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[
"If Alien scientists from 10 billion years ago made their own picture of the Cosmic Microwave Background, how different would it look from ours?"
] |
[
false
] |
Edit: Or earlier? Could anything be learned from it that we don't already know?
|
[
"The microwave background would have been hotter, by about 6 kelvin. (Fantastically, people have actually ",
"measured",
" the CMB temperature over time and shown it evolves as we expect.)",
"However, the ",
"picture",
" we usually see of the CMB doesn't contain the CMB's temperature but its temperature ",
", and that map wouldn't have been very much different, because all those temperature differences were ",
" onto the microwave background when it was emitted about 380,000 years after the Big Bang.",
"So what would change the picture? The temperature differences will somewhat shrink over time due to the overall temperature dropping. As the CMB becomes farther away in time, the same nonuniformities look smaller and smaller on the sky. There are also a few effects that directly change the CMB anisotropies as they move through the Universe, due to the photons making up the CMB being changed by the gravitational fields of galaxy clusters, interacting with gas, and so forth, but those are generally very small-scale effects that are difficult to see with precision instruments, much less the naked eye.",
" Interestingly, they actually exist (as I just learned during a Google search). One Stuart Lange did a senior thesis a few years back at Princeton asking almost exactly this question in detail: how does the CMB change over time? He focused in particular on how it evolves into the future (with the curious aim of trying to ",
"directly measure the expansion of the Universe",
" by taking two snapshots of the CMB a hundred years apart), but the pictures are still instructive. The thesis is ",
"here",
" and the pictures are on pages 75-77. Note that these are simulated pictures so the \"present\" CMB (figure 6.5) isn't our real one.",
"The important thing is that in cosmic terms, 10 billion years ago was not that long ago. The Universe has only about tripled in size in that time. That's about as much growth as the Universe will undergo in the next 10-20 billion years, so the first picture on page 77 (figure 6.9) looks roughly as different from the present CMB (figure 6.5) as the CMB 10 billion years ago looks from the real one today."
] |
[
"Picture an infinite ruler with 1 cm between the marks. Now, stretch it until there's 3 cm between the marks. It's still infinitely long, and all distances are tripled.",
"Edit: words."
] |
[
"It did, though the problem may lie in the choice of words \"tripled in size\". It might be more accurate to say that distances tripled. This applies to both the Universe and the ruler."
] |
[
"What happens to you during a panic attack?"
] |
[
false
] |
I have always wondered what happens to a person biologically during a panic attack brought on by an intense phobia or anxiety. Also to take that one step further but how those biological effects change your perception and senses to produce what ever the attack may feel like?
|
[
"Panic attacks are a very interesting example of the effect of our thought process in our bodies. It can be triggered by a small stimuli. Like brief dizziness or chest pain that by itself is nothing of importance. But the patient gives this event an importance much greater than what it really is. This creates anxiety and stress. Here is where it starts to escalate, the anxiety and stress generate a physical response. This mental states for our body mean that there is some danger we must escape so we start pumping large amounts of stimulants (adrenaline, noradrenaline) into our system. These have many effects, the patient perceives them and attributes it to the same pathology as the one causing the initial stress and anxiety. Of course this causes more anxiety and in turn a sustained release of adrenaline. At this point the patient thinks he is dying which perpetuates the process. "
] |
[
"From what I understand, a panic attack is a body's 'fight or flight' response. This results in increased heart rate, shallow breathing, adrenaline, rapid thoughts, etc. Your body is prepping you to run away (e.g. as in from a lion in the savannah), but the response can be triggered in circumstances where this is not particularly useful.",
"Source: i'm a kid with frequent panic attacks"
] |
[
"Really the person starts to think they are dying that is much worse than i could have imagined."
] |
[
"Ask Anything Wednesday - Engineering, Mathematics, Computer Science"
] |
[
false
] |
Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...". Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists. Please only answer a posted question if you are an expert in the field. . In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for . If you would like to become a member of the AskScience panel, . Past AskAnythingWednesday posts . Ask away!
|
[
"Short answer is yes. The block chain is really big and unwieldy. So far they've been able to get away with it, but in the future they will probably have to allow people to participate in the network without the full history of the blockchain. Their are also bandwidth limitations on the bitcoin network in terms of how many transactions can be processed per second which may be more difficult to resolve. Bitcoin at present is not capable of replacing more mainstream payment systems (eg, Visa)."
] |
[
"AI is not lacking a roadmap, its just that the things we are working on have nothing to do with the sort of sci-fi AIs you see in movies. ",
" strides have been made in the last five or so years in tons of AI subfields. Just no progress in the sort of inference engines that people in the 70s and 80s said would lead to Strong AI in a decade or so."
] |
[
"The Bitcoin network uses additional nodes to increase the security of the network, ",
". That means that the transaction throughput is limited to the throughput of the median node, ",
".",
"See my comment ",
"here",
"."
] |
[
"What is the maximum theoretical size for a sunspot?"
] |
[
false
] |
Edit: our sun, not other stars
|
[
"Do you mean a single sunspot or a complex cluster? Sunspots tend to break up into complexes as they grow.",
"Observationally, single sunspots get up to about 60Mm according to this comprehensive summary of the science from 2002: ",
"http://www2.mps.mpg.de/dokumente/publikationen/solanki/r45.pdf",
"\"Why do sunspots have the observed size and lifetime distributions? What places an upper limit on sunspot size?\" are given as open questions in the conclusions. Not sure what progress has been made since then."
] |
[
"Generally depends on the star and its magnetic field, but for the purpose of this answer I'm sticking with Sol.",
"First, to understand what a sunspot is and the underlying mechanisms.",
"A sunspot is a region of the sun where its sub-surface magnetic field has become twisted and knotted, then forced through the surface. The reason for this is that the sun, being a non-solid object, has different rotation rates. Its equator rotates once every 25 days, while the poles rotate once every 33 days or so. Magnetic fields like to stick with the plasma that's generating them, so with the difference in rotation, the magnetic fields start twisting and stretching around the sun. As stress builds up, the fields start twisting and generally becoming a tangled mess. At high enough field strengths, the field will start suppressing photosphere convection beneath the region. This in turn cools it, creating the dark spot.",
"Think of it like a rope or piece of wire. You can twist it back and forth a bit, and it will still mostly remain straight. But if you twist it too much, it'll try to loop back on itself to reduce the torsional stress. When this happens on the sun, a variety of magnetic phenomena occur, such as coronal loops.",
"Now, the size thing depends on how much energy is locked up in the exposed magnetic field, and how complex the field is. A simple up and down magnetic field (I believe its an alpha magnetic field) is not complex at all, and generally has 1 area where one side of the magnetic field is quite dense, producing a spot, while the other end is dispersed over the solar surface, producing little to no spots. These fields generally have a small amount of energy, are very stable, and once spawned generally spend their lives not doing much, maybe some light flaring if they get moody. At largest they're about the size of Earth.",
"As more energy collects below and builds, the sunspot grows and its magnetic field becomes twisted, with regions condensing and trying to mix together. As the magnetic field strength grows, the spot also grows as more and more convection below is suppressed. This energy wants out, it wants to be released. If the magnetic field lines from one internal part reconnect with a lower energy set somewhere else, the difference in energy is violently released in a Solar Flare. If the energy is being released slower than what is building below, the sunspot continues to grow until it reaches equilibrium. ",
"This leads to the meat of the question. How big can sunspots get? Your average sunspot is about the size of earth. A big one will reach Neptune sized. The monster sunspots are all the size of Jupiter or a bit larger. There's also sunspot chains, elongated regions on the sun where sunspots form in groups and clusters, and can be many tens if not hundreds of thousands of kilometers long. Large sunspot regions can last for many months, and present a threat to Earth-based space assets and astronauts each time they make a pass.",
"If you want to find out more, spaceweather.com has a very long running data archive (starting in 2001 I believe) showing the state of the main page every day and the data on the page, including imagery and a couple short blurbs about what the sun is doing or, if there's nothing too major the sun is doing, what else is going on in space weather. NASA also has the data archive for the Solar Dynamics Observatory freely available for perusal. You can input a range of dates, and the archive will spit out the images within that date range. You can watch short movies of sunspots doing their thing in various frequency ranges, from visible light, to UV, to Xray. You'll learn quite quickly our sun is quite the dynamic star, even though just looking at it from down here (Dont do it without protection though, you'll fry your eyes) it doesn't really look like it."
] |
[
"Yes we have, but due to the size of the object we're trying to pick out directly on another solar surface, its generally only the really big ones we can see directly (up to 100x larger than on Sol's surface). Others require various techniques to detect the spots. Naturally, such sunspots also generate x-ray activity which we can detect with orbital observatories. We've detected such x-ray activity around several red and orange dwarf stars, including Proxima Centauri, Wolf 359, and Barnard's Star. ",
"We've also detected considerable Xray activity from the II Pegasi system, specifically from II Pegasi A, the primary, which is a K-type subgiant that just left the main sequence. According to wikipedia 40% of its surface is covered in starspots."
] |
[
"Can you transplant organs across genders?"
] |
[
false
] |
For example can a man receive a woman's heart? Vice versa? What about transgendered?
|
[
"Gender is not a relevant criterium to judge possible organ donors. I only know about live organ donation, for example kidneys, but I assume that it is very similar with recently deceased donors. Your blood is tested for the amount of reactive antibodies, indicating how many of your white blood cells will recognize the foreign tissue as foreign and attack it. If your reactivitiy is under a certain limit the transplant will probably work. This reactivity is determined by how different HLA (human leukocyte antigen, a kind of molecular passport of your immune system) is between donor and recipient. The sex of the people involved isn't relevant. So to finally really answer your question: yes, absolutely, men and women can donate organs to each other, if they are a immunological fit. "
] |
[
"I remember seeing something recently about men being at higher risk of death after blood donations from ever-pregnant females, hypothesized to be as a result of immune system changes pregnant woman have to help protect the baby. A slight risk, but the study showed it to be statistically significant. Do you know of any similar issues for organ donations? "
] |
[
"To provide some anecdotal evidence to Opthalmic's explanation, my mum gave a kidney to a long time friend of the family who is a dude. I think it's been 10 years now and he's still going strong.:-)"
] |
[
"If the world is slowing down (ie. Spinning slower each year), would it have been noticeably faster millions of years ago?"
] |
[
false
] |
I say noticeably, I mean would a human being alive at that time (hypothetically) feel any different than they do in the present day?
|
[
"620 million years ago: the day was 21.9±0.4 hours"
] |
[
"It's slowing at a miniscule rate. Basically it's syncing up to the moons orbital speed. As the earth slows the moon moves farther away, about an inch a year. They'll never sync up though because before that can happen the sun will come to the end of it's life, grow to a red giant and engulf them both.",
"Edit: sun grows to red giant, not red dwarf lol"
] |
[
"So it is neither speeding up or slowing down? Or is it slowing at a miniscule rate?"
] |
[
"What would happen if a healthy person took the highly active antiretroviral therapy?"
] |
[
false
] |
[deleted]
|
[
"It would definitely reduce HIV transmission risk, if that's what you're asking. I don't think anyone knows how much it would reduce it, though. Most of the trials for this have been conducted in Africa with only single drugs or pairwise combinations, usually the cheapest ones available. I'm guessing that a full-blown HAART regimen, particularly including things like an integrase inhibitor, could have much more efficacy. ",
"There are some side effects of the drugs, though, particularly the protease inhbitors. They seem to cause metabolic changes like visceral body fat and increased glucose levels. HAART probably isn't something I'd want to take long term as a healthy person. The cost alone would be ruinous, as health insurance isn't going to pay for meds for someone without a diagnosis of being HIV positive. There's also a compliance issue, in that you'd have to take a lot of pills pretty regularly. Skipping a dose or two could dramatically reduce your protection level.",
"It also depends on what sort of contact you're trying to protect against. Female to male transmission by vaginal sex in the US is pretty low risk already. Addition of even one or two antiretrovirals to that would probably reduce the risk to very very low. If you're trying to protect against riskier contact, like male/male sex, or IV needle sharing, then a more active combination might be needed to reduce the risk to acceptable levels. It also depends on the meds that the infected partner has. If the partner were already on HAART, their viral loads might be so low that transmission is already relatively low risk."
] |
[
"it can make people with compromised immune systems live about as long as people with healthy immune systems",
"This is a wildly inaccurate description of HAART intervention. There are many, many reasons for immune deficiency beyond HIV infection, and obviously antiretrovirals do not affect these. It decreases the viral load and subsequent effects, nothing more. No infection means that the drugs will give you all the adverse effects and no benefits. The transmission prevalence rate for low-risk individuals is not high enough to justify the risk of routine prophylaxis or whatever else you may be thinking."
] |
[
"it can make people with compromised immune systems live about as long as people with healthy immune systems",
"This is a wildly inaccurate description of HAART intervention. There are many, many reasons for immune deficiency beyond HIV infection, and obviously antiretrovirals do not affect these. It decreases the viral load and subsequent effects, nothing more. No infection means that the drugs will give you all the adverse effects and no benefits. The transmission prevalence rate for low-risk individuals is not high enough to justify the risk of routine prophylaxis or whatever else you may be thinking."
] |
[
"How do solar flares and other types of activity of a star influence its movement through space?"
] |
[
false
] | null |
[
"Stellar activity will not influence an ordinary star's movement significantly at all. The total mass ejected by the Sun is around 10",
" solar masses per year. If you assume the ejected mass was travelling 50% of the speed of light in a single direction (it's actually traveling much less fast) it would change the Sun's speed by around 10",
" m/s, an incredibly small speed.",
"The story is different with higher-mass stars. In the extreme case of luminous blue variables like Eta Carinae, which can have mass loss rates of up to 10",
" solar masses per year, and as much as 1 solar mass/year during a strong eruption. This would change their velocity by up to 1% of the outflow speed if all of the ejected matter was moving in one direction (it's actually closer to spherically symmetric). Outflow speeds for Eta Carinae are up to 4000 km/s, so that would change the velocity of the star by around 40 km/s, which would be small but significant by Solar System standards in this most favorable case. But practically speaking, only events that destroy a star or one of its companions (like supernovae) are expected to change a star's velocity significantly. "
] |
[
"Thank you, in short: it has effect but for most thing it will be negligible, because the effect is very small?"
] |
[
"Exactly."
] |
[
"Why is the Higgs needed for atoms and stars to exist?"
] |
[
false
] |
"This symmetry breaking is required for atoms and other structures to form, as well as for nuclear reactions in stars, such as our Sun." on the Higgs wiki page. From what I understand the Higgs is the reason that Electromagnetism and the Weak force are two separate forces rather than one Electroweak force. And atoms can't form and combine together into stars while the Electroweak force is around. What about the Electroweak force is stopping atoms? I can't really find any details on what the Electroweak force is like. All I can find is that it has 4 version of the photon called W W W & B. Since they're all massless is the Electroweak force just like Electromagnetism? I also found , that says atoms and star could still exist if there was no Weak force. So is the Higgs like a necessary shackle on the Weak that allows us to exist?
|
[
"This blog post by Matt Strassler",
" discusses what the universe would be like if the Higgs field had a mean value of zero. That's a slightly different question than the one you're asking, but it's close enough to be interesting, I think.",
"Some highlights (edited slighty for brevity):"
] |
[
"Why is the Higgs needed for atoms and stars to exist?",
"Because there is no mathematical reason why particles such as the W and Z boson have mass -- they should be massless without a reason to have a mass. The Higgs mechanism provides a way to give the W and Z bosons (and other particles such as electrons) a mass.",
"From what I understand the Higgs is the reason that Electromagnetism and the Weak force are two separate forces rather than one Electroweak force.",
"More or less, yes.",
"And atoms can't form and combine together into stars while the Electroweak force is around.",
"Atoms can form and combine together but they will not at all resemble matter as we know it without the mass imbued by the Higgs mechanism.",
"What about the Electroweak force is stopping atoms?",
"Weak force processes would be completely different, which has a significant effect on the (in-)stability of various kinds of matter and various reaction and decay processes that occur, for example, in stars.",
"I can't really find any details on what the Electroweak force is like.",
"All I can find is that it has 4 version of the photon called W+, W0, W-, & B.",
"Since they're all massless is the Electroweak force just like Electromagnetism?",
"Not just like it. The massless W_0 and B_0 are neutral massless particles so they would be very similar to the photon. (The Z_0 is already very similar to the photon except it is short-ranged because it has a mass.) The W+ and W- would have electric charge, unlike the B_0 and W_0. I am not entirely sure what this would mean for their behavior.",
"I also found this hypothetical, that says atoms and star could still exist if there was no Weak force.",
"However they wouldn't be just like the atoms and stars we observe in the universe today. There would be some similarities but also many differences.",
"Really it's just the case that the physics in such a universe would be phenomenologically different because of the absence of the weak force."
] |
[
"Both are dependent on the universe's temperature. The electroweak merging temperature is around 10",
" K; the energy scale for proton and electron recombination is on the order of 10",
" K. So there are 11 orders of magnitude difference."
] |
[
"Why do lightbulbs need so much \"free space\" between the filament and the glass?"
] |
[
false
] |
[deleted]
|
[
"The bulb is filled with an inert gas (usually argon) that does not react with the filament. Throughout the bulb's life time, oxygen slowly seeps into the bulb, and once it passes some threshold, there is enough oxygen for the filament to oxidize and break, which causes the light to go out.",
"Therefore, with a large bulb volume, you increase the amount of oxygen that must enter the bulb volume (i.e. increase the life time) before there is a high enough fraction of oxygen to react with the filament. "
] |
[
"I seriously doubt that this has anything to do with it at all. More likely it's simply heat-transfer limitations. Incandescent bulbs operate with the filament basically as hot as it can get without destroying itself, and the transfer of heat out of the bulb will be limited by its surface area. If you make the bulb more powerful without making the bulb bigger, you'll make the filament hotter, and cause failures.",
"Incandescent bulbs also don't generally fail because of oxygen infiltration, they fail because at the temperature required for them to work, the filament is continuously vaporizing. The black soot that ends up on the glass of old incandescent bulbs is actually the tungsten from the filament, vaporized and then re-condensed on the glass. Halogen lights last longer with similar filaments because the halogen gas inside (usually iodine or bromine) reacts chemically with the tungsten and helps to deposit some of it back from the walls of the bulb onto the filament."
] |
[
"I'm not sure if slow continuous evaporation is the dominant failure mechanism either. Most of the tungsten deposits on surfaces of a blown bulb probably occur during the last few seconds prior to failure, during which time a defect has created a localized region of high resistance, localized heating, and accelerated vaporization in the local hot spot. The wire usually breaks in the hot spot by either grain slippage or partial melting. ",
"'Properties and failure modes of incandescent tungsten filaments', IEEE Proceedings"
] |
[
"Reddit, are you ready for my glass challange, I need your help!"
] |
[
false
] |
*repost from askreddit where they directed me to here. Hi Reddit, So, I have been lurking for some time, but I have no where else to turn. I have been trying to melt glass without bubbles for some time, and I just can't figure it out!!!!!! I have spent over a year and thousands of dollars. I am trying to make a small business, though now it is just a hobby because of this issue. I have a furnace that can reach 2100F or 1150C as a working temperature. I have kept the glass at that temperature for 12 hours, and there were bubbles everywhere. If I get the advice I need I will make something using this kiln, and ship it to them for free---> and it is up to you what you want me to make. I have no clue why this doesn't work!!! annealing is no problem, but the bubbles are. Should I use a vacuum furnace? If so, I "can" buy one, as I know it will be cost prohibitive in the long run to "rent"/oem this stuff. I am just curious if the vacuum will still have these bubbles in the glass. Also, what temperature does it need to be at and how long? or really if a vacuum furnace WOULD work? I spent a lot of money on this. I first built 2 furnaces, they were a disaster, then i bought another one that can reach those temperatures 2100F and 1150C, was crazy expensive, but my still work for the 2nd process if the vacuum furnace works. Please help! Edit: should also add that I do not use large pieces, rather small pieces, the warmglass website about stacking would not work Edit 2: not sure why i got a downvote, but from what i know askscience should be downvoted if it is not a scientific question. this is not ask google (which i googled for months), but a hardcore brain scratching question. thanks Edit 3: I am absolutely amazed at how wonderful reddit is. I probably saved a year, minimum, by spending a few hours here. Thank you to everyone for all the help, My battery will be dying very shortly and I am in the car, I am really the happiest that can be for a select few redditors in this thread. Thank you so much guys... I wish I could do something in return, as this helped me so much. thank you thank you!
|
[
"I might be able to help. I worked in glass formulation, raw material batching, and melting for over 8 years.",
"First thing first, what type of glass are you melting? Technically what you're doing at 1150C is softening the glass, not a true melt. If you're starting with a raw batch, that temperature won't cut it. If you're starting with cullet, depending on the chemistry you still might not be hot enough. ",
"You could also be seeing seeds (gas bubbles) from:\n1) Trapped air voids if the glass is to viscous from lack of temperature\n2) A difference in redox from room temp to a fluid phase could cause SO3 in solution to go out of solution and cause what's know as a reboil. It would like like tons of tiny gas bubbles in an annealed piece, almost like a freeze frame of boiling water."
] |
[
"Vacuuming the bubbles will not help. In industry the techniques are actually the opposite. You add things like water or bubble oxygen through the glass. Because those make large bubble and pass (usually) quite easily through the molten glass, they collect the tiny bubbles from carbonate and sulfate sources as well as pick up any trapped air voids that can form in low temperature melts. Water in the batch or bubbled up from below works well, but is not energy efficient. If you care about efficiencies or if you're trying to determine costs, avoid water if possible.",
"From your description however my gut is telling me you have an SO3 reboil issue combined with a high viscosity. Your top end temperature limits the viscosity you can achieve, and is in a range that can actually change the solubility of SO3 in your glass, causing the SO3 to come out and fill your melt with seeds. More often then not, once the SO3 comes out it's very difficult to near impossible to get it back in solution.",
"If you have any batch data on the glass cullet, send it to me. I'd like to see what's in it. If you have options to change around the source, try to find one with no or very little sulfate materials. Things like salt cake (sodium sulfate), gypsum and anhydrite (calcium sulfate), and potash (potassium sulfate) are common sources used in glassmaking. ",
"For your borosilicate glass, many of them have chemical coatings on finished glass depending on what the final use may be. If you're taking a final product and crushing it to use in a remelt situation, you're adding any one of hundreds of organic chemicals that can have numerous redox effects in a melt. Even if it's generic tube stock. These coatings are applied because the surface chemistry of borosilicates can be very reactive and actually behave as a deliquescent material. Try crushing up some material and let it sit in an area where you know there's decent humidity. Give it a day or so in a bucket or in a shallow pan. If you start seeing puddles, but never saw water on the as is material, there's a coating.",
"You could also do an LOI test on the material at about 200C to 500C, just stay south of the 800C or so softening temperature of Boro33. Look for a weight loss. It may only be 1% or even less, so use at least 4 decimal points. If that's not available, you might need to send it out for thermal analysis or contact the distributor."
] |
[
"Hi THere AlchemistPrime!! thank you so much for your reply, first off. ",
"What you said at first was extremely frustrating. I am melting Borsilicate 33 and soda lime glass. They are small chunkds of glass, right now I am using scrap glass for those two types, as I am not in production now..",
"your 2nd bubble question makes a bit of sense as there are crazy amounts of bubbles. so what temperature do you think i need? As I said, I CAN buy a vacuum furnace, but I do not want to have the same thing happen as with my current furnace. being a giant waste of space in my shop..."
] |
[
"Does air enter the vascular system after traumatic amputations?"
] |
[
false
] |
After an event that causes a traumatic amputation a tourniquet is usually applied to prevent exsanguination. Before the tourniquet is applied can/does air enter the vascular system or do the veins retract far enough proximally to prevent an embolism from developing?
|
[
"No, air embolism is not generally a concern in that situation. Even though veins are under less pressure than arteries, they are still at higher pressure than the surrounding atmosphere. Any open wound results in blood flowing outward, not air being sucked in."
] |
[
"Thanks for the answer, I was worrying about this the other day."
] |
[
"No. The circulatory system doesn't work on suction. It works on positive pressure, forcing blood forward through the system. All blood vessels are under greater pressure than the air outside, so puncturing a vessel will always cause flow from the inside out, not the other way around.",
"Air by itself will never simply flow into the bloodstream. That happens only when some external force pushes it in. For instance, air can enter the bloodstream when bubbles inside IV tubing are forced inward by the weight of liquid above them.",
"Also note that a small amount of air in the bloodstream is not as dangerous as TV and movies make it seem. Research shows that the circulatory system is able to cope with quite large air bubbles, with little ill effect, unless they are injected into certain critical vessels very near the heart or brain."
] |
[
"How does the fusion within stars work? Is it similar to a fusion reactor, and could we pull energy from it to power things?"
] |
[
false
] |
I have a basic understanding of how stars work (hydrogen bounces into each other to form helium which forms lithium which forms yaddah yaddah on and on until it's heavier and heavier). With this basic understanding, it makes sense in my head that one could harness this natural reactor to use it as a giant engine. Does that make sense? I'm writing a science-fiction story. I want to put a space station in the core of an artificial star. The idea is to have a station powered by a fusion reactor-type power source, and for it to basically be a star to an outside viewer (which would be the star of the system the story takes place in). If this sort of thing is stupid to ask in this subreddit, please direct me to an appropriate place, but dumb story or not I would still be interested in knowing if this is possible.
|
[
"Hi, ",
"your idea is not very realistic. Inside stars, you have temperatures of millions of degrees and pressures of billions of bars. Anything would just squished and ionized simultaneously in these conditions. Even if you ignore this, harnessing the produced energy would be difficult, because it is hard gamma radiation, which easily penetrates through any device you could use to gather electromagnetic energy. It would be more meaningful to use lower energy radiation such as visible or ultraviolet light. ",
"Also, you can't harness energy without an gradient. If you are inside a star, you are surrounded by plasma that has about the same temperature and pressure, so the energy can't do work. ",
"For these reasons, it would be more useful to have a station outside a star, that can harness the star's radiation, because the photons have a much lesser energy due to the collisions with the gas plus you have the required temperature gradient (hot surface of the star and cold universe)."
] |
[
"Yeah, the core of a fusion reaction is probably the last place you want to be. Having a small artificial star at the core of your space station would make more sense."
] |
[
"As Schublade points out, there is no ",
" way to do this, but you're writing science fiction, so lets look at it from that perspective. If you've ever seen the movie ",
", the characters pilot a ship into the liquid outter core of the Earth. It is able to survive the intense pressure and temperatures because the inventor of the craft shelled it in a material that he nicknamed ",
" that only becomes stronger the more pressure and/or temperature is applied to it. You could use that angle, and maybe incredibly powerful magnetic fields to maintain the station in the middle of the star. I'd also make the star a red dwarf as these are much cooler (although in the core its still incredibly dense and hot).",
"Or could you have the station ",
" just under the surface of the star, using its ",
" structural material to keep it from being destroyed, collecting solar plasma for energy? Maybe on the actual surface of the star could be a permenant ",
" that is the only outward sign that the station is there?"
] |
[
"How has life affected what the Earth looks like?"
] |
[
false
] |
How has biological life affected what the Earth looks like? If that's too broad a question I've got some specific ones below, and I'd love answers to any of them. Thanks for any interest in answering. Thanks again!
|
[
"Life has strong influences on many aspects of Earth processes",
". ",
"Some notable points include:",
" Life is largely responsible for ",
"atmospheric and oceanic oxygen",
", and influences the ",
"nitrogen cycle",
" and the ",
"carbon cycle",
".",
" Life alters ",
"erosion patterns",
" by altering precipitation rates, preventing land slides, reducing wind scour of soil, and contributing to soil production. ",
" It is plausible that atmospheric contributions by life may ",
"prevent depletion of land water",
" and thus maintain the \"wetness\" of Earth (as opposed to dry planets such as Mars).",
" Life is responsible for specific terrestrial formations/ecosystems such as coral beds, limestone and sand.",
" Man-made effects such as light pollution, ocean acidification, carbon release, etc.",
"One useful hypothesis that focuses on the question of ",
" is the ",
" which has three major tenants:",
" Biologically mediated feedbacks contribute to environmental homeostasis.",
" These feedbacks make the environment more suitable for life.",
" These feedbacks arise from Darwinian natural selection.",
" So, in sum, Earth topography, atmospheric chemistry, and oceanic chemistry are heavily influenced by life. There is a hypothesis that some of the effects of life on Earth processes evolved to drive ecological homeostasis and thus make Earth more suitable to continued life. ",
"The known contributions of life to terrestrial stability are especially important in light of the current ",
"mass extinction event",
" which already producing alarming ",
"state shifts",
" and ",
"tropic downgrading",
" of the biosphere. ",
" Updated the links that went through proxy, sorry most of these aren't open access."
] |
[
"The most obvious life-related features are probably carbonate formations (limestone, chalk), formed mostly of the skeletons of dead plankton. These can be kilometers deep and cover large regions, so they certainly have an effect on coastlines, though only to an extent: Tectonic activity forms the general shapes of the continents through mountain-building events, it's the shallow seas nearby these mountains that are filled in with carbonates."
] |
[
"...the oxygenation of the Earths atmosphere ~2 billion years ago still hasn't been figured out...",
"I was under the impression that this (the Great Oxidation Event) was fairly well understood to be as a result of cyanobacteria as oxygen sinks filled up (evident from banded iron formations)?"
] |
[
"How does schizophrenia effect people who lack a sense of sight and/or sound? Are visual and/or auditory hallucinations still experienced?"
] |
[
false
] |
Would these effects be different between those who were born without one or more of these senses, and those who lost these senses later in life?
|
[
"We haven't seen any blind schizophrenics yet (Sanders et al. 2003).",
"Deaf schizophrenics seem to have many visual and tactile hallucinations, with auditory hallucinations not usually attested (Schonauer et al. 1998).",
"References:",
"Sanders,Glenn S., Platek, Steven M., and Gallup, Gordon G. (2003). No blind schizophrenics: Are NMDA-receptor dynamics involved?. Behavioral and Brain Sciences, 26, pp 103-104.",
"Schonauer, K., Achtergarde, D., Gotthardt, U., & Folkerts, H. W. (1998). Hallucinatory modalities in prelingually deaf schizophrenic patients: a retrospective analysis of 67 cases. Acta Psychiatrica Scandinavica, 98(5), 377-383."
] |
[
"One of the hallmark features of schizophrenia is the noticing of connections between things that really have no connection. It takes learning to get to this point, which requires NMDA receptors. What I'm describing here is acquiring the information to support a delusion. ",
"An example would be, they go grocery shopping, and notice an orange that's been placed in the banana section. Recognizing it's out of place is an appropriate connection; deciding that it's been placed there by someone expressly to convey a message to you is something different. Once they've decided it's a message to them, they recall how the FBI has been screwing with their mind, and have been placing anomalies in their environment to convey the level of mind control they've gotten over this person. Suddenly, they recall how the dishwasher detergent lid didn't open at the last use, and they realize that the FBI is likely screwing with their appliances as well, just to make them question their own sanity. Therefore, appliance use and grocery stores are now venues of mind-control, and must be approached cautiously.",
"And the proof of all of this is the orange. ",
"And all of that took NMDA activity, because they're generating long- term memories of the event, and connecting it to other long-term memories. "
] |
[
"Interesting. I wonder why that would be when schizophrenia can simply include delusions, e.g. paranoia. So it would stand to reason (to me) that a blind person could simply have delusions but no visual hallucinations, or delusions that are accompanied by auditory hallucinations.",
"Could somebody explain in laymen terms why NMDA-receptors could possibly be involved with schizophrenia and other disorders? I am not a neuroscientist, so the above-cited article is a bit above my understanding."
] |
[
"How can a black hole created by a collapsed star have a stronger gravitational pull than the star it came from?"
] |
[
false
] |
Black holes can swallow up light particles, but stars don't have nearly that strong a gravitational pull. Is the area of effect of the gravitational pull simply smaller, but more powerful?
|
[
"It doesn't. The reason is that the same mass is compactified into a smaller region, so you can get closer to the black hole while still feeling the same amount of mass. If you're outside a star, you'll feel the same gravity as you would the same distance from a black hole of the same mass. But if you're inside that star, you'll only feel the gravity from the parts of the star interior to where you are (i.e., closer to the center) so you're only feeling some of the star's mass. With a black hole, all that mass is always interior to where you are."
] |
[
"If you continue this train of thought, you realise that anything can be turned into a black if you would be able to squeeze it hard enough. If you were to compact the earth to something the size of 8.8 mm (which, incidentally is app. the size of a red ant), it would become a black hole. This size is called the Schwarzschild Radius and is pretty easy to calculate. My Schwarzschild radius is 1.262×10",
" meters which is 9 orders of magnitude smaller than a proton. The sun's is 3 km btw."
] |
[
"In most gravitating bodies, their radius is larger than their ",
"Schwarzchild radius",
". This means that if you go inside the star or planet, the gravity doesn't keep increasing because the mass further out than you doesn't have a net effect. For example, at the very center of Earth, there is basically no net gravitational force (though there is plenty of pressure). So it's only when stars are very dense (denser than an atomic nucleus) that you can reach the extreme curvature needed for a black hole."
] |
[
"How often do animals known for their quickness or agility (like a deer or cheetah) tear ligaments or pull muscles?"
] |
[
false
] | null |
[
"Pulled muscles again do not occur very often. They have evolved to run and jump withstanding the associated stresses",
"It is also notable that many fast animals are significantly lighter than your average human being. Less weight means less torque on acceleration, so it takes a cheetah less 'power' to suddenly go from a standstill to speed."
] |
[
"Pulled muscles again do not occur very often. They have evolved to run and jump withstanding the associated stresses",
"It is also notable that many fast animals are significantly lighter than your average human being. Less weight means less torque on acceleration, so it takes a cheetah less 'power' to suddenly go from a standstill to speed."
] |
[
"Here's one next to a person- ",
"https://i.ytimg.com/vi/CEid3OzxE8U/maxresdefault.jpg",
"They are smaller than I thought, too."
] |
[
"How do we differentiate the Earth's magnetic field weakening due to a pending reversal instead of a complete shutdown like is suspected to have happened to Mars?"
] |
[
false
] |
From my understanding, it is suspected that Mars once had a magnetic field like ours, but because of its smaller size, the core eventually cooled and stopped its movement, causing the field to "turn off". How do we know the current weakening of Earth's field is not a similar process, but instead just a reversal?
|
[
"Loss of magnetic field is a gradual process which results from the cooling and solidification of the liquid outer core. We know from seismic studies we are nowhere near that point - it is still large and molten. Turning off of the magnetic field is ",
" a rapid on-off process.",
"The reason we're so far from it happening on Earth is the much bigger volume of our planet in comparison to Mars, hence the cores are bigger, better insulated, and the much higher volume to surface area ratio which means that cooling is less quick."
] |
[
"No, there is no fission. There is simple decay. Fission is driven by neutron bombardment, whereas decay is a natural process with a relatively much lower energy yield than fission. Fission ",
" occur in some very rare cases, but it is not considered a heat source within the earth.",
"The main elements responsible for earth's internal heat are U, Th and K, although by far the largest contributor is gravitational heating from the movement of dense material toward the core."
] |
[
"No, there is no fission. There is simple decay. Fission is driven by neutron bombardment, whereas decay is a natural process with a relatively much lower energy yield than fission. Fission ",
" occur in some very rare cases, but it is not considered a heat source within the earth.",
"The main elements responsible for earth's internal heat are U, Th and K, although by far the largest contributor is gravitational heating from the movement of dense material toward the core."
] |
[
"What is this radiation device at my school?"
] |
[
false
] |
[deleted]
|
[
"That's a ",
"Crookes tube",
". (Plücker version)"
] |
[
"looks like a ",
"cathode ray tube demonstrator",
"."
] |
[
"What do the warning tags say? even if they dont have names they might have numbers which could help figuire out what it is."
] |
[
"Reddit, here's a video of a powerful water cutter. If it can cut steel, what keeps the nozzle from being destroyed?"
] |
[
false
] | null |
[
"You're close here: the water is travelling parallel to the nozzle, so the nozzle does not wear much. The water strikes the steel, however, all of that energy is imparted into the steel, breaking it apart. "
] |
[
"Yes. And appearently, they use a jewel - like ruby or a diamond - to narrow the jet stream and thereby increasing the pressure:",
"http://en.wikipedia.org/wiki/Water_jet_cutter"
] |
[
"I would think that since you basically have a pipe flow within the nozzle (fluid moving more or less parallel to walls), then you would get a boundary layer of much slower fluid interacting with the nozzle walls."
] |
[
"What are the odds that any viruses or bacteria survived any missions to the moon and would they be able to do anything with the moon \"dirt\" to continue living or more?"
] |
[
false
] | null |
[
"That's not even remotely true, and you are in fact entirely wrong... there are plenty of bacteria that use anaerobic respiration, or are chemotrophisms to do survive in areas without oxygen. Absolutely nothing says all life on earth needs oxygen to survive. NASA in fact uses an equation to predict living cells on the voyager probes ",
"Relevent XKCD.",
" Part of the reason NASA makes their probes in clean rooms is to limit the possibility of taking something to another planet. I have no idea where you made this up from.",
"Take any general microbiology class in any college in the US and they will teach you about metabolic pathways in bacteria and how oxygen isn't required for them to survive.",
"Source: I am a microbiologist, I study MRSA and other ESKAPE pathogens."
] |
[
"That's not even remotely true, and you are in fact entirely wrong... there are plenty of bacteria that use anaerobic respiration, or are chemotrophisms to do survive in areas without oxygen. Absolutely nothing says all life on earth needs oxygen to survive. NASA in fact uses an equation to predict living cells on the voyager probes ",
"Relevent XKCD.",
" Part of the reason NASA makes their probes in clean rooms is to limit the possibility of taking something to another planet. I have no idea where you made this up from.",
"Take any general microbiology class in any college in the US and they will teach you about metabolic pathways in bacteria and how oxygen isn't required for them to survive.",
"Source: I am a microbiologist, I study MRSA and other ESKAPE pathogens."
] |
[
"Correct viruses are not alive. They are only broken pieces of DNA in a protein coat. They don't even have the basics of a simple cell. They are only tiny bags of DNA or RNA whose only purpose is to attach to the correct organism's cell and reprogram it"
] |
[
"Why does human hair grow so long? I've noticed that other apes and monkeys don't seem to have really long hair. Humans on the other hand can grow out the hair on their heads and get it pretty long."
] |
[
false
] | null |
[
"Why does human hair grow so long? The anagen phase tends to last several years on scalps. Other apes have far shorter anagen phases. ",
"Humans have thinner shorter hair over much of their bodies because we evolved to be long distant runners and sweating allows for very quick cooling. ",
"Obviously this isn't the case with our heads and genitals, where hair grows far longer than other apes. Reason? Sexual preference, like peacock tails. "
] |
[
"Which would, essentially, cause an increase in sex, therefore sexual selection, right?"
] |
[
"sexual selection is a popular idea, but there's also the hypothesis (e.g. ",
"here",
") that long head and pubic hair are for increasing surface area for pheromone distribution."
] |
[
"Texas hold'em probability question?"
] |
[
false
] | null |
[
"You're succumbing to a way of thinking that's very common and that intuitively makes sense, but incorrect: the Gambler's Fallacy (apt, in this case), also known as the Monte Carlo fallacy. Essentially, if two events occur independently, then it doesn't matter which order the two events occur in; the probabilities of each one's outcome remain the same. For example, if you flip a coin two times, the two events are you flipping the coin twice. Each time, you have a 1/2 chance of getting a heads and a 1/2 chance of getting a tails. Whether the first flip comes out heads or tails doesn't affect how the second flip comes out.",
"Getting dealt the losing hand 4 times and then having your opponent dealt the winning hand a 5th time does indeed have a chance of occurrence of 1 in 32. However, the probability of your opponent being dealt the winning hand a 5th time ",
" you've already been dealt the losing hand 4 times is still 1 in 2; your past losses do not affect the next hand."
] |
[
"Overall, my question is this: Say when you are playing 1 on 1, and you get dealt the losing hand 4 times. So that means that the chances of your opponent getting dealt the winning hand for a 5th time in a row is 1/(25)=1/32=3% right? So should that affect the percentages pre-flop? ",
"If you've already won four times, the chances of being dealt the winning hand for the 5th time are 1/2.",
"Your chances of being dealt the winning hand 5 times in a row are 1/32, but so are the chances of any other exact combination of 5 wins or losses. Your chances of winning the first, losing the second and third, winning the fourth, and winning the fifth are also 1/32, because there's only one possible way for that to happen. It ",
" more random but it's no more likely to happen by random chance. ",
"If you've won four hands already, there are only two possible outcomes for the first five hands: WWWWL or WWWWW. Both are equally likely. "
] |
[
"So that means that the chances of your opponent getting dealt the winning hand for a 5th time in a row is 1/(25)=1/32=3% right? So should that affect the percentages pre-flop?",
"Not really because the hand gets reshuffled after each hand, so your chances of getting the winning hand are the same for each hand, regardless of how many times you've won or lost. The gambler's fallacy means that gamblers often think that the probability is affected based on how many times you've won or lost previous hands. What you're asking about in this case is conditional probability, meaning that the outcome of one event affects the outcome of other events after it, but each hand is considered independent of every other hand, so the probability of winning or losing a hand is the same each time. The probability of winning or losing 5 times in a row is relatively slight, but that doesn't affect the outcome of each hand."
] |
[
"How much of the moon's original mass has been lost to impact damage?"
] |
[
false
] | null |
[
"None, in general it gains mass from impacts while dust and other debris is lifted from the surface the gravity from the moon is enough to recapture most of the debris and it will eventually settle back down on the surface."
] |
[
"A tiny amount. Most impacts only add mass to the moon - whatever is kicked up by the impact just falls back. A very few very large impacts have hit with enough force to send a few particles into space, but none in recorded history."
] |
[
"Thanks"
] |
[
"Does breathing salty air dehydrate you more than inland air?"
] |
[
false
] |
I'm wondering if the salty air when near the ocean, or on a boat can dehydrate the human body faster than if you were away from the ocean. Also, what amount of concentration of salt is in the air that you're breathing. Many times I have found piles of salt in my bags, when on a long voyage on a boat. Thanks for the information anyone can give me!
|
[
"Salt air is a real thing. As wind blowing over the ocean lifts sea water and vaporizes it, fine salt particles, ie salt dust, remain in the air. This salty air can be carried for some distance inland, but air that is closest to the sea has the highest salt concentrations. High humidity, fog, and rain can capture salt dust which then dissolves, and when that salt-carrying water condenses on surfaces, the salty condensate eats away at them. Surfaces such as wood and metal corrode much more quickly near the ocean. So yes, you do breathe in fine salt particles when you’re on the ocean. Whether it makes you thirstier, or not: I can only answer for myself that salt air makes me both thirsty and hungry,"
] |
[
"If you can smell something, it's physically in your nose. ",
"So I'd say that smelling saltwater spray does indeed dehydrate you a tad bit more than regular air."
] |
[
"If you can smell something, it's physically in your nose. ",
"So I'd say that smelling saltwater spray does indeed dehydrate you a tad bit more than regular air."
] |
[
"A few questions about the origin of life."
] |
[
false
] |
1-What is the most up to date theory on the origins of life? 2-In the Blind watch maker, Richard Dawkins talks about clay crystals acting as a building frame or something. can you please explain that to me. 3-What evidence do we have that all life originated from a common ancestor? 4-is it possible that there are multiple starts?
|
[
"So there are many different conjectures as to how ",
"abiogenesis",
" occured. There is no general theory of Most of them are basically imagined scenarios that are bound by the laws of physics, the chemical environment at the time, and the requirements of life. \nNo one has recapitulated abiogenesis ",
" and no one has observed it in nature either. One is compelled to deduce that it must have happened, but in what order and along what time frame? Some people say that organic monomers (Nucleic Acids, Amino Acids, and Phospho and Sphingo Lipids, etc) were necessary first, because darwinian polymeric chemistry is the first step, that is before cellular formation. A famous experiment by ",
"Stanley Miller and Harold Urey in 1953",
" demonstrated that organic monomers can form in conditions that might be similar what might have been on early earth with only small inorganic molecules present. Actually they tested many different kinds of environments and have many unanalyzed samples, still sterile and unopened. \nOn the other hand, some scientists assert that protocellular chambers existed in the micro-pores of sediment created by ",
"Hydrothermal Vents",
". (",
"here",
" is a free report on the paper i just linked). These vents exhibited electrochemical gradients through these micro-pores, which could facilitate the formation of organic monomors within the pores. Supposedly these monomers segregate based on charge/polarity and \"darwinian chemistry\" takes over. Eventually once there are proto-cells, most likely ",
"RNA would initially act as the hereditary material",
" and as ",
"Ribozymes",
". How proto-cells initially before binary fission when still trapped in micropores is currently unexplored. Perhaps they didn't develop replication until later on, like I said, it's a relatively unexplored question. Eventually though, they escape the \"cradle turned jail cell\" and eventually divide. Voila you've got life. Remember, it's taken a long time to get to highly regulated cell divison and metabolism, so these early forms of life might not strictly fit the \"common set of characteristics associated with life.\" (I abhor the notion that life has a definition that is constrained within our narrow understanding of the universe.",
"The same thing as I described in the hydrothermal vent situation happens in the clay crystals except that the monomers formed previously/elsewhere and were then trapped in clay crystals. They eventually escape the crystals and voila you've got life.",
"Strategolegend answered this well, though I might add that aside from genetic similarity, plants, animals and fungi share similar ",
"endosymbiont plastids",
" which have their own DNA. The fact that eukaryotes have ribosomes (A Riboenzyme multicomplex that translates mRNA into proteins) and that they are similar to those of prokaryotes also indicates we have a common ancestor. ",
"Basically there is no easy answer to this question. Most people say no, there was one start that gave rise to all life. This is not only parsimonius but supported by evidence that we (all life) are all derived from a common ancestor. However, early evolution has been proposed to be alinear, that is, ",
"different from the typical \"tree-of-life model\"",
". I will now speculate (stop reading here). Darwinian chemistry is not linear either, it is the idea that multiple instances occur one after the other until a stable quantity of chemical is formed and another reaction down the line towards life becomes favorable. When you are in the gray area of chemistry/biochemistry, it seems logical that multiple starts occured, but that only 1 or two actually resulted in dividing cells. Remember that it only has to happen once for the whole game to start.",
"Hope this answers your question and gives you 10 more to ask. Any mistakes in this discourse crept in after submission and are not the fault of the panelist."
] |
[
"A note regarding the speculation at the end: in early protolife, it is possible that multiple \"start\" events happened, including some mixing of early genetic materials. However, ",
"phylogenetic tests of all existing life",
" strongly support the idea that there is one universal common ancestor, making multiple ancestors exceedingly unlikely. So, if there were other start events, they did not persist to the present as separate lineages. This is what last universal common ancestor means.",
"To be perfectly clear, I am not in disagreement, but I thought some clarification would help."
] |
[
"thanks. That is exactly what I was trying to say. There would be a period of \"trial and error\" just to create a cell, but once it succeeded one time. ",
"AKA, multiple start ups, one success."
] |
[
"Why boil water for (instant) coffee?"
] |
[
false
] |
I understand that coffee will dissolve faster in hotter water but I don't understand why people heat water to a scalding temperature, only to let it cool down again. Not only does it seem to be a waste of energy but a waste of time too. I turn my kettle off before the water boils so I use hot water with my coffee. This means I can drink it immediately, I don't waste time or energy and I never burn my tongue! Am I missing something here? Is it unhealthy to drink warm coffee?
|
[
"I don't think this is so much of a science question, but anyway :) ",
"You should never really use boiling hot water for even normal coffee, as it scalds it and can give coffee a burnt flavour. Instant Coffee, is really just coffee which has already been steeped and dehydrated. There really is no need to use boiling hot water. ",
"Im sure there are a number of reasons people use boiling water",
"\n* They don't know better",
"\n* They want to add a colder liquid like milk or cream",
"\n* They arent drinking it immediately",
"\n* Some countries it may be a good idea to boil water before drinking it due to water borne pathogins and bacteria. "
] |
[
"More to the point, how else are you supposed to know when the kettle's ready? Sure you could build a super-fancy kettle with internal thermometers and some kind of blasted ",
" stuck to it that will scream at you when the water reaches the right temperature … or you could just wait for the whistle."
] |
[
"We have no problem with our drinking water, but I have been to some countries where I would definately not drink any tap water without boiling it first! Also when i've been camping/tramping, taking water from a stream you ",
" boil the water even though you only have instant coffee :)"
] |
[
"Can bird flu spread through eating infected chicken?"
] |
[
false
] |
Just curious how the transmission of this disease works.
|
[
"No human bird flu infections have been reported from proper handling of poultry meat or from eating properly cooked poultry or poultry products.",
"—",
"CDC: Avian flu transmission",
". Can I get avian influenza from eating poultry or eggs?",
". No. Poultry and eggs that are properly prepared and cooked are safe to eat. ",
"—",
"USDA Questions and Answers: Food Safety and Avian Influenza"
] |
[
"Idk man, campylobacter food poisoning is like a week of bloody diarrhea and vomiting, but at the same time people mostly recover on their own (or with antibiotics if it’s really bad) and the chance of death is incredibly low (.03%). Meanwhile, the current H5N1 strain of avian flu that’s going around in flocks has something like a 60% likelihood of death in humans when it’s been transmitted. ",
"Personally, I’m gonna take a week of bloody diarrhea over a 60% fatality rate."
] |
[
"Also think it is worth pointing out that bird flu wouldn't even be the worst thing you can catch from improperly cooked chicken meat or eggs. Dying a painful bloody diarrhea death is probably worse than bird flu"
] |
[
"Why are modern birds dinosaurs and not fish?"
] |
[
false
] |
I've seen it said many times (eg ) that modern birds are dinosaurs. But couldn't the same be said that all vertebrates with lungs are fish? What are the rules about whether descendant groups get excluded from a classification? Is this what's meant by "paraphyly"?
|
[
"This is a good question, and something that I very often see confusion about. The main issue here stems from the disconnect between technical, scientific names for groups of organisms and general English words. Pretty much all modern taxonomists agree that scientific naming conventions should reflect evolutionary history. So scientists try to place organisms into consistent groups composed of a common ancestor and ",
" of its descendants (i.e., monophyletic groups or clades). Groups that don't meet these criteria are either ",
"paraphyletic or polyphyletic",
" (the distinction between these two isn't important for your question). If it helps your to visualize this, then ",
"this figure",
" from Wikipedia is pretty good.",
"So, since birds evolved from within dinosaurs, a monophyletic definition of dinosaurs must include the most recent common ancestor of the group and ",
" of its descendants including birds; this makes a group that contains only extinct dinosaurs but no birds paraphyletic. However, the reason this is fairly easy to get across is because both the English words \"bird\" and \"dinosaur\" correspond well to specific scientifically defined clades (Aves and Dinosauria respectively). This becomes much trickier when discussing groups where there is a larger mismatch in the language used. The English word \"fish\" refers to a large number of aquatic vertebrates (and is even confusingly used for some invertebrates, e.g. starfish), but in this sense it corresponds to a paraphyletic group. If you look at ",
"this phylogeny",
", it's clear that tetrapods (i.e., land-living vertebrates) evolved from within fish in the same way that birds evolved from within dinosaurs.",
"To be clear, there's no issue here if we stick to using rigorous scientific terms. Tetrapods are a subset of sarcopterygiians, which are a subset of osteichthyans, which are a subset of gnathostomes, which are a subset of vertebrates, etc. Translating these terms to their common English equivalents is where I think a lot of the confusion on this point comes from: four-limbed land animals are a subset of lobe-finned fish, which are a subset of bony fish, which are a subset of jawed fish, which are a subset of vertebrates. This is the tricky part; we need to resolve the fact that the term \"fish\" as commonly used is paraphyletic. In the bird/dinosaur case, this is easy. Just count birds as dinosaurs, making dinosaurs monophyletic again (thus matching their scientific definition, which was always monophyletic anyway). When doing this with fish though, we run into a linguistic problem. If we decide to make fish monophyletic again by counting all tetrapods as fish, then we have synonymized the terms \"fish\" and \"vertebrate\"; they both refer to the exact same set of organisms.",
"Personally, while I believe it's very important to stick to monophyletic groups for serious scientific discussion, it's also clearly useful to have words that refer to some paraphyletic groups too. Replacing the English word \"fish\" with something like \"non-tetrapod vertebrate\" is obviously not going to catch on. In summary, I don't really think there's anything wrong with saying that birds evolved from fish, but since fish is not a rigorously defined scientific term people are likely to disagree or be confused. If you really want to discuss this kind of topic seriously, I think it does help to use the technical terminology to make sure everyone's on the same page."
] |
[
"Technically birds and all tetrapods ",
" fish in the cladistic sense. Incidentally, apes are in fact monkeys for this same reason, so the next time someone gets pedantic with you about this, you can get even more pedantic back at them",
"But \"fish\" is often used as a term for what's called a \"grade\". This is often used for a cluster of paraphyletic organisms which share certain characteristics and are often discussed as a group, but which aren't necessarily all closely related. It's mostly used for convenience rather than treated as a proper grouping. ",
"So why do we say \"birds are dinosaurs\" and not \"birds are fish\" (at least, not nearly as often?). Well, there's a couple reasons. First, there's no push to use \"fish\" to refer to traditional fish + tetrapods(reptiles, mammals, etc) because we already have a word for that group....vertebrates. That means people are mostly content to leave fish as a grade. There's no equivalent for dinosaurs + birds, so we just use dinosaurs for it all. ",
"Also, in a less technical sense, when you get right down to it, birds aren't really any more of an unusual group of dinosaurs than bats are an unusual group of mammals, and nobody wants to split bats off into their own thing. It's only because all the other dinosaurs were extinct and were discovered separately that we think of them as different, just like it might take you a while to connect living bats with other mammals if all you had from the rest was the bones of elephants and rhinos."
] |
[
"The main disconnect is between Linnaean Classification and modern cladistics.",
"From my own experience, even ~10 years ago the Linnaean system was the only one taught in my country's equivalent of High School. Cladistics weren't even mentioned once, even though they are of crucial importance to our modern understanding of evolution."
] |
[
"How far apart are raindrops vertically?"
] |
[
false
] |
On average, how long before 2 raindrops hit roughly the same spot one after another? I guess what I'm asking is, what is the average rate at which raindrops fall? If I place a raindrop sized object under a raincloud, how many raindrops will land on that object in 1 second?
|
[
"Using Google",
", let's estimate a raindrop is 0.2 cm in diameter, giving a volume of 0.034 cm",
" Rain is going to fall on some area of land. For now, say the area is a container 1 cm x 1 cm. Thus one raindrop landing in the container will raise the height by 0.034 cm. If the container filled up 1 cm in 1 hr, the average rate of raindrops was",
"1 cm / 0.034 (cm/raindrop) / 1 hr ≈ 29 raindrops / hr = 0.5 raindrops / min = 0.008 raindrops / s.",
"Now assume the raindrop is always traveling at terminal velocity. ",
"This table",
" gives us about 6.5 m/s = 650 cm/s. The raindrops will be spaced such that only one lands every 125 seconds (the reciprocal of the above rate). Thus one raindrop will be",
"125 s * 650 cm/s = 81250 cm = 812 m",
"away from the next.\nSo inside a 1 cm by 1 cm area, the rain will be spaced 812 m apart.",
"If you increase your \"search\" to an area of, say, 1 m x 1 m, you would find",
"1 cm / 0.0000034 (cm/raindrop) / 1 hr = ... ≈ 80 raindrops / s. Then the vertical spacing between raindrops anywhere in this area would be",
"0.0125 s * 650 cm/s = 8 cm. ",
"So as you look further out, the spacing gets smaller, which makes sense. Imagine if your search was in a very small area. What are the odds that another raindrop will fall in exactly the same place? It would probably take a long time. And in a very large area, you can imagine that somewhere two rain drops have to be hitting the ground at almost the same time."
] |
[
"Exactly the answer the question deserves - thanks for working it out for us!"
] |
[
"Double checked ",
"/u/I_hate_usernamez",
" and they're on the money. He's my estimate with slight different numbers. A medium rain gives about 5mm per hour. Let's use a drop size of 2mm and a drop speed of 10m/s.",
"Dividing the volume of water per second by the volume of air and the volume of a drop gives around 4 raindrops passing through each cubic meter air volume per second.",
"Note that each raindrop, if randomly distributed, is around 60 cm away on average from the nearest neighbor drop.",
"If our target is a 1cm x 1cm patch of ground, then we get 4 times 10 m/s times 1cm",
" = .004 drops per second over that patch. Invert this and we get an average of 4 minutes separation between drops. This gives a vertical displacement of about 2,500 meters.",
"Rainclouds are about that high up. This means that drops which hit the same spot on the ground have either just formed or not yet formed in the cloud compared to their falling cousins. In heavier rains, the both drops will likely be falling at the same time."
] |
[
"How do we forget?"
] |
[
false
] |
Warning, stupid question inbound. Does the human brain actually completely erase a memory when we forget something? Or does the thought/memory just go to a part in our brain where we cant access it? Sorry if this makes no sense, I am not a smart man.
|
[
"Great question, not stupid at all.",
"When I first read the question, my first thought was \"Well you tell me how we remember things, and I'll tell you how we forget them\". Meaning that it's hard to explain how a process is reversed if we don't really know what it is to begin with. I really should have my girlfriend answer this, as she's the memory expert (not a joke, she works on cellular mechanisms of memory). But here is my approach.",
"There are two basic possibilities:",
"1) Memory formation in reverse. Our very best bets about memory formation is that it revolves around the connection between neurons strengthening. In an extremely simplified view, for example, every day you place your keys on the kitchen table when you come home. This means that over and over the neurons that code for <your keys> and <your kitchen table> are activated at the same time. This causes any connections that happen to exist between them to get stronger, that is to say that the <your keys> neurons can cause the <your kitchen table> neurons to become active, and vice versa. Then you try to remember where you keys are. This actives the <your keys> neurons, which in turn activates the <your kitchen table> neurons, and boom, you think \"On the table\".",
"So one hypothesis is that forgetting is the reversal of this association. That the <your keys> neurons no longer can activated the <your kitchen table> neurons. This process of \"deconnection\" may just happen due to time, or more likely, because the repeated co-activation of the two population of neurons has stopped. That is to say, the <your keys> neurons fire, without the <your kitchen table> neurons being active, because, for instance, you're putting your keys on a keyhook now. This then causes active process to start, which reduce the strength of the connection.",
"2) Failure to recall the memory. We've known for a long time that people can often have memories stored in their brain, without the ability to actively recall them. Situations where someone will swear they don't know something, but if you ask them to guess, they will guess correctly. Think of it like a filing system, where the file is a memory. It works if you know where to find each file, but if I forget how to find each file, the filing system is useless, even though all the files are still there. We know the brain is capable of this kind of mistake, but does it play much of a roll in forgetting? Some people say so, and there is some evidence for it.",
"In reality, I believe the evidence points to 1) more strongly. It also suggests that continuing to remember things is an active process. That is, one the memory is formed, it is not set in stone, and it needs to be actively kept. On the other hand, we know that memories than have been \"forgotten\" can be reactivated very simply. Meaning that even after you forget, there are still traces of the memory there, somehow written into the structure of the brain. (Curiously, when you re-activate one of these forgotten memories, they are incredibly sensitive to being altered or erased)"
] |
[
"There is no evidence for this.",
"Well, obviously, I would disagree,. I would say there is a vast amount of ",
" for this. Is there ",
" of this? No. But evidence: there is truckloads. Most tellingly, there stuff coming out of Tonegawa's lab in the last 2 or 3 years. And of course the work by Nabavi et al., this year.",
"Also what part of the neuron stores the actual 'memory'? Is it the DNA or the electrical frequency :-)",
"Neither, obviously. And I'm honestly not trying to be a dick here, but the fact that you ask that question, in that way, kind of reflects that you aren't really very well informed regarding neuroscience. Which is totally fine, not everyone can be. But perhaps you would be better off asking questions, rather than asserting facts in this case.",
"Switching on, switching off (binary?) and linking neurons together, does not actually create a picture in the minds eye.",
"Citation Needed.",
"What process do neurons perform when you just imagine where your keys are?",
"They integrate charge and fire action potentials and release neurotransmitters.",
"Also, if this WAS the actual way that memories are formed and stored, then you would need far far more than 86 billion neurons to store all of the sensual information that even a very simple life would throw at a person!",
"Citation needed.",
"If memory was neuron related then please explain the recent experiments of primate recall v human recall.",
"Working memory doesn't rely on the same process as long term memory, so it's not especially relevant in this discussion.",
"Looking through your post history shows that we have very different views on the mind. I believe, because of the vast amount of scientific research dating back to the 17th Century BC, that the mind is the product of neural activity. You are of course welcome to disagree with that, but I feel it is disingenuous of you to come to a scientific forum and make statements of fact based on things which are not the result of scientific method."
] |
[
"It would be, if that was the only evidence. However, we also know that if you damage areas of the brain the are believed to code for the perception of a sense (i.e. the same areas that are activated when the perception is had) then the person can no longer perceive the sense. Likewise, if we activated the area artificially, then the person was have the perception. Thus these areas are necessary and sufficient.",
"But at this point that I have read what you have written in other subs. If you believe that the brain is basically an antenna for signals that are undetectable by modern physics, so long as you believe that the regions of the brain have specific functions, then I can not refute that. If you believe senses come into the brain, and then are transmitter via an undetectable signal to a higher dimension, from which returns signals are sent, again via undetectable signals to the the brain, I cannot state that this is not the case.",
"I would simply say that no current theory in neuroscience needs such phenomena, nor is there any evidence for it (i.e. neurons behave in a deterministic fashion depending on their input).",
"However, if you wish to believe that this occurs, I plainly cannot convince you otherwise."
] |
[
"How are the digits of PI actually calculated?"
] |
[
false
] |
How do we know that what we've calculated is correct? This Wikipedia page states that so-and-so of years past has calculated X digits of PI, but only Y are correct. Is there a formula for calculating the digits of PI? If so, is it something I can sit down and do on paper? This is the Wikipedia article I'm referencing above:
|
[
"Is there a formula for calculating the digits of PI? If so, is it something I can sit down and do on paper?",
"Yes and yes. There are a few formulas for calculating π actually. One of the simplest is really simple, called the ",
"Leibniz Formula for π",
":",
"π = 4/1 - 4/3 + 4/5 - 4/7 + 4/9 ...\n",
"This is not a particularly good way to calculate π because it converges (gets closer to π as you add additional terms) slowly compared to other methods, but it will serve to illustrate. (The wiki page I linked states that it takes ~5 billion terms to get 10 correct digits!)",
"How do we know \"how close\" we are to π after a certain number of terms? Well, each term is smaller than the last, and they alternatve adding/subtracting. So we know that π must be between the nth and (n+1) term.",
"For example, the first value is 4. The next is 4-4/3 = 7/3. So after two terms, we know that π must be between 8/3 and 4. The next term gets us to 8/3+4/5 = 52/15. So now we know π must be between 8/3 and 52/15.",
"As we add more terms, the digits of your bounds to π start to \"stabilize\" from the left. Once a digit has stabilized (because additional terms are too small to alter it), we are ",
" that that digit is correct.",
"Of course you might want a formula that converges faster, ",
"here's a write-up of various alternatives",
"."
] |
[
"Someone else has said ",
" we calculate digits, so I'll focus on how we CONFIRM such digits. I have actually worked on methods of calculating Pi in the past using computers, so if anyone is interested in different methods I can elaborate! ",
"When they say they calculated X digits and Y are correct, they're usually using some regular method to obtain those X digits. For example, the big news story about google recently breaking the record to celebrate Pi day. ",
"But the obvious question is, how do they know they're right? If they're calculating digits we didn't know before, how can they ",
" that? ",
"There are calculations that find the ",
" of Pi, aka all the digits. There are also formulas called \"Taps\" that give you ",
" digits of Pi. For example, it will tell you the 50th digit of pi, but none of the others. However, this is an inefficient way to calculate ",
" digit individually. ",
"Instead, if they find X digits, they use a \"Tap\" to confirm the last digits. You can be relatively sure that if the last 10, 20, etc digits are correct, the rest must be correct too. If there was some error in your calculation, it would grow out of control as time goes on."
] |
[
"You can watch someone doing it by hand here:",
"https://www.youtube.com/watch?v=HrRMnzANHHs",
"Matt Parker (The Standup Mathematician) is worth a watch, his channel tends to show serious mathematics with a humourous (and usually understandable to the novice) slant."
] |
[
"What will happen to the cores of planets during the \"heat death\" of the universe?"
] |
[
false
] |
I have a rudimentary understanding of entropy; heat transfers from a hotter object to a less hot object, eventually there will be an equilibrium temperature between the objects. The universe will reach that equilibrium in the future as well. So here's the question, with all the heat created by pressure at the core of a planet, will that heat bleed out or will cores remain molten? Or am I just misunderstanding what astrophysicists really mean by "heat death" or "big freeze"?
|
[
"There wont be any planets left when heat death finally occurs. There are several stages of metamorphosis, including the ",
" which ends with near complete nucleon decay (no more atoms), the ",
" which ends with all matter being bound to black holes and the ",
" where all black holes have evaporated and the unverse consists of loose photons, neutrinos, electrons, and positrons.",
"http://en.wikipedia.org/wiki/Future_of_an_expanding_universe"
] |
[
"Would it be fair, at that end point, to assume the universe has reverted to its state when the big bang occurred? Granted this assumption would imply that time did in fact exist prior to the big bang, even if in an infinitesimally small scale. ",
"This ultimately sounds like the potential playing grounds of a new big bang. Now, to back my position somewhat, there are some who believe that at the time of or prior to the big bang there was an equilibrium of energy. Such that all positive energy was equal to negative energy (I am greatly reducing this to layman's terms), but at some point that equilibrium was shaken resulting in a cataclysmic change that burst forth with new (how should I put this...?) forms of energy.",
"To round this off in plausible terms, let's assume for a moment that our idea of time is flawed, would it be possible that our universe formed within the confines of a previously \"dead\" universe? I may be greatly overstepping the boundaries of scientific theories that I am completely ignorant of."
] |
[
"Our entire idea of time revolves around two main concepts, which are the \"arrow\" of time (past and future within a reference frame), and the idea that time is actually another dimension of the universe which we can measure events against. ",
"In our mathematical model, we have no idea what the \"universe\" looked like before it came to be. The reason for that is we define the universe as spacetime as we know it, which didn't exist as we know it before its origin. This may seem redundant to say, but it's actually not; it is to elucidate the concept that our idea of \"time\" is contingent upon our current model.",
"What you're saying is entirely possible, but I think that it's actually unknowable; we are constrained within the boundaries of our own existence. ",
"On a meta-philosophical level, I think you may be able to say that there was a \"past\" existence prior to the formation of the known universe, but there is no scale available to give any meaning to that assertation nor do we have idea idea what that may have looked like."
] |
[
"If light always travels at the speed of light (perfect certainty in momentum), then how can it have a position?"
] |
[
false
] |
Light obeys the position-momentum uncertainty principle. Light always travels at the speed of light. Therefore, light never has a well defined position. But it's sunnier outside than inside. This seems like a contradiction. Where did I go wrong? Does it have to do with interference between various modes (each infinite in extent) that combine to form localized packets? I've googled/wikied this, but didn't find an answer (that I could understand). Thanks for your help.
|
[
"perfect certainty in momentum",
"This is incorrect. The momentum of a photon is",
"p = E/c = hf/c",
"i.e. the momentum is proportional to the frequency. A lower uncertainty in frequency means a higher certainty in position, and vice versa.",
"Technically, the distribution of the photon's wavefunction in position space and momentum space are related by a Fourier transform, which is where the uncertainty principle comes from."
] |
[
"Photons don't have positions. It's entirely reasonable to say that until a photon is absorbed (or scattered, same thing in this context) it doesn't exist at all, except as a little bit of non-localized momentum. At the instant a photon is absorbed, it ceases to exist entirely. So it never has a position where it ",
" It only has a position where it ",
" at the instant it was absorbed."
] |
[
"Not at all, no.",
"You're probably thinking of gravity as if it were the same as electromagnetism. It isn't. Gravity isn't an interaction. It's geometry. Light (and here by \"light\" I mean a large number of photons considered together) propagates through spacetime. As such, the trajectories it follows are functions of the local geometry between the emission and absorption events. A ray of light — again, a large number of photons, all considered as a unit — propagates along what's called a ",
" which is a trajectory of zero proper time. In flat spacetime, these geodesics are straight lines. In curved spacetimes, they're curves. No big deal, and the uncertainty principle never enters into it."
] |
[
"Confused about basic physics: So photons are the electromagnetic force carriers. How exactly do they mediate the influence that a negatively charged particle exerts on a positively charged particle?"
] |
[
false
] |
[deleted]
|
[
"Confused about basic physics: ",
"So photons are the electromagnetic force carriers.",
"That is not basic physics! That is very advanced physics.",
"If you want an analogy, imagine two people on skates on ice, and one of them is holding a pillow, and the other person grabs the pillow and takes it, and they repeat this process. The skaters will move closer together.",
"But really, the fact that opposite charges attract with a 1/r potential will tell you everything you need to know about electrostatics."
] |
[
"Are you asking how the 'virtual photon exchange' picture can explain attractive forces? The simplistic picture of little hard spheres emitting other little hard sphere breaks down in that situation. There was a ",
"previous thread",
" about this. There are a variety of ways of thinking about it, each with their own problems. When physicists actually do these calculations, they don't think in terms of these simplistic pictures, rather just use the maths and see what happens. If you do this, the attractive force becomes apparent. "
] |
[
"charged particles are basically spewing photons and absorbing them all the time",
"This is another thing which is only a kind of loose analogy. What actually happens is that charged particles do what the maths says they do, and a good way of looking at this maths is to say that there are 'virtual particles' being emitted and absorbed in various places. This is the essence of ",
"Feynman diagrams",
". Note that the first sentence of that wiki article says they are a 'pictorial representation scheme for the mathematical expressions governing the behavior of subatomic particles', i.e. ",
" an explicit picture of reality. ",
"i still don't really understand how the charge of the particles changes the sign of the direction of the force in this picture.",
"That's because that article I linked to before is only halfway there on the maths. Also it depends what you mean by 'understand'. If you mean, 'work through some correct maths and get an answer', then physicists 'understand' attractive forces. If you mean 'have a simple and complete analogy', then I (at least) don't 'understand'. ",
"what is the connection between this and the force that a magnetic field exerts on a moving charged particle?",
"A charge has an electric field. If you stand still with respect to the charge, you see an electric field. If you now start moving, the Lorentz transformations applied to the equations describing the electromagnetic field tell us that you will now see a magnetic field as well (the electric field and magnetic field are the same thing really, it just depends on how you view them). ",
"This was a warmup to answering your actual question. I hope it's clear now that electric and magnetic fields are the same thing. So, if you're watching a charge moving in a magnetic field, and then transform to the reference frame of the charge, you'll find that ",
" the magnetic field looks like an electric one. We know that in an electric field the charge feels a force, so there you go. If you're watching a stationary charge in a magnetic field, and try to transform to the reference frame of the charge, you'll find that the magnetic field is ",
" a magnetic field since the two reference frames are the same. So that's why you need the charge to be moving in order for it to feel a force from a magnetic field (or, rather, you need the charge to have a velocity relative to the frame in which you view the field to be purely magnetic)."
] |
[
"Geoengineering's Affect on Ocean Habitats?"
] |
[
false
] |
I read the article on what would happen if Geoengineers released aerosol particles into the atmosphere to reduce global warming. I noticed that they mentioned the Rainforest, but they left out any other habitat. So, AskScience, what would happen to the coral reef and deep sea waters if this was to happen? Original article:
|
[
"In short, increasing CO2 levels in the atmosphere would still be terrible for Coral reefs. Ocean acidification will increasingly make it more difficult for marine organisms to precipitate their skeletons, and corals will be most affected. As far as the more diffuse light goes, I think this is bad for corals but am not positive. Hopefully someone who is more familiar with zooxanthellae photosynthesis could weigh in.",
"Without something to prevent ocean acidification, it is likely we will lose the coral reefs as a biome; we already seeing them replaced with algal mounds which are not as productive or diverse, and don't build the reefs up. In time, they will erode away. \nAs for the deep sea, I don't think the effects would be as dramatic."
] |
[
"The direct effect of increased aerosol particles would be small - slightly less sunlight reaching the surface of the ocean. The indirect effect would be huge because this would allow ever greater amounts of fossil-fuel carbon to be burned. The radiative effects of the increased greenhouse gases might be balanced by the aerosols (and its not even clear that they can maintain this balance) but the effects on ocean chemistry would continue as all the fossil-fuel carbon slowly dissolves into the ocean. There are no geo-engineering 'fixes' for an acidifying ocean. All organisms which use calcium-carbonate for their shells/structure (corals, mollusks, some types of phytoplankton) would be detrimentally effected. ",
"Corals are already being lost at an alarming rate. Just considering what is already \"baked in\" (or \"in the pipe\") regarding carbon emissions, it is unlikely that coral will exist anywhere outside of aquaria in 100 years."
] |
[
"It's often repeated uncritically that aerosol geoengineering will \"do nothing\" to prevent ocean acidification, but the reality is more complex.",
"We know from past volcanic eruptions that the diffuse light created by stratospheric aerosol injections can potentially promote productivity in the terrestrial biosphere, although there is significant regional heterogeneity (Gu et al., 2003; Mann et al., 2012). This is the first indication that there is more going on than just a simplified, decoupled ocean and atmosphere response. Clearly we need to look at the interaction of the carbon cycle between all reservoirs, including the terrestrial sink.",
"When we do this using relatively simple (Earth system) models, we find that indeed the response from the terrestrial biosphere is very important in looking at the effects of aerosol geoengineering on ocean acidification (Matthews et al., 2009). What we see is that the lower temperature and increased carbon uptake by the terrestrial biosphere actually slows pH decrease a little relative to a non-geoengineering scenario (but has no change on aragonite saturation levels). Other experiments suggest that this increase in terrestrial carbon uptake might occur due to decreased higher latitude heterotrophic respiration and increased tropical productivity (Tjiputra and Otterå, 2011). These experiments indicate that while the cooler ocean waters are more soluble to atmospheric CO2, this is largely offset by a reduction in the ocean-atmosphere CO2 partial pressure gradient. ",
"It should be noted that these OA reductions are small relative to an unchecked emissions-driven scenario. ",
": Aerosol geoengineering may slightly reduce the rate of ocean acidificaiton due to increased terrestrial carbon uptake, but more study is needed. Even with geoengineering, ocean acidification is a serious threat to ocean life.",
": ",
"Gu, L., D. D. Baldocchi, S. C. Wofsy, J. W. Munger, J. J. Michalsky, S. P. Urbanski, and T. A. Boden (2003), Response of a Deciduous Forest to the Mount Pinatubo Eruption: Enhanced Photosynthesis, ",
", 299(5615), 2035–2038, doi:10.1126/science.1078366.",
"Mann, M. E., J. D. Fuentes, and S. Rutherford (2012), Underestimation of volcanic cooling in tree-ring-based reconstructions of hemispheric temperatures, ",
", 5(3), 202–205, doi:10.1038/ngeo1394.",
"Matthews, H. D., L. Cao, and K. Caldeira (2009), Sensitivity of ocean acidification to geoengineered climate stabilization, ",
", 36, 5 PP., doi:200910.1029/2009GL037488.",
"Tjiputra, J. F., and O. H. Otterå (2011), Role of volcanic forcing on future global carbon cycle, ",
", 2(1), 53–67, doi:10.5194/esd-2-53-2011."
] |
[
"When a newborn is flailing its limbs and moving around, is it consciously moving them or is it some sort of automatic function of a new human being?"
] |
[
false
] | null |
[
"It sounds like you're asking about some of the ",
"primitive reflexes",
". While they occur when an infant is conscious, they're involuntary. ",
"These reflexes disappear with age. They're understood to be inhibited as the brain develops (specifically the frontal lobe). Adults with disorders that affect the frontal lobes may exhibit primitive reflexes called ",
"frontal release signs",
"."
] |
[
"Here is something every new parent should lookout for as it is so neat.",
"At around 3 or 4 months of age a newborn will discover that it has conscious control of its arms and can make them move at will. To do this it will lie on its back and stare at the arm while moving it around. ",
"It is a fascinating process to watch happening."
] |
[
"We also tend to exhibit them in the last stages before death, they manifest as sheet pulling or grasping motions. It can be quite disturbing to watch even after you realise the movements are reflexive. "
] |
[
"Why does plaque build up on teeth, but not on oral piercings, such as lip rings/labrets or tongue piercings?"
] |
[
false
] |
[deleted]
|
[
"Plaque can and does build up on oral piercings, especially tongue jewelry. All jewelry, regardless of piercing location, should be cleaned regularly. Tongue jewelry can easily be cleaned while brushing your teeth. "
] |
[
"Teeth are porous and have uneven surfaces which it's easier for bacteria to adhere to (plaque is actually bacteria and their secretions) and harder to remove them from. If you look carefully you'll sometimes see plaque in the crevice formed where the ball attaches to the bar on oral jewellery, or if you want to gross yourself out, you can smell it. There is probably some plaque there, just not much. It would be rubbed off the smooth surfaces pretty regularly just by the movement of the jewellery in your mouth. "
] |
[
"No problem. "
] |
[
"Where is the electrical energy generated from power plants stored? Do they have like very big batteries of sorts?"
] |
[
false
] | null |
[
"Very little energy storage tech has been developed for city grid applications. Any electricity we generate, we must use immediately. Powerplants have been designed so that they are able to match as closely as possible the generation of electricity with the demand for electricity, reducing excess as much as possible. Typically this is done by coal or natural gas powerplants, as they are much faster at spinning up or slowing down generators than other types of powerplants."
] |
[
"I just want to correct you on one point. Hydroelectric is the fastest way to balance loads. Typically coal and natural gas respond in minutes, hydroelectric in seconds."
] |
[
"In the vast majority of the cases it is not stored. It is injected directly into the grid."
] |
[
"Is there a way to tell the difference between two atoms of the same element?"
] |
[
false
] |
Is there a way that a scientist could look at an atom, and then be able to tell that atom from any other atom of the same element? If so how? If not, why not?
|
[
"No. There is no difference. We know this because of quantum physics. Under quantum physics if you get the same state two different ways, you get interference. For example, if a photon goes through a slit on the right vs a slit on the left and ends up in the same place either way, it creates an interference pattern. But the end state has to be exactly the same. If you have some detector change based on which slit the photon goes through, there will be no interference.",
"If you have two of the same particle, and you swap their positions, it will interfere with the original state. This shows that they're the same state. If you switch the particles, the system isn't just too similar for us to tell apart with current technology. It is literally exactly the same."
] |
[
"The only way to distinguish two atoms of the same element is, if they are not build in the same ways.",
"1.) if they are different isotopes (i.e. one of the atoms has more neutrons than the other, like in ",
"radiocarbon dating",
")\n2.) if they have a different amount of electrons (i.e. one of the atoms is positively or negatively charged)"
] |
[
"You're basically right. The only differences I can see is if there one is an isotope of another, for example U-235 and U-238.",
"Other than that, the only other differences would be differences in position or velocity or temperature, which aren't really differences than one couldn't change.",
"But for two atoms with the same oxidation number (ie same number of electrons), same number of neutrons and same kinetic energy / temperature there is no difference other than their position."
] |
[
"Do scientists need to know the amount of an isotope present initially when doing radiometric dating? If so, how do they know?"
] |
[
false
] |
Hi everyone, this may be a dumb question, but I'm curious as to how we know what the amount of Carbon-14 was thousands of years ago? I've never considered this before, but I was speaking to a friend who is a YEC, and he gave me this analogy - "Radiocarbon dating is like coming in a room, finding a burning candle, and measuring how fast the candle burns. The problem is that even if we know how fast the candle burns, we don't know how tall it was in the first place." Personally, I'm an atheist, and I don't doubt the veracity of carbon dating (I find it hard to believe this many scientists would not have considered this "problem"). That said, I really didn't know what to say to him. I feel like he is (and to some extent me, because I couldn't answer his question) either missing the point, or misunderstanding how carbon dating actually works. I know what a half life is, and know that they are constant. I also understand that we use other dating methods to verify and create calibration curves for radiometric dating. My question is, are scientists assuming that the levels of these isotopes have been constant? And if so, how do know? From what I understand, we measure the amount of these isotopes present, and since they decay at certain rates, that allows us to come up with an age. My (very limited) understanding also assumes that we would have to know how much was present in the first place. Is this true? BTW: I just want to make this clear, I am not a YEC!! This comes from a question posed to me by one; it was a question I did not have a good answer for.
|
[
"Yes, we have to, and we do that by measuring the amounts of stable daughter isotopes present. ",
"I use U-Pb a lot, because C",
" is useless for materials in the age range I study. So, what I look for is zircon crystals, which are a very tough and stable geological material. When zircon forms, it is a natural trap for uranium, which nomally cannot leak out. As that uranium (U",
" ) decays, it follows the decay chain to radiogenic lead (Pb",
" ). ",
"So - we measure the ratio of remaining U",
" to U",
" in the rock, and the ratio of radiogenic to non-radiogenic lead. "
] |
[
"Radioactive elements decay through a specific chain of isotopes, until they reach a stable isotope which does not decay. There is a specific chain for ",
"U",
" , there is another for ",
"U",
" - the former ends at Pb",
" & the latter at Pb",
" , all of which can be dosed with extreme accuracy and precision. ",
"The way the data is treated is ",
"thusly",
".",
"For a much more detailled account of how this works out in the lab, see",
"Stern, R A, 1997, Radiogenic age and isotopic studies: Report 10; by Geological Survey of Canada; Geological Survey of Canada, Current Research 1997-F, 1997; p. 1-31, doi:10.4095/209089"
] |
[
"Your friend is right in thinking C-14 levels have varied enormously through. As I wrote previously, there are several factors that are responsible for that, and all the known ones are taken into account when using radioactive dating. That's (one of the reasons) why C-14 dating has gotten more and more accurate. Let's say we try to date something and we consider that C-14 concentration has been constant through ages. We'd get one figure. ",
"Then, we add the known supernovas. We get another figure. Then, nitrogen and carbon concentration through time as calculated from other souces (such as air bubbles in Antarctica). Another figure.",
"We keep adding data as we discover it and each time we get a more refined figure.",
"As far as we know, the half-life of C-14 and every radioactive isotope has been constant. There has been no perceptible change since we started measuring it a century ago. "
] |
[
"Where do elements heavier than iron come from?"
] |
[
false
] |
Since when a star begins fusing iron it dies, where do the heavier elements, i.e. copper, nickel, and so on up the table, come from?
|
[
"There are other nucleosynthetic processes that happen in nature. For example, the ",
"s-process",
", the ",
"r-process",
", the ",
"p-process",
", and the ",
"rp-process",
".",
"The s- and r-processes are responsible for producing most of the nuclides above the iron peak.",
"The rp-process happens on the surface of neutron stars, which have very strong gravity, so while heavy elements are produced, they don't really escape the neutron star, so they don't contribute to the abundances in the ISM.",
"And the p-process fills in a few gaps that both the s- and r-processes don't reach."
] |
[
"Technetium just happens to be the lightest element with no stable isotopes. It is produced naturally, it just decays quickly."
] |
[
"Is technetium a gap?"
] |
[
"Why are rainstorms frequently accompanied with lighting, but snowstorms/blizzards rarely (never?) have lightning?"
] |
[
false
] | null |
[
"Lightning requires energy. Lots of static electricity and heat to generate the charge differential that leads to lightning. Temperature difference between ground and air can do it, too.",
"Snow storms happen when it is cold. Meaning not as much energy source for lightning. When it does happen, it is called thunder snow."
] |
[
"Former meteorology major here. Lightning requires high cloud tops for a greater electric potential. These higher clouds typically occur with more potential buoyancy, meaning warmer temps down below and colder temps at higher altitudes. More water vapor also increases the buouyancy of air, and allows clouds to grow larger. In warmer months there is a lot of water vapor for added buoyancy and cloud formation, and a lot of potential heat energy at the surface for massive updrafts. Due to the latent heat of all the water vapor, clouds can rise for miles and still be warmer than the surrounding air as they condense. In the winter however there is less water vapor, and way less buoyancy because the surface doesn't have nearly as much heat energy available. The rate at which a parcel of air would cool as it rises is too high (it would start sinking again as the air around it would be warmer) before it got remotely high enough to make a cloud that can produce lightning. ",
"However, in rare conditions (this is starting to happen more frequently though with climate change), such as in snowstorms that have more moisture available, and with extremely cold temperatures aloft in some intense low pressure systems as well as lift caused by other factors, it can be below freezing at the surface and there is still enough buoyancy to make thunderstorms. Sometimes there is also a warm jet of moist air aloft that thunderstorms can grow on top of, while the bottom mile or so of an airmass is well below freezing, say if a shallow cold front came through. Warm rain can also fall into this cold air during a winter thunderstorm and turn into thundersleet, thundersnow, or graupel (soft hail). I've even seen a few winter snowstorms where there was large hail and heavy snow falling at the same time.",
"Hope this wasn't too dense but you get the idea :)"
] |
[
"I was snowboarding a week ago in minnesota during our record blizzard. The lightning lit up the snow so brightly."
] |
[
"A question about lab goggles, need help with comfort and sizing"
] |
[
false
] |
I'm currently working with an Arduino board and I have a project that requires some sort of goggles to fit certain expectations. Ideally the goggles need to be comfortable as they will be worn for long periods of time I would prefer goggles with a flat front Do they sell large goggles? i have things that need to attach to that flat front surface and a big area would be great I think im looking for those flexible ones that entirely cover the eye area, to protect from fumes Anyone have any suggestions or resources to help me sort through all those lab equipment sites? Brand names? Keywords? tl;dr im looking for lab goggles that are comfortable and large in size with full coverage, thanks AskScience!
|
[
"You can indeed find large goggles. I'd advise going to the nearest lab, trying on their goggles, and ask where they got the pair you like best.",
"On a side note, unless you are doing something really odd, Arduino work shouldn't require eye protection. Just don't jam the soldering iron in your eye."
] |
[
"Ah I should have clarified, the goggles arent for protection.",
"They are going to have Arduino components attached to them!"
] |
[
"In that case, I wouldn't go for lab goggles, but some \"fashion\" goggles. I see a lot of teenagers with bug-eye goggles on their heads, and I assume they're coming from somewhere. Probably the same place as steampunk goggles.",
"And just what are these goggles going to ",
"? "
] |
[
"Do dark surfaces contribute to climate change?"
] |
[
false
] |
Dark surfaces meaning asphalt-paved roads, dark roofs, &c.
|
[
"Yes. They absorb visible light and re-emit the energy as infrared light, which is absorbed by greenhouse gasses. Lightly-colored surfaces, on the other hand, reflect more of the incoming visible light back into space, so that energy doesn't have to find its way through the greenhouse gasses (as they are transparent to visible light). ",
"For this reason, the melting of sea ice creates a feedback loop. Sea water absorbs a great deal of incident light, especially compared to ice. As the ice melts, the Earth absorbs more of the energy from the Sun, which warms the Earth, causing more ice to melt, causing more absorption of energy from the Sun, etc. This is not the only feedback process involved in the climate (some are positive feedback loops while others are negative), but it is an important one. A negative feedback loop that works the same way is that a warmer Earth leads to more water evaporation, which leads to more cloud formation, which leads to more incoming sunlight being reflected away, thus cooling the Earth back down. How strong each of these various feedback loops is is one large source of uncertainty in modelling the future of climate change. (I want to be clear, though, that uncertainty in modelling the future is not the same as uncertainty in what is causing climate change - carbon dioxide originating from human activity is responsible for increased global average temperatures in the last several decades.)",
"We can see this effect in other planets as well. ",
"Venus reflects an incredible 77% of all the light incident upon it",
" (compared to Earth's 30%). Venus actually absorbs less energy from the Sun than Earth does, even though it's closer to the Sun! Yet Venus is hot enough that the first several probes sent there melted. Why? Venus has a thick atmosphere, dozens of times as dense as Earth's, and it's almost all carbon dioxide, so that Venus is extremely inefficient at re-radiating the energy it receives from the Sun. The greenhouse effect is strong enough to turn the 23% of sunlight that isn't reflected by the clouds into a hell-scape. "
] |
[
"Yep. They would basically act like ice patches that don't melt. In a compounding effect, white roofs in hot environments also mean less electricity is used for cooling, meaning less heat is generated ",
" less greenhouse effect generally."
] |
[
"Would it make a signifiant difference to the earth's energy balance if all roads and roofs in the world were somehow made white? "
] |
[
"Why aren't men and women the same size?"
] |
[
false
] |
Largely, I mean.
|
[
"\"Why\" is always a difficult question to answer - is it \"what mechanisms causes this phenomenon\" or is it more \"what is the benefit of this phenomenon\"?",
"In nature we can see that there are examples of vast differences between sexes (for instance male polar bears and gorillas can be 3 times as large as the females [but there are also species with larger females]). In higher animals many of the differences in appearance are related to reproduction. For instance, as one male can reproduce with many females, it is beneficial to have successful male offspring - which entails strong and large males.",
"Most of the observed difference is explained by genetic factors (although some researchers suggest that there are significant social factors for humans [e.g. that women are taught to eat less], but that is probably mostly ideologically motivated). Testosterone levels strongly affect muscle mass and differ significantly between males and females. Both estrogen and testosterone also have clear effects on bone mass"
] |
[
"While it is true that most societies have an approximately equal sex ratio, this is not because it provides a balance between optimal protection and resource allocation. It simply boils down to the fact that when there are more women in a society, it is evolutionarily advantageous to produce male offspring (more potential mates and less competition for those mates) and vice-versa. Over time, these selection pressures will balance the sex ratio. ",
"In terms of the evolutionary advantage of size dimorphism between men and women, it may simply boil down to sexual selection. In our evolutionary past, women may have preferred bigger, stronger men as they may have been able to protect and provide for offspring better. As women selectively mate with bigger and stronger men, those genes get passed on and the smaller men don't get to reproduce and pass their genes on. Men could also put selective pressure on women through their mate choices as well, though sexual selection is often driven by \"choosy\" females. "
] |
[
"\"what mechanisms causes this phenomenon\"",
"This would be \"how\" would it not?"
] |
[
"What if there is no quantum description of gravity?"
] |
[
false
] | null |
[
"Then things are extremely weird, because every other force of nature is described quantum-mechanically, but gravity isn't. I don't think any serious physicist considers this a possibility."
] |
[
"Right but physics in itself is extremely weird at the quantum level anyway, and physicists haven't found 95% of the universe, so clearly we are very early in our understanding.",
"",
"Is there any way to at least confirm gravity has quantum mechanical properties?"
] |
[
"Quantum mechanics is unintuitive to someone who's only experienced classical phenomena, but there's nothing illogical about it.",
"A universe where almost everything is quantum, \"stapled to\" classical gravity just doesn't make any sense.",
"Is there any way to at least confirm gravity has quantum mechanical properties?",
"Experiments have been done showing that a difference in gravitational potential causes a quantum-mechanical phase shift in cold neutron experiments."
] |
[
"Why does running water freeze at lower temps?"
] |
[
false
] |
Is there a temperature at which water will freeze no matter how fast it's moving?
|
[
"Flowing water has enough internal energy to resist crystallization. The water molecules are flying past each other, and so they are gaining energy from the jostling against the riverbed, each other, or their container. This gives them enough energy to remain above freezing temperatures."
] |
[
"The energy he's talking about is kinetic energy (the energy of motion). When you say that they are moving past each other too quickly to form intermolecular hydrogen bonds, you are saying that their kinetic energy is too high for the system to exist as a solid.",
"You're saying/thinking the same thing, just with different words."
] |
[
"It is due to the lack of nucleation sites for ice crystals. Same reason you can slowly chill a beer and then smack it on the counter and watch it all freeze over."
] |
[
"How does a genetic mutation propagate through the generations?"
] |
[
false
] |
I saw an article a while back about a Chinese kid who was born with weird eyes that let him see in almost complete darkness. I assume this is a mutation of some gene or genes that make the eye. How would that trait be passed down to his offspring? I figure that he would meet a woman with normal eyes and the baby would have a "watered down" effect since the mom was normal. As I understand it, this is how evolution works so how do you create a new type of eye that will become the norm for later generations?
|
[
"Genes don't get watered down, traits might.",
"\nThe genes are either passed on or not"
] |
[
"Genes are specific, discrete things. They're composed of discrete nucleotides.",
"A trait is often the combination of many, many genes.",
"When DNA is crossed through reproduction, genes are (more or less) chosen from each parent. Every gene in your body is more-or-less traceable to one of your parents (though your parents will have many in common and thus you wouldn't be able to tell).",
"Genes aren't watered down over time, but they can be removed if by chance they're not chosen in the reproduction, and the gene is taken from the other parent.",
"An example. Each letter is a gene, of which you have millions.",
"ABCDEF + AHIDJK -> ABIDJF",
"They aren't \"watered down,\" but not all of them are passed on. If you have multiple children, then they'll each receive a different half of your genes."
] |
[
"That makes a lot of sense. Thank you. I think I'll read some more information\nAbout it. "
] |
[
"Why is it that when I close my eyes tightly I hear a rumbling sound in my ears?"
] |
[
false
] |
Is there a name for it? What causes it?
|
[
"Pretty sure you're talking about ",
"Tensor tympani muscles",
", specifically voluntary control of."
] |
[
"Almost definitely right, but I think it's possible for it to be any muscles in the general area. If you hold your arm or fist up to your ear, you can even hear the rumbling noise from those when you tense up the muscles."
] |
[
"OH, YES. I have been wondering about this for so long, but I've had no idea how to ask the question without sounding crazy, just in case I'm alone. I can do it on the fly, so I had no way to ask. Thanks for answering, and thanks OP for asking."
] |
[
"Why do magnetic field lines leave at ninety degrees from an object?"
] |
[
false
] |
Apologies if this isn't worded too well. I'm taking physics in my final year of high school and we recently learned that in a magnetic field the magnetic field lines will enter and leave an object at ninety degrees. The only explanation I'm hearing is that 'it does because it does'. Is there any better explanation for this? Thanks for any replies.
|
[
"There are really two distinct cases to bear in mind:",
"In a magnetic material, like a bar magnet, the magnetic field is created by the material itself. The magnetic field lines don't leave it at always ninety degrees, it rather just acts as a dipole. ",
"The more important case is that of an electromagnet. Magnetic fields are created by movement of charge. When a charge (like an electron) is at rest you will experience an electric field from it. If it moves you will see a magnetic field. This field is always perpendicular to the direction the charge travels in. For example a normal electrical wire will have a magnetic field which curves around it if you pass current through it. ",
"Exactly which objects were you thinking about?"
] |
[
"Yes that's true. You can either derive the magnetic field from classical electrodynamics or do a lorentz transformation between the intertial systems of a point charge or a nearby current. Both yield the same answer.",
"As to why the field is perpendicular I can't really tell you. The is seldom a 'why' in physics, usually just a describtion. The magnetic field is described by the Biot-Savart equation, which tells us that it's perpendicular due to a cross product of the current and the vector pointing from the current to the point where you are examining the field. But it is really just a description of an experimental fact."
] |
[
"Why is the field perpendicular to the current? ",
"My understanding is magnetism is explained as \"normal\" electricity operating under Lorentz transform from special relativity. Do the maths and see currents behave as if there is a thing such as a magnetic field, so we just say there's one."
] |
[
"What is the most efficient way to learn? Can you teach yourself?"
] |
[
false
] | null |
[
"That's what I've ",
", but I'm thinking there just might be some science to it. "
] |
[
"I would also like to know this. I've got a hunch it has to do with dopamine and other related neurotransmitters during the learning process.",
"Like, if you enjoy music, and the process involves melody or rhythm, then you would be more responsive than just reading from a book.",
"Any studies on this avenue of learning. You should check out Ken Robinson's TED talk on multiple intelligences - that's what sparked my idea on this."
] |
[
"Learning is different for everyone, and some people learn with better methods than others. Some people can listen to a professor give a lecture on a subject and retain all the information. Some other people are better at learning with diagrams and visual aids, and may be better if they read about a subject. Others are best at learning by example, watching someone give examples in a subject and then giving some themselves.",
"There is no scientifically sound method of learning. We all learn better in different ways."
] |
[
"Why is it that animals, such as gorillas, can gain large amounts of muscle mass naturally. Whereas humans need to physically make an effort to \"get bigger\"?"
] |
[
false
] | null |
[
"Because humans and gorillas aren't the same species. Their muscles are adapted for force where ours are adapted for fine, precise control. "
] |
[
"I think he was refusing humans vs gorilla musclemass, not including the use of cars.",
"Even with cars it is a decent question, and here's why.",
"Gorillas live a VERY sedate lifestyle compared to humans. Very much like pandas if they were fiercely territorial. They find a nesting area do nothing but eat and sleep for a while, then trek a few miles rinse and repeat.",
"This gives rise to the question.",
"In all reality, comparing one animals to another in this manner won't give a specific answer. Genetic differences (biggest reason), lower amounts of the \"muscle stop\" hormone (which is still a genetic thing), they have a calorie weak but nutrient rich diet (humans are the opposite in current days), it could also be that their bodies have evolved to be optimal to their lifestyle. He have to our old lifestyle, but not our current, more sedated one.",
"Humans did not evolve to out run nearly any 4 legged animal by endurance over speed to simply to sit on a couch."
] |
[
"I think he was refusing humans vs gorilla musclemass, not including the use of cars.",
"Even with cars it is a decent question, and here's why.",
"Gorillas live a VERY sedate lifestyle compared to humans. Very much like pandas if they were fiercely territorial. They find a nesting area do nothing but eat and sleep for a while, then trek a few miles rinse and repeat.",
"This gives rise to the question.",
"In all reality, comparing one animals to another in this manner won't give a specific answer. Genetic differences (biggest reason), lower amounts of the \"muscle stop\" hormone (which is still a genetic thing), they have a calorie weak but nutrient rich diet (humans are the opposite in current days), it could also be that their bodies have evolved to be optimal to their lifestyle. He have to our old lifestyle, but not our current, more sedated one.",
"Humans did not evolve to out run nearly any 4 legged animal by endurance over speed to simply to sit on a couch."
] |
[
"What is this object in space?"
] |
[
false
] |
I'm currently on which allows you to see the milky way and local universe. I just randomly zoomed all the way in some where and saw What is it? It only shows up under visible light, at coordinates (-117.25,-11.55)
|
[
"Yep, that is an artifact from the optics. Maybe some combination of ",
"diffraction spikes",
" caused by the support beams holding up the secondary mirror and some ghosting effects. Could also be from improper flat field division. Look at the 3 images at the bottom of ",
"this page",
". A lot of calibration goes into producing a final science image. Raw images are often times ugly (uneven, littered with dust spots, riddled with oddly sensitive pixels, and scratched with cosmic rays)."
] |
[
"It looks very much like an image of a telescope mirror, which I ",
" could be caused by dust particles."
] |
[
"It's almost certainly an artefact from the telescope they used. Like how you see \"rays\" coming out of stars in some images."
] |
[
"How does centripetal force act to make the globe of death motorcycle stunt work?"
] |
[
false
] | null |
[
"For a motorcyclist riding inside the globe, the centripetal force is the normal force of the globe, pushing inwards."
] |
[
"What I don't understand is how a force that, from my understanding, pulls object inwards, seems to work to push objects outwards, like keeping the motorcycle glued to the outside of the ball, or a hammer throw. From the language used I would think that the force would be pulling the rider off the cage of the ball or that when a hammer thrower released the ball would then just come inwards and hit the thrower as opposed to actually being projected out and away. Does that explain my misunderstanding better?"
] |
[
"What I don't understand is how a force that, from my understanding, pulls object inwards, seems to work to push objects outwards",
"It's just uniform circular motion. Working in an inertial reference frame, there is no outward force. The force points inwards, so the acceleration points inwards. That's why the motorcycle curves inwards, and moves in a circular path. In this frame, there isn't any outward force."
] |
[
"Why does it seem like the Hubble Space Telescope can image distant galaxies with much better clarity than our own neighboring planets?"
] |
[
false
] |
It seems like HST photos of planets, when they exist, are incredibly blurry, grainy, or pixelated. Is it a focus thing? Is it just how incredibly massive those distant structures are, that they have a larger apparent size despite the vast distances? Or to put this another way, why don't or can't we use the Hubble for planetary science?
|
[
"I don't quite understand what you mean why you say that HST planetary photos are blurry. The photos of our solar system objects are outstanding, see ",
"this",
" as an example. Exposure times for Jupiter for example are about 10secs or so, so you are never going to spend orbits looking at a solor system planet. ",
"If you are talking about extrasolar planets that is an entirely different story. These planets are so far away that you are going to struggle to make out fine details since the details are smaller than the camera pixel size. The science done on these planets usually involves taking spectra of the planet and the host star to try and determine the atmosphere of the exoplanet. If you were to attempt to take spectra of these exoplanets using ground based telescopes you wouldn't be able to make out anything significant.",
"As for why galaxies appear clearer than exoplanets is very simply a numbers issue. While an exoplanet system might be much closer than a galaxy, the light from the star is many order of magnitude larger than the light from the planet. This is a result of the fact that the light from the planet is really light from the star that has been reflected. A simple estimate is that when an exoplanet passes directly infront of our line of sight with the host star, the overall light decreases by less than 1%. If the planet is to the side of the star the problem now becomes an exposure time problem, how do you take a picture of the planet without over exposing the star, whose light will cover up the planet. It is very tough to image exoplanets directly.",
"The HST is still used for planetary science, I'm not sure where you saw that it is not. Perhaps the majority of imaging by Hubble is not of planets but that is more due to the fact that most planets (excluding our solar system, which is extremely close compared to exoplanets) are close enough that ground based telescopes can obtain great results. ",
"As for your other questions:\n1. There are focus issues with Hubble, but nothing terribly important for planetary imaging."
] |
[
"For the same reason you can see a mountain from 10 miles away much more clearly than a grain of sand 50 feet away. The mountain is larger."
] |
[
"It seems like HST photos of planets, when they exist, are incredibly blurry, grainy, or pixelated. ",
"They are.",
"Is it a focus thing? ",
"Not for the most part. ",
"Is it just how incredibly massive those distant structures are, that they have a larger apparent size despite the vast distances?",
"Yes, to an extent. You can see andromeda as a smear in the sky, however you can only see mars as a pinpoint of light, and Pluto not at all. ",
"Or to put this another way, why don't or can't we use the Hubble for planetary science?",
"We do use it for planetary science, but taking photos of other planets is different than other galaxies. Exposure times need to be shorter because of relative motion, for instance. ",
"You can stare at a pinpoint in the distance for days and gather photons from those galaxies. You stare at a planet for days and you're going to see a weird smear of light. "
] |
[
"Is there a size limit to molecules? Could you theoretically have a hydrocarbon hundred of carbons long, for example? Thousands?"
] |
[
false
] |
[deleted]
|
[
"So some hundred or thousands is no problem. For example look at ",
"polyethylene",
", tehse are just straight hydrocarbon chains. The longest ones have a molecular weight of 5million which means about half a million carbon atoms.",
"So these molecules get unstable if they get longer. Right now I'm not sure about the right answer to why. IIRC (I have to find this in a book/lecture slides but I cannot remember where I learned it) it's because two orbitals in the same molecule aren't allowed to have the exact same energy. So with big molecules all the orbital energies get pretty close and then there's no more \"room\" for more orbitals and everything get's unstable."
] |
[
"So these molecules get unstable if they get longer. Right now I'm not sure about the right answer to why. IIRC (I have to find this in a book/lecture slides but I cannot remember where I learned it) it's because two orbitals in the same molecule aren't allowed to have the exact same energy. So with big molecules all the orbital energies get pretty close and then there's no more \"room\" for more orbitals and everything get's unstable.",
"I don't think that's true. The same happens in metals and metals don't become instable above certain dimensions. ",
"Back to topic. Most ",
"plastics",
" and ",
"elastomers",
" are just single molecules (+additives). Think about that when you change your tire."
] |
[
"Billions of a.a.s? Really?! The ones I've worked with are all just a few hundred.",
"But the DNA sequences encoding for these proteins will always be longer, given that each aa is encoded by a sequence of 3 nucleotides"
] |
[
"If helium balloons float upwards because it's less dense than air, shouldn't a container under vacuum also be lighter than air? Could you make an airship float using vacuum if you had a material light, yet strong enough to not collapse on itself?"
] |
[
false
] | null |
[
"Yes - and it's ",
"not a new idea",
".",
"The practical issue is that there's a big pressure differential between the atmosphere and the vacuum, and it's to support a balloon against that pressure, it has to be made of a very rigid strong material, which will be constantly under stress like a submarine. This is tricky to do while still keeping it light enough. If the shell is heavier than the displaced air, then you don't get any net buoyancy. So, there's no theoretical reason why it wouldn't work - it's just hard.",
"This is less of a problem with gas balloons (hydrogen, helium, hot air), because the gas inside provides pressure. So the balloon can have equal pressure on both sides, even if the gas is a different density."
] |
[
"Yes, but you don't gain that much.",
"For fixed pressure and temperature, the density of an ideal gas is proportional to its molecular weight.",
"For air, this is around 29 g /mol on average, for helium it's 4 g/mol, and for hydrogen it's 2 g/mol. A perfect vacuum has a density of 0 g/mol.",
"Buoyancy comes from the difference in densities. So the ratio of buoyant force on an otherwise identical airship filled with helium, hydrogen, and vacuum, is approximately 25:27:29.",
"As you see, you don't gain much buoyancy from using anything lighter than helium. Using vacuum means you need a much stronger, and therefore heavier, hull."
] |
[
"If we put this “vacuum balloon” in our atmosphere, the air pressure, which is 1 atm, converted to SI unit, would be 101kPa. So how much is 101kPa? 1 Pa (pascal) is a unit for pressure, by dividing force (in N, Newton) by area (in m",
" ), so 1 Pa = 1 N per m",
" . Then 101kPa should be 1.01 * 10",
" N per m",
" , under earth gravity, that close to the weight of 10306 kg or about 10.3 tons! Just imagine that much force! So it’s possible, but you would need a very very strong and very light material!",
"So let’s do some calculations! Say if you use a very light and strong material, graphene, with density of 2.267*10",
" kg/m",
" . With the air density bending 1.225 kg/m",
" , and the density of vacuum being 0, in order just for the ballon to reach the same density, the graphene can only be 1.225/2.267 * 10",
" , which is about 0.00054, or about 0.054% of the total volume!"
] |
[
"Do I need to be a scientist too read The Origin Of Species?"
] |
[
false
] | null |
[
"Oh thanks for telling me."
] |
[
"Oh thanks for telling me."
] |
[
"Not the right sub for such questions, but the answer is no, it is very accessible."
] |
[
"Is base 10 the right system to use?"
] |
[
false
] |
First off, I'm not much of a mathlete. By the time I got to 4th year (undergrad) differential calculus my brain had decided that was about all it could take and left the building. But a few nights ago I was reading a comic ( ) which has a scientist use a base of PHI ( ). The idea had never occurred to me that an irrational number could even be a base. However, it apparently can be. Fair enough. But one of the concepts the comic was trying to portray was that with this base numbering system shit starts to fall into place. I.E. It married the quantum and 'normal' systems so there wasn't any discrepancies, stuff like that. My understanding is that a base numbering system is just a representation of a concept. Not a concept itself (i.e. "A rose by any other name would still smell as sweet" sort of thing), so I didn't really buy into the idea that simply changing the base number system would make difference in mathematical results. However, like I said... I've never won any medals for math. So,
|
[
"does changing the base number system significantly alter any higher level math out there?",
"Absolutely not. Whatever your system, it just changes what you write, not what you mean. It is akin to asking if writing it in French changes the story of a book."
] |
[
"We routinely alter the number base to make certain types of math easier. For instance, Boolean is Base-2 (logic math), Hexadecimal is Base-16 (computer addresses), Radian Math Base-Pi (circular math), Duodecimal is Base-12 (time and lots of British Units), Babylonians used Base-60. ",
"So to answer your question, yes we routinely use different number bases to simplify math, but they are very difficult to implement on a very large scale (i.e. it's very hard to change the way a whole society counts)."
] |
[
"Is base 10 the right system to use? ",
"There's no ",
" right base. ",
"Just convenient bases for particular things.",
"Aside from how you write numbers and a little convenience with things like fractions, changing bases changes almost nothing of any importance.",
"(Write it as 'base ten', to save the 'every base is base 10' bit)"
] |
[
"Why do some materials like iron, gold and other bend, while other like coal or rocks break?"
] |
[
false
] | null |
[
"It all depends on what kind of bond and structures the atoms form. when talking about metals and rocks, crystal structures become very important. The crystal structure of a compound it decides by its composition and its preparation. Some crystal structures are very rigid and won't bend easily, other materials are actually a lot of tiny crystals that can move rather easily making the material bendy. \nThis is a very complicated topic and it is hard to not go into too much detail here. The short answer is that it depends on the way the atoms are arranged in the material. "
] |
[
"The answer lies in the difference in bonding between metals (iron and gold) and ceramics (coal and rocks).",
"\"In ceramics, however, dislocations are not common (though they are not nonexistent), and they are difficult to move to a new position. The reasons for this lie in the nature of the bonds holding the crystal structure together. In ionically bonded ceramics some planes—such as the so-called (111) plane shown slicing diagonally through the rock salt structure in Figure 3, top—contain only one kind of ion and are therefore unbalanced in their distribution of charges. Attempting to insert such a half plane into a ceramic would not favour a stable bond unless a half plane of the oppositely charged ion was also inserted. Even in the case of planes that were charge-balanced—for instance, the (100) plane created by a vertical slice down the middle of the rock salt crystal structure, as shown in Figure 3, bottom—slip induced along the middle would bring identically charged ions into proximity. The identical charges would repel each other, and dislocation motion would be impeded. Instead, the material would tend to fracture in the manner commonly associated with brittleness.\"",
"http://www.britannica.com/topic/composition-and-properties-103137"
] |
[
"There's one major phenomenon behind this difference: dislocations. Dislocations are a type of defect in a crystal. If you imagine a crystal as a lattice, a large array of evenly stacked atoms, a dislocation is a missing half plane of atoms. When you look at dislocations under an electron microscope, they look like spaghetti, lots of little lines.",
"When you apply a force to a crystal, it takes a lot of force to break the bonds between atoms, but not a lot of force to slide the bonds around a dislocation, letting it move. Moving dislocations let you change the shape of the material. Dislocations can glide along, but they can also tangle and even multiply (Check out a Frank-Read source on youtube!).",
"Dislocations exist in large quantity in almost all crystalline materials, but it some materials they just can't move very easily, and when they do move they build up fast. Dislocations not being able to move means that it becomes easier for the material to change shape by cracking instead of moving dislocations. Brittle materials are ones that crack before they ever bend very much.",
"Coal breaks because it has strong, directional bonds that mean that sliding a dislocation takes a lot of energy, so it's easier to crack. Rocks have complicated crystal structures, meaning you can't just slide one atom in a plane to move a dislocation, you have to slide a group of atoms before you get to a new stable point. Gold has a close-packed crystal structure with very little directional bonding, meaning it's really easy for the dislocations to slide. Iron has a different type of crystal structure called body-centered cubic, which has a little more directional bonding, meaning it's less ductile in general.",
"There's a lot of other things we can do to tweak the ability of dislocations to move in a material. Making it harder to move dislocations means the material becomes stronger, it takes more force to bend, but ti can also make the material more brittle, meaning it won't bend as far before it breaks. Adding impurities to the crystal is one way to do this. The mismatch in size of the wrong type of atom adds energy to the lattice that dislocations have to overcome. This is why carbon and iron together (steel) is so strong. There's tons of other things to do as well, it's a really cool field. In aluminum we cause lots of tiny crystals to form made of copper or magnesium and they slow down dislocations. Aluminum without these crystals, called precipitates, is very very ductile(bends a long way before breaking) and soft (doesn't take a lot of force). Have you ever bent aluminum wire in your hands? Aircraft grade aluminum has a lot of precipitates, and it'll crack much sooner, which is why airplanes are always being tested for cracks.",
"The field that deals with bending things without breaking is called plasticity, and it's pretty neat! Fracture and fatigue are two fields of study that involve how things break (which isn't as simple as I made it sound). I study both, trying to get metal to be strong and ductile and last longer by looking at these phenomena."
] |
[
"Do sociopaths yawn after others?"
] |
[
false
] |
I remember reading that the reason people yawn is a empathetic reaction from back in our pack hunting days. Since sociopaths don't have empathy, do they not yawn after others? (Assuming they don't fake yawn to conceal themselves.) Or is yawning beyond a traditional definition of empathy that is primarily concerned with emotions?
|
[
"\nWe require that all top level answers ",
" include at least ",
" sources to support their statements. If an answer does not have a source attached for support, the post will be removed.",
"\n",
"\nA source should be external corroboration that independently verifies your statements. These include, but are not limited to: journal articles, textbooks and educational websites. For more information, check out our ",
" on the issue.",
"Here are some examples of acceptable sources:",
"Source: Landau and Lifshitz. Mechanics. p. 14",
"http://www.cdc.gov/cancer/breast/",
"Self-referencing sources ",
"Source: me",
"Source: my cousin's wife",
"Source: petroleum engineer",
"\nYes, please do. :)"
] |
[
"Disclaimer: I'm an engineering student, not a psychology/neuroscience student.",
"This question interested me, so I've been researching around. I found an interesting article ",
"here",
". The article addresses the absence of contagious yawning in children with autism spectrum disorder, which isn't a direct response to your question--but it still yields some interesting insights into individuals that demonstrate a lack in empathy, as demonstrated in ",
"this article",
".",
"In the paper, they discuss showing participants video recordings of adults yawning and record the number of yawns from each individual. They also did a control where the videos were simply of adults opening their mouths (but not yawning).",
"What they found was that in children that were developing normally, there was a significant increase in yawning frequency when a video of an adult yawning was observed vs an adult merely opening their mouths. In children with autism spectral disorder (ASD), there was no statistically significant observed difference in yawn frequency when observing the videos of adults yawning vs. merely opening their mouths. The results are shown nicely in this ",
"plot",
". ",
"The paper states that the mechanism of contagious yawning isn't well understood. They also noted that people with ASD tend to fixate more on the mouth than the eyes of a person. Apparently changes in the eye region of a person's face are an indicator that they're yawning, and it's possible that the fixation on the mouth impedes the yawning stimulus in children with ASD.",
"Perhaps someone who is actually involved in the field can add to this. Or maybe there's a better paper. ",
"Source: ",
"Absence of contagious yawning in children with autism spectrum disorder, Senju et. al.",
"Source: ",
"The Empathy Quotient: An Investigation of Adults with Asperger Syndrome or High Functioning Autism, and Normal Sex Differences, Baron-Cohen & Wheelwright",
"."
] |
[
"why this thread in particular"
] |
[
"Why and how is it that a given batch of tea leaves of even moderate quality can be used to brew more than one successive batches of flavorfull tea, while coffee grounds cannot."
] |
[
false
] |
You can normally re-use tea bags and leaves at least 2, and even 3 times and brew good tea, while coffee brewed from previously used grounds is flavorless. But both drinks are normally caffeinated and infused from plant material - why does one release all of it's caffeine and flavor in one shot and not the other?
|
[
"Thank you for a detailed and illuminating response. It will be interesting to compare the info you get from your tea guy with the coffee data; my informal intuitive opinion would be that there is even less soluble material in the tea leaves, and yet they keep on brewing...",
"Also, anybody which can boast of having a \"tea sommelier\" at hand is in an enviable position. "
] |
[
"Thank you for a detailed and illuminating response. It will be interesting to compare the info you get from your tea guy with the coffee data; my informal intuitive opinion would be that there is even less soluble material in the tea leaves, and yet they keep on brewing...",
"Also, anybody which can boast of having a \"tea sommelier\" at hand is in an enviable position. "
] |
[
"Mostly because they are two entirely different parts (coffee seeds vs. tea leaves) of two entirely different plants, containing different chemicals, used in two entirely different ways - \"soaking in hot water\" is a wild generalization on preparation of both beverages.",
"Also, tea can release all of it's flavor in one shot - it just doesn't have the time. Tea contains some chemicals that are released immediately and quickly, and some are released after a longer steeping time and slower. The ones released early are usually the tastier and preferred ones."
] |
[
"Concerning DNA and the origin of life"
] |
[
false
] |
[deleted]
|
[
"Until someone invents a time machine I don't think we'll ever know for sure, but the most prominent theory is probably ",
"abiogenesis",
", the idea that individual molecules came together to eventually form more complex ",
"biomolecules",
", perhaps ",
"forming RNA",
" which could replicate itself and everything took off from there. I don't know if you can define exactly when it switched from inorganic matter to living matter, that would probably depend how you define \"life\". ",
"The \"information\" in DNA has accumulated over millions of years of evolution, with bits continually added, removed, and switched around."
] |
[
"This is not my field of study but, I think I read on here that the so called information contained in DNA you talked about is mostly used in the evolutionary debates and are insignificant. The information is counted by assigning bits to the DNA code. I say this because it is usually used in common discussions in the sense of being added to or removed as a progression of the evolutionary state but this type of discussion often leaves out the points where the amount of data i.e. the number of base pair might be the same between two samples but the functionality of the DNA may be different. This is a change in information but not in the amount and these discussions are generally concerned with amounts.",
"Alternatively, if you are talking about the information contained in DNA being a functional product instead of quantitative then I believe it is a result of biological chemistry (",
"Biochemistry",
") in which case the wikipedia page should be able to help. ",
"http://en.wikipedia.org/wiki/DNA"
] |
[
"This is not my field of study but, I think I read on here that the so called information contained in DNA you talked about is mostly used in the evolutionary debates and are insignificant. The information is counted by assigning bits to the DNA code. I say this because it is usually used in common discussions in the sense of being added to or removed as a progression of the evolutionary state but this type of discussion often leaves out the points where the amount of data i.e. the number of base pair might be the same between two samples but the functionality of the DNA may be different. This is a change in information but not in the amount and these discussions are generally concerned with amounts.",
"Alternatively, if you are talking about the information contained in DNA being a functional product instead of quantitative then I believe it is a result of biological chemistry (",
"Biochemistry",
") in which case the wikipedia page should be able to help. ",
"http://en.wikipedia.org/wiki/DNA"
] |
[
"Before we understood how light waves work, what was the historical understanding of refraction?"
] |
[
false
] |
I was taking a bath earlier and if I didn't know any better, I totally could have been convinced that my hand was physically shrinking when I dipped it in the water. Did people believe anything to that effect before we understood that it was refraction of light waves? Or did people generally understand it was some kind of trick of the light?
|
[
"I remember Bernoulli solved the Brachistochrone problem in the 1600s using light refraction. So by then the behavior of light was well understood. They didn't understand that it's both a particle and a wave, they didn't understand that it carries the electromagnetic field, and so on, but the basic behavior was well understood.",
"I would assume it's been known that it's a trick of the light since ancient times. Because if you try to spear a fish and you assume the fish is actually where it seems to be, you will not catch the fish. I don't have any information or sources to back it up though."
] |
[
"I actually have some time to write up an answer myself =) Most of this comes from ",
" by A. Mark Smith.",
"Accounts of refraction exist as early as Euclid's ",
" (4th-3rd century BCE). There are a bunch of ancient Greek works (and subsequent ones) called either ",
" or ",
". Roughly, optics was usually used to refer to the geometry of seeing things at a distance (e.g. parallel lines converging) and catoptrics was specifically focused on theories of reflection (specifically how different kinds of shapes of mirrors work). Euclid included a postulate on refraction in his ",
" so Smith uses that as a starting point. ",
"Euclid's sixth postulate is the only one about refraction and it actually describes something called a \"floating coin\" experiment: take a disk (a coin) and put it in a vessel (a glass). If you look at it from the right angle, it'll disappear from sight just below the rim. If you then pour water into the glass, it'll magically reappear into view and appear to float up. So, not really a law or rigorous or anything, just an observation and not explicitly called refraction or compared to reflection.",
"A mathematical account of refraction first appears about 500 years later in Ptolemy (2nd century CE), who is closely working off of Euclid's ",
" and ",
" (and other Greeks like Hero and Archimedes (whose own ",
" is lost but is references by other writers... see also final note below)). Ptolemy's analysis of refraction is extremely rigorous and seems to come out of thin air (or, at least, we don't have any other surviving earlier texts).",
"For a sense of what Ptolemy wrote, below is an extensive quote from Smith. There's a preoccupation with reflection because there had previously been geometric analyses of reflection. So a key question for Ptolemy was: are reflection and refraction the same / governed by the same principles? ",
"Ptolemy opens his study in book five by noting the fundamental similarities between refraction and reflection. For a start, both involve breaking of the visual ray. Physical, this breaking is due to the resistance of certain bodies to penetration by impinging visual rays. When the body's surface is reflective, its surface resists penetration completely, so the visual ray is fully broken by rebound (",
"). When the body is transparent, the resistance at its surface is only enough to deflect the ray as it passes through, so it is only partially broken. Refraction is thus a special case of reflection, in which the rebound is incomplete. The amount of deflection the visual ray undergoes in refraction depends on how much resistance it encounters, and that is a function of the relative \"density\" of the refractive body. Accordingly, when it passes from rare (",
") body, such as air, into a denser (",
") one, such as water, the visual ray will be deflected in a particular way. Likewise, when it passes from a denser into a rarer body, the visual ray will be deflected in a particular way.\" (Smith, p. 109-110).",
"This is a general, theoretical account based on properties of media to the extent that they were understood at the time. However, Ptolemy continues by describing geometrically what is going on (in a variation of Euclid's floating coin experiment) and this is quite in-depth (\"Let ABHD be a visual ray passing over the rim of the vessel...\"). Based on the geometric analysis, Ptolemy identifies some differences between reflection and refraction and then proposes several experiments that could be used to tell them apart and to confirm the equal-angles law of reflection. ",
"These experiments are amazing. Here is the gist: make a disk with equally spaced notches along it's rim (like a clock). Mark the middle of the disk with something that sticks out, like a pin. Hold the disk vertically (perpendicular to the ground) and submerge the bottom half of the disk in water. Use a little colored peg to mark a place along the rim of the disk. If the peg is at the very bottom of the disk and you are looking straight down (line of sight is top of disk --> marker/pin in center --> peg at bottom of the disk), then the peg and the marker in the middle of the disk will be perfectly aligned (no refraction). Now, move your line of sight from straight over the disk by 10 degrees along the side of the disk (i.e. to the 20 minute mark if you are thinking of it like a clock). Adjust the position of the peg at the bottom of the disk until it looks as if it is perfectly aligned with the marker in the middle. Because the bottom half of the disk and the peg are below the waterline, the position of the peg will appear shifted from where it is. Measuring the angle of how far off the peg is from where it would be on a straight line with the eye and the marker in the middle is a way of measuring the angle of refraction! Ptolemy measured this angle of refraction for both air-water, air-glass, and air-glass transitions (these are the three experiments) for different angles of incidence. The resulting measurements and was very close (within a degree for most) to modern theoretical values. (There are some nuances here about whether in his experiments the peg was below or above water and whether the water was covering the bottom or top of the disk, whether in certain media and from certain angles, the light would actually reflect internally complicating things, and some rounding procedure that he used for his values, etc. but it doesn't matter for the main point here.) ",
"So a pretty thorough geometric analysis of refraction. From these experiments, Ptolemy makes some generalizations about how refraction works and then concludes:",
"a \"marvelous fact will be apparent: namely, the course of nature in conserving the exercise of power.\" Ptolemy never addresses how this fact becomes apparent, but the appeal to conservation of power suggests that Ptolemy had in mind some overarching metaphysical principle, like, or at least analogous to, Hero's lest-distance principle, that governs the relationship between angles of incidence and refraction [",
"].",
"(I believe the last is supposed to be reflection, not refraction.)",
"I highlight this section because it brings us into collision with something that I have been avoiding: theories of how vision works (e.g. radiation or visual flux emitted from a point in the eye as a \"visual cone\", and whether these are real or abstraction and how this interacts with the medium, etc.). The geometric explanations are great, but if we want to get at ",
" light behaves this way, we need to have an understanding of light and sight and how light travels and through what. And that's a very different story. It's also important to remember that Ptolemy is especially interested in misperception. The remaining section of the book is concerned with several visual illusions like the ",
"moon illusion",
" and the key for Ptolemy was that a lot of them (and refraction and reflection!) could be explained by geometrical principles applied to ",
" vision and light worked. ",
"So, for me, the key takeaway is that, with Ptolemy, we have a geometric description of refraction and the measurement of a refractive index for several different kinds of media. Part of the explanation as to ",
" things look the way they do, though, is based on their understanding of how vision works at the time (some version of ",
"extromissionism",
") and their understanding of what makes different kinds of matter and media different (more or less \"dense\" in their understanding of density). ",
"Finally, a difficult note here is that we don't really have very many texts from before Ptolemy, so we don't know how much he was relying on other texts. As for Ptolemy's ",
", the oldest existing copy is a 12th century Latin translation of an Arabic version that no longer exists which itself was a translation from a Greek version... which also no longer exists. The existing text is also incomplete, actually cutting off in the middle of the book on refraction. So how much more was known at the time, we can't really say."
] |
[
"If you don't get an answer here, you can also try ",
"/r/askhistorians",
", ",
"/r/historyofscience",
", or ",
"/r/philosophyofscience"
] |
[
"How do plants cells and animal cells remove waste from their systems?"
] |
[
false
] | null |
[
"This depends on the nature of the waste. For small molecules, simple diffusion across the membrane allows the waste to be eliminated. This, by the way is why cells have a low ",
"surface-to-volume ratio",
" with regards to their size. A larger cell would take longer to rid itself of waste material (and also allow nutrients in).",
"Enzymes within the cell also break down waste products to smaller compounds so that they can be eliminated. Specialized vesicles, such as the ",
"lysosomes",
" of animal cells, perform this function. There is some debate as to whether plants and other organisms have lysosomes - many think that they have vesicles within the cell that perform similar functions, but they have not yet been clearly identified. "
] |
[
"Do you know of a site talking about the mechanisms of the lysosome like organelle in plants?"
] |
[
"I often use this reference from Miller and Levine ",
"http://www.millerandlevine.com/ques/lysosomes.html",
", mostly because of Miller's reputation as a cell biologist. There aren't a lot of articles in the popular science articles about plant lysosomes, but if you do a search on Google Scholar (for example) for \"plant lytic\" vesicles or vacuoles, you may find something more technical. ",
"I think that there is little doubt that plants have vesicles or vacuoles with a similar structure to the animals - they are probably just less specialized, which means that they would be difficult to identify among the thousands of vesicles in the cell."
] |
[
"Has popping joints been proven to affect local residents of other systems when popping the neck/shoulders/back?"
] |
[
false
] |
Lymbic/endocrine, etc
|
[
"It doesn't cause arthritis. Also, some info about the mechanics of knuckle cracking. - ",
"Johns Hopkins"
] |
[
"Please remember that this is not the place for anecdotes and everything needs to be sourced. Please no more laymen speculation. "
] |
[
"Popping the joints has some local effects. It causes a release of nitric-oxide, a very short lived vasodilator. It also has a temporary pain relieving effect and this is primarily why a person feels better after seeing a chiropractor. However, no effect outside the joint and immediate surroundings have been demonstrated."
] |
[
"Is earth relatively to other planets, considered 'small'?"
] |
[
false
] |
[deleted]
|
[
"It is bigger than three planets in this solar system and smaller than four. It is smaller than pretty much every one of the thousands of known extrasolar planets (might be some exceptions), but that is mainly due to our detection techniques."
] |
[
"But! Earth is the largest of the rocky ",
"\"terrestial planets\"",
"."
] |
[
"In our Solar System it is, but compared to all known rocky planets it's in the middle."
] |
[
"A ziploc bag is airtight, yet scents from inside the bag will still permeate the plastic over time. How do scent molecules do this without the exchange of air?"
] |
[
false
] | null |
[
"Small, nonpolar molecules can still diffuse through plastic. They basically dissolve in on one side and un-dissolve on the other side. ",
"If you want a more impermeable food containment strategy, use aluminum foil. "
] |
[
"That is sort of a unique case, because Helium gas is one of the smallest molecules that exists. As a result, it is notoriously difficult to contain and store."
] |
[
"True. But even a balloon filled with regular air shrivels after a few days."
] |
[
"Do the elements of supernovae stay within the range of the previous solar system? Is a solar system with a star of sufficient mass just recycling elements within that range?"
] |
[
false
] |
I get that nebulae can be many AU’s in diameter, but isn’t the distance between solar systems much larger to the point where there would be very little cross pollination between solar systems? Also what happens to planets that aren’t destroyed by supernovae? Are there gas giant sized planets drifting around within galaxies unattached to a star?
|
[
"Nah supernova remnants spread out really quickly, and mix into the general mess of low density gas called the \"interstellar medium\". The interstellar medium is the thin gas that fills most of the volume of the galaxy, and it's very turbulent - it gets stirred up by supernova and winds, and by the rotation of the galaxy. So the high-mass elements produced by the star and the supernova get spread around pretty quickly, and when some part of the interstellar medium condense to form a molecular cloud than will then collapse into stars, it carries bits of high-mass elements from all sorts of supernovae throughout the galaxy.",
"It's unlikely a planet would survive its star going supernova - they are extremely energetic events - but stars don't usually get completely destroyed when going supernova. There's a remnant - a neutron star or black hole - that's left behind, although it only has a portion of the mass of the original star. There might be enough left to keep some hypothetical planet bound, but it's unlikely, especially as the outflowing gas will push the planet too, and because supernovae are not symmetric - the star gets a big \"kick\" from the supernova, and could leave any hypothetical planets behind.",
"There should be rogue planets though anyway, but these would likely be slingshotted out by gravitational interactions rather than leftover after stars go supernova."
] |
[
"No. Supernova remnants expand far beyond the range of their original systems. For example, the Crab Nebula, the remnant of a supernova observed in 1054, has already expanded to a diameter of about 10-12 lightyears, and is still expanding at a rate of ~1500 km/s."
] |
[
"Not so much, there are \"planetary nebulae\" that are the end stage of stellar systems too small to go supernova & the radial velocity of these is near to the escape velocity of the system.",
"",
"Supernova remnants though can expand at up to 10% the speed of light & as they expand the shockfront sweeps up interstellar matter, mixing it with the heavier than Iron elements created by the supernova & as these collide with other shock fronts or denser matter can trigger new star formation",
"For example, analysis of the tiny spherical \"contrules\" found in Chondritic meteorites (theorised as pristive pre-solar matter fused by friction induced electrical discharges in space), reveal ratios between long lived heavy element isotopes that when plotted out form distinct clusters.",
"The average of these clusters is what normal solar system material approaches, which implies that this pristine material comes from several different places. I believe the data I saw implied at least 4 different Supernova shock fronts triggered the formation of our sun & contributed to the overall elemental abundances.",
"So yes, we are all made of star stuff, from long long ago in a star system far far away ...."
] |
[
"What are the long term effects of anti-depressants?"
] |
[
false
] |
[deleted]
|
[
"As others mentioned in this thread, there are many different types of anti-depressants. Your use of the words \"long term effects\" could refer to any number of things such as mechanisms of action or side effects. Because I have the time, I will try to cover both of these in as easy-to-understand language as possible.",
"I will discuss the three most common types of anti-depressants: monoamine oxidase inhibitors (MAOIs), tricyclic anti-depressants, and selective serotonin reuptake inhibitors. ",
"As the name suggests, MAOIs work by inhibiting an enzyme called monoamine oxidase (MAO) - specifically MAO-A. MAO-A's role in a neuron is to breakdown excess neurotransmitters including norepinephrine (NE), serotonin (5HT), and dopamine (DA). By inhibiting MAO-A, there is a greater amount of these three neurotransmitters available to be released into the synapse. However, the elevated levels of these neurotransmitters is not the relevant mechanism for its anti-depressant action, since the elevation occurs within hours of taking the drug (and it takes several weeks for the anti-depressant effects to occur). Recent research has suggested that the anti-depressant effects actually come from downregulation of the relevant auto-receptors/somatodendritic receptors, and an upregulation of second messanger signaling (specifically cAMP).",
"Minor side effects include weight gain, sleep disturbances, and danger of increased blood pressure if taken another drug that enhances NE function. But the most famous side effect is known as the \"cheese effect\". Besides the brain, MAOs also exist in the liver and are responsible for the breakdown of a chemical called tyramine (which is found in cheese, among many other foods). Without the MAOs to break down the tyramine, it can build up to dangerous levels and can sometimes be fatal. Patients taking MAOIs must avoid such foods. MAOIs also inhibit other liver enzymes such as the cytochrome P450 enzymes, which break down drugs such as alcohol, opiates, benzos, etc. Thus, taking any of these drugs will result in an intensified effect.",
"Tricyclics work by inhibiting the reuptake of NE and 5HT. After a neurotransmitter is released by a neuron and acts on its receptor, it is taken back (reuptake) by a transporter protein. Tricyclics work by blocking inhibiting these proteins so more neurotransmitters remain in the synapse. Different types of tricylcics affect NE and 5HT transporter proteins to different degrees. The anti-depressant effects again come after several weeks of administration and work by sensitizing and downregulating post-synaptic receptors.",
"Besides NE and 5HT, tricyclics also affect acetylcholine and histamine receptors. Histamine receptor blockade can result in sedation and fatigue, but often times patients who have trouble sleeping - a common symptom of depression - welcome this side effect. Blockade of acetylcholine receptors can result in dry mouth, blurry vision, and dizziness among others. Tricyclics can also be toxic if taken at about 10 times the regular dose, so they are oftentimes not prescribed for patients with suicidal ideation.",
"SSRIs work similar to tricyclics in that they block reuptake, but are more specific in that they only affect SERT - the serotonin reuptake transporter protein. They are also block reuptake more effectively than tricyclics. And again, like all anti-depressants (except acute administration of non-hallucinogenic doses of ketamine, but that's a whole other story :)) SSRIs require a few weeks before having an effect. Similar to MAOIs, SSRIs desensitize the relevant somatodendritic receptors and presynaptic autoreceptors, and also upregulate cAMP signaling. ",
"SSRIs are often prescribed first to patients due to their minimal side effects. These can include anxiety, sleep disturbance, nausea, and sexual dysfunction.",
"Overall, the main long-term effect of anti-depressants is, well, a reduction in depression symptoms. For reasons that we are not entirely sure of, anti-depressants affect everyone differently. It may take 3 or even 4 different medications before you find one that works for you. It also must be noted that while recent studies have increased our understanding of the neuronal changes that accompany long-term anti-depressant usage, it is by no means completely understood. There are also several other long-term effects that contribute to the anti-depressant mechanisms that I did not mention above, mostly due to their complexity. Several anti-depressants alter gene expression that modulate function of reuptake transporter proteins, several cause an increase in BDNF expression in the hippocampus, and several affect many transcription factors including c-fos and NGF1-A.",
"Sources:",
"Meyer, J.S. and Quenzer, L.F. (2005). ",
". ",
"And a B.S. in neuroscience, with a personal interest in psychopharmacology."
] |
[
"My apologies. I was simply recalling information that I had previously learned. Here are a couple articles you might be interested in:",
"http://www.sciencemag.org/content/210/4465/88.short",
"\nThis explores the possibility of decreased number of neuroreceptors due to extensive use of antidepressants",
"http://www.sexualidadysaludmental.com/imagenes/recursos/antidepres01.pdf",
"\nThis one delves into the possibility of sexual dysfunction as a resultant of altered neurochemistry in the brain"
] |
[
"Any comment on Tetracyclics and how they fit into this picture? Great post, btw!"
] |
[
"Does obesity exist in wild animals?"
] |
[
false
] |
I googled it but all I could find was half thought-out or misinformed opinions. Obviously, there are animals that purposely but on weight for hibernation or when giving birth, but I assume that well within the weight that a particular animal can handle doesn't hinder their life expectancy or abilities. Maybe I need a better definition for what obesity is when you compare across different animals. The reason I ask is because I have seen before some information which links obesity to a mental inability to stop eating or recognize that you are full. This is always seems a bit airy-fairy to me. Surely if such a condition exist, wild animals would be susceptible to it too? After plenty of answers which were very good, and a few great links. It seems the question is a bit harder than expected to answer. One of the problems includes defining what obesity is in other animals.
|
[
"If a wild animal's survival is affected by its eating habits and weight then it tends to die. If it doesn't it is easy to conclude that the gorging doesn't hinder it's survival. In other words it seems we have defined away the ability to have an \"overweight\" animal; either it is successfully managing its weight or it isn't and is dead."
] |
[
"Some animals come from environments where food is scarce, so they will eat pretty much anything that you put in front of them. There's never been any evolutionary pressure to put an upper limit on what they'll eat because starvation has always been the bigger problem.",
"However if the environment is changed then problems can occur. Normally, this happens when an animal is domesticated (reptiles especially are prone to being overfed, just took a quick look at care guides in any book store). However your question was specifically aimed at wild animals.",
"I can't find any specific, well documented cases of animal obesity in the wild, but given what's outlined in my first paragraph it's certainly possible. However I can't think of any reasonable explanation for a sudden abundance of food in an environment that previously contained little. So I'd need to conclude that while it is biologically possible, it's likely that environmental constraints would prevent it from being anything other an infrequent abnormality. In most cases a species has adapted to it's niche well enough that there's enough food to go around, but without much of a surplus."
] |
[
"Foxes don't just think \"Hey, food is a bit scarce this year, I better not have a few more babies.\" They have as many as they can every year. It's just that when there's more food available, more of the offspring survives. ",
"As a result, when there's plenty of food, the fox population quickly increases. If food source disappears or gets smaller, then the next offspring will starve and die, which in turn will result in a smaller population of foxes in that area."
] |
[
"If we can't predict the weather a week in advance accurately how can we predict the doomsday scenarios of Global Warming?"
] |
[
false
] | null |
[
"Weather and climate are not the same thing. I recommend starting with a simple google search for some background reading on the topic and coming back with a more specific question."
] |
[
"Ooo shots fired ;)"
] |
[
"My question is still valid why do I need a more specific question?"
] |
[
"When someone gets a transplant, if you wait long enough, do all the organ's donor cells get replaced by the recipients cells?"
] |
[
false
] |
[deleted]
|
[
"This would depend slightly on the organ, but in general I would say no. First of all, the \"all our cells get replaced in x years\" factoid is not true. Second, replacement of cells within an organ, if it happens at all, falls to the resident ",
"adult stem cells",
", which are likely to have been transplanted from the donor, since they reside in the organ. "
] |
[
"If they got replaced it would be from the donor's stem or just normal cells contained in the organ. As far as I know you have no cells in your body that retain the ability to turn into say a liver cell. They have all progressed past that point and are no longer totipotent (able to become any cell). The reason is that epigenetic silencing and regulation has progressed the cells past that point and reversing that is very difficult to impossible."
] |
[
"Part of the organ recipient procedure is being on immune suppressant drugs for the rest of your life. That wouldn't be necessary if your body replaced the donor organ. Cells in the donor organ live and reproduce just like your own cells."
] |
[
"Why is a screening test recommended every year for breast cancer but not for any other types of cancers?"
] |
[
false
] |
For breast cancer, a screening exam like a mammogram is done every year for women around a particular age. However for other types of cancers, screening annually is not recommended in the healthy population. So the question is: Why is breast cancer screened every year, but other cancer's are not screened at such a high frequency?
|
[
"The tests for different cancers vary a lot in terms of how expensive, how reliable and how invasive they are. For breast cancer, it just happen there is something relatively useful that can be done every year for little money. For bladder cancer, they do unpleasant things to you that I wouldn’t want to repeat every year, and it costs more."
] |
[
"I think cervical cancer is screened more than breast cancer women. ",
"Other cancers are screened too e.g. prostate cancer in men.",
"This is done where the benefits of screening (early detection) outweigh the risks (mainly false negatives), and where the health system can afford it."
] |
[
"There are other screening tests that are cost effective for the general public or select populations, such as colon cancer screening, lung cancer screening, prostate cancer screening.",
"These are not necessarily every year, though. For example, usually colon cancer goes through a pretty clear pathway from normal cells to adenomatous polyp to cancer and this process takes years, so the screening is only necessary every few years.",
"And breast cancer screening is only necessary every year if you ask a gynecologist or a cancer doctor. The United States preventative services task force (USPSTF) says that every other year is fine, any many primary care doctors follow this."
] |
[
"[physics] When looking at pictures of atoms, what am I really seeing?"
] |
[
false
] |
Am I seeing the nucleus or something else?
|
[
"You are basically seeing how much the apparatus you are using interacts with that atoms at each position along the surface being examined. You can read about the various methods ",
"here",
"."
] |
[
"thanks! precisely what I was looking for."
] |
[
"Just a little addition here, all the methods listed here are generally used to survey the ELECTRONIC degrees of freedom. If you want to image the NUCLEI (like you suggest) the best way to image them is through XRD provided they're in a regular lattice (x-ray diffraction) or gain other information (which unfortunately not so intuitive) if they're not (say if they're a polymer) which effectively gives you their positioning, crystal symmetry, inter-atomic distance, etc.",
"There are also ways to image things like: the local magnetic field (say something like uSR), and the energy quanta it'll accept or what is called the spectra (there are so, so many ways for this)."
] |
[
"Why is it apparently impossible to create a velocity profile for fluids with turbulent flow, but not laminar?"
] |
[
false
] | null |
[
"Turbulent water is incredibly chaotic, but laminar flow is smooth and easily predictable.",
"To add a little bit to this: laminar flow can be accurately represented with many different \"models\" of water behavior. Turbulent flow is nearly impossible to model correctly. For turbulent water, you need to track the more continuous overall fluid mechanics, you have to account for water molecules being participate in nature, and you have to worry about inter-molecular forces like surface tension, which can help create little spray droplets. These three models do not mesh well at all, and I'm probably still ignoring some of the important features that are needed to describe turbulent water."
] |
[
"When U try to determine the average conditions and write down the equations you get second-order statistical terms involving the cross-correlations between the velocity terms. When U derive the equation for the second-order terms it contains third-order statistical moments, etc. This is the turbulence closure problem and only approximations to it have been solved. "
] |
[
"The problem is that in fluid dynamics, you can't really smooth over small scale fluctuations without introducing an error. When you try to make a smooth large-scale average, the terms don't cancel out, and you end up with extra bits that you have to create some model for. Turbulence is a cascade of eddies that goes all the way down to the molecular scale, so there's velocity all the way down. So you need to either create a velocity profile that's accurate down to the individual molecules, or you need to make a large-scale average and include some approximate formulation for how you expect turbulence to go in your system. (This is particularly tricky in astrophysics where your turbulent overdensities eventually turn into supernovae).",
"With laminar flow, you have - by definition - a flow that doesn't have any interesting details below a certain scale length. So then you actually can smooth over the small scale bits and get an accurate answer, without going to the molecular scale."
] |
[
"Is antimatter related to energy in the same way that regular matter is related to energy?"
] |
[
false
] |
The matter that surrounds us is related to energy through the equation E=mc I know that when comparing matter and antimatter, for each property with an opposite (for example electric charge), a particle and it's antiparticle are opposite, but for properties without an opposite, they are the same. So are matter and antimatter related to energy in the same way, or do they somehow differ?
|
[
"Yes, they are related to energy the same way. An electron and a positron have equal rest mass, and thus equal rest energy (",
"); if both are moving at speed ",
", their kinetic energy non-relativistically will be ",
", and relativistically their combined rest and kinetic energy will by ",
"."
] |
[
"Got it. Thanks for the answer!"
] |
[
"You're welcome."
] |
[
"A question about memory"
] |
[
false
] |
[deleted]
|
[
"Although there are a lot of different ways to categorize memory subsystems in the brain, you are asking about the difference between ",
"recognition memory",
" and ",
"recall memory",
" ). ",
"Everyone can better ",
" things that they have heard/seen/learned/smelled etc than they can independently ",
" those memories on their own. It's the difference between simply matching-to-sample (which does not necessarily require cortical, top-down processing), and having to find the specific information you want in the web of connected items that is your declarative memory system (which requires your frontal lobes to deliberately rifle through your medial temporal lobes to find the info). While the information in both recognition and recall memory is vulnerable to decay (forgetting), the information in recognition memory is generally much more robust.",
"Your question is a bit more complicated by your example of not being able to recall where you left your phone an hour ago, because it adds the element of what you consciously, cortically attended to versus what you did not. The first step in being able to independently recall something is cortically attending to it long enough to encode it into your memory banks. ",
"Presumably, your cortical brain regions attended to 'GOURANGA' (you had to type it in or whatnot). However, generally, people do not ",
", cortically attend to things like where they left their possessions. Habitual actions are handled by subcortical brain regions that generally operate independent of cortical (what you might think of as more 'conscious') brain regions. While the information still goes into your memory to some extent (for example, you might have had the experience of suddenly 'remembering' leaving your phone in the refrigerator when you stumble across it there), it's generally much more accessible through recognition memory (which doesn't need much cortical input) than through free recall (which needs lots of cortical input). ",
"This is simplified to some extent, because it's not like your cortical system \"turns off\" completely while your subcortical system is handling a routine task, so sometimes your neocortex may have paid enough attention that you can dredge up the memory of where you placed your cellphone with some sincere effort.... but for the most part, your cell phone is whoknowswhere, while at the same time, you embarrassingly know all the words to ",
" when you accidentally catch it on Lite Rock FM. "
] |
[
"There is a difference between these two \"memory items\":",
"One, GOURANGA, is a very specific -and rather unique- thing. I only played GTA1, so I only remember it as the message you got when you mowed down the whole C-company at once, but anyway; you used the code as a means to a special end. It is, bluntly said, memorable.",
"The other, \"where did I put my key/phone/lighter\" is much less specific. When you come home you do it almost subconsciously, and even if you focused: You've put your phone in so many different locations that your brain will most likely not make the effort to store \"phone: on the shelf in the kitchen\" to long-term memory. It changes so often anyway.",
", on the other hand, that is biochemically done in the brain... I admit I don't know."
] |
[
"i thought those guys were joggers at first, but it turns out they're ",
"hare krishnas"
] |
[
"Does the earth's core (everything under the crust) move or flow?"
] |
[
false
] |
[deleted]
|
[
"Solid flow isn't the same thing as liquid flow. Solid flow occurs when a solid is heated close to its melting point. Ice is a very good example of a hot solid - glaciers flow at speeds that are easily measurable in time periods comprehensible to humans but it's still hardly comparable to a lazy river!"
] |
[
"Because there's a temperature gradient between the hot core and the cool crust, ",
"convection currents",
" will form in any material capable of flowing. The outer core is liquid metal, and flows quite readily. It's more viscous than liquid metal at atmospheric pressures, but not much moreso. The currents in the outer core are though to give rise to the dynamo effect that generates the global geomagnetic field.",
"The mantle is solid rock, but it's hot enough to be malleable - it, too, flows albeit over much longer timescales. Convection currents in the mantle are the main source of volcanism and \"hot spots\" in the crust."
] |
[
"So hypothetically if I could survive being thrown into the mantle, I could float around like it was the lazy river?"
] |
[
"What does it mean to say that \"Electromagnetism is a more powerful force than gravity\"?"
] |
[
false
] | null |
[
"The electrostatic attraction between a proton and an electron is about 10",
" times as strong as the gravitational attraction between them."
] |
[
"Not that this really matters, but to nitpick, your number is the ratio of the two forces when two electrons interact. For a proton and an electron, the ratio is on the order of 10"
] |
[
"Yeah you're right."
] |
[
"Astronomers, et. al. is it really possible to see detail like in this picture from earth?"
] |
[
false
] |
I live in an urban area, but I've spent long nights in deserts,forests, etc. without population for miles and miles, and I've seen detail like in in the night sky. So, in addition to basically asking 'Is this photo shopped?' I am also wondering, if it is possible, under what circumstances? Have I just not been stargazing from the right places?
|
[
"Its probably taken with a long exposure. By leaving the camera aperture open long, it lets in significantly more light, making for a more detailed picture."
] |
[
"Wouldn't the stars move and leave streaks in that long exposure? ",
"Here is the same arch, as far as I can tell, but with stars moving",
". ",
"If the camera were on an equatorial mount, I'd expect to see the arch move. ",
"Like the trees in this photo",
"."
] |
[
"In that first photo it looks like stars have rotated through about 90 degrees, so that would be an approximately 6 hour exposure. With a full frame sensor DSLR I'd imagine that you could get pretty good data from an exposure of even just 30s - 1m which would have minimal trails. It could also be a composite of the stars from a motorized mount long exposure with the foreground layered in from a static shot."
] |
[
"Why don't protons and electrons attract each other to form a electrostatic lattice?"
] |
[
false
] |
I was wondering why electrons orbit protons as opposed to joining with them to form almost a lattice structure between the positive proton and negative electrons. The protons and electrons do have a difference in size but not charge so I don't understand why they just orbit, and also why do protons with +1 charge join with neutrons? There's probably something I've missed as I don't know a great deal about it, and it's probably stupid, but I would have thought proton+electron makes more sense as it balances charge and acts more like ions
|
[
"I was wondering why electrons orbit protons",
"They don't, really. That's just a metaphor.",
"almost a lattice structure between the positive proton and negative electrons.",
"These are called atoms.",
"and also why do protons with +1 charge join with neutrons?",
"The strong interaction causes this."
] |
[
"Atoms aren't lattice structures? I think his use of lattice implies like a salt crystal, which electrons and protons decidedly don't do."
] |
[
"He said \"almost.\""
] |
[
"Can one attain a PhD in physics nowadays doing research in Newtonian physics?"
] |
[
false
] |
Just curious.
|
[
"Turbulence is still pretty much wide open."
] |
[
"Of course. You could do nonlinear dynamics or, as its also called, chaos."
] |
[
"Yep.",
"My galaxy simulations use newtonian gravity, because the corrections for GR on those scales are basically nothing. And nothing generally goes above a thousand km/s, so special relativistic corrections aren't important either. I've been doing isolated galaxy simulations, so I don't need to look at the expansion of the universe either.",
"There's still a huge amount of stuff that only really requires classical mechanics - GR, SR & QM effects are only important in certain regimes."
] |
[
"Is it more beneficial to lay on your left side, right side, or back when you have a stomach ache?"
] |
[
false
] |
[deleted]
|
[
"If the stomach ache you're referring too is caused by a buildup of stomach acids, then lying on your left side might be beneficial. This is purely due to the normal orientation of the stomach (preventing acid reflux due to gravity). The best position would be to lay with your head elevated."
] |
[
"There isn't any benefits for lying on any side...if there's a problem with your stomach, it will be there no matter how you lie down...but your stomach is on your left side, if that helps..."
] |
[
"Beneficial in what way? More comfortable? And what kind of stomach ache. If you have appendicitis you'll have a stomach ache, but you'll also get one if you just at a bad chimichanga. "
] |
[
"Why do Tau & muon particles not produce currents like Electrons?"
] |
[
false
] |
As I learnt, Electron, Muon & Tau particles come into the category of leptons. Electron, on its motion produces electric current. Then, why does Muon not produce Muonic Current (imaginary naming) & Tau -- Tauonic Current? From a few reads I got that these have many similar properties --motion, rotation, electric characters etc.-- but tau & muons decay very fast in comparison to electrons. Is there any other reason, why it is so? (please don't focus on language related errors. ;) ) edit: Suggest a few reads/links if possible.
|
[
"Any time charge moves — either negative ",
" positive — we call it \"current.\" Muons and tauons are charged, so when one moves, you get a current … very briefly. On the order of a millionth of a second for muons, a ten-trillionth of a second for tauons."
] |
[
"Every charged particle produces current if its moving. So they do as well."
] |
[
"Unless they're very very fast, and that extends their lifetime somewhat from our perspective."
] |
[
"If the minimum shutter speed of my phone camera is at 1/6000 of a second why can't I shoot slow mow videos with 6000 fps?"
] |
[
false
] | null |
[
"There are multiple reasons.",
"One is related to the way data is read from camera-sensors. With most sensors (especially in phone cameras), the entire sensor is not read in one go, but rather row by row. With a shutter speed of 1/6000, each row only collects 1/6000 of a second of light, but not all rows capture the same 1/6000. The speed with which a sensor can read out all its rows is called the \"readout speed\".",
"If there's a fast-moving object in the screen, then a sensor with slow readout speed will generate an image that is slightly distorted: the bottom of the object is shifted compared to the top, reflecting the fact that the various parts of the image were not recorded at the same time. This effect is called the \"rolling shutter effect\".",
"The readout speed ultimately determines the maximum framerate that can be captured. With a readout speed of 1/120 of a second, the sensor can deliver a complete frame 120 times per second, so videos up to 120 fps can be recorded.",
"A second constraint is the amount of data that is generated. A 6000 fps video generates 100 times as much raw data as a regular 60 fps video. All this data has to be stored in a temporary buffer and then processed into a video format (which greatly reduces the amount of extra data, since video-compression is very efficient when there are only tiny changes between frames, which is almost always the case at 6000 fps). This requires a large amount of high speed memory and a large amount of processing power."
] |
[
"A simple analogy: how long does it take you to crack open a can of soda? Maybe one second? If that's the case, why can't you drink 60 cans of soda in a minute?"
] |
[
"Wow, thank you for this detailed answer 👍"
] |
[
"Whats the difference between liquid and gas?"
] |
[
false
] |
I know this many sound like an extremely simple question, but on a molecular level, what's the difference between a liquid and a gas? From a young age we're shown a collection of diagrams showing how the structure of molecules in solids, liquids and gases differ. In diagram of the solid, they're touching, in the liquid, they're spaced apart and less structured, and in the gas, they're even further apart. My assumption has always been (feel free to correct me if I'm wrong), that difference between a solid and a liquid is the molecules 'touching', there molecular bonds. When a substance becomes hot enough that's its molecules have enough energy to break there bonds, it becomes a liquid. We have a definite point in which a solid becomes a liquid. Equally, there is a definite point when a gas becomes a plasma, when the molecules gain enough energy that there atomic bonds begin breaking down, making a soup of protons electrons and the works. ...but what's the definite point between liquid and gas? Are there any properties that a gas has the a liquid does not? Theoretically, if we had a liquid and a gas of the same density, how would they behave differently? Maybe a slept though a key part of my year 6 science classes and missed something. Help me atone for my younger laziness reddit!
|
[
"The molecules/atoms in solids aren't really \"touching,\" they are just held tightly together by weak intermolecular forces. There is an energy level at which the molecules/atoms are able to slide past one another despite the intermolecular forces, but are still held together: thus the liquid state. In a gas, however, each molecule/atom has sufficient energy to move entirely independently of it neighbors, which is why a gas will expand to fill it's container etc."
] |
[
"Briefly, condensed matter (i.e., solids and liquids) has a positive surface tension; gases do not. ",
"Put another way, it costs energy to form a condensed matter surface because such a surface is associated with unsatisfied bonds. There's no such implication with gases."
] |
[
"that difference between a solid and a liquid is the molecules 'touching', there molecular bonds",
"This is not true. Molecules in liquid are also \"touching.\" The difference is that bonds in a liquid can freely shift from one to another, while the bonds in a solid are fixed.",
"Equally, there is a definite point when a gas becomes a plasma",
"FYI, this is also not true. There is not a phase change point between gas and plasma. As you heat up a gas you'll just get more and more ions, not all of them ionizing at once.",
"Are there any properties that a gas has the a liquid does not?",
"The molecules in a gas are not \"stuck together\" at all. That's why it can freely expand to fill a space, while liquids maintain their volume even if they have room to expand. Gases also have no definite surface, while liquids do."
] |
[
"I've started studying quantum physics but have come across a problem I simply can't get my head around..."
] |
[
false
] |
From my understanding, in beta decay, a down quark in the neutron emits a W- boson, which then decays into a B- particle and an electron antineutrino, and then changes into an up quark. I know that a down quark weighs more than an up quark, but a W- boson weighs much more than the difference between them so where is this extra mass in the W- boson coming from? Is there another particle involved which gives its mass to the quark? Also, similarly, in positron emission, an up quark changes into a down quark and emits a W+ boson. Where is all this energy coming from that allows the up quark to change into a heavier down quark and also create the boson?
|
[
"These are two very good questions.",
"Starting with the B- decay: The issue here is that the W- that decays is actually not a real particle, but a virtual particle. A virtual W- does not necessarily have the same mass as a real W- boson, and exists solely to transmit the weak force. Where does the energy come from? It comes from the uncertainty principle. Remember that \\Delta(E)\\Delta(t) >= h\\bar/2. So if the W- boson exists for a small enough time, we can borrow some energy \\Delta(E) and still satisfy the uncertainty relation.",
"For the B+ decay: I'll give you a hint first: We can't see this decay in sole protons (we've never observed proton decay). The only way the reaction is kinematically allowed is if the total energy of the final state nucleus is ",
" than the original. So, in fact, the energy comes from changing the binding energy of the nucleus."
] |
[
"Thank you, the textbook made it seem as though a single proton simply changed into a neutron for no other reason than because. Even reading it again doesn't provide any better insight. ",
"As for the B- decay, are you saying that technically energy can be created, then, as long as the energy is then destroyed in a small enough time frame? Though only with these virtual particles. "
] |
[
"What does quantum foam mean? It sounds like gobbledygook to me! :)"
] |
[
"question about the old saying \"its like riding a bike, you never forget\", what is it about riding a bike that makes it so difficult to forget it?"
] |
[
false
] | null |
[
"Close. Motor skills. And rusty.",
"Good English for a non-native speaker! ...actually just straight up good English in general."
] |
[
"Riding a bike is, mostly, not something requiring \"training\", but rather just holding your arms straight and moving your feet. Most people can learn that in, like, less than 10 minutes, depending on their age. It's more about having the confidence in ",
" you can ride a bike, and not fall over. That might take a long time as a kid learning it, but if you already know you can ride a bike, you should have the motoric skills (think that's what it's called, english is not my native language) to ride the bike with ease, even after many years of being \"rusten\"."
] |
[
"It's to do with the part of your brain that you use wilst controlling / learning this skill. The motoric skills in general are relatively important to our human race, so we remember them for a long time as long as we do them from time to time. Imagine a primitive human in the savannah of Africa suddenly having the need to remember how to sprint when a lion is chasing him? "
] |
[
"Why don't ICBMs require a launch window?"
] |
[
false
] |
I've been following SpaceX's recent launches and there is always talk of launch windows and weather delays. At the same time conversations about ICBMs being launched at a "push of the button" are happening at the highest levels. My understanding is an ICBM is very similar to a multi-stage rocket used to launch a satellite for instance, so my question is, can ICBMs really be launched so readily? Is it because the accuracy of satellite placement needs to be much closer than a nuclear warhead? Is it the fact that a satellite is trying to hit a moving target (in the case of ISS rendezvous)? Or is the effect of weather just considered an acceptable risk once a decision has been made for a nuclear strike, whereas a routine rocket launches strive for 100% success? Does launching from a silo or using solid fuel mitigate the risk of weather? Is it known if nations would launch a salvo of ICBMs to account for failures (in addition to any existing countermeasures)? Thank you.
|
[
"A couple reasons.",
"Firstly, there is the fact that the launch is surface to surface not surface to orbit. The Earth rotates and thus the relationship between the position and momentum of a specific point on the Earth's surface (a launch site) and a specific orbit (inclination, phasing, etc.) of Earth or a specific orbit of the Sun (for interplanetary missions) is constantly changing, and for most launch sites there is only a short window of time with large breaks between (usually on the order of a day) when it is suitable to launch a given satellite into a specific orbit given the overall launch capabilities. However, the relative position and sub-orbital dynamics between two separate points on the surface of the Earth is always the same so there is no launch window for sub-orbital point to point trajectories.",
"Secondly, avoiding extreme weather is more of a matter of an excess of caution than an absolute necessity with launch vehicles. This is a numbers game. If you're launching one vehicle and spending hundreds of millions of dollars you don't want a 10%, 5%, or even 1% chance of failure due to wind sheer or lightning or what-have-you, so you'll just wait. If you're launching weapons of war en masse, that is no longer true. You launch a strike package containing perhaps dozens or hundreds of missiles from multiple locations and the overall total average failure rate of the whole shebang due to not only adverse weather conditions but also equipment malfunctions and so forth is already factored in and accounted for. Also, Apollo 12 flew through a thunderstorm and was struck by lightning and survived. Proof that you could engineer rockets to be more weather resistant if you put in the effort, but for launch vehicles the effort hasn't been warranted because they are already hugely expensive to develop.",
"Thirdly, on the same note, ICBMs ",
" generally more robust than launch vehicles. They are built stronger, they use solid fuels instead of liquid fuels (today), and they have higher thrust. This means they punch through the atmosphere much more reliably and with much less sensitivity to things like wind sheer than launch vehicles.",
"Fourthly, it is merely a coincidence that America's best location for a launch site (Southerly with ocean to the East, thus Florida) just happens is also an area of intense and frequent thunderstorm activity (with something like 1 out of every 5 days on average having a thunderstorm). This leads to a lot more launch holds due to adverse weather than other sites. Locations for other launch sites such as the high desert of the midwest or various parts of the open ocean for sub-launched SLBMs are on average much, much less likely to have launch interfering severe weather on any random day when a launch might be called for.",
" Compare the acceleration at launch of ",
"this Minuteman 3 launch",
" versus ",
"this Atlas V launch",
". The ICBM just screams out of the silo into the sky at many gees of acceleration, the Atlas V practically craaaaaawls off the launchpad at seemingly a walking pace until acceleration starts picking up as the rocket gets lighter (from expending propellant). Being built strong enough to withstand those gees means the ICBM can withstand much higher wind and weather conditions.",
": for fun you can also watch this launch of a ",
"sprint ABM interceptor",
": ",
"https://youtu.be/QiyldgYKy_U?t=52",
" (that bump you see in the launch is actually staging, the first stage burns for only 1.2 seconds)."
] |
[
"If you are launching ICBMs, it is hoped that this is an absolutely desperate last-resort measure. If you have time to think about the weather you should not be launching nuclear weapons at people. Also, the plan has always been to launch a lot of them at once, in order to overwhelm any defences, so you expect to lose some of them from the start.",
"Launching a rocket to Mars is kind of a one-shot deal, so you really want to minimize the risk, and it’s nowhere near as urgent."
] |
[
"Most space missions have a launch window because of the relative motions of the launch center and the mission target. For example, when SpaceX tries to rezvendous with the International Space Station they need to launch at a time that allows the rocket to intercept the space station. If this is not timed correctly then the rocket could get to orbit but the space station might be on the other side of the planet.",
"Sending anything into space is incredibly expensive. This includes spare fuel for extra maneuvers and spare supplies for spending extra time in space. Most missions are planned for a pretty specific timeline with a pretty specific set of maneuvers. The spacecraft carries enough supplies to reach the ISS \"when its overhead\" but not enough to launch at any random time and then go find and catch up to the space station. ",
"As before, this is a problem because of the motion between the launch site and the mission destination. Sometimes the mission destination is close by, and sometimes its farther away. ICBM's don't have this problem. If you build a nuclear missile silo in North Dakota and aim the rockets at Moscow, the relative positions of the launch location and the target never change. Once that ICBM is built, fueled, and programmed it can sit in that missile silo and be ready to go whenever needed. There are no external variables that would cause the ICBM to fail to have enough fuel to reach its target.",
"This is especially apparent when we consider launching to other planets. Both Earth and Mars, for example, move in an orbit around the sun. Only once every two years are these two planets at their closest point and sending a rocket to mars is economically feasible. You don't have to launch at the exact moment of least separation, but you need to be relatively close.",
"An even worse (better?) example is the Voyager missions. These missions took advantage of a particular alignment of all of the planets so that a single probe could visit multiple planets in sequence. This particular alignment only occurs once every 175 years, so hitting that particular launch window is literally a once-in-a-lifetime opportunity. These missions were able to visit Saturn, Jupiter, Uranus and (only Voyager 2) Neptune in a single trip. "
] |
[
"How could we travel faster than the speed of light?"
] |
[
false
] | null |
[
"We can't."
] |
[
"You're right. No, we can't currently because the amount of energy required to move an object that has mass approaches infinity as the object approaches the speed of light, as I understand it. But what theoretical ways could we get around this?"
] |
[
"None.",
"If you could, you could build a time machine, which makes physics inconsistent."
] |
[
"Is this a meteorite?"
] |
[
false
] |
I found stuck in my shoe today, it looks like shiny metal in a few spots where it was worn, the rest of it looks like a volcanic rock with lots of tiny bubbles. It is attracted to a magnet and is roughly 1.5cm long. Sorry for the poor picture I can take a better one tonight.
|
[
"Looks more like a chunk of slag to me. Any blast furnaces in the neighborhood?"
] |
[
"Sould slag be magnetic?"
] |
[
"If it's got enough metal in it. Depends on the slag, but the kind that looks like this often does."
] |
[
"What magnification is required to view DNA during mitosis??"
] |
[
false
] |
I remember back in highschool Biology class I had the opportunity to look at plant cells undergoing various stages of mitosis. I remember being fascinated by how clearly visible each cell wall was and how clearly I could see the strands of DNA and the cells duplicating during anaphase. I always wondered how much more magnification it would take to actually be able to see the nucleobases.
|
[
"You can't see individual strands of DNA without an electron microscope (very high magnification). What you saw under the microscope were ",
", which is DNA packaged together so tightly that makes the strands negatively supercoiled and will break without the help of various proteins inside the cell. These chromosomes are what come apart during anaphase. In addition, even the chromosomes can't be seen under an optical microscope without a stain. The cells you observed in high school were dead and stained. It is extremely difficult to see this in live cells. ",
"Even with electron microscopy, individual bases can't be seen. You can only see the backbone of the DNA molecules. "
] |
[
"I always wondered how much more magnification it would take to actually be able to see the nucleobases.",
"Bases are so small you have to move away from \"regular\" (light, electrons) magnification based microscopy and towards other technologies. Scanning tunneling microscopy and atomic force microscopy give you a way to directly 'image' materials. However these won't produce images of nucleotides in quite the way you may be envisaging. With these technologies we move a \"charged\" tip over a surface and by measuring the changes in the forces the tip experiences we can visualise the surface; here's two such papers:",
"http://www.pnas.org/content/103/1/10.full",
"http://www.ncbi.nlm.nih.gov/pmc/articles/PMC41681/",
"If you look at some of the images in those papers they probably don't produce the kind of images of molecules that you might have been imagining. Atomic and/or molecular resolution imaging is currently only achieveable by two methods; X-ray crystalography and NMR. In X-ray crystallography we'd prepare a crystallised sample of purified DNA, then we fire a beam of x-rays at the crystal and by measuring how the beam is deflected by the crystal we can infer where in the crystal the atoms are and in turn we can reconstitute the structure the bases and the DNA strand. NMR is basically a very, very high powered version of the MRI machines you find in hospitals, using radiowaves and high powered magnets we can probe a purified sample of DNA to find out information about the relative location of atoms in our sample. Like the x-ray method this information can be used to reconstitute the specific structure of the nucleotides and DNA strand",
"You can look up a whole world of atomic resolution imaging for proteins and DNA at the RCSB Protein Data Bank;",
"http://www.rcsb.org/pdb/home/home.do",
"There are quite a few structures for DNA deposited, here's a good one:",
"http://www.rcsb.org/pdb/explore/explore.do?structureId=4NZX",
"tl;dr; in short we can't really magnify our way to resolving individual nucleobases but there are number of alternative imaging technologies that can be used for this",
"edit: tl;dr 2: Molecular imaging is typically at the sub-Angstrom scale. With respects to conventional microscopy you might regard this as representing a factor magnification around 10",
" to 10",
" (given that an Angstrom is about 10",
" metres."
] |
[
"when you look at cells during mitosis what you see is actually chromosomes. These are tightly coiled wound and spooled double stranded DNA/protein complexes. To actually \"see\" a nucleotide with any clarity, you would need the use of x-ray crystallography or similar method such as NMR. You can begin to see the DNA strands with some clarity using electron microscopes, but the resolution isn't sufficient to distinguish the bases from one another. "
] |
[
"Do octopuses have specific limbs that would be arms and legs or are they all the same?"
] |
[
false
] |
[deleted]
|
[
"Your question also made me wonder about a follow up; do octopodes exhibit handedness?",
"I found this cool article: ",
"http://www.nature.com/news/2004/040615/full/news040614-1.html",
"In it it also says: ",
"Favourite arms are usually at the front of the animal, the team found. Meanwhile an octopus's rear limbs tend to shoulder much of the burden of locomotion, making them almost analogous to legs.",
"So it seems, that yes they do have semi-specific function and preference for tentacles but they all seem to be equally dextrous."
] |
[
"It’s interesting and colorful… maybe even pretty… but you and I must have very different definitions of “cute”.",
"(I can’t even tell where front and back are in that picture.)"
] |
[
"It’s interesting and colorful… maybe even pretty… but you and I must have very different definitions of “cute”.",
"(I can’t even tell where front and back are in that picture.)"
] |
[
"Sodium lauryl sulphoacetate - what's the deal?"
] |
[
false
] |
A friend of mine has bought some rather nice liquid hand soap that proudly boasts amongst other things that is has no parabens (good) and no sodium lauryl sulphate (apparently good). But I read the ingredients: it might not have sodium lauryl , but it does contain sodium lauryl . Now, as a non-chemist that looks like a very slight chemical change; if it a slight change, then really the advertising is disingenuous but not factually incorrect. But more interestingly, what if there is a big difference? Does that change matters much? So my question is: what, if any, differences in reactions are there between the two chemicals, with special reference to effects on humans. Thanks in advance! (Hope the question isn't too narrow, but I've found it can help discussion to at least have a nice, concrete question to start off with.)
|
[
"Here are some references.",
"http://en.wikipedia.org/wiki/Sodium_dodecyl_sulfate",
"http://chemicaloftheday.squarespace.com/todays-chemical/2010/9/14/sodium-lauryl-sulfoacetate.html",
"They appear to be very similar compounds, both chemically and in some of the symptoms/side-effects. Apparently SLSA is newer and appears to be milder, but this may be due to lack of data. It seems to be non-biodegradable and moderately toxic to aquatic life."
] |
[
"Sodium Lauryl Sulphate (SLS)- \"It is a known skin irritant and is absorbed through the skin and retained in the heart, liver and brain for long periods of time.\"",
"I would look at this with extreme skepticism. There is no way they could put this in every shampoo, toothpaste, etc. known to man, if that was true."
] |
[
"I'll be buggered. I spent ages searching for info and turned up very little.",
"I'd like to see some stuff from chemists and a bit more detail, but that's a fantastic start. Thank you!"
] |
[
"If a camera focuses on a mirror will all the things in the mirror be in focus too?"
] |
[
false
] | null |
[
"Yep. Your eyeball also has a lens just like a camera that needs to focus. ",
"You can do a simple experiment by taping a picture on your mirror and focusing alternatively on the picture or on your reflection. You can feel your focus changing and can see that only one of the images is in focus at a time."
] |
[
"No. Focal distance for objects seen in a mirror is sensor to mirror + mirror to object. You can focus on the surface of the mirror or on the reflect you see in it. "
] |
[
"What is sensor to mirror and what is mirror to object?"
] |
[
"Will there ever be a point in time on Earth when we won't be able to look at the entirety of the geologic record?"
] |
[
false
] |
Another phrasing: will there ever be a point in time where the beginnings of the geologic record will be wiped away by geologic forces?
|
[
"We are already missing large portions of the geologic record. While we have some material preserved from early portions of the Earth, e.g., ",
"the ~4.4 billion old zircon grains from the Jack Hills",
" which can provide a variety of clues about processes going on at the time of their formation (e.g., ",
"Ushikubo et al., 2008",
"), the oldest rocks that are exposed are ~4 billion years old (i.e., the ",
"Acasta Gneiss",
"), meaning that we have zero intact rocks from the first ~600 million years of Earth's history. Our gaps are not constrained to the very earliest history, e.g., the so-called 'Great Unconformity' represents several hundred million to nearly a billion years of missing time at the end of the ",
"Neoproterozoic",
" in many areas around the globe (e.g., ",
"Keller et al., 2018",
", ",
"McDannell et al., 2022",
"). The Great Unconformity is one of the largest, both in terms of time and spatial coverage, but certainly not the only large chunk of missing time within the rock record. Probably the largest missing bit of history relates to how plate tectonics work, and specifically that the maximum duration of oceanic lithosphere is ~200 million years, so our record of ~70% of the Earth's surface only goes back ",
"at max 200 million years",
". All of this is to say that there really was never a time when the geologic record was \"complete\" in any meaningful sense."
] |
[
"This completely satisfied my curiosity while also giving it something else to crave. Thank you!"
] |
[
"This is categorically untrue. ",
"I'm familiar with the video you're referring to and I have to say it is ",
" bad. I was a fan of Kurzgesagt, there's a place for pop-science as a tool to spark interest in a topic and no one can argue with the Kurzgesagt's production value. While I had noticed an instance or two of head-scratching simplification (to the point of near-falsehood) overall I felt they were rather good at boiling complicated ideas down into an easily digestible, interesting, and entertaining format. However, the video is question falls within the wheelhouse of my own scientific research (paleoclimatology and geochemistry) and is so badly mangled that I am left looking askance at the rest of their work.",
"I simply can't help but wonder, are there (m)any other Kurzgesagt videos equally, fundamentally incorrect? Perhaps pertaining to subjects on which I'm simply not knowledgeable enough to catch? ",
"Human civilization has fundamentally altered the chemistry of Earth's surface. Evidence of these alterations will persist ",
" hundreds of millions of years into the future; until the current, youngest, and best positioned (in respect to longevity) oceanic-crust subducts under its associated plate boundary. ",
"These alterations are massive in magnitude, global in reach, and chemically universal. Throw a dart at the periodic table and you'd be hard-pressed to miss an element on our planet's surface that now bears the indelible human mark. As a geochemist I will focus on chemistry, however any enterprising future geologist would certainly make note of many other lines of, more direct, physical evidence suggestive of an \"advanced\" society in the sediment record. ",
"Any single dataset discussed here, on its own, could ",
" be interpreted as a natural consequence. Though in many cases it would represent a singular event distinct from the rest of the geologic record (including other major events). However, when the body of evidence is evaluated as a whole: the massive isotopic perturbations of every stable isotopic system (particularly C, N, S, and O), ubiquitous elemental enrichments/depletions, the sudden appearance (and likely disappearance) of plastic in the sedimentary record, nuclear testing, ocean acidification, as well as the end-Holocene mass extinction event (which will likely scale along with the most massive die-offs in Earth's history by the time it is through), etc. It becomes ",
" difficult to imagine a future investigator avoiding the obvious interpretation: that a past civilization grew capable of modifying Earth's surface in a directed manner to its own \"benefit\".",
"Delving into some of these chemical records we might examine the massive perturbations to the carbon-cycle, beginning with landcover change and the agrarian revolution 10,000 years ago and spiraling into the industrial revolution and widespread combustion of fossil fuels today. These mechanisms not only change where carbon is store, it change the isotopic composition of carbon on Earth's surface. Beyond carbon we might look to the massive levers we pull on the nitrogen cycle when implementing the haber-bosch process, rare earth element mining, heavy industry, etc. the list is nearly endless.",
"All of these changes are recorded in the sediments. In the case of carbon, the isotopically light carbon we burn to power the modern world enters the atmosphere and is absorbed by the oceans. This C-12 enriched carbon is then utilized by phytoplankton to build their calcium carbonate (CaCO3) shells.",
"These phytoplankton eventually die and the vast majority are consumed. However their inorganic shells eventually make their way to the seafloor (generally riding fecal matter); the \"fecal express\", or \"marine-snow\". This material comprises the bulk of oceanic sediments over large swaths of the seafloor.The oldest parts of an oceanic plate might be topped by a layer of these microscopic shells reaching thicknesses measured in kilometers.",
"As paleoclimatologist we utilize these sediments as a primary archive of Earth's history. From drill ships we work to recover sediment cores from which we analyze the ancient carbonate shells (and so much more). This is a critical resource for reconstructing the perturbations in the carbon cycle through Earth history.",
"It's also how we know we are in for a ",
" bad time. Given the current magnitude of change (and how similar changes of far less magnitude are associated with mass extinction events). It is also how any future geologist, terrestrial or otherwise, would be able to ascertain our historical presence, should they have the desire to reconstruct our planet's history. Coupled with the rest of the elemental and isotopic changes going on in this geologic moment it would be plain to any future geologist looking, that a global civilization capable of massive industry was present in the here and now.",
"And while I referenced a preservation limit of 180-200 million years (at which point even the best positioned sediments for longetivity will be subducted back into the subsurface). The record will carry on in various reservoirs far past this point e.g. abducted ophiolites (marine sediment scraped onto the side of continents as the bulk of it's oceanic plate descends), in shallow basins, and on the continents themselves. These however only provide snapshots, rather than continuous records, of Earth history; and thus, the deep(er) past requires greater focus in stitching together a narrative.",
" Many are asking for sources, so here's some reading:",
"The carbon isotope record reflects the “discovery” of the New World some 500 years ago. As populations crashed in the Western Hemisphere, forests reclaimed enormous areas of previously worked, arable land. This reflects how forests store much more carbon (organic; isotopically light) per square meter than farmland.",
"How the sedimentary archive of lead(Pb) records the rise and fall of the Roman Empire",
"Urine salts highly enriched in soluble sodium, chlorine, nitrate, and nitrate-nitrogen isotope values preserve evidence of an exploding population of human beings associated with the rise of wide scale agriculture in Turkey ~10,000 years ago",
"Now, one might argue that a past civilization may not have been carbon based, may not have required sustenance or energy. May have been incorporeal plasma bodies slipping through space and time. I obviously cannot prove such a thing is impossible just as I cannot ",
" a null hypothesis. However, life as we know it follows the laws of thermodynamics. And ",
" that rises to a certain technological point will leave its indelible in the sedimentary record of its home planet.",
"At the end of the day I'm not arguing against the possible existence of some theoretical, completely alien civilization. I am arguing against Kurzgesagt's thesis that the evidence of ",
" civilization disappears after a few million years. A thesis that is categorically incorrect given the context of that video."
] |
[
"How fast would the planet have to decelerate to a halt in its orbit to cause objects to overcome gravity and fly off the planet?"
] |
[
false
] | null |
[
"9.8 m/s",
" That's the acceleration due to gravity at the surface of the Earth, so as long as the planet decelerates faster than that everything on the leading edge will overcome gravity. Everything on the trailing edge, of course, will experience up to 2g. "
] |
[
"Yes, humans can withstand 2g for a long time according to NASA research ",
"http://history.nasa.gov/conghand/mannedev.htm",
" figure 5. Remember this is only true for grown adults, small children with comparable weak bones would suffer from disformation of their skeleton."
] |
[
"Ignoring air resistance and earth's rotation because they make things hard,\nto leave the surface of the earth, 9.8m/s",
" However, this will really just toss everything a little bit in the air, while earth's gravity pulls it back down. So the earth is accelerating away from you at 9.8m/s",
" but you're falling towards it also at 9.8m/s",
" essentially being weightless. Since the earth is moving around the sun at approximately 29800m/s (on average), it will take earth about 3070 seconds (just under an hour) to come to a complete stop, at which point you'll fall back to the ground. (This ignores that earth will start accelerating towards the sun as it slows down in orbit)",
"If you're interested in a deceleration that will literally eject things off the earth into space so they won't ever fall back, it's a little more interesting.",
"The acceleration due to gravity is a= GM/r",
" G is something like 6.67 * 10",
" M is ~6 * 10",
" and r is ~6,300,000 on the surface of earth which should work out to ~9.8 (all with appropriate units in KMS). What matters is, the further you get away from earth, the less your gravity is. So if you were a sufficient distance away from earth in the earlier case, it's accelerating away at 9.8m/s",
" and you're accelerating towards at less than that, having the net effect of increasing your distance from earth. ",
"If you start on the surface and earth slows down at a>9.8, we need to find a(earth) such that by the time the earth stops moving, the total effect of (a(earth)-a(you)) over time = ",
"escape velocity",
"ignoring bad coding and a bunch of rounded numbers...",
"import math\n\nGM=400200000000000;\nfor asdf in range (99,110):\n a = 9.8;\n r = 6370000.0;\n v = 0.0;\n ae = asdf*0.1;\n t = int(29800/ae);\n for i in range (1,t+1):\n a = GM/r/r;\n v = v+ae-a;\n r = r+v;\n e = math.sqrt(2*GM/r)\n if (e-v) < 0.0:\n print ae\n break\n",
"My method involves guess and check, but I didn't try to find a closed form of those equations such that it's integratable, and writing a python script was easier.",
"10.2 m/s",
" is enough to permanently throw you into space. At first you're only accelerating at ~.4m/",
" .4 * 3000 = 1200 m/s <<11,200 (escape velocity at surface). But by the time you account for constantly decreasing gravity, at the end of an hour you're accelerating away from earth at around 8 m/s",
" and reach the decreased v = ~8,000m/s",
"Edit: (assuming you're standing on the 'front' of earth. At sunrise on the equator during an equinox would be one such place.)"
] |
[
"Does hearing bat squeaks indicate we are in their field of view? Do bats produce a focused enough echolocation sound that whatever can hear the sound is being observed by the bat?"
] |
[
false
] | null |
[
"Humans are not capable of hearing most bat squeaks (they're mostly ultrasonic), but bats are capable of producing remarkably focused sounds as well as adjusting the level of precision by altering the frequency and loudness of the sound they're using. A study published in nature found that on average, a bat call had a \"width\" of about 37º. That's about a tenth of a circle. That's pretty impressive."
] |
[
"Well, if you are behind something the bat cannot \"see\" you. Echolocation does not form a 3d map, but rather a picture that looks like it came from an eye. You can strand behind a tree and hear the bat just fine, but the bat will only \"see\" the tree,as that is the only thing that will bounce directly back to it"
] |
[
"The audible sounds you are hearing are mostly for communication purposes, not echolocation."
] |
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