title
list | over_18
list | post_content
stringlengths 0
9.37k
⌀ | C1
list | C2
list | C3
list |
|---|---|---|---|---|---|
[
"How can computers be able to calculate when they are only a bunch of inert materials connected via electricity ?"
] |
[
false
] | null |
[
"Hi ",
"/u/lucasmoulinx",
" ,",
"Unfortunately, there's a lot of misconceptions in your question. Let me try to point you in the right way:",
"A Turing machine is a model of computation. It is not real, most prominently because it possesses an infinite tape (storage). Contemporary computers are classified/modeled as \"linear bounded automata\".",
"Computers do not think. They perform the computations they are programmed to. Computers can take decisions in the sense that they are able to direct the program flow based on a binary choice - in other words, select one out of two instructions to execute based on a binary value. There is no straightforward way from which to program a \"thinking\" computer, and it is unclear if there ever will be.",
"Computers are most definitely not magic. :)",
"I'm not sure exactly where to point you. If you are interested in how computers are built, I can suggest a few computer architecture textbooks. Let me know.",
"If you want, you can also ask for more resources in ",
"/r/AskScienceDiscussion",
" ",
"Hope this helps."
] |
[
"Hello and thank you very much for taking the time to answer my question. I understand that computers cannot think, but what I meant was how are they able to make a choice or to select information by themselves? Again I am not certain to be clear or that my question even makes sense. Maybe I should as you said make some researches about how computers are built, because I have trouble picturing how to go from the abstract idea of an algorithm to the concrete building of a computer. \nAgain, thank you for your answer and if you have any resources you think might be useful for me to understand the physical concept of a computer, or calculation machine, do not hesitate to share them with me! "
] |
[
"Off-hand; I assume you have some sort of high-level overview of what a computer can do, but lack the low level insight. If so, I usually recommend ",
" by Tanenbaum. It will most likely be available at your local library, and parts of it may be available online as well.",
"You may also want to look at courses on computer architecture offered by various Computer Science departments, particularly USA-based.",
"I would encourage you to ask for more suggestions in ",
"/r/AskScienceDiscussion",
" - I will try to write a longer list there, and I'm sure helpful folks will suggest things I did not think of. :)",
"Cheers."
] |
[
"Is Turritopsis nutricula (the \"Immortal Jellyfish\") really immortal?"
] |
[
false
] |
As far as I understand, the "Immortal Jellyfish" can go back from being an adult to an infant, repeating this process indefinitely. Since most regular Jellyfish are doomed to die after a specific amount of time after reaching adulthood, this mechanism grants the "Immortal Jellyfish" as many life cycles as it wants. But is it immortal? After many cycles, I'd expect its DNA to have significantly mutated, leading to cancer, infertility, disease, and eventually death. And most importantly: What is the longest amount of time we have such a jellyfish to live? Is it much different than how long other jellyfish live?
|
[
"From the Wikipedia article you've mentioned:",
"Studies in the laboratory showed that 100% of specimens could revert to the polyp stage, but so far the process has not been observed in nature, in part because the process is quite rapid and field observations at the right moment in time are unlikely.[3] In spite of this remarkable ability, most Turritopsis medusae are likely to fall victim to the general hazards of life as plankton, including being eaten by other animals, or succumbing to disease.",
"That said, it's still an important discovery. ",
"There are also ",
"many other candidates for biological immortality",
" not to mention ",
"some of the longest lived organisms",
", because that would be rude not to mention them.",
"Also ",
"Lobsters can live for a long time according to reddit, but they really can't.",
". If they could they wouldn't because we'd eat them anyway.",
"edit: I would like to point out that it's likely the jellyfish in question gained this \"biological immortality\" to help its species survive in a very harsh and big ocean. They can be found all over the world, and it's believed this trait has helped them spread over the world. ",
"I would also like to note that I'm a layman."
] |
[
"I hate that I can't make a joke about my name in this subreddit!",
"It is biologically immortal, yes. So it has chance of living forever, albeit a small chance."
] |
[
"Of course! Death erases 100% of your previous life, so even a regenerative process that takes away 100% of my life would be no worse than death, with the potential for it to be better since I could learn about my previous self and thus have some continuity along with a fresh start."
] |
[
"The observable universe vs. the entire universe"
] |
[
false
] |
I was reading something and I thought.. "if we can't see past the observable universe, then how can we estimate a size of the universe?" Several sources later.. I took many things in from them, but some parts sounded like they were making up words. Help me out here, I'm explaining it in my own words the best that I can. Space is expanding at a constant rate into other objects that were once in some unobservable state. Two main theories. The first, that the expanding observable space is caused by something that is filling space between objects (dark energy), which in result, objects "slow down" (redshift) to an observable state. The second, that light originated in this location (and possibly others far away) of the universe and is expanding into the rest of it. I have a feeling I'm off on that second one, or really over-simplifying it. I'm still a little confused on how the entire universe is estimated at 93 billion *light years. Why is there a limitation put on it's size? Is/how is that measurable? I read about comoving distance but didn't really understand how that can tell you where an event happened. I think I understand it a little better than I can explain.. If anyone can build on that or correct me for someone with intermediary astronomy skills but a lot of interest, sweet! Feel free to blow my mind some more as well. *edit
|
[
"the entire universe is estimated at 93 billion years",
"Who says that? Even if you mean \"light years\", the universe is usually assumed to be infinite. Are you talking about just the observable universe?\nThen that number is not measured, but more calculated based on other measurements and the theory of general relativity.",
"Also, space is not expanding at a constant rate, but accelerating. This has been known for a little bit over 10 years now and the reason for this has been dubbed \"dark energy\" and we don't really know what it is.",
"You also have some misconception about the universe \"expanding into something else\", which is really not what it is doing, but I don't feel like writing a whole lot more. This misconception seems to be rather common though. One of these days I should attempt to create an appropriate animation of the big bang, although it's a challenge. "
] |
[
"The people who made that flash applet obviously are not cosmologists. They apparently stumbled upon the number of 93 billion ly and thought, \"if the universe is only 14 billion years old, how can that be the observable universe?\" and thus came to the conclusion, that the observable universe is 14 billion ly in size and the entire universe is 93 billion ly in size, but that is WRONG.",
"Because of the acceleration of spacetime, the observable universe is larger than the distance that light can travel in 14 billion years. Furthermore, cosmology knows more than one definition of \"distance\". Using one of the definitions, the size of the observable universe is actually exactly those 14 billion ly. But in a more useful definition for us, it is those 93 billion ly.",
"I haven't read this, so I can't tell you how good it is or if it is suitable for you, but on a first glance it looks ok.\n",
"http://de.arxiv.org/abs/astro-ph/0409426"
] |
[
"Point is, no serious scientist will conclude something they have zero information about. Almost every interview I read by a physicist answers the \"is the Universe infinite?\" question with \"we don't know\". That really is the only correct answer with our current level of understanding. ",
"It's like we are ants who have only explored the Smith's lawn trying to answer questions about the size and shape of the Earth. "
] |
[
"Our internal body temperature is 98.6 F, so why does it feel so hot when it's that temperature outside?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"medical advice",
"/r/AskScience",
"Please see our ",
"guidelines.",
"If you disagree with this decision, please send a message to the moderators."
] |
[
"I understand the guideline against medical advice, but I would argue that feeling hot when it's 98 degrees outside is not a medical condition, but rather is how most humans experience the world. Similarly, most feel cold when it's under 0F outside. Maybe not all, but certainly most.",
"I'm open to being persuaded otherwise, but I disagree that this is related to medical advice."
] |
[
"Oops! I'm sorry, I accidentally selected the incorrect response message (there are several when removing a post) -- I meant to select the one that said that this is a fairly common question and that you can find the answer by searching in the search bar for something like \"98 body temperature\". Unfortunately, because of the high volume, a lot of great questions and answers can get buried quite quickly. The search bar can be a great way of exploring ",
"/r/askscience",
"! Let me know if you have trouble finding a relevant post, and I can point you in the right direction."
] |
[
"How dark is space?"
] |
[
false
] |
Say I was floating around in deep space but protected in a space suit, the victim of a terrible star trekking disaster. If I was stranded far away from any known star or solar system, Would I be able to see my hand infront of my face? Would the ambient universal light from distant stars provide me with enough light to read a book while I float around awaiting my lonely death? How bright is empty space?
|
[
"As another post mentions, a good rule of thumb might be taking night-time with no light pollution, during a new moon. (I would add no planets here as well.) I poked around for some numbers... (Here: ",
"http://www.ee.ryerson.ca/~phiscock/astronomy/light-pollution/photometry.pdf",
")",
"What we're looking for is illuminance, which is how much incident light hits a surface for human perception (you mentioned wanting to see your hand). The figure it gives here is 2x10",
" lux, which is on the border of perceptibility (you could probably make out objects, but not read.)",
"You can definitely see the stars themselves (this is determined by luminence). Scotopic vision (",
"https://en.wikipedia.org/wiki/Scotopic_vision",
") can detect things down to maybe 3x10",
" cd/m",
" (threshold of vision), vs. \"night sky\" at 10",
" cd/m",
" on the chart.",
"Okay, but you mentioned \"deep\" space, and we are still talking about being inside a galaxy. Most of the universe isn't galaxies, but empty space. So let's imagine that we were far away from the Milky Way. At this point, you can give up any hope of seeing your hand. But what other galaxies could we see? What other galaxies are visible from Earth, ignoring the Milky Way and its satellites? Turns out only a handful can be seen. (See \"naked-eye galaxies\" here: ",
"https://en.wikipedia.org/wiki/List_of_galaxies",
")",
"But the universe is far far more cruel than this: at the largest scale, the universe is actually organized mostly into immense voids, and almost all of the galaxies are clustered together (into clusters, filaments and walls) sit between the voids somewhat like a foam. If by \"deep space\" you mean that you find yourself in one of these voids (and if you picked a random spot in the universe to be in, you'll probably end up here), I doubt you would see anything at all with the naked eye.",
"(See ",
"https://en.wikipedia.org/wiki/Observable_universe#Large-scale_structure",
")"
] |
[
"I'm not going to run numbers here, since the question is a little vague. This depends entirely on your definition of \"deep space\". If you mean, say, moving 4 or so light years away from our solar system and keeping that same distance from any other stars, then you're essentially talking about going to a dark sky site on Earth in the middle of the night, with the moon well below the horizon (new phase). In my professional experience, it is impossible to read a book in this light, but easily possible to see your hands and slowly and deliberately set up basic (read: not fiddly) equipment, such as portable telescopes, laptops, etc.",
"If we are talking about intergalactic space (halfway between the milky way and Andromeda, for example - on the order of a million light-years away), you wont be able to even see your own hand except as a shadow against the nearest galaxies - out there you wont be able to see any stars, only a few vague and very dim cloudy objects. Mostly you will see only blackness. Your eyes, once fully dark adapted, are remarkable instruments, but even they need more than the few scattered photons you will get from galaxies more than about 3 million light-years away. Even with a pretty decent (6 to 8 inch) amateur telescope, 15 million LY is about it.",
"So, any direction you look from out there where there are no galaxies within about 3 million LY (so, most directions you would care to look), you would see literally nothing. The blackest blackness it is possible to (fail to) perceive.",
"If you left our local group of galaxies and headed out into the space between groups, you would conceivably see absolutely nothing in any direction at all, even with a small telescope."
] |
[
"But what other galaxies could we see? ... Turns out only a handful can be seen.",
"So, essentially, any future intergalactic traveler would never see a view like ",
"this?"
] |
[
"How much gravity does an object need to visibly bend light waves?"
] |
[
false
] |
I know that dark matter bends light (gravitational lensing), but what is the lower limit for this kind of thing? Does the Earth have any effect on light waves?
|
[
"It does, but being able to see light bending depends a lot on the position of the viewer, in addition to the mass of the object. Gravitational Lensing in most of its classical examples like ",
"this",
" dramatic distortion happens with a galaxy billions of light years away. Light travels extremely fast, so the light has to travel a long way for the effect to be exaggerated enough to be visible. That being said, less massive objects than huge globular clusters produce only very subtle lensing effects. Einstein's original theory about the lensing effect was first experimentally verified by looking at the Sun's effect on nearby stars. The change in apparent position was extremely subtle, and would probably not be visible to the human eye. ",
"Tl;dr you need something galaxy-sized for an obvious distortion and it needs to be really far away. Anything that has mass (the Earth included) DOES bend light that passes near it, just not enough to really be visible.",
"P.S. also, gravitational lensing requires three things; a light source, an observer, and a massive object in between the two. This means that people standing on Earth would not see a lensing effect ",
", since there's not distance between the mass and the observer."
] |
[
"Thanks for the informative response!",
"Follow up question: can gravity affect sound waves the same way it does light waves? Given it was in a non-vacuum area of space and the object would not obstruct the path of the sound wave directly."
] |
[
"Well, sound waves are, by definition, pressure waves in a material (normally air for us humans). So the way a sound wave travels depends on the type and shape of the object or medium it is passing through. If an object is shaped or distorted by gravity, it will have a corresponding effect on sound waves that travel through that object. ",
"That being said, sound waves, unlike light, can't travel far (in terms of space-sized objects) because they die out quickly as their energy is dissipated through the medium, so you're not going to see 'sound lensing' in space."
] |
[
"How can sound travel as light in an optical cable? And does that mean the speed of sound can be increased beyond the sound barrier?"
] |
[
false
] | null |
[
"Where did you hear that “sound travels as light”?"
] |
[
"I was just assuming that since light is involved at both ends and the cable is optical based that the sound was traveling in the form of light"
] |
[
"What sound? It’s light everywhere."
] |
[
"Why can't I receive information from the future via delayed choice quantum eraser with a different beam splitter?"
] |
[
false
] |
It seems that you cannot send information to the past (aka receive information from the future) with delayed choice because the waveform interference pattern cannot be understood with the screen alone because you need to first examine the detectors to make sense of the dots on the screen. The current thinking seems to be that you cannot send information across time because in the scrambling "eraser" section of the experiment, we send photons through a beam splitter which results in 50% landing in detectors C and the other 50% in detector D. Due to the fact their interference patterns subsequently are perfectly out of phase, you cannot decipher waveforms with the screen alone because without being able to reference the information in the detectors, the screen alone just looks like a bunch of unorganized dots with no apparent interference pattern. However, is there a beam splitter available to science which could send most of the photons to one of the two detectors (for example, 99% go to detector C once they are in the eraser portion of the experiment). It would seem to me that if there's a beam splitter than can send most of the photons just to detector C (99% instead of 50%), you would pretty clearly be able to see either a waveform or not, despite a little bit of fuzziness. This idea also seems like it would not violate nature's rules about not having certainty about path information to get the waveform interference pattern. References:
|
[
"Ok well I've explained it 3 ways now, why your setup doesn't work and where your thinking is wrong. You don't seem to accept it, but at least keep in mind: either you've misunderstood or there is a trivially easy way to send FTL signals that has gone unnoticed by the worlds best and brightest for 100 years..."
] |
[
"Then you just have an almost totally unorganized blur for your C post selections, and basically a blank screen for your D post selections. The photons state is a 50-50 superposition for the two patterns (fringe/antifringe), the BS doesn't assign the state, just sorts (trasmits or reflects) based on it/in proportion to its weight. So, any BS which transmits not 50-50 will be sending a mixture of countervailing patterns to at least 1 detector, which washes out the interference an increasing amount as it approaches 100-0. Maybe easier to see if you instead ask: why can't the DCQE use just 3 detectors (replace C with a mirror aimed at D) and concentrate all the erased paths on 1 location? Because then the photons aren't spatially sorted by patterns at all and the setup is self defeating."
] |
[
"No, I just always receive the unfiltered C+D combined pattern, which is always a blur/blob. Nothing you do before or after can change this for me. I can't filter my measurement result to just the subset of my photon impressions that paired your Cs until you tell me which ones were Cs for you. For which you will need to send a lightspeed signal.",
"And, if you choose to send 99% to C, this won't be very interesting to me, once you send me the report of which photons were C photons. It will at best filter my blob down to a fringe pattern overlaid with 98% of an anti fringe pattern. This will not really look any different than the full C+D blob I had pre filtering."
] |
[
"Why are \"god rays\" (light rays coming through clouds) not parallel but seem to come from a point light source much closer than the sun?"
] |
[
false
] | null |
[
"They ",
" parallel. Think about what happens when you look at a long set of parallel lines, like a railroad track. ",
"They look like they converge",
" in the far-off distance. That's why the rays that you see appear to diverge from a point.",
"PS The scientific name is ",
"crepuscular rays",
".",
"Edit: lot's of people are having trouble believing the idea that they actually are parallel beams of light. Yes, they will be affected by the fact that the Sun is not infinitely far away, and by the fact that the sun is not a true point source, so they are not 100% completely parallel, but their deviation from parallel is so tiny that it is negligible on the scale of the Earth. Also, the shadows will have a ",
"penumbral",
" part as well, so they will be slightly smaller as they go, but the penumbral angle is only 0.25 degrees, which will be barely noticeable even on scales of 100s of miles or kilometers.",
"Take a look at this example of ",
", which are the same thing but on the opposite side of the sky. You can see clearly that the shadows converge again on the opposite horizon, something that only essentially parallel lines could do."
] |
[
"Thanks for the new wallpaper!",
"Hecklingfern has it right - those sun rays only look like they're vertical. They're actually angled. Something you learn when you start following weather around in the summer is that distances in the sky are very deceptive. The supercell thunderstorm that looks like it's almost right on top of you might actually be 20+ miles away. ",
"We humans are pretty good at judging relative distance on the ground. If the tree is blocking your view of the car, then you know the tree is closer than the car. If one object is a lot blurrier than another object, it's probably farther away. ",
"But once you lift your eyes skyward, you lose a lot of those visual cues. What you think is a solid cloud might actually be 2 clouds 10 miles apart - they just look like a solid cloud because one happens to be behind the other and a similar color. You don't figure it out until something happens to give you a visual cue, like an airplane flying between the two clouds. ",
"Because we're so bad at judging distance with things we see in the sky, a long shaft of sunlight can look like it's going straight up and down when really it's angled toward you quite significantly. Get several of them next to each other in parallel, and you get the optical illusion that they're radiating from a hole in the cloud. "
] |
[
"Thanks for the new wallpaper!",
"Hecklingfern has it right - those sun rays only look like they're vertical. They're actually angled. Something you learn when you start following weather around in the summer is that distances in the sky are very deceptive. The supercell thunderstorm that looks like it's almost right on top of you might actually be 20+ miles away. ",
"We humans are pretty good at judging relative distance on the ground. If the tree is blocking your view of the car, then you know the tree is closer than the car. If one object is a lot blurrier than another object, it's probably farther away. ",
"But once you lift your eyes skyward, you lose a lot of those visual cues. What you think is a solid cloud might actually be 2 clouds 10 miles apart - they just look like a solid cloud because one happens to be behind the other and a similar color. You don't figure it out until something happens to give you a visual cue, like an airplane flying between the two clouds. ",
"Because we're so bad at judging distance with things we see in the sky, a long shaft of sunlight can look like it's going straight up and down when really it's angled toward you quite significantly. Get several of them next to each other in parallel, and you get the optical illusion that they're radiating from a hole in the cloud. "
] |
[
"Is it possible to see nerves in a cut of meat from the grocery store?"
] |
[
false
] |
Obviously in various cuts of meat you can see skin, bone, muscle, fat, tendons, ligaments, etc. Is it possible to see nerves too? This is the closest I'll ever get to dissection/surgery so I'd like to make the most of it!
|
[
"Yes. Nerves veins and arteries usually are bundled together, in a sheath, through muscle groups.",
"The sciatic nerve, forms around the level of the gluteal muscles and goes down the leg, is quite large above the knee.",
"So I'm thinking ham hock?"
] |
[
"Yes, I believe so. I've never slaughtered a cow or pig myself and I don't really know how the locations of the particular cuts work out, but judging from the size of some human nerves (brachial plexus, sciatic, etc.), it should definitely be possible to see some in a cut of beef or pork. ",
"Here",
" is a labeled human arm dissection, and you can see a gloved hand in the bottom right for scale. As you can see, the median nerve is pretty thick."
] |
[
"In some cuts, yes. For example, I like to smoke pork shoulders, and I have found remnants of the brachial plexus in some. I think they generally try to cut temp out, though."
] |
[
"Explain Antimatter and Matter to me."
] |
[
false
] |
I know there's a lot of material out there on Antimatter and Matter, but most of it is extremely technical and precise. This isn't a problem, but it also isn't what I'm looking for. I'm looking for the explanation you give to Timmy, Kid Physicist. He's seven years old, likes penguins, and wants to know more about the world around him. He heard about antimatter on some Sci Fi show he watched, and now he wants to know what it is. Help Timmy out.
|
[
"Here you go, Timmy."
] |
[
"Well here's the basic idea:",
"Think of your basic particles subatomic particles - proton, electron, neutron. (Protons and neutrons have further sub-particles, but we'll ignore this.)",
"Antimatter is still ordinary matter. It doesn't have negative mass. It isn't repelled by gravity. It's just opposite charge.",
"The antiparticle of an electron is a positron. It has the same mass, but positive charge.",
"The antiparticle of a proton is an antiproton. It has the same mass as a proton, but a negative charge.",
"We don't run into antimatter that often. If a matter particle meets it's antimatter companion, both particles are completely annihilated and converted to gamma rays. So, you generally don't find any antimatter around a large planet like Earth made of normal matter. The only place we see it is inside particle accelerators where it's made from scratch. ",
"So, if you somehow run into an antimatter duplicate of yourself, don't go over and give them a big old bear hug. ",
"According to my rough math, if you each weighed 150 lbs, this would produce a massive nuclear fireball with the energy equivalent of 186,000 Hiroshima-size bombs going off simultaneously. "
] |
[
"I would say even a teaspoon's worth would be orders of magnitude to large."
] |
[
"Are there any gemstones that have applications in the scientific community?"
] |
[
false
] | null |
[
"There's lots of instrumentation made out of precious gems. Examples include ",
"diamond anvil cells",
" for examining extremely high-pressure compounds, ",
"diamond and sapphire lenses",
" used for camera optics that can function at Venus surface temperatures, as well as ",
"ruby lasers",
"."
] |
[
"It was natural... and, aparently, it's an interesting case in ",
"tax law",
" (!!??).",
"When you import optical elements to the US you had to pay taxes on it, and if you \"re-exported\" them later you got your money back. So a lawyer for the Hughes Aircraft Company had to argue that launching a probe is the same as exporting it",
"edit: the internet teaches me the weirdest shit "
] |
[
"Within geology there are a number of precious and semi-precious stones that are useful in determining the geologic history of rocks and regions. In many cases, aspects like the trace element geochemistry (e.g. relative abundances of things like light and heavy rare earth elements or isotopic composition) or the geochemistry/mineralogy of inclusions (i.e. other smaller minerals within a larger mineral) within gemstones document the chemical, temperature, and/or pressure environment of formation (and thus reveal something of the history of the rock in which that gemstone formed). This is especially true for garnets which are incredibly chemically diverse (and that diversity is tied to the conditions under which they formed) and get used (geochemically) for all sorts of things, ",
"here is just one random example",
". Other examples of gemstones which under certain circumstances can be useful are ",
"diamonds",
", ",
"beryl (i.e. emeralds, aquamarine, and a host of other names)",
", ",
"corundum (i.e. ruby or sapphire)",
", and ",
"tourmaline",
" (this is not an exhaustive list, just the ones that come to mind). In some cases, the properties that make a particular example of a mineral geologically interesting (e.g. inclusions) may make it less appealing as a gemstone, but this is not always the case."
] |
[
"What is going on neurologically when you switch from voluntary to involuntary breathing?"
] |
[
false
] |
Have there been imaging studies of the respiratory center while this takes place?
|
[
"See this previous post",
"Brainstem respiratory neurons control automatic breathing. When you begin to breathe 'consciously,' this voluntary breathing is initiated by the cerebral cortex but interacts with automatic breathing via projections from the cortex to the brainstem respiratory centers. For example, corticobulbar (cortex to brainstem) projections suppress automatic breathing during breath holding. The cortex can also directly control breathing via direct projections to respiratory muscles (eg. cortex to phrenic nerve projections).",
"Thus breathing control is not strictly hierarchical but rather a very complicated circuit. You can have lesions that affect voluntary breathing but not automatic breathing, lesions that affect automatic breathing but not voluntary breathing, or lesions that affect both types of breathing, depending on the extent and location of the lesion."
] |
[
"More like those patients have to be ventilated."
] |
[
"You can have lesions that affect voluntary breathing but not automatic breathing, lesions that affect automatic breathing but not voluntary breathing, or lesions that affect both types of breathing",
"Do people get lesions on their automatic breathing, meaning they have to be permanently aware of their breathing?"
] |
[
"Since antibiotic-resistant bacteria are often less competitive than other species of bacteria, could introducing another bacteria that is harmless to humans but can outcompete the resistant bacteria be a useful treatment for multi-drug resistant infections?"
] |
[
false
] | null |
[
"http://www.sciencemag.org/content/312/5782/1944.short",
"\"Antibiotic resistance is also often associated with a reduced competitive\nability against antibiotic-sensitive strains, in the absence of the antibiotic\""
] |
[
"Since antibiotic-resistant bacteria are often less competitive than other species of bacteria",
"Source?"
] |
[
"That is primarily because it cells that are antibiotic resistant have to expend energy and nutrients to being antibiotic resistant. ",
"However, your idea does not take into account that nearly all antibiotic resistance is acquired by bacteria horizontally--that is, susceptible bacteria acquire genes for resistance from resistant bacteria on plasmids or transposable elements. Therefore, introducing susceptible bacteria to a population that carries resistance may lead to a larger population of resistant bacteria once those resistance genes have been transferred to the susceptible population. ",
"However, I would like to point out that many infections of antibiotic resistant bacteria arise in situations where the normal, healthy bacterial population has been severely reduced; e.g. surgery, when the wound site is kept highly sterile. Often, the best ",
" against an antibiotic resistant infection is having a diverse and healthy population of susceptible bacteria that can out-compete the highly resistant strains. However, introducing more bacteria to an antibiotic resistant infection is not an appropriate ",
" to combat it. "
] |
[
"What happens when something hits the edge of the universe?"
] |
[
false
] | null |
[
"As far as we know there is no end to the universe. "
] |
[
"It isn't an intuitive result, without studying the subject, I don't think anyone would have good reason to understand the result."
] |
[
"Yeah. But what happens. I don't want to fall out. "
] |
[
"Why do planets orbit elliptically?"
] |
[
false
] |
[deleted]
|
[
"You don't need relativity to explain elliptical planetary orbits",
"."
] |
[
"An ellipse is the most energy efficient shape for an orbit. I think the easiest way to explain it would be to point out that an oval is composed of the intersection of 4 circles, of 2 different radii. Each point on the oval is exactly the distance of the radius from at least one circle. The arcs of each circle join smoothly, but the change in direction is not smooth. If an object were moving along the arc of one of the larger circles it would have a path described by ",
" circle. Once the object \"hits\" the tangential to one of the smaller circles, it's path is now described by a ",
" arc, defined by a different radius. For the object to orbit in an oval it would require \"switching\" to 4 different curves.",
"An ellipse on the other hand is defined by two focal points and any point along the ellipse is a distance that is the sum of the distance to both of those focal points. A single arc describes the path around an ellipse. An elliptical orbit allows for a balance between the curvature of space created by the mass of the object at one of the focal points and the inertia of the orbiting body.",
"In other words, the ellipsis is one curve. An oval is composed of 4 joined curves (or arcs form a circle), and while the join is smooth and continuous the change in direction around each is not.",
"This might also help. Imagine a planet orbiting a star with the star being the center of one of the smaller circles (to closely match the configuration of an elliptical orbit). As the planet \"hits\" one of the switching spots, it's orbit will would now follow a circular path of a certain radius (the radius of the smaller circles that compose the oval, which is now different and discrete from the radius of the larger circles from before the switch). This means that the object's inertia from its velocity while it was on the previous arc would now have to be gone. It is in a stable orbit, at a fixed radius from the star.",
"There is no reason for that radius to change (ignoring orbital decay, changes in mass of the planet or star, influence from other objects, etc.) again, for it to switch back to the second arc. The circular orbit is an elliptical orbit, a circle is a specialized ellipse, so now we have the planet traveling along an elliptical path again and no way to describe that path changing (ignoring the same causes listed above).",
"Hopefully that helps explain and didn't just confuse you more."
] |
[
"A shape that would not conserve angular momentum would not be energy efficient, would it? An oval would not conserve angular momentum, but then one might ask why ",
" is. I tried answering the question without talking about conserving angular momentum and avoiding the acceleration that would cause the change in velocity, since that sort of begs the question."
] |
[
"Do cars in higher elevations get better gas mileage?"
] |
[
false
] |
I’d think so, because there’s less air to create drag, but then again, maybe less/thinner air affects the engine somehow.
|
[
"You're right to point out that it's a combination of both factors. Fuel efficiency goes down since there's less oxygen for the combustion (although with a turbo the effect may not be so simple) but in spite of this mileage will go up because drag goes down massively. Since drag is involved it's going to depend on the type of driving as well, for low-speed driving drag isn't as important"
] |
[
"You're right to point out that it's a combination of both factors. Fuel efficiency goes down since there's less oxygen for the combustion (although with a turbo the effect may not be so simple) but in spite of this mileage will go up because drag goes down massively. Since drag is involved it's going to depend on the type of driving as well, for low-speed driving drag isn't as important"
] |
[
"This is one area where electric cars have a major advantage.",
"The \"Hot/High\" problem decreases internal combustion engine performance, which is only partially offset by decreased air resistance. This is a major thing for aircraft.",
"Electric cars on the other hand lose no power due to altitude or temperature, and enjoy the same benefit of lower density.",
"On the other hand, electric cars get noticably worse range in winter with the denser air (and sometimes need to warm the pack)."
] |
[
"Ask Anything Wednesday - Biology, Chemistry, Neuroscience, Medicine, Psychology"
] |
[
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!
|
[
"Cure is a bit strong of a word. THC has anti-cancer properties, and there have been many studies on it.",
"Head and neck.",
"Lung cancer",
".",
"Breast cancer",
".",
"There are many more, if you want I can provide some. The biggest problem is that there are some inconsistent methodologies giving somewhat conflicting opinions on THC and cancer.",
"So while there have been studies, they sometimes conflict. But there is a noticeable pattern of THC inhibiting specific types of cancer that is undeniable. For example, several papers have noticed the link between THC and the epidermal growth factor receptor-overexpressing lung cancers, with THC inhibiting growth of the cancer, but the mechanisms aren't well understood.",
"There should be no real difference between method of consumption other than differences in amounts of carcinogens.",
"I don't know much about the psychological aspect, but these treatments are somewhat controversial in that, again, there is a conflict in the literature about efficacy for these ailments."
] |
[
"Are male and female brains different? Like, could a very educated and experienced neuroscientist look at scans and data etc., and tell them apart? ",
"Edit: And if so, when do the differences become apparent? Puberty? And what does the brain of a person identifying as transgender. - like Jenner , who specifically stated their brain was female - look like? Female? Male? Something in the middle?"
] |
[
"Yes the newest hypotheses is that so called ribozymes are RNA molecules with catalytic properties, these are thought to jump start the whole central dogma."
] |
[
"If carboxylic acid is created spontaneously when water is left in a beaker for a day or so, why isn't the world's lake all carboxylic acid?"
] |
[
false
] | null |
[
"You mean carbonic acid.",
"The reason is that only limited amounts of carbon dioxide are absorbed in water to begin with. The amount of carbonic acid is limited by the equilibrium of dissolved carbon dioxide, bicarbonate ion, and carbonic acid."
] |
[
"Yes, because with more carbon in the air it shifts the equilibrium so that the water will take in more carbon as well therefore having higher concentration of carbonic acid."
] |
[
"that's not at all true. CO2 in the ocean is rising rapidly in response to atmospheric increase in CO2.",
"https://ocean.si.edu/conservation/acidification/ocean-acidification-graph"
] |
[
"What's going to happen to the polar bears as the ice caps shrink? Evolution or extinction?"
] |
[
false
] |
I watched a show recently describing how as the sea ice melts earlier, polar bears are going to be threatened because they won't have enough time to hunt enough seals to build up their fat stores for the summer months. This made me wonder, as the earth warms further what will happen to polar bears? Will they simply go extinct or will a variant of existing polar bears remain (perhaps those who are more efficient at converting seal food into fat or those that can swim further/hunt better without the ice). Has there been any research done into this?
|
[
"Well extinction is a distinct possibility as a loss of sea ice results in very large evolutionary hurdles. On the other hand with less ice and snow, selection pressures favour darker bears, and as they can interbreed with grizzlies its possible they might just converge back into a single species."
] |
[
"Extinction is not evolution. Evolution can only occur if the DNA is passed on. That is using evolution in the strict sense. "
] |
[
"upvoted for reference to pizzlies."
] |
[
"How/why did the original continental landmass, Pangaea, form?"
] |
[
false
] |
Are there any theories out there that provide insight in to the formation of land on our planet, and why it started out as a single, large mass of land?
|
[
"Pangea was not the first supercontinent in Earth's history. Supercontinents, as you probably know already, form when several regular continents collide and stick together. There is something known as the supercontinent cycle where, about every 300 to 500 million years, the Earth's continents all join together to form a supercontinent before breaking apart. Vaalbara, Kenorland, Columbia, Rodinia, and Pannotia were previous supercontinents that existed as far back as 3 billion years ago. The earliest supercontinents, like Vaalbara (or Ur) were tiny compared to continents today because they constituted (as far as we know) the entirety of the planet's continental crust at that time though by once Pangea formed there was a lot more continental crust to work with.",
"It appears that the oldest blocks of stable continental crust, Precambrian shields, are what's left of the first islands in Earth's history. Back before continents had formed there was just oceanic crust forming at spreading centers and being recycled at subduction zones. At these subduction zones, island arcs formed that are somewhat analogous to modern arcs such as Indonesia, the Philippines, and the Aleutians in Alaska. As more and more arcs formed they began to collide and, over time, accreted into the first continents, albeit ones much smaller than modern day ones. Once these continents were formed they began to bump into and stick to each other. However, unlike when they were island chains, they did not necessarily stay stuck together and, after a time, would break apart. ",
"Why continents regularly get together and then break up is still debated but it all has to do with the transfer of heat from within the mantle. It would seem that the breakup of a supercontinent is due to the fact that they trap heat underneath them and, as it gets hotter and hotter under the supercontinent, it eventually reaches a point where the heat forces the crust apart.",
"I'm glossing over a lot of items here but it's a very big topic so I hope that answers your question.",
"Edit: ",
"This article",
" has a fairly good overview of tectonics and supercontinents.",
"Edit 2: I forgot to mention that when it comes to the old supercontinents like Vaalbara, Kenorland and Columbia their arrangement is much less clear than it is for Pangea because there is less data to go on."
] |
[
"This is a good question and one I would like to take my time with. I'm a little preoccupied so I'll get back to you on this."
] |
[
"This is a good question and one I would like to take my time with. I'm a little preoccupied so I'll get back to you on this."
] |
[
"So Voyager has left the solar system. Could we catch up with it if we wanted to do a targeted exploration?"
] |
[
false
] |
Voyager was a craft designed to examine the outer planets, so I'm guessing it has very limited instruments left that can measure interesting things about space outside the heliosphere. So if we wanted to send out a craft specifically to explore the environment in interstellar space, would it take another 37 years to get there or could we send out a probe that would use much less time? Would it help if we target the mission specifically to reach interstellar space? Is there any new tech that has come along since then that would be used for such a mission if planning and production started today?
|
[
"of course we could. We could it even in the 70´s. its just a question of money.\nThe speed you need to leave the sun Gravitation is around 46 km/s. Because the earth spins around the sun you just need 16 km/s.\nVoyager 1 and 2 both use a multi slingshot acceleration flight plane where jupiter and saturn both gave them a big kick of acceleration to leave the solar system.(Voyager needs the most the time traveling between the Planets because the flight plane was on efficiency and not speed). The slingshot plane helps them to reduce own acceleration and increasing the amount of payload.\nIf you want to move fast as Voyager 1/2 you would start with higher start acceleration in space and just use a saturn slingshot therefore you just need a big rocket not more science. If time is not the problem than you would use today an Ion engine because of its high efficiency. other with a typical rocket engine."
] |
[
"Voyager took advantage of several gravity assists (using planetary gravity as a 'slingshot' of sorts) and a good alignment of planetary orbits to achieve escape from the solar system.",
"The planetary alignment is kind of a only happens once every N years kind of thing. ",
"We don't really have technology yet that could do much better time wise, and would need much more fuel to make up for the lack of good alignment for gravity assists. We don't have propulsion systems capable of flying straight there. "
] |
[
"With conventional technology, yes, it'd take that much unless you want to spend billions to use a huge rocket. But a couple of modern concepts using solar energy could be faster. Take a look at ",
"this thread",
" for details."
] |
[
"If i had a bowling ball in the middle of outer space. Could a m&m orbit around it?"
] |
[
false
] |
What size ball would you need to get something like an m&m to orbit around it?
|
[
"Yes, but very slowly.",
"A plain old circular orbit is described by the following equation:",
"a = w",
" r",
"with a being the acceleration (in this case, due to gravity), w the angular velocity (in radians per second, for reference: a full circle corresponds to 2 pi radians) and r the orbital radius.",
"The gravitational acceleration is given by Newton's Law of Gravitation:",
"a = M G / r",
"with M being the mass of the central object (the bowling ball), G the Newtonian constant of gravity and r the distance to the center of mass (the center of the bowling ball).",
"According to Wikipedia, a bowling ball should have a mass of at most 7.26 kg, so lets use that value. An m&m orbiting at a distance of 1 meter from the center of the ball would have an orbital period of about 3.3 days. So that's how long it would take the m&m to complete a full orbit.",
"If the m&m is instead only 30 cm from the center of the ball (which is less than 20 cm from its surface), the orbital period is about 13 hours.",
"If the m&m orbits just above the surface, at a distance of 12 cm from the center (Wikipedia tells me that regulation bowling balls have a radius between 11.80 and 11.92 cm), the orbital period is 3.3 hours.",
"Note that the mass of the m&m doesn't play a role as long as it is sufficiently small. Because the m&m also exerts a gravity force on the bowling ball, it is more accurate to say that both objects orbit a shared center of mass. But when the mass difference between the two objects is very large, the center of mass of both object is practically the same as the center of mass of the large object and you can consider it stationary. The situation with 2 bowling ball would look different, as you'd clearly see both balls orbiting a single point in between the two balls."
] |
[
"Worth noting that you have to give the m&m just the right push to put it in the orbit around the bowling ball. The escape velocity is sqrt(2GM/r), which for a 7 kg bowling ball at a distance of 1 m is just 0.00003 m/s. (G is 6.67e-11 m",
"/ kg s",
".)",
"Any faster initial velocity (from 1 m from the center of the bowling ball), and you won't get an orbit."
] |
[
"It is absolutely possible to position something with 30nm accuracy with the right tools, and sub atom accuracies are doable with the right instruments."
] |
[
"Could Someone please explain to me the science of the octave in music?"
] |
[
false
] | null |
[
"First let's explain the science behind a \"note\". A note is just a name given to a particular frequency of air vibrations, which is what gives that note its tone. For example, an A in the middle of the piano in standard tuning is nothing more than a vibration at 440 Hz, meaning when that key is pressed on the piano, a hammer strikes a string that naturally vibrates 440 times a second, which makes the air around it vibrate at 440 times a second - a vibration that propagates through the air to your ear.\nUsing that same A as an example, on the piano 12 keys to the right, there is another \"A\", this one an octave higher. It is an octave higher because that string naturally vibrates at twice the frequency (880 Hz - 880 times a second), which vibrates the air around it at 880 Hz, which is the vibration that reaches your ear.\nTo summarize: an octave is a relationship between two sound frequencies (or rates of vibration) in which the relationship is 2:1. A 200 Hz tone is the octave up from a 100 Hz tone.\nInterestingly, 2:1 is the simplest geometric mathematical relationship, giving us the most innately stable/consonant musical tone relationship - the octave. Deriving further, 3:2 relationship between frequencies gives us the \"perfect fifth\", the second most innately stable tone relationship. Flipping the relationship (2:3) gives us the \"perfect fourth\" which is a perfect fifth in the opposite direction. 4:3 gives us the 3rd and 6th and so on. The tritone, an extremely dissonant interval that the Catholic Church actually banned at one point in time calling it the devil's interval, has a very ugly mathematical relationship that I cannot recall at the moment. And this is why I am an engineering student who loves music."
] |
[
"It all boils down to a mathematical concept called \"Fourier transformation\". This guy named Fourier figured out how to turn any series of values (like the pressure in air at subsequent points in time) into a collection of pitches. That turns out to be extremely useful for many things. ",
"One of the cool things about Fourier transformation is that any ",
" waveform is just the sum of several pure tones ",
". A flute makes a pure(ish) tone, but a horn making the same note sounds quite different. The difference is that the horn sound has the main tone mixed in with overtones at integer harmonics (2x the base frequency, 3x, 4x, etc.). It's worth repeating: ",
".",
"So your auditory system has adapted to treat multiple frequencies separated by an integer factor as parts of the same complex tone. That's good, since it's usually true -- if you have a bunch of random noises around you, most of them won't happen to share any integer harmonics: two notes that are exactly an integer multiple apart are almost certainly part of the same tone.",
"There are some exceptions to that rule. In particular, some devilish fellow might be playing a ",
" on a musical instrument. Chords are auditory puns. For example, a C major chord is middle-C, middle-E, and middle-G. Those notes happen to have the frequency ratio 1 : 5/4 : 3/2. Multiply all those numbers by 4 and you get the sequence 4:5:6 -- all the notes in the C chord happen to be multiples of another note with a much lower tone! Whoah. In this case, the lower tone happens to be C two octaves down. Your auditory system identifies the chord as part of a single complex sound at the much lower pitch -- even if that pitch doesn't actually exist in the music.",
"That's the basic theory of chords and pitches mixing. The pitch scale is a ",
" scale -- each step up or down the scale ",
" frequency by a certain amount. Going up or down an octave multiplies or divides by 2. The reason that notes an octave apart sound like \"the same note\" is that they are so closely harmonically related -- practically every sound around you contains a base pitch and its second harmonic. If you listen carefully, you can also get that same \"sameness\" from a note and the fifth-interval an octave up. A fifth interval is a ratio of 3/2 in frequency, so a fifth and an octave gives you a ratio of 3. Since it's an integer ratio (not a fraction), the two notes (say, C-below-middle, and middle-G) have a little of the \"sameness\" that you normally associate with octaves only. But octaves have so much of that \"same\" sound that we give notes an octave apart the same name.",
"Now -- why are octaves \"octaves\", and why are there exactly 12 half-steps in an octave? That's because of something called the \"circle of fifths\", which musicians frequently mutter about (and which you can google for more information if you're not one). The easiest way to construct a scale is by starting with a base note somewhere (say, A-440, but any frequency will do), and then constructing third harmonics of it. Each time you go up in frequency a factor of 3, you get a nice harmony (the octave-and-a-fifth). Then you fold the new note downward by octaves until it is within a factor of 2 of the original frequency, and start over. If you do that 12 times you'll create 12 separate notes, and arrive ",
" back where you started -- 1.36% higher in pitch than the original note. That's really discordant if you play it next to the original note, but if you tweak each of your derived notes ever so slightly, you can sort of smooth things out so that all the frequencies work right to form new chords with one another. You'l find that you created exactly 12 notes and defined the half-step scale. But you had to fudge the frequencies, because you had to sweep the discord under the sonic rug somewhere. This is reasonable not just for aesthetic reasons but because, if you didn't know the math, you might think you'd just screwed up the tripling step a tiny bit each time. When people say the Western scale is based on a lie, this is the lie they mean: the circle of fifths cannot work perfectly, because no matter how many times you multiply your original frequency by 3, you will never arrive at a power of 2 -- but you can fudge it if you're close enough. ",
"Through the ages there have been several different \"temperaments\" used, in which people tweaked the notes of the 12 tone circle of fifths in various different ways, to try to make particular chords sound particularly good -- at the expense of other chords. These days, we use an \"equal-tempered\" scale where each half step is exactly a factor of 2",
" above the previous one. If you're playing a bendable instrument (like the flute, the trombone, the violin, or the human voice) and you are a good musician, you will unconsciously tune each note slightly higher or lower depending on the chordal context of your particular note, to harmonize better with the rest of the orchestra. You ",
" bend the notes on a piano, which is why pianos have multiple strings singing each note -- it fuzzes out the resonance of each note, so it's harder for your ears to pick out the harmonic discrepancies. (There are ",
" strings so you can't hear the slightly-detuned strings beating, as you could if there were just ",
". The bass bridge usually has two strings per note, but by the time you get down there the resonances are so cruddy that you can't really hear the beating anyway).",
"The 8 primary notes (A-G) you can get by stepping ",
" forward on the circle of fifths and and ",
" backward, to get three notes separated by fifth intervals (for example, F-below-middle, middle-C, and middle-G). If you create major chords for each of those three notes (and fold all those new notes into a single octave), you'll find that there are 8 unique pitches, which are the pitches of the major scale. That's why we call it an \"octave\" - oct for 8. Since going down a fifth (and folding into the main octave) is the same as going up a fourth interval, you can immediately see why IV,V,I and similar chord progressions are so common in Western music -- they're the very basis of our musical scale.",
"Incidentally, not everyone agrees on that scale. The equal-tempered Western scale can generate harmonic sequences up to 7/8 of the original (if you play a C7 chord with the low G and two lower C's, you are playing the 1, 2, 3, 4, 5, 6, and ~7 harmonics of the lowest C). But any higher harmonics fall between the notes. Middle-eastern and Indian music uses higher harmonics, and therefore has lots of quarter-step or smaller intervals that sound strange to our ears. The German tradition calls that 7/8 harmonic of C by its own special name - 'H', as the next note after G, a fact Johann Sebastian Bach exploited by working his own name (BACH) into a counterpoint line in his last great composition.",
": What, I summarize 900 years of musical theory and you're complaining it's a wall of text? F*ck you, go back and read it."
] |
[
"Of the various harmonic relationships such as octave (2:1), perfect fourth/fifth (3:2), perfect third (4:3), why do we perceive only the octave to be the \"same\" note?"
] |
[
"In sample standard deviation, why do we divide by (n - 1)?"
] |
[
false
] |
I understand that it is because of the sample size generally being lower than the population average, hence we just minus one from in order to obtain slightly more accurate results to emulate the population. However, I don't understand why 1 was chosen. Does anyone know the origin of the choice of the number 1? Why not 0.5, why not 2? Is there an actual mathematical origin of the use of 1 in the formula?
|
[
"This is a sort of boring answer to your question sadly, but here it goes:\nSo let's say you try your first instinct and choose to divide by n. Then following a lot of algebra, you see that your expected sample variance will be (n-1)/n * (sigma), where sigma is the true variance. See here for details: ",
"https://maxwell.ict.griffith.edu.au/sso/biased_variance.pdf",
"\nIt's just long and tedious is all.",
"So we say to ourselves, hmmm, well this is too small, and we want it to equal sigma! So how do we fix it? Well we want to get rid of the (n-1)/n term, hence we multiply by n/(n-1), but recall originally that we multiplied by 1/n in the beginning (back when we were so naive), and so this is equivalent to multiplying by 1/(n-1) to start with.",
"TL;DR: It works out algebraically. "
] |
[
"According to the textbook I am studying, \"probability and statistics for scientists and engineers\" page 15...",
"It should be clear to the reader that the sample standard deviation is, in fact, a measure of variability. Large variability in a data set produces relatively large values of (x-x)",
"[I don't know how to format the squiggly line over the second x]",
"... and thus a large sample variance. The quantity (n-1) is often called the ",
" estimate. In this simple example, the degrees of freedom depict the number of independent pieces of information available for computing variability. For example, suppose that we wish to compute the sample variance and standard deviation of the data set (5, 17, 6, 4). The sample average is 8. The computation of variance involves",
"(5-8)",
" + (17-8)",
" + (6-8)",
" + (4-8)",
" = ... = 0.",
"The quantities inside paranthesis sum to zero... ... Then the variation does not involve ",
" ",
" from the mean. In fact, since the last value of x - x is determined by the initial n-1 of them, we say that these are n-1 \"pieces of information\" that produces s",
" Thus, there are n-1 degrees of freedom rather than ",
" degrees of freedom for computing sample variance.",
"Think of it like this. You have ",
" sample points. But they can only vary between each other. Imagine you represent the sample points as spaces on a paper, and you divide them either by cutting the paper, or drawing lines between the areas.",
"The number of cuts you had to make to create ",
" pieces is (n-1). You know this. Cut a paper in 2 with 1 cut, cut a paper in 3 with 2 cuts, and so on. The cuts represent the variances, and the pieces of paper represent the sample points. Or to be more technically accurate, the size of the spaces between your pieces on the table is more analogous to the variance. The end pieces are at the edges of the container (i.e., your domain), and can't move out. So the pieces can only ",
" in the (n-1) spaces you created.",
"*",
" fixed some grammar, spelling"
] |
[
"This is the right answer, however I'd add that there is an intuitive interpretation behind this.",
"Think about it this way, what would the standard deviation of a sample of size one be? It should be undefined, because the idea of standard deviation doesn't make sense with only a single sample. Dividing by (n-1) implies that the standard deviation is undefined for n=1 (division by zero)."
] |
[
"What exactly is the 4th Dimension?"
] |
[
false
] |
Ok so my basic understanding from Carl Sagan videos and other things like that is that it is just a higher spacial dimension than ours. But why do we think that it exists, what evidence has pointed us to thinking that there is a 4th dimension. And why is time associated with it? Is it just because its the next logical direction to move in (length, width, depth, time?)
|
[
"So let's start with space-like dimensions, since they're more intuitive. What are they? Well they're measurements one can make with a ruler, right? I can point in a direction and say the tv is 3 meters over there, and point in another direction and say the light is 2 meters up there, and so forth. It turns out that all of this pointing and measuring can be ",
" to 3 measurements, a measurement up/down, a measurement left/right, and a measurement front/back. 3 rulers, mutually perpendicular will tell me the location of every object in the universe. ",
", they only tell us the location relative to our starting position, where the zeros of the rulers are, our \"origin\" of the coordinate system. And they depend on our choice of what is up and down and left and right and forward and backward in that region. There are some rules about how to define these things of course, they should be perpendicular, and once you've defined two axes, the third is fixed (ie defining up and right fixes forward). So what happens when we change our coordinate system, by say, rotating it?",
"Well we start with noting that the distance from the origin is d=sqrt(x",
" +y",
" +z",
" ). Now I rotate my axes in some way, and I get new measures of x and y and z. The rotation takes some of the measurement in x and turns it into some distance in y and z, and y into x and z, and z into x and y. But of course if I calculate d again I will get the ",
". Because my rotation didn't change the distance from the origin. ",
"So now let's consider time. Time has some special properties, in that it has a(n apparent?) unidirectional 'flow'. The exact nature of this is the matter of much philosophical debate over the ages, but let's talk physics not philosophy. ",
" we notice one important fact about our universe. All observers measure light to travel at c regardless of their relative velocity. And more specifically as observers move relative to each other the way in which they measure distances and times ",
", they disagree on length along direction of travel, and they disagree with the rates their clocks tick, and they disagree about what events are simultaneous or not. But for this discussion what is most important is that they disagree in a very ",
" way. ",
"Let's combine measurements on a clock and measurements on a ruler and discuss \"events\", things that happen at one place at one time. I can denote the location of an event by saying it's at (ct, x, y, z). You can, in all reality, think of c as just a \"conversion factor\" to get space and time in the same units. Many physicists just work in the convention that c=1 and choose how they measure distance and time appropriately; eg, one could measure time in years, and distances in light-years. ",
"Now let's look at what happens when we measure events between relative observers. Alice is stationary and Bob flies by at some fraction of the speed of light, usually called beta (beta=v/c), but I'll just use b (since I don't feel like looking up how to type a beta right now). We find that there's an important factor called the Lorentz gamma factor and it's defined to be (1-b",
" )",
" and I'll just call it g for now. Let's further fix Alice's coordinate system such that Bob flies by in the +x direction. Well if we represent an event Alice measures as (ct, x, y, z) we will find Bob measures the event to be (g*ct-g*b*x, g*x-g*b*ct, y, z). This is called the",
" Lorentz transformation",
". Essentially, you can look at it as a little bit of space acting like some time, and some time acting like some space. You see, the Lorentz transformation is much ",
" a rotation, by taking some space measurement and turning it into a time measurement and time into space, ",
" a regular rotation turns some position in x into some position in y and z. ",
"But if the Lorentz transformation is a rotation, what distance does it preserve? This is the really true beauty of relativity: s=sqrt(-(ct)",
" +x",
" +y",
" +z",
" ). You can choose your sign convention to be the other way if you'd like, but what's important to see is the difference in sign between space and time. You can represent all the physics of special relativity by the above convention and saying that total space-time length is preserved between different observers. ",
"So, what's a time-like dimension? It's the thing with the opposite sign from the space-like dimensions when you calculate length in space-time. ",
"We live in a universe with 3 space-like dimensions and 1 time-like dimension",
". To be more specific we call these \"extended dimensions\" as in they extend to very long distances. There are some ideas of \"compact\" dimensions within our extended ones such that the total distance you can move along any one of those dimensions is some very very tiny amount (10",
" m or so)."
] |
[
"The point of t being ",
" (you can equally call t+ and space-, and we choose this convention often times when we work with energy and momentum) is that it creates what's called a \"hyperbolic\" geometry. so if a line of constant distance from the origin in \"standard\" geometry is given by sqrt (x",
" +y",
" ), the equation for a circle, the line of constant value in a hyperbolic geometry is sqrt (-t",
" +x",
" ), a hyperbola. Then one can do a whole bunch of hyberbolic maths here, but it's one of the reasons why ",
"rapidity",
", the hyperbolic arctangent of v/c adds algebraically in relativity, when velocities do not. Essentially it's the right type of geometry to explain what we observe.",
"Yes the link for privileged 3+1 is a bit anthropic, but the point I wanted to make is that scientists ",
" considered more space and more time dimensions. The universe we occupy only has 3 extended spatial dimensions and 1 extended time dimension. Universes with other space-times are ",
" different than our own, to the tune of being overly simplistic or wildly unpredictable or unstable. A lot of people, especially recently, have been asking questions about \"what if there were more space/time dimensions.\" I just want everyone to know, we ",
" considered it, and the best answer is what we have. "
] |
[
"There's two different concepts here. One is that the universe has three spatial dimensions and one time dimension, so that \"The ground floor of 3rd street and 5th avenue at 7 PM\" is a four dimensional coordinate. The is other is four dimensional space, which is a mathematical construction."
] |
[
"If I was floating in space and didn't have a point of reference, would I be able to tell if my body inverted 180 degrees from my original position?"
] |
[
false
] | null |
[
"You could tell if you were holding a gyroscope."
] |
[
"if you were slowly rotating in space with no reference points then you would not know you are rotating because your 'state' never changes; you are always rotating and always will (until you are nudged still again).",
"Not true. Rotation will always have centripetal acceleration and consequently a measurable force. You would be able to feel this spinning provided it was of a reasonable speed."
] |
[
"most likely yes. in order to invert your body a force would have to be applied to start moving you and then another force to make you stop moving and those forces would be felt (nudge on your shoulder or stabilizer firing), this would by a dynamic system. but if you were slowly rotating in space with no reference points then you would not know you are rotating because your 'state' never changes; you are always rotating and always will (until you are nudged still again)."
] |
[
"Why do car engines 'tick' after being turned off?"
] |
[
false
] | null |
[
"When the engine is running, it will heat up itself and the components near it. Heating something causes it to expand. Once the engine is turned off, it will cool down again which causes the materials to shrink back to their original state. The different parts of the engine are made of different materials, so the heating, cooling, expanding and shrinking happens at different rates. This can cause some friction and snapping, which causes the ticking sound you hear.",
"The same happens when the engine is heating up, just after starting it. However, these sounds are very hard to hear, because they're being drowned out by the normal operating noise of the engine."
] |
[
"That's true. That's just one part ticking then. If you had multiple parts of different size all cooling and snagging on friction at the same time, it wouldn't be a constant function. Adding multiple parts would increase the degrees of freedom in the heat transfer rate equations, and you would have some ridiculous polynomial function for ticks per second."
] |
[
"the repeated ticking that I hear after turning my car off in the summer is evenly paced ticking. I doubt that internal parts all cool at the same rate (1 per second for ~20 seconds)?"
] |
[
"Why can't powerbanks charge while being charged?"
] |
[
false
] | null |
[
"They can. For instance, most cell phones can be used while charging. This is generally called \"pass-thru\". Unfortunately, with external batteries, most manufacturers and/or retailers don't actually say which support it. ",
"The reason it's not universal is because it creates more of a thermal load, since twice the power is flowing in and out. This means the device must monitor and control the combined input and output, rather than the two independently."
] |
[
"Forgot to provide my link...",
"https://www.pcmag.com/roundup/351446/the-best-battery-packs-for-your-phone",
"Not exactly a wide selection, but if you're looking for one, hopefully it'll give you a start."
] |
[
"It's only more complicated if you are making unsafe batteries. A pass through battery with the appropriate safety considerations is more complex than one without."
] |
[
"Why You Can't Tickle Yourself"
] |
[
false
] |
[deleted]
|
[
"Is there a question here?"
] |
[
"Someone posted a few days ago with a question about tickling and since I went to the trouble to type this up for an answer I figured I'd see if anyone appreciated me posting it."
] |
[
"TL;DR so i tickled myself on the foot and it worked. qed"
] |
[
"Do a freshly laid egg and a freshly hatched chick have the same number of calories? If not, where do the extra calories come from?"
] |
[
false
] |
If the chick has more calories, it must be getting the extra energy from somewhere...?
|
[
"No, the egg would have more calories. The egg has all of the materials, including energy, needed to form the chick. The process of forming the chick involves chemical reactions that are driven forward by the use of the stored energy. The process is not 100% efficient and the energy lost escapes from the egg as heat. On top of that the chick moves in the egg, it's heart beats, it's nerves fire, all of which use calories, which is lost in the end as heat."
] |
[
"Nope. You need a temperature differential to do work. The mother bird is just making sure the eggs don't lose heat."
] |
[
"Bird eggs have no mechanism to convert heat energy into something like glucose that is usable for metabolism. If a mother bird sits on an egg and warms it, it transfers energy to the egg in the sense that it warms it up, but that energy is simply the heat in the egg, and is lost when the egg cools down. It's not transformed to other substances and stored.",
"Think of it like leaving your car out in the hot sun. The sun adds energy to your car, but it won't let you drive farther."
] |
[
"Can gravitational waves escape black holes?"
] |
[
false
] | null |
[
"No. Nothing can."
] |
[
"...sorry what? Plane of existence? "
] |
[
"This is ",
". If you set up your weak field theory around a background like so",
"g = g_0 + h, h << 1",
"You'll find h features waves that move in the bg metric g_0 and are affected by it."
] |
[
"[Medicine] Improper alcohol detoxification can kill a person. How then can people rehabilitate alcoholics?"
] |
[
false
] | null |
[
"have them (the addict) continue to consume alcohol as needed to avoid serious withdrawal symptoms.",
"However, the amount consumed per day is decreased continually over a span of several days, so that their dependance on ethanol is gradually reduced to zero."
] |
[
"Switch to other longer acting drugs that work on the same receptors (diazepam or other benzos) and then taper down the dosage at a safe and tolerable rate. Cold turkey is very rarely an effective method of overcoming moderate-severe cases of physical dependency because even overlooking the risks of seizures and strokes relapse rates are very high due to how psychologically challenging it is to overcome acute withdrawal."
] |
[
"In the hospital for the treatment of acute moderate or severe alcohol withdrawal, there is usually a \"detox cocktail\". This main aim is to treat/prevent seizures, lower craving, and supplement vitamins to prevent encephalopathy. ",
"To prevent seizures/craving from acute alcohol withdrawal, you have benzodiazepines (chlordiazepoxide, oxazepam etc) or carbamazepine. To treat seizures you usually use shorter acting benzos like lorazepam.",
"To prevent encephalopathy, you often see pabrinex (vitamin b and c) prescribed, then followed by a combination of vitamin B compounds and thiamine. You can also get lactulose and rifaximin prescribed to prevent ammonia buildup in the gut which can cause encephalopathy."
] |
[
"I've read that certain sharks will kill their siblings before birth. What purpose does this behavior serve, and isn't it a waste of resources for the mother?"
] |
[
false
] | null |
[
"Remembered this from an animal behavior course:\n",
"http://en.wikipedia.org/wiki/Siblicide",
"I'm pretty sure this is obligate siblicide. The surviving shark will typically be the stronger of its siblings and will have gained resources. ",
"You can think of it as way to have more biological diversity. Instead of just producing one individual progeny with only one combination of genetics which may or may not be optimal, you can have multiple progeny with different combinations and then just have them duke it out so that the most genetically fit individual will survive. A key assumption here is that the survivor will typically perform better than its deceased siblings would. ",
"The wikipedia article also mentions that this type of behavior may actually be counterproductive for the mother. (It may reduce or impair her reproductive fitness)"
] |
[
"the question isn't \"what is best for sharks as a species?\"",
"the question is \"what genes are best at surviving?\"",
"a shark that eats it's siblings is going to have less competition and do better for himself, assuming that sharks don't help each other out very much. if so sharks that do such a thing are going to out-compete their siblings and reproduce their genes better."
] |
[
"This is what it's all about. Selection favors genes that survive, not necessarily genes that benefit \"the species\"."
] |
[
"How hot are the coals in the coal bed of a campfire that has been burning for a while?"
] |
[
false
] |
We were camping on the weekend and a few of us thought around 500-600 degrees celcius, some thought over 1000 degrees celcius.
|
[
"Wood coals burn at 3-600 degrees. You can get them hotter by providing lots of oxygen (like in a blacksmith's setup) but the way to tell is by the color of the coals. \nBased on the Black-body radiation (since coals are black, this is a good approximation) you start to see a glow at about 500 deg C, and it is easily visible at about 600C. At 800 it starts to get more yellow, and at about 1200 it is almost white. This is a very rough guide, but not to bad for this purpose. \nIf you really want to settle it next time, get a piece of aluminum foil, which melts at ~660 C. So that would be a good way to settle the bet. I think you'd have to try pretty hard to get aluminum to melt over a wood fire. "
] |
[
"It should also be noted that coals which have burned for a while will be covered in ash, which will make approximation by color difficult. If the coals are from wood, the type of wood and dryness will also affect how hot it burns.",
"And yes, over a small fire you'll likely never melt foil - just build a bigger fire. We frequently toss aluminum cans in bonfires and fish the melted and distorted metal out of the ash later. It's fun!"
] |
[
"Thank you!"
] |
[
"How does putting a phone into a ceramic bowl amplify sound?"
] |
[
false
] |
Recently I saw that you could make your own "speaker" by putting a phone into a ceramic bowl, how does this work exactly?
|
[
"Sound waves spread out in all directions and bounce off of solid surfaces. So if you put your phone in a bowl, the sound bounces off all of the interior surfaces of the bowl and exits out the open side. The bowl basically works kind of like a lens for sound waves."
] |
[
"I apologize for the abstract nature of my comparison. I didn't mean to imply that sound waves behave like light, simply that the way a bowl focuses a soundwave is approximately like how a lens focuses light."
] |
[
"In both cases, waves are redirected by interaction with things, but I think that's as far as the analogy goes.",
"And that is only as far as I was trying to take the analogy, but seeing the error of my ways I renounce my comparison and will flagellate myself in the name of ",
"/u/horsedickery",
"."
] |
[
"If standing 1 foot away from a cellular tower antenna burns you and causes headaches, why doesn't standing in a city full of thousands of towers have an effect on you?"
] |
[
false
] |
[deleted]
|
[
"If you put your hand a centimeter away from a lightbulb, you feel the heat (or might even get burned). Now have a room full of lightbulbs in the ceiling and tables - you don't get burned. You might get some heating over time if the room is small, but that's negligible.",
"It's because there is an inverse square relation between intensity and distance to the emitter."
] |
[
"I have never heard of this, and I work in the industry. I am constantly in close proximity to cell towers and have never had headaches or gotten burned or heard of anyone who has. The only thing I could think of that might cause this is if you had a peace of metal on you which was acting as an antenna and heated up and burned you. "
] |
[
"It is all about power density, or watts per square centimeter. Cell towers typically put out a certain number of watts of radio frequency (RF) and do so in all directions. The further from the tower, the less watts of RF per square centimeter. It drops off pretty quickly."
] |
[
"Are LED or compact flourescent bulbs still more cost effective for lighting if you live in a cold environment where you need to heat your home with some source of heat anyway?"
] |
[
false
] |
Are LED or compact flourescent bulbs still more cost effective for lighting if you live in a cold environment where you need to heat your home with some source of heat anyway? The primary argument against incandescent bulbs as i understand it is that they waste so much electricity as heat not light. But if you are going to have to hest your house anyway and could therefore be offsetting additional heating with the heat from the incandescent bulbs then arent incandescents just as cost effective to operate? Assuming the alternative from of heating would be the same price as electrical heating to operate. (not gas etc) So shouldnt hypothetical people living in the northpole for example continue to use incandescent bulbs?
|
[
"There has been some similar questions before, like ",
"this",
", ",
"this",
" and ",
"this recent one",
".",
"It all boils down to: Only if you use resistive heating devices like an electric radiator it doesn't matter if you spend electricity on that or something else like lights or appliances. Also if you don't need heating in a good part of the year but still need light during that period then using LED's will lead to less energy wasted.",
"Whether it will be the most cost effective is hard to answer as it depends on what kind of heating you have, it's price, price for electricity etc. But LED's will last many, many years whereas traditional light bulbs only last a few and I think almost in terms of this an LED bulb will be cheaper.",
"So to the hypothetical question:",
"So shouldnt hypothetical people living in the northpole for example continue to use incandescent bulbs?",
"Yes if the electricity is produced locally inside the house/tent. In research stations such as those on the southpole they use diesel generators for electricity, but whether they rely on electrical heating or central heating by using the waste energy from the generator I don't know - but it would make sense to use as much of the \"waste heat\" to heat the building before turning to electrical heating."
] |
[
"How much you feel is not important. The thing is, you can only get two types of energy out of light bulbs: visible light and infrared. The infrared part contributes to heating your house. "
] |
[
"The heating cost differential between electricity is about half in favor of gas.",
"Therefore in the winter the led only sabes you half as much because you have to make up for the heat loss with gas heat which is half as expensive as the electricity would have been.",
"No if you were all solar panels with excess capacity and no gas there wouldnt be any difference"
] |
[
"What is happening when a fabric gets stained?"
] |
[
false
] | null |
[
"When a fabric is stained (or intentionally dyed for that matter), molecules which absorb visible wavelengths of light as a result of their electronic structure become attached to the fabric molecules. Usually, the stain is held in the fabric by weaker intermolecular interactions (Van der Waals force, hydrogen bonds, etc.), and it is not chemically bonded to the fabric; therefore, it is possible to remove the stain with detergent, which helps the staining molecules enter solution. ",
"In some cases, typically with intentionally used dyes, the colored molecules become chemically attached to the fabric; these dyes are thus significantly more difficult to remove. One example is the use of mordants to form a metal complex which binds the dye and the fabric together via a metal ion. "
] |
[
"Coincidentally, I just answered a question on ",
"how bleach works",
". It doesn't remove the staining molecules, just destroys the chromophore (part of the molecule which makes it colored). "
] |
[
"If you bleach a colored material does this remove the bonded molecules? or simply add others to the mix that cause the fabric to appear white?"
] |
[
"Ask Anything Wednesday - Biology, Chemistry, Neuroscience, Medicine, Psychology"
] |
[
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!
|
[
"I think this is the right thread for this.",
"I've noticed that when my eyes are exposed to bright light before they adjust I have trouble keeping my eyelids open. However, the total amount of light received seems to matter - I'm able to keep one eye fully open and the other closed with about the same amount of effort as keeping both half open even when fully opening both is difficult. ",
"So, my question is: why does the amount of light received by one eye seem to affect my ability to open the other when both are exposed to bright light? "
] |
[
"How close are neuroscience and psychology to being combined in the teaching of the mind? They are still taught as separate entities, but we know mental illness comes from chemical/physiological impairments. "
] |
[
"Are humans devolving because of advances in modern medicine? Are we circumventing 'survival of the fittest' by keeping people alive through illness and injury?"
] |
[
"Other types of quarks?"
] |
[
false
] | null |
[
"Up, down, strange, charm, bottom, and top."
] |
[
"Can the last 3 do anything?"
] |
[
"Yes, but they’re not stable either."
] |
[
"What makes us distinct from other animals?"
] |
[
false
] |
Sorry for the slightly philosophical question but I am writing an essay on this topic and would like a more scientific answer to this question. To give some background I am using Hans Jonas' 'Tool, Image a Grave' where he argues that that it is our ability to make tools and images and also conceive of death (especially our own) that makes us different (more advanced). Again, sorry for the philosophy but I am looking for a scientific explanation.
|
[
"Our brain. Specifically our highly developed neocortex. Read the quote below and if you want more answers click on the link and do some searches for \"neocortex\" or \"human brain\" or whatever key words you think will help.",
"From Carl Sagan's \"Dragons of Eden\" found ",
"HERE",
"and clearly the most recent evolutionary\naccretion, is the neocortex. Like the higher mammals and the\nother primates, humans have a relatively massive neocortex. It\nbecomes progressively more developed in the more advanced\nmammals. The most elaborately developed neocortex is ours\n(and the dolphins' and whales'). It probably evolved several\ntens of millions of years ago, but its development accelerated\ngreatly a few million years ago when humans emerged.",
"EDIT: another good passage",
"The evidence suggests that in our ancestors of some tens of\nmillions of years ago there was a neocortex, but one in which\nthe left and right hemispheres served comparable and\nredundant functions. Since then, upright posture, the use of\ntools, and the development of language have mutually advanced\none another, a small increment in language ability, for example,\npermitting the incremental improvement of hand axes, and vice versa. The corresponding brain evolution seems to have\nproceeded by specializing one of the two hemispheres for\nanalytic thinking."
] |
[
"From a biological standpoint, we're not very different at all; a lot of our genetic sequence is shared, not just by primates, but other organisms too. Our basic needs are identical, the \"building blocks\" that make us up (proteins, lipids, etc) are all found in one way or another in other species, and even our nutritional requirements are almost exactly the same.\nFrom a scientific perspective, humans are animals, plain and simple. Our differences arise from some of the things you mentioned; knowledge of our own death, self-consciousness (not found exclusively in humans), and other reasons that are more philosophical/psychological.\nOne could argue that a larger and more developed brain sets us apart, but then again there's many animals with brain functions far beyond ours in certain respects."
] |
[
"The attempt to define what's unique about humans is primarily a philosophical question, rather than a scientific one. Biologically, there are large numbers of things that are unique about humans, just like there are unique features of literally every other species. ",
"Definitions like \"man is the animal that makes tools\" exist to comfort people that we're not \"merely animals\". "
] |
[
"What does gravity feel like of Europa?"
] |
[
false
] |
Hello! I was wanting to know what gravity would be like on one of Jupiter's moons, specifically Europa. Would there be a massive tidal effect that takes place doe to Jupiter's massive size? If so how drastic is it? Would the entire moon be shifted towards Jupiter? Would this cause an odd speed for acceleration due to gravity?
|
[
"Europa is close enough to Jupiter that it is tidally locked. That is the same side of Europa always faces Jupiter. Also, the moon becomes slightly elongated at its closest approach to Jupiter, and returned to mostly spherical as it moves away from its closest approach. It is thought that this flexing can make a possible subsurface ocean.",
"However if you were on the surface you would experience around 13.4% of the gravity we have on Earth regardless of how close you are to Jupiter."
] |
[
"The gravity on Europa is 1.315 m/s², or about 13% of Earths gravity. The tidal force on Europa is about 0.00132 m/s² (",
"source",
"), which is about 1/1000th of a decrease, so you wouldn't notice it.",
"On a planets surface, a tidal force is a 'negative gravity' force that is at its maximum on either side closest and furthest from the body causing the tide.",
"If a small object orbits a large object, it has a natural stable orbit that is a balance of orbital speed and proximity to the large object. Further out, it orbits slower because it requires less centrifugal force to counter the gravity pulling the small body in (like how Pluto orbits every 248 years). A solid body with significant size, like a moon, has a stable orbit around its center of gravity. The side of the moon close to the large body is orbiting too slow, and is slightly sucked in. The farther out side is orbiting too fast, and is sorta flung out."
] |
[
"Ok this is one of those ask science questions that is fun because it's not to difficult to figure out yourself, given the right tools. To find the force from gravity F = G",
"m/r",
" Where G is the universal gravitational constant, M is the planet's mass, m is the mass of you, and r is your distance from the planet's center. Calculate the force from gravity from Europa and from jupiter. The difference of those values is the force of gravity you would experience."
] |
[
"Will a hole drilled into a metal block get bigger or smaller when the metal block is frozen?"
] |
[
false
] |
Let's say you have a 1" cube of steel, and you drill a hole straight through the middle, top to bottom. Now it looks like a bizarre square metal donut. You take that square cube, throw it into the freezer overnight, and take it out in the morning. Would the drill bit no longer fit inside the hole due to the hole's diameter shrinking, or would it pass through freely due to the contraction of the metal causing the diameter of the hole to increase?
|
[
"This is exactly how we attach the turbine disk to the shaft in a T-700 helicopter engine."
] |
[
"This is exactly how we attach the turbine disk to the shaft in a T-700 helicopter engine."
] |
[
"There's a way to think about this that makes the answer obvious:",
"Suppose instead of drilling the hole you just draw a circle on a face of the cube. When the cube cools down it shrinks. It's pretty obvious that the circle you drew will shrink too.",
"Ok, now imagine you had drilled a hole where that circle is drawn..."
] |
[
"How did organisms in nature evolve to use sequences and angles like the Fibonacci Sequence in their structures?"
] |
[
false
] |
Inspired by . How did the Nautilus evolve its shell like that? Is there some advantage to it being that shaped? Why are the sunflower thingies spread out in successive 137.5 angles? What evolutionary advantage is there to having structure based on these sequences?
|
[
"This",
" may be of interest to you. And ",
"this",
" as well. Essentially it seems that the fibonacci pattern arises out of geometry rather than being hard coded into structure."
] |
[
"So the Fibonacci sequence produces geometric shapes that require less energy to form? Excellent links and upvoted for that, but that doesn't quite answer my question with regard to animals like the Nautilus. The shell shape I presume would be genetic, so Fibonacci sequence-inspired shells must be selected for, correct?"
] |
[
"The important thing to recall is that genes don't code for gross structure, just the proteins which are responsible for constructing it and (abstracted - this is done by other proteins coded for by other genes) the situations in which they should be expressed. In this regard, the material of the shell and the stage of development at which it appears (and from that, its position on the creature) are controlled by genetics. The specific structure they take is governed by the physics of the environment in which it occurs. ",
"The first article is actually a fascinating read in its own right."
] |
[
"Why do cells multiply when they're about to die?"
] |
[
false
] |
I seem to hear a lot that after the growth stage, cells will still multiply with one of the new splits dying and the other carrying on. Either this is a gross misunderstanding of the process or it was grossly under-explained. So, I guess the first question is why do cells dies anyway? It would seem to me that any reason they would would carry on to its successor. Waste products? Osmosis dictates that both new cells would have it. Corrupted DNA issue? Would be transcribed similarly (and probably with its own errors; I remember hearing about chromosomes getting slightly shorter each time they're copied). So what purpose would splitting a cell actually serve if it's not explicitly for the macro growth of the organisms it's a part of?
|
[
"Just because this is a topic so close to me, I'm going to add an almost useless comment:",
"Stem cell division does not have to be asymmetric --- i.e. one remains a stem cell and one differentiates. It is possible (and indeed often) that the daughters both differentiate or both remain in cycle; the overall balance only needs to be maintained on average. The precise balance which controls this is/should be interesting. In the specific case of intestinal crypts, I believe both models are seen: the paneth cells appear to undergo strict asymmetric division, and indeed are responsible for the overall crypt maintenance but are incredibly slowly turning over; whereas the much more active Lgr5+ stem cells located halfway up will undergo all types of fates, and are the main contributors to the active maintenance of the somatic tissue."
] |
[
"Cells in the body are lost all the time. For instance a significant proportion of your stool is cells from your intestine. These are the cells of the intestinal epithelia. The cells are fully differentiated and do not divide. New cells are developed from areas of the intestine called crypts which contain adult stem cells. These stem cells are able to replicate. Of the two daughter cells, one remains a stem cell and the other moves off toward the villi.",
"So, organisms use cell division to maintain proper structures within the body. Cells sometimes need to die in order to maintain these structures. Most cells in your body are differentiated and do not appreciably divide.",
"In other situations, by replicating slowly over time, DNA errors can be caught by arresting DNA replication. The arrest can cause a kill signal to be sent, killing the cell but saving the organism."
] |
[
"Interesting stuff. I think the principle model of asymmetric division is the hair follicle. This might be an interesting further reading topic for the OP."
] |
[
"Any news on the attempt to photograph a black hole?"
] |
[
false
] |
I'm an aspiring astronomer, and I have yet to see any news about it, is there anything I missed?
|
[
"I'm guessing the OP is talking about the ",
"Event Horizon telescope project",
"."
] |
[
"http://www.reddit.com/r/askscience/comments/ori40/scientists_plan_on_taking_the_first_picture_of_a/",
"It's on the front page right now."
] |
[
"The Event Horizon imaging project is still very much in the early stages. These things take time. If/when they succeed you'll definitely hear about it. "
] |
[
"Why is string theory empirically untestable? Couldn't we build a microscope powerful enough to see \"strings\"?"
] |
[
false
] | null |
[
"Imagine you could only measure the shape of a statue by bouncing various sports balls off of it and seeing how they return to you. You could start with basketballs which gives you a kind of pillar shape, as best you can tell. Then baseballs, and you start to see rough features. Then golf balls, then bbs. The smaller the ball, the finer the resolution you can see. ",
"Well everything has an intrinsic wavelength, especially small particles. Well the smaller the wavelength, the better your resolution can be. It's why you can't use an optical microscope to resolve an atom, the wavelength of visible light is bigger than the atom. What's interesting is that the wavelength is ",
" proportional to the momentum of an object. More momentum = smaller wavelength. In some ways that's what we're aiming to do with particle accelerator experiments, reduce the size of wavelength to measure ever smaller lengths."
] |
[
"I recall that to build an accelerator capable of probing the length scales of strings is on the order of the orbit of pluto. Like we'd have to build a particle accelerator the size of our solar system to be able to \"see\" strings. So in a way, it's empirically testable, just not feasibly so with modern understanding. However there are other predictions the theory makes that we hope to test in the future."
] |
[
"order of the orbit of pluto",
"That is, with current accelerator technology, I think. If we had more powerful bending magnets, we could theoretically do it with a smaller accelerator.",
"Of course, that doesn't help us right now. The string scale is believed to be many many many many orders of magnitude above energy scales we can reach today. If reaching the string scale is the only way to get good evidence of string theory, none of us will be alive to see it (unless there is alien intervention)."
] |
[
"Is it possible to scale/climb under electric fences by simply diverting the current to ground using a rod or conductor of sorts?"
] |
[
false
] |
I recently watched a documentary on North Korea that followed a guard who defected through the DMZ. In his interview he said that he used a plastic pipe (insulator) to temporarily divert the current to ground by bridging the gap between the wires and dirt with it, following him propping up the low current wires with a wooden stick and climbing under. I mean it clearly worked once but how feasible is this? Did he just get lucky? As I understand it electric fences are just wires with a high voltage but since there is no voltage differential there is no current movement until someone (usually a person) completes the circuit..so if the circuit is completed using a more conductive object then the human body wouldn't it take the path of least resistance ie not through you? Here is the doc. Maybe halfway through they discuss this.
|
[
"It might be more likely that the fence he snuck through simply wasn't energized at the time. North Korea's power grid isn't exactly known for its robustness..."
] |
[
"In your example, yes - the guy probably got lucky and did not brush the fence. However, what you are asking might be possible in the right circumstances - it depends on how the fence circuit is constructed. In all likelihood, the fence is a floating DC circuit, meaning it has no electron sink until you touch the wire. Your ability to defeat such a circuit then depends on how much steady state current the power source can deliver, and how much current you can sink. If you can ground the wire near the source, you might be able to sink enough current that the source voltage will sag to a safe level, but the farther you go from the source, the larger the resistance in the wire becomes, and the more current you will have to sink to sag the voltage to a safe level. Of course, this assumes that the source doesn't have a current limiter built in to prevent such things, which seems likely, otherwise you'd be replacing fuses every time someone touched the fence. ",
"What should work though, is building yourself some clothing lined with foil or mail and tied with wire to a ground, preventing your flesh from being the best path to ground when you grab the wire with your gloves. You could also do something like use old tire rubber to build an insulating suit or \"blanket\" to separate you from the wires. Or, you could just use very well insulated bolt cutters to cut a hole in the fence. ",
"Edit - if it were me, I'd put a capacitor bank between the fence and the source. It is possible that this guy (or something else) discharged the bank with the pipe, allowing him to climb under while they recharged, which may explain why his friend didn't make it if the banks recharged."
] |
[
"Why would current flow to ground through the insulator?",
"I may be missing something, but it seems like he just poked the wire out of the way with something that wouldn't conduct so that he could crawl under without touching it."
] |
[
"Is there any sort of case in which a particle and antiparticle collide which does not result in annihilation for both particles? Can a positive particle survive a collision with an antiparticle?"
] |
[
false
] |
I just listened to the Radiolab on Symmetry and it raised this question in me. Thank you for your time :D Additionally, is it possible for an electron and positron to collide, resulting in the destruction of the positron, but the electron survives?
|
[
"Bhabha scattering also has a t-channel where the electron and positron don't annihilate.",
"The more specific example you provided can not happen because it violates a series of conservation laws, mainly charge."
] |
[
"By definition vertices on a Feynman diagram describing a process will always have three branches, and as a general rule of thumb the particles going in won't be the same ones coming out. With that said there are some radiation processes which \"preserve\" the parent particle. Famously, electrons do this when they emit light . The old electron is still in some description still \"alive,\" though to be honest, the description of an electron decaying into an electron and photon works just as well. Other bremsstrahlung processes exist as well, ",
"Higgs bremsstrahlung",
"Here's another example of such a particle exchange which leaves the \"original\" particle still kicking, ",
"ZZ fusion",
"I could talk about gluon radiation here too, which is very similar to how electrons radiate photons, but gluons carry color/anticolor charges so the quarks that produce such radiation are \"changed\" themselves, so I don't think you're interested in that process. ",
"Lastly, electrons and antielectrons can scatter off each other without annihilating. ",
"This cartoon",
" sort of shows the process heuristically."
] |
[
"Firstly, the notion of collisions of elementary particles is not obvious. As these behave quantumly, for an interaction between a particle and and an antiparticle, there is only a finite probability of annihilation, that depend on the particles positions, velocities, and collision cross section.\nThere are more conservation laws that should be obeyed, such as charge conservation, energy conservation, baryon conservation...\nFor your question, charge conservation prevents the survival of the electron is the positron is destroyed.\nThis also means that for example an antielectron and a proton will not annihilate. I don't know what would happen for proton-antineutron reaction, as they share some quarks."
] |
[
"If you used anti-protons in particle therapy, would they behave like protons, electrons, or positrons?"
] |
[
false
] | null |
[
"They would behave like protons, but they’d also be able to annihilate."
] |
[
"Either a positive or negative charge at very high energy will have the same effect: it will knock electrons out of atoms."
] |
[
"yeah ok. Thanks"
] |
[
"Do black holes have any 'size'?"
] |
[
false
] |
I know black holes are very massive and that we don't really know what happens inside them, but I was thinking... Once a black hole 'swallows' something, does that new mass make it bigger and more powerful? Or once a black hole gets started it is always the same no matter how much stuff falls into it? I mean, do the particles actually stay there, but in a very very compacted way, or they just cease to exist? Can we know how much stuff fell into a black hole by measuring its gravity or something? Or they all just look the same to us?
|
[
"The main misconception about black holes is that they behave like vacuum cleaners. They don't \"swallow\" things, things fall into them.",
"But yes, black holes increase in mass as things fall in."
] |
[
"As far as I'm aware (I'm not up-to-date with theoretical black hole physics, but I have a physics degree!), the black hole itself is usually considered to be a dimensionless object (singularity), that has mass. It therefore has infinite density. ",
"However, there is a distance (the Schwarzschild Radius) from the black hole within which NOTHING is able to escape (not even light). So it can be useful to consider this as being the \"size\" of the black hole in some way, although it's more a volume in which the black hole dominates.",
"As the black hole gets more massive, the Schwarzschild Radius also gets bigger, though the black hole itself is though to remain a singularity."
] |
[
"the black hole itself is usually considered to be a dimensionless object (singularity), that has mass.",
"The term \"black hole\" generally refers to the region of space bounded by the event horizon as measured by a far away observer in the asymptotically flat region of spacetime. The thing you're describing is just called \"the singularity\"."
] |
[
"Can lake Mead ever refill?"
] |
[
false
] |
Basically the title…are we in a long period of drought or is this the new normal? Is there any realistic amount of rain/snowpack in a wet year that would get the lake back to its 1980s levels?
|
[
"I like to use dice to explain it to people. If every year the lake loses 35 units of water, but every year you get 10 six-sided dice of input, it'll fluctuate but stay stable. Sometimes you roll a 60, sometimes a 10, but usually between 30 and 40. Climate change takes away dice. With 9 dice, it'll take a long time to notice the difference. 8 will be subtle but obvious, and by the time you get down to 6, only the most extreme rolls will even cover your losses. If we're at 7 dice, even if you roll all 5s and 6s once in a while, the house will win in the end."
] |
[
"are we in a long period of drought or is this the new normal?",
"More the latter than the former. In terms of us considering this a drought, that's specifically in reference to past climatological means, i.e., there is less precipitation than an average baseline from decades past. Generally, in the context of pervasive and fast changes in climate, drawing the line between short term trends (e.g., a drought) and new climatological realities is challenging. For the American Southwest though, looking toward the future, across a range of projections in terms of different ",
"RCPs",
" (i.e., projected emissions) and different modelling frameworks, the projection for much of the region is significantly less total precipitation than \"average\", where again generally the average is not the recent conditions but longer-term and older climatological means (e.g., ",
"Wang & Kotamarthi, 2015",
", ",
"Seager et al., 2013",
", ",
"Greene & Seager, 2016",
", ",
"Tillman et al., 2020",
", etc). Indeed, several of these sources explicitly state in one form or another that aspects of the current \"drought\" conditions are expected to essentially be the new normal, or close to it (and in some cases, worse, e.g., expected decreasing amounts of infiltration and thus less groundwater recharge as described in the Tillman paper).",
"Is there any realistic amount of rain/snowpack in a wet year that would get the lake back to its 1980s levels?",
"In a single year? Especially in the context of the projections above? Probably not. To boil it down to the simplest level, it's a relatively basic set of math. Specifically, the amount of water being extracted from the system for human uses consistently exceeds the amount being added via precipitation and that deficit is projected to continue, so broadly, the only way the reservoir will appreciably go back up is if the amount being extracted is (drastically and consistently) reduced to below the average amount being added via precipitation. Certainly, a few wet years could help and there will always be variability, i.e., even in the context of projected significant reduction in long-term means, there can still be isolated, or maybe even sequences of wet years, but on average, the projections suggest a much drier future for this region, closer to the current conditions than the past. In the face of the projections, and in a scenario with no meaningful reduction in usage or significant changes in the projections (the latter of which is unlikely given current trends) or barring some extremely large infrastructure project (e.g., desalination and pumping, diversion of other major rivers, etc) that each pose a range of different challenges, it's less a question of if the reservoirs will effectively run dry, but when."
] |
[
"Is there any realistic amount of rain/snowpack in a wet year that \nwould get the lake back to its 1980s levels?",
"Note that when the dam was first built (with fewer downstream demands on the water than there are presently), it took it all the way from 1934 to 1941 to fill. Even if everything works the way it was planned to a century ago, the plan was to use about 90% of the river's flow in any given year, and very gradually capture the surplus to fill the reservoirs and start generating power.",
"If future usage is less than future river flow, the reservoirs will (slowly) refill, over a period of several years. If not, they won't."
] |
[
"Does black is an actual color or a shadow?"
] |
[
false
] | null |
[
"Objects do not have color. Color is a psychological, not a physical property. Objects, like you wrote, have surface reflectance properties which determine which wavelengths of light are absorbed/reflected and how they are reflected (e.g. diffuse). ",
"We experience objects as black when our cone receptors are ewually minimally stimulated or not at all stimulated (e.g. when no visible light reaches our eye). ",
"Which wavelengths of light end up reaching our eye depends on the nature of the light source and the material of the object (and the medium through which the light travels). That's why, under certain lighting conditions, your sweater might appear green and in others it will look blue -- the physical properties of the sweater haven't changed, but which wavelengths are reflected off of it (and how your visual system interprets the nature of the light shining on it) affects how it appears to you."
] |
[
"Wow, this really changed my perspective of viewing everything in this world right now. Thank you so much for explaining it. Does everyone knows this? I mean this is super mind blowing!! To think that every objects do not have color at all!"
] |
[
"Colloquially we speak of objects having color and this being a stable property because for the most part, we have similar visual systems. In the same way, most of us agree that the same things taste sweet, but that's because we are detecting sugar and have the same sensors for doing so, not because \"sweetness\" is an inherent property of the food. ",
"This is most apparent when we think about colorblind individuals: they do not see objects as colored in the way that non-colorblind people do, but the underlying objects are the same for both! If a majority of people were colorblind, perhaps they would all agree on the \"true color of things\" and it would be non-colorblind people who see things anomolously and incorrectly."
] |
[
"How does a CME disrupt electricity?"
] |
[
false
] |
So I just saw a video by a Youtube channel called RealLifeLore talking about Coronal Mass Ejections. And I got curious. He talks about the possible damage and that electricity may be shut down by such an event for years. Why is it lasting such a long time? Wouldn't it only be during the time the ejection actually hits us?
|
[
"Even though the electromagnetic disruption from a CME is temporary, if it is powerful enough to fry every transformer, computer chip, and electrical switching station in the country, they would all need to be physically replaced, and that would take a much longer time."
] |
[
"Plus, even when the Sun emits a big one, it's less than a 1 in 2 billion chance that it will be headed towards Earth.",
"(from the Sun's perspective, the solid angle subtended by the Earth is.. quite small)"
] |
[
"Why do you think the utility company gives a dam about it?"
] |
[
"How long would it take for a hand crank generator to fully charge a AA battery?"
] |
[
false
] |
Obviously there's a couple of variables here, such as crank speed, battery capacity, and so forth. Please feel free to make assumptions on an average use-case. Using this kind of thing;
|
[
"Most rechargeable chemistry AA batteries have energy capacities of ~2-3 Watt-hours, charge capacities of ~2000 milliamp-hours",
".",
"A healthy person can maintain an output of 75W",
", so recharge could conceivably be done in minutes.",
"However, the real limitation of recharge rate is the internal resistance of the battery. Discharge/recharge currents generally need to be limited to about 400 mA or less to prevent overheating and explosion. So for a typical rechargeable AA battery with a capacity of ~2000 mAh you are talking several hours to safely charge the cell.",
"EDIT: I should add that it is difficult to continuously deep cycle most batteries, so you actually get a small fraction of this energy out, so recharge doesn't take quite as long as these calculations suggest, but you're still talking the better part of an hour for most AA cells."
] |
[
"Why thank you! Here's to hoping we can get some excellent answers!"
] |
[
"I read this and actually said aloud, \"That's an excellent question!\""
] |
[
"What makes the australian black bean - castanospermum australe - poisonous?"
] |
[
false
] |
Wikipedia didn't specify what chemical actually made it poisonous, and several other links also didn't specify it.
|
[
"Well you might figure this, but Castanospermum contains at least one toxic substance and it's called castanospermine (heh). I'm unsure whether there are more toxic substances. ",
"Castanospermine is a glucosidase inhibitor. I could explain to you what that means if you're really interested but that's a whole other topic. "
] |
[
"There might be very little difference.",
"\nCastanospermine has been reported to have an anti-diabetic effect, and it has long been noticed that a lot of alkaloid plants actually have an anti-diabetic effect. This might be the main cause. ",
"Interestingly, compare the chemical structure of ",
"castanospermine",
" to a major anti-diabetic drug, ",
"miglitol",
".",
"\nThey are very much alike.",
"\nSo you could imagine that because anti-diabetic drugs are specifically developed they would probably have a very high target specificity. They are meant only to inhibit alpha-glucosidases. Thereby they should only have a specific effect on glucose metabolism, and very little other effects. ",
"Because castanospermine has a slightly different structure, you could imagine that it could also have an effect on other glucosidases/proteins. For example, castanospermine also affects ß-glucosidase and sucrase",
" ",
"Other differential effects might be caused by differences in biological processing/uptake, dose and possible interactions with other (potentially toxic) susbtances in the Castanospermum.",
"1:",
"http://jocpr.com/vol6-iss8-2014/JCPR-2014-6-8-288-293.pdf",
" "
] |
[
"That sounded familiar so I googled it, and found that anti-diabetic drugs are alpha glucosidase inhibitors. So I'm interested in knowing how it's different from that"
] |
[
"Are there any major advantages to flapping wings, or are fixed wing aircraft something we have truly improved upon nature? Given advanced enough materials and power supply, could ornithopters theoretically be practical compared to fixed wing and rotor craft?"
] |
[
false
] | null |
[
"Short of a propulsion system powered by explosive flatulence, our aircraft design, while very efficient, is simply impractical for animals. In the same way, cars with wheels are more efficient than limbs but a living organism can't support a wheel. Our machinery is certainly simpler and requires less energy but is only practical for man made mechanisms with replaceable parts and deliberately designed with physics in mind rather than by chance powered evolution."
] |
[
"This actually depends on the size of the flier.",
"For a large wingspan, non-flapping will always be better. This is because large units of air have less \"surface tension,\" behaving more like what you think about when you envision your own arms flapping.",
"At smaller distances, the surface tension of air is higher. The animal is pushing on more individual particles as a ratio of particles:bodymass, and this allows for greater relative pressure of wingflappery.",
"This is why insects seem to have such an easier time flying than birds do. For more, read up on this page: ",
"https://en.wikipedia.org/wiki/Navier%E2%80%93Stokes_equations"
] |
[
"Air does not have surface tension, nor anything of the like. Flapping wing flight is governed by relative frequency and relative velocity.",
"Insects are far less efficient than birds, although their small size does allow them to hover, making use of dynamic stall and wake recapture.",
"Telling someone interested in flight to look at the Navier Stokes equations is about as much use as telling someone interested in race-car performance to read about Newton's laws of motion. While perhaps relevant the step between theory and application is far too large to be left as an exercise to the reader."
] |
[
"All all rechargeable battery chemistries inherently degrading, or are there technologies either practical or theoretical that would allow for rechargeable batteries that barring mistreatment keep the same capacity?"
] |
[
false
] | null |
[
"There are lots of Electrical energy storages devices that do not degrade with direct usage. Their issue is that they either are very expensive, or have limited power to weight or volume.",
"Flywheel energy storage. Used everywhere, ultra robust. Problem? Cost and minimum size required.",
"Flow Batteries. Hydrogen Fuel cells being the most common. Problems? Low efficiency, high cost, difficulty in generating clean Hydrogen.",
"Every electrochemical battery with a self-contained anode, cathode, and electrolyte degrades over time. The only question there is the number of cycles before they must be recycled. We can improve the number of cycles, but anything with a redox reaction that doesn't allow us to separate the materials, purge and recycle them, is going to degrade with use. There are just so many more paths for it to degrade, then there are for it to improve. Entropy works only in 1 direction."
] |
[
"There are advancements being made in this area. Personally, I believe we are on the verge of a rechargeable battery that will keep the same capacity almost in definitely. Here’s an interesting read on one such technology. ",
"SOURCE"
] |
[
"For large-scale installations, there are already flow batteries (",
"https://en.wikipedia.org/wiki/Flow_battery",
") which would qualify, but I think you're more likely thinking about smaller, consumer-grade and sized batteries. There are thin-film lithium-ion batteries under development which have shown no degradation in capacity after 1200 charge/discharge cycles. They are predicted to have a lifespan of 40,000 cycles before capacity drops to a level necessitating replacement, which would mean over 100 years of daily full recharges.",
"There is also the original Edison battery, the nickel–iron battery. These are VERY durable, tolerant of abuse, and still hold a high capacity after thousands of charge/discharge cycles. They're not very energy dense however, and are relatively costly to produce. ",
"https://ironedison.com/shop/batteries/nickel-iron/nickel-iron-ni-fe-battery/",
"The best batteries overall that we have on the market now, readily available and at a decent price are lithium-titanate batteries. 5000 to 10,000 cycles, but at a lower voltage than standard Li-ion batteries, so a much lower energy density. They make up for it with a very much higher recharge rate though, reports are they can recharge to 100% in under 10 minutes. Mitsubishi and Honda are using these batteries in some applications, and Samsung has some niche applications (s-pen) that benefit from the fast recharge."
] |
[
"How much physical space is needed to store the data of every possible game of chess?"
] |
[
false
] |
And also what is an informed estimate of the total amount of info/data our universe holds. IE if you were to model every atom. it's location etc, store all of it as a binary number, how many orders of magnitude greater would it be than total chess game permutations (which I hear is c. 10
|
[
"Yes, well I don't think it would be possible given the total number of atoms in the observable universe.",
"The total number of chess permutations is indeed 10",
" according to the paper 1950 ",
"Programming a Computer for Playing Chess",
" and is known as the Shannon number.",
"The ",
"number of atoms in the observable universe",
" is around 10",
" to 10",
" so one can see how brute force to solve the problem of winning chess will not work.",
"And also what is an informed estimate of the total amount of info/data our universe holds.",
"I think this depends on how accurate you would want to measure the positions of the relevant particles. More accuracy results in more data, and of course given the Heisenberg uncertainty principle one cannot know both the position and momentum of a given particle with perfect precision. It would therefore be impossible to know with absolute accuracy all of the data you wanted, even in principle."
] |
[
"The reason we consider only the observable universe as the universe we can interact with is not just semantics. If you imagine your actions as being on a world line and possible interactions in a light cone, then there are certain things outside of that light cone. Given the expansion of the universe there are regions that we can have no interaction with even hypothetically because their recession velocity will be greater than c, the speed limit of the universe. ",
"While it may well be the case the universe is flat and infinite, that doesn't mean we can interact with all of the volume of it. Indeed if anything, given what I've just stated and assuming the universe is infinite, we can only interact with a tiny proportion of the total universe. "
] |
[
"endlessly produce new matter ",
"I don't know of any good evidence for this. This seems like a speculative idea not rooted in solid evidence."
] |
[
"Why doesn't frequency affect current in the photoelectric effect?"
] |
[
false
] |
[deleted]
|
[
"If electrons are discharged with greater energy, doesn't that mean they move faster and the current should be faster?",
"So I see where you are coming from. Let's talk a bit about the experiment to shed some light on this.",
"We have two plates of metal as part of an electrical circuit. When we apply a voltage one place becomes negatively charged and the other positively charged, just like a standard capacitor. On the negatively charged one we shine a light, if the frequency of the photons from this light is high enough (to exceed the work function) then we can eject electrons. Once an electron is ejected then it is free to move in the electric field that we established between the plates, i.e. it will be accelerated towards the positive plate where it rejoins the rest of the circuit.",
"What is important to remember, and indeed was the exciting result of this experiment, each photon can only eject a single electron and only if it has enough energy on it's own (i.e. two with half the energy can't join forces to eject an electron together).",
"Ok, so what are currents and voltages? Current is a measure of the amount of charge flowing per second (the number of electrons) C s",
" , voltage is the amount of energy that these electrons have J C",
" . Normally if we crank up the voltage then we cause the electrons to move faster and so our current is increased, however in our circuit we have a break, the capacitor.",
"Since the current is the number of electrons per second then to increase the current we need to shift more electrons, not give more energy to each electron. Each photon can only liberate one electron therefore the only way to get more electrons is with more photons, not with higher energy photons.",
"I don't really understand amplitude. I know that amplitude is the measure of the top or bottom half of a wave and that this is a measure of how much energy a wave carries",
"So for a regular wave yes. If you have a wave in sound then if you pump more energy in (without changing the frequency) the amplitude grows. With light each photon of the same frequency has the same energy. The way that these em oscillations work is that if you put more energy into one it doesn't make the amplitude greater it makes the speed at which they oscillate greater, a rapid change in E-field causes a rapid change in B-field which causes a rapid change in E-field etc. etc. This manifests as a higher frequency not a higher amplitude (per photon).",
"So if I have a laser that emits only photons at one frequency and I want to increase the amplitude, how do I do that? Well you send more photons. If you think of a photon as a discrete package of energy then 2 photons has twice the energy of 1.",
"In our photoelectric experiment that means if we have twice as many photons and each photon has enough energy to eject an electron then we can eject twice as many photons! So our current (electrons per second) doubles.",
"Lastly, does the charged metal eventually totally lose its charge or become positive as the light shines on it?",
"So a piece of metal just sitting there would but ours is part of a circuit, the current is the same at all parts of the circuit so when there is no light shining (and no electrons leaving the plate) then the current is 0, so the rate of change of the charge on the negative plate is 0. When you shine a light the electrons leave the plate sure, so the charge drops but they rejoin the circuit on the opposite plate and complete the circuit, current flows all the way around and replenishes the charge that was ejected from the negative plate.",
"If you had a piece of metal not part of a circuit then you could still eject electrons from it by shining a light of sufficiently high frequency onto it's surface. However, each electron that is ejected will leave the plate slightly more positively charged meaning the work function would grow (it takes more energy per electron to eject them). If you continually ejected electrons in this manner eventually the energy per photon of your light will no longer exceed the energy required to eject an electron and the process would halt.",
"In fact, now you have a slightlly positively charged object so it will attract free electrons in the air (including the ones you just ejected) and would, over time, return to neutrality."
] |
[
"is increasing amplitude pretty much the same as increasing the intensity?",
"Not really.",
"The thing is amplitude doesn't really have a nice analogue in light. Photons aren't really little wave packets, you could talk about the strength of the electric field of a photon but that isn't simply defined.",
"I personally see no reason to talk about the amplitude of a photon, especially since as you know, photons have their energy defined ",
" by their frequency and nothing to do with an amplitude. This is in contrast to a water wave or a sound wave where their energy is dictated by both the amplitude and frequency.",
"With photons you can increase the energy (by increasing the frequency) but this doesn't change the magnitude of the variation of the E-field. The real nitty gritty of this is deep down in QM.",
"The one interesting case is that of a coherent light source (a laser) where the photons are all oscillating in phase and as such behave as a single wave with energy density proportional to the square of the electric field amplitude.",
"Hope that helps a little."
] |
[
"is increasing amplitude pretty much the same as increasing the intensity?",
"Not really.",
"The thing is amplitude doesn't really have a nice analogue in light. Photons aren't really little wave packets, you could talk about the strength of the electric field of a photon but that isn't simply defined.",
"I personally see no reason to talk about the amplitude of a photon, especially since as you know, photons have their energy defined ",
" by their frequency and nothing to do with an amplitude. This is in contrast to a water wave or a sound wave where their energy is dictated by both the amplitude and frequency.",
"With photons you can increase the energy (by increasing the frequency) but this doesn't change the magnitude of the variation of the E-field. The real nitty gritty of this is deep down in QM.",
"The one interesting case is that of a coherent light source (a laser) where the photons are all oscillating in phase and as such behave as a single wave with energy density proportional to the square of the electric field amplitude.",
"Hope that helps a little."
] |
[
"If I spill my coffee onto a piece of paper, what determines the rate at which the fluid advances through the paper?"
] |
[
false
] |
[deleted]
|
[
"Sounds possible, but I suspect he would see the slowing down even with an infinite pool. In doing ",
"thin layer chromatography",
", I have noticed that the rate at which my solvent front advances up the plate slows down as it gets farther up the plate. In that case I don't have an ",
" pool of solvent, but it is large enough that the change in volume of the pool is probably negligible. "
] |
[
"To me that argues against it being a vapor pressure based phenomenon. The vapor pressure of water is pretty low, I wouldn't worry about losing it to atmosphere and if you're doing your TLC in a closed jar that should negate any vapor pressure effects."
] |
[
"Do you mean a thin strip? The amount of liquid is still constant and finite. The adhesive property of the paper is going to have to pull more and more water as the area of saturation gets larger and eventually it is going to be overpowered by the cohesiveness of the water. It isn't just pulling the water at the \"front\". It has to pull all of the water behind it, to fill the empty places in the paper. As more water is absorbed the adhesive forces between the paper have to do more work (more mass, greater distance). Since those adhesive forces are somewhat constant they are eventually going to be (or approach being) inadequate.",
"Maybe I don't understand what you are asking or what you are trying to understand. I'm not sure why you would be surprised that it would slow down."
] |
[
"Despite the diversity of life, no form has three sexes. Why exactly?"
] |
[
false
] | null |
[
"I took a class on the evolution of reproduction. We actually do see multiple sexes (mating types) in certain species like Physarium (a genus of slime mould) which has >500 sexes (but it still only takes two individuals, who are not the same sex, to make a baby).",
"The main problem that limits most species to 2 sexes is the issue of mitochondrial inheritance. Basically, when the two gametes fuse, only one of them can donate its mitochondria (if they both did, the cell would die). So, nature's solution was to create two general mating types: Male (DNA only donors) and Female (DNA and mitochondria donors).",
"In most species with multiple sexes, the mitochondria donor seems to be determined by a \"rock-paper-scissors\"-type of game."
] |
[
"Ah, I heard someone talk about this on a podcast the other day and it made alot of sense. So, while I can't say \"it's definitely because of X\", here is some food for thought.",
"With the two sexes we have, the male is gametes are very small, they basically just contribute some genomic DNA. The female gamete is very large, and has everything else.",
"What would a 3rd sex be?",
"If it were to be compatible with ",
" other gametes, then it would need to be a large cell, like the female egg, so that it could accept the male sperm. While that might work, how would two very large cells (the new sex and the traditional female sex) fuse effectively? ",
"It might work if all three sexes had an intermediate gamete size, but, as seen with sperm, there's an advantage of \"cheating\" by reducing your gamete size. So, even if there were a system with equal gamete size, any mutations that reduced the size of one gamete could provide a selective advantage. This would then push the paradigm to what we have today - multitudinous small gametes trying to fertilize a large gamete."
] |
[
"Not a biologist, but I do remember reading about this question year ago. My understanding is as follows:",
"The main reward for sex is sharing of genetic information. Species that reproduce asexually evolve much more slowly and have troubles adapting to new environments.",
"Adding a third (or fourth) sex wouldn't add a large enough benefit over two. A species might be able to adapt to a new environment a little faster, but the risks, and energy involved are too much of a hindrance. Mating can already be a complex issue in order to get two individuals to agree on the act. Adding a third vastly complicates things. The risk simply isn't a reward and if a third sex were to appear it would be quickly selected against."
] |
[
"Do Turbo Engines have more cylinder pressure than NA engines?"
] |
[
false
] |
Background: Friend says turbo engines (typically) run lower than naturally aspirated engines, and concluded turbocharged engines don't require as high of octane as an NA engine of the same compression ratio. From my experience with ECU tuning, I know that maximum Manifold Absoulute pressure is often (roughly) double in turbo engines compared to NA (NA is retricted to atmospheric pressure: 1ATM/~14.7psi/~1013mbar) Question: for compression ratio, peak MA pressure (MAP), and means of induction.* Does a turbocharged engine produce higher cylinder pressure than a naturally aspirated engine? Additional question: Assume the same scenario as above, but now compare at an equivalent MA pressure. Say both engines cylinder pressure is measured when both engines are at 1ATM (maximum MAP for NA, but typically half maximum MAP for a turbo engine) In this scenario, which engine will have a higher cylinder pressure?
|
[
"Your friend is right and then wrong.",
"Yes, turbocharged engines usually have lower static compression ratio. For example my Subaru had 8.5:1. While NA engine is typically 11 to 13. But why ?",
"To compensate for higher air pressure from turbocharger. To make more force you need more pressure that comes from explosion. By forcing more air in, you can add more fuel and generate more pressure.",
"Turbocharged engines tuned for performance need better octane fuel, because you are trying to compress air that is already compressed, meaning that temperature raises more quickly."
] |
[
"The primary reason for lower compression ratios on engines with forced induction is that the compression process (from turbocharger or supercharger) heats up the air, and even with an intercooler, the increased temperatures raise the risk of pre-ignition (or detonation, or knock). Higher octane increases the auto ignition temperature, allowing for greater pressures in the same engine without knocking. The engine static compression ratio can also be lowered to reduce how much the air will be heated by the compression stroke.",
"But this is actually not necessary. It is just an extra safety margin that is favored by people who really really don't want to take more risk than necessary. For example there is a turbocharger kit for the Porsche 11:1 CR flat 6. It is limited to 4psi, but it still provides a rather large increase in power, because you will make more power for a given boost pressure with a higher CR.",
"However... all of this is largely beside the point of your question. There is an easy way to shortcut all of the nuances of the variables when you are looking for cylinder pressures: Torque. More cylinder pressure = more torque on the crankshaft. So the way to get the answer to your question is to examine different engines with different CRs, different boost pressures, etc... And just look at what makes more torque.",
"I have had the same 1.8L engine boosted, and dynoed, at pressures from 5psi to 15psi, and with CRs of 10.5:1, 9.5:1, and 8.6:1. (and have had other non-boosted versions of the same car/engine) All on 93 octane, so that was a controlled variable. I could run more boost on track without knock with the 8.6:1, but the torque/power peaks didn't actually vary much. Naturally Aspirated doesn't change this. Cylinder pressure is directly related to torque.",
"Anecdotally, I vastly preferred lower boost and higher CR for a given power level, since the turbo reacted quicker from a higher off-boost mass going through the turbine, and when spooling it gets to it's lower peak boost much faster. The end result is that the car had much better partial and transient throttle dynamics, which made road course \"racing\" (non competitive) vastly better"
] |
[
"great response, thank you"
] |
[
"Is there any scientific evidence or reason that you gain weight by eating late?"
] |
[
false
] |
I almost exclusively eat late, ranging anywhere from 9pm to 11pm. I just need to be relaxed and have time to enjoy eating. When my kids are awake I have to be alert and take care of them,so I don't eat just a few bites with them and prepare dinner after they are asleep. People who know about of this habit tend to state that it's not healthy as you gain weight and sleep bad. Now I'm interested, is this just a myth or are there any studies or explanations supporting this?
|
[
"Directly - no. Calories are calories and whether you eat late or early doesn't seem to change much in terms of nutrients.",
"However, there has been research that suggests that people who eat late tend to ingest more calories:",
"https://pubmed.ncbi.nlm.nih.gov/25439026/",
"There is also evidence that people who eat late ingest food of lesser quality:",
"https://pubmed.ncbi.nlm.nih.gov/23036285/",
"There is also proof that late night eating is associated with poor eating habits: ",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4214609/",
"Interestingly, it seems that hormonally there is an urge created to eat more the more tired you are: ",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3763921/",
" Eating at night isn't special nutritionally, however, it is tied to behaviour that increases weight gain."
] |
[
"Interestingly, it seems that hormonally there is an urge created to eat more the more tired you are:",
"Huh, don't you get tired when you are really hungry too? I wonder if it's your body getting them confused"
] |
[
"When you're tired your body tells you to sit, eat and relax.",
"When you eat a lot your body tells you to sit, relax and digest."
] |
[
"If gravity affects time, can time affect gravity?"
] |
[
false
] |
Layman science fiction nerd here, please be gentle. I've read that in places where there's lots of gravity, time is affected (speeds up? can't remember) My question is this: In a theoretical situation where excessive time is produced, is gravity affected? If so, how, what are the parameters, does more time give more or less gravity?
|
[
"General Relativity says that time passes more slowly in a gravity well.",
"In a theoretical situation where excessive time is produced, is gravity affected?",
"Since time isn't really 'produced' by anything, there's no way for something like this to happen."
] |
[
"In a theoretical situation where excessive time is produced",
"It's hard to answer your question, as I have no idea what this means."
] |
[
"Wait, time slows down with excess gravity? As in, we age less on Earth than in empty space? I thought it was the opposite."
] |
[
"Would it be ecologically feasible to reintroduce cheetahs into the western US?"
] |
[
false
] | null |
[
"Could it be done? Yes it's quite possible if there were a proper prey item available. Should it be done? No"
] |
[
"proper prey item",
"Jackrabbits.",
"Also: The theory is that the reason ",
"pronghorns",
" are so fast is that they used to be the chief prey item for the North American Cheetah. ",
"(Pronghorns aren't real common now, but if we got real gung-ho on the cheetah re-introduction program, we'd probably want to also increase the numbers of pronghorns to provide them with prey.) "
] |
[
"Oh, I had been under the impression they were related to old world cheetahs. Thanks.",
"Also they have been extinct for only about 10,000 years actually, from what I have read."
] |
[
"What determined the earths final orbit position and how did it begin its orbit as opposed to just moving closer to the sun?"
] |
[
false
] |
I have read explanations as to the reason why we are not pulled into the sun as we are in orbit moving sideways around the sun. Many websites have used the analogy of swinging around a ball on a string as an example. What isint clear is how did the earth first enter into the correct distance that its orbit now inhabits in relation to the sun and what made it stop moving closer to the sun and start moving sideways around the sun instead? To clarify say the earth was being pulled into the sun before it reached its set distance that made up its orbit. Did another force act on the earth to begin its movement sideways and thus begin its orbit? Or was earth just always in its set orbit distance and if so what made it move sideways initially to counter the straight pull towards the sun?
|
[
"The 'correct'ness of orbiting bodies is basically self-generating. Bodies without 'correct' orbits (those that are too slow or to fast etc and so are less circular) collide with the Sun or some other body, or are flung out into deep space. After billions of years, everything thats left looks nice and planned, but its only because things that are't 'correct' got eliminated.",
"The Earth didnt really form, then shift into its orbit, rather small objects started clumping in area of the solar system, and that original clump was orbiting the sun. The clump's gravity pulled in more clumps, and more clumps, all the time orbiting the Sun: The earth formed in an orbit. If at any time the clumps orbit was 'incorrect' the clumps orbit would have changed, either still being 'correct' for the new, bigger clump, or colliding with the Sun or proto-Mars etc."
] |
[
"Do you mean Earth's ",
" orbit? Because simulations show that the planets are not in stable orbits, long term, and wander in and out quite a bit. The Earth will still be wandering when the sun swells to red giant state and either evaporates it all away or slows it down by friction and swallows it completely."
] |
[
"The reason the earth did not initially fall straight into the sun is conversation of angular momentum - things that are spinning need to keep spinning (unless acted on by an outside torque). In this case the \"spin\" in question is the tangential velocity of the earth relative to the sun.",
"With slightly more math: Angular momentum is given by mass multiplied by tangential velocity multiplied by radius from the center: L = (m) x (Vt) x (r)",
"As the forming earth gets closer to the sun, the radius between them decreases. Because angular momentum stays the same, its tangential velocity ",
" increase. This is the same thing you see happening with figure skaters that are spinning and pull their arms in: they spin faster. The increased tangential velocity creates a centripetal force that pushes the earth back out, making it miss the sun.",
"So basically, as long as there is some angular momentum in the big blob of matter that becomes the solar system (and there was), then not all planets and asteroids are going to fall straight in. (A few unlucky ones with very low angular momentum will fall in, but we don't know about them... cause they fell in.)",
"As others have pointed out, once things are orbiting getting the 'final' orbits is incredibly hard - tons of interactions and collisions and semi stable orbits. But angular momentum has to be conserved, so it all keeps spinning about the sun.",
"Also: that second article, the one from medium, is ",
". Its hard to know when looking at a new subject so I really don't blame you, but pretty much nothing in it is true."
] |
[
"Why is proving Riemann so important?"
] |
[
false
] |
According to "The Math Book," (by Clifford a Pickover) proving the Riemann Hypothesis is the most important open question in mathematics. Say a mathematician did it tomorrow...what would the implications be? What use would come from it and how would we seeit manifested in quantum theory, or in our day-to-day lives?
|
[
"Here",
" is a list of some important consequences of the Riemann hypothesis. As you can see, they are mostly mathematical in nature. You would not see it immediately manifest in your day to day lives, as is the case with just about any mathematical research being done nowadays. I'm also not aware of any implications in Quantum mechanics. I'm not sure why you are asking about that specifically.",
"The importance of RH is more related to the fact that it"
] |
[
"A practical thing that might effect the everyday world would be credit card security which uses primes to create a very difficult security systems. It's difficult because primes are still very mysterious to us and how it is distributed. The Riemann hypothesis, from what I understand is that it suggests that all primes are equally distributed which helps find a structure in the primes."
] |
[
"I'm also not aware of any implications in Quantum mechanics.",
"http://en.wikipedia.org/wiki/Hilbert%E2%80%93P%C3%B3lya_conjecture#Possible_connection_with_quantum_mechanics",
"Searching for Riemann hypothesis and quantum mechanics turns up multiple papers."
] |
[
"In 4 - vector space-time geometry, why is the time component negative?"
] |
[
false
] | null |
[
"For background on the OP's question, see ",
"this",
" post from earlier today. The question is: in spacetime, vectors have four components (one for time and three for space). The length of a 4-vector (the technical name for these) with components (t, x, y, z) is defined as",
"length",
" = -c",
" t",
" + x",
" + y",
" + z",
"If you ignore the time term, this is just the Pythagorean theorem. But why does the time term have a minus sign?",
"In effect, this is just a definition, but it's a very useful one. This length equation defines a 4-D geometry which we call spacetime. In that spacetime you can talk about rotations through the four dimensions, and it turns out that if you do such a 4-D rotation to the coordinate system you put on the Universe, you get out a new coordinate system which is equivalent to the coordinate system that someone else, moving relative to you, would use.",
"In high-school physics, we require that the laws of physics don't care how you rotate the spatial coordinates. You can look at the Universe upside down if you want to, but the laws of physics you measure are still the same. F is still equal to ma and so on. If we demand the same thing for space",
" rotations, it turns out that the funny effects of special relativity - time dilation, length contraction, the constancy of the speed of light, E=mc",
", etc. - all drop out of that naturally. So this minus-sign convention accounts for all of special relativity.",
"It also has the nice feature of separating out the \"causal structure\" of spacetime. Take the 4-vector describing your velocity. The spatial components are your spatial velocity, and the time component denotes how the time on your watch compares to the time coordinate you're using (it's another word for measuring time dilation). Now take the length-squared of that velocity 4-vector, using this minus-sign convention. It turns out that massive particles (travelling below the speed of light) always have a negative length-squared, massless particles (travelling at the speed of light) have zero length to their 4-velocity, and the velocity between two points in space at the same time (or, alternatively, the velocity of an unphysical particle travelling faster than light) has positive length-squared. If your length-squared is positive, you're violating cause-and-effect, since (in some coordinate systems) you're moving instantaneously or even backwards in time."
] |
[
"One way to look at it: ",
"Space is \"circular.\" If you want to draw a line connecting all the points that are equidistant from one center point... you draw a circle. (or sphere in 3-D)",
"Space-Time, on the other hand, is \"hyperbolic.\" To draw all the points equidistant from one \"event\" (a location in space at some specific time (as measured by one particular observer)), you draw a hyperbola.",
"In space, no matter how you rotate a circle, it remains a circle. In Space-time, your rotation is called a \"lorentz boost\" It is, mathematically, very much like a rotation, but for hyperbolic spaces. What is interesting is that as you boost from one observer to another, the hyperbola you've drawn remains the same \"shape.\" Just like the circle in plain space.",
"This is starting from the mathematical definition of space-time and working backwards. The more conventional way would be to start with the rules of relativity. Start with some origin, and plot the point x=0, t=1. And then transform that to some other moving observer, and plot that point. And keep transforming it to every observer... and you'll see that it traces out a hyperbola. This tells you that the fundamental geometry is hyperbolic, not circular. "
] |
[
"If (ct)",
" is greater than x",
"+y",
"+z",
" your length takes on a complex value; I assume this would be the case for a particle moving faster than c. He's asking how one should interpret the imaginary part of that complex length.",
"And if I've misinterpreted and that ",
" what he meant, then I would still like an answer if you have one."
] |
[
"If visible photons are absorbed by atoms and then re-emmited at the same wavelength, why can light not pass through dense matter?"
] |
[
false
] |
For example, if you shine a light on a concrete block which appears grey, why don't photons travel through the block by this re-emmission of absorbed photons?
|
[
"Light traveling through materials scatters. This includes air, water, glass and opaque materials. When it scatters, it is not necessarily re-emitted at the same wave length, or in the same direction. The particle that absorbed the photon may de-excite by emitting two photons with lower energies than the original. In this way, visible light is absorbed and re-emitted as heat. Alternatively, the the light may undergo a reflective scattering, where the photon is re-emitted roughly back towards the source.",
"With transparent materials, due to the structure of the material, light has a low probability of undergoing such interactions. In opaque materials, the probability is higher. Opaque materials that are thin enough, or not ",
" opaque as other materials sometimes show a glow when sufficiently bright light is shone on the opposite side - this is an indicator that light is getting through (transmission), but that there is some interference in the path of the light."
] |
[
"Light can pass through dense matter. It's just a matter of how likely it is for each photon to get through unscattered and unabsorbed. As a photon passes through just about anything besides vacuum, there is a finite chance that it will be scattered (direction changed) and/or absorbed. The thicker the material, the longer the \"gauntlet\" it has to pass through before it makes it out the other side, but the effects are typically exponential with thickness and strongly dependent on wavelength and material. If you were to polish your piece of concrete down to a thin enough layer, then some light would get through it. This is true even of metals (which transmit visible light very poorly). In our lab, it is commonplace to use glass with various thicknesses of metal deposited on them to control the power of a laser beam. We call them neutral density filters.",
"If you are interested in these, check out this page: ",
"http://thorlabs.com/navigation.cfm?Guide_ID=21",
" . These are some of the many tools we use to get stuff done.",
"Thorlabs is like the Wal-Mart of optics, but what they make is good enough most of the time."
] |
[
"Adding a bit more to this to more fully answer the quesiton:",
"When light is absorbed by a substance, only light of specific wavelengths is absorbed and only light of specific wavelengths is reemitted. The rest is scattered. For a block of concrete, visible light is scattered rather than absorbed while infrared light may be absorbed and reemitted. The wavelengths of light that are capable of being absorbed and reemitted has to do with how much energy is required to bump an electron in the material up one energy level (orbital). The wavelengths that are reemitted are dependent on the amount of energy preferentially released when an electron drops from an excited state into a lower excited state or its ground state."
] |
[
"Obviously, there are solids that float in liquids. Are there liquids that float in gases (specifically air)? Solids in air?"
] |
[
false
] | null |
[
"In a practical sense, I'm not aware of any liquids light enough or gases heavy enough to allow this to happen. If you take one of the densest gases, radon, its density is something on the order of 10 g/L, and if you take a very light liquid, say an alcohol, they have densities on the order of ",
" g/L. This is all at STP, obviously. Gases are compressible, so you could probably fiddle with pressure to get the densities higher, but we're talking about heavy gases being orders of magnitude less dense than light liquids, so I doubt it's possible."
] |
[
"When densities of these solids are given it is as if they are in a vacuum. Aerogels are extremely porous, which gives them their low density. In a radon atmosphere the pores would fill with radon gas and as radon gas + aerogel is heavier than radon gas alone the aerogel would sink.",
"I am a material chemist have handled aerogels in air - they are very light but they don't float!"
] |
[
"That boat only works because there is air inside it. If that video is an example of a \"solid floating in gas\", then so is a hot air balloon."
] |
[
"Why are things that aren't fission products themselves, become \"radioactive\" and are dangerous? (IE Clothes, metal, etc)"
] |
[
false
] | null |
[
"They are contaminated. If you’re in an environment where there’s radioactivity dissolved in the water, in the dirt, in the form of dust in the air, etc., you will carry that contamination with you."
] |
[
"Well what makes them contaminated? Fission makes things radioactive, the things contaminated have simply just been around it and effected by it. What makes it continue to resonate radioactivity?"
] |
[
"They have collected radioactive dirt, water, and dust, in and on their bodies and clothes, and inadvertently carried it with them."
] |
[
"Why do human males have external penises, rather than penises that only come out for copulation?"
] |
[
false
] |
It seems that for most animals, penises only emerge during sexual arousal. Why are humans different? Is it a feature we share with other primates?
|
[
"Yes, it is a feature we share with other primates in a sense. The reason for it is likely both physiological and social. ",
"Primates have an amazing diversity when it comes to penile morphology. There have been entire books written on it. Most have a penile spine called a baculum that assists copulation. This is important as it helps speed the process up when sex needs to be quick and it also assists in removing sperm. Some primates do not have baculums. We are one of those. ",
"Human penises are interesting first because of their shape. It is theorized that the mushroom shape at the end of the penis acts in a way that would remove a competitors sperm from the vaginal tract. If you were to examine the penis of a bonobo or chimpanzee you would see that it is quite long and is used for a similar purpose. Females will often copulate with several males to confuse paternity in some situations and this is an effective strategy to ensure your babies get produced. ",
"Many primates penises' are relatively outside the body, but ours is much more so due to its incredible length. Comparatively speaking our penises are huge. Yet, we have tiny testicles. If you examine a chimpanzee or bonobo you will see they have HUGE testicles. This is because they compete more for access to mates. If you look at a gorilla you will see they have itty bitty testicles. This is because they compete less for mates as silverback males control a harem of females and depending upon the species also their non-silverback offspring. ",
"So when we began walking on two legs an interesting problem began to arise. Typical signals for female receptivity were gone. When many primates are in estrus (particularly chimps and bonobos) you know. Everyone knows. It's quite...obvious. So when we began to walk we switched to a method of concealed ovulation (hidden estrus). Females could no longer show when they were receptive and so our social system had to change. Now we could talk all day about how this happened, why and what not but I won't because it is lengthy. ",
"I will get to the point in saying that when we became bi-pedal we had to find other mechanisms for reproduction. It is likely that our penises became longer and lost their spines to be able to adapt to female vaginas and mating pressures (such as other males or lack thereof). Our large obvious penises may have even been a sign for female choice. Females choose mates based upon different factors for some like orangutans it is about their cheekpads and long calls. For others it is purely sexual. In spider monkeys for example, during a particular season their testicles swell and females will often choose the male with the biggest testicles. Some squirrel monkeys pelage will become more colorful during times of female receptivity. In all of the above cases the males who are chosen typically exhibit the highest quality genes and produce the healthiest offspring. This choice then is important in maintaining populations. ",
"So overall it is quite a complex question and a complex answer, but quite interesting. "
] |
[
"Questions like this are incredibly difficult to answer experimentally, so most potential explanations will rely on post-hoc rationalization - in other words, trying to fit the data into your explanation rather than the other way around.",
"I can think of a number of potential explanations, but these would merely be hypotheses and I can't think of a method to go about proving them. You could perhaps do a comparative study looking at other mammals with external penises and look at mating habits, etc, but the explanation could also be something social, or related to posture, etc. ",
"Sorry for the non-answer. I'm not an expert on animal physiology and a quick search of the literature didn't return any promising leads, but as no one else responded, I thought that at least I'd give you this much."
] |
[
"Here's a little gallery of primate penises I just found for some morphology comparison.",
"Chimpanzee",
" | ",
"Bonobo",
"\n| ",
"Orangutan",
" \n| ",
"Proboscis monkey",
"\n| ",
"Vervet monkey",
"\n| ",
"unknown species",
"\n| ",
"unknown species",
"\n| ",
"unknown species, surly expression",
"It's really weird that they all appear to resemble a circumcised human penis more than an intact human penis, isn't it? I wonder why so many people say human male foreskin is a \"vestige from primates\" like it's a tail or something, when apparently most species of primates have extremely short foreskin that looks more like the human penis ",
" circumcision.",
"* Are there any scientists here who would like weigh in on the popular misconception of foreskin as vestigial? I have never heard a primatologist mention foreskin before.",
"Dixon never touched the issue, did he?"
] |
[
"When they say the most common cause of death among children is accidents, do they mean car accidents only or any unintentional action that causes death (chocking by food or sh) ?"
] |
[
false
] | null |
[
"Who is “they”? Unless you present a source no one can answer accurately."
] |
[
"Oh sorry for that, i was reading on amboss a resource for medical students about leading cause of deatg in children aged from 1-18, and they say that leading cause of death is accidents and don't elaborate which ones."
] |
[
"In the US it’s firearms as of the last 2 years, so you need to give details on the source"
] |
[
"What makes spinal cord tissue different than other tissue than can repair itself when damaged?"
] |
[
false
] | null |
[
"I'm not entirely sure what the context of your question here is, but I will assume you are asking why spinal injuries can cause permenant damage and disability.",
"The answer is that nerves do not repair. The nerves you have when born are largely going to be the same nerves you have when you die. This is for several reasons but a large one is that the neurons that make up these nerves are VERY long by cell standards. It's impractical for new neurons to establish themselves to replace old ones. Spinal cord damage that severs neurons therefore can't really be healed."
] |
[
"The central nervous system is composed of both the brain and spinal cord and contains cells called \"neurons\" that are used to transmit the electrical information we perceive as thoughts and senses. These neurons transmit information via the use of long extensions of the cell body called axons that are frequently coated with an insulating myelin sheath (white matter). These cells typically form networks throughout childhood and infancy and the production of new neurons dramatically ceases around the time of birth. Recent evidence has shown that there is some ability in the adult brain to produce new neurons (cognitive stimulation methods as well as some antidepressents), however for the most part regrowth does not occur.",
"The growing of these cells occurs at a short yet critical time and does not continue throughout adult life. Neurons do not experience cell death in the same way that other cells within the body do due to the extremely complex nature of the pathways they form, coupled with reasons I listed above including: interference from ogliodendrocytes, rapid formation of scartissue, and lack of growth factors in the ECM. "
] |
[
"That and also the fact that the spinal cord is like a mega cable, made up of thousands and thousands of smaller cables, for a full recovery every severed cable needs to find its second (severed) part, and this is usually impossible, although theoretically possible, the factors are listed above. Extra fact the neurons grow for about 1 mm per day, so some sort( minimal) recovery is possible "
] |
[
"Why do sneezes often come in pairs?"
] |
[
false
] | null |
[
"I've asked many different boards so far and this is the first time anyone's even responded. I guess I'm making progress!"
] |
[
"Sorry that your best response is essentially: insufficient data. I'd be quite surprised if anyone's come across a truly explanatory theory as to why this is the case. First I'd say that I personally experience the classic double-sneeze, however, I've encountered many people that get any number of sneezes each bout that seem to cluster in groups from 2–6. My best guess would be that the responsible neuronal circuit triggered remains sensitive (that is, remains excitable after the initial refractory period) after a sneeze. The duration (measured in number of firings/cycles) this sensitivity lasts is probably dependent on the individual (with 2 sneezes being most typical). The why? No idea. Maybe 2 sneezes afforded the sneezor a higher survival benefit than the singly sneezor over the course of mammalian history."
] |
[
"I call bullshit on anyone who even attempts this one."
] |
[
"Could FTL neutrinos be used for extraterrestrial communication?"
] |
[
false
] |
[deleted]
|
[
"So I'm not a particle physicist, but I do know that neutrinos are so small they rarely interact with larger matter like atoms. A hundred billion neutrinos are streaming through every square centimeter of the Earth every second, only one of which will interact with something (",
"source",
"), but it takes a huge liquid filled room and special cameras to be able to detect them on the rare event they do interact.",
"Considering how much energy would be needed to get them to cross the threshold (assuming this is possible), it would be remarkably inefficient, as the receiving party would have such trouble even detecting them. It would be like flinging scrabble letters at each other in a dark room."
] |
[
"Even accepting assumptions 1 & 2, there may be some issue with 3&4. ",
"In the paper about the Opera experiment (",
"http://arxiv.org/abs/1109.4897",
"), they looked into energy effects on neutrino speed a little, analysing both the entire event history, as well as sub-dividing it into \"low\" and \"high\" energy regions (end of section 8). This gave measures for distributions with mean energies of 13.8, 28.2 and 40.7 GeV. There was a ",
" variation with energy in these results - neutrinos arrived 54.7 ns early for the lowest energy, compared to 68.1 ns early for the highest energy. However, this variation is swamped by the statistical noise (on the order of +-20 ns), so it's not a significant result, suggesting the neutrino speed is close to energy-independent, at least in the tens of GeV energy region.",
"It's important to note that the above time difference is the difference in speed ",
" for these neutrinos. If you express it in terms of a fractional change in speed, the particle's speed has increased by fraction of 6*10",
" when the energy has tripled.",
"Even if you accept assumption 3&4, this gives rather silly results if you try to apply things like a linear or exponential curve to it. If we assume the low- and high-energy time delays are indeed correct and fit simple functions to them, it suggests energies of more than 1 Joule per particle are needed to reach 2c if you assume a linear extrapolation and ignore the non-zero velocity at 0 eV. If you assume it's exponential it's even worse - something like 10",
" eV to reach just 2c (not a typo, ten to the power of 27 thousand. Like I said, silly results).",
"And then, as others have said, the cross-section for these events are ",
". SN1987A produced 10",
" neutrinos in a burst which led to ~20 events detected on earth. That was at a distance of 168k light years, but seeing the same number of events at a distance of, say, one light year would require ~3*10",
" neutrinos, assuming a uniform emission. Even if you could get this down to, say, a micro-radian beam (better than most/all modern lasers), you still need on the order of 10",
" neutrinos to see non-trivial numbers of events at one light year. ",
"So, even with the optimistic 1 J estimation for a neutrino going at 2c, that's 10",
" joules of energy dumped into the neutrinos to get a couple of bits (optimistically) 1 light year in 6 months. For comparison, this is one hundred trillion times more energy than the sun outputs each second.",
"So... yeah. It doesn't look good for this method for sending messages, even with the most generous assumptions about the Opera results."
] |
[
"I am a particle physicist, and I approve this message.",
"Actually, the OPERA experiment gives you an idea about what you would need to do in order to transmit a message, based on our current understanding of neutrinos. A neutrino beam from CERN is being shot at the OPERA detector in Italy with a certain timing structure so that other sources of neutrinos can be cut out.",
"Eventually, (and this is how they measured the speed of light) it's possible to see that timing structure. You could send messages by changing the structure of the beam. However, you would either need an extremely large detector so that it could be read out in one shot, or you would have to send the same message many times.",
"The main issues would probably be aiming the beam and addressing beam dispersion."
] |
[
"Does scratching at irritations like bug bites harm or delay the healing process at all?"
] |
[
false
] | null |
[
"It will cause more histamine release and more immune cells to infiltrate the area, causing more irritation. Theoretically it might have the potential to fight against certain microbes, but in terms of healing, it would not help. ",
"First of all, the scratching causes more damage to the area. Then the immune cells release substrates that can damage the tissue matrix which is not good for healing. "
] |
[
"It's important to keep in mind that not everything has an evolutionary advantage simply because it is a trait that evolved. "
] |
[
"Why then have we developed such an intense, hard-to-resist itch response? Animals often will scratch themselves to the point of skin loss and infection, which seems like a very bad trait for survival.",
"I can understand a slight itch response to dislodge an insect or object, but beyond that, what benefit does an ongoing, intense itch response have?"
] |
[
"Is there anything “special” about the visible spectrum?"
] |
[
false
] |
Our eyes perceive light in the visible spectrum, which is just one small part of the full electromagnetic spectrum. We can differentiate hundreds of colors out of this relatively narrow spectrum of light. My question is, is there anything special about the part of the EM spectrum that our eyes can see that allow us to distinguish red from blue from yellow? If we instead had evolved to “see” in what we consider the UV or microwave regimes, would an eye be able to perceive different colors? In other words, is the visible spectrum the only spectrum where we could have so much differentiation in color?
|
[
"Hi, I'm a astrophysicist.",
"There's absolutely nothing special about visible light in principle. Our sun emits light ",
"fairly predictably across IR, visible, and UV",
" (although it also emits in other wavelengths). We can only see a tiny fraction of that spectrum",
"citation needed]).",
"However, our eyes evolved underwater",
", and of those wavelengths, ",
"visible",
" passes through water best. Thus, it would be the wavelength that underwater organisms could see the most with.",
"Some other organisms can see UV (bees) and sense IR (certain snakes, though not with their eyes). But we actually already know of people who could see UV",
", and you don't really see a new color. It's just blue. But it does look more intensely blue, purple and white. (though, again, UV itself is just blue)",
"If we could see more UV, the world would look different because flowers and some other objects have UV patterns to attract pollinators in a form of coevolution. But most of our buildings would look sort of similar.",
"As for IR, that's how night vision glasses see, just in false color. You'd be able to see how how an object was in different spots, and windows could become opaque (though a similar problem would occur with UV). There's not a wildly large number of things see here on earth in IR other than temperature, but space would look very different.",
"As a final note, here's some neat demonstrations of the ",
"galaxy",
", ",
"earth and space scenes",
", and ",
"sun",
" in different wavelengths. Obviously, they're all false-color, but it's a start towards answering your question.",
" eyes evolved relatively early, technically before fish",
" anyone who's had one or both lenses removed from their eyes can see down to 300nm"
] |
[
"The differentiation between colors is also an artifact of our biology. We have three types of cones that are sensitive to red, green, and blue respectively (roughly, they all have an absorption spectrum). A human that sees UV light is just seeing blue because that's the only cone that gets any signal. If we had more cones in different parts of the electromagnetic spectrum, we would identify distinct colors for all of the corresponding wavelengths."
] |
[
"Geosciences here. To go along with this, the Earth’s atmosphere has what we call atmospheric windows, which are wavelengths of the EMS that can pass through. The visible spectrum passes through at a high rate while much of the spectrum does not."
] |
[
"Can you identify which forest ash came from by analyzing the ash?"
] |
[
false
] |
With the California Bay Area currently being covered in ash from wildfires across the state, I am wondering if you could analyze the ash that is falling on the ground here and determine which forest it came from. If not, what, if any, information could you determine? Thank you!
|
[
"Generally I would say no.",
"In specific cases yes. For example, if the soil in a particular forest is enriched in, say, the elements selenium and vanadium, you might be able to assert that this particular ash sample possibly came from that forest. ",
"In a court of law, IMO, a SME for the other side would shred that assertion.",
"What you can do is build a profile of trace elements from various sources (forest ash samples) and say that you particular sample matched some profile, but IMO it’s still pretty iffy, unless there’s some really uncommon elements present."
] |
[
"I could see if different trees put out different compositions of ash you might be able to say what sort of tree it came from, and that might help you differentiate the source. A coworker did a project where they put wood smoke through a mass spec and demonstrated they could figure out what species it was from, so maybe you can do the same thing with ash?"
] |
[
"That’s a surprising finding! Thanks..."
] |
[
"Why does alcohol interact with so many other drugs?"
] |
[
false
] |
A lot of drugs carry a warning to not mix with alcohol. Is it just because it's legal and widely used or is there a chemical explanation?
|
[
"Oh wow, lots of misinformation in this thread. Yes, alcohol has CNS effects. Yes, it affects other organ systems. But ",
". The source of its interaction is its metabolic pathway.",
"Alcohol is oxidized in the liver, primarily by the enzyme Alcohol Dehydrogenase. However it is also oxidized by the cytochrome P450 enzyme CYP2E1. Alcohol consumption upregulates CYP2E1. This enzyme also metabolizes lots of drugs, including many anesthetics. So if you drink while on these drugs, the drugs are metabolized more quickly.",
"Metabolizing drugs more quickly does three things. Firstly, and most obviously, it means that the drug is consumed and therefore less effective. Secondly, it means the the drug's metabolic by-products build up more quickly. This effect can be very dangerous, and is the source of most Tylenol (paracetamol) toxicity. Thirdly, some drugs are given in an inactive form, and their metabolization by CYP2E1 ",
" them. In this case, alcohol will quickly (and sometimes catastrophically) increase the amount of active drug in your body."
] |
[
"and humans have used it for so long, our bodies have numerous adaptations to its consumption",
"Really? So does this mean I have a higher alcohol tolerance than someone from several hundred (thousand?) years ago, despite never having had a drink? Or that mean we now just metabolize it faster and don't stay drunk for as long? Or am I just totally misinterpreting this line? "
] |
[
"and humans have used it for so long, our bodies have numerous adaptations to its consumption",
"Really? So does this mean I have a higher alcohol tolerance than someone from several hundred (thousand?) years ago, despite never having had a drink? Or that mean we now just metabolize it faster and don't stay drunk for as long? Or am I just totally misinterpreting this line? "
] |
[
"How does a plant seed know which way is \"up\"?"
] |
[
false
] |
I guess since they are buried deep in the ground with no sunlight or without any other way of knowing which way it should grow to get the surface.
|
[
"I believe seeds have the ability to detect the directing of gravity (gravitropism), but they can also detect temperature gradients and hence direction to the surface."
] |
[
"A bunch of other commenters have mentioned that plants can sense gravity, but nobody's explained how! The answer is that they have starchy components (amyloplasts) in some of their cells that are heavier than the cytoplasm, making them sediment at the bottom of the cell. A hormonal growth signal then emanates in the direction of the part of the cell where the amyloplasts accumulate (i.e. down).",
"You can see this for yourself by tipping over a fast-growing potted plant. The side of the stem facing down will grow faster, causing the shoot to gradually bend upright again. Plants use the same mechanism - uneven distribution of growth hormones in response to sensory input - when they grow toward light, etc.",
"Animals can sense gravity, too - it's what we usually call our sense of balance, and of course it really responds to acceleration of any kind. Some animals have balance organs ",
"with a similar mechanism",
" to the granules in plant cells; others (like humans) have balance organs with ",
"accelerating fluids",
" that push little sensory hairs around."
] |
[
"If I were a smartass, I'd talk about how the vacuum of space does no one favours.",
"More seriously, yes! We have been experimenting with plant growth in space in both shuttles and on the ISS since the 80s. Root formation is described as 'disorderly' or 'random', because they have no \"down\" to aim for.",
"The shoots grow towards light, as they normally do."
] |
[
"Why do we need a Higgs boson to impart mass to particles?"
] |
[
false
] |
Isn't mass just energy? Or does energy not interact with gravitational fields in the right way? How then could a Higgs particle have a ridiculous energy of 250 GeV (one possibility that hasn't yet been ruled out) if it gives itself mass?
|
[
"So there are these things called ",
" What they are and now they work aren't important right now; just know that they're a thing.",
"Four elementary bosons have been conclusively identified. There's the photon, which is the boson of the electromagnetic field. Then there are the W and Z bosons, which are related to radioactivity. And finally there's the gluon about which we don't care right now.",
"The photon and the W and Z bosons are close cousins. They're actually part of the same underlying … well, ",
" since going into more detail than that is more than we want to get into right now. Just consider the photon and the W and Z bosons to be the fruit of the same electroweak tree.",
"Except the photon is ",
" while the W and Z bosons aren't. This is a mystery. Photons and W and Z bosons are very closely related, so there has to be some ",
" why the weak bosons have mass while the photon doesn't.",
"The Higgs mechanism is what gives the W and Z bosons mass. All of space is filled with a scalar field, called the Higgs field. The W and Z fields are coupled to the Higgs field; the electromagnetic field isn't. So the weak bosons have this property we call \"mass\" — which is distinct from all the ",
" things we also call \"mass\" — while the photon doesn't.",
"The only way to detect the Higgs field experimentally is by looking for its excited state, which is what the Higgs boson is."
] |
[
"I forgot about photons, and that by mass one might mean the m2 = E2 - p2 variety (in c = 1 units because that's how I learned it).",
"What? No. That's completely wrong. Photons are ",
" and mass is independent of momentum.",
"So the Higgs boson is basically a necessity of QFT",
"No, it's part of the Standard Model.",
"What happens if we don't find it?",
"We keep looking. Nobody seriously believes that the Higgs mechanism doesn't exist. It fits the data too well. The question isn't whether there is a Higgs mechanism, but rather what the details of that mechanism are. That's what we seek to pin down empirically.",
"I read today that we haven't found it in the middle of the predicted energy range.",
"We also haven't ",
" for any meaningful definition of the phrase. Imagine you have a theory — mathematically sound and consistent to the limit of your ability to examine it on paper — that when lightning strikes a golf ball it turns the golf ball into delicious candy. So you go out to a golf course on a stormy night, drop a golf ball in the middle of a green and wait. Are you going to declare your theory a failure if lightning fails to strike the golf ball? Of course not! Because your theory says nothing about the likelihood of lightning striking a golf ball; it ",
" what the ",
" of lightning striking a golf ball would be. You can't say the theory's been tested experimentally unless you do, in fact, get lightning to strike a golf ball.",
"And now imagine your theory doesn't say lightning turns golf balls into delicious candy … but rather that when lightning strikes a golf ball, ",
" that it will turn the golf ball into delicious candy. Will you declare your theory a failure if you don't get candy on your first try? What about your first ten tries? Your first hundred?",
"For all intents and purposes, we can say with total truthfulness that we have no yet ever looked for the Higgs boson. The amount of data that's been collected is so small compared to the amount of data we'll need before we can draw any conclusions at all that it essentially rounds down to zero.",
"but is the Higgs boson predicted by one of those SU(whatever) models",
"Yes. The Higgs field is a complex spinor under SU(2). Below a critical energy, spontaneous symmetry breaking causes three of the four components of the field to couple with the W",
" and W",
" and Z bosons, and the fourth component gives rise to the Higgs boson."
] |
[
"It's bad science reporting. It's like the kid who sulks because he's looked everywhere for his toy, even though he really spent three seconds glancing around his room before having a pout."
] |
[
"How can light sails exist if \"light\" has a nonzero mass?"
] |
[
false
] | null |
[
"This is an ",
"FAQ"
] |
[
"Not necessarily, I'm specifically wondering if there is a proof that the mass is 100% zero as opposed to as absurdly close to zero as possible.",
"I realize this question basically questions the whole basis of the current energy without mass formula. ",
"My only current proof that the mass is not one katrillionth of an atom of mass is that even at that mass, it would take a large amount of energy to generate photons with a light bulb that travel at the speed of light, and photons would theoretically lose speed over time if they had any surface area."
] |
[
"Oh I misread the question, I read it as \"how can light sails exist if light has no mass?\".",
"Why would light having mass mean a light sail couldn't exist?",
"People have done experiments looking for a photon mass. You can only ever put an upper bound on the photon mass but it is currently something like 10",
" atomic mass units."
] |
[
"Electromagnetic radiation; can electronics actually give you cancer or headaches, or render you impotent, as some people claim?"
] |
[
false
] |
As an engineer, I find it frustrating that some people genuinely believe that household electronics can do collateral harm. "Bad waves" from televisions can give you cancer, a cellphone in your pocket can make you infertile. But then again, I can't seem to find solid proof that they are indeed, completely safe. Is there still a lot of uncertainty on the effects of EMI on human health? Are there any conclusive research papers on this subject?
|
[
"I tried digging around. The answer appears to either be no, inconclusive or conflicting. Now I'm confused, too!",
"Here's one short paper from ",
"John Hopkins University on cell phones",
" (pdf file)",
"WHO says ",
"EM fields possibly carcinogenic",
". Says inadequate to draw conclusion.",
"Here's one on ",
"non-specific symptoms and tinnitus",
". No risk.",
"Here's one on ",
"extremely low frequency EM fields and leukaemia in childeren",
". No risk.",
"Children and phones",
". No risk.",
"EM study of ELF EM in adults",
". May be a risk of meningioma especially around power lines.",
"Interesting paper on ",
"DNA being a fractal antenna!",
". ",
"Electric and magnetic fields at power frequencies.",
". possible carcinogenic at high levels",
"Childhood cancer and magnetic fields from high-voltage power lines in England and Wales: a case-control study.",
". Not statistically significantly "
] |
[
"Let's do some theory to tackle the idea. ",
"Electromagnetic waves are photons. The only way photons could interact with your body are either exciting the electronic state of a bond in your biochemical makeup (like UV tanning --> skin cancer), or by triggering some resonant frequency in your molecules/cells (like a microwave). ",
"Now, cell phone waves are very low energy - they have to be in order to pass through solids (or else solids would absorb them). Electronic excitation in the bonds in your bodily molecules tend to require energies from something like a UV photon or higher. The energy difference between ",
"radio waves",
" and ",
"UV rays",
" is 6 orders of magnitude (Factor of 1 million). So, it is ",
" unlikely that the cell phone radiation waves could trigger this form of cellular damage. ",
"The second type is resonant frequency disruption. What this is is how a fairly low-intensity, low-frequency wave can slowly excite something into a high-frequency, high-energy form. For example, when you're pushing someone on a swing set, you're pushing lightly, but at a frequency that is, after a while, enough to make large amplitude swings. ",
" The FCC has investigated radio frequencies that might be resonant on biological species and has banned dangerous frequencies. You can ",
"read more about it here",
" and ",
"here",
" Theoretical physics says no, EM waves are unlikely to harm you. "
] |
[
"I don't think microwaves use a resonance phenomenon for heating. How I have always understood it is that the water molecules, a dielectric, aligns (rotates) to the electric field in the micowave oven. This dipole rotation has a region between where subjected electric field oscillations are \"oscillating slow, with enough time to align fully\" and \"oscillating too fast for the molecules to noticably be affected\"; between this region it is various amounts of \"oscillating just enough to impart enegy info the dielectric material\""
] |
[
"Is the ionic radius of Cu2+ bigger than Cu as an atom? If so then why?"
] |
[
false
] |
I could not find any help on the internet. Any help would be very much appreciated :)
|
[
"No, Cu2+ has fewer electrons than Cu. Whenever electrons are removed from an atom its radius gets smaller. This happens because electrons push against each other so as electrons are removed the outer ones can move closer. If you want to think about orbitals, Cu has an electron in the 4s1 orbital and Cu2+ does not."
] |
[
"thanks a lot. I guess there was an error in my school exam ;)"
] |
[
"Cu2+ as an ionic radius of 0.73 angstrom, Cu has an atomic radius of 1.3 angstrom.",
"Cu has more electrons orbiting it, in order to relieve high energy electron interaction effects the electrons orbiting Cu expand the orbital, increasing the atomic radius.",
"Cu2+ has less electrons orbiting it, less electron repulsion effects, electrons may sit closer to the nuclei as a result. In addition, Cu2+ is more positive than Cu, and this positive charge attracts negative electrons, causing electrons to sit even tighter to the nuclei, once again, decreasing the ionic radius."
] |
[
"Is time infinitely divisible, or is there a minimum quantum value for time?"
] |
[
false
] |
I suppose the same question can apply to space. Matter and energy have minimum quantum values, and matter/energy warp spacetime around them, so it would seem natural to assume that spacetime would also have some kind of minimum divisible amount, but at the same time that would seem to suggest that existence is digital rather than analog, and that seems like the sort of thing we'd have heard about if it were true...
|
[
"Energy does not have a minimum quantum value. When you measure the energy of a particular quantum system, the energy that you measure can only be particular values. These values are different for different systems, and there is no universal energy 'quanta' which all energy eigenvalues are multiples of.",
"The same is true of time. There are no discrete divisions of time in the universe. At least, we have no reason to believe that there are."
] |
[
"FYI, it's very straightforward to define and use smaller intervals of time than the Planck time -- just divide it by any number! Super easy. :) The Planck time isn't necessarily \"special\" -- it's just a natural unit for time in Planck units.",
"The Planck time ",
" be the smallest ",
" interval of time -- but that does not imply that smaller intervals of time do not exist, do not make sense, cannot be defined, or cannot be used in calculations. All of those are still distinct possibilities.",
"The only real \"problem\" with using times less than the Planck time is that it is expected that quantum corrections to general relativity's classical predictions will become significant at that time/distance scale, which means that particular theory loses its predictive power at that scale. This is more a problem with general relativity than anything though, arising due to general relativity being a purely classical theory while quantum fluctuations are on the order of the Planck scale.",
"From that article you linked to:",
"For processes that occur in a time t less than one Planck time, the dimensionless quantity tP / t is greater than one. Dimensional analysis suggests that the effects of both quantum mechanics and gravity will be important under these circumstances, requiring a theory of quantum gravity.",
"Also, there ",
" be some indirect evidence that time is ",
" quantized on the Planck scale, at least if certain quantum theories of gravitation like loop quantum gravity are valid:",
"According to Lieu and Hillman,[5] speculative theories of quantum gravity \"foam\" where there are space–time fluctuations on the Planck scale predict that images of extremely distant objects should be blurry. However, blurring was not seen in the Hubble images, which was claimed to be problematic for such theories.",
"Of course, those theories are not widely accepted, but they are the most viable theories where space and time are quantized on the Planck scale."
] |
[
"FYI, it's very straightforward to define and use smaller intervals of time than the Planck time -- just divide it by any number! Super easy. :) The Planck time isn't necessarily \"special\" -- it's just a natural unit for time in Planck units.",
"The Planck time ",
" be the smallest ",
" interval of time -- but that does not imply that smaller intervals of time do not exist, do not make sense, cannot be defined, or cannot be used in calculations. All of those are still distinct possibilities.",
"The only real \"problem\" with using times less than the Planck time is that it is expected that quantum corrections to general relativity's classical predictions will become significant at that time/distance scale, which means that particular theory loses its predictive power at that scale. This is more a problem with general relativity than anything though, arising due to general relativity being a purely classical theory while quantum fluctuations are on the order of the Planck scale.",
"From that article you linked to:",
"For processes that occur in a time t less than one Planck time, the dimensionless quantity tP / t is greater than one. Dimensional analysis suggests that the effects of both quantum mechanics and gravity will be important under these circumstances, requiring a theory of quantum gravity.",
"Also, there ",
" be some indirect evidence that time is ",
" quantized on the Planck scale, at least if certain quantum theories of gravitation like loop quantum gravity are valid:",
"According to Lieu and Hillman,[5] speculative theories of quantum gravity \"foam\" where there are space–time fluctuations on the Planck scale predict that images of extremely distant objects should be blurry. However, blurring was not seen in the Hubble images, which was claimed to be problematic for such theories.",
"Of course, those theories are not widely accepted, but they are the most viable theories where space and time are quantized on the Planck scale."
] |
[
"What is the nutritional content of human flesh?"
] |
[
false
] |
Hypothetically if someone were to substitute human flesh instead of meat along with a balanced diet, how would it impact on their health? Positives? Negatives?
|
[
"In the amazing though somewhat academic work, \"Dinner with a Cannibal.\" The author discusses the survivors of a plane crash in Chile(?) who were forced to turn to cannibalism to survive. Essentially, the human body provided all the nutrients they needed to live (high in fat and protein) however they began to have digestion issues until they started eating the viscera (organs) which cleared that up. They were as healthy as people who survived a plane crash and then were forced to survive off snow and semi-cooked meat would have been, none of them developed prionopathies. There are multiple tribes around the world which have been cannibalistic as part of a war or funeral ritual. None of these tribes had any known (obviously we stopped these rituals when we came in so it's hard to say) medical issues except the Fore people.",
"The Fore people practiced funerary cannibalism (eating the dead as part of a funeral) and are an interesting and heavily debated case, they obviously developed a prionopathy (a transmittable infections protein disease that is caused by a misfolded protein forcing a properly folded protein into it's misfolded shape) from eating other dead humans. What is debated is whether this prionopathy was new because they ate an outsider who had CJD (a genetically transmissible prionopathy), or if it was new because they had recently begun practicing funerary cannibalism. (it is fairly clear the prionopathy was new). Many groups of humans around the world have a natural resistance to prionopathies leading some to speculate that humans may have engaged in cannibalism often enough that this trait evolved. (Prionopathies it might be noted, are only found in the brain and cereberal spinal fluid. The protein that lead to mad cow disease probably came from the CSF as it's difficult to properly butcher an animal so that none of the CSF gets on the meat. There is some indication that prioniopathies may exist in other tissues, which is why brits can't donate blood in America, but I have never seen a good proof of this. Prionopathies cannot be sterilized out of meat by cooking. They are stable into a high temperature range.)",
"There is new research that indicates that Alzheimer's disease may be a transmissible prionopathy. (Incredibly controversial and and I don't believe it I might add). Basically if you inject one mouse with one of the Alzheimer causing proteins from another mouse, it will develop AD. It's unclear what, if anything this means for humans as very few humans grew old enough to develop Alzheimer's in pre-industrial socieities where funerary or ritualistic cannibalism would have been practiced.",
"Obviously, other than prionopathies the other major consequence of cannibalism is that diseases transmit very easily from human to human (as opposed to from cow to human, we have slightly different immune systems). As people who die over a period of time, especially in hospitals, are susceptible to secondary infections as their defense mechanisms break down, eating people carries a risk of infection unless the meat is cooked very thoroughly.",
"Also, as humans are top of the food chain, we tend to bioaccumulate many heavy metals and fat soluble toxins. I'm not sure the statistics on this, but this would be another concern with eating humans, especially over a long period of time. (And the reason you should probably not eat dolphins.)"
] |
[
"Well, ",
"the person who commented on \"tastes like pig\" may be right.",
" Because of the amount of salt we take in with our daily diets, and the similarities between people and swine (we can even substitute organs), I'm not surprised human meat is compared to pork. ",
"That being said, the biggest negative health effect in my opinion has to be the spread of communicable diseases. If you eat human flesh, whatever was ailing that person could easily be spread to you. There were cases Africa of people succumbing to a disease which essentially caused their brain to become porous. This was caused by the spread of prions through cannibalism. It's a similar disease to mad cow disease. "
] |
[
"From what I understood of that, it's only transmitted through the consumption of brain matter, something to do with a protein only found there.",
"(edit: what greath was saying below)"
] |
[
"Can I propose a solution to the non-contributors that post to askscience?"
] |
[
false
] | null |
[
"Hmmm... that's putting a lot of trust in the moderators, and I've seen one or two lame posts by the mods themselves. What's the benefit, though? If someone posts crap, they get downvoted to hell and/or deleted."
] |
[
"What's the benefit, though? If someone posts crap, they get downvoted to hell and/or deleted. ",
"It would remind people to make insightful posts. I'm definitely for this, good idea OP."
] |
[
"It would remind people to make insightful posts",
"Why? Isn't that what upvoting is supposed to do? Will I get brownie points whenever I make an insightful post?"
] |
[
"If energy can be never be created or destroyed, and as the universe is expanding, would there come a time where all energy is so dissipated that things have little to no, energy and hence would freeze?"
] |
[
false
] | null |
[
"There are no (nontrivial) global conservation laws for energy in GR. There are some spacetimes in which conservation laws can hold, but there is no law that holds for all spacetimes. That is, the statement that \"energy cannot be created or destroyed\" is not necessarily true in GR. Indeed, energy conservation typically is a consequence of time-homogeneity of an associated Lagrangian function. But since the universe is expanding, it is clearly not time-homogeneous.",
"That being said, the concept of ",
"heat death of the universe",
" is likely the closest to what you are asking. The idea is that the universe will achieve thermal equilibrium; the free energy is zero. That is, no work can be performed via temperature differences. One problem with such a proposition is that it is not clear how we should define the entropy of the universe (particularly, a gravitational field), whence the question of whether the universe will achieve maximal entropy is not, at the moment, precisely stated. It's not even clear whether a gravitational field can be described by thermodynamics.",
"This is about the limit of my knowledge on the subject. It seems to me also that since dark energy remains more or less at constant density as the universe expands, then this energy can be viewed as just sort of appearing out of nowhere. (This goes back to what I stated earlier about the lack of global conservation laws.) An expert in cosmology can much better answer the fine details."
] |
[
"Yea, the eventual heat death of the universe.",
"\n",
"From this article",
": \"Every star will die, nearly all matter will decay, and eventually all that will be left is a sparse soup of particles and radiation. Even the energy of that soup will be sapped away over time by the expansion of the universe, leaving everything just a fraction of a degree above absolute zero.\""
] |
[
"There is a great short story by Isaac Asimov that is related to this: The Last Question (",
"http://www.multivax.com/last_question.html",
")"
] |
[
"What could have emitted the \"Oh-My-God\" particle (a likely proton caught traveling with 99.99999999999999999999951% of the speed of light?"
] |
[
false
] |
The doesn't mention its origin.
|
[
"Well, the short answer is that we don't know, but analysis of the most energetic cosmic rays shows that a lot of them originate in one part of the sky (see ",
"here",
") at least hinting at the location of the source. Now the Ice Cube neutrino detector under the South Pole is starting to see super-high energy neutrinos that may be correlated in their origin with super-high energy cosmic rays, which will help narrow down the source.",
"As for the physical mechanism, it could be something involving the accretion disk of a supermassive or rapidly rotating black hole. These are hypothesized to be efficient particle accelerators. This is educated speculation on my part."
] |
[
"Particles shouldn't go that fast for too long. The ",
"GZK",
" limit sets a suggests a threshold before the speed of the cosmic ray is great enough to blue-shift the Cosmic Microwave Background (",
"CMB",
") to high enough energy in the frame of the cosmic ray to slow the cosmic ray down. This only holds over extreme distances, so if it's something that we can explain with astrophysical structures we know of, then it must be nearby (relatively speaking).",
"However, ",
"/u/iorgfeflkd",
"'s link says there is a location in the sky (to very high likelihood, 4 sigma 99+%). If it is a black hole, you have to answer why that black hole is special, and why these ultra high energy cosmic rays aren't then coming from all black holes, showing us where in the sky the near black holes are.",
"One possible acceleration method for these ultra high energy cosmic rays comes from coupling with ",
"Mirror Matter",
", should it exist. There is some evidence calling for an exotic matter such as this, so its existence would solve several problems, which is exciting. It's foundation is something really off the wall, but to start: there is a property of particles called ",
"parity",
"), which is a measure of reversibility in coordinates of a physical system. A good 1 coordinate reversing example is a ",
"mirror image",
". Well, in the late 1950s, we found that parity is ",
"violated",
"#Parity_violation) (not conserved) in our universe. Many experiments since then have attempted to get higher precision limits at to quantitatively how much parity is violated, and currently no data exists to suggest that this parity violation is in part to this mirror matter sector, but should there be evidence with current generation experiments, it would be 1.) cool, and 2.) a possible explanation to your question. I won't be able to get into the mirror matter coupling, but due to its present scientific non-discovery, I think there are more interesting things to learn about as a layman.",
"Long short answer, we don't know."
] |
[
"What is the long answer?"
] |
[
"Where does the light come from during a nuclear explosion?"
] |
[
false
] |
I know a lot of the bright light associated with a nuclear explosion (like a nuclear weapon going off) must be associated with the fire. However, would a nuclear weapon give of light in, say a vacuum, where there was no fuel for fire?
|
[
"I know a lot of the bright light associated with a nuclear explosion (like a nuclear weapon going off) must be associated with the fire.",
"Why do you assume light is associated with fire? What about chemiluminescence (e.g. glow sticks) or glow-in-the-dark materials? What about fireflies or lightbulbs? Why exactly do you assume the emission of light needs fire?",
"It's a good question. I'd just like to see you refine your question a little bit so I can understand what you're thinking."
] |
[
"Visible light is the result of electrons moving from an exited state to a ground state, the energy between the two states being given off as a photon. In the case of a nuclear reaction, the energy needed to move an electron to its excited state is provided by the nuclear reaction. These excited electrons then give off a photon as the drop back to the ground state. In combustion, the energy is derived from the rapid oxidation of organic compounds. The light given off by a nuclear explosion is not due to combustion (though a nuclear explosion does cause fires). As such, a nuclear explosion in a vacuum would still give off light. "
] |
[
"Building off of what radaroffline and Yuforic said:",
"A nuclear explosion provides immense amounts of energy (in many forms like blast, multiple forms of radiation, heat, etc.) through fission/fusion reactions (depending on the nuclear weapon). That energy transfers to electrons in an electron shell and causes that electron to jump to a higher state. When the electron returns to its ground state, the energy is given off as a photon which we can see. Since there is such a large amount of energy being given off from the explosion, that's why they say there is a \"blinding light\". The great amount of heat given off can cause fires but it doesn't necessarily mean the explosion is fire."
] |
[
"Why don't step up transformers violate the law of conservation of energy?"
] |
[
false
] | null |
[
"V = IR applies to Ohmic circuit elements, where there's a linear relationship between the voltage and current.",
"V = IR does not apply ",
" the insulating gap of a transformer, and there's no need for any resistance to change for the transformer to function.",
"How can it possibly self-limit it's own current?",
"I'm not sure what you mean."
] |
[
"I get that, I'm not taking about the insulating gap. I'm talking about the circuit on the other side of the transformer, the circuit that the secondary coil powers. I and V in that circuit are connected. How can you have a high voltage but a very low current without introducing resistive elements into that circuit? If the voltage is high, the current must be high too."
] |
[
"I'm talking about the circuit on the other side of the transformer, the circuit that the secondary coil powers.",
"Then what is the resistance you're referring to? Is ",
"this",
" the question you're asking?"
] |
[
"How can I calculate the power output of a Fresnel reflector/Parabolic concentrator"
] |
[
false
] |
I'm currently working on a project for my engineering degree and am struggling with calculating outputs for a solar oven. I mainly want to focus on viability within the UK and am unsure what to use as a Q value (for the amount of energy provided by the sun) within my Stefan-Boltzmann equation. I've seen the average proposed as 1kW of raw sunshine on the earth surface, however I've also seen that the distance from the equator means that this value is only 60% of that within the UK (600W). My main question is because this is diffuse light is this then negated because of the concentrating aspects of the reflectors or do I have to use 600W as my base value?
|
[
"The amount of solar energy that you have to work with is going to be in the form of Watts per square meter - energy per area per time. The area in this case is the area of your reflectors - this is your maximum starting value. That energy is then concentrated into a smaller space ... but the amount of theoretically available energy isn't going to change."
] |
[
"I'm still not sure that I'm following you correctly. ",
"For peak values in a particular spot, you're either going to have to measure yourself, or find measurements that someone else has taken. I don't know of a way around that. ",
"For the ... diffusivity affecting things - if you're worried about the radiation diffusing between the sun and the reflector, then this should already be accounted for in the numbers that you have. If you're worried about the diffusion between the reflector and the oven, then this should be negligible, unless the distance between the two is enormous. ",
"If I'm missing the question again, let me know and I'll try to help."
] |
[
"Sorry, I should have stated I meant 1000W/m",
" is the output of the sun on average, which goes down to 600W/m",
" in the UK (assuming the midday sunshine) so if for example the surface area of my reflector was 1m",
" what would be the energy output. I'm aware I'll change this through emissivity (for aluminium I've read it's between 0.02 and 0.09) however it's the initial value for solar irradation I need to pin down before I can continue and work out theoretical times for how long it would take to boil water etc maknig various assumptions."
] |
[
"Why would the addition of a yellow subpixel to the usual RGB increase the picture quality if the input remains the same?"
] |
[
false
] |
I mean, if the signal coming into the TV with the extra suibpixel is the same RGB signal that would be displayed on your typical RGB TV then where would the extra colorspace information come from? Wouldn't an RGB monitor by default offer the best possible picture, ie a 1:1 representation of the incoming RGB signal without any interpolation signal degredation? I was looking for a new TV and came accross Sharp's Aquos line which prompted the question. Link:
|
[
"There is no extra colorspace information. These televisions do some onboard signal processing to derive or augment a yellow channel, and that's about it."
] |
[
"The theory is that the color mixtures that produce yellow aren't precise enough. To get yellow (and other non primary colors), we are essentially mixing RG. The RGB signal might be (128)(128)(0) to get a dark mustardy yellow. The TV that had RGB(Y) would interpret that signal as (0)(0)(0)(128). Add in some intensity issues that may lead to bleeding and a sharper image doesn't seem unreasonable.",
"Having said that, I would expect it only be truly noticeable in a side by side comparison."
] |
[
"If there was perfect RGB fidelity, then it shouldn't help.",
"But it is possible that it can help augment the imperfect output of the other three pixel colors."
] |
[
"Why are creases in paper impossible to smooth out?"
] |
[
false
] |
What about the material of paper makes that so difficult compared to, say, a folded cloth?
|
[
"This image",
" shows the difference in a fold in paper (top left) and polyester fabric (bottom right). As you can see, the polyester fibers bend and deform, but are not damaged and can therefore be smoothed out. They are also woven together, so individual fibers won't be separated from the cloth. Cellulose fibers are easier to damage and, as the enlarged photo shows, can separate from the rest of the sheet more easily because they are not woven together. These changes to the material are not reversible, so some evidence of the crease will remain."
] |
[
"They're from ",
"this paper",
" about origami robots, but I just found it on Google."
] |
[
"where did you find those images? they're amazing"
] |
[
"What is the scientific/ biological explanation behind female menstrual cycles syncing?"
] |
[
false
] | null |
[
"Menstrual synchrony seems to be just plain chance, as far as I know. Menstrual cycles of women greatly vary, and supposed synchrony is usually noticed with a wide range. Given a group of women whose cycles can have a difference of two weeks, and which last only a few days to over a week, they'll eventually occur at roughly the same time, before moving apart again.",
"Maybe there's something else to it and it really does exist, but evidence is slim and research pretty inconclusive. Probability seems to provide the best answer."
] |
[
"To add to this, the mechanism often proposed is that it's due to pheromones. The problem is that there's no evidence that humans use pheromones. The vomeronasal organ, which in other species is used to detect pheromones, is either non-existent or inactive in human beings. So even if we did send out pheromones, we wouldn't be able to detect them."
] |
[
"It's now thought to be mostly a myth. Because most (but not all) menstrual cycles are 28 - 35 days (that will vary person - person and even within the same person) and last ~5-7 days (again, SO much variation there) if you have a large enough group of women, at some point they'll overlap. "
] |
[
"How possible is it to access oil and natural gas fields by drilling from a place lying hundred kilometres away from the field?"
] |
[
false
] |
Is it scientifically possible that Iran can access oil fields of Saudi Arabia or that Turkey, Kazakhstan access Russian oil fields by drilling horizontally? Moreover, can they transport oil this way and can it be detected by the other country? This picture illustrates what I mean
|
[
"That article should give you your answer. The lengths mentioned are apparently our current maximum lengths. Even if you double the longest mentioned one, it wouldn't be very far relative to the \"hundreds\" of km from your question."
] |
[
"Thank you for your reply. Actually bend drilling at right angle is of minor if of any importance. ",
"I'm more interested in if it actually possible to access oil fields lying hundreds of kilometres away from a place you start drilling. ",
"edit: here is something I found after a short research on the Internet",
"https://en.wikipedia.org/wiki/Extended_reach_drilling"
] |
[
"Unlikely to happen as you've drawn, since how would they bend the drill bit at the right angle?",
"However, they can certainly ",
"drill diagonally and drillholes do not have to be straight",
"."
] |
[
"If our internal organs only contain pain receptors, why is it that when I eat/drink something hot or cold, I can feel its temperature in my stomach?"
] |
[
false
] |
My anatomy and physiology textbook (published in 2011 so it's fairly recent) states "As a rule, pain receptors are the only receptors in viscera whose stimulation produces sensations." So why can I feel, for example, ice cold water as it travels to my stomach?
|
[
"The book may simply be incorrect, depending on how it classifies thermoception--or more charitably, it might not be putting things the best way it could. Thermoceptors/thermoreceptors (both spellings used) ",
" present both cutaneously ",
". Because of the involvement of you-know-what-cranial-nerve, these ones are sometimes called the ",
"vagal thermoreceptors",
".",
"The sensation of heat and cold has sometimes been classified as part of nociception in the past, which may be the sort of scheme your book is operating under. It's my general understanding that they are more commonly viewed as distinct now, however.",
"As an additional nit to pick at the line in your book, mechanoreceptive systems around the stomach, lungs, and bladder (often called the \"stretch receptors\") also produce visceral somatosensory information and are generally never understood as nociceptors. Can you consciously tell when you have to pee? Yeah, me too, which means they do indeed \"produce sensation\" by any conventional definition I am familiar with. Even by the forgiving standards of your book's hedge, \"as a rule,\" I'd say that I definitely experience sensations related to these visceral mechanoreceptive systems much more often than visceral pain.",
"As a second and maybe weaker nitpick, I might add that the proprioceptive sense probably has a lot of top-down central control and input from the vestibular system, but probably does also incorporate a certain amount of input from muscles, tendons, ligaments, etc., all around the body. While we usually don't think of our proprioception as a \"sensation,\" that may be because we're quite used to having it around. (Read the story of Christina--\"The Disembodied Lady\"--from Sacks' ",
" if you want to know the terror of losing proprioception entirely). ",
"And to go out as far as I can on the branch here, I'm not sure, but I think it might be possible that the peripheral chemoreceptors monitoring your blood pH produce sensation, or at least contribute to a complex sensation. (Can you tell when you're deprived of oxygen? Try holding your breath for a while and feel the burn--that's the one I'm talking about.) Chemoreceptors for this purpose are also located centrally (sitting there on the ventrolateral medulla), and testing whether or not you still experience the subjective sensation without the central chemoreceptor area seems like a tough one to get past the IRB."
] |
[
"Sure, we're big-elongated-doughnut deuterstomes and all, but that didn't exactly look like the point the book was making. Receptors peppering the stomach lining would usually pretty easily qualify as \"in the viscera,\" (given the usual use of the preposition there) unless there's a point being made off-camera here about embryonic development."
] |
[
"I was just trying to explain how the book's ",
" correct in a very abstruse way, but I suppose the simplest answer is that they should have said it differently.",
"unless there's a point being made off-camera here about embryonic development.",
":D"
] |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.