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[
"[Biology] Pouyannian mimicry: How do plants evolve to mimic members of the animal kingdom?"
] |
[
false
] |
I did what little research I could without a background in biology, outside an intro course in my undergrad. I would really appreciate if a botanist could break this science down.
|
[
"The key thing here is that evolution is not directed, it's not like the plant is thinking, if I look more like that insect, it will be attracted to me, and then spread my pollen for me.",
"The mutations to the plant are random, some mutations result in a flower that more closely resembles an insect (shape, color, even smell), some mutations don't. The flower that more closely resembled a insect, happen to attract more insects, which results in increased spread of pollen. This increases the fitness of that plant. \nThe plant is not aware of that fact that its appearance is attracting insects, it's just that the plant that over time mutated in such a way that they did look like plants were more successful than plants that did not. "
] |
[
"Same concept. Nothing directs a walking stick to look like the tree its crawling on. But somewhere back ages ago the insects that had these chance mutations that made them look like a part of that tree were less likely to be detected by predators (or more likely to sneak up on prey) and, therefore, more likely to pass on their genes complete with mutations."
] |
[
"So do animals just so happen to resemble leaves or twigs as well? This is all just natural selection and not an emerging field of study? I can accept this answer, but it's not that satisfying. "
] |
[
"What would happen if you actually did eat those \"do not eat\" silica gel packets?"
] |
[
false
] | null |
[
"Most likely: nothing. The silica gel itself is inert and nontoxic. It is placed in the bag of food to help reduce moisture/humidity which may spoil said food. It is marked with 'DO NOT EAT' because it is a non-food item mixed in with food items, and may also present a choking hazard. ",
"Given the fact that the purpose of the packets are to desiccate, a person might have extremely dry mouth or constipation after eating them. If anyone does accidentally ingest a packet, a call should be placed to poison control at 1-800-222-1222"
] |
[
"”Most likely: nothing. The silica gel itself is inert and nontoxic.”",
"”If anyone does accidentally ingest a packet, a call should be placed to poison control”",
"I think you captured the reason OP is asking this quite accurately, how can it be harmless, yet require medical attention?"
] |
[
"Well, anytime anyone ingests (accidentally or intentionally) something they shouldn't, poison control should be called. That's just the protocol, at least in my area. Sometimes it's for documentation/epidemiological data reasons, other times its to confirm appropriate management or correct prescribed therapy. Often it feels like a waste of time for all parties involved."
] |
[
"Do galaxies have an electric current?"
] |
[
false
] |
Stars are electric objects. The have magnetic poles. Do galaxies have magnetic poles and a current of interstellar electricity charging the sun by flowing down the spiral arms of the milky way?
|
[
"Stars are electric objects. ",
"I guess that's not wrong but not how I would put it. It has currents which generate the magnetic fields but it's not strongly charged.",
"Anyway, galaxies do have magnetic fields (see a recent ",
"image",
" by Planck of our own galaxy) but these are extremely weak in comparison to, say, the local Earth magnetic field. I don't think they have very strong poles, magnetic fields typically will follow the structure of the interstellar medium (ISM) in the galaxy (see ",
"here",
" and ",
"here",
" for two examples of other galaxies).",
"The interstellar medium does have many free electrons. Again, I guess it's not wrong, but I would not call it interstellar electricity. Magnetic fields play a role in how the ISM moves but I think (am fairly sure but not positive) that turbulence in the ISM plays a larger role, at least on \"smaller\" scales, especially since the ISM is pretty consistent with being isotropic (a magnetic field would make one direction more important, so it would be anisotropic), though some measurements debate this. As you get to galaxy-wide scales, magnetic fields may play a more important role."
] |
[
"Right I'm not talking about a cosmic thunder bolt. But a current moving in a uniform direction among the galactic arms"
] |
[
"Right I'm not talking about a cosmic thunder bolt. But a current moving in a uniform direction among the galactic arms"
] |
[
"Does chlorine that settles in to ground when irrigating lawns or draining swimming pools degrade into something else, or remain unchanged?"
] |
[
false
] |
I work in water utilities. 99% of residents in my city irrigate their lawns with city water, and we like chlorine to be 1.8-2.1 in this city. All run off from irrigation and when people drain pools and the like seeps into their lawn, and all water eventually makes it to the lake system. It's common knowledge here that chlorinated water once "filtered" through ones lawn removes nearly all the of the chlorine from the water by the time it makes its way back into our lake system. So my questions is, does all that chlorine sit in the ground unchanged? Or does it eventually degrade into something else?
|
[
"Chlorine gas is very reactive and can oxidize most organic matter it comes in contact with. It does not stay chlorine for very long in an high-organic load environment such as soil. The chlorine in treated water will gain two electrons from something in the environment and become two chloride ions (Cl-)."
] |
[
"Lawns are foolish, as far as that goes.",
"Usually, yea. The firebreak concept they originated from is still relevant in the rural areas around me, though. Ur seen houses saved from wildfires by a decent lawn. "
] |
[
"Using potable water in this way is foolish but universal. Lawns are foolish, as far as that goes.",
"Chlorine atoms are very reactive and exist as hypochlorous ions in water. They react with organic soil molecules, forming hydrocarbons and similar chemicals. Some will evaporate as Cl2 gas into atmosphere. "
] |
[
"Of the infectious diseases that were the leading causes of death in the 1850s, which ones are now easily curable and which are still dangerous?"
] |
[
false
] |
I found this display at a science museum in San Diego which showed the leading causes of death in 1850, all infectious diseases. If I (a 20-something woman with normal medical history) were diagnosed with any of these tomorrow morning, will I survive and/or be cured? Which of theses diseases are still a real threat?
|
[
"Some of these are single infections, while others are diseases with multiple infectious causes. I'll address them one by one. ",
"TB: Quite treatable with a multi-drug regimen, although antibiotic resistance is increased in parts of the world. Still a huge killer worldwide, but in the developed world, you should be good. ",
"Dysentery/diarrhea: There are many causes, but usually very treatable with oral rehydration therapy, AKA drinking lots of water with salt and sugar in it. It's that simple, yet we didn't figure this out until well into the 20th century, and it took the 3rd world teaching the 1st world. It's pretty embarrassing. We also just have less because of clean water. ",
"Cholera: Same as other kinds of diarrhea but even more so. For every cup of water you poop out, you drink a cup of salty sugar-water. Antibiotics can help, but you should have the cure in your kitchen. ",
"Malaria: Generally treatable with antimalarials (also some resistance) though you'll have a bad time, and severe cases can still kill. ",
"Typhoid: Treatable with antibiotics and rehydration. ",
"Pneumonia: Depends on the cause (different bacteria, viruses, even fungi) and other factors. Often treatable and not a huge deal in healthy folks, but still a common cause of death in people with a lot of other medical problems. Deaths from COVID typically involve pneumonia, so yes, this is one to fear.",
"Diphtheria: If you were dumb enough not to get the vaccine and get a bad case, we'll shoot you full of horse antibodies, stick a tube down your throat, and you'll survive. Get the vaccine.",
"Scarlet fever: Rare because we treat strep throat with antibiotics anyway, but treatable. ",
"Meningitis: I live in fear of it. Different causes, but they all mean infection has breached vital barriers and is in a very bad place. Treatment takes bacterial meningitis all the way down from \"certain death\" to \"still worse than Russian roulette.\" If you survive, full neurologic recovery is not guaranteed.",
"Whooping cough: Easy to treat in adults, still gnarly in babies. Prevention is in the same vaccine as diphtheria, get your damn booster."
] |
[
"depends on where you live. If you are in a developed country those are mostly treatable. In an developing country not so much. TB is now drug resistant and may be the biggest threat. Malaria also can be drug resistant is remains a major threat to people world wide. whooping cough, diptheria, pneumonia, are vaccine preventable. typhoid, scarlet fever, dysentery and cholera are treatable."
] |
[
"Malaria.",
"\nIn reality it is the most dangerous disease around. According to the WHO, in 2020 there were an estimated 241 Million recorded cases of malaria and this resulted in some 627,000 confirmed deaths. Yes, it is treatable and yes you can take anti-malarial medication before travel, but these are only 93% effective. Even if you do not die, the symptoms can be life changing and severe, most people do not die from Malaria itself, but from secondary infections or complications caused by a damaged immune system. The WHO estimates that more than 18 million people die each year as a result of malarial infection, but that most deaths are recorded as being caused by the secondary/opportunistic infections and complex medical conditions, thus do not get recorded correctly."
] |
[
"Is it better to drink something hot or something cold when you have a sore throat?"
] |
[
false
] |
I've been drinking hot tea all my life and found out all my friends eat ice cream.
|
[
"I believe that warm drinks have been shown to ameliorate common cold symptoms. The ",
"website for Cardiff University's Common Cold Centre",
" looks to have some interesting information along these lines.",
"EDIT: for ease (please see the page linked-to above for references though):",
"Any form of hot drink will provide relief from the symptoms of sore throat and cough. The hot fluid has a demulcent and soothing action and tasty drinks containing slightly bitter flavours such as lemon and citric acid are particularly beneficial. Spicy foods and hot soups are also beneficial as they promote airway secretions which have a calmative action on an inflamed throat. Hot drinks in combination with paracetamol provide long lasting relief from pain related symptoms and fever. There is little evidence to support the effectiveness of the small doses of oral decongestant and vitamin C contained in many of the hot drink formulations."
] |
[
"Interesting. This confirms my anecdotal evidence.",
"When I get a cold I like to go to the local Vietnamese place and get a big bowl of spicy soup with some hot tea with lemon and honey. Always makes me feel better."
] |
[
"Yeah i've heard that hot drinks, spicy food, lemon and honey are all (independently) good for colds, so you've pretty much hit the motherload there.",
"Incidentally, i believe, and it never ceases to amaze me, that honey was used as a basic antiseptic (edit: antibiotic?) by the Vietnamese when performing surgeries during the American War."
] |
[
"Have extremophiles always been extremophiles?"
] |
[
false
] |
That is, are the ancestor of those bacteria and other weird lifeforms that live in the harshest environments on earth extremophiles as well or did all extremophiles evolve from organism that lived in more friendly environments? How much do we even know about extremophile evolution?
|
[
"We know a little about extremophile evolution by tracking the 16S ribosomal RNA in different species (or similar techniques). This allows us to map the phylogeny of different species, and so far seems to point at the fact that the oldest living organisms we know of were some kind of thermophile (heat loving).",
"It's important to realise that we define 'extremophiles' as those organisms that live in environments that are 'extreme' to ",
". The organisms themselves don't really care whether it's extreme or not, they just live their lives and adapt if necessary.",
"However, most extremophiles that we know of still utilise the same basic machinery that most 'normal' life we know of does, but they have particular mechanisms to protect or prevent or repair damage from the harsh environment. So for example, most psychrophiles still utilise liquid water in their metabolisms, they just have developed particular ways of keeping the water liquid in a cold environment. Or halophiles which have developed ways to reduce the osmotic gradients and allow them to retain water. This kind of thing leads us to the belief that 'normal' organisms are normal, and the extremophiles have developed ways to counteract their particular extreme environments, but there's no smoking gun we can point at to show that this is true."
] |
[
"There are many schools of thought. Some people think that the chemical environment of the warm \"smokers\" (i.e. not necessarily the black smokers people normally connect with undersea vents) was itself how life arose, with a natural proton gradient created by the reaction of seawater and rock allowing the first metabolisms to start. So yes, it's entirely possible.",
"And to each ",
" extremophile, everything else is an extremophile."
] |
[
"Isn't there a school of thought that says life first organized in the high energy environment of hot water \"smokers\" and only after some types developed mutations that allowed them to get energy from sources other than hydrogen sulfide reactions did life populate other environmental niches around the globe? ",
"TL;DR: to an extremophile, we're the extreme ones"
] |
[
"How long would it take after a vaccine for COVID-19 is approved for use would it take to make 250 Million doses and give it to Americans?"
] |
[
false
] |
Edit: For the constant hate comments that appear about me make this about America. It wasn't out of selfishness. It just happens to be where I live and it doesn't take much of a scientist to understand its not going to go smoothly here with all the anti-vax nuts and misinformation. Edit 2: I said 250 million to factor out people that already have had the virus and the anti-vax people who are going to refuse and die. It was still a pretty rough guess but I am well aware there are 350 million Americans.
|
[
"Usually the regulatory hurdles would be large. If you do the discovery, optimization, process development, risk assessments etc. and then start your clinical trials with what you've got, you've already chewed up a lot of time. If you're confident you could start manufacturing (and in my opinion this would be fairly simple as far as biologics go) during your trials and have it ready by the conclusion - risky but smart bet.",
"You'll see that JnJ is manufacturing 800 million doses at risk, which means they're confident enough in a conservative candidate that they think the conclusion of a successful clinical trial will coincide with their stockpile being complete. From a pharmaceuticals standpoint that is a huge, huge, huge accomplishment if they pull it off, even with some regulatory barriers relaxed. Even this is anticipated to take a little under a year-ish.",
"EDIT below -",
"It isn't uncommon to get the ball rolling towards commercial batches if your process is set/validated etc. and you anticipate a successful conclusion, and in my opinion vaccines are a lot \"simpler\" to make than other biologics because there is quite a bit of expertise in the area, but yes they're accelerating the process at what (in my opinion) is an impressive pace. That's what I was trying to emphasize.",
"I did *not* want my comment on what they're doing to sound like an overhyped Buzzfeed article, but having had to go back and dot i's and cross t's for filings, I remain in awe of how fast they're going."
] |
[
"The Bill and Melinda Gates foundation is ",
"funding initial construction of ",
" 7 vaccines ",
".",
"Edit: wording; many factories are built for each vaccine"
] |
[
"Here's a good peer-reviewed perspective piece from Amanat et al. in Immunity published April 6th.",
"30120-5) They outline many challenges with developing a vaccine for SARS-CoV-2, including but not limited to:",
"Bao et al., 2020",
"current Good Manufacturing Practices (cGMP)",
" ",
" ",
"I highly encourage reading the paper or at least giving it a skim. It's open access to the public and has a lot more details about SARS-CoV-2 in general and the different vaccines being tried.",
"Edit: fixed links and added a little more context for one of them"
] |
[
"Is it possible (ignoring heat), to make a light bright enough to shine through solid things like sheet metal or wood?"
] |
[
false
] | null |
[
"It gets exponentially harder with thickness. For example, suppose you have a sheet of paper just thick enough to block half the light. Two of them will block 3/4ths of the light. Three would block 7/8ths, etc. How many sheets thick is a block of wood? A block of wood would be like a ream of paper, and block about 1-10",
" of the light. You could turn the entire visible universe into light and you won't even come close to sending a single photon through."
] |
[
"If you could create a light source strong enough sure, the only problem is that with the technology we have right now, it would create enough heat to cause spontaneous combustion. ",
"Theoretically yes, a strong enough pinpoint light source would be able to shine through any material, but the amount of energy involved starts to stretch physics if your material gets thick enough. "
] |
[
"I mean theoretical possible."
] |
[
"What volume of outer space would you need to inhale to take a single breath?"
] |
[
false
] |
Of course, outer space is very much devoid of oxygen, but if you were to take an average breath, what volume of outer space would you need to suck up each time?
|
[
"I will read your question as \"Given the ratio of the gas densities in interstellar space and on earth, what volume of space contains the same number of molecules as your lung?\" in order to give an order of magnitude estimate.",
"Assume your lung volume to be about 2 liters, give or take.\nOn earth under standard conditions (1 atm, 0 C) that means you have about 0.1 mole = 6x10",
" molecules in your lung.",
"The density of the interstellar medium is widely varying. The relevant wiki page lists between 10",
" and 10",
" atoms per cm",
" Lets assume you are trying to draw this breath in one of the denser regions, so 10",
" atoms per cm",
" or 2x10",
" atoms in the two liter volume of our lung.",
"So we need 3x10",
" times the lung volume of space, which is 60x10",
" litres = 60x10",
" m",
" = 60 km",
"So anywhere upwards of a few hundred cubic ",
" will do. ",
"Of course, as you point out, there's very little oxygen in that breath."
] |
[
"yes, as a rule of thumb 75% H 24% He and the rest heavier elements. (Except when you run into an asteroid, perhaps even with an iron core. That would not be a pleasant encounter for your ramjet)"
] |
[
"Guessing it would be mostly hydrogen that floating around. There have been theoretical designs for spaceships that use electromagnetic scoops to collect ions for a drive. This frees them from having to carry mass to be expelled for thrust. I do recall Robert W. Bussard's original estimates (1960) for the availability of hydrogen was found to be too optimistic so the drive wasn't feasible."
] |
[
"How can the Casimir effect come from harmonic oscillator ground state energy if the latter is arbitrary?"
] |
[
false
] |
In many explanations of the Casimir effect (e.g. or Casimir's original paper ) it is argued with the ground state ("vacuum") energy of harmonic oscillators. In fact the quantization of the classical harmonic oscillator has an ambiguity which leads to an arbitrary ground state energy (see e.g. chapters 6.3 and 6.4 or (if you're able to read german) chapters 4.4 and 4.5). For relativistic theories it is even necessary to have E_0 = 0.
|
[
"That derivation of the Casimir effect is simplified with the assumption that the fine structure constant is infinite, which allows it to be derived much more easily. A full derivation considers the relativistic van der Waals attraction between two real plates, which is more complicated and less handwavy: ",
"http://arxiv.org/pdf/hep-th/0503158.pdf"
] |
[
"I think it is actually pre-dated by a van der Waals argument ( just reading Casimir's first paragraph in the link you posted). I think it is an example of how a handwavy explanation is presented so often that people mistake it for the real thing, sort of like how Hawking radiation comes from particle-antiparticle pairs that half-escape the black hole."
] |
[
"Baez writes about it here:\n",
"http://www.obscure.org/physics-faq/Relativity/BlackHoles/hawking.html",
"\"...this argument also does not correspond in any clear way to the actual computation. Or at least I've never seen how the standard computation can be transmuted into one involving virtual particles sneaking over the horizon, and in the last talk I was at on this it was emphasized that nobody has ever worked out `local' description of Hawking radiation in terms of stuff like this happening at the horizon....\"",
"You can do the same sort of calculation for an accelerated observer in flat space to get a similar result:\n",
"http://en.wikipedia.org/wiki/Unruh_effect",
"Now, accelerated observers still have cosmological horizons, so maybe the heuristic explanation still holds, but if it does I expect it's tied to subtle aspects of what a particle is."
] |
[
"A few questions regarding light and the effect it has on how we view things"
] |
[
false
] |
Assuming faster-than-light travel was possible: Person A is travelling from Earth at 0.9c, would they see any events happening on Earth occur very slowly? Person B is travelling from Earth at c, would events on Earth appear to have frozen? Person C is travelling from Earth at 2c, would the events on Earth appear to be in reverse, and in real-time motion? Person D is travelling Earth at c, would events on Earth appear to be happening twice as fast?
|
[
"Only your first questions is answerable- and you are correct, a person traveling towards the Earth would see events on Earth taking place slowly (according to what you mean by very slowly- the gamma factor would 0.9c is 2.2, so things would appear to be moving at about half speed). ",
"The problem with your other questions is what you'd expect, faster than light travel isn't possible (that we know of). Now, there are hypothetical questions that are answerable (what would it be like if our planet were a cube? Well, planets can't be cubes, but you can still discuss the implications. Or, what would happen if the sun suddenly lost half of its mass? Well, mass must be conserved, but thankfully the physics describing conversation of mass are independent of the physics describing orbital dynamics, so as a fun exercise, we can still discuss it). But the only physics we have that discuss what happens when we go fast is the same physics that tells us we can't go faster than c. So, we can make no predictions about the outcomes of what would happen when traveling at c or faster. "
] |
[
"No, general relativity does not allow for paths which travel faster than c. "
] |
[
"i was told that faster than light travel is possible, but crossing the threshold towards lower than the speed of light or vice versa is impossible. Is this true?"
] |
[
"Why don't contacts for people with astigmatism come in small steps along the axes?"
] |
[
false
] |
Looking into contacts and I have relatively bad astigmatism. The optometrist said that contacts come in steps of about 5 degrees, 10 degrees for the less severe. Why is that the case? I can tell a very clear difference of 1 degree in my spectacle prescription, will I be able to get good contacts?
|
[
"The fundamental problem is the cost of maintaining inventory.",
"A prescription for a person without astigmatism just has a quantity of correction in diopters: +1.5 or -4.5 or whatever. So if a contact lens manufacturer does these in .5 diopter increments, and covers from -10 to +10, they'd have to stock 21 sizes (assuming 0.0 was available, for color change only).",
"Now add in astigmatism.",
"The astimatism portion has two numbers: the \"cylinders\" or strength of astigmatism, and the axis, a number from 0 to 180.",
"So the manufacturer used to have to stock 21 strengths. Now multiply this times (for 10 degree increments) 18 to cover the varying axis values, and strengths from 0.5 to 8.",
"Now the manufacturer has to machine and stock 21 * 18 * 14 = 5,292 SKUs. If they stock in 1-degree increments, change that 18 to 180, or 52,920 SKUs.",
"Add the fact that contact lenses expire, and you can see that the cost of maintaining inventory could get astronomical.",
"Maybe this will change one day when contacts are machined at order time. Just-in-time 3D printing of contacts, anyone?",
"Anyway, that's the reason. It's too expensive to stock every possible combination when you allow too much precision."
] |
[
"Because these are not made custom for you. They're stocked in a warehouse, and doing 1 degree increments would mean stocking fifty thousand different prescriptions instead of five thousand prescriptions. That's the fast answer I buried in too much text above. :)"
] |
[
"My question is more focused on why they don't do smaller increments for the axis? I'm not concerned whether or not they have to order my prescription in, more why they can't do it in 1 degree increments instead of 5-10? Maybe I misunderstood my optometrist?"
] |
[
"Could mining asteroids for water have a negative effect on the ecosystem/environment"
] |
[
false
] |
With the idea of mining asteroids for resources becoming a reality would introducing more water into the environment have a negative impact? Since the water that's been on the planet has pretty much been the same throughout history can it even be predicted what the effects would be?
|
[
"Would you be surprised to learn that the ",
"mass of the asteroid belt",
" is about the same as the ",
"mass of the oceans on Earth",
"? The former is only 25% more mass.",
"Now how much of the asteroid belt is actually water? The majority of the asteroid belt is ",
"carbonaceous chondrite in composition",
". This type can have water content up to 22% by mass, but is typically closer to 5% range. Using this rough estimate, ",
".",
"Now we know that ",
"about 2% of Earth's total water is in the form of ice",
". If all this was melted, sea levels would rise ",
"about 200 feet, or 60 meters",
". So if we managed to bring a third of the asteroid belt's water to Earth, that's how much the sea level would rise.",
"But the odds are we're not going to bring a third of the asteroid belt to Earth, even in the distant future. I'd say the odds are we won't even bring a third of a percent of the asteroid belt to Earth in the foreseeable future. So I don't think sea level rise would be much of an immediate concern, and I can think of no other ill effects Earth might suffer from adding a relatively small amount of water."
] |
[
"Is it really becoming a reality?"
] |
[
"apparently there are a few companies working towards it. one is heavily financed by the creators of google and james cameron. i read an article earlier today about how a passing asteroid on friday has 400 Billion $ worth of resources that were mostly water on it. "
] |
[
"Why do I remember trying to fall asleep, but not actually the falling asleep itself?"
] |
[
false
] |
Pretty much title.
|
[
"I had [what I assume was] a lucid dream once as I was falling asleep. It felt like I was being sucked into a black hole and sounded like bullet trains whizzing passed my ears. I joked to my roommate that this is why people don't remember falling asleep, it's traumatizing. He's in medical school, so I expected his usual snide, \"well actually..\", but all I got was a single eye brow raise and an intrigued sounding \"huh\". There's no science here and I'm 99% joking, but food for thought."
] |
[
"Because it's a different state of consciousness - your brain activity switches to a resting state and you aren't able to form memories or experience things in a way that's meaningful to you. The electrical activity of the brain actually changes when you switch from waking to sleep states (doesn't turn off, but changes frequency)"
] |
[
"Very interesting. Thank you."
] |
[
"Is a rubber band really a single molecule?"
] |
[
false
] |
I read it and just would like a clarification and perhaps a little more explanation. Thanks!
|
[
"It's a bit of a grey area. You start with individual polymers, which are all their own molecules, then you bind them together in ways that are not entirely dissimilar from the way different atoms in a single molecule are bound. So you sort of end up with a molecule-of-molecules, in a sense.",
"Chemistry is far more complicated and variable than we all learned in school. Or so my chemist friends keep telling me, usually right before they throw me out of their parties for being dumb."
] |
[
"I'll attempt to clarify because it could be slightly misleading to simply call it a single molecule.",
"Rubber begins as a mass of oriented polymer chains which are free to slide past each other. These don't have particularly good material properties, it's like trying to pull on a clump of spaghetti. It's like a bunch of little kids holding hands in a bunch of parallel lines.",
"| | |",
"| | |",
"| | |",
"But during the vulcanisation process, the chains of molecules get sulfur put onto them. Sulfur interacts extremely strongly with itself, and will react with other sulfhydryls to form a covalent bond between parallel chains known as a disulfide bond (or disulfide bridge). ",
"This effectively links every single long polymer chain to every other one, forming a large cross-linked network. Now it looks like:",
"|_| |",
"| |_|",
"| | |",
"Now that all the chains are bonded to one another, we call the entire thing an entire \"molecule.\"",
"But it certainly doesn't start out like that (Although it can, when polymerizing a tri+functional monomer)."
] |
[
"You never drop that on their asses?"
] |
[
"What makes an object sharp? How does it cut or pierce through other objects?"
] |
[
false
] |
I never understood the concept, so I’m not sure if this is a stupid question or not. Update: Right now I’m busy with lectures, but I’ll read the comments afterward. Update: wow, didn’t expect this many people to comment. Thank you everyone for answering my question!
|
[
"As ",
"u/fael_7",
" said, a sharp edge basically concentrated the force applied. If you weigh 60kg and walk on your toes in sand, you will leave deeper footprints than if you walk on your entire foot, right?",
"Same idea, basically. If you apply an equal force using a sharp point it edge compared to a blunt surface, that force is pressing on your \"target\" on a more concentrated area, increasing the pressure (force divided by area) you can apply.",
"If this localized pressure can break the material (either on a macroscopic scale by separating individual pieces or segments, or on a molecular/atomic scale by breaking bonds) and if your sharp tool is strong enough to withstand the force being applied with it, so as not to break itself, you will cut.",
"It can be complicated to describe it exactly as different materials have different properties and mechanisms for failure (being broken or cut) so if you are unclear or want to ask about a specific example, please do. "
] |
[
"This gif might help understand what is happening.",
" In the case of that image it is a blade slicing through steel when viewed through an electron microscope.",
"It is actually quite interesting what is happening here. As you can see the edge of the blade at this scale is actually surprisingly rounded. There also appears to be a buildup of steel at that rounded tip which doesn't particularly go anywhere despite the material sliding along for either side of it.",
"I've seen some other gifs where occasionally that little buildup falls one way or the other, but almost immediately some material finds its way into forming a new buildup.",
"One thing to keep in mind is that it takes a lot of force to basically smash apart the granular structure of metal, but on the scale of this image it is easy to focus a small amount of force into a tiny area, thus \"becoming\" a large amount."
] |
[
"If this localized pressure can break the material (either on a macroscopic scale by separating individual pieces or segments, or on a molecular/atomic scale by breaking bonds)",
"This is where I get confused. Take the specific example of using a kitchen knife to cut an onion. I am assuming that it is 'cutting' rather than just mushing the onion. But what is happening at the lower physical scale? There are some metal atoms moving down and horizontally relative to the onion molecules. Does it split individual cells open? I figure that it does, which is how the chemicals get out that cause your eyes to water. Is the pressure literally inserting the metal atoms between cell wall molecules? ",
"Also, why does moving the knife make it easier? I figure that it has something to do with shear forces. ",
""
] |
[
"Could a planet orbit the sun on a vertical plane as opposed to the horizontal plane of the other planets?"
] |
[
false
] |
I am not sure of terminology, but assuming that all the planets are on the same horizontal plane could another planet orbit on a vertical plane?
|
[
"Bet of a mess here so I'll make a bit of a tl;dr top-level response:",
"Planets form in a flat plane because they all form from a disc of gas.",
"But if you somehow got a planet in vertical orbit ",
" the gas disc had dissipated, it should continue quite happily, and there are indeed small objects in the solar system that do have very very high inclinations in their orbits."
] |
[
"No, electron orbits are not supposed to resemble those of planets. Someone else can likely answer this better, but electrons do not act like planets partly because they have both particle and wave-like properties. ",
"An electron's orbit can be characterized better with the atomic orbital model, which predicts around where you would be able to find an electron. In the case of a single electron orbiting a nucleus, the electron cloud, or area where it might be, is sort of more like how you would find atmosphere on a planet in that it kind of envelopes the planet. The electron clouds can be very different though depending on how many electrons are in the atom and several other factors. ",
"Edit: ... Why do people keep downvoting alliace? He/she had a legitimate question that is a pretty common misconception. An insightful answer to such a question would be beneficial to many people. "
] |
[
"How come electrons circle the nucleus at vertical angles then? Aren't their orbit supposed to ressemble that of planets?"
] |
[
"Keep hearing that we are running out of lithium, so how close are we to combining protons and electrons to form elements from the periodic table?"
] |
[
false
] | null |
[
"I work for one the largest lithium producers and refiners. We certainly don’t think lithium is running out. We get a lot of ours by drying brine combined with earth in old volcanic zones. The left over salts have a decent concentration of lithium. This helps avoid so much mining too, but there are a couple lithium mines in America and a big one in Australia. "
] |
[
"Lithium is the 25th most abundant element on earth. It's contained in the earths crust at concentrations of about 25mg per kg. i.e. There's ",
" of lithium around, it's just really spread out. We are not ever going to \"run out\" of lithium. What we're having trouble with is sources of highly concentrated, cheap to mine lithium. This is an engineering problem... how do we extract it cheaply? It's in sea water, it's in your front yard, it's everywhere... how do we get it out of all that stuff in a way that's cheap and not environmentally damaging? ",
"https://en.wikipedia.org/wiki/Lithium#Terrestrial"
] |
[
"We can and do use nuclear reactions to produce specific isotopes of specific elements, however it's very expensive, and generally not commercially viable except to produce radioactive nuclides which can't be found in nature (for medical purposes, experiments, etc.)."
] |
[
"How does diamagnetism, paramagnetism, farramagnetism fall into the spectrum? or do they fall into the spectrum?"
] |
[
false
] | null |
[
"What's \"the spectrum\"?"
] |
[
"The electromagnetic spectrum."
] |
[
"I see. They don't really fall into the spectrum - the electromagnetic field created by a magnetic material is defined in terms of its static magnetic moment. So there's no radiation at work here. ",
"Alternatively, there's a sense in which you can interpret static electromagnetic fields as a zero frequency (or infinite wavelength) electromagnetic wave. This is just in the sense that a electromagnetic wave which does not actually oscillate in time is a static field, so zero frequency is a non-oscillating wave."
] |
[
"Hey AskScience, give me your best shot for an intergalactic positioning system."
] |
[
false
] |
The universe is a big place. Say, I want to meet you at a certain moon of a certain planet of a certain star of a certain galaxy at 15.00h tomorrow (local time) and that moon moves thausands of kilometers until then in respect to a eg. a sol centered coordinate system (like this one: ). I would either have to give you coordinates where I will be at that time relative to eg. our sun / the earth, or you would have to have some navigation computer that can be given some coordinates (of even unknown objects) and translates them into "real" coordinates for any certain time. What information has to be contained in such coordinates that can predict where that thing will float around in space for any given time? How do (real world) star charts encode star information? x,y,z relative to us at t-zero, plus some kind of interpolation function where that thing will be later? Wouldn't that be really unwieldy for a moon of a planet of a star in some distant galaxy?
|
[
"Actually, its not that hard to interpolate where planets/the sun are going to be at any given time, since gravity is a pretty easily predicted thing. In fact, we have GPS satellites buzzing in all different orbits at any given time, and yet we do a pretty good job of keeping track of where all of them are.",
"One important thing, though, is that due to relativity, time is different for everyone at different speeds. This would require that we define a \"intergalactic inertial reference frame\" so that everyone could calculate the correct time, similar to how we use time zones today."
] |
[
"an intergalactic inertial reference frame...",
"The CMB would be perfect, no?"
] |
[
"Radial velocity is from redshift, angular is from position snapshots. The mass is less precise, you get it by comparing with better known objects of similar nature, which boils down to using the spectrum."
] |
[
"Why do we have such effective antibiotics but no true equivalent for viruses?"
] |
[
false
] |
Are viruses that much harder to treat or is it just that there has not yet been the "penicillin - moment" equivalent to antivirals? Edit: Wow! Post is an hour old and already has several awesome answers. Thanks everyone! I feel better having learned something today. I'll definitely be visiting more often; lots of interesting posts to read!
|
[
"It's mostly metabolic. Bacteria are living cells with DNA and metabolic enzymes. They can live and divide on their own like other one cell organisms. This gives antibiotics a method of attacking the bacteria- interfere with, or \"poison\", the metabolism and you can kill them.",
"Viruses are packets of DNA that enter the host cells and take over the metabolism- using the host cells to replicate themselves. The can't reproduce on their own. Without a host cell, it is difficult to even call them living organisms. This makes it very difficult to target a virus using antibiotics- interfering with the viral metabolism means interfering with the metabolism of host cells."
] |
[
"Good Question. Killing viruses and bacteria are very different propositions. Viruses are small proteins with a little bit of genetic material (and sometimes enzymes), whereas bacteria are prokaryotic cells. Killing viruses is harder than bacteria because for most viruses, you need to break their capsid (strong protein coat) and denature their DNA to effectively kill them. Bacteria, on the other hand can be killed simply by lysing their cell membrane. Furthermore, bacteria are easily targeted because of a number of surface molecules that remain fairly consistent (e.g. mannose residues, lipopolysaccharides, peptidoglycan, etc.), within and across species, that are distinct from host surface proteins. It is relatively easy to create drugs that specifically target bacterial cells. Most viruses cannot be killed by a drug that would not be toxic to humans, because you would need a strong chaotrope to disrupt their capsid, which would also disrupt host cells. Therefore, most antivirals act by enhancing the host response to the virus since they cannot effectively target the viral molecules themselves. As has also been mentioned in this thread, viruses have a high degree of antigenic variation, which makes generation of antiviral antibodies difficult. "
] |
[
"It's the equivalent of saying \"this\". All posts should contribute meaningfully to the thread. If you find a post enlightening or educational, I would direct you to the lightbulb to the left of each post."
] |
[
"How do you calculate the distance of stars etc from Earth?"
] |
[
false
] | null |
[
"Supernova in general are not the same intensity. A particular type of supernova - Type IA, which are hypothesized only to occur in binary star systems where one star is a white dwarf, produce a consistent light curve which can be used along side of a measured light curve to figure out the distance to the galaxy in which the exploding star resides"
] |
[
"Astronomers are able to calculate the distance from earth to a celestial object through a method called Parallax. Astronomers record the position of an object in the sky on two different nights (it's easiest when the time intervals are half a year apart). Then, since we know the diameter of the orbit the earth takes around the sun, we can pretty much triangulate the position of the celestial object. However this method is only usefull for objects that are within 100 light-years of earth, anything beyond that and the parallax shift is too small to give a reliable distance.",
"http://en.wikipedia.org/wiki/Parallax",
"Diagram of how it works: ",
"http://i.imgur.com/o6DoiYk.gif",
"If an object is beyond 100 light-years, astronomers use Cephid variable stars. These stars vary in brightness over time, which allows astronomers to determine the star's true brightness. By comparing the apparent brightness of the star to its calculated true brightness astronomer are able to calculate the distance from earth to the star.",
"http://en.wikipedia.org/wiki/Cepheid_variable"
] |
[
"I've heard of parallax, but I find it interesting that supernovaes are generally the same intensity."
] |
[
"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!
|
[
"Hare's checklist includes a lot of things that are very common and not so worrisome on their own--this includes stuff like impulsivity, irritability, promiscuity, irresponsibility, and proneness to boredom. Few of us have never bought something we didn't need on a whim, or said something in annoyance or anger. Quite a few normal people would sleep with an attractive stranger given the chance, and I know I've overslept or missed paying a bill before. As for proneness to boredom, well, here we are on Reddit. See pages 2 and 3 for the actual checklist: ",
"http://www.insidetime.org/resources/Misc_Info_Downloads/Hares_PCL-R_Checklist.pdf",
"Callousness/lack of empathy is indeed on the list, but I'd argue society and upbringing have a far stronger role in shaping prejudices, especially racial ones. In-group bias tends to be a factor no matter where you go. ",
"Anyway, for an actual idea of what it might look like, there's a book written by a researcher who found that he had numerous markers associated with psychopathy, yet led a relatively stable life, which he credits to a loving childhood. His words:",
"http://www.smithsonianmag.com/science-nature/the-neuroscientist-who-discovered-he-was-a-psychopath-180947814/#soc8wzydagsQhQrP.99"
] |
[
"There are numerous pathogens that cause upper respiratory infections (URIs). In an otherwise healthy individual, the pathogen is most commonly a virus, and sometimes a bacterium.",
"Some pathogens (but not all) produce characteristic smells. For example, a tell-tale sign of Streptococcus infection (strep throat) is \"rotten egg breath\". Pseudomonas is the most common cause of outer ear infection (otitis externa), and has its own characteristic smell, which has been described as \"sweet\", though I personally wouldn't use that adjective.",
"Some of these odors are from something the pathogen directly produces, while others are products of the immune system attacking the infection."
] |
[
"Hi! I was wondering some things about psychopathy. Robert Hare mentioned in an article that there is a test for it and that everyone exhibits some bit of it. I was hoping you guys can shed light as to what a mild version of psychopathy looks like. Is racism or general prejudice a part of that? "
] |
[
"How far is the horizon from a human point of view?"
] |
[
false
] | null |
[
"When you are on a sphere of radius R and look out to the horizon from a height h, the distance to the horizon is sqrt{2Rh}.",
"For a typical person, this is about 3 miles or 5 km, if you're just standing up on the Earth.",
"This site",
" has an online calculator that tells you how far away the horizon is as a function of height, as well as an explanation of the geometry that determines this distance.",
"Edit: As a couple of people have pointed out below, I neglected to mention that sqrt{2Rh} is an approximation, valid when the height h is much less than the radius R. For a perfect sphere, the exact formula is sqrt{2Rh+h",
"}=sqrt{2Rh(1+h/2R)}. For the Earth, one must also correct because the Earth isn't a perfect sphere."
] |
[
"Well, on a good day, the sun can be seen with the naked eye, and that's over 92 million miles away."
] |
[
"Well, on a good day, the sun can be seen with the naked eye, and that's over 92 million miles away."
] |
[
"Fingerprints: What is the evolutionary reason and do any other mammals have then besides primates?"
] |
[
false
] |
Seriously, what is the point of the pattern on our hands and figerprints. Why did this happen?
|
[
"Fingerprint grip theory rejected",
"BBC article that doesn't fully reject the notion of improving grip for specific surfaces, but seems to reject the \"improved grip\" notion in general.",
"\"Ennos believes that fingerprints may have evolved to grip onto rough surfaces, like tree bark; the ridges may allow our skin to stretch and deform more easily, protecting it from damage; or they may allow water trapped between our finger pads and the surface to drain away and improve surface contact in wet conditions. Other researchers have suggested that the ridges could increase our fingerpads' touch sensitivity.\""
] |
[
"Grip. Without them, we wouldn't be able to grip objects we're holding nearly as well. They're random patterns, which makes them great for identification, but that isn't their primary function."
] |
[
"I didn't say we couldn't grip, I said we couldn't grip as well as we can with them. It's an improvement."
] |
[
"Physiology Blood type question, how can universal recipient receive any type of blood and universal donor can donate to any blood type without the transfused blood cells being attacked and destroyed?"
] |
[
false
] |
Explain why a) the UNIVERSAL DONOR can donate red blood cells to any of the blood types and b) the UNIVERSAL RECIPIENT can receive red blood cells from any of the blood types without the transfused blood cells being attacked and destroyed.
|
[
"Blood type describes the type of antigens (structures used in immune system response) found on a person’s red blood cells. The letters (A, B, & O) refer to sugar-based antigens. There are A antigens and B antigens. We use type O to refer to blood cells with neither A or B antigens. The plus/minus (Rh D) refers to a protein-based antigen. Plus blood types have the Rh D antigen, while minus types do not have it. ",
"The immune system recognizes antigens as either native or foreign to the body. Any blood cells with foreign antigens will be attacked by the immune system; this is why blood types must be taken into account for blood transfusions. Red blood cells without these antigens will be accepted by any immune system. This is why O- is the universal donor; it does not have the A, B, or Rh D antigens, allowing it to avoid detection. In contrast AB+ is the universal recipient; it has all 3 antigens and therefore the immune system will be accepting of any blood type. ",
"As a quick example, we can think about a type A- person (only have the A antigen) donating to our universal donor (O-) and our universal recipient (AB+). The universal recipient has A antigens in its blood already. So the universal recipient’s immune system is accepting of the A- blood. On the other hand, the universal donor does not have A antigens in its blood. So the universal donor’s immune system will attack the type A red blood cells. This will cause a transfusion reaction which can range from mild to life-threatening.",
"Source 1",
", ",
"Source 2"
] |
[
"Note that this all refers to just the packed red blood cells without the blood plasma. If you just put whole blood from a type O person into a type AB person, the red blood cells in the transfused blood won't be attacked but the A and B antibodies in the plasma will attack the native red blood cells.",
"So, to make \"universal blood\" you need type O red blood cells (that don't have surface antigens A, B, or Rh) with type AB plasma (that doesn't have A or B antibodies). Or use saline instead for the plasma.",
"At least that is how I understand it.",
"Ref: \"With regard to transfusions of plasma, this situation is reversed. Type O plasma, containing both anti-A and anti-B antibodies, can only be given to O recipients. The antibodies will attack the antigens on any other blood type. Conversely, AB plasma can be given to patients of any ABO blood group due to not containing any anti-A or anti-B antibodies.\" -",
"wikipedia"
] |
[
"You've gotten a few detailed answers here, but the short is whole blood is no longer transfused regularly. Instead we transfuse blood components (red cells, plasma, platelets, etc). If you transfuse whole blood there will be some degree of reaction unless donor and recipient have the same blood type (and even then there might be if the blood is not crossmatched, as there are hundreds of blood group antigens outside of A, B, and D aka Rh)."
] |
[
"Does running on an inclined treadmill involve significantly more work than running on a flat treadmill?"
] |
[
false
] |
Conventional wisdom says yes. Even calorie burn estimators say you use a lot more energy on an inclined treadmill. But there's no net displacement in opposition to gravity. I guess you could theoretically be slightly elevating your body with every step and then be slightly lowered by the machine on the back-step, but it seems like the mechanics of running are such that you're mostly only beginning to support your body weight against falling when your foot is out in front of you with the majority of the propulsion occurring only after your front foot is nearly under you. Plus it just seems like your body would kind of naturally move differently when not required to actually combat gravity by climbing from a kinesthetics standpoint. I guess this would ultimately depend on an individual's gait, which can be pretty idiosyncratic. Is running/walking consistent enough of a movement to draw conclusions based on physics? If not has there been any statistical study of this question? (Couldn't figure out how to add a second flair.) Are all of those treadmills that say you're burning like 50% more calories on the incline mode full of shit and just using numbers based on actual uphill running? Or is there a legitimate scientific basis for those kinds of claims?
|
[
"gravity isn't the only force you have to work against, there's also the force stopping gravity from plunging you straight through the treadmill, into the ground, and down towards the core of the earth. This is called the \"normal force\" - always pushes in a direction \"normal to\" (ie, at right angles to) the surface.",
"Place a ball on flat ground - gravity pulls it down, and the ground pushes it up. The ball doesn't move.",
"Place the ball on slopy ground - the ground always pushes away at right angles to the surface - so now the ground ",
" counteracts gravity, but since it's pushing at an angle, the ball has some acceleration down the hill. ",
"Gravity + the normal force = a net force downhill.",
"So, on a flat treadmill, you aren't fighting gravity, the normal force does that. You just have to run at constant speed, moving your arms and legs and fighting friction between you and the surface. ",
"On an inclined treadmill, gravity + the normal force combine to add an ",
" force pulling you backwards. You have to run to fight that too, so you burn more calories. "
] |
[
"I'm not sure what you are confused about, no offense. It is demonstrably true that running up hill requires more work than running on a flat surface. Why would an inclined treadmill be any different?",
"Or is the key to your question in the use of the word \"significantly\"? As in, can a treadmill incline enough to simulate a steep hill? Is that what you are asking?"
] |
[
"Yeah, but balls are fixed (more or less) rigid structures. It doesn't really take any energy to keep a ball from collapsing on a flat surface, but it also can't alter its shape and center of gravity to keep from rolling on a slope. Humans do have to use energy to maintain muscle flexion to stand upright, but they can also alter the shape and position of their point of contact with the ground relative to their center of mass such that standing on a slope does not require significantly more energy than standing on a flat surface.",
"Think instead of a robot that moves using a single thick wheel at its base and maintains an upright position by balancing itself using gyroscopes. It seems to me that this robot would not expend more energy on an inclined treadmill than it would on a flat one.",
"I see what you're saying about the normal force adding a backward component, but it seems like altering your stride to make your center of mass farther forward relative the position of contact between you feet and the treadmill would shift all that extra work to the friction between you shoes and the treadmill."
] |
[
"straw in a glass of water"
] |
[
false
] |
so me and my friends couldn't agree on why water stays in a straw when it's in a cup of water and if you cover the top and lift the straw, the water stays in the straw but falls out when you let go of the finger at the top of the straw. so I just thought I'd ask reddit to see what the correct explanation is? since I've seen several different explanations on the internet and from person to person. edit: i guess i'm having trouble figuring out the forces at work here, the water stays in the straw means there's an upward force counter acting gravity right? and that force is gone once i let go of my finger? what is this upward force? i kinda get surface tension but how come gravity is not able to overcome surface tension if the finger seals the straw but can when i let go of the finger?
|
[
"No, when it is that big the surface tension is not strong enough to hold the water together."
] |
[
"Pressure and surface tension.",
"The water can't fall out all together as a whole because air has to take it's place, and air can't get into the straw while the top is held.",
"The water won't fall apart and fall out drop by drop because there is surface tension holding it together."
] |
[
"Would it work with a giant straw? Say 50ft long with a 5ft (circumference) opening?"
] |
[
"Why is raw chicken considered more dangerous than other raw meats?"
] |
[
false
] |
Or maybe it's just poultry in general but why is it generally forbidden to eat chicken that is in any way raw? Raw fish is eaten all the time and its acceptable to eat meat that is somewhat raw in the middle. Is there just a stigma to chicken meat that has made it seem more dangerous or are chickens (and their eggs) simply more receptable to harmful bacteria?
|
[
"This is true for the most part; Chicken carcasses are disemboweled by a high speed automated machine which often rips open the intestines of the poultry, releasing fecal matter into the birds' body cavities.",
"Furthermore, in post-processing the chickens are often mass-chilled in a huge bath of chlorinated water, raw chickens, and their residual shit-matter. ",
"Source: I work as a butcher."
] |
[
"This is true for the most part; Chicken carcasses are disemboweled by a high speed automated machine which often rips open the intestines of the poultry, releasing fecal matter into the birds' body cavities.",
"Furthermore, in post-processing the chickens are often mass-chilled in a huge bath of chlorinated water, raw chickens, and their residual shit-matter. ",
"Source: I work as a butcher."
] |
[
"that's...disgusting"
] |
[
"If the mass and size of the universe are plugged into the schwartzchild radius, it’s a black hole. Why is this brushed off as a coincidence?"
] |
[
false
] | null |
[
"It's not a coincidence, it actually means that our universe is flat! If you take the ",
"Friedmann equations",
" and compare the Schwarzchild radius for the mass contained within the Hubble length to the Hubble length, you will find that they are equal for a flat universe. This doesn't mean that the universe is a black hole though.",
"Sean Carroll provides some excellent insight ",
"here",
", and Viktor Toth gives a breakdown of the relation ",
"here"
] |
[
"It doesn't. The Schwartzchild radius based on R=2GM/c",
" is 2x10",
" meters while the radius of the observable universe is 4.4x10",
" meters.",
"Also the Schwartzchild radius has a restriction of non-rotation which I don't know/can't speak to if that is present.",
"Edit: The numbers I found to do the math may be off."
] |
[
"That's because the definition of the mass contained within a hubble sphere is based on the critical density i.e. the density required to halt expansion.",
"Any higher density should result in stuff being pulled back together. ",
"Some searching shows that our universe is approximately the critical density meaning at infinite time expansion should halt."
] |
[
"How can the universe be 93 billion light years across and only 13.7 billion years old?"
] |
[
false
] | null |
[
"Please see the FAQ"
] |
[
"It's the first one under the Astronomy section."
] |
[
"It's the first one under the Astronomy section."
] |
[
"Has there ever been a moment in time where the human population on Earth was lower than previously? Is the birthrate enough to outnumber the deaths of wars and pandemics?"
] |
[
false
] |
Further, does this fluctuation have any adverse effects? Given the finite size of this planet, would there be an ideal population size? I'm sure there's plenty of room with how we are currently building upward and the eventuality of humans developing outward into the ocean. Before those next advancements, I'm curious. These questions stem from recently reading discussions involving global fertility rates, global temperature increases, the continued spread of disease, and an alleged increase in deaths resulting from a natural disaster. Thanks in advance! Note: Repeat submission due to not flairing the post, as per the rules. Anthropology seems to fit, and I'm curious what folks who work in that field have to say in response to these questions.
|
[
"Both World Wars led to significant decreases in total population. ",
"Do you have a source for this? AFAICT, there was no period during the 20th century when total world population was in decline. Yes, the growth rate was significantly reduced during the world wars and the Spanish Flu pandemic, but did not drop below zero. ",
"It appears that the most recent extended period of world population decline may have been between 1606 and 1647 (see ",
"https://ourworldindata.org/world-population-growth#all-charts-preview",
"), possibly the result of ",
"overlapping regional epidemics of bubonic plague",
"."
] |
[
"It's believed that, about 70,000 years ago, the ",
"Toba volcanic eruption",
" caused a dramatic climate disruption that wiped out much of the human population, reducing the total number to 3000 to 10,000, producing a genetic bottleneck."
] |
[
"Both World Wars led to significant decreases in total population.",
"No, they led to decreases in worldwide growth rate but not a decrease in population."
] |
[
"In a really long line, if the first person moves forward, what's the average time until the last person moves. (That is, what's the speed of wave propagation in queues)?"
] |
[
false
] |
I was waiting in a long line (queue) at a theme park yesterday and started wondering: how long does it take from the time that the first person moves until the opening gets to me and I can step forward? That is, what's the speed of wave propagation in queues? I'm picturing waves of people moving forward though the line, and it's kind of a neat image. I've tried Google searching a bunch of related phrases but haven't turned anything up. Surely someone has measured this. Although I can't really think of any practical implications. Any ideas?
|
[
"Slower if the people have luggage. But it doesn't always propagate as neat wave either. I don't think you can assign a meaningful single number to it."
] |
[
"If it were a line of heavy railway carriages connected by springs, then it would be a perfect wave.",
"Humans of course have personalities and make choices, but you can make an average model of how they will react.",
"Perhaps ",
"https://en.wikipedia.org/wiki/Crowd_simulation#Crowd_dynamics",
"would give you an idea at least of how to get an answer. There is software to model crowds, so presumably it could model queues too."
] |
[
"There are too many variables. Cell phones, number and types of luggage or number of items each add to the complexity of moving the queue as well as transaction times.",
"Realistically, we've all been stuck in lines that barely move while adjacent lines sped along. The trend in efficiency seems to be a single line splitting to several tellers. I see this in DMV, and self automated check out kiosks in mega stores. December and early January would be good times to sample the various length of time under different schemes."
] |
[
"How does general air traffic deal with orbital space launches?"
] |
[
false
] |
Is this a predetermined window around launch areas, or is it easy enough for general air traffic to pick up on any orbital bound satellites or spacecraft so that it may be avoided?
|
[
"Generally speaking, any time there is a rocket launch occurring there will be a temporary flight restriction (TFR) places within 20-50 nautical miles of the launch site prohibiting air traffic from entering. Those TFRs are published by the FAA at all sources that a pilot should be expected to check before embarking upon a flight (Flight Service Briefings, etc).",
"Looking at ",
"the Orlando TAC chart",
" you can see the large blue shaded area on the right side over Kennedy Space Center. There are a number of other blue hashing makings to indicate other restricted areas which may or not be active. Whether or not these areas are active are, again, always expected to be part of a standard preflight briefing.",
"The FAA takes the violation of these areas very seriously. Pilots should expect a suspension of certificate privileges, if not also a fine, for doing so without authorization from the controlling agency.",
"When the shuttle was going to launch, a TFR would be placed around NASA KSC which would extend to 40 NM No-Fly zone radius with an additional 10 NM \"Air Defense Identification Zone\" where all aircraft were operating under radar contact and either a defensive VFR or IFR flight plan to allow Orlando International (KMCO) to avoid having to shut down.",
"Source: I worked as a flight instructor based in Vero Beach (KVRB, just outside of the restricted zone) for half a decade. Actually saw a student violate the NASA TFR during a check ride. Long story, but it wasn't really his fault so they let him off with a suspension."
] |
[
"Prohibited airspace is temporarily declared around the launch site by the FAA.",
"This information is made known to pilots by notices called NOTAMs (Notices To Airmen)."
] |
[
"That's pretty fascinating. Thank you."
] |
[
"How radio (and wifi) waves don't interfere with each other and send the same information to every location?"
] |
[
false
] |
Picture: Mainly I don't really understand how radio waves work. I presented several question here, in order for you to help me understand, but the big question is " " Let's start with location - PC1 (the black one) receives data from the router (the red one). This can also apply to FM radio. If I move my laptop, I still receive the same data, so there are waves of information everywhere - but each second it transmits different data, meaning that near the transmitting station, there is a different data that the one that had to travel all the way to the other end of the room/house/street. So why moving the receiver doesn't disrupt the signal? Now look at the blue waves - they hit the wall and get back to the receiver ( waves do get projected from walls right? Well I don't know about wifi, but there are different types of waves right? ) so the receiver gets at least 2 different signal at any given time. Shouldn't it also disrupt the signal? If we talk about a wifi for a second - in every part of the room there are different set of "1"s and "0"s, and it received "1"s and "0"s simultaneously from all the wall projections. Additional info: I was radio specialist in the army in my country, was AP physics in high school and currently doing computer science major. So I do now understand that specific topic, but I do have some background if you don't want to ELI5. : Well this is a hard question to write without a picture so I did some horrible job with paint ( I don't have Photoshop on the pc ).
|
[
"Wow great question. ",
"First, off you are correct, signals do bounce off the room and you receiver is obtaining multiple copies of the signal. And because the wavelengths are so small (WIFI is less than 3 cm), a small very fast change could absolutely destroy your packet. ",
"The solution is primarily ",
"channel equalization",
"). Indeed, lets say we send x(t), and we receive a x(t) + b x(t-q) + c x(t-r) + n, where n is a noise term. We can view the received signal as the signal x(t), convoluted with the \"channel,\" in this case aδ(t) + bδ(t-q) + cδ(t-r) (and an additive noise term). This channel has a certain frequency response, and in essence channel equalization flattens out this curve. This, in essence, makes the channel appear like aδ(t). "
] |
[
"So why moving the receiver doesn't disrupt the signal?",
"The speed with which you move the computer or receiver is small compared to the speed of light (how fast radio signals travel) so it doesn't noticeably affect the timing of the arrival data.",
"Now look at the blue waves - they hit the wall and get back to the receiver ... so the receiver gets at least 2 different signal at any given time. Shouldn't it also disrupt the signal?",
"Concrete walls don't reflect low-frequency radiation (radio, wifi) well enough to create significant interference, and there is a lot of hardware and software rejection built into wifi cards to filter noise when digitizing noisy frequency. However, if you do have a lot of wifi networks in similar frequencies, you will notice some lag on your network as your computer sometimes rejects data packets due to the noisy environment.",
"If we talk about a wifi for a second - in every part of the room there are different set of \"1\"s and \"0\"s, and it received \"1\"s and \"0\"s simultaneously from all the wall projections.",
"This goes back to the two above points: the timescale it takes to move the device around the room is far longer than the timescale of the data transmission. Also, it's ",
"a bit more complicated",
" than what you seem to be describing, which is amplitude modulated data transmission from wifi radio waves, but the same principle applies. Also, as above, you won't get much reflection from walls unless you happen to live in a house with metal walls."
] |
[
"Wow - this and the other two replies made so much sense. Thank you very much. Now I understand that it's actually a negligible problem, so my reasoning was correct, just not up to scale. And that there is also math included that helps figure out the real signal without the noise.",
"Thank you for your answer."
] |
[
"Can electromagnetic forces also cause spacetime frame dragging? Like what one would observe a few miles from a magnetar?"
] |
[
false
] |
Could extremely strong rotating magnetic fields cause spacetime distortions or frame dragging?
|
[
"Yes, electromagnetic fields deform spacetime. Everything that has energy density (and/or momentum density or momentum flux) contributes to curving spacetime. This is quantified by the stress-energy tensor T, which sources the curvature in Einstein's field equation",
"[; G_{ab} = 8\\pi G_N T_{ab}. ;]\n",
"where G is the Einstein curvature tensor (which is the trace-reverse of the Ricci curvature tensor), and G_N is Newton's gravitational constant (and I have set c=1).",
"Now electromagnetic fields have a stress-energy tensor",
"[; T_{ab} = F_{ac} F^c_{\\ b} - \\frac{1}{4} g_{ab} F_{cd} F^{cd} ;]\n",
"where F is the electromagnetic field strength tensor.",
"It turns out that gravitomagnetism is sourced by the time-space (rather than space-space or time-time, i.e. the 0i rather than 00 or ij) components of the stress tensor. For the electromagnetic field, this corresponds to an electromagnetic ",
", not just a static magnetic field."
] |
[
"I wish I could understand what I just read"
] |
[
"Equations"
] |
[
"Can the Large Hadron Collider be used to make new elements?"
] |
[
false
] |
I know that the GSI Helmholtz Centre for Heavy Ion Research uses an accelerator to produce these elements, but I doubt there is any accelerator out there that is bigger than the LHC and would be able to smash more elements together.
|
[
"Hi Apollo, in it's current configuration, the answer is yes and no. I'll explain the no first:",
"No, because the LHC operates energies that are too keep nuclei intact. The normal way to create heavy elements is to slam two lighter elements together. If you were going to take the 7TeV proton beam or the 3.5TeV lead ion beam and smash it into a target, the target would be destroyed. Just take a look at the binding energies of atoms compared to these beam energies: ",
"Millions of eV versus ",
" of eV",
".",
"Yes, however, because there are lots of less energetic interactions that take place as the debris from collisions hit various parts of the detector structure. In the 6 year on-and-off run history of the LHC, it's likely that some of these interactions have resulted in new elements. There's just no way to find them!"
] |
[
"So what your saying is that the LHC is just too powerful? "
] |
[
"Yes. When the ions in breeder reactors collide, they act similar to balls of putty hitting each other and merging. There are some simulations you can look up. ",
"In the LHC, they act more like water droplets hitting one another. There is so much energy that instead of the nuclei fusing normally, the individual particles react with each other and convert to a variety of non-nucleons, spraying everywhere. "
] |
[
"Does the weight of all the paint added to an aircraft over the course of its life significantly change its max payload and/or fuel burn rate?"
] |
[
false
] | null |
[
"Yes, it does. For that reason, you don't just paint over an old paint job on an airplane. You stip it down to the metal, then prime and paint again.",
"I always thought it was pretty smart of American Airlines to go with the \"bare aluminum\" look for their planes - think of all the poundage they saved!"
] |
[
"A quick search on it gave me \"up to 1100 pounds on a 747\" on some airline forum. ",
"The same forum also said that AA does not in fact save any money. Yes they get better mileage, but they spend more on corrosive treatment for their planes. In the end, I would call it same same. "
] |
[
"Did it give any numbers or say if it was relative to current fuel cost? With the price of oil up where it is these days, I would estimate that the better mileage is worth the cost."
] |
[
"What kind of bacteria would grow in the glass of water I leave by my bed overnight?"
] |
[
false
] |
Is it a harmful amount by the time I wake up and need a sip of water. Assume average temperature is 10 degrees Celsius, in the range for bacteria growth.
|
[
"The use of chlorine and chloramine in drinking water render it free of pathogens at the point of delivery (your tap); other areas use ozone, which does not have as strong a residual effect. These products are added in order to get rid of potentially pathogenic organisms; much of the rest of the world does not enjoy assured freedom from nasties such as cholera, dysentery, giardia, typhoid fever, hepatitis A, leptospirosis, and so forth.",
"However, these organisms do not spring from empty space; they come from biological sources that contaminate your water. These are unlikely to be present in your room, barring any afflicted housemates coughing in your glass of water.",
"So, while spores and the occasional live organism might find their way into your drinking glass, these are ubiquitous and you inhale them with every breath anyway. That they have found a glass of water to land in is hardly exceptional; there is little else in there to inspire spore germination and subsequent growth. Plain tap water is pretty good at keeping organisms from growing, unlike (for example) a glass of lightly sugared water with some chemical fertilizers added.",
"So- between residual disinfectant levels, and that there are no nutrients to inspire bacterial or fungal \"blooms,\" your tap water on the bedstand is safe."
] |
[
"Take two bottles: just open one and do with second one as suggested above.",
"And compare."
] |
[
"Backwash bacteria from your mouth.",
"Don't believe me? Got any partially consumed bottles of water? If not, drink half a bottle as you normally would. Sit it in your hot car for a week. Open the bottle and take a whiff... GAG."
] |
[
"What is the universe expanding into?"
] |
[
false
] | null |
[
"If I open in browser on my phone in new version I still see the FAQ in the sidebar and can access it. I'm using the rif app and it works fine there as well... weird... would you mind please sending a modmail describing your setup (mobile, new version, etc.) and what it shows when you try to access FAQ. Someone will look into it. Thank you! ",
"Hope the post above answered your question"
] |
[
"Please see the FAQ"
] |
[
"The guidelines and FAQs pages say they are no longer being updated and are blank."
] |
[
"How does potassium get from food to a cell?"
] |
[
false
] |
What happens once food enters the intestines, what process recognizes potassium? How does the potassium move from the intestines to a cell in your finger that needs it?
|
[
"There are quite a few points I wish to supplement / correct.",
"I believe the Hydrochloric acid helps to 'ionize' the potassium (K+) and other ions from however they were stored in the food. For example, NaCl (table salt) would be ionized to Na+ and Cl-, with the help of this highly acidic environment.",
"Potassium is very soluble in water and does not require acidic environment to be ionized, as well as for sodium. However, as most potassium are stored within cells in the food, you do require a harsh condition to break cells apart and release the potassium.",
"little molecules that were once food get absorbed through receptors and channels on the surface of the small intestine gut cells",
"Potassium is absorbed throughout the entire alimentary tract, including those above small intestine.",
"The small intestine has almost zero bacteria",
"The entire alimentary tract contains bacteria. Different species colonize different parts of the tract, including small intestine.",
"potassium can then be absorbed by your finger cells through a 'potassium channel' or a 'monovalent cation channel'",
"I'd say they get into cell mostly through the Na/K ATPase. They move out of cell via potassium channel",
"open and snap shut depending on things like the voltage across the cell",
"Like I said, potassium gets into cell via Na/K ATPase, which is constantly acting, and are not regulated by voltage across cell.",
"K+ levels are also changed by a few hormones in the body like adrenaline and ADH",
"ADH does not directly regulate levels of potassium. You might be thinking of aldosterone. For additional information, potassium level is also affected by insulin.",
"I guess your grad work no longer involves physiology, or at least not GI?"
] |
[
"There are quite a few points I wish to supplement / correct.",
"I believe the Hydrochloric acid helps to 'ionize' the potassium (K+) and other ions from however they were stored in the food. For example, NaCl (table salt) would be ionized to Na+ and Cl-, with the help of this highly acidic environment.",
"Potassium is very soluble in water and does not require acidic environment to be ionized, as well as for sodium. However, as most potassium are stored within cells in the food, you do require a harsh condition to break cells apart and release the potassium.",
"little molecules that were once food get absorbed through receptors and channels on the surface of the small intestine gut cells",
"Potassium is absorbed throughout the entire alimentary tract, including those above small intestine.",
"The small intestine has almost zero bacteria",
"The entire alimentary tract contains bacteria. Different species colonize different parts of the tract, including small intestine.",
"potassium can then be absorbed by your finger cells through a 'potassium channel' or a 'monovalent cation channel'",
"I'd say they get into cell mostly through the Na/K ATPase. They move out of cell via potassium channel",
"open and snap shut depending on things like the voltage across the cell",
"Like I said, potassium gets into cell via Na/K ATPase, which is constantly acting, and are not regulated by voltage across cell.",
"K+ levels are also changed by a few hormones in the body like adrenaline and ADH",
"ADH does not directly regulate levels of potassium. You might be thinking of aldosterone. For additional information, potassium level is also affected by insulin.",
"I guess your grad work no longer involves physiology, or at least not GI?"
] |
[
"Thank you! That was great! "
] |
[
"What do atoms look like?"
] |
[
false
] |
[deleted]
|
[
"Their shapes are difficult to calculate and even more difficult to visualize. ",
"Here",
" is a nice image of several states of an electron in the simplest kind of atom (Hydrogen, with a single proton and a single electron). The state of the electron is like a 3D dimensional \"cloud\", with the density in a spot essentially representing the probability of the electron spending time there. It is difficult to show density visually, so this picture shows the \"level curves\" of that density, in the same way that topographic maps of the earth show level curves of elevation. ",
"Although these shapes are beautiful and fascinating, most calculations in physics and chemistry are more focused on things we can directly measure, like energies of photons that are emitted when the electrons transition between these states. "
] |
[
"All of those are \"hydrogen-like\" configurations where there is only one electron. It works for any size nucleus, but when there are more electrons they start to interact with each other and it gets very complicated."
] |
[
"http://blog.everydayscientist.com/wp-content/uploads/pentacene-AFM.png",
"On the bottom left is an atomic force microscope image of a pentacene molecule. You can see that the atoms are arranged similarly to the chemical diagram. It's not actually a picture of atoms though, it's a map of how much attraction the microscope tip felt. Similarly, this is an image of atoms being assembled by a scanning tunnelling microscope, which is like an atomic force microscope that shoots electrons. You're not looking at atoms, it's more like the electrical resistivity at a given spot. ",
"http://education.mrsec.wisc.edu/background/STM/images/quantum-corral-1.jpg"
] |
[
"What is used as nutrition to cultivated cell meat? And how much antibiotics is used?"
] |
[
false
] |
Where does the nutrition to the cells come from. And can you avoid using antibiotics completely
|
[
"You can avoid antibiotics, but most tissue culture uses some. It is really difficult to do industry-sized cell culture without antibiotics.",
"Also, they use fetal bovine serum as a nutrient, which is essentially baby cow blood, so it isn’t vegan and isn’t very sustainable at this point. Maybe someday they can avoid this."
] |
[
"To elaborate, fetal bovine serum (FBS) is added to the medium primarily due to its concentration of growth factors (encourages growth) and globular proteins (amino acid source). It is typically only a small fraction of the volume of most media. ",
"Most of the culture's metabolic need is provided by the glucose (sugar) and derivatives (pyruvate) that make up the bulk of the media. ",
""
] |
[
"Thank you"
] |
[
"If you are traveling at speeds close to the speed of light, would you disrupt the motion of things nearby?"
] |
[
false
] |
If you are traveling through space at a speed very close to the speed of light, would your mass increase to a such a level that it would begin to disrupt the motion of other bodies nearby? Like, if you whizzed through our solar system is there the potential to throw the orbits of planets off kilter?
|
[
"Rather, when something going really fast crashes into something else, it has a momentum that is greater than just the product of its mass and velocity. This new ratio of momentum to velocity is what was called \"relativistic mass.\""
] |
[
"This is a very widespread misconception. In actuality, there is no such thing as relativistic mass. So the answer to your question is a simple, unadorned \"no.\"",
"The mass is invariant between frameworks, but that does ",
" mean that the gravitational force is independent of velocity. You then have to use general relativity, which is very complicated, but the result ",
" depends on velocity. You can't just substitute the invariant mass into Newton's formula for gravity."
] |
[
"This is a very widespread misconception. In actuality, there is no such thing as relativistic mass. So the answer to your question is a simple, unadorned \"no.\""
] |
[
"Since our stomach acid is a strong acid, when we drink water does it react with that acid and form H3O+ in our stomachs?"
] |
[
false
] | null |
[
"The stomach acid is already a watery solution and dissociated. The H3O+ is already there."
] |
[
"What is stomach acid actually?",
"Hydrogen-Chlorine(HCl)?"
] |
[
"Yeah, HCl at a pH between 1 and 3."
] |
[
"Could you dry wet clothes very quickly by generating a vacuum around them?"
] |
[
false
] |
And if you built a machine that could do this, would it be more energy efficient than a tumble dryer?
|
[
"You can, but you will still need to add additional heat to dry them quickly. As the water boils at the lower pressure, heat is removed from the clothes and remaining water. Since the heat of vaporisation of water is much higher than the heat of fusion, the remaining water will quickly freeze in the clothes. Additional heat is required to retain the water in liquid state so that it can continue to evaporate/boil.",
"I had thought about making one of these using a magnetron (from a microwave) as a heat source and vacuum pump from a vacuum bagger!",
" I actually tried this a few years ago with a vacuum sealer (",
"similar to this one",
") and some wet strips of cloth. I am an \"I've run out of clothes, time to wash\" person and thought a rapid dryer would be handy! Still haven't tried it with the magnetron yet though... ",
"AskScienceFair",
" anyone?"
] |
[
"water boils at low pressure."
] |
[
"Yes you can, and I suspect that it would not. It takes a lot of energy to draw a vacuum."
] |
[
"Is it possible, under special circumstances, that noble gases could be forced into molecules?"
] |
[
false
] |
Basic chemistry courses always state that noble gases don't create molecules with other atoms, but I know in higher levels of chemistry there is a little wiggle room to the rules. An example I always refer back to is that pH can be outside of the 0-14 scale, it's just not told to basic chemistry students.
|
[
"Yes, it is possible. It's hard but not impossible to get a noble gas to make a bond. Generally you accomplish this by bonding with an element like Flourine.",
"An example is Argon Flourohydride, which decomposes at -256 C (i.e. 17.1 K). See its wiki page ",
"here",
". Also notable is the stable but incredibly reactive Hydrohelium (HeH",
") cation, which is the strongest known Brønsted acid. "
] |
[
"Yes, xenon in particular has a number of compounds. XeF2, XeF4, and XeF6 are all possible and (relatively) stable. The basic hybrid orbital theory (\"octet rule\" and such) that is taught in introductory chemistry is not sufficient to explain these compounds, but suffice to say that when you're taught the ",
" mechanics behind bond formation (molecular orbital theory, if you're curious) these things aren't outside the rules at all. "
] |
[
"As the others have said, noble gases can form a number of compounds, which are usually pretty reactive. As a rule of thumb, the heavier the noble gas, the more compounds it forms. While He, Ne and Ar extremely reactive molecules, Kr and Xe form a number of relatively stable compounds. ",
"KrF",
" for example is stable up to about 0 °C for a few days and is considered to be an even stronger oxidizing agent than elemental fluorine.",
"The ionization potentiol of Xe is so low that it forms not just fluorine compounds (XeF",
", XeF",
", XeF",
"), but even oxides (XeO",
", XeO",
"). There are even funkier molecules, like xenates (salts of xenic acid H",
"XeO",
") and perxenates ((salts of perxenic acid H",
"XeO",
") and my personal favorite, the ",
"tetraxenonogold(II)",
"-ion."
] |
[
"Why do plants need mitochondria?"
] |
[
false
] |
If plants can produce ATP in chloroplasts, why do plants have mitochondria?
|
[
"They produce ATP in chloroplasts, but they ",
" use aerobic respiration! Excess oxygen is released as a waste product, but they have no trouble using some of it again in the mitochondria."
] |
[
"Also think about seeds, when they germinate they are not yet photosynthesizing and are still able to perform complex molecular tasks in order to establish. Another example would be the pollen tube, it needs to grow through the style to the ovary without photosynthesis."
] |
[
"I'm glad to hear you are enjoying your plant classes, plants are truly wonderous. I highly recommend you learning about fungi as well, they rock :D"
] |
[
"Is advertising effective on people with disorders such as aspergers?"
] |
[
false
] | null |
[
"Depends upon which advertising strategy they're using, the severity of the specific deficits of the person, and what method was used (internet banner ad, mail, TV commercial, etc.). What specifically did you have in mind? We might be able to link it to a cognitive strength/weakness and help explain why it might or might not work."
] |
[
"The kind of ads i had in mind were things like beer commercials which show people having a good time or doing something funny followed by the product name."
] |
[
"Well, anything that's going to be a 'bandwagon' approach isn't going to work subconsciously, most likely because of a lack of social identification with the people involved. But I'm not an Aspie and I can tell you that those types of commercials don't work with me, either. :)",
"Now, would they remember the product name? Probably. Would they go buy it? Probably not."
] |
[
"How do we know for sure the Mariana Trench is the deepest point in the ocean?"
] |
[
false
] | null |
[
"We have a low resolution survey of the entire ocean floor. That constrains pretty well what the overall topography is like, and certainly the very deep sections are incredibly restricted in location - they're all related to subduction trenches. Whether the Challenger Deep is the very deepest section or not is a bit of an open question, as we haven't got high resolution bathymetry for all of the deep portions. There are few places that could challenge it, however."
] |
[
"Like where?!"
] |
[
"I don't know Pacific bathymetry well enough to say I m afraid. There may not even be any plausible candidates. "
] |
[
"Question about Curiosity mission and space probes"
] |
[
false
] |
While I'm absolutely thrilled at the successful launch of such a high profile mission, I can't help but have some doubts about its ultimate goals. Doubtless some great science will be done and new discoveries will be made. However if we're going to be looking for evidence of life wouldn't the resources be better spent on sending a mission to Titan, Europa or Enceladus? Are there any practical reasons why we haven't sent probes to these moons? Do we simply keep sending probes to Mars because of proximity and technological limitations?
|
[
"Well, there's a mission planned for Europa in 2020 and a probe landed on Titan in 2005. It's not like 100% of planetary exploration is devoted to Mars."
] |
[
"There are some daunting technical challenges with reaching the liquid part of the ice moons. I'd like to see a 2 component mission with an impactor followed by a autonomous ROV-type sub, coupled with an orbital telecom relay. A bit like the way we've handled the Deep Impact program on Tempel 1. But you'd have to scale things up considerably to have an impact which would break through the ice crust of Enceladus of Europa. But drilling is not going to cut it, and its in the liquid phase that you want to get.",
"Otherwise, while no doubt interesting, well just be able to do surface observation of the ice (which should be pretty barren, although some organic material might be present in trace amounts), and perhaps radar imagery through the crust. Fun and interesting for sure, but not the answer to the questions on top of everybody's mind: are there critters swimming downs there?"
] |
[
"Europa in 2020 ",
"Ganymede too!"
] |
[
"Can someone explain chalcophiles to me?"
] |
[
false
] |
I completely understand how certain elements will preferentially form ionic bonds and enter the rock phase as lithophiles. I completely understand how other elements will preferentially form metallic bonds and enter the iron core as siderophiles. The distinction between ionic and metallic bonding is clear enough. But what is it about sulfur? Why do certain elements “love” sulfur but not oxide or silicate anions? What characteristic of the sulfide bond makes metal-sulfides behave different from ordinary ionic compounds? Does it have to do with sulfide being a larger, “softer” (more polarizable) anion than oxide?
|
[
"Yes, it's basically polarizability. See: ",
"https://en.wikipedia.org/wiki/HSAB_theory"
] |
[
"Thanks."
] |
[
"Thanks."
] |
[
"If a human settlement is established on Mars, would the lower gravity make pregnancy/childhood difficult or impossible?"
] |
[
false
] |
Once a human has developed to a certain point on Earth, then I could see them going to Mars and surviving, but until that point it seems that lower gravity could adversely effect embryological development and/or a newborn's development. Besides just muscular/skeletal development, are there other vital biological processes or structures that are dependent on a certain amount of gravity for proper functioning?
|
[
"There's a good ",
"review",
" of pregnancy in microgravity. Pregnant rats have produced relatively normal offspring in microgravity, though with reduced weight and bone calcification."
] |
[
"Mars has gravity rather than microgravity, it is just significantly less than here on earth. The studied aspects of animal fertility and birth so far suggest that those cycles on mars will be less risky than in space however there will still be moderate to significant adaptions in physiology to martian gravity. In other words, if you are born on mars and come to earth, you're gonna have a bad time."
] |
[
"Gravity actually has a large influence on our physiology. Astronauts who have been in a gravity-less state for a few months have to \"rehabilitate\" for a significant period upon return. Our bodies are very strong at adapting, and no (or lesser) gravity means you're using muscles a lot less than here on earth, making you very weak, which in term has a lot of other consequences. "
] |
[
"[Biology] How do animals, both mammal and non-mammal handle eating active, living prey?"
] |
[
false
] |
As a human, I can’t imagine eating an entire living organism whole, and NOT experience severe indigestion. What with it still alive, for a time, in my stomach wiggling about. So how do animals tolerate this?
|
[
"I amby far not a professional so I will delete this answer when somebody with more knowledge will answer but nearly no animal eat active living prey.\nThe only animals I can think of who eat a whole animals at once are snake, some birds and fish. (If you have any other example I'm interested).\nSnakes usually kill them first by chocking or poisoning the prey first. They also have powerful muscles who are able to destroy the body of the prey after ingestion.\nBirds who eat mice or any other animal without cutting them usually kill them with their beak or claw, targeting the neck and destroying the nervous system in the spine, which would make the prey unable to move even if alive.\nFor fish... I would say that usually they eat prey who are so small compared to them that there is no danger at all, it would be like human eating raw octopus: once it's in the stomach, the prey have no chance of fighting or hurting the predator's body.\nHope it helps, even a little !"
] |
[
"Baby eels in Japan, baby octopus in Korea, maggots from casu marzu in Sardinia, grubs, ants, shrimp in China, oysters, sea urchin ..."
] |
[
"Tbf I think humans are the species that eats most other species alive.",
"What makes you think that? I cannot imagine having eaten anything alive - besides accidentally swallowing a tiny fly."
] |
[
"Is this Russian methane release as ominous as it sounds?"
] |
[
false
] |
[deleted]
|
[
"It's Arctic methane release. Your title made it sound like the Russians are releasing it."
] |
[
"There is already ",
"a discussion",
" on this on ",
"/r/askscience",
" ",
"I think that ",
"things_break's reply to limitnz",
" does a good job with this."
] |
[
"FWIW, TIL that there are estimated to be ",
"1.3 billion cattle in the world",
", so a few billion tones is a few annual-world-cow-outputs (or, ",
", as we like to call them around here)."
] |
[
"Is it possible to achieve a temperature higher than the temperature of the surface of the sun using a system of lenses only using the energy of the sun?"
] |
[
false
] |
Every sun ray has an energy of E=v*h. By focusing all the rays emitted by the sun to a single point on earth, would it be possible to achieve a temperature of over 6000K?
|
[
"No you cannot make something hotter than the surface of the sun by focussing sunlight onto something.",
"What you do when you focus sunlight is basically increasing the apparent object size of the sun for the object being irradiated. (This is called the ",
"brightness theorem",
")",
"In the extreme case, you could make it so that the object in question \"looks\" at the surface of the sun in any direction it is looking.",
"The two objects (sun and target) would then move toward a thermal equilibrium until they reach the same temperature. Effectively (assuming the target is small) this means the target reaches 6000K and the temperature of the sun remains as it is.",
"Simple thermodynamics.",
"edit added reference to brightness theorem",
"edit2: To make it clear, you cannot focus all the energy radiated from the sun onto an arbitrarily small surface. As a direct consequence of the brightness theorem the maximum is the output corresponding to a surface on the sun of the same size as the target surface. No matter how you arrange lenses and mirrors, there is a limit how strongly you can concentrate the sunlight."
] |
[
"But every object radiates some energy: the hotter it is the more energy it radiates. So it will reach a temperature such that it loses as much energy because of its thermal radiation as it gets from the Sun (if there isn't any convection or conduction). Since it loses energy in all directions, the best you can do is bring energy from the Sun from all directions. And it will reach an equilibrium when the object loses as much energy per direction as it gets from the Sun, which means it will be as bright as the Sun. And since the thermal radiation brightness is directly related to the temperature, it means it will be as hot as the Sun."
] |
[
"You can increase the intensity at the target, but you cannot increase the brightness of the source.",
"To illustrate why: Say you have a source of roughly 2cm at a meter distance. The angle from which light is reaching the target is roughly one degree. If you now put a convex lens between target and source you can increase the amount of light that reaches the target. But you will also increase the angle from which the light comes.",
"If you do the math, you will notice that the light per solid angle (i.e. the brightness) will not change.",
"edit: Also, you are welcome. This is an intriguing question because everybody can understand it and first instincts kind of contradict what you learned about physics :-)",
"edit2: You can describe lenses without interference also for light sources without conherent light."
] |
[
"Is there any liquid lighter than air?"
] |
[
false
] |
Is there any liquid (or even a solid) that, under room temperature and standard pressure, has a lower density than air? I'm studying engineering, first year, and I was asking myself this question while learning physics :)
|
[
"No. The particle densities in a gas are far below anything that can be achieved in solids or liquids, in which intermolecular bonds are important."
] |
[
"The answer is the same but the question removes the constraint of air being the gas."
] |
[
"The answer is the same but the question removes the constraint of air being the gas."
] |
[
"Does the last rep of lifting weights help more than the first?"
] |
[
false
] |
Basically what I mean to say is: do the harder reps later on of the same weight provide more value than the first/easier ones? edit: I guess by "provide more value" i mean help you build muscle more.
|
[
"'stimulate muscle growth more effectively'"
] |
[
"They'll definitely have an answer, but it won't fulfill the same criteria of scientific supportedness."
] |
[
"Citation? Wouldn't it make more sense that later reps break more fibers? If you have a partially broken muscle then those fibers are not working, correct? So you have an effectively weaker muscle at the last reps meaning more exertion is required to complete the rep. Wouldn't this mean that the fibers are under more strain and therefore more likely to break? The first reps take out the weakest and the last take out stronger ones?"
] |
[
"What does one mean by positive and negative approach in quantum theory?"
] |
[
false
] | null |
[
"any updates on this question ??"
] |
[
"any updates on this question ??"
] |
[
"any updates on this question ??"
] |
[
"Preparing figures for publication?"
] |
[
false
] |
[deleted]
|
[
"When I first started publishing I worried about this stuff too. I brought up the issue to my adviser. His response was, \"just ignore it and we'll deal with it if they ask.\"",
"I ignored the rules, the journals never cared (like you mention, the dpi was always high enough)."
] |
[
"It's a fine way to deal with it. I used to be the managing editor of a scientific journal. When I took it over, the instructions for authors still reflected the requirement for old-fashioned hand-drawn figures that couldn't be easily resized, or had to be photographed and resized at great expense. I guess other journals have the same ancient instructions. Now that everything is digital, the typesetters can easily resize stuff provided it is provided in a high enough starting resolution (at least 300 dpi)."
] |
[
"It's a fine way to deal with it. I used to be the managing editor of a scientific journal. When I took it over, the instructions for authors still reflected the requirement for old-fashioned hand-drawn figures that couldn't be easily resized, or had to be photographed and resized at great expense. I guess other journals have the same ancient instructions. Now that everything is digital, the typesetters can easily resize stuff provided it is provided in a high enough starting resolution (at least 300 dpi)."
] |
[
"Can the Sun be used in gravity slingshot maneuvers to propel probes to neighboring stars?"
] |
[
false
] |
Assuming we can develop a probe that can survive and fly above the Sun's atmosphere, could we use the Sun in a gravity slingshot maneuver to help propel a probe to a neighboring star? says that something outside our solar system could use the Sun in a gravity assist, but doesn't talk about something inside using it. This implies we'd need black holes or neutron stars to achieve relativistic speeds. So the follow up question is: could we use our sun repeatedly to attain relativistic speeds?
|
[
"This would work in theory, but you'd need a huge amount of propellant and a relatively small spacecrat.",
"The problem is, to get to the sun, you have to scrub off the 30km/s orbital velocity of the Earth. There are two ways you can do this. ",
"Use a series of gravitational assists from Venus and Mercury to slow you down",
"Go out to the orbit of Jupiter and do a burn to lower your aphelion distance",
"Both trajectories take a lot of energy, and to make it worthwhile you need to take a lot of propellant with you to make your perihelion acceleration burn. There's a careful balancing act that needs to be done here. You need to weigh the mass cost of taking extra propellant with you to the amount of energy you'd gain from the ",
"Olberth effect.",
"Unless you're able to take a huge amount of fuel with you, it would likely be more efficient to use Jupiter's gravity to accelerate you out of the Solar System.",
"EDIT: So to actually answer the OP's question",
"Using the Sun to accelerate isn't really as effective within the Solar System because we're deep in the Sun's gravitational well, and wouldn't gain as much energy by falling as we would if we're falling towards the Sun from outside its gravity well.",
"Further, the best case scenario for using the Sun as a gravity assist would require a lot of time energy. The most acceleration would be gained by getting yourself in an orbit that takes you close to the Sun, then performing a burn that takes you as far out from the Sun as possible. This orbit will take tens of thousands of years to complete, but when you come back you will be traveling at a couple of percent the speed of light. This burn will be ",
" effective, and will provide the maximum amount of energy you can get from using the Sun as a gravitational boost.",
"However, in that time you could have already been well on your way to the next star and be using that as a gravitational boost instead."
] |
[
"It might be useless to use the Oberth effect near the Sun with the delta-v we have in space craft right now. But if we're talking about going to neighbouring stars then I think we can assume that we have a whole lot more delta-v available. And we don't need all that much more for the Sun slingshot to be effective.",
"For the direct approach where you just immediately cancel some of Earth's orbital motion and then use your remaining delta-v at perihelion, this becomes worthwhile somewhere around 30 km/s of delta-v remaining at Earth orbit. Certainly much more than any space craft to date has had but not a ridiculous amount.",
"But there is also a better way of doing this. If you can escape the solar system in the first place, then what you can do is get to an escape orbit that just barely escapes (and you can use Jupiter or any other gravity assist here). Wait a few years, or decades, and when you're somewhere beyond Pluto's orbit, cancel nearly all your orbital motion, which will require very little delta-v that far away. Now you're falling towards the Sun and can loop around it arbitrarily close. Then use your remaining delta-v there. With regards to how much delta-v we can put in space craft, we're already at the point where this could get us a much better escape speed from the system. Although the problem is that you first spend several decades just flying around the solar system before escaping it. But if we're talking about interstellar travel, then a few decades here and there shouldn't really matter. And this method will not get you to anywhere near light speed so the whole interstellar travel would still be quite impractical.",
"It should be also noted (and the person I'm replying to probably knows this already but others might not) that this isn't really a gravity assist in the usual sense. Usually you grab some of the momentum of the planet you use for gravity assist to speed yourself up. That's not what happens here, instead we just use the Oberth effect near the Sun. I'm sure there have been several questions about gravity assists and Oberth effects in this subreddit if you need more details about either."
] |
[
"The speed of Solar Probe Plus is purely from falling towards the Sun from the orbit of Venus. Venus provides the gravity assist to get into that orbit, but the rest is just an effect of its new orbit around the Sun."
] |
[
"Is it possible for a planetary body or a star to have a spiral orbit instead of a planar ellipse/orbit?"
] |
[
false
] |
Title.
|
[
"Planets will (insanely slowly) radiate energy through gravitational waves, spiralling into the star. So you could say they all have spiral orbits. But insomuch as you can approximate gravity using Newton's law of universal gravitation, the planet will always move in a conic section. Namely an ellipse, parabola, or hyperbola. (The parabola is escape velocity, not the thing where you drop an object on the ground and it makes an extremely eccentric ellipse that you approximate as a parabola.)"
] |
[
"Does this count?",
"\n",
"https://en.wikipedia.org/wiki/Apsidal_precession",
"\nThis motion happens for a number of reasons including third body interaction, tidal or rotational perturbations and famously general relativity."
] |
[
"AFAIK the earth's orbit around the sun is 'spiral' moving \"'Nth to Sth\" (up and down?) of the suns equator and back again every 33,000yrs or so",
"IIRC It's often when the earth is at it's farthest distance away from the sun during one of these periods that ice ages have occurred"
] |
[
"How do islands get internet?"
] |
[
false
] | null |
[
"Mostly via cables that run over the sea or ocean floor. The same way that we connect the Americas to Eurasia.",
"Smaller islands, where it's not worth the investment to lay cables will use some form of satellite internet."
] |
[
"Smaller islands, where it's not worth the investment to lay cables will use",
"Or radio lines on the surface. If there's a line of sight (with towers), microwave links is a good alternative. This is used for instance on offshore installations in the north sea."
] |
[
"Just to quibble a bit with your last sentence - photons are much better. That's why most new backbone is fiber and not copper."
] |
[
"Why do some people who contract infections show no symptoms?"
] |
[
false
] |
How are some (most) cases of influenza, etc asymptomatic? Does this mean the body has fought and removed the virus without giving symptoms?
|
[
"Almost all symptoms of a infectious disease is caused by the immune systems response and not the pathogen itself. The objective of an infectious pathogen is to actually remain undetected by the immune system as the more pathogenic it is, then the less likely it will be able to reproduce and infect another host, as either the immune system will kill the pathogen or the host will die. ",
"Viruses are especially are good at hiding from immune systems as they are able to rapidly evolve to form new strains capable of evading immune systems. This is why you need a new flu shot each year as the genetic variation is random and some strains evolve to be more pathogenic then others and cause flu outbreaks etc, which is bad for both us and the virus.",
"Therefore most of us are actually infected with pathogens right now but only a small portion of us have an immune reaction and usually only to a particular strain of each pathogen, otherwise cohabitation would be impossible."
] |
[
"Is not having symptoms (w/o vaccination) identical to having been vaccinated? Is it immunity or just not having pathological readtion "
] |
[
"There are two parts of your immune system; the innate and adaptive immunities. When you get sick the symptoms you see are primarily caused by the innate immunity which is your immediate reaction to infection.",
"But when you get vaccinated, you're introducing your immunity to a weakened pathogen so you'll technically become mildly sick (so mild that you won't even notice symptoms). This gives your B cells which are part of your adaptive immune system a chance to produce antibodies so that the next time you encounter the pathogen it is killed much faster with more or less no ill effects as the innate system is barely activated. ",
"So yes the symptoms would be the same but because the pathogen is eliminated much faster in vaccinated individuals you don't really get a chance to see any. If the infection is bad enough though then you'll definitely see the same symptoms.",
"Hope this helps and wasn't to jargony. Happy to answer any more questions :) I'm an immunologist btw "
] |
[
"Poison Control Education for 8th graders. Any ideas? [X-Post r/AskReddit]"
] |
[
false
] |
I have the duty of coming up with some sort of presentation regarding 'Poison Control' to a group of 8th graders. So far I have a few ideas on what I want to talk about, but I definitely need more and some type of activity or worksheet. My ideas so far include The dangers of mixing bleach and ammonia products How taking too much Tylenol (acetaminophen) can be very dangerous Inhalants such as Pam can coat the lungs and cause suffocation Not to 'warm up the car' with the garage door shut Burning 'pressure treated wood' in the house can cause a release of toxic gases, including arsenic. Consuming large amounts of orange juice can cause hyperkalemia (intro into how large amounts of 'benign' substances can be harmful) Flee/Tick collar are not for human use. Warfarin = Rat Poison (Dose makes the poison) I am trying to stay away from any anti-drug stuff. I have the bit about inhalants, and tylenol, but I feel like those relate to house-hold poisons more so than other drugs. If anyone has any other ideas on things people may not realize are dangerous, please I am open to suggestions. (I am partnering with Poison Control and have looked at everything they have to offer.) Thanks everyone. [X-Post from AskReddit] I did not receive much input there and am hoping you all have some ideas.
|
[
"Warfarin = Rat Poison (Dose makes the poison)",
"Eighth graders won't have any idea of what Warfarin is. I doubt many college students would either. ",
"Use water. Same concept, more relateable. "
] |
[
"It sounds like you have a great cross-section of common things that can be dangerous if used improperly. I might also bring up antifreeze (which is sweet) and some shampoos as being toxic is used improperly. I would also talk about carbon monoxide broadly (e.g. from a broken furnace), in addition to specifically in the context of cars. A lot of being safe is about having the right mindset when you encounter something new. ",
"This brochure",
" from the American Association of Poison Control Centers has a few more examples (particularly of biological materials that can also be poisions), as well as a general outline of good poison control behaviors. Highlighting that more than just industrial chemicals can be harmful is a good idea.",
"My students tend to be older, but I find that students of all ages respond well to being put in a position to help others. Perhaps have them work out a plan to make sure that their homes are poison safe, and how to talk about their family or friends about poison control."
] |
[
"You should make them all memorize the poison control center hotline #. (800)222-1222"
] |
[
"If the universe and our solar system are in motion and subject to shift over time will this eventually affect the accuracy of our modern calendars?"
] |
[
false
] |
If our universe and solar system are expanding as so many sources put forth will the fact that we have a static calendar eventually become an issue? Will adjustments need to be made at some point in the coming centuries?
|
[
"Actually, the Solar System isn't expanding - the overall expansion of the universe has to compete with gravity, and gravity wins on all but the very largest scales. Even nearby galaxies have \"peculiar velocities\" which differ from Hubble expansion, due to interactions with our galaxy and others. There's a bit of discussion on this ",
"over here",
"."
] |
[
"Even though the expansion of the universe isn't a factor as Dannei stated, Coordinated Universal Time (UTC) is updated from time to time with leap seconds to adjust for uncertainties and changes in the rotation of the earth. "
] |
[
"Thanks much for the explanations. Interesting to think about individual solar systems held together by the glue of gravity whilst the rest of the universe expands. I'd love to know more about the history of the mathematics and science that went into the creation of the modern (adjustable) calendar. "
] |
[
"How do kangaroo foetuses know where to go?"
] |
[
false
] |
I have just seen that a month after conception, the baby kangaroo is essentially born where it weighs around 1 gram. It then climbs up to the mothers pouch, where it remains for 3 months. How does it know that it needs to climb upwards, or that it needs to find the pouch? In fact, how does it even know about the pouches existence? Thanks :)
|
[
"Not sure about kangaroos, but possum mothers use their spit to slick down a line of fur leading from their uterus to their baby-holding area. The possums then crawl up there since it's the easiest way to go."
] |
[
"Same way human babies grow and learn to crawl, then walk themselves and same way birds know how to build nests without ever being taught how to",
"Its instinct and intrinsic preprogrammed brain functions that these birds and kangaroos are doing. You can have 10 baby animals and 10 mothers yet each will know who their own mother is. Bird use sound and each one that's born is exposed to the mothers sound of calling and is always able to identify the mother. Other animals use sight, smell, etc. ",
"It's nature and animals are way more intelligent than you may think they are. Check out some documentaries on animals. Saw one on crows recently in which it was revealed some crows could remember human faces up to 2 years and warn other crows by calls when the same face that proposed danger showed up even after 2 years! Another species of crows uses creates tools by biting off the leafs off a small twigs and then using them to reach deep places they otherwise couldn't with their small beaks."
] |
[
"Fascinating. Restating the question: How does the mother possum know to do this?"
] |
[
"Are there extinct subatomic particles?"
] |
[
false
] |
Or are there elements that don't exist anymore? If a lot of crazy things happened around the time of the big bang, and that was an insanely long time ago, does that mean there could be elements or particles that no longer exist?
|
[
"There are many particles that were produced in abundance in the early universe, but which are very rare today. Matter we see today is primarily made of electrons, up quarks, and down quarks; we also see light (photons) and neutrinos.",
"But there are all sorts of unstable particles that we can create in the lab (some of which we see via cosmic ray events and some of which might exist occasionally in extreme conditions at places in the universe today), but which shortly after the Big Bang existed in abundances comparable to their counterparts. These include the muon and tau (like electrons in many ways, but heavier), and 4 additional types of quarks (strange, charm, bottom, and top). In addition, antiparticles for all these objects -- the ones we no longer see today and the ones we still see today -- existed in abundance. In addition, the W and Z bosons and the Higgs boson were produced easily in the extremely early universe.",
"In addition, there was a really early phase in the universe in which quarks and gluons existed freely, rather than being bound up into mesons and baryons, as they are today."
] |
[
"Not in the way you are thinking about them, no.",
"Particle physics may change at different energy scales, but that has not changed. In other words, as soon as we reproduce interactions at that energy scale, we reproduce the exact same physics that existed when that was the average energy scale of the universe."
] |
[
"the laws of physics are founded upon the belief that physics is the same everywhere and always has been with relatively little evidence (a small segment of time in an extremely small patch of space)",
"This is simply not true. We have evidence from spectral lines, the cosmic microwave background, studies of supernovas, and the abundances of nuclei in the universe that the same laws of physics have been in operation for nearly 13.8 billion years (Big Bang nucleosynthesis took place in the first several minutes after the Big Bang) and across the vast distances of the universe that we have observed."
] |
[
"How accurate/accepted is my physics professor's assertion about the passage of time?"
] |
[
false
] |
I am a college student and one of my courses this semester is an intro to college physics. My professor has a tendency to break off from discussing vectors into tangents on various topics including metaphysical ideas and advanced (I think very advanced, but painted in broad, vague strokes) physics. When speaking on the topic of time recently he asserted that the modern thinking is that, contrary to the way people typically think of time - fluid and infinitely subdividable - there is a extremely small but finite (I think he spouted off a number in teerms of nano seconds) period of time beyond which time cannot be subdivided for the sake of describing rates of change in the universe, because no change occurs in the gap. If this is a real theory hopefully it will ring some bells. Can anyone speak to the validity of this idea?
|
[
"Perhaps he was referring obliquely to the ",
"Planck time",
"?"
] |
[
"Well, as you can see ",
"here:",
"The resulting candidate for a theory of quantum gravity is Loop quantum gravity, in which space is represented by a network structure called a spin network, ",
".",
"One of the theories for quantum gravity (Loop quantum gravity) use the idea of quantum time. But it's one of many and we are not sure if it's the best one.",
"Sorry, i'm not being very helpful, because we are still in active research on that point."
] |
[
"I also believe that is most likely what he was referring to, given he seems to be saying that it is rather meaningless to subdivise it any further, rather than say that it can't be."
] |
[
"Perfect hollow spherical mirror. Let some light in, what happens?"
] |
[
false
] | null |
[
"Well your question answers itself, a perfect mirror will not convert any light into heat but such a mirror will never exist."
] |
[
"If the shell was thin enough and you waited enough time, the photon could quantum tunnel it's way through the shell and escape."
] |
[
"Try a search",
"."
] |
[
"Ugh, boring question: when sucrose is dissolved in water, does it disassociate into fructose and glucose, or stay as sucrose?"
] |
[
false
] | null |
[
"Yes. The acid catalyzes the reaction that breaks the bond between the fructose and glucose rings. This takes sucrose, which is prone to crystallization because it is very pure, and turns it into a mixture of sucrose, fructose, and glucose, which is much less prone to crystallize out. ",
"Adding invert sugar (the term for syrup from hydrolyzed sucrose), glucose syrup, corn syrup, trimoline, honey, or any other syrup that is a mixture of glucose and fructose will have a similar crystallization-preventing effect as the acid. Acid basically makes invert sugar in the pan, but is difficult to accurately control the exact extent of the reaction. For caramel this doesn't matter as much but it's tricky to use acid when making hard candy, for example. Adding syrup is more repeatable.",
"Another way to do it is use invertase. This is an enzyme that will catalyze the sugar inversion in the same way that acid will. This reaction is often used in making cherry or liquor cordials as you can make the candy center with a fondant that will solidify in order to cover with chocolate, but a drop of added invertase will liquify the sugar inside the chocolate shell over time. "
] |
[
"If you look closely at the ",
"glycosidic bond",
", you'll find that it is an ",
"acetal",
". As acetals are labile in acid, the hydrolysis rate depends on the acidity of the solution. At pH 7, it occurs very slowly - ",
"half-life of about 500 years",
" (Figure 2)."
] |
[
"Is that why some cooks add lemon juice when dissolving sugar to make caramel?"
] |
[
"Why are aluminium foils so used in physics experiments setups and what for?"
] |
[
false
] |
Very often, when visiting labs, or on pictures in articles, I've seen parts of experimental devices wrapped up with aluminium foils. Here is I randomly found with google. What is it for, and why aluminium?
|
[
"I work with many clean systems and vacuum systems, and I use aluminum foil because it's cleanable and doesn't leave lint. It also stays in place over an opening without needing a string tie or something, and actually has quite a bit of strength if you use the heavier stuff. ",
"I also use it to wrap pipes that need to be heated or baked, and I suspect that's why you see it so much and what it's being used for in the photo you linked. To reach very high vacuum (read: very low pressure), you need to bake the pipes out to drive off volatile molecules and water. Aluminum foil wraps keep the heat-tape and insulation tight around the pipe without being flammable (inflammable, whatever). ",
"Edit: I see the last question: why aluminum? It's cheap and makes nice foils. Also grammar."
] |
[
"Most aluminum foil you buy is actually rolled two sheets at a time, and it has a bit of oil or lubrication between them. It doesn't matter at all for people at home, but with clean parts it's unacceptable. We buy foil made specially without lubrication on it. For critical parts, you clean it with a solvent and clean wipe first. Air blasting isn't really necessary because the foil comes without many particles. The majority of the usage is when you open up parts that were ultra clean, and covering the ports with the foil just keeps stuff from getting in there. "
] |
[
"SPX_hbar mostly touched on this, I'm going to rephrase what s/he said and expand a bit.",
"In our lab we have a lot of vacuum chambers that we need to use with very low pressures inside. One of the things that makes chamber pressures worse is water -- water has a very high vapor pressure at room temperature, but low enough that it will take forever to just evaporate through the pumping apparatus alone. So whenever we let air into the chamber (it happens rarely) we need to \"bake\" it to 100-200C to drive off all the water.",
"The cheapest way to bake a chamber is to buy a bunch of heater tapes, wrap the chamber in the heater tapes, and then cover the heater tapes and chamber with aluminum foil to insulate them and to distribute the heat evenly.",
"This is a huge pain to do, so usually people leave as many heater tapes and as much aluminum on the chamber as possible between bakes.",
"I've never seen someone clean aluminum foil. But we also have a separate brand of aluminum foil (without the oil that SPX_hbar mentions) that we use for purposes involving ultra clean equipment -- any time something is going to touch vacuum we use the special (more expensive) foil.",
"Another way to do this without as much aluminum foil is to build an insulative tent around your equipment and put space heaters inside to provide the heat."
] |
[
"How would air get trapped in a solid crystal?"
] |
[
false
] |
Currently on the front page is a gif of a quartz crystal which contains a pocket of water. The pocket of water also contains an gas bubble. How is it possible that such a formation could form?
|
[
"Inclusions of water in crystals such as quartz frequently contain a small bubble. The bubble commonly contains water vapor, but can also contain other gases such as CO2 or natural gas. The inclusions of water plus vapor generally form because of some growth defect during the growth of the crystal as the crystal precipitates out of aqueous solution, with the quartz crystal growing around a small pocket of water. Once the pocket of water is completely encased in quartz, we call it a fluid inclusion. These inclusions can be air- and water-tight. If water is trapped in these inclusions at depth at elevated temperature and pressure, the water is less dense than under surface temperature conditions. As the quartz crystal is moved to the surface by tectonic uplift and erosion, the water that is encased in this tight container cools. With cooling, the water has the tendency to contract. Because of the air-tight containment, this tendency for contraction will eventually cause the water to cavitate and to exsolve a vapor bubble. In other words, the small bubble forms after the formation of the inclusion, when the quartz crystal moves from greater depth and higher temperature to the surface (generally by natural processes). It is also possible that gas is trapped at the same time with water, for instance in a boiling system where liquid water and water vapor (and air) are both present. But this is not the general case. Other inclusions can trap oil and water. It is also not uncommon for water inclusions to contain small crystals of salt.",
"These inclusions come in all sizes. If they are very large, they are called geodes. More commonly, inclusions are sub-millimeter in size and require a microscope for observation. The vapor bubbles are even smaller, perhaps only a few micrometer for inclusions that are 10-50 micrometer in size. While often not recognizable with the naked eye, fluid inclusions give quartz the milky appearance. Clear quartz is relatively free of inclusions.",
"The behavior of inclusions can be predicted if the phase behavior of the fluid is known (as taught in a chemical thermodynamics class). Alternatively, using controlled heating and freezing experiments conducted under a microscope, we can determine the temperature of crystal formation and the composition of the trapped liquid. This is known as fluid inclusion microthermometry.",
""
] |
[
"Could you link to the gif? I've seen gifs of a very large, but fake inclusion. They made it by taking a big quartz crystal and using clear epoxy to make fake fluid filled inclusions."
] |
[
"Just google fluid inclusions for images. Fluid inclusions in quartz that show the behavior described above can be created artificially in the lab in an epithermal cell, i.e. a device that can be heated and pressurized in the presence of an aqueous solution of silica. While \"fake\" they just look like inclusions formed under natural subsurface conditions. Epoxy generally has a different refractive index so it can be easily distinguished from the quartz under the microscope."
] |
[
"How common is our Moon's orbit which causes it to always show us the same face to Earth?"
] |
[
false
] |
As stated in the title, is it common for other planetary moons to show the same face to the body they orbit? If not, are there any theories as to how our moon's orbit evolved as such. If so, what causes this to happen?
|
[
"It's quite common, essentially all the large moons in the solar system are tidally locked to their planet. It's not a random occurrence, it happens because the gravitational gradient from the planet exerts a drag on the rotation of the moon that gradually slows it down until its rotation and its orbit are in synch. "
] |
[
"They do! In other solar systems. Most of our planets are too far from the sun for tidal locking, but Mercury has spin-orbital resonances such that it experiences three days every two years.",
"These guys",
" managed to calculate a temperature map of an extrasolar planet using clever spectroscopy and found that it's hottest at a point almost directly under where the sun is directly above, but swept aside slightly due to wind."
] |
[
"Why don't planets suffer the same effect from their sun?"
] |
[
"What does the top of a lightning bolt look like?"
] |
[
false
] |
Since the lightning bolt isn't actually attached to anything and the top of it is hidden in the clouds, I was wondering what the upper edge/boundary of a lightning bolt is shaped like. Is it just a mass of electricity? Does it fade into nothingness near the top? I can't quite picture how the source would appear.
|
[
"So essentially there's an avalanche of electrons that starts at the cloud and propagates towards the ground. ",
"Does this help your explanation a bit? After reading your reply it instantly reminded me of this gif."
] |
[
"When it touches the ground there is a trail of ionized air (from the avalance) connecting the charged cloud to ground. Current can then flow en masse through the ionized path and you get the main flash"
] |
[
"If the bolt is directed from the cloud to ground, it will fade into nothing. I'll try to explain why with a simplistic description of lightning. The lightning bolt is essentially an arc that propagates from cloud to cloud, cloud to ground or ground to cloud. Let's assume cloud to ground. You have a build-up of negative charge (electrons) in the cloud and a potential difference between the cloud and the ground. Because of the potential difference, bound electrons in air particles that come near the cloud can get stripped off and accelerated toward the ground. If the potential difference is large enough (ionization potential of air), by the time the electron interacts with another atom, it will knock off another electron. Then both will accelerate.",
"So essentially there's an avalanche of electrons that starts at the cloud and propagates towards the ground. Near the cloud there are fewer electrons in the avalanche so there is less to see.",
"Now, in reality, we actually don't know yet the details of lightning formation and how the charge builds up. This is still an area of research."
] |
[
"Does rain fall in a pattern?"
] |
[
false
] | null |
[
"If you're asking does rain fall in a pattern on the ground in your front yard, the current consensus is maybe, but not significantly for most applications. While there will be a distribution of drop sizes (i.e., basically a bunch of small drops and exponentially less large drops), these drops are traditionally assumed to be randomly dispersed in space. Now because they're randomly dispersed you can still end up with clusters where one patch might get more rain than another patch, but this is due to randomness. Some more recent research has shown that there is some slight deviation from randomness, but these measurements are inherently hard to make [1]. While this non-randomness is going to be negligible for hydrologists and farmers, it can be really important for micophysical equations in our weather models.",
"If you're asking if it rains in large scale (multiple kilometer or larger) patterns, it absolutely does. For example, near the equator is the ",
"intertropical convergence zone (ITCZ)",
" which is a band of thunderstorms like a belt across the globe. This happens because of converging and rising air. Conversely, there are large deserts on either side of the equator in the tropics due to this same air descending.",
"[1] ",
"https://journals.ametsoc.org/doi/abs/10.1175/1520-0469(2000)057",
"<0901:OTSDOC>2.0.CO%3B2",
"Edit: link formatting "
] |
[
"The rain may seem to come in waves due to the wind gusts often occurring in downpours. There's also likely turbulence based clustering that you see, especially near the surface and in intense rain. In stratiform situations (think steady rain all day) these \"waves\" of rain are likely less prevalent due to less wind and turbulence. ",
"Going further into your 3D question, rain absolutely varies in the vertical. Within cloud due to the rain drop growth processes and terminal velocities. Small drops are formed first, but also have the lowest terminal velocity and dominate the rain drop size spectrum near the cloud top. As you go further down into the cloud the spectrum broadens and you get larger drops."
] |
[
"What about in 3D space? It often seems in downpours that the rain is coming in waves. Is this my imagination, of an actual phenomenon ?"
] |
[
"Is there any correlation between eye color and light sensitivity?"
] |
[
false
] |
I have very dark (almost black) eyes and am very sensitive to light. I basically have to wear sunglasses any time i'm outside. Is this at all because of my eye color?
|
[
"Well, sensitivity is somewhat dependent on your medical history etc. But it is a fact that people with lighter eyes allow more sunlight to pass through the eye itself and so are at a greater risk of problems associated with uv exposure. People with dark eyes absorb the light and so are less likely to feel these effects. This is the general rule of thumb when talking about absorption in the color spectra, but humans are so diverse we cannot just attribut sensitivity to eye color alone. "
] |
[
"But it is a fact that people with lighter eyes allow more sunlight to pass through the eye itself and so are at a greater risk of problems associated with uv exposure. People with dark eyes absorb the light and so are less likely to feel these effects.",
"That's definitely not what my optometrist said when I asked him this same question. I don't feel qualified to give a proper answer to OP's question, but I was told that it's the ",
"pupil size/reflex",
" and ",
"pigmentation ",
" (that is, inside the eye)",
" that correlates to light sensitivity, which AFAIR has little if any correlation to iris color."
] |
[
"True true, i asked my optometrist that as well and you are right. Perhaps I phrased my answer poorly. My comment was regarding the iris, which is the colored muscle of the eye which influences the contraction/dilation of the pupil itself. The retina doesn't have color per say. The retina is the back of the eye and is what actually absorbs the light that passes through the pupil to form an image. In terms of coloring the retina, I can only think of the cone and rod cells if that is what you are referring too?"
] |
[
"Does fusion occur inside black holes?"
] |
[
false
] |
I understand that fusion only occurs under extreme temperature and pressure. So this got me thinking; does it also happen in black holes, where there is astronomical amounts of gravity?
|
[
"No, and I don't think anybody can explain it better than our 'own' ",
"RobotRollCall",
"."
] |
[
"You are way past fusion even before you get to a black hole. Precursors to black holes are usually neutron stars (unless the original star is more than 3 stellar masses which is enough to collapse it directly into a black hole). ",
"Neutron stars are already so dense that their gravity has gone beyond the limit of electron degeneracy (point at which electrons and protons can no longer repel each other against gravity) and has fused most of the protons and electrons into neutrons (usually recoiling when doing so and creating one huge blast aka. supernova). ",
"It is now a ball of pure neutron matter aka neutron star (usually about 20km across and about as heavy as our sun). If such a star happens to come close to another neutron star or any other star for that matter it will either slam into it (in case of another neutron star) or strip it of it's matter until it's own mass exceeds that of 3 solar masses at which point neutron degeneracy occurs which is short for the opposing forces keeping the neutrons apart can no longer battle against the rising gravity and the neutron star collapses into a singularity. At this point what happens to the neutrons is beyond us. Weather neutron-neutron fusion occurs and something is released is beyond us since the gravity at that point is so massive that information can only escape via hawking radiation. Also things like infinity start creeping up out of the woodwork and basic laws of physics get all crapped up. ",
"There are theoretical models that predict the existence of quark stars which are neutron stars who's gravity has overwhelmed the repelling forces inside neutrons, forced neutron-neutron fusion which in turn has turned the star into a super-dense soup of constituent quarks. However no such stars have been found so far so who knows ... there are even more exotic things in theory ... like Strange Stars etc. "
] |
[
"Not just atoms, gravity in a black hole is so strong that nuclear particles like protons and neutrons can't exist - gravity overcomes the forces that maintain their structure. It's the breakdown of this subatomic structure that leads to the final collapse to a black hole."
] |
[
"How do surgeons remove an entire tumor without leaving microscopic pieces/cells which can cause a relapse?"
] |
[
false
] | null |
[
"Leaving microscopic pieces and cells is a known problem, and in fact surgery itself can in some circumstances trigger metastases since cancerous cells are relesed into circulation: ",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5380551/",
"Its a known problem and active field of research. Obviously the goal is to minimize this, and one technique is to use as large margins as possible when operating."
] |
[
"They don’t. Cells can have escaped and lodged elsewhere. That’s why many tumor removals are followed by chemo or the equivalent for that cancer. And why many times, that cancer comes back but in a secondary area."
] |
[
"That's what happened to me. Fortunately my doc ended up getting it all eventually."
] |
[
"Why galaxies are flat? Why there are no spherical galaxies but only disc shaped galaxies?"
] |
[
false
] |
Gravity should be same in all 3 dimensions then why galaxys are flat , and we don't see a sphere with a black hole at the centre and stars revolving around it around the whole sphere, why disc shape?
|
[
"There are spherical galaxies! We call them \"ellipticals\" though - they have a bit of angular momentum, so they tend to be somewhat \"smushed\" or \"stretched\" spheres.",
"There is nothing stopping stars from orbitting all over the place - and when disc galaxies merge, often the stars get so stirred up that it forms an elliptical galaxy in the end. However, stars tend to ",
" in a disc. We only have disc galaxies because the stars are basically staying in the configuration they started with.",
"While stars can orbit any way, ",
" tends to form a disc. Stars almost never collide with other stars (except if they form together as a binary etc), but gas particles in space do actually collide with each other quite often. This means that you can't just orbit anywhere you want - the gas particles will bump into each other and lose energy. Eventually it settles down into the lowest energy configuration you can get while still conserving angular momentum - and that's a disc. The stars then form from the gas of this disc, and tend to stay roughly in a disc.",
"Over time, the stellar disc does stir itself up a bit, and ends up a bit thicker than the gas disc. Generally, we have a \"thick disc\" of older stars, a \"thin disc\" of younger stars, and a very thin disc of gas.",
"As a side note: the supermassive black hole isn't really important here, as far as gravity goes. The vast majority of the mass is in dark matter, stars, and gas. Stars orbit within their own shared gravitational potential - they aren't affected by the supermassive black hole unless they're basically right on top of it."
] |
[
"Interestingly enough, dark matter tends to be in a big sphere surrounding and encompassing the galaxy it's part of. And due to this, we suspect that it does not interact with itself either! It's also why it's probably best labeled as 'Dark Gravity'."
] |
[
"If it falls into a black hole yes, it's never coming out. But it's much less likely to fall into a black hole than normal matter.",
"When matter (both normal and dark) gets pulled into a back hole it only rarely gets sucked straight in. It first gets captured by the gravity well and starts orbiting the black hole. Eventually it gets slowed down by friction and collisions and falls into the hole.",
"But dark matter doesn't get affected by friction or collisions. So once it starts orbiting a black hole it just stays there, never slowing down or falling in.",
"For dark matter to fall into a black hole it would have to be aimed directly at it, and that happens so rarely that it's almost (but not totally) impossible."
] |
[
"What 'green' technologies are barely helpful/harmful to the environment?"
] |
[
false
] |
I read an article a few years back in PopSci that mentioned hybrid cars not being that good for the environment when you look into the creation of nickel batteries. The idea was that a Prius has to drive 100,000 miles to make up for the carbon footprint of it's creation. So I'm curious what 'green' technologies are we being sold that are not helpful to the cause or worse hurting the cause.
|
[
"Biodiesel made from corn is a huge waste."
] |
[
"Analysis on the problems inherent with biofuels - \n",
"http://www.unep.org/resourcepanel/Publications/AssessingBiofuels/tabid/56055/Default.aspx"
] |
[
"Many forms of recycling are not actually beneficial, depending on the process used, type of material, distance to treatment plant/source for new version, etc."
] |
[
"What defines flavor? Why do some people find things pleasing and others not?"
] |
[
false
] | null |
[
"Sight and hearing come from well studied receptors that work along easily measurable physical scale, i.e. light and sound frequency. ",
"However, for taste and olfaction there are are thousands of receptors each keyed to different molecular structures that don't follow patters (at least not in the way light does). In addition, these receptors, unlike those for sight, are not necessarily shared by all humans (",
"e.g.",
").",
"So think of this analogy: there's a painting you like it, but your friend doesn't. Unless one of you is colorblind, you are probably sensing the same lightwaves reflected from the canvas and paint. Now imagine if you could see colors your friend can't (or vice versa). The latter would be like taste/olfaction.",
"Then, there's not only a subjective side to flavour, but also a physical inability for some people to sense some tastes or smells you can.",
"EDIT: To clarify, I also talk about olfaction because smell works along with your taste buds to create flavours. Just try covering your nose while eating, the flavour can change quite a bit."
] |
[
"huh, that's too interesting. I think I might give these a go."
] |
[
"huh, that's too interesting. I think I might give these a go."
] |
[
"Could we ever bring back a long extinct species from prehistoric DNA?"
] |
[
false
] |
What is the most likely method that Humanity will find/recover prehistoric DNA? Is there any chance of recovering the DNA of even a simple organism or spore from amber?
|
[
"Japanese, Russian and South Korean scientists are currently attempting to clone a Mammoth.",
"http://www.telegraph.co.uk/earth/wildlife/9139976/South-Korean-and-Russian-scientists-bid-to-clone-mammoth.html"
] |
[
"There is a group making mammoths again."
] |
[
"The answer is probably not. There are a few people who have claimed to be able to recover tiny snippets of DNA from insects preserved in amber, but those claims have failed many attempts to repeat their findings. DNA just doesn't last that long, even if it's preserved in amber. And amber is probably the best-case scenario for recovery. Even then, the snippets recovered are so tiny that it would require an absolutely monumental effort to recover enough to build a complete genome sequence for even a bacterium. They are recovering tens of base pairs, and even bacterial genomes are millions of base pairs, many orders of magnitude larger.",
"Even after you reconstructed what the sequence is, you'd still need to actually go and build it if you wanted to resurrect the organism. That's a similarly monumental effort, which might not even be possible due to problems like imprinting and other epigenetic regulation mechanisms. The DNA sequence alone isn't sufficient to just resurrect an animal. You'd probably need a closely related species to act as a surrogate to provide the imprinting factors that are present in an egg. If those factors aren't compatible...",
"EDIT: I was talking only about SERIOUSLY prehistoric animals, like dinosaurs. For much more recent extinctions (since the last ice age), like wooly mammoths or quagga, we've got good enough DNA samples that we could reconstruct the species, or possibly even clone them."
] |
[
"Will water boil faster if it's moving?"
] |
[
false
] |
Boiling water is when it's molecules move really fast right? So if the water is moving and rippling would it boil faster? Also is that the reason the oceans don't freeze? Because they are always moving?
|
[
"Truthfully, shaking boiling water will cause it to boil slightly faster, due to the shock waves passing through it. The decreased pressure during rarefaction will speed up boiling at that point slightly. It's insignificant, though. The added energy from shaking is also negligible.",
"Also is that the reason the oceans don't freeze?",
"Oceans don't freeze solid since ice floats. The surface freezes and forms an insulating barrier between the water and the overlying air. Sure, there is transference of energy through the ice, but as the ice thickens, this becomes quite slow."
] |
[
"Why do you think it is trolling?"
] |
[
"Why do you think it is trolling?"
] |
[
"Is it possible for a mountain to escape the atmosphere?"
] |
[
false
] | null |
[
"In general, no, or at least not without a very improbable atmosphere.",
"This is a little difficult since one has to define some threshold where the atmosphere ends, when in reality atmospheres don't have a sudden cutoff like that. However, the height of both atmospheres and mountains scale by the same factor: gravity.",
"Mt. Everest is very close to the limit of how high a mountain on Earth can be; much taller, and the base can no longer support the massive weight of the mountain. Similarly, consider Olympus Mons on Mars - gravity there is almost 3 times less than on Earth, and it's no coincidence that Olympus is almost 3 times taller than Everest. It, too, is close to the height limit, but on Mars.",
"Atmospheres don't have a height limit, but we can look at a property known as its \"scale height\", which is a measure of how high one has to go before the atmosphere gets 37% thinner. This height also scales with gravity; the weaker gravity is, the taller the scale height.",
"However, the scale height also scales with two other things: the temperature of the atmosphere (the hotter it is, the taller it is), and the average molecular weight (the lighter the atmosphere, the taller it is). Since Mars is quite a bit colder than Earth and has an atmosphere made of CO2 (heavier than our nitrogen/oxygen atmosphere), its scale height is only about 1/3 taller than Earth's: 8.5 km on Earth, 11.1 km on Earth. ",
"So, since Mars' scale height is not 3 times as tall as you would predict from just gravity, Olympus Mons sticks up into the thin atmosphere a bit more than Earth. Atmospheric pressure at the top of Olympus is about 12% of what it is near the plains. On Earth, the pressure at the top of Mt. Everest is about 32% of what it is at sea level.",
"In order to get a mountain that peaks out into even thinner atmosphere, you'd need a planet that's even colder, and made of an atmosphere that's even thicker. Gravity won't get you there, since mountain height and scale height both scale the same with gravity."
] |
[
"In general, yes. On Earth, no.",
"Mountains' height is limited by the strength of gravity, the shear strength (or compressive strength, depending on geometry) of the rock, and the density of the rock. So on Earth, the maximum height for a mountain is roughly 10 - 15 km. If this mountain is already on a high plain, then the actual elevation is the height of the mountain plus the elevation of the plain, but high plains are governed by the same physics.",
"There's also some fuzziness on the maximum height of an atmosphere. On Earth, this is about 100 km, but in reality, the atmosphere is a continuum of particles that decrease in density as you go higher. But it should be obvious that on Earth, the atmosphere is about an order of magnitude higher than the tallest mountains.",
"On a planet with very little atmosphere, it would be possible to build a mountain higher than the atmosphere. The moon, for instance, has virtually no atmosphere, so a mountain there could be considered to be \"above\" the atmosphere."
] |
[
"The idea that the difference in gravitational acceleration between Earth and Mars is the sole driver for the difference in the maximum height of mountain ranges is pervasive, but also not quite right. Of equal (and perhaps larger depending on the relative differences) importance is the fact that the support of mountains (or any mass) is largely through flexure of the crust so the height of mountains are fundamentally dictated by the effective elastic thickness of the crust (i.e. the thickness of an idealized elastic beam necessary to support the mass and display the same topography as observed). The crust of Mars is much thicker and more rigid than that of Earth's, so estimates of the effective elastic thickness under Olympus Mons is ~200 km (and may reach up to 300 km in other places on Mars), where as on Earth, estimates of effective elastic thicknesses are usually 10-50 km in oceanic crust and can reach up to 100 km in areas of thickened continental crust (like in mountain ranges). So, gravity is an important factor (as this will obviously play into the amount of flexure), but couching mountain height in those terms only ignores the massive difference in crustal rheology between Earth and Mars. For those interested, the excellent book \"Isostasy and Flexure of the Lithosphere\", by A.B. Watts provides a nice discussion of all this."
] |
[
"What is it about having extra stores of fat on one's body that makes it so unhealthy?"
] |
[
false
] |
There are many studies that show that being overweight increases risks of all types of diseases. But is it really just having extra fat on one's body that leads to increased health risks? Or could it be some other factor, like overweight people eating less healthy foods? I don't really see why just having fat on your body would inherently be bad. It's just stored energy, isn't it?
|
[
"One issue is that the extra fat can deposit in arteries. This can lead to several health problems, the most obvious being heart attacks from blocked arteries."
] |
[
"Visceral fat responds more to glucocorticoid with lipolysis, and releases more FFAs into circulation, which is thought to contribute to insulin resistance. It also produces a number of cytokines that have systemic effects both on the endocrine system (along the lines of metabolic syndrome) as well as vascular system (atherosclerosis).",
"To add to my original point, obesity is also a risk factor for cardiovascular disease (from increased metabolic demands in addition to vascular disruption) and respiratory disease (from the effects of body habitus). ",
"It's also associated with a number of cancers."
] |
[
"Additionally, visceral adipose tissue appears to have greater proportion of activated immune cells that contribute to chronic, low grade inflammation, which is associated with many comorbities of obesity. Additionally, adipose must be substantially vascularized, which leads to a greater work load on the heart, eventually leading to hypertrophy and the associated health issues with it. "
] |
[
"Is the number of faults on Earth's surface generally an increasing function of time?"
] |
[
false
] |
As time is measured over billions of years? Would this also apply on exoplanets?
|
[
"Interesting question.",
"While new faults are occasionally created, most fault motion (earthquakes) occur along already existing faults.",
"So new faults are occasionally added, but old ones are also removed through subduction and erosion. Quite what the balance is I'm not sure, and certainly there are many ancient preserved faults in the geologic record which haven't been active for many millions of years. However, my guess would be that as the volume of continental crust on earth is increasing through geological time, I would conclude that the number of faults is also gradually increasing.",
"I wouldn't want to try and put numbers on it though."
] |
[
"most fault motion (earthquakes) occur along already existing faults.",
"I second this. The Earth's crust is permeated with faults, and when a new deformation process begins it usually just reactivates and then modifies pre-existing structures. ",
"My instinct would be that the number of faults on a geologically active exoplanet would approach a quasi steady state fairly soon in the planet's history. "
] |
[
"This may be correct near the surface, particularly where an existing fault line is a zone of weakness which releases stresses intermittently. However, if there is mineralisation associated with a fault, it could become stronger than the rock in which the fault first formed. "
] |
[
"Why is it so unbearably uncomfortable when a body part \"falls asleep\"?"
] |
[
false
] | null |
[
"5) The brain perceives this situation as that horrible and unique tingling sensation everyone hates, rightfully so.",
"FTFY"
] |
[
"5) The brain perceives this situation as that horrible and unique tingling sensation everyone hates, rightfully so.",
"FTFY"
] |
[
"Haha, indeed. I'd like to add that the \"pins and needles\" effect is called paresthesia. Thought it would be appropriate to mention that here. "
] |
[
"How would the drake equation be affected if one were to consider AI to be an Extra Terrestrial civilization?"
] |
[
false
] |
I was meditating on the words of Carl Sagan when I started thinking about robot civilizations. Would it be possible for an intergalactic species to contact us via robotic spacecraft? If so, would this have a functional impact on the fraction fc? (the fraction of civilizations that develop a technology that releases detectable signs of their existence into space ).
|
[
"I think you are over-thinking this? I mean, yes, if we had some knowledge about the proportion of civilizations which developed and sent out robotic spacecraft, then we could incorporate that into our calculation of fc. But we don't. We don't have any data on fc, because we don't know of any alien civilizations, so any number we put in there is pretty much a guess."
] |
[
"You can read up on the Fermi paradox. Self replicating machines basically throws a curve ball. We can reason that an intelligent species would eventually create self replicating machines to explore the universe. From the speed they replicate at and the age of the universe, it can be reasoned that self replicating machines should be everywhere. The fact that we do not see them at all is part of the Fermi paradox. ",
"As for impacting the Drake equation, I think you would need to change it up a whole lot due to colonization from the AI. You would need to modify the formula to account for civilizations that develop this technology (maybe adding a new variable) and than predict at what time in the universe this would have likely happened. After, you take the time difference between now and that time, and apply the colonization Drake equation over that time to see how many planets have AI on them. You then add the number from the original Drake equation (chances are that the AI planets would dominate and the original Drake equation can be ignored). All of this is just fancy estimations and don't really have any purpose other than to spark discussion."
] |
[
"great question. but i think that for an artificial life-form to have been created, an actual thinking life-form had to emerge in order to create it. so for this secondary life-form to contact us it would be less likely than the drake result."
] |
[
"Why is gravity often considered to be the weakest of the fundamental forced when its effects can be felt so far away from the source?"
] |
[
false
] |
How is gravity weaker than say the electromagnetic force? Jupiter is far more influenced by the sun's gravity than the sun's magnetic field. Why do scientists mean when they say gravity is the weakest?
|
[
"It's weaker in the sense that if you take two charged particles (let's say two electrons), the electrical force between them is much much stronger than the gravitational force between them. Both forces act according to the same general form (they fall off as 1/r",
" and they are proportional to the respective masses/charges), but the constants in the electrical force equation are many orders of magnitude larger than their equivalents in the gravitational force equation.",
"So, why is gravity the dominant force on cosmological scales? Because there is only one type of mass: positive. All objects with mass are attracted to each other. By contrast, there are two types of charge, and the forces may be repulsive (same) or attractive (different). Since different charges attract, most matter ends up being electrically neutral.",
"At a large distance, this means that the attractive and repulsive electric forces balance out, because there is no net charge. Gravity, which is only attractive, is therefore left to summate and win the day."
] |
[
"Easiest test, Hold a pin with a magnet above the floor. In so doing, the electromagnetic force of the magnet in your hand is able to resist the gravitational force of the entire planet earth pulling on the pin. ",
"Similarly, you have two 1 gallon jugs of water, sitting one meter apart. The repulsive force of the electrons is cancelled out by their attraction to the nuclei. But if you could cancel out that attractive force, the repulsion between the ",
"two jugs would exert more force than the weight of an entire second planet earth resting on top of our current planet earth."
] |
[
"As for strong and weak nuclear forces, those only act over small scales."
] |
[
"Does mammals have menopause like humans? And do they have sex \"for fun\" even after they ate unable to reproduce?"
] |
[
false
] | null |
[
"Only primates, mostly old world primates (great apes, macaques, baboons), can be generally said to \"menstruate\" (here's a few papers about the evolution of menstruation: ",
"1",
" and ",
"2",
") so only they would have the possibility of going into menopause. It seems like the research has mixed results and scientists ",
"disagree",
" over whether non-human primates can be said to enter menopause, which is defined by the end of menstrual cycles (most mammals have \"estrus cycles\" instead.) Menopause refers to a specific sequence of physiological and reproductive changes, the consequences of which lead to decreased fertility, among other things. ",
"That being said, even animals that do not undergo menopause undergo a much decreased level of fertility to the point where they are basically unable to reproduce. Their oocytes are just too old (remember, females make all their eggs before birth) so even if they still ovulate, they cannot be successfully fertilized and implanted. There's also some age-related fibrosis of the reproductive tract that makes it less able to nurture a fetus, even if you transplant a young egg.",
"EDIT: added more sources"
] |
[
"Bonobos have orgies to resolve conflict between groups. I believe this frequently includes homosexuality. (EDIT: homosexuality --> nonreproductive sex.. I'm not sure if this is what you're wondering, but hopefully it helps!)"
] |
[
"IIRC only Orcas are known to undergo menopause. Dunno about their sex lives afterwards."
] |
[
"How can a part of the brain be simultaneously less active and more connected?"
] |
[
false
] |
A lot of research about the effect of psychedelics on the default mode network shows in the default mode network but between the default mode network and other nodes or networks (and sometimes more connectivity between nodes in its own network). How can a part of the brain be simultaneously less active more connected? Doesn't connectivity imply activity? I've Googled this, because it seems like it should be a simple answer, but I can't find anything.
|
[
"Brain connectivity can be structural or functional.",
"Structural connectivity usually uses DTI to map the white matter pathways to see how much white matter connects various regions. This is not directly related to activity.",
"Functional connectivity uses fMRI, EEG or the like to see what the *correlation* is between activity in 2 different areas. So you would typically choose a 'seed' area (say, a region of DMN) and then see how the waveform of activity (up/down over time) corresponds to the waveform of activity in other areas. You could have low activity and a high correlation, if every time an area goes up by a small amount, another area also goes up in some consistent corresponding amount.",
"Another thing to keep in mind is that more efficient networks are often less active under similar conditions. So for example in certain conditions (e.g., degraded white matter) you can have more activity as the brain tries to compensate and get the job done despite lower effective connectivity."
] |
[
"Thank you. I hope a clarifying question is alright:",
"So when two areas have high functional connectivity, it's possible for that connectivity to be negative? Activity in one area goes up and activity in another area goes down (maybe because one area is inhibiting the other or for some other reason, I don't know). I ask because I think I was under the assumption that functional connectivity = both areas increasing activity in each other. But maybe it's more about any kind of communication, whether that be one-way or two-way or inhibitory or excitatory. And if that's the case, can researchers tell what type of communication it is?"
] |
[
"Thank you so much. That really helps."
] |
[
"Can I use my regular sunglasses to see the transit of Venus?"
] |
[
false
] |
[deleted]
|
[
"If you read the article you linked they have a big NO! section that says specifically not to use sunglasses, as they will not offer the right kind of protection from the sun."
] |
[
"No.",
"Your sunglasses are nowhere near enough protection.",
"Welder's Glass #14 (I think this is the darkest of all welder's glass but hopefully someone else can say for sure) ",
"is deemed suitable for direct viewing",
"."
] |
[
"Yes, you should be able to find, if not the glasses, then the material the glass is made of at a home hardware store. ",
"You'll notice the difference if you actually put on a pair of the $1-$2 glasses. While you can look at the sun and see it quite clearly, you can't see ",
" while wearing them. Those glasses block out a good 98-99% of visible light, which is required to safely look at the sun. "
] |
[
"RE: This news about a star seeding the universe with water - Isn't water fairly easily formed on a planet anyway?"
] |
[
false
] |
Pertaining to Combining hydrogen and oxygen to make water is a relatively low energy reaction from what I know (as well as separating water back to them). I don't think the problem is amount of these elements in the universe, but rather that many planets are inhospitable to the water sticking around due to temperature, lack of atmosphere/magnetic field for protection, lack of a solid surface, etc... I see so many people talking about "Oooh this could be where our water came from!!" I just don't see it being that big of a deal. Am I wrong? EDIT: I have to say though, I'm surprised the H2O molecules are intact after being ejected at such speed and energy
|
[
"I'm not sure this is as well-established as you imply. The ",
"D/H ratios of comets",
" are wrong for them to be the only source of water on the Earth. The most likely alternative is that the water was present in the material that formed the Earth and was subsequently outgassed from its interior. Regarding the OP's question, there is a lot of water in the interstellar medium; a star jetting out water is only one contributor."
] |
[
"Most of the water on Earth came from comets bringing it to Earth. We know this be the Deuterium ratio in the water. There is alot of water on dust grains in interstellar dust, but the question is in what state? Most of the water is in ice form. I read this article and they of course make it sound like amazing news. We know there is loads of water out there on dust grains where new stars are formed. But in vast quanities it is not. "
] |
[
"I'm not sure that is entirely correct either. The available evidence doesn't point to comets as being a likely source for water as rocksinmyhead pointed out above. Also even if water was present in the early material it probably wouldn't have stuck around for accretion."
] |
[
"Would the same baseball player generate more power with a heavier or lighter bat?"
] |
[
false
] |
Say he can choose from a 30 oz bat or a 36 oz bat, which would generate more power hitting the ball? How would a player determine the optimal weight for which bat size to use?
|
[
"A heavier bat would usually generate more power because a slower swing builds up more momentum. A lighter bat may carry more kinetic energy but this figure is not very important when compared to the rate of energy transfer between the bat and ball. Getting the best energy transfer requires a proper balance between mass, speed and the elastic properties of the bat and ball."
] |
[
"I think the reason wooden bats are preferred are because they are more flexible than metal bats, and this flexing action increases the duration of contact, and energy transfer. "
] |
[
"Well just based on the formula KE = mv",
" a bat swung 2x faster than a bat twice as heavy would have twice the kinetic energy so I would say the lighter bat would generate more power if it resulted in a sufficient increase in swing velocity. I think this is also why the MLB uses wooden bats and not metal ones."
] |
[
"Since Mars doesn't have a magnetic field, how would this affect our ability to use electricity-based technologies there?"
] |
[
false
] |
[deleted]
|
[
"It would make no noticeable difference on any of those things."
] |
[
"Electronics would be more susceptible to solar radiation, but I'm not sure there would be GIC's (Geomagnetically induced currents) on mars like there are on earth without a magnetic field around the planet.. "
] |
[
"A planetary body lacking a dipole magnetic field, shouldn't impact the feasibility of permanent dipole magnets. I would think motors and the like would still function normally in the martian atmosphere.",
"But, our astrophysicists probably know better...."
] |
[
"I've heard that heat is the \"least useful\" form of energy. What does this mean? To do with entropy."
] |
[
false
] |
This was mentioned by Brain Cox in his program (UK only link, sorry) at around 35 minutes in. But he didn't really explain why one form of energy is a "lower quality" energy than another.
|
[
"100% of work can be transformed to heat but not 100%percent of heat can be converted to work. "
] |
[
"Sory I can't watch the programme so I can't comment on exactly what he said.",
"Entropy is strange and unintuitive concept, yet it is very practical and very well understood.",
"Unlike most of the laws of physics the ",
"second law of thermodynamics",
" is not time reversible, and states that over time in a closed system the entropy will increase. Aside: this can be taken as a definition of the ",
"arrow of time.",
" I digress.",
"In practical terms what this means is that in order to do \"useful\" work (useful work can be used to reduce entropy) you need high grade (low entropy) energy and then do the work using that energy and then release as waste low grade (high entropy) energy such that the ammount of entropy increase from the waste is greater than the entropy lowered in the doing of the work.",
"As an example the sun emits (relatevly) low entropy high quality energy (UV and visible light) which is absorbed by plants and PV solar cells lowers entropy by performs work assembling people and plants and hydrocarbons. But the earth radiates energy in the form of heat (IR light) which is the same ammount of energy at a higher entropy, lower quality grade.",
"Your, car, radio, computer, body takes in high quality energy in the form of electrcity or hydrocarbons and uses that energy to do work (potentially lower local entropy) but emits heat as the low grade output energy.",
"Ultimately all energy will end up as heat because heat is the lowest quality energy there is and once everything is at the same temperature then no work can be done since heat engines require a temperature difference.",
"See ",
"heat death of the universe."
] |
[
"Thank you this seems like a great answer :)"
] |
[
"Where does the energy go during the latent heating phase?"
] |
[
false
] |
I understand temperature is the average kinetic energy of a substance, basically how fast the disordered motion of each molecule is. What I don't understand is why the temperature should stop increasing at the phase transition temperature until the latent heat has been overcome? For a solid melting, why do the molecules collectively "decide" to stop moving faster once they reach the melting point, wait until they get enough energy (which is going where? Loosening/widening the intermolecular bonds?), and then what causes the sudden phase transition, followed by increasing in temperature normally again? Why does the phase transition depend on the overall temperature of the bulk instead of being more or less molecule-for-molecule? Also, why is the latent heat different for fusion and vaporization for water, what exactly is different about the hydrogen bonds in ice and in liquid if the molecules are the same? Please explain in physical instead of mathematical terms, I want to know what's going on with the molecules themselves in space. Thank you for any answers.
|
[
"OK firstly let's start by considering what temperature actually is.Temperature is a measure of the ",
" of the particles within an object.",
"When you put energy into something (heat) the energy is absorbed by the particles within the object. In a solid, nothing can move, so the heat energy goes into vibrational energy (which is a form of kinetic energy) - this increases the temperature of the object.",
"As you hit the melting point, there is still energy transfer into the object, but it doesn't cause further increases in vibrational energy so the temperature remains the same. The object now contains more energy though, but it is in the form of ",
", not kinetic. The energy has been used to break some of the attractions between the particles.",
"Now the particles don't \"collectively\" do anything. This is best illustrated at the vapourisation stage so I'll come back to this.",
"Continuing to send energy into the object and you now get increased translational energy as well - the particles can move around in a liquid, as well as continued increases in vibrational energy.",
"When you start to close to the boiling point, some particles ",
" will gain sufficient energy to break all the attractive forces to neighbouring particles and escape into gas form. You can observe this if you put a thermometer in water as you boil it - the container will start to emit vapour before boiling point itself is reached. (Remember the temperature is a measure of the ",
" kinetic energy.) If particles at the bottom of the container do this though, as they move through the liquid towards the surface, they lose their extra energy to the particles they pass.",
"So the phase transitions don't really depend on the temperature of the whole - it's just that when they occur in individual particles that have more energy than their neighbours, the phase change is reversed as their neighbours steal some of the extra energy. But increasingly as you get closer to boiling point, more of these transitions don't reverse. When all of their neighbouring particles are of a similar energy, there is less opportunity for energy loss (crudely speaking).",
"The concept that for any liquid, some molecules will have sufficient energy to become gaseous is quantified by the term ",
" the partial pressure of the gas \"emitted\" by a liquid at a certain temperature. For pure water at 100C the vapour pressure is 1 atm. If the phase transition all happened at once, then the vapour pressure graph would be a sudden jump from 0 (all the water is liquid) to 1 (all the water is gas). Here's what it actually looks like:",
"http://zimmer.csufresno.edu/~davidz/Chem3AF97/ChW/vaporpressh2o.html",
"As you can see you have gaseous water above the surface of the liquid at all temperatures above freezing point.",
"As far as hydrogen bonds go - there is no difference. You just don't break all the hydrogen bonds going from ice to water - just enough to enable the molecules to escape the rigid lattice structure. In ice each water molecule will form 4 hydrogen bonds. In liquid water, the bonding is more varied and fluid.",
"In summary - phase changing is a slow process, but because temperature measures the average ",
" energy, we see the increase in temperature stop while the bulk of the particles in the substance make the phase change, but this doesn't mean that all the particles make the change at the same time."
] |
[
"The short answer is the molecules do not collectively decide to move slower or faster on phase transition. When you achieve boiling point of water for example, by continuously providing heat you will see that the water is gradually turned to steam, but the total temperature will go higher than 100°C only after all water is converted. Usually this energy required for phase transition is used to break intermolecular bonds, in case of turning to vapor, the bonds are completely broken, while when turning from solid to liquid it would instead reconfigure the bonds from a crystal structure to a more relaxed configuration that permits more movement for the molecules."
] |
[
"Based upon my understanding…",
"The kinetic energy is not uniform, so you’ll have some molecules with higher and other with lower kinetic energy. When two molecules interact, if there is enough kinetic energy, it will break the intermolecular bonds, causing a phase change for one of those particles. As this only able to happen on the higher energy molecules, removal of them necessarily reduces the average (because math). ",
"This is a reduction of the temperature, except energy is being added back to the system. If you are adding only a little energy, in general there will be very few cases where there is enough energy to transition, so you’ll see a slow phase change for the bulk object. But if you add a lot of energy, there will be lots of cases where this happens. ",
"The medium will find a balancing point where the energy in and energy out balance (there will always be some minor fluctuations). This balancing point will be the transition temperature, which the medium holds at. If you spike input energy, you’ll see a very brief spike in temperature, but the accelerating phase transition is causes will catch up and bring it back down to the balancing point. ",
"Note: the balancing point isn’t fixed and external factors can, and do, effect it. Pressure, for example, is a big external factor."
] |
[
"There's such a thing as finite but edgeless space, so is there such a (hypothetical) thing as bounded but infinite space?"
] |
[
false
] | null |
[
"You are mixing up a lot of terms here, and so it's a bit confusing what you're asking. So please clarify.",
"So I am assuming that by \"space\" you mean a manifold, and so the only reasonable ways to interpret \"finite\" and \"edgeless\" would be \"compact\" and \"without (manifold) boundary\". If so, then, yes, such a manifold exists. (For instance, a circle.)",
"\"Bounded\" generally means that distances between points cannot be arbitrarily large. But do you mean to say \"with boundary\"? For instance, a closed disk is bounded and has a boundary. An infinite strip is unbounded and has a boundary. Boundedness has nothing to do with whether a manifold has a boundary.",
"I don't know what you mean by \"infinite\" since it can be taken to mean ",
" things.",
"Do you mean to ask some sort of physics question? It's hard to tell what you mean by \"reach in a finite amount of time\". I have several ideas of what you mean, but it's better if you just clarify yourself."
] |
[
"\"Is there such a thing as bounded but infinite space?\"",
"Bounded in this case means with a boundary. When I say infinite, I specifically mean \"you will always have more space no matter how much you take up\"",
"\"Could one theoretically have a space that has borders that can be reached in a finite amount of time, but containing an infinite amount of space?\"",
"I'm not asking in a physics manner at all. What I mean is, is there a finite path one can draw between any two points?"
] |
[
"When I say infinite, I specifically mean \"you will always have more space no matter how much you take up\"",
"Again, I really don't know what you mean. Those aren't mathematical terms.",
"It sounds like you want \"infinite\" to mean either \"non-compact\" or \"unbounded\" (if, say, there were a notion of distance in this manifold). But these two properties don't have anything to do with each other. (Generally speaking, compactness is a property of the topology and boundedness is a property of the metric.) I'm reasonably guessing you actually mean \"non-compact\". So as for your question \"is there a non-compact manifold with boundary?\", then the answer is yes (e.g., the interval [0, ∞)).",
"I'm not asking in a physics manner at all. What I mean is, is there a finite path one can draw between any two points?",
"If your manifold is also a metric space, then the distance between any two pair of points is finite. But you asked about \"borders that can be reached in a finite amount of time\", and that seems to imply you have some sort of idea of path parametrization in mind.",
"I think a big problem here is that many of the words you are using are either not mathematical terms or they ",
" but you are using them in contradictory ways (contradictory to both how they should be used and to how you use other related terms in your question). So it's very difficult for me to understand what you are asking exactly."
] |
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