title list | over_18 list | post_content stringlengths 0 9.37k ⌀ | C1 list | C2 list | C3 list |
|---|---|---|---|---|---|
[
"What is at the center of a Neutron Star?"
] | [
false
] | Reading about them makes my head hurt. I can't even begin to comprehend the forces at work on the surface, let alone in the middle of one. | [
"It's difficult to say, because neutron star cores are in a regime (high pressure, low temperature) that is difficult to produce experimentally. Cole Miller at UMD has a nice ",
"page",
" on neutron star interiors. I enjoyed the following description of the transition from crust to core:",
"As the density i... | [
"Is the density increase in a linear fashion towards the center? Other than the linear increase is the density homogeneous?"
] | [
"This is a very wrong description.",
"The energy from fusion actually has no bearing on core collapse supernova. The force keeping a star's inner core from collapsing into a neutron star is electron degeneracy pressure. What happens in a type-II supernova (which forms a neutron star) is that interior pressure in ... |
[
"When I leave my parking voucher on my dashboard for a few weeks and the sun fades the print, where does the ink go?"
] | [
false
] | null | [
"Most store receipts are printed on thermal paper, as well. The advantage is there is no ink to ever replace. If you look around thermal printers are pretty common. If you use a blow dryer on low, hold the receipt about an arms length away and apply heat slowly to the receipt and you can get faded text to reappe... | [
"Oh, awesome thanks! really interesting. I've never heard of a thermal printer.",
"Also does this mean that windshields are not UV protective?"
] | [
"Oh, awesome thanks! really interesting. I've never heard of a thermal printer.",
"Also does this mean that windshields are not UV protective?"
] |
[
"Have astronomical observatories progressed to the point where we can see the disc of a star yet?"
] | [
false
] | Given that stars are very small compared to their distance from us (except for Sol of course) has science/technology reached the point where we can see a star's disc in the way that even a simple child's telescope can make out the planetary discs? | [
"The star Betelgeuse (a red star in Orion) is big enough and close enough that we can look at its surface as a finite area (as opposed to a point). ",
"Here's a picture",
" from the Very Large Telescope."
] | [
"Stellar bodies have a quite complicated internal structure. What you have quoted is the average density. The density at the core will be much higher."
] | [
"The density isn't uniform; there may be a dense region in the center where fusion occurs. It's a red giant, meaning it has cooled down, contracted, re-ignited, and that re-ignition caused the outer atmosphere to expand."
] |
[
"Would organisms on a \"super-earth\" be larger or smaller, on average, than organisms on Earth?"
] | [
false
] | null | [
"For the non-math-savy: \"increased by a factor of 2",
" means \"increased by about 25%\". So a 160 lb person would weigh about 200 lbs on this theoretical planet."
] | [
"I won't comment on biology, but I will make the point that larger planets don't increase gravity as much as people think.",
"Assuming a similar density to Earth, the gravity at the surface is g=GM/r",
" where M=density * 4/3 pi r",
" , so g = constant * M",
"Thus, for double the mass, gravity has only incr... | [
"It depends on the strength of the gravity more than the mass. If you find a planet with 4x Earth's mass, but only 2x Earth's radius, then the gravity would be the same as on Earth. This comes from the ",
"gravitational force equation.",
"The size of single biological cells is inversely proportional to the stre... |
[
"When you delete something off a phone or computer, where does it actually go?"
] | [
false
] | [deleted] | [
"Data is merely a series of bits (1s and 0s) and bytes (8 bits..more efficient in a lot of ways).",
"So...you have this device which stores that information. Well, you also have to store ",
" you stored that information. Let's say that you want to store a 2MB song on an 8GB device. There are somewhere near 4,0... | [
"To add to that, when you hear someone talk about restoring data, all they're doing is finding out where those references used to be. Any bits that haven't been overwritten yet will still be intact, or \"recoverable\". It's harder than it sounds, especially when you bring fragmentation into the mix. Fragmentatio... | [
"The data you download on your computer is not something being \"added\" to your hard drive, but more like setting certain bits to off, and the others to on.",
"Think of your harddrive like a giant switchboard with 100 switches, arranged 10x10. ",
"Each switch",
" can either be on or off. ",
"At the beginni... |
[
"How would multiple moons affect a planet's tides?"
] | [
false
] | There's a hypothetical oceanic planet with multiple moons which vary in size, rotation speed, etc., but are all large enough and close enough to have a tidal effect. Is it reasonable to expect that this planet would not experience diurnal tides? I think what I'm asking is: Could this arrangement sufficiently complicate tidal patterns such that the planet's ocean is only at peak tide once every great while (i.e. all moons are in a certain relative position)? | [
"If this hypothetical world was completely deep ocean then the tides from the multiple moons would be superimposed on each other. With one moon we experience 2 high tides per day since the tidal bulge points towards the moon as well as away from it (actually not quite, since the ocean takes some time to respond the... | [
"This is a possibly counter intuitive point that I didn't get into in my top level comment: you get spring tides on Earth even if the Moon and Sun are on opposite sides of the Earth (see the Wikipedia link from my top level comment for a diagram) because what you need is for the ",
" to be lined up. So you don't ... | [
"That said, instances of all the moons lining up would be rare, so the huge huge tides would also be rare.",
"Planets with multiple large moons often wind up with orbital resonances. Jupiter, for example, has a 1:2:4 resonance with Ganymede, Europa, and Io.",
"Resonances tend to favor non-aligned positions, so... |
[
"Why is it harder to keep one's balance when you close your eyes?"
] | [
false
] | [deleted] | [
"The human body has three different pathways to detect equilibrium/balance: vision, the vestibular system (the tiny hairs in fluid filled canals near your ears), and proprioception (this is a fancy word for the ability to detect what our body posture is at any given moment). Like I said these 3 systems work togethe... | [
"WilliamTheLow's comment sort of addresses this as well. ",
"Think of your ability to balance as a tripod. The three legs are your vestibular system (modulated chiefly by fluids in your inner ear), your proprioceptive system (information sent from your muscles back to your brain about where the muscles are positi... | [
" refers to the collective contribution of all sensory modalities (sight, audition, olfaction, balance, etc.) to positioning one's self in space. Yes, your balance if influenced primary by the ",
"vestibular system",
", but integrative information from the visual system supplements our body's sense of position.... |
[
"Is IQ difference detectable with MRI or EEG? In other words, do high IQ brains look or record any differently from those with low IQ scores?"
] | [
false
] | null | [
"Detectable differences exist by MRI.",
"Here's a great review.",
"Abstract for the lazy:",
"Genetic influences on brain morphology and IQ are well studied. A variety of sophisticated brain-mapping approaches relating genetic influences on brain structure and intelligence establishes a regional distribution f... | [
"This",
" is a PDF of the Annual Review that ren just linked to, for those interested readers who don't have a subscription to the journal. "
] | [
"I found this tidbit in the PDF interesting: From childhood to adolescence \"areas performing more basic functions mature earlier; areas for higher-order functions (emotion, self-control) mature later. The prefrontal cortex, which handles reasoning and other executive functions, emerged late in evolution and is amo... |
[
"Is global climate change, (aka global warming) a legitimate problem?"
] | [
false
] | null | [
"Nice try Bill O'Reilly."
] | [
"Nice try Bill O'Reilly."
] | [
"A study by Stanford University researchers examining expert credibility in climate change has confirmed that ",
". The vast majority of skeptics who signed onto joint statements denying man-made climate change \"have not published extensively in the peer-reviewed climate literature,\" the study found.",
"http:... |
[
"Question about simulating chemical reactions"
] | [
false
] | I was wondering if we know enough about the interactions between various molecules to accurately model how they interact with one another, say in a computer simulation. For example, given molecules X and Y at temperature and pressure Z and W, can we know how they will interact in a general way? How much energy is released from those interactions? What states of matter the two compounds and their resulting compounds will be in? Etc etc. I guess I'm wondering if that kind of thing is simulate-able in a reliable way. Thanks! | [
"There are several methods that are commonly employed to do just that. It's actually my job is to design and apply simulation methods to tackle problems.",
"The methods we have are actually pretty reliable, but one of the large remaining issues deals with computational efficiency versus computational accuracy. ... | [
"That's good to hear. Do you happen to have any links to more in-depth explanations of the various algorithms?"
] | [
"If you want the basic description you can find some quick links using a google search. Just search for Molecular Dynamics, Monte Carlo Molecular Simulations, and Density Functional Theory. That should pop up a whole host of information. ",
"If you want really detailed explanations then you might want to pick ... |
[
"Would the big rip scenario be able to overcome even the binding force of a black hole, and if so, what sort of energy would be released when breaking the bond in a singularity."
] | [
false
] | [deleted] | [
"All black holes are expected to evaporate over time by emitting Hawking radiation. So realistically a singularity shouldn't persist over time even if nothing close to a Big Rip happens.",
"Ignoring that, though, then a Big Rip still wouldn't \"rip a singularity apart.\" The thing about a cosmological solution li... | [
"Dimensionless; a point has no size."
] | [
"A point is defined as infinitely small,"
] |
[
"Does your body prioritize water usage after you drink it?"
] | [
false
] | Does your body use the water for specific places first then uses excess after for less important functions? For example will water always go to your brain before your stool? If so what regulates this. How does your body know where the water needs to go? If someone was badly constipated will the water directly go to the intestine/colon first? | [
"So when you are dehydrated does your blood actually become more viscous?"
] | [
"So when you are dehydrated does your blood actually become more viscous?"
] | [
"Related question: how long does it take for the body to absorb and distribute a glass of water throughout the body?"
] |
[
"How big of a magnifying lens would be needed to burn things with the \"moon\"?"
] | [
false
] | I understand it is actually the sun's power, but the exact same idea as burning ants or lighting things on fire with a magnifying glass. I imagine rather large and the height would be different. Maybe ladders and multiple people would be required. Thanks | [
"one at least 500,000 times larger than one needed to burn things with the sun as that is the difference between their brightness levels.",
"http://en.wikipedia.org/wiki/Moonlight",
"in other words, you would need a huge fucking lens."
] | [
"That's 500,000 times larger in area. So only about 700 times larger in diameter. I've burned things with a 3 inch magnifying glass. So you need a diameter of about 175 feet."
] | [
"Lenses do not need to be thick in the middle",
"."
] |
[
"Since photons have energy, do they have ability to transfer that energy to move an object?"
] | [
false
] | null | [
"Since photons don't have mass, they can't transfer momentum.",
"That's not true. A photon has energy and momentum, even though it has no mass."
] | [
"Google told me different"
] | [
"Then the site you found is wrong."
] |
[
"How do you know if the sun is setting or rising?"
] | [
false
] | If you didn't know where you were or what time it was, and the sun is just above the horizon, how do you know if it's the beginning of a day or the end? I know you could wait around and see which direction the sun goes, but I mean for one instant, how can you tell? | [
"In some cases you might be able to guess based on the air temperature and by what kind of climate/season you appear to be in, since it's generally colder at sunrise than sunset. But that wouldn't always work.",
"If you happened to have a compass on you you could check whether the Sun's in the east or west.",
"... | [
"Your Coriolis effect solution wouldn't work very well for someone near the equator"
] | [
"It wouldn't work very well for anyone. The Coriolis effect is not in practice really observable for anything small over a short time. If you allowed a longer period of observation, you could use a Foucault pendulum but at that point you could just look and see which way the sun had moved.",
"The concept of a per... |
[
"What is the oldest expression we still use in modern times?"
] | [
false
] | Expressions like "to the bitter end" are relatively new, but are there some which made it over from old cultures? And how old would they be? | [
"A lot of enduring phrases are usually religious in origin simply because preaching in olden times was the main way to convey an idea. \"A drop in the bucket\" can be linked to Isaiah 40:15 (KJV) for example. Now if this became an everyday expression more recently or not is harder to prove, but the strong imagery i... | [
"And because religious texts have survived in written form for thousands of years."
] | [
"Good question. As I understand it, though, ancient Hebrew is still spoken today in Israel, so biblical expressions seem like a likely source of old expressions still in use. ",
"It also strikes me that some modern expressions were recreated from ancient sources. For example, I believe “by Jove” has not been in c... |
[
"What would be better to store information on for the long term? Digital media (optical hard drives, flash, etc...) or a piece of paper?"
] | [
false
] | If I want to store a book for example, but I want to make sure it will remain readable as long as possible. Should I store it on a digital media like an HDD or an SSD, or just store the book in it's physical format (paper and ink)? There is of course the option to always make a new copy every once in a while but I'm interested about what format would last longer. | [
"Bricks. Electronic media can last 20 years, maybe 50. Paper can last for hundreds of years, we have paper that is over 1000 years old. But we have baked clay tablets that are thousands of years old, and clay pot shards older than that. Carved stone may last longer if it is the right kind of stone, but clay is easi... | [
"If the method of reading the information disappears then it is the same as if the information is gone. Hard drives may theoretically be able to stay uncorrupted for a long period of time but that doesn't mean they will remain relevant. ",
"In the past several decades we have already begun running into problems w... | [
"Just because a certain technology falls out of use does not mean that it cannot be reverse engineered to retrieve the data from said source. This is also assuming that the ability to read from a certain device has been completely eradicated from the entire human race which is unlikely. Even if it were so, it's not... |
[
"Assuming it was ridged enough and there was enough liquid, can a straw be so long you simply couldn't drink through it?"
] | [
false
] | null | [
"Yes.",
"A straw works because the pressure inside the straw is less than the ambient atmospheric pressure. So the atmosphere pushes down on the liquid and forces it up the straw.",
"One atmosphere of pressure can support a column of water only about 10 meters high (p = ϱgh)."
] | [
"Unless your straw is tiny, then capillary action is negligible. For example straw with a 0.4 mm diameter would only draw water up about 70 mm. Compared to the 10 m result neglecting capillary action, that's less than a 1% difference"
] | [
"The equation is p = ϱgh, as I already wrote. p = pressure, ϱ = density of water, g = gravitational acceleration, h = height of water column. This is just Bernoulli's principle for a fluid at rest."
] |
[
"Is there sound on mars and if so do we have recordings of it?"
] | [
false
] | We were able to get recordings of titan so it would make sense to also have a recording of mars | [
"Well obviously we didn't need to bring a machine, Mars makes all the Snickers anyway."
] | [
"It's not actually static noise, a microphone on mars would listen mainly to the rover's own noise and martian winds. Everything else is highly unlikely to happen, such as volcanic activity or meteor impact. In any case, Mars atmospheric pressure is just 0.1% that of Earth, while this is enough for sound to propaga... | [
"It's not actually static noise, a microphone on mars would listen mainly to the rover's own noise and martian winds. Everything else is highly unlikely to happen, such as volcanic activity or meteor impact. In any case, Mars atmospheric pressure is just 0.1% that of Earth, while this is enough for sound to propaga... |
[
"How does the drug 5-fluoroorotic acid select against URA3 in haploid S. cerevisiae?"
] | [
false
] | From my understanding, diploid yeast strains, specifically in Candida albicans, select against URA3 through homologous recombination. How does this selection work in a haploid strain? I've only been told that it "works" and I'm curious as to the mechanism of the selection. | [
"The Protein encoded by the URA3 gene can use 5-Fluoroorotic acid as a substrate and turn it into 5-fluorouracil which is toxic and therefore kills the yeast. It does not matter if these yeasts are haploid or diploid. If they carry a copy of the gene they will die."
] | [
"Yes it is a loss of function. So 5FOA no longer gets converted and, since it is the same enzyme, uracil synthesis is disrupted."
] | [
"I understand that much so far, I'm referring to the mechanism through which that selection occurs. Is it just a loss-of-function point mutation that is being selected for, or is it something more than that? "
] |
[
"How are we able to observe Earthrise from the moon if the moon is tidally locked with Earth?"
] | [
false
] | I was thinking of an Earth rise conceptually; wouldn't the Earth stay in one spot in the moon sky because the moon is tidally locked to Earth? I saw and now I'm wondering if the moon isn't perfectly tidally locked or if the video was taken during ascent/descent. | [
"First, the video was taken from the command module as it orbited the moon.",
"However, while the moon is tidally locked, there is a motion called libration, resulting is slightly more than 50% of the moon's surface being visible from the Earth. So, if you were on the moon in the right position (near the edge as... | [
"The video in question is taken from orbit, most likely. The spacecraft is moving from the far side to the near side, explaining the \"rise\" of Earth. That said, Earth does appear to move around a bit in the Moon's sky due to ",
"libration",
". When observed from locations near the lunar limb (the edge of the ... | [
"Huh that's pretty neat, thanks for the response!"
] |
[
"How exactly does a neuron communicate with a muscle such as a tendon in a hand?"
] | [
false
] | What is the exact process of me moving my finger? | [
"There is also the cerebellum. Information can either be 'stored' (ie about learned movements you've done in the past - and things to do with muscle memory. This is the basis upon which practice improves one's ability to play a musical instrument for example), as well as signals from the motor cortices being 'fine-... | [
"Neurons connect to muscles via the neuromuscular junction:",
"http://en.wikipedia.org/wiki/Neuromuscular_junction",
"The neurotransmitter is acetylcholine. Botox (botulinum toxin) interferes with this signaling, as does nicotine and many other cholinergic toxins."
] | [
"First off, think of the tendons as cables that connect muscle to bone, think of the ligaments as flexible support cables attaching bone to bone. Neither of these have any physical ability to contract. The muscles do the work."
] |
[
"What senses do animals have that humans don't?"
] | [
false
] | null | [
"http://en.wikipedia.org/wiki/Senses#Non-human_senses",
"One they don't list is the infrared-sensing organ of pit vipers: ",
"http://en.wikipedia.org/wiki/Infrared_sensing_in_snakes"
] | [
"Some animals can detect polarized light (some hatchling turtles for example) and Mantis Shrimp can see circularly polarized light. The also have 12 different colour sensing cells (humans have only three). Most non-mammal vertebrates can see more colours than we can. Green sea turtles have septochromatic vision and... | [
"Electroreception"
] |
[
"Why do microwaves have hot spots?"
] | [
false
] | null | [
"A ",
"standing wave",
" is setup in the microwave cavity because the microwaves reflect inside the cavity and interfere. Where they interfere constructively, you get anti-nodes, the hotspots, and where they interfere destructively, you get nodes, cold spots. Here's an ",
"animation of a standing wave",
"."... | [
"You don't want to eliminate it in a microwave. The energy of the wave has to be dissipated somewhere and you don't want it going into the walls of the microwave or back into the cyclotron. By having nodes at the walls you save a lot of power."
] | [
"Is this like an audio standing wave? In a studio control room, they eliminate dead spots for certain frequencies by doing things like adjusting the dimensions so the walls aren't parallel. Would this work in a microwave?"
] |
[
"As a black hole loses mass (due to Hawking radiation), does it eventually lose its event horizon? Would a super-heavy star suddenly appear when this happens?"
] | [
false
] | null | [
"The size of an event horizon is related to the mass of a black hole - as the event horizon shrinks due to mass loss, the rate of mass loss also increases. Eventually you get a tiny black hole that just vanishes in a burst of gamma rays. You don't suddenly get a huge amount of mass reappearing in one place - it's a... | [
"Only black holes smaller than ~4.55*10",
" kg are currently warmer than the CMB and lose mass as a result. "
] | [
"Surely it would have a minimum size as it picked up energy from e.g. the CMB? To be honest I don't understand black hole evaporation :-)"
] |
[
"How does an electric circuit actually work?"
] | [
false
] | I recently learned that in a circuit, when an emf is created due to potential difference, it starts to work. But I also learned that the electrons themselves move at a very slow pace. So what exactly is at play here? If the appliance doesn't receive electrons, how does it work? | [
"Electricity travels at the speed of light essentially, not the drift velocity of the electrons. When you close a switch or start a power source, an electromagnetic wave travels the circuit. As the wave travels, so do voltage and current, and hence the movement of electrons. ",
"Now, the wave isn't quite light. L... | [
"I always thought about an electron leaving the battery bumping a nearby electron, bumping a nearby electron. Imagine a line of people where they are all next to each other. The last person in line pushes forward a yard, person directly in front of them goes forward a yard, all the way to the front where you've g... | [
"Which is accurate, but leaves the question of how the electrons bump and at which speed the bumping will move at. The answer comes down to the electric field they each have and the net electromagnetic field they establish. "
] |
[
"Why do electrons fill up orbitals when atoms bond? Why are atoms more unstable without full orbitals?"
] | [
false
] | I would like to know what actually causes electrons to act in this manner. I know all about how an atom 'prefers' to have a balanced amount of electrons orbiting it. But why do the electrons 'oblige' and become shared? It seems strange and I can't come up with an answer, nor can my chemistry teacher. I'm not really sure if this is worded correctly, but I am extremely curious, and would rephrase as best I can if the question isn't understandable. | [
"Short answer:",
"\nQuantum Mechanics ",
"Long answer:",
"\nElectrons don't have a an exact position as it were, as you might well probably know. Instead they have a wavefunction. These wavefunctions, due to electrons being fermions, must be anti-symmetric and when the wavefunction of two electrons overlap (... | [
"I didn't explain in too much excruciating detail (to do that I would need to write a textbook). A well is a potential well (like a gravitational well, but in this case for electric stuff) and wavefunctions are mathematical constructs that when you \"square integrate\" you get the probability of the electron's posi... | [
"There is some debate about that actually. The most common and readily taught interpretation is that it is just a mathematical construct that describes the probability of finding an electron in different locations, known as the ",
"Copenhagen Interpretation",
". Different interpretations range in testability.",... |
[
"How far away from the nucleus does 100% of the electron cloud extend?"
] | [
false
] | The electron cloud is usually defined as the volume where between 90 and 97% of the electron resides. Using modeling software you can alter the parameter to see the cloud expand to 99% or 99.99%. Is there some portion (1X10 of the cloud existing a meter away from the nucleus? How about a lightyear away? Can we use this for ftl communication somehow? Does quantum nature or the Plank length act as a limit to this idea? I've tried looking through physical chemistry and quantum physics literature before, but it was too far out of my field and I gave up. | [
"The long-distance behavior of the radial wavefunctions for atomic orbitals is exponential decay. So there is no distance after which they go to zero."
] | [
"My answer above is just talking about the wavefunction of the electron in non-relativistic QM; not field theory.",
"But yes, it's a rapidly decaying function of r that asymptotically approaches zero in the large distance limit."
] | [
"So the electron field is kind of like an idealized pond, with the electron as a ripple in it? It doesn't take long for the ripple to be almost imperceptible, but it has an infinite extent throughout the pond.",
"Is that about it?"
] |
[
"Do DNA error checking routines exist?"
] | [
false
] | When files are copied on a computer there is an error checking routine which compares the original to the new file as it is being written. Is there an error checking routine for DNA which just breaks down as we get older or does error checking not exist? Might errors be intentional so that new approaches might be tried out? | [
"You could prob specialize just in the DNA repair/error recognition pathways. ",
"1st is all Very few cells stay alive throughout our lifetime and avoid apoptosis. Those that do have telomerase activity which essentially puts a protective end on their chromosomes so DNA isn’t degraded with each replication. ",
... | [
"You can run an entire lab focusing on mismatch repair due to cytosine methylation, much less DNA repair mechanisms in general. Huge field, and was the focus of a recent set of nobel prizes."
] | [
"Huge area of research. Error repair is really relevant to cancer therapy because error repair reduces the chances that a cancer cell will die from drugs or radiation that cause DNA damage. ",
"On the flip side, NASA is extremely interested in drugs that could enhance the function of DNA repair enzymes. Radiation... |
[
"Climate Change Question: Oil consumption will presumably crash on a global level over the next several months to 1 year. Will we see a commensurate dip in measured atmospheric CO2 in 2020?"
] | [
false
] | null | [
"CO2 is removed from the atmosphere on time scales of ",
"decades to millenia",
". Even if we stopped ",
" human emissions of CO2 right now, we wouldn't see a significant drop back towards natural levels for many years. I went into a lot more details about subtleties involving different types of pollution and... | [
"I felt it was important to quickly add a big picture consideration. Whilst oil consumption may decrease for a short while, in the long run fossil fuel use may increase quite a bit. For example, using coal to generate energy is a quick (and dirty) way to try and get out of an economic slump, and some countries are ... | [
"Thanks for these thoughtful answers. Looking at the Moana Loa curve, it doesn't seem to reflect other economic downturns (1970s, 2008?) ... is the presumption that this one will be so radical that it will be visible nonetheless?"
] |
[
"Are objects on the space station affected by gravity differently than the station?"
] | [
false
] | If an astronaut on the space station were to release an object in the middle of a room imparting no force on it, would the object remain in that relative spot to the space station or would the earth's gravity eventually pull the object to the wall closest to the earth? This is assuming no altitude changes from the station. | [
"If you left it at the space station's center of gravity, it would float there, undisturbed, because the station is in free fall ",
" that point. (This is how center of gravity is defined. For other kinds of center, you might run into problems, but in any case all reasonable \"centers\" will be pretty close toget... | [
"I believe in practice one of the more significant non-orbital-dynamics effects on floating objects is air currents from the station's forced ventilation - the ventilation intake screens are sometimes referred to as \"",
"the Lost and Found department",
"\". Said ventilation is ",
"absolutely necessary",
"... | [
"It's basically tidal effect - every part of the station, including objects inside, tends to stay in its own orbit. So objects closer to the Earth will drift forwards, and those farther - backwards. "
] |
[
"Can entropy exist without time?"
] | [
false
] | I was sent a book by a relative recently that uses some entropic arguments to prove the existence of God. One of them is contingent upon the idea that if the big bang was part of a bang crunch cycle, then entropy over the entirety of a string of crunch bang cycles would have to decrease spontaneously with each crunch. Since entropy is intimately related to the establishment of time, and there is purportedly no time before the big bang, is there such a thing as entropy before the big bang or across bang/crunch cycles in such a universe? | [
"That's not really a question we can answer, not using physics. The laws of physics are derived from an examination and experimentation of our universe. Whatever preceded (God, a multiverse, whatever) our universe was by definition ",
" our universe, and therefore our laws do not apply, nor do any rules or observ... | [
"Not entropy per se, but the second law of thermodynamics. In a universe where entropy can decrease history is unreliable, as physical information about the past is lost. "
] | [
"No, entropy merely provides a direction for time. Without entropy past and future would be indistinguishable, just like either end of a given spatial axis."
] |
[
"I keep hearing over and over that the big bang originated from a point the size of a pea, or a pin head, or some other tiny object. This was repeated again in the first episode of COSMOS. How do we know this?"
] | [
false
] | I understand fully that the universe is expanding out from a single point. I understand that this is a detectable and verifiable fact. What I don't get it is how science has come to the conclusion that this origin point was so tiny. Even if the origin point was said to be the size of Jupiter at the time of the big bang, that would still seem unreasonably small considering the incredibly vast amount of material in space. But a pea? A pin head? That is an incredibly specific claim. How was this determined? What is the evidence? : To clarify my question better: We are told the origin was the size of a pinhead. That seems oddly specific given the amount of unknowns about the early universe. How do we know it was a pinhead, rather than a basketball, or the size of a minivan? | [
"My understanding may be flawed, but here is what I know. ",
"Everything we see in the universe, from neighbouring galaxies up to galaxies that are far-away and the cosmic microwave background, is running away from us. That is ",
"Hubble's law",
". We can look at this, measure it, all the way to the ",
"CMB... | [
"According to NASA, we believe that the ",
" universe was once a point, but if the universe is infinite (as data does not currently contradict) then the entire universe was also infinite before the big bang. ",
"http://wmap.gsfc.nasa.gov/universe/bb_concepts.html"
] | [
"This is why science communicators shouldn't talk about how the universe \"began\". As you say, we don't understand how it came into existence, we only know (so far) how it arrived at the current state from a state at the limits of our understanding of physics.",
"That's completely different from knowing how the ... |
[
"What would happen with an magnetized metal in vacuum? Would it demagnetize?"
] | [
false
] | We are assuming no other form of radiation except background radiation. | [
"A permanent magnet is either made of iron, cobalt, or nickle, and it is formed from the alignment of the metal's atoms so that the magnetic fields of each individual atom points in the same direction. Other materials will spontaneously demagnetize because their atoms wont stay aligned, though some will align in th... | [
"Is a candle hot enough for most magnets to rearrange? Along a similar line of thought, are there any/many materials that start to retain a magnetization when they are cooled sufficiently?"
] | [
"The temperature at which a permanent magnet loses its magnetization is called the ",
"Curie temperature",
". For iron, cobalt, and nickel, it's about 1000 K, 1400 K, and 600K respectively. The ",
"hottest part of a candle burns at about 1400 C",
" or 1670 K, so it would demagnetize all of these.",
"Along... |
[
"Is there any way to identify the quality of a Tungsten ring"
] | [
false
] | The other tungsten ring question brought up discussion as to the disparity in pricing. I've looked into them before, and heard the more expensive ones are cut from a chunk of tungsten (I'm not sure if it'd be an extrusion or how else this block is formed), and that cheaper tungsten rings are sintered from powder into their shape, and are significantly weaker. Is there any truth to this? Is there a way to identify the manufacturing process when shopping? | [
"Are you talking about tungsten carbide (common) or metallic tungsten (uncommon)? Jewelers frequently use the two interchangeably which only adds to confusion."
] | [
"Its all about density. ",
"No commercial tungsten carbide products (be they jewelry or cutting tools) are made from monocrystalline TC. Materials of such high hardness are very difficult to work with, and achieving shapes of any complexity is prohibitively expensive. As a result commercial products are almost wi... | [
"Thanks! That helps clarify quite a bit!"
] |
[
"Is it physically possible to have a one-sided object that isn't a loop or something like the Mobius Strip?"
] | [
false
] | I was pondering the other day of if something besides the famous Mobius Strip can only have one side. For example, is it physically possible for a piece of paper to have one side that you can write on, while the other side ceases to exist? I have never studied physics, so I'm not sure of the possibilities. | [
"A ",
"klein bottle",
" fits what you are describing. I seem to recall I'm not supposed to just give a link in this subreddit, but I don't know what else could possibly be said. "
] | [
"Nothing wrong with links! Would be cool if you linked to the non-mobile version though."
] | [
"A solid paper sphere would seem to fit the bill."
] |
[
"What is the highest temperature any solid material/element can take without changing states?"
] | [
false
] | Im not talking just melting point either. Sublimation too. I know tungsten has the highest known melting point of any element at 3695 K, but I read somewhere that there are also other alloys that can take hotter temperature. I know carbon sublimes at around 4098 K so i'm wondering if there is anything that can go beyond those temperatures without a phase transition. Compounds are allowed too. Edit: Under earth's atmospheric pressure at sea level. | [
"Then hafnium carbonitride is the best I can find.",
"https://www.sciencedirect.com/science/article/pii/S0272884220307793",
"No direct measurement of the melting temperature, but a comparison that the melting point is higher than for tantalum hafnium carbide (~4200-4300 K)."
] | [
"It depends on the pressure. ",
"Under high pressure diamond is solid up to much higher temperatures",
", for example."
] | [
"Let's say, earth's atmospheric pressure at sea level"
] |
[
"Could you make glass out of the sand on mars? If so, how different from 'earth glass' would it be?"
] | [
false
] | null | [
"Ordinary ",
"soda-lime glass",
" is primarily made out of silicon dioxide (SiO2), sodium oxide (Na2O, the \"soda\"), and calcium oxide (CaO, the \"lime\"), plus small quantities of a few other oxides. Various Mars rovers have measured the ",
"composition of the Martian \"soil\"",
" and found that it conta... | [
"Hmm, an interesting question. The atmosphere of Mars is <1% of the pressure of Earth's atmosphere, and mostly consists of carbon dioxide. The lack of atmospheric oxygen would actually be useful, as it means you don't have to provide an inert atmosphere to stop the bath of molten tin from oxidizing (the tin dioxi... | [
"Does the atmosphere of Mars differ enough from Earth's that melting metal for the \"float glass\" technique would be difficult or impossible?"
] |
[
"Why do consistent electric streams jump around rather than have a smooth transition?"
] | [
false
] | Similarly in a plasma globe, the arc of electricity will move around smoothly, then suddenly jump to another favourable spot. My question is, what is causing the stream of electricity to move away from its initial attraction, then sudden jump to another one? | [
"The stream of electricty is a flow of electrons and this stream will always flow from low potential (its origin) to highest potential. The highest potential part is what causes the jump between favorable spots. Electric potential changes with atmospheric and environmental conditions. In the example of the plasm... | [
"The environment does not push around the stream but the stream flows through the environment as it is. Differences in the atmosphere such as moisture pockets that have developed determine the path. The stream being a flow of electrons takes the path of least resistance...mostly. Think of it like pouring water ... | [
"So the \"environment\" in which the electrons are passing through can push the stream around until a new (more direct) stream is formed?",
"Does that mean, the more uniform the medium is, the smoother the stream will be (stay)?"
] |
[
"How do parasitic wasp identify their prey?"
] | [
false
] | Thinking about, for example, the cicada hawk, how does the female identify cicada adults as her prey? Is it based on odor or some other chemical signature from the prey animal? Is it based on visual cues like body shape? Is it based on sound? And building on this....could a parasitic wasp be trained to identify a different prey animal? For example, could they be taught to lay their eggs in different insect species? Or, if an egg is transplanted to a different species, would that egg hatch into a wasp with a taste for that new species? | [
"Remember, insects don't have brains per se, they have ganglions, bundles of nerves throughout their body that process everything. They are not smart in a way that they think about stuff, they just do it. It's basically programmed into them from birth via genes, the ganglions react to certain stimuli in a certain w... | [
"You start to extrapolate this behavior and ask yourself where “response to stimuli” ends and real intelligence begins. A smarter spider might have an extra routine build into its synapses that allows it to determine some optimal jump. But, is it intelligent? Well no, it’s just got extra capabilities compared to no... | [
"Probably more than you care to hear, but this is ",
"r/askscience",
" and I'm a scientist, so...",
"I was an animal behavior major as an undergrad, took all sorts of behavior courses taught by some of the premier scientists in the US at the time - game theory, naked mole rats, bee waggle dance, all that stuf... |
[
"Do snow covered mountains still erode?"
] | [
false
] | If the temperature on the mountain never reaches below zero, I figure the only source of erosion is the wind. But when the mountain is covered with snow, does it not act as a barrier between the wind and the mountain? | [
"Yes, snow covered mountains still erode, sometimes in a spectacular fashion. ",
"You have to keep in mind that snow cover is not static, but represents a dynamic equilibrium between precipitation and slope stability. When that equilibrium is disrupted, say by a surfeit of fresh snow, mass wastage ensues and aval... | [
"Water flowing from under a glacier is often milky white due to the finely ground rock particles, which is called rock flour. Once the larger particles have dropped out the water is often shockingly and beautifully blue, due to the Rayleigh Effect. The same phenomenon makes the sky, some human eyes, and various o... | [
"That was very informative, thanks!"
] |
[
"[Physics] How can a singularity be possible given the Pauli exclusion principle?"
] | [
false
] | I know that electron and neutron degeneracy prevents the collapse of stars below the Chandrasekhar limit but how does it not prevent stars with masses greater than the limit? The singularity means all the mass particles occupy the same position and velocity. Is there some other state or theory to explain this occurrence? | [
"The singularity means all the mass particles occupy the same position and velocity.",
"Not quite. They share positions but not necessarily velocities, which means they can pile on each other just fine if they have enough energy (adding more particles means they must be higher velocity to be in a different state,... | [
"The singularity doesn't act like any other point in space, so you cannot assume that if a particle falls in and stays there that it has zero momentum. Spacetime (or at least our model of it) ends at the singularity, so it doesn't even really make sense to say that a particle can stay there, because that would requ... | [
"Another way to say it is that all ",
" inside a black hole lead to the singularity. "
] |
[
"Is modern infrastructure heat dissipation a concern for global warming?"
] | [
false
] | A genuine after-thought that's now on my mind, figured this would be the right place to ask something like this (not some anti-global warming thing, because I feel like this has that vibe just asking it). With all the technological advancements in the last 20-150 years, many household appliances and automobiles generate a ton of waste heat. We counteract this with re-search into heat dissipation tools like radiators/ heat pumps (and more) to transfer waste heat. In some cases appliances that require heat and then output it as waste etc. I know the earth has ways or methods to radiate heat away, but with the C02 issues in the atmosphere. It has me wondering if nature can't counterbalance these things by natural processes anymore. Is it possible that we're at a scale (with how big the population & the sheer amount of appliances/ products of the modern era being actively used around the globe) where this could be a possible factor of concern for global warming? or is this just a bogus afterthought? | [
"Not presently. Waste heat is small compared to radiative forcing driven by greenhouse gases. ",
"Flanner, 2009",
" estimated that globally waste heat contributed about 0.028 W/m",
". The forcing from greenhouse gases is ",
"3.0 W/m",
" (Figure 4)",
", or a bit over 100 times more. The Flanner paper doe... | [
"Not about houses but:",
"135 billion barrels of oil\n5.8 million BTU per barrel\n783,000,000,000 BTU released by oil alone. ",
"About 15 years ago I calculated the specific heat of the earth up to the first 5km of the crust and all the world's oceans. It should be much hotter than it is but it's nearly impossi... | [
"only waste heat produced by coal, petroleum, nuclear and natural gas would be a net positive on Earths heat budget. Energy gathered via renewables or hydro would have no effect and since we are quickly switching to renewables and I expect we will be at about 100% renewable use in 100 year I don't see this as an is... |
[
"Will we eventually run out of radioactive materials/Isotopes?"
] | [
false
] | Since all the radioactive substances will eventually become stable, even if it takes billions and billions of years, would the universe theoretically run out at some point in time? | [
"You can always make new radioactive substances with nuclear reactions. As long as stars exist that process happens naturally, too (although long-living low-mass stars are not particularly good at that)."
] | [
"Therefore, of all the bismuth-209 there is in the universe, half will still be radioactive after twice the universe's life span. ",
"Am I missing something? Twice the universe's current life span is some 2.8 x 10",
" years. That is still 9 orders of magnitude less than the half-life of Bismuth-209."
] | [
"Therefore, of all the bismuth-209 there is in the universe, half will still be radioactive after twice the universe's life span. ",
"Am I missing something? Twice the universe's current life span is some 2.8 x 10",
" years. That is still 9 orders of magnitude less than the half-life of Bismuth-209."
] |
[
"The effects of adolescent marijuana use on a developing brain?"
] | [
false
] | Many times here on Reddit you will see pro-legalization/anti-legalization threads for marijuana. Many of these threads also condone not smoking at least until the mid-20's due to the brain still developing and marijuana possible being harmful to underage users. Is there any evidence to support the claim that marijuana can harm the brain during the development process? | [
"Yes, temporarily. ",
"According to this study",
" many of these effects are resolved after 3 months of abstaining use. It recommends further study however, and new studies may reveal if there might be any long-term effects.",
"From the abstract - \"Adolescents who use marijuana heavily tend to show disadvant... | [
"Listen, I clearly said these instances are debatable. I'm not trying to spread false information here, I smoke marijuana myself, quite frequently, and in medical school. You can argue if you'd like, just don't go pointing a finger in my face saying that I am just bullshitting. That's all I'm going to say about ... | [
"Gynecomastia?",
"Oh ",
" I don't defend marijuana in the slightest, but you're spewing 1930's level propaganda here. "
] |
[
"How powerful would a magnet need to be to stop a bullet? What about to alter its trajectory so it is deflected?"
] | [
false
] | null | [
" \nThanks to pbmonster and filterplz for calling me out here - there is an effect by which a non-charged body can be stopped by a magnetic field - ",
"link",
". What follows is a simple examination of what system could be used to stop a bullet, assuming the bullet is a point-like particle with a net charge.",
... | [
"Theoretically, if you have a long enough chain of magnets, set up in a tunnel kind of fashion, you could slow the bullet through eddy-current fields. This is the principle that the fastest roller coasters in the world use to stop the coaster cars, in a smooth stop. If you run an aluminum fin over a magnet (needs t... | [
"I don't have an exact answer but I remember MythBusters doing a test on this in their James Bond special.",
"http://mythbustersresults.com/episode95"
] |
[
"What way would a compass point on the Moon?"
] | [
false
] | Would it point towards wherever the Moon's very weak magnetic field is strongest from that location? Or would it point towards the Earth? | [
"The moon is about 65 times further away from the Earth's core than Earth's surface is. Magnetic dipoles like the Earth's magnetic field decay in strength by 1/r",
". So the Earth's field as detected on the moon should be about 275,000x weaker than on the surface of the Earth.",
"TL;DR No."
] | [
"You'd also need a pretty good compass, since the field is about 1000x weaker."
] | [
"You'd also need a pretty good compass, since the field is about 1000x weaker."
] |
[
"Can you synthetically produce DNA base pairs? If so, could you map out a person's entire DNA strain and synthetically produce a copy of undamaged DNA from an earlier time and reintroduce it into a sick person via a virus vector to reverse damaged DNA?"
] | [
false
] | null | [
"Yes, synthesizing DNA is very common in modern genetics. We most commonly use it to create short sequences called primers, but the length isn't a large limiting factor. Even at the extreme lengths, we can stitch together sequences to get whatever we want.",
"We could synthesize an entire genome, but that would b... | [
"I forgot about Venter, I think that was first.",
"I was thinking of the early work of the ",
"Church lab",
" and ",
"this",
" recent follow up."
] | [
"Many viruses don't really work that way, and even for retroviruses this seems like an inefficient treatment. There was a very ",
"high profile case",
" out of China where a doctor introduced a known change in DNA to human embryos (twins) using CRIPSR to make them immune to HIV. This was a bit of a scandal as e... |
[
"If the Earth is closest to the sun in January, are Southern Hemisphere summers hotter than Northern Hemisphere summers?"
] | [
false
] | [deleted] | [
"No. It turns out that the slight difference in seasonal sunlight due to Earth's elliptical orbit is almost exactly cancelled out by the difference in land mass between the northern and southern hemispheres. Because the southern hemisphere has more ocean it heats up less in summer than the northern hemisphere. If a... | [
"Still no. Thermal inertia moderates atmospheric temperatures, the heat absorbed by the oceans is not dumped to the atmosphere straight away and we measure atmospheric temperature. A lot of that heat moderates winter temperatures. ",
"Measurements show",
" that the Northern Hemisphere not only has warmer summer... | [
"Yes, ever so slightly, in theory. The heat from the sun is dependant on how much incident radiation the earth gets; sunshine is literally the one and only method of getting solar energy to us (neglecting the solar wind, which is very minor compared to radiation)",
"The difference is actually really small though.... |
[
"What is different about parallel programs at a coding level?"
] | [
false
] | Some background (you can skip this and refer back to it after you read the question, if you need): I am a chemist by training but I work to develop a software package that is used to simulate various molecular properties but running a simulator. Like any simulator there are a set of rules that governs the motion of all of the particles in the system. The major difference is that these rules are not the regular laws of physics, but rather we use quantum mechanics. The equations of quantum mechanics can't be solved for an interesting system ( well can't be solved in a finite amount of time) so there is a huge variety of methods we use for different things the subtle differences between these are not very important, but some of them are very slow and scale poorly when applied to larger systems. In order to improve the speed of some of these methods I am working to modify the procedure so that the calculation can be split up into smaller parallelizable parts. I am writing a proposal to get funding for me to work on this project, and part of the proposal requires that I address any skills I have that will assist me, and those which I would need to learn before moving on. That leads to my question. I have been working on this software for a while and am able to write C++ that is satisfactory to be pushed into master repository. Other methods have been updated with parallel code but the people who developed them are not from our group or have left before I arrived, and I can get in contact with them. I just want to know is making a program parallel just a matter of writing some kind of infrastructure to manage the individual pieces of the whole calculation. OR is it done using an entirely new programing language. In short would I have to re-write all of these codes in a new language or just add too it to make it parallel? As you can probably tell from this post I do not know anything about parallel programing, so if more clarification or details are needed I would be happy to answer your questions. Thank you in advance! | [
"If you're asking if threading (\"parallel programming\") can be done in C++: yes, most definitely!",
"However, it requires a bit a different style of programming. You need to be very careful with resources (memory) to never get two threads manipulating the same bit of memory. If a bit of memory can't be changed ... | [
"\"Threading is hard!\" -- Beginner programmer",
"\"Threading is easy!\" -- Intermediate programmer",
"\"Threading is hard!\" -- Advanced programmer",
"Typically, when people say \"parallel programming,\" they mean treading. The main difficulty of threading is sharing of information, since each thread has acc... | [
"You know, if you're using super computer level hardware, it may be beneficial to skip past threading as a parallelization strategy and use message passing. This is generally the programming tool of choice for high level scientific calculations and simulations. One common implementation is ",
"http://www.open-mpi... |
[
"Is there a reason why the planets after mars are gas planets?"
] | [
false
] | On the flip side is there a reason why the planets up till mars are terrestrial? It feels more than a coincidence to me but couldn’t get much with google. | [
"Yes. It's actually a simple answer. But it's also not my field, so feel free to jump in astronomers.",
"As planets form, a critical parameter to their final size are the types of material available for them to accrete. Close to the sun, there is no ice because it's too hot. But far from the sun, ices are stable.... | [
"There's this thing called the ",
"frost line",
", the distance from a star past which it's cold enough for water ice to form. Past the frost line, planetesimals are able to accumulate water ice, thus becoming more massive more quickly, eventually being massive enough to retain huge amounts of gas."
] | [
"The process of planet formation is something we don't really fully understand. There is a lot of research into it and many competing ideas. ",
"So I'd say that we don't have one single answer to your question at the moment. "
] |
[
"How does exercise promote muscle growth?"
] | [
false
] | I've just started going to the gym recently and this question just struck me and I didn't know the answer; hoping some of you guys can help! | [
"There are a few different things that promote muscle synthesis, a lot of which feed in to activating the master protein synthesis regulator, mTOR. Nutrient abundance (eating enough protein in your diet), hormones (insulin, IGF-1, testosterone, etc), and mechanoreceptors all have a positive effect on muscle synthes... | [
"This is exactly what has been taught for at least 30 years (you remember correctly). This seems to be the standard line except that no one has actually done any real studies. They are all hypothetical. This is a great article on the subject: ",
"https://medium.com/@SandCResearch/does-muscle-damage-cause-hypertro... | [
"This is exactly what has been taught for at least 30 years (you remember correctly). This seems to be the standard line except that no one has actually done any real studies. They are all hypothetical. This is a great article on the subject: ",
"https://medium.com/@SandCResearch/does-muscle-damage-cause-hypertro... |
[
"how do pharma labs choose the name of the meds they produce?"
] | [
false
] | Do they follow any naming rules? from my point of view, if some names give a hint at what the medicine does/cures, most of them just look like someone found a funny name. Is there any existing rule for that? | [
"They can pretty much give it whatever ",
" name they want, and generally go with something that their marketing folks tell them sounds good and conveys the effect of the drug (eg lopressor to lower blood pressure). The ",
" names generally follow a set of nomenclature rules where a certain suffix denotes a ce... | [
"Oooh! Just want to add something to your monoclonal antibody thing.",
"The naming scheme for them also includes where they were derived from, such as chimeric, human, humanized, rat/mouse, etc. AND what their target is.",
"So for example, ",
"ada= prefix with no meaning",
"lim = targets the immune system",... | [
"Here are the USAN list of (name) stems",
", for anyone interested."
] |
[
"Burn from an ice cube on salt.. is the burn from the temperature or the chlorine?"
] | [
false
] | [deleted] | [
"It'd be from the temperature. Salt on ice is neither more dangerous than salt by itself or salt mixed with water. Chlorine ions really like to hold on to that extra electron they get from sodium. It takes outside energy (like in electrolysis) to make the chlorine give it up and become dangerous."
] | [
"As you've described it, it's definitely damage from the ice. The reason for the salt is that it lowers the melting point of the ice, allowing for there to be water on the person's skin which is, even if for just a moment, actually colder than the freezing point of water in the person's skin cells."
] | [
"As you've described it, it's definitely damage from the ice. The reason for the salt is that it lowers the melting point of the ice, allowing for there to be water on the person's skin which is, even if for just a moment, actually colder than the freezing point of water in the person's skin cells."
] |
[
"What is this 4,61 km big thing moving over the ocean floor and leaving a visible trail?"
] | [
false
] | I stumbled over this video, and I would really like some awnsers other than "aliens". This looks really intriguing and I wonder why i never heard of this before. I posted it to but videos are not allowed there. There must be a normal explanation for this, right? | [
"Ok, wow. First off, to save anyone else from having to give that video another view on youtube, ",
"the coordinates for the area discussed are here",
". ",
"In terms of breaking down what we can see here, a ",
"post and its subsequent links from yesterday are relevant",
". The bathymetry you see in googl... | [
"wow, thx!",
"i love this sub for people like you!",
"i knew that there needed to be a reasonable awnser, i just couldnt come up with any explanation by myself.",
"very intersting the thing with the underwater rivers! who knew such a thing could exist?",
"it just looks so weird because it has a constant wid... | [
"River width certainly can change along its length due to many factors, but it's also very common to have reasonably similar widths along a river for a decent distance. While submarine channels share some commonalities with rivers on land, I'm not as versed in their dynamics, but to me it's not at all strange looki... |
[
"Why does crossbreeding (seem to) work better with plants than animals?"
] | [
false
] | How come we see plants like and and not random mixes of animals? Have we just not tried (not saying it would be a good idea) or are there (more) genetic limitations than in plants? Or are strawberries/pineapples and tomatoes/potatoes similar enough, like in cases of and ? EDIT: disregard my terrible examples (thanks to ) | [
"Good question, but bad examples. Pineberry is not a cross of pineapple and strawberry (rather, it's two different cultivars of strawberry, as stated in the link you link), and pomatoes are tomatoes grafted onto potatoes (and therefore not cross; also as stated in the link). But it does seem like there are more in... | [
"Animals and plants use their genome in a different fashion. Animals typically encode similar but different protein in a 'compressed state' and use alternative splicing of mRNA while plants encode similar but different proteins with seperate genes. For example genes going ABC ABD ABE and ABF in plants may be AB(C/D... | [
"Yeah, it works better that way. A lot of it has to do with making sure the chromosomes ldivide nicely during meiosis and complement one another well. ",
"This",
" looks like a pretty nice description that. One of the reasons plants might cross more easily is there numerous whole-genome duplication (i.e. autopo... |
[
"When a star collapses into a black hole, does the density of the singularity continue to increase forever?"
] | [
false
] | From what I understand, once the star exceeds the electron degeneracy pressure, there's no known force in the Universe that will prevent the star from not only collapsing but to collapsing. That being said, is the density of the singularity of Sagittarius A* higher than it was, say, yesterday morning if we had some way of measuring it? | [
"It doesn't really make sense to consider the density of the singularity. You can consider the mean density of the entire black hole within the event horizon, which actually decreases as the black hole gets bigger. If you treat the center as a singularity, it has infinite density, like an electron has infinite char... | [
"Basically, if there's a mathematical singularity in a model it means that the math is failing at describing physical reality. For example, there's also a singularity at the surface of a black hole but it goes away with a coordinate transformation so it isn't something physical. A mass distribution like that also b... | [
"Probably not, but that's how they're treated formally because it works well for describing what happens on the outside."
] |
[
"Would a car accelerating to 50 MPH do more damage to a second car, then a car decelerating to 50 MPH?"
] | [
false
] | I know it seems simple, at the point of collision they both will have been going 50 MPH, One is gaining momentum while the other is losing it. Yet the car that is decelerating came from a higher speed so has a forward momentum. But then again they are both at 50 mph, anyone have any insight? | [
"If they are going the same speed and have the same mass, the collision is the same. Momentum and energy are both independent of acceleration--both only depend on velocity.",
"The only possible difference is the affect that the breaks or the engine might have in the moments after contact. One would imagine this... | [
"One significant difference that I can think of is that a braking car will have its front end lower (assuming a front engine)."
] | [
"*Effect, not affect. "
] |
[
"Is heat dissipation in nuclear powered submarines problematic from a stealth standpoint?"
] | [
false
] | many of these reactors have outputs upwards of 100MW, and the vast majority of that energy must be dumped into the ocean as heat. can this be exploited to find military submarines? | [
"There's a decent thread on the Straight Dope about this:",
"http://boards.straightdope.com/sdmb/showthread.php?t=617076",
"In short, not really. The sheer volume of water around the boat compared to the amount of coolant the boat discharges means that the heat is dissipated pretty rapidly. Also, water is a s... | [
"The reactor rating might be that high, but it won't run that hard in a stealth situation, if ever. Still 10MW is a lot of heat, but as others have said, water holds a lot of heat without drastically changing its properties, and it's hard to \"see\" IR wavelengths through water. "
] | [
"I just straight up don't believe this. Water stops radiation extremely well, that's why radioactive waste is kept in pools. I can't imagine a noticeable amount pushing through any large distance in water. ",
"To me your comment seems completely unsubstantiated, I think you should really find a source "
] |
[
"Are most of the pain receptors in the skin? If you were skinned alive, would you feel much pain after the skin had all been removed?"
] | [
false
] | This of animals skinned alive made me wonder how much pain these animals really are in. Not that I'm condoning the practice, just wondering. | [
"Just in case anyone is curious, that video (if it's the one I'm thinking of) is currently the only video on the internet I genuinely wish I hadn't seen. And I've seen all sorts of videos."
] | [
"The three types of pain receptors are cutaneous (skin), somatic (joints and bones), and visceral (body organs)."
] | [
"This is absolutely not a credible source. "
] |
[
"Does the gravity on the moon increase as you go closer to the core?"
] | [
false
] | The moon has gravity of above 0.166g on the surface. If one were to dig a tunnel underground, would the gravity be higher as one approaches the core? If so how deep would one have to deep? 100s of km? My thought is that would it be possible to have these underground bunkers in the moon where gravity would be closer to that on Earth? | [
"The opposite, actually. ",
"When you stand on a spherical object, be it the moon, earth, whatever, the entire mass of it is below you and thus you are feeling the gravitational pull in only that direction. Now, if you dig a ways down some of that mass will now be above you and will be pulling you up ever so slig... | [
"For Earth the point with the highest gravitational acceleration is at the core/mantle boundary, about 8% higher than on the surface. This comes from the very high density of the core.",
"The Moon doesn't have such a strong density gradient, and 8% more wouldn't get you anywhere close to Earth-like gravity anyway... | [
"I want to point out that this is true if the sphere has uniform density afaik. If not, the opposite can happen. Consider, for example, the system Earth + atmosphere. The atmosphere certainly has mass, but gravity is stronger on the surface of the Earth than just outside the atmosphere."
] |
[
"Does sound waves become muddled with noise if the medium it travels through is very hot?"
] | [
false
] | My rudimentary understanding of temperature has always been that particles "jiggle in place" more "violently" when their temperature increases. So, I wondered whether an increase in temperature in the medium a sound travels through, has an effect on the noise that medium introduces to a given acoustic signal. I imagine it would have no noticeable effect since sound is a more macro phenomenon, but it never hurts to ask :) | [
"Sound waves do actually move faster in warmer air. Like you said, hot air molecules move more freely than cold molecules, and so the warmer the molecule, the faster a sound wave travels through the air. This can actually contribute to higher or lower pitches in musical instruments, depending on whether the area th... | [
"How can the speed of transmission through the air affect the pitch? How fast a signal travels doesnt affect the frequency of the signal, does it?"
] | [
"If you look at the differential equations that describe wave propagation and study them in musical instruments, you'll find the solutions to musical instruments (usually the eigenfunctions/values of a wave equation in a well, eg 1d wave eq with closed closed boundary condition) will depend on the speed of wave pro... |
[
"Why isn't Nikola Tesla as highly revered as he should be?"
] | [
false
] | Growing up I didn't learn much about Nikola Tesla, elementary school was more focused on Thomas Edison and electricity, the wright brothers,Alexander Gram Bell and many others. I do not even remember Nikola Tesla's inventions being brought up till my dad told me about that and I read a book about it. Why isn't Tesla really taught in schools and why do people in the general public not know about him? | [
"We have a frequently used unit of magnetic flux named after him, but nothing like that for Edison. Also, I was under the impression that besides his useful research Tesla was quite a crackpot."
] | [
"Also, it's only been since the 2nd half of the 20th that we started to really understand and use fields and electromagnetism. His life dream, wireless power transmission is a fairly recent practice (commercially at least) so it's only now that we're starting to really appreciate how far ahead of his time he was. M... | [
"Don't forget the Prestige, in which he is not only capable of inventing a teleporter/instant-replication machine, but he also ",
" Can't beat that."
] |
[
"A question I had since high school, and probably needs an expert on magnetic shielding to answer."
] | [
false
] | No teacher or later professor was able to answer it really. But maybe I was just expressing myself insufficiently. Ok, here it goes: Imagine a brushed dc motor. Now replace the coil with a normal magnet. The result is a motor that can only do half a turn. Now get another such motor, connect them at the shaft 180° phase shifted. Now the motor shouldn't move at all. Now shield the magnetic field on one of the motors. It should move 180°. Shield the other motor, it should move 180° further. Alternating the shielding should keep the motor moving. If you connect those shields with the common shaft to rotate at the same axis 1/2 the speed, the alternating shielding is done by the motor itself. Now you have motor that doesn't need any external power supply, but has stored all its power in the contained magnets. It will run at under 50% efficiency and will have limited power output, but it will run without pause until the magnets lose their power, which means possibly for centuries. The weak/difficult point of this is obviously the magnetic shield. There are so many different ways to shield magnetic fields, all of them are difficult and for specific applications. So the question is, is there some form of shielding suitable for this application. I may even be possible to tap the induced currencies by the moving magnetic fields to increase efficiency. | [
"the alternating shielding is done by the motor itself.",
"You seem to think that moving shields in a magnetic field requires no energy - it's something you could do for free. You're wrong. There will be ",
"Foucault currents",
", plain old magnetic forces (if the shields are ferromagnetic), etc. etc.",
"Yo... | [
"It's not the materials. It's the principle. It won't work."
] | [
"Go ahead, change your design then, until \"high school physics\" don't defeat you anymore. Not vague \"it seems there are methods\" type of claim, but precise detail instead. Go on, just try. See if it works. ;)"
] |
[
"Why does animal fat turn from translucent to white/opaque when it cools?"
] | [
false
] | [deleted] | [
"Dissolved in what...?"
] | [
"Well it isn't water because the fat is all fat, fat and water are immiscible. Please don't just speculate on here, we can all guess."
] | [
"You're right it obviously can't be water so it must be just a mixture of different fats. It's impossible to say exactly what the solvent was, but the concept I explained still explains the OP's question as to why it is translucent in hotter temperatures and yet opaque in cooler ones."
] |
[
"A friend of mine claimed supermassive black holes \"create\" galaxies. To what degree is this true?"
] | [
false
] | He gave me a wishy-washy clarification that the galaxies were created by the black hole because the black hole "sucked in all the stars around it." I suspect he's full of shit. Wikipedia suggests the SBHs at the center of most galaxies are created the galaxy is formed. It does suggest that the black hole plays a significant role in the evolution of the host galaxy, however. So, , what say you? Was my friend correct? | [
"Well, we can't say he's wrong or right! This is an unsolved problem in astrophysics, I'm afraid.",
"Some models say the supermassive black holes caused galaxy formation, and others say galaxy formation caused the SMBH formation. Either way, most people agree that at least most galaxies have a SMBH at their cen... | [
"Just to clarify, not every galaxy has an SBH at the centre. Most dwarf galaxies and smaller galaxies have no SBH. In addition, the Triangulum Galaxy (M33) is a relatively large spiral galaxy that likely has no SBH at the center (",
"http://en.wikipedia.org/wiki/Messier_33#Structure",
", ",
"http://arxiv.org/... | [
"it might not even be either one exclusively"
] |
[
"Is commercial bee production helpful in addressing colony collapse, and do commercial bees suffer?"
] | [
false
] | I am a 12 year vegan who does not eat animal products, including honey, because I believe most commercially-raised animals suffer. I know plenty about the commercial production of other animals and have decided to avoid those products, but how are commercial bees produced, raised, treated and disposed of? Does commercial bee production help address colony collapse? What about bi-products of honey production, or of using bees to pollinate crops? Does commercial bee production cause pollution? I'm trying to make a completely educated decision about honey, inclusive of its impact on the environment, colony collapse, and the bees themselves. | [
"Hey,",
"I very much doubt that much pollution comes from commercial beekeeping. The only source I can think of would be from transporting colonies large distance. The bees are essentially given a perfect home in a hive that's better than anything else they would find, so they stay there and do their own thing. B... | [
"Commercial honey production is all done by the bees. They simply live in apiaries because it is designed to be a very suitable place for a nest. Commercial honey production can in a way help with colony collapse because commercial bees still produce reproductives which may be released to build homes elsewhere is... | [
"I think honey is ok. I know they use smoke to calm the bees to get the honey. They also use special honey combs that prevent the queen from laying eggs in them but still allow the storage of honey, thats what we use. We can also use the beeswax they produce. Not sure if they pollute, I doubt it since the bees do m... |
[
"Can animals feel shame? Can an animal be insulted?"
] | [
false
] | null | [
"source?"
] | [
"source?"
] | [
"Why do we have to have this comment on every \"animal\" thread? I'm sorry, but OP was crystal clear, and this comment does not bring anything to the discussion. Plus, ",
"with a bit of googling",
":",
"2 . any such living thing other than a human being."
] |
[
"When we break a bone, is it nerve receptors in the bone that register the pain, or receptors in the muscles around the bone?"
] | [
false
] | null | [
"Bones are covered by a membrane called the periosteum, which is very sensitive to pain."
] | [
"Injuries cause the body to release a cocktail of signaling molecules and other factors that lead to inflammation. Inflammation is another source of pain that may arise in the surrounding tissues as well. You often have to take a systems approach if you want to understand things like pain."
] | [
"Is that why when we \"bruise a bone,\" its the periosteum that gets injured?"
] |
[
"Does the average psychopath know they are a psychopath?"
] | [
false
] | And a corollary question: what is the estimated frequency of antisocial personality disorder among the general population? Thanks for all the replies! I am still catching up, reading them. A summary (shoot me a PM if I've erred in this!): It has been pointed out many times that "Psychopathy" and "Sociopathy" tend to be used interchangably, while "Anti-Social Personality Disorder" is considered to be quite different, based on behaviour rather than personality. I think I recall reading that the DSM only focuses on ASPD. There seems to be some disagreement on the subject of whether Psychopathy is inborn or not, and relatedly, whether it is something a person can be "a little bit of". I had always thought it stemmed from a structural difference in the brain. I haven't read anything so far which would suggest this. I have asked if it was heritable before, but received no consensus. (ASPD, however, seems to be at least partially, if not fully, based on learned behaviour.) Perhaps unsurprisingly, the general consensus tends to be that psychopaths may recognize that they are different than others, but few of the estimated 1% of people who are thought to be psychopathic would go out of their way to actually get themselves diagnosed. Typically such a diagnosis is not important except in the case of delinquency, which blurs the line between psychopathy and ASPD, as explained above. | [
"Everyone please remember this is not the place for personal stories or anecdotes. Please refrain from posting them. "
] | [
"Psychologist generally refer to psychopaths as having ",
"antisocial personality disorder",
"You are essentially asking whether they have ",
"insight",
" into their condition, which is mediated by being ",
"egosyntonic or egodysitonic",
". ",
"Some people with personality disorders like who they are... | [
"I just realized no one has answered your second question. The prevalence rate in the general population is about 1% (Coid, Yang, Ulrich, Roberts, & Hare, 2009). In prison, it is around 25% (Hare, 2001). ",
"I am going to talk to my thesis advisor in an hour so I will ask her about the other question. (I am doing... |
[
"What shape do orbitals take when angular momentum quantum number, l>3?"
] | [
false
] | While studying electronic structures why do we limit our studies to f orbitals ( l=3)? Can electrons occupy orbitals other than s,p,d,f? The angular momentum quantum number is always one less than the principal quantum number. When explaining the aufbau principle of filling electrons in shells, several texts depict the 5th shell to have four orbitals, sixth shell has 3 orbitals, and it keeps decreasing as n increases? Is this depiction erroneous? | [
"There are hydrogenic wavefunctions for every possible set of quantum numbers, you can find the functions in tables online.",
"L is not always n - 1, it can take on any value from 0 to n - 1. Orbitals beyond f certainly exist. The naming scheme goes s, p, d, f, g, h, ... alphabetically."
] | [
"To reach g-block elements (elements where some electrons occupy g orbitals in the ground state), yes.",
"But every atom has an infinite amount of bound mean-field orbitals, with arbitrarily high orbital angular momenta. So lighter elements have excited states where some number of electrons may occupy g orbitals,... | [
"Got it. L can take up values from 0 to n-1. However for it reach l=4, the atomic number has to be greater than 120 ( super heavy elements?)."
] |
[
"How does the immune system already have the DNA to make antibodies for new viruses?"
] | [
false
] | So I get exposed to a newly evolved virus, and my body will eventually "learn" to make a protein to combat it. How? Does that genetic code already exist in my DNA and my body is just turning it on or do my cells edit DNA to make a specially designed antibody? If it's the former, what happens if a virus evolves that doesn't match any DNA code I have for antibodies? Or is that not going to happen because they are using antigens that have to match my cell's proteins? If it's the latter, doesn't that go against the "central dogma" of DNA that info only flows in one direction? (DNA --> Protein) | [
"The immune system \"learning\" that people talk about is called ",
"V(D)J recombination",
" it's the process where your body produces B cells but randomly sorts variable sections of genes in order to produce a huge repertoire of potential antibody diversity. Once one of these mature B cells binds an antigen, i... | [
"You evolve the antibodies. The first step is V(D)J combination mentioned by other posters, where as it develops the new B cell recombines some possible starting sequences for antibodies to make a novel starting sequence. The new B cell is then exposed to a variety of antigens. If nothing binds, it quietly dies. I... | [
"So correct me if I'm wrong, but the body is basically trying random antibodies until something works. So then, why is there a consistent 2-week timeframe for developing immunity after exposure? Shouldn't that mean the body can get lucky/unlucky and take much shorter or much longer than 2 weeks?"
] |
[
"Why don't lakes all have unique collections of fish species?"
] | [
false
] | I know a lot of lakes are connected to rivers and other lakes, or are man-made and artificially stocked, but what about freshwater lakes that have been isolated for a long time? Has it just not been long enough? | [
"Isolated lakes that are geologically young often do not have fish at all. In North America this is (or was, before introduction of fish by humans) the case for many of the mountain lakes that were formed by retreating glaciers. Fish don't easily spread to a highly isolated mountain lake, especially if there are so... | [
"One theory:\n",
"Birds",
"Some wading birds relocate fish eggs that get stuck to their legs, thereby aiding in fish dispersal to other parts of a river or marsh."
] | [
"Thanks. I guess I was just under-informed and didn't realize that there actually are several examples of unique fish populations."
] |
[
"Why don't we use Calcium Channel Blockers in Asthma treatment?"
] | [
false
] | My understanding is that, like beta agonists, calcium channel blockers reduce the controllability of smooth muscle. As such, wouldn't a calcium channel blocker act in a similar way to a long acting beta agonist, and therefore be useful in treatment of severe asthma? | [
"We do. ",
"There's a fair bit of research done using magnesium sulfate, which is a calcium channel blocker. ",
"It's not a first-line drug, though, because the results are a bit mixed. Some studies show it gives some benefit in conjunction with the standard therapy, and some show it doesn't do anything signifi... | [
"I don't know of any calcium channel blockers than can be aerosolised for inhalation. In any case most of the CCBs don't seem to have any action upon airway smooth muscle. There are different types of calcium channels and different CCBs affect different calcium channels in different organs, and none of them affect ... | [
"They actually work in completely different ways!",
"Currently studying this now and looking at a big flowchart if that's any help.",
"Basically, in smooth muscle contraction in asthma, you have one side of the contraction cycle where cAMP activates Protein Kinase A, reducing the concentration of calcium inside... |
[
"If gravity can bend light, doesn't that mean the moon isn't where it looks like it is in the sky?"
] | [
false
] | I mean, if we see the moon as the light from the Sun reflecting back off the Moon, wouldn't the gravity of the Sun bend that very light back toward the Sun to make it look like it's a different place in the sky than it actually is? And wouldn't the gravities of the Earth and the Moon come into play as well? How do we know where everything actually is? | [
"The answer is not really. Light will always bend (even to some extremely small degree) but with weak gravitational sources this is not measurable. In addition, the way your phrasing it makes it sound like the Sun's gravity is \"pulling\" on the photons, which it is not.",
"Here",
" is a picture of one of the f... | [
"I appreciate this question. I performed a quick calculation and found that the angle of deflection of the light coming off of the moon from the sun is of order 10",
" radians. Thus the deflection distance from where the light is directed from the moon to where the light lands on earth is very roughly 10 m. Compa... | [
"As others have said, the gravity will deflect the light only by an immeasurable amount. On the other hand, ",
"atmospheric refraction",
" may bend it by a fairly large amount when the Moon is near the horizon. So much so that it wouldn't really be a stretch to say that the Moon isn't really where it looks to b... |
[
"How indistinguishable is cubic zirconia from real diamonds?"
] | [
false
] | [deleted] | [
"Cubic zircon is, in many ways, \"diamond lite\". While diamond has a refractive index of around 2.5, CZ is around 2.15. On the moh's scale, diamond is a 10 while CZ is a respectable 8. Hell, they even weigh about the same (diamond is a bit lighter). For all intents and purposes, they are indistinguishable with the... | [
"Until you get to thermal conductivity."
] | [
"This is pretty far off on all parts. They are quite easy to distinguish. Diamond isn't a \"bit lighter\", it's nearly half as dense. CZ also has higher dispersion, which you failed to mention. This means that Diamond doesn't necessarily catch the light better, I would actually give the edge to CZ on that count. "
... |
[
"Does the gravitational potential energy of the universe increase as it expands? And can energy be extracted from it?"
] | [
false
] | As space expands, is gravitational potential energy being added to the universe? And if it is, can it be harnessed? For instance, can it be transformed into mass/matter? | [
"On the one hand, yes. If you add more space between two bodies, they'll have more potential energy because of the longer distance along which they can gravitationaly pull each other.",
"However, since the universe IS expanding, there are basic forces that overpower gravity, so that potential energy is only theor... | [
"Dark energy isn't needed for expansion. It's only needed for accelerated expansion."
] | [
"The size of matter wouldn't explain all we're seeing.",
"For instance, red-shifted light"
] |
[
"Is the universe 13.8 billion years old everywhere?"
] | [
false
] | null | [
"No. As others have stated, time dilation messes around with the passage of time, and some parts of the universe will have experienced a different passage of time since the Big Bang. ",
"The one remaining piece of the puzzle, however, is asking the question: if the universe is 14bn years old.....says who?",
"Wh... | [
"As I understand, if you moved at a relativistic speed relative to Earth, you would measure the age of the universe to be smaller in your frame of reference. Can once say, then, that there exists a unique frame of reference wherein the age of the universe is maximal?"
] | [
"My gut instinct would be that 13.77bn is the maximal age (it's easy to slow time in GR, hard to speed it up), but the problem with that statement is that \"maximal\" only makes sense if you can get everyone to make a simultaneous report of the age of the universe in their reference frame, and then sort them for th... |
[
"Why does spitting into swim goggles stop them from fogging up?"
] | [
false
] | I swim a lot, and play underwater hockey, and my mask or goggles fog up in about 5 minutes unless I spit in them first and rub it around. I'm sure many of us are familiar with this trick. They stay clear for over 2 hours after this. Is there a good explanation for this phenomenon? | [
"The fogging on glass is the result of tiny water droplets clinging to the surface of the glass. They cling to the glass and to each other because water has a pretty high surface tension. Spit has chemicals which act as surfactants. Surfactants are chemicals that break the surface tension of water and cause them to... | [
"Thanks! That's cool! What are the surfactants in spit? I know it has some enzymes like amylase, but I don't know what else is in there."
] | [
"I don't know what the surfactants are, and I'm not sure it's been researched but, yes, I would suspect it's one of the enzymes."
] |
[
"Humans have one ear on each side of their head so how do they differentiate between sounds coming from the front/back or above/below?"
] | [
false
] | null | [
"Experience. The ears are not symmetrically shaped in the up/down or front/back directions, and therefore the same sound will enter the ear subtly differently depending on whether it's in front of you or behind you. You can only tell this difference from sounds you are already familiar with, which is why it's easy ... | [
"You spend your early years learning to triangulate sounds by not just amplitude differences in each ear, but also the effect your body has on absorbing sounds. When a sound comes from below, for instance, much of the sound energy is absorbed by your body and you have associated this filtered signature with a speci... | [
"This might seem a bit obvious, but humans can move their head in any direction they want. This comes into play more than people realize in terms of distinguishing where hard to locate noises are coming from."
] |
[
"From my understanding, anything that enters a black hole is brought to a singularity at the center of the black hole. How does this not go against the Pauli Exclusion Principle? Are all fermions ultimately annihilated?"
] | [
false
] | null | [
"Two ways of looking at this. The singularity of a black hole is current off-limits to modern theory. That is to say that no good verifiable theory current exists that reconciles contemporary astrophysics and quantum mechanics with the singularity of a black hole. It may need new physics, and there have been some a... | [
"Can someone please explain why this answer wrong?"
] | [
"For starters, the idea that ",
"something falling into a black hole witnesses the entire history of the universe is incorrect",
"."
] |
[
"When I write with my pencil on paper, what force keeps the graphite shards on the paper."
] | [
false
] | As near as I understand it, when I write with a pencil, I rub my crystalline graphite along the paper. The fact that graphite has incredibly strong bonds in its one plane, and quite weak bonds normal to that allows for friction to rip off huge chunks of graphite quite easily. My question is how do they stay on the paper? I can't come up with any satisfactory explanations. | [
"The paper is a tangle of fibers. The shards of graphite get stuck in the tangle of fibers."
] | [
"This is the major factor, the other is that graphite is a carbon chain surrounded by hydrogen atoms on all sides. These hydrogen atoms are capable of having weak electronic attractions with portions of the paper, which can strengthen the adhesion.",
"Edit: having\nEdit 2: Changed magnetic to electronic"
] | [
"Magnetic is not the right word, I think you mean electronic."
] |
[
"Have we found any evidence that eukaryotic organisms have existed at any point in time outside the 5 kingdoms?"
] | [
false
] | Since we have plenty of examples of other levels of the taxonomic tree of life going extinct (individual species, genuses, etc), what's the furthest "branch" we can go out from the center that is now extinct? Was there an entire class, phylum, kingdom or maybe even domain of organism that no longer exists today? | [
"Short answer: Probably, maybe, possibly, yes.",
"It's important to remember that taxonomic classification is a human construction, and nature doesn't always follow the boxes we try to put it in. The validity of the 'five kingdoms' concept is actively being discussed (along with the rest of taxonomy), and if you... | [
"Protista is more or less just a place to dump any eukaryotes that don't fit into the other 3 eukaryotes kingdoms, so in that sense there are not any eukaryotes outside of the 4 of them, but that's obviously just a case of messy taxonomy."
] | [
"Oh wow, I just read this in the page about Acritarchs:",
"A recent discovery has greatly extended our knowledge of acritarchs. Large (50μm)[5] acritarchs have been found in silica-based rocks of Archaean age in South Africa. These rocks date to 3,200 million years ago, which makes them the second oldest life to ... |
[
"Would there be any differences if the moon was twice as far away but twice as large?"
] | [
false
] | Sorry if this has been asked before, I did a search but couldn't find anything. Basically what the title says. If the moon was further away it would affect tides, but if it was also twice as big would it have the same effect that it does now? Would the lunar cycle be twice as long? What other changes would there be? Thanks | [
"It depends what you mean by twice as big. Tidal forces scale as the inverse cube of separation, so if it was twice as far away and twice as massive, the tides would be four times as weak."
] | [
"If it was twice as massive, its radius would only be 2",
" as big, because volume is proportional to the cube of the radius. So it would look much smaller.",
"It would ",
" the same if its radius was twice as big, but then its volume and mass would be 8 times as big and if it was twice as far away, then tida... | [
"I'm reading the OP's question as \"if the moon was twice as far away but had twice the radius would we see any difference?\"",
"As others have pointed out the tidal affect falls off as ",
"1/r",
" but a moon with double the radius of our moon would have 2",
" times the mass of the moon, so with the total t... |
[
"How would you create Antimatter and for what purpose?"
] | [
false
] | Hi , I was just wondering how we would create antimatter? Also what would you use it for, other than researching it's properties? Thanks :) | [
"PET-scans are named after \"positron emission tomography\". So they are used in medicine. The positrons eventually interact with the body to generate gamma-ray pairs which are measured by the device. They are the product of the radioactive decay of some isotopes. "
] | [
"At CERN in Geneva antimatter is created by firing a high energy proton beam at a block of Iridium. There are many particle processes involved and most of the outgoing particles are fast decaying Mesons Baryons and Leptons.\nA small part will be Positrons and Antiprotons which are, as long as isolated, stable. \nSi... | [
"I create antimatter by eating bananas. A small portion of the potassium is radioactive, and occasionally decays by emitting a positron. ",
"Humans emit very small amounts of antimatter all the time."
] |
[
"How does a planet's orbit change as one of the suns in a binary-sun solar system starts do 'die'?"
] | [
false
] | Given a solar system with a binary sun, where one of the suns is noticeably smaller than the other; given that such a system has only one planet with its companion moon. The smaller sun starts to die. Will the orbit of the lone planet expand or contract? Will that planet's year get longer or shorter as the sun dies off? Thanks! | [
"Stars give away energy as they radiate (thus reducing their mass) but are also acquiring new mass from from surrounding sources, so stellar masses fluctuate over time, and yes typically they net lose mass over time. However, why do you associate the act of a star \"dying\" specifically with some noticeable change... | [
"White dwarfs, neutron stars, and other stellar remnants generally have masses that are fractions of the original star's mass. White dwarfs only exist after a mid-sized star has shed its outer layers, and that shedding process during the asymptotic giant phase causes the star to lose a substantial amount of materia... | [
"Yes, but then each scenario has vastly different final masses and one must specify the final form. However, my question to the OP was stated to probe whether there may be a misconception that a bright body behaves in some way different gravitationally than a dim one of equal mass."
] |
[
"Does electrical stimulation of muscles have any medical benefit?"
] | [
false
] | null | [
"Okay then. Here's your answer: yes. And here's your evidence. Have a good read.",
"http://www.physther.net/content/65/2/186.short",
"http://www.physicaltherapyjournal.com/content/68/5/660.full.pdf",
"http://www.physther.net/content/63/4/494.full.pdf",
"http://www.physther.net/content/85/4/358.full"
] | [
"It does. I have been to physical therapy numerous times and have used this. It helps \"teach\" muscles that haven't been used for whatever reason. It also sort of assists muscles that are too weak to exercise. "
] | [
"Thanks."
] |
[
"Can your balls get tangled up?"
] | [
false
] | I mean, it seems like they pretty much stay where they are but is it possible that during some of the day they can spin around eachother and get tangled? | [
"Yes. ",
"Testicular Torsion",
" can be very dangerous if left untreated, and you could lose a testicle."
] | [
"yes. it's called ",
"testicular torsion.",
" now go away while i curl up in the fetal position and whimper."
] | [
"I'm not expert, but thanks to an episode of The Venture Brothers I am aware that ",
"this",
" is a thing."
] |
[
"How close are we to using quantam entanglement to transmit binary data?"
] | [
false
] | I was playing a game where they used this to communicate vast distances faster than light. | [
"Well, first of all, you can't use entanglement to transmit actual data. It's difficult to explain why, but imagine you have two boxes. One of them contains a red sock, and one of them contains a green sock. You do not know which is which until you open them - in fact, it is not determined which box is which until ... | [
"To be completely fair, I've oversimplified the situation a lot. It is possible for quantum events to influence each other in a way that would require faster-than-light travel, but no useful information can be transmitted by such means.",
"It is possible to extend the sock box experiment with a machine that, at t... | [
"No, because you'd need to entangle it with the other photon of the pair, which is sitting in my lab and sealed from outside interference."
] |
[
"Are there any real and tangible examples of the Butterfly Effect?"
] | [
false
] | For those that haven't heard of it, here's the definition from Wikipedia. In chaos theory, the butterfly effect is the sensitive dependency on initial conditions in which a small change at one place in a deterministic nonlinear system can result in large differences in a later state. The name of the effect, coined by Edward Lorenz, is derived from the theoretical example of a hurricane's formation being contingent on whether or not a distant butterfly had flapped its wings several weeks earlier. | [
"A pendulum consisting of two rods (so basically a pendulum with a pendulum attached to it) is an easy example. Small differences in the initial state will make the system behave completely differently. It is still a predictable system though, but in order to make any senseful predictions one would need very accura... | [
"Rolling dice is the easiest example. Physically, a die is nothing more than a cube. It obeys the laws of physics in very predictable ways. Yet the tiny, tiny variations in the initial state of the die as it is thrown are enough to make its result more-or-less completely unpredictable.",
"If the roll of the di... | [
"Absolutely. The intial state of the die as it is being thrown can vary very little in terms of momentum, angle, facing, etc... but once it starts bouncing around it becomes very hard to predict how those individuals changes will result in the die landing. That's the main reason dice have been used for so long as... |
[
"Is there friction associated with dark matter?"
] | [
false
] | The context of the question being that if we someday travel to another star system, would this be a factor in the time it takes to get there/energy we'd have to use, etc.? How would we measure such a thing? Is there any evidence from the Voyager probes that they're slowing down? | [
"There was a recent paper showing that there is friction from dark energy (sort of). "
] | [
"Any chance you could elaborate?",
"Also, being that the question asked about dark ",
", is it possible for dark matter to apply friction to objects? I would think not, since it doesn't participate in EM interactions (although its gravity might do something to objects floating through it)."
] | [
"http://pra.aps.org/abstract/PRA/v82/i6/e063827"
] |
[
"What are the physiological processes that make us want to sleep?"
] | [
false
] | I mean if there is anything which builds up in your brain while you are wake, and when you sleep, it gets cleared. How does your brain know that it is tired? Is there any evolutionary explanation for this phenomenon? | [
"Thanks for great explanation. Do you also know how excess adenosin is pumped out from the brain while sleeping? As far as I remember unlike muscles and tendons, brain has no plumbing system to remove the waste."
] | [
"Thanks for great explanation. Do you also know how excess adenosin is pumped out from the brain while sleeping? As far as I remember unlike muscles and tendons, brain has no plumbing system to remove the waste."
] | [
"This",
" is the paper that showed metabolites are flushed out during sleep. The mechanism seems to be ",
"pulsation of cerebral arteries",
".",
"In addition, the brain's metabolic rate is lower in non-REM sleep than during wakefulness. This results in less accumulation of metabolites (including adenosine) ... |
[
"Where did all the sand in the Sahara Desert come from?"
] | [
false
] | null | [
"The sand is primarily derived from weathering of Cretaceous sandstones in North Africa. When these sandstones were deposited in the Cretaceous, the area where they are now was a shallow sea. The original source of the sand was the large mountain ranges that still exist in the central part of the Sahara. These moun... | [
"Actually yes. It's where some of our best fossils of ancient whales come from. ",
"https://en.wikipedia.org/wiki/Wadi_El_Hitan"
] | [
"So underneath the Sahara could be fossilized remain of old trees or animals?"
] |
[
"How does the human body physically lose weight?"
] | [
false
] | null | [
"But why after sleeping? Wouldn't I weigh the same right after I had my last meal? Between that point and the point I wake up, I haven't lost any mass."
] | [
"There would be some slight increase in weight loss because of the energy in expanding and contracting the diaphragm to breathe more quickly, but this is very minimal if there is any energy difference at all. What would essentially happen is that you'd be breathing more oxygen then your body needs so some excess wo... | [
"I see. The level of CO2 you exhale is not constant, and the level is determined by the amount of waste your body wants to get rid of. So if you're not actively burning fat, you'll exhale less CO2, despite how much you're breathing. "
] |
[
"What is the biggest sphere that can exist in the universe from a mathematical standpoint, and only assuming that the Planck length is correct?"
] | [
false
] | Ok, first of all, , in case anybody wonders. I was just hypothesizing the following: Imagine a perfect sphere lying on a perfectly flat plane. The sphere is infinitely light and doesn't flex, nor does the plane, so that they only connect in one point. Read the following paragraph looking at the "image" below. Look at a section of the sphere that passes through its center. Look at the point where this section touches the plane (A=B). Walk along the circumference of this section for the Planck length, to C, and observe that the distance of this point to the plane is the Planck length (the distance between C and D). What's the diameter of the sphere? | [
"At this scale there is no edge of anything to walk along. The Planck length is 10",
" times smaller than the smallest neutrino, 10",
" times smaller than an electron, and 10",
" smaller than a hydrogen atom. You're talking about the edge of a sphere like it would be something that exists at this scale but ... | [
"Wait, isn't the sphere continuous? Unbounded? Wouldn't that mean that it could be of any size, so long as that size is greater than the planck length?",
"A sphere greater in diameter than the planck length will always have at least a part of it's circumference that is equal to the planck length."
] | [
"A sphere greater in diameter than the planck length will always have at least a part of it's circumference that is equal to the planck length.",
"So let's name A and B the two ends of this part of the circumference of length ",
" (Planck length).\nThere's a plane passing through A and this plane is tangent to ... |
[
"Can a lake be so deep that it's own pressure creates ice?"
] | [
false
] | I know that at lower air pressure water boils at lower temperatures. Logically, at areas of high pressure, water should freeze at higher temperatures. Is it theoretically possible that a lake is so deep that it's own pressure causes water to become ice at the bottom? If so, how deep would that lake have to be? And, if possible, what would happen to any ice since it is less dense as a solid than a liquid? | [
"Logically, at areas of high pressure, water should freeze at higher temperatures. ",
"It doesn't, until you get to ~200 MPa. Water is weird that way. ",
"Is it theoretically possible that a lake is so deep that it's own pressure causes water to become ice at the bottom? If so, how deep would that lake have t... | [
"The freezing point of water is depressed under increased pressure up to about 200 MPa. A lake would have to be about 20 kilometers deep to have that pressure at the bottom. This is only 15 or so times deeper than Lake Baikal and twice as deep as the Mariana Trench. "
] | [
"Logically, at areas of high pressure, water should freeze at higher temperatures.",
"at very high pressures, the pressure forces the water molecules into a conformation that is unfavorable for ice formation. the angles for the bonds get all funky, so the freezing point actually ",
"."
] |
[
"How was the permeability of free space derived?"
] | [
false
] | It seems really strange to me that it is a constant with respect to pi. What were the calculations to derive that the permeability of free space is equal to 4π×10 V·s/(A·m) | [
"Well... there's a fixed relationship between the permitivity and permeability of free space (c",
" = 1/(ε0μ0)). In the SI system of units, meters and seconds are both defined, and therefore c is fixed. We then ",
" the permeability of free space, which in turn fixes the permittivity of free space.",
"So in ... | [
"The value is defined and the pi apear as a result, I think nice explains it nicely: \n",
"http://en.wikipedia.org/wiki/Magnetic_constant"
] | [
"Start reading at the bottom of ",
"page 2.",
"I could give further explanation, but I think that presentation is rather concise. "
] |
[
"Is there a safe way to modify the human dna?"
] | [
false
] | null | [
"Look into CRISPR Prime editing. It’s a powerful form of Cas protein and guide RNA that is theoretically a safer form of gene editing than traditional CRISPR. This is because it doesn’t require the generation of a DNA double strand break which is the most dangerous DNA lesion for the cell. And also because it’s bee... | [
"Safe is relative as it has to be balanced against the need to change. ",
"But generally speaking, there is no currently safe way to do that, but we do have new technology that can do that, most famous is CRISPR/CAS9. ",
"There is too issues preventing this from being used outside very experimental setting",
... | [
"PS: it's CRISPR, not CRISPER",
"PS2: what's LF DNA?"
] |
[
"When Neil Armstrong made his first footsteps on the moon, did the dust make a crunch similar to walking on freshly packed snow?"
] | [
false
] | null | [
"Probably not. The lunar regolith has the consistency of fine dust or sand. It was probably more like walking on really dry soil (the kind that goes everywhere when you walk on it) than snow. Even though there is very little atmosphere on the moon, the astronauts would have been able to hear themselves walking arou... | [
"but he was wearing a space suit which had air inside of it. So him stepping onto the surface could absolutely have transmitted sound through the suit to his ear."
] | [
"Space suits aren't exactly the best conductors of sound waves.",
"If there was any sound, it would most likely be Baffled before it left the astronaut's boots. ",
"edit: better word usage"
] |
[
"How far back can we trace the etymology of our words?"
] | [
false
] | When I look up a word like "fire" in the dictionary it gives a cursory explanation that it comes from "fir, old english." But at some point words had to have formed out of pre-civilization unsophisticated communications. How far back can we track our oldest words? To phrase my query another way; can we trace any words back to grunts and unstructured vocalizations of cavemen and neanderthals? | [
"Most linguists agree that the farthest historical linguistics can get is 5,000 to 10,000 years. There are a few linguists who claim that they can go farther, but most linguists don't buy their arguments.",
"English, Russian, Ancient Greek and Sanskrit are Indo-European languages. Their ancestor language, late ... | [
"/u/ygam",
" has already answered part of OP's question, but there are a couple of problematic assumptions in there that need to be addressed.",
"First, OP asserts that:",
"at some point words had to have formed out of pre-civilization unsophisticated communications",
"We have no reason to believe that lang... | [
"Basque is a linguistic isolate, which means it has not been demonstrated to be related to any other language. So it is spoken in Europe, but is not related to any other language in Europe (or any language that we have evidence of)."
] |
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