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[
"I have read online that some fabrics have antimicrobial properties. Is this true? How does this work?"
] |
[
false
] |
[deleted]
|
[
"Antibacterial metal-infused clothing contains copper, which as a surface material has antimicrobial properties due to several chemical interactions it can have with bacterial cells.",
"Effects described here: ",
"https://cuverro.com/resources/faqs/how-does-copper-kill-bacteria",
"Copper-infused clothing has been shown to have antibacterial properties, however according to this article ",
"http://community.dur.ac.uk/wp-content/uploads/sites/9/2018/02/Investigating-the-antimicrobial-properties-of-copper-infused-fabrics.pdf",
", it seems to depend on the thickness and absorbency of the material. ",
"The bamboo plant has natural antibacterial agents to prevent unwanted growth on the living plant, but there are conflicting claims on whether or not those agents are lost in the textile manufacturing process, with most reputable agencies concluding that there are no antibacterial benefits to processed bamboo clothing.",
"This study examined the antibacterial effectiveness of prepared bamboo fibres against other plant fibres: ",
"https://www.swst.org/wp/meetings/AM12/pdfs/papers/BAF-1.pdf"
] |
[
"I forgot to mention hemp here but in this article it appears that hemp fibres do have antibacterial activity possibly due to cannabinoids or other bioactive compounds:",
"https://bioresources.cnr.ncsu.edu/resources/antibacterial-properties-of-hemp-and-other-natural-fibre-plants-a-review/"
] |
[
"Additionally, many silver infused hospital scrubs are advertised as bacteria resistant while various studies have found no beneficial effects to their use. One therefore has to be careful that using these doesn't produce a false sentiment of security. ",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3382727/",
"https://www.researchgate.net/publication/334198599_Medical_textiles_with_silvernanosilver_and_their_potential_application_for_the_prevention_and_control_of_healthcare-associated_infections_-_mini-review"
] |
[
"Is it safe to boil water in a plastic container?"
] |
[
false
] |
I've recently learned that boiling water in a plastic container such as a water bottle is survival tactic. I can understand this in unusual circumstances. However, I'm wondering if this would release other toxic bits into the water by doing this.
|
[
"A lot of reusable water bottles now advertise BPA free so many are safe from BPA probably even when boiling. However, that's not to say that there aren't more potentially harmful substances in plastic containers that might leach out. BPA is used in other containers also like for lining metal cans for food and beverages. ",
"According to Science Daily:",
"Prior to boiling water exposure, the rate of release from individual bottles ranged from 0.2 to 0.8 nanograms per hour. After exposure, rates increased to 8 to 32 nanograms per hour.",
"However, they also go on to say that \"it is still unclear what level of BPA is harmful to humans\" and that cumulative exposure should be considered.",
"I a survival situation however, I find it difficult to imagine that one would use a plastic vessel for boiling water. I am, however, assuming that there would be no electricity and thus no microwave and that you are not heating the water in a plastic vessel over an open flame. ",
"http://www.sciencedaily.com/releases/2008/01/080130092108.htm"
] |
[
"A lot of reusable water bottles now advertise BPA free so many are safe from BPA probably even when boiling. However, that's not to say that there aren't more potentially harmful substances in plastic containers that might leach out. BPA is used in other containers also like for lining metal cans for food and beverages. ",
"According to Science Daily:",
"Prior to boiling water exposure, the rate of release from individual bottles ranged from 0.2 to 0.8 nanograms per hour. After exposure, rates increased to 8 to 32 nanograms per hour.",
"However, they also go on to say that \"it is still unclear what level of BPA is harmful to humans\" and that cumulative exposure should be considered.",
"I a survival situation however, I find it difficult to imagine that one would use a plastic vessel for boiling water. I am, however, assuming that there would be no electricity and thus no microwave and that you are not heating the water in a plastic vessel over an open flame. ",
"http://www.sciencedaily.com/releases/2008/01/080130092108.htm"
] |
[
"I'm almost positive plastic will boil water. The parts of the plastic containing water cannot melt. ",
"this",
" vid.",
"Points of interest will be at 3:20, 6:40, and 11:50 along with his video comments."
] |
[
"What exactly is meant when by electrons being negatively charged, protons positively charged, and neutrons having no charge?"
] |
[
false
] |
I understand that protons are positively charged, electrons are negatively charged, and neutrons have no charge, but why? What exactly is "negative" about an electron and "positive" about a proton? I understand that positive repels positive and positive attracts negative, but beyond these properties how does a positively charged particle behave differently from a negatively charged particle? I read that the charge of a particle is determined by its response to the electromagnetic field, but how?
|
[
"guessed, and got the answer wrong",
"Not true, that's a popular myth. It's based on the wrong idea that positive charges are not real, and that electric currents are flows of electrons.",
"Electric current in human bodies is a flow of positive sodium and an opposite flow of negative chloride ions. When you get shocked, two interpenetrating clouds of opposite-charged particles are flowing through each other in opposite directions. In electrolytic conductors, no electrons flow at all, and the charge-drift is in two different directions at the same time.",
"Electric current in plasma is two opposite flows: electrons in one direction and positive gas ions in the other. Same idea applies to liquid metals.",
"Electric current in proton conductors is a flow of positive charges. No electrons. (Go look up Proton Conductor.)",
"Aaaaaaand ...electric current in solid metals is a flow of negative electrons.",
"How can Franklin have chosen \"wrong,\" when the polarity of flowing charges depends on which kind of conductor is carrying the current?",
"So, while current \"flows\" from positive to negative,",
"No, it doesn't.",
"The vector for Amperes in conductors is always in the positive direction. A flow of negative charges has its vector backwards, but that has nothing to do with the motion of the charges. Or said more simply: if Franklin had chosen things the other way, then while it's true that all the Proton Conductors would then have their charge flow opposite to their current's vector, all the electrolytic conductors would still be the same as now: two clouds of opposite charges flowing in two directions simultaneously, regardless of the ",
" vector associated with the Amperes. The charge motion in electrolytes is not the electric current direction. To find out the amps, you have to flip the direction and the polarity of the negatives, then add that current to the positives.",
"So, Franklin was wrong in thinking there could be a single \"kind\" of electricity, since, in his original proposal, he thought that one polarity of charges carried all the mass of the conductor atoms, while the other polarity of charges was massless. This is wrong in general. It doesn't apply to currents in dirt, ocean, human flesh, and fluorescent lamps. It does apply to ",
" metal conductors, sort of.",
"Finally, when looking at an antimatter flashlight from an opposite universe, Ben Franklin would still be wrong, since physics is supposed to describe electric currents in all cases: antimatter metals, AND electrolytes, AND hydrogen plasma currents, AND proton beams, ...even cold solidified copper, etc."
] |
[
"We can do a little bit more than just say \"charge exists,\" and leave it at that. There is a principle of the universe called U(1) gauge invariance. U(1) gauge invariance explains a variety of things -- why there is a photon, why the photon is massless, and why there are electromagnetic fields and waves. It also implies that every field has a charge given by a real number (this is non-trivial; other forces have charges are given by matrices), and so those charges can be positive or negative or zero. It also tells you the difference between positive and negative charge and between different magnitudes of charge, and tells you the form of the electromagnetic forces on charged particles.",
"Now we still can't answer why there is U(1) gauge invariance or why there are matter fields or why those matter fields have the specific charge values they do, so certainly there are things we still just have to assert. But U(1) gauge invariance does explain many of the properties of charges and electromagnetism with one principle."
] |
[
"We can do a little bit more than just say \"charge exists,\" and leave it at that. There is a principle of the universe called U(1) gauge invariance. U(1) gauge invariance explains a variety of things -- why there is a photon, why the photon is massless, and why there are electromagnetic fields and waves. It also implies that every field has a charge given by a real number (this is non-trivial; other forces have charges are given by matrices), and so those charges can be positive or negative or zero. It also tells you the difference between positive and negative charge and between different magnitudes of charge, and tells you the form of the electromagnetic forces on charged particles.",
"Now we still can't answer why there is U(1) gauge invariance or why there are matter fields or why those matter fields have the specific charge values they do, so certainly there are things we still just have to assert. But U(1) gauge invariance does explain many of the properties of charges and electromagnetism with one principle."
] |
[
"What happens if you repeatedly melt glass?"
] |
[
false
] |
If you have glass and you melt it, then allow it to cool and harden, then melt it again and repeat a few times, will the glass become brittle? What change will happen to the glass?
|
[
"Glass is already tremendously brittle.",
"But to respond to the substance of your question: glass doesn't have a memory. It doesn't remember that it's been melted 50 times before in the last 24 hours instead of 1 time. So the parameters that affect the properties of glass are simply those of the most recent melt/solidification cycle."
] |
[
"It exists as its own creature now. Let it float freely on the currents of the internet, educating mildly curious people around the world :)"
] |
[
"Glass is complicated. Tempering is usually done in a separate step after it has been shaped - it is reheated until gooey and then cooled. Annealed glass can start liquid and is brought down gently, but not so gently that it has time to crystallize and devitrify."
] |
[
"What causes very salty water to be visibly different from pure water when the two are initially combined?"
] |
[
false
] |
I work as an RA in a neuroscience lab and regularly have to dilute a 10x saline solution. Whenever the concentrated salt water is added to pure water there are visible "waves" much like you see on the highway on a hot day. After it is fully mixed these waves are no longer apparent. Is this due to different densities between the solutions or is the charge from ions causing refraction in some regions and not others? Something else entirely?
|
[
"It is due to the different indices of refraction. You can see ",
"this table here",
"What you see when there's a mixture of two indices is called a schlieren."
] |
[
"I understood that different refraction properties cause these visual differences, but was curious as to why they are different (density, ionic charge). ",
"Schlieren is an awesome new word though, thanks! "
] |
[
"The refraction properties go back to the polarisabilites of the molecules/atoms in the solution. Because you have sodium an chloride in one part and none of those in the other the refractive indices of the solutions differ. At the surfaces of these different solutions the light will change direction just like it would at the surface of a lense. This makes the schlieren (German word) visible, they fade away as the \"two types\" of liquids mix and there is no \"surface\" left."
] |
[
"Are quantum leaps in FLOPS feasible with current technology?"
] |
[
false
] |
[deleted]
|
[
"You have built a computer that utilises each of the 10",
" atoms in the observable universe as a core. Each of these cores is capable of running at the fantastic rate of a million-billion-",
"googol",
" ( 10",
" ) expressions per second. Your computer has been running for 13.7 billion years (4.3x10",
" seconds) since the dawn of the universe. Your solution is currently a total of 0.000000000000000000000000000000000000000000000000000000005% (5x10",
" %) completed...",
"So unfortunately 10",
" expressions will never be solvable no matter how good technology gets. Also, true ",
"quantum leaps are actually incredibly tiny",
"!"
] |
[
"That is the most upsetting, yet strangely gratifying thing I've heard today. On one hand, it's a sad realization of just how large the number is. On the other hand, I suppose it means that my analytical research is actually useful and won't just be obsolete one day (Like many-a-paper of last century). Thanks for the realization!"
] |
[
"For a while, computing trends followed an empirical observation known as ",
"Moore's law.",
" (It's not a causative law, it's just an observation). It states that computing powers have been growing exponentially for some time. That's pretty nifty, but if you talk to anyone who knows their stuff about this, there's a limit to the law which we know no way past. So far a great deal of progress has been made by making transistors smaller and smaller, so you can fit more of them in a CPU. But there's a fundamental limit to this process, because transistors have to be made of atoms, and thus at least the size of an atom.",
"Realistically this means that a fundamental breakthrough, the likes of which are unknown to anyone right now, would have to occur in order to reach computing power of the magnitude you mention.",
"In fact, 10",
" is such a huge number that there are other limits we can use. If you have to save the result of each of your 10",
" simple expressions, there are more numbers to save than there are protons in the observable universe."
] |
[
"Is the strength of a magnetic material based solely on the amount of pure magnetic material present? And are iron,nickel and cobalt equal in their magnetic strength? Why/why not?"
] |
[
false
] | null |
[
"You also have the interactions of mixes of materials. For instance the alloy ",
"Alnico",
" is a mix of aluminum, nickel, iron, copper, and cobalt. But the mix makes a much stronger magnet than any of the pure ingredients. With aluminum and copper considered completely non-magnetic.",
"The composition of alnico alloys is typically 8–12% Al, 15–26% Ni, 5–24% Co, up to 6% Cu, up to 1% Ti, and the balance is Fe",
"The mix effect is even stronger in the ",
"rare earth magnets",
". ",
"The greater strength of rare-earth magnets is mostly due to two factors. First, their crystalline structures have very high magnetic anisotropy. This means that a crystal of the material preferentially magnetizes along a specific crystal axis but is very difficult to magnetize in other directions. Like other magnets, rare-earth magnets are composed of microcrystalline grains, which are aligned in a powerful magnetic field during manufacture, so their magnetic axes all point in the same direction. The resistance of the crystal lattice to turning its direction of magnetization gives these compounds a very high magnetic coercivity (resistance to being demagnetized).",
"Second, atoms of rare-earth elements can have high magnetic moments because their orbital electron structure contains many unpaired electrons, in contrast to other elements, in which almost all of the electrons exist in pairs with opposite spins, so their magnetic fields cancel out. This is a consequence of incomplete filling of the f-shell, which can contain up to 7 unpaired electrons. In a magnet it is the unpaired electrons, aligned so they spin in the same direction, which generate the magnetic field. This gives the materials high remanence (saturation magnetization Js). The maximal energy density BHmax is proportional to Js2, so these materials have the potential for storing large amounts of magnetic energy. The magnetic energy product BHmax of neodymium magnets is about 18 times greater than \"ordinary\" magnets by volume. This allows rare-earth magnets to be smaller than other magnets with the same field strength."
] |
[
"You also have the interactions of mixes of materials. For instance the alloy ",
"Alnico",
" is a mix of aluminum, nickel, iron, copper, and cobalt. But the mix makes a much stronger magnet than any of the pure ingredients. With aluminum and copper considered completely non-magnetic.",
"The composition of alnico alloys is typically 8–12% Al, 15–26% Ni, 5–24% Co, up to 6% Cu, up to 1% Ti, and the balance is Fe",
"The mix effect is even stronger in the ",
"rare earth magnets",
". ",
"The greater strength of rare-earth magnets is mostly due to two factors. First, their crystalline structures have very high magnetic anisotropy. This means that a crystal of the material preferentially magnetizes along a specific crystal axis but is very difficult to magnetize in other directions. Like other magnets, rare-earth magnets are composed of microcrystalline grains, which are aligned in a powerful magnetic field during manufacture, so their magnetic axes all point in the same direction. The resistance of the crystal lattice to turning its direction of magnetization gives these compounds a very high magnetic coercivity (resistance to being demagnetized).",
"Second, atoms of rare-earth elements can have high magnetic moments because their orbital electron structure contains many unpaired electrons, in contrast to other elements, in which almost all of the electrons exist in pairs with opposite spins, so their magnetic fields cancel out. This is a consequence of incomplete filling of the f-shell, which can contain up to 7 unpaired electrons. In a magnet it is the unpaired electrons, aligned so they spin in the same direction, which generate the magnetic field. This gives the materials high remanence (saturation magnetization Js). The maximal energy density BHmax is proportional to Js2, so these materials have the potential for storing large amounts of magnetic energy. The magnetic energy product BHmax of neodymium magnets is about 18 times greater than \"ordinary\" magnets by volume. This allows rare-earth magnets to be smaller than other magnets with the same field strength."
] |
[
"Great answer, thank you so much! I had come across several of these points searching the internet but none that answered my question so completely. Also, given you are looking at a diagram of magnetic field lines around a magnetic object, is the magnetic force stronger along these lines than in between them? Or is it a simple representation and the field is uniform throughout?(except getting weaker with distance)"
] |
[
"How does the brain decide when to release dopamine?"
] |
[
false
] |
As we know, dopamine is responsible for making us feel good after we do some action (often stupid acts). How does brain knows which acts deserves dopamine release and which don't ?
|
[
"As always with most neuroscience-related questions, we don't have a well-worked out theory for how value is represented and learned in the brain. That said, we do know some pieces of the puzzle. First of all, nervous system function is very tightly related to patterns of neural firing in different systems. These patterns influence the patterns in other regions due to how they are connected. Ultimately, neural firing patterns are translated into motor actions. ",
"Neurotransmitters and neuromodulators influence the system in virtue of how they effect neural firing patterns. There is nothing in the chemical itself that makes it play the functional role that it does. As others have stated, there are many systems that utilize dopamine, not all of which are related to reward (e.g. Parkinson's disease is critically related to dopamine but causes primarily motor deficits).",
"I'm guessing that the thrust of your question is this: dopamine seems to be telling some brain areas that something good just happened - but what is telling the dopamine system that something good just occurred? This is a good question and leads to the ongoing investigation into the representation of value in the brain, which includes both subcortical structures like the Nucleus Accumbens as well as cortical structures like medial prefrontal cortex and orbitofrontal cortex. Ultimately, what I think your question highlights is that the view that dopamine is a pleasure chemical which tells the brain something good happened is highly oversimplified. "
] |
[
"Dopamine is responsible for so many things! There are actually 4 major dopaminergic pathways which have varied functions like motor control and assisting in endocrine function.",
"The one you are referring to though is the mesolimbic dopamine pathway. This is the widely discussed \"reward pathway\". Basically dopamine is released from the ventral tegmental area (VTA) and acts at the nucleus accumbens (NAc).",
"So then the question is what activates VTA? This is where the answer gets kinda vague, because it's a lot. Amygdala, hippocampus, prefrontal cortex, cingulate gyrus, olfactory bulb and so on... So you can reason this action is important (PFC) or maybe have a large emotional response to it (amygdala) or see it as something novel and exciting (hippocampus)... and many brain regions converge and activate the mesolimbic pathway and you get this feeling like, \"this is great, we should keep doing this.\" At it's most basic level, there is a high level of cognitive input, and what is necessary for survival feels good.",
"In the case of \"some stupid acts\" like drug use, you are literally jacking your nervous system so you feel some supra-physiological level of dopamine release. This is dependent on the given drug and it's mechanism of action."
] |
[
"Yeah, you described the mesolimbic pathway pretty well. However, dopamine has more recently been considered for learning behaviors, helping our attentiveness to pair operant behaviors with associated rewards, not necessarily acting as a pleasure chemical itself. They think glutamate is that pleasure chemical. (Not saying what you said was outright wrong, but this is just a new idea being thrown around)",
"A pretty simplistic view has DA responsible for movement and motivation (like you mentioned)"
] |
[
"Does our brain having to flip everything we see as a result of our upside-down retinas impact/decrease reaction time?"
] |
[
false
] |
I recently learned that our retinas are upside down, thus our brain has to flip everything we see in order to well... Not see everything upside down, so I've been wondering if the extra task of fliping the image cause a measurable decrease in average reaction time.
|
[
"I was skeptical simply because it seems like it would a difficult and unpleasant experiment to do.",
"You underestimate how inquisitive and dedicated scientists can be. Some of them have worn those glasses for days at a time, and the brain does adapt.",
"https://en.wikipedia.org/wiki/George_M._Stratton#Wundt's_lab_and_the_inverted-glasses_experiments"
] |
[
"Your brain does not have to flip anything. The image on your retina is only inverted relative to another upright person looking at your eyeballs. Your brain does not have a separate pair of eyes. Information from the bottom part of the retina just corresponds to the upper part of the world.",
"By analogy: if you are holding a map in your hands, north on the map always corresponds to north in the world no matter which way you are facing or how you hold it. You don't have to align the map with the world in order to read it."
] |
[
"I dont know if this is true, but I read that if you give a person glasses that flips things upside down the brain will after a period of time flip it. I was skeptical simply because it seems like it would a difficult and unpleasant experiment to do."
] |
[
"Any techy's about or Internet service provider experts?"
] |
[
false
] | null |
[
"Hi ",
"/u/deano2440",
" ,",
"Your question is quite vague. Mobile and \"landline\" networks differ because they have different objectives. Thus, they use different technologies - there is no one-size-fits-all solution.",
"If you have more specific questions, feel free to resubmit.",
"Cheers."
] |
[
"Thank you, well, in my local area, the internet is soooooo bad, legit.\nDuring gaming, I am often DC'd due to the connection of my internet. However, i do not disconnect or have any issues when i hotspot the PC to my phone which runs 4G! \nI just thought if I am able to get better/stronger connection from a hotspot vs my landline then surely the future leads to extinction of fibre optic?"
] |
[
"edit: in my area (maybe different in other areas)"
] |
[
"If you have already done PCR what are the reasons you would want to transform bacteria with your PCR product?"
] |
[
false
] |
[deleted]
|
[
"E.coli replicates the plasmids with extremely high fidelity, at least 100 times better than the best available polymerases . Also an overnight culture can easily give you milligrams of plasmid DNA. plasmids can also be used to transform other organisms like bacteria, yeast, even human cells. "
] |
[
"plasmids can also be used to transform other organisms like bacteria, yeast, even human cells. ",
"This is usually the reason. If all you care about is the sequence you can sequence the PCR product directly (eg. if you want to be really sure your primers are amplifying exactly what you think they are). You clone it into bacteria because you're going to use the plasmid for something else later on, the sequencing is basically a quality control step to confirm that you've made the plasmid correctly and that no mutations have been introduced.",
"There are some exceptions where you clone your PCR product into bacteria where you don't need to anything besides sequencing, like bisulfite sequencing."
] |
[
"This is basic cloning. In this particular case yes, they just want you to be familiar with the technique. In a molecular biology lab there are a ton of reasons why one would want to clone a piece of DNA. This is the basic methodology used for making recombinant dna products and can be the first step for things like gene therapy or mutagenesis experiments for example."
] |
[
"Does a series always either converge or diverge, or is there a middle ground?"
] |
[
false
] |
And what would that mean?
|
[
"It does not converge to 1/2. It is divergent, hence it has no sum.",
"However, the \"Cesaro-sum\" of this series is 1/2. But the Cesaro-sum is not the same as the sum. "
] |
[
"A divergent series is one that does not converge, so there is technically no middle ground. Divergence doesn't necessarily mean it goes to infinity or -infinity, though, if that's what you're asking - for example, (-1)",
" is a divergent series:",
"-1, 1, -1, 1, -1, 1, -1, 1, ..."
] |
[
"Some types of divergences can be \"tamed\" and given reasonable answers. There are various summation methods which agree with normal limits when they exist, but can also assign \"sums\" to series that don't have a limit. A basic one is Cesaro summation: replace the series at each step with the average of all its values so far. So we have",
"-1, (-1+1)/2, (-1+1-1)/3, (-1+1-1+1)/4,....",
"=-1,0,-1/3,0,-1/5,0....",
"which has zero as its limit. Not coincidentally, this is the long term average of the values. Cesaro summation smooths out the oscillations so that they actually tend to the average instead of wandering around it.",
"The bit about using a geometric series is actually referring to the ",
" associated to the above sequence. So if you form the sequence of partial sums, you get",
"-1, (-1+1), (-1+1-1)... ",
"=-1, 0, -1, 0, .....",
"and the \"smoothing\" method above spits out -1/2. It would have spit out 1/2 if we started with 1 instead of -1 (where the partial sums go 1,0,1,0,...), and this is the situation that ",
"/u/iplanckperiodically",
" refers to.",
"I didn't use the geometric series argument here, but there's usually a single \"correct\" answer for these things which various \"extended summation\" methods will all give you, even as they approach the calculation from totally different perspectives."
] |
[
"Why are thermoplastic polymers more easily recycled than thermosetting polymers?"
] |
[
false
] |
I've read that thermoplastics can be recycled but their properties degrade in the process (why?) Thermosettings are hard to recycle but I don't get exactly why?
|
[
"Thermosetting plastics solidify through a chemical reaction which forms links between short polmyer chains (cross-linking). These cross links are permanent bonds which lock the structure in place, making the shape rigid. ",
"Thermoplastics on the other hand are just frozen liquids. They're not too dissimilar to ice, except the size of the individual molecules is potentially millions of times larger, meaning they freeze at a much higher temperature as they struggle to move around. Just like ice, if you heat them up enough, the molecules get enough energy to slide over eachother, and hey presto you have a liquid that you can reform then refreeze.",
"To deform you thermoset plastic you'd need to break those crosslinks, which isn't really straightforward/ possible!"
] |
[
"yep, comes down to what happens when you heat it. Thermoplastics melt and you get a liquid, so you can put it in a new mold, mix it with stuff etc. Thermosets change chemically when they set, so when you heat them up they just degrade and burn but won't melt. Much harder to make something new when it won't melt."
] |
[
"Thanks a lot! "
] |
[
"Why do bees die after they sting? Biology"
] |
[
false
] | null |
[
"For a bit of clarification, bees only die when they sting certain animals - notably mammals - most reptiles, birds and other insects they can sting repeatedly."
] |
[
"Second post as this is less factual and more speculative and thus might get downvotes...",
"When bees sting and the stinger remains, so does the venom sack and associated muscles. This will continue to pump venom, even after the bee is swatted away, and be harder for an animal to remove (while killing the bee would be easier). Delivering higher doses of venom would be important for predators which are larger (bears, badgers, humans etc) than for other insects (wasps, bumble bees etc).",
"It may be that over time dying, but leaving the stinger attached and delivering more venom was more beneficial to colonies on the whole than surviving but delivering less venom.",
"Given the workers don't reproduce individually, total colony health is the important factor here. An average hive holds 5000-10000 bees, with a worker lifespan of 6 weeks (and a maximum reproductive rate of up to 2000 eggs/day). I don't know the number of stings needed on average to drive off common predators, but if you speculate that it is likely in the region of tens or hundreds then the impact on the colony is relatively minor compared to the total size of the colony (provided that attacks are below a certain threshold and not damaging to the hive structure itself)."
] |
[
"Not a scientist, but, here is how I understand it:",
"The bee's stinger is an excellent tool in insect-on-insect combat. It's only when they use their stinger on larger animals such as humans that they run into the problem of dying after a sting.",
"I'm not totally sure on why this happens, so, I'll let someone else do the explaining. What I\"m trying to get across with this post though, is that the stinger does have a purpose."
] |
[
"If water is such a good electrical conductor, why don't millions of fish die every time lighting strikes an ocean?"
] |
[
false
] |
Unless they do of course, but we never hear about it or have mass schools of dead fish wash up on our shores after every storm
|
[
"I am by no means an expert but I think that the electrical resistance of the fishes body is the main reason this doesn't happen. Compared to the resistance of the water the fish is just a higher resistance parallel resistor. ",
"I am under the impression that the charge is built up at the surface, meaning the potential is only between the air and water, I am interested to hear what happens to the electricity after the strike if there is anyone who can explain that."
] |
[
"Water itself is actually ",
" a good conductor. It is all the impurities within the water, such as the minerals, that make it appear to be a good conductor.",
"As to lightning travelling, it is the same reason an electric eels shock only goes so far... which I am wracking my brain searching for the memory. I believe it also has to do with the contents of the water and how it can vary from meter to meter, eg salt content, minerals, etc."
] |
[
"I expect fish do die, yes.",
"Sea water is a good conductor, so I assume the current spreads more or less spherically. The damage done to tissues, I'm guessing, is inversely proportional to the volume of that sphere. (Though it could be the surface area.)",
"An electric eel, assuming a half-second discharge (a guess), is apparently ",
"1 amp at 750 volts",
", or 750 J.",
"According to wikipedia, a lightning bolt carries an average of 500 megajoules of energy, much more. To produce the same energy density as an electric eel shock, you'd need a sphere 87 times the radius (or a hemisphere with 174x radius, since only spreads out in the hemisphere below the water surface).",
"So, if an electric eel can zap stun fish a meter away (total guess on my part), then a lightning bolt would be stunning fish 170m away, a total volume of 4/3 pi r ",
" or 0.022 cubic km.",
"Once more, according to wikipedia, lighting occurs 1.4 billion times a year, a quarter of those striking the ground. 70.8% of the earth's surface is water, so that's 247.8 million cloud-to-water strikes per year.",
"Multiplying that by the stun volume per strike and that's 5.451 million cubic kilometers of shocked water yearly. Let's simplify and say that all the fish in the ocean live in the top 174m of the earths' water, which is a volume of around 62 million cubic kilometers.",
"So, 11% of the earth's fish are shocked by lightning every year. :-)"
] |
[
"Why exactly is a 100% efficient process impossible?"
] |
[
false
] |
[deleted]
|
[
"Friction is a good culprit in mechanical systems, but equivalent types of loss occur in other systems (e.g. viscosity leads to drag in fluids; randomization of electron paths leads to ohmic resistance in electrical systems).",
"I think the concept you're reaching for is this: it is never, in practice, possible to create a completely ordered system, and slight amounts of disorder in any energy-transducing system will yield loss of ordered energy (mechanical, electrical, chemical) to disordered energy (heat at uniform temperature). Friction is due to lack of order in the physical shape of sliding solids on the molecular scale, or to viscosity in liquids or gases -- which in turn is due to momentum transfer by disordered molecular motion perpendicular to applied shear. Electrical resistance is due to disorder in the electron-nucleus interaction in a conductor. Etc.",
"The problem is that such statements have to be so general (to encompass all the forms of disorder and of ordered energy) that they just boil down to restatements of the second law of thermodynamics."
] |
[
"What does efficiency mean to you? Yes you can keep a current going forever. But if I throw a ball in space it will also keep going forever. There isn't any energy gained out of the system."
] |
[
"The answer is, once again and always, entropy. If you do the math, for an ideal system with net entropy dS = 0, the efficiency is n=1-Tc/Th, where Tc is the temperature of the cold side, and Th the temperature of the hot side."
] |
[
"What are actual humanity endangering threats of Global Warming/Climate Change?"
] |
[
false
] |
Like - rising sea-levels. That's gradual isn't it? People can either see the sea getting closer every year and move, or if they want to stay where they are so bad, they can build sea-walls or whatever. Rivers and coast-lines have moved throughout history and people have had to move. Or the rising temperature and crops - if it gets hotter up in northern latitudes can't you just grow the varieties that were being grown further south up north, if the heat is bad for northerly varieties? Or desertification, the Sahara didn't used to be a desert, now it is. If some places become deserts, then people will have to move, or try to prevent desertification. So, that's the gist of my question - I always see people talk about Global Warming as a threat to humanity, like our survival as a species, and I don't see it. What am I missing? Sure, it'd suck to be living a place that goes underwater/becomes a desert, and you'll have refugee crises/famine/disease, but would the scale really be any larger than modern refugee crises/famines/disease outbreaks given that the timescale is in decades? Moreover, those seem like 'third world problems' - what threat does GW present to a first world country like the US that presumably has the ability to prevent things like desertification, build sea-walls, import heat-resistant varieties of crops/genetically engineer new ones? Sorry if this is a little rant-y, I want to describe my understanding of the issues, so that an expert (or someone more well-informed) can address them explicitly.
|
[
"The agriculture issue is not trivial.",
"Assuming the climate belts migrate to more polar latitudes you have to appreciate that firstly, that means the agricultural land has to move a long way from teh traditional population centres. That means very significant population displacement, even if you ignore the sea level problems.",
"Then you ahve to consider the type of ground and logistics. North of our agricultural belts we have enormous forests. Clearing vast swathes of forestry is difficult, but stabilising a rich soil is the work of millenia, not decades. You only have to look at the terrible soil erosion problems across the amazon basin where forestry has been cleared for agriculture to see the problems.",
"Then you have the issue of establishing an entirely new logistics network to provide access to this new agricultural land to your population centres. ",
"This map",
" gives you a reasonable idea of how our road networks are currently located, and the paucity of transport in the more extreme latitudes we would require.",
"I would also argue that countries like the US still can't do anything about desertification. Sea walls are also not a long term solution for sea level rise - they are fine for protecting agains occaisional tidal surges or storm surges, but they are not suitable for literally extending your coastline. ",
"Heat resistance is also not the main issue for crops - it's how the warmer climate changes the rainfall and groundwater conditions. You can grow a tomato plant in temperatures a few degrees hotter - what you can't do is grow a tomato plant when the region you're growing it in is no longer receiving the rainfall it needs, and the soils are parched. ",
"You can engineer your way out of these problems on a small scale, but there is no way you can do it on a national scale - the US, Russia, Australia and China are the only nations that could even really consider such mega engineering, as they have landmass which covers several climate belts. The practicalities are still way beyond even contemplating though. Most countries do not have that option at all. "
] |
[
"We will almost certainly survive as a species, yes. However it'll have ",
" economic effects.",
"Sure, people can move, but they shouldn't have to. A raise in sea levels is going to destroy a lot of unique ecologies. Yes, some of those effects of those ecologies might be repeated, but not necessarily.",
"Weather patterns overall will likely change, it'll take time for people to move their crops, it only takes a year of crop shortages for food prices to skyrocket. Humans will survive, civilization will survive, but it wont be ",
". ",
"We're talking about bigger economic drains than the great depression, and we're talking about much longer term.",
"When people argue against global warming, they're not arguing that ",
" climate change is bad, they're arguing that extremely rapid, manmade climate change is bad. A sudden shift in climate will very likely shatter ecologies the world over, from oceanic to temperate.",
"We could see mass die offs of animals that we've come to see as staples of our world. Will the world go on? Yes, of course. Will we survive? Almost certainly. Will the costs be ridiculously high? Probably.",
"Basically, all of humanity is putting out a set of substances which could cost all of humanity untold amounts of wealth in dealing with it. Why ignore it, and have some very serious potential problems crop of in the future when the cost of avoiding the entire situation is so small by comparison.",
"It's like insurance. We're going to make sure we don't make any more changes to the environment than ",
", because the alternative could be anything from \"very little problem\" (very unlikely) to \"end of humanity\" (also very unlikely) with a high probability of \"untold amounts of fortune spent dealing with the problem.\" "
] |
[
"Like - rising sea-levels. That's gradual isn't it? ",
"It is gradual, but as we just saw with Sandy, even gradually increasing seas can cause sudden and disastrous damage to inland areas that seem safe on a day-to-day basis if they are hit with a storm surge. Sandy was not a hurricane when she made landfall, but her storm surge just topped a record set nearly 200 years ago by a category ",
" hurricane, almost entirely due to the rise in sea levels since that time.",
"Or the rising temperature and crops - if it gets hotter up in northern latitudes can't you just grow the varieties that were being grown further south up north, if the heat is bad for northerly varieties?",
"It's not that simple. Northern latitudes tend to have thin, rocky, acidic, and nutrient-poor soils - not good for plants. ",
"Also, concerning your reference to importing/developing \"heat-resistant crops,\" it's important to note that there is a physical limit on how \"heat resistant\" any plant can be. Photosynthesis is a temperature dependent process. It shuts down around 95° F and ceases entirely by 105° F.",
"Or desertification, the Sahara didn't used to be a desert, now it is. If some places become deserts, then people will have to move, or try to prevent desertification.",
"The issue here is how extensive the desertification could become under some of the higher emissions scenarios. Check out the maps from this study: ",
"https://www2.ucar.edu/atmosnews/news/2904/climate-change-drought-may-threaten-much-globe-within-decades",
"Joe Romm also talks a lot about desertification. You may find this post a good starting point: ",
"http://thinkprogress.org/climate/2012/10/14/1009121/science-of-global-warming-impacts-guide/",
"Also keep in mind that severe weather in general is really bad for crops, whether droughts, floods, wind, hail, heat, cold, or whatever, and climate change is expected to increase the frequency and severity of severe weather in general.",
"I don't think climate change - even severe climate change - is likely to drive the human race to extinction, but by the middle of the century we're expected to have 9 billion people on the planet. I think the scale will be much, much larger than modern humanitarian crises."
] |
[
"How do carcinogens actually cause cancer?"
] |
[
false
] |
Specificity would be awesome.
|
[
"SO many ways. First, it's worth understanding the surprising level of regulation of when cells can grow and divide. Some proteins favor growth and division, some oppose it. The genes that code for these proteins can get altered by anything that can bind to DNA/react with it/break it. Cells are pretty impressive at copying and repairing DNA, but over a lifetime, even a tiny risk of error means a decent chance of cancer. In general, cancer requires that proteins in favor of growth/division get over-activated (a \"proto-oncogene\" becomes an \"oncogene\") or that proteins suppressing growth/division (\"tumor suppressors\") get knocked out. ",
"A classic example of a tumor suppressor is p53, a protein with many functions in responding to DNA damage, making sure it's repaired and shutting things down until it is. (If things are bad enough, p53 can even kill the cell.) By some estimates, over half of human cancers have a p53 mutation. It's not to say that it's the cause of all those, but it sure helps.",
"So, how do the carcinogens actually cause DNA damage leading to mutations? Chemical carcinogens can react with DNA directly or form other reactive compounds that do so. Ionizing radiation like an X-ray basically involves high-energy particles that smash into DNA. Viruses, which depend on our cells working constantly to make more virus, often have mechanisms to stop normal cell regulation, which can lead to cancer. HPV is known for causing cervical cancer, partly by making a protein called E6 that binds p53 and inactivates it. Some viruses even integrate their genome into a cell's, activating nearby proto-oncogenes. My personal favorite carcinogen is asbestos; it's been suggested that it can have such incredibly thin fibers as to physically mess with chromosomes and screw up mitosis.",
"Less specifically, but very importantly, practically anything that leads to chronic inflammation can lead to or at least support cancer. Part of this is simply that tumors need plenty of blood flow if they want to grow recklessly, but there's probably a lot of other stuff going on that's beyond my understanding. ",
"TL;DR: Mostly by messing with DNA in a way that lets cells grow and divide like crazy."
] |
[
"This was a great answer; exactly what I was looking for. Thank you "
] |
[
"As you probably know, cancer is caused by pathogenic mutations in your body cells DNA that result in abnormal proliferation. Carcinogens can be genotoxic or nongenotoxic. For example, radiation is genotoxic as it directly disrupts DNA. Smoke contains pyrolytic products that bind do DNA and disrut it this way. Nongenotoxic mechanisms are relatively minor, acting as tumour promotors by exerting effects on cell pathways. "
] |
[
"Is the universe on a plane?"
] |
[
false
] |
[deleted]
|
[
"Is the universe on a plane like a disk or only the galaxies that spiral inward?",
"Only the galaxies. There is no reason to believe the universe as whole acts as a rotating sphere - aka disk.",
"Why does it look like a spiral galaxy seems to rotate on a plane? ",
"Conservation of angular momentum."
] |
[
"The problem with the determining the shape of the universe is that there is and there probably will never be any way to see it. We are trapped inside an ever expanding sphere of space-time called the observable universe. The only way to know otherwise is to see an impact of the side of the universe on something (maybe another universe next door) or observe the edges in the cosmic background radiation. Nothing like these conditions are suspected as being possible. But basically for what we can see its pretty much the same in all directions. For what lies beyond or even to know our position in the greater unknown and never seen universe is unattainable. Alas, we can never know how big the universe is beyond what we see right now and it will never get better since the universe is expanding faster then the speed of light. Bummer. ",
"But if you look around the internet you will see that some scientists will say things like the universe is \"flat\". If you have heard this then you, like me, might have though \"that's kind of a bizarre thing to say.\" You can clearly move in your local universe by going back-forth, up-down and left-right. You seemingly have proved that the universe (at least locally) is not flat. Maybe you should see about collecting that Noble Prize :) ",
"But wait a second, \"That's not what we mean\" says the scientists. No prize for you. Well the problem isn't the answer since we have established a universe with 3 spacial dimensions, the problem is the context of the question. To understand what a scientist means when they say the universe is flat you need to know that they are usually talking about the topology of the universe. That means that they are talking about boundaries, mutable shapes and relative or related positions. The classic example is the understanding that a Möbius strip has one side and one edge. Really cool when you think about it. An ant on a Möbius strip can move from what we perceive as the inside strip part to the outside strip part while travelling in a straight line without crossing any boundary. cool. ",
"So anyway, what does \"flat\" mean? Well that means that the universe in terms of topology obeys \"flat\"geometry. If for example we beamed 3 lines on the scale of the observable universe in the shape of a triangle and we measured the internal angles we will find that the angles sum to 180 degrees. Just like they do on a flat surface. AHA! thats the connection! It also implies that the universe is comprised within nothing more then the 3 dimensions of space and 1 of time. If it can be demonstrated that other dimensions exist then they must be wrapped up and very very very tiny without an effect on the grand scale of the universe. ",
"For fun, what if the universe was curved (in 4 dimensions) to look like a sphere (again - a 4 dimentional sphere- don't fret too much about the concept at this point) then we would see a curve in the universe that would cause the internal angles of our universal sized triangle to be >180 degrees. The same principle can be applied to a saddle shape or torus or donut shaped universe. Pretty much any value for our giant triangle other then 180 will indicate a non-flat universe. ",
"If the universe were not flat then the implications would be astounding. Depending on the topology of the universe an observer could see the same galaxy from different sides, at different points in time. Maybe if it was so curved we could see the otherside of our own Milky Way as it existed in the past. Oh well, a flat universe is sufficient. And its the one we occupy so I am cool with it. ",
"But yea, I agree with most people. When asked about shape the scientist should say \"the topography of the universe is flat meaning no matter haw big you make it, a triangle is still a triangle and the dimentions you see are the ones you get. but as far as we can observe the shape of OBSERVABLE space-time is a 3 dimensional sphere\". At least that way we would not get confused with the answer ;)"
] |
[
"No. The universe is shaped like a giant, expanding bubble. Many galaxies really are often shaped like rotating disks -- thicker than a plane but oriented along a plane."
] |
[
"Does a steel bar resist bending until a certain amount of force is applied, or does all force bend it, however slightly?"
] |
[
false
] |
[deleted]
|
[
"Yes. All solids undergo small elastic deformations due to even small applied forces. The ratio of applied force to displacement (normalized by the area and length) is called the elastic modulus, or simply modulus. The elastic modulus for steel is around 200 GPa. Interestingly, this extends to even tiny displacements that we don't normally see - this is how sound propagates in solids.",
"What you are likely used to is observing permanent, or plastic deformation. This only occurs when we exceed a certain inherent stress - the yield stress. The yield stress of many common steels can be quite high, around 1 GPa. It therefore takes a lot of force to deform a piece of steel by a large amount, with the force scaling with the area of the piece. So it seems like the steel is unmoving, just because we cannot bend it as much as we are used to. ",
"In this specific scenario, you would need to take the geometry into consideration by calculating the bending moment of the beam (wikipedia \"Bending\")."
] |
[
"So to clarify, your saying that steel will bend under any force, but it will move itself back into place unless a sufficient amount of force is applied and it is bent to a certain extent, yes?"
] |
[
"1 GPa is a typical value for Ultra-high strength steels UHSS which are actually some of the most widely used grades, eg car paneling. But \"steel\" comprises a huge array of alloy families, with yield strengths ranging from < 200 MPa to over 1500 MPa. You are probably used to high- strength low alloy steels (HSLA) which typically fit your range.",
"The exact properties of the steel will greatly depend on the composition and subsequent heat treatment of the material you get, which should be indicated by the supplier"
] |
[
"What stops inter-species crossbreeding? If a horse and a donkey can make a mule, why can't we crossbreed say a dog and a cat?"
] |
[
false
] |
Also, what other inter-species crossbreeds are there?
|
[
"Horse and a donkey is a great example. As are dogs.",
"Speciation isn't a switch. You don't suddenly get a new species in one generation, rather it is a very long gradation of between divergent phenotypes.",
"The idea of a species is largely a human construct that doesn't capture all the detail of nature.",
"We can say that donkeys and horses are clearly related. They can even interbreed. However, their progeny isn't always fertile, in fact mules are often sterile. The reason for this isn't because the mating impacts fertility specifically, it simply shows that fertility is fragile and that when things start to break it is often the first to go.",
"So we can say that as two populations split, they collect something that makes them gradually incompatible.",
"Now lets look closer.",
"As two populations diverge and no longer breed (for whatever reason) differences in nucleotides between the two populations start to collect within each group. Mutations are almost always neutrally fit, but occasionally there are deleterious mutations. Selection however quickly removes these by reverting it or masking it through a second site change (mutation B compensates for mutation A for example). ",
"As deleterious mutations occur and are masked in separate populations, the species diverge. Depending on how divergent the two populations are, changes the effect seen in hybrid progeny (like mules).",
"Hybrids, between vert closely related populations or within populations show no particularly notable effects due to hybrids. Business as usual.",
"Hybrids between mildly divergent populations exhibit ",
"heterosis",
", improved fitness as ancestrally homozygous deleterious alleles are masked by heterozygous alleles. Dogs are a example of this, Mutts are far more fit than purebreds.",
"Hybrids between substantially divergent populations show deleterious effects. Masked mutations as described above called Hybrid Incompatibilities are uncovered in the hybrid because it may not possess the second site masking mutation. This creates sterile mules and unfit organisms like the Liger. ",
"Hybrids that are extremely divergent (like dogs and cats) have so many incompatibilities at the DNA level that hybridization on the molecular level (between DNA strands) simply cannot occur. "
] |
[
"It's nice to see that searine's here already and has done a good job explaining the basic ideas. I'd like to take a moment to talk through a bit more explicitly some of the genetic incompatibilities he mentions.",
"Consider two arbitrary genetic loci. The \"A locus\" and the \"B locus\". Imagine that your entire population consists of individuals who are of the genotype AABB. That is, they all carry two copies each of the \"big A\" allele and two copies each of the \"Big B\" allele. Imagine that the A locus and the B locus each code for a protein of some sort, and that these two proteins must interact in an appropriate way in order for the organism to develop properly.",
"Now, imagine that your population splits into two separate ones. We'll creatively call them population 1 and population 2. Imagine that a mutation occurs at the A locus in population 1, and at the B locus in population 2. So what you now have are two separate populations in which most individuals are AABB, but where 1 individual is AaBB in population 1, and another individual is AABb in population 2.",
"Imagine that both of these two new mutations are successful (i.e. organisms who carry them do well and survive, perhaps even better than the individuals who carry the ancestral alleles), and thus you wind up with population 1 being full of individuals who are aaBB, and population 2 being full of individuals who are AAbb.",
"So, what happens when these two \"budding species\" have secondary contact, and an individual from population 1 tries to mate with an individual from population 2? Well, if you do your two locus ",
"punnet square",
", you'll find that all progeny from this mating will be of the genotype AaBb. ",
"So what's new here? The small a allele and the small b allele have never seen one another before. They arose independently in separate populations, so we don't know how they'll interact when they're found together in the same individual. It's quite possible, even perhaps likely, that they might not work well together, and thus individuals who are AaBb in genotype might be less viable or less fertile than \"pure\" member of populations 1 and 2, who are either aaBB or AAbb. This all depends to some extent of the dominance relationships among the alleles. It may be that you need to have an aabb genotype in order to see negative effects, in which case the AaBb individuals will experience reduced fertility, because some portion of their progeny ",
" be of the aabb genotype, no matter who they mated with, or it could be that the AaBb genotype is sufficient to cause that individual itself to have serious viability problems, in which case it just won't survive. It's also very possible for these effects to be much less severe than I've made them out to be. However, you can have multiple independent sets of these things (known as Dobzhansky-Muller incompatibilities) running around the genome, and thus they could add up to have a fairly serious effect, even if each one individually only has a small effect.",
"Thus, there is ",
" against hybridization in this case, so you tend not to have hybrids form, or if you do, they don't tend to be able to interbreed with members of either of the parent populations, and thus you actually have natural selection acting to maintain separation between the species. ",
"It depends a lot on the context and the genetics of the particular species we're talking about. In some cases the selection acting to keep the species separate may not be strong enough, and they may collapse back into a single species if enough interbreeding occurs. Alternatively, the selection against hybridization might actually work as selection ",
" members of the two different \"species\" to not breed with one another, as individuals who can recognize who is part of their species and who is not will be able to avoid the reduced fitness that comes with producing sub-par hybrid offspring (this process is known as reinforcement).",
"Of course, in the case of dogs and cats we're long past this point. Those species have been isolated for some time, and may even have undergone more serious physiological evolution to prevent fertilization, or even if fertilization could occur, there's likely been sufficient chromosomal rearrangement such that the process of mitosis would never work properly, and you'd wind up with seriously messed up cells as soon as they tried to divide."
] |
[
"Reproductive isolation are mechanisms that prevent interbreeding to occur in nature. You can read all about it here! ",
"http://en.wikipedia.org/wiki/Reproductive_isolation"
] |
[
"What would a spaceship experience if it flew through a nebula?"
] |
[
false
] |
I was just checking out some photos of the pillars of creation and was wondering what would it be like. Are they all made of just gasses, or is it more like a debris filled.
|
[
"Wildly disappointing, unfortunately. All that gas is spread out over a truly incomprehensible area of space, and up close it would likely be too dispersed to see much. It’s really only from such massive distances away that we can really appreciate their splendor"
] |
[
"Basically gases, that's right. There are different kinds of nebulae, with some being pulled together from the interstellar medium and then birthing stars, to others being created as dying stars shed or explode outer layers. But really in all of those cases, you're talking about gases of some kind.",
"The ",
"Carina Nebula",
" recently re-imaged by JWST is a star-forming region. These regions form when cold interstellar gas - of order a few 10s of Kelvin cold! - clumps together and then gravity takes over. While they are dense in the interstellar sense, they are not dense by terrestrial standards, getting up to maybe 1 million particles per cubic centimeter - the rule-of-thumb value for the interstellar medium is about 1 particle per cubic centimeter. Contrast that with about 10",
" particles per cubic centimeter in our atmosphere! The reason these nebulae can appear opaque is because there's a ",
" of material because space is so big. Over time, stars are forming inside of the Carina Nebula, and you'll then also start to get planets around those stars, but you're not likely to run into them because space is so large. The gas early on will be molecular, along with interstellar ",
"dust",
" particles, which are essentially clumps of molecules. As protostars/stars start to form, the energy they output will break apart the molecules into atoms, and then eventually even ionize the gas, ripping the electrons from the nuclei. This process is actually happening in the image linked above. ",
"Inside the Carina Nebula is itself another nebula, the ",
"Homunculus Nebula",
" surrounding the dying massive star Eta Carinae. This star is thought to be a good candidate for the next galactic supernova, and right now in its last death throes, it is ejecting ionized gas from its atmosphere - ionized because of all of the high energies involved. It should be noted that because the star itself produced heavier elements through nuclear fusion, the gas that it ejects will be more \"enriched\" in these materials than the gas that went into creating the star and the rest of the Carina Nebula on average. The ejecta interacts with particles in the medium of the surrounding nebula, leading to interesting shock fronts there too."
] |
[
"Nebulae are clouds of extremely sparse gas. The maximum density might be a million molecules per cubic centimeter, which is less than one-trillionth as dense as air. Most parts of the clouds will be even less dense than that. A spacecraft would need sensitive detectors to even notice that it had passed into the nebula. ",
"The only reason we can see them at all is that they are so huge. They may be hundreds of light-years in diameter. Even a very sparse and wispy gas can block light when you are trying to look through a quadrillion miles of it."
] |
[
"From what I understand, we have a lot of trouble surgically reconnecting nerves. That being the case, how do transplants work? If we can't really reconnect nerves, how does the transplanted tissue function?"
] |
[
false
] | null |
[
"Nerves like those directing muscle movement - aka motor nerves, need to be in the right \" orientation\" because they map all the way into our spine and brain in a set pattern. A specific patch of your brain controls your pinky versus ring finger, but both are carried by the same nerve sheath in your wrist. Similar things are true for sensory nerves and preserved patterning. It's difficult to even connect these nerves surgically, let alone hypothetically ensure proper orientation.",
"Also, motor neurons do not regrow leasily. The cell body is located all the way a the spine, and cutting a distant part of it causes the nerve to undergo so much of a \"shock\" that it might die. They can regrow, but it's rare and we don't quite know how yet.",
"Many organs don't need nerves to function full - the might work on endocrine functions. Also, many organs are supplied by autonomic nerves - different from motor/sensory. These are basically \"on/off\" signals - or rather \"faster/slower\" signals that don't need a specific orientation to work. These nerves are also less complex, and tend to regrow somewhat easier. A lot of times, these nerves follow the vessels that supply the organ. Therefore connecting the organ circulation is sufficient to start the nerve regrowth."
] |
[
"It used to be stated as fact that nerves don't grow. Now we know that is not true. Nerve reconnection requires skilled micro-surgeons but it is being done, fairly routinely now. ",
"http://www.hopkinsmedicine.org/health/articles-and-answers/ask-the-expert/behind-hand-and-arm-transplants-1",
" ",
"For a nerve to heal, it needs to be reconnected at the site of injury. Once this happens, nerve fibers start growing inside the connected nerves at the site of the nerve repairs, away from the body and towards the new body part, at a maximum rate of one inch per month. The new limb should regain nerve signals approximately within three to eighteen months, depending on the part of the body. However, results are never guaranteed.\nBrandacher: The growing nerve uses the donor nerve as a scaffolding. As the nerve grows towards the new limb, it can stimulate the structures it encounters. So, patients might experience a slight burning or tingling sensation. Over time, groups of muscles begin to reinnervate (regrow nerves) until the entire limb is functional. ",
"Also, 3D printed nerve guideways are working for severed nerves in mice. ",
"http://www.qmed.com/sites/default/files/ck_images/McAlpine-Nerve-Regeneration-Guide.jpg"
] |
[
"Had a similar surgery back in 95. Same result. 20 years later a small portion of my ankle is still numb. Everything else came back, but right along the scar is still numb. It took 10 years, but the foot finally got feeling back. I also had an intense \"light socket\" feeling on the scar when it was pressed. Couldn't wear mid-rise shoes. Low tops or high tops only. That finally went away at about year 15. Hope yours is faster. "
] |
[
"Why is it that certain age groups are subject to hearing certain frequencies? Such as the mosquito tone."
] |
[
false
] |
I'm sure most people have heard of the mosquito tone or the tone that only young people can hear, but why is it that only younger people can hear this tone? Same question applies to other frequencies, why does it just cut off at a certain age?
|
[
"It doesn't \"just cut off\", but it does decrease with age. The portions of the human cochlea used to perceive high frequencies are the most metabolically active portions of the cochlea, and thus the most susceptible to die from lack of nutrients/oxygen from overstimulation. Pretty much everyone loses some of them with age, and as a consequence loses some of their high frequency hearing."
] |
[
"Could you elaborate on the reason that they require more energy?",
"I'm not familiar with the studies that show basal hair cells are more metabolically active. Maybe they (outer hair cells) are because they have to deal with higher frequencies at the base. ",
"Is it because high frequencies are detected near the cochlea's entrance, so all frequencies must go through that region?",
"The cochlea is tonotopically organized with higher frequencies in the base to lower frequencies in the apex. Sound stimulus causes a traveling wave in the cochlea. For the wave to get to the apex, it'll pass the base. Mouse studies have shown that if you play broadband noise of between 4-10 kHz (lower frequencies for the mouse) at something like 100 dB SPL for 2-4 hours, much of the outer hair cell loss is in the base of the cochlea. So yes, the organization probably contributes.",
"Edit: Hopefully made things more clear."
] |
[
"Could you elaborate on the reason that they require more energy? Is it because high frequencies are detected near the cochlea's entrance, so all frequencies must go through that region?"
] |
[
"Why is it that humans and many animals make loud noises when in pain?"
] |
[
false
] | null |
[
"Instinctual trait to tell others that there is something bad in the vicinity, and that they need help. "
] |
[
"Also important for animals that play. Dogs and wolves, for instance, can bite when they play. A yelp when in pain will tell their partner to stop. This is one way pups learn how to be gentle and how hard is too hard to bite when playing."
] |
[
"You know what the OP meant. This nitpicking adds nothing."
] |
[
"Have there been any models that predict what conditions are necessary for Great Powers to engage in war in the modern era?"
] |
[
false
] | null |
[
"Absolutely--there is a robust literature surrounding the prediction of conflict, although it does not tend to revolve around \"great power\" conflict specifically. You can grab your data from recent history and then plug whatever predictor you want into a logistic regression. Some factors important in the prediction of conflict include, and I quote, ",
"population size, infant mortality rates, demographic composition, education levels, oil dependence, ethnic cleavages, and neighborhood characteristics",
"."
] |
[
"This fascinating paper you linked to predicts a global decline in conflict. Is the model they are using strong enough to justify a sense of relief?"
] |
[
"These are some of the strongest indicators of impending conflict, and the paper made conclusions based off of those variables. It's only logical that the effects would transfer into real-world situations."
] |
[
"Is there any dark matter in my room right now?"
] |
[
false
] |
[deleted]
|
[
" Maybe. It depends what dark matter is.",
" ",
" is a bit of a catch all term. It's just meant to describe the bulk of the apparent gravitating mass in the universe which is not luminous. We don't know what it is yet. The evidence is really really good that it exists, we're just not sure what it is. ",
"Generally, 'dark matter' is used to refer to a presently unidentified kind of matter. For example, some people think that maybe there were just a whooole bunch of black holes floating through space, waaay more than any model for stellar evolution might predict, and since black holes don't give off light they would constitute 'dark matter'. But this isn't a favored answer for a long list of reasons. ",
"A more popular idea presently is that dark matter is some kind of particle. Aptly called 'particle dark matter.' This kind of dark matter would be a heavy and abundant particle which just doesn't interact with the electromagnetic force, so it doesn't give off light and it doesn't really clump into planets and stars the same way that atoms do. There are a lot of hypothetical candidates with all sorts of fun names, like sterile neutrinos, WIMPs, and axions. ",
"If one of these hypothetical candidates really is the dark matter, which whizzes around and could be all over the place, then there is probably some passing through your room right now, streaming through the earth like a ghost."
] |
[
"Good question, and the answer is 'Yes.' The two main detectors at the Large Hadron Collider, for example (ATLAS and CMS) both reconstruct \"Missing Energy\" as one of the variables they look for in each collision."
] |
[
"Good question, and the answer is 'Yes.' The two main detectors at the Large Hadron Collider, for example (ATLAS and CMS) both reconstruct \"Missing Energy\" as one of the variables they look for in each collision."
] |
[
"Do currents stop at extreme depths, or are the oceans always moving, everywhere?"
] |
[
false
] |
[deleted]
|
[
"Yes there are currents at all depths, but the magnitude of the currents is generally smaller at depth. . In the early days of oceanography it was thought the deep ocean was nearly motionless but once they were able to actually make measurements they discovered sizable varying currents. This article on the ",
"Storms of the Sea",
" is a good summary. The mesoscale eddy field seen in animations like the ",
"perpetual ocean",
" are strongest at the surface but they have effects which reach all the way to the ocean bottom.",
"The isolated deep trenches such as Mariana Trench or Kermadec Trench probably have very little flow in them but even there the water is not perfectly still. "
] |
[
"That's a good point about water mass properties being characterized by the water properties in their formation regions. It's one of the key diagnostic properties of ocean structure and was used to infer ocean circulation long before we had direct measurements. I would consider movement of water masses part of ocean circulation and thus currents. The ",
" rate of flow of this water masses is driven by density gradients but that slow average is achieved on top of a fairly energetic eddy field. In general, if you place a current meter in the deep ocean you will see velocities corresponding to variability of the mesoscale eddy field while the velocities associated with the average flow of water masses are an order of magnitude weaker. It takes long records and lots of averaging to see the circulation inferred by the distribution of water masses."
] |
[
"I was going to mention water masses and their movement in thermohaline circulation, but I don't believe they are considered currents, is that correct?",
"That said, there is slow movement of water in deeper parts of the ocean driven by differences in density due to salinity and temperature. I think the most interesting aspect of this is that water masses \"obtain\" these characteristics based on where they \"form\". You can actually tell where a parcel of water came from based on its properties (as well as its relative position in the water column), Antarctic Bottom Water vs North Atlantic Deep Water for example."
] |
[
"Is it possible for an asteroid (or spaceship) to actually \"skip\" off the atmosphere?"
] |
[
false
] |
My understanding is that when people talk about objects "skipping" off the earth's atmosphere, it generally doesn't mean "skipping" in the sense of a stone skipping on a pond. Instead (my understanding is that) it refers to the fact that an object approaching the earth on a non-orbital trajectory that enters the Earth's atmosphere at a shallow enough angle will not bleed off enough speed through drag (and other atmospheric forces) to enter into orbit of the earth. The object is slowed, but ultimately exits the atmosphere on an escape trajectory. This would, for example, be the kind of "skipping" they were concerned about with respect to the Apollo 13 mission. That said, is it possible for an object to actually "skip" an object off the atmosphere in a manner similar to skipping off a pond? I don't see any reason it shouldn't be possible. Stones skip off water due to creation of lift and an object entering the atmosphere certainly can also create lift. I don't see any reason that lift couldn't be enough to lift the object back out of the atmosphere similar to a skipping stone. As a follow up, I suppose that generating lift wouldn't increase orbital velocity, so the stone like type of "skipping" couldn't propel an object into an escape trajectory that didn't enter the atmosphere already on an escape trajectory. Since intuition and orbital mechanics generally don't play well together, is that intuition correct?
|
[
"In general, no. Objects can certainly have an orbital trajectory that grazes the Earth's atmosphere at a small enough depth that it doesn't lose sufficient energy to deorbit; this actually happened with an asteroid ",
"in 1972",
", but this is not the \"skipping\" process you are describing. ",
"A stone skips because it meets a sudden interface between the two media (air and water) which exert different forces on the stone; the imbalanced forces in the vertical direction cause it to skip back into the less resistive medium (air). There isn't an analogous interface in the atmosphere, as it has a smooth density profile. So in general, random objects like asteroids won't \"skip\" off of the atmosphere. ",
"What about more optimized/controllable objects like ",
"lifting bodies",
"? This could perhaps work. Imagine you are flying an unpowered glider toward the Earth at a speed much greater than escape velocity and at a very shallow approach that would impact the Earth in the absence of air resistance. Specifically, pick a \"starting point\" where you enter the atmosphere; let v_total be the speed of the object at this point and v_radial be the radially inward component of this velocity. If your lifting body has an effective lift/drag ratio at very high altitudes and very high (orbital) speeds which is much greater than v_radial/v_total then you should be able to \"skip\" off of the atmosphere. However, this assumes a limit as the object moves arbitrarily fast and that such a lift/drag ratio at that speed is possible to achieve; a more careful calculation might yield that this is not possible."
] |
[
"This could perhaps work.",
"It does work. That's how you run a skip-glide reentry - you dig into the upper atmosphere in such a way that you slow down in horizontal velocity and meanwhile actually start flying back up into space again due to lift, then \"re-reenter\" and land somewhere further downrange. I suspect that you might not be able to skip off and go flying out on an escape trajectory unless your initial velocity (and heat shielding!) is truly insane, but you can definitely make it \"back out of the atmosphere similar to a skipping stone\" as per the earlier parts of the OP."
] |
[
"Kinda like Neil's X-15 flight.",
"https://www.airspacemag.com/daily-planet/neil-armstrongs-x-15-flight-over-pasadena-59458462/",
""
] |
[
"Can I \"give\" antibodies to people as I give them diseases?"
] |
[
false
] |
For example, if I have Influenza and have already developed antibodies for it, can I (with a sneeze or blood transfusion) "pass" those antibodies to someone else (Assuming we both have the same blood type)?
|
[
"That's an excellent question. You are equally likely to pass a single antibody or a single virion to your friend. The single copy of the influenza virus will make millions of copies of itself once it gets into cells, the antibody will not. That means that the virus will take off and colonize the host, the antibody won't.",
"So, no, you can't \"give\" someone your immunity, unless you have someone in a lab purify your antibodies and inject them into someone else"
] |
[
"Yes, patients are given antibodies routinely in the clinic. There are ",
"many monoclonal antibodies approved by the FDA",
"; however, these are most commonly given as cancer therapeutics or for autoimmune diseases. ",
"For the situation you are describing (i.e. giving antibodies for influenza), this is not the best way to immunize the patient. If you wanted to keep the person protected against a pathogen you would have to continually give them doses of antibodies, since eventually the antibodies will be degraded. It makes more sense to give them an inactive form of the virus so then the body can develop memory B cells. Then the second time the body encounters the virus, it produces a large amount of antibodies and kills the virus (referred to as secondary immune response). "
] |
[
"wrt to the second part of this blokes answer, this is actual treatment for certain diseases and goes by the name passive immunity. also, blood type would be completely irrelevant as it is MAINLY for red blood cells only."
] |
[
"Why is there sometimes a halo of light around a plane's shadow on the ground (at least when seen from the plane)?"
] |
[
false
] |
I took on a recent flight, during landing (as you can see by the size of the trees, we're not very high up). It looks as if the ground around the shadow is actually being more brightly illuminated than the surrounding area. That seems super weird to me.
|
[
"That's called a ",
". Sunlight gets reflected/refracted twice inside the droplets that are in the air. In your picture it isn't very clear, you have a thin cloud veil. Google \"glory, optical phenomenon\". It's something similar to what happens in a rainbow. There are two theories: here light also travels around the surface of the drop instead of just bouncing inside, therefore the angle is smaller and you get a closed circle. Another theory suggests wave interference inside the droplets."
] |
[
"Plenty of things are called sun dogs, that aren't sun dogs. :-)",
"\nSun dogs are ",
"patches of color to the left or right of the Sun",
" (never anywhere else -- if so, they are likely some other form of ",
"ice halo",
")."
] |
[
"Cool, thanks!"
] |
[
"Does visible light have properties other than being visible to humans?"
] |
[
false
] |
It seems like most of the other types of EM radiation have some property that's much less arbitrary than "we can see it," i.e. X-rays are similar in magnitude to atomic crystalline structures so we can do crystallography, microwaves are capable of fast energy transfer to water molecules, etc. If we couldn't see 350-750nm, would it be interesting at all?
|
[
"Oh, definitely! For starters, these are generally the colors of light that make it through the atmosphere from the Sun in highest abundance. We're using the most common photons to see. Beyond that, these energies are very important to biological life, due to the chemistry involved. To explain, I need to clarify something about the structures (and energies) of molecules.",
"You can think of electromagnetic radiation as having different 'sections' based upon the sorts of things that it does to molecules. Photons around the 'radio' portion of the spectrum make molecules rotate. Photons in the infrared range, like where you microwave is, make molecules vibrate. Above those energies (starting around 800ish nm, though lower for special systems), photons begin to have enough energy to cause the electrons in molecules to go to other energy levels in the system.",
"At very high energies (like x-rays or the extreme UV), these energies can knock very low-lying (core) electrons out of atoms, and generally cause a lot of \"chaos and destruction.\" More to the point, photons in this region can be absorbed by basically ",
" atoms, so they aren't very selective.",
"However, photons in the visible part of the spectrum are ",
" high enough in energy to cause excitations if the structure of a molecule is correct (for instance, if there is a metal atom present), but not in most of the other \"everyday\" materials--your typical chunks of carbon, nitrogen, and oxygen. When these photons ",
" cause excitations, they're only between the highest-occupied states and the lowest-occupied (typically), which means that a ton of extra energy isn't bouncing around the system.",
"This is amazing for biology. Processes like photosynthesis have evolved to absorb light only at certain complexes that funnel the energy into doing useful chemistry, rather than damaging the molecule. You can think of it as the \"Goldilocks effect:\" visible light is high enough in energy to do useful chemistry, but low enough that it doesn't cause damage to surrounding systems."
] |
[
"Wait! Does it mean that visible light and green chloroplasts are another example of processes happening in a Goldilocks zone? Would we expect alien animals to see in similar wavelengths and alien plants to be green?"
] |
[
"Visible wavelength lasers are crucial for biological science and microscopy. We can attach fluorescent markers to cells that will emit a different visible light if lit with the right wavelength. Different cells often bond with different markers, so by looking at what's fluoresced when you light up a sample of cells, you can figure out all sorts of things. One specific example is regular blood cells versus HIV infected blood cells. Using the aforementioned technique in a process called flow cytometry, you can test for HIV infection."
] |
[
"Why do men go bald while females don't?"
] |
[
false
] |
I know not all males go bald, but I know that many do. I am yet to encounter a female going bald though. Is there a specific reason for this?
|
[
"Yeah, but hair loss isn't the exact same thing as baldness. I understand that women have thinning hair, receding hair lines, and bald spots, but how come we never see a woman with a shiny bald head and the cul-de-sac of hair like we do men? Are they all just wearing wigs?"
] |
[
"Yeah, but hair loss isn't the exact same thing as baldness. I understand that women have thinning hair, receding hair lines, and bald spots, but how come we never see a woman with a shiny bald head and the cul-de-sac of hair like we do men? Are they all just wearing wigs?"
] |
[
"This is mostly not true:",
"Balding is multifactorial, with several lines of evidence suggesting that it most likely functions by a diathesis–stress model. Since androgens and androgen receptors (AR) are the initiating cause of androgenic alopecia, their genetic corollaries are a subject of much research. Some involved genes are not X-linked, with men whose fathers show hair loss 2.5 times more likely to experience it themselves regardless of maternal report.",
"If male pattern baldness were an X-linked trait, it would be impossible for fathers to pass it on to their sons. There may be genes on the X chromosome that are linked to male pattern baldness, but they're only a minor contributing factor. Testosterone is necessary to cause male pattern baldness, which is why it's less common in women.",
"Source: ",
"http://en.wikipedia.org/wiki/Androgenic_alopecia"
] |
[
"How can black holes conserve angular momentum while being infinitely small? Do they spin infinitely fast?"
] |
[
false
] |
[deleted]
|
[
"While, as per the other comment, it's true we don't have a complete answer to this, the speed of light does not impose a limitation into how much angular momentum you can pack into an object of given size. Momentum does not increase linearly with velocity in relativity, and you could, in principle, continue packing more angular momentum into an object and the surface velocity will continue getting incrementally closer to light speed, but never reach it."
] |
[
"So basically angular momentum is analogous to kinetic energy (and linear momentum?) in that it is unbounded as you asymptomaticly approach the speed of light?",
"That explains where my confusion came from about singularity size.",
"Points about quantum gravity below a certain size have been made as well, and it sounds like that is an open question in physics, but I think my original question just stems from a misunderstanding of rotation under relativity. Thanks for addressing that!"
] |
[
"I found the relativistic definition of momentum ",
"here",
", which is just the Newtonian definition times the Lorentz factor. As you can see, as v approaches c, the denominator will approach zero, meaning the term as a whole approaches infinity."
] |
[
"How do the blind perceive space for motor control?"
] |
[
false
] |
I've been learning lately and reading some papers about how the superior colliculus receives input from the eyes and that's sent to pre-motor etc. But how is auditory or somatosensory integrated into this system? In a blind individual would the superior colliculus be taken over by auditory input? Or does auditory normally have input from another part of the brain that would just grow much larger?
|
[
"Most people think that there are five senses: Touch, taste, smell, hearing, and seeing. (haptics, olfactory, etc...) But there are actually a few more. There is thermoception, ability to tell temperature, which is not based on touch. Nociception, the sense of pain. Equilibrioception, ones sense of balance. And finally, to answer your question, proprioception, or the relation of ones limbs to their body and the other limbs.",
"Proprioception is how the blind still have motor control. To demonstrate this, close your eyes, and try to touch your nose."
] |
[
"so the question boils down to \"how can we calibrate proprioception without sight?\" "
] |
[
"Probably the same way we can calibrate (roughly) the temperature that will burn us, without touching it. Humans are probably born with a certain level of innate coordination, like how a fawn can run only a few minutes after being born."
] |
[
"Does it take more or energy to launch an object into orbit towards the East or West?"
] |
[
false
] |
Specifically with reference to the effect of the rotation of the earth?
|
[
"The site of the ESA's ",
"Guiana Space Centre",
" was selected because of its proximity to the equator. That way, the space craft gets some free extra kinetic energy from the earths rotation.",
"See also ",
"here",
":",
"A final point to make is that this speed bonus also explains why rockets are launched towards the east. Since Earth rotates west to east, launching an orbital satellite in that direction maximizes the effect of the rotational speed bonus.",
"So: "
] |
[
"Just to add to this, there are very few satellites that have been launched westwards. The only country that does is Israel, to avoid flying over the neighbours."
] |
[
"That's a hilariously sad fact."
] |
[
"With how many drops of water could you mix a single drop of blood and still be able to determine the DNA of the blood sample?"
] |
[
false
] |
[deleted]
|
[
"In theory an infinite amount, assuming there is no contamination in the water. In practice you will be limited by either the capacity of your centrifuge (>4 liters is tough to spin on most centrifuges) or the DNA isolation column (which could probably be made larger, but are designed generally for <10 mL)."
] |
[
"DNA has a relative density of 1.7. If you spin a homogenized cell extract for 10 minutes at 1,000 g you will get a nice pellet of DNA. You can then pour off the supernatant and resuspend in whatever volume you want. This processed has been done millions of times for >70 years.",
"While DNA is a discrete molecule, your analogy to homeopathy is not relevant. You only need one copy of DNA to do basic sequencing due to PCR technology. "
] |
[
"There's other ways to enrich which would bypass the centrifuge/column limit, e.g. evaporation or WBC pull-down using antibodies."
] |
[
"I'm trying to understand the whole current is equal to the voltage divided by the resistance and I think I'm misunderstanding it."
] |
[
false
] |
What I understand is this: voltage would be the same thing as power if it weren't for resistance. So If I had 3 volts divided by 1 ohm it would still be three volts. So does that mean a volt is measured assuming there is one ohm of resistance? And if that's the case then what you're really doing to find current is saying okay turns out there's more resistance than we assumed(1 ohm) so the actual voltage is a little lower than we initially thought which in turn reduces the power output. Is that right? Although if that was the case why couldn't they just do this: voltage/current * voltage
|
[
"Ok, please don't take this the wrong way, but you have a base misunderstanding so let's break it down together;",
"---What I understand is this: voltage would be the same thing as power if it weren't for resistance. --- \nBut, it is not... You're thinking about it backwards. Power would be the same as voltage if it weren't for resistance. But, mayhaps I misunderstood you. \nYou go on to say (given the prior statement) \n--- So If I had 3 volts divided by 1 ohm it would still be three volts. ---\nYes, it would be 3 volts potential, AND it would be 3 watts of power... But if you're thinking 3 volts divided by 1 ohm is volts, that is incorrect. The unit of measure is very important. Just because you're dividing by one does not mean the ohm unit of measure is not important.",
"--- So does that mean a volt is measured assuming there is one ohm of resistance? ---\nInteresting question. A SINGLE Volt is ",
" as; the difference in electric potential across a wire when an electric current of one ampere dissipates one watt of power.\nSo, in that sense, you are correct, a volt is ",
" with the assumption of 1 ohm of resistance. \nHowever; the more (scientifically) useful definition of volt would be; potential difference between two points that will impart one joule of energy per coulomb of charge that passes through it.\nThis definition would be more useful in explaining how Voltage is ",
" because voltage is not measured assuming one ohm of resistance. Without going into detail, voltage is ",
" by how much of an impact that 'measured-voltage' has on a field that is constant(when compared to the measurement).",
"Ok, so I've been up awhile so hopefully that's all made sense. So, the assumptions you've put out pre-empt the question you've asked, but let's address the question as I understand it.",
"Ok. So, by 'if that's the case then what you're really doing to find current' etc. I understand you as asking how are we finding current?\nWell, in the real world, when a meter is used - We again compare a constant field to a changing field, this is dependant on whether or not we're finding AC current or DC current. \nBut if we're using math, then we don't backtrack: 'Okay, turns out there's more resistance than we assumed... so... voltage is lower than thought'\nVoltage is an independent measurement. \nResistance is also an independent measurement. (though some might argue impedance is)\nAnd finally, Current is fully dependant on the resistance (impedance) of the circuit.",
"So, because of all the above reasons I've listed, we cannot take voltage/current *V to equal power.... look at the units ",
"Power? = Voltage / Amps * Voltage \nPower? = (Joules/ Coulomb)(Second / Coulomb) * (Joules / Coulomb)",
"Power? = (Joules",
" * sec)/ Coulomb",
"\nWhere as power = Joule / Sec ",
"Ok, so, I know enough that I probably misunderstood some of your understanding of the subject, but hopefully this is enough for you to figure out yourself where the gap is in the grasping of these terms. If it doesn't, It always helps me to take a break, do not think at all about it, and re-read the explanation or subject matter a few hours later"
] |
[
"I was reading the last part where you put second/coulomb and I'm wondering what's the difference between coulomb per second and second per coulomb. They sound the same but mathematically they would be pretty different right?"
] |
[
"I was reading the last part where you put second/coulomb and I'm wondering what's the difference between coulomb per second and second per coulomb. They sound the same but mathematically they would be pretty different right?"
] |
[
"Would it be possible to create an upside down cone shaped ceramic ice cube tray that wouldn't explode?"
] |
[
false
] | null |
[
"They probably do to some degree, but from everything I've seen on freezing dynamics they are designed to freeze from the top downward and push the cube slowly upward as it goes. This is also the explanation most commonly given for the times when you get a whole tray that just shatters instead of coming out as nice cubes. If the freezing doesn't happen from the top down but just the outside in you can get a situation where the outward force holds the cube in place with excessive stress, and when you try to pop out the cube you just release all the stress instead."
] |
[
"This is pretty much how most ice cube trays already work, the sides slope so that the bottom is smaller than the top and the expanding ice pushes the cube upward to relieve the stress from freezing expansion. If you wanted to make a ceramic ice cube tray you certainly could, though depending on what kind of ceramic you might need to glaze or polish the surface. If the ceramic was porous enough to absorb some of the water then it could potentially freeze and split."
] |
[
"Interesting, I was under the impression that the plastic trays were flexing to some degree under the pressure."
] |
[
"Do forests have natural life cycles, or will they go on indefinitely without interference?"
] |
[
false
] | null |
[
"Trees, yes. Forrests, maybe not how you are thinking. Theyare referred to as \"stochastic\". Trees fall, other species move in for a bit, old tree type returns. Fire wipes out a patch, grasses, followed by bushes reclaim, but the Trees come back. Over a long enough time scale, because of Tectonic motion, the Trees may end up at a latitude they are not well adapted to. The forests that once grew on the land thar is now Antarctica certainly got well and truly screwed."
] |
[
"They wax and wain. They move, they change.",
"Even where I grew up, the woods are always changing. Some of our woods are old growth that have been changing over as the old White Pines die from blister rust. That opens up the canopy and regen comes up in it's place. Usually Aspen and Alder. In the meadow, where no White Pines have sprouted in hundreds of years, suddenly they start to spring up like magic when they feel the old tree has died. They compete until one major tree grows and the others whither. The Red Pines are expanding into the meadow to the east. When I was a kid, it was almost completely open. Now it's almost 100% covered with Red Pine. The twisted blue cedar remains the unchanged in it's little enclave. Unchanging. Next to the cedar swamp is the black spruce bog. All muskeg and skinny trees that could be 400 years old for all we know. Once you're inside the bog, it's pitch black at high noon. The ground is untrustworthy, you should stay out in the summer.",
"The creek meanders and new oxbows form. Where an oxbow lake appears, the Balm of Gilead comes up along with Diamond Willow. The Bam grows faster than weed. Many feet per year. Eventually, the oxbow dries up, the creek keeps moving, the beavers cut down all the Bam and aspen and make a new dam. Now there's a new pond for a while killing off some of the trees which will attract creatures that will live in the dead tree stump.",
"Tomorrow, new things will happen."
] |
[
"Ooh, so there's a lot to discuss on this topic! So back in the mid twentieth century, when the science of ecology was just getting started, there was a popular theory that forests were essentially indefinite without disturbance. After a disturbance like a tornado or forest fire, ecological succession would occur and end in a stable 'climax community' of tall canopy trees, understory trees, and finally forest floor vegetation, and that the climax community was essentially static. The terms super-organism and old-growth forests were coined to describe these systems, and many ecologists considered these ancient forests to be in perfect balance, where every single species had an important role to play, no species could be removed from that system without a fundamental breakdown, and once that balanced climax forest was created, it would remain forever until some new disturbance arrived. (Here is one of the most popular early papers on the topic: Clements, F.E., 1936. Nature and structure of the climax. Journal of ecology, 24(1), pp.252-284. - just google scholar it, the pdf is free if you want to read it)",
"However, we don't really think of forests this way anymore. Forests are essentially just ecosystems that are defined by the presence of large trees. If you have large trees, you have a forest, and large trees are remarkably competitive in areas with the climate to support their growth and where disturbance is infrequent or not severe enough to kill them. So if there is relatively little disturbance and suitable climate, some kind of forest will tend to remain for as long as conditions allow it to. However, the specifics within each forest will change dramatically in response to thousands of factors: presence of pathogens and herbivores, climate, moisture levels, man-made and natural disturbance, and much more.",
"Probably the biggest factor in determining the 'longevity' of a forest is disturbance, which varies depending on conditions. In the eastern United States where conditions are humid and moist, the main disturbance factor (exculding man made ones like logging or deforestation) is actually small scale wind throw events. In those forests, as trees get really old and big, they eventually become so heavy and catch so much wind that a particularly bad storm will uproot them, knocking them over. They often then fall into other trees so you get a 'domino effect' of one to a few dozen trees falling over in the forest. That creates holes in the canopy which allows in more light and a small area of a different community type that is often closer to a grassland or shrubland than a forest. However, this doesn't last long as new trees grow tall and surrounding branches close in to cover up the hole in the canopy. There has been plenty of research on this type of disturbance, but here is one example looking at the extent of these disturbance events (Ulanova, N.G., 2000. The effects of windthrow on forests at different spatial scales: a review. Forest ecology and management, 135(1-3), pp.155-167.)",
"However, in fire-mediated forests, like those of the pacific northwest, fire is the main disturbance factor. Everyone's heard about the giant, terrible forest fires that have been rampaging through the region in recent years. Those are serious, forest-ending disturbance events (at least for a few dozen/hundred years until the canopy can re-establish itself), but they are not the norm. Normally, every inch of these forests will burn once every 5-10 years (a period known as the fire-return interval), and because the fires are so frequent, all they do is burn off the underbrush and take out any old/rotting/weak trees - an effect not unlike the gap phase disturbance model of eastern forests. The only reason we have so many massive firestorms nowadays is because of smoky the bear - human efforts to put out any and all forest fires as soon as they start created a giant buildup of fuel and dead stuff on the forest floor for decades, so now when the forests inevitable do catch fire, all the fuel burns like crazy and creates flames so big that they destroy healthy canopy trees as well. Humans meddled in the natural nutrient cycling regimes of those ecosystems, and now we're paying the price for it. (Steel, Z.L., Safford, H.D. and Viers, J.H., 2015. The fire frequency‐severity relationship and the legacy of fire suppression in California forests. Ecosphere, 6(1), pp.1-23.) I should note here that this does not occur in Eastern forests because the main mechanism for cycling dead plant matter in these systems is decomposition, not fire. The environment is generally so moist and humid that fungi can break down even gigantic dead trees in a matter of just a few years, so the fuel does not build up as plants die. Furthermore, the fire return interval for most eastern forests is around 500 years, 100x less than for fire-mediated ecosystems.",
"So to get back to your core question - the answer is complicated. If you're asking whether forests just naturally 'peter out' due to lack of resources or some such over time, the answer is generally no. In a healthy forest ecosystem, all nutrients are cycled back into the system somehow, be it from fire or decomposition, and even though individual trees may die and species regimes may shift over time, some sort of forest canopy will almost always remain as long as climate and disturbance regimes allow it to.",
"But as we've seen with recent wildfires, human intervention in natural forest ecosystem processes can cause huge cascading effects that can wipe out entire forests if we're not careful. Whether those human destroyed forests will return is something that remains to be seen. Now that there are so many invasive species, we realistically cannot expect the same trajectory of ecological succession that we've seen in the past, so the species composition of our regrowth forests will be different, but it is likely that some form of forest will eventually regrow in those areas."
] |
[
"Carbon is such a critical component of complex molecules because it can form 4 covalent bonds. Can silicon be used in a similar way?"
] |
[
false
] | null |
[
"Yes, in some sense. The chemistry is similar, but the products will likely be very different. Take carbon dioxide, a very simple, rather plentiful, and essential gas for life on Earth. The silicon counterpart is silicon dioxide, commonly seen as sand or quartz. So in theory, life could develop using silicon, though it would be very different from what we're used to. "
] |
[
"The only option that yields a gas would be fluorine, but fluorine atoms can only bond to one atom while oxygen can bond to two, so silicon fluorine chemistry is a lot less complex than carbon oxygen chemistry"
] |
[
"Not really.",
"The issue goes beyond just the number of bonds that carbon (or silicon) can form. The types of bonds and their stability are important. Carbon can form single and multiple bonds to itself and other atoms. These compounds can be reactive enough to do all sorts of interesting chemistry, but stable enough that they don't just fall apart in water. Life as we know it wouldn't be possible otherwise.",
"Silicon chemistry is quite a bit different. The Si-Si single bond is more labile than a C-C bond, and double bonds between silicon and itself or other atoms are rare. While most biochemical processes for carbon-based life involve manipulating compounds with double-bonds, you can't do that with silicon. The types of molecules you can make are much less diverse."
] |
[
"Is it possible to gain more than one pound of weight after eating one pound of food?"
] |
[
false
] |
[deleted]
|
[
"No. Even with a perfect 100% efficiency of conversion (which is not possible) the best you could do would be one pound. Exceeding that is impossible due to ",
"http://en.wikipedia.org/wiki/Conservation_of_mass",
"."
] |
[
"You took in 1 pound of matter. How would your body convert 1 pound of matter into >1 pound of matter?"
] |
[
"Sort of.",
"For example, salty food can make you retain water longer than you normally would. If you got on a scale 4 hours later, you might weigh 1.1 lbs. more than you would have if you hadn't eaten."
] |
[
"How does seedless produce get planted and reproduced?"
] |
[
false
] | null |
[
"There are different cultivars of watermelon that have different chromosome counts? That sounds like an extreme variation within one species (wait, are they even still one species?). How did this happen?"
] |
[
"There are different cultivars of watermelon that have different chromosome counts? That sounds like an extreme variation within one species (wait, are they even still one species?). How did this happen?"
] |
[
"A regular watermelon has 22 chromosomes. Using Colchicine makes the watermelon have 44 chromosomes. \nBreeding the first watermelon with the second creates a watermelon with 33 chromosomes. They technically have seeds, those little white soft ones that you don’t even notice are there, they just don’t fully develop. ",
"Basically. This is extremely generalized, but it’s the jist of what happens.",
"Edit: I only put the first number of the amount of chromosomes and not the second (guess my numbers were supposed to be diploid, tripled and tetraploid and my morning brain wasn’t having it?). I had just woken up, my b. \n",
"Here is an article about it from MSU"
] |
[
"Can plant roots penetrate a sheet of rubber?"
] |
[
false
] | null |
[
"Yeah. Seed lands in crack of a sidewalk, the roots begin to spread, water gets in the cracks and freezes expanding the cracks even more, etc. That's how it breaks down isn't it?"
] |
[
"Hmmm...what I meant was, if you have an inch-thick sheet of rubber, and cover that in 5 feet of dirt, and plant seeds in the dirt on top of the rubber, will the roots of the seeds eventually penetrate the rubber or will they grow around it?"
] |
[
"Sidewalks and roads (pretty much anthing made of rock) break apart after plants dig their roots in and grow bigger",
"Oh really?"
] |
[
"Do we experience less gravity during day time, because of the pull from the sun counteracting Earth's gravity? How big is this effect?"
] |
[
false
] | null |
[
"Correction: the sun also pulls on the earth, and this will greatly reduce the effect of the sun's gravity if you were to stand on a scale on earth (even though the sun is pulling you up, the earth is also being pulled up towards you. The residual effect is the difference between the sun's gravity at the surface vs the center of earth which is only. 008% of the strength you calculated (assuming you stand with the sun directly overhead). So the real impact on your weight on a scale would be only +/-4 milligrams."
] |
[
"There is a very small effect due to the relative positions of the sun and the moon (mainly the moon), but it's not due to their direct pull on us but rather due to the reshaping of the Earth due to the tidal influence of those bodies, which modifies the gravitational field by about a part in ten million. See the gravitational part of ",
"this article",
"."
] |
[
"This is wrong. I also once thought this and tried to measure the difference in gravity using very sensitive equipment at work (",
"by a bond tester",
") lifting a weight repeatedly during the day and the night. The tester is accurate enough to eliminate effects like temperature on the measurement. I found that my hypothesis was wrong; the measured force was the same.",
"The reason is that we are in free fall around the sun (together with the earth). The really simple way to see this is to consider another example: the ISS. You could apply the same formulas to the space station, but it is rather obvious that the astronauts do NOT experience the pull of the earth in that way. They are in free fall around the earth. The same is true for us and the sun."
] |
[
"Does rainwater really clean the air?"
] |
[
false
] |
[deleted]
|
[
"Water condenses around little specks of dust and dirt in the air, so it does get those little bits of matter out of the air. ",
"Acid rain has nothing to do with the dirt in the air. It's dependent on how much carbon dioxide is in the atmosphere. More carbon dioxide means the rain becomes more acidic"
] |
[
"Look at air quality levels in your local paper, watch what happens after it rains. Particulates and NxOx molecules are certainly \"cleaned\", and any local paper can demonstrate this.",
"Acid rain is caused by sulfur and NxOx reacting with the water to produce sulfuric and nitric acids. Again the rain is clearly removing these molecules from the air, so it is \"cleaning\" the air in a literal sense. Seriously damaging acid rains are caused by sulfurs released by coal burning.",
"And yes, the air is cleaner when it rains. NxOx molecules precipitate out of the air more heavily on hot days, so low tempratures generally also improve air quality."
] |
[
"I'll look into that, but I seriously doubt my local newspaper would have any detail more elaborate than \"bad air day\" and \"good air day.\" The city I live in is seriously lacking in people who would understand any more detail than that. And I'm not saying that to be rude. It's actually true. "
] |
[
"When you break a bar magnet in half, it reforms north and south poles. The process repeats with additional breaks. Why, and how far \"down\" will I continue to get these magnetic poles?"
] |
[
false
] |
I understand that magnetism is basically formed by the uniform up or down spin of electrons, ( I could be wrong about this. I'm not even close to an expert.) If I'm correct, why does breaking a magnet cause these electrons to re spin in the appropriate configuration? Also, if I break a magnet in half, and then again and again... at what point will I stop seeing opposite poles?
|
[
"You are thinking about this the wrong way.",
"Think about magnets likes legos. North is the \"top\" of the lego with the little circles (male side), and South is the bottom of the lego with the cavity (female side).",
"At what point does the lego \"switch\" from the top to the bottom? This question doesn't really make sense",
"Similarly, if you have a big tower of legos, don't you see that no matter where you break it, the bottom is already going to be a female / South side, and the top of the new piece will already be North / male ?",
"Do you see how if you break the tower, you don't need \"two new poles\" to be created? they are there simply because you split the tower, and they were already oriented with the rest of the magnet (north side up, south side down). "
] |
[
"They don't re-spin. ",
"Think of the smallest \"unit\" of magnetism as pointing one direction. One direction it points will be \"north\", and the other is \"south\".",
"This is a fundamental aspect of magnets (di-poles). ",
"When you add a bunch of these units together facing the same direction, their strength becomes cumulative, and they make a \"larger\" magnet. ",
"So as you can see, when you break a magnet down, nothing needs to \"spin\", because the fundamental nature is they have a north and south pole all on their own. "
] |
[
"Individual electrons have a magnetic field. So far as we know, the electron is a truly fundamental particle and there is no way to divide it further. ",
"It might (and by might, I mean probably not) be possible to have a ",
"magnetic monopole",
", which would be like a north-only bar magnet. "
] |
[
"Is the CMB cold spot legitimate proof of the existence of a parallel universe?"
] |
[
false
] |
I've read that many physicists/astronomers believe that cold spots in space are imprints to other universes. Also what would a cold spot look like in person? Just vast emptiness or could there actually be a wormhole-like structure in that area?
|
[
"None of those things, it's just a place in the sky where the CMB is slightly colder, as is expected from its statistical fluctuations."
] |
[
"Note that the difference between a cold spot and a hot spot in the CMB is ",
"0.0002 Kelvin",
". There is nothing interesting there to observe. The spots are no proof of a parallel universe but are grounds for hypotheses."
] |
[
"The non-Gaussian cold spot detected in wavelet space in the WMAP 1-year data, is detected again in the coadded WMAP 3-year data at the same position (b = -57, l = 209) and size in the sky (around 10 degrees). The present analysis is based on several statistical methods: kurtosis, maximum absolute temperature, number of pixels below a given threshold, volume and Higher Criticism. All these methods detect deviations from Gaussianity in the 3--year data set at a slightly higher confidence level than in the WMAP 1-year data. These small differences are mainly due to the new foreground reduction technique and not to the reduction of the noise level, which is negligible at the scale of the spot. In order to avoid \"a posteriori\" analyses, we recalculate for the WMAP 3-year data the significance of the deviation in the kurtosis. The skewness and kurtosis tests were the first tests performed with wavelets for the WMAP data. ",
". The frequency dependence of the spot is shown to be extremely flat. Galactic foreground emissions are not likely to be responsible for the detected deviation from Gaussianity. ",
"http://arxiv.org/abs/astro-ph/0603859",
"(emphasis mine)",
"A 1.85% statistical anomaly is imho not unlikely enough to warrant more exotic explanations.",
"Did perhaps the Horizon episode with Laura Mersini prompt you to ask this question? You can read about some of her research here:",
"http://en.wikipedia.org/wiki/Laura_Mersini#Research"
] |
[
"In theory, would it be genetically possible for two humans to repopulate the earth?"
] |
[
false
] |
Say a man and a woman are forced to repopulate our species after an apocalyptic event. Would genetic defects remain a major problem even after 10,000 generations++? How diverse could we become genetically?
|
[
" yes this could happen. The bottleneck is so slim, however, that it really remains up to chance. It really depends on how many recessive alleles are present in the founders and how deleterious these alleles are. Consanguinity has led to all sorts of genetic diseases that still affect populations today (hemophilia in the European royal families, Tay-Sachs in the Ashkenazi Jews, etc). Because of meiotic crossing in the gonads, these founders would be wise to be as prolific as possible, as the patchwork of chromosomes they pass on to their progeny would be a vital source of genetic diversity.",
"This would be a phenomenal feat of odds, as childbirth and infancy ",
"in pre-industrial society",
" is very dangerous. Plus you've got other factors- disease (even without humans around, ",
"we can still get quite sick",
"), predators, injury, getting enough food, etc.",
"Basically, it's possible but very unlikely."
] |
[
"If you have a limited number of spaces on a space ship, you raise a very good point. By sending more females than males, you loose genetic diversity, but you gain in number of children that grow to childbearing age.",
"But as long as we are going scifi, you send a 100% female crew with a vast supply of frozen sperm. Every child sired by a different male. Then you select for only female children until you run out of unique sperm donors. You get maximum genetic diversity and maximum population boom.",
"EDIT: It has been pointed out below that we could send frozen eggs also, to increase genetic diversity even more rapidly. Instead of creating 5 siblings, for example, a single woman could create 5 completely unrelated children."
] |
[
"maybe my post is best suited for this question! You need (on average, for any species) 4169 individuals but the conservative estimates for mammals are around 7000 and there's only direct evidence for 12000 or so. ",
"http://www.sciencedirect.com/science/article/pii/S0006320707002534",
"since these are individuals, divide by 2 for # couples"
] |
[
"How much orbital debris needs to accumulate around the Earth before we start forming rings that we can see from the ground? How long will this take?"
] |
[
false
] |
Is this even possible?
|
[
"Search for ",
"previous answers to your questions",
" before you post them :) "
] |
[
"Oops. I usually do, but I forgot this time. Sorry about that!"
] |
[
"Well, your question does specify a ",
" ring, so forgetfulness aside, your question is different. In light of the provided link, though, the answer seems to be the same \"no,\" but slightly more emphatic due to the extra requirement of visibility. "
] |
[
"can your hands \"prune\" in the salt water of the ocean?"
] |
[
false
] |
is this phenomenon caused by osmotic pressure, which would mean that you never prune if the water is saltier than your body, or does it work through some other mechanism that can work regardless of salinity?
|
[
"It's not caused by osmotic pressure, it's a regulated neurological phenomenon. If you cut the nerves to the hand, you don't prune. If you cut the blood supply to the hand, you don't prune. If it was osmotic, why does it only happen on the fingers and toes, and not on, for example, the forearm or chest?",
"I don't think the mechanism is known, but it is ",
"theorized",
" that it is a regulated process that has something to do with improving grip in a wet environment. ",
"Primary journal",
" here. I think it's open access. There's a pdf behind that link, by the way.",
"And yes, it does happen in salt water, too (just personal experience on that one, though)."
] |
[
"Not a dumb question at all - the leading ",
"mechanism",
" involves electrolyte balance so it's quite reasonable to hypothesize that it works differently in salt water - from first principles of osmosis one would expect a difference. My experimentation-as-surfer (er, anecdotal evidence) is that the end result is the same - wrinkled fingers."
] |
[
"not everyone can just go in the ocean whenever they want, thanks"
] |
[
"Is it true that certain foods can increase your short term mental alertness?"
] |
[
false
] |
[deleted]
|
[
"I had a HS teacher do the same with me and as I have judged science fairs, this is a common project for young kids (give some friends peppermint and see if they remember a list of words better than controls).",
"The claim for peppermint seems to be more in the smell as opposed to eating it. ",
"Here is one recent study",
", though the results were not nearly as impressive as the abstract would lead you to believe. ",
"Here is the take home figure from the paper.",
" "
] |
[
"And its actually worse than that. Checkout table 1. They measured 17 variables (and possibly others not listed) and for each variable did three tests (control vs mint, control vs ylang, and mint vs ylang) and found 7 \"significant comparisons\" at the p<0.05 level (you would naively expect about 3 by chance). All the significant comparisons showed ylang was worse than the control or peppermint (lower accuracy, or longer time). So if anything this study shows, don't use ylang-ylang if you want to perform well on their battery of tests.",
"They later did data drudging and created ",
" new variables via grouping measured variables together (into categories not predicted to be significant ",
") and low and behold found some significant differences. Even then the intragroup variation was still much greater than the difference between groups. I'm not saying the study couldn't have found a quite subtle effect, but they have made a relatively weak or merely placebo effect. (The two test conditions were oils they could smell, the control was water. Maybe multiple control group of an detectable aroma not associated with brain function?)."
] |
[
"I've heard these things as well but I've never seen any data to support it.",
"You already mentioned caffeine, and that is basically the only food-product that I know that temporarily increases cognitive functioning. "
] |
[
"If the strong force will pull protons together just as strongly as neutrons, why don't we see nuclei with just 2 or 3 or more protons without any neutrons? Why aren't there any helium ions with no neutrons?"
] |
[
false
] | null |
[
"The diproton does exist. It is very unstable.",
"https://en.wikipedia.org/wiki/Isotopes_of_helium",
"While the strong force is strong, it still competes with the electromagnetic force. So protons still repel each other. This is one of the reasons why larger nuclei have more neutrons than protons. "
] |
[
"Something like ",
"this",
"? There is some evidence for dineutrons. The problem for neutrons is that they are not the lowest bound state. They want to decay into protons. That is why free neutrons decay. Being in the nucleus \"stabilizes\" them. The modes of decay become limited and they are essentially prevented from decaying. The reason you don't see systems with 5 neutrons is because they do not last long. In many cases, the system is not bound. Being bound is the general definition to claim that the system exists. The best way to explain it is whether the system consisting of multiple neutrons are bound together as 1 system before decaying."
] |
[
"A neutron is not an electron and proton stuck together any more than a proton is a neutron and a positron stuck together. A neutron is two down quarks and an up quark. A proton is two up quarks and a down quark. Neither of them have any electrons or positrons."
] |
[
"Massive bodies orbit in conic sections under Newtonian gravity. What shape would a photon's orbit be?"
] |
[
false
] |
Assuming it makes sense to think of photons as bodies of constant speed and ignore relativistic effects. Does the shape of the orbit of such a body have a name?
|
[
"There is no consistent way to talk about photons in Newtonian physics, which makes sense since they are quantum mechanical objects after all. Specifically, there's really no such thing as a massless object in Newtonian physics. I suppose the best you can say is that if m = 0, then the net force acting on that object must be 0 also by Newton's second law. Hence photons (really, we should talk about light waves or light rays) cannot be deflected by any force, including gravity, in Newtonian physics. So they travel in straight lines, which are an example of a degenerate conic section.",
"(edit: Please do not downvote posts for asking genuine questions.)"
] |
[
"You asked about how photons orbit in Newtonian gravity and prefaced the question by noting that ",
" objects orbit in conic sections. Well, ",
" objects don't exist in Newtonian mechanics, but if they did the best you could say is that they travel in straight lines.",
"Now you seem to be asking about orbits with constant speed? First of all, it's incorrect to characterize the orbit of a photon (even in GR) as an orbit with constant speed of ",
". Second of all, orbits with constant speed certainly exist in Newtonian gravity for ",
" objects; the orbits have to be circular. But obviously there is no limit to the speed of that object.",
"The main problem of your question is that you are trying to ask a question that combines principles from two contradictory theories. Do you want to talk about massless objects or do you want to talk about orbits with constant speed or do you want to talk about objects with speed ",
" (which is ",
" an upper bound for speeds in Newtonian mechanics)?",
"If you want to know about orbits of photons in GR, then that has a well-defined answer. Null geodesics for a Schwarzschild black hole are circles in Schwarzschild coordinates and consist of great circles on the so-called ",
", at Schwarzschild radial coordinate r = 3GM/c",
" where M is the mass of the black hole. For more complicated black holes, photons do not necessarily have any closed orbits. For a Kerr black hole (rotating black hole with no charge), the null geodesics consist of both equatorial circles and some very complicated open loops away from the equator. The coordinates of choice are Boyer-Lindquist coordinates, which are really elliptical coordinates. So the orbits themselves, unless they are completely equatorial, look nothing like circles or ellipses."
] |
[
"As I have said ",
" times, photons do not exist in Newtonian mechanics. At best you can say that since they are massless they are not deflected by any forces whatsoever and so their orbits are just straight lines. If your simulation is not based at all on GR, then I have no idea what this simulation is intended to show. They should all be straight lines if you claim you are basing this on Newtonian physics.",
"Again... you are trying to pick and choose aspects of two different theories and combine them in some nonsensical way. If you are using Newtonian mechanics, the orbits of a massless particle are straight lines and the orbits of massive particles are conic sections. If you are using GR, the orbits of a photon are more complicated, and circular orbits are possible. There is no combination of the two theories that makes sense."
] |
[
"How fast does something need to spin to look like it's not moving?"
] |
[
false
] |
I was looking at a D20 (20 sided dice) and was wondering how fast it would need to spin for it to look like it was still? Would it be possible? This would be looking directly at at, not through a camera.
|
[
"There is no definite answer to your question. Despite others have mentioned movie theaters as a \"proof\", it is not that simple. It depends on several factors for individual images to be fused into a continuous movement. Among others, like e.g. attention, these factors are general brightness and contrast. It works for movies at a rather low framerate because it is mainly dark in cinemas and also the movie itself is not very bright. The darker the images, the earlier fusion starts.",
"Furthermore, it depends on the region the stimulus is displayed. For peripheral vision there are different thresholds than central vision."
] |
[
"Eye's don't see in FPS, they see a continuous stream of light. It's been proven that trained eyes are capable of distinguishing a single different frame (with enough detail to identify what the frame was) out of 200 frames shown in a single second. As another user stated, it's simply around 30 FPS that movement begins to look smooth."
] |
[
"Eye's don't see in FPS, they see a continuous stream of light. It's been proven that trained eyes are capable of distinguishing a single different frame (with enough detail to identify what the frame was) out of 200 frames shown in a single second. As another user stated, it's simply around 30 FPS that movement begins to look smooth."
] |
[
"Why can some people seemingly fall asleep on command while others can hardly sleep at all?"
] |
[
false
] |
[deleted]
|
[
"I would love to hear an answer on this as well. I am able to fall asleep very easily, and my wife takes an hour or two to really fall asleep. Since she's been pregnant, (20 weeks or so,) she falls asleep on command, and we talk about why this is all the time. While not all that scientific, I've always thought it's because she is a big worrier, and her mind is full of worries when she goes to sleep. I, on the other hand, like to go to bed with a clear mind, I deal with my worries before I get to bed, so my mind isn't \"active\" when I try to sleep. My answer isn't biological in nature, but it is somewhat scientific. I've often found that people who generally take longer to fall asleep just have much more active minds when bedtime arrives - whether it be worry or something else. As for a neurological reason, I would be really intested in hearing an actual scientist's perspective!"
] |
[
"Knowing why/how would be interesting to know. A \"cure\" would be great. I really envy my gf, she can start snoozing within a couple minutes of laying down, while I lay awake, miserable and tired."
] |
[
"This is not a science answer, but from personal experiences it really seems genetic. You should conduct a survey and ask your friends who have varying levels of difficulty sleeping if their immediate family members are the same way. I'll expect a full report in 2 weeks."
] |
[
"How does Optical Image Stabilization work in an expensive camera lens?"
] |
[
false
] |
To me, the image appears more smooth as if controlled by a gyroscope, but I know that is not exactly how it works. Does anyone have an engineering insight on this?
|
[
"It isn't typically accelerometers. Such MEMS devices are relatively new. Most established camera systems such as Canon's IS use gyroscopes.\nA lens group mounted in the gyro resists camera shake redirecting light ",
"Here is a video of the IS lens in action:\n",
"http://youtu.be/C60ehMe3wQ8"
] |
[
"looking back at my sources, I have no idea why I said accelerometers. I must have been out of it. ",
"Sweet video"
] |
[
"Every company does it a tad differently, but in general, they all work on the same principle of using accelerometers to detect movements and adjust either an element in the lens (if it is lens based) or the actual image sensor in the camera itself.",
"Nikon has a relatively nice page explaining the technology. Nikon's VR is lens based: ",
"http://www.nikon.com/about/technology/rd/core/software/vr_e/index.htm",
"EDIT: I accidentally a sentence"
] |
[
"If joules are understood solely as energy, how can they be negative?"
] |
[
false
] |
[deleted]
|
[
"It depends on context. If you have some process that involves energy, like a chemical reaction, negative energy often represents the amount of energy ",
" necessary for that process to take place. Another example is atomic or nuclear binding energy, which is often treated as negative. For instance, the inner electrons of the gold atom have around 80 keV of binding energy. If a 90 keV photon knocks one of those electrons out, it is emitted with 90 + (-80) = 10 keV of kinetic energy."
] |
[
"If you're talking about ",
"enthalpy",
", then it has a very important meaning in distinguishing exothermic and endothermic reactions."
] |
[
"The difference in energy between two states, for example."
] |
[
"Can I plug a generator into the wall socket to power everything on that line"
] |
[
false
] |
If I were to take a generator and plug it into my wall socket when the power is out would everything on that breaker be able to receive the power and could I power things on other breakers. I am not trying to do this just more curious if I'm thinking of this correctly.
|
[
"No it wouldn't work. Your branch breaker shares a bus with all the other branches in your house so you'll be trying to power your entire house off the 15A circuit your generator is connected to. Maybe if you turned off all the devices that you don't wish to use (don't forget the permanent devices like central air!)"
] |
[
"Assuming you disconnected the line (by turning of the relevant breaker), it should work after some fashion. But remember that wall sockets aren't dimensioned to drive an entire line, so trying something like this could easily cause an electric fire."
] |
[
"Yes, it will power all the lines. The power will flow back though the circuit breaker to the mains distribution and the other circuit breakers.",
"You would have to open the main circuit breaker because if power comes back it will most probably desyncronize your generator and possibly destroy it (very dangerous). It's not a proper installation."
] |
[
"Benificial autocanibalistism in extreme survival situation?"
] |
[
false
] |
So the hypothetical situation is this: you are stranded on a rock in the middle of the ocean with no food (this includes a lack of all flora and fauna inhabitting said rock) but ample rainwater. The rock has worn away in a manner where it is impossible to fish without permanently returning to the ocean, which would be a problem if you had a boat but you don't. Given that you have the supplies and know how to amputate a limb with minimum loss of blood, and nullify any infection would there be any benefit in doing so and eating said limb? I know this is kind of strange but once a question pops in my head it is hard to let go...
|
[
"The inflammation and reaction your body would have to losing a limb from sawing it off would far outweigh any benefit from eating your limb. Also, the body is already reabsorbing the proteins in your muscle for fuel, so theres no real need to do it through your mouth/stomach. "
] |
[
"Layman here but this is an easy one to tackle.",
"Your cells do that automatically as part of their normal metabolic processes: they often breaks down complex molecules they're \"made of\" to extract energy in order to sustain themselves if the calories intake is insufficient (some cell cannibalism/dead cell recycling is also involved). That's why you get thinner after not eating.",
"Severing a limb would definitely be far less efficient than that.",
"One may argue that it would save on future energy consumption (less body mass to maintain) but, given the short time you'd have left, energy expenditure for just shock+healing would vastly outweight the benefits.",
"That aside, your body cannot synthesize essential amino acids, minerals and so on. Your severed limb would be out of those much needed substances just as much as the rest of your body would be.",
"There are probably tons of other implications a qualified panelist would mention (and I hope some will turn up)."
] |
[
"Your's and mustfndnewname's points are ones i have considered as well, i suppose i should have worded the question better (Can it prove to be more benificial to canabalize a part of yourself rather than allow yourself to emaciate.) I hadn't thought of the fact that your body would be uniformly non-nutritious though, that point made me facepalm. "
] |
[
"How can a Half Blood Moon exist?"
] |
[
false
] |
On 24 March 2022, at around 3:00am, from the UK, I could see a red half-moon. At first I thought "Oh must be a lunar eclipse" before double-taking and realising it was almost a half moon (just coming into third-quarter). (this picture doesn't actually do it any justice, it was much redder). I did some research to see if there was a way the moon could appear this way somehow, and I also tried googling it to see if it could have been some sort of atmospheric disturbance or something, like the same way the sun appears redder in the sky at sunset and sunrise, but I didn't see anything related to the moon. The moon wasn't on the horizon, however it was low, but not at a height you'd expect to see such a dramatic change in colour. Also, as the moon rose in the sky, it stayed red. What am I missing here?
|
[
"It's only possible to have a Lunar Eclipse during a Full Moon - because that's when the Moon is on the far side of the Earth from the Sun - and the 24th of March was a slightly over half Moon, as in your picture. Though you ",
" get half-red half-black moons, but the black shadow has to curve the other way. If you imagine a big red circle, with a smaller black circle in the centre inside it, and cut out a Moon-sized circle on the edge of them, then that's what it'd look like. The smaller black circle is the Earth's \"umbra\" - the full shadow that totally blocks out the Sun's light - and the larger red circle is the Earth's \"penumbra\" - the partial shadow that blocks out part of the Sun's light, and filters some of it through the atmosphere.",
"So, there couldn't have been a Lunar Eclipse on that date, and a Lunar Eclipse wouldn't look quite like that anyway. It definitely had to be an atmospheric effect. Note that in the UK we have been having particularly clear weather over the last week, so you might be noticing the Moon more than normal."
] |
[
"Have a look at this article from the Guardian:",
"https://www.theguardian.com/uk-news/2022/mar/16/saharan-dust-shifting-across-europe-hit-britain"
] |
[
"That's an interesting article. The photo was actually taken in the north of the UK though. I do believe it to be an atmospheric phenomenon of some sorts however."
] |
[
"Is there a limit to how small a star can be? If so, what is the theoretically smallest star possible and why?"
] |
[
false
] | null |
[
"About 80 times the mass of Jupiter. Below that, they don't have enough mass to get the intense heat and pressure in the core required to fuse hydrogen. These objects are called \"brown dwarfs\", and generally look more like ",
" Jupiter than a star. The line between a small brown dwarf and a large gas giant is actually a bit fuzzy."
] |
[
"Astro physics put in terms I can understand. Thank you sir!"
] |
[
"Here's my take. We want an object that is massive enough that when we are on the surface we cannot jump up to reach escape velocity. It needs to be made of a realistic material that we can obtain and put on its own. The densest such material is Osmium and it'll lead to the smallest radius. The highest vertical jump I've seen on youtube is 62 inches, which is roughly 54 inches height difference from take-off to highest point. This gives a vertical velocity of take-off of 5.282 meters/second. Playing around with the various equations for potential energy, kinetic energy, escape velocity, density and volume, I have the figures",
"radius = 1487.62 meters\nmass = 9.3373*10",
" kg",
"If the object were made of iron it would have",
"radius = 2518.91 meters\nmass = 1.58059*10",
" kg",
"This is in the ballpark of the size of Deimos, one of the satellites of Mars. As the wikipedia page mentions, its escape velocity is 5.6 meters/second, meaning that pretty much no human on Earth can escape its gravitational pull. Althought, if someone were to give you a boost, that's most surely achievable!"
] |
[
"How is a genome built?"
] |
[
false
] |
Sorry to bring religious apologetics into askscience, but I was watching video and, while logical refutations for the majority of the annotations came to me easily enough, I found myself stumped trying to find literature that could help me understand the mechanics which allow a genome to expand (the point stating the difference between the genome of the simplest bacteria and the relatively complex human genome). I get the feeling there's already a pretty solid explanation or ten but I'd appreciate it if anyone could point me in the right direction.
|
[
"What do you mean, expand? Like in size, e.g. 3 billion base pairs vs 1 billion?",
"Well gene duplication events copy and duplicate a region of a chromosome. These events have occurred extremely frequently and have become a major source of evolution. There are lots of different mechanisms that can lead to this- \"errors\" during recombination, particularly in regions with a lot of repetition, retrotransposition events (retrotransposons actually make up a huge percentage of our own DNA) where a region of DNA makes copies of itself and inserts it else, or even whole chromosomal duplication events. Most of our large DNA size is due to a large amount of \"junk DNA\" that doesn't contain genes and have been a result of these duplication events; organisms like bacteria or yeast have much more compact genomes that do not have as much non-coding DNA."
] |
[
"It was indeed."
] |
[
"That's pretty much what I was trying to ask :D",
"Thanks for responding so clearly. This leaves me with a number of phenomena to investigate...Wikipedia here I come."
] |
[
"Dear AskScience, is sound \"real?\""
] |
[
false
] |
We're all familiar with the old question: If a tree falls in a forest, and nobody is around to hear it, does it make a sound? Is it possible that we can answer this question through reference to the physics of sound and the biology of hearing? Sound is vibration. Our ears are sensitive to certain vibrations, and when we come in contact with those vibrations, our ears alert our brains to their presence. "We" then "hear" the corresponding sound. (The distinction, in discussions like these, of brain and self is always extremely baffling.) My question is, is there anything objectively "correct" about the sound we experience in response to a given vibration, or is it merely the product of a fixed, but ultimately arbitrary, convention of evolution - a code, or translation, if you will? Obviously the sounds are with the vibrations, and the whole system is self-consistent. If some hypothetical extraterrestrial scientists were studying the human brain and they (somehow) knew what one vibration sounded like to us, they could reasonably deduce what other vibrations would sound like to us. But is it not also possible that those same aliens would experience those same vibrations in an equally self-consistent, but wholly different way? If this is indeed the case, then, in my opinion (as a humble Philosophy undergrad), a tree falling in a forest make a sound. It makes vibrations. Sound is something that's heard - the subjective product of the objective vibrations filtered through and translated by our neurological hearing apparatus. If this is correct, then the other old philosophy cliche - how can you and I be sure we experience color in the same way? - would apply equally well to hearing. Thoughts?
|
[
"Isn't it really just a matter of definition? Settle on a definition and you have your answer."
] |
[
"You're just playing with definitions. Is sound real? If you define sound as vibrations in the air, it is. If you define it as some hard-to-decode neural pattern, sure. If you define it as a thought, well, that depends on if you define thoughts to be real.",
"Anyway, if you intend to go down this route, it helps to define what counts as real first :)"
] |
[
"I think you are looking for ",
"/r/askphilosophy",
".",
"Our ",
" is our interpretation of vibrations in the air. What you define ",
" to be is largely up to you."
] |
[
"Is there any sort of evolutionary explanation as to why humans find baby animals cute?"
] |
[
false
] |
There is something about baby animals that invokes a deep emotional response in humans. You'd think that a baby animal would be seen instinctively as as easy catch for dinner. But instead, we want to pick them up and hug them. Other predatory animals seem to have no problem chasing after a baby animal of a different species. And humans don't have a problem chasing after an adult animal for food. I've always wondered about this. Perhaps because if humans were to kill off baby animals, they couldn't reproduce and there would be a shortage of food in the future (thinking in terms of more primitive humans in localized populations)? Thanks
|
[
"They have the same traits (such as large eyes) that make us think human babies are cute."
] |
[
"I would guess that not going derpy over every infant is the learned behavior. People generally don't like strangers fawning over their babies, so you learn not to. Pets are different. "
] |
[
"I would guess that not going derpy over every infant is the learned behavior. People generally don't like strangers fawning over their babies, so you learn not to. Pets are different. "
] |
[
"If measurement causes the wavefunction to collapse, and everything is constantly interacting with everything else in the universe via gravity, why haven't all wavefunctions collapsed all the time?"
] |
[
false
] |
[deleted]
|
[
"Crudely, wavefunction collapse means the following. You allow your quantum system S to interact with a set of degrees of freedom M. The interaction entangles the state of S with the state of M, so that the probability distribution of some observable OS of S are correlated with observable OM of M. But perhaps you don't care about OM and only want the marginal distribution for OS. Averaging over OM produces an effective collapse: the probabilities governing future behavior of S now behave as though, at the time of interaction with M, OS took various values with probability set by the Born rule. This is what you would expect from classical probability theory, but differs from quantum mechanics because it eliminates the effects of interference between quantum mechanical amplitudes.",
"So, you might think that everything is interacting with gravity, and we don't care about the state of the gravitational field, so why doesn't averaging over it classicalize all probabilities? The reason is that gravity is weak: interactions with gravitons are rare. The quantum systems we look at are affected by gravity in the sense that their motion is influenced by the background gravitational field, but they are very unlikely to change the state of that field by entangling with a graviton."
] |
[
"EM is approximately a trillion trillion trillion times more powerful than gravity. Even on earth, gravity effectively doesn't exist when compared to electromagnetism. "
] |
[
"EM is approximately a trillion trillion trillion times more powerful than gravity. Even on earth, gravity effectively doesn't exist when compared to electromagnetism. "
] |
[
"The speed of light and earth like planets"
] |
[
false
] |
When science searches the cosmos for "earth like" planets, are they actually searching for planets with a similar make up as ours? If we are, how do they figure out which will be earth like considering that the speed of light causes them to see so far into the planets "past"?
|
[
"From what I've heard/seen, most the planets we've found are on the order of tens to hundreds of light-years away, meaning we're look at them only a few hundred years in the past. ",
"Example: ",
"Here's",
" a 600 light-year away planet",
"After a little googling I found an ",
"article",
" that has some other planets found."
] |
[
"Two answers to your question!",
"As snailbotic pointed out, all of the planets we are looking for/found are rather close to Earth. I don't know the exact number, but I would venture a guess that they are all within 1000 light years. ",
"When we look for \"Earth-like\" planets, we're not necessarily looking that they have clouds and water and grass. We're looking that they're about Earth sized at about Earth distances from their star. It will take further investigation to determine what their atmospheres are composed of."
] |
[
"In addition to the other responses, I'd like to point out that the vast majority of exoplanet researchers aren't looking for \"earth-like planets.\" Of course, finding such would mean instant fame. But most researchers have their own topics of interests: things like hot jupiters, mdwarfs, multiple-planet systems, even simply refining exoplanet techniques."
] |
[
"Why don’t we use salt water for toilet water? Wouldn’t it save millions of gallons of freshwater?"
] |
[
false
] | null |
[
"Saltwater is more reactive and corrosive than fresh water, for one. Harder to maintain, I'd expect.",
"Also, you would still want fresh water to your house for showering and cooking, so you'd have an additional set of pipes running to each building."
] |
[
"As others have said, there are problems with salt water.",
"The solution is \"grey water\". This is water that is relatively clean but not drinkable. Think rainwater, or what goes down the plug in your shower or bath, even what comes out of your washing machine. All of this is perfectly good to flush a toilet with and basically wasted. You can install a secondary system that takes and filters grey water to use for toilets. But as piping fresh water to your house is mostly trivially cheap, it's usually more expensive than its worth. "
] |
[
"In extreme cases it is used. For instance Hong Kong has a dual water system. ",
"https://en.m.wikipedia.org/wiki/Water_supply_and_sanitation_in_Hong_Kong"
] |
[
"Can we make sounds with our vocal chords that are not in the audible frequency range?"
] |
[
false
] | null |
[
"It depends how you define \"sound\". Do you mean the fundamental perceived pitch, or can we include the highest frequency present in the vibration?",
"If you can make a clicking sound, a click can approach a ",
"dirac delta function",
", which has energy at every frequency. It is the identity operator in time domain convolution. Convolution in the time domain is multiplication in the spectral domain, which shows that a dirac function must have power at every possible frequency.",
"While you cannot make a dirac delta with your vocal chords (and a true dirac delta isn't really going to be measured anywhere in nature), a simple click can easily contain components far above the range of human hearing. The throat and mouth act as a low pass filter so the higher frequencies are attenuated of course."
] |
[
"I should add that this is not the only possible way to make an ultrasonic vocalization. Just showing that at least one is possible."
] |
[
"Just an interesting aside - there is ",
"evidence",
" to suggest that those who are \"hearing voices\" are making subvocalizations in line with whatever it is they're hearing. Essentially, your vocal cords are demonstrating subtle activity but not actually producing audible sound, while you hear the voices internally."
] |
[
"Why do the containers of vacuums need to be strong?"
] |
[
false
] | null |
[
"Yeah, that's it. You need your chamber to be able to withstand the inward pressure force, or else it will implode."
] |
[
"PSI stands for pounds per square inch. Just estimating the size of that tube to be 10 meters in length and 1 meter in diameter, its surface area is 48695 in",
". Assuming the pressure difference between outside and inside is 14.5 PSI, the force acting on the tube is over 700000 pounds."
] |
[
"hmmm, good point. Theoretically though, if you could get a material that could withstand an inwards force of 15psi (as an example) would that be sufficient to prevent an implosion? Or are there more forces at work>? "
] |
[
"Does a person using a skateboard expend less energy than a walking person traveling the same distance?"
] |
[
false
] |
Yes, I know. Strange question. But I was watching a neighbor pass by my house on a skateboard today, and I started wondering about the physics of it. Obviously, he was moving between points A and B on his journey faster than he would be walking. But then again, he also has to occasionally use one foot to push against the ground several times to keep the momentum of the skateboard moving forward at a higher speed than if he was just walking. My question is basically is he ending up expending the SAME amount of total energy by the "pushing" of his one foot while using the skateboard as he would if he was just walking the same distance traveled using two feet? Assume all other things are equal, as in the ground being level in the comparison, etc. My intuition says there is no such thing as a "free energy lunch". That regardless of how he propels his body between two points, he would have to expend the same amount of energy regardless whether he was walking or occasionally pushing the skateboard with one foot. But I'm not sure about that right now. Are there any other factors involved that would change the energy requirement expended? Like the time vs distance traveled in each case? EDIT: I flaired the question as Physics, but it might be an Engineering question instead. EDIT 2: Wow. I never expected my question to generate so many answers. Thanks for that. I do see now that my use of the words "energy expended" should probably have been "work done" instead. And I learned things I didn't know to begin with about "skateboards". I never knew there were...and was a difference between..."short" and "long" boards. The last time I was on a "skateboard" was in the late 1960's. I'd hurt myself if I got on one today.
|
[
"To be fair, it is unlikely they were using subjects who weren't experienced with walking."
] |
[
"A study was done two years ago by Colorado State University for 15 experienced longboarders.",
"\"The gross metabolic cost was ~2.2 J kg(-1) m(-1) at the typical speed, greater than that reported for cycling and ~50% smaller than that of walking.\"",
"http://www.ncbi.nlm.nih.gov/pubmed/25085605"
] |
[
"Just noticed this study was done on longboards. They are overall a much smoother ride and require much less work, so I'd be interested to see this study done for a short board. "
] |
[
"Why is Fluorocarbon hydrophobic?"
] |
[
false
] |
If I understand it right, hydrocarbons are hydrophobic because of the non-polar interactions. But what makes Fluorocarbons MORE hydrophobic? Fluor-carbon interaction are very polar aren't they? so wouldn't that make them soluble in water?
|
[
"Great question!",
"Your most common PFC is CF4. Draw a Lewis structure of this molecule and notice that the four C—F bonds are symmetrical about the central carbon atom. You’re correct that each of these bonds is polar, and ordinarily that does make a molecule hydrophilic, but in order to be hydrophilic the ",
" dipole moment of the molecule has to be ",
".",
"The electrons are very attracted to the flourines, but they’re attracted to ",
" of the flourines and so the average position of the electrons is evenly distributed. Thus, no permanent dipole moment."
] |
[
"Short answer: My guess would be that fluorocarbons are more hydrophobic than hydropcarbons because FC's are bigger. ",
"Here's a paper",
" which supports that, stating, \"[T]he extra work of cavity formation to accommodate a fluorocarbon, compared to a hydrocarbon, is not offset by enhanced energetic interactions with water.\"",
"Long answer with my reasoning:",
"I think this is a case where it's useful to recall just what hydrophobicity is. Nonpolar molecules only associate through instantaneous dipoles (London Dispersion Force), which are always going to be weaker than a permanent dipole on a polar molecule like water. Therefore, the \"driving force\" of hydrophobicity is not the hydrophobic molecules themselves, but the ",
" molecules. Remember that \"unfavorable\" or \"unstable\" interactions are only unfavorable/unstable ",
", and therefore interactions between water and nonpolar molecules are unfavorable only insofar as ",
". A single water molecule in a sea of hydrophobic molecules has no better option than interacting with those nonpolar molecules; it has no preferred orientation. However, when there are other water molecules in the mixture, the dipole-diople interactions between them will be stronger than the induced dipole interactions. Once water molecules form mutual interactions, they fall into a potential energy well and are \"disinclined\" to leave. To look at this yet another way: ",
"Now consider the behavior of a shell of water molecules surrounding tetrafluoromethane as opposed to regular old methane. The former is substantially larger than the latter, meaning it takes more water molecules to cover it. For every water molecule that is in direct contact with CF4 or CH4, there is a favorable dipole-diple interaction that is not happening. The direct contact of two CF4 molecules, therefore, displaces more water molecules - which go on to form favorable dipole-dipole interactions - than two CH4 molecules would. Conversely, the intrusion of a single CF4 molecule into a homogeneous region of water must overcome more stable water-water interactions than that of a molecule of methane."
] |
[
"Ok thank you,",
"But what properts makes Fluorocarbons MORE hydrophobic than hydrocarbons? I am making a presentation about Fluor in skiwax and why is is hazardous. But I am also gonna explain why Fluor works so good as a skiwax. That must be because it is very hydrophobic, right? I’ve also found out that paraffin is used, and paraffin is non-polar, which makes it hydrophobic. But there must be something that makes Fluor better than Hydrocarbons(paraffin)"
] |
[
"How do I know what atomic mass is correct on the periodic table when different tables have different atomic mass for certain elements?"
] |
[
false
] |
I am home schooling my 8 year old son and would like to start teaching him the elements on the periodic table. I have made flash cards for all 118 elements on the periodic table including symbol, atomic number, element name and atomic mass however different periodic tables seem to have different atomic mass for certain elements. I have added the other name and symbol for the elements that are known by two names, like 112, Copernicium is also known as Ununbium, but am unsure as to which atomic mass I should attribute to the cards when I get different AM from different tables. Anyone able to tell me which table is most accurate? Thanks in advance.
|
[
"Don't make your kid memorize all the element masses to four decimal places. Do make him understand what the position of an element in the table can tell him about its properties, how to estimate molar mass from the number of the element, what the atomic shells will look like and what this means for reactions, etc.. The periodic table is structured the way it is for several reasons, and understanding those reasons is more important than simply memorizing it. If your son goes on to do chemistry in college/university, one thing he ",
" likely have in tests for reference is a periodic table of elements. Knowing how to use that is more useful than simply being able to reproduce it from memory. "
] |
[
"This.",
"The ability to read, comprehend, analyze, and ",
" information is an infinitely more useful skill to teach than ",
" rote memorization ever will be."
] |
[
"Copernicium is the new name for 112. The previous name was a placeholder. Also, I wouldn't worry about those. They are synthetic. Focus on teaching the meaning of the mass. Also, the mass is based on isotopes and percent abundance in the world...so Carbon is actually different masses than what you see on the table because there are different isotopes of Carbon.",
"edit: to clarify placeholder - the synthetic elements have to wait for confirmation from another lab. Once they are confirmed, IUPAC decides on a name to replace the placeholder."
] |
[
"Light and sound are both waves. Does light have octaves too?"
] |
[
false
] | null |
[
"Sidenote: ",
"If \"musical note A\" were defined to include every wave with a frequency of (440 * 2 ^ x) where x is an integer, then the 40th octave of A would be 483785116221440 Hz, which falls within the color red.",
"The \"41st octave\" (under this crazy definition), would be outside the visible spectrum."
] |
[
"An octave is \"the interval between one musical pitch and another with half or double its frequency\" ",
"Source",
"You can have double or half the frequency of a certain wavelength of light, so sure. Also see ",
"\"Electromagnetic spectrum\""
] |
[
"The relevant numbers are frequency, not wavelength.",
"http://www.wolframalpha.com/input/?i=frequency+of+visible+light",
"But yes. 450 to 750 Terahertz",
"Also interesting, there's a weird gap in our understanding and manipulation of electromagnetic frequencies just above radio waves and just below infrared light: \n",
"http://en.wikipedia.org/wiki/Terahertz_gap"
] |
[
"How far off is GATTACA style engineering?"
] |
[
false
] | null |
[
"I don't think its a good idea to play with that kind of stuff in our lifetime. With only a handful of semi-successful transgene tested in humans, the idea of engineering many your of kid's genes presents a lot of unknowns that might be better tested in mice first. I'll note that 4 of the ten patients in the famous ",
"SCIDs gene therapy clinical study",
" developed leukemia because of viral insertion near an oncogene. There have been recent developments in gene therapy and some apparently successful trials with non-viral and site specific viral vectors. For instance, an adeno-associated virus was used to treat a rare genetic blindness in children. ",
"Many genes still have functions that are not elucidated and regulation of gene expression is a phenomenon appearing to be more complicated with every new discovery about it.",
"It takes a long time to learn about these kinds of things which are fundamental to understanding how we might undertake safe genetic engineering.",
"At the moment the gene therapies that are being explored focus on ameliorating genetic diseases, cancer, or viral infections. It may be that in our lifetime, our children will not have to experience these sadnesses.",
"Personally I don't feel that neo-Eugenics would be all that great at this point. Undoubtedly people will think the grass in greener on the side where you have super-children, but there are many unknowable consequences that might be less than appealing."
] |
[
"So probably not in my child bearing life time?"
] |
[
" to get it past the ethics committee."
] |
[
"Why are galaxies shaped like spirals? Why doesn't the spiral structure stretch out and disappear after a few galactic revolutions?"
] |
[
false
] |
The center of a galaxy must be rotating many times faster than the outer limbs due to the laws of angular velocity, right? (Like how Mercury rotates much faster than Earth... or is that a false analogy?) It would seem like the neat spiral pattern would pretty quickly get spread out into longer and thinner bands, until they were eventually unrecognizable. Why doesnt that seem to happen?
|
[
"Short answer: Because dark matter!",
"The short answer should have been \"density waves,\" because the spiral structure would be possible with or without dark matter. Dark matter does affect the rotation of a galaxy, but it is not responsible for the spiral shape (nor does the observed rotation curve - based on that information, spirals would still wind up since the farther material still takes longer to orbit - same orbital speed but larger orbit).",
"The animations on this wikipedia page",
" do a very good job at illustrating what's happening, and it really has little to nothing to do with dark matter."
] |
[
"Short answer: Because dark matter!",
"The short answer should have been \"density waves,\" because the spiral structure would be possible with or without dark matter. Dark matter does affect the rotation of a galaxy, but it is not responsible for the spiral shape (nor does the observed rotation curve - based on that information, spirals would still wind up since the farther material still takes longer to orbit - same orbital speed but larger orbit).",
"The animations on this wikipedia page",
" do a very good job at illustrating what's happening, and it really has little to nothing to do with dark matter."
] |
[
"There are many ways you can get spiral structure. Because the inner gas and stars take less time to orbit than the outer gas and stars, any structure will get sheared out into a spiral-ish shape. So it's quite common to get things like ",
"flocculant spirals",
", where instead of a couple of big spiral arms, you have a vague spiral shape made up of lots of sheared-out spiral segments. Each spiral segment will continue to \"wind up\" until it's no longer recognisable as a spiral, but by then you'll have new concentrations of mass to get sheared out into new spiral segments, so you can get a messy spiral going for a long time.",
"For the tidier ",
"\"grand design\" spirals",
", then this is most likely some sort of ",
"density wave",
" - like a sound wave through the interstellar gas and stars. This wave consists of the density of gas and stars going up and down as you go around the disc. Because it's a ",
" and not a solid structure, it isn't affected by the winding problem.",
"When the gas gets denser, you get a lot of new stars forming. The brightest stars only last for less than 10 million years, so places where we've recently formed stars are the brightest parts of the galaxy. The spiral arms aren't actually that much more dense in stars than the gaps between the spirals, they're just a lot brighter because that's where all the big young bright blue stars live.",
"If you look at ",
"this image",
" again, you can see that not only are the bright blue-white stars in the spiral arms, but the grey-brown ",
" is also concentrated there, and this traces where the gas is densest. So it isn't just the stars forming a spiral, the gas is there too. You can also see red splotches throughout the spiral arms. These are \"H-alpha\" regions. They are gas that has been recently ionised by newly formed stars. So these tell you where the stars are forming - and you can see they're mostly forming in the spiral arms."
] |
[
"G-force, pushing vs. pulling? can you tell?"
] |
[
false
] |
Hi! I just listened to a podcast discussing cars, and I couldn't quite grasp their statement, which was: Some people prefer engines in the back (Porsche f. ex.) instead of the front (most normal cars) not just because of the driving physics (weight distribution, traction etc.), but because they enjoy the feeling of being pushed rather than being pulled. Made me think - is there any noticable difference? Is it possible in a blind test to determine if you are being pushed or pulled? For experimental purposes, let's eliminate factors such as rear wheel drive vs. front wheel drive vs. four wheel drive, suspension, etc. Every voice in my head says there is no way to tell the difference, but it would be nice to hear your thoughts.
|
[
"Any rear-wheel drive car is still ",
" you, regardless of where the engine is. ",
"To flip it on its head, if a rear-engine car were front wheel drive, would it still be pushing you?",
"It's not a question of where the engine is converting chemical energy into kinetic energy, it's where this kinetic energy is being applied to the road. ",
"Even so, the reason rear-wheel-drive layouts tend to 'feel better' is that as the car 'squats' back due to inertia, it puts weight over the driven axle, whereas in a front wheel drive car, it unloads the driven axle. Things like that, and the ensuing understeer/oversteer behavior bias of FWD and RWD makes RWD the more 'fun' or 'preferable' configuration for the type of people you describe.",
"Where the engine is, however, doesn't change whether the driven wheels are pushing or pulling you. That doesn't make any sense. "
] |
[
"Yes, you can tell where the weight of the engine is when you're accelerating and cornering, but when they're saying 'pushing vs pulling' I have to think they're talking about whether a car is front wheel drive or rear wheel drive. "
] |
[
"Interesting question. There's already good answers in this thread, I just want to touch on something else.",
"I don't think you'd be able to tell the difference between pushing or pulling. The reason I think this is the case is because the force applied by the road onto the tires and then to you the driver. But I think the important part is ",
" that force ends up getting to you.",
"The tires turn and they roll without slipping and the same force of static friction felt by the tires is applied to the axel of the drive tires (rear for rwd front for fwd). Then it is connected to the rest of the car, suffice to say the body of the car. Your seat is connected to the body of the car, and so are you.",
"I think because the force is distributed throughout the whole car for both drive types, I doubt you'd notice a difference. Realistically the differences you'd be able to feel would come during turning, where the drive type is most important."
] |
[
"If a fruit like a pear is grown in a no gravity condition, will it still be pear-shaped?"
] |
[
false
] |
[deleted]
|
[
"Some pears are round. Do a google image search for \"round pear\" and you'll see them. Further research showed a specific pear that's round called ",
"pyrus pyrifolia",
".",
"Further exploration yielded this ",
"PDF paper",
" detailing a pear-shaped tomato being linked to the genes. Now, this article quickly became too technical for me so I'm not entirely sure what it all says but check it out yourself and see what you think.",
"So, the shape of the fruit is due to its genes and not its environment. Another ",
"article",
" supports this in that the length and perimeter of the fruit was governed by its genes. Again, far too technical for me but you may enjoy it.",
"Hope that helps."
] |
[
"Yes, the genetic makeup of the plant determines the shape of the fruit. But gravity acts upon the plant while it produces these fruit. You don't know how this influences the shaping of the fruit, maybe this shaping process depends on gravity. The typical pear shape is what the plant produces under the conditions found on earth. Just because the genetic code of 2 plants is the same that doesn't mean they will necessarily produce identical fruit in completely different environments. ",
"The space pears may grow just fine",
", but you can't really know for sure."
] |
[
"Gravity doesn't do much at all.",
"Read my first level reply. I'm the son of a apple and pear farmer, I've seen pears grow in every direction, including entirely upside down, end result is always the same."
] |
[
"If the symptoms of COVID-19 are so similar to flu/cold symptoms, how did doctors discover this was a brand new virus?"
] |
[
false
] | null |
[
"COVID symptoms are not really similar to flu/cold. They tend to be more severe. The doctors saw a bunch of very severe flu-like illnesses and got suspicious. ",
"There are two major misunderstandings floating around, making people think that this isn’t as serious as it is. ",
"First, public health people said this is like flu. To public health people, ",
". The flu is lethal. It kills hundreds of thousands of people a year. To public health people, influenza is the worst killer they see, year after year and year. ",
"But most people don’t realize this. They don’t know what flu is. They think it’s a mild disease. So when public health people ",
" them, this is as bad as flu, they heard the opposite message that was supposed to be delivered. ",
"Next, people heard Chinese medics say that 80% of cases were “mild”. They think that means sniffles, a little cough. That’s not what the Chinese meant. ",
"In China, they ranked the disease as “mild”, “severe”, and “critical”. ",
"Mild” was a positive test, fever, cough — maybe even pneumonia, but not needing oxygen. “Severe” was breathing rate up and oxygen saturation down, so needing oxygen or a ventilator. “Critical” was respiratory failure or multi-organ failure.",
"—",
"Bruce Aylward",
"So “mild” isn’t just mild. It’s everyone who doesn’t need supplementary oxygen. ",
"All those people who are taking comfort in the “80% of cases are mild” don’t know what they’re talking about. Certainly some cases are genuinely mild. There may even be a few asymptomatic cases (but Aylward says ",
", so don’t count on that). ",
"A lot of those “mild” cases are going to be like the worst case of flu you ever had. Maybe you won’t need a ventilator to stay alive, but you will feel like a truck hit you, for a week. ",
"Even for the 80% of people who get “mild” disease, this is often going to be a really unpleasant experience."
] |
[
"And this is how jargon can cause miscommunication. The average person will interpret \"mild\" as nothing to worry about. Surely people versed in effective communication saw that coming..."
] |
[
"i work in pharma/vaccine manufacturing. ",
"They are already doing this. Once we identified the genome of SARS-CoV-2 they begann identifying target proteins to make the vaccine. Then you have to make the vaccine, two ways of doing this, either making mRNA that codes for the protein or grow cells to create the protein itself. Both these processes take months. For example a current biologic product i work on takes about 40 days from thaw to bulk drug substance for just one batch! And even once all that is done you are still not even sure if the protein target you selected will provide the immune response we are looking for. ",
"Its near impossible to do all that work safely and effectively in less than a year"
] |
[
"Why doesn't our brain go haywire when magnetic flux is present around it?"
] |
[
false
] |
Like when our body goes through MRI , current would arbitrarily be produced in different parts of our brain which should cause random movement of limbs and many such effects but it doesn't why?
|
[
"The current produced would have to be strong enough to overcome our neuron's threshold for activation. All neurons have a base level of electric activity called a resting membrane potential, which is about -70 millivolts (mV). In order to cause that neuron to send an electrical impulse we must depolarize that same neuron to about -55 mV. This can either be done internally, with the release or intake of various electrically charged ions in and out of the neuron, or externally by inducing a current strong enough to penetrate the skull, depolarize the neuron, and be focused to be specific enough to hit just one neuron or a cluster of geographically associated neurons. This can be achieved with very strong and local electromagnetic transducers, such as with transcranial magnetic stimulation (TMS). Although an MRI produces a powerful electromagnetic field, the current it produces in the human body is not typically enough (strong enough, specific enough, or possibly even at the correct angle enough) to cause specific or generalized depolarization of the neurons resulting in activation."
] |
[
"Electrical current doesn’t flow through nerves like it does in wires, where a magnetic field ",
" induce a current. Instead, it’s an active process involving the movement of ions across the cell membrane that occurs in a moving gradient down the length of the nerve, which a magnetic field does not affect in the same way."
] |
[
"This is all accurate in principle, but as an electrophysiologist I feel i should mention that plenty of neurons rest around - 60 to - 55mv. And while the depolarization threshold varies a bit by channel types expressed, I've never seen it as low as - 55mv, -35mv or higher is more typical."
] |
[
"If Mercury's year is only 88 Earth days, why is it's transit across the Sun so rare?"
] |
[
false
] | null |
[
"Mercury usually passes above or or below from our perspective.",
" I'm doing this on my phone's calculator while watching Dubs/Blazers so someone correct me if I screw any of this up. Quick math:",
"Radius of the sun is 695700 km. Earth to sun is 149.6 million km. Mercury to sun is 57.91 million km. Mercury orbit to earth orbit is 91.69 million km. Similar triangles says that an object 91.69 million km from the earth has to be within about 426000 km of the earth-sun line to appear in front of the sun. If that were the highest Mercury ever went, its orbit would have an inclination of 0.421 degrees. It's real inclination is just about 7 degrees. Didn't take into account the fact that Mercury is a disk and not a point but that's negligible compared to its inclination. I'm less sure about your location on the earth being negligible but it probably is too.",
"The planets basically have to line up when Mercury's within a couple of days (hours? weeks?) of crossing from below the ecliptic to above it (or above to below). If Mercury is ascending or descending and the earth is somewhere else, we don't see it. If the earth is looking \"through\" Mercury's ascending or descending node and ",
" is somewhere else, we don't see it. If they're lined up and Mercury isn't on one of the nodes, it passes above or below and we don't see it.",
"edit: What ",
"/u/kteac",
" brought up is called the synodic period and that's a factor too. Two things at slightly different speeds take a while to line up again. Ever listen to the click of your own turn signal while watching the one on the car in front of you? Their frequencies won't be exactly the same so it takes a while to line up again. The synodic period of the earth and Mercury is (365*88)/(abs(365-88)) = 116 days so that's how often you even have a chance, not 88 days. Not a huge difference but it's something. Also, since that's not a nice multiple or division of 88 days, the place Mercury is in its orbit is going to be different every time it passes between us and the sun.",
"also edit: Jesus, so many typos. That's what I get for trying to do this in overtime."
] |
[
"While Earth orbits the sun every 365 days, Mercury orbits the sun every 88 days. However, Mercury's orbit is tilted, which means it will only pass directly between the Earth and the sun 14 times in the next 100 years. Aside from today, the next time will be in 2019 and after that, 2032.",
"I pulled this from an article about it, ",
"Link",
". I'm hoping this an acceptable answer for this sub, if not I apologize."
] |
[
"It has to do with the orbit incline.",
"http://www.vox.com/2016/5/8/11612978/mercury-transit-watch-2016"
] |
[
"Why does light travel faster in a vacuum?"
] |
[
false
] |
If atoms are mostly empty space, and photons are infinitely small anyway, shouldn't they always travel at the same speed?
|
[
"Yes, but when going through a medium photons are being absorbed and retransmitted. This causes the apparent slowdown."
] |
[
"Actually, classical electromagnetics is a worse way to explain the slowing of light. You can take the macroscopic view and work with flux quantities (B and D), but that doesn't actually really explain it at all. The microscopic view does, but you have to construct an infinite series of induced dipoles and scattered fields. The interference pattern from the infinite sum is a reduced velocity forward propagating wave."
] |
[
"The way it was explained to me was that waves are remitted in all directions and through interference and superposition the lightwave retains its direction of propagation."
] |
[
"Can we deduce any properties of an element from its emission spectrum?"
] |
[
false
] |
Edit: Thank you for the answers!
|
[
"You can get the nuclear mass. If you compare the emission spectra of different isotopes of the same element (e.g. hydrogen and deuterium) there are small differences in energy - the isotopic shifts. These can be measured with high precision and do give you the nuclear mass. ",
"I've done the experiment as an undergraduate where we looked at H and D emission lines in the lab, and it was a pronounced and easily measured effect.",
"The reason this appears is this: When you are solving the Schroedinger equation you will usually transform into the centre of mass system, and during that transformation the effective mass appears naturally.",
"You will also get higher order effects, e.g. from the increased nuclear radius, which changes the overlap of the electron wave functions with the nucleus. A small change, but the precision with which we can measure the resulting energy shifts is very high."
] |
[
"Theoretically, yes. Envision spectra are caused by transitions between different energy states of an atom. The wavelength of the emission, and to some extent the width of the line, do reveal a lot of information about the different energy states. It is theoretically possible to take that information and use it to calculate the electron energy levels, then use those to determine things like molecular bonding possibilities and such. However, it is far far far easier and more accurate to determine that information in other ways. Further, by the time that you had the knowledge to use emission spectra like that, you would probably already know more about the energy states then the spectrum could tell you. "
] |
[
"I am currently going through Balmer Series in college and don't really understand what's special about those emission lines "
] |
[
"Is it true we know more about our moon than we know about our oceans?"
] |
[
false
] |
I hear this a lot and I just thought I'd ask this here.
|
[
"Yes, in that it is much easier to explore and learn about the moon then it is the oceans. Mostly in that the oceans are so complex. Only with modern technology have we really begun to understand how different factors interact in the oceans. One issue is that the marine science lags behind terrestrial science simply because one is easier to study then the other."
] |
[
"But that sounds like a relative thing, as in, it's a lot easier to know everything about a thumb tack than an amoeba. It may be more accurate to say that we can characterize the Moon more fully than we can characterize the oceans, but the total body of knowledge about the oceans is greater than the total body of knowledge about the Moon."
] |
[
"As a geologist, I would say no. I typically file that statement under such phrases as, \"we only use 10% of our brains\" - something the general public considers fact.",
"When I consider how much mapping still needs to be done on Earth in areas that have been explored for over a century, it occurs to me that a couple hundred pounds of rock from one or two locations is a criminally small data set. "
] |
[
"When thermite burns on ice why is there an explosion?"
] |
[
false
] |
The Mythbusters did this and didn't have a good explanation as to why. Video here: I've heard two explanation. Hydrogen being released from the oxygen and detonation or a Steam explosion. Neither seems to be wholly correct to me. As for a steam explosion I would think there would need to be a pressure vessel to contain the steam long enough to build pressure and there isn't one. For a hydrogen explosion again there would need to be something keeping the hydrogen in close until the air-hydrogen ration would allow a detonation as opposed to a simple burn off. So, do we know what causes this and if not, what do you think would be a viable experimental protocol to find out?
|
[
"It is a steam explosion. Breaking down of water molecules is not an instantenuous reaction, and it needs a certain catalyst. Instead, water evaporates very quickly, and as we know from Clapeyron's equation (ideal gas law), hot gas likes to expand, and it does so very quickly, releasing so much energy, that it's able to scatter chunks of ice and burning thermite all over the place."
] |
[
"The explosion you see in a ",
"grease fire with water in it",
" is also a steam explosion. No pressure vessel needed."
] |
[
"Explosion is just a rapid gas expansion, that's all there's to it. There doesn't need to be a container in order for gas to explode, if enough hot steam is created. Following that logic, there would have to be a container in order for explosives to work, but that's not true. "
] |
[
"What is it with spinning?"
] |
[
false
] |
[deleted]
|
[
"Well, the short answer is that central forces are everywhere. In 3-d space in general there's no preferred direction, so forces like gravity and electromagnetism are emitted with spherical symmetry. ",
"Orbits happen with forces that point towards the center, like gravity or EM attraction between opposite charges. Let's imagine you have a giant rock hurtling towards Earth from Klendathu, a la Starship Troopers. That rock can do one of three things:",
"It can get trapped in Earth's gravitational well and smash into the surface",
"It can miss Earth's gravitational well, bend its trajectory slightly, and keep on cruising through space",
"It can get the balance between its own kinetic energy and Earth's gravitational energy juuuuust right, so that when its trajectory bends due to gravity the centrifical force generated is exactly equal to the force of Earth's gravity on the rock. ",
"Of course, all three of these possibilities occur all the time, but you never notice the first two because they don't last very long.",
"For electrons the picture is slightly different: the electron is trapped inside the nucleus' potential well due to electromagnetic attraction, but cannot collapse to the center due to the Heisenberg uncertainty principle. Since it doesn't have enough energy to break free, it stays trapped."
] |
[
"The electron can actually collapse to the center in some cases, unstable proton rich nuclei can actually undergo decay by \"electron capture\". Since the wavefunctions of inner electrons overlap with the nucleus, there is a small chance of a weak interaction where the electron is changed into an electron neutrino, and the proton into a neutron.",
"I also don't think that Heisenberg plays a conceptual role here.",
"The question is why can something like a Hydrogen atom not collapse into some lower energy state than 1s where the probability density of the electron would presumably be concentrated more closely to the nucleus.",
"The answer is just that if you solve the radial part of the 3 dimensional time-independent Schrodinger equation for the 1/r potential, there is a minimum energy solution (the 1s state) for which the electron wavefunction is finite. I don't know of any more conceptual way of saying this. ",
"You could appeal to common sense by saying that if the electron was allowed into an arbitrarily low energy bound state to the nucleus, then one could extract infinite energy from the system, which is silly. So the purely mathematical outcome of a lowest energy bound state is to be expected."
] |
[
"The electron can actually collapse to the center in some cases, unstable proton rich nuclei can actually undergo decay by \"electron capture\". Since the wavefunctions of inner electrons overlap with the nucleus, there is a small chance of a weak interaction where the electron is changed into an electron neutrino, and the proton into a neutron.",
"I also don't think that Heisenberg plays a conceptual role here.",
"The question is why can something like a Hydrogen atom not collapse into some lower energy state than 1s where the probability density of the electron would presumably be concentrated more closely to the nucleus.",
"The answer is just that if you solve the radial part of the 3 dimensional time-independent Schrodinger equation for the 1/r potential, there is a minimum energy solution (the 1s state) for which the electron wavefunction is finite. I don't know of any more conceptual way of saying this. ",
"You could appeal to common sense by saying that if the electron was allowed into an arbitrarily low energy bound state to the nucleus, then one could extract infinite energy from the system, which is silly. So the purely mathematical outcome of a lowest energy bound state is to be expected."
] |
[
"How does the body generate heat?"
] |
[
false
] | null |
[
"In birds and mammals, the heat comes specifically from the mitochondria in the cell ",
" a series of spatially separated redox reactions called an electron transport chain, or ETC (thanks ",
"/u/onthisday420",
"!) to create ATP, which other cells use for energy, AKA, \"metabolism\". Some recent studies have found the mitochondria in cells to be as hot as 50C (122F). ",
"Source",
"It's important to note that body heat generation is a bit more complex than what I've explained here, and some animals, such as bats, exhibit different body temperature regulation when sleeping. ",
"Source",
"Here's some info about electron transport chains and the generation of heat:",
"Electron Transfers Release Large Amounts of Energy",
"Electron transport chain in mitochondria",
"Edit: including info provided by ",
"/u/onthisday420"
] |
[
"So they really are power houses?"
] |
[
"In birds and mammals, the heat comes specifically from the mitochondria in the cell breaking down glucose to create ATP",
"Not just glucose. Other substrates can be broken down/converted into pyruvate, such as triglycerides. These breakdowns/conversions also give off heat. "
] |
[
"What are the earliest known occurrences of depression? How was it recorded?"
] |
[
false
] |
Any answers?? Thanks!
|
[
"I've learned it's on mesopotamian clay tablets, with a description of symptoms and treatments - although it was handled by priests, since they thought it was caused by demonic possession or curses (by either a god or a human). Does trying to find out which cause \"applied\" in each case as early psychotherapy?",
"The eighth and ninth clay tablets of the Gilgamesh epos describe his grief and wanderings after Enkidu's death, with an account we would read as depression today.",
"Later on Herodot and Plutarch describe it as a disease in their medical texts, but they called it melancholia."
] |
[
"Layman comment: but I feel like there's references in medieval Europe to kings falling to deep malaise / melancholy.",
"Also would be interesting to look at early buddist philosophers and ask how they were so so early on the drop to realizing nothing is real in the way we think of it, and what biochemically may have made that a widely swallowable truth",
"But hey I'm just a know nothing commentor so... Ask others!"
] |
[
"It was reported among the ancient Greeks, as was a treatment they sometimes used, throwing the patient off a short cliff into the sea. (I read about this many years ago when I wrote an educational monograph on depression for Bristol-Myers Squibb when they were launching the antidepressant nefazodone.) Presumably it existed before this, but I don't know when it was first recognized as a disease. FYI, Hippocrates (ca. 400 BC) thought that all illnesses resulted from an imbalance in the four humors: blood, yellow bile, black bile, and phlegm. If you substitute these with the neurotransmitters serotonin, norepinephrine, and dopamine, he may not have been that far off from what we know now (which isn't much)."
] |
[
"Is a scientific theory speculation?"
] |
[
false
] |
Someone keeps telling me a theory is just speculation. I don't believe that is the case. Can askscience weigh in? Maybe with some credible sources?
|
[
"In science, there is a really big difference between Theory, as in Scientific Theory and theory which is what you'd use in everyday language. Let me illustrate this:",
"The roof is leaking, my theory is there is a hole in the roof.",
"While the average Joe, calls this his theory, it's what in science would be referred to has a hypothesis. There is an observational fact: The roof leaks, and an idea to explain that fact. This hypothesis can be easily tested. You can test a hypothesis with an experiment. For instance, does the roof leak when it rains only or does it do so at other times?",
"If it's rained several times in the past few days and you only noticed it leaking when it rained, then you have evidence to back up your hypothesis. However this doesn't prove it. You can never prove a hypothesis, only gather an insurmountable pile of evidence. Let's say you find a hole in your roof. Now you have two striking pieces of evidence to support your hypothesis. But this still doesn't prove you right.",
"The next day you find a copper pipe leaking water and you realize the hole was in the wrong place. Suddenly your hypothesis was proven wrong, even with substantial evidence for it. You see in science, you can never prove anything, but only gather mountains of evidence for it.",
"Okay, with hypotheses properly defined we can move on to what a scientific theory is.",
"In science, a scientific theory is a collection of hypotheses which agree with experiment and observed facts which are connected together with an overall narrative of sorts. Theories are meant to be large, giant ideas. For instance:",
"There are literally hundreds of scientific theories which all are huge ideas which explain large chunks of natural phenomenon. To gain the title \"Theory\" they must stand not only the test of time, but agree with as much observational facts as possible.",
"Scientific theories can in fact be completely wrong and scrapped, such as the theory of a geocentric solar system. However, usually scientific theories are so good at their jobs that even when proven wrong they need not be completely destroyed.",
"Newtonian classical mechanics is factually wrong. However, it is still used and given merit because it still works as long as you realize it's limitations. The limit of general/special relativity which is the modern description of gravity becomes classical mechanics at slow speeds and sizes.",
"Just as often, scientific theories can simply be \"tweaked.\" It is highly unlikely that cell theory will meet it's demise because the evidence for it is nearly infinite. However, new evidence can come to light that may say challenge certain parts of it. Instead of throwing out the whole theory you can simple add or modify certain parts into.",
"The big bang theory had such an event when the idea of inflation had to be added to the theory. We didn't throw out the whole idea, but we simply added a new part to it.",
"Sorry this is long, but I really wanted to give you a good course in scientific literacy. Speculation is reserved for hypotheses, which are specific and easily proved wrong. Scientific theories are much larger ideas with many internal hypotheses and facts woven together. While a hypothesis can easily die, a scientific theory can either die, be limited, or modified.",
"I suggest you read \"The Demon-Haunted World\" by Carl Sagan. He takes a very good approach to explaining what science is and what it isn't and why it's a collection of the best ideas anyone has ever had."
] |
[
"No, a scientific theory isn't speculation.",
"Let's put it this way. A speculation is a possible explanation based on what you observed. In scientific terms, this can be said to be a hypothesis. A theory is a hypothesis that has experimental and theoretical backing. That means that a theory is a hypothesis that has strong evidence backing it up other than the facts provided by the observation itself.",
"So go tell that \"someone\", yes, a theory is speculation. However, it is speculation so extensively tested and matched with other independent observations that it can be considered to be fact until a strong counter-example is presented."
] |
[
"Thanks."
] |
[
"How much time would a flight attendant 'gain' over their career?"
] |
[
false
] |
So I was talking to my aunt who said that she was on a plane that was the last flight of one of the attendants before she retired. She also commented that the attendant in question "looked every minute of 60 years old." Now I know that because of time dilation, she would have 'gained' a small amount of time by travelling at high velocities, but how much? Assuming that she was working as a flight attendant full-time for at least 30 years, would she have gained a few seconds or a minute of time or what? Would she legitimately be "every minute of 60?"
|
[
"There have been several tests that measured time dilation due to flight. ",
"A recent one",
" measured a shift of 246 ns on a trip from London - LA - Auckland - Hong Kong - London.",
"Let's assume a flight attendant makes a journey roughly equivalent to that twice a week, 45 weeks a year, for 40 years. ",
"That's 246 ns * 2 * 45 * 40 = .0008856 seconds. ",
"Edit: Just reviewed the ",
"original experiment",
" and forgot to include directional effects. Eastward you actually lose time, Westward gain (-40 and 275ns, respectively). Assuming her East/West flight time roughly evened out over her career, the actual net gain would be the average, or 117.5ns. That gives a total dilation of .000423 seconds. "
] |
[
"The time dilation effect would have only a very minor impact, less than a second, so no."
] |
[
"On michio kaku's \"sci fi science\" he had an interview with an astronaut that had spent 3 years in space, his life was extended with something shorter than .001 second, so the effect of it isn't that great"
] |
[
"Can someone please explain time dilation to me?"
] |
[
false
] | null |
[
"It's just foreshortening. Time isn't special, it's just another direction (like \"north\"). ",
"Einsteinian relativity unifies the concepts of \"motion\" and \"rotation\" -- as in, you're always zooming along at ",
" in some direction or other. If you're sitting at your desk, you're zooming directly \"later\". If you are in a jet fighter plane going north, you're actually zooming in a vaguely \"later by north-later\" direction. If you're going really, really fast, you might be going closer to directly north-later. ",
"Elapsed time as measured by your wristwatch measures distance along the direction you're traveling (for example, later by north-later). Time as measured by your wall clock measures distance due later. Each clock's time is foreshortened from the perspective of the other one. ",
"Using more conventional directions, if you go a mile northwest, you'll only actually travel about 0.7 miles due north, because your track is diagonal. (You'll also cover about 0.7 miles due west). Likewise, if you use the semi-cardinal points for reference and go a mile north, you'll only actually travel about 0.7 miles northwest, for the same reason (and also 0.7 miles northeast). That explains how time dilation can (bizarrely if you don't \"get it\") work both ways: your buddies at home think your wristwatch is running slow, because they're measuring time in the \"due later\" direction and your wristwatch is measuring in the \"north by north-later\" direction. But you think the wall clock is running slow, for exactly the same reason.",
"All of that said, there's one more little caveat. Normally, stuff is foreshortened by a factor of cos(theta), where theta is the angle you rotate the distance you want to measure, away from the distance you are actually measuring. But when you project between temporal and spatial directions, the foreshortening uses ",
" instead of normal trigonometry, and you have to use the \"cosh\" and \"sinh\" functions instead of \"cos\" and \"sin\". They're similar but not exactly the same. The difference between cos(theta) and cosh(theta) is what makes the speed of light a natural limit."
] |
[
"Have you seen this video by sixty symbols? It's quite understandable. ",
"http://www.youtube.com/watch?v=jlJNsRZ4WxI"
] |
[
"http://casa.colorado.edu/~ajsh/sr/time.html",
"There is an interesting gif there that illustrates how the time appears. The blue ball, which is moving, sees the white ball as being a normal rate, but the red ball sees a difference between the two (red thinks that blue's is slower)."
] |
[
"Why does disinfecting a wound cause it to \"sting\"?"
] |
[
false
] |
Using first-aid spray, hydrogen peroxide, alcohols, etc. causes that sharp stinging feeling when applied to an open wound. I know this has to do with the death of bacteria, but why exactly does it feel like that?
|
[
"Intact skin has layers of dead cells that protect it, but when the skin is broken, tissues are exposed. If they come in direct contact with alcohol, they are damaged. Alcohol takes lipids out of the membranes of cells, allowing dehydration, killing your cells and thereby causing pain. "
] |
[
"These disinfectants are essentially poisons. They kill cells, whether they are single cellular organisms, ore cells of a larger being. You feel a sting because the disinfectant kills some of your cells, but your body is perfectly capable of handling that. "
] |
[
"Most of the reason is that peroxide is actually not a very effective disinfectant. It doesn't kill many bacteria, and also doesn't kill as many of your mature cells, which means you experience less pain.",
"A contributing reason is that H2O2 has a fairly short shelf life. If you've had a bottle of household peroxide sitting around for a couple of years, most of the peroxide has probably fallen apart into water and oxygen. That solution isn't going to sting any more than tap water."
] |
[
"I'm sitting in central Florida, where did the rain that is falling from TS Debbie come from. Did it evaporate from the gulf, or is it local moisture?"
] |
[
false
] | null |
[
"I think OP was asking not where the storm came from, but where the water itself came from. We've all seen satellite images tracking storms, and know they move across the water. But more specifically, does the water rise and fall into the sea, creating a chain reaction that fuels the storm, or is it literally a swirling mass that is kept aloft the whole difference? So for these storms that formed in western Africa, is it possible that the last time Atomskie's raindrops touched down, they were dew on a Western Sahara palm?"
] |
[
"Atlantic Tropical Storms are essentially just weak hurricanes. They form from evaporation of the warm ocean water off the coast of western Africa, and are then carried west by the tradewinds (a dominant easterly airflow) to wreak havoc on the Caribbean and Gulf region.",
"If it's raining in Florida, the humidity will be at 100%, and you wouldn't be seeing enough additional evaporation to add more moisture to the storm than it is currently expending."
] |
[
"The water is being pulled out of the Gulf, the heat of the water allows incoming air to evaporate large quantities of the ocean. The water is then uplifted through adiabatic processes(as well as the upper level low) and condensed as precipitation which falls over wherever it happens to fall.. ",
"For Debbie. the water is gulf based.. ",
"Neat animation.. Can see the center of rotation and the latest round of gulf water falling over over the panhandle. ",
"http://weather.rap.ucar.edu/satellite/displaySat.php?region=US&itype=ir&size=large&endDate=20120626&endTime=-1&duration=12"
] |
[
"Can we create \"new\" organ systems?"
] |
[
false
] |
With stem cells, I am under the impression that you can kind of "zap" them into doing different tasks and becoming different types of cells. Does this mean that you can only zap them into being things that already exist, like liver cells or skin cells? Or are you actually able to make them do ANY job? If you can make them do anything, does this mean that we can create entirely new organ systems in the body to do completely new functions and ultimately allow us to directly evolve ourselves? I have mentioned this to people and for some reason they usually don't fully grasp what I am saying. When I say "new organ systems," think about the ones you already have. Digestive, Respiratory, blah blah blah. Each system has its own job to help the body survive. A new system would be an organ(s)/gland(s) that do something like..... notify you when you are near radiation? Or one that sends cells throughout the body to endlessly hunt/kill cancer cells? (im still working on good ideas for new organ systems lol..) But the idea is that you would be able to do some sort of function that you could never do before that would help you survive. Sorry if that last part was too simple. I have just had too many people require that extra explanation.
|
[
"Every cell in your body (that has DNA) has a set of recipes for every organ your body contains (probably some exceptions there too, since this is biology; I'm thinking gut microflora?). The thing is that most cell fates require the cells to go through a series of successive, irreversible ",
"differentiations",
". The reason stem cells are useful is because they're undifferentiated so you can still coax them into following whichever course you'd like.",
"If you want to induce the cells to make some new system that doesn't naturally exist in the genome, there's no intrinsic reason why you'd need to go back to the undifferentiated state since they don't contain that recipe either way. However, there could be some aspects of some terminally differentiated cells that make them really hard to turn into anything else. So if you were trying to make something new, you'd probably want to start with some kind of moderately differentiated precursor of the most similar natural cell type, but you probably wouldn't have to go all the way back to a pluripotent stage. "
] |
[
"Stem cells can only differentiate into whatever the DNA inside them encodes for.",
"Creating a new organ system would be mostly pointless and incredibly difficult. However, if you applied extensive gene therapy to many, many stem cells, and then injected them into the person's body, it could be possible."
] |
[
"Yes, we'd need to engineer the new organs. There are no instructions to follow other than those for the organs we already have. The body does not check for DNA when rejecting cells, it checks for other factors which stem cells can replicate."
] |
[
"Roast beef turns grey-brown when fully cooked, but smoked meat becomes red, instead. How does smoke change how the meat cooks? What's the chemistry of this reaction?"
] |
[
false
] | null |
[
"You might be referring to the pink smoke ring that can be found in smoked meats. This is caused by a reaction between nitrogen monoxide and carbon monoxide in the smoke and myoglobin in the meat. More information: ",
"http://amazingribs.com/tips_and_technique/mythbusting_the_smoke_ring.html"
] |
[
"Roast beef is supposed to be red in the middle also but what most people see and eat that is labeled Roast Beef isn't Roast Beef or not very good Roast Beef. ",
"This is what good Roast Beef is supposed to look like",
"Roasting and smoking both use low heat but long cook times which browns only the outer layer of meat leaving the interior red, the more red and less brown the better."
] |
[
"If you cook it long enough it will loose it red color but then all you'll have is ashes and chew sticks for your dog. :)"
] |
[
"What would happen if I fired a gun on the moon?"
] |
[
false
] | null |
[
"Because saltpeter (a part of gunpowder) has oxygen as a component, the gun will still fire and cause the bullet to move.",
"With no air resistance and lower gravity, the bullet would travel farther and faster than on Earth.",
"But as the escape velocity of the moon (~7,000 feet per second) is higher than the muzzle velocity of any small arms, the bullet would still land somewhere on the surface, however."
] |
[
"I doubt it'll be a huge difference. Compared to the pressures behind the bullet a drop of 1 atm pressure in front won't matter too much, especially considering the short time it spends in there."
] |
[
"I wonder how much the lack of air resistance in the barrel would increase muzzle velocity. Some exotic cartridges can get muzzle velocities of 4-5,000 ft/s. I doubt it would get all the way to 7,000, but I wonder how close it could get."
] |
[
"How exactly are neutrinos and dark matter related?"
] |
[
false
] | null |
[
"Neutrinos are an example of dark matter because they do not interact with light. But the total energy of the neutrinos in the universe is very small, so they are only a very small fraction of the dark matter that exists. Also, we know that dark matter is \"cold\" and clumps together due to gravity based on many kinds of evidence. Because neutrinos are always \"hot\" (their thermal energy is much larger than their mass-energy), most dark matter can't be made of neutrinos.",
"So most dark matter cannot be neutrinos- which is why people will say that neutrinos are not the source of dark matter."
] |
[
"The amount of neutrinos from the big bang can be measured indirectly: They influence the cosmic microwave background. No, there are not enough neutrinos around (at least not the type of neutrinos we know). There is also ",
"PTOLEMY",
", a proposed experiment to measure these neutrinos directly."
] |
[
"They might not be. Neutrinos are an example of a particle which does not interact via electromagnetism, so they are proof of concept in a sense: we know dark matter doesn't interact electromagnetically.",
"Neutrinos, as observed, can't explain dark matter. But they show other possibilities."
] |
[
"Is my car engine more efficient on hot or cold days?"
] |
[
false
] |
Let us define "Hot" and "Cold" to be in the vicinity of 80 F and 30 F respectively.
|
[
"It depends on how long you're going to be operating it for, and if you live in the real world.",
"Cooler intake air will be more dense and have higher mass flow per piston-cycle. Getting more mass of oxygen into the cylinder will allow more fuel to be burnt, making each cycle produce more power (but also use more fuel). Cooler intake air also reduces knock (premature explosion of the fuel-air mixture due to heating via compression).",
"Cooler temperatures will also make your various lubricants more viscous and thick. Proper engine oil shouldn't be affected by this at such mild temperatures listed in your query, but can be affected when things drop below -30 centigrade. Oils are engineered nowadays to have the same viscosity within a wide range of temperatures. The real losses come from places that are lubricated with grease, like wheel bearings. These warm up relatively quickly though.",
"Starting out, your engine block will be cold, the intake air will be cold and the exhaust gasses will cool rapidly within the cold exhaust ducting. Rapidly cooling exhaust gasses is unwanted since you'll observe greater back pressure. This reduces engine air flow, and thus efficiency. All of these systems warm up as you drive. As they warm up, your efficiency will increase.",
"So, if you're driving 5-10 minutes to the shops, your efficiency will be worse.",
"If you're driving 30 minutes on the highway to work, not in stop-go traffic, your efficiency will be better at cooler ambient temperatures than warmer.",
"Carnot efficiency (as outlined in another reply) is only a small part of the equation."
] |
[
"No problem.",
"So what happens, is, you get rapidly cooling exhaust. Cooler gas mixtures generally have higher kinematic and dynamic viscosity. They are also more dense.",
"Both of those result in making it more difficult for the fluid to flow.",
"Higher viscosity means that the fluid will essentially be 'stickier' and attach to the walls of the pipe and resist flowing more. Think molasses in a syringe versus water. The molasses will be much more difficult to push through the pipe.",
"Higher density means that each unit volume has higher mass. Higher mass means more force is required to accelerate the fluid out of the way. It's as though there's a steel plug in the pipe upstream of your flow (this is, of course, exaggerated). The gas will have greater inertia, and thus resist movement more than a warmer less dense gas.",
"Your intuition is correct for things like solids and liquids. Less dense means less volume. However, with gasses it's not quite so simple. Gas always expands to fill its container. So when a gas flowing in a pipe cools down the line and gets more dense, it's still filling the whole volume. But, if it's the same volume, how has the density changed? Well, in order to conserve mass, the velocity of the gas is reduced. In idealized pipe flows, the mass flow rate of the gas will be constant from inlet to outlet (If you have more than one inlet or outlet, you can simply add them all up accordingly).",
"Mass flow rate = Mass per unit time (kg/s)",
"Mass flow rate = Density * Area * Velocity (kg/m",
" * m",
" * m/s) > (kg/s, as all of the length units cancel out)",
"Assuming a straight pipe, Area will remain constant. So if Density increases, Velocity must decrease to compensate.",
"In the end, you wind up with a slow moving, stickier, heavier fluid impeding the flow of the warmer, faster, slicker, lighter fluid upstream.",
"This is why high end exhaust systems don't just stick the fattest pipe possible coming from the engine exhaust ports. If the pipe is too wide, the fluid can cool down too much before it is released to the atmosphere and cause impaired flow."
] |
[
"You're probably going to get answers about Carnot efficiency but they will be wrong. Car engines are incredibly complex machines and are limited by a ton of factors before Carnot efficiency. Real world efficiency drops during the winter, but I am not qualified to talk about why"
] |
[
"Are there any known organism that is so photophobic that they can actually die from too much exposure to common sources of light?"
] |
[
false
] |
And no, I dont mean the heat that usually comes with most light source. I mean . And by "common" I mean not something that can only be produced in a lab or in space like gamma or x-rays. I mean sunlight or a torchlight.
|
[
"So related to your question, there was a famous tree in northern British Columbia called \"Kiidk'yaas\" or simply \"The Golden Spruce\". It had a mutation that would cause needles to die if they received direct sunlight even though the tree needed sunlight to survive. ",
"This tree managed to grow quite large due to constant fog that essentially gave the tree just enough light to grow but not enough to kill it. Survival of this type of tree is extremely rare.",
"Sadly someone cut this tree down because some people don't want the world to have nice things."
] |
[
"The guy that cut it down was \"protesting the forestry industry\". The tree was considered sacred to the Haida Gwaii people of British Columbias West coast. He cut the tree in such a way that it would fall in the next big wind (\"a series of deep cuts\") in January 20th 1997, the tree fell 2 days later. He claimed responsibility through the media and was arrested and returned to Haida Gwaii to stand trial where he was released on bail. He went missing 4 days before his February 18th court appearance and is presumed dead. \nHe probably didn't die well, the BC wilds are a harsh place in that area (most areas of BC really) and people across the country were very angry. ",
"There is a book about it called \"the Golden spruce\""
] |
[
"Lots of (most?) unprotected ",
"organisms will succumb to radiation damage after sufficient exposure to sunlight. See ",
"this study",
". Melanomas and the like will accomplish the same thing in humans and other unprotected animals."
] |
[
"Big rip question"
] |
[
false
] |
If the big rip is the ultimate fate of the universe, is it possible that dark energy's action on quarks could lead to some sort of spontaneous matter production (due to confinement)? Possibly to such an extent that such an event would resemble the big bang? I'm pretty sure I've made (many) mistakes or misunderstandings above so spare me no correction.
|
[
"If the big rip is the ultimate fate of the universe…",
"It isn't. At least, there's no reason to think it is. The \"Big Rip\" idea came out of a paper published last decade, 2003 or somewhere around there I believe, that started with the ",
" that the scale factor could go infinite in finite time. It was a what-if paper. Everything we know about the universe — which isn't everything there ",
" about the universe, obviously, but it's an awful lot — says the scale factor will increase exponentially but that it will not diverge.",
"…is it possible that dark energy's action on quarks could lead to some sort of spontaneous matter production (due to confinement)?",
"It actually doesn't matter. If the scale factor were to diverge — and again, zero reason to think it could — then every point in the universe would eventually be behind its own cosmological horizon. Nothing that happens anywhere could affect anything that happens anywhere else. The universe would ",
" not be in a state that in any way resembles its own early history; in the early history of the universe the scale factor was very close to zero, while in this hypothetical scenario it's literally infinite.",
"But again, I can't emphasize strongly enough that this has nothing to do at all with reality. You can say \"What if the scale factor diverged?\" and answers would be offered, but it's no different from saying \"What if the scale factor went up on Tuesdays and down on Thursdays,\" or \"What if the scale factor were linked to the wholesale price of tea?\" It's just pure counterfactual speculation."
] |
[
"It's speculation, but not ",
" out of a hat speculation; their paper was based on rigorously showing that the scale factor ",
" diverge if dark energy exists and has certain parameters. Since dark energy is part of the standard model, and the parameters needed for a big-rip are within the error range of current empirical estimates, it's not completely absurd."
] |
[
"Everything we know about the universe — which isn't everything there is to know about the universe, obviously, but it's an awful lot — says the scale factor will increase exponentially but that it will not diverge.",
"Just out of curiosity, do we know what value it will probably converge to? If so, what is it?"
] |
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