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[
"What does general relativity have to do with the fate of the universe?"
] |
[
false
] | null |
[
"Cosmology is a branch of general relativity.",
"The concept of spacetime doesn't even exist in Newtonian gravity. The universe is once and forever Euclidean in Newtonian gravity."
] |
[
"Ok, then why do you need the concept of spacetime to consider the fate of the universe? It seems like old-fashioned 3-d space and gravity would be sufficient."
] |
[
"Because it's not correct. "
] |
[
"What will airlines do when fossil fuels run out?"
] |
[
false
] |
"My grandfather rode a camel. My father drove a car. I fly my jet. My grandson will ride a camel." - Old Saudi saying Baring an unprecedented and totally unforeseen technological advancement, energy in a post-fossil fuel world will be in the form of electricity (generated by nuclear power, solar, wind, etc.) or biofuels, from crops. Electric cars and buses work fine, but I can't imagine a commercial airplane being powered by electricity. For starters, the batteries would be too heavy. So, are aviation-grade biofuels possible? Is it feasible/possible to have a jet engine capable of running on 100% biofuel? Will we return to the days of the 1950's or 60's, when an air trip cost a month or two of salary and rail (coal) or bus (will be expensive too) or ocean liner (coal) may be the transport of choice?
|
[
"So, are aviation-grade biofuels possible? Is it feasible/possible to have a jet engine capable of running on 100% biofuel?",
"Absolutely. It's a huge focus in engineering R&D by all the major aircraft/engine manufacturers. ",
"You can read about it here.",
" There have been many commercial flights that used a blend of biofuels and regular jet fuel, as well as some 100% biofuel flights.",
"Electric cars and buses work fine, but I can't imagine a commercial airplane being powered by electricity. For starters, the batteries would be too heavy.",
"You're correct; a massive improvement in battery energy density would be needed to make this feasible. The propulsion itself (electric fan) is relatively simple and definitely feasible with current technology.",
"Really, running present-day turbofans with biofuels isn't a matter of scientific possibility, but more just tweaking the design of turbofans (which naturally have been highly optimized for traditional hydrocarbons) to better use biofuels."
] |
[
"... no."
] |
[
"... no."
] |
[
"How do we know what kind of eyesight an animal has?"
] |
[
false
] | null |
[
"If you're asking how we can tell how far an eye can see, that's just a simple lens problem from physics you measure it out and get the answer. ",
"If you're asking how we know that for instance a dog is colorblind, you can open up the eye and see how many rods vs cones are there since a dog has none of the cones or very few its color blind but can see in the dark well.",
"(sort of source)[",
"http://en.wikipedia.org/wiki/Photoreceptor_cell",
"]"
] |
[
"/u/zardif",
" explained mammals well, so I'll speak about non mammals. They tested how much jellyfish could see by painting a plastic rod different colours and seeing what rods the jellyfish would swim around and which rods it would swim in to (in different light, florecent paint, etc). "
] |
[
"I was going to outline this, but couldn't say it any better, so I'll just add on how the horse shoe crab has been used a lot in explaining how vision works in creatures with less complex eyes than mammals.",
"http://www.ncbi.nlm.nih.gov/m/pubmed/19578331/",
" "
] |
[
"How big of a threat are the ancient bacteria in the arctic due to the melting of ice?"
] |
[
false
] | null |
[
"The question you're asking is exactly why they seem dangerous at all -- because we don't know to what degree they would affect us.",
"A lot of the issues involving virulence are attributed to the host's ability to respond to an alien strain. Therefore, if we are not trained in recognizing symptoms, treating symptoms, and other proper measures for full recovery, then it is much more likely that a strain of bacteria will be highly virulent (as it would be able to multiply and spread without individuals recognizing and treating it).",
"Think of COVID -- the reason why it's been so bad is because newest mutations were not being recognized as symptoms of COVID, and therefore, hosts were not able to undergo proper isolation and treatment.",
"Also, there are large possibilities that these bacterial strains are not affecting us (humans), but other living hosts. As our current world's state of biodiversity is adapted enough to current conditions, the introduction of a new parasite could be detrimental to other hosts which are not well-adapted to such things which they had previously never interacted. Basically, we don't know what effects it would have on every single individual species, and that uncertainty is enough to believe that it could limit the (already dwindling) biodiversity we now have.",
"Additionally, there is the issue of how fast the permafrost is melting which would make such issues as identifying strains, treatments, etc compoundingly difficult with how many new strains would be in the ecosystem.",
"So, I know this all sucks, but the answer really is that we would have no true way of knowing (at least for certain bacteria -- scientists have been able to defrost dormant bacteria in the permafrost in order to identify them, but we can only go back so many years in Earth's history worth of permafrost before we are unable to isolate and identify parasites). The fact that we have to ask the question of how dangerous they are (and cannot fully study or anticipate it) means that the best we can do is prepare for the worst -- not only for ourselves but the whole ecosystem's biodiversity."
] |
[
"I’m a bit late — but that may not work either. Penicillin is good against certain types of infectious bacteria (mostly gram-positive types), but not effective against viruses, due to the mechanism of action that penicillin uses. There’s also the issue of antibiotic-resistant bacterial strains popping up too, which I believe is already exists as certain bacteria are resistant to penicillin.",
"Since we don’t know whether these dormant bacteria are gram negative or gram positive, or if these dormant pathogens are actually viruses instead of bacteria, we unfortunately cannot rely on penicillin alone. :( ",
"Stocking up antibiotics/vaccines are also a costly issue and may not even be used much — see the controversial case of the UK and the stockpile of swine flu vaccines.",
"A good measure would be to continue strict health & sanitation practices and to encourage people to monitor their health!"
] |
[
"This is what I figured. It hasn't been long enough to really find out. Thank you!"
] |
[
"How does your body produce antibodies to fight bacteria to which your body was never previously exposed to?"
] |
[
false
] | null |
[
"A B cell is a specific type of white blood cell, whose most important job is to make antibodies. An antibody is just a protein. All antibodies have a similar overall shape, but they vary at a particular spot on the protein, which is where the antibody binds to whatever it binds to. One cell will make zillions of identical antibodies, but the next B cell over will be making zillions of antibodies that have a different shape at the binding site.",
"Like all proteins, antibodies are encoded in the B cell DNA. All cells in your body have identical DNA, so how do you get different cells making different antibodies? That's one of the coolest things your body does. For starters, the antibody genes (plural because there are a couple of different parts to the antibody) are modular. Each part of the gene is present in multiple, slightly different copies. The cell rearranges its DNA, picking one copy of each part and smushing them together. This gives a huge number of possible antibodies to start with. In addition, as the B cell matures, it just flat-out adds random bases into the middle of the gene, where the variable bit is encoded. Look up V(D)J recombination if you want to learn more about this part.",
"There's more to it, as the body makes sure it's not going to react to anything that should be there, but the end result is that each B cell is making its own uniquely shaped antibody. Between all of the B cells in your body, you're pretty well covered against anything that might come along.",
"As an added bonus, when something DOES come along, and one specific B cell's antibodies start reacting to it, that specific cell starts reproducing like crazy, making lots more B cells to make lots more antibodies. And to make things even better, those new daughter B cells deliberately start mutating their antibody gene, trying to refine the antibody so that it works even better. This is called \"somatic hypermutation\". Those mutants that produce better antibodies reproduce more, while those that don't, don't. It's a little mini-evolutionary arms race in your blood stream.",
"And THAT is literally the only interesting bit in all of immunology."
] |
[
"I don't like the term \"proto-antibody\", especially as a synonym for \"B cell\"."
] |
[
"There are components of the recombination called recombination-activating genes (RAGs). Multiple RAGs combine to the DNA and depending where they attach will determine the variable region of the antibody. These RAGs basically create hairpin loops to \"splice\" parts of the germline to create the mRNA that will actually be processed. Therefore you can have zillions of combinations.\n",
"http://imgur.com/VP8VXNQ"
] |
[
"Is there a reason we prefer instruments to start flat when tuning by ear?"
] |
[
false
] |
When I've talked to musicians about tuning by ear, they often say that it is easier to hear the pitch differences and tune accordingly if it is going from flat -> in-tune, as opposed to sharp -> in-tune. For instance, when tuning a guitar, often musicians will make the string they want to tune wildly flat and then bring it up to tune as opposed to making it sharp. Is there a known reason our ears would favor this transition more than a sharp-> in-tune transition?
|
[
"I'd say because it's less likely to slip back out of tune when you're finished. When going from sharp to flat, the string drags on the nut a bit and the small amount of string between the nut and machine head is unnecessarily slack."
] |
[
"Musician here. no research done on this but from experience in learning about music/theory is that its just more \"comfortable\" and usual to go from \"down\" to \"up\" yanno?",
"its like counting. you usually count 1-2-3-4-5 intead of 5-4-3-2-1.",
"or if you're studying intervals, more often than not, they begin with ascending and then follow up with descending"
] |
[
"Right! I'm a musician too and I've always found it more comfortable, but I was not sure as to why besides just being used to it. Someone I talked to who works in auditory perception says it may have to do with how the ear recognizes the different parts of a sound as the waves come in, but she wasn't too sure."
] |
[
"How does CERN/LHC deal with soil movement?"
] |
[
false
] |
I was watching a video on the LHC and this question popped into my mind that I couldn't find an answer to online. Which is how the LHC in Geneva accounts for soil movement, expanding soils, and things like that, given that it's such a massive structure? Wouldn't it eventually throw their measurements off? I know they need a remarkable amount of precision to electromagnetically shoot particle beams into one another.
|
[
"There is also the central LHC monitoring system:",
"https://op-webtools.web.cern.ch/vistar/vistars.php",
"https://op-webtools.web.cern.ch/vistar/vistars.php?usr=LHC3",
"Now offline, too. Will be back early 2021."
] |
[
"There is also the central LHC monitoring system:",
"https://op-webtools.web.cern.ch/vistar/vistars.php",
"https://op-webtools.web.cern.ch/vistar/vistars.php?usr=LHC3",
"Now offline, too. Will be back early 2021."
] |
[
"Not at the LHC, but I have worked with scientists at Argonne National Lab's ",
"Advanced Photon Source",
" lab, which runs an electron beam at 99.999% the speed of light around a multi-KM diameter circle.",
"They were noticing disturbances in the electron beam - it was not traveling in the center of its desired path; which obviously caused issues with their electron beam and experiments.",
"The issue was construction that was going on over a mile away. This construction was causing ground vibrations that were interrupting the electron beam. The vibrations were imperceptible to people - on the order of micro-g's - but even those low acceleration levels were enough to disturb the beam.",
"In this case, they were just monitoring the vibration levels in order to determine when their beam would be usable; they did not have any active vibration control built into the system. I would imagine that would be near impossible - a huge engineering project on its own."
] |
[
"Why do mutations occur in the first place?"
] |
[
false
] |
If you plug 2+2 into a calculator 1 million times, it will give you '4' every time. Why is DNA any different?
|
[
"If you plug 2+2 into a calculator 1 million times, it will give you '4' every time.",
"Is not absolutely true. The logic error rate is determined by the signal to noise ratio. All things above absolute zero have thermal noise and this leads to a calculation of the error rate. ",
"Bit error rate",
"."
] |
[
"There are several ways a mutation in DNA can arise. Some types of errors are due to the fact that the proteins and enzymes that replicate DNA and other nuclear material are not infallible. DNA polymerase along with the regulatory processes which follow during replication have a fidelity of about 1 error in 10 billion base pairs replicated. The beautiful thing about these machines is that there’s a degree of chaos at work, the random vibration of molecules, proximity to other chemical reactions, slight changes in temperature or pH can all affect their ability to do their job correctly. Mutations can also result from any ionizing radiation, think UV radiation from the sun. An unlucky highly energetic wave (or particle if it’s easier to imagine) slamming into DNA and causing a double stranded break altogether. Usually the repair isn’t difficult, but also not as accurate in recreating the original sequence.",
"It’s also theorized that some random mutation is evolutionarily beneficial to a population, because it can indirectly lead to genetic variability. "
] |
[
"I actually bet if you had someone run that experiment with a person, you'd get something besides 4 before you got to a million."
] |
[
"Why do magnets only attract ferrous objects?"
] |
[
false
] |
Are there magnets that attract or repel things which are not ferrous? A magnet, say for ceramics or for silver? If not, why not?
|
[
"It should be mentioned that levitation of a frog is through ",
", whereas the attraction of materials to magnets is through either ",
" or ",
". In the frog case, the water molecules align to make a magnetic field ",
" that of the applied field, so you get a repulsion. For iron attracting a material, the electronic spins in those materials make a magnetic field in the same direction as the applied field, so you get an attraction."
] |
[
"There is no special magnet for non-ferrous materials. There is only one kind of magnetism.",
"In order to be affected by a static magnetic field, an object needs to have a magnetic moment (i.e., N and S poles). When a ferromagnetic material is placed in a magnetic field, it develops these poles. We say that it is easily \"polarized\".",
"Other materials can be polarized, but the response is much weaker. One can, for example, ",
"levitate a frog",
" in a strong magnetic field."
] |
[
"I was talking about the magnetic field itself, not the response of a material to it. I agree that there many possible responses, but there is only one stimulus. I think that is what OP was asking about. He asked whether there might be \"A magnet, say for ceramics or for silver?\""
] |
[
"I randomly generated 30 numbers and added up 5 at random. Is there a non-trial and error way to figure out which 5 numbers I added? Is this an example of a P vs. NP problem?"
] |
[
false
] |
[deleted]
|
[
"One general technique which can save you a lot of time in these sorts of problems corresponds to the maze-solving notion \"instead of searching from the start to find the end, try searching from both the start and the end at once until you meet somewhere in the middle\".",
"For your problem, this would mean making a list of all the sums you could get from 2 out of your 30 numbers; making a separate list of 2,423,070,010 (your answer) minus all possible sums you could get from 3 out of your 30 numbers, and then look for overlaps. In general, for a list of n numbers, this takes time O(n",
" instead of the O(n",
" that the naive algorithm would take, a significant improvement."
] |
[
"If we know it's five numbers, the brute force solution is O (n",
" ). If wet don't know how many numbers, this is subset-sum, which is known to be NP-complete. I think. "
] |
[
"Here's one way to do it in Python. (The algorithm here is Θ(n",
" log n) rather than Θ(n",
"), but the sorting operations can be optimised with some care.)",
"from itertools import combinations\n\ndef find_quintuple(input_list,N):\n triples = sorted(combinations(input_list, 3), key=sum)\n doubles = sorted(combinations(input_list, 2), key=sum)\n j = len(doubles)-1\n for (i, triple) in enumerate(triples):\n s = sum(triple)\n while s + sum(doubles[j]) > N:\n if j == 0:\n return None\n j -= 1\n if s + sum(doubles[j]) == N:\n return sorted(triple + doubles[j])\n return None\n\ninput_list = [7908023, ... , 953565826] # full list omitted for brevity\n\nprint(find_quintuple(input_list, 2423070010))\n# this prints [222140204, 337291249, 465093839, 537600752, 860943966]\n",
"Edited to add: I missed out a couple of details when I wrote the code because I was in a bit of a rush; it doesn't enforce that the triple and double are \"disjoint\", so find_quintuple([1,2,3,4,5],9) will return [1,1,2,2,3], for example. Not going to bother fixing this since ",
"/u/thestoicattack",
" has a better version below."
] |
[
"What is nowadays real world application of Reed-Muller codes?"
] |
[
false
] | null |
[
"Oddly specific. ",
"Reed-Muller codes",
", for those wondering, are a type of error correction code. Error correction codes being a code that adds redundancy to data to ensure that... errors can be corrected. For example, consider sending a 0 for 0 and a 1 for 1. If there is an error in this scheme (e.g., a 0 was sent but a 1 received) then the receiver is SOL. On the other hand if I send 000 for 0 and 111 for 1, a single error (e.g., sent 000 received 010) can be corrected since 000 is the more likely of the two codewords.",
"Reed-Muller codes found use in ",
"deep space communication (PDF; pg 11)",
" because of how efficient they were in terms of redundancy and decoder complexity. That being said, they were not in fact ",
"capacity",
" achieving, and fell out of fashion in favor of ",
"turbo codes",
", ",
"LDPC codes",
", and ",
"Polar codes",
". ",
"Polar codes are the most interesting of these because they can be shown to be capacity achieving. They also share a large amount in common with Reed-Muller codes, ",
"as discussed in the paper which originally proposed polar codes (PDF; see page 5 section D)",
". ",
"Polar codes are currently being used for error correction codes, and ",
"source coding (PDF)",
". In fact, polar codes have been selected for use in 5G."
] |
[
"Whoaa thanks man, really helpful. You even give the references... ",
"I'm working on some paper about reed muller, but well all i ever heard is that reed muller codes had been used in voyager 2 or something mission. I ",
" that's a long long time ago... for now BCH has done the job better involving binary correction even tho it's more complex to decode...",
"And your reply just prove how wrong my thinking was... appreciate it eric...",
"Edit: reed muller was used in mariner 9 mission"
] |
[
"Well good luck. It is surprising that you are taking a class where you are learning about error correction without being given real world applications. In some ways, error correction as the implementation side of information theory.",
"Error correction codes though are actually necessary for all practical forms of communication in order to maximize communication rate. In situations where they are not used, such as wired internet, they are opting for lower complexity decoders instead of higher rates of communication. "
] |
[
"Are there any tenable and/or mainstream critiques to the many-worlds interpretation and the \"multiverse\"?"
] |
[
false
] |
Or are these interpretations of fairly accepted? What are some alternative points of view? These theories seem so odd to me, and it seems there would be other points of view on the topic that perhaps don't get as much attention, or perhaps are still in their infancy.
|
[
"Okay. First let me say the very first and most important thing. Science tells us what to expect when we measure something. Quantum mechanics and the associated scientific theories work ",
" well in this scientific regard. The moment we ask what happens between measurements, we leave science for the world of philosophy. So what I'm about to say is ",
" philosophical. It's informed with scientific concepts, but it ",
".",
"The multi-world interpretation (MWI) would be ",
" better named the multi-state interpretation(MSI). You see there's this comic-book principle that people go to when they hear multiple worlds. They go to this idea that you exactly mention, that there is a world out there where I had Chinese for dinner last night and not Indian. But MWI is not ",
" like that.",
"MWI or MSI works like this: We know a particle can be in a quantum superposition of states. We can interact this particle with another particle and that system can be described as a superposition of states. MSI just keeps going. What if these particles interact with more, and more until every particle of a detection machine is in a superposition of states that is all correlated to the particle it's trying to measure. Even the particles that make up our memory of the measurement outcome would be in a superposition of states.",
"Thus MSI proposes that the ",
" universe is in a universal wavefunction with superpositions at many different scales. Single particles, particle detectors, etc. That we remember one specific result rather than some other is just the fact that we could never tell the difference between having a memory for sure or having a super-position of memories.",
"And that's the rough outline of MSI/MWI. It's not science. Just philosophy. You can accept it or not, and the universe doesn't care one way or the other. It's not incompatible with other interpretations either like the transactional interpretation. It is pretty incompatible with the Copenhagen interpretation however. But again, science is blind to these philosophical distinctions until we find some evidence that can distinguish one interpretation from another. (which may actually be unlikely to ever be found)",
"(Previously posted",
" here",
")"
] |
[
"TL, DR: The interpretations of quantum mechanics are philosophical, and are intended to provide a mental model of what's happening. They are not theories, make no predictions, and any discussion on them is a matter of opinion, not science."
] |
[
"Everything there is, kittenboobies."
] |
[
"Why does my mucus become green or yellow when I have an infection?"
] |
[
false
] |
It's common knowledge that when your mucus turns colors, you have some kind of infection. What is it about the infection or our body that makes this happen?
|
[
"When a part of the body becomes infected it produces signals to alert the immune system to the developing problem. Cells and other immune components follow these signals by a process called chemotaxis to home in on the affected area. In the case of colds, white blood cells called neutrophils are amongst the first on the scene and arrive via the blood stream. Upon arrival the neutrophils mount an attack. They attempt to engulf (swallow) the pathogen (a virus in the case of colds) and at the same time they produce antiseptic chemicals that wipe out other pathogens nearby. These chemicals are so potent that even the neutophils don't escape and are destroyed, committing suicide to fight the spread of infection. Generally, enzymes are responsible for the production of the antiseptic chemicals and it is these that give mucus the green colour. Enzymes often require ‘helpers’, called co-enzymes, to function properly and it is more specifically the co-enzyme iron (ferrous form) that lends the green colour to mucus. One such iron containing enzyme in neutrophils is myeloperoxidase. Myeloperoxidase produces the antiseptic chemical hypochlorous acid, the type of bleach commonly used to sanitise swimming pools. Interestingly, it is similar iron containing enzymes in wasabi that make it green too."
] |
[
"Thanks for the detailed explanation!"
] |
[
"So, it is appropriate to assume: The more potent the infection, the more green the mucus will be; while if the infection is less potent, the mucus will be more of yellow colour?"
] |
[
"What is the escape velocity of our galaxy, perpendicular to the disk?"
] |
[
false
] |
[deleted]
|
[
"The escape velocity for our region of the galaxy was estimated in 2013 by the ",
"Radial Velocity Experiment",
" (a.k.a. RAVE Survey) as being about 537 km/s. To put that in perspective, the speed of Voyager I relative to the Sun is about 17 km/s.",
"If we really wanted to escape the galaxy, attempting to do it perpendicular to the disk wouldn't make much sense. In that case, since our starting velocity perpendicular to the disk is close to zero, we'd have to provide nearly all of that 537 km/s with the spacecraft's propulsion system - about 30 times the speed of Voyager I.",
"We'd be much better off attempting that in the plane of our solar system's orbit, because it allows us to exploit the solar system's orbital speed and just add an incremental amount to escape the galaxy. Our solar system orbital speed is about 220 km/s, so to escape the galaxy in the plane of our orbit would \"only\" require about 317 km/s - less than 19 times the speed of Voyager I.",
"Sources:",
"The RAVE survey: the Galactic escape speed and the mass of the Milky Way",
"\n",
"The RAVE Survey: Constraining the Local Galactic Escape Speed"
] |
[
"That's really interesting... I suppose there would be more stars available to do a gravity assist as well, though there'd probably be enough to do it in the vertical plane anyway. Though at those speeds I imagine the margin for error gets smaller and smaller...",
"Hard to think of a practical reason to want to go to another galaxy, but it's still fun to contemplate."
] |
[
"That calculation applies when you're orbiting outside a spherically symmetrical object. The galaxy isn't spherically symmetrical, and we're orbiting within it, so our escape velocity is affected not only by mass towards the center, but also mass that's further out from the center than we are. The distribution of mass also comes into play, particularly if there's dark matter that's not evenly distributed.",
"It's not a simple calculation, which is why something like the RAVE survey was needed to determine a value."
] |
[
"How do computers accurately perform calculations which involve irrational numbers such as Pi and e, if these numbers have infinite digits?"
] |
[
false
] | null |
[
"Computers typically only use an approximation for irrational constants like pi and e. And for any other non-integer values.",
"The commonly used \"double precision floating point\" type has an accuracy of 15-17 significant decimal digits. That means that numbers such as pi and e, which have 1 digit before the period will have an accuracy of at least 14 decimal digits after the period. For almost all calculations, this is more than enough.",
"If necessary, computers can work with more precise approximations, but the increased accuracy incurs a large performance penalty.",
"There's also computer algebra software, which performs algebraic manipulations like a human working on a math problem would. This software leaves constants like pi and e as they are, without replacing them with approximated values, while performing the requested computations. If necessary, approximations for these constants are substituted at the end of the process. Computer algebra packages are specialized software that is typically used in scientific applications. However, one freely available example is Wolfram Alpha, which is a web interface for the computer algebra package Mathematica."
] |
[
"This is not true. While floating point arithmetic is often used, plenty of systems use fixed precision or infinite precision math. There are also plenty of systems that use bit lengths for numbers that are neither 32 nor 64 bits."
] |
[
"Yes.",
"Because in a calculation that involves multiple variables, the accuracy of the outcome most strongly depends on the accuracy of the least accurate of those. Suppose you want to calculate the length of a circular orbit to the level of accuracy where you're limited by the standard floating point representation of pi, then the radius of this orbit should be known to at least this accuracy as well.",
"If you look at the orbit of Earth, this would mean you'd need to know the Earth-Sun distance down to the centimeter."
] |
[
"If two different species have similar genome sizes, is it likely they contain the same number of genes?"
] |
[
false
] |
[deleted]
|
[
"Genome size is the number of base pairs in the entire DNA sequence of the species. Most of that DNA is non-coding, meaning not part of genes. So a larger genome could just mean more non-coding DNA, and the same number of genes."
] |
[
"First off it is not so easy to define gene. That aside genes vary in the number of base pair. ",
"This page",
" shows the wide range found in humans. Going across species (families, etc.) make it even worse. The alleles (variations) of a particular gene in humans are reasonably similar in size but that can change as we look at population further and further apart."
] |
[
"Genes and DNA are very interesting and we are still only scratching the surface of their capabilities. I remember about 6 years ago in highschool biology I was taught that a good portion of human DNA was ",
" DNA. I remember blurting out, \"No! That's not possible!\" The teacher explained that someday I may disprove it but that is where the current understanding is now.\nWe've come a long way since then. Junk DNA, for the most part is a myth. Scientists were used to looking for coding DNA, which basically is the DNA that codes for the direct production of a protein. Many species have DNA that may code for the production of other molecules, like mRNA, for example-not necessarily proteins. Other regions of your genome may only be accessed during certain periods of development. Other regions of DNA may have a pleiotropic effect and code for multiple things under different conditions.\nWith that said, genome length does not necessarily correlate to ",
". Humans on average have about 20,000-30,000 protein coding genes which account for 2% of or genome. That roughly comes to 3bil base pairs, there are some (",
") plants (and fish) that have over ",
" basepairs. \nSometimes species have adaptations that allow for a more \"consolidated\" genome-selection can only act upon structures that already exist, this sometimes leads to streamlined, efficient adaptations or sometimes yields strange adaptations that don't make much sense (i.e. laryngeal nerve in giraffes, or the ",
" being essentially a primate version of the woodpecker). There is no reason for nature to sometimes yield genomes that look goofy in comparison to others.\nHumans, because we build cool things and are who we are like to think of ourselves as the pinnacle of 'evolution'. It is important to remove this anthrocentric view as much as possible from, especially, science."
] |
[
"How do we get clocks (digital & analog) to 'know' when a second has passed?"
] |
[
false
] |
[deleted]
|
[
"Through very different ways. ",
"Analog clocks (is that the name for them? I'm unsure, but I'm talking about clocks with pendulums) know time by their pendulums. How long it takes a pendulum to swing is not dependent on the size of the swing, ",
"only on the length of the bar",
". Thus, even as the pendulum swing gets smaller, you can keep accurate time by keeping track of the number of swings. ",
"Digital clocks most commonly use a quartz crystal. Quartz crystals will oscillate when an electric field is passed through them. This rate of oscillation is not dependent on the current, so again, even as the battery starts to die, it will remain accurate. So keeping track of how many times the crystal vibrates you can keep track of time. "
] |
[
"I think analogue refers to the display being hands instead of numbers, the mechanism is probably called mechanical.",
"Just wanted to add that not all mechanical (clockwork?) clocks use pendulums, they can also use balance wheels which are much cooler and I imagine much more common in smaller clocks (including watches). They work the same, spin backwards and forwards at a known rate regardless to how tight the spring is wound.",
"We also have atomic clocks I guess which complete the standard set, they work the same as in quartz clocks but instead of a quartz crystal as their reference frequency they use the photons emitted from hyperfine (really narrow in terms of energy) transitions of atoms, normally caesium.",
"edit: ",
"video",
" of a balance wheel, pretty sexy right? notice how it oscillates back and forth and is brought back to the centre each time by that spiral spring thing. "
] |
[
"To specify; Analogue refers to something continuous(like a sun watch), and digital to something in pieces or quantitative(hourglass, with individual grains of sand). Cool video btw. "
] |
[
"Where/How Is Physics Codified?"
] |
[
false
] |
Is there any straightforward and reliable way for a layman to keep up with what the latest findings are in cosmology, particle physics, etc.? Since I started following a few months ago, I've learned that much of what I thought I "knew" about physics is now known to be false, and that discoveries in the last 10-15 years have led to important new conclusions. I would guess that real physicists keep up by reading around in academic journals, going to conferences, corresponding with colleagues, etc. For a nonprofessional like myself, I have neither the time nor the academic grounding to do those things, not to mention the budget to subscribe to the journals. I've also learned on reddit that much of what is written about science in popular journals directed at layman is pseudoscience, shoddy journalism, and in some cases "not even wrong." Alas, what should be the ideal avenue for we laypeople fails the reliability test. I've learned more here in the last several months than I had in the previous few years, so currently my best option seems to be keeping tuned in to the excellent contributions by the scientists here. Yet something a bit more programmatic and structured would be very welcome. As an example, is the latest accepted version of the Standard Model codified in one place anywhere--and is there a version of this that is understandable by a nonprofessional? Any suggestions? TL;DR - What's the best way for a layman to stay current in physics?
|
[
"Science journalism is a decent place to ",
" Think of it like a wiki article (just worse sometimes). Try to find if the article is referring to a peer-reviewed journal article. See if you can find that article, maybe check arXiv for a pre-print copy of it. Be careful about arXiv in general, because it isn't peer-reviewed itself. Some of the things posted to it ",
" be peer-reviewed in the future. "
] |
[
"But be weary of things in the \"General Physics\" section.",
"Another thing I'd recommend is just reading the abstracts (or even the titles) of Physical Review Letters. They should be free, and written for a wider audience to understand, and you'll get a sense of what's being done even if you don't know the details."
] |
[
"Thanks. I hadn't heard of arXiv before... after checking it out just now, I'm pretty sure I'll be spending a lot of time there."
] |
[
"Why is it that whenever I use some mouth wash, my tongue burns when I place it on the bottom of my mouth?"
] |
[
false
] | null |
[
"My tongue tends to burn when I place it on the top of my mouth. Usually if i press a bit harder, it hurts a bit more."
] |
[
"Mouth wash is typically fifteen percent alcohol... That's why. "
] |
[
"The one I am using is 0% Alcohol, no joke!"
] |
[
"Is there a logical explanation as to why we put open containers of baking soda in refrigerators? If yes, what does it do and how?"
] |
[
false
] | null |
[
"Baking soda (NaHCO3) or sodium bicarbonate is a basic salt, so if the odours that your food is giving off (known as volatile organic molecules) are acidic, they will then react with the base and form a sodium salt. Salts are much less volatile and will not have as strong of an odour."
] |
[
"I missed a point, it will also absorb basic organic molecules because sodium bicarbonate is also acidic (being both a base and an acid is called ",
"amphoterism",
"). It acts as a ",
"buffer",
" and can absorb both basic and acidic ",
"volatile organic compounds",
" emitted by your food and drinks. [EDIT: added some links]"
] |
[
"you can hit the edit button if you want to fix your first post : )",
"also foul smells tend to be amines aka nitrogen containing compounds. for example putrescine and cadaverine. these types of amine compounds are produced by decay organic matter that is slowly chemically breaking down (usually due to bacteria)",
"http://en.wikipedia.org/wiki/Putrescine",
"http://en.wikipedia.org/wiki/Cadaverine"
] |
[
"When you pull a hair, does the bulb come out with the shaft? If so, how does it grow back?"
] |
[
false
] | null |
[
"Sometimes when I pull out a hair, it has a thin transparent layer around the bottom bit. What is that?"
] |
[
"Why, then, after so many years of plucking my uni-brow does it insist on growing back. I would think I'd have damaged at least a few of those suckers."
] |
[
"You will have, but there are a lot of follicles. Plenty of women are still drawing their eyebrows on because they overplucked in the 70s. "
] |
[
"Does heavier propeller mean more thrust?"
] |
[
false
] |
In both aviation and maritime. If you think about it, only the shape and the RPM of the propeller must affect the airflow/waterflow, so logically you would try to make the propeller as light as possible, but especially ship propellers are made quite heavy sometimes weighing tens of tons, while making it from a lighter material would save fuel. Aircraft propellers seem much lighter than the watercraft propellers, probably due to air having much less resistance. But how do you calculate the ideal propeller weight and density of the material?
|
[
"The weight of the propeller and its density don't effect the thrust that it is capable of putting out. Its shape and RPM (as you noted) are the direct factors that determine its output thrust.",
"Now the density of the material combined with its shape will give you the weight of the propeller, so you could so the weight of the propeller does determine its thrust.",
"Finally the propeller has to be capable of withstanding the force of the trust it is outputting (Newton's third law). This means for your propeller to put out a large thrust, it needs to be strong enough to withstand that thrust. That is usually done by it being a dense material that can withstand the stresses.",
"So that would be the answer, if you want to have a propeller that puts out a large thrust it will need to be made of a material that can withstand that force. The large the force the heavier the material."
] |
[
"In maritime, I don't know how much weight and density of the prop matters. What matters is the pitch of the propeller. Being able to control the pitch allows you to move fwd or back as well as control the amount of water going through the screw. ",
"I'm sure density is related to this, I just don't know how other than displacing water via its weight. "
] |
[
"Strength and stiffness is also important, as you don't want your propeller blades flexing or yielding under load. So they have to be made of a stiff enough material and built thick enough that they can withstand the stresses involved. Such designs would have the side effect of being heavier."
] |
[
"How do we know that any of the laws of physics are constant?"
] |
[
false
] |
Obviously the laws of physics are more or less constant in our day to day lives, Newtonian laws have held up nicely, but this is a relatively small portion of the universe. I recently chanced upon article which describes about how there may be variation in alpha, which describes electromagnetic forces. This lead me to wonder, since all of our observations are limited to such a small section of space how could we differentiate observations due to our environment from scientific law? What leads us to believe that gravity, or the passage of time or planks constant aren't "distorted" in our local space similarly to how light is refracted when moving between a liquid and a gas?
|
[
"Our observations aren't limited to a small section of space. We can see things very, very far away.",
"And what we see when we look at very distant things amounts to the best evidence we have of the universality of the laws of physics: the universe is ",
" and ",
" What that means is that wherever we look in the sky, from right-next-door to billions of light-years away, we see pretty much the same ",
" So we know that if the laws of physics vary, they can't vary very much. Otherwise we wouldn't see stars and galaxies everywhere. We'd see other things … or more likely nothing, since if you change the laws of physics ",
" it turns out matter can't exist.",
"Of course, we ",
" know that things like the passage of time are affected by the environment around us. We can observe this directly, but putting clocks aboard orbiting satellites. But that's not a case of the laws of physics changing from point to point. It's a case of the passage of time not being constant, but rather dependent on the geometry of spacetime. The passage of time went from being a given to being a consequence of something more fundamental.",
"And this shapes our idea of what reality is. If something varies from place to place, or from time to time, then it's not a given, is it? It's a consequence of something else, something which ",
" fundamental and universal."
] |
[
"My point about local observations was that pretty much all of our scientific observations have been conducted within a limited range.",
"If you define \"limited range\" as some thirty-odd billion light-years, then yes. In an infinite universe, a sixty-billion-light-year sphere is ",
" But the underlying point is that wherever we look, we see a universe that's consistent with a single set of fundamental physical laws that apply everywhere and at all times.",
"If for whatever reason, redshift or observed radio waves were distorted within our local space we would have nothing to calibrate it against.",
"Sure we would. If a particular energy transition in a particular atom results in an emission of a particular photon ",
" and we see photons of that energy ",
" then we have a good idea that the same underlying laws that dictate how atomic transitions work apply everywhere.",
"It makes sense that any large scale modification to physical constants would quickly devolve to the realm of science fiction.",
"It's science fiction because you're starting with a conclusion and feeling around for evidence to contradict it. Is it possible that a trillion trillion light-years from here the gravitational constant is different by a quarter of a percent from what we measure? Of course it is. But there's no reason to believe that to be the case. There's no evidence to support such an assertion."
] |
[
"That's a good point. I can definitely appreciate that the dispersal of matter throughout the universe is a good case for constants. My point about local observations was that pretty much all of our scientific observations have been conducted within a limited range. If for whatever reason, redshift or observed radio waves were distorted within our local space we would have nothing to calibrate it against. I suppose the real argument against this would be that physics is so harmonious from, the math to the actual cosmological behavior . Modifications in one constant would influence others which in turn would be observable. It makes sense that any large scale modification to physical constants would quickly devolve to the realm of science fiction. Thanks for helping me out."
] |
[
"why do objects bend space/time?"
] |
[
false
] |
I was recently watching a documentary on gravity and started to wonder how and why matter bends/warps space and why that causes gravity. also EITMLI6
|
[
"We don't know, and we probably won't ever know. \"Why\" is a very tricky question, and it can't usually be answered scientifically. We can measure ",
" something happens, and we can come up with predictive models of ",
" will happen, but to say ",
" something happens requires going beyond that. We can say, scientifically, that objects tend to accelerate toward one another. We can say that this is true for massless objects like light just as much as for massive particles, so that, for example, light passing near a star appears to follow a curved path. We can also say that a good ",
" for this behavior can be given by treating spacetime as a curved manifold where the curvature is related to the local energy density according to a certain rule (Einstein's field equation). But ",
" that particular relation should hold, or ",
" the behavior should be able to be modeled with such a mathematical description at all, is a question that we can't really answer."
] |
[
"Here's a simple thought experiment that should give you a little intuition for why mass bends space.",
"Imagine you're in an elevator. You stand still, jump up and down, whatever. Are you on earth? Past experience says \"yes,\" but here's ",
" possibility. What if, instead of an elevator in the Empire State Building, we put you in free space and stuck a rocket booster to the bottom of this room and blasted you at 9.8 m/s",
" (the same gravitational acceleration as our planet)? ",
"You'd feel the exact same as if you were on earth",
"!",
"So Einstein said the two situations have to be equivalent: ",
". That's the key here.",
"Now make a pinprick through your elevator wall. A beam of light shines through horizontally. In free space light travels in a straight line, right? Well how about if your elevator is actually accelerating via rockets? The light starts at the pinhole, you move up a bit. The light (which travels at a constant speed) crosses the room more, you move more than a bit (remember, your velocity is increasing every moment). ",
"The light moves a little more, you move ",
" more",
". So the beam appears to bend in your rocket toward the floor! Does that make sense?",
"Now here's the punchline: since you can't tell the difference between being in a rocket elevator and being in a gravitational field with the same acceleration, the same result must hold (light bending) if we're sitting pretty near a mass! Mass must bends light just like rockets!",
"But we said earlier that light travels in a line. It takes the shortest distance between two points. But if light is bent, and it takes the shortest path between two points, the shortest path between two points must be bent, like two points to an ant on the surface of a sphere, or a torus maybe. So from our simple thought experiment, we discovered that masses bend light, and thus the shortest distance between points, affecting spacetime.",
"I apologize for the crappy pictures, but they were the best Google gave for this famous ",
" (thought) experiment. If you want to learn more, I suggest looking up the following stuff: The Equivalence Principle, Geodesics, and The Principle of Covariance. Also, read ",
" which is a cheap and super-accessible book on the sexy physics and underlying philosophy behind it (interestingly enough, the physicist who wrote that book was in the first lecture presenting relativity taught by Einstein himself). Cheers!"
] |
[
"thank you! I have been struggling with this concept for a while now, this is so helpful."
] |
[
"What color is the sun?[astronomy]"
] |
[
false
] |
So basically if we were able to fly to our sun and be a safe enough distance away, think moon from earth scale, what features would we see and what color would it be?
|
[
"This color",
". Above the atmosphere, the sun is white with a blue-green tint as a result of its peak wavelengths. Through our atmosphere, the sun's peak wavelengths are greener. However, the sun is still considered white in both cases because its emission strikes every single visible wavelength fairly evenly. \nIf you want to assign a color to the sun, though, then you'd say it's green, based on peak wavelengths. The reason we usually consider the sun yellow is because it's always referenced to a blue sky, and so appears yellower in contrast.\n",
"This",
" this is a great visualization of the solar spectrum, both in space and through out atmosphere."
] |
[
"Thanks so much! I've always been curious as to what we would see. "
] |
[
"No. So what's happening here is they are putting a large filter over the star. Now because red light waves travel further then any other light wave they get through the filter. "
] |
[
"Does vitamin C really improve connective tissue health?"
] |
[
false
] |
Many coaches and "fitness experts" suggest suppplementing vitamin c for joints health/recovery, but i couldnt really find any good research about it, is there any scientifical proof about it?
|
[
"Collagen is synthesized in your body as an inactive precursor called procollagen, and to make the final product the body needs the compound called vitamin C as a cofactor. Cofactor means it is a molecule necessary for certain chemical reactions to take place, but we can't make this molecule ourselves and need it from the diet. This chemistry is fairly well understood.",
"Collagen is the principal component of connective tissue, and even makes up 25-35% of all proteins in your body by weight. Your body is constantly breaking tissue down and re-assembling it, remodelling after minor injuries and performing structural maintenance. Insufficient dietary vitamin C will result in poor connective tissue health as new collagen can't be made, and most famously a condition called ",
"scurvy",
"."
] |
[
"From what I know of biochemistry (2nd year med student), excess vitamin C would simply be excreted either through the urine or through faeces. Our bodies don't really store vitamin C in any way. Vitamin C helps enzymes, proteins that make chemical reactions happen. Compare this to trucks that transport cargo; if you increase the number of trucks but not the number of drivers or cargo, you won't really notice any difference in the amount of work being done. Excess vitamin C when not needed won't be put to good use, and since it isn't stored, I would wager it doesn't affect recovery in any significant way. (Despite this, ",
" overdoses will cause symptoms such as diarrhoea, urinary calculi and hyperferremia (too much iron) because vitamin C plays a role in iron uptake too.)",
"The adverse effects of mild vitamin C deficiencies are not known exactly, but I would assume there would be a mild, perhaps not clinically significant, reduction in collagen synthesis.",
"This website",
" is maintained by doctors in the UK and might have some more answers."
] |
[
"Vitamin C is a vital nutrient, but deficiencies (e.g. scurvy) are extremely rare in modern life. As such, supplementation is generally considered unnecessary. ",
"Later in life, nobel prize winner Linus Pauling came to wrongly believe Vitamin C was a cure for everything- and the myth is still out there.",
"For more:",
"http://www.vox.com/2015/1/15/7547741/vitamin-c-myth-pauling",
"https://www.sciencebasedmedicine.org/high-dose-vitamin-c-and-cancer-has-linus-pauling-been-vindicated/",
"http://www.quackwatch.com/01QuackeryRelatedTopics/pauling.html"
] |
[
"When an animal becomes extremely endangered, how do they reproduce without inbreeding?"
] |
[
false
] | null |
[
"They dont. This leads to an extreme lack of biodiversity and an increase in diseases and deformation. We see this with dogs, and breeding them. There are so few pure bred dogs, that many pure bred dogs ha e deformities and diseases. I know a dog with diabetes."
] |
[
"They do reproduce with inbreeding and this will cause their genetic diversity to be greatly diminished. A lack of genetic diversity can be very damaging to a population. A good example of this is cheetahs. Their population was decimated a few thousand years ago causing a massive \"genetic bottleneck.\" Their population was a able to make somewhat of a comeback after the event but this led to much inbreeding as a result of the low population. Today cheetahs genetic diversity is so low you can take an organ from any cheetah and transplant it into any other cheetah. This lack of diversity leads them to be susceptible to many diseases and other conditions."
] |
[
"They inbreed, it's the only option for them. An interesting example of this is with the wolf population on Isle Royale, an island in Lake Superior. The wolf population has dwindled down to 2 or 3 over the years and so the wolves are horribly inbred. The few wolves left are pretty sickly and deformed. "
] |
[
"Why does tilting a mug reduce the foam head when pouring a beer?"
] |
[
false
] | null |
[
"If you don't tilt the glass and pour the beer directly toward the bottom of the glass, the beer travels a longer distance, splashes at the bottom, and continues to mix with beer that is poured later. This agitates the beer a lot, adding air bubbles, and ultimately more foam. Tilting the glass reduces the distance traveled by the beer before hitting the glass (thus reducing the effect of the splash). Less agitation, less air, less foam.",
"There is also the consideration of where the dissolved carbon dioxide must go. A slow pour allows more carbon dioxide to release. Tilting the glass also increases the surface area of the beer that is exposed to the air, thus allowing more carbon dioxide to release per second. So less C0",
", fewer bubbles, less foam."
] |
[
"So most of this is accurate, but not all of it. I don't mean to sound pedantic, but this is ",
"/r/askscience",
"This agitates the beer a lot, adding air bubbles, and ultimately more foam.",
"The key is agitation. \"Adding air bubbles\" imples that it has something to do with mixing with air - this is not the case. The agitation and turbulence cause the dissolution of CO2, which is seen as head or foam.",
"Tilting the glass decreases the free fall distance of the stream, which is one factor in helping to decrease the head production. Another factor is that the beer hits the glass side and flows to the bottom is a mostly laminar fashion, and there is less turbulence at the bottom of the glass, because some energy has been dissipated by friction within the fluid and between the glass and fluid.",
"There is also the consideration of where the dissolved carbon dioxide must go. A slow pour allows more carbon dioxide to release. Tilting the glass also increases the surface area of the beer that is exposed to the air, thus allowing more carbon dioxide to release per second. So less C02, fewer bubbles, less foam.",
"This part is all false. A slow pour will release ",
" CO2 than a quick pour, for the reasons described above. Surface area is mostly irrelevant, but releasing more CO2 would generally result in more head, so this hypothesis is invalid."
] |
[
"Thanks! Great answer!"
] |
[
"Energy and matter are the same stuff. Can two quanta of energy occupy the same point in space?"
] |
[
false
] |
[deleted]
|
[
"(not on panel)Firstly there is no particle called 'energy' :) energy is just one of the conserved quantities. (Hmm treated differently in thermal physics, though it seems, should recheck that)",
"Presumably the energy is where the particle is. And wavefunctions(and corresponding probabilities) of particles can readily overlap, so i'd say yes it can occupy the same point.(But don't think saying 'the energy can overlap' is very meaningful) However, if they can take in the same state, the answer is different:",
"Identical bosons can share the same state, whereas ",
"fermions",
" ",
". Forgot how that was, had to look it back up.",
"Reading it again, i can make the following explanation. Since the particles are identical, there has to be a symmetry in swapping the particles, however, the theory of QM doesn't hand one itself.(classically) It gives you two options, either the wavefunctions of the identical particles ",
" be antisymmetric ",
" symmetric. Fermions are antisymmetric, bosons symmetric. An immediate consequence of this is that two fermions cannot be in the same state, because that would be symmetric.",
"Apparently in relativistic QM, you can actually also derive that half-integer spin is fermion and the rest boson. But i don't know how that works."
] |
[
"I'm just going to upvote you instead of making a long winded post, because you capture most of the answer here.",
"A lot of this question depends on how you define \"in the same space.\" If you mean \"what is the probability that I will find ",
" A and B at this location\" then that's the probability of them being in the same state (if position is the only defining property of their state). There are still internal degrees of freedom that define their state though, so you can actually say that two electrons could be found in the same place, but no more. For bosons such as photons, you could in principle find many of them in the same place this way (i.e. there is no limit).",
"As you said, in regular QM you put this behavior in by hand, after reasoning and handwaving about how you cannot in principle meaningfully assign labels to particles and track them through space, but in QFT it comes out as the only way things can work."
] |
[
"Trying to be handwavy enough to not flood with math and yet mathy enough to not be pure handwaving.",
"The statistics of the particles basically comes in QFT from the behavior of the quantum operators which add or subtract particles of a given species and a given momentum from a state they act on. Multiparticle states are basically just a chain of creation operators acting on the vacuum, times some wavefunction. Lets call our creation operators for a given state (call it p, but keep in mind I'm folding spin states in there too) \n a*_p and our annihilation operators a_p.",
"If the fields satisfy one kind of quantization condition, then you find that the operators satisfy:",
" a_p a_p' - a_p' a_p = 0\n a_p a*_p' - a*_p' a_p = {1 if p = p', 0 otherwise}\n a*_p a*_p' - a*_p' a*_p = 0\n",
"Consider what happens in a two particle state",
"\n ψ(p,p') a",
"_p'|0>\nthe third equation tells us we can switch the order of the two operators with no issues, but this is the same as exchanging p with p', so the wave-function ψ must be symmetric under the exchange. Similarly if p=p', things are just dandy, so we can keep adding particles in this same state with no problem. There's nothing special about this being in the momentum basis, but it's easy to work with it.",
"BUT, the funny thing is it turns out this only works with field that transform in certain ways under the Lorentz group. Scalar, Vector and Tensor fields, which we identify in the nonrelativistic case with spin 0, 1 and 2 respectively.",
"If you take a dirac spinor and apply the same quantization conditions, you find that the Hamiltonian is not bounded from below! More particles = lower energy, and the universe blows up. Oops. So instead you must impose a slightly different condition which leads to the operators (lets call them b this time) satisfying: ",
" b_p b_p' + b_p b_p' = 0\n b_p b*_p' + b*_p' b*_p = {1 if p=p', 0 otherwise}\n b*_p b*_p' + b*_p' b*_p = 0\n",
"note that the signs in the middle have flipped! This has consequences for multiparticle states. Consider",
" ψ(p,p') b*_p b*_p' |0>\n",
"equation 3 now implies that if we trade the two creation operators, we pick up a minus sign! Since trading the creation operators is the same as trading p and p', the wavefunction ψ must be antisymmetic. Furthermore if p=p' then equation three implies that the combination of the two operators is minus itself, so it must be zero. Therefore you only get one fermion in any given state.",
"So, the commutation or anticommutation relationships of the creation operators tells you both how many particles can be in a given state (1 or as many as you want) and dictate the symmetry that the wavefunction must have."
] |
[
"Why haven't we been able to develop a HIV vaccine yet?"
] |
[
false
] |
Why do we have vaccines for viruses such as smallpox and the common cold, but yet haven't been able to develop a vaccine for HIV yet?
|
[
"Because the virus is constantly mutating. The envelope protein only has a few conserved regions while the rest - particularly the big loops that come off the surface - are highly variable. Plus, the surface is covered with glycans that shield the surface making it difficult for the immune system to interact with parts of env. ",
"There was a phase 3 trial a few years ago called RV144 but it only had ~30% efficacy. "
] |
[
"Actually there ",
" a really promising treatment currently in development which blocks the interaction of the virus with the human protein which allows it to export virus particles from the human cell. Since the human protein does not mutate, this part of the virus cannot mutate to avoid the interaction and so resistance to this as a treatment should be greatly reduced.",
"It's not a vaccine, but it is a treatment and unfortunately with current medication we are still not able to treat HIV progression nearly as well as we would like to.",
"You can read the actual research here: ",
"http://pubs.acs.org/doi/abs/10.1021/cb800193n",
". The full paper is available online but I will save the host a reddit DDOS."
] |
[
"If the envelope protein is mutating, how come it keeps the parts that stick to the immune system cells? Couldn't a vaccine or serum be made to interact with those parts? "
] |
[
"How does a dog detect low insulin levels?"
] |
[
false
] |
Me and my roommate thought it might have something to do with a change in the composition of your smell or breath but we are not entirely sure
|
[
"I can smell when a diabetic is getting hyperglycemic. It's just a specific scent. ",
"I am sure it's the same for a dog. ",
"I read about an older lady that could smell when a person was getting Parkinson's disease. ",
"Once you recognize a scent you just know when you smell it again. And scent is chemical identification. ",
"You can ",
"read about Joy Milne the Parkinson's sniffer here",
"."
] |
[
"I don't know precisely what the dogs are picking up on, but diabetic people's breath have a distinct smell that humans can notice, too.",
"It's causes by raised levels of ketones in the blood, which comes from the increased breakdown of fat when sugar is unavailable, either due to starvation or diabetes. Intense dieting, especially with a ketogenic diet (hence the name) can also cause it."
] |
[
"It's quite unlikely they smell insuline levels, they probably smell sugar. If your blood glucose goes up your metabolism changes, cells start burning more sugar, your kidneys start flushing out sugar, probably your skin too. So there are a bunch of potential chemical clues there."
] |
[
"I’m a chemist so I should know the answer to this question but I don’t. Why is Technicium a synthetic radioactive while the two elements above it on the periodic table (Manganese and Rhenium) are naturally occurring elements?"
] |
[
false
] | null |
[
"There's no single reason. Out of the ~3000 known nuclides (at least 7000 are predicted to exist), only a lucky few (less than 300) are stable.",
"No element is \"entitled\" to have ",
" stable isotopes (except maybe hydrogen, barring proton decay). Although it turns out that most elements up to and including lead do have at least one. Technetium and promethium are the two exceptions.",
"A nuclide is theoretically unstable if there exists at least one energetically possible decay mode. (Even if this is the case, it could still be \"observationally stable\", if its half-life is so long that we haven't observed it to decay.)",
"But anyway, if you look at all of the isotopes of Tc or Pm, even the ones near the valley of stability, they are unstable to beta decay. What makes the decay energetically possible is the difference in binding energies between the parent and the daughters. The binding of a nucleus is a complicated balance of forces, and it just turns out that every isotope of these elements has an isobar (a nuclide with the same mass number) with a higher binding energy. So in every case, there is a beta decay which is energetically possible."
] |
[
"Now that's a wondrous thought... is there such a thing as a \"Nuclear\" Periodic Table rather than the \"Electronic\" Periodic Table we know and love?",
"After googling a bit, it seems that there is! Or, at least one group has attempted to construct one: ",
"https://link.springer.com/article/10.1007/s10698-020-09365-5",
"That is very neat!"
] |
[
"Couldn't explain this any better.",
"I'd just like to add that for the purposes of nuclear physics / chemistry, comparing an element to the rest of its group on the periodic table (like OP does in the title, comparing Tc to Mn and Re) is misleading.",
"The overall structure of the periodic table comes from the electronic structure of atoms.\nNuclear properties like radioactivity instead come from the structure of the nuclei.\nSince the interactions of electrons and that of protons and neutrons are quite different, the nuclear properties and the chemical/electronic properties of an element don't have to be similar at all."
] |
[
"Shellfish is such a broad term but if you are allergic to it you can't have any at all. So what specifically in shellfish are people allergic to?"
] |
[
false
] |
Shellfish is such a broad term but if you are allergic to it you can't have any at all. So what specifically in shellfish are people allergic to?
|
[
"The main thing in shellfish that causes an allergic reaction in humans is a muscle protein called ",
"tropomyosin",
". It's not necessarily true that if you're allergic to one kind of seafood you're allergic to all of it (or even all shellfish). ",
"Here's a brief summary",
" of the results of a few studies done in 2008 and 2009 that talk about discovering some other seafood proteins (besides tropomyosin) that can cause allergic reactions."
] |
[
"You're welcome! I'm glad I could help restore your \"faith\" in reddit haha"
] |
[
"Awesome, I was afraid I wouldn't get a response. I love reddit for things like this! Thanks so much"
] |
[
"Is storing solar energy under the form of pressure a thing?"
] |
[
false
] |
I was brainstorming ways to store solar energy or do something useful with it while its available. The most practical things seemed air conditioning and cryptocurrency mining. But why not use a compressor/water pump to fill up some tanks, in combination with a valve and turbine, to use that pressure for energy at a later time?
|
[
"the energy density of compressed gas is terrible, on either a volume or weight basis.",
"there are much more compact ways to store energy, such at in a chemical reaction (Batteries) or gravitational field (dam)",
"https://en.m.wikipedia.org/wiki/Energy_density",
"from the table there, 300 bar (full had cylinder) gets you at most 0.5 Mj/kg. hydrogen gas gives you more than 200 times more storage, per unit weight."
] |
[
"Nevertheless it was still tried:",
"Huntorf plant in Germany (290 MW) diabatic. 580 MWh energy, 42% efficiency.[23]",
"McIntosh plant in Alabama, USA (110 MW) diabatic. 2,860 MWh energy, 54% efficiency.[23]"
] |
[
"Kind of a similar concept, ",
"pumped-storage hydroelectricity",
" is a good way to store excess energy from intermittent sources like solar or wind. The idea is pretty simple, you use excess energy to pump water up a storage container. When you close it off, energy is stored as gravitational potential energy. When you need it, you let it flow down and through a turbine like a normal hydroelectric dam."
] |
[
"In DNA tests, how do geneticists determine what a person is ethnically?"
] |
[
false
] |
[deleted]
|
[
"How is it that people vary in size, shapes, colors?",
"There are things known as SNPs (Single nucleotide polymorphisms) which really just are common mutations in the population that cause variation within the population. ",
"tracing origins",
"The distribution of SNPs is used for DNA fingerprinting. SNPs are inherited and you share ~50% with your mother and ~50% with your father. Another common way to look as ancestry is utilizing mitochondrial DNA (inherited maternally) or utilizing the Y chromosome (inherited paternally). Check out the terms mitochondrial Eve and Y-chromosomal Adam if this wasn't enough to clear up how it works.",
"determine ethinicity",
"Simply compare SNPs or sequence of mDNA/Y-chromsome with genomes from different ethinicities and calculate similarities."
] |
[
"This is a thorny issue. There isn't a genetic test that can determine what your race/ethnicity is, although attempts at identifying ",
"gene clusters",
" that correlate to self-reported race and ethnicity have been made. In general each SNP we identify has only a weak correlation if any to what race people identify with, and forming clusters from these SNPs is very method dependent. Y chromosomes and mitochondrial DNA are better at tracing human migrations from the past (since they don't mix between parents) but for race you still only get a correlation, not a clear answer. See ",
"Noah Rosenberg",
" at Stanford for research about clustering, though he focuses on other things too. ",
"Humans are remarkably homogenous genetically, much more so than chimps, our closest relative. So we are looking for subtle differences in the DNA. While we think that appearance is determined genetically, we very rarely can identify what genes correspond to any one feature. Instead we identify genes that correlate. Even ",
"eye color",
" can only be predicted to about 90% accuracy. ",
"If you sign up for 23 and me, you can get information on your genetic origins, but be aware it will not be definitive by any stretch. In my experience they are pretty good about explaining their results to you (if you read the fine print)."
] |
[
"Yep! They send you a kit, you swab your cheek and send it back",
"Environment will also play a role. For example, access to good nutrition tends to increase height. I will try to pick some links for articles on Central American ancestry. My memory of Mexico and the Dominican Republic is that ancestry markers run the gamut from 100% indigenous to 100% Spanish, plus African, and everything in between. I guess we thank colonialism?",
"Good luck!"
] |
[
"technical math question on filtered white noise"
] |
[
false
] |
Hello. This is a very technical question. I hope this is ok. Consider a random process F(t) defined by: F(t) = (f * W) (t) where: f is some filter which we know W is a white noise process '*' is the convolution product Is it possible to calculate the random process F(t + tau) | F(t) = x ? (F(t + tau) knowing the value the random process actually took when it was at time t) Or some sort of covariance leaving from value x ? Feel free to just give me pointers to the theorems with which you can answer this question without too much developpement. I will be able to finish the work. Thank you
|
[
"For a sufficiently narrow bandpass filter, sort of. The amplitude and phase will still be random, but you'll have obviously reduced the variance in frequency to the point where it's fairly predictable.",
"What do you mean by covariance leaving from value x?"
] |
[
"No, it is not possible to predict the outcome of stochastic processes given current conditions. You can sometimes estimate within an interval where the value should lie. ",
"Source"
] |
[
"No, you cannot perfectly calculate the value of a random process at an unobserved time. You should be able to say something about its distribution in this case, which would allow you to predict a value for the process. Kalman filtering may be helpful here."
] |
[
"Can I change a recoring of my voice so it sounds as it does to me when I'm speaking?"
] |
[
false
] |
[deleted]
|
[
"Technically this is absolutely possible!\nYou would basically want to \"EQ\" the recording until it matches what you hear in your own head (using EQ, compression, etc.). This would of course be totally subjective, since you're the only one who really knows how you sound in your own head. ",
"This would be complicated and probably tedious, but technically possible. "
] |
[
"Technically yes. However the microphone will not pick up the vibration in the exact same way that your eardrum will, so you would still end up with tonal differences in the recording. But with the right microphone and the right placement you could probably get close. Would take a lot of trial and error though. "
] |
[
"Technically yes. However the microphone will not pick up the vibration in the exact same way that your eardrum will, so you would still end up with tonal differences in the recording. But with the right microphone and the right placement you could probably get close. Would take a lot of trial and error though. "
] |
[
"When Earth was this warm (and warmer) in the distant past, how did it affect plant and animal life?"
] |
[
false
] |
I continue to hear that it's been X-hundred-thousand years since the last time Earth was this warm. , for example, show that the Earth was about as warm as today ~125k years ago, ~240k years ago, ~325k years ago, and ~410k years ago, and I'm guessing some of you could provide longer-term graphs with older and warmer periods. I also continue to hear that today's temperature variation is causing mass extinctions, which makes me wonder how these past temperature local-maximums affected life. Do we know? What theories and evidence do we have?
|
[
"There is a recent thread that has been posted about this here: ",
"http://www.reddit.com/r/askscience/comments/1dc95m/greenhouse_gas_levels_highest_in_3_million_years/",
"You asked about warmth levels, and because greenhouse gas levels have been positively associated with warmer temperatures, I would like to redirect you to here. There are many questions in there that answer your question as well. (:"
] |
[
"Thanks! That's what made me think to ask this, and I didn't want to hijack the thread since that was focused on the causes and I was looking for effects, but looks like a lot of relevant info has been added since I last looked!"
] |
[
"50 million years ago, during the Eocene, the earth was so warm that the Arctic had a climate similar to the southeastern US. It is thought that the deciduous habit of larches, bald-cypresses, and dawn redwoods originated as an adaptation to the darkness of the polar winter."
] |
[
"How the heck does smart shade makeup (Almay) work?"
] |
[
false
] |
Almay makes a foundation called "smart shade" that is supposed to change to match your skin tone. It comes out of the tube looking white with little black specks in it, but as you rub it into your skin, it turns to a fleshy colour. What kind of sorcery is this? Help me !
|
[
"This actually turned out to be a very interesting question, and I'm glad you asked it (I think I might even write/draw it up on my blog). For all the rest of the men who doesn't know what RainbootRobot is talking about, she's referring to ",
"this",
", and The Internet seems to suggest it actually [works] (within a range of complexion).",
"Some more digging yielded this ",
"patent",
", claiming an \"emulsion makeup compositions for keratinous surfaces which change color upon application\". Taking apart the patent language, I believe this is what's behind SmartShade. This foundation, apparently, is different from other formulations in that the pigments are not dispersed to start with, but instead captured in little droplets of emulsion. (The chemistry there is interesting, but I don't think you need to know that to appreciate the real issue.)",
"The pigments and the carrier solution are not the same polarity: one is hydrophilic, the other hydrophobic. When it's applied next to the skin, the hydrophilic pigments diffuse out from the hydrophobic media, and disperses itsel now on the keratinous surface (skin). And this, straight from the horse's mouth,",
"In the case of a composition applied to skin such as foundation makeup, the development of the color directly on the skin from a non-skin matching color to a skin matching color ",
"In other words, it's all smoke and mirrors -- which is why \"SmartShade\" foundation comes in \"light\", \"light-medium\", and \"medium\" ;)",
" - ...and for a more graphical explanation, this is the writeup in ",
"comic form",
"!"
] |
[
"Wow, thank you! The comic is especially helpful. Oh marketing, the fine art of lying and getting away with it."
] |
[
"Good morning - my pleasure. I had a second look at their marketing stuff, and I think they worked quite hard to make sure it's legal ",
". So it says things like, ",
"The lightweight formula starts out white and adjusts to right\" ",
"in which \"right\" technically could be anything. The most adjustable thing here is the interpretation ;)",
"On that note, the comic's been picked up by a few feminist blogs, and they have some scalding words for the cosmetic industry as a whole - apparently it's a very loosely regulated industry with lots of money at stake, so snake-oil is just about everywhere."
] |
[
"Do dock leaves have a non-placebo effect on stings?"
] |
[
false
] |
I've searched around a bit and haven't found a satisfying answer, so thought I'd ask here. The idea that dock leaves grow near stinging nettles because 'nature provides a cure' or 'where there's a need, evolution will provide' always seemed like baloney to me. But I'd prefer to actually know rather than having an equally-invalid gut reaction. So is there any evidence for rubbing a dock leaf on a sting providing any kind of chemical relief or soothing beyond what we would expect from the placebo effect?
|
[
"A quick google and I came up with ",
"http://skeptics.stackexchange.com/questions/3031/does-rubbing-a-dock-leaf-on-a-sting-from-a-stinging-nettle-help-to-reduce-pain",
" which reports that Dock contains an antihistamine which would easily explain why they work.",
"Another quick google and I can see other reports that this is the case... "
] |
[
"Well, yeah, but those two are pretty much the same thing, wouldn't you say?"
] |
[
"I always understood the reasoning to be that nettle stings were acidic and dock leaves were alkaline (or vice versa). Putting the latter on the former therefore neutralizes it. But a little googling suggests that they are both acidic (or at least most species in the same genus of dock leaves are, and I find no reputable source telling me that dock leaves are an exception). See ",
"here",
" and ",
"here",
".",
"Also, the wikipedia article suggests both baking soda (alkaline) and lemon juice (acidic) as remedies, which challenges the neutralization interpretation.",
"Some interesting speculation that I came across can be found ",
"here",
"."
] |
[
"How does water form bridge? (GIF in decription)"
] |
[
false
] |
Water bridge formed by electric current but how does this phenomenon occur?
|
[
"Short answer: \"the scientific community agrees that surface polarization at the water surface when a high tangent electrical field is applied is responsible for the extraordinary stability of the system.\"\n",
"Source",
" (Wikipedia)",
"Long answer",
" (interesting material!)"
] |
[
"I imagine that it is energetically more favourable for the system to allow the current to flow through the water bridge than for the water to stay put. ",
"In the paper cited by ",
"/u/hyseptik",
", they used a potential difference of 15 kV with a current of 0.5 A. That's a power of 7.5 kW. Now if 10 mL of water rises 1 cm to form the bridge and is held there for 1 second in Earth's gravity, the power required to do that is a mere milliwatt.",
"Hm... those orders of magnitude seem a bit off, but you get what I'm getting at."
] |
[
"Do you think it might be possible to use this property on a large scale for some sort of transportation device? I'm thinking something like the chutes from Bionicle, if you're of that era..."
] |
[
"How does food get carried to every single cell in your body?"
] |
[
false
] |
I'm mainly thinking about how blood vessels can't possibly connect to every single cell in your body. If so, how do remote cells get their food from? (Also just to confirm, the chemical reaction that turns glucose into energy happens inside a cell right?
|
[
"Capillaries do a good job of communicating with tissues throughout your body, but don't come into contact with every cell. A couple of things help out with this. One is ",
"interstitial fluid",
" which bathes cells and contains glucose. Also, some cells communicate with each other through various ports including ",
"gap junctions",
" which allow the cytoplasm of one cell to mix with the cytoplasm of another and support the transport of ATP (energy) from one cell to another.",
"Glycolysis",
" (the breakdown of glucose to pyruvate) happens in the cytosol (watery part of the cell), but the big thing that helps us make lots of energy occurs in the mitochondria and is called the ",
"citric acid cycle",
"."
] |
[
"This answer here. Beat me to typing it."
] |
[
"This isn't exactly my field, but I'm relatively sure that most cells are located within a few cell thicknesses of a ",
"capillary",
"."
] |
[
"Can human or non-human cultural behaviour be coded into genes?"
] |
[
false
] |
J.T. Bonner in "The Evolution of Culture in Animals" defines culture as "the transfer of information by behavioral means, most particularly by the process of teaching and learning. It is used in a sense that contrasts with the transmission of genetic information passed by the direct inheritance of genes from one generation to the next." What I am wondering is that if there is any behavioral trait in humans or non-human animals, which falls under this definition as "culture", but has been passed on from generation to generation under such a long time that it has transformed from a mere cultural behavior into one which is genetically coded? For example, could the migrational pattern of birds have at some point started off as a behavioral pattern where one individual/group of individuals randomly migrated and this information was "culturally" (in Bonner's sense) passed on to the next generation until it eventually became genetically coded?
|
[
"Cultural behavior, strictly speaking is not genetic. However, if it provides an evolutionary advantage, then genes that favor this culture will become more prevalent. I don't see that it couldn't turn those cultural behaviors into instinctual behaviors, but I don't know of an example of that.",
"For instance, Capuchins in Brazil teach eachother to open nuts with tools. Genetically they adapt to be better at tool use, better able to learn from eachother. It's possible that an instinctive genetic instinctual desire to smash round things together would develop could develop in at least some of the population. It's vague enough to be reasonable, it would help with their adaptation to the tool use, and definitely wouldn't hinder their survival and reproduction.",
"Now say some event took place and many or all of the adults died off or were somehow unable to teach. The monkeys that bashed things together instinctually would be the first ones to get back into being able to eat and those genes would dominate the next generation. If an event like this happened periodically at the right time, I could imagine that the process of peeling, drying, breaking the nuts could be encoded genetically. But culture transfers so much easier that I think it's unlikely unless you were to set up a giant experiment to set out specifically to do that. Otherwise the population would work just fine teaching eachother and would benefit more from being better able to learn than instinctually know the entire process.",
"In humans, we see some genetic deviations because of culture. Consider something like lactose tolerance. Animals generally become lactose intolerant after they wean. They don't need to survive on milk, and there might be some energy savings from not producing those enzymes, and it might help to ensure they wean so that the mother can have more babies. But we have agriculture in western Europe for some thousands of years and milk is all of a sudden a good way to turn inedible material into sugars fats and vitamins. People who can make use of this energy are more fecund, and genes that stave off lactose intolerance spread around the population, making lactose intolerance the exception rather than the rule in that population. This is an environmental change (diet) brought about by a cultural change (agriculture and the keeping of livestock for milk)",
"In the end though, culture can affect genetics. But I don't think that the default is for genetics to emulate culture, more to adapt the organism to support an advantageous culture. "
] |
[
"Human Universals is a popular book which studies the universality of human behaviours, based on Donald Brown's research. Certain behaviours (e.g. smiling) were found to have a universal meaning (there were 67 'universals' in total).; though you can probably find an exception to the universals if you look hard enough (we could consider this pathological behaviour). It seems reasonable that at least some of these behaviours (e.g. smiling) can be attributed to genes. Here's a list of the 'universals': ",
"http://en.wikipedia.org/wiki/Human_Universals",
"."
] |
[
"Execellent question. I downvoted everyone because I don't think anyone tried to answer your question. OP is not asking about the definition of culture, nor the genetic basis of human behavior. Instead I think she/he is asking a much more awesome question of could the line between the two be blurred over time. Starting cultural, but then causing a genetic shift.",
"Unfortunately, I don't think anyone in the world has an answer.",
"For humans, we've seen lot of cultural transmissions, but figuring out how they might impact genes has three big challenges: 1) Almost by definition, it involves a research project that spans many, many generations 2) that project wouldn't exactly be PC 3) there are very real and very tricky problems of ",
"causation",
". Correlation is not causation, and there are strong and reasonable ethical concerns about, lets say, intentionally mutating human genes and releasing those mutants into the public.",
"In animal species that pass information culturally, all of the problems are smaller and manageable but I've never heard of a really good effort that would answer your question. If someone knows of one I'd love to know!"
] |
[
"Can you catch 2 strains of covid at the same time?"
] |
[
false
] | null |
[
"Yes. There was a RadioLab podcast 2 weeks ago (",
"COVID Crystal Ball",
") about how an immunocompromised patient had multiple variants and how they could actually track which ones were winning the battle to be the most virulent (not sure if that is the best way to describe). Essentially is was a small microcosm of what is happening on the global stage. Really interesting and scary listening to how the virus was evolving."
] |
[
"Damn. Thats crazy."
] |
[
"maths shows that one contaminated with the covid generates more copies than required to statistically create a mutation. \nbut this new variant will eventually not be able to reproduce again (cell host contamination)"
] |
[
"Could Earth have become tidally locked around the Sun, like the Moon is around Earth?"
] |
[
false
] |
The implications for life on Earth are fascinating if this were to happen.
|
[
"It's not a past thing, it's a future thing. Over long enough time, this is the preferred configuration. The amount of time this would take for the Earth would be much longer than the expected lifetime of the sun. The time for Earth to get locked to the moon is faster, but still over billions and billions of years."
] |
[
"The amount of time this would take for the Earth would be much longer than the expected lifetime of the sun. ",
"Because of the moon, the Earth can never be tidally locked to the sun. Since the moon is so much closer than the sun, its tidal effects are greater and the earth will become tidally locked to the moon. Once that happens, the sun will never be able to change that, unless the moon escapes from earth, first.",
"As the Earth's rotation slows down to become tidally locked to the moon, that angular momentum that it lost goes into the orbital angular momentum of the Earth-moon system, increasing the moon's distance from the Earth. That distance won't ever increase to the point where the tidal gradient from the sun overpower's that from the moon, though. In fact, tidal forces from the sun will slowly rob angular momentum from the Earth-moon system, causing the moon's distance to decrease, which in turn speeds up earth's rotation. The result is that as long as the moon isn't blown to smithereens, the earth can never be tidally locked to anything else. ",
"There is additionally no possible configuration in a 3 body system where one object is simultaneously tidally locked to both of the others. "
] |
[
"Nope! The only possible way for that to happen is for the moon (or whatever the least massive body in the 3-body system is) to be in the L1 Lagrange point, but at that point you can hardly call it a satellite of the earth. The L1 Lagrange point is itself unstable, anyway, but in principle you could have the moon in an approximately stable orbit around it. The system would inevitably fall apart at some point, though, without constant correction.",
"The L4 and L5 points are stable, though, so as long as the 'moon' were very small compared to the planet and star, you could imagine the earth and 'moon' tidally locked to the sun, and therefore also to each other (but not because of their own mutual interaction). But again, an object in a Lagrange point isn't orbiting the Earth anymore, so it's a very different scenario from our own."
] |
[
"What is the origin of Aboriginal Australians?"
] |
[
false
] |
How did homosapiens come to Australia? Were they the same people from Africa? I'm under the impression that homosapiens came from Africa, then went to Europe; it seems hard to accept that they made it all the way to Australia around the same time. I'm reading the prehistory of Australia on wikipedia right now, but it is creating more questions than answers for me.
|
[
"Try ",
"History of Indigenous Australians",
" and discuss the questions which the articles bring up for you in addition to your main interest."
] |
[
"you accidentally put two brackets and broke your link. As a sidenote the ",
"image that illustrates this article",
" is one of the contributions I made to wikipedia I'm most proud of... "
] |
[
"old site with good info"
] |
[
"Why is nuclear decay logarithmic?"
] |
[
false
] | null |
[
"The probability that a particular radioactive atom will decay in any given amount of time does not itself vary with time (so far as we have observed). This means that as a sample of atoms is decaying away, the number that decay in any time span is simply proportional to the number of atoms that are left.",
"Math tells us that if you have a quantity that changes at a rate proportional to itself, the result is an ",
"exponential function",
"."
] |
[
"You mean exponential?",
"Basically it's because if any nucleus has a probability to decay in a given time, if you have two nuclei the probability of a decay is twice as high (could be either one in that time period that goes), and if you have a million it's a million times as high. So you can say that the rate at which decays occur is proportional to the number of decayers. And when an atom decays, it is no longer the same atom: the total number is reduced by one.",
"So you can say \"the derivative of the number of atoms is proportional to the number of atoms\" and if you've studied calculus, you'll know that the only function (besides zero) that fulfills that criteria is the exponential."
] |
[
"The mathematical term for this function is technically \"exponential,\" not \"logarithmic.\"",
"Imagine you have a billion people rolling a hundred-sided die, all in sync with each other. When you roll a 42, you're killed. Roughly 1%, or 10 million, will lose on their first roll. Roughly 1% of those remaining (another 9.9 million) will lose on their second. Because there are fewer people rolling as the rounds progress, fewer people are eliminated each time--they key is that the relative number (1% of those remaining) stays constant, due to the underlying process/mechanism."
] |
[
"Why does water in my toilet rise and fall on a really windy day?"
] |
[
false
] |
Aren't most municipal sewer and water systems completely underground? If that's the case, why would high wind have any affect on the water in my toilet?
|
[
"From ",
"Wikipedia",
":",
"The venting system, or plumbing vents, consists of pipes leading from waste pipes to the outdoors, usually through the roof. Vents provide a means to release sewer gases outside instead of inside the house. Vents also admit oxygen to the waste system to allow aerobic sewage digestion. Vents provide a way to equalize the pressure on both sides of trap, thereby allowing the trap to hold water, which is needed to maintain effectiveness of the trap.",
"So what's happening is that wind blowing past the vent opening causes the pressure to fluctuate, resulting in changes in the water level in the water in the various traps around your home's plumbing system."
] |
[
"Take a look at this toilet cutaway illustration",
" The water sitting in your toilet acts much like the trap farther downstream from it. When the water in the bowl is lower, the parcel of water is free to move up or down the piping behind the bowl without spilling any additional water down the pipe.",
"On a windy day, the air flowing over the peak of your house is traveling faster than that of the air inside. Due to ",
"Bernoulli's principle",
", which states that \"an increase in the speed of the fluid occurs simultaneously with a decrease in pressure\", this will cause the air pressure to fluctuate near the plumbing vent, which is ",
"connected to your toilet's drain system farther downstream",
" (past the traps) and leads down from the roof.",
"The pressure differential will 'suck' the water in bowl partially back up the pipe behind the bowl, where it will recede and rise in an erratic manner (it's actually the air inside the house forcing the water out). This cycle will likely coincide with the frequency of the gusts outside , and make the water in your toilet appear to be possessed. ",
"EDIT: Crap. Looks like everyone responded while I was typing this up. Oh well."
] |
[
"Thanks folks. You can likely tell me and basic plumbing have never met."
] |
[
"The Mars rover found that Martian soil is composed of about 2% water. How significant is this number? What about compared to the Sahara? What else should we expect after finding this water on Mars?"
] |
[
false
] |
[deleted]
|
[
"It means ",
"much-less-than",
" (seriously)."
] |
[
"So most rocks on Earth contain water in them a granite will include a few percent water (3-5 is a good range) and you don't see anyone trying to get water from a stone... So compared to Earth this is not super wet but it is a lot wetter than the moon where it's really dry. ",
"TL/DR: This is a marginally exciting result."
] |
[
"Moon rocks are <<1% water"
] |
[
"Does cracking your windows actually help them from being blown out during a hurricane?"
] |
[
false
] |
If keep a few of my windows cracked during hurricane Sandy will it actually help keep them from shattering? I've thought about this and am really torn between pressure differences acting as force across the area of the closed window vs the wind gust's pressure against the window will make that difference in pressure negligible...
|
[
"Not scientific at all, but somewhat relevant personal experience.",
"I was in a tornado 4 or 5 years ago where water was seeping in sealed emergency exits. I know the pressure is worse in a tornado, but I'm guessing that if you had windows cracked you would have massive amounts of water in your house. Board up your windows."
] |
[
"The best protection you should do is simply cover them in plywood. Sudden large pressure changes are more a tornado thing than with hurricanes."
] |
[
"TL;DR: It's best to board up your windows if you're expecting a hurricane.",
"Mythbusters actually tested something similar (Season 7 Episode 16) with regards to the pressure differential in a house during a Category 2 hurricane. While it should be noted that they weren't testing the windows in particular, said windows remained intact when confronted with just the wind. ",
"The real damage came when they added water and debris to the test. Water, with the windows opened, has the potential to ruin much of the house and belongings held within. Debris will end up breaking windows and allow water in, not to mention damaging anything in its way while inside. The most common, way to protect one's home would be to board up the windows with plywood or tough plastic.",
"The ",
"National Hurricane Center",
" has some more information about hurricane preparedness, though I couldn't find much on protecting one's home."
] |
[
"Why doesn't ice sink in water like most solids, and how rare is that?"
] |
[
false
] |
[deleted]
|
[
"When most things freeze, the reduced activity of the particles reduces their ability to escape the forces that are trying to pull them together and this is why most things shrink and become more dense as they are cooled.",
"As I understand it, water is an exception to this because of the structure of the molecule. Initially water behaves like most other things as it is cooled until a certain temperature (roughly 4C) - after this point the water begins to arrange itself into a different structure because the hydrogen bonds more and more easily than the oxygen as the temperature falls and the resulting structure has a lot of \"space\" in it which causes the water to expand and become less dense. ",
"As with anything mixed together, whichever has less density will float to the top while the denser material sinks to the bottom and that is why ice floats in water."
] |
[
"No, logic! Go away!",
"I was expecting a pun thread from top to bottom. "
] |
[
"Most solids don't sink if they're in the right shape.",
"Just a reminder to phrasing your question carefully. The question is answered by somebody else so I'll just add one thing: it's extremely rare for the solid form of a substance to be less dense than its liquid form."
] |
[
"Male orgasms are much more intense if you masturbate and stop right before ejaculating for a few times before actually doing it. Why does this method work?"
] |
[
false
] |
[deleted]
|
[
"Most nerves use something called cascades (proteins use it too but proteins use hormones instead of cations). The cascade is basically when something small causes large changes and an increasing avalanche effect/chain reaction (this is why you can't stop an orgasm once you hit the vinegar strokes). If the levels hit a certain point, the cascade will be triggered and the final effect can be much stronger than what caused it, but if the event is even one atom off from causing the cascade, nothing will happen. When your penis is stimulated, the molecules responsible for causing the ejaculation/orgasm begin production or transportation to the nerves associated with the action. The closer towards orgasm the nerves get, the higher the concentration of these molecules becomes. If the cascade is not triggered, the molecules won't do anything and continue to build up (arguably the chemical basis for \"blue balls\" though psychological evolution plays its part too). When the orgasm actually happens after being pushed to the edge multiple times, not only are the nerves primed for a strong response, but the molecules that make it happen are in such high concentration that the effect of the orgasm seems multiplied many times over. Also this probably has something to do with desensitization but that's to do more with the relative feeling rather than what causes the differences. "
] |
[
"Also works for women,."
] |
[
"Not that I know what I'm talking about:",
"Why is it that if one is interrupted after a few approaches towards the crest of cascade (I suspect Reddit will produce a \"Cascading\" meme now) is the cascade stumbling and rather poor? ",
"If the hormonal load behind the levee has built up so high, what is it that can muddle an orgasm? Is it simply a matter of psychology where the mind is diverted just as something great happens?",
"So much opportunity for innuendo. Must resist."
] |
[
"Where do all the \"breakthrough\" medicines we hear about go?"
] |
[
false
] |
So often you hear about super intriguing medical breakthroughs that science has discovered. Many things seem like they would completely eliminate a heath problem or an illness, but then years later you still have not seen the results. What happens to all these miracle drugs and surgeries we hear about (like the one or two a week that pop up on reddits front page)? And maybe more specifically the things we see working on lab mice?
|
[
"It has to do with drug development and treatment testing. As you progress through phases, treatments run into snags. What worked great in an animal model loses steam in a human trial. After the open ended human trial, maybe it doesn't separate from standard treatments in randomised trial. Perhaps a side effect is discovered. Unfortunately many drugs die this way. ",
"My pharmacology prof had a great saying. \"bleach kills cancer on a petri dish\". He meant that something might look great in the lab but translate horribly to human physiology. ",
"The truth is, many compounds and treatments look very promising early on but comet out afterwards. Thus is the perils of drug development, and one of the reasons research and development costs are high. When a successful drug or treatment is launched it must recover the costs of all the failed ones. "
] |
[
"Another part of this is that the follow-ups are most often not covered by the popular media - they simply report the discovery. A follow-up look at scientific/medical journals after the development/testing phase will help identify which of these are actually \"breakthrough\" medicines. ",
"For example, a new ",
"class of antibiotic",
" has recently been discovered that has a huge potential - but if could be several years before it hits the market, and then sometimes, this will be under a commercial name. ",
"Follow-up on some search engines to see where the discoveries are now."
] |
[
"Here is a comment I wrote",
" a while back for ",
"/r/explainlikeimfive",
".",
"The short answer is this: is the stage of research reported? It's likely not, or you don't pay too much attention to that. Many of these are very, very early stages of research, and later trials eliminate the vast majority of candidates. Not only that, the many stages of testing take many, many years."
] |
[
"Is bullying evolutionarily related to the idea of humans forming groups (tribes), then ridding themselves of those seen as weak?"
] |
[
false
] | null |
[
"Is bullying evolutionary related to ... ridding themselves of those seen as weak?",
"Not directly, no.",
"Here's an informative article on ",
"The Origins of Bullying",
", which examines bullying across human cultures and across species.",
"One of the core factors in bullying appears to be establishing dominance and maintaining a social order, and so most bullying even among our primate cousins does not result in \"ridding themselves of those seen as weak\", or in killing.",
"However, as the article points out, there are cases where bullying can result in killing. Interestingly, among chimpanzees at least, the victims in these cases aren't necessarily \"weak\" members of the group, but rather those who have violated social norms - sometimes these are strong and fit individuals, and a group will gang up to bully them into conformity.",
"I'm thinking that if a deformed, sickly, unusual, or weak looking baby was born into a group it would be in the best interest of the group to kill the person to keep the others from having to support it, or it being unable to keep up. ",
"Killing babies doesn't really count as bullying. On that subject, the paper ",
"Infant Killing as Evolutionary Strategy: Reality or Myth",
" (PDF) reaches a relevant conclusion:",
"\"Most witnessed cases of infant killing appear to be simply genetically inconsequential epiphenomena of aggressive episodes. At this stage, there is little evidence to suggest that infant killing is anything but a rare and evolutionarily trivial phenomenon. No evidence of genetic inheritance or direct selection for the trait has been provided, just non-quantitative plausibility arguments based on anecdotes.\"",
"The paper goes on to address the weaknesses of these sort of ",
"just so stories",
", a.k.a. ad hoc fallacies:",
"\"Until more specific evidence is available [...] the burden of proof remains, as it always has, with those who favor the sexual selection hypothesis. It is both important and enjoyable to formulate scientific hypotheses, and it is not difficult to fit them into an evolutionary framework. However, this in itself is not science. Good science begins when one collects the relevant data needed to test these hypotheses.\""
] |
[
"Maybe I was too narrow in my line of questions, because the article you posted (excellent, thank you!) seems to agree with my basic idea. ",
"Bullying, it seems is part of our normal behavioral repertoire, it is part of the human condition.",
"...",
"Humans have taken an ancient behavior that used to provide an advantage in survival and reproduction and altered its intensity and impact through language and culture. ",
"...",
"The tendency to bully, or coerce, others is natural and deeply rooted in our evolutionary history, and emerges in any group of toddlers playing freely. ",
"I was probably too specific by focusing on physical differences when social differences would serve the same purpose of creating an outcast. It seems, however, the two are essentially interchangeable. I've seen, and we've all probably heard of, good looking or otherwise fit people having unusual habits or hobbies being bullied, and likewise \"abnormal\" people that followed all of the social norms also being bullied. It seems both are categorically the same.",
"I wasn't implying merely infanticide, just that the differences may be noticed early in life and set them on a path of inevitably being bullied, and that not being killed for those differences may be a product of modern society, morals, and laws rather than the refrain of early man. ",
"The idea being that if children were taught that it was OK, ",
" that it was encouraged, to kill others then we'll see a large percentage of those that are bullied simply killed for it. Since the end result of that action would be a group that is both fit and sexually appealing, it would seem a positive trend that's worth continuing. Along comes an enhanced sense of morality, along with deterrents such as laws and becoming an outcast yourself by killing someone, and we have this hairline balance we see today in schools. "
] |
[
"I wasn't implying merely infanticide",
"No, but a similar principle applies, i.e. the relatively infrequent cases of bullying that result in killing, and the non-lethal outcome of the majority of bullying cases indicate that the killing of unfit members is not the evolutionary \"purpose\" of bullying.",
"the differences may be noticed early in life and set them on a path of inevitably being bullied, and that not being killed for those differences may be a product of modern society, morals, and laws rather than the refrain of early man. ",
"The evidence doesn't seem consistent with the idea that \"not being killed for those differences\" is anything new or unique to humans. The evidence indicates that bullying is designed to establish social dominance and enforce conformance, and being killed as a result is a relatively infrequent outcome. Here's a quote from the article I linked:",
"\"In most cases the bullying-like behaviors experienced by male chimpanzees are temporary and relatively harmless. The most common form of intimidation involves a dominant male puffing himself up, with all of his hair standing on end, and walking toward or by another male. This is usually enough to compel the subordinate, or lower ranking, male to pant grunt (a short “uhh, uhh, uhh” vocalization which is repeated several times and serves to recognize the dominance of another chimpanzee), don a fear grimace and put their hand out in a palm up begging gesture.\"",
"You also write:",
"The idea being that if children were taught that it was OK, not that it was encouraged, to kill others then we'll see a large percentage of those that are bullied simply killed for it. ",
"Again, the evidence from other primates doesn't support this.",
"Since the end result of that action would be a group that is both fit and sexually appealing, it would seem a positive trend that's worth continuing. ",
"The end result of bullying that's actually observed is more social conformance. There are numerous problems with what you're saying: bullying is not primarily about killing unfit members of the group; and bullying is not about killing sexually unappealing members.",
"Here's a good summary from the article:",
"\"In all three instances the males that were killed appeared to have broken social rules or norms, and bullying-like behaviors that erupted into violence were used to attempt to get them to conform. Among chimpanzee, and many other primate societies, proper socialization and conformity are critical for maintaining social order and consistency, just as they are in humans. Individuals whose behavior challenges, disrupts or are considered unusual are often the targets of aggression, and that aggression continues until those individuals change their behavior. Bullying-like behaviors are not only present in many primate species, they are often utilized to accomplish the same goals. Bullying-like behaviors are used to enhance an individual or coalition’s competitive ability, or to coerce others into changing their behavior to conform to the rest of the community. Bullying-like behaviors provide the individuals who engage in them with advantages over their targets, through enhanced status or access to resources, or both. If this sounds familiar, it’s because humans use bullying behaviors to achieve the same ends.\"",
"Back to you:",
"Along comes an enhanced sense of morality, along with deterrents such as laws and becoming an outcast yourself by killing someone, and we have this hairline balance we see today in schools. ",
"It's presumably true that bullying results in a lower incidence of killing amongst humans than other primates, but even in other primates, bullying is not used to cull undesirable members of the population to the extent you're speculating about, and its primary purpose is very different than that."
] |
[
"Why don't I ever experience destructive interference of sound waves from two speakers?"
] |
[
false
] |
I would think that, if I had two speakers on my desk, playing the same sound, the speakers would have a small chance to play the sound back just right so that they interfere and the sound is made quieter. I would assume that the speakers are not playing the sound exactly synchronized all the time, so I would expect to hear (if not often, but at least every now and then) the sound canceling out and being quieter. However, I have never experienced this, so why?
|
[
"Maybe because you don't typically listen pure tones. For complex waves, like songs, or almost any real world audio, there are many frequencies present. And so if some frequencies are occasionally attenuated, you may not really notice.",
"Try it with pure tones. λ = v / f, so for sound typically v = 343 m/s. For a pure \"A\" at 440 Hz, I calculate λ ~ .78 m. ",
"You should be able to set up this experiment with pure tones. Make the distance from your ear to speakers 1 and 2 be d1, d2 and set d1-d2 = λ/2. (This can be done by placing the speakers λ/2 apart and standing so that your position, and that of both speakers are collinear)."
] |
[
"You have two ears. The likelyhood that both would fall in a null point, and that the null point would be stable at those two points (reflections and stuff mess with that), is very low as the wavelength drops. The whole shebang is massively complicated by the rich spectral content of music and the complexity of the room/speaker system. That said, our ears are 1600hz apart, roughly, and you can probably guess 400Hz or lower (4x the distance between your ears) would start making that possibility likely. ",
"And if you play tones through a subwoofer and walk around a room, you'll find that this does indeed happen. Subwoofer positioning makes a ",
" impact on how it sounds in a room. Subs also usually have a phase reversing switch or even an analog phase control in an attempt to manage constructive and destructive interference. Most high end setups use two or more small subwoofers to spread the energy input around the room to try to avoid this, and ",
" good setups ",
" ",
"careful sub positioning",
" and measurement, because poor positioning can ruin low frequency response.",
"It also happens with higher frequencies, but the effects are much more complicated and difficult to hear without training. They show up in ",
"objective measurement",
" though. ",
"EDIT again: ",
"Interestingly, the interaction of multiple sources in the same speaker (IE, tweeter and midrange drivers, as well as the baffle they're mounted to) are a major concern for speaker designers. You could easily mount two drivers in such a way that the listener would hear a massive ",
"hole",
" at the crossover frequency.",
"TL;DR:\nIt ",
" happen. Play some tones, and move your head around while listening really, really carefully. Lower frequencies will be much more obvious."
] |
[
"You can test it thoroughly by setting up a pair of speakers, and then moving around the room a little bit and seeing how the sound gets louder and quieter depending on where you are in the room, provided both speakers are playing the same pure tone."
] |
[
"Does language/culture affect our emotions ? Example : If the English language did not accommodate complex emotional words like \" indignation \" and such , would we still recognize them the way we do now ?"
] |
[
false
] |
[deleted]
|
[
"This is an ancient and complex debate in linguistics, really the best thing is to start at the right ",
"wikipedia article",
" and explore for yourself from there. "
] |
[
"There is little scientific research which suggests that any idea contained in vocabulary cannot be transfered from one language to the next(though it must be said that grammatical differences do effect understanding, though in a slightly different manner, I will attempt to discuss this later). when europe was expanding into the \"third world\" during the 17, 18 and 19 centuries some effort was made to find out about things such as this before the apparently less complex languages became over run. One overiding result was that it was always possible after a certain amount of time to convey extremely complex ideas, differences in comprehension were difficult to find. For your example of indignation even though a corresponding word may not exist in another language that does not mean that the idea of indignation could not be conveyed, the areas where this begins to breakdown is in matters of opinion such as colour(if you have ever been to japan you would notice that their \"green\" for go traffic lights could well be mistaken for blue in western society). now grammaticaly it can be odd those who speak fluent mandarin for instance would note that the context of any given tense can be very different to those of latinate languages(european born). For instance if i were to say \"i went to dinner\" in English it would be odd for me not to also convey the time or with whom I went to dinner with, wheras( I believe) in mandarin it would not be out of place for this sentence to stand alone. There are other examples which exlpain similar discrepancies though I can't think of them off the top of my head. I hope this helps, struggling a little with a french keyboard and a broken wrist i apologise if it is difficul to read."
] |
[
"Here's an interesting article from NYTimes last year, quite thorough too."
] |
[
"If a bullet were traveling at 100mph"
] |
[
false
] |
This is all hypothetical, but, if a bullet were traveling at 100mph ad you were traveling at 99 mph away from the bullet and you have some distance between you, say 50ft. Would the bullet hurt you when it finally came in contact with you? Or would it just poke you and be slowed down by the speed you are going? I know this seems stupid but its just something me and my friends came up with last night.
|
[
"This is the fundamental concept behind on-orbit spacecraft rendezvous",
"Dissenters PWNED. Awesome."
] |
[
"I agree. Questions like this aren't stupid and often spawn really amazing answers and side topics. "
] |
[
"I agree. Questions like this aren't stupid and often spawn really amazing answers and side topics. "
] |
[
"Tsunamis and submarines?"
] |
[
false
] |
[deleted]
|
[
"same thing as the boat. The wave will pass with little notice. Tsunamis aren't really anything until the energy starts to mash up against land masses. Out in the open ocean there is nothing like that. "
] |
[
"I haven't downvoted you, and I am not disagreeing with your physics. The similarity in perception is between a tsunami hitting a beach and a rogue wave hitting a ship: a single event that makes an otherwise normal ocean dangerous and remarkable."
] |
[
"can't really agree with you that a rogue wave is similar to a tsunami though. ",
"a tsunami is a deep water, long period wave while a rogue wave is typically a confluence of ocean swells which combine to be more substantial than the other swells. "
] |
[
"How does a modern smartphone antenna work? Why don't we anymore need the long antennas from the 90's?"
] |
[
false
] | null |
[
"A few things happened. First, signal processing got a LOT cheaper, which means that you can work with an extremely weak signal using inexpensive IC's (something that only NASA used to do for interstellar space probes is done routinely on your phone today.) Second, new signaling formats were adopted that take advantage of this enhanced signal processing capability on your phone processor (i.e. 3G, 4G, etc.) Finally, there have been ongoing incremental improvements that can squeeze more signal from a relatively small antenna (for example fractal antennae.)",
"Edit: unfortunately, I think it's also true that phone today suck a bit more than they did in the 90s in terms of reception. "
] |
[
"Edit: unfortunately, I think it's also true that phone today suck a bit more than they did in the 90s in terms of reception.",
"Interestingly, this is not at all related to the antenna, but rather population density. Network bandwidth is actually channel speed times channel capacity. Channel capacity is limited by the tech the phones use (4G is 4G, a faster tower doesn't make the phone talk at faster than 4G speeds). The number of channels can be somewhat increased with advanced towers (I believe three channels using directional antennas on each tower is pretty normal, more advanced towers will probably increase this in the future). To get more channels the solution is to add more towers. To add more towers the range of every tower needs to be reduced. This is done by decreasing the power level of the towers and the phones communicating with them to prevent towers from interfering.",
"The result is that in the 90s nobody used cell phones, so one tower could cover many square miles of land using a high power, this one tower had the bandwidth to support everyone in it's coverage area, this high power and low tower count meant that there were actually very few bad reception areas, phone could adjust to significantly reduced signals.",
"Today everyone and their mother uses cell phones, in areas like cities, cell phone towers are installed every couple blocks, these towers operate near the lowest possible transmission power, and just a small reduction in signal will kill it completely. Additionally, in areas with very high population densities, this may still be too many people for the tower to support (you can easily get a few thousand users per block in cities). They end up installing towers in these areas with ranges of a couple of floors, the corner of your building might actually be a dead zone (because they don't want that tower interfering with the tower across the street). With these towers you can end up with dead spots measured in feet and multiple dead spots per block which can't be fixed because they can't get the rights to install the tower on the optimal floor. Older high power towers had larger dead spots that were easier to manage and fix."
] |
[
"Modern phones use sheet antennas. There's a sheet of copper in your smartphone for your wifi antenna and a separate sheet for your mobile data antenna.",
"As for why, modern phones are expected to send/receive a lot more data, and as a general rule (with a large number of complications and exceptions) you can accurately receive weaker transmissions more clearly with less energy spent on amplification by using a larger antenna.",
"Update: okay, so while validating the now deleted comment to this I checked, and iphones use some distinctly non-sheet antennas: The iPhone series all seem to use case antennas like ",
"this",
". ",
"As opposed to sheet antennas like ",
"this laptop wifi antenna",
", or android antennas like ",
"this.",
", which is what I'd call typical of android and blackberry phones. It probably spends its life glued to the inside of the phone case."
] |
[
"If electric currents make magnetic fields, and electrons in atoms are constantly moving, why isn't everything magnetic?"
] |
[
false
] | null |
[
"Every single atom has a magnetic moment. In materials however the direction of this magnetic moment is (generally) randomly distributed, resulting in no net magnetic moment of the material.",
"Magnetic materials can realign their atoms giving a uniform magnetic moment in the same direction."
] |
[
"Yes. By raising the temperature of the magnet to the ",
"Curie temperature",
". You could also do it by waiting a very very long time."
] |
[
"Ferromagnetic is like your fridge magnets, ",
"https://en.wikipedia.org/wiki/Ferromagnetism",
"The intrinsic magnetism of the metal atoms are \"lined up\" to form a large coherent magnetic field."
] |
[
"Why do electrical transformers give off a blue color when they arc/explode?"
] |
[
false
] |
The video from ESPN last night showing the transformer explosion and subsequent power outage at Candlestick Park got me thinking. I asked everyone at work, and no one has a good answer... any help?
|
[
"Blue is the color that our atmosphere glows when ionized; it's mostly nitrogen. Other gasses will glow different colors, which is why neon signs glow red."
] |
[
"Ah. Safe to assume ozone is formed during this ionization?",
"Thanks for the answer, I appreciate it. "
] |
[
"Sure. Oxygen glows pink."
] |
[
"Why does cancer occur so often now?"
] |
[
false
] |
It seems like twenty years ago I rarely heard of it, and the further back in history the least likely-hood people died from it. I know technology plays a role, but why does it happen so much these days. Also, what killed so many people before the presence of cancer was so common?
|
[
"Cancer is a disease of old age. Cancer is formed when a cell in the body undergoes a series of ~4-7 mutations, successively breaking cellular machinery designed to keep the cells from replicating out of control. Since each mutation even has a very small chance of happening, the chance of these mutations accumulating becomes higher the older you are.",
"Before antibiotics and modern medicine, people tended to die of infectious disease. As we got better at curing these, we began to see more deaths due to diseases of old age and a sedentary lifestyle - heart disease and cancer. So, somewhat paradoxically, any advances in medicine which cause people to live longer will increase the rates of cancer.",
"Your timeline is a little off... 20 years ago we were in the midst of one of the largest public awareness campaigns (War on Cancer). The past 20 years has actually seen a decrease in mortality in almost all non-lung cancers. But you are correct in spirit - if we go back 100 years or more, cancer is much less common.",
"Lots more info here"
] |
[
"Lots of times, juvenile cancer can be traced to a congenital mutation in an oncogene. ",
"Retinoblastoma",
" is the classic example. But it sounds like you are well aware of this.",
"You can glean a little more insight if you look at ",
" cancers are more prevalent in young people. Across all ages, the most common cancers are in the skin, lungs, breast, and prostate. In adolescents, the most common cancers are in the blood and brain.",
"One hypothesis for this goes back to evolution. I apologize in advance for not using the correct terminology here - evolution isn't my thing. Our immune system and brain is one of the more recent \"advances,\" so to speak. And in general, tumor suppression mechanisms across the animal kingdom have evolved to perform very well up until the age that a species stops being reproductively viable. The exception, of course, is brain and blood cancers in adolescent humans.",
"So the hypothesis is this:",
"-our immune system and brain gives us a large evolutionary advantage",
"\n-the selection pressures that would improve the cancer defenses are dwarfed by selection pressures related to the actual function of these systems",
"You can read this paper",
" for more info on evolutionary hypotheses behind cancer"
] |
[
"Less common or less detected? Medicine has a come a long way in a very short time."
] |
[
"How does testosterone decrease fat body mass?"
] |
[
false
] |
I was looking at a and I couldn't really pick apart WHY the fat is lost.
|
[
"According to ",
"some",
" ",
"reading",
" I've done, testosterone does not significantly decrease the total fat mass of your body. Rather, it increases ",
" in the form of lean muscle tissue. This can, in and of itself, decrease total fat content simply because ",
"muscle cells are metabolically active",
". However, if you have a citation for at least a few studies stating that testosterone directly leads to fat loss, please share them."
] |
[
"Your statement was",
"I have never heard of that. I have, however, heard that test increases muscle gain, so your body fat percentage goes down as you mentioned. I suspect, this is the info OP has gotten slightly wrong.",
"My statement was",
"According to some reading I've done, testosterone does not significantly decrease the total fat mass of your body. Rather, it increases fat-free mass in the form of lean muscle tissue",
"I don't see how those statements differ, aside from the particular choice of words used.",
"Test changes the behaviour of the indicidual to a more competitive state, I believe, and this could lead to higher efforts, which would burn fat.",
"In the studies I cite above (the links in \"some\" and \"reading\") the exercise frequency and intensity of participants was controlled for, and therefore behavioural changes were not a factor. As well, unless citations are provided, this comment appears to involve speculation, which is discouraged on ",
"/r/askscience",
". It does sound like an interesting suggestion, but does require some citation. Alternatively, you can post such suggestions on ",
"/r/asksciencediscussion",
" to get some feedback from the Reddit science community."
] |
[
"That clarifies your comments a bit more, thanks. And I apologize if I offended you. The wording of your statement made it appear as though you were offering some sort of correction in the first line \"I have never heard of that.\" although I can see where the disconnect in interpretations may have stemmed from."
] |
[
"What is the physics behind the wave-like motion of this bridge before it collapses? Also, what were the engineering mistakes?"
] |
[
false
] |
[x-posted to ]
|
[
"False!",
"It's a widely spread myth, but the collapse was ",
" caused by resonance. In order to create resonance, it would need to receive a periodic force, as you described it. But the wind was approximately constant. The collapse was apparently caused by ",
"aeroelastic flutter",
" which, I have to admit, I don't completely understand."
] |
[
"False!",
"It's a widely spread myth, but the collapse was ",
" caused by resonance. In order to create resonance, it would need to receive a periodic force, as you described it. But the wind was approximately constant. The collapse was apparently caused by ",
"aeroelastic flutter",
" which, I have to admit, I don't completely understand."
] |
[
"As ",
"/u/TarMil",
" pointed out, it was due to aeroelastic flutter. Basically, the further the bridge had been pushed by the wind, the easier it was for the wind to push it. This lead to larger and larger vibrations."
] |
[
"How could that 16-year old have possibly survived stowing away in the wheel-well of a that 35,000 ft altitude California to Hawaii flight? 5 hours of no pressurization, no heat, low oxygen; how did he not die?"
] |
[
false
] | null |
[
"Perhaps the landing gear area is mostly airtight, keeping the air inside pressurized to some degree. Another idea is that the kid simply passed out shortly after takeoff and re-awoke after landing--he stayed in a state of half-hypoxia during the flight and got enough oxygen because he was asleep/low bodily requirements."
] |
[
"Perhaps the landing gear area is mostly airtight, keeping the air inside pressurized to some degree. Another idea is that the kid simply passed out shortly after takeoff and re-awoke after landing--he stayed in a state of half-hypoxia during the flight and got enough oxygen because he was asleep/low bodily requirements."
] |
[
"The BBC article",
" explains that he was, indeed, unconscious during most of the flight."
] |
[
"Thin strings of smoke near atomic explosion. What is it?"
] |
[
false
] |
Hey I was watching a video about atomic bombs and I noticed that next to a few of these atomic bomb explosions there were about 10 thin strings of smoke. Like right in the beginning of this video: Are these strings put there to watch how the blast wave moves or is there an other reason? Thanks
|
[
"The smoke pillars are in roughly equal distance to each other. That means they are probably placed there on purpose and not an incidental by-product. My guess is that they are used to determine a) the pressure wave and/or b) the wind direction to estimate the fallout (area,density)."
] |
[
"Henkersjunge is correct: Taken from: ",
"http://www.atomcentral.com/atomic-smoke-trails.aspx",
"In order to study the velocity of the shockwave front, rocket trails were located perpendicular to the line of site and the shockwave was photographed as it passed in front of these trails. The progress of the shockwave was then followed by observing the \"hooks\" in the rocket trails at the shock front. These hooks are due to the change in the index of refraction of the air at the shock front.",
"The rockets were fired at 85 degree angles radially away from their respective photostations in order that the trails would appear as straight lines on the recording films.",
"Other methods of recording the shockwave effect included \"jatos\" and morter puffs. The Jetos were smoke generators located along a line 500 ft from the blast line and parallel to it. These were timed so as to set up a column of smoke before arrival of the shock wave.",
"The mortar puffs were essencially a type of commercial fireworks, sometimes known as aerial salutes, the only change being that the yellowish smoke burst was replaced by a white smoke for better visibility. "
] |
[
"They are smoke trails left by rockets that are set off just before (a second or two before) the explosion. The point is as you surmise, to see the blast wave move through the air. ",
"In ",
"this video",
", even though the feed is grainy, you can distinctly see them being launched right as the countdown nears its finish (2:15)."
] |
[
"Assuming no water or insect damage, at what age will the kiln-dried pine wood making up my roof trusses become brittle and unable to support itself?"
] |
[
false
] |
I don't really know what happens to wood that is dried and protected from moisture, that is what I am asking I guess. How long before wood is unusable as wood just because of time alone? Imagine this: we build a concrete waterproof room that is temp and humidity controlled for all eternity. We put a pine kiln-dried 2x6 across the middle of the room, half-way up. The room is sealed forever. How long before the board breaks and falls?
|
[
"This Buddhist temple in Japan has wood from about 1500 years ago, \n",
"http://en.wikipedia.org/wiki/H%C5%8Dry%C5%AB-ji",
"It is thought to be one of the world's oldest wood buildings. So, at least 1500 years.",
"If the wood is kept in a controlled humidity and temperature and pest free, I can't imagine what will destroy it."
] |
[
"Wood is mostly cellulose fiber and Lignin, right? They're both stable biopolymers, and I expect they'll last essentially forever in the absence of chemical attack. ",
"Wood will tend to get a lot stiffer over the first couple of years as it loses water, but that slows down asymptotically. There are wooden articles that are thousands of years old from the pyramids in Egypt that seem to be in totally fine condition.",
"This site",
" is selling wood up to 50,000 years old. It was \"preserved\" by being buried, so I'm thinking a controlled environment would preserve wood for a good while longer than that.",
"Another data point: The Schöningen Spears are ~400,000 years old, and still intact. I couldn't find any references to how strong they are after that time, but from the pictures, they don't seem to be in very good condition."
] |
[
"Haha oldest post I've ever replied to. No idea what link got me here. This comment was very thought-provoking. I started reading your wood comment thinking you were being a smart ass, but noticed it was in posted to science so I figured I'd give the comments a chance.",
"This comment made me think of something interesting: as we humans have advanced, more and more of the items we make are fit for ever-longer preservation. Earlier humans: stone tools, bits of flint and a freak piece of wood here or there that got preserved in unusual conditions. Mid-humans, 6000 years ago: Fertile Crescent civilizations, copper age-bronze age transition, metal tools, detailed clay pots. Last 100 years: Styrofoam, millions of plastic forms, all the modern science equipment and materials. And the population producing them has exploded.",
"Looking back will look like a tsunami wave of artifacts - small at first but as it nears it surges upward into a mountain of debris. "
] |
[
"Do you think Synthetic Humans should be given human rights?"
] |
[
false
] | null |
[
"Speculative questions are better suited for ",
"/r/asksciencediscussion",
"."
] |
[
"Ok, thanks"
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"/r/AskScienceDiscussion",
"Please see our ",
"guidelines.",
"If you disagree with this decision, please send a message to the moderators."
] |
[
"Are we--and all multicellular life--just giant biological synergies between our cells?"
] |
[
false
] |
I mean, there isn't really anything that makes our cells any more special than bacteria, as far as I'm aware. Is it possible that complex life just originated from a few cells suddenly finding out that it is easier to reproduce when attached to different cells? Edit: not even sure that synergy is the exact phrase I'm looking for, just couldn't be bothered to search for the right one.
|
[
"I mean, there isn't really anything that makes our cells any more special than bacteria",
"Our cells actually differ a LOT from bacterial cells in important ways.",
"Our cells are able to communicate with each other through a variety of specific and functionally distinct pathways that do not exist in bacteria (e.g. Notch-Delta, Hedgehog, canonical and noncanonical Wnt, TGF-beta, etc). This allows animal cells to talk to each other, and to set up local and spatial differences in cell identity, which then allows animals to produce different tissues in different places.",
"Our cells are capable of communicating at a distance, both by releasing diffusible proteins and by physical extensions. This means that our cells can produce macroscopic patterns, which then allows us to have tissue types and organs.",
"Our cells are capable of setting up and maintaining long-term changes in how the DNA code is read, which then allows us to have permanent cell fates. This is why a muscle cell can stay a muscle cell for a long period of time, instead of suddenly changing to a nerve cell or a fat cell depending on highly variable local factors. Without that sort of permanence or semipermanence, you simply cannot grow a body and expect it to keep its shape.",
"Our cells are able to connect to each other in ways that bacterial cells just cannot, such as tight junctions and via basement membranes. This allows our cells to come together to produce structures that are capable of bending and folding to create complex shapes, and to hold their shape under force. This is critical if you want to create complex organ systems (where cell folding is important in setting up different parts of the system) and if you want your organism to maintain tissue integrity (i.e. not fall apart under the slightest movement). ",
"Our cells are capable of short-term changes in state that do not affect long-term cell identity. This allows cells to do things like generate action potentials, which is the basis of our nervous system, muscle function, and so on. Without that, animals would be unable to coordinate cell behaviors in order to accomplish organism-scale behaviors.",
"In other words, yes, animal cells are very different from bacterial cells."
] |
[
"No problem!",
"The cellular-to-multicellular transition is pretty poorly understood, so it's reasonable to be kind of confused about it. Especially if you're just trying to approach it from a conceptual/evolutionary perspective, and unfortunately the organisms we have at the base of Metazoa are all pretty weird and don't really exhibit any sort of coherent evolutionary trend, so a lot of this is pretty speculative. We know that metazoans evolved bit by bit, but how these different key components of metazoan development and cell biology evolved is obscured by the lack of diverse early-branching metazoans. We've got ctenophores, we've got sponges, we've got placozoans, and we've got jellyfish.....and that's it. But sponges and placozoans may be secondarily simplified, and ctenophores are surprisingly complex in ways that differ from all other animals, so we don't really know what the earliest ancestor of all modern animals even looked like.",
"And on the other hand, many single-celled organisms are more complex than meets the eye, with specialized cytoplasms in certain parts of the cell, with localized cytoskeletons and localized membrane structures (e.g. primary cilia), even multiple nuclei with specialized transcriptional environments. So all these components of cell specialization are already present in many unicellular organisms....within a single cell. Some of these cells also take on specific cell fates for extended periods of time within the organism's life cycle, so they have the transcriptional machinery to change from one cell type to another.",
"So there are pieces there in some single-celled organisms, but how you go from that to an animal isn't entirely clear. But it is still credible."
] |
[
"Multicellularity evolved multiple times independently (e.g. animals, plants, and fungi). And there's even some cases where previously multicellular organisms became unicellular again (bakers yeast). There are a lot of advantages to communal living, from there cells start to specialize because that increases efficiency (some cells can turn off genes and processes provided by other cells), and then eventually cells become dependent on others for basic survival and reproduction and then you have a multicellular organism. There are actually some primitive multicellular bacteria, but the complexity is very limited (probably because of lack of mitochondria, but that's another topic)."
] |
[
"Why is escape velocity so high?"
] |
[
false
] |
Why is the escape velocity for earth 11.2 km/s? Can someone explain why it needs to be such a high speed? Why can't a vehicle just travel at a steady 1 km/h until is out of reach of the planet's gravity?
|
[
"It can, it would just need to be thrusting the whole time. Escape velocity is the speed you need to escape without adding any more energy - just coasting. That is why escape velocity depends on altitude - the higher up you are, the less speed you need to go the rest of the way."
] |
[
"Earth's radius is 6,371 km. The benefits of launching from a few extra kilometers higher up are far outweighted by the logistical effort required to transport rocket parts up to the mountains. ",
"What does help though, is launching from near the equator, due to Earth's spin. Launching over the sea also prevents collateral damage if the rocket falfunctions and comes crashing back down. ",
"And here's a \"fun\" fact about Israel's rocket launches:",
"Due to Israel's geographic location and hostile relations with surrounding countries, launches take off due west, over the Mediterranean Sea. This is done in order to avoid flying over hostile territories. This is also to prevent possible debris from falling above populated areas. This limitation imposes a penalty of roughly 30% on its lifting capabilities.",
"Israeli satelites orbit the Earth in the opposite direction compared to other satelites!"
] |
[
"It could. But you’d need to continually apply that acceleration. ",
"Once you reach escape velocity you no longer need to apply any force. You can essentially hit neutral and coast the rest of the way and the earth can’t stop you. "
] |
[
"How is the right amino acid brought to ribosomes?"
] |
[
false
] |
So what I know is that the mRNA is brought to the ribosome with a code for an amino acid. I also know that the tRNA with a matching codon and correct amino acid are brought to the ribosome for assembly. But how is the right amino known? Does the ribosome read the mRNA and call for a tRNA or do the tRNA keep trying to fit the codon in the ribosome till it fits then goes and brings the amino acid. Thanks i have a test on this is a couple of hours.
|
[
"But how is the right amino known?",
"Put simply, it doesn't 'know'. All the amino acids are attached to tRNAs and they all diffuse around until they meet a ribosome that requires that particular one, as determined by the codon of the mRNA. It can't \"call for it\" it just waits for it. "
] |
[
"All the amino acids are attached to tRNAs",
"This is the key part.",
"While I do not know the exact mechanism, hopefully someone can expand on the following I do know: There are specific enzymes, at least one for reach amino acid, that bind the correct amino acid to the correct tRNA. It also has to do with the structure of the tRNA (and IIRC, the specific anticodon sequence), recognized by the enzyme, so that it 'knows' which tRNA it is dealing with and thus which amino acid needs to be attached at the top. ",
"As for the tRNA transfer to ribosomes, that happens somewhat randomly. Or perfectly random through diffusion only. As for building in the correct ones: incorrect ones simply don't get build in. If the anticodon of the tRNA does not match the codon of the mRNA, binding of the amino acid to the protein chain does not occur, and the tRNA leaves the ribosome to make space for another tRNA. "
] |
[
"This animation",
" shows the process of translation nice and simply and ",
"this one",
" shows DNA > protein in more detail. ",
"They're not included in those videos, but ",
"Aminoacyl tRNA synthetases",
" are the enzymes that transfer amino acids onto the tRNA. "
] |
[
"How did different species evolve to have different numbers of chromosomes?"
] |
[
false
] |
Even different species of apes have different numbers of chromosomes. Since they are presumably descended from a common ancestor at some point, doesn't this mean that there have been multiple instances of breeding between two animals with different numbers of chromosomes that was successful? My understanding is that if the chromosomes don't match up, the offspring will be sterile, mentally handicapped, or both.
|
[
"All great apes apart from man have 24 pairs of chromosomes. There is therefore a hypothesis that the common ancestor of all great apes had 24 pairs of chromosomes and that the fusion of two of the ancestor's chromosomes created chromosome 2 in humans. The evidence for this hypothesis is very strong.",
"The Evidence",
"Evidence for fusing of two ancestral chromosomes to create human chromosome 2 and where there has been no fusion in other Great Apes is:",
"1) The analogous chromosomes (2p and 2q) in the non-human great apes can be shown, when laid end to end, to create an identical banding structure to the human chromosome 2.",
"2) The remains of the sequence that the chromosome has on its ends (the telomere) is found in the middle of human chromosome 2 where the ancestral chromosomes fused.",
"3) the detail of this region (pre-telomeric sequence, telomeric sequence, reversed telomeric sequence, pre-telomeric sequence) is exactly what we would expect from a fusion.",
"4) this telomeric region is exactly where one would expect to find it if a fusion had occurred in the middle of human chromosome 2.",
"5) the centromere of human chromosome 2 lines up with the chimp chromosome 2p chromosomal centromere.",
"6) At the place where we would expect it on the human chromosome we find the remnants of the chimp 2q centromere.",
"Not only is this strong evidence for a fusion event, but it is also strong evidence for common ancestry; in fact, it is hard to explain by any other mechanism.",
"I dare you to ask a christian that question."
] |
[
"\"a creationist that question\"",
"FTFY"
] |
[
"Chromosomes can separate or fuse into new chromosomes, such as in the case of our own ",
"chromosome 2",
". "
] |
[
"In view of recent reports of thylacines possibly being caught on tape in Southern Victoria, what kind of follow up would normally be carried out to authenticate such potential sightings."
] |
[
false
] |
And any relevant comments on the hypothetical possibility that thylacines might perhaps not yet be extinct, what would come next should their actual existance be confirmed, and other related subjects are welcome of course. see:
|
[
"Nothing, really. ",
"According to ",
"Tasmania Parks & Wildlife",
", there have been hundreds of reported sightings of thylacines since the last known individual died in a zoo in the 30s, but no proof beyond unclear videos and hearsay. This new video isn't even the first thylacine \"sighting\" ",
"this month",
". There have also been several search expeditions over the past several decades, none of which found any evidence of living individuals.",
"With hundreds of anecdotal reports and several professional searches, the fact that we don't have any confirmed tracks, droppings, DNA, carcasses, or even good pictures, is really the best 'evidence' that these animals aren't out there. One more long-distance grainy video isn't really enough to get scientists in gear, especially since that animal looks a whole lot more like an injured ",
"mangy fox",
" than a ",
"thylacine",
", and that video was taken on the mainland where thylacines are thought to have been extinct for 2,000 years. ",
"If we DID get conclusive information - good images, DNA, or a dead thylacine - then I would think the local wildlife organizations would mobilize. They would need to identify as best they could where the animals were, how many there were, what habitats they were frequenting, and what they were eating. From there, we could start making plans for how to protect their habitats. ",
"They would almost certainly consider capturing one or more to test for genetic diversity or to establish a captive breeding program - which would probably be necessary if their population is small, which is likely considering they've evaded detection for a century. ",
"If their genetic diversity is too low, it may be a struggle to save them. Unlike rhinos or peregrine falcons, the thylacine doesn't have any close relatives who could lend some genetic support through cross-breeding. "
] |
[
"To be considered conclusive you'd ideally need a dead or live animal, although DNA evidence ",
" be considered conclusive if it was substantial enough (eg. if droppings of thylacines started showing up). I don't really think any amount of video evidence could truly be considered conclusive, especially how easy it would be to fake. And even leaving that aside most videos are kind of inconclusive, eg, the one linked could be a mangy fox with an injured leg."
] |
[
"I'd add a simple anatomy observation. In the longer video the length of the rear feet clearly rules out it being a thylacine. The thylacine has a very short rear foot. ",
"google images",
"In the video at this point",
" (1:30) you can clearly see that this animal has exceptionally long feet, very much like a fox."
] |
[
"Is there a way to speed up the process of radioactive decay?"
] |
[
false
] |
I'm curious if there is any method that we have to speed up the rate of decay in radioactive materials? For example, a radioactive material that normally has a half life of 1000 years and making that half life shorter.
|
[
"You can make it happen on demand by hitting it with a moderately zippy neutron or other high-energy particle. If you use the high-energy particles from fission to force other fissions then you have invented the concept of a nuclear reactor - or a bomb if you did it all at once.",
"Arguably smashing the nucleus instead of letting it decay naturally is cheating and not really changing the half-life, but it is a way to get rid of radioactive materials before their time."
] |
[
"If we knew of such a way, then all of our efforts at Radio Carbon Dating to learn about the past would have to be called into question. The fact is, the most accurate clocks in the world use radioactive decay as a standard by which to measure time itself. I would be very surprised to hear if anybody anywhere had found a way around that."
] |
[
"Correct, save for the atomic clock bit. A cesium clock uses the vibration of electrons to count time, they are not dependent on radioactivity. Decay through the weak force is statistical in nature, so you can't use that to measure fine time intervals. Over long time scales, that statistical average is pretty darn accurate though. You could \"slow\" decay down if you were to put the sample in something traveling near light speed. Take home point: in a rest frame, radioactive decay time is always going to be the same."
] |
[
"Is it possible to take dead wood, and soak it with calcium mixture to make it slowly become bone as wood decays and bone slowly grows into the shape of the wood?"
] |
[
false
] |
Is this possible? Even if not, i'd like to learn the mechanics of those systems, so any explanation would be great and well-appreciated
|
[
"...well what do you know.",
"Popular article: \"Turning wood into bones\" ",
"http://news.bbc.co.uk/2/hi/europe/8446637.stm",
"Journal article: \"From wood to bone: multi-step process to convert wood hierarchical structures into biomimetic hydroxyapatite scaffolds for bone tissue engineering\" ",
"http://pubs.rsc.org/en/Content/ArticleLanding/2009/JM/B900333A",
" ",
"http://www.lebsc.it/wp-content/uploads/2011/02/7_Tampieri_J-Mat-Chem.pdf"
] |
[
"Something tells me OP didn't tell us everything..."
] |
[
"Can someone explain the chemistry behind this?"
] |
[
"Why is it that there can be water vapor in the air when it's cooler than its boiling point?"
] |
[
false
] |
When the air is below 100 degrees Celsius, how can there still be gaseous water mixed in?
|
[
"Because ",
"vapor pressure",
"."
] |
[
"It's because water has a finite vapour pressure even below the boiling point.",
"Microscopically, some water molecules in the liquid state shuffling around at the interface just randomly gain enough energy to leave the surface and go into the gas phase."
] |
[
"Sorry to reply to such an old thread, but I'm trying to figure this out without asking it as a new post.",
"Could you say that the boiling point of ",
" water is less than 100C (based on the pressure or whatever around it?). ",
"I've been searching for an answer to this that I can understand, and I think the problem a lot of people are having is that different people define these words differently. In school, I learned that boiling point = temperature that liquid becomes gas. I'm starting to think that it's not quite that simple :)"
] |
[
"Am I wrong? Should I go back in my textbook or not?"
] |
[
false
] | null |
[
"There's plenty of tests and experiments that have been done that show significant change in the genetic make up of a population, done both ",
"artificially",
" and ",
"naturally",
". ",
"Those links just scratch the surface on a huge field of research showing that the evidence for evolution is extremely extremely strong. ",
"So yeah, I'd say you were wrong. "
] |
[
"The best synonym for theory in this context is \"framework.\" The framework of evolution.",
"If somebody is deriving the behaviour of particles in a two dimensional universe, are they working on a theory or not?"
] |
[
"Yes, it's wrong. Every sound experiment has a null hypothesis and is tested to a certain level of statistical significance. Because you can't prove a positive, you define it as a negative and prove that wrong.",
"If you were trying to breed MRSA in a lab, your null hypothesis would be \"the culture does not gain resistance to methicillin\", and the significance level would be a certain percent change in cell deaths when exposed to methicillin. The experiment would then try to prove the null hypothesis wrong.",
"So in trying to prove whether there is evolution occurring over several generations your null hypothesis would be \"there is no change in DNA makeup of a population in response to outside pressures\" and there would be a significance level specifically defined. This null hypothesis has been proven wrong, repeatedly. Ryguy offered two great examples."
] |
[
"Theoretically, how small can a microchip be fabricated?"
] |
[
false
] |
I keep hearing of new CPUs going from 65nm to 45nm. Is there a limit on how small we can make them?
|
[
"When you hear 45nm or 22nm or 14nm (which is the latest Intel technology, planned to be released sometime in the next two years), they are referring to the gate length of the minimum sized transistor in the chip. The ",
"L in this picture",
"\n refers to this length. In reality, the technology node (say, 14nm) does not directly correspond to the physical gate length of the transistor, but it has been close enough for a long time now. ",
"However, the fact that the gate length is getting smaller is having a smaller and smaller effect on the performance of these transistors. ",
"This",
" is what the latest Intel transistors look like. Making the gate surround the channel like that helped improve transistor performance way more than actually reducing the length, because it curbs the so-called short-channel effects. ",
"Anyway, this is the top of the line transistor for logic applications in the world. Making it smaller is extremely hard. Intel projects that 10nm is the last node and after that the short channel effects dominate the current flow too much and the gate actually loses control over the channel. Essentially this means that the transistor doesn't act like a voltage-controlled switch anymore. However, this is not the only topology to make transistors. Look up Single Electron transistors that use Quantum Dots to achieve transistor action, which can be scaled down to dimensions like 5nm diameter. ",
"Btw, microchips themselves have been around the same size from each generation, as making the chip itself bigger increases chance of faults and reduces yield, plus it's really hard to cool bigger chips. The size is around 250mm",
" for Intel processors."
] |
[
"There is ",
"talk",
" of single atom transistors.",
"However, the current trend in economics seems to make this unlikely. As ",
"/u/lookatmetype",
" said, it is unlikely large scale silicon fabs will progress beyond 10 nm."
] |
[
"I worked in molecular computing research briefly (although we were developing materials for data storage); there is definitely funding for the research side.",
"How viable manufacturing is is a different question; in our research all the theoretically viable target molecules we found were near impossible to synthesise and I imagine that issue exists elsewhere, too."
] |
[
"What happens to black holes at the heat death of the universe?"
] |
[
false
] | null |
[
"After a very very long time they would radiate away in the form of Hawking radiation."
] |
[
"According to what we know about quantum gravity, once the CMB's temperature becomes lower than Hawking radiation's because of cosmic expansion, they would slowly start to lose mass by said radiation, until they eventually evaporate completely. The time for a stellar mass black hole to evaporate would be of the order of 10",
" years."
] |
[
"Does the virtual particles needed for hawking radiation still appear when entropy gets lower?"
] |
[
"Can different species ever evolve into the same one?"
] |
[
false
] |
For example, if large populations of the were transferred to a habitat where there was only one constant source of food (theoretically), would any two of these species evolve into the same species because of the parallel habitat and way of life?
|
[
"A quick search of the literature turns up ",
"this example",
" of the three-spined stickleback, a Canadian fish. In this case, two species of fish which were closely related to each other but inhabited different depths of a particular lake combined to form a single population with greater genetic variation.",
"Note that the authors of this study believe that this was possible because the two species were, until relatively recently in their genetic history, a single species. Thus they had never really lost the ability to interbreed. They had just stopped mating with each other due to this depth separation and so had become two genetically distinct populations. There is no reason to believe this would be impossible for other recently diverged species such as finches with different beaks.",
"Because of issues such as gene-placement and exact chromosome count, which do not appear to face strong selective pressures in any environment but which prevent the development of viable offspring in mating between members of two significantly diverged species, it is unlikely that two species which are very different now could converge to form a single species in the future no matter how alike in phenotype (physical form and behavior) they became."
] |
[
"Adaptations would be the same but it is unlikely that they would be able to successfully mate."
] |
[
"Convergent evolution is where separate species evolve into very similar forms. They can't interbreed, but the whole organism, or certain parts, will look nearly the same."
] |
[
"Is radioactive decay temperature-dependent?"
] |
[
false
] |
Does the rate of radioactive decay for an isotope vary with temperature? For example uranium-235 has a half-life of 703.8 million years, but would cooling to absolute zero (or very close to absolute zero) have a significant influence of the rate of decay?
|
[
"Typically is not, the nucleus is so much smaller than the atom that it doesn't \"care\" what's happening around it (imagine a marble at the center of one of those giant human hamster balls). There are maybe a few small exceptions. ",
"One could argue that the electron-capture mechanism (sometimes called inverse beta decay) depends on the probability of the electron being found in the nucleus, which depends on the lattice arrangement which depends on temperature. The difficulty with testing this is that the functioning of particle detectors for measuring decay also depends on temperature. There were a few studies purporting to find temperature dependence, ",
"but a more precise study",
" did not.",
"There's also the phenomenon that a superheated gas might have atoms that experience time dilation and appear to have slower decay rate. It's not feasible to make a gas that hot with current technology, but slower decay rates of nuclei have been observed in a particle accelerator."
] |
[
"Low temperature doesn't freeze time... Two stationary things (wrt eachother) experience the same time."
] |
[
"I'm having a hard time discerning where I feel this explanation is wrong because all of that is sound thermodynamics.",
"I would like to discuss time dilation further however in the sense that cooling to absolute zero would in essence freeze the atom in perpetuity to an outside observer.",
"Given that, the lowest state of the system would appear frozen and I am not sure how this system could break the fundamental law of thermodynamics.",
"However, given that energy must be input into the system to observe the system itself I feel that the quantum mechanics are above my current understanding as to how that would impart enough energy into the system to behave the same at 1K as 99999999k.",
"Interesting for sure.",
"Any thoughts on how decay would be intrinsically tied to observation on the quantum mechanics level?"
] |
[
"Has the change from plastic to paper straws had any quantifiable impact on the environment?"
] |
[
false
] | null |
[
"Plastic straws and stirrers are ",
"estimated to comprise 1.9% of marine litter",
", a small fraction of the ",
"50% of manufactured plastics which are disposed of after single-use, leading to 150 million tons of annual plastic waste worldwide",
". Marine litter is ",
"eaten by creatures such as the Lysan Albatross",
", though those pictures appear to show mainly bottle tops in the dead birds it seems likely something will eventually eat plastic straws and be damaged by them."
] |
[
"2% is a lot. I always thought it was much less. Gonna focus on my straw choices now!"
] |
[
"It bothers me thar I still get a single use plastic topper lid with my paper straw. I don't care about the straw either way, and given the choice I'll just drink like a normal cup without a lid/straw. But it seems... off to be just replacing straws and not lids as well. Though it's probably harder to come up with a single use non plastic lid.",
"And with covid my ability to use a reusable mug when getting a coffee on the go is gone as well. I'm okay with them not wanting to touch my mug, it makes sense. I just stopped going for coffee I guess."
] |
[
"is the nuclear fallout from japan going to cause health problems in the USA?"
] |
[
false
] |
[deleted]
|
[
"In short, no.",
"http://www.reddit.com/r/askscience/comments/sqdjk/would_the_collapse_of_the_fukushima_reactor/c4g4f3g"
] |
[
"There is no \"fallout\". This is more indicative of nuclear explosions. Radioactive exposure-wise, no. Not even close."
] |
[
"Thanks for the link! =P"
] |
[
"Why is vision grainy at night or in dark areas?"
] |
[
false
] |
At night time why does human vision appear grainy?
|
[
"Because your central vision (where you have color perception) is high resolution (higher density of light-sensing cells) but low-sensitivity (requires more light to detect) whereas your peripheral vision is low resolution and high sensitivity (and so works better in low light than color vision).",
"From an evolutionary perspective, because the color of the bear that is going to kill you is irrelevant, whereas the color of the fruit you are about to eat is important."
] |
[
"That's true but you explained it poorly. The center of your vision falls on the part of the retina called the fovea where a lot of the cones are. The rods are more present outside of the fovea. So at night whenever you look at something, anything you are directly looking at you're going to have a harder time seeing than if you look at it from slightly off centre due to the fovea basically becoming a blind spot in low light situations"
] |
[
"Also natural night time light is biased towards the blue end of the spectrum because of Rayleigh scattering. Because of this night vision is more reliant on blue cones which are ",
"sparsely populated compared to red or green cones",
"."
] |
[
"Could a black hole ever be harvested?"
] |
[
false
] | null |
[
"The stuff inside the event horizon could never be brought outside of the event horizon."
] |
[
"Qv ",
"Penrose process",
"."
] |
[
"With that being said; black holes evaporate via hawking radiation so you could harvest that.",
"Large black holes evaporate much slower then smaller black holes.",
"That being said, my reasoning is that since small black holes would be relatively safe, when I say small I mean artificially small black holes, of a few hundred tons.",
"Would converting 230 tons of mass into a black hole produce a 100% mass to energy conversation? If we could collapse that 230 tons, it's lifetime equals 1 second via black hole calculator i'm using and would that not be a perfect conversation of mass to energy?",
"I'd make a huge giant sphere filled with salt, in the middle we convert 230 tons into a black hole, the resulting emitting energy would be vaporize a lot of the salt, melt the rest. Highly pressurized salt, heat energy used for electricity generation.",
"Plausible?",
"On second thought... If a black hole converted it's 230 tons of mass into energy via hawking radiation within 1 second, wouldn't that essentially be a bomb?",
"http://xaonon.dyndns.org/hawking/"
] |
[
"When does your body start to break down muscle instead of fat?"
] |
[
false
] |
yep
|
[
"There is always a muscle turnover rate. Meaning your body is constantly breaking down and rebuilding new muscle. Its breaking down somewhere around 500 grams of protein a day, give or take a couple hundred grams. Its also synthesizing new muscle every day about the same rate as the breakdown. Now the change in size depends on balance. Protein breakdown > synthesis means catabolism. The opposite means anabolism. Dieting and not enough protein will increase breakdown. Now if you train, it increases both breakdown and synthesis. But the turnover is a net positive, meaning add some amino acids to your diet and the synthesis is more than the breakdown. Now during a caloric deficit, it is taxing on your body both hormonally and energy wise. So its much harder to build muscle, you can only hope to maintain. You lose body fat on a diet because your body is eating less than what it takes to maintain your bodily functions, basically tapping into your fat reserves to fuel your life. ",
"tl;dr Your body is ALWAYS breaking down muscle and fat."
] |
[
"WRONG!"
] |
[
"ok Thanks cause all the bodybuilding stuff I read make it seem like you need to constantly workout and get protein supplements otherwise your body will just randomly start breaking down protein cause it requires the most energy to maintain"
] |
[
"Why don't horses lie down very often? How can they sleep while standing?"
] |
[
false
] |
I have never seen a horse lie down and in a recent Reddit discussion many people said it is not common for horses to lie down.
|
[
"Being able to go from sleeping to instantly running is probably a pretty good evolutionary advantage."
] |
[
"Horses can sleep standing up because they have a specific ",
"\"stay apparatus\"",
" in their limbs. Basically, it allows horses to transfer the load of the body from muscles (which use energy and are relatively unstable relative to tendons or bone) to connective tissue structures or bone. This eliminates the requirement for the horse to use muscle tone to keep the limb steady and hold up the front of the body. ",
"This",
" gives links to explanations of all the parts of the stay apparatus."
] |
[
"Thanks! That explains the standing up part but are there any other animals that sleep while standing, or lie down less often?",
"Also is there any evolutionary (or any other kind of) advantage of such behavior?"
] |
[
"Do any animals other than humans like spicy food?"
] |
[
false
] | null |
[
"Spiciness, caused by the chemical Capsaicin, appears to be an adaptation of plants to prevent mammals from eating their fruit/peppers. Birds, which are immune to Capsaicin, appear to be the intended consumer of these fruits, which is understandible considering they fly and can, thusly, disperse the seeds over a wider area.",
"As to why some humans have developed a fondness for Capsaicin, there's some evidence that Capsaicin inhibits bacterial growth and, in this way, helps preserve freshness in food. Spicy food is less likely to make you sick than non-spicy food due to this quality."
] |
[
"Askscience downvotes anecdotes."
] |
[
"Capsaicin is actually also an ",
"analgesic",
" for birds, so not only are they unable to taste the spiciness capsaicin actually is a pain reliever."
] |
[
"From a quantum mechanical standpoint what happens to random physical objects when unobserved?"
] |
[
false
] |
Let's say I have sealed off my bedroom from any outside interference (no radio waves, etc.). I leave my room and turn off the light so there is absolutely no observation/photon involvment. Every object in my bedroom is has become in the scientific sense of the word, "unobserved." If such a controlled environment could exist what exactly would be going on inside my bedroom? Would the physical objects in the room still exist in the same sense as I think of them existing or would they be taking on an additional form as well as existing in the sense I know? Second part: Let's say I enter the room and turn the light off behind me. No photon bombardment of any sort. Would my mere presence be considered an observation? I guess what I'm wondering is this: Could I somehow experience the dual nature of subatomic particles or is that inherently impossible?
|
[
"Firstly, it would be impossible to seal yourself of like that at a macroscopic level. You still have thermal blackbody radiation being emitted from everything in your room. As well as thermal and acoustic vibrations being transmitted through the objects and the air.",
"Secondly, observation refers to more than just sight/light. It refers to any measurement of a system. So any interaction with your environment would count, as well as the interaction of the environment with any of your other senses. If you are experiencing the room in any way, that is an observation (in this context).",
"If you want to see the effects of quantum mechanics, that is much easier. Just set up one of many standard experiments, like the double-slit experiment."
] |
[
"The objects in your room will probably stay the same with 99.99999999% probability.",
"Yes, there is always a slight probability that electrons, protons, and neutrons will appear in locations that are energetically unfavorable, but those probabilities are exceedingly rare. Ground-state electrons won't leave atoms very often. Atomic nuclei won't decay or fuse together very often. Particles won't tunnel into places you wouldn't expect; at least not on a massive scale.",
"As a general rule of thumb, you don't have to consider quantum mechanical effects in systems larger than a \"De Broglie wavelength\", which is about 150 nanometers for the typical electron."
] |
[
"It's how the math works out. Essentially, it boils down to Planck's constant.",
"If Planck's constant were much, much higher, then we would see quantum effect in the real world.",
"If Planck's constant were much much lower, then we wouldn't experience quantum effects at all."
] |
[
"Is there any significant advantage for computer applications to be in 64-bit compared to being in 32-bit?"
] |
[
false
] | null |
[
"There are some, although the list is fairly short.",
"Firstly, 64-bit processors provide 64-bit addressing, allowing for access to a ",
" of memory -- vastly more memory than is practical to actually have on a physical machine. Using a flat 64-bit memory model",
" a 64-bit computer can a) store an address pointer in a single register, and b) address up to 2",
" bytes (16 exabytes) of memory.",
"This has certain additional advantages; an issue faced with 32-bit Windows is that applications could generally only access 3GB of RAM, as Windows uses 1GB of virtual memory addressing space in each process for the operating system kernel. As a flat 32-bit address can only address 4GB of total RAM, removing this 1GB per process only left 3GB available to the application",
" With a 64-bit address space this isn't a concern -- nobody has 16 exabytes of RAM",
" and so the kernel can inhabit a portion of virtual memory that simply can't exist on a real PC, giving a single process access to all available RAM on a system. A 64-bit processor can access all this memory with high efficiency, as your can LOAD an address pointer into a register in a single clock cycle.",
"Secondly, a 64-bit processor is more efficient at math with a large number of significant digits. A 64-bit number is capable of describing 2",
" times more values than a 32-bit number. When working in 32-bit mode, an unsigned integer greater than ~4.29 billion (or greater/less than roughly +/- 2.15 billion for a signed integer) will require multiple LOAD/STORE and clock cycles to complete, whereas a 64-bit processor can complete the calculation in a single clock (as the entire value can reside in a single 64-bit register). This can come up in certain scientific computing scenarios using very large numbers requiring high precision, and provide a performance boost by requiring fewer register LOADs, fewer registers (leaving them free for other values), and fewer instructions to perform the calculation.",
"Lastly, while not directly a benefit of being 64-bit, some families of CPU (like 64-bit processors from AMD and Intel) are faster owing to having a lot more general purpose registers than their 32-bit counterparts. This is less a property of being 64-bit itself than the move to 64-bit allowing for a new standard for number of general-purpose registers. So as to maintain a high level of compatibility with pre-compiled software it is usually considered very challenging to add registers to an existing CPU design; but as the move to 64-bit required applications to be recompiled anyway, it gave AMD (and later Intel) the opportunity to remedy the low number of general purpose registers in their 32-bit processors",
" Having more general purpose registers allows compilers to make better decisions as to what to load into registers and how long those values can stay in the registers -- with a low number available, you typically have to spend a lot more time shuffling values between registers and cache/RAM in order to do computations, reducing efficiency. But again -- this was mostly purely because it was an advantageous time for more registers to be introduced, rather than some natural property of 64-bit processors. A brand-new, non-compatible 32-bit processor could just as easily be designed with more registers",
" -- it's easy to forget that there are also non-flat (",
"segmented",
") memory models; in some processors (such as Intel processors) use of segmented memory requires the use of two registers to hold an address making this memory system much less efficient, requiring two LOADs per address.",
"\n",
" -- in reality, the MMU on your CPU/motherboard is going to have a much lower limit as to how much physical memory it can address.",
"\n",
" -- note that this doesn't mean that Windows in its entirety could only use 3GB of physical RAM -- the other 1GB would be virtually mapped to other processes that need it.",
"\n",
" -- just as a guide, 16 exabytes of RAM is the equivalent of over 67 ",
" 16GB RAM sticks!!!",
"\n",
" -- you can potentially design a CPU that uses higher-bit addressing than it can process; Intel CPUs running in Real mode do this to provide access of up to 1MB of RAM using a 20-bit segmented address, even though the original \"real mode\" CPUs were only 16-bit. However, you lost some processing efficiency as you needed to load two 16-bit values into two 16-bit registers",
" using an extra clock cycle for a second LOAD and reducing the number of general-purpose registers available to your program by one. Physical Address Extensions (PAE) on some 32 and 64-bit Intel processors can allow up to 64GB of RAM by using a somewhat similar segmented addressing system (albeit with more bits).",
"\n",
" -- so you noticed 16 + 16 != 20. Intel CPUs running in real mode take the 16-bit segment and shift it left by four bits, and then physically add (as in via binary addition) the 16-bit offset to it, giving a 20-bit address. As a side effect to this, there are 2",
" different ways to address each byte in the system.",
"\n",
" -- the 80386 had only 8 general purpose registers (although some of them had fixed uses in certain contexts). x86_64 boosted this to 16 general purpose registers.",
"\n",
" -- which is exactly what happened for the PowerPC architecture, which featured 32 general purpose registers in their 32-bit G4 CPU. "
] |
[
"True, but the size of the floating point registers does not necessarily match the size of the integer registers. Intel's 32-bit processors and even their 16-bit processors with a math coprocessor could do 64-bit and 80-bit floating point math. "
] |
[
"Excellent response, thank you."
] |
[
"What are some issues that quantum field theory and general relativity have that make it so they don’t match?"
] |
[
false
] |
[deleted]
|
[
"There are a few issues the two theories have.",
"For one, they predict that different things should happen inside a black hole. Relativity suggests that the curvature of spacetime should be so extreme inside a black hole that all matter will end up in an infinitely dense point, called the singularity. Quantum mechanics says that this is impossible, because the Heisenberg Uncertainty Principle tells us we can't know both the location and momentum of a particle with precision.",
"Relativity describes the behavior of gravity as a curving of spacetime. Quantum mechanics barely acknowledges the existence of gravity at all...and when it does, it suggests that gravity should have a quantum field and a massless force-carrying particle called the graviton (which is virtually impossible to detect due to the insane energy levels required).",
"Relativity suggests that things falling into black holes can never escape. Quantum mechanics suggests that black holes will eventually evaporate via Hawking Radiation over unfathomably long timescales."
] |
[
"General relativity is a classical theory which ignores quantum mechanics. Yet it describes gravity being sourced from matter and energy which we know is described by quantum mechanics, so we expect that GR needs to be made quantum mechanical. In particular, since matter can be in some superposition, it doesn't seem to make much sense to keep GR as it is - we seem to need a quantum version of GR which allows superpositions of gravitational fields.",
"There has been some interesting work on quantum gravity, and intriguingly, it seems to correspondingly show that quantum field theory will not be able to describe it at all energies. While ",
"/u/humanino",
" is correct that the effective quantum field theory description is fine at low-energies, at high energies we expect gravity to involve black holes, and we do have some good hints that the physics of black holes have a certain amount of non-locality which is inconsistent with quantum field theory. This is incapsulated in the ",
"holographic principle",
", suggesting that a full quantum gravity theory is described by a quantum field theory (or more generally, some quantum theory without gravity) which exists in a lower dimensionality than the quantum gravity theory itself. This is still not entirely understood, but there are some pretty amazing and beautiful examples of this explicitly popping out of certain toy theories.",
"So there are likely aspects of both GR and QFT which will need alteration for quantum gravity."
] |
[
"What does this mean tho??",
"Simply put: we have 2 theories that, under known circumstances, agree very well with experiment. In very particular regimes these theories fundamentally disagree with each other and produce wildly different results. ",
"does it mean that one of the theories is wrong??",
"Scientists don't look at their theories in terms of being \"right\" or \"wrong\". We tend to ask ",
" the theories are useful - under what circumstances do our theories produce answers that concur with experiments. None of our theories perfectly describe nature in all regimes and Physicists (begrudgingly) understand the limitations of our theories. "
] |
[
"Why Do Certain Chemicals Cause Different Individuals To Experience Similar Complex Thoughts/Hallucinations? Where Is The Information Coming From?"
] |
[
false
] | null |
[
"There might be confirmation bias going on here, just because \"many report\" is not necessarily indicative of the expereinces of most users. My own experience with DMT was like a kaleidoscope with no other \"entities\".",
"All brains are wired differently but pretty much all of them use the same chemical schematics to do the job, so shared expereinces can come from that. A chemical change that causes one person to perceive an unknown entity may cause the same effect in another, or it may not. ",
"Keep in mind with altered states of conciousness it be difficult to perceive what is influencing you, one person may say \"I'm bring eaten by butterflies!\" And cause the rest to manifest the same hallucination. "
] |
[
"Schizophrenics provide some interesting insight into the topic, ",
"EASE",
" and ",
"EAWE",
" provide a really thorough list of common experiences and for some it's pretty easy to see how the delusions can come about to rationalize simpler more understandable experiences. For example I knew a schizophrenic person who was convinced everyone but him had telepathy and all of his \"evidence\" was simply that everyone seemed to know how each other were feeling when he didn't, but it was obvious they were just reading affect/facial expression/body language and he was completely unable to. "
] |
[
"Schizophrenics provide some interesting insight into the topic, ",
"EASE",
" and ",
"EAWE",
" provide a really thorough list of common experiences and for some it's pretty easy to see how the delusions can come about to rationalize simpler more understandable experiences. For example I knew a schizophrenic person who was convinced everyone but him had telepathy and all of his \"evidence\" was simply that everyone seemed to know how each other were feeling when he didn't, but it was obvious they were just reading affect/facial expression/body language and he was completely unable to. "
] |
[
"What is actually happening when I see a 'shooting star'?"
] |
[
false
] | null |
[
"Just a clarification: The heat's not really from the drag force, it's mostly from compression forces of the rocks being supersonic."
] |
[
"Just a clarification: The heat's not really from the drag force, it's mostly from compression forces of the rocks being supersonic."
] |
[
"You are seeing a rock burn up in the atmosphere as it falls down towards the ground. Most rocks will disintegrate into dust as they fall and never actually reach the ground. The rocks are moving up to 50 miles per second, so as it stars to hit the air, the air heats up and burns the rock.",
"Many rocks come from the kuiper belt. It's the area beyond pluto where tons of tiny rocks, dust and more dwarf planets are. As they are nudged and run into each other, some fall out of orbit and into the middle part of solar system, running into earth."
] |
[
"Is it possible to give a planet without an active core a magnetic field?"
] |
[
false
] |
I'm mostly thinking of Mars, inspired by a top post in this sub about compass use on the planet. I know the reason Mars is barren is it's lack of a protective magnetosphere, but could the planets core be jump started or an artificial field be developed? Obviously both require vast amounts energy but let's pretend such energy is available for said purposes.
|
[
"I don't really know where the research is now but NASA talked about the feasibility of placing a magnetic field-generating satellite at the Mars-L1 Lagrange Point to shield Mars from the solar winds as seen in the diagram: ",
"https://3c1703fe8d.site.internapcdn.net/newman/csz/news/800/2017/1-nasaproposes.jpg",
"https://m.phys.org/news/2017-03-nasa-magnetic-shield-mars-atmosphere.html"
] |
[
"Wouldn't want to upset the belters though"
] |
[
"Wouldn't want to upset the belters though"
] |
[
"Please forgive my ignorance."
] |
[
false
] |
I'm going to use made up numbers and hope I still make sense. This question has been bugging me for weeks now. If I am on a spaceship traveling for 10 years at 99.9% the speed of light - I will have aged 10 years while someone on earth will have aged 500 years <please remember: made up numbers> So, if I were to get in my spaceship, and travel to a solar system 5 light years away (and back) -- (please exclude acceleration) -- I'd age 10 years, but to anybody back on earth I'd take 500 years. The solar system is 5 light years away (round trip 10) I'm traveling essentially the speed of light there and back. If I'm travelling 99.9% the speed of light why does it take me 500 years to reach my destination? Or alternatively If (travelling 99.9% SOL) it takes 10 years round trip from an Earth-relative position to make the trip - - - -- How quick is the trip for me aboard the spaceship? How fast did I travel? Again, please please excise my complete ignorance. Ignore me if I'm asking a dumb question. Kind regards, DAL82
|
[
"Or alternatively If (travelling 99.9% SOL) it takes 10 years round trip from an Earth-relative position to make the trip -- How quick is the trip for me aboard the spaceship?",
"This is correct. If you travelled at near light speed 5 light years and back, on Earth 10 years would have passed. The trip for you would be much shorter than 10 years."
] |
[
"Length contraction would make it appear to be much less than 10 light-years to you."
] |
[
"Great, I can visualize that.",
"But what I can't visualize is what MY speed would be. ",
"I'd manage to travel 10 light years in far less than 10 years. ",
"EDIT: Thanks for your quick reply. :)"
] |
[
"At what rate is heat lost in a vacuum."
] |
[
false
] |
How quickly will an object radiate it's heat in a vacuum and how does this compare to loss of heat in a atmosphere?
|
[
"5.67 * 10",
" joules of energy every second per square meter of exposed surface times the temperature of the object raised to the fourth power. It is less than in the atmosphere because of the loss of conduction to air."
] |
[
"That number assuming a blackbody radiator?"
] |
[
"Yes."
] |
[
"How far could Baumgartner travel if he wore a winged suit during free fall."
] |
[
false
] | null |
[
"You can't just multiply like that because gliding requires air resistance, which was notably absent for a good part of the stratojump."
] |
[
"Yes, in a first-order approximation you can.",
"You get less lift (i.e. you fall faster) but you also need less force to move horizontally. Both because of the lower air density. All that changes is the absolute glide speed. You will (once you're up to that) follow roughly the same trajectory as in denser air, just faster.",
"It's a bit counterintuitive, but that's how it is. The effect of air density cancels out. The glide ratio stays (roughly) the same."
] |
[
"Wikipedia says:",
"On 31 July 2003 an Austrian, Felix Baumgartner, jumping from 29,360 ft (9 km), successfully crossed the English Channel in 14 minutes using a wingpack, having covered over 35 km (21.8 mi).",
"That would mean he had a glide ratio of 35/9 = 3.9",
"For his Stratojump the distance would be 39km * 3.9 = ",
"Edit: You have to take into consideration, that the glide ratio is not constant for all altitudes.",
"Edit 2: Quote from SaliciaKeyz ",
"A wingpack and a winged suit are two completely different things.",
"This is correct, according to Wikipedia the glide ratio would be 2.5, the distance therefore about "
] |
[
"What deadly viruses could we feasibly eradicate in the future - which ones will probably always be around?"
] |
[
false
] | null |
[
"Polio has once been wide-spread, now it's limited to two countries and could get eradicated in the near future: ",
"https://en.wikipedia.org/wiki/Poliomyelitis_eradication",
"Not a deadly virus, but dracunculiasis might be close to eradication: ",
"https://en.wikipedia.org/wiki/Eradication_of_dracunculiasis",
"More potential candidates: ",
"https://en.wikipedia.org/wiki/Category:Infectious_diseases_with_eradication_efforts"
] |
[
"Theoretically speaking, any virus that only infect humans have the potential to be eradicated. Viruses that can also live in animal hosts cannot be eradicated by current technology. Even if you vaccinated the whole human race, any subsequent generations born afterward can still get infected through animals."
] |
[
"I think HIV is a candidate for future eradication if medication is made available to all who need it. With treatment, Viral load can be brought down to such low levels that a HIV positive individual could (not should) have unprotected sex and not pass the virus on. ",
"It’s also worth noting that HIV is much less deadly these days with proper treatment, however it’s still a very serious virus.",
"here’s a short article on the subject "
] |
[
"How can I weigh more in the evening than in the morning without eating or drinking?"
] |
[
false
] | null |
[
"That's got to be scale error. Normally people continuously lose mass due to respiration (because for every O2 you breathe in, CO2 leaves, and there's also some loss if water vapor. Perhaps your scale's readings vary slightly with ambient temperature? "
] |
[
"I thought it was scale error also. I also know that my bathroom is 70 degrees plus or minus 1 degree. I check the temperature both times. I also accounted for scale error by weighing in ten times each time and averaging them out. "
] |
[
"Mysterious! But it's got to be the scale somehow... I teach physiology, and humans who aren't ingesting or excreting anything always lose weight, detectably, every hour. We even do a lab on it. Unless you're photosynthesizing I don't see how it can be real.",
"It may just be that you've had one of those statistical flukes - they do happen now and then. Keep at the data collection and see if you repeat it. "
] |
[
"Why don't trees freeze and fracture? Or do they?"
] |
[
false
] |
How does a tree stay warm? Or does it?
|
[
"The short answer is that they can: ",
"http://en.wikipedia.org/wiki/Exploding_tree",
"However, they typically don't for several reasons. First of all, under certain conditions, water can remain liquid at temperatures below what would normally be considered its freezing temperature. This is known as ",
"supercooling",
" and is usually what happens with the water in trees' vascular tissues. Second of all, even when they do freeze, they're still unlikely to fracture because wood is a relatively soft material that, in most cases, will be able to absorb the resulting stresses without breaking."
] |
[
"Vascular system works on capillary action, trees don't have hearts.",
"True.",
"So the water in these vessels are only a few molecules across...",
"False. They're unfathomably wider than that.",
"It's due to a lack of ",
"nucleation sites",
"."
] |
[
"Trees can freeze and fracture! In fact, I saw one that had done so in the crazy midwest cold that struck last week. Super cold temperatures can overcome the following three mechanisms I've explained below.",
"Trees and other cold-tolerant plants do a couple neat tricks to avoid having all there cells explode in the cold. The first thing plants begin doing is altering their cell membranes to remove water out into spaces between cells. You could consider this a dehydrating step. Less water to freeze inside the cells that could lead to cellular damage. ",
"The second way trees can prevent freezing is to produce a sort of \"anti-freeze\" within it's cells. It does this by increasing sugar concentrations, which lowers the freezing temperature of the fluid within cells (inhibits water crystallization). This is very similar to how salt is used to melt and prevent ice formation on the roads. The salt is lower the freezing temperature.",
"The third trick involves both the first and second mechanisms. As the cells dehydrate and the sugar concentrations increase, you can imagine you get this thick syrupy mixture. The cells gets harder and harder as the cell dehydrates further and the temperature gets colder. The cells remains unfroze and forms almost a solid as it remains in suspended animation until warmer weathers. "
] |
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