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[
"How can bosons ever evolve to be in the same state?"
] |
[
false
] |
Bosons are characterized by being the ability to be in the same quantum state at the same time, e.g. a laser can be made by "piling" a bunch of photons into the same state. However, doesn't unitarity guarantee that if two quantum systems start out in different states, they stay in different states? Or can this only occur when wave functions collapse? If so, it seems like wave functions collapsing into the same waveform would be very unlikely, and I don't understand how we would see practical differences between fermions and bosons.
|
[
"I mean you engineer the device to produce many particles in the same state. They don't \"randomly\" just evolve into it. You're neglecting the whole device that is making that.",
"A many particle system of Fermions can't have multiple fermions in the same state. States need to be antisymmetric in exchanging particles which makes this impossible. For bosons the many possible wave function is symmetric in that respect. You can have multiple particles in the same one particle state.",
"Also I don't think it's accurate to say that you put many photons in the same one particle state. You rather produce a lot of photons with identical properties."
] |
[
"There seems to be some misunderstandings going on because to be honest I don't understand any of your follow ups. Have you seen the math of a laser? (Gerry / Knight, quantum optics book, chapter 4 talks about interactions of atoms with classical and quantized electromagnetic field.) You have product states of the atom (an higher energy state |a> and lower energy state |b> of the atom) and electromagnetic field (Fock states |n> where n is the number of photons of a particular frequency ω which corresponds to the gap between |a> and |b>). A typical state of the system is a product of such things, like |i> = |a>|n> (atom in excited state, photon field contains n photons). You look at transitions to states like |b>|n+1> (atom in lower energy state, emitted a photon). (see video here ",
"https://www.youtube.com/watch?v=EB3AhLU_g2s",
"). You don't even have multiple fermion like systems here (say two electron in an atom).",
"None of this has to do with collapse. You have time evolution driven by an interaction between atom and electromagnetic field. You don't have wave functions of photons that would collapse into particular states or anything. This just isn't how any of this is formulated. So I can't follow what you are saying.",
"I'm not saying that probabilities of wave function collapse according to a uniform distribution, but it always is a stochastic process.",
"I don't know where you are getting this from because I didn't mention any such thing. What I said was basically the system is made to emit photons of particular properties in significant numbers. You don't have to \"wait around\" until the photon states evolve into what you want to have, or something like that.",
"I understand that a device can coerce particles into a state that is \"very close\" to an Eigenstate",
"Again you seem to be thinking of collapse all the time, but it has nothing to do with it. The states occuring here are states of fixed photon number |n>. The system is the photon field (of frequency ω). n is also called occupation number and means that the state with energy ħω is occupied n times. This is only possible for bosons. Bosons allow any natural number (including 0) as occupation numbers for any state. For fermions only possible occupation numbers are 0 and 1 (there can't be two fermions in the same state).",
"but at the end of the day the probability that the wavefunction collapses to a particular state is arbitrarily small, no matter how the device is engineered.",
"I don't think that's accurate nor do I see the connection to the question.",
"Is it more accurate (at least from a practical viewpoint) to say that fermions require an increasing amount of energy to be placed increasingly similar states, whereas bosons can be placed in very similar states without that large energy requirement? If so, I think that makes sense as a meaningful distinction.",
"No. See what I said about symmetry and antisymmetry of the multiparticle state. This is what accurately distinguishes bosons from fermions.",
"https://www.ks.uiuc.edu/Services/Class/PHYS480/qm_PDF/chp9.pdf",
"Naturally when you fill a system with fermions, at temperature T = 0k (ie no thermal population of higher energy states), given that multiple fermions can't go into the same state, they will fill lowest energy states first and then fill higher up states, whereas a boson system at T = 0k has all bosons in the lowest energy states. Maybe this is what you mean, but it's not how you accurately define fermions and bosons.",
"You rather produce a lot of photons with identical properties.",
"Is this a consequence of N-particle systems being fundamentally different than 1-particle systems? I.e. you can't represent an N-particle system as a combination of N 1-particle systems? ",
"Also no. The state of a multi particle system can be built from ((anti)symmetrized) product states of 1 particle systems.",
"Maybe some of this helps, but I think we're kinda talking at crossp-purposes. Maybe you need to give concrete example of a system with concrete math. Maybe you've read some concrete thing and have some questions regarding that."
] |
[
"The time evolution for a laser is not unitary. There is strong coupling to the environment that allows the thing to work. Likewise, a Bose-Einstein condensate created using atomic vapours relies on coupling to the environment, otherwise it cannot cool down."
] |
[
"How do I go about looking for an academic paper? (more in description)"
] |
[
false
] |
I am looking for a certain article that I remember seeing on reddit a few months ago. It involved an experiment some zoologists did in the 1970s by transporting lizards in the pacific from a "hostile island" to a "tropical paradise". This change in environment prompted a radical change in anatomy and behavior yet not DNA. I haven't found the article yet but would be happy if anyone can point me in the right direction. Also how would i go about finding the original paper (or any academic paper for that matter) to verify the validity of the article? And does reddit have any insights?
|
[
"If you don't have a subscription to any kind of journal database (Web of Knowledge, PubMed, etc), you can try Google Scholar.",
"However, without more details to search under it might be very difficult to find the specific paper you're looking for.",
"Usually I'll search under key words such as the author, species name, concept and/or technique, if you can find any of them it would make it a lot easier to find."
] |
[
"First Google hit for \"Lizard Evolution\"",
".",
"This reveals that ",
"Duncan Irschick",
" is probably the dude in question. He's made it easy for us by having a cool website!",
"Publications and pdf files for D. J. Irschick",
".",
"Except that's a lot of words and I'm feeling lazy. Skimming the \"Media Attention\" section of the lab website makes it clear that \"rapid evolution\" is probably the key phrase. You could go back to the publications page and look for that, but it's quicker to do a ",
"Google Scholar search",
".",
"Is this what you are looking for?",
"Rapid large-scale evolutionary divergence in morphology and performance associated with exploitation of a different dietary resource",
"?"
] |
[
"This sounds like work done with Anoles in the caribbean. I suggest using google scholar to search for ",
" and experimental evolution. And then going into the references of those papers."
] |
[
"How do infants and toddlers who barely speak get diagnosed with eye problems, when we have no way of knowing if they're able to see things just the way they are ?"
] |
[
false
] |
Recently saw a video where a baby got correction glasses and was able to see it's parents properly for the first time. How do parent get to know their kids have issues with seeing and even if they do, how are doctors able to correctly prescribe them glasses
|
[
"Parents may include an eye examination as a routine check on an infant's health.",
"There are diagnostic tools that will measure the focal point of an eye's lens. Myopia, nearsightedness, is caused by the lens focusing in front of the retina. Hyperopia, farsightedness, is caused by the focus behind behind the retina."
] |
[
"Beyond eyeball checking diagnostic tools, parents can also pick up on signals from their kid.",
"For example, if you kid looks in a book sees a bus and says \"Bus!\" cause they like buses, but then you walk by one on the street 40 feet away that is within the child's central vision and they do not react, you can be reasonably sure that the child didn't see the bus. If this is a common issue and not a once-off, it would be a sign that you need to take your child in for a vision test to determine what kind of trouble is occurring.",
"This is why it is very important to pay attention to your child's behavior over time to understand how they are responding to stimulus.",
"Also, on average children have full visual faculty between 6 months and 1 year of age, including acuity, depth perception, and color vision. If your child is older than 1 year old and has problems with vision, you should be consulting with a doctor."
] |
[
"To get the prescription, they use ",
"retinoscopy",
" with infants, which is a technique for objectively measuring the error the eye.",
"There's a similar fully-automatic technique called an \"autorefractor\" that can measure this as well, and you've probably even had it done if you've got glasses. It's the machine where you look at some goofy little image of a house that goes bzzzzz and goes in and out of focus for a minute. They typically use the result as the starting point for the \"this or that\" process, to save a bunch of time-- but the final \"which is best\" has a bit of opinion in it, too, so they show you a bunch of \"pretty close\" options and ask which you like best. The autorefractor doesn't work well for infants, since you can't tell them to stare at something for any length of time."
] |
[
"What's stopping us from having cars that drive themselves?"
] |
[
false
] |
It seems like the communications technology is there so what gives? Is it costs, logistics, safety issues? When can I finally tell my car to drive to work and go back to sleep?
|
[
"Communications technology is not the only requirement: the main obstacle to producing cars that drive themselves is pattern recognition. It is easy to include road and navigation data in a driverless system, and a car with this information could navigate from point A to B. Issues arise, however, once unknown factors come into play.",
"For example, consider your daily drive to and from work and the observations and decisions you make along the way. Is that kid going to run out in front of me? Is that a rock (avoid) or rabbit (annihilate - Australians will understand) on the road? Can I run over that fallen tree branch or should I swerve to avoid it? The traffic light ahead appears to be broken, which signal should I consider instead? Humans are excellent at visually identifying a vast number of objects quickly and accurately under highly varying environmental conditions. Computers are not. In their defence, however, computers are far better at certain split-second decision making given accurate data (take ",
"electronic stability control",
" as a vehicular example).",
" A ",
"book on autonomous vehicles",
" for those interested."
] |
[
"Google actually has some that they're working on which are capable of driving on public roads. I believe at the moment they're required to have someone in the drivers seat to use them legally, but they're working on getting Nevada to allow them to run fully autonomously. Check out ",
"http://www.smartplanet.com/blog/thinking-tech/googles-self-driving-car-gets-a-green-light-from-nevada/7505",
" ."
] |
[
"Liability. ",
"Yes, there are technological hurdles, especially in terms of pattern recognition and infrastructure, but we could address those. However, even if we developed a safe and practical car, the company that sold it would be liable if anyone got hurt, and in the real world something will always go wrong somewhere eventually. There's just no profit in opening yourself up to that type of liability."
] |
[
"Is it by coincidence that we consider North as \"up\" on maps and globes?"
] |
[
false
] |
[deleted]
|
[
"Jerry Brotton wrote an interesting book called ",
" that does cover this specific topic in terms of map orientation.",
"Unfortuantely, I am out of town, and don't have access to my library to provide you the relevant passages. I will check back on this thread next week when I get home to see if there has been a valid response to your question, and if not sufficiently answered, will be able to add Brotton's comments on this. "
] |
[
"Did an early cartographer just consider that they were in the upper hemisphere of Earth, and drew it like that, so it became the norm?",
"No. In fact medieval European cartographers generally drew maps with East being up. There have also been Japanese maps with no clear up. All labels where placed so that the capital city would be above them, when read right."
] |
[
"It's actually a general rule in Astronomy, called the ",
"right-hand rule",
". Basically you extend out your right arm, and curl in your fingers to your palm in the direction of rotation of the object. Then, the direction that your thumb is pointing is considered \"North\". This is how all celestial objects are labeled when it comes to their directions. (except for the Milky Way, which was labeled before the direction of rotation was known, so \"South\" is \"North\")"
] |
[
"How does something as large as a city affect the crust/mantle below it? Could a city become so large and heavy that it would collapse or compress the earth underneath?"
] |
[
false
] |
Always wondered how something as massively heavy and all-covering as an urban area (with sewers and sediment of more ancient city walls below etc) manages to not just sink.
|
[
"I'll try to make this as clear as possible. ",
"Firstly, your answer is no (at least with respect to the crust/mantle). As far as compress the earth underneath, speaking in purely scientific terms, any weight will compress the earth underneath, whether it is 100,000 lbs or 1 oz. The degree of compression is what you are wondering. ",
"You can see from ",
"this",
" boussinesq chart that the load of a ",
" foundation member the weight is distrbued such that at a depth approximately 6 times the length of the footing, the load \"felt\" by the soil is only about 10% of that at the surface. Now, I'm sure you're wondering why don't we just make a 3 inch diameter pile and load it with 1,000,000 lbs and say \"well, at 18\" the load is dropped to 100,000, so we'll double that make it 3 ft and call it a day!\" That won't work; notice I said \"properly loaded\", this means you have to take settlement into account, at an improper load, the foundation will sink (kind of like a hypodermic needle going into skin). So you need to size the footing to avoid this.",
"Building foundations are designed by geotechnical engineers. The first step in this process is to determine the soil properties below the proposed building; this includes getting information on soil properties deep below the surface (hundreds of feet sometimes) using differing methods (SPT, CPT penetrometers, ground penetrating radar, geophone/shear wave recording, etc) Then based on certain methods of settlement (Schmertmann's method is one, also using Boussinesq force distributions) you can determine the structural capacity of the soil. If you have the approximate weight distribution of the building, you can size your footings so that the force doesn't \"over-stress\" the soil. This would result in various failure, either the foundation \"rolling\" over (due to eccentric loading or eccentric support, think two soils next to each other that have different strength), or much more commonly (as noted below with the Mexican example) settlement. ",
"Now, with the soil properties known if it is determined that you can't support all of the load on the surface of the ground, you need to do deep foundations. Commonly these will either be \"drilled shafts\" or \"driven piles\". For huge buildings, it will almost always be a drilled shaft because these are basically holes drilled into the ground (commonly over 10 ft in diameter) then a reinforcement cage lowered in, then concrete filling it. A driven pile, is basically a column that is driven into the ground and don't get much bigger than ~30 inches in diameter. Drilled shafts can be several hundred feet deep. This type of foundation relies more on side friction between the concrete and soil (think about a 100 ft deep, 10ft diameter concrete member buried in sand. It has over 3000 square feet for friction to act on. This is a HUGE amount of resistive force. ",
"If you determine that the weight of the building will be too large, then you need to redesign it (either by using light weight concrete, which is about 50-60% of the weight of normal weight concrete or by using more steel as it is stronger when compared pound for pound). ",
"Think about it this way, when you go to the beach and stand in the water, you start to sink , but only a couple inches. So what has happened is that your feet don't provide enough force on the surface to keep you up, so you start to settle ",
" is equal to your weight. ",
"On this note, 1.) quicksand is not a thing. You can have sand in what is known as a \"quick\" condition, which is where water is flowing upward. and 2.) in this situation, you will not drown (unless you can't swim), sand is about twice as dense as water, so if the water gets to a fully quick condition, it will just become buoyant sand, meaning it is about the same density as water, and you can swim through it.",
"If you want more clarification, let me know.",
"Source: Masters degree in geotechnical engineering, working on Ph.D.",
"EDIT: Thank you to whomever gave me gold!"
] |
[
"Well, I'm a geotechnical engineer, and you're both right. You're just talking about different things. Preconsolidation pressure is most definitely thing. And we don't just imagine it. We measure it. It's very important for estimating ",
" due to an applied load, which is needed if you want your floors to remain smooth and level, and if you don't want cracks to develop in your concrete. Bearing capacity is also a thing, but it has more to do with whether the applied load is going to cause a ",
" failure in the soil, which could cause your whole building to tip. The allowable bearing pressure is dependent on which of the two failure modes is critical. Unless your geotechnical engineer is very experienced, and familiar with the site soils, s/he should always be calculating both. And for the record, DrunclePhil's linked paper is exactly what he thinks it is, and what it describes would indeed help prevent excessive settlement after construction. "
] |
[
"Well, I'm a geotechnical engineer, and you're both right. You're just talking about different things. Preconsolidation pressure is most definitely thing. And we don't just imagine it. We measure it. It's very important for estimating ",
" due to an applied load, which is needed if you want your floors to remain smooth and level, and if you don't want cracks to develop in your concrete. Bearing capacity is also a thing, but it has more to do with whether the applied load is going to cause a ",
" failure in the soil, which could cause your whole building to tip. The allowable bearing pressure is dependent on which of the two failure modes is critical. Unless your geotechnical engineer is very experienced, and familiar with the site soils, s/he should always be calculating both. And for the record, DrunclePhil's linked paper is exactly what he thinks it is, and what it describes would indeed help prevent excessive settlement after construction. "
] |
[
"What exactly are the mechanisms inside the core of an atom which determine exactly when it will decay?"
] |
[
false
] |
I mean it seems random to us, but like anything else it must be governed by some mechanism right? Google did not help me with this at all.
|
[
"You ",
" determine when it will decay; it's fundamentally random (according to certain interpretations of QM)."
] |
[
"But if its random then how is it caused?",
"Whenever your system can reach a state of lower energy without violating any relevant conservation laws, it ",
" do so. So an unstable nucleus will decay to a nucleus with a lower mass.",
"There must be something that happens to causes it to go from \"not releasing a particle in this instant\" to \"releasing a particle in this instant\" right?",
"That might be what you classical intuition tells you, but in quantum mechanics, that's simply not the case. The unstable state has a probability density which exponentially decreases with time. If you put a detector nearby and wait for a decay product to be detected, when it occurs will be random."
] |
[
"Does that mean the universe is not deterministic?"
] |
[
"Mathematically, what does it mean to \"control for\" a factor? And can I trust a study that claims to do so?"
] |
[
false
] |
For example, a hypothetical study might say "controlling for alcohol intake, smoking increases the risk of heart disease". For an example of something I'm unsure about trusting, towards the end of TED talk, the presenter says that his results, (about the relationship between income inequality and well-being), still show up after controlling for "poverty or education or so on". Generally, I don't know what to make of social science studies that claim to control for 'big' things, like education or income, which seem to correlate with so many other things. How does this controlling work, and what determines what we can accurately control for?
|
[
"Before I get around to answering your question, I want to clear something up:",
"Generally, I don't know what to make of social science studies that claim to control for 'big' things, like education or income, which seem to correlate with so many other things.",
"I see the word \"correlate\" used a lot when people provide and interpret results. When people use \"correlate\" in every day speech it typically means \"thing 1 goes along with thing 2\". You might think of, for example, the higher the median income in a town, the better the education level. Often, people think of correlating as being one positive and another positive. ",
"But when a scientist uses the word correlate that's not what they mean. Typically, a correlation (as in the statistical measure) means that there is a ",
", wherein it ",
". But that correlation could be median town income goes up, and so does education quality, or it could mean that as median town income goes up ",
". It's still a correlation, just a negative one. The metric of correlation is just the slope of a line. The meaning of a \"correlation\" from a scientist usually means \"a significant correlation\" in one direction or the other. ",
"I'm going to dance around an answer before I give one to you. It's not just a mathematical thing. Mathematically, it's specific to statistical approaches, but more broadly it's about experimental design and the ",
" you collect for your study.",
"I'll give you a not-so-hypothetical: ",
"This ",
" to be accepted as a somewhat factual statement for years in the medical community. But it wasn't true. At the time of early studies there were lots of caffeine users who were also ",
" and more specifically, ",
". The statement to go along with that now, if it were a study of caffeine use, would be:",
"But in that statement, we can't take away \"Nicotine is the culprit!\" unless we test it. The goal of this not-so-hypothetical (though, I'm truncating) was to test caffeine and health.",
"the presenter says that his results, (about the relationship between income inequality and well-being), still show up after controlling for \"poverty or education or so on\".",
"What this person is telling you is that their study is on the following:",
"If they were to just do some statistical test on the relationship between inequality and well-being, they could get a result, or they may not. But right away you'll have lots of social scientists saying \"woah woah woah... did you ",
" for things?\" Pretend you're a social psychologist studying the effects of ",
" on well-being...",
"From your perspective, there are ",
", or ",
" for the other person's study. They're investigating income inequality and well-being, but your research says there is an effect of poverty on well-being already. So the data the other person has might not reflect anything about income inequality and well-being... ",
". ",
"So, as you might be alluding to, \"controlling for ",
"\" pops up much more frequently in social, psychological, neuro, bio and other fields, but you don't see the term nearly as much in chemistry, physics, math, etc... So, why is that? ",
"Well, in an experiment, you set out to measure (and test) something. I'll provide a very, very simplified example: From a physicists perspective, what they are measuring is what they are measuring (sans error for instrumentation/observation). That is, when they measure ",
", they really are measuring ",
".",
"But if you have a psychologist measure ",
", who says they are measuring ",
"? A psychologist measures outward behaviors, usually through simple things like reaction time or surveys or simple tests (e.g., memory). But when you test a human, who knows what ",
" could be ",
" (confounding) the number you record from them? ",
"Humans, animals, and societies/social settings, are incredibly complex. You are made up of millions (probably billions or even more) \"variables\", from your DNA all the way up to what you just snacked on (did it have caffeine or sugar? is it your favorite item or does it disgust you and you ate it out of kindness for someone who is learning how to cook?). ",
"If I were to go out and give everyone within a 3 mile radius a survey and ask them to tell me about their well-being and income I might have a good idea of the general sense of well-being of people, with respect to their income. But I could find out if people are happier in general when they are middle-aged or when they in a certain part of town... I should find out. My results of just 2 measures might not be ",
" and might in fact, ",
". If I can account for other things that might effect well-being (being very old or very sick, being in a bad part of town, etc...) then I get a better sense of exactly how income inequality and well-being are related. ",
"And that's \"controlling\": basically, I need to \"take out\" how much influence each of the other (possibly) confounding variables might explain in this relationship. What I'm left with, is my answer.",
"How does this controlling work, and what determines what we can accurately control for?",
"This is a pretty deep question. So, the first fairly tried-and-true way of \"controlling\" is to get as many samples as you can (I'm lying a bit here, but it's OK for now). When you have more and more samples you can say that the relationship you do find happens less and less by chance. ",
"Controlling for specific variables needs to happen in a lot of experiments, but there is no way to control for ",
" (the millions, billions, or more I pointed out). So, you can account for lots of variables that have already been shown to influence whatever you are measuring. If you're an economist or sociologist studying income and \nwell-being, you should be reading up on psychology and education literature to find out what they know about other variables, and that way you can \"take them out\" of your analysis so that whatever is left, is real.",
"And finally, if a study (especially in the social sciences) doesn't control for something, that's when you should be a bit skeptical until you find out more. Sure, there are lots of ways to account for things without controlling for them, but on the level of social sciences, variables should be controlled for. ",
": A really good point came up from jjberg2: there are two definitions for the word \"control\" when it comes to statistical methods. See jjberg2's comment ",
"here",
". The OP appears to be asking about the \"controlling for\" definition. "
] |
[
"in a statistical 'generalized linear modelling' sense, 'controlling' for a factor is a way of partitioning some amount of variation in a set of observations, to account for known variation associated with different factors. For example, if you're looking at how nutrition affects adult height, and you know that males and females have different mean heights to begin with, you could 'control' for sex in an analysis by including a term in the model which accounts for this mean difference. By partitioning out this mean difference, you can then study the remaining variation to see whether there is still an effect of nutrition, after controlling for the sex difference. \nHowever, what this means is if you have very correlated variables, controlling for one will eat up so much variation that you won't have the power to detect the effect of the second variable. This is where good study design helps to minimize the amount of correlation between the things that you're studying. Social science can't really do experiments in this sense, and their models tend not to be very powerful as a result (ie the correlation between the variables of interest mean that it is difficult to reject falsehoods), by controlling for many factors, you are constraining the amount of actual variation that you can associate with a factor of interest, after accounting for the other factors."
] |
[
"The simplest way to control for a variable is just to make it into an independent variable. For example, continuing with your alcohol/smoking example, a researcher could group the subjects not only by tobacco intake, but also by alcohol intake. In this one could use an ANOVA to analyze the effects of both alcohol and smoking, as well as the interaction of the two, on heart disease. Alternatively, one can condition the variables in the smoking set on the variables in the alcohol set. In this way, the question being asked would be, 'given the rates of alcohol intake for subject x, does smoking increase risk of heart disease. The two methods are related, however conditioning upon extraneous variables typically is used more frequently in Bayesian statistical analyses. Both attempt to minimize confounding effects of the unwanted variable on the dependent variable."
] |
[
"What kind of scientific evidence do we have that global warming is caused by CO2 or any other greenhouse gasses?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"You question is either commonly occurring or has been recently posted on ",
"/r/AskScience",
". It may also be answerable using a Google or Wikipedia search.",
"To check for previous similar posts, please use the subreddit search on the right, or Google site:reddit.com",
"/r/askscience",
" ",
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"our FAQ",
".",
"For more information regarding this and similar issues, please see our ",
"guidelines",
".",
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"message to the moderators."
] |
[
"Here are a few pasts thread on the topic:\n",
"https://www.reddit.com/r/askscience/comments/avedpr/ive_seen_the_charts_for_temperature_rise_the/",
"https://www.reddit.com/r/askscience/comments/bpq8vg/what_proof_do_we_have_that_co2_is_a_greenhouse/",
"https://www.reddit.com/r/askscience/comments/btdtje/what_makes_certain_gasses_carbon_dioxide_freon/",
"https://www.reddit.com/r/askscience/comments/b0dact/if_carbon_dioxide_is_only_00391_percent_of_the/"
] |
[
"Here are a few pasts thread on the topic:\n",
"https://www.reddit.com/r/askscience/comments/avedpr/ive_seen_the_charts_for_temperature_rise_the/",
"https://www.reddit.com/r/askscience/comments/bpq8vg/what_proof_do_we_have_that_co2_is_a_greenhouse/",
"https://www.reddit.com/r/askscience/comments/btdtje/what_makes_certain_gasses_carbon_dioxide_freon/",
"https://www.reddit.com/r/askscience/comments/b0dact/if_carbon_dioxide_is_only_00391_percent_of_the/"
] |
[
"With MRI Magnets being ridiculously strong, Why don't they affect compasses, systems, animals, etc ?"
] |
[
false
] |
I have heard that MRI magnets are something like 60,000 x stronger than the earth's magnetic field. If this is true, with thousands of them in operation world wide. Why aren't compasses, animals who navigate by the earth's north pole, instruments, and even the earth's magnetic poles affected by them ?
|
[
"Mainly size. The Earth's magnetic field has is poles at opposite ends of the planet so the field covers the entire world. But with a magnet such as one from an MRI the polls are very close together and so the field is pretty tight, and doesn't really extend far beyond the actual magnet. "
] |
[
"This! And that is on purpose. MRIs are designed in a way to create a high magnetic flux density in a small volume (where the patient is placed). Limiting the spatial extent of that field is crucial to achieve those high flux densities.",
"A spatially larger field with similar flux density ",
" influence its environment; also it would increase energy consumption by the MRI."
] |
[
"A colleague recently re-purposed an old medical MRI magnet for use in a detector system. The stray fields from the magnet are a big concern, with modern magnets taking great care to have both shielding and compensation coils so that outside the magnet no strong residual fields exist. The regulations pertaining to such magnets are strict. They still carry warning labels, but the stray fields are much reduced. You also get a rapid decrease of the stray fields with distance from the magnet. ",
"All of this reduces the effect of MRI magnets on wildlife, compass needles, CRT screens (no longer used), credit card magnetic strips in my pocket (definitely worth protecting) etc.",
"You will find ",
"this",
" interesting reading, with a list of references to further safety related documents."
] |
[
"Am i as genetically similar to my daughter as my daughter is to my mother? (and other genetic questions)"
] |
[
false
] |
I understand human beings have 23 pairs of chromosomes each, and in only the last pair determines the sex, however, I received 23 half pairs of chromosomes from my mother and then have passed on said chromosomes to my daughter. Does this mean that my mother is as genetically similar as I am to my daughter as my daughter is to me? could someone determine genetically that my mother is the grandmother of my daughter, as they could determine my paternity to my daughter? Also a woman has 1 egg in her body per menstrual cycle, does the arrangement of half pairs change per cycle? if a woman has a child what determines which chromosomes would get passed on to her child the chromosomes she got from her mother or her father or a mix of both? Because a woman only has 1 egg that gets fertilized could we determine genetic problems that might be present in that child by examining that 1 egg in a lab beforehand?
|
[
"Well, for one thing, you have your mother's mitochondrial DNA but your daughter doesn't have yours."
] |
[
"OP is male."
] |
[
"OP is male."
] |
[
"Do animals experience menstrual cramps?"
] |
[
false
] | null |
[
"Yes. However, not many animals menstruate. Humans and old-world primates are about the only animals that undergo menses with the exception of bats. "
] |
[
"Having offspring that don't coincide with seasons means that you have to be able to provide food and protection any time of year."
] |
[
"It's not, and that's why it makes sense. Having babies that need food and protection at any time of year is hard. Having babies that are basically helpless for several years is also hard. That's why very few organisms have those qualities."
] |
[
"Does the ammount of muscle cells in the body increase through exercise?"
] |
[
false
] |
[deleted]
|
[
"The answer is a bit complicated, and depends on the type of exercise. Your typical mature muscle cells don't undergo mitosis to increase the number of cells following exercise. There are satellite cells that reside next to muscle cells that asymmetrically decive to replenish the muscle cells. Muscle cells are also a little strange in that a single cell can contain multiple nucleuses. ",
"This topic was (and to a lesser extent today) very much debated within literature. I've included a link that it pretty well written.\n",
"hyperplasia vs hypertrophy ",
"Apologize for formatting and spelling from mobile."
] |
[
"Thank you"
] |
[
"Going along with that, muscle cells gain more nuclei during exercise, and have a literal muscle memory, as if you stop working out for a while, the nuclei remain and help get back to the former muscle mass prior to stopping."
] |
[
"Is thermal motion truly random?"
] |
[
false
] |
Excuse my ignorance in advance. I keep seeing these visualizations of thermal motion and it's just energetic atoms or molecules bouncing off of each other and walls. What makes this truly random? It seems like given the initial conditions the motion is predictable.
|
[
"It seems like given the initial conditions the motion is predictable.",
"What do you mean by random? In a classical situation with little balls bouncing off walls like you describe then the process is indeed - in principle - predictable. By \"random\" in this sense we mean that the objects positions and velocities have some clear statistical distribution and there are no spurious correlations.",
"If you're alluding to a quantum mechanical description then any form of \"little balls bouncing off walls\" is not a correct description. Though it's worth pointing out that without measurement quantum mechanics is also deterministic. Even with \"quantum weirdness\" the behaviour of a large ensemble has an average behaviour that follows emergent, deterministic models (this is called \"statistical mechanics\", which is basically the behaviour of many, many quantum particles)."
] |
[
"If we ignore, for now, the complexity of even trying to model the motion of Avagadro's Number of particles, we can try and determine whether the initial conditions are even predictable.",
"One example of initial conditions might be a small number of particles at low temperature i.e. a Bose Einstein condensate.",
"https://en.wikipedia.org/wiki/Bose%E2%80%93Einstein_condensate",
"In this, the particles have been cooled to the point where there are few available states for them to occupy. In these conditions, the question of which particle is in which state is believed to be truly random, on a quantum wavefunction level.",
"Warming this state up, it seems that the resultant state must also be truly random, even if running a model of all the particles motion and vibration was even possible."
] |
[
"This actually becomes an issue in creating very low pressures. Eventually the gas stops acting statistical and you have your ping pong balls. You need to use different types of pumps like turbo pumps which basically smack the molecules in a certain direction towards the roughing pump. Also you put cryotraps which absorb heat from the molecules and slow them down more lowering the pressure. Crazy stuff."
] |
[
"Since when water freezes, it expands, how is it that ocean level would rise when iceberges melt. Shouldnt they lower due to the decrease in ice?"
] |
[
false
] |
It just logicaly doesn't make sense. Is there something I am missing?
|
[
"Floating ice will not affect sea level. However, the ice on land (Greenland, Antarctica) will flow into the sea when it melts, thereby causing the sea level to rise.",
"If all the ice on Greenland were to melt, the sea level would rise over 7 meters."
] |
[
"Adding onto this. Drop an ice cube into a glass of water. The water amount will remain close to the same when the ice cube melts. :)"
] |
[
"and most of the ice is actually on land",
"https://water.usgs.gov/edu/watercycleice.html",
"Remember that rising seas would not damage the planet - they've gone up and down dramatically before - but they would have an enormous impact on human societies due to the way we've built our infrastructure. Most major population areas are near water, for obvious reasons."
] |
[
"A simple F=MA problem that frustrates my brain."
] |
[
false
] |
I have had a basic physics question that I can't really settle within myself. If a car is moving at a constant speed then the forces acting on it must be equal to zero... Yet what happens when you take something like friction into effect? Would you or would you not need another force to overcome the friction and therefore make the car's acceleration equal to zero? More fundamentally, what would the net force on the car be?
|
[
"If your car is coasting along (ie engine not actively powering wheels) and you include friction, then your car will be slowing down gradually. Friction between the wheels and the ground (rolling friction) would manifest as a force in the direction opposite of the car's movement, resulting in a small acceleration in the same direction.",
"If you want a car to travel at a constant speed while considering rolling friction, you must be applying energy to the wheels by some mechanism to oppose the losses due to friction. You'll still have the rolling friction force going in the opposite direction, but you'd have an equal and opposite force driving the wheels forward to get you a net force of 0.",
"Would you or would you not need another force to overcome the friction and therefore make the car's acceleration equal to zero? More fundamentally, what would the net force on the car be?",
"You would indeed need some other force to cancel out the friction to result in zero acceleration. And if you have zero acceleration, the net force will be zero."
] |
[
"Assuming the car is undergoing no acceleration, the net force acting on the car is zero. Thus the forward force being generated by the combustion within the engine (assuming a combustion engine of course...) is just equaling all of the frictional forces acting against the car (the friction of the movable parts of the car rubbing against each other, the friction of the air against the car, or aerodynamic friction, and the friction of the tires against the road)."
] |
[
"Oh my God THANK YOU. I think the last sentence especially helped me understand this."
] |
[
"Does dimethyl mercury evaporate at room temperature?"
] |
[
false
] |
I saw a video on this… about the chemist that died back in 1997. Pretty scary stuff. I was wondering does this evaporate completely? Like someone can’t put some on a commonly touched item to contaminate people…. Or can they?
|
[
"It has double the vapor pressure of water at room temperature, so it'll dry up relatively quickly. This, and the risk of gassing yourself with the vapors (plus the risks intrinsic in creating the substance in the first place), makes it an impractical contact poison."
] |
[
"Okay so I will start with a direct answer with little context, \"It depends on how you define evaporate\". Does any amount of dimethyl mercury enter the vapor phase? Yes, is it very much/is it a rapid process like the evaporation of acetone? No, not exactly, but it has double the vapor pressure of water, thus evaporates at a higher rate than water at room temp.",
"Something for your knowledge regarding questions like this in the future, chemical compounds all have defined \"physical properties\" that can be looked up and referenced or even used to help identify an unknown material. They can be found on many sites ranging from the basic info on Wikipedia, to in depth information from NIST. These include values like boiling point, vapor pressure, molar mass, etc. ",
"To your question about leaving some to intentionally poison people, I mean you could yes, it comes down to why would someone who has access to a hard to acquire compound willingly release something that is toxic to themselves and anyone nearby (which would result in you being charged criminally, as well as environmental damages) and is a long term environmental pollutant",
"I \"could\" go rob a bank, but the logic in my head tells me it's not worth it and wrong to do.",
"example for dimethyl mercury: ",
"https://www.chemeo.com/cid/50-560-4/Mercury,%20dimethyl-"
] |
[
"I saw vapor pressure, but I wasn’t for sure exactly how that translates to me"
] |
[
"Field of a permanent magnet"
] |
[
false
] |
Assuming constant magnetization of the material, how does the field of a permanent magnet (lets say a bar magnet) depend on its shape and size? For example, if I wanted to induce the most possible current in a loop by moving a magnet, and the cost of the magnet is dependent on weight or volume, how could I compare magnets of different shapes and sizes but the same material?
|
[
"Well, the magnetic field of a permanent magnet is just the aggregate field of the magnetic moments of its component atoms (or molecules), so to get the total field, you would simply take the sum of each magnetic dipole moment.",
"Realistically, you can't do that, but assuming constant polarization and knowledge of the specific* amount of your material, you can get some pretty good (i.e. within a few digits of precision) estimates by integrating over the desired volume.",
"*My use of the word specific here is similar to that of specific heat, specific gravity, etc; the specific amount is the number of moles of a material in a given volume. I feel like there should be a better word for that, but it's late and i'm starting to see cross-eyed, so whatever."
] |
[
"If OP knows the shape and material, and assumes the material is uniform, s/he can approximate field strength around the magnet numerically. ",
"I have done similar numerical solves, but I am hesitant to sink in lots of time helping OP, unless this is something s/he wants to do, i.e. not a random whim. "
] |
[
"If you want to maximize energy, minimize losses. Any flux from the magnet that is not passing through your wires is putting energy into magnetizing the air. You must minimize the air gaps.",
"It also depends on how fast you plan to move the magnet. At high speeds you need to consider eddy currents that will flow in metallic parts of your system, other than the wires. If the entire assembly is made of insulator you will not have this problem, but that is somewhat uncommon."
] |
[
"How does the frequency of treatment affect recovery time and rate?"
] |
[
false
] |
[deleted]
|
[
"Talking about leukemia treatments and radiation is sort of a pandoras box because then you start talking about the supplemental chemotherapy as well as the subtype of leukemia. Let's just talk about antibiotics.",
"MRSA stands for Methacillin resistant staphalococcus aureus. Basically it's a bacteria that has become resistant to many standard antibiotics. Typically the treatment for MRSA is a really potent antibiotic called vancomycin. If you're on a vancomycin you will get blood tests ordered frequently that check the peak and trough of the medication.\n",
" is the point when the drug reaches the highest concentration in your body\n",
" is the point where the drug reachest the lowest concentration in the body.\nThe doctor has to schedule the drug is that the peak doesn't get too high where the body experiences toxic reactions, but the trough isn't low enough that the drug isn't working at all. The range between where the concentration isn't toxic, but is still exhibiting a beneficial effect on the body is called the ",
". The drug has to constantly be in this therapeutic window. If the trough is consistently too low, the bacteria can react to the drug by mutating and becoming resistant to that antibiotic. Vancomycin resistant MRSA IS NOT COOL! That's why antibiotic regiments are a huge issue because patients have trouble being compliant with their drug therapy leading to drug resistant bacteria. Hope I helped. ",
"So that drug HAS to be taken 30 times in the 30 days (hypothetically speaking)."
] |
[
"Sorry. There is not enough information to answer this question. What kind of medicine are you talking about here, and recovery from what kind of illness?",
"Antibiotics have peaks and trough that have to be kept in therapeutic range so scheduling is key, for instance.",
"There are no general rules of thumb with treatments that say \"Oh if I speed any medication, I get better faster\""
] |
[
"I guess this sort of answers my question actually. I edited the initial question to be a little more specific. The purpose was that it could have been any ailment; I wanted to know how important is the scheduling of treatment to the overall recovery process. And does the scheduling become more important when treating leukemia with radiation therapy vs treating MRSA with an antibiotic."
] |
[
"Ref: Voyager leaving Heliosphere and traveling through interstellar space."
] |
[
false
] |
Wouldn't electromagnetic signals and from interstellar space travel travel further with lower signal to noise ratio, i.e., be easier to interpret over great distance, given that the background radiation is a well know quantity. Or can we produce comparable signals with enough power from within solar system?
|
[
"You're onto something, but you've stated it a little awkwardly. First, for a receiver at earth, the noise power in the receiver is independent of the distance to the transmitter. It's more influenced by the direction (in the case of a tracking antenna) and atmospheric effects on earth. (Rain both attenuates the inbound signal and has a higher noise temperature.) Even as the transmitter (Voyager) moves farther away, the flux density of the power at earth is still dropping off as the square of the distance. Iorg has a good point though, that travelling through media other than (almost completely) empty space will introduce additional attenuation of the inbound signal. So, no, the best case scenario is that for a transmitter that is continuing to recede from view, SNR doesn't ever increase, it just decreases more slowly per unit distance."
] |
[
"Sorry friend, I think you might benefit from working some figures out for a couple cases to see my point. Imagine a satellite moving from 2m to 3m, and the ratio of their path loss (1/3",
" / (1/2",
" = .444.. Now one from 4m to 5m, (1/25)/(1/16) = .64. While it's true that the power level has decreased in both cases in moving a distance of one meter, look at what else happened. Travelling one meter in the first case reduced the power level to 44% of what it was. In the second, the power level is reduced to 64% of what it was, still moving over one meter. By the time you get out to 100 meters vs. 101 meters, the power level is reduced for 1 meter to 98.01% of its start value. Therefore, my statement that free space loss decelerates at father distances per unit length stands. ",
"Your second point is also incorrect. We're dealing with extremely low power levels on receive. The reception and fidelity of the digital transmissions are heavily dependent on SNR (as bit error rate increases rapidly when the signal is near the noise level.) So both parts of atmospheric effects are important: The variance of the noise (which is what's important, btw! SNR is calculated using the power received from the transmission divided by the noise variance!) will increase because rain has a higher noise temperature, AND the signal is decreased by an additional .1 - .5 dB due to the rain. "
] |
[
"There's gas and dust in interstellar space that absorbs radiation. "
] |
[
"Why do people take iodine pills for radiation exposure?"
] |
[
false
] |
I just learned about the synthesis of triiodothyronine and thyroxine and it got me wondering what benefits does iodine have against radiation exposure? Like when people in Chernobyl were given them
|
[
"During a nuclear explosion, one byproduct is radioactive iodine (I-131). This can bioaccumulate in the thyroid and damage it or lead to thyroid cancer. One way to prevent that is to swamp the body with non-radioactive iodine (mostly I-127) so that you don’t absorb the radioactive version."
] |
[
"It's a bit like giving ethanol for methanol poisoning then?"
] |
[
"Your thyroid gland takes up iodine naturally, and radioactive iodine-131 is a common waste product from nuclear plants. Taking iodine pills in a nuclear emergency basically saturates your thyroid with safe iodine so that it doesn’t absorb iodine-131."
] |
[
"Why do black men tend to develop keloids instead of regular scar tissue, and why don't we see keloids present in other races?"
] |
[
false
] |
Does it actually occur in other races, simply at a lower rate? Why don't black men develop normal scar tissue? Is this also an issue with black woman? If not, why is it limited to only black men?
|
[
"Good question, and the answer is not completely understood (typical). ",
"Firstly, we do know that individuals predisposed to keloid (and hypertrophic scar) formation have increased expression of TGF (transforming growth factor) beta (they also have increased VEGF and CTGF) following skin trauma, which is the primary regulator of fibroblast proliferation, and subsequent collagen formation. As ",
"/u/coolmanmax2000",
" already said, the primary component of keloids is the collagenous connective tissue. During normal scar formation, TGF-beta expression is negatively regulated following completion of scar formation, but this is not true in the case of keloid formation. mRNA expression for procollagen type 1 is also seen, consistent with the excess type 1 procollagen seen in keloids. Expression of apoptosis related genes are also underexpressed, eluding to the idea that these fibroblasts are not dying appropriately.",
"It is true that the different races have varying incidence of keloids (to answer your question directly: yes, other races do get keloids, but yes, with lower incidence rates), but to date I am unaware of any particular genes associated with keloid formation. That said, a number of susceptibility loci have been identified linking susceptibility to keloid formation (in a Japanese population, it is likely these will vary across different races) but these loci were unsuccessful in identifying genes responsible for the pathogenesis of keloids. Familial cases of keloid formation suggest an autosomal dominant inheritance pattern with variable penetrance. Still, no causal gene mutation has been identified. ",
"A quick scopus search for papers from 2013 identifying genes linked to keloid pathogenesis has been promising for future development (see source 9, it's the most exciting genetics wise and answers the 'why' part of your question best!).",
"Sources-",
"Nakaoka et al. 1995. Acta Derm Venereol.",
"Fujiwara et al. 2005. Br J Dermatol.",
"Uitto et al. 1985. Proc Natl Acad Sci USA",
"Wolfram et al. 2009. Dermatol Surg.",
"Sayah et al. 1999. J Surg Res.",
"Chike-Obi et al. 2009. Semin Plast Surg.",
"Marneros et al. 2001. Arch Dermatol. ",
"Nakashima et al. 2010. Nat Genet.",
"Hahn et al. 2013. Wound Repair Regen.",
"EDIT:\nSo this question was bugging me after my initial answer, and I found another paper from last year (2012) by Halin et al. in APS (archives of plastic surgery). I think this is the best information out there to answer your question best. Japanese genome studies have linked chromosomal regions 2q23, and African American family genome studies linked chromosomal region 7p11. Han Chinese family genome studies excluded 7p11, but found sites 15q22.31-q23, 18q21.1 and 10q23.31 for this family. Note that the 18q21.1 site contains sites for the SMAD 2, 7 and 4 genes, which regulate TGF-beta signalling pathways. No link between TGF-beta and Caucasion populations have been made as of yet (which may explain why the incidence is so low in this population as ",
"/u/ketchy_shuby",
" pointed out). That been said, HLA-DRBA*15 is linked to keloid formation in Chinese and Caucasion populations. Hope that helps! :)"
] |
[
"Keloids form more frequently in Polynesian and Chinese persons than in Indian and Malaysian persons. As many as 16% of people in a random sampling of black Africans reported having keloids. White persons are least commonly affected."
] |
[
"But why?"
] |
[
"Catalyst - Do you need a catalyst to convert CxHx - H2O + CO2, Carbonmonoxide - CO2 and NOx - N2 + CO2 or would those reactions also happen without the catalyst?"
] |
[
false
] |
[deleted]
|
[
"Let me clarify your reactions as best as I can understand them:",
"CxHx <--> H20 + CO2",
"2CO + O2 <--> 2CO2",
"the last one was tricky to understand. Do you mean:",
"N2 + O2 <--> NOx ?",
"For your answer, these are all combustion reactions. You should do some general reading on combustion. Wikipedia's article is very good. The short answer to your question is something has to overcome the initial energy barrier -- either a chemical catalyst, or heat (i.e. spark plug in a gasoline engine)."
] |
[
"Upvotes to semitones; there will be some overlap with our answers.",
"CxHx -> H2O +CO2",
"This is a combustion reaction, so oxygen is needed on the reactant side. A little bit of energy is required to start the reaction, so no catalyst is required.",
"CO -> CO2",
"CO oxidation can occur with oxygen as the reactant, similar to combustion. There IS research with using catalysts for low temperature CO oxidation. This is important for proton enhanced membrane fuel cells where small quantities of CO in the H2 feed will poison the platinum catalyst. Gold catalysts have received some attention for this application due to near-100% selectivity of CO -> CO2 around room temperature. ",
"The water-gas shift reaction (",
"http://en.wikipedia.org/wiki/Water_gas_shift",
") also uses catalysts to react CO + H2O <-> CO2 + H2.",
"NOx <-> N2 +CO2 ",
"This isn't a reaction, however....",
"N2 + O2 <-> NOx",
"This oxidation is a byproduct of industrial combustion where air is used as a source of oxygen (air is ~79% N2, 21% O2); this is thermal, so there is no catalyst. NOx are a class of environmental pollutants that further oxidize in the atmosphere (oxygen radicals are the catalyst).HNO3 (nitric acid) is eventually formed, leading to a constituent in acid rain."
] |
[
"You don't \"need\" a catalyst for any reaction. They can all happen by themselves but a catalyst makes it go faster."
] |
[
"Physics How do time and space connect to become what is described as spacetime?"
] |
[
false
] |
Repost because my last attempt got caught up in the spam filter. If time can be seen as a spatial dimension, then the units should be able to be comparable, right? For example, 1 meter in the y dimension of space is equal in magnitude to 1 meter in the x dimension of space. So then, 1 meter in the y dimension would be equal in magnitude to how many seconds in the t dimension? Also, I feel like the Planck length might be useful for this, but I'm not sure how.
|
[
"To add to the distinction with what little I know, four-vectors' (vectors in 4 dimensional spacetime) magnitudes are calculated with something kinda similar to the Pythagorean theorem:",
"R (dot) R = (ct)",
" - ( x",
" + y",
" + z",
" )",
"The fact that the term with time and the term with the spatial dimensions are separated by subtraction, in combination with both terms being squared, suggests that time can be equated, in a way, to an imaginary spatial dimension.",
"Anyone who knows better than me and sees something wrong, please correct me. I'm here to learn as well!"
] |
[
"Sorry for the late reply. I can't thank you enough for this. This is a very difficult question to word, and finding an answer has been very hard. This is exactly what I was looking for."
] |
[
"Sorry for the late reply. I can't thank you enough for this. This is a very difficult question to word, and finding an answer has been very hard. This is exactly what I was looking for."
] |
[
"Assuming that a person could float in space without being killed, how much further does he have to be to see the entirety of Jupiter at once?"
] |
[
false
] | null |
[
"further than what?"
] |
[
"From the atmosphere of Jupiter"
] |
[
"Oh. Please post calculation requests to ",
"/r/theydidthemath",
"."
] |
[
"Can a Rh negative male be injected with Rh positive blood to harvest Rhogam?"
] |
[
false
] |
Since Rhogam is a blood product made from Rh- mother exposure to Rh+ fetal blood, could a male be injected with Rh+ blood to get the take advantage of the immune response and harvest his IgM before the body starts creating the IgG? I couldnt find if this is done or not, and was brought up in class. Edit: Is it done? And If not, why?
|
[
"No.. That's what you want. You only have a four month window to get the byproduct of sensitization. Once your body starts creating the IgG it's game over for making rhogam (IgG can be passed through the placenta, and antibodies against fetal blood is never good)... And a main reason that there has been shortages in the past. We want the product of sensitization, IgM (which cannot be passed through the placenta) which is only made for a short time. ",
"Edit: Once an event occurs, and fetal blood ends up in the maternal system, if there is immuno-incompatibility we get an immune response...small incompatible transfusion would the exact way to get the outcome we want. "
] |
[
"No.. That's what you want. You only have a four month window to get the byproduct of sensitization. Once your body starts creating the IgG it's game over for making rhogam (IgG can be passed through the placenta, and antibodies against fetal blood is never good)... And a main reason that there has been shortages in the past. We want the product of sensitization, IgM (which cannot be passed through the placenta) which is only made for a short time. ",
"Edit: Once an event occurs, and fetal blood ends up in the maternal system, if there is immuno-incompatibility we get an immune response...small incompatible transfusion would the exact way to get the outcome we want. "
] |
[
"We know we have a 72 hour window from the trauma causing the crossover of the blood till we can give the Rhogam before the IgM cascade to IgG will be inevitable in mothers. We know 72 hours because of the way the testing was done (in pregnant women in prision..If a trauma happened on friday, nobody was qualified to give the rhogam until monday). It could be longer, but you cannot ethically hold a med in a possible placental rupture.",
"The total time it takes the body from sensitization and creating IgM to creating IgG is four months. My question was, do we/can we use this to our advantage. By the way...this is a human blood product if i'm not mistaken... "
] |
[
"How much do we know about abiogenesis?"
] |
[
false
] |
As far as I know the science behind how life began at the current time is almost 100% hypothetical. That's for pretty obvious reasons: it's pretty hard to do experiments to try and replicate the process without simulating an entire solar system, and there's no fossil evidence or anything like that left for us to study. So what I'm wondering is, are we actually at a stage where we can put kind of likelihood on abiogenesis occurring, or are the proposed mechanisms more of a "well this could be plausible, but we have no idea whether it actually plausible" situation? It seems useless to look at our own existence when it comes to probability, since no matter how likely or unlikely it is to happen, we would always find ourselves somewhere where it did. So I'm just wondering about likelihoods extrapolated from the study of abiogenesis itself.
|
[
"Your question summarizes one of the most important issues related to this field of study (and related to the larger field of evolutionary biology, in general): we have a sample population of one. All life on Earth (that we have observed) is descended from a common ancestor, and thus the product of a single successful abiotic origin. This is a big reason why the search for extraterrestrial life is scientifically important. The chance of encountering other intelligent life is very low, but finding microbial life seems increasingly likely. If/when we do, we will have doubled our sample population and will finally have something different to check our ideas against.",
"It is also important to understand that all science is based on probability. We know nothing absolutely, we only know what is more or less likely. There are plenty of relevant and informative experimental investigations related to the origins of life. None will absolutely confirm how life began on this planet, but plausibility goes a long way. Again, this will be especially true if/when we find life elsewhere in the universe to apply and test our theories against."
] |
[
"Definitely, finding another set of life from a separate abiogenesis event would be amazing from a scientific point of view, especially if we were able to study its biology. I'm sure biologists dream about that sort of thing.",
"Also I just came across a paper that did a bayesian probability anaylsis which concluded the discovery of another population of life would greatly increase the odds of abiogenesis and life being fairly common, so there is that aspect as well."
] |
[
"Remember that if we're working under the assumption that life is unique to the earth in the whole universe (not impossible), then we're utterly wasting our time looking for the answer to how it began. ",
"The real answer would have to be so mind-numblingly far-fetched that it could never be replicated in a lab."
] |
[
"How long could you actually swim in a swimming pool full of liquor before your body succumbs to alcohol poisoning as the liquor absorbs into your body?"
] |
[
false
] | null |
[
"From ",
"Quora",
":",
"You would find it much harder than usual to swim and may drown in an unusually horrible way, for two reasons:",
"1) Distilled liquors have quite a bit lower density (and thus less buoyancy) than a swimming pool because alcohol is lighter than water. You cannot float in 80 proof alcohol -- even with lungs fully inflated, your body is denser than the liquor and you will sink if you stop swimming.",
"2) The fumes will probably cause you to choke and cough. It will be extremely difficult to get a good breath of air, and what you do inhale may cause you to get drunk to the point of passing out. Then you will pass out, inhale liquid, and die. What I don't know is whether the asphyxiation or alcohol poisoning will kill you first."
] |
[
"If it were changed to standing neck-deep in a pool of ethanol with some method of breathing clean air how long would it take?"
] |
[
"Assuming the body's orifices are tightly sealed and that the concentration of alcohol outside the body is significantly higher than that inside (which is valid for a pool with significantly higher volume than the body and will remain valid well past when the alcohol reaches fatal concentrations), the rate of transfer should be constant (unless prolonged exposure alters the alcohols ability to diffuse through the skin). Time until probable death could be calculated if we knew the permeability per unit area of human skin to alcohol, the submerged surface area, the pool's alcohol content, and the volume of the body's water. I've only ever seen such information for organs through which alcohol is typically exchanged (intestine), not the skin. "
] |
[
"Is it possible to calculate the g-forces one would experience at the event horizon and/or the singularity of a black hole?"
] |
[
false
] | null |
[
"But once matter is there... it can never get back out of that area bounded by the event horizon. "
] |
[
"But once matter is there... it can never get back out of that area bounded by the event horizon. "
] |
[
"I've asked this several times, but never got a reasonable answer.",
"Why is speed used to define the point of no return?",
"Escape velocity is a concept thus: the speed at which you have to go to escape a gravity well ",
".",
"On earth, for instance, we can escape Earth's surface by never actually reaching of exceeding the escape velocity at the surface: you just need enough at the surface to get farther away, and the farther you go, the lower the escape velocity gets. To really escape, at some point you have to exceed the escape velocity, but that velocity keeps getting lower the farther you go.",
"It seems like escape from a normal gravity well is a question of energy to overcome the gravitational potential, not just instantaneous speed.",
"BUT with black holes, all we ever talk about is the Schwartzchild radius, which is only defined by speed.",
"Why is that?"
] |
[
"What would have been on the land when “life” first crawled out of the water?"
] |
[
false
] | null |
[
"If you mean 'animals', the first animals to colonize the land were arthropods during the Silurian. ",
"Near lakes, rivers, and the coast, there would have been very primitive plants (think moss and bryophytes) and early land fungi. The rest of the land would have been largely barren."
] |
[
"Neil Shubin has a very interesting book called “Your Inner Fish” that discusses how life transitioned from water to land. I won’t try to repeat his points here as I would be doing so by memory, and it’s not my area of expertise. But this book as well as his others are great for this question."
] |
[
"Animals may have sporadically ended up on land prior to plants evolving, but the first actual land animals postdate primitive plants. Land plants emerged in the very late Ordovician, with early land animals emerging during the Silurian."
] |
[
"Apparently all US Presidents, save one, are related. Given the time scale, is this really that remarkable?"
] |
[
false
] |
Question is based on this video, A fb friend prone to conspiracy theories posted it and I'm curious to get some insight on whether or not this is at all something by which to be impressed, especially given that the common ancestor was a British King from the 12th Century.
|
[
"No. It's not even the slightest bit remarkable.",
"You have two parents, 4 grandparents, 8 great grandparents, 16 great",
" grandparents, 32 great",
" grandparents, etc. In general, you have 2",
" great",
" grandparents.",
"If we take 25 years to be your average generation time, and start the clock in 1986 (when Obama was 25), then there have been on the order of (1986-1200)/25 ≈ 31 generations between 1200 and Barack Obama.",
"Let's make it a round 30.",
"This means that 2",
" = 1,073,741,824 people alive in the year 1200 were Barack Obama's great",
" grandparents.",
"But that's almost certainly impossible, as ",
"according to a variety of sources",
" (links to the actual sources are in the wiki article), the population of the entire world was about 400,000,000 in the year 1200. ",
"What's happening here is that most of Obama's great",
" grandparents actually fulfill that role many time over, via independent routes through the pedigree. So although you can trace a billion different lines back through the pedigree from Barack Obama to the year 1200 (with half a billion going through each parent, a quarter of a billion going through each grandparent), many of them wind up merging back together just a few generations back up, because of this inbreeding phenomenon. So there certainly aren't a billion independent ancestors in the year 1200, but there are definitely hundreds of thousands, and probably many millions",
"In any case, it's clear that as you go back through time, the number of ancestors that any given individual has absolutely explodes. These approximations I've listed for Obama apply to all other US presidents as well, and all other individuals alive today.",
"As such, it's a virtual certainty that the pedigrees of different individuals would eventually start to overlap, no matter who they are, and given that all US presidents have been of European descent (Obama only 50%), I don't think this result is even the least bit surprising. She was guaranteed to find it. The only issue was exactly how far back she would have to go, and whether good records existed that far back. It seems almost certain that there were many other people alive at the same time as this British King who are also ancestors of most or all US presidents, but that the records are simply better in royal bloodlines, so that's who she found.",
"Just for fun, ",
"here's",
" a recent paper by some folks in my lab about using genetic data to understand these sort of patterns of ancestry in Europe."
] |
[
"How remarkable is it that Van Buren is not part of that family tree (as far back as the girl traced at least)?"
] |
[
"JJBerg is 100% correct. Absolutely unremarkable. ",
"This",
" is an excellent overview (written at the layman level) that you may want to send your friend.",
"Key point:",
"Until you understand the fundamentals of genealogical math, you will likely remain impressed with these famous cousin connections, but once you do - not so much. In a nutshell, many people who lived more than three or four hundred years ago now have millions of descendants (yes, millions), and inevitably, a few of them will be famous. And while it used to at least be worthy of note that people would take the time to ferret out these hidden links among living progeny, the growing number of massive genealogical databases makes this less and less remarkable. Those on the prowl for potential headline-grabbing cousinships also know exactly where to look:",
"\"Colonial times in North America constitute a famous cousin sweet spot. They're long enough ago that genealogical math has had a chance to work its magic, but recent enough that there's often a paper trail to follow. That's why - if you pay attention the next time you hear a famous cousin revelation - the touted connections almost always involve a shared colonial American or French-Canadian ancestor. And the living celebrities will rarely be more closely related than seventh cousins. In fact, they're most often eighth, ninth or tenth cousins. About the only exceptions to this pattern are those who are related even more distantly, generally through a royal ancestor who lived back before America and Canada existed.\"*",
"By the way, I have colonial American ancestry and ",
"here's",
" a sampling of my \"famous relative\" breakdown from Ancestry.com. It goes on for pages and pages."
] |
[
"If light travels at \"c\", then does that mean stars will continue to \"appear\" if you have a telescope pointed in one direction?"
] |
[
false
] | null |
[
"Yes, but it will be a real-time process. Imagine that we have 3 stars with no velocity difference between them. Star A is at x=0, B at x=5 Ly, and C at x=10 Ly. No relative ",
" velocity, so we can imagine that each star is using the same clock. At t=0, A and B explode. For the next 5 years, an observer where A was will see B and C shining on as they were, B will see A and C shining, and C will see A and B shining. This is because photons generated by the explosions haven't had time to cover the vast distances between each star. At the t=5 years point, an observer at A will see B explode, an observer at B will see A explode, and an observer at C will see B explode ",
" A will still look content. It isn't until year 10 that C finally sees that A has exploded. ",
"Likewise, whatever additional, further out stars we might see in our telescope by staring at a single point must have formed far in the distant past. Thus, they already exist, and the star that made them already died, we just haven't seen it because of how far away the star is. Sometime in the future, we'll see the photons of it's birth, heavily redshifted, and we'll observe it for as long as humanly possible. Yes, we will sees stars bursting into fusion for the first time, however, there are experimental difficulties with measuring stars that far away, so don't expect to be able to easily distinguish the new stars you see. Also be wary of weak sources and variable sources. A nearby variable star noticed for the first time could look a star catching fire for the first time, until it returns to the off position.",
"Edit 1: was tired, how did no one catch this..."
] |
[
"I don't see how that relates to stars appearing. Ten days is a very long exposure time, and probably needed for distant light sources. But ten days is an extremely short time interval to actually see any difference in the depth of the observable universe.",
"I would be more inclined to believe it was to see \"deep\" rather than to see how the depth changes. But I'm not an astronomer."
] |
[
"At the time of the big bang, the universe was the size of a point",
"This isn't correct, as far as we know."
] |
[
"Does microwaving alter food nutrients?"
] |
[
false
] |
I have been microwaving eggs and it has been suggested to me that the microwave rays burn the protein/fats/nutrients. Is this accurate?
|
[
"I did a couple of pubmed searches, and I couldn't find any readily accessible information. One study showed that microwave prep slightly reduced the beneficial effects of legume starch, but they were comparing microwave prep to raw beans, not to beans cooked via another method.",
"This",
" seems to have some good information, so I'll just quote them extensively.",
"In addition to being more selective, microwave-oven energy is also more penetrating than heat that emanates from an oven or stovetop. It immediately reaches molecules about an inch or so below the surface. In contrast, regular cooking heat goes through food rather slowly, moving inward from the outside by process of conduction.",
"Some nutrients do break down when they’re exposed to heat, whether it is from a microwave or a regular oven. Vitamin C is perhaps the clearest example. So, as a general proposition, cooking with a microwave probably does a better job of preserving the nutrient content of foods because the cooking times are shorter.",
"As far as vegetables go, it’s cooking them in water that robs them of some of their nutritional value because the nutrients leach out into the cooking water. For example, boiled broccoli loses glucosinolate, the sulfur-containing compound that may give the vegetable its cancer-fighting properties as well as the taste that many find distinctive and some, disgusting. The nutrient-rich water from boiled vegetables can be salvaged and incorporated into sauces or soups.",
"Is steaming vegetables better? In some respects, yes. For example, steamed broccoli holds on to more glucosinolate than boiled or fried broccoli.",
"But this is nutrition, and nothing in nutrition is simple. Italian researchers published results in 2008 of an experiment comparing three cooking methods — boiling, steaming, and frying — and the effect they had on the nutritional content of broccoli, carrots, and zucchini. Boiling carrots actually increased their carotenoid content, while steaming and frying reduced it. Carotenoids are compounds like lutein, which may be good for the eyes, and beta carotene. One possible explanation is that it takes longer for vegetables to get tender when they’re steamed, so the extra cooking time results in more degradation of some nutrients and longer exposure to oxygen and light.",
"Edit: Also some good stuff on ",
"wikipedia",
" :",
"Several studies have shown that if properly used, microwave cooking does not change the nutrient content of foods to a larger extent than conventional heating, and that there is a tendency towards greater retention of many micronutrients with microwaving, probably due to the shorter preparation time."
] |
[
"All cooking changes the nutritional content of food.",
"This blew my mind when I first found this out. Especially with regard to how cooking affects how many calories are made available to the body: ",
"http://blogs.discovermagazine.com/crux/2011/12/08/why-calorie-counts-are-wrong-cooked-food-provides-a-lot-more-energy/"
] |
[
"All cooking changes the nutritional content of food.",
"This blew my mind when I first found this out. Especially with regard to how cooking affects how many calories are made available to the body: ",
"http://blogs.discovermagazine.com/crux/2011/12/08/why-calorie-counts-are-wrong-cooked-food-provides-a-lot-more-energy/"
] |
[
"Could we change the course evolution takes?"
] |
[
false
] |
I was thinking about the movie and I got to thinking, is it possible to change the course human evolution takes in order to give us special abilities, such as breathing underwater? From my understanding of evolution, and please correct me if I'm wrong, things evolve to adapt to their surroundings for survivability. Could we force our bodies to adapt to certain situations and mutate ourselves (our future generations)?
|
[
"We cannot ",
" our bodies to adapt to our environment in the evolutionary sense. For people who aren't well educated in evolution and natural selection, the term \"adaption\" is a tad confusing.",
"The previous theory of evolution is known as the Lamarck's theory of evolution (",
"http://en.wikipedia.org/wiki/Lamarckism",
"). His idea was that organisms would change their physical bodies in an attempt to survive harsh conditions not previously lived in. Organisms that do survive pass on whatever changes to their off-spring. Since Darwin, this theory has been proven false.",
"Let's throw down a scenario here. 100 people live within a biosphere, reproducing like normal people would. They absorb oxygen through lungs as we do today. But something happens within their environment that that requires them to ONLY have dark skin (anyone without dark skin dies off). So let's say that 90 lighter-skinned people die and 10 darker skinned people survive. The remaining ten reproduce to create a population of solely dark skinned people. The remaining ten have \"adapted\" to their environment. Adaption is a genetic advantage that an organism has BEFORE a change in environment.",
"So with that said, would it be possible for people to humans to evolve to breathe underwater? Assuming that some people have the ability to breathe underwater (say, have gills) and breathe on land (lungs) before whatever disaster happens, then maybe. If those remaining gill/lung humans met together and reproduce the entire human population with gills and lungs, then yes, people would be able to breathe underwater.",
"So to change the course that evolution takes, we would have to genetically change a set of people to have whatever adaption before whatever disaster occurs so they survive and repopulate the human race.",
"tl;dr - ",
" yes, realistically not a chance.",
"Feel free to correct anything I posted. "
] |
[
"First off let's remember that evolution is not something that happens overnight or even over a lifetime. Evolution is a result of natural selection. Natural selection is the concept that traits will be passed on by survivors. It goes well with survival of the fittest which means that an organism that is more well suited for it's environment will pass it's genes on to offspring. So basically a more fit individual is one that is able to not only survive in their environment but pass those traits on to future generations. Natural selection is based around the idea that traits that more easily facilitate successful breeding and successful offspring will be the ones continuing to pass on these inherited genes. New traits are introduced through mutations. Many mutations are not good as they are not normal, however some are actually advantageous. For example a nocturnal creature low on the food chain would be more likely to survive if they were black as opposed to glow-in-the-dark. Now what if the normal color was glow-in-the-dark and the mutation was black? Well that black creature would probably survive and pass it's genes on to more offspring, that combined with the limited mate selection due to so many being eaten we would see a small change in the populations expression of a certain gene. Naturally over many MANY generations the glow-in-dark individuals would die out and black would be the new color. Why? Because the color black helped better facilitate the creature not only living in their environment but also passing that trait to their successful offspring. So evolution occurs as a result of natural selection choosing traits that facilitate successful breeding and successful offspring.",
"With that said. It's not very practical to think that any lineage of people would actually be able to focus on changing a trait as major as that in any sort of conceivable time frame (thousands if not millions of years). It would also not be very ethical to breed humans and restrict or force them to breed with other humans based on which traits they express. So for something like having humans developing gills this probably could not happen feasibly. It would just be too hard to breed humans enough times to get a mutation with gills. Evolution works well and it's very hard to trick. So is it possible? Well I suppose so but it's not likely to ever happen, well at least not without an initial mutation which would be hard to create. However, if you wanted to stick with the breathing under water thing, over a long enough period of time you could probably breed a group of humans to have amazing capabilities to hold their breath underwater. If you only allowed humans to mate with other individuals with above average abilities to hold their breath for enough generations you could theoretically create a human that could hold their breath and stay active for say 20-30 minutes. It's not practical and it would take a long time. But it's possible.",
"There have been many cases of selective breeding so organisms exhibit favorable traits. Such as selectively breeding corn to exhibit traits such as size. Individuals have used this technique of selective breeding throughout history. But they have never created traits that didn't some to exist naturally through some mutation.",
"The idea of being able to manipulate genomes as they are being formed in the womb to genetically engineer your offspring is another issue entirely. There is no telling what we will discover and what will be able to manipulate artificially. Something such as human gills may be possible through a technique such as this in the future.",
"TL;DR Evolution and natural selection work with current traits. Gills could not be expressed in humans unless there was a human with a mutation expressing gills first. Evolution doesn't create traits it regulates which ones are passed on."
] |
[
"Possible? Yes\nPlausible? No",
"Human race will most likely perish before anything like that happens. Don't mean to sound like a buzz kill :)"
] |
[
"Can the immune system target specific elements inside the cell?"
] |
[
false
] |
[deleted]
|
[
"It kind of depends what you mean by \"target\". The immune system can certainly ",
" elements inside the cell, and determine that they are foreign and need to be destroyed. The immune system can't really specifically remove those foreign elements, though (though there have been arguments that under some conditions it can). In general if a cell contains harmful foreign elements, the immune system rapidly identifies it and destroys the whole cell.",
"You ask about mitochondria specifically. In fact mitochondria are strongly recognized by the immune system and treated as harmful. This shouldn't be surprising in principle, because of course ",
"mitochondria are symbiotic bacteria",
", and the immune system is tuned to recognize and destroy bacteria. Normally, though, mitochondria are invisible to immunity because they are intracellular; it's mainly after cells are damaged that mitochondria are exposed to the immune system and can lead to responses.",
"Mitochondrial damage-associated molecular patterns (DAMPs) are molecules that are released from mitochondria to extracellular space during cell death and include not only proteins but also DNA or lipids. Mitochondrial DAMPs induce inflammatory responses and are critically involved in the pathogenesis of various diseases. .. ",
"--",
"The Roles of Mitochondrial Damage-Associated Molecular Patterns in Diseases",
"There are two major pathways by which cells provide information about their internal components, to the cellular components of the immune system like lymphocytes and neutrophils. ",
"In one, there are a large number of intracellular sensors that monitor cells for general ",
"pathogen-associated molecular patterns",
" (wikipedia link). These trigger pathways that eventually result in the cell producing ",
"cytokines",
", like ",
"interferons",
", that activate and recruit immune responses.",
"In another branch, there's a complex process that constantly surveys intracellular protein production, and moves samples to the outside of the cell where lymphocytes can analyze the cell and respond to those that have abnormal components. This is called ",
"antigen presentation",
".",
"But again, the response is not so subtle. Instead of delicately removing the abnormal component, the whole cell is typically destroyed, presumably preventing the intracellular pathogen from completing its life cycle and amplifying its numbers."
] |
[
"Interferons and interleukins are two good examples of it.",
"Interferons can be produced by infected cells or immune cells in response to infections or tumors. One of their functions is to slow down replication of RNA to slow down the replication of the pathogen or the cancer cells. And interferons also targets other cells to lower their vulnerability against the infection.",
"Interleukins (or cytokines) are mostly regulators of the immune response. They activate and target immune cells against pathogens or antigens, they control their replication, the production of antibodies and the differentiation of the many immune cells (like memory lymphocytes, useful against a second infection). Cytokines are produced by immune cells but also many other cells in your body and another of their functions is to regulate the immune response to avoid self-immune reactions. A cytokine storm is an acute disproportionate cytokinic response to an infection. That's what caused so many deaths at the begining of the COVID pandemy."
] |
[
"The immune system can't really specifically remove those foreign elements, though (though there have been arguments that under some conditions it can). In general if a cell contains harmful foreign elements, the immune system rapidly identifies it and destroys the whole cell.",
"That definitely depends. Systems like CRISPR-Cas and piRNA, for example, are capable of removing foreign elements without damaging the cell. ",
"Of course immune systems vary dramatically depending on the organism you investigate."
] |
[
"How did they carry out genetic identification before the human genome project?"
] |
[
false
] |
Ok, so I keep seeing references of DNA fingerprinting around the 1900s to 2000s. I see the reference to engineering E. Coli to create insulin. Or identification of genetic diseases using the various blotting styles. The question I have here is... How did they know what gene and sequence to look at? I know they can certainly find the sequence using the right polypeptides and marking techniques. But the question here is how did they know what the specific sequences were? How did they know that this specific sequence coded for insulin? Or that this specific sequence was for Tay Sachs?
|
[
"So DNA sequencing techniques were available before the Human Genome Project. The main drawback was that they were slow and laborious, and could only sequence very small amounts of DNA (think hundreds to a thousand or so base pairs, which is on the order of the size of a gene). So, it was feasible to get the sequence for insulin, but it wasn’t to sequence the extraordinary amount of base pairs that constitute the human genome. That is, until we developed much faster, high-throughput sequencing methods that made it possible."
] |
[
"Most genetic studies involve a technique called \"polymerase chain reaction\" developed in 1985.",
"In this technique, a strand of DNA get copied repeatedly, in the millions, to make it detectable and readable.",
"Interesting Background here",
" ",
"The technique is done by adding enzymes and raising and lowering the temperature.",
"There were clear limits to the maximum size of the copyable DNA strand and it took dozens to hundreds of reactions performed manually to get good results.",
"It was highly, highly laborious and costly.",
"As time progressed, the process was improved and automated, also very much stimulated by the human genome projects.",
"Today, PCR is performed by highly efficient \"thermal cyclers\" heavily lowering cost and time needed to identify DNA. It's a wondrous technique honestly.",
"So, the famous PCR tests performed nowadays? Thousands of thermal cyclers worldwide are amplifying genetic material from mucus to search for viral material. Hence the name."
] |
[
"We still knew about genes before the human genome project, we just didn't know all the genes. Before the human genome project we could amplify small parts of the genome with ",
"PCR",
" and sequence them.",
"The genes themselves were first discovered centuries ago. Many genes were first discovered by breeding plants and fruit flies and identifying patterns of inheritance. Of course the sequences wouldn't be known until much later, the first gene was sequenced in the late 70's. But the concept of a heritable unit is very old.",
"Insulin is actually a perfect example. Insulin is a protein made of amino acids, each amino acid is coded by 3 letters of DNA in the gene (but even this wasn't known until the 60's). We discovered the amino acid sequence of Insulin in the 50's, before we knew the DNA sequence. Quick bio refresher: our genetic code is stored in DNA as A T G and C much like the 1's and 0's in a computer. The DNA sequence is then converted RNA (basically the same thing) and then translated into proteins which use a different code. Back in the 50's protein was a big deal and for the most part no one knew much about DNA. Scientists knew that proteins were made of amino acids in chains but they didn't know the sequences. ",
"Frederick Sanger",
" wanted to find the amino acid sequence of insulin and he came up with a genius (nobel prize winning) idea. He knew how to identify the amino acid at the end of the chain but not the ones in the middle of the chain. So he took many insulin proteins (many chains) and broke them up into chains of all sizes, separated them by size and read the end amino acid. Then he took all these end reads and put them together in the order of size and got the sequence.",
"Sanger later took this idea of reading the ends of amino acid chains and applied it to DNA creating ",
"Sanger sequencing",
". It works the opposite way, by building chains and stopping them at different points, you still get many chains of all sizes and read the end of each though. We have much faster methods now but it all came from someone trying to discover the primary structure of insulin."
] |
[
"If I throw a baseball at 90 mph, does that mean my hand must be travelling at 90mph before it releases the ball?"
] |
[
false
] | null |
[
"At least the tips of your fingers have to. You see, once the ball has left your hand, there is no way it is accelerating anymore. That means, the ball has the highest velocity just as it leaves your hand. Your hand therefore has a speed of 90 mph at the moment you throw.",
"Edit: Holy, that thing has blown up since I was here last. Just to clarify, my argumentation does not include effects like added rotational energy of the ball. You are welcome to discuss. However, in my opinion, these effects are not exactly in the magnitude of the translational energy involved here. ",
"For all those arguing with momentums that can further accelerate the ball after it has been thrown (no flick involved): No. Have a look at conservation of energy."
] |
[
"This is in contrast to a football or soccer ball which is compressed during a kick and comes off the foot faster than the foot is moving."
] |
[
"Baseballs do that too, but they do it when being struck by a bat. See: ",
"http://www.maxbats.com/images/bats/find-your-max/ball-compression.jpg"
] |
[
"Southern Blot Help. My blots keep coming out looking like attached figure\"E\", in which it looks like all the genomic DNA is being hybridized. Any Advice?!?"
] |
[
false
] |
Please look at . Not sure why, but it happens all the time. I can barely make out the bands and I need to determine if there is another band about 1000bp shifted. Any advice would be really appreciated.
|
[
"Could you be using to much dye? (I cant remember what it's called) It looks like there's an even streak across the entire lane, which is probably dye not DNA fragments. ",
"Sorry if it's no help, I just started running those this month, and still haven't mastered it myself"
] |
[
"If the DNA is not dyed, how are you getting a good look at it? In my lab, we view the gel under a UV light to see they dyed DNA"
] |
[
"Try ",
"r/askscitech",
" as well."
] |
[
"Why does it feel so good to get a \"back rub\"- but not as good to get a \"front-rub\"-? -and please hold back any sexual jokes."
] |
[
false
] |
Are the nerves/muscles more superficial? Is it because of extensors vs flexors? I've always wondered about this-
|
[
"Your back muscles are under the strain of holding you upright all day. ",
"Your front is mainly softer tissue. ",
"Your back protect your internal organs and is rigid. ",
"Your lower front would allow the massager to press on those organs. "
] |
[
"Front rubs feel ",
", especially on the upper pectorals and anterior deltoids. Maybe you're not giving/receiving in the right places?"
] |
[
"And how does a person go about doing this? I'm not really sure if I am using my core muscles or not; I don't know how to tell."
] |
[
"The farther one looks into space, the farther one looks back in time."
] |
[
false
] |
Hi everyone. It is sometimes confusing to me when people maintain that the farther one looks into space, the farther one also looks back in time. I am a layperson in physics, but from what I know about special relativity, it seems that one cannot posit an inertial frame of reference for all of the universe. So how can one attach a given date to a distant event one sees in space? Should one not say that those events are taking place now, immediately, in one's own frame of reference? Can the concept of "now" even be used in this context? There is some time I have been thinking about this question, and I thought reddit could provide an answer.
|
[
"Cosmologist use what they call comoving coordinates, where a stationary observer sees the universe as isotropic. All the galaxies are more or less stationary in this coordinate system. As you can guess, this 'grid' follows the expansion of the universe and the proper time experienced by comoving observers is roughly the same for all of them. This frame isn't anything special physically, it's just convenient."
] |
[
"Based on your question, it seems you're implying that an event can only be said to have happened once YOU receive information that it has happened. ",
"And before it's said, the friend surprise visiting and seeing a star from 1000 light years away blow up are not different when looked at from an information propagation perspective, which is what this question is truly about (I think?).",
"Just to explain myself a little more, as I sometimes doubt my ability to be clear:",
"Friend surprise visiting you = a supernova sending out light = information being sent that you are unaware of before the information reaches you",
"Knock on your door = your eyes receiving the supernova's light = notification that a previously unknown event has happened",
"If you are able to say that a supernova whose light is just reaching you is happening right now in your frame of reference, then wouldn't you have to say that a friend who surprise visits you left their house in your frame of reference the moment they knocked on your door?"
] |
[
"If someone throws a baseball at you, what good would it be to say that he threw the baseball when you caught it?"
] |
[
"Can any flavor (e.g. \"blueberry\" or \"cheese and onion\") be expressed as a combination of relative amounts of the five basic tastes (sweet, bitter, sour, salty, umami), just like colors can be expressed as RGB?"
] |
[
false
] |
, then: , then: why not? What do people mean when they say there are "five basic tastes"? What other factors are necessary in order to recreate a taste?
|
[
"No:",
"The five basic tastes are what the taste buds on your tongue can detect. Flavor, however, is much more than that. It works in conjunction with the nose. That is why you do not smell a lot when you have blocked nose.",
"It might be possible to decompose the taste (only tongue), but even the taste is not only the amount in the five parts, but also the temporal distribution (you might have noticed that some foods appear to change their taste a while you chew them) not to mention texture."
] |
[
"Flavors are determined by a staggering array of chemical compounds, but there is some work being done towards a theory of complementary flavors. ",
"Here's a research letter regarding it."
] |
[
"I was reading the wiki entry for Taste after a similar question some time ago and there is apparently a sixth taste: ",
"metallic",
"."
] |
[
"Is there any way to prove that anything really exists?"
] |
[
false
] | null |
[
"This is really a philosophy question and should be posted to a philosophy sub."
] |
[
"I'm looking at the question from a physics point of view, like is there a certain type of atom analysis or something to prove existence of other things, are there electrical impulses from the brain that prove consciousness?"
] |
[
"You are presupposing that atoms exist. This is really a philosophy question."
] |
[
"Is there a limit to how bright a light source can be? In other words, is there a limit to the density of photons in a given place at a given time, or is this hypothetically limitless given a sufficient source?"
] |
[
false
] |
Assuming you had a limitless source of photons, could a limitless amount of them be concentrated into a beam of light, or is there a limit to their density?
|
[
"They have energy density, so they gravitate.",
"They don't have rest mass."
] |
[
"In theory, if you were to concentrate enough light in a volume, the light would collapse to form a black hole. However, there's not a practical method for doing such a thing."
] |
[
"It would be more accurate to say that rest mass is one potential form of energy, and all energy contributes to gravitational effects, regardless of what form it might be."
] |
[
"How do GPS receivers get their position from GPS satellites?"
] |
[
false
] |
So I know that GPS receivers look for satellites and calculates its position based on that, probably through triangulation. But how does the receiver communicate with the satellite? Does the receiver send out radio signals that get picked up by satellites, or do the GPS satellites continuously broadcast radio signals that the receiver listens to? If the former, how does the satellite sort through a million requests for information from everyone using GPS at any point in time? If the latter, doesn't the satellite require a lot of power to operate? Does solar power provide enough energy for the satellite to continuously broadcast?
|
[
"GPS satellites have very precise atomic clocks (which are monitored and kept accurate by very, VERY accurate atomic clocks on the ground). They are also told their orbit parameters by the monitoring ground stations. This very precise time and pretty darn precise location is broadcast by the satellites continuously to be picked up by a GPS receiver. GPS is a one way system, signal is sent from the satellite constellation and picked up by receivers in GPS navigation devices. Edit: they are all solar+battery powered, the original satellites could generate around 400 watts of power, later models could generate 700+ watts.",
"The receiver compares the time of acquisition from 2 or more satellites with the time of transmission as reported by each satellite and from the small differences can calculate the \"time of flight\" of each satellite signal. With that information it can calculate the distance to each satellite and with the reported satellite positions can calculate where it is in 3 dimensional space. More satellites being monitored can be used to improve positional accuracy because of the slight inaccuracy in each satellite's \"knowledge\" of its own position."
] |
[
"Wouldn't the satellites also have to transmit their own location for the receiver to be able to triangulate? ",
"Also, why would the transmission area be the shape of Europe? GPS works in the oceans, too, so it would make more sense for the transmission area to be anything with a line-of-sight to the satellite (understandably at least a certain amount over the horizon, if necessary, I guess). "
] |
[
"Wouldn't the satellites also have to transmit their own location for the receiver to be able to triangulate? ",
"Also, why would the transmission area be the shape of Europe? GPS works in the oceans, too, so it would make more sense for the transmission area to be anything with a line-of-sight to the satellite (understandably at least a certain amount over the horizon, if necessary, I guess). "
] |
[
"Why does exercise help us lose weight?"
] |
[
false
] |
Obviously, exercise allows you to burn more calories more quickly, but wouldn't that just cause you to become hungrier faster, meaning you'll eat more? So that in the end, regardless of how much exercise you're doing (or not doing), all that matters for weight loss is that you eat less than your body says it wants you to eat. Am I missing something here?
|
[
"Yes, the key is to spend more than what you take in.",
"all that matters for weight loss is that you eat less than your body says it wants you to eat",
"Not really, because if you are not active enough the body will find other ways to cover the deficit, such as reducing muscle mass to reduce upkeep energy requirement."
] |
[
"To clarify: muscle loss is still weight loss, so OP is correct. But yes, exercise and sufficient protein intake will help make sure that more of the lost mass is actually fat and not muscle."
] |
[
"In order to burn a pound of fat, you need to expend 3800 more calories than you take in. If you exercise more, and eat more, you'll essentially stay the same weight. (This isn't exactly true, but it is the gist.)"
] |
[
"How can stars cool down as they gain energy?"
] |
[
false
] |
With the semi- recent talk of a gas reaching negative Kelvin values I decided to check out how this was possible. Apparently the confusion arises from our interpretation of temperature. After reading a helpful explanation ( ) I think I understand the mathematics of it but not so much the theory. Why is it that as energy is added to stars, and black holes, etc. they are less 'willing' to give up energy. Similarly there are objects that as they gain energy they become less entropic. What's the explanation behind that? Edit: Spelling
|
[
"They don't \"cool down\" as they gain energy, they actually become hotter (as in more willing to transfer heat). Temperature (in a thermodynamic sense) is not a measurement of how hot something is. From the laws of thermodynamics we can define temperature (T) as a measurement of how much entropy increases (dS) per added heat energy (dQ). ",
"dS=dQ/T \n",
"(They use the equation upside-down in the article, but it's still essentially the same)",
"Entropy is (simplified) number of possible unique configurations energy can take in a system.",
"Normally the more energy into a system, the more ways it can be configured. But in extreme cases energy already exist in most configurations, and when energy is added it will occupy some of the remaining configurations and there will be ",
" possible configurations left, and thus entropy ",
" with the addition of energy.",
"And if we put a negative value for change in entropy (dS) in our equation, temperature will also be negative.",
"EDIT: Expanded explanation to include entropy.",
"EDIT2: Answering a question.",
"Why is it that as energy is added to stars, and black holes, etc. they are less 'willing' to give up energy.",
"The article's bolded definition \"Temperature measures the willingness of an object to give up energy\" is misleading and isn't well-defined for negative temperatures. 0 Kelvin would be where an object is not at all willing to give up energy. Negative Kelvin is a new scale of \"willingness of an object to give up energy\" above any positive temperature. The second law of thermodynamics states that the entropy of an isolated system ",
" decrease, and as entropy decreases with the addition of energy in a negative temperature system, energy cannot transfer for a system with positive temperature into a system with negative temperature without violating the second law of thermodynamics. "
] |
[
"Great Explanation. Follow up question- How is it that the discovery of the Quantum Gas that goes into 'negative Kelvin' can actually result in a combustion engine with a >100% efficiency? "
] |
[
"http://www.sciencedaily.com/releases/2013/01/130104143516.htm",
"It says, \"Matter at negative absolute temperature has a whole range of astounding consequences: with its help, one could create heat engines such as combustion engines with an efficiency of more than 100%. This does not mean, however, that the law of energy conservation is violated. Instead, the engine could not only absorb energy from the hotter medium, and thus do work, but, in contrast to the usual case, from the colder medium as well.\nAt purely positive temperatures, the colder medium inevitably heats up in contrast, therefore absorbing a portion of the energy of the hot medium and thereby limits the efficiency. If the hot medium has a negative temperature, it is possible to absorb energy from both media simultaneously. The work performed by the engine is therefore greater than the energy taken from the hotter medium alone – the efficiency is over 100 percent.\" It sounds simple, but I don't understand it at all"
] |
[
"Are the orbits of the planets in our solar system flat, or largely on a similar plane? Why? If so, are planets in other solar systems the same?"
] |
[
false
] | null |
[
"The solar system formed from a disc of gas, which is why all the planets formed in the same plane. This disc formed from the collapse of a cloud of gas. As interstellar gas is pretty turbulent, any chunk of gas will have a bit of spin to it, which basically gets amplified as it cools and collapses under gravity, until you get a disc. And as this spin comes from random turbulent motions, every solar system basically has its own spin, and therefore its own plane. So each solar system is flat, but they're all pointing in different directions to each other. They don't generally coincide with the plane of the Milky Way, except by coincidence sometimes."
] |
[
"While many discs will be flat and aligned with their host star they are not as simple as was once though. ",
" ",
"Misalignment between the hosts spin vector and the discs orbital vector are pretty common (",
"Franchini et al. 2018",
"). Some ways this can happen is by truncation of the molecular cloud by a nearby passing companion, more turbulent acretion, magnetic star-disc interactions and more. Although it is possible some observations of star-system misalignments are actually due to momentum transport within the star leading to the atmosphere of the host star having a different spin vector from the interior ",
"Aerts et al. 2019",
". ",
" ",
"We can also have warped discs. This is essentially a twisting of the flat disc so that the inner and outer portions are misaligned. In the late stages of protoplanetary discs we can also have fragmented inner and outer portions of the disc which can be misaligned ",
"Benisty et al. 2018",
". This can result in very high mutual inclination between the inner and outer disc (with some suggesting polar discs are possible). These effects on discs have been observed in both simulations and observations but the mechanisms involved are not well understood.",
" ",
"While the disc exists planets are embedded within it and hence their orbits follow within the disc. Once the disc dissipates then things change and we can have dynamical interaction between the planets (such as planet-planet scattering) which can result in high mutual misalignment. Further, if there is a nearby massive companion (for example in a distant binary system) then the Kozai-Lidov mechanism may act to misalign the system.",
" ",
"One such interesting problem in exoplanets is the so called Kepler Dichotomy. That is the over abundance of single transiting systems (systems where only a single planet transits). It is thought that this is either because there are two populations of systems, single planet systems and multiplanet systems, or that ~50% of systems are actually misaligned ",
"Ballard and Johnson 2016",
". Last time I checked all Kepler multis are flat to the same extent as the solar system but this may just be because of observational bias in the techniques.",
" ",
"Just thought I would add this in as a lot of our \"well the Solar system is like this and so all systems must be like this\" has been getting slowly destroyed by the advancements in exoplanetary science in the past 20 years."
] |
[
"To put some numbers to the \"flatness\" of the Solar System:",
"The invariable plane of a planetary system is the plane passing through its barycenter perpendicular to its angular momentum vector. (In the Solar System, about 98% of this effect is contributed by the orbital angular momenta of Jupiter, Saturn, Uranus, and Neptune). ",
"The invariable plane may be regarded as the weighted average of all planetary orbital and rotational planes. In the Solar System, the orbital planes of 6 planets align within ",
" of the invariable plane. Only Mercury (6.3°) and Venus (2.2°) exceed this threshold. So the Solar System is quite \"flat\"."
] |
[
"If two different viruses invade one cell, which virus wins?"
] |
[
false
] | null |
[
"It depends! Very complicated question with many examples.",
"I actually do a pre molecular/immuno technique to see if a cell is infected by one virus by trying to infect it with another that has a much more pronounced effect. ",
"If the second virus can't infect then you know that the cell was infected with the first."
] |
[
"It’s very unlikely to happen at all",
"There are viruses like Hepatitis D which can only reproduce if a cell is infected with another virus, in this example that is Hepatitis B. Considering there are viruses that require coinfections to reproduce I wouldn't claim it is very unlikely to happen."
] |
[
"That's rather interesting. I had never thought you could do that. May I ask if this is research or a testing lab?",
"As a follow up if I may, could we use a stronger virus that is benign or easily eradicated as a counter agent to another virus that is more pathogenic? Perhaps as a form of prophylaxis?"
] |
[
"Is there a scientifically viable explanation of quantum mechanics that suggests the universe is deterministic?"
] |
[
false
] | null |
[
"Determinism usually means that you can ",
"fully predict the future given the initial conditions of the system.",
" If you have those initial conditions you will never be surprised.",
"In De Broglie-Bohm, all of those initial conditions exist but you still cannot look at them. Determinism with no spoilers is a really weak form of determinism if you even want to call it that.",
"In Many Worlds, even if you had all pieces of relevant information (which you still can't get), there is no singular future to predict. In this interpretation the multiverse as a whole is deterministic from some outside perspective but it doesn't allow outside perspectives. Call it determinism with lots of qualifiers.",
"You can also bite the bullet and accept the Copenhagen interpretation, which gets rid of the unobservables but introduces the concept of frighteningly pure randomness and unpredictability.",
"All of these are equally valid ways of interpreting the experimental results and the math. Pick whatever you like, unless De Broglie's pilot wave or your alternate-universe twin have already picked for you."
] |
[
"Determinism usually means that you can ",
"fully predict the future given the initial conditions of the system.",
" If you have those initial conditions you will never be surprised.",
"In De Broglie-Bohm, all of those initial conditions exist but you still cannot look at them. Determinism with no spoilers is a really weak form of determinism if you even want to call it that.",
"In Many Worlds, even if you had all pieces of relevant information (which you still can't get), there is no singular future to predict. In this interpretation the multiverse as a whole is deterministic from some outside perspective but it doesn't allow outside perspectives. Call it determinism with lots of qualifiers.",
"You can also bite the bullet and accept the Copenhagen interpretation, which gets rid of the unobservables but introduces the concept of frighteningly pure randomness and unpredictability.",
"All of these are equally valid ways of interpreting the experimental results and the math. Pick whatever you like, unless De Broglie's pilot wave or your alternate-universe twin have already picked for you."
] |
[
"Both ",
"de Broglie-Bohm",
" and ",
"Everettian (ie Many Worlds)",
" interpretations of quantum mechanics are deterministic. "
] |
[
"How easy is it for a person to lose and gain brain cells?"
] |
[
false
] |
[deleted]
|
[
"Well my neuropathology teacher told us that there is still some sort of neurogenesis on adult brain on the sub ventricular area and the hippocampus area (Like you gain a few hundrerds neurones every day) but you have a few thousands that die every day too.",
"As for glial cells, they keep the capacity to divide themselves even into adulthood.",
"So basically it's super easy to get/lose new neurons/new glial cells, you just have to wait."
] |
[
"To further, further add, the number of neurons isn't really as important as you might think. Moreover losing them, through a process called pruning, is part of the normal development of the brain. In fact, a lack of pruning has been associated with mental disabilities including autism, and disorders such as schizophrenia. ",
"We're supposed to lose neurons. This is probably (partially) why we forget the name of our 6th grade history teacher and can't remember the capital of Canada. But we tend to keep the connections we need the most and trim the fat throughout our lifespan. "
] |
[
"To further, further add, the number of neurons isn't really as important as you might think. Moreover losing them, through a process called pruning, is part of the normal development of the brain. In fact, a lack of pruning has been associated with mental disabilities including autism, and disorders such as schizophrenia. ",
"We're supposed to lose neurons. This is probably (partially) why we forget the name of our 6th grade history teacher and can't remember the capital of Canada. But we tend to keep the connections we need the most and trim the fat throughout our lifespan. "
] |
[
"Hypothetically, if Time Travel were to exist, how would we measure the rate of travel?"
] |
[
false
] |
[deleted]
|
[
"(time of object/system/reference frame/whatever you're attempting to time travel relative to)/(time as experienced by you/those within or passing through the time machine)"
] |
[
"It really depends on the type of time travel.",
"To make an analogy with something we know, forwards time travel, the rate can be measured with the Lorentz factor, which can be thought of as a ratio between time passed for you and time passed on Earth (or wherever).",
"If you're travelling faster than light then your Lorentz factor is imaginary; perhaps the absolute value of that imaginary number could be used as a measure."
] |
[
"Seconds per second."
] |
[
"Why is that, when things are heated up, they turn orange, red, or yellow?"
] |
[
false
] |
Like iron. Heating it up to melt it causes it turn yellow or orange. Why not blue or green?
|
[
"The name of the effect you're asking about is ",
"\"black body radiation\"",
". All objects (including you) emit light, with the frequency of that light depending on how hot the object is.",
"The ",
"color",
" of light is determined by its frequency, or mixture of frequencies. The order matches the ",
"rainbow",
", going from infrared (which you can't see) to red to green to blue to ultraviolet (which you can't see) as frequency increases.",
"However, you won't see hot things cycle through the rainbow as they heat up. Objects hot enough to emit blue light also emit a lot of red light (and everything in between). So what you see is more like \"adding up\" the rainbow, with the colors going from ",
"red",
" to ",
"red+green=yellow",
" to ",
"red+green+blue=white",
" instead of ",
"red",
" to ",
"green",
" to ",
"blue",
".",
": ",
"Infrared vision",
" works by detecting black body radiation emitted by your body, which is hotter than the environment and so emits infrared light of a slightly higher frequency."
] |
[
"Good answer. Note that a better name for the physical effect is \"thermal radiation\". Blackbody radiation is a really an idealized model of thermal radiation, which typically does not hold exactly true to the thermal radiation spectrum coming from real-life objects."
] |
[
"All objects above absolute zero emit thermal radiation as the vibrations of atoms in the material are spontaneously converted into electromagnetic radiation. This radiation covers a broad range of frequencies, and the spectrum of frequencies emitted depends on the temperature of the material. At room temperatures, the peak of the radiation spectrum is in the infrared range, and almost no visible light is emitted by the material. While our eyes don't see any glowing, infrared cameras can actually capture this thermal radiation just fine - this is what you are seeing when you see \"heat vision\" or similar things in movies and games. As the temperature gets higher, the spectrum of the thermal radiation changes and the peak starts moving to higher and higher frequencies. Once the temperature reaches about 500 C, the radiation peak reaches a frequency that our eyes can see, and we see a dull red glow. As the temperature continues to increase, the frequency peak rises and the color changes to orange, yellow, and if it gets hot enough, a whitish-blue.",
"Interestingly enough, this range of colors is exactly the same range of colors that we see when we look at stars through telescopes. Cooler stars are red, warmer ones like our sun are yellow, and short-lived intensely hot supergiants are a brilliant white-blue. This is because the light we see from stars is the same thermal radiation you see when you heat up a piece of iron with a blowtorch.",
"You can read more about it here:\n",
"http://en.wikipedia.org/wiki/Thermal_radiation",
"\n",
"http://en.wikipedia.org/wiki/Black-body_radiation"
] |
[
"A question about the expansion of the universe."
] |
[
false
] |
Let's say that I could find 2 galaxies equally as distant from each other as they are from our galaxy to form an equilateral triangle in space. Provided that we could get an accurate measurement of the distance between them and came back and observed them at a later date would it still form an equilateral triangle? Would the distance between all three be the equal? Have there ever been any experiments conducted to check this? I understand they are studying supernovae to use as standard candles for measurements over large distances so maybe this is something we have not been able to do yet. I guess the heart of my question would be is the expansion of space uniform? When I hear people in physics and astronomy talk about red shift they simply state that every where we look galaxies are speeding away from us. Why do they say almost, are there any anomalies we have found?
|
[
"First, keep in mind that galaxies have their own motion and direction regardless of expansion. So in your example, the three galaxies are moving on their own - with their own local groups, etc.",
"Expansion does not actually move galaxies - but rather, simply creates more space between them.",
"Since the force of gravity is much stronger than the force of expansion - any time there is enough gravity (e.g., energy/matter) there is no expansion. So expansion happens more in the dead of space - rather then in galaxies, etc.",
"Edit: Yes, and some galaxies are coming towards us (blue shifting) - such as Andromeda in our local cluster which will eventually collide with the Milky Way."
] |
[
"scientists don't tend to do things like that.",
"http://en.wikipedia.org/wiki/Metric_expansion_of_space#Observational_evidence"
] |
[
"Fair enough, I forgot about the motion of galaxies in relation to being pulled by gravitational forces. So let's say we could observe the motion of the galaxy and add/subtract their regular motions from the measurement. I understand that the expansion comes from empty space but I am still curious if we have been able to determine it's uniformity or lack there of. "
] |
[
"Why is it typical to feel an uplift in mood after a psychedelic trip dispite causing downregulation of 5ht receptors?"
] |
[
false
] |
Assuming the user was not traumatized for some reason, which is quite rare, it's often reported ingesting a psychedelic drug leaves you with a lasting sense of well being, happyness, and connection to others. See the john's hopkins research for instance. It's also been shown in rats that 5ht receptors rapidly down regulate upon injesting said chemical and this is what causes tolerance, generally returning to normal in about a week. So giving our current understanding on serotonin's effect on mood do we have any ideas on this currently? This would seem to be in opposition to how SSRI's work in increasing 5ht activity, how can a reduction in said activity cause the same effect?
|
[
"Serotnin's reputation as a happiness hormone is undeserved. It's role is more of as a stressor and if a person benefits from SSRI's it's quite debatable that it has anything to do with increasing serotonin levels. Danny Roddy summarized the ",
"research on serotonin and psychedelics in a recent post",
"."
] |
[
"That article kinda read like someone trying to cherry pick data and mold it around their own idea of what's happening. I don't believe SSRI's work particularly effectively for treating depression, to say so is oversimplified, but while that is why they were designed they anticipated there would be side effects due to their method of action. Imo it's a very crude way of achieving their end goal, but it's what we currently have. ",
"If serotonin makes you stressed out and depressed how do you explain mdma's effect? I don't buy it's simply due to a release of cortisol, that sounds rediculous. If that were the case prednisone would be abused. Sure it can give you a slight increase in mood, but it's hardly noticable, especially compared to mdma. I could maybe be persuaded serotonin does the opposite of what we thought, but an increase in mood simply from cortisol is absurd."
] |
[
"MDMA effects levels of serotonin, norepeniphrine, dopamine and oxytocin. Norepeniphrine is a catcholamine, so that energizes people (makes them want to dance their ass off). Oxytocin is undoubtably the hormone that makes people feel all love-y and huggy and like everyone is their best friend. In the theory of serotonin as stressor, then this would be why people experienced clenched jaw, sore low back and a depressive/burnout phase in the week(s) after usage."
] |
[
"Where did dust come from?"
] |
[
false
] |
[deleted]
|
[
"It’s made up of everything and anything pretty much, although the thing that’s commonly said is that a high percentage of dust is dead skin cells. Technically it came from space but in the end we all did and everything does. "
] |
[
"As long as we have air flow to pick up and carry fine particles of skin and sand and notes and their “emissions” etc. we will always have dust. If you think of how much dust could exist in the air in a sealed room and you see how dusty an old closed up house gets, there is a ",
".",
"All cleaning up does is move the dust buildup around to somewhere we can’t see it."
] |
[
"As long as we have air flow to pick up and carry fine particles of skin and sand and notes and their “emissions” etc. we will always have dust. If you think of how much dust could exist in the air in a sealed room and you see how dusty an old closed up house gets, there is a ",
".",
"All cleaning up does is move the dust buildup around to somewhere we can’t see it."
] |
[
"How does jump height scale with animal size?"
] |
[
false
] |
So I have a book on mathematical dynamics that does a few fun calculations with biology. One of the claims that is reasoned is that the height an animal can jump does not scale with the height of the animal. Does this claim actually bear out in reality? Can a flee jump a comparable height to a larger animal, for example?
|
[
"Yes, but work is force*distance. My legs are much longer than a flea's, so they exert force over a longer distance, thus doing more work."
] |
[
"I see what the misunderstanding is. You are answering whether jump height is proportional to L. That is, is jump height ~L",
" My question is whether jump height is constant with respect to L. That is, jump height ~L",
" Which asks whether size doesn't matter for jumping."
] |
[
"Their legs are long, the hind pair well adapted for jumping: a flea can jump vertically up to 7 inches (18 cm) and horizontally up to 13 inches (33 cm).[3] This is around 1200 to 2200 times their own body length, making the flea one of the best jumpers of all known animals (relative to body size), second only to the froghopper. ",
"http://en.wikipedia.org/wiki/Flea"
] |
[
"How precisely did Einstein get led to postulate that the speed of light is invariable for all frames of reference?"
] |
[
false
] |
I understand that the speed of light in a vacuum is constant in all frames of reference. Further, I understand that due to this one fact, Einstein was able to derive (with his theory of special relativity) many amazing things, such as length contraction of moving objects, time dilation, energy-mass equivalence, and so on. Basically, he started at the invariance of and came up with the rest. But what led him to figure out that was invariable in the first place? Was he the first to postulate this? I guess I'm asking what was known about light at the time, and what did Einstein come up with, and what led him to his conclusion that was invariable for all frames of reference.
|
[
"He looked at Maxwell's equations, the ones that determine the speed of the EM field, and he looked, and he looked...",
"And then he went \"huh, that's funny, the speed of the EM field is this constant divided by that constant, ",
". So the speed never changes. Well, that's bizarre. So, if we assume for an instant that this is ",
"...\"",
"And the rest is history."
] |
[
"Obligatory Irregular Webcomic"
] |
[
"This won't be quite what you're looking for, but it at least fills in a small piece of the puzzle.",
"Before Einstein was born, light was known to have wave like properties. A natural follow up question was \"What is the medium that light waves travel through\". Scientists at the time assumed that medium existed, and when about trying to observe it. The ",
"Michelson-Morley",
" experiment tried to observe the \"Luminiferous Aether\". It failed miserably. It wasn't definitive proof, but it was pretty strong evidence that the aether wasn't actually there.",
"Now, it was possible to modify the existing theories and still have an aether. One way to explain the experimental results is to say massive bodies (like the earth) drag the aether as it passes through it... similar to a boat dragging water as it floats by. You could imagine a relatively static clump of aether constantly moving along with the earth.",
"Another possible explanation: When some object moves through the aether, its length is contracted along its direction of motion (relative to the aether). This made sense until they re-ran the MM experiment with arms of different lengths. To explain the null result in the new experiment they had to also assume time dilation (again when an object moves relative to the aether).",
"So when Einstein comes on the scene he tasks himself with the job of explaining the MM experiment results. I don't know his thought process, or what actually prompted him to assume a constant speed of light (and to see where that took him), but when he was done the MM experiment was explained, and there was no need to invoke this incredibly timid aether."
] |
[
"What happens on an atomic scale when water is boiled?"
] |
[
false
] |
So my college entry biology professor (with a doctorate) just told my summer school class that when water boils, the hydrogen and oxygen atoms split and bind to each other, forming H2 and O2. I have always been taught that water vapor is just water molecules that are heated to a gaseous form. Also, if what he said is true (which at this point, I have trouble believing) than why does the ensuing H2 gas and O2 gas not react with my kitchen stove and blow my house apart when I do something like cook pasta?
|
[
"Your biology professor is incorrect. There is no chemical change in the water. The H2O does not split into H2 and O2.",
"You have been taught correctly, that water vapor is gaseous water.",
"For your hypothetical, if you ",
" have H2 and O2 gas, they wouldn't necessarily explode unless you have an ignition source at a temperature above the flash point (so, a gas stove). Alternately, they will spontaneously combust if they are heated above the autoignition temperature of hydrogen (~500°C)."
] |
[
"Oversimplified, but when water boils, enough heat has been added to water molecules that they gain kinetic energy, causing the interactions between water molecules to become more transient and letting some water molecules escape into the gas phase (water vapor). ",
"In contrast and also oversimplified, in order to make H2 and O2 diatomic gas molecules from water molecules, the molecular bonds between the hydrogen atoms and oxygen atom in a water molecule must be actually broken in order that H2 and O2 molecules can form, such as in ",
"electrolysis",
". "
] |
[
"Thank you, I thought she was wrong, but I couldn't point to an exact reason as to why. "
] |
[
"Could electrolysis of water efficiently provide fuel for a hydrogen fuel cell?"
] |
[
false
] |
Well, I not quite sure how a hydrogen fuel cell works. However, I do know that the energy produced comes from the exothermic reaction of hydrogen and oxygen coming together to form water (I think it gives off about 55 kJ of energy per one mole O and 2 moles of H). But, wouldn't it take 55 kJ to decompose water into H and O? If this is the case, then it would take more electricity to make the hydrogen than would be gained from the fuel cell, since fuel cells are not 100% efficient. Or, am I just missing something about Fuel cells?
|
[
"No, you're right. But that doesn't mean hydrogen fuel cells are worthless. Hydrogen Fuel cells are not energy creation devices, they are energy transportation devices. They are a way to carry energy, in a very dense way. ",
"Why is this useful, you may ask? Let's look at a car, for instance. A standard V6 car is only about 13% efficient (aka- the exhaust is only 13% cooler than the flash point temperature of gasoline). A power plant, however, is upwards of 40% efficient. Thus, if we use power from a power plant to make hydrogen in order to fill up hydrogen fuel cells for cars, we still have a net gain (over 2x) of efficiency to propel a car. "
] |
[
"Yes, that's the first law of thermodynamics. The reaction of H2 and O2 to water takes the same amount of energy in both directions. But due to heat losses/the second law of thermodynamics, neither the fuel cell or electrolysis cells would ever be 100% efficient. ",
"So there's little point in using electrolysis in producing hydrogen to put into a fuel cell, where your end goal is getting electrical power. But fuel cells can still be useful if you produce your hydrogen by some other means (for instance, directly from sunlight using clever chemical catalysts that we're currently doing a lot of research into). ",
"The point here is that chemical compounds serve as very good forms of energy storage, and that fuel cells have the ability - in principle at least - to produce electrical energy much more efficiently from them than combustion does."
] |
[
"70% efficiency is incredibly high, actually. And burning hydrocarbons isn't \"green\" but it isn't necessarily less green than using electrolysis, as that electricity has to come from somewhere. And somewhere most likely means a fossil fuel burning plant. "
] |
[
"When you inhale dust/ dirt/ pollution, does it stay in your lungs? And if so, does your lung clean itself?"
] |
[
false
] | null |
[
"There are special immune cells in the lungs called alveolar macrophages. These cells engulf inhaled particles, and degrade them using enzymes and acids (inside lysosomes).",
"However, certain types of dust particles cannot be degraded. This includes coal, aluminum, asbestos and silica. These particles accumulate inside the macrophages, leading to a disease known as ",
"pneumoconiosis",
". A rare form of this disease is called ",
"pneumonoultramicroscopicsilicovolcanoconiosis",
"."
] |
[
"What happens to those things that are trapped? What happens if it’s not trapped?"
] |
[
"What happens to those things that are trapped? What happens if it’s not trapped?"
] |
[
"During the Ice Age did deserts exist?"
] |
[
false
] |
[deleted]
|
[
"Those areas are simply too cold for the water to be in a useable state for life, but, it's the lack of precip that really matters."
] |
[
"The dictionary does not provide a scientific definition, only a colloquial one. Scientifically, a desert has little precipitation, or available moisture. Parts of Antarctica absolutely are deserts."
] |
[
"Maybe I'm mistaken I always thought deserts were defined by the lack of precipitation, but maybe not."
] |
[
"Is climate change responsible for the current droughts and starvation in Africa?"
] |
[
false
] |
I've read that climate change affects Africa proportionately, and that many large bodies of water have already dried up. Is climate change responsible for the current droughts and humanitarian crisis in the Horn of Africa?
|
[
"Disclaimer: Not a climate scientist",
"Although an increase in the frequency of events like this is what you expect from climate change, I think you cannot say whether or not any single event is due to climate change."
] |
[
"In the long term, I'd say local politics and economics are the primary cause. If they had a stable government that fairly enforced property laws, a decent education system, and a primarily capitalist form of economics, the problem would at the least be far less then it currently is. That is to say they'd be making reasonable amounts of money, and they'd be able to buy food and farm equipment on the global market. This would increase the global cost of food slightly, but as a result more land would be farmed and fewer people worldwide would be starving.",
"That said, the current drought would certainly still be causing humanitarian issues. And we have to make a distinction between weather and climate. The drought is weather, and while it may be more ",
" in a particular area because of climate change, we can't say for sure that it wouldn't have happened anyway."
] |
[
"That's a good question. From what I understand, it is really hard to separate the effects of climate change and drought from the other relevant factors like geopolitics, agricultural policy, military conflicts, and global food markets, but hopefully someone more qualified than I can give a good answer."
] |
[
"[Physics] How do the integral and differential forms of Faraday's law and Ampere's law not conflict at points away from \"source?\""
] |
[
false
] |
For Faraday's law, imagine a loop enclosing a changing magnetic field (orthogonal to the plane of the loop), but larger than the area where the field exists. The integral form predicts that an E field is induced at the loop since dBflux/dt is nonzero, but the differential form predicts that no E field is induced there since dB/dt=0 there. Similarly, imagine a long straight current carrying wire. For a loop enclosing this wire's cross section, the integral form of Amperes law predicts a B field will be produced there since the enclosed current is nonzero and dEflux/dt=0. However, the differential form predicts B=0 outside of the wire since the current density is 0 outside of the wire and the E field is constant. What am I missing here?
|
[
"For Faraday's law, imagine a loop enclosing a changing magnetic field (orthogonal to the plane of the loop), but larger than the area where the field exists. The integral form predicts that an E field is induced at the loop since dBflux/dt is nonzero",
"If the loop encloses the entire magnetic field, then dBflux/dt is zero, since magnetic field lines are always closed, as magnetic monopoles (almost certainly) don't exist.",
"Similarly, imagine a long straight current carrying wire. For a loop enclosing this wire's cross section, ... the differential form predicts B=0 outside of the wire since the current density is 0 outside of the wire and the E field is constant.",
"The differential form of Ampere's law is curl(B) = J + dE/dt, ignoring some constants. The differential form predicts that curl(B) is zero outside of the wire which is true. However, this doesn't mean that B is zero: curl(B) is nonzero at the location of the wire, which establishes that B forms a vortex-like pattern like ",
"this",
". ",
""
] |
[
"Yeah the curl there is everywhere (0, 0, -2); his link doesn’t actually show the B-field of a thin wire.",
"The B-field outside a thin wire does wrap around it, but it decays proportional to 1/r away from the current, ",
"like this.",
" whereas the linked one actually GROWS farther away from the center. ",
"If you calculate the curlB in cylindrical coordinates, you only get a contribution from the φ-component,",
" which after multiplied by r is constant, with a 0 derivative; therefore curl",
" is “everywhere” zero, despite the field itself being nonzero. I say “everywhere” in quotes because there’s actually a 1/r factor in the curl operator, so the differential form of Ampere’s law becomes undefined at the location of the wire (where r = 0). This is a very similar situation to the divergence of a point charge, where the entire contribution to the flux of ",
" through some closed surface comes from the infinitely dense charge at the center, and div",
" = 0 everywhere else. Here, the entire contribution to the circulation of ",
" around a line current comes from the infinitely dense current right at the center, and the curl is ",
" everywhere else. Note that curl",
" = ",
" does not imply that ",
" = ",
".",
"For a straight line current, you can picture that while the B-field does wrap around the wire everywhere, it does so more and more weakly the farther away you go, so the decaying of the field with distance “catches up” with the wrapping, and does so in such a way that geometrically, it exactly counteracts the curling around the center at every other point. I know this is hard to visualize (it is for me), but if you directly calculate curl of ",
" = (0, k/r, 0), with k is some constant (this is the field of a straight line current), you see that it's everywhere zero, except where it blows up at r = 0.",
"So using the differential form, we conclude that the current density is ",
" everywhere outside the wire, which is what we want, but we cannot use the differential form to evaluate the current density in the wire, because curl",
" is undefined there. This is okay, because on a thin wire, we expect the current density to be infinite, like the charge density of a point charge."
] |
[
"This is what I was missing - the curl from the visual rotation is counteracted by the decaying strength of the field. This solves both problems. Thanks so much!"
] |
[
"What exactly are the repercussions from this year's drought on the international food supply?"
] |
[
false
] |
What can we expect in the next few years?
|
[
"There has not been a \"lack of food\" in a long time, the warehouses has always been bulging. The distribution and economy is the real thing in this equation, and for us in the rich world, we will maybe see a small rize in price due to lesser supply. It will be far more severe in the poorer parts of the world, because they cannot afford to buy from our supply. "
] |
[
"There has not been a \"lack of food\" in a long time, the warehouses has always been bulging. The distribution and economy is the real thing in this equation, and for us in the rich world, we will maybe see a small rize in price due to lesser supply. It will be far more severe in the poorer parts of the world, because they cannot afford to buy from our supply. "
] |
[
"One of the aggravating factors is EISA (Energy independence and security act) which mandates a certain quota of ethanol be blended into auto fuels. with a huge reduction in corn production, and an unwillingness on the government's part to suspend the quota requirements, there's going to be problems. Mexico will likely have tortilla riots."
] |
[
"Can a black hole be filled?"
] |
[
false
] |
If a black whole is a 'hole' than it should fill up if enough stuff is put inside of it. I guess the answer to this could also be in what context 'hole' is being used. If by 'hole' it means "An aperture passing through something" and filtering it back into space, then if it's being put back into space, and space is ever expanding, then it's not possible to it to get filled up, rite?
|
[
"A black hole cannot get filled up. As more matter is added to the black hole, the black hole gets larger.",
"What surrounds the black hole is a surface called the ",
". Once something crosses the event horizon, it can no longer go back out. The term \"black hole,\" then, should not be taken literally, but rather as a technical term that conveys a useful metaphor."
] |
[
"Exactly. The definition of the event horizon is that its the point where light cant escape the black hole. Since nothing can move faster than light, its impossible to reach escape velocity."
] |
[
"at the speed of light ",
"No, if light cant escape, then something going the same speed as light cant escape as well.",
"(or faster) ",
"Depends on how fast, but still impossible."
] |
[
"Best Science periodical?"
] |
[
false
] | null |
[
"Cat 2 are supposedly written for a general scientific audience, but are pretty damned specialised. You could add New Scientist to the first category? "
] |
[
"Why not approach this empirically (since we don't really know your level of expertise, anyway). Go to a library and take a look at the journals you're interested in, and see if you can understand the articles.",
"My guess is that you'll find something like ",
" or ",
" more suitable for your purposes than ",
" or ",
", but a little experimental investigation on your part should help you figure this out."
] |
[
" may be good for you. As a plus, it is now free with a membership to the American Chemical Society. "
] |
[
"Why was there (if any) a selective pressure for increased genetic variation & diversity in humans?"
] |
[
false
] |
I am having a slightly difficult time thinking about why there was a pressure for the genome to produce more variation and increase diversity between individuals (i.e. in humans) via mutations, chromosome crossing over, the tendency to be attracted to mates that are more distantly related, and using sexual (vs asexual) reproduction. I might be phrasing this question or thinking about it in the wrong way, in which case feel free to rephrase. My first thought was that natural selection works on selecting from variation between individuals, but I don't think natural selection would work to make it easier for it to work on .. itself? That reasoning seems circular. Is it more so due to producing better defenses (and more variable targets) against infectious organisms? Or is there something else I'm missing? Thanks!
|
[
"The more diversity in a population, the better that population can survive against some major event. Therefore, genetic variation is very advantageous.",
"Unfortunately, there is not as much natural selection active in humans today as there was in earlier human species. All the technological advances have made most genetic disadvantages less of a problem.",
"For example, I wear contacts(prescription is -1.00). Out in the wild, I would probably die quicker than others because I wouldn't be able to see predators and threats from as far as others. Since I can wear contacts, I have no longer at any disadvantage."
] |
[
"I could see how genetic variation does increase the chance that the population doesn't get wiped out by a major event -- but how did the selection occur in the first place? Doesn't that invoke \"group selection\" as a potential mechanism? I'm not sure I'm convinced by your explanation. "
] |
[
"Natural Selection was never about the survival of an individual. Natural Selection occurs at the individual level, but affects the group as a whole.",
"How did it begin? After the first non lethal mutation. If you have two individuals with non-identical genomes, one will most likely be better adapted to survive in a given habitat."
] |
[
"Alternative to Google Scholar?"
] |
[
false
] |
Recently I've noticed cropping up in Google Scholar more and more, as well as some self-published 'journals'. Is there something similar to Google Scholar (e.g. broad spectrum) but something limited to reliable journals?
|
[
"What you show is disturbing. The fact that it implies some sort of peer review is truly devious.",
"Depends on what field you are in.",
"arxiv for example is a pre-publication repository for physics. Maybe bio has something like it. ",
"If you have access to a university library ISI web of science is the best there is. It is not free to general users, however; universities can justify the expensive subscription."
] |
[
"Google Scholar never promises that there's been peer review, I've turned up lots of publications that are 'grey' literature (internal government publications for example). It's a tool, that's all it is. It's like showing a hammer sometimes bends nails and then asking for a new tool.",
"Google Scholar gives me more flexibility than Web of Science but I know I've got to be careful of what it's pulling off the web. It's a tradeoff. That 'Answers in Genesis' comes up sort of sucks, but it's pretty obvious what that journal is all about."
] |
[
"PubMed is awesome for anything in the sciences and social sciences, and serves as a good quality filter. ",
"I have been known to then use it in conjunction with GoogleScholar to see if the full article is available for free somehow on the internet (if the abstract is not sufficient for my purposes). ",
"Additionally, don't forget the power of just emailing the corresponding author and asking for a copy of the paper. To be sure, the turnaround time is nothing like the insta-net gratification we've come to rely on, and the failure rate is non-zero, but it's a nice, old-school workaround that beats paying individual access fees. "
] |
[
"Is it possible to stop Mercury (Hg) from moving through soil when placed in a landfill?"
] |
[
false
] |
I noticed my local rubbish tip was dumping some mercury, and I just wondered - due to it's liquid nature, and most toxic substance's tendency to leech throughout the soil - how do they manage to keep the substance at bay? Do they make it form a compound or something?
|
[
"You noticed this how and where? It's illegal in a lot of places to dump mercury "
] |
[
"You can test whether the mercury will leach from the waste after its processed (i.e. reacted with a precipitant as you said). Whether it leaches or not depends on the chemical form of the mercury and how stable it is. A stable example would be if you embedded the mercury in glass (",
"vitrification",
") then there's a pretty low chance that it'll leach over time. An unstable example is organic mercury compounds which can be water soluble and are often bioactive.",
"Here's a basic description of the leaching test: ",
"http://en.wikipedia.org/wiki/Toxicity_characteristic_leaching_procedure",
"With a lot of caveats, if it passes the TCLP test and some other criteria, then you can put it in a landfill. I'm a little hazy on the specifics at the moment, but the guidelines originated with ",
"RCRA",
" and laws that followed."
] |
[
"yet they still allow people have mercury dental fillings in some countries"
] |
[
"Could anyone explain how entanglement can not simply be explained by the two entangled particles \"seeing\" each other and fixing their states at creation?"
] |
[
false
] | null |
[
"I wish it were that simple. Bell's theorem says it isn't."
] |
[
"Mainly QM doesn't allow the entangled particles to have a local hidden state (e.g., something dependent on local variables) prior to being measured. The reason is bell's inequality/bell's theorem, which has been experimentally tested (essentially verifying no local hidden variables). Difficult to explain concisely in a brief reddit comment (without eqns/diagrams), so here are some links to good explanations.",
"http://www.iafe.uba.ar/e2e/phys230/history/moon.pdf",
"http://en.wikipedia.org/wiki/Bell%27s_theorem#Overview",
" ",
"http://www.upscale.utoronto.ca/PVB/Harrison/BellsTheorem/BellsTheorem.html"
] |
[
"Am I getting this right(?):",
"No",
"Essentially verifying no local hidden variables means that the observation/measurement was predicted perfectly by a set of mathematical laws, and those laws, which performed perfectly, also violated locality. Nobody ran an experiment directly proving that local hidden variables were not present. Rather, the experiments showed that the previously predicted mathematical model is sufficient to describe the experimental outcome. It is Bell's theorem which suggests that since such a model is sufficient to describe the experimental outcome, AND that such a model does invoke non-locality, then local hidden variables are not necessary. They are only ruled out because they are not necessary. ",
"John Bell found a theoretical discrepancy between the standard QM prediction and an extremely generic model of local hidden variables (that should encompass them all). He found a basic property (Bell's Inequality) that if (local) hidden variables were allowed should always be satisfied. However, using the QM framework you get a prediction that breaks that property. Doing the experiment (Aspect et al), they found QM's prediction is right, local hidden variables is wrong. It is much stronger than we don't have a local hidden variables theory or don't need one; we have demonstrated that all local hidden variables theories are in disagreement with experimental data."
] |
[
"AskScience AMA Series: We are experts on NASA's efforts to grow crops in space including a harvest just in time for Thanksgiving! Ask us Anything!"
] |
[
false
] |
Since 2015, using NASA hardware, scientists and researchers have worked with astronauts on the International Space Station to conduct a series of experiments to grow, harvest and eat a variety of crops in space with seeds sent from Earth. The most recent experiment has the ISS crew growing Mizuna mustard using two different light recipes and multiple harvests, with the experiment's final harvest scheduled for later this week. This work builds upon decades of NASA and international research into growing plants in space. These experiments are advancing the knowledge required to successfully grow a large variety of crops on long-duration missions, such as a crewed mission to Mars. Being able to crops grown in space provides many benefits including supplementing the astronauts' packaged diet with essential nutrients and combating diet fatigue. Here answering your questions are: We will see you at 2:30 p.m. Eastern Standard Time (19:30 UT), ask us anything!
|
[
"Which plants have surprised everyone the most with their performance and which ones have the most potential for going to Mars?"
] |
[
"Hello! As I am part of the team responsible for researching new crops on the ground to be applied in space flight, the plant that I found to interestingly not do as well in flight than it did the ground was a cabbage called Tokyo Bekana. Also, while screening some peppers a variety that grew very large and tall (too large for current plant growth hardware VEGGIE and Advanced Plant Habitat, APH), dwarfed itself and became a manageable size when grown in APH analog hardware. ",
"-L.S."
] |
[
"Do plants grow differently in low-gravity conditions, and if so, how does that impact your research, the choice of crops to bring on a trip, and the requirements for their growth space?"
] |
[
"How do the Chinese send signals back to earth from the dark side of the moon if it is tidally locked?"
] |
[
false
] | null |
[
"Before landing Chang'e 4, they launched a relay satellite named Queqiao that stays at a point past the moon where it can see both Earth, and the far side of the moon.",
"https://en.wikipedia.org/wiki/Chang%27e_4#Queqiao_relay_satellite"
] |
[
"The relay is in a halo orbit around the Earth-Moon L2 Lagrange Point: ",
"https://en.wikipedia.org/wiki/Halo_orbit"
] |
[
"Worth mentioning Larange points aren't stable orbits, and require station keeping fuel burns in order to stay there, which means anything you put there is gonna have a finite time. Granted, ALL satellites being put into any orbital regime for a specific task will require station keeping in order to be able to perform their task, but the Larange points require a lot more finesse. "
] |
[
"Light travels faster in vacuum than through air, so is there a material that could slow light down in a way that we could see it traveling?"
] |
[
false
] |
So light travels at 299,792 kilometers per second through vacuum and at ~200,000 kilometers per second through air. That's almost 100,000 kmps slower, what's the slowest that light can travel through a material and what material?
|
[
"In principle: Yes. Light has been slowed to below 10 m/s.",
"https://en.wikipedia.org/wiki/Electromagnetically_induced_transparency",
"I don't have time right now, might write more about it later.",
"Edit: The key here is the introduction in the section \"Slow light and stopped light\". Make the absorption depend critically on tiny frequency changes (kHz range) and you get very slow group velocities for a narrow wavelength range."
] |
[
"Light travels slower through materials, but not as slower as you said: light speed in air is almost identical to the one in vacuum, in fact in vacuum is 299 792 458m/s, while in air is about 299 720 000. This isn’t such an huge difference, and also other materials can’t slow light down so much that we could see it travelling. If u wanna know more look on the internet for refractive index, which is a number that describes how much fast light travels through that material"
] |
[
"I found this list: ",
"https://en.m.wikipedia.org/wiki/List_of_refractive_indices",
" \nThe highest is the value of the index, the slowest the light goes through the material, according to the formula v=c/n, where v is the speed through the material, c is the light speed in vacuum, and n is the refractive index. \nThe highest value is germanium, whose index is about 4, which is too low to make the travelling of light visible, indeed it slows light down at only the order of magnitude 10",
" which is too big to make visible the travel of light. \nThe only way to see light travel is make it travel long distances."
] |
[
"How much energy is required for D-D fusion???"
] |
[
false
] |
[deleted]
|
[
"There's no single number, but a good measure is the Coulomb barrier. ",
"Here",
" is a calculator, which gives a barrier energy of 476 keV.",
"Most environments in which DD fusion is occurring are not at 5.5 Gigakelvin temperatures (476 keV divided by Boltzmann's constant), so tunneling is playing a large role in the reaction rate.",
"Here",
" is the actual cross section for this reaction (not the Maxwellian-averaged cross section, or reaction rate, that a lot of fusion people seem to like to plot). This is the basic nuclear data, that doesn't depend on the environment (temperature and density).",
"So you can see that there isn't really anything suddenly changing at the Coulomb barrier energy."
] |
[
"Thank you!!!"
] |
[
"You can calculate that from the cross section."
] |
[
"Are all animals/insects/birds etc equally skilled in tasks necessary to their survival? Do \"stupid\" animals/\"smart\" animals exist (especially in the wild)?"
] |
[
false
] |
Asking this question after watching a video of a spider spinning its intricate web so it got me wondering as to whether in this example a spider would make mistakes while spinning its web or always get it right the first time, or would a bird always make a perfect nest (eg. the nest of the weaver bird). Video of spider spinning web:
|
[
"Brains are expensive. They take energy that could otherwise be used for moving, growing defenses, or just makin' more babies. All animals existing live in a sweet spot that allows them to do as well as they can with what they have and the requirements of their environment. Being smarter is not always a benefit, if it means a trade-off in other areas. ",
"That said, there is natural variability in all traits, including intelligence. If a mutation makes an animal \"smarter,\" and that increase in resources towards intelligence is worth the energy devoted to it, the animal has more babies, and that trait is passed on in more offspring generation after generation. It could also have a neutral or even a negative effect, and would then be less likely to be passed on.",
"The variation we see in nature is a result of this complex selection. Generally, in a stable population, we don't see animals that are too dumb to survive, or animals that are so very much smarter than others, because those sorts of inequalities would lead to shifts in the population. We do have evidence that this happens, though, and it's part of the whole theory of evolution.",
"Source: biologist who works with relatively smart and dumb animals.",
"tl/dr: yes, but extremes are either weeded out or take over, so most animals you see are just competent at their jobs."
] |
[
"Another interesting point is that the amount of variability in a trait is strongly influenced by the pressure of selection on that trait. If intelligence is strongly linked to fitness, we would expect to find very little variability in the genes governing intelligence. If intelligence played only a small role in the fitness of the animal, we would expect to see a much broader distribution of intellectual abilities in the population."
] |
[
"There will necessarily be animals that are better at surviving in their environment than others. The animals that are better at surviving in their environment will reproduce more often, and those less equipped will reproduce less often (or die all together). This is the basis behind Darwinian natural selection."
] |
[
"In relation to a /r/adviceanimals post, how do we know the sun made its 18 revolution around the galaxy?"
] |
[
false
] | null |
[
"Well, we know the sun is 4.5 billion years old. By carefully studying the motions of nearby stars, we know that the disk of stars in our galaxy, which the sun is a part of, ",
"orbits at roughly 220km/s",
". And we've also measured to distance to the center of the galaxy to be about 25,000 light years.",
"Plugging it all in",
" gives you 18-20 orbits around the galaxy.",
"All of these numbers are very uncertain though, and tracing our sun's exact path backward even half an orbit is impossible at this point. We're just assuming that the sun was formed in the disk and has been orbiting the center of the galaxy at roughly the same speed and distance for it's entire life. We don't know that for sure though."
] |
[
"One would assume 4.5 billion. A year is how long Earth goes around the Sun, so if the Sun is 4.5 billion years old, etc..."
] |
[
"Get the age of the Earth and you have your rough number. As with the Sun's rotation around the galaxy, we might not have been moving at the same speed, in the same position all that time."
] |
[
"What is happening when paper gets wet?"
] |
[
false
] |
I was curious as to why paper gets mushy and totally changes texture when it gets wet. I have read that paper is made mostly from cellulose, and was thinking that when it gets wet, the water causes hydrolysis between the monomers, which in turn causes the mushy texture because the bonds are broken. I don't know if this is true at all, or whether the cellulose used in paper has the same structure as the one that I know of. Any ideas as to what is happening at a molecular level?
|
[
"Paper is mainly held together via hydrogen bonds",
", wetting (introducing water) disrupts the bonding ",
" cellulose fibres. The cellulose chain itself are held together by covalent bond, and would not be affected easily by wetting. That's why cellulose hydrolysis requires ",
"specialised and energy intensive methods",
"."
] |
[
"My chemistry is quite shoddy, so I won't be able to go into great detail in terms of the physical chemistry (bond strength and energy) involved. However, I can say that ",
"water",
" is quite good at forming hydrogen bonds itself. It seems that, when water is introduced to the fibres, ",
"the molecules can competes for hydrogen bonds with the fibres",
"."
] |
[
"To know what's happening it might be good to look at how paper is made. In the simplest methods, pulp fiber from wood (or cotton or other fibrous material) is chipped and ground and made into a slurry of cellulose and lignen, it then goes through a mechanical alignment process which forces the slurry through a blade that aligns all the fibers into the desired 'web' such that after the following processes it will adhere better. Next the web of slurry is pressed and dried, the water content of the slurry is removed and the pulp web of cellulose and lignen is then rebound through pressing. ",
"So basically when paper is wet, it's lignen and cellulose is becoming unbound, essentially returning it to its slurry state. Depending on what types of fibers and what additives were used in the paper making process determine how well the web is bonded, it could be as tough as a grocery bag or as fragile as tissue paper which just dissolves when wet."
] |
[
"If an object is in orbit, meaning it is in free-fall, what stops it from accelerating indefinitely?"
] |
[
false
] | null |
[
"It's constantly accelerating, but the direction it accelerates in keeps changing, so the average acceleration is zero and it always has around the same momentum. If it's in a circular orbit, it's always accelerating perpendicular to the direction of motion, so it doesn't speed up or slow down. It just changes direction."
] |
[
"Gravity is what changes the direction of the satellite. The object is pulled toward Earth's center of mass which may speed it up or slow it down depending on whether the object is working with gravity or against it. A good example of this is a highly elliptical orbit. At the point where the object is the furthest from the Earth, it is moving quite slow, as gravity has slowed it down (since it was fighting gravity all the way there.) When it near the Earth, it is moving quite fast, because gravity sped it up. A circular orbit is traveling at just the right speed that is neither working with or against gravity, so its direction changes while it maintains the same speed.",
"Wikipedia has some graphics demonstrating how orbits work.",
" The animated GIFs are particularly helpful."
] |
[
"It just clicked, thank you! The gifs really helped."
] |
[
"On an infinite square grid of perfect one Ohm resistors, what is the equivalent resistance between two points that are a knight's move from each other?"
] |
[
false
] |
I've been reading XKCD for years at this point, and I like looking into things that appear in the comics. What is the resistance here, how would you work it out, and why is it so incredibly hard?
|
[
"I was given this as a homework problem in a graduate E&M course. Interestingly, for two points next to each other in the lattice, there is a simple argument to show that the equivalent resistance is R/2. But as soon as you try any other two nodes - the knight move or even just a diagonal - you need much heavier machinery.",
"There is ",
"this mathpages",
" article which goes through it. I haven't read their whole article; it seems rather long, as my handwritten solution is just over 2 pages (it looks like I did it differently). We were also allowed to use Mathematica for the integrals, so we skipped many of the steps. (I know how to do the integrals analytically using contour integration, but it's pretty tedious).",
"The trick is to set up an infinite set of equations using Kirchoff's law at every lattice point. Imagine you have inserted a current I at the point (0,0) and are removing a current at (2,1), where (x,y) are integer coordinates on the grid. Then at every lattice point, you need to have total current coming out of the node is conserved: I(x,y) R = V(x+1,y) + V(x-1,y) + V(x,y+1) + V(x,y-1) - 4 V(x,y) = 0. Except at the two points where you've inserted/removed current, you need to include this on the right-hand side: ",
"V(1,0) + V(-1,0) + V(0,1) + V(0,-1) - 4 V(0,0) = I_in R",
"V(3,1) + V(1,1) + V(2,2) + V(2,0) - 4 V(2,1) = -I_in R",
"Here, I_in is the total current flowing through the circuit. I'm using R as the resistance of each resistor (so R = 1 Ohm in the xkcd comic). Then after explicitly solving this infinite system of equations for V(x,y) as a function of I, we can find the equivalent resistance as R_eq = (V(2,1) - V(0,0))/I_in (the I_in dependence will always cancel out, which you can prove via dimensional analysis).",
"Ok, but how do we actually solve this infinite set of equations? As a condensed matter physicist, I immediately recognize this as equivalent to solving some non-interacting tight-binding quantum lattice model, so I did what a condensed matter theorist would do. I introduced the discrete Fourier transform:",
"V(x,y) = ∫dk1 dk2 V(k1,k2) e",
"where the integrals go from -pi to pi. Anyways, placing this into the infinite set of equations reduces to a simple algebraic equation for the V(k1,k2). I think the mathpages is doing a very similar thing but using a slightly different method. Then to get V(x,y) you need to do a rather nasty integral, but it can be done in practice.",
"I can give more details on the intermediate steps above if desired. The answer is (4/pi - 1/2)R. We also did the diagonal case. I can check my solution later when I'm back in my apartment to see what that equivalent resistance is.",
"EDIT: Just pulled out my handwritten solution. I fixed some errors above. The equivalent resistance between two nodes connected by the diagonal of a square is (2/pi)R. To obtain the equivalent resistance between two arbitrary nodes, I have to perform an integral which I'm not sure can be done as a function of the nodes. (This integral is presumably equivalent to equations (9) and (13) in the mathpages article, since I got the same answer for the two special cases considered). ",
"The mathematical procedure above can be thought of as obtaining the inverse (or \"Green's function\") of the discrete Laplacian on the square lattice. This is very similar to solving the discretized free Schrödinger equation, which is how I recognized how to solve the problem once the system of equations was set up."
] |
[
"In case nobody can answer it in a shorter way, this is an old puzzle: ",
"http://www.mathpages.com/home/kmath668/kmath668.htm"
] |
[
"This question is indeed about the inverse of the Laplacian on a square lattice. However, this inverse is not well-defined! (The Laplacian of a constant potential vanishes.) When doing the integrals, you have to discard a few infinities, as the infinite grid of resistors is not quite physically reasonable.",
"Remember that the full Greens function also depends on energy E. In this case, it has a singularity at E=0."
] |
[
"When did humans start falling in love?"
] |
[
false
] |
According to , monogamy came with STIs. If that's the case, when did love come along? Did it exist before we became monogamous? Or was it a result monogamy?
|
[
"It's an interesting question, but I believe the vagueness of it is why it didn't get answered. First you have to define what love is, then you have to define what monogamy is. I'll put my own answer at the bottom if you don't want to read everything in between.",
"Is love a deep rooted emotion of the soul, a set of chemical changes in the body and brain that induce an individual to take a mate, or a choice of commitment to another person? In the third case, does that dedication require exclusivity? Under any of these definitions, is it possible to love, and be loved by, more than one person at once?",
"What about monogamy? Where does serial monogamy (i.e. the mating systems currently practiced in most Western countries) fit in? Is it the most common definition of having only a single sexual partner at once, or can the concept of monogamy only exist within the institution of marriage? Can a person that has had more than one sexual partner in their lives be called monogamous? Can a person who has been divorced be called monogamous within their next marriage? ",
"What about people who have sexual relations outside of wedlock? What about those who only have one sexual partner at a time but tend to frequently fall into and out of non-marriage relationships? Any STI-preventing properties of monogamy are substantially weakened when a strict monogamy of one sexual partner for life is not observed, and I don't think I have to explain how extremely rare that is, from unmarried teenagers sneaking off to have a roll in the bushes to young \"on again, off again\" couples to divorcees to unfaithful spouses frequenting brothels or \"visiting\" the shopkeeper in the village center.",
"Further muddying the waters, there are non-Western (Western being influenced by modern Western European culture; this did not functionally exist prior to the Colonial period) cultural marriage systems going back thousands of years that don't fit neatly into one category. Some were polygamous, or in other words, \"poly monogamous,\" either through one male and multiple females (polygyny) or one female and multiple males (polyandry). All of these arrangements still exist today, just not as commonly. In this system, a single member of one sex is paired with multiple members of the other, but all of the relationships exist as discrete pairs without any sexual relationships happening outside of each pair, and the members of the multiplied sex have no relations with one another. So in a polygynous relationship, which is the most common arrangement, the females are strictly monogamous while the male is not strictly monogamous but is tightly constrained to sexual relationships within the same small pool of partners as one pair at a time.",
"This has already gotten extremely complicated and we haven't yet included same-sex relationships, multi-lateral marriage, or polyamory, all of which have existed in varying forms with varying rarity and varying cultural acceptance going clear back to the invention of writing, and probably well before that.",
"So to answer the question at all, one has to impose definitions of love, monogamy, and marriage that vary wildly depending on the cultural background in which one was raised. Further, applying modern sexual definitions to historical arrangements is both effectively impossible and one of the highest orders of folly in anyone studying the past. ",
"So to take it all back to the beginning: did love exist before monogamy? If it's a deep-seated emotion, then it almost certainly existed at the dawn of our species. If it's the chemical change in the brain telling someone to take a mate, then it not only existed before monogamy, it's very likely to have existed clear back to the point that our genus branched off of the evolutionary path of the other great apes, and then a couple million years before that. Depending on how loose you are with the definition, back to the origin of sexually reproducing life, although I would stop at the great apes since anything less closely related to us than that probably wouldn't experience it anywhere near the same way. If it's a commitment to another person, then we can be certain it existed at least as long as institutionalized marriage if one takes marriage as concrete proof of such a commitment. The oldest evidence of institutionalized marriage is about 4500 years old, but it probably existed a long time before that, and the actual dedication to other people is very likely to be older still.",
"Ultra TL;DR: Probably at the origin of ",
", yes, no."
] |
[
"Thanks for your thoughtful answer! "
] |
[
"You can't really ask techical questions about something like \"love\" without VERY clearly operationalizing what you mean by the term. Otherwise, as a simple example, one might point out that most children love their parents, and that this would not make much sense to have been all that related to monogamy or not, since children start loving their parents long before they become sexually mature, monogamously or otherwise.",
"You might then specify \"romantic love\" but is that actually different than other love? Or is it co-opting the same emotions, but just adding in physical intimacy or other slight differences that modify the base emotion? ",
"And of course there are many different ways people feel love, even only with romantic partners, and you may not want to include the full spectrum or all possible mixes. Etc."
] |
[
"Redshifting- What is it in a nutshell?"
] |
[
false
] |
Also, how do wavelengths come into play with red shifting? How does redshifting prove the Big Bang theory?
|
[
"As for evidence of the Big Bang? Nothing's conclusive yet, but many of the galaxies we can see display a Redshift, which imply they are currently moving away from us, which is a good indication of Universal Expansion",
"The evidence is quite strong and at least the basics of the big bang model are considered as proven. General relativity predicts an expanding universe where the redshift is proportional to distance (further objects move away faster), which is precisely what is observed. The expansion causes the universe to cool, and the rate of expansion is consistent with the 2.7K temperature of the cosmic microwave background radiation."
] |
[
"Redshifting is when an object appears with a slightly longer wavelength, towards the red/infra-red end of the electromagnetic spectrum, hence redshifting. This occurs when an object is moving away, meaning we observe a longer wavelength. The wavelength observed is essentially the wavelength emitted, plus how fast it is moving away. ",
"The reason this is evidence (not proof, but evidence) for the big bang theory is that everything we observe is redshifted, meaning it is moving away from us. This suggests that we all initially started from a single point, and then exploded and are now moving away from each other. ",
"Hope this helped :)"
] |
[
"Redshifting is the same principle as the Doppler Effect, but applied to light!",
"You've probably experienced the Doppler Effect before. The most commonly used example is that of a truck horn which increases in pitch as it approaches you, then fades away as it passes you, making that EEEEEERRRRRRROOooooooowwwwnnnnnn sound.",
"As the truck approaches you, each sound wave it emits takes less time to travel to your ears. What results is an essential \"bunching\" up of soundwaves, resulting in a shorter over all wavelength and higher pitch. The EEEEEERRRRRRR. ",
"Then the truck begins to pass you and move away from you. Now the source of the noise is moving away and each successive soundwave takes LONGER to get to you, resulting in a spacing out of soundwaves and a LONGER overall wavelength. The OOooooooowwwwnnnnnn.",
"Now Redshift is the Doppler Effect with respect to light! As a light source, most obviously a star, moves away from you, the light wavelengths you observe get \"spaced out\", making them appear more red. This red is the equivalent of the \"OOooooooowwwwnnnnnn\". Blueshift, of course, is the exact opposite, where the light source moves toward you, resulting in you observing more \"bunched up\" wavelengths, the equivalent of the \"EEEEEERRRRRRR\".",
"As for evidence of the Big Bang? Many of the galaxies we can see display a Redshift, which imply they are currently moving away from us, which is a good indication of Universal Expansion caused by the Big Bang. If things were Blueshifted, then things would be on their way back toward us, which may happen if the Big Crunch theory proves to be true. You don't wanna be around when that happens."
] |
[
"Does every planet massive enough to support an atmosphere (e.g., as dense as Mars's) actually have one?"
] |
[
false
] | null |
[
"Temperature also plays a big role.",
"This is a super important point. ",
"For a specific case in comparative planetology, check out the difference between Mercury and Titan. Mercury is about 2.5x as massive as Titan, and has an escape velocity that's about 65% greater. However, Mercury also has daytime temperatures that are 7 times hotter than Titan.",
"The result is that Titan has an atmosphere about 50% thicker than Earth's, while Mercury essentially has no atmosphere. (Technically Mercury does have some sodium atoms that get briefly bound to the planet...but if you were able to gather this \"atmosphere\" all in one place, it would have roughly the same mass as a Volkswagen Bug.)"
] |
[
"Temperature also plays a big role.",
"This is a super important point. ",
"For a specific case in comparative planetology, check out the difference between Mercury and Titan. Mercury is about 2.5x as massive as Titan, and has an escape velocity that's about 65% greater. However, Mercury also has daytime temperatures that are 7 times hotter than Titan.",
"The result is that Titan has an atmosphere about 50% thicker than Earth's, while Mercury essentially has no atmosphere. (Technically Mercury does have some sodium atoms that get briefly bound to the planet...but if you were able to gather this \"atmosphere\" all in one place, it would have roughly the same mass as a Volkswagen Bug.)"
] |
[
"Mass and temperature are both very important. Earth and the Moon are both at the same distance from the Sun, but only Earth has an atmosphere because it's so much more massive than the Moon."
] |
[
"How are we finding such intact remains of Neanderthals, yet Denisovans/other homonins remain out of grasp, so to speak?"
] |
[
false
] | null |
[
"Neanderthals lived in some of the most heavily dug-over regions on the planet--Europe and the Near East. No doubt the prevalence of archaeologists has something to do with the prevalence of known fossils."
] |
[
"My knowledge of archaeology/anthropology is limited at best, but I would speculate that the easy answer (or at least one of them, considering the multitude of potential reasons) would be the availability of Neanderthal bones and dwellings to archaeologists.\n Being our nearest ancestor and having only recently become extinct (relatively speaking), there are simply more remains to be found than other, earlier archaic homo sapiens.",
"\nAlso, it may be that there were significant cultural/anthropological differences between species -e.g., burial rituals, preferences for certain types communal living arrangements, etc- that would preclude easily excavatable remains.\nIn any case, it's an interesting question!"
] |
[
"Person with anthropology degree here (admittedly sociolinguistics was more my jam). Plainly put, the longer the period of time, the more time there is for something to destroy the remains. There are two types of fossils mainly - trace fossils (footprints and the like) and body fossils. Body fossils are your concern. Proportional to their extant numbers, not many organisms die under the specific circumstances which lead to fossilization. A corpse sitting out for any length of time will not only decay, but be subject to predation by scavengers. So the fossil-to-be has to be rapidly encased or covered quickly after death, to protect it from both predation and erosion. Pompeii is an excellent example of this. ",
"There are several ways this can happen: being trapped in amber (most common for small organisms like insects), permineralization (water carrying minerals replaces certain minerals in the body and eventually leaves behind basically a rock sculpture of what was there before. fascinating stuff you should look into it), molds that retain the imprint of the organism long after it has decayed. ",
"Even after a fossil is formed, there is no guarantee that it won't be destroyed. Natural cataclysms, eventual erosion, landscape change. There's also the fact that the older a fossil, the deeper in the ground it will generally be. Neanderthal remains are simply easier to find, even by accident. I can go into stratum layers if you want, though it might be something you already know, so I don't want to assume. ",
"Now, admittedly Denisovans specifically aren't a subject I had a lot of knowledge going into. But it would seem that the reason for the sparcity of remains is another factor of fossilization: environment. It seems that Denisovans at one point lived contemporaneously with and even interbred with modern anatomical humans and neanderthals (",
"source",
"). Genetic evidence points to a significant presence in Southeast Asia (",
"source",
" ), whose wet, warm environment is not conducive to preservation of remains."
] |
[
"How long can individual cells go without food?"
] |
[
false
] |
I ask because I was wondering if it were possible for a cancer patient to starve themselves to the point where the rapidly dividing cancer cells die but their body can be saved.
|
[
"not very long. one method of cancer therapy, however, is starving the cells of glucose, since most cancer cells almost exclusively use glycolysis to make energy; while normal cells have several other pathways they can use. if you cut off the glucose, the cancer cells die, but your normal cells live."
] |
[
"So is fasting prescribed for patients often? "
] |
[
"no, they are given glycolysis inhibiting drugs. you can look here for more info:",
"http://en.wikipedia.org/wiki/Warburg_effect#Oncology"
] |
[
"How does THC intoxication work?"
] |
[
false
] |
[deleted]
|
[
"From what I understand, while you feel high the THC is actually bound to cannabinoid receptors in your brain. However after separating from the receptors your body begins to metabolize the THC. That process creates metabolites of THC, or little traces of what it used to be. It's those metabolites that create a positive result on a drug test.",
"Additionally, THC is a lipid (fat) unlike most drugs. Because of this it's not excreted as quickly from your system, and it also allows the THC to bind to some of the fat in your body, prolonging how long you'd test positive."
] |
[
"It is a lipid, it's not a fat. \"Lipid\" just means that it likes nonpolar solvent environments, such as oils (e.g. butter) and nonpolar organic solvents (e.g. butane). \"Fat\" means a triester of glycerol and three fatty acids, which THC definitely is not.",
"Different molecules get taken different places at very different rates by all the different transport mechanisms in your body. THC gets out of your brain long before it's out of the rest of your body, and some other drugs, like certain antidepressants, you have to take for weeks before they start to build up to therapeutic concentrations in your brain."
] |
[
"To add on to this, the reason THC activating cannabinoid receptors produces a \"high\" is the distribution of the receptors in the brain. They are located in the ",
"hippocampus, hypothalamus, amygdala, and basal ganglia",
". The ",
"hippocampus",
" is the key region of the brain where short-term memory is consolidated into long-term memory, and its impairment is responsible for the effects cannabis has on memory. The ",
"hypothalamus",
" contains multiple nuclei (collections of brain cells) responsible for survival, including those that control eating, which is the reason cannabis has such potent appetite stimulating effects. The ",
"amygdala",
" is a key brain region involved in emotions, particularly fear, and heightened amygdala activity could explain the paranoia cannabis has for some people. The ",
"basal ganglia",
" are a group of nuclei in the brain that have functions in habit learning, memorizing routines, and motivational behavior."
] |
[
"How does a FM Radio antenna deal with the echoed signals?"
] |
[
false
] |
Hello, When voice is transmitted over a radio, the transmitter transmits it in all directions, and a few of them reach the receiver antenna (in either straight line or through reflections) with different delays. But why doesn't we hear the echo like we do with Sound?
|
[
"This is called “multipath interference” and it’s definitely a problem for radio communication. But the effect between two copies of a wave a few nanoseconds to microseconds apart is a weakening or garbling of the signal, not something you can hear."
] |
[
"Back in the days of VHF television transmissions, ghost images due to receiving reflected signals was sometimes experienced. Those ghosts were only a fraction of a single scan line on the screen behind the main image. That works out to be something around one microsecond delay, far less than the time for one cycle of the highest audio frequencies, competely imperceptible."
] |
[
"Yes, and if the delay was sufficient to hear it, the extra added path length would attenuate the signal so much that it would be too weak for the radio to actually pickup."
] |
[
"If you place a pot of water in the freezer, will it freeze from the edge inwards or the center outwards?"
] |
[
false
] |
[deleted]
|
[
"From top/edge inwards to the center.",
"Explanation:\nWater has the highest density at about 4°C [1]. The temperatur of the water in the pot is roughly even, with just slight variations (since the cooling is slow and the water has enough time to evenout). However, these variations make a difference.\nWater at 4°C will flow to the bottom, any warmer OR colder water will float above it. Even if the entire pot is below 4°C, the coldes part will be on top. Therefore, the pot (and any other body of water eg lakes) will freeze from the top.",
"If the pot (the container) itself is cold enough, it is possible that some water will freese on its inside surface. However, the effects described above will still apply: You will get a U-shaped portion of ice (in cross-section) with a liquid part inside. So basically, the container wall becomes thicker. If the surrounding temperature is cold enough, it might freeze from top as well, leaving you with a ball of ice with a liquid core, all inside the pot.",
"Btw: Having the highest density above the freezing point is something very rare. It's called ",
"negative thermal expansion",
" [2]. It might be a driving factor for the existance of life, since otherwise our oceans would have frozen from the bottom up and never completly melted between ice ages.",
"[1] ",
"https://en.wikipedia.org/wiki/Properties_of_water#/media/File:Density_of_ice_and_water_(en).svg",
"[2] ",
"https://en.wikipedia.org/wiki/Negative_thermal_expansion",
"Edit: ",
"leaving you with a ball of ice with a liquid core",
"Maybe you have seen this when making ice cubes in the freezer: Sometimes you end up with an ice cube that has a liquid core (and/or even a bubble) inside. That's the same process."
] |
[
"Well you proved me wrong. I thought edges and bottom first, to inward. I learned something. Thanks."
] |
[
"Water will freeze at the 0°C temperature. So basically the ice limit will follow the area of 0°C. So if you use a simple bottle or a bowl it will freeze from the exterior inward as it is there that the exchange of energy will take place. That is why for instance a frozen river has its top frozen, beacaus it is the air which is cold, the ground underneath is generally hotter."
] |
[
"Does one experience \"lag time\" when viewing a black hole?"
] |
[
false
] |
I just watched . I can't stop thinking about what two people would experience when A watches B enter a black hole - both with lights that flash every second. For Example: When B draws near the black hole, as time slows and the light blink longer and slower, wouldn't the light emitted grow dimmer, longer lasting, and slower to occur to A? And wouldn't the lag time between where B is, and where A "see's B at" increase? (Like how the stars we see in the sky are long dead but the light remains?). As A gets drops nearer the black hole wouldn't "everything" get brighter (more light photons getting to the eyes faster)? To the point they are blinded by light?
|
[
"For Example: When B draws near the black hole, as time slows and the light blink longer and slower, wouldn't the light emitted grow dimmer, longer lasting, and slower to occur to A?",
"This is spot on! The quick answer is that as we watch an object approach the event horizon of a black hole, we will see it 1) move ever more slowly and its light will become increasingly 2) redder and 3) dimmer.",
"To get a better sense of what is going on, imagine that you are an observer at point A and you are observing a laser fall into a black hole while sending light towards you. Now let's say that the laser emits light in the form of pulses at a fixed wavelength, ",
"as shown in this diagram",
". As you watch this signal, you will see that the closer the laser gets to the event horizon, the redder and dimmer the light will look. The reason for this effect is that as the laser moves into the higher gravitational potential of the black hole it will experience a ",
"gravitational time dilation",
", which will effectively ",
"stretch the light it emits",
". This stretching will cause both the pulses to separate from each other (making the light dimmer), as well as the the wavelength of each pulse to increase (making it redder).",
"Now here comes a key part of the story: ",
" Instead you will see the laser asymptotically approach this point without ever quite reaching it. In other words, as you watch the laser you will see it move slower and slower until its motion would seem frozen right at the event horizon. Moreover, you won't really be able to observe it for long. As the laser will approach the event horizon, the pulses will become so rare that the beam will become too dim to be detected. On top of that the wavelength of the light would start to increase so much that you simply wouldn't be able to detect it. In the limit of the laser falling into the event horizon, you would have to wait infinitely long to receive a pulse that has an infinite wavelength."
] |
[
"You are exactly right, there has to be a last pulse/photon, since in its own frame of reference object B will at some point cross the event horizon. However, as you wait to receive those last few photons, the time you would have to wait between pulses would grow longer and longer. In fact, this waiting time will approach infinity in the limit of waiting for the last pulse before the laser crosses the event horizon. This effect happens for the same reason that we can never see B cross the event horizon: because of time dilation, the time needed for B to cross the event horizon is infinitely long. "
] |
[
"I cant see how it would in practice asymptotically approach the EH without crossing it from A's point of view. I think the pulses would indeed stretch out as you describe, but must eventually Doppler shift and then disappear (stop). From the point at which B leaves A to the point at which B actually crosses the event horizon, there will be a finite and known number of pulses that were transmitted from B. This number observed by A cannot be exceeded. Am I missing something?"
] |
[
"How do they keep radiation from contaminating the water which evaporates out of the top Nuclear Power Plants?"
] |
[
false
] |
Okay, so in Water Moderated Reactors, I understand that they use rods to contain the radioactive materials (usually Uranium-235), and because of the nuclear reactions these rods get really hot and they use the water to cool them down which is where all the water vapor comes from. (Please correct me if I'm wrong about any of this) So what confuses me is how do the keep the radiation inside of the rods? If it contaminated the evaporating water wouldn't that result in toxic rain? And because we know this is bad and don't want it to happen I have to believe that we've done something to prevent it. I know lead blocks all sorts of radiation but lead contamination would be almost as bad as fallout. So how do we do it?
|
[
"There are separate cooling loops. The water coming off of the huge evaporating towers has not seen any radioactivity, it has been encased in pipes and separate tanks the whole time and used to cool off the inner loop which as far as I know consists of water that may have radioactive impurities."
] |
[
"So in nuclear reactors fission heats water in a closed system. Once the water is heated is goes through a pipe system that is cooled with a second set of fresh water that doesn't have any contact with radiation or the contaminated water. So the heat is transferred to clean water that is then used to power the turbines and eventually comes out of the cooling towers.",
"It is when this system is breached that you have a problem and radioactivity leaking out.",
"Also, a minor comment: Most of the uranium used is 238 with about 3% 235. Some 238 undergoes fission, too, when hit by neutrons from 235 fission or when it becomes plutonium-239 through neutron capture. "
] |
[
"The vast majority of nuclear power plants use pressurised water reactor (PWR) and boiling water reactor (BWR) designs. In both cases the water running through the reactor pressure vessel is in a closed loop. In a PWR this heats a second closed loop which provides energy to the turbine, whilst in a BWR the the turbine runs off steam being produced within the reactor itself. ",
"In both cases the coolant is an additional open loop that comes after the turbine. ",
"Here",
" is a GIF showing the PWR design.",
"I don't know if it's a wording issue, but you appear confused about the difference between radiation and radioactive materials. ",
"I think that it's important to understand that radiation isn't a thing to be kept inside the rods. Reactors only work because neutron radiation is being emitted by rods, moderated by the water in the pressure vessel, and then being absorbed by other rods to cause fission and maintain a chain reaction. Other types of radiation are of course also being produced, but all of it essentially travels in straight lines and any travelling in an outward direction will quickly be absorbed by the water and reactor walls.",
"What you probably mean to be concerned about is radioactive byproducts. Radioactive material could contaminate the coolant, and as it travels through the reactor it will release radiation wherever it may be at the time. The majority of the dangerous material is contained within the fuel rods, and should only escape in substantial quantities in the case of the rods being damaged somehow. The coolant will however always be contaminated by activation products - when an atom (from the coolant or the vessel walls, or anything else around) absorbs radiation it may itself be transmuted into a radioactive isotope. Activation products are unavoidable, and they are a lot of the reason that the chained coolant loops are used. The inner-loop coolant, and anything else in close proximity to the reaction itself, eventually has to be disposed of as radioactive waste itself even if it was inert at time of production."
] |
[
"In logographic written languages such as Chinese, where characters broadly represent things/concepts/words, do they invent new characters when new things are invented or new words are coined?"
] |
[
false
] |
The same goes for Japanese kanji characters – do they invent new ones?
|
[
"In Chinese, if it's a loan word from another language they find a combination of characters that approximate the pronunciation of that loan word. A lot of characters have the same pronunciations, after all. If they can, they select characters with positive and relevant meanings, but otherwise they just try to not be silly or stupid. See ",
"this explanation",
" for how \"Coca Cola\" is translated into Chinese. In Japanese, it's much more straightforward: they have an alphabet, katakana, that is used exclusively for foreign words.",
"For new inventions, Chinese usually combine pre-existing characters to describe the new thing. As previously said, a lot of characters have the same pronunciation so most \"words\" are actually \"compound words\" consisting of multiple characters. For example, a computer is 电脑, Diànnǎo, written with the characters for electricity and brain. The internet is 互联网, Hùliánwǎng, meaning roughly mutually connected net.",
"Japanese has two alphabet system, hiragana and katakana, in addition to kanji. As such, they could come up with any new word and just spell it out phonetically in hiragana, just like with English. They could then find some combination of kanji to match those sounds to give the word extra meaning, but that's a tricky thing since most kanji can be read in multiple ways, but that's another topic altogether.",
"Source: Am Chinese."
] |
[
"I think others will answer your question more directly, but just to clarify: Chinese is not logographic.",
"Estimates are that around 3% of characters have logographic origins, and you can't characterise a whole system by 3% of it. One of the terms which is certainly less romantic, but more accurate is that Chinese characters are morpho-syllabic. That is, each character represents a morpheme of meaning and a syllable of speech.",
"Most characters are compounds of two components. Most commonly, but not always, one component will be a clue the meaning and one a clue to the sound. These clues have a wide variance of reliability. ",
"Think of a rebus like [picture of an eye] [picture of a heart] U, which I hope you can picture. English speakers will work out that this means \"I love you\". The pronunciation of eye is used to substitute for \"I\", the heart for the idea of love and the sound the letter U for \"you\". That might give you a little bit of an idea how many characters work by analogy.",
"Apart from anything else, most characters that are supposedly logographs don't look like pictures of the things they represent to outsiders. For example, 日 used to be a round shape in earlier scripts, but no-one who doesn't know the system would guess that it's a sun, in the same way that they can work out what pictures of males and females on toilet doors represent.",
"Source: teacher of Chinese and lecturer in Chinese literacy education. I can provide sources if anyone's interested. You could do worse than start by reading John De Francis \"The Chinese Language: Fact and Fantasy\""
] |
[
"I know about the Japanese kana – I was just wondering if the Japanese are making up more/new kanji. I understand that the existence of kana lessen the need for that, but still: Do they ever do it?",
"No, they don't really do that. In Japan there are about 2000 Kanji that people are supposed to learn in school, and that's about it. Only highly educated people know more than that.\nThe exact number of Kanji that are taught in school changes from time to time. Also the school board occasionally drops or adds some Kanji. But those that are added are not new. They have already existed before and are now simply regarded more important than before. ",
"For new words the Japanese basically only use Katakana."
] |
[
"How much % banana are we?"
] |
[
false
] |
[deleted]
|
[
"Clarification, 60% of ",
". Which is a very small percentage of the entire genome sequence."
] |
[
"about ",
"60%",
", apparently."
] |
[
"about 25%",
"This is easily calculated after one considers the fact that there are only 4 nucleotide bases from which to choose, therefore two completely random strings of DNA will always be at least 25% identical to each other on average."
] |
[
"Is mountain air really the healthiest/least polluted air?"
] |
[
false
] |
Is there less polution in the mountains (for example the Alps in France) than in some desolate village at sea-level?
|
[
"It's not so much the altitude as it is proximity to large cities and prevailing wind patterns. There aren't a lot of large cities with manufacturing and chemical processing plants near the French Alps, for example, and the higher you go, the smaller the population is - therefore, the air is much cleaner. ",
"In Hawaii, some of \"most pure\" air in the world is blown in from the Pacific, because although these winds originate in China, they travel over the pacific for approximately 3 weeks before making landfall in Hawaii which allows all the pollution to settle out."
] |
[
"A lot of the pollution does not settle in the ocean.",
"http://discovermagazine.com/2011/apr/18-made-in-china-our-toxic-imported-air-pollution#.UpLdcz_9WSo",
"http://aliciapatterson.org/stories/china%E2%80%99s-rise-creates-clouds-us-pollution"
] |
[
"There are many type of 'pollution', different components in air. The O2, CO or CO2 level are tolerable in certain interval, it just gives you a headache. But there can be different chemicals, becteria, viruses, dust, heavy metals, or even hazardous waste or radiation carried by the dust.\nThe air cleaning 'things' are different too. Rain cleans dust and phisical substances, plants refreshes CO2 to O2 (daytime), UV light will kill bacteria and viruses, and some things heavyer than the 'air' (CO, Butane, dust, etc) will just sweep out in the calm air. Lighter gasses will pass to upper atmosphere (freons). And there are other special cases, like CO2 or suplhur can dissolve in water, even rainwater. Carbonic-acid > light type of acid rain or suplhur > acid rain.",
"So, when the suplhur and dust pollution is high coused by the coal firing (London, 60 years ago) Red snow or acid rain can be fall elsewhere (Sweden's high mountains.)"
] |
[
"How much neutron star material would it take to equal the mass of earth?"
] |
[
false
] |
From "A neutron star is so dense that one teaspoon (5 milliliters) of its material would have a mass over 5.5×1012 kg, about 900 times the mass of the Great Pyramid of Giza." This made me wonder how much neutron star material would it take to equal the mass of earth? Also, if you were able to break off a piece with mass equal to the earth, would it expand, stay the same size or explode? Sorry if these questions are ridiculous. Neutron stars (like much of the universe) boggles my mind!
|
[
"Taking the density at 4.5×10",
" kg/m",
" (there's a range of possibilities, but that's about average), a neutron star with Earth's mass would have a volume of 13,276,000 m",
" , equivalent to a sphere of radius 146 metres.",
"If isolated from the neutron star's gravitational pressure, a small section of neutron star matter would likely decay fairly rapidly to normal matter, but we don't know very much about the true structure of material in a neutron star, which makes it difficult to predict its behaviour in different scenarios."
] |
[
"You're right.",
"1.086 x 10",
" teaspoons = 5.355 x 10",
" mL = 5.355 x 10",
" cm",
" = 5.355 x 10",
" m",
" = 5,355,000 m",
"As far as how many oil supertankers that is - depends on the size of the oil tanker. ",
"I will mention that if you had a perfect rectangular prism the height and base of the Empire State Building - you would have a volume on the order of magnitude of 2,700,000 m",
" So just a little bit bigger than 2 Empire State Prisms and you'd have the same volume."
] |
[
"\"How much\" could either refer to an amount of volume or mass (or moles I suppose), but the context of his question clearly indicates that he means volume."
] |
[
"Why is There a Speed of Sound? Shouldn't the Speed of Sound Vary With the Intensity of the Source?"
] |
[
false
] | null |
[
"Nope, it only varies with the density of the medium in which it travels.",
"Think of it this way: you drop a pebble and a big rock into a lake. The waves created travel at the same speed, the pebble's waves are just smaller and fade to nothing sooner than the big rock's waves."
] |
[
"This is a common misconception of intensity, speed as applied to particles and speed as applied to waves.",
"We are used to the notions of speed of particles - we throw rocks, pitch baseballs, play darts etc. For these, it seems intuitive that the \"harder\" we propel the object, the \"faster\" the object will be.",
"The problem with sound is that it is not a particle. It is a wave that is caused by a disturbance. Think of it this way: to create a wave on a string, you actually shake the string up and down (think of skipping ropes). The action or lay term \"force\" is actually at 90 degrees to the direction of the wave on the string. Shaking the string harder creates waves with higher crests and troughs, shaking the string faster creates waves that are higher in frequency, but the speed of the wave will not change because you are moving the string at 90 degrees (or orthogonal) to the direction of the wave. ",
"(Strictly speaking these are transverse waves and sound is longitudinal, so there are differences here, but it's an analog.)",
"It is possible to vary the speed of the wave by varying the medium - for example, changing the tension of the string or its material etc. Thus, sound speeds in water and air are different."
] |
[
"The speed of sound in a medium will also depend on the ",
"bulk modulus",
" of the material (describes responsiveness to pressure) in addition to the density."
] |
[
"I know a catalyst works by lowering the activation energy but how does it do that?"
] |
[
false
] | null |
[
"One way that this can work is for the catalyst to orient the reactants in a way that is favourable for the reaction to occur. The reactant-catalyst interactions are low energy, so easily formed, and they position the reactants in such a way that they can react with each other easily. "
] |
[
"It depends on the exact catalyst, but generally it works like this. If the reaction A+B->AB has an activation energy of X and a third substance C undergoes the reactions A+C->AC with activation energy Y and AC+B->AB+C with activation energy Z, and Y+Z<X, then the reaction will proceed through the favorable catalyst cycle. ",
"Disclaimer: I might be misremembering this."
] |
[
"To put it simply: usually the catalyst offers a different reaction path that has an lower activation energy. So, it's not the same reaction with a lower activation energy, but rather a different reaction leading to the same product from the same reagents + the catalyst, and the catalyst is regenerated at the end. The exact way it does that can vary from one or the other tough. Some orient the reagents in a way that is more favorable to the reaction, others facilitate the formation of the product bonds or weaken the bonds that needs to be broken on the reagents and so on."
] |
[
"Can non-ionizing radiation heat air and water?"
] |
[
false
] | null |
[
"I can't really answer that without speculating."
] |
[
"Yes. This is how the sun (primarily) heats the Earth."
] |
[
"Do you think there's a signicant heating impact from human made emr ? (A la climate change)"
] |
[
"Why do some airplanes have raised wingtips?"
] |
[
false
] | null |
[
"Winglets",
" reduce the aircrafts drag by reducing ",
"wingtip vortices",
". This increases overall efficiency, which can save substantial amounts of fuel. They can also improve stability and handling by increasing the ",
"aspect ratio of the wing",
") without increasing the actual wingspan."
] |
[
"very accurate. They do save a lot of fuel particularly on long flights. That is why they are most commonly seen on larger jets."
] |
[
"Also the payback time through fuel savings is something like 6 months for an older plane retrofitted with winglets."
] |
[
"How does the air inside the tire of a moving car behave? For example does it \"spin\" at a similar rpm to the tire? Also what effect does centripetal force have on the air if any at all?"
] |
[
false
] | null |
[
"Tire engineer here,",
"The air does move, and it will be lagged behind the carcass (which is lagged behind the wheel a bit, kind of). The air will lag, but not very much, and the effects are minimal.",
"Currently even the most advanced tire models (F1 or aircraft) do not even model the effect you are talking about. There just isn't enough mass of air to make a difference compared to all the other things going on when tires are in use.",
"As for the centripetal force, this is negligible, again, because the air has so little mass. Tires also rotate a lot slower than most people think. Even NASCAR tires at 200 mph are only turning about 2400 rpm (2.22m rollout), which is really slow as far as centripetal forces on air are concerned. Still about 2300g though (V²/r)/9.81",
"The volume of one of those tires is about 0.4m³ which means at 1.2kg/m³ and say, 5 atm (70 psi is realistically the highest pressure a right side tire will use at Charlotte) the air in the tire will have a mass of about 0.5kg. Even if we consider all of this to be at the loaded radius, the total centripetal force at 2300g is about 10kn (2500lb). ",
"This may seem like a lot, but distributed around the circumference of the tire it means this is about the same as 2 psi more pressure. ",
"Compare that to the centrifugal force of the actual tire, which is more like 10kg, and it looks pretty insignificant (230kn and 45psi effective)."
] |
[
"I can't say I've ever modeled tires with water in them, but there are two interesting things that would happen off the top of my head.",
"One is that the flow of water would add a huge damping effect, meaning that if your tire got stuck suddenly, the flowing water would give it a huge boost of torque, as the water is still moving at the speed you were going. This could be much, much higher than the torque the engine can apply, given the amount of mass and the radius of the tire. This would be really noticeable in increasing the acceleration time between tires filled with air. I can see how this would be useful as you don't want to stop the tractor if you hit a bump, and adding engine capacity is not always feasible.",
"The other thing is that if the tire isn't completely full, there will be a sloshing frequency in the water, which can be an advantage when you are stuck. If you go drive / reverse at this frequency, the sloshing will amplify the normal gravitational rocking that is done when you are in soft soil and the tire is in a hole. Ideally the slosh frequency would be near the natural rocking frequency for your tractor.",
"Of course, there's just the plain old fact that more weight makes the tractor get more traction in soft ground with such large tires."
] |
[
"As an aside, a lot of tractor tires are liquid filled to add weight. Solution of calcium chloride, I think, to keep from freezing. My old tractor was filled about 90% with liquid, and each tire with rim weighed about 500 pounds. Guess they are going too slow to notice any sloshing effect, though."
] |
[
"A question about visible lasers."
] |
[
false
] |
I recently bought a 5mw visible green laser. If I'm in a well lit area, I can't see the beam. However, today I noticed that if I aim the laser at a mirror in my room, so that the returning beam goes right past my head, I can see it. But I can only see the beam after in hits the mirror. Does anyone have an explanation for this?
|
[
"Photons can scatter in air - the effect is called ",
"coherent scattering",
" and affects a lot of processes having to do with light and air.",
"Scattering at small angles (a tiny deflection of the photon) is more likely than scattering at large angles (a big deflection). So when you shine the laser away from you at the mirror, light has to scatter almost 180 degrees to get to your eye. When it reflects off of the mirror, it is traveling towards you, and only has to deflect a small angle to enter your eye."
] |
[
"Yep. Also, watch out. It's not too far from almost by your eye, to in your eye, blinding you. If you want to continue enjoying the fun and science of lasers, you should really invest in appropriate eye-wear."
] |
[
"I will be sure to pick some up as soon as possible."
] |
[
"Why do the colours on my computer monitor appear in negative when i tilt my screen?"
] |
[
false
] | null |
[
"The LCD (TN type panel) consist of many layers of filters. by tilting your screen, it makes some of the filter not work as design.",
"Here is short youtube video explaining how LCD works.",
"http://www.youtube.com/watch?v=jiejNAUwcQ8"
] |
[
"To add to this, there exist IPS-type panels (such as what's used on the iPad and other high-end devices) which are in general more costly than TN panels but provide uniform color for viewers 178 degrees around the front of the panel. ",
"For example, I am typing this on a Dell UltraSharp U2412m IPS monitor. Monitors like this are preferable when you want to change orientations between horizontal and vertical at will, make a mobile device that needs to look good both in front of your face and flat on a table, or have multiple people standing around a screen and seeing the same, accurate representative of an image (whether it's a movie, photo, or medical diagnostic scan).",
"Edit: rephrasing for clarity."
] |
[
"Light coming at a flat angle from the screen has passed through a thicker layer of liquid crystal than intended, and is thus more rotated. Colors that were supposed to be blocked may thus pass, and colors that were supposed to pass are thus blocked.",
"Some more details.",
" ",
"Photons",
" (light particles) are electro-magnetic waves, the magnetic field being ",
"90 degrees",
" rotated compared to the electric one. For simplicity, consider only one of the two fields (say the electric one). Seen from the front, this would look like a flat line. Hence, you could say that the photon is \"horizontal\" or \"vertical\", or somewhere in between.",
" You may imagine a ",
"polarizer",
" as prison bars. If the light is in the right orientation (polarization), it can pass between the bars. If it has the wrong one, it will hit the bars is thus blocked by the polarizer.",
" Normal (unpolarized) light is made of photons oriented in random directions. After crossing the first polarizer, only half of the photons remain (say vertical ones). Because the second polarizer is in the opposite direction (say horizontal), all the remaining photons are blocked.",
" Placed between two polarizers in opposite directions, this allows you to control where light may pass through (e.g., by rotating the light 90 degrees) and where it should not (e.g., by not rotating the light).",
" If you look at it with too flat an angle, the photons reaching your eyes will have crossed a thicker layer of liquid crystal than intended, making it rotate more than intended. If it should have been rotated by 90 degrees but crossed twice the thickness that it should have crossed by design, then it rotated 180 degrees, which brings it back vertical if it started vertical. Thus, light that should have passed through is now blocked."
] |
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