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[
"Why does the chain \"screen\" that goes across my fireplace not get as hot as the other metal or rocks around it?"
] |
[
false
] |
There are two chain curtains that close from either side across the front of my fireplace. I assume to keep sparks and other flaming debris from coming out of the fire and into the living room. Any time I adjust them, or open and close them to add more wood, they never seem more than slightly warm, even though they are less than a foot from the fire and coals, while the tools and surrounding rock are hot to the touch. Why is that?
|
[
"no cite available:",
"I ",
" it's because it functions like a radiator, the chain link would effectively have a lot of surface area to transfer the heat to the surrounding air. "
] |
[
"Not only does it have a high ratio of surface area to volume/mass, but it's in the airstream that feeds the fire, so the combination of these two factors keeps the curtain cool."
] |
[
"I would suggest there are two factors here:\n1. The chain fence is colder because it has large surface area and is further away from the fire."
] |
[
"Does a vehicle get better fuel economy over its life if you wax it and keep it clean versus never washing or waxing it beyond the initial factory clean?"
] |
[
false
] |
I notice when a car is very dirty, the paint feels rough. When I wash, and especially after I wax my car, it feels very smooth, almost slippery. So I wonder if this makes it more aerodynamic, and thus improves fuel economy. And if so, by how much?
|
[
"A dirty car gets a better mileage than a clean car. The added weight of the dirt is insignificant compared to the mass of the car. The dirt helps to break up the laminar flow around your car into a turbulent one, which reduces the aerodynamic drag. Its the same effect that makes golf balls fly further (dimples). The Mythbusters have done an ",
"experiment",
" on that."
] |
[
"Mythbusters is hardly rigorous when it comes to their science, but it is fun and anecdotal.",
"For drag, there are two kinds of drag at play here, viscous drag and pressure drag. Viscous drag is the drag due to the friction of the air flow against the surface. Pressure drag is the drag that comes about from the air flow separating from the object and recirculating. For a car, you could consider it more of what is called a bluff body. A sphere is a good example of another bluff body. This is in contrast to a streamlined body, like an airfoil.",
"For bluff bodies, the pressure drag tends to contribute much more due to the difficulty the air has in smoothly following the surface. For streamlined bodies, the viscous drag tends to dominate. Now, there are two types of flow at the surface of objects (called the boundary layer): laminar and turbulent. Laminar is nice and neat and everything is organized essentially. For turbulent, there are many small disturbances and air is swirling around right next to the object a lot. Now, laminar is great for reducing viscous drag. Turbulent however, has much more viscous drag. However, due to all that extra activity in turbulent flow, it tends to stay attached to the surface longer.",
"So for bluff bodies, you WANT turbulent flow since that reduces the pressure drag more than it increases the viscous drag"
] |
[
"Wow that's the opposite of what I'd think. Thanks"
] |
[
"Why do black holes spiral into each other and get picked up by LIGO, instead of just orbiting each other like everything else in the universe?"
] |
[
false
] | null |
[
"When objects orbit each other, they emit gravitational waves, which slow down the system. However, in almost all cases this effect is too small to be noticeable - the slowdown gets faster when gravity is stronger. You can only really detect it once you're dealing with very very strong gravitational fields. We have observed binary neutron stars whose orbit is very slowly decaying, for instance. So the idea is that binary black holes that are very close to each other have such strong gravity that their orbits decay really fast and they merge.",
"The actual tricky bit is how to get the black holes that close to each other in the first place. If two galaxies with supermassive black holes merge, you'll end up with one galaxy with two supermassive black holes in it - but they'll be nowhere near each other. The supermassive black holes will tend to \"sink\" to the centre of the galaxy, as they lose kinetic energy by scattering nearby stars and gas - this is called \"dynamical friction\". However, this only works until they are a few light years apart. This is called the \"final parsec problem\", where a parsec is a unit of length that is a bit over 3 light years - we're not sure how supermassive black holes get from being about a parsec apart to being close enough that gravitational waves take over and the orbit decays. It may be something to do with interactions between the accretion discs or other gas around the black holes - but this is a field of active research, and I'm personally running some simulations right now, provided I got the submission script right this time."
] |
[
"you can understand this simple by conservation of energy. the gravitational waves carry energy away from the obiting system. this means that that system has to lose this same energy somehow. this is what brings them closer and closer together."
] |
[
"Static mass have static potential wells, moving masses dont. Gravity has a finite speed so it takes some time for spacetime to react to a change in position of the object causing it's deformation. This deformation of the spacetime is what is taking your energy, energy being convertable means you trade potential/kinetic for bending energy. Lost potential/kinetic means closer orbits, since the wave losses get stronger and stronger the closer your masses get the quicker the orbits decay.",
"The effect is similar to how electric charges give of radiation if accelerated."
] |
[
"If Jupiter is only made of gas then why did we notice impacts on its surface with Shoemaker Levy"
] |
[
false
] |
I remember seeing black dots on its surface when the meteorites smashed on the planet. If its only made out of gas, then why did we see black impact holes?
|
[
"Those were impact holes in the clouds."
] |
[
"Jupiter is not only made out of gas. In the center, the pressure and temperature is too big for gas to exist.\nBut the marks you see is because the atmosphere was disturbed where the meteorites hit it, and it takes some time for it to get back to 'normal'. Of course, it always changes, some spots disappear and new ones appear, because of 'weather' patterns."
] |
[
"It happened for the same reason we see meteors as \"shooting stars\" or exploding bolides. The chunks of comet hit the atmosphere, they were really, really large, and they immediately converted all their kinetic energy into heat and went BOOM like giant bombs. ",
"A similar (though thankfully smaller) event happened in ",
"1908 in Russia",
". A chunk of comet or an asteroid that didn't hit the ground (grazed the atmosphere or exploded ",
" the atmosphere), resulted in a very big explosion, like a very large, high altitude nuclear bomb."
] |
[
"Does each individual sperm carry different information?"
] |
[
false
] |
This just got me thinking as I thought cells were created by replicating themselves so in my thinking that would make each one identical. But then how do siblings look different if everything is decided by the information in the sex cells? Basically what makes siblings look and grow differently?
|
[
"Yes",
"This is part of the process of sexual reproduction. During spermatogenesis the cells called spermatocytes undergo a process called meiosis which shuffles maternal and paternal genetic information. Each primary spermatocyte has two copies of each chromosome, pairs, one of which was inherited from the father, and one of which was inherited from the mother. As spermotogenesis proceeds the cell splits in two and one copy of each chromsome ends up in each of the two secondary spermatocytes. It gets more complicated but the bottom line is that sperm carry a random 50% of the father's DNA, and eggs carry a random 50% of the mother's DNA, and these combine to make a new human. As each person has 23 pairs of chromosomes the genetic variation between siblings is quite signficant.",
"TL;DR There is a process that 'shuffles the deck' of genetic information during the creation of sperm and eggs, so the information in each sperm and egg is actually quite different."
] |
[
"You're thinking is half right. ",
"All the cells of the body (somatic cells) replicate by splitting into two identical cells. This is called mitosis. ",
"However, sperm cells in men and eggs in women are generated by this thing called miosis, which is different than mitosis. ",
"To explain it, we need to get into the DNA of the cell. DNA is in the cell as these things called chromosomes. We have 23 pairs of chromosomes (so 46 total). In mitosis, the cell doubles these and then splits them evenly between two new cells. So both cells have identical 46 chromosomes.",
"In the sperm and egg cells however, miosis splits the chromosomes in half (so they get one of each pair, so 23 total). Then, when the egg and sperm meet, they combine to form the complete set of 46.",
"So when the sperm or egg are made, they only get one of each pair, so if a parent has two different chromosomes in the pair, then they would only get one, and the siblings could get different ones."
] |
[
"The process that creates sperm (and egg) cells is called meiosis. It's like mitosis, where the chromosomes duplicate then spilt, but with a few extra steps where some genes transfer and the chromosome pairs themselves split. ",
"Your genome consists of 23 chromosomes from Mom and 23 equivalent chromosomes from Dad. During mitosis, each chromosome duplicates so that when the cell splits, each one has the proper amount of DNA. Meiosis picks up after Mitosis. At this point you have two identical cells (except for the process that creates egg cells. One cell will become the egg cell and the other is an empty cell called a polar body. This is broken down and reabsorbed.) ",
"Now, a gene exchange occurs. One of your mom's chromosomes gets up next to one of your dad's chromosomes and parts of the genome jumps around between them (that's right, your parents are still swapping DNA inside your balls/ovaries right now). This ensures genetic diversity. At this point, it's time to divide again. The cell currently has 23 pairs of chromosomes in it. When the cell gets ready to divide, the chromosome pairs are split randomly- the one from your mom goes to one cell and your dad's to the other. This happens randomly to each chromosome pair until the cell is divided, at which point only minor development is necessary before it's ready to be squirted into a sock. ",
"To answer your question, each sperm cell is perfectly genetically unique. Consider that there are 2",
" ways to split the chromosome pairs (~10 million), and vastly more ways to exchange genes before division. "
] |
[
"Dear chemists, why do personal hygene products list water as \"eau\" or \"aqua\" in the ingredients?"
] |
[
false
] |
'Chemistry'
|
[
"This actually isn't a science question for chemists. It's more of a MARKETING question.",
"The whole world of personal hygiene, and in particular anything associated with upper-end women's cosmetics or \"age treatments\" or various perfumes, benefits tremendously from good marketing.",
"Eau and Aqua, synonyms for \"water\" in other languages, sound so much more elegant and refined than just plain old water does. They make the component of the recipe seem European, and mysterious, and made with 'special' ingredients. ",
"And that fine-sounding name translates directly into a greater level of appeal, meaning people are willing to spend more on the \"specialness\" of the product because they consider it more \"elite\". So companies can charge extraordinary prices for these higher-tier products compared to, say, a generic-brand body wash or a moisturizing hand cream that's sold in one-quart plastic bottles."
] |
[
"\"Eau\" literally means \"water\" in French, and \"Aqua\" means \"water\" in Latin."
] |
[
"Well, this makes a lot of sense. Thanks for your input, man."
] |
[
"Why doesn't milk curdle in your stomach acid?"
] |
[
false
] | null |
[
"It shouldn't ",
"; curdling is just the separation of curds and whey and there's no real chemical change affecting the constituents of the milk. This is how cheese is made after all.",
"It is possible that you feel nauseous due to psychological reasons - curdled milk does look pretty disgusting! Also, if the milk has curdled naturally because it has been left for a long period of time, then the bacterial content is probably quite high and it could be that making you nauseous/sick."
] |
[
"As far as I'm aware ",
"it does",
". Why do you think it doesn't?"
] |
[
"That's more to do with it being a gallon that it being milk!"
] |
[
"Is there a limit on how much information the brain can retain?"
] |
[
false
] |
Does the human mind, or do minds in general, have a storage capacity?
|
[
"I think this question would better fit in ",
"/r/AskScienceDiscussion",
", but anyway: ",
"We do not (yet) exactly know how memory is stored. We know about plasticity, which is the brain's ability to form new connections between neurons, we know about firing patterns associated with certain types of memory, but we have no clue how this works together in the big picture. Therefore, it is absolutely impossible to make any assumptions on \"storage capacity\" of the brain.",
"If I might add something: When questions like this come up, I always imagine that people imagine the brain to work like a hard disk or a storage unit: There's a directory of where stuff is found and than the brain locates this bit and retrieves it. Although I said above that we don't know how memory works, we have some ideas how it does ",
" work. The hard disk model is one of those cases. Also you need to remember that while it is easy to quantify digital information (how many bytes?), how would one quantify information stored in the brain? How would you know the information \"the clear sky is blue\" takes up more or less \"space\" than \"The first moon landing took place in 1969\"? This is just not how the brain works. ",
"Also it might be worth mentioning that if we can't remember something, it's most likely because the brain decided to filter that information out and not store it in the first place. However, it doesn't do so because it wants to \"save space\", but because we most probably go nuts if we could remember everything. There are people with disorders where this filtering doesn't work. They literally remember everything that ever happened to them. This is called ",
"hyperthmesia",
"."
] |
[
"I agree with ",
"/u/HereForTheFish",
" in general.",
"That being said, there have been a few studies in pigeons where they looked at limits of paired associate memory (shown two pictures, pick the \"correct\" one). ",
"Vaughan and Greene (1984)",
" found that pigeons could retain this kind of learning for 100+ items for two years without intermediate exposure. More recently, ",
"Cook, Levison, Gillett, & Blaisdell (2005)",
" found that pigeons could learn about 850 image-response associations over the course of several months, but as more images were presented, the total number of retained associations remained constant. They argue that this is the first evidence for any kind of memory limit (I'm assuming they are excluding working memory). In a second study, ",
"Fagot & Cook (2006)",
" replicated the results in pigeons (800-1200 item-response pairs) and also tested baboons, who were able to learn, over the course of three years, 3500-5000 item-response pairs and did not seem to have reached a limit."
] |
[
"You may want to take your question here: ",
"/r/cogsci",
"As HereForTheFish points out this can be a difficult question because some of the physical processes involved are still not yet understood.",
"That said, there are long standing models and reliable \"memory capacity\" measurements.",
"Cognitive Psychology is a sub-discipline of Experimental Psychology which has attempted to quantify memory capacity. In the classical models, there are typically three types of memory: Sensory, Working*, and Long Term Memory.",
"*Working is sometimes used interchangeably with Short Term memory in the literature because the concepts overlap. However, there are important differences between the definitions for these stores which I really don't want to get into here. ",
"Memory capacity is really interesting from a Cognitive Psychology perspective. Interestingly, it is one of the reasons for its very existence as a field of study. Without boring you with a lot of historical details, Behaviorism was the dominant discipline within Psychology (particularly Experimental) for most of the early 20th century. This is important to mention because Behaviorism assumed internal mental processes as unnecessary. In their view, only overt Behavior is necessary to understand mental functioning. In the 1950s, several researchers published articles challenging this assumption. One such article was written by George A. Miller (",
"The Magical Number Seven, Plus or Minus Two: Some Limits on Our Capacity for Processing Information",
"). This article directly challenged the Behaviorist assumptions by demonstrating that memory capacity was influenced by how an observer (subject;participant;etc...) grouped, or chunked, the information. Moreover, this was evidence that mental processes not only influenced direct overt behavior (remembered items on a task) but that behavioral output could be examined to learn something about the Psychology of the observer (i.e. their mental state). In short, their experiences (familiarity etc...) influenced how information was chunked.",
"Example:)",
"If you give a participant a list of discrete numbers and only allow for a brief exposure you would expect them to remember about 7 (+ or -, 2 of them). However, if you organize those numbers into a meaningful group (e.g. phone number listings) a participant will recall 7 (+ or -, 2) phone numbers listings. Phone numbers in the US are 7 digits long, so the participant would be demonstrating memory for 35 to 63 individual numbers (within the listings). Basically, they would be able to remember more overall numbers because the meaningful chunks remembered are made up of them.",
"Based on this and other research many Cognitive Psychologists believe Working Memory capacity to be somewhere around 7, + or -, 2 chunks. Further, these chunks can be rehearsed and stored in Long Term memory. They also can be grouped into additional chunks which will further influence how much can be integrated into future Working Memory tasks. For this reason, many Cognitive Psychologists believe limits on Long Term Memory to be unknown, but extremely large (sometimes considered infinite in models, for practical purposes). There are some interesting case studies that seem to demonstrate this point (though in an abnormal population). A. R. Luria describes an of a particularly robust human memory in his book ",
"The Mind of a Mnemonist: A Little Book about a Vast Memory",
".",
"In conclusion, we can measure some of the functional limits for different types of memory stores we assume to exist. However, the total amount of information depends on how we apply meaning to that information (how we chunk the information). This, in turn, can be measured to some degree as well. However, because meaning/chunking is individual, and fluid (it changes with learning etc..), something like total Long Term Memory capacity would be very difficult to measure/calculate. ",
"Edit:) grammar; ugh, I need an editor."
] |
[
"What makes skin itchy?"
] |
[
false
] |
besides an obvious skin irritation like a cut or rash, what causes spontaneous itches on our skin? I have been wondering this for years and the only this I can think about it body hair. I have no clue.
|
[
"You get an itch when sensory neurons on the top skin layers become irritated. This will stimulate them, and as a result, a signal will be transmitted through unmyelinated nerve fibers to the cerebral cortex of the brain to illicit a scratch response. This stimulus can be very small, like a dust particle in the air, so it may seem like the itch comes out of no where. However, in the case of mental illness, an itch can arise without any sort of stimulus. "
] |
[
"If I may expand on this question, what is it about the act of scratching which relieves the itch? For things like mosquito bites, not particles irritating the skin."
] |
[
"Simple. You have skin that's irritated. Once you scratch it you are removing those skin cells. Irritation is almost always superficial. "
] |
[
"Is it accurate to suggest that any time you can see the reflection of a person that they can see you 100% of the time too?"
] |
[
false
] | null |
[
"No.",
"You see an object in a mirror because light has reflected off of it, hit the mirror, then reflected off the mirror, and traveled into your eyes. Light is well allowed to travel on reverse-paths, but that only means light from your eyes will eventually strike that other object. ",
"Now if that object is the other person's eyes, then they will see you. In other words, if you can see their eyes, they can see yours.",
"But what if that object is not the other person's eyes? Then you have not determined yet whether there is a light ray that travels from you into their eyes. So they may not necessarily be able to see you. It could be the case that see part of you or it could be the case that they see none of you.",
"But what is certain is that if either of you can see the other's eyes, then both of you can see the other's eyes. (And that's probably all that really matters for the majority of us who want to make sure we don't look creepy in some reflection on the bus or subway.)"
] |
[
"Either a mirror that is only reflecting light in one direction,",
"There is no such thing. That would violate all kinds of laws of physics. Light paths don't have a direction. If light can make it from point A to point B, then they can make it from point B to point A. That's why we can use nifty things like Fermat's Principle of Least Time in assessing optical set-ups.",
"\"One way glass\" is just slightly mirrored glass where one room is in darkness and the other is very bright. The light still goes two ways. If the police turn on the light in their booth, both rooms can see each other equally well."
] |
[
"Either a mirror that is only reflecting light in one direction, or a particular setup of the light sources that only illuminates one side or the other."
] |
[
"If our tears are salty, why does salt water sting our eyes?"
] |
[
false
] |
I've always been curious as to why my eyes burn underwater in the ocean but my tears always taste salty.
|
[
"Great question! Let's consider any differences in those two types of saltwater. Now aside from microorganisms and other nutrients and minerals present in seawater the main difference is that the oceans are saltier than our tears. That is not to say our tears are not salty- medical fluids such as IV drips or contact solution have a small amount of salt in them to match the fact that our bodies have small amounts of salts dissolved (Na, K, Ca, Cl mostly). Pure water would be bad to put into a person actually, and small amounts of salts prevent over or dehydration. tl;dr In short, more salts in seawater than tears- so it stings. Tears don't sting because they have as much salt as your body already is working with in them."
] |
[
"Sweat is generally more salty to prevent bacterial growth in what would otherwise be an inviting environment for them- warm moist skin"
] |
[
"To add on to this, I've noticed that sweat does sting your eyes, so I'm assuming it's more salty than tears? Is there a reason for this?"
] |
[
"Can scars form on the inside of the body as well?"
] |
[
false
] | null |
[
"Sure can! They are usually a result of invasive surgery, but can form from injuries such as deep cuts, stabbing, or really any internal injury that would result in scarring if it occurred externally. ",
"I assume by “inside” you mean there’s no scar on the skin, but regular scars do extend into the body. Think of them like an iceberg. You only see the part that protrudes through the surface ",
"https://health.clevelandclinic.org/4-best-ways-to-take-control-of-abdominal-adhesions/"
] |
[
"Sometimes scar tissue can result from non surgical internal injuries or infection like cysts resulting from infected hair follicles, scarred stomach tissue from ulcers, endometriosis from infected endometrial tissue that can’t be shed because it occurred in the wrong place, or scarred lung tissue from tuberculosis infection. "
] |
[
"Yes, they are called adhesions and they bind two parts together that shouldn't be together. Say you have appendicitis that doesn't get treated for a while. You can get adhesions from the chronic inflammation and infection."
] |
[
"Can I give up depth perception for a larger field of view?"
] |
[
false
] |
Would my brain ever get used to seeing what I "normally" see with one eye and say behind me?
|
[
"I would have to say no.",
"The brain comes wired for binocular vision. The primary visual cortex is organized into ocular dominance columns, which means that there are alternating rows of cells that correspond to each eye. Hubel and Wiesel won a Nobel prize for discovering this.",
"http://en.wikipedia.org/wiki/Ocular_dominance_column",
"If the input from both eyes doesn't match at a young age (as we often see in eye misalignment AKA strabismus), the brain deals with this by choosing a dominant eye and ignoring the other one. This is called suppression. Eventually, cells in the ocular dominance column of the ignored eye die off. This is called amblyopia.",
"http://en.wikipedia.org/wiki/Amblyopia",
"As we get to around 10 years old, we lose our ability to suppress and there is no more potential for amblyopia.",
"If you were to do this to a young child, one of the eyes would become ambylopic and the brain would essentially ignore its input. If you did it in an adult, it would cause double vision. The brain doesn't deal with double vision particularly well. This probably has to do with the organization of the brain and the dominance columns. Because input from both eyes is interpreted together, double vision is disorienting. ",
"You would be able to \"see\" the things behind you if you focused on them, but it would likely be very bothersome. The brain possesses some ability to adapt (plasticity) but isn't able to overcome discrepancy between eyes. "
] |
[
"Is suppression similar to why we don't see bullets or is that a myth? "
] |
[
"We can't see bullets because they move quickly.",
"Suppression is the brain ignoring input from one eye."
] |
[
"Why do I feel like I'm still riding a roller coaster when I'm lying in bed after a day at the theme park?"
] |
[
false
] |
My best guess is that it has something to do with balance and the inner ear.
|
[
"Just like when you stare at those weird optical illusions and look away to see everything distorted, your inner ear gets used to the frequent motion and actually adapts to it and deeming it normal. So when it stops, things can feel a bit skewed for a short period of time while your inner ear adapts to the new motionless environment."
] |
[
"Your neurons react to the regular stimulation during the day. If this happens long enough your neurons take this new aroused state as a new baseline. When you are at home, your environment is now dramatically different from that new baseline, giving the perception you are still moving."
] |
[
"It isn't necessarily a threshold. Your perception of what is going, in this case movement and propioception, is based on patterns of neuronal firing. By changing the baseline the accelerated or decelerated pattern (not related to what is going on, colors have various speeds of firing in the optic nerve) becomes the new baseline. So when the pattern changes once again at home that change in pattern is once again perceived as movement. Sorry if it feels like I am repeating myself it is kind of hard to explain without drawing it out and all that."
] |
[
"Can we use a black hole as gravity-assist to propel a spaceship to near light speed ?"
] |
[
false
] |
This might probably be a ELI5 question, but the fears of the creation of micro black holes at CERN had me thinking this. Couldn't a space ship travel outside the event horizon of a black hole to boost its speeds capable of interstellar travel ?
|
[
"The force applied at the highest speed point of the fall is translated into greater kinetic energy",
"Just to clarify, firing rockets at the fastest point of the fall isn't efficient because burning fuel at this point magically has more energy. It doesn't. It's most economical to fire the rockets at this point because it allows you to pay the least amount of energy to gravitational overhead."
] |
[
"Yes, this is plausible, but probably not all the way to light speed. The ",
"gravity assist wiki has a brief discussion of this",
" (which I found by googleing 'gravity assist using black hole' BTW).",
"It's also important to note that gravity assists do not change the magnitude of the velocity of the flyby craft relative to the flyby body. A spacecraft in a flyby trajectory around Jupiter will enter and leave Jupiter's sphere of influence with the same magnitude velocity (only rotated). But with respect to the heliocentric frame, the spacecraft will be moving faster, and Jupiter will be moving slower. So a flyby past a black hole will only change your velocity with respect to a galactic inertial frame. "
] |
[
"The wikipedia article on ",
"Gravity assist",
" makes for some good reading.",
"To answer your question: there are two types of gravity assists. One is the passive slingshot, such as the one used to launch the Voyager probes. This is what is actually referred to as a gravity assist. This works by slingshotting around something that is in motion with respect to something else. Jupiter is moving with respect to the solar system, so Voyager could slingshot around Jupiter to gain speed relative to the solar system. Slingshotting in this way around the sun would be ineffective, since the sun is stationary with respect to the solar system.",
"A powered slingshot, on the other hand, can use the ",
"Oberth effect",
" to gain velocity with respect to the object it is slingshotting around. This works by falling into the object's gravity well, then firing rockets (or whatever propulsive force) at the fastest point of the fall (in this case, the closest approach to the gravitational body). This works for two reasons:",
"The ship loses mass from burning fuel. As such, when it leaves orbit, it actually suffers less negative acceleration that it gained falling into the gravity well.",
"The force applied at the highest speed point of the fall is translated into greater kinetic energy due to how fast the object is already moving. In a simplified explanation, the energy gained from applying the force is equal to F*d. A faster moving object covers a greater distance while applying the force (assuming equal time spent applying it) and thus gains more energy."
] |
[
"Do nonlinear differential equations truly have no analytic solutions or have we just not discovered a method of solving them?"
] |
[
false
] |
I have the understanding that nonlinear ODEs/PDEs are usually solved by linearization with a taylor series, but I'm wondering if they could be solved exactly if some extremely clever mathematician came up with a new method, somewhat like how integration by parts can be used for integration.
|
[
"We don't have any ",
" solution, but it doesn't mean we don't know how to solve some of them."
] |
[
"I don't think it's proven to be impossible but I guess everybody highly doubt it. For example, solving the Navier-Stokes equation (a PDE used in fluid mechanics) is already worth a million dollars: ",
"http://en.wikipedia.org/wiki/Millennium_Prize_Problems#Navier.E2.80.93Stokes_existence_and_smoothness",
"If a general solution is found in the next centuries, it would be a tremendous breakthrough."
] |
[
"I can explain without referencing that. Basically, I can express some computer in terms of non-linear differential equations describing charges in the wires, transistors, and such.",
"Now, I can have this computer computing something, starting from initial state at time 0, and arriving at answer on some time t.",
"If there was an easy, general method to just skip the simulation and find the state of the computer at time t without performing the number of operations proportional to t, it would be an universal optimisation. I could use that method to speed up any computations.",
"Needless to say it sounds implausible that such optimization could exist, perpetuum mobile style; I am not sure if there is a formal proof of it's impossibility but in general I know that the ability to implement arbitrary computation is usually taken to mean that general 'analytic' solution which doesn't involve number of computations proportional to t is not possible."
] |
[
"How do moving electrically charged particles cause magnetism?"
] |
[
false
] |
I understand that magnetism and electricity are 2 side of the same coin and that one causes the other. But why? How come an electric current create a force that isn't in the direction of the momentum of the electrons?
|
[
"What you are asking is an extremely deep question. This is the puzzle that eventually led to Einstein developing his theory of special relativity.",
"You are correct that magnetism and electricity are \"2 sides of the same coin.\" Specifically, they are related by Lorentz transformations from the framework of relativity. That is, magnetism arises from viewing electric fields in a different frame of reference. As a very loose analogy to understand what's meant by this, consider being in a traveling train and tossing a ball up and down. You will only see the ball moving up and down. However, if I am standing outside the train, I'll see the ball move sideways with the train as well; the change in perspective introduces some new apparent phenomenon.",
"We see explicitly that (inertial, i.e. non-accelerating) reference frames will play an important part in electromagnetism, since the formula for the total force on an object due to electromagnetism is F = qE + qV x B, with q being the charge of the object, E being the electric field, B being the magnetic field, and importantly V being the velocity of the particle (the x just indicates a vector cross product between V and B; it's not important for understanding this discussion). Consider the case of moving through constant and uniform electric and magnetic fields for simplicity. Just by changing our reference frame so that we travel along with the object, the velocity we measure goes to 0. Hence the magnetic force would apparently be 0. But the total force on an object shouldn't change between reference frames. So the conclusion is that the change of reference frames also changes the observed electric and magnetic field, so that the trajectories a particle takes are consistent between the two reference frames. In other words, electric and magnetic fields transform into each other under the effects of special relativity. (Edit: I think my example here was unclear and may not be correct; this page explains another example much better than I can ",
"http://galileo.phys.virginia.edu/classes/252/rel_el_mag.html",
")",
"By the way, as for why magnetic forces are not in the direction of a current, that stems from the cross product (v x B) that appeared in the Lorentz force law I'd mentioned earlier, which produces a resulting vector that is perpendicular to both of the vectors which are being cross-multiplied. Cross products are all over magnetic equations, and ultimately it stems from applications of Stokes' Theorem in Maxwell's Equations, which relates a line integral over a closed line to a surface integral of a cross product."
] |
[
"I read the linked article. It doesn't say anything about protons having increased mass, does it? It did say that, due to Lorentz contraction, the protons are grouped more closely in the rest frame of the electrons. (And electrons grouped more closely in the rest frame of the protons.) (By a factor of (lambda v",
" c",
" in both cases.) The moving charged particles have a higher charge per unit length (of the wire) because the moving charged particles are closer together, i.e. more charge per unit length, than the non-moving particles."
] |
[
"Thanks, I really appreciate your answer!\nFollow up question: in the link you posted, the increased charge of the protons is attributed to to their increased mass due to special relativity. Does an increase in mass always cause an increase in charge? Does that mean moving charged particles have higher charges than static ones?"
] |
[
"Can someone grow out of having ADD?"
] |
[
false
] |
Or does it just become a matter of learning to manage with it?
|
[
"Thanks! As I myself have ADD, I was curious. "
] |
[
"I'm going to disagree with NawtAGoodNinja if (s)he's implying you can't change these behaviors if you're intentional about it and argue that if he wants that answer to have any merit, he needs to have a citation. ",
"In any behavior of interest, it's important that we understand the construct on a variety of levels. For that reason, NIMH has created what's called the Research Domain Criteria. It breaks down each construct into units of analysis which are inter-related (",
"https://www.nimh.nih.gov/research-priorities/rdoc/research-domain-criteria-matrix.shtml",
"). ",
"Many individuals in fields related to psychology look at these constructs at levels that we don't have great interventions (Genes, Molecules, Cells, Circuits, Physiology), they conclude based on their findings that you cannot change anything. However, we understand more and more that these units of analysis have a two way relationship on each other (see epigenetics) instead of a one way relationship that is rather old hat (the nature/nurture argument). ",
"A behavior analysis approach is going to argue that by changing behaviors we \"learn\" which by definition has an impact on the smaller units of analysis. Secondly, most individuals not in the medical field (psychiatry) reject reification of clinical constructs. That is, ADHD isn't a thing, there's not a biological agent like a bacteria or genetic deficiency causing it. Instead it's a series of behaviors that cluster together that may or may not have corresponding biological/physiological/genetic markers. ",
"Breaking it down, ADHD seems to be defined by 4 core behaviors (Barkley RA. Behavioral inhibition, sustained attention, and executive functions: Constructing a unifying theory of ADHD. Psycholo Bull 121: 65-94). According to Barkley, these are behavioral inhibition, working memory, regulation of motivation, and motor control. Researchers for awhile now have proposed intervening on working memory in children (an intervention that looks kind of similar to playing simon says) and there's now promising research that this can produce outcomes (Klingberg, T., Fernell, E., Olesen, P. J., Johnson, M., Gustafsson, P., Dahlström, K., ... & Westerberg, H. (2005). Computerized training of working memory in children with ADHD-a randomized, controlled trial. Journal of the American Academy of Child & Adolescent Psychiatry, 44(2), 177-186.) Indeed Klingberg concluded \"This study shows that WM can be improved by training in children with ADHD. This training also improved response inhibition and reasoning and resulted in a reduction of the parent-rated inattentive symptoms of ADHD.\" ",
"A more recent article came to the same conclusion citing medication as an impacting factor as well (Holmes, J., Gathercole, S. E., Place, M., Dunning, D. L., Hilton, K. A., & Elliott, J. G. (2010). Working memory deficits can be overcome: Impacts of training and medication on working memory in children with ADHD. Applied Cognitive Psychology, 24(6), 827-836.). ",
"So like many behaviors (depression, anxiety, etc.) behaviors that are not consistent with ADHD can become the at strength repertoire. Like other changes in behavior, it takes time, effort, patience, and commitment. You will not \"grow out of it\" if you don't try to change the behaviors. "
] |
[
"It's not likely. Generally, symptoms become more manageable with age (the subject learns to reduce the symptoms of their disorder with the help of specific coping mechanisms and adequate medication), but it is ",
" rare to outgrow the disorder."
] |
[
"Can a diurnal predatory species evolve to become nocturnal if their prey is nocturnal? And vice versa? And can it shift back in the other way?"
] |
[
false
] |
Let's say there's an island with hawks who are active during the day; rabbits who are active during the day, and raccoons who are active during the night. Hawks eat rabbits and raccoons. Slowly, due to some unrelated factor like disease, the rabbit population starts to diminish, so raccoons become an increasingly important food source for the hawks. Over time, can the hawks evolve new behaviors and physical features to make them better at night hunting so they can catch more raccoons? Let's say hundreds of generations have gone by and the hawks have evolved owl-like senses and nocturnal patterns to get really good at catching raccoons in the dark. Could the raccoons then start adapting their behavior and/or physiology to become more active during the day and less likely to be eaten by these formidable night-hawks?
|
[
"The raccoons that stay out are night and have lighter colors (are visible) are more likely to be eaten by night hawks. Whereas the ones that feed during the day and perhaps blend in easier at night due to darker colors are better at surviving and over time then overwhelm the previously “normal” raccoon population."
] |
[
"It’s back when primates were small squirrel-like creatures. Many tens of millions of years ago. It’s a bit disingenuous to say it was humans. It was a distant ancestor of primates in general."
] |
[
"Evolution will always favour the individuals that are more well-adapted to the surrounding environment, whether that may be related to predation, avoiding predators, sexual selection, environmental factors etc. A hawk with slightly better eyesight at night-time will most likely catch more food and therefore has a higher chance of reproducing, in the same way that a racoon which is better camouflaged at night will have a higher chance or survival. Overtime the characteristics of these individuals will guide the evolution of, in this case both the hawks and the racoons. The characteristics would by then, have changed the hawks and racoons so much, that both would be regarded as new species. ",
"However, this progress is not something that happens overnight but instead over several thousands of years. So, if the rabbit population suddenly diminishes due to decease and the hawks cannot hunt at night they will most likely die out. ",
"It is worth mentioning that evolution is not working in a steady flow and that after mass extinctions, an establishment in completely new species is always observed “rather quickly”, filling out the previous, now new “empty habitats”."
] |
[
"How can one calculate the volume of a holey cube?"
] |
[
false
] |
Take a cube with, say, sides of a 10 cm length, and then you drill a hole with a radius of 1 cm perfectly through the centre of each face to the other side. The volume should be the volume of the cube, minus the volume of three cylinders with a radius of 1 cm and a length of 10 cm, right? But that doesn't take into account the area where the cylinders intersect. Now, I've heard something about the Steinmetz solid, but as far as I know, that only covers the area where all cylinders intersect, ignoring the corners where only two cylinders intersect. How do I calculate the volume of a "holey cube"?
|
[
"You can use the ",
"Inclusion-Exclusion Principle",
" to find the volume of the three intersecting cylinders. If the three cylinders are C",
", C",
", C",
", then the Inclusion-Exclusion Principle says that",
"where I'm abusing notation a bit to just use C",
" to also mean the volumes. The volumes of the two intersecting cylinders, called ",
"bicylinders",
", are 16r",
"/3 each. The volume of the three intersecting cylinders, called ",
"tricyliners",
", is 8(2-sqrt(2))r",
". So the volume of three intersecting cylinders of height H and radius R is "
] |
[
"Calculating≠Measuring"
] |
[
"Or better yet.. put the cube in some water and see how much it displaces."
] |
[
"Have there been any cases of extinct species making a a comeback? If so, how is this possible?"
] |
[
false
] | null |
[
"There have been cases of animals being classified as extinct and then rediscovered as to not be extinct. But it terms of animals being extinct, they have stayed that way.",
"The South Island kokako, a bird in new zealand, was classified as extinct but over recent years with claimed sightings, the bird has been reclassified as data deficient and there is a $10,000 reward for a confirmed sighting of the kokako"
] |
[
"The word you are looking for is De-extinction.",
"There is a method called Breeding back. To do so you breed animals who are close to the extinct one and breed them to look and behave like the original. But if that really is a comeback of the extinct species or just the creation of a lookalike is arguable.",
"You can find more on that here:\n",
"https://en.m.wikipedia.org/wiki/Breeding_back",
"There are also several attempts to bring back extinct creatures by cloning them from conserved DNA. The Mammoth is on that list for example as well as the Tasmanian tiger or the passenger pigeon, but as far as I know no real attempt was made so far but it should work in theory.",
"More on that here:\n",
"https://en.m.wikipedia.org/wiki/De-extinction"
] |
[
"It is possible for a species that was ",
" extinct to not really be extinct and have the population rebound for whatever reason, and ",
"it has happened before",
". But for a species actually extinct, it would not be possible without interference."
] |
[
"Can evolution happen faster? Is it a flat rate of growth for the most part? How does evolution speed up or slow down?"
] |
[
false
] |
[deleted]
|
[
"Selective breeding by farmers is evolution where farmer-selection takes the place of survival of the fittest. It is the same process as natural evolution, but it proceeds faster because we ",
" breed from the individuals that we select. You can see this in brassicas (cale, cabbage, broccoli, sprouts) and in horses, dogs, cats, chickens, turkeys and salmon."
] |
[
" There are four main evolutionary forces: mutation, genetic drift, gene flow and natural selection. Mutation is -generally- a slow process, genetic drift, gene flow and natural selection can be either slow or fast, depending on the intensity in which they occur. Considering all possible combinations in the intensity of this forces, evolution ranges from totally steady to a-few-generations-fast.",
"Hi, evolutionary ecologist here!",
"First of all, I'll link you to some other answers I've given about evolution that will be helpful to broaden your understanding in the subject. Next I'll give direct answers to your inquiries.",
"Here I explain ",
"the main evolutionary forces and the role of mutation",
".",
"Here I explain ",
"how natural selection works",
".",
"Finally, here I explain ",
"how much every evolutionary force contributes to evolution",
". ",
"Now, I'll tackle your inquiries in parts, starting with: ",
"Biological evolution is the ",
". Evolution isn't directional, there aren't \"more evolved\" states and evolution is historical, ",
" what happened in the past affects what can happen in the future. Evolution implies a change, you don't need to have a new species to say that there was evolution. If a change in the traits occurred, evolution is going on. ",
"So, to measure \"evolution speed\", we would have to measure how much are the traits changing in each generation, if there is a great change, we could say that evolution is going \"fast\" and viceverse (although, \"fast\" or \"slow\" are concepts that make no sense since evolution is within a ",
"deep-time",
" concept).",
"There are four main evolutionary forces: mutation, genetic drift, gene flow and natural selection. Each affects in a specific way the change in traits and each has a particular \"speed range\". I won't explain each one here since I already referred to previous answers with similar content somewhere else.",
"a. ",
". In this graph you can see that ",
"average mutation rate varies among organisms",
", if you consider only bacteria and eukaryotes, mutation rates are around 10",
" - 10",
" changes in the DNA sequence per genome (this is 0.000000001 - 0.0000000001 changes in DNA sequence in each genome replication event). In this other graph, you can see that, ",
"with a mutation rate ",
" = 10",
" it would take around 60 000 generation to change the frequency of a trait ",
" from 100% to 50%",
". This is, with mutation alone.",
"b. ",
" but it depends in how strong the event was. This force relies on chance, and it acts by changing the proportion of organisms that will have offspring, it can happen by ",
"founder effect",
" or ",
"population bottleneck",
". Because it relies on chance, ",
"simulations of genetic drift look like this",
", but ultimately in a few generations an allele/trait will be fixed (100% present) or lost (0%) and this is a great change.",
"c. ",
" because it is related with the exchange of traits. At final stances, gene flow completely homogenizes the populations. If in an isolated population you let the flow of traits from another population, the isolated will change greatly in the first stages, but this will decrease over time, because both population will start to be very similar.",
"d. ",
". If the pressure is lax, natural selection will act slowly; in the other hand, if the pressure is high, natural selection will impact strongly in the population, changing it in a few generations.",
"The evolution rate changes depending on the intensity of each evolutionary force. You can have an average mutation rate with no genetic drift, no gene flow and low selective pressure or any other combination, sometimes evolution could not be happening at all! Evolution intensity varies wildly in time.",
"As an example of how fast can evolution be, think about domesticated crops or antibiotic-resistant bacteria, both are cases of ",
" (sometimes referred as \"artificial selection\" to distinguish when the human were involved in the selection process. Here I talk about the ",
"domestication process of corn",
" and here I talk about the ",
"relation between penicillin and antibiotic tolerance in bacteria",
". ",
"If you have any further inquiries or doubts, let me know!"
] |
[
"There is a thing called 'punctuated equilibrium' that posits that evolution happens in phases of slower and faster rates. ",
"Changes in environment will cause animals to adapt and evolve quickly, with those best adapted surviving and passing on their traits and those less able to survive dying out. ",
"An extinction of one animal will often open a niche in the ecosystem and allow another species to evolve into that niche and take it's place.",
"Small isolated populations of animals will often evolve faster than a large population that is able to interact and breed with other populations of the same species. Large populations tend to equalize the gene pool to a certain degree, causing variants to be less able to take hold, while a small or isolated population has less chance to 'cancel out' these variations. ",
"All that considered, evolution is always very slow, taking hundreds if not thousands of generations to bring about any significant changes. "
] |
[
"Are new viruses spontaneously mutated? In one million years will humans be immune to all viruses on Earth?"
] |
[
false
] |
[deleted]
|
[
"Long story short, yes, they are. Since viruses reproduce so quickly and stuff is always trying to kill them, they evolve on a much more rapid scale. Otherwise we would have been immune a long time ago. It's also why it's so hard to find suitable cures for some viruses, because they can become resistant so quickly. "
] |
[
"But isn't there a limited number of mutation possibilities",
"Strictly yes, the number of possible mutations in calculably finite. In practical terms no.",
"If a virus had only 1 protein (unlikely) and it was 100 amino acids long then the number of possible sequences that protein could adopt is of the order of 10",
" variants. For comparison we estimate that there are only 10",
" stars in the universe.",
"The sequence-space even a single small protein can explore is vast.",
"Of course not all those possible sequences will be useful nor even do the same job as the original protein but even if we throw away ",
" >99.999999% of them our protein can likely still explore somewhere around 10",
" \"useful\" sequences. ",
"But our thought experiment is pretty unrealistic most viruses will have at least 10 and as many as 100 proteins. There's a lot of space for practically limitless adaptation",
"(for the sake of brevity I'm glossing over the relationship between sequence-structure and the host immune system, lots of minor changes in a sequence can still be detected by a primed host immune system. So not all virus protein variants would be novel to the point of being undetectable)",
"Edit: Corrected the exponential error as per the comments below"
] |
[
"Small mathematical nitpick: If you took 10",
" combinations and threw away 90%, you would be left with 10",
" combinations, not 10"
] |
[
"What percentage of stars in our night sky are actually galaxies vs actual stars?"
] |
[
false
] | null |
[
"If you mean visible to your eye without a telescope, there is only ONE galaxy you can see - the Andromeda galaxy. It's not very bright, but if you are in a fairly dark sky you can see it as what appears to be a faint fuzzy cotton-ball, which is the bulge of stars near the center of the galaxy. A sufficiently dark sky and large enough telescope will let you see the spiral structure around that fuzzy cotton-ball, which is ",
"really something to see",
", but it's not something the average person is going to get through an eyepiece in your back-yard. (That photo is also not what you can see with an eye-piece, your eye will pick it up in black and white and without as much depth.)"
] |
[
"Good point! Showing my own bias towards what I am used to being accessible in a backyard, there. There's no way to confuse those with a star, though."
] |
[
"Triangulum (M33) is also visible with a naked eye under exceptionally dark skies."
] |
[
"If time slows down with heavier gravity than earth, does it speed up with less gravity then earth?"
] |
[
false
] |
Comparing to earth time
|
[
"Comparing to earth time ",
"This is the important point to keep in mind. Anyway, the answer to your question is ",
" As an example, GPS satellites in orbit around the Earth are further outside our Earth's gravitational well and thus experience less gravitational time dilation—by about 45 microseconds difference per Earth day. Conversely because the satellites are moving so quickly to be in orbit, their relative motion time dilation means they'll be slower by about 7 microseconds per Earth day. These two effects fight eachother and GPS satellites must content themselves with being ~38 microseconds per day faster per Earth day. This manifests in the broadcast frequency they send out.\n",
"http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit5/gps.html",
"GPS has been operational since 1995, so if we didn't correct for relativity, they'd be off by about 1/3 of a second by now."
] |
[
"The \"faster\" time you gain by leaving the Earth's gravity only goes so far and plateaus off as you head further away to about 60 microseconds per Earth day.",
"You have to think of about this in reverse, out in empty space, time is moving normal and uniform (relative motion aside), it is us Earthlings who are slow compared to everyone else. If you want crazy gravitational time dilation like 65 \"space years\" to one Earth year, then you're going to have to make Earth very very massive or very very dense.",
"This it to contrast dilation from relative motion which doesn't have limits and depends on how fast you're moving compared to others, exploiting this physics, you could easily make 100,000 years on Earth seem like 1 year to you via the twin paradox."
] |
[
"If I understand the concepts of relativity correctly the speed up or slow down of time is only seen by the outside observer.",
"For the person traveling at relativistic velocities the clock is ticking over at the same rate as it always has. This means that if that person is 30 years old at departure and travels for 30 years they are going to be 60 years old from their own perspective.",
"For the outside observer it would be something less than 60 depending on travel velocity as a percentage of the speed of light."
] |
[
"Is repetition the mother of learning? And if so why?"
] |
[
false
] |
[deleted]
|
[
"It depends on the type of repetition. Yes, repeating and spacing out study boosts how much material we remember. This was discovered decades ago and there are still many ",
"studies",
" investigating why this happens. So if studying for a test, your mom was right when she said it’s better to break it up over several days rather than force a crash study session right before a test. ",
"But just rereading a textbook isn’t the best strategy of repetition. The important part of the learning process is the “retrieval” component—the process of pulling a thought out of memory. In the context of studying, this means quizzing yourself. So it turns out that testing is not just an assessment of learning, but a ",
" for learning",
" as well. People who spend time self-testing on material are more likely to remember the material than people who just restudy it. It requires more work, but it seems like the more mental sweat it takes to dig something out of memory, the more securely it will be settled into memory for the future. ",
"On a similar note, the repetition works better if you repeat your study in different environments. There’s an old ",
"study",
" that showed this (and this has been repeated in many different ways), where researchers found that students who studied vocabulary lists in two different rooms (one windowless and cluttered, the other modern with a courtyard view), did far better on a subsequent test than students who studied twice but in the same room. The idea for why this happens is the brain makes unconscious associations between the material being studied and the environment in which you’re studying. By forcing your brain to make multiple associations with the same material, the information becomes enriched, which slows down forgetting. "
] |
[
"Would spinning in my spinny chair count as a different study environment? So if I recited a list of elements from the Period Table staring at a computer screen and then recited the same list as I spun around in my chair, would my brain register the blurred room as a new environment? ",
"I instinctually did this in high school and wonder if my brain was being very very smart because it knew there was no way it was gonna get me to go to a room that was not a cluttered, windowless, hot-pocket's riddled depression cave."
] |
[
"Maybe! Context definitely is a broader thing than just the room you're in. There's evidence that context can even be instantiated through your ",
"mood",
" or the ",
"music",
" you're listening to. Even your physiological state can be a context. ",
"One of the weirder studies",
" showed that people who were intoxicated with alcohol during both study and test performed better on memory tests than people who were drunk for only one of the two sessions (although obviously people who were sober for both study and test sessions performed the best). ",
"The idea is if you test yourself in the same context that you were in when you were studying the material, that context acts like a cue for memory. By varying the context in which you study, the memory becomes deeper. So by studying both in the still chair and in the spinning chair--I'd guess--you got extra mental cues for the material."
] |
[
"Can you tell mars is red just by watching the sky?"
] |
[
false
] |
I find it amazing that old scriptures and temples in India describe mars as the "red planet". How would they have done that without telescopes and stuff?
|
[
"The word planet, derived from Greek, means \"wandering star\". A very appropriate term for early astronomers to use since those \"stars\" seems to move about relative to all the other \"fixed\" stars.",
"Certainly other languages used different words, but they would be translated from something like \"wandering star\" to planet."
] |
[
"Yes, on a dark night you can see it as a red dot, what suprises me however is that they call it a planet. How old are these scriptures?"
] |
[
"Yes, it is quite obviously reddish even to the naked eye."
] |
[
"Is it possible to build up enough static electricity to actually damage yourself?"
] |
[
false
] | null |
[
"Static electricity is a difference in electric potential energy, it is a relative difference of charge carriers. What hurts you is the electric discharge that can result from static electricity. The electric discharge occurs by finding or creating a path to conduct charge carriers to balance out the difference in electric potential. When i say it creates the path, the electric potential has so much energy that it can convert an ordinarily insulating material into a conductor, temporarily. This is what happens when lightning strikes, it forces the air to conduct electricity, and i think it goes without saying that lightning can hurt us."
] |
[
"Capacitance is the ability for something to store charge. It's described in units if ",
". In engineering, choosing the right capacitance is critical for a very wide range of applications, from energy storage to filtering. It effectively describes the number if electrons (charge is measured in ",
") that are present for a given voltage. Crudely, you can think of capacitors as a reservoir of potential energy, like filling a bucket water and hoisting it up. The capacitance describes how much charge the \"bucket\" holds for a given voltage.",
"Over-volting a cap (being too generous with voltage from a supply) can damage the dielectric that stores the electrons. Effectively, you push the storage ability to a limit where the chemical breaks down and there's usually a terrific surge of current. Humans are only able to hold a few pF. You can try to probe it crudely by touching the proves of an LC meter.",
"So what does this mean? It means that when your body has been charged up by the potential energy of tens of thousands of volts (by wearing wool socks and walking around, or by driving your car, etc.) The discharge can occur if you handle a good conductor, especially if it has a path to ground.",
"You can be personally over-volted, but your fate is similar to burning a capacitor. :)"
] |
[
"I don't think so, not in the conventional sense, mostly because of where the charge is stored and the path it would take off you. Even if you rubbed your feet on the carpet then touched something a million volts the other way... I doubt the path and amps would deal real damage. I suppose there is always a threshold though. ",
"I don't consider vdg machines and blasting people with lightning the same as generating a static charge on a person and releasing it in the spirit of the question."
] |
[
"Who owns the moon?"
] |
[
false
] |
If I wanted to make a spaceboat, go to the spaceisland and build a spacehouse, who would i have to negotiate with? Are there landowners? Could I start my own town?
|
[
"No nation can own it according to this treaty.",
"http://en.wikipedia.org/wiki/Outer_Space_Treaty"
] |
[
"The barriers to settling the moon aren't political, they're economical and technical. If any nation ever gets close to setting up a colony or gathering resources from the moon, it will probably spark a new legal discussion. In practice it might be similar to how Antarctica is currently administered."
] |
[
"Well, I'm talking about the present day. Presumably if there's a time when we have the need and the technology to go to the moon, we'll define the laws about colonization then, but we can only speculate now."
] |
[
"Do we know of any viruses which insert DNA fragments into the human genome?"
] |
[
false
] |
[deleted]
|
[
"http://en.wikipedia.org/wiki/Lentivirus",
"Lentiviruses transfer RNA into animals cells. ",
"Agrobacterium can transmit DNA between plant cells and is used very heavily in the production of genetically modified crops/plants, but has also been shown to infect and transmit its T-DNA into the human genome under certain circumstances. ",
"http://www.pnas.org/content/98/4/1871.long"
] |
[
"Many viruses can insert themselves into the human genome. The HIV virus is one of them. Once inserted it becomes inactive until some process activates it, so such endogenous viruses cannot be cured by conventional means."
] |
[
"To elaborate on that, as far as I know there is no DNA containing virus that does this. HIV is retrovirus that contains RNA, which is a little bit different and can't be integrated into the genome.",
"So what the virus does about this, it brings along some of its own pre-made proteins that help to convert RNA into DNA and then with the help of other proteins this newly made DNA strand gets integrated randomly into the host cell.",
"So, to answer OPs second question, as far as I know the integration is random, although it probably does depend on certain sequences to start off the process. These sequences are likely to be found all over the genome though and there is no preference for any particular region of the genome."
] |
[
"Do subatomic particles have an exact mass or ranges of mass?"
] |
[
false
] |
Nothing is exactly 4 kg in classical physics, there's always a rounding error. Is that true at the subatomic level as well? If so, what is responsible for the variance in masses between different particles of the same category?
|
[
"Stable particles have an exact mass, unstable particles don't.",
"One form of the uncertainty principle says that the uncertainty in time and in energy (or mass) multiplied together must be above a certain amount. If you are measuring the mass of a particle, you want to maximise the uncertainty in time, so that you can minimize the uncertainty in the particle's mass.",
"If the particle is stable, you can make the uncertainty in time as large as you like, and so can measure the particle's mass to arbitrary accuracy. But if the particle decays, that limits the uncertainty in time of the measurement, which introduces an uncertainty in the mass that you measure because of the uncertainty principle."
] |
[
"Excellent answer. Also a note for the OP that these uncertainties you are talking about are ",
" to the quantum particle itself, and do not result from measurement technology (as is the case in classical physics of measuring the exact mass of a 4 kg object). No matter how exact your measurement technology becomes, you can never reduce the quantum uncertainty dictated by the Heisenberg Uncertainty Principle. "
] |
[
"Relativistic mass isn't very useful in any context. Rest mass does not change."
] |
[
"Are all babies female before the third month of pregnancy?"
] |
[
false
] |
I don't recall where I saw this, but, is that true? For what I can remember, the article said that we are all female until the third month of pregnancy, then, the gender is defined and you become a girl or a boy.
|
[
"This is one of those pseudo-intellectual misconceptions that can get confusing if not explained properly.",
"A female body is the default early fetal ",
" regardless of what the explicit ",
" is. The distinction is important.",
"Males (XY) have a gene on the Y-chromosome (the SRY gene) which, when activated, results in male sexual differentiation and a male body phenotype. If the SRY gene fails to activate for whatever reason (or the fetus has androgen insensitivity) then the female body phenotype will persist despite the XY genotype and you can get a male sex with a phenotypically female appearance (but the person will probably have undescended testes, etc). So yes, we all \"start\" female in a sense but only so much as the Y chromosome has not been activated yet to make a difference.",
"tl;dr In the absence of a Y chromosome every fetus would develop as a female. It is the activation of the Y chromosome during gestation that results in the male body appearance. Sex is determined at fertilization (XY vs XX)"
] |
[
"At around 10 weeks ",
"virilization",
" occurs which is the start of sexual differentiation.",
"That said when the egg is fertilized it has either an XY set (male) or XX set (female) so at that moment the baby's gender is determined."
] |
[
"Are hermaphrodites the result of SRY gene failing to activate?"
] |
[
"How soon could we overtake the Voyager I probe with modern technologies?"
] |
[
false
] |
If we were to build a modern probe and launch it in the direction of the Voyager I probe, currently the farthest man made object from earth, how much time would it take to over take it and become the new farthest object. Is this even possible considering the current distance and limitations to our technologies? If so what kind of time scale would we be looking at? If it can not be done what is an estimate before it would be possible? Just some random thoughts i had today....
|
[
"I checked, and your numbers are correct, and Im literally in 'holy shit' mode.",
"Once up to speed, 200,000mph for 55,000 hours (or 291 days) would go the 11B miles.",
"So we can make a thing that can catch up to a probe launched some 35 years ago in under 2 years. Mind freaking blown, off to learn about ion engines now."
] |
[
"I checked, and your numbers are correct, and Im literally in 'holy shit' mode.",
"Once up to speed, 200,000mph for 55,000 hours (or 291 days) would go the 11B miles.",
"So we can make a thing that can catch up to a probe launched some 35 years ago in under 2 years. Mind freaking blown, off to learn about ion engines now."
] |
[
"Acceleration in space is easier because there are fewer opposing forces to overcome such as a planetary gravity or drag."
] |
[
"How do companies know how many Calories are in food?"
] |
[
false
] |
It's probably a really simple question, but how do fast food companies know how many calories are in each thing they serve?
|
[
"Essentially, they burn it.",
"Food calories are a measure of the chemical energy available in the food. Basically, food gives us energy because of the energy in the chemical bonds in the sugars, starches, et cetera, that are present in the food. Subjecting these food substances to exothermic reactions breaks up the molecules into simpler, lower-energy forms, and gives off heat in the process. This heat can be measured.",
"So, more or less, they put a sample of the food into a special chamber. The chamber is then heated with a heating element that can be carefully monitored. Inside the chamber, the food burns, giving off heat. Then using accurate temperature measurements and some math, you can work out how much hotter the chamber actually got than it would have if there hadn't been a sample in it at all. That allows you to calculate the total energy output of the sample, and thus, how much energy was in it to begin with.",
"Source: Read it in a Science News article many, many years ago."
] |
[
"A quick addition to that is that practically, this method is not done for all foods. They simply know the amount of calories present in a gram of sugars, proteins, fats, etc., and calculate the total calories based off the amount of components present. It's always an average calculation, but the numbers are pretty accurate for most foods."
] |
[
"I do want to stress that the answers given so far are right, but ultimately do not answer your question due to the relevance of today. ",
"If you were to do a quick search, you often get the bomb calorie meter used as an explanation so it's easy that it's passed off as the answer.",
"The problem is, and this is what no body has mentioned.",
"We don't use that anymore, and the bomb calorie meter was slightly flawed, and an easier method was devised.",
"To quickly state why the Bomb Calorie Meter was slightly flawed I am not going to go into a full explanations on the workings, p2p_editor and DrIlilis gave great examples of that, but the method of measuring the energy content measures the total energy content of the food.",
"The thing is however, there is quite a bit in foods that we simply can't break down and our bodies can't get the energy from, but yes heating it can still release the energy in a bomb calorie meter. Things like cellulose, sure a Cow can break it down, a human can not. Fibre is another example.",
"So what system is used today and how do we know how many useful calories are in food? ",
"We use the Atwater system. The Atwater system is pretty simple actually. I'm going to explain the basics.",
"Essentially food energy or calories are measured in kcal/g. The only problem is different food has different calories so it's not as simple as measuring the weight in grams and times that by kcal per gram... Or is it? Well it almost is!",
"See the total weight of the food means very little, what means a lot is the breakdown of the weight. If you know how much protein, carbs and fat a food contains, you can demonstrate it's energy content.",
"Protein 4.5 kcal/g",
"Fat 9 kcal/g",
"Carbs 4.5 kcal/g",
"So the equation can come down to (Carbs * 4.5) + (Fat * 9) + (Protein * 4.5) = total carbs.",
"Now there are other things as well such as fiber, polyols and organic acids which contribute to food energy as well.",
"http://en.wikipedia.org/wiki/Food_Energy",
"The system works better then the bomb caloriemeter because it ensures you are not getting other sources. If for example I mixed wood pulp into my product and it was safe and it made it taste delicious and people loved them and didn't care, why should my product have to account for the calories from cellulose in the food? ",
"I just wanted to correct that a little because people give the answer bomb calorie meter when that's not what is used today."
] |
[
"How do mRNA vaccines avoid being chopped up by the human body's cell enzymes?"
] |
[
false
] |
I read this passage in a NYT article: The mRNA molecules our cells make can only survive a matter of minutes. so that the cells can make extra virus proteins and prompt a stronger immune response. But the mRNA can only last for a few days at most before they are destroyed. How does this work? What is it about particular strands of mRNA that makes them accessible for protein production but also prevents them from being destroyed for a while?
|
[
"Naked RNA would be rapidly degraded by exonucleases before it entered the cell. To prevent this, the mRNA is enclosed in lipid nanoparticles that protect it from extracellular RNAses and also helps it transfect (get into) the cells it needs to enter. mRNA is supposed to come from the nucleus - any mRNA that comes from outside the cell is a hallmark of a virus and is going to trigger some anti-viral responses. The lipid nanoparticles also help protect the RNA from some of the receptors (like TLR 7 and 8) that would otherwise trigger antiviral responses that could shut down translation and speed up degradation of the mRNA.",
"Once it is inside the cell, the mRNA will be translated into spike protein by ribosomes and the proteins will then be processed and presented on MHC-I and II molecules so that T-cells can be activated (just as happens with natural viral proteins).",
"The mRNA will eventually be degraded by endonucleases. This is ",
": it limits potential adverse effects, you don't want the mRNA hanging around and being translated forever! But you also want to be sure that it isn't degraded ",
" rapidly that barely any spike protein gets made and the adaptive immune response isn't sufficiently activated.",
"There are a number of methods that can be used to increase the stability and half-life of the mRNA by making it harder for certain RNA-degradation processes to work and/or increasing the efficiency of translation prior to degradation. For example, you can elongate the poly-A tail, or modify the 5' cap, or make nucleotide modifications.",
"The Pfizer vaccine makes a few nucleotide modifications (with single incorporations of 1-CH3-pseudouridine) which helps prevent innate immune responses from destroying the mRNA before it can be translated, and also increases its translation. It's believed that the increased translation is because it decreases the hydrolysis of the mRNA by phosphodiesterases. ",
"Both vaccines also use similar consecutive proline substitutions to force the relevant spike protein chains into more stable pre-fusion conformations. By stabilizing the protein product in this way, mRNA can be active for a shorter time because the protein product is more likely to stimulate the correct immune responses."
] |
[
"The difference is the ability to reproduce and spread to other cells. When you say a virus will \"cause the cell to produce something it isn't meant to\", it's not just some arbitrary thing it's producing. By definition, a virus has to get the cell to make more copies of the virus. The vaccines can't do that. They only contain the RNA code necessary to make the spike protein (one part of the virus that is involved in helping it get into new cells). They don't contain code for copying the RNA or for making a new lipid nanoparticle to shuttle it to a new cell.",
"I suppose you could try to describe the vaccines as a virus missing some key components, but those components (the ability to replicate its genetic material and spread to new cells) are defining characteristics of a virus. Without that, it's just a piece of DNA or RNA that would pose no threat to the body beyond the initial infected cell."
] |
[
"Man, if you take a step back and look at this, it's amazing how humans are able to understand our body at the cellular level to basically hack it to develop this immunity to a specific virus. Science rocks!",
"At the same time, its also amazing how some humans would rather believe literally anything else but science...."
] |
[
"Is the irregular shape of the periodic table caused by imperfect classification or just because that's how the universe is?"
] |
[
false
] |
It just seems to me that the table should be a perfected organized shape instead of having hydrogen and helium alone at the top and then the Lanthanoids and Actinoids being shown oddly at the bottom
|
[
"This is more a problem of our way of showing it than nature itself. The sort of odd shape of the table is mostly due to the different electron orbital types that can appear around and atom and what that means for reactivity and such.",
"Also, it is important to note the \"The Periodic Table\" isn't a physical law, just one picture that we can use to organize what is going on. There are quite a few alternate periodic table ideas out there, but the one most people think of has been chosen as a pretty good baseline and history has now probably cemented it as our baseline forever (",
"here are a couple alternates",
" or just search google images for a bunch more).",
"For the \"main\" periodic table, if you break the table into chunks you can see the different orbitals for electrons to fall into. The first two columns (push He next to H) represent the s orbital. The transition metals represent the d orbitals. The nonmetals (13-18) represent the p orbitals. The Lanthanoids and Actinoids represent the f orbitals. The fact that certain orbitals can only hold a certain number of electrons and that certain orbitals don't appear until you get far enough along in the proton/neutron/electron count then gives you this weird shape with different blocks. Since we have chosen to lay out the elements in atomic number order we are forced to leave gaps in the higher rows to be filled further down when those orbitals appear.",
"IMO, the thing might be a little easier to figure out if you moved He next to H, put the Lanthanoids/Actinoids in where they belong, and then put empty boxes where you would find the orbitals that don't exist. The table would be massively wide and have tons of empty space at the top, but it would make more sense when learning things."
] |
[
"Part of the reason the periodic table is laid out the way it is, is expediency. Strictly speaking if you were to lay out the lower parts of the table following the rules of the upper part of the table, it'd look like this:",
"http://www.chemistryland.com/CHM130W/03-BuildingBlocks/Chaos/PeriodicInnerTrans.jpg",
"That's not particularly helpful, is it? The lightweight elements are even further apart! Plus remember the original periodic table was laid out at a time when we didn't know that many of the heavier elements even existed. Hypothetically, if there were elements that were even heavier than the actinides (there aren't. The nuclei are too unstable) they'd insert ANOTHER gap into the table, pushing H and He, and Be & B, even ",
" apart!",
"The periodic table as it exists gives us a pretty straightforward way to understand the outermost electron shells (valence electrons) that you're dealing with for each of the elements, and chemistry is the study of the behavior of those elements, (among other things). H, Li, Na, and K all have singleton valence electrons, and are all very very reactive as a consequence, because nature abhors a naked electron. He, and Ne, have filled up valence shells with 2 and 8 electrons residing in them, respectively. Ar also has 8 electrons in it's valence shell, but adding additional electrons to the 4s orbital turns out to be less energetic than adding to the 3d orbital, which is why you get K and Ca before the table widens with the 10 elements of the transition metals, corresponding to the 10 electrons that can fill up the 3d orbital.",
"Point is it does make sense, if you focus on the valence electrons. Ultimately, the periodic table is a simple visual reference, created at at time when when many of the elements in it were only theoretical, so it's not surprising it's assembled like a camel, with all the humps."
] |
[
"I've read that the elements on the left edge are unstable and the ones on the right edge are stable and as you go from left to right the elements become progressively more stable. Is that wrong?"
] |
[
"What's the easiest way to prove to a layperson that the speed of light is an upper limit for all speeds?"
] |
[
false
] |
My dad and I got into an argument today about the existence of aliens, and I said that while I think they probably do exist in the universe, I didn't think they'd ever visited here because of how long they'd have to travel. My dad thinks that we just haven't "learned" how to travel faster than light. I have a background in science, and my dad doesn't. While I can try to explain to him that we've done experiments and that the speed of light as an upper limit has been thoroughly established, he's never been exposed to any of that so he just rejects it, saying things like "Well when I was a boy cell phones were a dream, so who knows what we will dream up next?" and that we find errors in scientific findings all the time. Is there any easy-to-explain result that you can use to demonstrate that the speed of light is an upper limit? What I really am looking for I guess is some experimental evidence that relies on the speed of light being an upper limit and comes from an experiment a layperson could understand, or a piece of technology that wouldn't work if the speed of light weren't a limit. Something that demonstrates a real-life consequence of the speed of light, and that he could therefore relate to.
|
[
"Tell him that he's right in one way (people love to hear that, it makes them way more open to hearing what you have to say), there are theoretical mathematical workarounds to bypass the speed of light, but they're cheats. You simply cannot travel accelerate to the speed of light, because it takes an infinite amount of energy.",
"It's easy to go from .0c to .00001c. It's harder to go from .00001c to .0001c, and harder still to get to .001c. Once you get into .8c and .9c the amounts of energy go up exponentially. At some point, because exponents get so big, you need all of the energy in the universe to go even a little faster... and you're still at .99999999999(repeating for a long time, but still not forever...)c.",
"Tell him about wormholes, and then explain the complications of those to him later. But don't just say \"You're wrong. Here's MATH,\" because people aren't receptive to that.",
"Give a little honey before you make them eat their veggies, then a little ice cream at the end. "
] |
[
".99999999999(repeating)c",
"That would be c (0.999(repeating) = 1), and you can't reach that speed."
] |
[
"Good catch, I didn't so much meaning repeating forever as for a long time. ",
"1/3,2/3,3/3, blahblahblah. "
] |
[
"Is there an escape velocity for leaving the solar system?"
] |
[
false
] |
Would an object need to travel faster than a particular velocity in order to leave the suns orbit? Or do I have the concept of escape velocity completely wrong?
|
[
"Yes, there is. Escape velocity depends on how far you are from the primary - generally the value given is for the surface of the primary. If you are at the distance of the Earth from the sun (1 AU), then you need to recompute this. It's really easy: escape velocity is the velocity that makes the kinetic energy equal to (minus) the potential energy",
"1/2 m v",
" = G M m / r",
"so that KE and PE cancel, and you can reach infinity with no KE to spare. Any less, and you wouldn't be able to leave. Manipulating the above gives",
"v",
" = 2 GM / r",
"the GM for the sun is better known than the mass M, so let's plug that in, along with r = 1 AU. We get",
"v ~ 42 km/s",
"that's a bit scary if you think that Earth's orbital velocity is around 30 km/s, a bit more and we would fly away... why is it so?",
"The reason is the virial theorem. It says, that under some conditions, gravitational systems satisfy:",
"KE = 1/2 |PE|",
"(kinetic energy is half the potential energy in modulus). Then if you do the calculation that means that orbital velocity is 1/sqrt(2) escape velocity. Sure enough:",
"30 * sqrt(2) ~ 42"
] |
[
"Not exactly: if a spacecraft is slower than 42 km/s AND is no farther from the sun than 1 AU, then it is trapped. The distance matters. Basically the condition is whether the total energy (kinetic plus potential) is positive or negative. Negative energy means you're bound (your orbit is an ellipse), positive means you're unbound (it's an arc of hyperbola).",
"Also, it does not matter where you're headed! The direction doesn't matter. If you are at 1 AU from the sun, and moving at 50 km/s in ",
" direction, you'll leave the solar system",
"EDIT: please stop commenting \"unless you go directly towards the sun\""
] |
[
"Relevant side note: It is even true that at your current position you need to travel faster than a critical speed in order to escape from the Andromeda Galaxy (a faint fuzzy barely visible in the night sky). You are unlikely to guess this escape velocity correctly: ",
"http://www.science20.com/hammock_physicist/you_andromeda_and_largest_structure_universe-100856",
" "
] |
[
"Planks constant states that the position uncertainty of an electron times the momentum uncertainty must be greater than or equal to planks constant divided by two. Why is this? What would happen otherwise, or what is preventing it to happen? Or, how do we know this?"
] |
[
false
] | null |
[
"You mean the uncertainty principle. It's because position and momentum are incompatible observables in quantum mechanics. The Hermitian operators which represent them don't commute, so they cannot be simultaneously diagonalized. Eigenvectors of one are not eigenvectors of the other.",
"From the postulates of QM, it's fairly straightforward to prove that any pair of non-commuting observables obeys a similar minimum uncertainty relation.",
"What would happen otherwise would be like classical mechanics. The position and momentum of a classical particle can be known simultaneously to arbitrary precision."
] |
[
"Planck's constant is a measurement. There is no way to derive it. The measurements are not done via position and momentum of particles, however, they are done via the energy of photons and similar quantities.",
"Alternatively, you can fix this constant to a specific value to define what a kilogram is, something that will probably happen in the next years."
] |
[
"I do mean the uncertainty principle, thanks! I've been reading about it. But I'm just a layman, so I probably didn't express it well. ",
"You say that \"position and momentum are incompatible in QM\". And I get that. But I don't understand how that relates to H in the equation. ",
"I guess my next question is; how do we know that planks constant is \n6.62607004 × 10-34 m2 kg / s is the number? "
] |
[
"Is it possible/practical to harness potential energy given by gravity?"
] |
[
false
] |
[deleted]
|
[
"There are schemes in place that make use of GPE for storage - many smaller hydroschemes consist of two linked storage reservoirs, the upper reservoir can be refilled by pumping the water in the lower reservoir back up.",
"The market price of electricity fluctuates greatly over 24 hrs, typically being cheapest overnight when demand is lowest, so pumping when it's cheap and generating at peak demand can be quite profitable. Any natural flow into the upper reservoir is just a freebie.",
"Aside from the financial gain for the operator, it also provides a very rapid response to system frequency droops (caused by over-demand)."
] |
[
"To clarify this, the only way to practically use gravitational potential energy is if you did not have to expend any/much energy to give your object that potential energy. Hydroelectricity is a great example of this because we, as humans, do not put any effort into 'moving' the water upstream; we simply take advantage of it as it flows downstream again."
] |
[
"To clarify this, the only way to practically use gravitational potential energy is if you did not have to expend any/much energy to give your object that potential energy. Hydroelectricity is a great example of this because we, as humans, do not put any effort into 'moving' the water upstream; we simply take advantage of it as it flows downstream again."
] |
[
"How much radiation does the earth release when it's at equilibrium temperature, relative to the amount of radiation that the earth absorbs?"
] |
[
false
] |
I'm pretty bad at science and know very little about climate change - but I've been trying, slowly, to learn more about the topic. A few people on Reddit have been telling me about how the earth's equilibrium temperature changes whenever the amount of greenhouse gases in the earth's atmosphere changes. On a very basic level, I understand that the equilibrium temperature of the earth is whatever the earth's temperature is when the amount of radiation emitted by the earth into outer space is equal the amount of radiation absorbed by the earth. I also understand that some of the radiation released by the earth doesn't make it to space (at least, not right away), because it gets trapped in the atmosphere by greenhouse gases. So that would seem to suggest that at any moment, the amount of radiation "released" by the earth's molecules is greater than the amount of radiation "emitted" by the earth into space. And if the earth is at equilibrium temperature, with the amount of radiation emitted equal to the amount of radiation absorbed, then...that would seem to suggest that the earth releases more radiation than it absorbs (because of the transitive property; if radiation emitted is equal to radiation absorbed, and if radiation emitted is less than the total amount of radiation released, then radiation absorbed would also have to be less than the total amount of radiation released). Someone told me though, that the amount of radiation released by an object will always be equal to however much radiation had been absorbed by the object. I only have a very rudimentary understanding of the processes involved - and clearly, I must be thinking about this the wrong way, since the math doesn't seem to work out. Could someone try to clarify this for me? Thanks! :)
|
[
"Equilibrium temperature is the temperature at which Earth re-emits the same amount of energy as it absorbs. However the equilibrium temperature is not fixed. It depends on a lot of different factors, like for example the reflectivity (albedo) and the emissivity. \nGreenhouse gases indeed increase the equilibrium temperature by absorbing thermal radiation from the surface instead of letting it pass through the atmosphere into space. Earth then becomes warmer and the energy carried by the thermal radiation increases until the re-emitted radiation equals the absorbed solar radiation again. At this point Earth has reached its new equilibrium temperature. The energt emitted in the form of thermal radiation by Earth depends on the temperature to the 4th power, so even small changes in the temperature can significantly change the amount of energy emitted by Earth.",
"one thing to note is, that Earths equilibrium temperature constantly changes. The amount of ice, vegetation and atmospheric composition etc. etc. are all variable and all affect the equilibrium temperature. "
] |
[
"Equilibrium temperature is the temperature at which Earth re-emits the same amount of energy as it absorbs. However the equilibrium temperature is not fixed. It depends on a lot of different factors, like for example the reflectivity (albedo) and the emissivity. \nGreenhouse gases indeed increase the equilibrium temperature by absorbing thermal radiation from the surface instead of letting it pass.",
"Just to add to this, greenhouse gasses reduce the emissivity of the earth. That is, the amount of energy given off at any given temperature. This means it needs to increase in temperature before the total thermal energy emitted again equals the energy absorbed from the sun. "
] |
[
"Strictly speaking the amount emitted would be slightly greater than the amount absorbed at equilibrium, due to internal heating. However this is a very small effect."
] |
[
"are there any large systems of planets that orbit a bigger planet rather than a star?"
] |
[
false
] |
I suppose that would just be a rouge planet with a lot of moons but does it happen often? could you find planets with the size and quantity as the ones in our solar system orbiting one the size of jupiter? or would they all just drift away or crash into eachother or something? (sorry if this is a dumb question)
|
[
"We have detected some planets around brown dwarfs, which are about 13-75 times the mass of Jupiter, and don't count as stars because they aren't massive enough to produce fusion. This is at the very lower limit of where we can detect planets though, and we've only found a few of these.",
"For rogue planets of Jupiter mass or below, these are extremely hard to detect at all, let alone whether they have any satellites. There are a number of candidates that ",
" rogue planets, but very few have been confirmed."
] |
[
"Is there a reason you would exclude the Jovian system as an example of this? 79 moons orbiting a planet the size of Jupiter would qualify as a large system. Ganymede is bigger than Mercury so would qualify as a planet if it orbited the sun rather than Jupiter. ",
"If you are only interested in exoplanets with no star, well that would be hard to find. Most exoplanets are detected by perturbations in the observation of a sun. Minus the sun they would be darned hard to detect."
] |
[
"That's not the reason pluto was declassified as a planet. Pluto is certainly large enough to be rounded by its gravity. Pluto fails the third requirement since it has not cleared the neighborhood of its orbit.",
"The reason Ganymede is not considered a planet is mainly that planets must by definition orbit a star or stellar remnant."
] |
[
"How to calculate force on a cube with negative pressure?"
] |
[
false
] | null |
[
"Would I be correct in thinking that taking sea level pressure at 101325 Pa and then taking away my internal pressure of 0.00378 Pa... would that leave me with the N/m2 being exerted on my cube from the outside?",
"Yes, assuming the pressure is constant on the outside of the box. Now just integrate this over the surface area of the box."
] |
[
"You'd look at the ",
"Knudsen number",
" to decide whether or not fluid mechanics is valid for your situation."
] |
[
"You'd look at the ",
"Knudsen number",
" to decide whether or not fluid mechanics is valid for your situation."
] |
[
"Question about black holes / Hawking radiation:"
] |
[
false
] |
So, I was thinking about black holes today, and had a thought which confused me somewhat. There is a common thought experiment where people ask what would happen if a clock were thrown into a black hole, and it can be shown that, from the perspective of an outside observer, the clock would slow down as it approached the event horizon, never actually reaching it. Presumably, this means that from the clock's 'perspective', time would be passing at a normal rate, but events happening in the rest of the universe would appear to speed up more and more as it approached the black hole, eventually traveling infinitely fast. However, won't this mean that, from an outside perspective, objects would never cross the event horizon in a finite amount of time, and if so, wouldn't that mean that the black hole would decay due to Hawking radiation before the clock ever reached it? If so, does this mean that it is impossible for a black hole to acquire more mass than it started out with? This conclusion doesn't seem right to me, but I'd appreciate it if anybody who knows something about black holes could explain where I have gone wrong in my thinking.
|
[
"I'm pretty sure it's the other way around. As the clock approaches the event horizon, it experiences time dilation effects, \"stretching\" time in its own reference frame. After it passes the event horizon, it is no longer possible to communicate with the clock (i.e. read the time from it) as the information transfer necessary would have to occur at superluminal speeds. At this point, for the outside observer, the clock is essentially destroyed, but from the clock's perspective the black hole seems to get closer and closer",
"."
] |
[
"Presumably, this means that from the clock's 'perspective', time would be passing at a normal rate, but events happening in the rest of the universe would appear to speed up more and more as it approached the black hole, eventually traveling infinitely fast.",
"That's not actually correct. While events outside ",
" appear to speed up, they will ",
" approach infinite speed. The problem is not symmetrical between our infalling observer and our stationary observer.",
"However, won't this mean that, from an outside perspective, objects would never cross the event horizon in a finite amount of time",
"Yep.",
"wouldn't that mean that the black hole would decay due to Hawking radiation before the clock ever reached it?",
"The addition of Hawking radiation (and other quantum effects in the curved spacetime) actually produces some non-trivial new physics. For example, in the case of a spherical collapse, it's actually possible for the collapsing object to completely evaporate ",
" any event horizon is formed. Moreover, even when a horizon ",
" form, it's not necessarily true that a freely-falling observer will cross it; the horizon may evaporate out from under them. There's also the technical distinction between apparent horizons and event horizons that becomes (more) significant as we have to consider that some observers will see a horizon even if there isn't a ",
" horizon.",
"In the case that we include Hawking radiation ",
" have something cross the event horizon, our distant observer will see it become highly redshifted and 'smeared' over the horizon; eventually, the outgoing radiation will swamp this redshifted, thermalized light and it will just be seen as another part of the radiation from the evaporating black hole.",
"If so, does this mean that it is impossible for a black hole to acquire more mass than it started out with?",
"Nope, but what happens when one ",
" is largely unknown. We know that the area of the event horizon should increase, but just how that all goes down hasn't yet been determined."
] |
[
"Sadly for the poor clock, it reaches the singularity in a finite amount of time, even in its own frame of reference. The slowing down and fading an outside observer can witness is only an effect of photons being unable to escape the event horizon and does note correlate to any kind of time slowing down."
] |
[
"Why don't we ever sneeze while sleeping?"
] |
[
false
] | null |
[
"When you're awake, allergies, particles etc. can stimulate the nerve cells in your nose. The cells send a signal to the brain and you sneeze to get whatever's causing the stimulation out.",
"When you're asleep, though, much more stimulation is required to initiate a sneeze, due to an inhibitory neurotransmitter known as GABA which specifically inhibits the areas of the brain which are more active when you're awake. This state is known as REM atonia. You also, in general, have fewer particles enter your nose when asleep.",
"However, enough external particles WILL cause you to sneeze, but you will wake up to do so."
] |
[
"anecdotally, my GF wakes up a few times a night to sneeze and goes right back to sleep."
] |
[
"I was going to ask the OP how he knows he doesn't sneeze. You'd have to set up a camera/microphone to be sure. Maybe it just doesn't wake you or you don't recall it after falling right back to sleep."
] |
[
"Why is ∞* 0 ≠0"
] |
[
false
] |
It looks like a simple math. I mean, I know infinity is some number very very big, but regardless of the magnitude of infinity, I would assume if I multiply that number with 0, then I would get 0.
|
[
"infinity is some number very very big",
"This is the wrong way of looking at things. Infinity ",
" a number - it is a concept used to describe something limitless. ",
"Generally, the instances when infinities are \"part\" of equations are those when you have a function (eg. f(x)), which has parts where certain ",
" values will return an error, such as divide-by-zero. However, we can still evaluate the ",
" of such a function."
] |
[
"Problem here is that we can ask ourselves multiple questions that all are proper interpretation of 0*infinity:",
"extended real number line",
"cardinal multiplication"
] |
[
"Infinity is not a real number, so it can't be treated as such. "
] |
[
"Are mind palaces, like in BBCs Shelock, real? If so how effective are they?"
] |
[
false
] | null |
[
"Mind palaces are real, though not like the one shown on TV of course. the idea is that we remember locations better than facts, so if we create a location we are familiar with (real or fictional), filled with triggers that links to facts, then we create what is a mind palace. a complicated mind palace takes a lot of practice, and constant \"revisits\" to make sure everything is still there. "
] |
[
"oh for sure, I mean if there are people who can recite pi to the 100,000th digit then a huge mind palace isn't impossible. mind palace is after all a technique/tool, and its potential depends on the user. "
] |
[
"It seemed a little crazy to me especially after Season three Episode three where the creepy black mail guy (what ever his name is) has piles of information on hundreds of people stored in his head. Thanks for the response"
] |
[
"I want to understand the difference (and importance of the concept) between impedance (as in \"75 ohm coax wire\") and grade-school resistance (as in \"I = V/R\" and \"P = I squared R\")."
] |
[
false
] |
I am very comfortable with the concept of grade-school resistance. I tried to read the about impedance, but I think I need a explain-it-like-I'm-five explanation, if anyone would be so kind...
|
[
"In general, ",
" is the complex (as in 'complex numbers', with a real and imaginary part) form of ",
". Z = R+jX. Z= ",
", R = the (real) ",
" you are familiar with, X= the (imaginary) ",
".",
"This complex ",
" comes in play when describing relations between voltage and current when capacitors and inductors are involved. The impedance of a capacitor is Z=1/(jwC), the impedance of a coil is Z=jwL (w=2.Pi.f with f the frequency of the signal). You use the ",
" in the same way as the ",
" to solve a circuit, but you will end up with complex currents and voltages (and frequency dependent).",
"Now, a ",
" of for example a coax cable is something specifically for transmission lines. In short, transmission lines are involved when the length of the current paths (like a long coax-cable) are longer than the wavelength of the signal on that path. I'll try to explain this intuitively. Assume you have a source with an internal resistance (impedance) driving a load resistance (impedance). When the signal paths are short or the signal frequency is low, a change in the source voltage will immediately be seen at the load and the source will 'feel' this load. However, when the signal frequency is higher and the signal paths are longer, the source voltage will already have changed before the 'previous' voltage reached the load resistance (impedance), so the source cannot directly 'feel' the load resistance (impedance). What the source ",
" feel is dependent on the characteristics of that transmission line (distributed capacitors, coils and resistors). The resulting impedance is what the source 'feels' as load (not entirely correct, this is when there are no reflections from when the signal bounces off the load resistance. Assume a infinitely long transmission line.). This ",
" of a transmission line is dependent on frequency an defined for a specific frequency range (the range in which the for example coax cable is used)",
"To avoid the reflections I was talking about, the load impedance (at the end of the transmission line) should be the same as the characteristic impedance of this transmission line. This is why it is such an important value when designing electronics, and why there are certain standards (50 Ohm, 75 Ohm), to make sure that different devices connected to different coax cables still work as expected."
] |
[
"Electrical concepts are usually explained first in terms of direct current because DC is a special case where these concepts are pretty simple (V=IR). You can think of impedance as being composed of two different components. An impedance value holds two pieces of information, resistivity to electrical current, and what we call reactance. In DC systems that reactance component is 0, so we just call the \"impedance\", \"resistance\".",
"When we have alternating current we have a new attribute of the system we need to keep track of. We have the voltage and current as we do in DC systems, but now we have a relative phase between those two waveforms. Lets take a simple test case where we have a voltage source that produces an alternating current where the voltage is \"in phase\" with the current, i.e. there relative phase is 0. Certain electrical elements can \"pull\" the voltage's waveform behind the current's, or vice versa. An inductor \"pulls\" the current behind the voltage, a capacitor pulls the voltage behind the current. We say \"the voltage leads or lags the current by x degrees/radians\". As Pienix explained, impedance is a complex number, where the real part holds the information on resistance and the imaginary part holds information on the phase shift between voltage and current. The sign of the imaginary part tells you weather the current or voltage leads."
] |
[
"I'll take a stab at this and try to explain it on a simpler level. ",
"/r/ascience",
" engineers, please be kind to me ;)",
"When you get in to impedance you're getting into alternating currents not direct currents more easily solved by Ohm's Law although when you add everything up you still use Ohm's Law.",
"It's best to first look at the concept of ",
"reactance",
". Impedance is reactance plus DC resistance.",
"In your case to go further it get's down to ",
"inductive reactance",
" where a coil/wire/cable/etc ",
". Opposing a change in current (or voltage with capacitors) is the key to understanding impedance. The higher the inductance and the higher the frequency, the higher your impedance will be. This is very useful concept for designing filters.",
"Capacitors work just the opposite. The smaller the capacitor and the lower the frequency the higher your capacitive reactance will be. This allows very low value capacitors to be used in relatively high frequency microwave applications but we would need much larger capacitors in relatively low frequency audio applications.",
"For cables that are 75 ohm for audio/visual or 50 ohm for radio applications and are ballpark numbers, this is more important for ",
"impedance matching",
". Having an impedance mismatch means that you're loosing or not effectively using the signal in the cable. This can be very bad in higher power applications. Getting in to transmission line models will just confuse you.",
"As an example, if you use a 2 ohm speaker, which is measured in impedance for a certain frequency and will have a much lower DC resistance, in a small amplifier designed for 8 ohm speakers then you could damage the amplifier because of the severe impedance mismatch caused will allow excess current to flow.",
"So, something that opposes a change in current (for inductive reactance) or a change in voltage (for capacitive reactance) at a certain frequency plus the DC resistance gives you your impedance.",
"Not that you're more confused, I found an article that give some analogies for impedance in cables.",
"http://www.bluejeanscable.com/articles/impedance.htm",
"I hope this helps."
] |
[
"Would Dinosaurs have been red or white meat?"
] |
[
false
] | null |
[
"Red vs. white meat is largely a function of how the specific muscles are utilized. The 'red' in red meat is from high amounts of myoglobin for oxygen retention and mitochondria that are used for aerobic respiration and are generally found in higher abundance in slow-twitch muscles that are used for extended periods of time. In contrast, fast-twitch muscles that require rapid bursts of power but fatigue quickly tend to rely on anaerobic respiration more and therefore have less myoglobin and fewer mitochondria, making them more whitish in appearance. In fact, most animals have both types of muscles (analogous to white meat vs dark meat in chicken). ",
"This, combined with the fact that chickens and other birds descended from dinosaurs, would seem to indicate that different dinosaurs would have different ratios of slow-twitch and fast-twitch muscles. This means that dinosaurs would have both white meat and dark meat, just like chicken!",
"Going further, it's more likely that dinosaurs that were grazers or persistence/pack hunters and moved around all the time would have more red meat and smaller dinosaurs that perhaps would rely on their speed to escape from predation or to catch prey themselves would have more white meat. ",
"Source: medical student with a lifelong fascination of paleontology. "
] |
[
"Taste in meat is due to so many factors, including presence or absence of different types of fats/oils and whether there's stored glycogen there. Also, since animals do tend to taste differently based on their diet... it is really pretty impossible to know or conjecture. The safe answer would be to say they taste like birds... but ",
"who really knows?"
] |
[
"more important, how would it taste ?",
"edit : not sure its possible to begin answering that, not a joke, I am serious"
] |
[
"Why don't scientists clone endangered species as a means to increase their population?"
] |
[
false
] | null |
[
"One of the most necessary factors in long term species survival is genetic diversity. Cloning would lead to an increase in organisms, however there would be a massive genetic drift toward one genotype (or a few) and increase the likely hood of future offspring having deleterious (harmful) genes or mutations. There are a whole lot of other factors that have to do with fitness of the cloned organism but genetic drift leading to a bottle neck is a big deal in population and conservation genetics.\nSource: I'm a molecular, cellular and developmental biology major (senior) taken a few conservation genetics classes in my time. "
] |
[
"Species become endangered because they lose their natural habitat, not because they fail to breed. Cloning them would not restore their habitat.",
"Edit: typo."
] |
[
"Cloning is not easier than breeding non-clones. Generally, it's harder.",
"Cloning is not done by some scifi replicator, but simply by implanting a zygote into a host-mother's womb and having it grow as normal. To clone, that zygote is prepared by a tricky process of implanting a nucleus into an egg. To non-clone, it's just ordinary semen+egg in a test tube."
] |
[
"Why was the number 299,792,458 chosen as the definiton of a metre instead of a more rounded off number like 300,000,000?"
] |
[
false
] |
So a metre is defined as the distance light travels in 1/299,792,458 of a second, but is there a reason why this particular number is chosen instead of a more "convenient" number? Edit: Typo
|
[
"The principle was to keep the definition consistent with previous measurements, within their uncertainty. We already had a definition for the metre, just not as precise as the current definition, and we want the new definition to be as consistent as possible, but just easier to measure precisely. Rounding to 300,000 km/s would change the definition of the metre by about 0.07%. That would just make life different for everybody: we'd have to specify if we're talking about the \"old\" metre or the \"new\" metre, because that 0.07% change is big enough to matter. It'd change the circumference of the Earth by about 30 km, for instance - a big enough difference that it's measurable, even if it's small.",
"Rounding down to the nearest 1 m/s means that instead of a 0.07% change, the change is ~0.0000003% at most. So, that changes the circumference of the Earth by <10 cm at most. That's small enough that it would typically be within the measurement error, and it's close enough that we can treat the metre as unchanged without causing any problems."
] |
[
"It'd change the circumference of the Earth by about 30 km, for instance",
"to illustrate the impact, if we built a metal ring with a circumference 30km larger than that of the equator, it's diameter would be ~9km more than that of the earth.",
"that ring would float about 4.5kms above everyone's head."
] |
[
"The meter ",
" was defined as 1/10,000,000 the distance from the equator to the North Pole at the longitude of Lyon.",
"Then people figured out that this wasn't a great way of developing a precise unit of length due to difficulty measuring, and the fact that the value might even change due to Earthquakes, and it could only be referenced at one spot (the line through Lyon) and they searched for a definition that was a universal constant. Eventually the speed of light was chosen (there were electrum rod references in between), and it happened to be 299,792,458. It's a pure fluke that it's so close to 300,000,000"
] |
[
"Why does sodium move inside the membrane during an action potential?"
] |
[
false
] |
I get that at resting potential, the inside of the membrane is less positive than the outside. Nevertheless, wouldn't potassium cation ion still make the inside of the membrane overall positive? If both the inside and outside of the membrane are overall positively charged, then during depolarization, what is driving Na into moving towards yet another positively charged region? Likewise, what force is causing K to move to the outside of the membrane (which is also positively charged)? Can someone please explain to me the underlying biophysics?
|
[
"There is a protein integrated into the plasma membrane of cells called the “Na+/K+ transporter”. This protein is constantly using ATP in order to push sodium ions OUTSIDE of the cell. This “Na+/K+ transporter” protein is therefore creating a Na+ ion gradient with a lot of Na+ outside of the cell and very little Na+ inside the cell. Therefore, as long as another protein which is called a “Na+ ion channel” is open, then Na+ ions will happily rush into the cell down their concentration gradient (the Na+ ion crosses the plasma membrane barrier by flowing through the opened Na+ ion channel). The Na+ flowing down their concentration gradient and is thermodynamically favorable with a negative Gibbs free energy and will occur spontaneously, which is very intuitive.",
"Also, It’s negatively charged inside the cell (technically speaking the electric potential is lower inside the cell relative to outside the cell, creating a voltage difference and the reasons for this voltage difference is actually quite complex). Nevertheless inside the cell is more negatively charged relative to outside the cell. Therefore as long as those “Na+ ion channels” proteins are open, then those positively charged Na+ ion will happily rush into the cell because its attracted towards the negatively charged cytoplasm (negatively charged cytoplasm inside the cell will attract the positively charged Na+ to move inside the cell). This is also thermodynamically favorable with a negative delta Gibbs free energy and will be spontaneous.",
"Therefore, these two thermodynamically favorable forces (the chemical concentration gradient of sodium ions rushing inside the cell PLUS the electrical pull of the positively charged Na+ ions attracted towards the negatively charged cytoplasm) both of these forces add up (Gibbs free energy is additive) and make it very thermodynamically favorable and spontaneous for positively charged Na+ ions to rush inside of the cell, as long as there are “Na+ ion channels” open to allow those Na+ ions to diffuse inside the cell and cross the plasma membrane.",
"Below is a video link that goes into more detail ",
"https://m.youtube.com/watch?v=x7DyzG6geX8"
] |
[
"Also if you’re curious, the reason why there is a transmembrane voltage potential in the first place is because of the K+ ion gradient (maintained by the Na+/K+ Transporter). The K+ ions move outside of the cell down it’s chemical concentration gradient through “K+ leak channels”, and this process is moving positive charges out of the cell and this process creates a transmembrane potential. ",
"Below is a link to a video if you’re more curious on more details",
"https://m.youtube.com/watch?v=x7DyzG6geX8",
"The truth is it’s a bit more complex, in reality there is a “transmembrane voltage potential” with energy in the form of electric potential energy charging the plasma membrane as if it were a capacitor. This charged capacitor can dissipate energy and in that process provide a thermodynamic force allowing ions to move in or out of cells depending on their charge. So saying the cytoplasm is negatively charged is a bit of a simplification."
] |
[
"The inside of the cell has negatively charged macromolecules that can't leave the cell, allowing it to have Na+ and K+ ions while still remaining a negative charge. The cell keeps that charge in a few ways, there are ion channels (leak channel) that allow Na+ and K+ into and out of the cell. They follow their concentration gradient through these. There is also the sodium potassium pump which punps 3 Na+ out and 2 K+ in which would make the cell more negative as it is losing one positive ion."
] |
[
"A health concern is the failing of antibiotics as bacterial become immune to them. Is the same situation true of vaccines or is it not in any way similar?"
] |
[
false
] | null |
[
"Hi eagle332288 thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Medicine"
] |
[
"'Medicine'"
] |
[
"Are orbital altitudes correlated to required orbital velocities relative to earth?"
] |
[
false
] |
So the ISS chills at about 300km above the surface of the earth and travels at about 27000km an hour, how much can that orbital velocity vary? Since the moon does it's thing at 375,000km and travels at 1km a second (3600km an hour?) is it reasonable to assume that the further away a body is, the slower it can/must orbit to stay stable? All those numbers are pretty roundabout and I know all bodies are tugged on by other massive bodies in the solar system, for simplicity I'm curious about earth's gravity taken in isolation (if possible). I also know the moon is slowly drifting away, I'm curious about time spans observable by humans. For fun, what would happen if you appreciably altered the speeds of the ISS and the Moon both faster and slower?
|
[
"So the ISS chills at about 300km above the surface of the earth and travels at about 27000km an hour, how much can that orbital velocity vary?",
"If the ISS were in a perfectly circular orbit, the velocity would not vary at all. Its orbit isn't perfectly circular, but after a small amount of searching I can't find how not-circular (elliptical) it is, but it definitely will be, even if just a little bit. When it's further away from the Earth it will be travelling slower, and when it's closer it will travel faster. This is ",
"Kepler's second law or planetary motion",
", there's a nice gif in that link.",
"Since the moon does it's thing at 375,000km and travels at 1km a second (3600km an hour?) is it reasonable to assume that the further away a body is, the slower it can/must orbit to stay stable?",
"Yes. In these situation it's often useful to take limiting cases, which means to take things to extremes. Imagine an object infinitely far away from the Earth. How fast does it need to go to maintain orbit? It doesn't need to even move at all because it doesn't feel Earth's gravity because it's infinitely far away! So all it needs is zero velocity. So you are correct in saying that the further away something is the less velocity it needs. ",
"Here",
" the following formula is derived:",
"where v is orbital velocity, r is the orbital radius, M is the mass of the thing that's being orbited and G is the universal gravitational constant. So for extremely large r, v becomes very small, as I described above. ",
"I'm curious about earth's gravity taken in isolation (if possible)",
"The above explanations all rely on this, in practice there are non-negligible effects from the Sun. ",
"what would happen if you appreciably altered the speeds of the ISS and the Moon both faster and slower?",
"If gave the ISS (or the Moon) a push, its orbit would become more elliptical. If you pushed it hard enough, it might escape Earth. "
] |
[
"Orbital speed and altitude are intimately related. For low eccentricity orbits, ",
"v ~ sqrt(m2",
" *G/((m1+m2)/r))",
"So the speed varies inversely with the square root of the semi-major axis.",
"For all non-circular orbits, which is basically all orbits since they all have some eccentricity in real life, the speed increases as the orbiting object nears the orbited object, and decreases as it goes away.",
"So if you gave a short boost to the ISS on one side of its orbit and in the direction of its velocity, the far side altitude would be increased, and the far side speed would be increased, while the side where you gave the boost would remain the same in altitude, and would have the added boost of speed.",
"If you reversed this boost, you would slow the speed down at that point, which would lower the altitude at the opposite point, and increase the speed at the opposite point. Unless the altitude was decreased enough to cause the orbit to intersect with the sphere of the Earth, in which case the speed of the ISS would at some point become zero."
] |
[
"If you pushed it hard enough, it might escape Earth.",
"Depending on how you pushed it, it could also dip the orbit low enough to burn the ISS up in the atmosphere. This takes much less delta-v (change in velocity, thus requiring less fuel), so it would be a more realistic option for evil geniuses."
] |
[
"Does Compton Scattering produce multiple photons?"
] |
[
false
] |
Lets say we have a stationary electron with energy E = m c and an incident photon with energy E = hf , where f is the frequency. After the scattering event, the scattered photon will have energy E=hf where f >f and the electron will have energy E=sqrt(m c + p c ) then by conservation of energy we have: hf + m c = hf + sqrt(m c + p c ) My question is that after the collision the electron will have acquired some momentum and if that is the case then its velocity must have changed. Would this not mean that hf + m c > hf + sqrt(m c + p c ) since the electron would have radiated some energy away as it was accelerating and would that acceleration result in more photons?
|
[
"I like the definition of Compton scattering as seeing a photon + electron in, and then a photon + electron out, which implies that the energy will be conserved. But it's wrong to say that bremssstrahlung doesn't exist in quantum mechanics and has no relevance here. Understanding the effects of bremsstrahlung was incredibly important in the development of QED, where perturbation theory is plagued with infrared divergences from the massless photons. In that sense, the OP's intuition is actually very good, since considering the processes with extra photons with vanishingly small energies in the final state turns out to be the correct solution for eliminating these divergences. You're correct that we should consider the process where we only see one final state high-energy photon, but we need to add in all final states with extra bremsstrahlung photons that had so little energy we couldn't measure them to get the physically correct answer."
] |
[
"Nope. ",
"The actual mechanism behind the scattering event is not actually specified in the usual derivation of Compton scattering. It's treated like a mysterious black box where we simply see one photon and one electron enter the interaction, and a different photon and a different electron leave. To understand ",
" and ",
" the electron and photon interact, you'd need to tackle the problem with the mathematics of QFT. It's like the intro-physics problem where two billiard balls undergo an elastic collision; the collision is assumed to be instantaneous and you're never able to define a proper acceleration. ",
"I'm assuming that the radiation you're referring to is Bremsstrahlung radiation, which is a purely classical type of radiation emitted by a charged particle when it accelerates. You should be careful when you try to extend classical results like that to the sphere of quantum mechanics. "
] |
[
"The energy of EM radiation decreases like 1/r",
" with distance from the (sufficiently far) source, so the second change should have much less energy than the first. The total energy (in the charges + radiation) will be perfectly conserved of course, so the second wave will have less energy than the original wave."
] |
[
"If you have a spacecraft that’s designed so it rotates and keeps gravity at 1 g…"
] |
[
false
] |
...how fast would the spacecraft be able to go before humans were unable to travel on it? I’m thinking in terms of interstellar travel where we’d need to be on the craft for a long period of time. Similar to how the Earth orbits the Sun at about 108,000 km/h but has enough gravity and rotation (I assume this is the cause) so we don’t feel like we’re going 108,000 km/h. Would the spacecraft be able to travel at 108,000 km/h and beyond if the rotation was enough to keep a constant 1 g? I guess that’s also assuming the spacecraft is able to generate the necessary speed and built to withstand the pressures put upon it.
|
[
"Unfortunately, you are a bit confused about exactly what kind of conditions are inhospitable. It's not how fast you are going, it's how much you are accelerating. The fact that being in an accelerating frame of reference feels the same as being in a gravitational field is one of the key insights underlying Einstein's theory of general relativity.",
"Basically, the spacecraft can go arbitrarily close to the speed of light with humans on it (in, for example, the Earth's frame of reference), as long as it isn't accelerating too much faster than 1 g.",
"Now, to answer your question. If your ship is already going a certain speed (relative to the earth or the sun or whatever), it can be going at any speed less than the speed of light. The fact that it's rotating and creating \"artificial gravity\" is independent of the speed if it's not accelerating."
] |
[
"It would need to accelerate relatively slowly. Depends on how fast you want to go and how long you're willing to accelerate for. One cute idea from science fiction is to have a spacecraft that accelerates at 1 g for the first half of the journey, then turns around and decelerates at 1 g. Travel aboard such a craft would be very comfortable and would reach relativistic speeds rather quickly, but it would take tremendous energy to keep up such acceleration.",
"Here's what you want:\n",
"http://en.wikipedia.org/wiki/G-force#Human_tolerance_of_g-force"
] |
[
"so we don’t feel like we’re going 108,000 km/h",
"You never feel speeds. You only feel accelerations.",
"The spacecraft could go any speed you like, so long as it is slower than the speed of light. The rotation which would give you the simulated gravity is entirely separate from the speed the ship travels. An observer inside the ship wouldn't feel any difference if they were traveling at 1000000000 mph or sitting still, as long as they were rotating."
] |
[
"Relativistic effects in gear systems."
] |
[
false
] | null |
[
"Thanks! I'll do that. I'll crosspost it, and let a mod close it here if they determine that's something that should happen. I'll provide a link here for people to follow."
] |
[
"The cross post is ",
"here",
"."
] |
[
"A good home for this question would be ",
"/r/AskScienceDiscussion",
"."
] |
[
"What actually causes the internal resistance of a battery?"
] |
[
false
] |
Batteries have a characteristic which we call internal resistance. I'm an electronic engineer and I understand how this effect manifests itself. It acts like a resistor being in series with the output of the battery, however it is not a "real" resistor but to an engineer it makes our lives easier to think of it that way. I've always thought that the internal resistance was basically due to the battery's limited ability to produce current. i.e. As you try to draw a large current from the battery, the battery struggles and that is analogous to having an increasing series resistance. However, I've been thinking about how batteries can get hot as they discharge. The heat generation is always put down to the current flowing though the internal resistance of the battery which implies that the internal resistance is acting like an ordinary resistor(/conductor). So now I'm confused. Do charges flowing through the electrolyte experience an electrical resistance? Or something similar? Or is it something else entirely? , What actually internal resistance? What is the cause of the heating?
|
[
"There is in fact an electrical resistance associated with batteries, which causes ohmic heating just like the resistance of any other circuit element. However, it's generally made up of a lot of different components and not only depends on the type of battery, but can change non-linearly with state-of-charge, rate of discharge, age, or even between different manufacturers of the same type of cell. A few contributions are:",
"A roughly fixed resistance, due to finite (ionic) conductivity of the electrolyte. You can think of the lost heat as being due to \"friction\" from the ions and molecules in the electrolyte rubbing against each other as they move.",
"The ",
"kinetics",
" (roughly speaking, activation energy) of the chemical reactions happening inside the battery.",
"Poor diffusion of solid-state reaction products: in a NiMH or Li-ion battery, H+ and Li+, respectively, must diffuse through a solid material after reacting at its surface. Since charged particles are moving, this can be thought of as a diffusive \"current\" and it is possible to ",
"mathematically transform",
" the diffusion coefficient into a resistivity.",
"Buildup of solid products on the surface of electrodes: in lead-acid batteries, PbSO4 naturally builds up during discharge, and in Li-ion batteries, electrolyte degradation products build up over many charge/discharge cycles. This causes similar problems to the solid state diffusion mentioned above.",
"As ",
"u/tuctrohs",
" mentioned, it's often possible to quantify different contributions to the resistance separately by measuring impedance of the battery as a function of frequency, since each process usually occurs on a different timescale and thus will get \"frozen out\" at high enough frequency. This type of experiment is called ",
"Electrochemical Impedance Spectroscopy",
". However, in practice it can be difficult to do this, because you have to already have some idea of what you're looking for in order to make sense of the data."
] |
[
"There are multiple contributions, including the electrical resistance of the plates, the diffusion process in the electrolyte and the reactions at each plate. Which one dominates can depend on whether you are testing a steady draw or a pulsating draw. The impedance vs. frequency can be used to tease out, to some extent, the contributions from each of these (and perhaps more that I'm forgetting). That technique is called \"electrochemical impedance spectroscopy\". The results are often modeled as RC chains, with the different resistors in the model representing (roughly) the different phenomena giving rise to the resistance."
] |
[
"/u/tuctrohs",
" and ",
"/u/almightycuppa",
" both gave correct answers, but maybe failed to directly address your questions, which seem to be more straightforward: ",
"\"What actually IS internal resistance? What is the cause of the heating?\"",
"Generally speaking, the \"origin\" of internal resistance of a battery is the same of that of a pure resistor, even though the exact mechanisms may differ because the nature of the nature carriers are different: electrons in pure resistors, ions in batteries. The reason why both of them heat up is also the same, and you've heard of it: Joule heating. ",
"Depending on the level of detail, the electrical/electrochemical description of Joule heating can more or less complex. It can be translated into mechanical terms as the \"friction\" to the flow of charge carriers within a medium (electrons in metal, or ions in an electrolyte). Closer to reality, while the Li-ion battery is being charged, the charge carriers (Li",
" have to move from the cathode (e.g. LiCoO2) to the anode (graphite), passing through the electrolyte (e.g. LiClO4). As Li",
" diffuses within these materials, it interacts with atomic species within, losing energy in the form of heat. This energy loss translates as a resistance in the electric circuit. ",
"A second reason for batteries heating up/cooling down is called thermochemical heating/cooling. Depending on the chemistry of the battery, some of the electrochemical reactions can be endo or exothermic (according to the direction of the current, and even moment during cycle), leading to temperature changes. However, this effect can be negligible compared to Joule heating, as long as the battery is used within the designer's safety recommendations, to avoid thermal runaway."
] |
[
"How the Universe began."
] |
[
false
] |
I am curious. I guess I am unclear about the space that our universe is expanding into. Since it is expanding then where did this space come from?
|
[
"Space was, and continues to be created by the expansion/inflation of the Universe after the Big Bang."
] |
[
"Thank you all for your responses. It has really helped me understand things a bit better. I still have one question. The simple fact that there was a particle sitting there (before the explosion) means that space has already in existence does it not?"
] |
[
"Space itself expands. It needs no medium to expand into because it creates its own. The balloon analogy is used quite often. As the balloon expands, the space between two points on the surface of the balloon continues to increase. You don't need to add anything onto the surface of the balloon, it just expands. ",
"Now the other question of what exists outside the universe, or what the universe sits in, is more complicated/theoretical. "
] |
[
"I just learned about the MarsOne project, and I was just wondering, what is NASA's take on the matter? Also, is the project a realistic and viable option? What exactly would be necessary for it to be successful?"
] |
[
false
] | null |
[
"Its a bit vague about the details. The main problem is money."
] |
[
"So would NASA be willing to actually contribute to the project. I've heard of NASA wanting to send people to explore Mars, but it seemed like a slower process, you know? It didn't sound like they would just dump people on the planet for the rest of their lives."
] |
[
"So would NASA be willing to actually contribute to the project",
"Maybe they would pay for a seat, hard to say.",
"It didn't sound like they would just dump people on the planet for the rest of their lives.",
"That might be the best thing to do. In ten years when my son is an adult I would consider doing something like that."
] |
[
"Diffusion: why is it molecule specific?"
] |
[
false
] |
I was taught in my biology class that if we have add two types of ions with similar with similar charge and size to a water beaker solutions, these ions will distribute uniformly with respect to themselves and NOT with respect to other ions in the solution. That is, say we have Na+ and K+ ions in our solution. After a long amount of time for diffusion to commence, all the Na+ will be uniformly distributed (ignoring the K+), and all the K+ will be uniformly distributed (ignoring the Na+) in the beaker. My question is why is not possible (or is it) that if we look at the beaker after a long time, maybe the left side has a much larger number of K+ ions than the right side, and the right side has a much larger number of Na+ ions than the left side, such that overall the + ion distribution is approximately uniform (as if the Na+ and K+ were just a single type of ion)?
|
[
"The question you are asking is one of ",
"statistical mechanics",
". This ",
"exemple",
" is very close to what you are asking. ",
"In a nutshell, when your solution has at equilibrium, all configurations of the ions that respects the external conditions (pressure, temperature, etc) are equiprobable (i.e. the microscate has the same probability). ",
"So a situation where your suggested ",
" of ions would happen is not forbidden. It could happen. But the problem is that it is very, very unlikely. ",
"To see this, let's say the Na+ ion has a 50/50 chance of being on the left side of the beaker and the solution is very dilute so there is no ion-ion interactions to worry about. For all the Na+ ions to be on the left, the odds would be 1/2",
" where N is the number of Na+ ions (say, on the order of a mole, 6.02 e+23), i.e. damn near zero. The same holds for the K+ ions. ",
"Basically, think of it as throwing a coin for each ions. The odds of throwing a \"billion billion\" coins in a row and coming every time head is negligeable. Most likely, out of a \"billion billion\" coin throws, half will be heads (Na+ in the left side) and half will be tail (Na+ in the right side). "
] |
[
"What you said makes perfect sense in the one ion case, but I'm still a little hazy on the two ion case. I have one more follow up question that would probably help correct my understanding:",
"Say we have two beakers of water connected with a one-way permeable membrane from beaker A to beaker B. Beaker A has 1M Na+ solution, and Beaker B has 1000M K+ solution (an extreme case). In the end, will this system stabilize as Beaker A (0.5M Na+) and Beaker B (0.5M Na+, 1000M K+)? ",
"I would think the repulsion of the K+ ions would have a non-negligible effect on the Na+ ability to diffuse and make it more probable that a state with a higher concentration of Na+ in beaker A would be more likely in the long term (t=infinity). "
] |
[
"Well, first a little word about solutions. I was careful in my initial post to describe an ",
"ideal solution",
". In an ideal solution, the ions are independent. If the solution is non-ideal, then things can start to get strange. As you correctly start to surmise. ",
"I'll break your exemple into two step. ",
", Let us start with a beaker with 1 M Na",
" and 1000M K",
" (ignoring the fact you probably can't get to that concentration, let's just use this as a strawman, a gedanke experiment) but without your proposed membrane. Because of the symmetry in the system, you will end up with a uniform concentration of Na",
" and a uniform concentration of K",
" For sure, there is now interaction between the two, but the equations of the system are symmetric, no physical location in the beaker is different than another one, so when running our stat mech calculations, we will still end up with uniform concentrations. My previous mathematical exemple still applies. ",
", now, if I get to your exemple, I have ",
". The probability of a K",
" ion moving across the membran is now zero. All K",
" ions are stuck on one side. We have already agreed that at such a strong concentration, the solution is no longer ideal, so the Na",
" ions and the K",
" ions now interact with each other. I think it is safe to assume that at the start of your proposed experiment, the ",
"chemical potential",
" of an Na+ ion is not the same on one side of the barrier than it is on the other. I.e. an Na+ ion has a different \"free energy\" on the two sides of the membrane due to the asymmetry of conditions existing. ",
"But at the end of your experiment, the chemical potential of Na",
" ions must be the same on both side of the membrane, in space of the difference of environment on each side. (by definition of thermodynamics equilibrium ...in stat mechs's parlance, the distribution of Na",
" ions must obey Maxwell Boltzman statistics at the end of the experiment...the two \"phrasing\" (thermodynamics vs. statistical mechanics) can be shown to be equivalent) ",
"The way this happens is, as you guessed indeed, by having different concentrations. The concentration would reflect the difference in free energy that the Na",
" ion experiences on each side. If I can assume the Na",
" ions are still an ideal solutes (but make no such assumption for K",
" ions, and I take those as a \"constant\" of our experiment), then the concentration on each side of your membrane will be given by ",
"Maxwell Boltzmann statistics",
". ",
"Hopefully this is clear...if not, I can try to rephrase it. ",
"P.S: note that the functional dependence of the chemical potential on concentration ",
" the Maxwell Boltzmann statistics. So that if we were to study this problem solely through thermodynamics, we'd still get the right answer. Just like we did by looking at it through the statistical mechanics lens. "
] |
[
"Anyone familiar with GST fusion proteins and how they are prepared?"
] |
[
false
] |
[deleted]
|
[
"Which part of the preparation are you having trouble with? I haven't actually used GST in particular but it is a similar concept as with any fusion tag. ",
"First step is the molecular cloning - The DNA sequence that encodes the GST tag is known, so you fuse this sequence in-frame with whatever protein you are interested in to form the fusion protein. This is probably done in a plasmid that has some other elements that are needed. I can go into more detail if this is where you are having problems.",
"Second step is to transform a host - Assuming you want to make your GST fusion protein in some organism other than what you made the plasmid in (likely ",
"), you are going to have to get that piece of DNA into whichever organism. This step really depends on what your host is. A lot of bacteria will just take up foreign DNA under certain conditions, with plants you use a bacterium called Agrobacterium... not sure about animal cell lines and all that.",
"Third step is to purify the fusion protein - Again this depends on exactly what you are trying to do, but if you are using GST you are probably trying to \"pulldown\" your fusion protein and possibly find protein that interacts with your protein of interest. You do this by taking advantage of GST's high affinity to glutathione by using by small beads (usually agarose or sepharose) that are coated with glutathione to separate your fusion protein and anything that has high affinity for it from all the other junk. ",
"Again I could give you more detail at any step, but that is the basics."
] |
[
"Usually the tag is already in an expression plasmid. What you do is cut that plasmid and your gene (eg. hp300) separately with a restriction enzyme and you can combine them by mixing and putting in ligase, an enzyme that combines pieces of DNA. You then put your new plasmid with your fusion protein into a host (",
") to make more of the plasmid. ",
"Transforming your host is standard no matter if it is prokaryotic or eukaryotic. Even if you want to express your protein in ",
", there are different strains for making plasmids and expressing proteins.",
"Based on what you said, it sounds like they purified their GST-hp300 protein using the GST tag, and then tested it for HAT activity. Briefly, what they would probably do is take a culture of cells that have that plasmid from earlier, make the cells produce lots of that protein typically by adding some chemical, and then collect the cells. The cells are ruptured in some way to release all the proteins in them. But some other proteins may have HAT activity right? So you need to separate the protein you are interested in from all the other junk. As I mentioned before, what you do is incubate your cell extract with these Glutathione beads, the GST binds them tightly, you wash away everything else and then release the protein from the beads and collect it. You can then test for HAT activity using your assay, either before or after removing the GST (assuming you have a cleavage site too). "
] |
[
"First off, thank you for responding. We have no textbook and it gets crazy searching online.",
"Anyways, for the first step if I understand correctly, GST tags onto a terminus of a protein (ex/ hp300) which is inoculated into a plasmid. Culture is grown and we have cloned sequences? ",
"I don't think we have to deal with transforming hosts...unless this is a standard procedure(?). Are we talking about putting the fusion proteins from protozoa to metazoa or just any host to host?",
"The third step is definitely the most difficult component to comprehend and imagine. HAT activity is observed for the GST-hp300 (and this I suppose is shown with the purification of the GST fusion protein?). I do remember the professor mentioning something about \"pulling down\" (again wish there were textbooks for this class). ",
"If it's possible can you elaborate on the third step. I can msg you with the article if that helps. Thank you for your insightful and helpful comment!"
] |
[
"Why does metal turn red when it is heated?"
] |
[
false
] | null |
[
"Everything glows red when heated to a certain temperature because of blackbody radiation. It's just metal is one of the few things we deal with that doesn't combust or melt before it can get that hot."
] |
[
"It's not about how sensitive our eyes are as that they are attuned to the visible spectrum of light. As things get warmer, they release higher energy photons, this is why things get red-hot, red being the lowest energy visible light, before they get white hot."
] |
[
"The OP is clearly a layman, and although you have provided a link to technically correct information, the OP is unlikely to learn anything from it. Perhaps explain the content in layman's terms."
] |
[
"Is this statement true? \"as we emit more and more carbon dioxide into our atmosphere, each increment results in less and less warming.\""
] |
[
false
] | null |
[
"Yes, this is true. If you look at the two formulae in ",
"Wikipedia's entry on radiative forcing",
", you'll see that temperature change varies linearly with radiative forcing, and radiative forcing for carbon dioxide varies logarithmically.",
"That is why climate scientists often speak of change in equilibrium temperature per ",
" of CO2. Each doubling increases the equilibrium temperature arithmatically."
] |
[
"This would only be a valid argument if you assume that any dangers or issues that can result from increased temperatures increase linearly with rising temperature. It doesn't seem to hold true if you are talking about specific climatic break points, or if the first serious negative impacts occur a comparatively lower CO2 ratings. ",
"figuratively speaking, if you start poking holes in a parachute, the fifth or sixth hole may not make the guy fall any faster, but it doesn't mean he isn't already screwed."
] |
[
"This is askscience. Every question is asking for a response that is backed up with data and understanding."
] |
[
"Can you measure absolute velocity in space without a frame of reference?"
] |
[
false
] |
Say you are in a patch of space a few light years across in all 3 dimensions and you have no frame of reference, say for some reason you cannot see any stars, its pitch black. Could you measure your speed? Would it be of experimental interest (say, just to have a lab that is at rest relative to space itself) ? (One method I thought about would be based on the speed of light being constant: Imagine you are in a spaceship. You extend a detector array that includes a highly accurate atomic clock about a light second to your left. You then fire a laser at the thing and see if it hits. If you aim directly at the array and hit, then you are at rest, if not, you need to alter the angle of the laser beam to hit the detector. Based on the distance of the array, the angle on the laser beam and the runtime of the beam, you should be able to calculate your forward motion. You would of course need to have 3 arrays and 3 lasers to accurately dertermine your speed in 3 dimensions.) Edit: Thanks everybody!
|
[
"No, you can't, because there's no such thing as absolute velocity. The speed of light being constant means it's constant in ",
" reference frames; in general, there is no local experiment you can run to determine any sort of absolute speed."
] |
[
"Because the twin in the spaceship ",
". Acceleration isn't relative."
] |
[
"Let's say you have several hundred cans of super-magic-rocketfuel. You use one, and discover that it propels you forward at 10% of the speed of light, relative to your friend who was watching.",
"As you make your journey, you use up 200 such cans, and each time you use one, you begin moving faster than before. Yet, as you pass several star systems, the residents of each of those star systems will clock you as going some speed lower than the speed of light. You never really reach the speed of light, relative to ",
" observer.",
"Let's say that your friend came through earlier and laid out mile markers at every light minute. You've used the first 200 cans of super-magic-rocket fuel, and now you realize that you are passing 20 of these markers each minute! But, the markers are closer now than your friend said that they would be. They're a lot smaller also. All of space is compressed. You're going sub-light speeds, but since space is compressed you get to your destination faster than you thought possible for sub-lightspeed travel.",
"You put on the brakes since you've now reached the far side of the galaxy. Everything expands back to the normal size, and you meet and greet the aliens living at your destination. The next morning you pack up and head home, using the same rocket fuel. You're excited to tell your friends and family back home that you made the trip across the galaxy and back in just a few weeks.",
"But, when you get home, you discover that millions of years have elapsed while you were gone. While the galaxy shrunk for you during your trip, time dilation made you age less, and you never realized people back home experienced thousands of years in a blink of your eye. Now all your friends and family are gone, and the civilization you knew is just a historical footnote. Whoops."
] |
[
"How far can a flea see? Does it always know where it's going to land, or does it jump and hope for the best?"
] |
[
false
] | null |
[
"It would have to be the latter. The insect's size, and thus the size of its eyes, limit the visual resolution that it could have even under ideal conditions. And there's also processing power in the flea's brain - I very much doubt if they have enough neuronal complexity to pick out landing spots, even if they could see them. So it's more of a \"jump for it, because most of the time that works\" process."
] |
[
"I would only add that to a flea, his terminal velocity is low enough he never impacts with enough force to damage anything. So jumping into the unknown is not much of a bet for him. "
] |
[
"Would size play a factor in what force is needed to cause damage? Is this more related to the strength of the flea's body chemistry? Would a flea the size of a human be able to jump off of a skyscraper and be fine?"
] |
[
"If time slows down in gravitational fields, does it come to a complete stop in singularities?"
] |
[
false
] |
[deleted]
|
[
"I just want to tack onto this that singularities aren't thought to be a physical thing, but rather a failure of our model. The fact that our description of black holes contains a singularity at the center doesn't mean we expect an infinitely dense point to lie at the middle, but rather that our description of black holes is insufficient. There is also a singularity at the event horizon, but this can be eliminated by a coordinate transformation."
] |
[
"We have no idea what happens in singularities. However time does slow down ",
" singularities. If you were to watch someone fall into a black hole from far away, you would see it taking infinite time for the other person to pass through the horizon. In fact, from your perspective, they wouldn't \"pass through\" the horizon at all. They'd just spread out evenly over the horizon, extremely slowly."
] |
[
"I want to add on to this, though, that while it takes an infinite time for someone to fall into the event horizon from the perspective of an outside observer, from the perspective of the (spaghettified) observer falling into the black hole, a finite time passes as he crosses the event horizon."
] |
[
"For the economists: beyond ideology, is capitalism a sustainable economic policy?"
] |
[
false
] | null |
[
"is there a point at which capitalism will cease to be a viable economic policy?",
"Depends on your definition of \"viable\". I would say we passed that point many decades ago.",
"From a more charitable definition, it will happen once the cheap liquid fuel becomes no longer cheap enough, and once the environmental costs of production are actually taken into consideration by the rule of law."
] |
[
"It is not sustainable. You hit on precisely the right point - capitalism not only requires continual growth, but continual growth at constantly INCREASING rate. Any time this growth is not met, you get economic collapse. At best this results in a boom-bust cycle.",
"One attempt to provide a framework for a permanently sustainable society is Technocracy (and arguably the only one that has been thought up that does not require a degree of Luddism) (see also ",
"r/technocracy",
".)",
"M. King Hubbert (A geologist who worked for Shell oil and the man responsible for the idea of peak oil) wrote the ",
"Technocracy Study Guide",
" detailing the results of an extensive project (The Energy Survey of North America - undertaken by the Technical Alliance, which included Charles Steinmetz, Richard Tolman, Thorstein Veblen and others) explaining the failures and shortcomings of existing economic systems (including capitalism) as well as outlining a solution founded on scientific principles.",
"I wrote up an ",
"Intro to Technocracy",
" which summarizes the guide in which it is explained why capitalism must reach a state of failure if you're interested and want something shorter than the full study guide."
] |
[
"You're wrong.",
"Technocracy tends toward physics, and views \"left\" \"right\" and everything in between as outdated, obsolete thinking.",
"Socialism is still economically based on the price system, just as far right free market capitalism is. The price system ITSELF is fundamentally flawed. The socialist-capitalism model corrects SOME issues with free-market capitalism in goals similar to what technocracy would provide (universal health care etc.) but does so using very different means. ",
"Socialism still relies on generating income as money and taxing that, so you can still lose services or have an \"economic collapse\" in the event of a downturn, resulting - in extreme circumstances - in starvation and deprivation, despite the fact that society did not lose the ability to produce the food or other resources needed. Thus access is dependent on continued economic success, which is dependent on exponential growth.",
"In a technate on the other hand, services don't need to be denied due to lack of funds or profitability (since there is no money). Wealth exists in the form of only that which is actually of value - energy, materials, goods and services. If more of something is needed to provide medical care, it is produced. Production is geared toward the demands of society, rather than limited to what someone has already earned and is owed."
] |
[
"Why do very few high order derivatives not show up very often in equations of motion?"
] |
[
false
] |
I’ve seen a lot of equations of motion in terms of velocity and acceleration. But I’ve never seen ones where d x/dt for n > 2 show up or even the n-th integral of x with respect to t ever pop up. This even seems to happen in what I’ve read about quantum mechanics and relativity, (although I haven’t read much about relativity). Why would the laws of physics pretty much limit itself to only using distance, velocity, and acceleration when there’s an infinite amount of higher order derivatives that it could use?
|
[
"If higher time derivatives would appear anywhere in a fundamental equation it would almost certainly lead to a violation of energy and momentum conservation.",
"The acceleration is linked to a change in kinetic energy (the time derivative of it is m v a), the velocity is what determines the kinetic energy, and the position tells you something about potential energies. If a force could induce a third or higher derivative then the change in kinetic energy wouldn't be linked to a change in potential energy any more."
] |
[
"The Lagrangian for classical electrodynamics is not of the form \"kinetic energy minus potential energy\". There are terms that are velocity-dependent that mimic the role of a potential in the Lagrangian, but they are not actually potentials. A true potential would have the property that the change in kinetic energy of a particle along its trajectory is a difference in that potential.",
"Higher time derivatives don't really show up very often because Newton's second law is a second-order equation. So you should not expect third-order or higher time derivatives to appear in applications, unless that application specifically examines some property of those derivatives. (For example, if you want to find a trajectory that minimizes the maximum possible jerk, then, sure, you will consider a third-order time derivative. But the equations of motion that dictate the motion of the particle do not require anything to do with the jerk.)",
"The fact that Newton's second law is second-order is essentially what allows us to derive conservation of energy and momentum in general systems. So as ",
"/u/mfb-",
" said, higher-order time derivatives would not generally allow us to derive any sort of energy conservation. Conversely, if you accept energy conservation as a fundamental principle, then the equation \"dE/dt = 0\" (or m",
"/2 + U(",
") = const.) is really just the equation \"",
" · (m",
" - ",
") = ",
"\", which is just \"",
" = m",
"\", which is second-order in time.",
"Higher ",
" derivatives show up all over the place: general relativity, elastics, fluids, electrodynamics, etc. But that's because fundamental objects in these fields are higher-order tensors (rank 3 or higher), whose rank roughly corresponds to the order of spatial derivatives involved."
] |
[
"There you run into violation of conservation laws as well. You can introduce something like an effective potential in some cases but that doesn't have the same role."
] |
[
"Why do men tend to go bald in the typical horseshoe shaped pattern?"
] |
[
false
] | null |
[
"Hi, I see many posts have been deleted here so hopefully mine won't be. I'm currently a medical student and I did my senior thesis on male pattern baldness. Essentially, the medical science behind male pattern baldness isn't fully completed. We do know that there is an extremely strong link between the expression of ",
"DHT",
" on the scalp and places of balding. If a male has the genetic marker for male pattern baldness (which is almost always passed down through the mothers side) we begin to see DHT levels spike at the temples and the vertex. However due to biochemical differences, each male is different....the horseshoe pattern is just the type that most men experience but not all. Of course studies have also shown that men who don't have male pattern baldness but rather a receding or \"maturing\" hairline also have spikes of DHT in these areas. So there is definitely a strong linkage. ",
"To add, there are many pharmaceutical and herbal regiments known as DHT blockers which cater to a market for men wishing to keep their hair...however their effectiveness is debatable. ",
"Edit: grammar"
] |
[
"Higher levels of 5-alpha reductase are found in the frontal and vertex region of the scalp versus the back and sides. 5-alpha reductase converts testosterone to dihydrotestosterone (DHT), a hormone which causes miniaturization of hair follicles in (mostly genetically) susceptible individuals."
] |
[
"Here's something on the subject: ",
"http://www.ncbi.nlm.nih.gov/pubmed/8077349"
] |
[
"Why do free neutrons decay?"
] |
[
false
] |
[deleted]
|
[
"They don't decay in the nucleus because decaying in a nucleus would increase the binding energy of the nucleus more than the difference in energy between (a neutron) and (a proton, electron, and antineutrino), which means it is more energetically favorable to stay as a neutron than to decay inside the nucleus.",
"The reason why is because protons have electric charge and they repel eachother. That means additional energy is required to overcome the Coulomb potential between the repelling charges to keep them in a bound state. So, rather than decaying and adding more repulsion to the nucleus (which will require more energy in the bonds of the strong force to overcome that repulsion), staying as a neutron is favored since it doesn't require adding more energy."
] |
[
"Because the decay products (a proton, electron, and antineutrino) have less mass (and therefore energy) combined than the neutron did before it decayed."
] |
[
"A nucleus is unstable if the product of some reaction (like beta decay) has less mass than the initial state. The mass is determined by how the nucleus is structured. For stable nuclei (again just considering beta decay here), the potential nucleus from a neutron turning into a proton is higher in mass than the initial nucleus."
] |
[
"Are supposedly \"habitable\" exoplanets that have 5 times the mass of Earth really habitable?"
] |
[
false
] |
I just read a new article stating that a habitable exoplanet has been found. However, it states that it has 5 times the mass of Earth. Doesn't that mean that it will have 5 times as much gravity? It seems like that would make the planet inhabitable, having the much gravity. Am I wrong?
|
[
"Habitable usually means that the surface could support liquid water (assuming the atmosphere is right for that). In terms of mass and gravity, a planet 5 times the mass of Earth would actually probably have surface gravity closer to twice that of Earth, because the greater radius of the planet reduces the gravitational pull you feel."
] |
[
"Okay so, ignoring all the constants involved to simplify the math (justifiable), and assuming the exoplanet is the same density as earth (not necessarily justifiable, but it simplifies the comparison), start by considering the classical form of the gravitational interaction: ",
"F = (mass1 * mass2) / (distance between the masses)",
"So, yes, if you simply replace mass1 with 5 * mass1, you'll get 5 * F. But, remember that we decided that the exoplanet has the same density as the earth! So now, we have to look at how a planet's radius (which is effectively the distance used above, for an object on the planets surface, by ",
"Shell Theorem",
") changes given a change in mass but not density. Given that density is constant, a change in mass is proportional to volume, and a the volume of a sphere is proportional to the cube of its radius, so that:",
"(ratio of masses) = (ratio of radius)",
" This in turn can be substituted into the earlier equation, while holding mass2 constant (because the person is the same mass in both situations) to give:",
"(ratio of force) = (ratio of mass)/(ratio of radius)",
" = (ratio of mass) / (ratio of mass)",
" = (ratio of mass)",
" So, if our (ratio of mass) = 5, then (ratio of force) = 5",
" = 1.71. Since the force of gravity on the surface of the earth is 1g, the force of gravity on the surface of the exoplanet would be 1.71g.",
"Edit: formatting"
] |
[
"Keep in mind that the size of the planet has an effect on surface gravity. Just because it has 5 times the mass doesn't necessarily mean it has 5x the surface gravity. "
] |
[
"What makes a caterpillar become a moth or butterfly?"
] |
[
false
] | null |
[
"First, the caterpillar digests itself, releasing enzymes to dissolve all of its tissues. If you were to cut open a cocoon or chrysalis at just the right time, caterpillar soup would ooze out. But the contents of the pupa are not entirely an amorphous mess. Certain highly organized groups of cells known as imaginal discs survive the digestive process. Before hatching, when a caterpillar is still developing inside its egg, it grows an imaginal disc for each of the adult body parts it will need as a mature butterfly or moth—discs for its eyes, for its wings, its legs and so on. In some species, these imaginal discs remain dormant throughout the caterpillar's life; in other species, the discs begin to take the shape of adult body parts even before the caterpillar forms a chrysalis or cocoon. Some caterpillars walk around with tiny rudimentary wings tucked inside their bodies, though you would never know it by looking at them.",
"source"
] |
[
"A caterpillar doesn’t choose so to speak. A moth and a butterfly are two different species. However, both species go through a similar process of metamorphosis. This is where they cocoon and after a few days or so emerge as a butterfly, or a moth. But one can’t just become the other."
] |
[
"I never knew I wanted to know this, until now!",
"Thanks for the research!"
] |
[
"Why aren't there animals today that are as large as dinosaurs were?"
] |
[
false
] | null |
[
"A lot of today's animals are larger than dinosaurs. An African elephant is larger than the majority of the dinosaurs that ever lived.",
"Dinosaurs ",
" bigger for a number of reasons:"
] |
[
"Makes sense, thanks!"
] |
[
"Well, the ",
"largest animal ever to have existed",
" is still around today. Here are some size ",
"comparisons",
".",
"But, I'd say land animals aren't that big now because (a) it isn't advantageous to be that size in the current environment and/or (b) it just hasn't come up in all the random mutations that drive evolution. Also, the whole extinction of the large-sized dinosaurs thing probably has a lot to do with it."
] |
[
"Are there any downsides to camouflage?"
] |
[
false
] |
Animals that are cryptically colored can hide from predators. This seems too perfect. Is there any trade off that the prey may face?
|
[
"Camouflage that is ideally suited to one environment will stick out like a sore thumb in different areas and may end up reducing the effective range of that particular animal."
] |
[
"Mating.\nThis is like the biggest point.\nDon't get eaten, but still be seen by the girls :)",
"Since most animals don't have a opposable thumb, they have a hard time filling out their online-dating-profiles.",
"But seriously, that is the biggest problem, that the females are mostly attracted by coulerful males, but they get eaten quite fast, so it's a fine border."
] |
[
"Camouflage is considered a primary defense mechanism as opposed to a secondary defense mechanism (ex: when a lizard severs its tail to get away) or a tertiary mechanism (emetics, some sort of toxin). However, organisms can't afford to maximize all three of these types of defense mechanisms. An organism that is cryptic will typically not have any defense beyond being cryptic and if found they have nothing left in their arsenal. "
] |
[
"Because violet light is closer to UV and X-ray light than the other colors, is violet light at all more likely to give someone cancer?"
] |
[
false
] | null |
[
"The key to understanding the damage caused by photon radiation (light and electromagnetic radiation) is whether or not it is capable of creating ionization when it impacts another material. Ionization is when an electron is stripped from an atom, which causes it to become charged and reactive, and possible to break apart whatever molecule it's part of. The molecule of most concern is DNA. Our bodies are quite good a repairing or killing off cells that have mutated or broken DNA, but not perfect. Roll those dice too many times and your risk for a skin cancer increases.",
"Violet/blue (visible) light is not at a high enough energy level to ionize the elements that make up animal skin/tissue. UVA and UVB are."
] |
[
"Blue/violet light can cause some damage, particularly to the retina of the eye:",
"http://en.wikipedia.org/wiki/High-energy_visible_light#Blue-light_hazard",
"There are also some studies showing Mitochondrial DNA damage from blue light:",
"http://www.jbc.org/content/280/22/21061.full"
] |
[
"UV light isn't ionizing radiation either.",
"The process by which UV light causes cancer is not through ionization, but through chemical creations.",
"Ultraviolet light can cause burns to skin[8] and cataracts to the eyes.[8] Ultraviolet is classified into near, medium and far UV according to energy, where near and medium ultraviolet are technically non-ionizing, but where all UV wavelengths can cause photochemical reactions that to some extent mimic ionization (including DNA damage and carcinogenesis). UV radiation above 10 eV (wavelength shorter than 125 nm) is considered ionizing. However, the rest of the UV spectrum from 3.1 eV (400 nm) to 10 eV, although technically non-ionizing, can produce photochemical reactions that are damaging to molecules by means other than simple heat. Since these reactions are often very similar to those caused by ionizing radiation, often the entire UV spectrum is considered to be equivalent to ionization radiation in its interaction with many systems (including biological systems)."
] |
[
"what is karposa sarcoma when related to a person with aids? what percent of people survive?"
] |
[
false
] | null |
[
"Kaposi's sarcoma is a systemic disease that presents with a very specific appearance on the skin and mucus membranes of affected individuals. It is caused by a different virus than the HIV virus. The virus is not typically capable of creating symptoms in an individual who is not immuno-compromised, so this is why patients with AIDS are more likely to present it.",
"In terms of how many survive, most AIDS patients eventually die from an acquired infection."
] |
[
"The causative virus is human herpes virus 8. It can rarely cause Kaposi's in people without HIV, typically in people from Greece or Turkey, but the vast majority of cases are seen in HIV patients or organ transplant recipients. In many HIV patients it is an incidental finding of little importance that won't greatly impact their disease course. It often appears when they are initially diagnosed or when they have very advanced disease and may be a sign of how advanced their disease is, but the KS will not greatly impact them. However, in some patients it can be symptomatic and very fast growing. In these patients, the KS itself can adversely impact there survival, and it's generally this group of patients that will receive chemotherapy. "
] |
[
"All good additive information, I don't follow it a ton, but I see it from time to time."
] |
[
"Are all forces just interactions between fields?"
] |
[
false
] | null |
[
"I was trying to say that there always are different formulations of what is happenning. The key point is that in the gauge theory you have a particle which mediates the force, in the other case the change of spacetime results in the change of motion."
] |
[
"Field theory is just our way to describe what is happening around us. It certainly is not the only wayy to describe nature, but most of the time it is the easiest and has the most predictive power.An example for a description without (gauge) fields can be general relativity. You can either formulate everything in terms of geometry or you can describe it with a classical field theory lagrangian involving a Spin-2 field (both give the same result)"
] |
[
"In both cases it is a field theory, just not expressed in a lagrangian formalism."
] |
[
"Why do Newton's corrections to critical pressure and temperature exist for hydrogen and helium?"
] |
[
false
] |
In my chemical engineering book, we are told to adjust the critical pressure and temperature of hydrogen and helium by 8K and 8 atm when calculating reduced pressure and temperature. Why? Why are the actual values 8K and 8 atm lower? why not just define them as the corrected value?
|
[
"Someone else may have to correct me on this, but I believe this is related to the Joule-Thomson effect, where helium and hydrogen have anomalous behavior, being very much non-ideal gases.",
"I don't remember enough about the topic offhand to go into it in detail, but I'd read up on the ",
"Joule-Thomson Coefficient",
" for at least a hint as to why hydrogen and helium are unusual."
] |
[
"http://pubs.acs.org/doi/abs/10.1021/ie50523a054?journalCode=iechad",
"This should explain it. So the critical temperature and pressure are not incorrect. However when using critical temperature and pressure in reduced P & T calculations, the resulting relationship between compressibility factor and reduced pressure and temperature is inaccurate. However by using a correction factor of 8 atm and 8k you can still use your standard Tr = T/Tc with a compressibility chart with high accuracy.",
"Why this is I'm unsure, I'm only a 3rd year materials engineering student.",
"TLDR: Because Newton said so."
] |
[
"I don't think they're non ideal",
"This is wrong. Hydrogen and Helium can often by ",
" as ideal gasses, but they do not always behave as such. ",
"In the case of the Joule-Thomson effect, the individual gas particles are interacting with one another, so they are definitely ",
" behaving like an ideal gas. "
] |
[
"When stirring a liquid clockwise in a glass, how does the liquid move with the straw?"
] |
[
false
] |
[deleted]
|
[
"Friction and especially friction because water tend to pull itself once in motion (which is why it clumps into drops). Essentially what is happening is the friction between the straw and objects causes them to move, and the friction with the glass causes it to slow. If the centripetal force is high enough, the water will move (centripetal means circular) and pull water with it. \nTl;dr: frictional force from straw > frictional force of glass. Water pulls itself."
] |
[
"Water polarity has nothing to do here. It's all friction.",
"Do a quick wikipedia search on Dynamic Viscosity if you're interested :) there you'll find insight in the relationship between movement and friction in layers of liquids.",
"The concept is quite weird though. It's counter-intuitive, at first, to think that liquids' motion is determined somehow by friction (with itself and with whatever it's touching), but with a few examples it ends seeming almost obvious :)"
] |
[
"Due to molecular forces between the solid and the fluid, fluids almost always closely obey a 'no-slip' condition near a boundary, meaning that the fluid is moving at exactly the same velocity as the solid right at the interface. You can look at this video for a demonstration:",
"https://www.youtube.com/watch?v=cUTkqZeiMow",
"This is because there is an attraction between the solid and the fluid, and this will dominate the flow in a very small region near the boundary. The rest of the fluid is indirectly affected because each little bit of fluid has some tendency to follow the fluid touching it. This tendency of fluid is called \"viscosity\" and varies between fluids. For example, air has a relatively low viscosity, for water it is higher, for tree sap it is even higher, and for tar it is really high. Molecular attractions can affect viscosity, but it is present even in a gas with negligible attractive interactions, and arrises from the effect of collisions of molecules."
] |
[
"pregnancy/cancer test for males: why is checking for cancer by looking for levels of 'Human chorionic gonadotropin' not a regular test?"
] |
[
false
] |
somebody had a male friend who used a pregnancy test which became positive, the community told him to go to doctor to check for cancer, he has a small tumour on one testicle. Turns out that levels can come from cancer. Why is this not a standard tool for diagnostic medicine? (I hope this does not stray too close to giving out medical advice)
|
[
"Just typed this out elsewhere to kind of the same question:",
"This is completely true and yet it does not at all mean that this is a good way of detecting cancer in men.",
"In medicine, a test is not only graded on how sensitive it is (how likely you are to have cancer and for the test to come back positive) but also how specific it is (how likely you are not to have cancer, but still get a positive result)\nThe trouble is that in order for a screening test to be effective, it needs to be both specific and sensitive.\nIt also needs to be cost effective.\nSo in order to make a good screening test you need to ask yourself not only how good is the test, but also, even if we had a perfect test that never gets false positives or negatives (there is no such test), how much of an improvement can we expect in each patients prognosis (or for the cynic, how much money can we save on each patient's treatment).",
"I have not looked this up (So it is my opinion) but I suspect that incidental findings of the cancers (note two cancers do not occur in males and are already diagnosed with serum b-HCG levels in women who will already clinically appear pregnant) that you have mentioned will not drastically improve mortality/morbidity rates when compared with clinical presentations.",
"TL:DR - it is not the cost of the test, but the cost of the consequences of a bad test that matter."
] |
[
"Keeping in mind that HCG (and other tumor markers) can be used to aid in diagnosis and then be tested to obtain a baseline for subsequent monitoring of progression of disease, treatment response and for recurrence. So it isn't that the test is completely ignored.",
"But yes, for the most part tumor markers and screening have a questionable utility in cancer diagnosis. "
] |
[
"Imagine you have a test that has 100% sensitivity, but is only 75% specific. ",
"Now lets for argument's sake assume incidence rate of actual cancer is exactly 5%.",
"If you test 100 people. you will get 5 TRUE positives. and ~25 ",
" Positives. If you test 1000 people, you'll get 50 TRUE positives and 250 ",
" positives.",
"but you have no idea of knowing if a false positive is a false positive. so you move forward and treat those 250 False Positives as if they were true positives. Treatment for Cancer is Horrible. It's expensive and you sure as fuck don't want it unless you're 100% sure you need it. "
] |
[
"Would a child reach adult intelligence in time if their growth was halted?"
] |
[
false
] |
If a 3 year old child stayed the same physically for 30 years, would they reach the intelligence of an adult? How much is growth versus learning?
|
[
"The brain goes through a profound pruning stage during adolescence, and certain brain areas undergo different stages of maturation at different stages of childhood, adolescence, and young adulthood. If those developmental processes were halted, the child would definitely never have an 'adult' brain/mind; however, it's not easy to guess how 'smart' they could become anyway, because we don't have any examples to work from."
] |
[
"By definition, if a child stayed 3 years old for 30 years their brain would remain the same and therefore would be incapable of the kinds of things older children are normally able to do. If you're asking how much can a 3 year old learn, without the constraints of time, then there would only me marginal improvement over the time period. For example, individuals with down syndrome generally don't get more intelligent over their adult lifetime, but they can manage to gain knowledge that is commensurate with their abilities. "
] |
[
"What do you mean by \"stayed physically the same?\" If taken literally and fully down to the last atom, obviously not, because the structure of the brain would be exactly the same."
] |
[
"Why do we define the imaginary unit as the square root of -1 and not as another undefined quantity?"
] |
[
false
] |
What's so special about -1? Why don't we use ln(-1) or 1/0 or anything else?
|
[
"This is kind of like asking why we define \"2\" as the \"first integer after 1\" instead of \"cos(pi/3)\". The symbol \"2\" is just a picture that we assign to the first integer after 1 for convenience, if we assigned this picture to something else, then we'd have a different object. ",
"\"i\" is just a picture and we happen to a root of x",
"+1=0. If we were to assign this picture to something else, then we'd have a completely different object. It should also be noted that sqrt(-1) ",
" a defined quantity, it is defined to be a root of x",
"+1=0, just as sqrt(2) is defined to be a root of x",
"-2=0. All numbers are made up. The imaginary unit is just a real as 7 or sqrt(5) or anything else.",
"The reason why we're concerned with sqrt(-1) is because of polynomials. If we have a polynomial, then we can try and find an input that gives us zero. For instance, if I have the polynomial \"x+7\", then this is zero at x=-7. But to the ancient Greeks, this was a meaningless solution because negative numbers weren't a thing, someone had to come along and say: \"Look, we really need to be able to have solutions to x+7=0, I know that it doesn't exist in the traditional sense, but let's just say that this equation does have a solution and let's assign the picture \"-7\" to this newly invented number.\" The Pythagoreans discovered early on that they really needed a solution to the equation x",
"-2=0, but they showed that it didn't exist in their number system, so they invented a new number that was a solution to this equation and they assigned the picture \"sqrt(2)\" to it. We also need to be able to have numbers that are solutions to equations like 3x-5=0, which didn't exist in original number systems. So we invent a new number and declare that it is a solution to this equation and, whatever the hell it is, we assign to it the picture \"5/3\" so that we can keep track of it. This is how all fractions are invented: as solutions to equations.",
"Solutions to polynomials not only pop-up all the time, but when you invent solutions using them what you get in return is a nice number system that obeys all the rules that we enjoy and take for granted. Somewhere along the lines, people discovered that they really needed a solution to the equation x",
"+1=0, so they invented it and since it was invented using a polynomial, we get a nice number system in return. If we look for a solution to e",
"=-1 (ie log(-1)), then things don't naturally fall into place and we don't really get a well defined \"number\" or a good number system because it's not originating from a polynomial. (For instance, log(-1) can be equal to ipi, 3ipi, 5ipi etc, so it's not a well defined quantity). If you take any polynomial that does not have a solution, you can invent a solution to it, assign a picture to it, and include it into your number system and you'll get a new number system. In fact, the only way to get a new number system from an old one using solutions of some equation is by adding roots of polynomials. This is actually a statement with a proof.",
"But one very special thing about i=sqrt(-1) is that if we include this number into the real line, then we get the complex numbers and in the complex numbers every single polynomial has all of it's zeros. So because every polynomial has all of it's roots in the complex numbers, there's no polynomial that doesn't have a solution so there are no new numbers to invent, so the Complex Numbers are (in a way) a totally complete number system that cannot be extended in a natural way. It's full. This is what the Fundamental Theorem of Algebra says. Though, if you add i=sqrt(-1) only to the rational numbers, there are many more number systems we can make from this, it's important that we start with the reals."
] |
[
"Most highschools are only concerned with computing real roots of polynomials, getting into the real \"meat\" of algebra would fly over >99.99% of high schoolers heads"
] |
[
"As someone who has taught college algebra, if my students were remotely interested in learning why things worked, I'd love to talk about that with them in my office hours. In class, there's only a short amount of time to cover a lot of things.",
"I personally try to show the derivation of the quadratic formula, by doing examples where we complete the square for an equation like, say, 3x",
" + 5x + 2 = 0, alongside completing the square for the general form of the equation ax",
" + bx + c = 0. But I absolutely understand why many professors and teachers won't go over that -- between time pressure and the students lacking interest, it may be better to use the time on other things."
] |
[
"Can lithium float on tungsten hexafluoride?"
] |
[
false
] |
[deleted]
|
[
"No! At least not at atmospheric pressure... ",
"",
"The density of lithium is 534 g/L and the density of tungsten hexafluoride is 12.4 g/L. If you could compress a liter of WF6 to 41 atm or so, and it survived and behaved like an ideal gas and didn't undergo a phase change you might be able to."
] |
[
"You could answer your own question with a few seconds googling.",
"Lithium has a density of 534 grams per liter.",
"Tungsten hexaflouride has a density of 12.4 grams per liter as a gas.",
"Lithium is 40 and a bit times as dense. So...No."
] |
[
"Sorry haha, i was given false information."
] |
[
"During astronomical night, how much solar radiation reaches the ground?"
] |
[
false
] |
On a moonless clear night (Sun is below 18° below the horizon and Moon is too dim / too deep below the horizon to cause any effect on the dark night sky), how much solar radiation (including IR, visible and UV) still reaches the ground?
|
[
"Almost none. The main causes for ",
" (rather than starlight) to reach the ground in true nighttime would be reflection off planets -- especially Venus and Jupiter -- and the zodiacal light, which is sunlight reflecting off dust grains in the solar system.",
"If I'm doing the math right, the largest contribution is ",
"zodiacal light",
", whose total whole-sky brightness is a bit brighter than Venus and 250 million times fainter than the Sun."
] |
[
"Is it really solar radiation if there’s absorption and re-emission?"
] |
[
"Don't neglect airglow from upper atmospheric oxygen & nitrogen molecules recombining from nitrous oxide NO back to O² & N² following a full day of absorbing solar UV"
] |
[
"How do cells in the body become determined and organized correctly?"
] |
[
false
] |
Apologies if this has been asked before, I searched here and at sciencefaqs and nothing popped up. I'm having trouble understanding the nature of cell determination in the body. My understanding of this is from high school biology so it's patchy at best, but from a single undetermined cell develops a set of different cells. How does the body organise cells in the correct areas, why doesn't a heart tissue cell grow in the liver or on the skin for example? Also, what stops skin cells from spreading into other areas. When the fetus is developing when does cell organisation begin? Is it gradual or instantaneous? Sorry if this is obvious or poorly worded.
|
[
"http://www.reddit.com/r/askscience/comments/g7p8i/how_do_cells_know_their_location_in_the_body/",
"I liked this answer from user mamaBiskothu",
"Imagine a bunch of kids playing some role-playing game. At least in my country the way it goes is that we just kinda decide who's going to be who, and we start the game: Say I will tell \"I'll be a farmer, and you be a peasant that works in the field\" and another is told to be the feudal lord, while a girl is told to be the farmer's house-wife (my country is known to have very sexist cultures).\nSo then we start the game, and everybody goes about with their assigned roles. Everybody kinda knows what almost all these roles entitle to them as duties, should they get assigned such roles. A farmer goes to work, a farmer's wife will cook food for him at home (ahem). When we play tomorrow, I could be assigned the feudal lord and I will know what I should do for the same. All our brains know from past experiences what they should do for any normally given roles.",
"That probably summarizes also how our body's cells coordinate with each other during development. Every cell has recorded in its genome the program to follow if it is specified to be any cell it wants. All it needs are the exact cues. How are the programs structured? as highly intricate patterns of gene expression that results in a plethora of inter-connecting gene-interactions which will in-turn give out various phenotypic outcomes (extending dendrites and an axon if you are a neuron for eg). So if you take a single cell out and provide it the exact cues (knowing all that we can know about its genome and working), we can in theory make it differentiate into any of the 100 trillion cells in your body. So in essence and in a very simplistic sense, a cell's location in the body is fully found by the cues it gets.",
"What are these cues and where do they come from? Cues are mostly protein or hormone signals that are either released by other cells, or are presented on the surface of neighboring cells. But it all boils down to the same way the kids determined within each other on who will become what. Obviously some kid started the assignments, and sometimes there are kids who are dominant and will always start the assignments, while othertimes all the kids are equally timid and one kid will just randomly man-up and suggest that he be the farmer. Both concepts have been found to be occuring in our cells too, for these patterning events.",
"If you imagine this game in a more massive scale involving hundreds of kids, then its a chain reaction: one kid can say, you be a farmer, and this kid can say to everyone next to him to all be farmers! And then all these farmers can then yell, \"whoever hears us will now be a peasant, and pairs of people can choose between them who will be the husband and who will be wife. Amen.\" And then it would be settled. They effectively drew a circle around themselves that specified all the peasants for that game (we are assuming a completely cooperative bunch of 100 kids). They also instructed these peasant families to decide between themselves who will be husband and who will be wife.",
"Now imagine that kind of assigning program getting executed from the moment of fertilization for many years, only maybe a million times more complicated. For example, Cue A could be a diffusing signal from a distant cell, and could have different effects depending on the concentration of this signal, and the enzymatic properties of this signal would mean that there will be a cut-off point distance from the main signal cell, away from which you have no effect.",
"Imagine such a Cue A emanating from the root of your budding arm, and its cut-off distance is 12 cm or so (which is somewhat determined by the variant of the Cue A gene, lets assume). The cells at the tip of the \"budding hand\" would already have gotten a plethora of cues that have kind of instructed them that they need to divide as long as they get Cue A. So these cells will divide till Cue A signal concentration drops off below the treshold, effectively making a crude arm thats 12 cm long from the signal-sending cell (which itself would've been instructed to send Cue A because of the program started by the cues it received a moment before).\nOther cues within these divided cells will now start to kick in, and these cells will literally \"organize themselves\" in a similar way, using similar mechanisms to form a fully patterned hand.\n (Entertainment: ",
"http://www.youtube.com/watch?v=dy9QeosTh7w&t=1m40s",
")",
"Similar combinations of cues and their timings decide the patterning of other parts of your body; we do not know the exact cue patterns that determine all these various patterning mechanisms, but we know the different types of cues that happen and the most important cue genes that are involved in these process.",
"Needless to say, these genes are important in a lot of things in our body, including cancers (many of these cue genes are involved in cell division control). They are also the ones that even with small variation cause gross changes in one's body (like the extra finger) and it is suspected that a sum of multiple small variations in these genes (which is basically modifying kinetics of various enzymatic signal reactions) that determine our physical characteristics like height, body sizes, etc.",
"edit : formatting"
] |
[
"Thanks for this! I read through the whole thread and that was the exemplary answer for me as well. It's really fascinating."
] |
[
"I will leave it to someone more well versed in developmental biology (it was never my strong point) to attempt a succinct answer, but in the mean time I think reading up on Hox genes is what you're going to want to do:",
"http://en.wikipedia.org/wiki/Hox_genes",
"http://www.nature.com/scitable/topicpage/hox-genes-in-development-the-hox-code-41402"
] |
[
"With all the advantages Solar Sails have over Fuel, why aren’t they being utilized more?"
] |
[
false
] | null |
[
"Deploying a piece of foil a few tens of microns thick spanning kilometers while in 0g is not easy. Even deploying cables is hard. I don't think anything longer than a few tens of meters have been deployed in space (",
", see comment below).",
"They are also not that interesting when you are in Earth orbit because they are too low thrust when deep into a gravity well. And there are not that many interplanetary missions. Those missions also usually have funding for scientific studies and people are reluctant to put their mission in danger with a high risk new tech."
] |
[
"Whats not the same? All I commented on was the statement:",
"I don't think anything longer than a few tens of meters have been deployed in space",
"We have. The shuttle deployed a cable 20km long with a satellite on the end of it.",
"The reason for the deployment isn't relevant to the length."
] |
[
"Ah, i missed the part about not even deploying cables in space. I thought we were talking about solar sails, and read your link and was confused. I'm sorry."
] |
[
"Would running with or against the rotation of an artificial gravity ring in space significantly change the effect it had on you?"
] |
[
false
] |
If this was the case could you completely negate the affect of gravity by sprinting against the rotation resulting in the situation where you were floating in place as the ring was rotating without you.
|
[
"Yes, you can change the effects of the \"effective gravity\" force by running with/against the rotation of the ring. Whether or not it's a significant effect depends on the ratio of your running speed to the linear speed of rotation of the ring. If the rotation of the ring is fast compared to your running speed, you won't notice much change.",
"Also since we're talking about somebody moving in the co-rotating frame, I should at least mention that the ",
"Coriolis force",
" may come into play."
] |
[
"Astronauts running around the \"ring\" in Skylab. The station is not spinning.",
"https://www.youtube.com/watch?v=S_p7LiyOUx0"
] |
[
"Also, astronauts demonstrating running around the inside of a circular portion of the space station. Even though the station was in zero-g, they were able to generate enough centripetal force to get the traction needed."
] |
[
"Are we the only animal to have deciduous (baby) teeth, and what is their function?"
] |
[
false
] |
[deleted]
|
[
"No, all mammals have deciduous teeth. ",
"Pic",
". Except for elephants and manatees, who replace teeth often, mammals are \"diphyodont\"- have 2 sets of teeth. Other species have several sets of teeth (fish, reptiles) and are called \"polyphyodont\".",
"The function? Teeth don't really grow in size and an infant's jaws are not big enough to fit full-sized teeth. Baby teeth serve as a template for the adult teeth as the jaw grows and allows us to be able to eat in the interim between weaning and the stage of growth that allows the jaw to be big enough for full-size teeth.",
"EDIT: added info."
] |
[
"Not sure about the function, but I can confirm dogs and cats have them too."
] |
[
"Good post...Just some more details to follow up:",
"The basic tooth plan for other vertebrates is a bunch of simple teeth constantly falling out and being replaced. Mammals have complexly shaped teeth which have to fit together closely to work right. In order for this precision fit to happen, teeth can't be constantly getting replaced. So we get one set as youngsters with small jaws, and a second set once we have grown larger.",
"Elephants (I'm not sure about manatees) have the same number of molars as seen in the basic mammal plan, they just pop them out one at a time in conveyor-belt fashion. "
] |
[
"Why doesn’t anybody want to find more stable isotopes of existing elements?"
] |
[
false
] |
With all the talk about discovering new elements, other elements are just left behind. Take astatine, for example. While it theoretically has a stable isotope, it’s still heavier than any isotope discovered or created. It’ll surely be easier to add more neutrons to astatine than try to make element 119 or 120. With the many, possibly unique properties of the those near the end of the periodic table, it seems like a no-brainer to try and look into those as well as discovering new ones.
|
[
"We are very interested in discovering new elements, and new isotopes of already-discovered elements. And people are actively working on doing this in labs all over the world, every day.",
"However, it's unlikely that there are any yet undiscovered nuclides which will be stable."
] |
[
"Take astatine, for example. While it theoretically has a stable isotope",
"Where did you get that from?",
"We are discovering new isotopes of known elements frequently, they just don't get any attention in the popular press. For elements up to uranium we know all the isotopes near the stable region already. The newly discovered isotopes are all far away from it and they are all short-living. It is not expected that one of them is stable.",
"Here is a graph",
". Black = stable, any other color = discovered and unstable"
] |
[
"Bismuth-209 is marked as stable in the graph, but it decays by alpha emission with a half-life of 20.1 exayears. I'm very angry about this oversight.",
"Edit: The half-life was even longer than I remembered!"
] |
[
"What is Quantum Computer? How do they work? What are the differences between that at the computer I'm asking this question from?"
] |
[
false
] |
And anything else interesting about the field. Thanks in advance! (Just noticed the small derp in my first question and the larger derp in my last. I'm a tired man.)
|
[
"A quantum computer uses the key concepts of quantum mechanics—superposition and entanglement—to solve some problems more efficiently than a classical computer.",
"At the heart of it, you have quantum (as opposed to classical) bits, which can be realized in many different physical architectures, such as photons, trapped ions, neutral atoms, spins in solid states and superconducting circuits. The difference between these quantum bits and the classical bits in your computer is that they don't just assume two discrete logical states—'0' or '1'—but arbitrary superpositions of those (e.g. a qubit can simultaneously be in a state \"'0' and '1'\"). If you have many qubits in collective superpositions you get entanglement.",
"These quantum bits are the quantum information carriers and they have to interact with each other to realize quantum logic gates and eventually an algorithm. The best known quantum algorithm is Shor's; it factors large numbers into its constituents in polynomial time, while the best known classical algorithm scales exponentially.",
"We haven't got many interesting algorithms yet where quantum computers will really shine, but one area we're really interested in is to use them to simulate other quantum systems. Say you've got a quantum systems that's hard to understand and even harder to control, like a big molecule, or even a protein. So instead of trying to use that thing directly, we can simulate it's Hamiltonian (that best describes the system according to our understanding) on a quantum computer which is easier to set up. These simulations than help us figure out how the system behaves in reality.",
"EDIT, you may also be interested in the technological status quo: single photons have achieved up to 8-qubit entanglement, but at terrible quality and really low rates. They do not currently constitute a very scalable approach to quantum computing. ",
"Trapped ions are doing much better: up to 14 entangled qubits have been realized, and they have done nice quantum simulations with 6 and more qubits. The quality is quite good and their immediate future in terms of scaling this to higher numbers is looking quite good. ",
"Superconducting circuits are catching up very quickly, they're currently playing with three-qubit gates, teleportation, error correction and so on—the usual first steps which are necessary to demonstrate the level of coherent quantum control you need for quantum computation. ",
"Solid-state qubits have long looked too hard to realize but all of a sudden they're also addressing and reading out single qubits, and the first entangling gates are in the pipeline. Once they've got that sorted, they could overtake the other technologies really quickly because their technology is based on a multi-billion dollar device fabrication industry.",
"Unfortunately though, ",
" of these technologies will have a really hard time to move beyond a few tens of qubits. It's not even quantum coherence or other fundamental physics that's holding us back, it's things as profane as you can't get enough lasers into a single room to set up, manipulate, and read out 20000 ions. Or, alternatively, a few tens of thousands of superconducting qubits would need a whole power plant to stay cool."
] |
[
"D-Wave is using superconducting circuits using hundreds of qbits to do quantum annealing, which isn't general quantum computation but it is still pretty impressive and useful.",
"They can help with stuff like pattern recognition, protein folding, traveling salesman problems and the like and are quickly scaling up the qbits."
] |
[
" explains how they work very well. I have done several research papers on the topic, and the main difference that a user would notice is the speed. A quantum computer is not a linear speed increase, it is exponential. For example, since every qubit exists in both states simultaneously, the equivalent amount of binary bits is 2",
" where n is the number of qubits. Three qubits is equivalent to 8 binary bits. This is especially attractive for security applications, since theoretically the quantum computer is 2",
" /n times faster (it does not come out to this practically). Still, it would absolutely destroy current encryption algorithms and leave every computer system in the world vulnerable. Even with only tens of qubits, it is still a huge revolution. Only 50 qubits is the equivalent of ",
". 90 qubits is 128 yottabytes. "
] |
[
"If alcohol is so deadly to bacteria, why is it safe for humans to come into contact with?"
] |
[
false
] |
I have been told alcohol is such a effective disinfectant because it is too powerful for things like antibiotic resistance to apply. If it is do deadly to bacteria, why can I pour rubbing alcohol on my arm and not observe any harmful effects (not even minor skin irritation)?
|
[
"Alcohol (whether isopropanol or ethanol) will kill almost any cell it comes in contact with. It does this by dissolving the cell membranes which are made of lipids that are not soluble in water, but very soluble in alcohols. It is exactly the same for bacteria and for our cells if the cells are exposed. The factor that protects your skin is that it contains a thick layer of inert/dead cells and highly cross-linked extra-cellular proteins. This makes a layer that is quite resistant to alcohols (and almost everything else), at least for short-term exposure."
] |
[
"Part of the issue missing from the other responses thus far is what percentage alcohol are we talking about? If I'm working in lab, 70% ethanol is generally considered sufficient to decontaminate a surface. Many hand sanitizers have less than that. And much of what you drink is also less than that. So while your average bourbon ",
" kill some bacteria, it won't do it as efficiently or as well as a higher percentage of alcohol."
] |
[
"Actually, alcohol is a common irritant in many acne medications. Also, aftershave with alcohol tends to dry the skin out and cause irritation. I am not an expert in cellular biology, but these seem to indicate that, in fact, alcohol does have harmful effects on human skin."
] |
[
"Why are there holes in the ozone layer, as opposed to the ozone redistributing itself around the layer to be equally thin everywhere?"
] |
[
false
] | null |
[
"This is due to a polar vortex, a rotating low pressure zone above both the north and south poles, that minimizes the air exchange above these regions. The vortex limits the inflow of ozone to the depleted regions. The polar vortex above Antarctica is typically stronger than the one above the arctic, hence the ozone hole over Antarctica is generally more severe than the one over the arctic. "
] |
[
"To be specific, it is because the chemistry that depletes the ozone occurs on the surfaces of tiny ice crystals that only form in high enough concentrations at the altitude of the ozone layer during the late winter and early spring at the center of the polar vortex. In areas outside the center of the vortex the ice crystal are dispersed by the winds of the vortex, but in the center of the gyre, they tend to concentrate and form clouds. The ice crystals serve as a base on which ",
" Chlorofluorocarbon compounds condense and begin acting as a catalyst for the ozone depletion reaction. In effect, it forms a giant catalytic converter hundreds of miles wide, chewing up all the ozone that comes near it. "
] |
[
"Looks like the above was not completely accurate. The chemicals condense on the polar ice clouds, but are not active until they are activate by the return of sunlight in the late winter/early spring. The clouds act as traps, gathering the chemicals into high concentrations. Then, when the sun strikes the cloud, they are all photochemically activated and released into the atmosphere in a large pulse that catalytically reacts with ozone, although at that point, no longer on the surface of the ice crystals "
] |
[
"Does a volcano erupting reduce the pressure in other nearby volcanos, or is each magma pocket independent?"
] |
[
false
] | null |
[
"The majority of volcanoes have independent magma chambers. Usually when magma finds it's way to the surface it's only going to form one volcano, not two.",
"If you've got linked magma chambers then you get what's called a volcano complex. Or a complex volcano. It's kindof a matter of if you want to think of it as multiple volcanoes sharing a magma chamber, or a single volcano with multiple vents that are far apart. In either case this should be what you're interested in.",
"They're relatively uncommon, but quite a few exist. Usually what happens is that a large stratovolcano collapses into a caldera and with the center blocked new vents open up at multiple locations around the rim. ",
"In any case there's a really interesting documented event of what you mentioned happening in 1912 when Novarupta erupted, and Mount Katmai, 6 miles away collapsed when the magna underneath it shifted over to Novarupta. Was the largest eruption in the 20th century. There's still research going on today figuring out exactly what happened."
] |
[
"Thank you for taking the time to answer. I was curious if the magma was a planet-wide pressure system, and if a bit of that pressure was released, it could lower the chance of a volcano erupting on the other side of the world, or at least other volcanos on the fault line (forgive me if that sounds dumb.) It seems even in the volcano complex, the impact is very localized. Going to research Novarupta now!"
] |
[
"Reduce may not be the correct word but if you say alter, you’re more on the right track. Take the case of Iceland where Eyjafjallajökull and nearby Katla are independent from each other but have a tendency to erupt within a geologically short time of each other. Katla’s magma chamber is still connected to the core and additional magma is available to keep up the pressure, so the relationship is not straight forward and science hasn’t quite figured out why one erupts so soon after the other."
] |
[
"Synthesizing an Acid Halide from an Alcohol"
] |
[
false
] |
I took an Organic Chemistry midterm today, and did some really funky stuff on a multi-step synthesis problem. I got myself in a situation where in one of the steps I needed to create an acid halide/Ester (Cl-C=O-Oet) from an alcohol (I am guessing methanol, but any alcohol under 4 carbons would work) as one of the steps. Is this even possible???? I missed these points, but I have the feeling that it is possible to do so I am trying to figure out how I can defend myself and get back my A in the class...so far no luck.
|
[
"You can make ethyl chloroformate. May I ask how you backed yourself into this corner?"
] |
[
"Well, if you wanted to start with ethanol, we need to oxidize it a lot to get there. First we could oxidize to the aldehyde using either PCC or a Swern oxidation. Then you could do a Baeyer-Villager oxidation to make the formate. Then KMnO4 oxidation to get the acid, followed by chloride substitution with thionyl chloride would get ethyl chloroformate.",
"But, a simple aldol might work better."
] |
[
"Why not just react ethanol with phosgene/triphosgene to give you ethyl chloroformate in a single step?"
] |
[
"Do non-humans exhibit signs of autism/autism spectrum disorders?"
] |
[
false
] |
[deleted]
|
[
"I can't answer your question in full. But what I do know is that we regularly create ASD type symptoms in animals for testing/research purposes. So broadly, yes, artificially altered animals can exhibit signs of autism. If you are asking if it is observed to occur naturally, then I am unsure. As a neurologist I can see no reason why not. "
] |
[
"Building off of this, we use animal models that share certain behavioral traits with ASD (altered sociability, stereotypic behaviors, altered communication). But no, the animals aren't said to have autism, as that's anthropomorphizing, but we'll refer to them as a model of autism due to the behavioral phenotype and usually genetic or molecular markers that are related to the human condition. Also, no model of autism or Rett Syndrome perfectly recapitulates the human condition so we use these models to study how the changes in Mecp2 (altered in Rett Syndrome) expression impacts things like neurodevelopment, brain function, behavior, and contribution to sex differences seen in these disorders."
] |
[
"This is a good question and well-worded. Had you asked \"do animals get autism\" there would be no way to answer because an autism diagnosis must be based on human frame of reference. That seems obvious, but it's key to recognize there can never be an autistic animal. As soon as the symptoms leave human context, it's not really autism.",
"This",
" is a good reference from one of the leaders in the field of autism research.",
"there are many biological steps between genes and behavioral outputs; moreover, the social and environmental contexts that shaped human behavior compared with that of rodents have been highly divergent over the course of evolutionary time. Thus, behaviors resulting from mutations introduced into the mouse genome might best be construed as no more than potentially useful readouts of underlying neural processes. Drugs act on molecular targets, not directly on behaviors or other symptoms. Thus, predictive validity for therapies requires good conservation of the molecular mechanism by which activation or inhibition of a molecular target affects a well-chosen readout that correlates strongly with a human symptom",
"The hallmarks of autism are 1) social disorder and 2) stereotyped behavior. Obviously this super broad and you could fit just about any average user into the autism box with this diagnosis. It's up to the doctor to make the call about whether the behavior is pathological. ",
"It's even more difficult with animals in nature because we can't really monitor their social interactions the same way as with people. Sure, with monkeys we can measure eye contact or watch for things like over-grooming, but we could never know if these are because of \"autism\" or he/she just doesn't like the perfume you're wearing and it makes him/her itchy. ",
"Studying autism in research is a different story. We can make animals with a genetic mutation that copies a mutation found in human autistic patients. If we see a sudden change in animal behavior because if this mutation, we can be pretty sure there is some overlapping biology being screwed up common between the patient and the animal. ",
"TLDR: Yes",
"Edit: while writing this ",
"u/kaijuawho",
" expanded nicely with some specifics ",
"Edit2: fixed link and some phrasing "
] |
[
"Is there an explanation as to why I've dreamt the same dream, with me dying in that dream, 3 times within the past 3 years?"
] |
[
false
] | null |
[
"Hi ",
" thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"We can't speculate about this here."
] |
[
"Where should I post this? And what does it mean to flair a post?"
] |
[
"In the event of a large scale nuclear war, involving two super powers like the U.S. and Russia, how long would it take for survivors in underground shelters to be able to repopulate the earth?"
] |
[
false
] |
Basically, I'm interested in how long it would take for the Earth to be habitable to survivors again. I would really appreciate any information you guys can have!
|
[
"I think you're over estimating the impacts of nuclear fallout. Even if the whole world was targeted, there would be lots of survivors."
] |
[
"I do not know why you are being downvoted. Life on earth has survived SIX major extinction already and our nukes now are CLEANER then the ones we dropped on japan"
] |
[
"Your figure is dramatically exaggerated. There was nowhere near 1,000,000 deaths from the Chernobyl accident."
] |
[
"Would the DNA taken from my red beard hairs be the same as that from my majority black beard hairs? If so, what makes the red hair red?"
] |
[
false
] |
My beard consists of 4 or 5 red beard hairs. What is the science behind those hairs?
|
[
"Gene expression. Just like the DNA sequence in your nerve cells is identical to the DNA sequence in your skin cells, the thing that differs is gene expression. ",
"All the steps of protein synthesis can be regulated to alter gene expression and even rate of protein breakdown can be regulated to alter phenotype. Ask if you want examples or further explanations."
] |
[
"That's so interesting. I've never thought of it like that. I guess my question then is at what level is this change occurring?",
"I don't know very much about biology, so I apologize for asking really basic/dumb questions in advance. The difference between cells becoming skin or hair probably takes place at an early stage right?",
"Skin becoming my regular skin or a birth mark, and hair becoming its usual black or the odd red - is that a different stage of protein synthesis?"
] |
[
"The DNA is the instructions on what every kind of cell in the body does. When cells are created, only a small subset of these instructions are actually used by the cell. Small proteins determine which bits get used"
] |
[
"Homosexuality and genetics."
] |
[
false
] | null |
[
"This question has been addressed several times, please use the search function."
] |
[
"Thank you. I found a lot about the genetic side. Has there been anything on the behavioral side? This post is stemming from a discussion when we realized all of our gay friends have rough childhoods (various abuse, absentee fathers). Is there any research correlating abuse to homosexual tendencies? "
] |
[
"It's out of my field, but there may have been comments related to it in the history of /AskScience, maybe search some more, if you can't find anything, feel free to post a question, and mention that you did a search, it will help us mods approve the question."
] |
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