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[
"Do robotic prosthetic limbs work on a two-way or one-way communication system with the brain?"
] |
[
false
] |
[deleted]
|
[
"The journal Nature has this (free) and relatively jargon-free ",
"feature on neuroprosthetics",
".",
"As you'll read in that link, the current neuroprosthetics are all one-way. They read what is happening from the brain to decode what hand movements to make. There is no feedback from the prosthetic hand itself to the person, but it is something that is being worked on."
] |
[
"I will add that visual feedback remains, meaning that individuals can see, for example, if they are applying too much or too little pressure to pick up a water bottle"
] |
[
"I will add that visual feedback remains, meaning that individuals can see, for example, if they are applying too much or too little pressure to pick up a water bottle"
] |
[
"Is there a natural bias in favor of even numbers in mathematics?"
] |
[
false
] |
For example: An odd number multiplied by an odd number equals an odd number. An even number multiplied by an even number equals an even number. But an odd number multiplied by an even number equals an even number. Is this just a coincidence, an strange quirk in math, some sign that the universe chooses order over chaos, or what?
|
[
"An odd number divided by an odd number (assuming the numbers are divisible) gives an odd number. An even number divided by an even number can equal an odd number. ",
"Multiplication of natural numbers produces more even than uneven numbers. However, this is not a general result or trend in mathematics.",
"Edit: Also Mathematics is a construct based on a set of axioms (things you assume are true) and oddities in that construct do not necessarily have implications on the nature of the universe."
] |
[
"Remember that a number is \"even\" if it has at least one 2 in its prime factorization. Multiplying two integers together just combines their factors and never destroys any, so any product of a multiple of 2 with another integer must be a multiple of 2. In the same way, any product of a multiple of 17 with another integer must be a multiple of 17. It's not that the universe is \"biased\" towards multiples of 17 or of 2 or of anything else; it's just the way multiplication is defined."
] |
[
"You can apply maths for many useful purposes such as Physics or Informatics.",
"However, properties inherent in Maths built on a specific set of axioms do not reflect properties of the universe.",
"You can only use math to make predictions about the universe after linking formulas to properties.",
"edit: I am not denying the legitimacy of maths. I am only stating that you need to make certain assumptions (which then cannot be proven) to begin with. 1+1=2 is a perfect example of such an assumption (though you would need to define properties of 2)."
] |
[
"Can we make pairwise genome-wide association studies? Have any been done?"
] |
[
false
] |
I'm pretty sure that some genes work best in synergy with each other, and it would be interesting to see if we could do that on the IQ phenotype - as described at
|
[
"Tes, that stuff is done in GWAS. But, for GWAS it's too hard to say that there are interactions. We can note how a SNP of one gene marker and a SNP of another gene marker ",
" contribute to a phenotype but this only tells us about the alleles.",
"To really know if they are working together you need expression data, like mRNA, miRNA and methylation."
] |
[
"Can you provide more detail in your question regarding pairwise? Do you replicability across GWAS or literally pairwise comparisons of the SNPs between people (basically sequence alignment...)?",
"Are you curious about the work in GWAS to include more phenotypes or other markers?",
"Something else?"
] |
[
"Like - basically - interactions between genes.",
"It could be possible that there's little effect between two individual genes - say - DRD2 and MAO genes, but that they have a significant effect when expressed together (if they were expressed as the DRD2:MAO term)"
] |
[
"How can asymptomatic cases cause long-COVID? Doesn't that stem from the damage caused by the initial symptoms?"
] |
[
false
] | null |
[
"Typically, most symptoms aren't caused by the actual infection but the immune response to it afterwards.",
"Someone could feasibly have a weakened immune system and have little of the normal symptoms of infection but still have a pretty widespread infection of the body."
] |
[
"There are both good and bad sides to a weakened immune response.",
"Sometimes, when people have an overactive immune response the vast majority of the damage to the body is actually caused by the inflammation and controlled cell death of the immune response. On the other hand, having a weakened immune system can slow how fast the body reacts to an infection giving it more time to spread and grow within the body. This means that when the body do finally have an immune response it will be even larger and affect more of the body.",
"When this happens sometime doctor will prescribe immuno-suppressants like corticosteroids to temporarily suppress the immune response.",
"The ideal however is to have the fastest immune response as possible to control the infection before the viral load of the body gets too large. The faster the immune system responds to a potential infection the more the collateral damage to the body is controlled.",
"This is why vaccination is so important for novel viruses that the body hasn't ever been exposed to before. Because these kinds of viruses take the longest for the immune system to react to since they can often go unnoticed at first by the immune system."
] |
[
"There are both good and bad sides to a weakened immune response.",
"Sometimes, when people have an overactive immune response the vast majority of the damage to the body is actually caused by the inflammation and controlled cell death of the immune response. On the other hand, having a weakened immune system can slow how fast the body reacts to an infection giving it more time to spread and grow within the body. This means that when the body do finally have an immune response it will be even larger and affect more of the body.",
"When this happens sometime doctor will prescribe immuno-suppressants like corticosteroids to temporarily suppress the immune response.",
"The ideal however is to have the fastest immune response as possible to control the infection before the viral load of the body gets too large. The faster the immune system responds to a potential infection the more the collateral damage to the body is controlled.",
"This is why vaccination is so important for novel viruses that the body hasn't ever been exposed to before. Because these kinds of viruses take the longest for the immune system to react to since they can often go unnoticed at first by the immune system."
] |
[
"9/11 - One question no one ever seemed to ask..."
] |
[
false
] | null |
[
"There's not really a solution for that. Maybe if they could all get to the roof and rescue helicopters got to them. Other than that I don't believe there is a realistic way to rescue people."
] |
[
"Actually there are several patents for systems out there (google escape elevator systems) These tend to have a high economic cost so they would not be plausible for use in normal high rises."
] |
[
"Yeah... let's just say we know some crazy mofo who works in Canary Wharf that keeps base jumping equipment in their office..."
] |
[
"Why is gravity not a violation of the second law of thermodynamics?"
] |
[
false
] |
Note: I come from a chemistry background and this is an astronomy question, so I may be off on some of my assumptions. This is a question I've struggled with for a long time and haven't been able to get a clear answer from my previous professors: The second law of thermodynamics states that the total entropy of a system will increase (or at least not decrease) over time. From a chemistry perspective this was exemplified by molecules in an isolated system being organized in the most diffuse manner possible. So if I had 10 particles bouncing around the inside of a box, then doubled the size of the box, over time the particles would on average be farther apart from one another. This was given as one example of the disorder increasing. However, the matter of the universe tends to congregate into comets, asteroids, planets, stars, galaxies, local groups, etc. This is, of course, because matter has mass, and gravity causes mass to be attracted to mass. So, over time the matter of the universe is collecting into relatively small areas. To me, this sounds like a decrease in the entropy of the universe. If entropy was increasing I would imagine that collections of matter would be disintegrating into the void of space to produce the most uniform and diffuse distribution of matter possible. Why not? Why isn't gravity a violation of the second law of thermodynamics? EDIT: Thank you all for your input. It seems that the incorrect assumption is that positional entropy is representative of total entropy, which actually includes other factors like the relative heat given off.
|
[
"Something similar was asked about attracting magnets recently. The answer is the same: When the things come together due to an attracting force, the potential energy that's equivalent to that force has to go ",
" (First law of thermo!). ",
"If two asteroids attract each other, they'll accelerate towards each other, and eventually collide. Where does the kinetic energy go? It becomes heat. And ",
" means entropy. So while the entropy is lower strictly in terms of how stuff is dispersed, the ",
" entropy is higher because of the change in temperature."
] |
[
"How about some ",
"Entropic Gravity",
"?",
"Here's an interesting paper entitled: ",
"Can Gravity Decrease Entropy?",
" -",
"In the calculation I just did, it's a bit hard to see exactly why the entropy of the gas cloud goes down as it shrinks. As the gas cloud shrinks, each atom roams around a smaller region in position space. That tends to ",
" the entropy. But as the gas cloud shrinks, it gets hot - so each atom roams around a bigger region in momentum space. That tends to ",
" the entropy. "
] |
[
"GUAH, ANOTHER CHEMICAL ENGINEER. ",
"/ontopic/\nYeah, you'd initially think that gravity would essentially reverse entropy, but the heat generated by the release of the potential energy when the objects come together offsets that and keeps the second law of thermodynamics alive :P"
] |
[
"Which country spends more? A cold one keeping warm, or a warm one cooling down?"
] |
[
false
] | null |
[
"Know a little about cold weather engineering although it is not my area. I'll explain what I can.",
"In most cases it is cheaper to heat than to cool.",
"Air conditioning compresses a gas like freon, or nowdays R-22 into a liquid, then when it goes through the phase change back to gas it pulls heat. At this point its in the condenser which is the cold side the equation. Then the coolant goes back to gas when it hits the evaporator (which is outside).",
"Compressing the gas creates heat, the motor creates heat, if it's especially hot out the evaporator becomes less efficient and the pump must work harder. You also have to factor in how fast the heat transfers through the evaporator fins, and how much the air going though the condenser will be cool. Resistances in the gas lines, lines and other parts heat soaking.",
"A large house with a high enough R rating can be heated through the winter for a few hundred dollars, whereas to cool it through a very hot summer will cost considerably more.",
"With heating the electricity can go strait to elements, and then into the air, or even more efficiently gas to gas elements. ",
"Also, what happens often in the far north like Fairbanks people become very creative about heating systems. Many houses have an outdoor wood boiler, or a gravity furnace, high efficiency wood, gas, or oil stove, or some other supplemental heating systems. There's a lot of debate going on as to whether or not to ban the wood burning systems because the air quality in the winter is very, very bad because all the particulate sinks and the air is so still that just lingers. ",
"Another case worth noting is that UAF heats all their buildings off of steam pipes that run strait from their coal fired powerplant that also makes the electricity. ",
"That kind of system can't be done for cooling, because cooling isn't a byproduct of so many different processes, and it's much more complicated to achieve cooling.",
"Keep in mind many people will allow their houses to get hot and just sit around keep themselves cool with fans and such, or if the house is empty they'll let the temp become very hot. ",
"Likewise, in a cold climate people may put on more layers of clothing, or keep a woodstove lit. So that balances out somewhat.",
"But in a cold climate, unless the house has been winterized the pipes will burst if the furnace stops ticking. So a furnace warming a house will likely kick on and off at pretty regular intervals, whereas AC is likely to be used at peak hours only.",
"This is another factor because depending on how the power is being generated a lot of power companies will charge less at night, for large industrial and commercial properties at least because the power is less in demand and the systems that generate it have a fairly constant output. It's either that or store it in flywheels, or in the case of Fairbanks the worlds largest warehouse full of car batteries. ",
"Since peak demand hours are invariably around high noon, AC in intrinsically more expensive.",
"I'm hoping I got that all right, if not I'm sure others will chime in. There are probably exceptions to each. Maybe a house in a cold climate has a really poor R rating and electric baseboard heating would costs more to heat than a house in a hot climate that's well insulated and has high efficiency room-by-room cooling. Humidity is another factor, it may not feel as hot or as cold if you're at the coast or far inland respectively. Poverty, if a place absolutely cannot afford cooling it's a luxury item in a lot of places.",
"But between a truly hot, and a truly cold place the hot place both first-world and industrialized the highest aggregate cost of dealing with temperature will probably be cooling."
] |
[
"It's a loaded question, unfortunately. There are far too many factors that exist with heating and cooling a building. These include climate (how cold is cold, how got is hot?), humidity, tolerance of occupants (80 degrees versus 70 degrees means a big difference) , energy rates, etc. To generalize, heating is usually cheaper than cooling as described in another comment. There are certainly some cases where this isn't true. ",
"Source : I'm a professional HVAC engineer and energy modeler. I've done energy and costs analysis for buildings around the world. "
] |
[
"The other factor to consider is thermodynamics, whose laws we obey in this house, young lady.",
"Any electrical devices you have will produce waste heat, and speaking for one house, all year, in the winter, this heat contributes to warming the house (raising the temperature isn't doing work) , but in the summer, the AC has to work harder to overcome this heat.",
"It's another example of why the mandated switch away from incandescent bulbs has not worked so well, a 100 W bulb produces 100W of heat in a cold room (they're also used to heat egg incubators).",
"The new LED traffic lights for example, we're found to need electric heaters to melt snow and ice because they ran so much cooler than the old style. "
] |
[
"How much bigger is the universe than the \"observable\" universe?"
] |
[
false
] |
We can only see billions of years in any direction. Has new stuff formed further out than that?
|
[
"The size of the Universe is unknown; it may be infinite. It depends on how big the large scale curvature of space is. According to the current measurements universe is either flat and infinite or very nearly flat. It is estimated that universe is at least 250 times the size of observable universe. ",
"sources:",
"WMAP also confirms the predictions that the amplitude of the variations in the density of the universe on big scales should be slightly larger than smaller scales, and that the universe should obey the rules of Euclidean geometry so the sum of the interior angles of a triangle add to 180 degrees.",
"http://map.gsfc.nasa.gov/news/",
"Applications of Bayesian model averaging to the curvature and size of the Universe\n",
"http://arxiv.org/abs/1101.5476"
] |
[
"And that is just the estimate for the minimum possible size. "
] |
[
"The term 'flat' does not mean a piece of paper laid out on a table, like the Earth was one envisioned to be. It is a topological term that means the curvature of our 3-dimensional universe is 0. ",
"Read this",
" to enlighten yourself. There have been many observations made that very strongly suggest that the curvature of the universe is 0 (to some margin of error)."
] |
[
"How does magnetic tape/magnetic disk storage work?"
] |
[
false
] | null |
[
"The surface has a magnetic dust embedded in it.",
"The write head can magnetise parts of it as it moves, this is done by making the head an electromagnet and having the surface move below the head.",
"To read the data the head moves through the magnetic field of the tape and this creates a small current.",
"Moving magnetic fields and such.",
"https://en.m.wikipedia.org/wiki/Electromagnetic_field",
"The way that the magnetic fields encode data can vary depending on disk vs tape, and each company has its own magic tricks.",
"But imagine an audio tone, it changes every second, a high pitch tone = 1 and a low pitch tone = 0\nIt’s easy to record a tone on a magnetic tape.\ngo and read about FSK encoding.\n",
"https://en.m.wikipedia.org/wiki/Frequency-shift_keying",
"NOTE: that last bit is not how it’s done, it’s an example of how data could be stored.",
"Modern hard drives use an advanced version of PSK\n",
"https://en.m.wikipedia.org/wiki/Phase-shift_keying",
"Over time new tricks to stuff more data into less space have come along.",
"Add error correction and ability to correct bad data and you can do what looks like magic."
] |
[
"I can answer this one, I'll be using layman's terms but I'll try to be thorough. We'll start with magnetic tape as it's slightly simpler, and then I'll explain how disk storage works differently. There is a third form of magnetic storage that was very widely used until the 1960s which is magnetic-core storage, but that is much more complicated and I'd suggest looking up the wikipedia page if you want to learn more about that as well.",
"First let's just look at what these things actually are. Magnetic tape is actually just plastic tape - not much different from, for example, sticky tape. But it is coated in a thin-layer of very sensitive ferro-magnetic material. So that's step one. Magnetic disk use a similar coating, but it's coated over a metal disk. ",
"To understand how it work, firstly we need to break it down a bit because there are two parts to data storage: writing it and reading it and with magnetic storage these processes happen by somewhat different methods.",
"Writing works by moving an electromagnet over the surface of the coating, changing the voltage in it to represent the data. For simple analog music recording the voltage wave is simply a replica of a sound wave. For digital storage you only switch between a higher and lower intensity voltage. Changing the voltage changes the strength of the electromagnet. When you put a magnetic material near a magnet - it gets magnetized as well. So now as the coating moves past the writing head - it gets magnetized but not uniformly, each bit gets more or less magnetized depending on how strong the electromagnet in the writing head is at that particular moment (whether this is a wave-pattern or a digital pattern is not that important otherwise).",
"So once you've done this, the magnetic coating has different levels of magnetization at each part - an exact replica of the differences in voltage that were supplied to the write head. You've stored your data.",
"So how to read it again ? This relies on a process known as electro-magnetic induction. The basic principle is that if you move a conductor through a magnetic field it induces a current in the conductor. It only works if the conductor is moving or the magnetic field is changing - but if either condition is true, a current is induced. The voltage of that current is directly proportional to the strength of the magnetic field.\nThis has very many applications in electrical and electronic engineering. Varying magnetic fields using AC powered electromagnets and induction create transformers which we use to step voltage up or down for different applications. Radio antennas work on a refined form of induction (this is VERY simplified), and any rotary power generator is using induction (with a moving magnet) to actually generate electricity - all wind, fossil fuel, geothermal, nuclear and hydro-power stations use this method. In fact solar-optical power is the only commonly-used form of power generation to use any other method.",
"In the case of magnetic storage, you take your electro-magnet from before - but you power it down entirely. So now it's not a magnet anymore, just a coil of conducting wire which is quite sensitive to magnetic fields. Move the magnetic coating over it, and the changing magnetic field induces a current in it - which you can measure, and it will match exactly the pattern (but not quite the intensity since no system works without energy loss) of the current fluctuations you had used to write.",
"That's the fundamental principle on which magnetic storage works. Now with tape storage it's easy - because the coating just slides by, in one direction, with a constant speed - it's as simple as just making sure it moves at the same speed during both reading and writing.\nDisk storage is more complicated. Because now you're moving the coating in a circle - and a circle is wider at the edges than in the center. It takes the same amount of time to make a rotation - so that means a spot on the outside edge travels a great deal further in the same amount of time as a spot in the center.\nVelocity is distance over time. So the outside edges move much, much faster the inside edges. \nDo we need to compensate for this ? Actually no. Because all it means is that, in the center, the distance between one bit and the next is much smaller, the data is more tightly packed - while it's more spread out at the edges. This is very different from how optical storage works by the way - in compact disks (and their descendents like DVD's and Blueray) the distance between two bits is always the same. This is achieved by increasing or decreasing the rotation rate of the disk depending on whether you are writing/reading on the outside edge or the inside edge. The result is what is called Constant Linear Velocity (meaning a line along the disk will always pass the heads at the same speed) - but that's not practical with magnetic disks (among other things because they are much heavier).",
"It does however have an interesting side effect - it reduces the usable lifespan of the disks themselves. Magnetic disks are better than tapes because they can read and write much faster - you can move the heads into any section of the disk at a moments notice and go read/write there. With a tape - you have to go through the entire tape to get to the piece you want.\nBut there is a price to pay for that. The spinning disk generates a centrifugal effect, and the sprayed on coating is being subjected to this. Over time the coating gradually slides off as a result of this, and the disk deteriorates until it fails. Tapes don't have this problem.\nThat's why we use disks for day-to-day storage and tapes for long-term backups. It gets the best use out of the benefits of each and minimises the impact of their downsides."
] |
[
"Thanks, great explanation!"
] |
[
"What should you do if parents comes into a clinic and says they doesn't want their children to be vaccinated?"
] |
[
false
] | null |
[
"Consider it identical to any other refusal of treatment, because that's all it is.",
"You need to first find out ",
" they object to vaccination. A lot of the time it's \"I read once on this website it makes them autistic.\" You can then offer information about the correlations (that most of us have accepted doesn't exist) and causations.",
"Make sure they're informed of the risks of ",
" vaccinating their child. Be very clear, this is where you have the most chance to convince them it's in the best interest of their child.",
"At the end of the day, be prepared to lose. A lot of people with objections like this are too proud admit they could be wrong, and it is ",
" right, to refuse care so long as the child is their legal guardian.",
"Informed consent, basically."
] |
[
"Oh okay, I see. Thank you!"
] |
[
"In the US, each state has it's own laws about the subject. Washington recently changed their laws, so that might be a good starting place."
] |
[
"How is quantum tunnelling the reason our sun shines ?"
] |
[
false
] |
My daughter shared video ted talk by Jim Al-Khalili titled "How Quantum Biology Might Explain Life’s Biggest Questions ". I understand the basic concept of quantum tunnelling but not how it applies to our sun.
|
[
"There are nuclear reactions occurring in the sun that involve particles tunneling through each others Coulomb barriers. Nuclei repel because they’re positively charged, but even if they have a low relative kinetic energy, they can still tunnel in order to react with each other."
] |
[
"The important thing about quantum tunneling is that barriers that cannot be overcome classically with the amount of energy typically available, can be overcome with some chance quantum mechanically. That's all there is to it. So processes that are classically impossible or unlikely will happen with a higher frequency if you take quantum theory into account.",
"In the sun this applies to the electrostatic barrier between like charges (protons)."
] |
[
"The sun is made up of nuclei (protons and neutrons) which undergo nuclear fusion.",
"The protons repel each other because they have the same electronic charge, but still fuse due to the tunneling effect.",
"The energy emitted from the fusion is done so as light."
] |
[
"Why does a wet dog smell?"
] |
[
false
] | null |
[
"From ",
"this",
":",
"\"Molecules have to leave the smelly objects and get to your nose through the air and that means that these molecules must be very small and volatile. That's to say they must be easily evaporated. The chemicals that make dogs smell are mostly what we call volatile organic acids and they are produced by bacteria from the fats that are breaking down from sweat; and that's maybe why we find these body odours unpleasant. They signal a presence of bacteria and decay and death to us. ",
"Their [dogs] skins mostly have ",
" bacteria, which don't produce much in the way of a smell at all, but they've also got some yeasts too which are really pongy. ",
"But why does the smell seem worse when the dog is wet? Here, I think we have to go into some physics. The amount of evaporation of a substance is related to the concentration of the compound on a surface it’s evaporating from and the amount of compound that's in the air, just above the surface.",
"So how might that change when it’s wet? Well, if the organic acids are dissolved in water on the fur of the wet dog, as the water evaporates, the concentration of those smelly acids increases, so they'll evaporate more, so there are more molecules in the air for us to smell.\""
] |
[
"So how might that change when it’s wet? Well, if the organic acids are dissolved in water on the fur of the wet dog, as the water evaporates, the concentration of those smelly acids increases, so they'll evaporate more, so there are more molecules in the air for us to smell.\"",
"But wouldn't the highest absolute concentration be before the dog gets wet? Therefore, shouldn't it stink more when he's dry? Maybe I'm missing something, here."
] |
[
"You're not smelling the acids on the dog. The water gets on the dog, the acids get in the water, the water evaporates and takes the acids into the atmosphere, you inhale some atmosphere through your nose, the acids are sensed, and you smell them. ",
"Dogs don't sweat all over the way humans do, so there isn't usually much, if any, moisture to carry the acids up to your nose. Even though there are probably more acids on the dog, without some way of getting them into the air, you're going to have to rub your nose on the dog to smell them."
] |
[
"What would happen if a sun, larger than a black hole, went into the black hole?"
] |
[
false
] |
[deleted]
|
[
"I think what the OP is asking is whether the black hole can tear a hole through the inside of the star in a direct collision (not merely a close orbit). Since the black hole's radius will be a small fraction of the diameter of the star, it takes a \"bite\" out of the core. And repeat this process as the star's now extreme elliptical orbit causes subsequent \"head on\" collisions. ",
"I think if the star were large enough or moving fast enough, this could happen. Also, the first collision could be a direct hit to the center of the star, but it's unlikely (if the star survived) that subsequent orbits would be head on, but rather grazing. Also, if the black hole has less mass than the star, then it might orbit inside the star eating it from the inside out. ",
"This is probably best answered with a scientific physics simulation since there can be many black hole variables like mass, spin and the size of the accretion disk, etc. "
] |
[
"Here's a computer simulation of what would happen: ",
"https://www.youtube.com/watch?v=thkKrW23vNU"
] |
[
"\"Larger\" has to be defined in this context as well.",
"Are we referring to net mass, or measurable size? Of the singularity, or of the total amount of mass spiraling towards the event horizon?"
] |
[
"Why haven't humans adapted to their environment in the same way animals have?"
] |
[
false
] | null |
[
"If you take a polar bear to that country it would have quite a difficult time. Likewise if you take a desert creature to the arctic it may have some difficulty. "
] |
[
"I think you may have misinterpreted my question, I'm asking: ",
"\"Why humans haven't developed similar traits as animals to cope in extreme climates?\""
] |
[
"Unfortunately, the general answer to \"why hasn't something evolved\" is \"because it hasn't been selected for\". Although there are plenty of changes that we might point to if we are looking at our local environments, for example differences in amount of hair or skin tone or even type of ",
"earwax",
" depending on where you live. "
] |
[
"How can I calculate the magnetic field strength required to stop a metal projectile such as a bullet?"
] |
[
false
] | null |
[
"For context I'm a student and I'm writing a theoretical research paper on the possibility of doing this.",
"I'm a little lost on where to begin. I understand the concept of eddy currents but I'm not sure how to link kinetic energy of the bullet to the magnetic field strength,conductivity of the bullet(assumed to be 70% copper,30% zinc) and how distance affects the magnetic field strength."
] |
[
"Please post calculation requests to ",
"/r/estimation",
" or ",
"/r/theydidthemath",
"."
] |
[
"Alright thank you!Apologies "
] |
[
"Do short-lived species, such as fruit flies, evolve/adapt quicker because of shorter, more frequent generations?"
] |
[
false
] |
On paper you would think so right? since the driving force behind evolution is the variations of traits passed from generation to generation. An example I can think of would maybe be cats with thumbs, isn't that a relatively new common mutation?
|
[
"It's just polydactyly",
" (i.e. an extra digit).",
"I don't really know why the OP thinks cats area good example of a short generation time though. Cats have generations times on the order of multiple years, which is a long time in the world of biology. A better example for the OP is the evolution of antibiotic resistance in bacteria, which has happened well within the length of a single human lifespan."
] |
[
"Where are you finding cats with thumbs?"
] |
[
"All else being equal (a big assumption), evolution will proceed faster on the per year scale in populations with shorter generation times, yes.",
"Can you clarify where cats with thumbs comes into this?"
] |
[
"Are canker sores (apthous ulcers) contagious? If so/not, could you please show me the peer-reviewed article showing this?"
] |
[
false
] |
[deleted]
|
[
"Here's",
" the mayo Clinic's basic health information page on canker sores (not cold sores, those are different, but often confused.)",
"It says that they are not contagious."
] |
[
"Thank you, I found that one, but it doesn't link to a scientific article that shows the information to be researched."
] |
[
"Here's",
" an article about the recurrent form, I did not get a chance to read the whole thing, but it doesn't mention direct transfer as one of the standard causes.",
"The references might be a good place to start looking for more in-depth information."
] |
[
"Pharaoh's Snake: Can someone please explain what is happening here?"
] |
[
false
] |
Is this actually solid mass? What happens next? Does it disintegrate? What is left behind? What does it smell like?
|
[
"It's not a solid mass, it's a very porous light sponge-like material, it will crumble to dust if you crushed it and you could ultimately reduce it back to a powder about the size of what they started with. "
] |
[
"I'm more annoyed at the ridiculous use of a rattlesnake sound effect."
] |
[
"was a minute and 20 secs off him dumping the powder really necessary?"
] |
[
"Why do I faint after flu shots?"
] |
[
false
] | null |
[
"We can't really comment on isolated incidents / personal anecdotes without resorting to speculation."
] |
[
"Speculation is fine. I am curious to hear if anyone has had a similar situation and knows what it is or if there's any doctors that have experience with this."
] |
[
"We don't allow that on this sub."
] |
[
"What is the speed of gravity? I.e. If the sun just disappeared in a moment, how long would it take for earth to go out from its orbit?"
] |
[
false
] |
[deleted]
|
[
"There is no such thing as instantaneously in this universe. The earth would fall out of orbit in 8 minutes, the speed of light "
] |
[
"Dude, you are completely 100% wrong. I don't know where you read that, or if you just came up with it on your own, but you heard wrong, completely wrong.",
"The speed of information aka the speed of light aka the speed of gluons aka the speed of gravity is all the same. All massless things (such as gravity) travel at this speed.",
"We would stop feeling gravity at the same time we saw it vanish... after 8 minutes. "
] |
[
"Gravity is said to travel or \"ripple through space-time\" at the speed of light. ",
"Prior to Einstein's Theory of Relativity, we thought (as did Isaac Newton) that if the sun disappeared, the Earth would immediately cease its orbit and continue off into space along a tangent to the point in orbit.",
"Einstein said this is wrong. Just as it takes light 8 minutes to travel to us from the Sun, it would have to take at least this long for information like gravity to travel to us. So he says, we would still be orbiting for 8 minutes until a gravity wave hits us."
] |
[
"How can a single speaker cone vibrating reproduce the sound of all the individual instruments of an entire orchestra at once?"
] |
[
false
] |
I imagine the cellos causing the speaker to vibrate, then I imagine adding in the violins, and then the percussion, and then the woodwind etc. and how their vibrations would all interact with each other. How can this all be reproduced accurately on one speaker cone?
|
[
"Riding a sine wave on a sine wave. ",
"Say you had a high freq sound wave going steady, and then you played a low wave at the same time. You would actually be able to observe that as the low wave caused the cone to move back and forth slowly, it would at the same time be vibrating quickly along the low freq wave.",
"Move your hand up and down. Hold it still and shake it. Now shake it while moving it up and down. High freqs and low freqs work together like that."
] |
[
"Here are some graphs I made to help",
"Edit: made frequencies further apart"
] |
[
"Sound is a pressure wave in time. Objects in the world move, and bump the air molecules around them. These molecules then bump into molecules farther away, and so on and so forth until finally the air molecules bump your ear drum and your sensory system interprets the bump as sound.",
"Music, and individual notes in particular, are very specific waves of pressure in air. These waves are described by frequency and amplitude. We perceive frequency as pitch, and amplitude as volume. If you think of a guitar, you can pluck a big heavy string and it will vibrate slowly and produce a low tone. Then, you can pluck a lighter string, which vibrates faster and produces a higher pitched tone. You can also get higher pitches by tightening the string (the sort of sound you hear while tuning or using slide guitar), or by shortening the string (by pinching it higher on the fretboard).",
"Next, if you pluck the string lightly, it will only vibrate a little bit, creating a smaller amplitude, and exciting the air around it less, which results in a quieter sound. Or, you can pick it really hard and send it vibrating all over the place and get a louder sound as a consequence.",
"Now, the interesting thing is that all of these different sounds are caused by just one thing - molecules hitting your ear drum. Your ear perception system records the amount of pressure on your ear drum at a particular moment, and that's it. All of the complexity of the orchestra is perceived by this same two-dimensional sensor (pressure by time), since your ear can't perceive two different pressures simultaneously.",
"So what happens when you have two strings, or a whole orchestra, playing together at the same time? Scientists call it SUPERPOSITION, which is one of the coolest scientific terms ever. It looks like ",
"this",
". or ",
"this",
". You can see how the faster wiggles are shifted by the bigger waves to create signals that carry both of the frequencies simultaneously.",
"So, in complex music, this is exactly what is happening. The bass plays the slow waves, and the violins and such overlay that slow wave with lots of different fast wiggles. Our brain is quite good at teasing those two sources apart given the combined signals, and with some training a professional musician can not only tell you all of the notes that are being played, but the frequency relationships between them. Just another thing that makes our perception system absolutely astounding.",
"Finally, since I work in the computer vision domain, I can't help but include this related example. Superposition is present in all sorts of things:\n",
"look at this image close up, and then back up",
"You should see two different people. Why? Because once you move away, your vision system cannot pick up on the high-frequency content of the fine edges any more, and you form a completely different image based on the low-frequency information. Once you start dealing with signals, you start seeing EVERYTHING in terms of superpositions of waves of various frequencies, phases and amplitudes (otherwise known as seeing it in Fourier Space). One more way in which being a scientist changes the way you look at the world.",
"TL;DR: what keepishop said"
] |
[
"Are giant space animals possible?"
] |
[
false
] | null |
[
"You'll need an astrobiologist for this one. On top of that, this question will pretty much yield only speculative answers as we haven't found any life in the dead of space yet. May I suggest reposting this instead to ",
"/r/asksciencediscussion",
" ?"
] |
[
"I would agree.",
"I'll just post my standard astrobiology answer -",
"Yes, we can imagine any kind of animal that could for example feed on interstellar hydrogen as it swam through space. ",
"But doing so is completely incompatible with life as we understand it. Doesn't mean it's impossible, but according to our current understanding of life, it is highly improbable."
] |
[
"Energy? Check.",
"Materials? Sort of check.",
"Water? No.",
"There is abundant sunlight for a solar-powered creature. Raw materials like carbon and nitrogen are available in comets and asteroids, but these are ",
" widely distributed. Spacewhales might benefit from low-fuel propulsion options like solar sails.",
"Water is available, but it has no liquid phase at or near zero pressure. You might be able to get away with an incredibly well-insulated and pressurized shell, but that would be silly and is pushing the bounds of plausibility hard.",
"There's also the question of how such a creature could evolve. Space would be unfriendly to earthlike microbes even under the best of circumstances. Microbes can survive space, but they cannot divide in space due to water freezing or sublimating.",
"This would require a radically different way of building living things. An advanced culture might design a spacewhale out of boredom though, or release vaguely whale-shaped Von Neumann robots."
] |
[
"Historically many fields of science have been quite dogmatic about certain theories and wound up being wrong. To the scientists on this board: Is there anything you personally believe that would be considered outside the mainstream of your field, perhaps even heretical?"
] |
[
false
] | null |
[
"I'm not going to answer your question (because I don't have anything that fits) - but I am going to address your comment.",
"Science is indeed very often wrong, or misled, by experimental results. But that is the nature of science. Each answer we obtain adds or subtracts from the weight of an observation. Very often an observation leads down new avenues and new discoveries.",
"The point is... science is about the refinement of knowledge. (and I'm going to step out on a limb here...) this is one (of many) things that separate science from most religions - religions tend not to change their thinking (they have to dragged, kicking and screaming, to accept new concepts and ideas) whereas science embraces change and new knowledge.",
"That said... scientists can be quite dogmatic because lots of times a new idea is counter to what has been experimentally observed - and it takes quite a bit of confirmation to change that perception (we are, after all, only human)."
] |
[
"Yep: P = NP. But I'm no where near as educated about the subject as the professors who taught me. Very much so considering one of them is Stephen Cook."
] |
[
"I'm a respectable materials scientist, but I still think the jury is out on what happens when you load lots of deuterium into palladium (you can take palladium metal and make the D to Pd ratio nearly 1:1). An experiment on this subject led to the cold fusion controversy, which killed all research on the topic. If I had to guess, I don't think this system will be useful as an energy source, but I suspect that there's interesting things to be learned from studying it. I think it's a real shame that people shy away from this area."
] |
[
"Is there something in our body that gives a clue about our [species, not individual] approximate lifespan?"
] |
[
false
] |
For instance, if an alien species abduct a single human, would they be able to find out that we're supposed to live a maximum of 80 to 100 years? And if it's possible, how young could that person be so that prediction is still accurate enough? (All of this using known, earth science, obviously)
|
[
"There are some ways to do this; you can pretty cleanly draw correlations between resting heart rate and life expectancy (slower heart, longer life) and between body mass and life expectancy (bigger body, longer life)",
"That said, we ",
" supposed to live this long. Humans are an incredible outlier in both of those correlations, because we developed medical technology."
] |
[
"No. At this point we aren't even close to a biological model of aging in humans nor can we tell if there's a hard limit to how old humans can get. The only reason we can make reasonable estimates of max age is because we can analyse people throughout their lifecycle, something I assume the aliens can't.",
"Even if they'd have super advanced computing to simulate out bodies I don't think they'd be able to model how old we get because the limiting factor on earth is caused by exposure to external factors. I think the only way aliens could find that out if they took someone that recently died."
] |
[
"Are you aware of anyone who has put together a regression of those correlations? I’d love to see what they suggest about the “natural” human lifespan.",
"Edit: based on the averages in this paper (",
"https://pubmed.ncbi.nlm.nih.gov/9316546/",
"), human lifespan should be less than 20 years, assuming resting heart rate of 80 bpm. If I did the math right."
] |
[
"Can space reach the point where it can't become any smaller?"
] |
[
false
] |
[deleted]
|
[
"No. There are speculative theories that space might be discretized like this, but none of them have evidence going for them (and some have evidence going against them). ",
"We have every reason to believe that arbitrarily small volumes in space are meaningful; we don't quite know how to describe things once you get to the scale of a Planck length, but it makes no sense to conclude that the Planck length must be some sort of minimum. It'd be like noting that your car starts breaking when you go at 200 km/h, and concluding that 200 km/h is the absolute fastest a car can ever go."
] |
[
"It's important to note that the Planck length is the smallest length we can \"describe and still make sense of because our current theories break down there, not necessarily because space itself can't \"get any smaller.\""
] |
[
"Someone with more expertise in this area will likely have a better explanation than me, but ",
"this article",
" on the Planck Length might interest you. From what I understand (not an expert, just a curious layman) this is about as small as we can really describe and still make sense of, which I feel is what the spirit of your question is after.\nI've wondered about this as well and would love to hear someone that has a better idea of what they are talking about weigh in."
] |
[
"Can I \"integrate\" special relativity (stepping between nearby IRFs) to get GR?"
] |
[
false
] |
I've always seen SR described in terms of inertial reference frames, not really "dealing with" acceleration. Well, what if I compute forces on an object during some small time interval "taking SR into account," move the object into a new inertial reference frame based on those forces, and repeat? If I make the time intervals small enough the acceleration during any interval will be negligible. Will I get GR predictions, or is something else missing? Here's an explicit example: Say I have a test particle in orbit around a star of mass M. A (naive, but easy to understand) way to predict its orbit numerically is to integrate "v_1 = v_0 + <vector towards the star> * G M / r * dt." But in SR I see the test particle's clock running slow, so maybe the test particle experiences forces during my dt for only dt * sqrt(1 - v_0 / c If I integrate "v_1 = v_0 + <vector towards star> * G M / r * dt * sqrt(1 - v_0 / c will I get a path prediction consistent with GR? I actually tried an experiment with that model years ago and recall I was able to get precession of the perihelion of very fast/close elliptical orbits, but I never validated those orbits against a known-good GR simulation, and I simply don't trust myself with the GR math.
|
[
"This is an interesting question! I hope it doesn't get overlooked by the panelists, but if it does, it might be worth posting in ",
"r/askphysics",
" as there is likely to be at least one person with experience in numerical relativity who could help you out.",
"GR is a bit outside my comfort zone, but I do know that gravitation is due to the curvature of spacetime, and the whole business of the mathematics of GR is to determine the degree of that curvature. If gravity is input into your calculation without deriving it directly from the Einstein field equations, then at best you are only approximating the curvature of spacetime with G M / r2, but I would be uncomfortable saying anything beyond that."
] |
[
"This is actually an exercise in Goldstein's ",
":",
"Show that the relativistic motion of a particle in an attractive inverse-square law of force is a precessing ellipse. Compute the precession of the perihelion of Mercury resulting from this effect. (The answer, about 7'' per century, is much smaller than the actual precession of 43'' per century that can be accounted for correctly only by general relativity. The other planets produce a precession greater than 500\" per century.) ",
"I'm not sure there is an interesting answer as to why this isn't enough - the general theory of relativity just has more to it. I would, however, like to point out that precession of elliptical orbits is actually the normal state of affairs for other central force laws - force laws with stable, closed orbits (Hooke's law and inverse-square, for example) are special. One way to see this is to consider a small perturbation from a circular orbit in an arbitrary central force. In general the period of radial oscillation will be different from the rotational period, leading to precession (or spirographs, depending how poorly the two match up). ",
"EDIT: The Wikipedia page on ",
"Bertrand's theorem",
" goes into what I mentioned in more detail."
] |
[
"Thanks for the reply and the links to Classical Mechanics and Bertrand's Theorem. I guess I shouldn't be surprised that the integration trick doesn't work. If that was all it took to go from SR to GR then GR would be taught as a little appendix on top of SR instead of a whole new topic.",
"You said that the general theory just has \"more to it.\" Can you elaborate on that? Is the gravity well the (main) problem? I mean would (something like) the integration method I described work if the acceleration happened to come from a rocket instead of the pull of a star? That would violate the equivalence principle, right? There must be a more fundamental problem with the idea of approximating acceleration by stepping between nearby IRFs."
] |
[
"When I heat up water in the microwave and then pour it into a bowl, it always clings to the side of the container I'm pouring from and spills all over the place, spout or not. Why?"
] |
[
false
] |
[deleted]
|
[
"If you look though the side of a glass of water you can see the water is not flat across but actually curves up the side a bit. I believe this has to do with the interaction between the glass, the water and the water's surface tension. I don't know how this interaction exactly works. But I'm pretty sure that when you pour the water out of the bowl, it is this same effect that causes the water to not pour straight down but instead causes some to run down the side of the bowl and onto your feet. "
] |
[
"What you're talking about is capillarity. It comes from the difference in attraction of liquid molecules to each other vs. to the container. In the case of water and glass, the glass tends to be charged, so water molecules are more attracted to it and thus \"climb up\" the walls (opposed by gravity). Surface tension enhances this effect, but isn't necessary (surface tension comes from the intermolecular ordering of the water molecules - fluids without surface tension still exhibit capillarity).",
"To address the OP's question, there's a balance of forces: capillarity (the tendency of the water to stick to glass), surface tension (the tendency of the water to stick to itself), and gravity. The first tends to be 1D (force is proportional to the length of the water-glass-air interface), the second is 2D (i.e., force is proportional to surface area), the last 3D (force is proportional to volume). When you pour slowly, not a lot of liquid comes out of the glass, so the first two tend to win out. If you pour more quickly, gravity will win out and your feet will stay dry."
] |
[
"Have you tried with cold water too? Maybe make 2 videos with cold and hot water? Because regardless of the container heating up too, the decreased surface tension of the hot water should actually have the opposite effet and let it disconnect from the container more easily.",
"But maybe I'm just an idiot and the decreased viscosity makes it bend around the corner more easily."
] |
[
"How is testicual cancer (or any cancer in less than vital organs like cervix, breasts etc.) potentially lethal?"
] |
[
false
] |
Of course, I am going under the assumption that such a cancer will, untreated, ultimately lead to death. I am, however, not exactly sure how. What I am thinking is that, as organs like the testicles, ovaries, and breasts are (seemingly) not vital to staying alive, it is not that cancer in itself that will cause death. Rather, it is the metastasis to vital organs (or several non-vital leading to increased stress, in some way) that will lead to complications in those organs. Am I on the right track with this way of thinking? If not, why?
|
[
"Shorter: Cancer can ",
" - tumors can spread - they are not confined to where they start. ",
"Some cancers may be considered more dangerous than others due to the ways they commonly metastasize. Breast cancer, for example, can result in a spread of tumors to the bones, brain, lungs, and liver (among other locations). ",
"More learning for OP at: ",
"http://en.wikipedia.org/wiki/Metastasis"
] |
[
"Shorter: Cancer can ",
" - tumors can spread - they are not confined to where they start. ",
"Some cancers may be considered more dangerous than others due to the ways they commonly metastasize. Breast cancer, for example, can result in a spread of tumors to the bones, brain, lungs, and liver (among other locations). ",
"More learning for OP at: ",
"http://en.wikipedia.org/wiki/Metastasis"
] |
[
"Yes, you are thinking about it the correct way. Either the cancer kills you by infiltrating more vital organs, think liver, lungs, brain and shutting them down or it does it by something called paraneoplastic syndrome. That's when the cancer cells start behaving in a way that disturbs the rest of the body without it being a metastasis, an example is an electrolyte imbalance called hypercalcemia which you can get from lung cancer cells that produce a protein that looks like a hormone that elevates calcium levels. Paraneoplastic syndrome can cause all sorts of weird things.",
"But in general, it's not the damage done to the testicles that's the problem with testicular cancer, you are completely right there."
] |
[
"What happens to magnetic field when a north pole is near a south pole?"
] |
[
false
] |
I'm trying to understand magnetism currently and had this question: Let's say I have a line of u-shaped magnets all facing the same way (north poles next to north poles and vice versa). What happens if I switch one of these magnets? My theory is that it would reduce the strength of the magnetic field, but I can't find any sources on this.
|
[
"I'm not sure what your scenario is, can you draw it? ",
"If you have the same poles facing each other, the magnetic field between them would be weaker. If you have different poles, it would be stronger. "
] |
[
"My theory is that it would reduce the strength of the magnetic field, but I can't find any sources on this. ",
"You're right. When there are two magnets next to eachother, their magnetic fields add together. That means:",
"0.001 Tesla in the \"left\" direction + 0.002 Tesla in the \"right\" direction = 0.001 Tesla in the \"right\" direction",
"Tesla, by the way, is the unit that magnetic fields are measured in. Eath's magnetic field is about 0.00002 to 0.00006 Tesla at the surface. "
] |
[
"Magnetic fields follow the principle of superposition just like electric fields do (E total= E1 + E2 + E3 +... where these are all vectors. So B total = B1+B2+B3+...). So if you have two magnets facing where the South people of one magnet touches the North pole of the other (end on end) the total magnetic field would be stronger than just one magnet. If you have two magnets facing North to North or South to South their magnetic fields would decrease by a factor dependent on the strength of the independent magnetic fields.",
"Superposition becomes super helpful in free space. "
] |
[
"What evidence do we have for an early hot universe - or: Are there alternative theories for matter generation and the cosmic microwave background?"
] |
[
false
] |
Hi, answering in another post got me thinking; AFAIK we deduce from redshift that space is expanding as time increases, and from the CMB we deduce that the younger the universe was, the higher its energy density. My question: How certain are we that these assumptions are correct? Are there alternative theories out there explaining the origin of matter and the CMB? Could it be that while space is expanding, the energy density gets somehow replenished, and the CMB does not mean what we think it does? In essence: How axiomatic are our cosmology models?
|
[
"Well, to be specific let's say what the current model is. We know everything is expanding, so if we trace back in time, we assume (with other data along the way) that there existed some time in which everything was packed very densely together. Infinitely dense perhaps. Now let's play that tape forward and for the first 300,000 years or so, the universe is so hot that atoms can't form. The electrons are too energetic to orbit a nucleus. So because of all of these free-floating charges, light can't travel very far. The universe is hot and opaque. But as it cools down, eventually the electrons lose enough energy that they can orbit the nuclei to form the first atoms. Now that the universe becomes predominantly neutral particles light can travel freely for the first time. ",
" is the CMB. Light finally being free of the plasma that preceeded atoms. ",
"No other theory put forward has quite the explanatory power of the Big Bang/inflationary model, though scientists are actively still reviewing data to confirm whether the model explains everything we can observe. Your third question: Where would energy density come from? Essentially you're proposing a large-scale violation of the conservation of energy, something that we've never seen any evidence for. So it seems to me to be unlikely. "
] |
[
"Conservation of energy is pretty darned axiomatic."
] |
[
"It wouldn't have been a stupid question ",
" To the contrary, the energy-time uncertainty relation is a very important aspect of quantum theory.",
"I wish I were sufficiently educated to explain it.",
"Or even fully understand it."
] |
[
"Why does xenon an inert gas interact with flourine?"
] |
[
false
] |
Isn't it accepted in science that inert gases do not chemically interact to form molecules with other elements? Why is xenon different from the other inert gases?
|
[
"\"Xenon reacts directly with fluorine because fluorine is a very powerful oxidizing agent (hence it gets reduced and it gains an electron from Xenon). Xenon has larger radii; therefore the electron attraction to the nucleus is weaker in comparison to the smaller noble gases. Fluorine on the other hand is very tiny and highly electronegative, so it would steal an electron from fluorine, forming a compound.\"",
"\nSource"
] |
[
"I'm going to add on to this with a mini-lecture on chemical reactions in general. Despite the mystique many people attribute to chemical reactions, they generally fall into only a few categories of reactions which are in reality the same thing - redox or, Reduction-Oxidation. ",
"The reason this is true isn't really that interesting - we just look at reactions as being redox reactions because an exchange of electrons, the indicator of a redox reaction, is almost always occurring across a reaction. There are a few ways redox reactions can occur, but they basically come down to exciting an atom or a molecule enough to exchange electrons with something else.",
"Now, to the point - just about everything is reactive if given the right conditions. We can literally shoot electrons at a chemical to make it react in normally impossible ways. So, inert isn't really about \"doesn't react\", but about \"doesn't easily react\". Once again science gives us a wishy-washy explanation of the universe that doesn't feel as concrete and comfortable as we'd like :/."
] |
[
"The noble gases, inc. Xenon, are commonly said to be inert. In fact they're just unusually stable, not totally inert under all circumstances.",
"A simple way of looking at it is that Fluorine's 'reactiveness' is just bigger than Xenon's 'unreactiveness'."
] |
[
"Has there ever been an animal with visual acuity based on movement?"
] |
[
false
] |
Watching Jurassic Park for the millionth time. I know that the idea of T-Rex only being able to see you if you moved has been debunked, but it got me wondering. Has there been an animal that this could have been based around? Or was this just some crazy idea?
|
[
"Theoretically it would be pointless because they could just move their head to see everything. ",
"But the line from the movie came from the sex-changing frog they used in the film to splice in DNA. The frogs had poor eyesight and only identified prey and predators based on movement patterns. So at the time we thought that they couldn't actually see things that weren't moving, even though we now know they see stationary objects but their visual processing doesn't bother distinguishing it from scenery if it isn't moving like something they need to respond to."
] |
[
"I'm not aware of this applying to the entire visual field of any animal, but most animals have something like this for at least a part of their visual field, including you! Take your left index finger, hold it up in front of your face (about 10 inches away), point to the right (so that your hand /arm is parallel to the ground), and slowly move your hand to the left while keeping your eyes fixed directly in front of you. At some point, you won't be able to see your finger anymore when you are looking straight ahead, but if you move your eyes to the left you should still be able to see your finger. Ok, now look straight ahead (your finger should be invisible) and wiggle your finger. It should suddenly, magically, pop into view! ",
"This is because in our peripheral vision we have many more rods than cones and because signal from many rods is pooled together. Rods are sensitive to changes in the intensity of light and are most helpful for motion perception. Because signal from many rods in the periphery is pooled, we don't have good spatial resolution there. "
] |
[
"But the line comes from a paleontologist, and he's talking about T-rex, not frogs. That's some sloppy writing, then, I suppose. "
] |
[
"How can chemists predict the resulting products of alkane cracking?"
] |
[
false
] |
For example - if we break down decane we can produce propane + heptane or perhaps pentane + hexane, etc. How can we dictate the result and choose between what we want the product to be?
|
[
"Ah okay, that definitely makes sufficient sense. I sort of figured that perhaps we'd just want one or two specific products from such reactions, but thinking about it now I realize that it'd be kind of inefficient and a bit of a waste of time.",
"Thanks for your answer!"
] |
[
"Ah okay, that definitely makes sufficient sense. I sort of figured that perhaps we'd just want one or two specific products from such reactions, but thinking about it now I realize that it'd be kind of inefficient and a bit of a waste of time.",
"Thanks for your answer!"
] |
[
"I see. Thanks again! ",
"May I ask though, why are chiral molecules useless?"
] |
[
"How does a black hole consume matter?"
] |
[
false
] |
What I'm wondering is: If we could open a tiny black hole by/in a rock, for the short amount of time it would take to consume a part of the rock, would the rock break into pieces? Or would it be sort of smeared (couldn't find a better word) into the hole? What got me thinking was this picture: I'm just using a rock as an example..
|
[
"An object near the surface of a black hole experience massive tidal forces because one end feels a stronger gravitational field then the other, so it gets stretched."
] |
[
"Thank you!"
] |
[
"If we could open a tiny black hole",
"This isn't really an answer to your question, but based on your wording, it looks like you're under a mistaken assumption. Please feel free to ignore this if I'm wrong.",
"Anyway, a black hole is not a hole, and isn't something that \"opens\". A black hole is a massive body where the matter is compressed densely enough that the gravity caused by the mass of the black hole is able to prevent light from escaping."
] |
[
"Which is denser; Tungsten or Gold?"
] |
[
false
] | null |
[
"I'm not going to let this out because the answer can easily be found on google.",
"The density of tungsten is 15.63 grams/cc and the density of gold is 19.3 grams/cc. I hope that helps"
] |
[
"Fair enough. I looked did a bit of searching, but even wiki (which should be a good source for something like this) had contradictory results.",
"Here",
" is a listing of tungsten at 17.6 g/cm",
" and gold at 17.31 g/cm",
" . My CRC (64th) lists W at 17.6 and gold at 17.28, but that's liquid state. Everywhere I look, I get different numbers that vary way beyond any sort of margin of error. I'm confused, they are both stable elements.",
"I guess I'm looking for a source considered authoritative to chemists that I can show someone else."
] |
[
"The website you gave me lists Gold at 19.3 and tungsten at 19.25 which is closer than I put it but the order stays the same. "
] |
[
"Medical Physics: what is it?"
] |
[
false
] |
I read the Wikipedia article, and I'm still not clear. It seems related to diagnostic imaging and whatnot, and I knew that already, so I have a few questions: 1) How is it different from an engineering discipline? It seems very focused on devices like MRIs and whatnot. 2) Is someone in medical physics a physicist proper, or are they typically specialized physicians? 3) What does someone in medical physics actually ? (Like how a theoretical physicist does math, or an experimental physicist designs experiments and experimental apparatuses) Basically, I'm looking for some perspective and context for discipline. And please, feel free to elaborate past my list of questions. Part of the problem is that I'm which questions are most useful. Thanks!
|
[
"Medical physics student here. Depending on your definition, there's around 3 broad specializations for the field: Health physicists, imaging physicists and radiotherapy physicists.",
"Health physicists are mostly concerned with radiation protection and shielding. They're a bit more rare than the other two in the profession, and they're found in hospitals, nuclear plants, and government agencies.",
"The duties of the imaging/radiotherapy physicists will vary based on which hospital/health center they work at. For example, at some places the physicists might be the ones doing quality assurance on the machines to ensure that they are giving the right amount of radiation at the right place. ",
"Imaging physcists will usually perform a bunch of in-depth tests (especially for mammography machines) on imaging equipment to check resolution, contrast, radiation dose, etc. Radiotherapy physicists usually perform yearly/quarterly/monthly extensive QA on all radiotherapy equipment where a bunch of parameters are verified (I can't really start naming them without getting into the lingo of the profession) and sometimes they also perform the daily routine checks.",
"Physicists are also the ones who will approve a radiotherapy treatment plan before it is delivered to a patient. They also often are the ones who come up with the more complicated treatment plans. Essentially, the oncologist (a physician) will prescribe doses and constraints to specific regions on a CT scan (for example, the oncologist could say that they want X units of radiation to be delivered to at least 95% of the volume of a tumor, but they want less than 15% of the volume of a nearby healthy organ to get more than Y units of radiation). It becomes an optimization problem that requires some knowledge to achieve. ",
"Modern education for medical physics is usually at the graduate level and as far as my experience goes, it requires a bachelor's degree in physics.",
"edit: I mostly described the jobs of clinical physicists, there's the whole academic side where they do research on new treatment modalities and ways to more accurately deliver dose to patients, MRI pulse sequences/coil design, new ways to use ultrasound imaging and all that fun stuff."
] |
[
"From what I know, Medical Physicists work mainly in radiation therapy and nuclear medicine.",
"Radiation therapy uses highly energetic beams (photons, electrons, protons or ions) to destroy tumors. These beams are deadly but invisible. The physisicst's work is to insure the correct dose gets delivered to the correct position, as prescribed by the doctor. Taking this huge responsability requires a good knowledge of particle physics, as well as a good practical sense. In addition, these physicists often do research on the practical aspects of radiation therapy: planning, motion compensation, simulation of dose deposition, and so on.",
"In nuclear medicine, we use radioactive isotopes as a tracer inside the patients (PET or SPECT). Again, handling these dangerous isotopes requires a physicist."
] |
[
"I am finishing my PhD in medical physics hopefully before new years. My research and experience is in functional CT imaging and intensity modulated radiotherapy of cancer, but I have been around for a while so I have had my hands in a bit if nuclear medicine, MRI, ultrasound and other things.",
"The majority of clinical medical physicists work in cancer radiotherapy - either brachytherapy which is the implantation or temporary insertion of radioactive sources into the tumor or external beam radiotherapy mostly using x-rays but some times electrons, protons and more exotic particles.",
"As a clinical medical physicist you are in charge of the day to day QA of treatment plans, QA on delivery machines, trouble shooting problems during operation and finalizing treatment plans. The oncologist will delineate the target, radiotherapists will delineate organs and dosimetrists will set up the plan, the physicist will then either approve the plan or tweak it to achieve the most conformal dose to the target with the least risk of causing complications.",
"Imaging physicists mostly deal with calibration, QA and maintenance of software and hardware - they are often not as clinically involved if they work on MRI or CT, however nuclear medicine physicists do get involved as they are required to ensure the safe handling of the machinery and radioactive substances.",
"As a medical physicist you have to know your particle and nuclear physics which of course means E&M, you also need to understand image detector design, semi conductor detector design, linac design."
] |
[
"If two identical twins produced an offspring (gross), would the offspring be some kind of genetic clone?"
] |
[
false
] | null |
[
"This wouldn’t be possible since identical twins would be the same gender."
] |
[
"If this was possible (other people have mentioned the same-sex thing) then the child would not be a clone of the parent(s). ",
"Any genes where the parent was homozygous would still be homozygous. However, only 50% of the genes where there is heterozygosity would still be heterozygous. The others would become homozygous. ",
"It’s this increase in homozygosity which causes the negative effects of inbreeding."
] |
[
"Actually, it is possible for identical twins (twins born through a process where a single fertilized egg splits into two) to be born with different genders in the presence of genetic defects. If the gene determining gender is xxy, when the egg splits it is possible to have one xx and one xy egg after the fact.",
"This is absurdly rare, but it is possible."
] |
[
"Does cupping your ear with your hand improve your hearing significantly? How about in terms of sound quality?"
] |
[
false
] |
[deleted]
|
[
"As DrWurm pointed out, you are forming a reflector with your hand, and directing more acoustic energy into your ear. It is worth noting, however, that you are preferentially increasing high frequency sounds. This is because for low frequency waves the wavelength can be on the order of ten meters long, and your hand is too small to significantly alter the path of the wave. For high frequency waves the wavelengths are on the order of centimeters, and waves act like \"rays\" that can be effectively gathered by these simple reflectors.",
"As a result, these reflectors can sometimes increase \"noise\" if you are specifically trying to listen to a sound below the threshold of the reflector. That's why audio guys don't simply slap a parabolic reflector on every mic they use."
] |
[
"I agree with this. I will add that cupping a hand behind the ear adds 6-8 dB to high frequencies (some at frequencies >1000 Hz, more >4000 Hz)"
] |
[
"Cupping your hand over your ear creates a sort of directional parabolic receiver around your ear. You're bouncing in more sound energy than would have otherwise made it into your ear. ",
"Parabolic microphones are basically the same concept",
"."
] |
[
"In case it hasn't been brought to your attention, there's a new subreddit, \"Explain Like I'm Five\" that might do well to have some of our scientists checking it out."
] |
[
false
] | null |
[
"RULES:",
"No science questions. Those belong in ",
"r/askscience",
"."
] |
[
"Seems reasonable to me. There's already a subreddit for science questions, this one, so it makes sense to keep those questions here.",
"Also, I'm not sure I see how this is any different from ",
"r/answers",
"..."
] |
[
"Whoa, didn't notice that. Seems a little much to me. :/ Maybe they'll change that."
] |
[
"If 2 people with walkie talkie's fell past the event horizon of a super massive black hole, would they be able to talk to each other with their walkie talkies?"
] |
[
false
] | null |
[
"I thought the basic geometric description of inside the event horizon was basically \"all directions point to the singularity\", in that case one-way communication would be possible if one person was \"in the way\" of the others path to the singularity, but two way would not be possible."
] |
[
"The standard view is that in a basic non-rotating super massive black hole the gravitational gradients just inside the event horizon can be low enough that you not have to worry about spaghettification for several hours, and that there is no local measurement that you can make that would tell you that you have passed the event horizon, and thus walky talkies would continue to operate. (If you are still in one piece then light speed signals (those propagating the forces that hold you together) are clearly still possible, and so there will be orientations of the 2 people that will allow for communication, although my intuition is that there will also be arrangements of the two people (eg opposite sides of the black hole) that do not.) ",
"One intuitive way to think about this is the ",
"'river model'",
" imagine that at the event horizon spacetime is moving towards the singularity at > c. So even photons can't escape and everything gets carried along in the river of spacetime, but that for the objects themselves, other than rapidly approaching the singularity things go on much as normal at least until you get closer. ",
"Of course in practice however the answer depends a lot on exactly what description of blackholes turns out to be correct, and the honest answer at the moment is that we don't know. For instance some people propose that just inside the event horizon is something called the ",
"firewall",
" which has been proposed to deal with the black hole information paradox and which represents a maelstrom of energy just inside the event horizon. This view seems to be falling out of fashion again though. "
] |
[
"Pretty sure OP is asking about two people being able to communicate if both are inside the event horizon. Is the answer still no? Could you elaborate?",
"/r/AskScience",
" should be more than one word answers."
] |
[
"Why does mixing mustard and honey together make a compound that is far runnier than either one by themselves?"
] |
[
false
] |
I poured out some mustard and it was pretty thick. It didn't move. Honey slowly poured down the side of the plate. However, when I mix them, it becomes quite liquid, almost like a thick soup. Why is this?
|
[
"In ",
"/r/askscience",
", it's considered bad form to guess or speculate, especially in top-level posts.",
"But you should definitely consider that mustard is thick because of the presence of a natural emulsifier, called mucilage. That's why a bit of mustard allows you to mix oil and vinegar. The emulsifier ensures that the thickness of the mustard isn't overly affected if the amount of water in the mustard is changed.",
"Honey, on the other hand, is thick because of the absence of water, and honey is also naturally hygroscopic.",
"Honey, when mixed with any other substance containing water, will, because of its hygroscopic properties leech water form the other substance. That accounts for the runniness of the honey, when mixed with mustard.",
"I cannot speculate on why the resulting mix is even runnier than the mustard."
] |
[
"In ",
"/r/askscience",
", it's considered bad form to guess or speculate, especially in top-level posts.",
"But you should definitely consider that mustard is thick because of the presence of a natural emulsifier, called mucilage. That's why a bit of mustard allows you to mix oil and vinegar. The emulsifier ensures that the thickness of the mustard isn't overly affected if the amount of water in the mustard is changed.",
"Honey, on the other hand, is thick because of the absence of water, and honey is also naturally hygroscopic.",
"Honey, when mixed with any other substance containing water, will, because of its hygroscopic properties leech water form the other substance. That accounts for the runniness of the honey, when mixed with mustard.",
"I cannot speculate on why the resulting mix is even runnier than the mustard."
] |
[
"I don't really know for certain, but I do know that the viscosity of honey is very sensitive to temperature. Mixing two viscous substances together will add some heat and may be enough to explain the increased fluidity that you observed.",
"Maybe you could set some honey, some mustard, and a mixture of the two at room temperature for about 20min before doing the experiment again."
] |
[
"Why is pykrete so strong?"
] |
[
false
] |
[deleted]
|
[
"Drop a crystal from the second floor vs. a piece of wood. There are several different material properties contributing to what would be colloquially called strength. Hardness, tensile strength, compressive strength, shear strength are all different and independent properties that one might call \"strong\". In the case of pykrete, preventing the formation of large crystals is actually the goal, as crystals tend to shatter easily. The wood pulp will prevent cracks from propagating which increases shear strength, and i suspect the increased elasticity is what helps with compressive strength. The hardness will be lowered, but since most applications will involve a multitude of forces, getting a material with overall more \"balanced\" properties will make it more useful. For example, you could make phone screens out of crystal (say sapphire or diamond) and it would be scratch-proof but shatter pretty much every time when dropped. Or you could make a phone screen out of PET or plexiglass and you could throw it against a wall without shattering the screen, but it would get scratched just from carrying it in your pocket."
] |
[
"Because the stresses used to define them are very different and thus different molecular structures react differently.",
"To pick some macroscopic examples, picture a rope vs. a stack of bricks. The stack of bricks will have excellent compressive strength, whereas the rope doesn't. If you put something on top of the rope, it will be squashed, but the stack can support heavy loads until individual bricks get crushed.\nOn the other hand, the rope has good tensile strength, i.e. you can pull it without it breaking, whereas ataching something to the top of the stack of bricks and pulling will lift the attached bricks only, \"breaking\" the stack.\nAnd if we look at shear strength, both aren't great, the rope will bend and the stack will fall over and scatter."
] |
[
"Because the stresses used to define them are very different and thus different molecular structures react differently.",
"To pick some macroscopic examples, picture a rope vs. a stack of bricks. The stack of bricks will have excellent compressive strength, whereas the rope doesn't. If you put something on top of the rope, it will be squashed, but the stack can support heavy loads until individual bricks get crushed.\nOn the other hand, the rope has good tensile strength, i.e. you can pull it without it breaking, whereas ataching something to the top of the stack of bricks and pulling will lift the attached bricks only, \"breaking\" the stack.\nAnd if we look at shear strength, both aren't great, the rope will bend and the stack will fall over and scatter."
] |
[
"What happened with the Black Death? Is it still around? Can it come back?"
] |
[
false
] | null |
[
"What happened is that it ",
"killed a lot of people",
". ",
"Yes, ",
"it is still around",
".",
"A future major outbreak is unlikely unless it mutates or is used as a bioweapon, because it is preventable (through sanitation) and treatable (with antibiotics). "
] |
[
"The Black Death is an appearance of Yersenia pestis that presents itself by swelling the lymphnodes to ungodly sizes. Yersenia pestis also presents itself as pneumonic and septisemic plague which each cause their own, deadly problems. Originally carried by fleas on the backs of Rattus rattus, the black rat, on merchant ships from Asia to Europe where the fleas on the black rat were then transferred to humans causing widespread transference. Yersenia pestis is still a problem today and can be transferred by squirrels! It is not as big a deal anymore because we have much better sanitation, I mean in medieval Europe people threw their feces out the window as a means of disposal. They didn't wash themselves. They had terrible urban sanitation, and even when people had latrines they dug them right up against the god damned water supply. Also we have antibiotics that treat Yersenia pestis and from what I understand, because it is so uncommon, it's not developing resistance like other bacteria.",
"Interesting note though, some historians doubt the validity of the idea that the \"Black Death\" that struck down so many medieval Europeans was actually the Bubonic Plague. For one, the rapidity of the transmission of the virus seems to indicate a much more virulent disease. Merchants weren't exactly Amazon Prime with two day delivery in those days. Some believe that the more likely culprit was something more akin to the Spanish Flu. They believe that the reports of swollen lymphnodes may have been exaggerated and that while bubonic plague was an issue, people began associating all sickness related deaths with it rather than seeing that there were actual two separate illnesses going around. I mean these people did believe that this was a punishment from god rather than an actual microorganism. ",
"I should point out that the overwhelming consensus remains that the bubonic plague was the culprit of the widespread pandemic that plagued Europe consistently. I should also point out that my limited understanding of this is as a historian and not as a scientist. "
] |
[
"For one, the rapidity of the transmission of the virus ",
"Note: ",
" is a bacterium, not a virus."
] |
[
"Does the location of a mosquito bite have any impact on the itchiness or swelling at all?"
] |
[
false
] |
I recently received a ton of bites, some of which swelled up much more than others. I realize that a possible/ most likely answer is that I was bitten by different types of bugs. But still: if I received a bite closer to a large vein, or in a particular area, would it itch or swell more?
|
[
"its about the concentration of blood vessels and tissue in the area. More of either or both = more swelling, redness and yes itching."
] |
[
"Anecdotally I've had bites on my face, which seem to itch and swell quite a bit less than other places. "
] |
[
"Do you have any evidence of this?"
] |
[
"What kills you when you burn to death?"
] |
[
false
] |
Ok so the title sounds a bit silly but my question is, What exactly is shutting down or ceasing to function when one burns to death? Obviously burning skin probably wouldn't you (not quickly anyway) and pain cant kill people AFAIK So what is the fire doing to your body that causes you to die? is it heatstroke? does the fire burn through your skin and begin directly damaging organs? i was of the understanding fire killed you long before it was able to do this.
|
[
"Obviously burning skin probably wouldn't kill you (not quickly anyway)",
"If your skin is burned deeply enough and widely enough, it can compromise circulation and also breathing as the skin tightens and blood vessels are compressed and the chest is unable to expand. In such circumstances an escharotomy can be performed, putting long incisions in the burned skin to allow the chest to expand without the skin needing to stretch.",
"It's very not pretty, in case you were thinking of googling it."
] |
[
"Seriously don't Google this. This looks just like my pork belly, but people."
] |
[
"how is a heart attack stimulated (sorry can't think of a better word) when in a fire? as in, what is causing the blockage of the artery? Is it any different due to the fire? "
] |
[
"What causes the entire sky to turn a deep red?"
] |
[
false
] |
About 5-7 years ago, I recall having a large thunderstorm where I live (Vancouver Canada). One thing that stood out about this thunderstorm was that afterwards, the sky was red. That's a picture I took after the rain subsided. It was shortly after sunset, and I asked several friends who live between 5-10km away about it, and they also recalled a red(dish) sky. What causes this?
|
[
"The sun is white light (all colours - or at least enough to serve as an approximation). As light enters the atmosphere, short wavelength light gets scattered, whereas longer wavelengths are able to \"make it around\" particles in the sky (water molecules - clouds, etc). Once the shorter (blue) wavelengths are scattered, you are left mostly with the longer wavelengths (reds) which reach your eye - so you see a red sky.",
"This is also the reason why the setting sun seems more red in appearance. The sun being lower in the sky means that it travels through more atmosphere to reach your eye, and more opportunities for the blue wavelenghts to scatter, leaving only the reds.",
"For the thunderstorm, the increased density of the clouds would be enough to have more scattering of the blue wavelengths."
] |
[
"Just a minor correction: while individual molecules in our atmosphere (nitrogen and oxygen) cause blue-heavy Rayleigh scattering, water vapor and clouds cause Mie scattering, which is not wavelength dependent. This is why on very humid days the sky appears more white, while very blue skies are usually only seen in dry desert conditions."
] |
[
"Is there any reason it never happens inbetween and produces a green sky?"
] |
[
"Is the movement of tectonic plates ever going to stop?"
] |
[
false
] |
So I'm not a physicist or geologist. But I am a well-read amateur in physics, and I took a few geology courses in college. Doesn't thermodynamics require that the earth eventually bleeds off enough energy that it cools even further and eventually becomes more solid; which is to say, won't the tectonic plates eventually stop moving? Or does the sun supply enough energy to keep the planet hot? Or is it the radioactivity of elements that are farther down inside Earth that keep it warm?
|
[
"Eventually, yes. But the heat inside the Earth is supplemented by radioactive decay, slowing the internal heat loss down. In addition to this, some of the plate tectonic processes at work don't require convective motion to continue functioning, such as ridge push and slab pull. "
] |
[
"So is it basically one of those questions where the answer is, \"Yes, but the Sun will expand and envelop us before it happens\"?",
"Edit: typo"
] |
[
"Pretty much. The core of the planet is hotter than the surface of the sun, and you may note that precious little of that heat reaches us here. It'll take a long, looong time for it to cool down to background levels."
] |
[
"Our bones repair themselves, why don't our teeth?"
] |
[
false
] | null |
[
"The evolutionary need to maintain or keep this trait never developed. If this were a problem that significantly inhibited reproduction, we'd have a different tooth setup today. ",
"I would love to grow more teeth, but my ancestors were able to stay alive long enough to reproduce despite their potential loss of teeth. So were my bald family members. I'd love to grow my hair back too, but going bald isn't stopping men from reproducing. Evolution does not optimize us unnecessarily. "
] |
[
"For most of human history, the key reproductive years would have been just about the same time that you were completing the move from deciduous (baby) teeth to permanent teeth; i.e. in your teens. ",
"Evolutionarily speaking, there wouldn't really have been much selective pressure for anything at all that happens after your 20's."
] |
[
"The move to permanent teeth completes roughly around age 20 with the arrival of wisdom teeth. ",
"The peak age for hormonally-induced sexual lust is in the teens. ",
"Both boys and girls acquire their secondary sexual characteristics and the ability to reproduce in their early teens.",
"All through recorded history, and as recently as a couple of hundred years ago in the western world the typical age for marriage and motherhood was in the mid-teens.",
"Millions upon millions of people all over the world are ",
" reproducing in their teens.",
"All the evidence suggests that this is our biological norm. "
] |
[
"How does a spinning black hole differ from a stationary black hole? Also, can we tell the difference between the two just by looking at their gravitational signatures?"
] |
[
false
] | null |
[
"A spinning black hole is ",
"stationary",
". Which is distinct from ",
"static",
".",
"The difference between a spinning black hole and a static one is the spinning. There ",
"can't",
" be anything else.",
"And yes you can, in principle, extract these numbers (modulo any degeneracy, I've not thought about that part) from gravitational experiments."
] |
[
"To add to ",
"/u/Para199x",
", here are a few key differences:",
"Regarding your second question, yes, and astrophysicists do this measurement in a clever way by observing the spectral lines of ions in the accretion disk near the black hole. These spectral lines are affected in a way that depends on the rotation of the black hole, so it can be measured."
] |
[
"A spinning black hole has two event horizons, one inside the other.",
"Does this mean that events that are in between the two horizons can have causal relationships, but events between the horizons and events within the inner event horizon cannot?"
] |
[
"If I were the size of an atom, how long would it take to walk across the tip of a sewing needle?"
] |
[
false
] | null |
[
"From ",
"this scanning electron microscope image",
", one can generously estimate the point of a sewing needle to have a diameter of 50µm. You would therefore have to walk approximately (π/2)·50µm ≈ 80µm to get across. The diameter of an atom is in the range ",
"0.06 nm (for Helium) to 0.5 nm (for Francium)",
". The length of an adult human step is ",
"around 75 cm",
". So if you were the size of an atom, you would have to walk a distance equivalent to anywhere between 120 km and 1000 km.",
"There is interplay between ",
"step length, step frequency, and walking speed",
", so to estimate the time required to walk across the needle tip, it may be best to assume an average walking speed of 1 m/s. In this case, it would take you anywhere from 33 hours (if you were the size of a Francium atom) to 278 hours (if you were the size of a Helium atom). If you hike 8 hours a day, it would take you sometime between ",
" and ",
" to complete the trek.",
"TL;DR: This is not a day hike!"
] |
[
"Wow, that's a great way to put in perspective how tiny atoms really are. Thank you!"
] |
[
"The point of the needle is (approximately) in the shape of a hemisphere, so to get to the other side, OP would only need to traverse ",
" a circumference."
] |
[
"Why isn't ECMO / Bypass used for resuscitation in Cardiac Arrest?"
] |
[
false
] |
If someone is in Cardiac Arrest, they're dying due to lack of ventilation and circulation due to their heart not pumping. Lets say a huge MI caused the onset of arrest. Why can't they hook them up to ECMO or bypass and allow them to live that way until they can fix the MI that threw off electrical conduction in their heart? Surgeons stop hearts all the time for heart operations as well as heart transplants.
|
[
"I am an ECMO specialist and have been for 15 years. ECMO for cardiac arrest is already in use in the form of ECPR, which stands for Extracorporeal CPR. It isn't widely used because it can only be reasonably instituted in a hospital that has an active bypass team in place, and physicians (usually surgeons) who are skilled at cannulation. ECMO can be up and running in 20 minutes. If that patient is getting high-quality CPR during that time, brain death is not a given. \nNew techniques and equipment have enabled very rapid cannulation in the femoral vessels via the Seldinger technique, and it can be done with CPR in progress.\nHOWEVER: 1)very few institutions have the staff or equipment for this timely intervention. The ECMO should only be started in an institution that has an ECMO team (not just a bypass team) or the patient would need to be transported to such a place for continued care. \n2) The staff starting the ECMO need to be knowledgable about when it is ethical/appropriate to initiate ECMO. Nobody can die on ECMO, but anyone can be dead on ECMO. For example: it should never be started on someone whose condition is not survivable or reversible. \nECPR should never be done for a PEA arrest.\n3) Finally, to reiterate; successful ECMO can only be done in experienced, high-volume institutions on a limited patient population. ECPR is indeed already being done nationwide. The hospital where I work certainly does it and has for quite sometime. Our outcomes are similar to general ECMO outcomes and national outcomes. "
] |
[
"I am not a doctor and I don't play one on TV (I am an EMT, but that doesn't qualify me to say much) but here is what I know about reactionary ECMO.",
"As a field therapy, it is probably not indicated. A lot of cardiac arrests happen outside of a hospital and it would be prohibitively expensive and difficult to have a surgeon on an ambulance with an ICU nurse to establish ECMO. It would also probably take too long.",
"Now in hospital care, that is a different matter entirely. A couple studies have been done that I will link at the end, but the short version is this. A well set up system can establish ECMO in 5-10 minutes, plenty of time to avoid serious hypoxic brain injury if you are lucky. This obviously can increase patient outcome noticeably. It is very invasive, so it is probably only really going to be used after the rest of the book has been tried and failed.",
"But if you have a ECMO machine standing by, a surgeon ready to start the catherization and an ICU nurse to take over once everything is established (as one might in a level 1 trauma center). Patient outcomes will be improved noticeably.",
"http://www.ncbi.nlm.nih.gov/pubmed/21057309?access_num=21057309&link_type=MED&dopt=Abstract",
"http://www.ncbi.nlm.nih.gov/pubmed/22899771",
"http://icvts.oxfordjournals.org/content/12/6/929.long",
"That last article may be behind a pay wall for anyone not on a campus with access to NEJM, but it was a child study, done on a small group of post surgery and medical cases in the ICU.",
"With rescue ECMO, 17 [of 42] (40.4%) patients survived. Survival to discharge with CPR alone in hospitalized patients ranged from 8% to 22%",
"Doubling of survival rates?! Less dead babies?! Sounds really good. And it is, unfortunately, there is a huge risk of massive infection from those gigantic catheters sticking out of major vessels. There also appears to be a risk of neurological deficit, though this is also the case for traditional resuscitation.",
"So, overall, it looks like this is a promising new technique. Some great preliminary data indicates efficacy. Of course, more studies are needed, and concerns of logistics, availability and cost can never be discounted when considering new treatment modalities (and make no mistake, ECMO, which requires perfusionist or ICU nurse monitoring 24/7, semi invasive surgical procedure and complicated machinery is going to be flipping expensive) but this looks promising.",
"Look for ECMO saving lives in a hospital near you in 5 years"
] |
[
"True, but the amount of evidence for this particular application of ECMO indicates to me at least that it is new for this application. So the technology is not new, the technique of using it on sudden cardiac arrest victims in a hospital setting is (or at least seems to be, im not an expert x.x)"
] |
[
"How do spacecraft take off from the Lunar surface?"
] |
[
false
] |
[deleted]
|
[
"Like so",
". It is much easier to get to orbit on Moon, for several reasons.",
"First the gravity on the surface is low so you only need low thrust to lift anything. That means that you need less powerful and less massive engines. Also all the supporting structures of the spacecraft can be much lighter.",
"There's no atmosphere, so you can pretty much put all your effort into getting to orbit instead of getting above the atmosphere. And nothing is lost to atmospheric drag. And again, because the spacecraft doesn't have to be able to withstand a whole range of outside pressures and supersonic wind, the structures of the spacecraft can be much lighter.",
"And then finally, orbital velocity, and escape velocity too but the lunar module of Apollo only got to orbit, are that much less on the Moon. Orbital velocity is about 1,600 m/s while on Earth it is 7,800 m/s. When you put those numbers into the ",
"rocket quation",
", you get that the Apollo Lunar Module ascent stage needed to have about 40% of its mass as propellant, while a rocket getting to Earth orbit needs to have about 95% of its mass as propellant. So if you want to lift 2,000 kg of payload to orbit, on the Moon your whole craft has a mass of about 3,300 kg. On Earth 40,000 kg. ",
"And that's just an idealised scenario. On the Moon it almost works like that but on Earth it gets even worse. The Earth rocket needs more massive engines, more massive structures to hold it all together, that ridiculous amount of propellant needs all kinds of pumps to even get it to the engines, and so on."
] |
[
"This xkcd",
" gives a good visual representation of the amount of energy required to escape earth compared to the moon. The short answer is yes, it does take much less energy to escape the moon than it does to get there from earth."
] |
[
"The Apollo Lunar module consisted of two parts, the descent and ascent stage, as you can see in ",
"this illustration",
". The descent stage was left on the moon and used as a platform for take-off.",
"According to ",
"\"Apollo Experience Report - Mission Planning for Lunar Module Descent and Ascent\"",
" (PDF alert) the ascent stage produced about 3500 pounds of thrust with a burn time of a little more than 7 minutes (page 19-20 in the PDF, 13-14 in the actual document)."
] |
[
"How did aircraft navigation systems work before GPS?"
] |
[
false
] |
I always wondered how things like ATC or autopilot navigations worked before the days of GPS. Certainly it wasn't all map-based, was it? How could a pilot land in foggy conditions without an exact positioning system?
|
[
"There is a system of radio beacons on the ground that aircraft can detect and track with specially tuned equipment on-board (VOR, NDB). These stations broadcast a signal on a known frequency, and all the pilot has to do is tune the navigational radio to that frequency, and if it's in range, you can track yourself toward or away from it. ",
"These systems still exist on aircraft and are still used as navigation points even WITH GPS in use. "
] |
[
"There are a bunch of really interesting navigation systems that were used - many of them are still in use.",
"One simple system is ",
"VOR",
". Scattered throughout the country are various radio towers. The plane has a receiver that tells which direction (relative to the plane) the signal is arriving from. While in the air, you can cross reference that against charts to determine your position.",
"Then there's the ",
"LORAN",
" system, which is very similar to GPS. Throughout the world, there are radio beacons that broadcast a signal. The plane has a system which records the time difference between different incoming signals, and triangulates your position. You tell it where you want to go (e.g. a certain airport), and it tells you what heading to fly and how far you have to go.",
"The simplest autopilot system will simply keep the wings level, and keep the plane on a given heading. ",
"Let's say know that you need to fly at 185º for 60 miles. You set your heading at 185º, and turn on autopilot. 10 minutes later, your LORAN tells you that you are 5 miles east of your intended path - turns out you had a slight crosswind. So you correct your heading to 200º to get back on track. Once you get closer to your destination, you look for VOR signals from nearby airports to confirm you are in the right area. Eventually you spot the airport, and then you are set. "
] |
[
"Inertial navigation",
" which is still used as a backup.",
"before gps we had ",
"LORAN",
"and before either of those, there was of course ",
"dead reckonig"
] |
[
"How random is random?"
] |
[
false
] |
How difficult is it to make something entirely random? What methods can be used to ensure truly random number generation? Is it even possible? And which, if any, applications require these methods?
|
[
"It is impossible to generate truly random numbers using a compter.",
"Nah, it's not. Look up Lavarand, an R&D thing that came out of Silicon Graphics in the 90s. What you meant to say there is \"It's impossible to generate truly random numbers purely algorithmically.\" Generating true random numbers using a computer is actually pretty trivial, all things considered. It's just that pseudorandom numbers can be generated purely algorithmically, and they're totally fine for nearly all applications in the real world."
] |
[
"It is impossible to generate truly random numbers using a compter.",
"Nah, it's not. Look up Lavarand, an R&D thing that came out of Silicon Graphics in the 90s. What you meant to say there is \"It's impossible to generate truly random numbers purely algorithmically.\" Generating true random numbers using a computer is actually pretty trivial, all things considered. It's just that pseudorandom numbers can be generated purely algorithmically, and they're totally fine for nearly all applications in the real world."
] |
[
"It is best to define what we mean by random. First, we can only define randomness for a sequence of symbols (numbers). There are two different, but similar, criteria for if a sequence is random or not. One is if it has a positive ",
"entropy rate",
". A positive entropy rate would mean that if you were watching these numbers pop up on a screen, and you had arbitrarily good memory and pattern-figuring-out abilities, you still wouldn't be positive as to what the next number would be.",
"The second criteria is that, for a long sequence of these numbers, the ",
"Kolmogorov complexity",
" is approximately equal to the length of the sequence. This basically means that there is no way of compressing the sequence into a short description.",
"As others have discussed, computers alone can not really generate truly random numbers because computers always follow some concrete set of instructions and only have their internal data to work with. This means that, at least according to the second criteria I listed, we can summarize a really long sequence of \"random\" numbers easily: run this loop of code N times.",
"But, given some external source, computers can generate numbers that are random (access to radioactive decay, etc). Typical linux and unix computers these days have a file called /dev/random which is made up of numbers that the computer gathers such as hard drive temperature fluctuations, the time between key presses, etc -- things that can be reasonable considered random."
] |
[
"If light always moves at the same speed in a vacuum, does that mean we can use it to find a stationary point in the universe?"
] |
[
false
] |
Say light is coming at you from the front at 1.1 light speed, and from the rear at 0.9 light speed. Would that mean you are moving away from a stationary point in the universe at 0.1 light speed? Is this a method used? If not, what ways do scientists do it?
|
[
"Say light is coming at you from the front at 1.1 light speed, and from the rear at 0.9 light speed.",
"Light will be coming at you from the front at light speed and from the rear at light speed as well.",
"The speed of light is independent of your reference frame. So if I'm on a hypothetical spaceship traveling at 0.5 c and I would turn on its headlights, the light from that would be traveling at a speed of 1 c when see from aboard the spaceship. However, an observer standing on a nearby planet would also see this light travel at a speed of 1 c."
] |
[
"They would measure your ship at 0.5 c and the beam from your headlights at 1 c.",
"You (on board the ship) would measure the planet passing by at 0.5 c compared to your rocket. You would also measure the speed of the beam from your headlights at 1 c.",
"The speed of light is the same in every reference frame, even though that appears incredibly counterintuitive and clashes with the notion we have of speeds being additive (a person walking at 5 km/h through a train traveling at 50 km/h is seen by someone standing next to the tracks as traveling at 55 km/h)."
] |
[
"Unfortunately, this viewpoint is incorrect. First, there is nothing such as a \"stationary point\" or \"center of the universe\". The big bang did not happen \"somewhere\" (as in \"somewhere in this universe\") because the big bang IS the universe. I think the first concept to forget is that this big bang is like an explosion in a physical sense that we understand. ",
"Second, the entire notion of a reference frame is difficult to understand and it is easy to misunderstand (using \"supernatural\" metaphors etc). In its essence though, the best understanding we have is that the speed of light in a vacuum is an invariant, regardless of how fast an object is travelling. The IMPLICATION of this is pretty mind-blowing (and has been verified experimentally so it isn't speculative) - every object in this universe perceives space and time differently! What is 1 km to you, is not 1km to an object traveling quickly, what is 1 second to you is not 1 second to another person on a train travelling 200km/hr."
] |
[
"How much would the distance grow between two atoms near the colliding black holes due to the gravitational waves?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"Gravitational Wave Megathread",
"If you disagree with this decision, please send a message to the moderators."
] |
[
"Well, it doesn't! Should I submit it again?"
] |
[
"I did a rough calculation for you. The strain amplitude A is proportional to 1/D for gravitational waves (D=distance). The strain is the fractional length change (change in length divided by the total length). For a distance of 410 megaparsecs (1 parsec = 3.26 lightyears), we measured a strain of 10",
" So that means A = k/D where k is a proportionality constant. k = AD = 10",
" x 410 Mpc = 4.1 x 10",
" Mpc. If I plug in for the distance of a parsec away from the black hole binary, let's say, then you get A = k/D = 4.1 x 10",
" Mpc / (0.000001 Mpc) = 4.1 x 10",
" That means that lengths change by that amount. So it depends how separated the two particles are. For a particle separated by 1 meter, the distance change will be 4.1 x 10",
" meters, or 0.41 picometers (0.00041 nanometers)."
] |
[
"Which vitamins and supplements are scientifically proven and witch are just new age?"
] |
[
false
] |
The guy in the office next to mine offered me a free "biophotonic" scan: I simply held my hand on a machine to get some kind of number to prove my over all health. He also sells a combo-pack of vitamins and supplements, and even do my brain screamed "you're being scammed", i bought one to keep the office peace. So my question is, will eating 70mg of (for example) Quercetin and 60 mcg of selenium, or any of the other 20 ingredients really do me any good? Edit: I just saw my funny spelling error in the headline...
|
[
"On a side note: Biophoton scans, and the whole concept of \"biophotons\" are ",
"utter bullshit."
] |
[
"Pretty much all vitamin supplements are unnecessary. Only in the rarest of cases will someone actually develop a vitamin deficiency. Starvation (not the diet-starvation type, but the two grains of rice a day for extended periods of time type of starvation) or gastrointestinal diseases (Crohn's) for example.",
"PS: Selenium\n",
"http://ods.od.nih.gov/factsheets/selenium.asp"
] |
[
"Vitamins and micronutrients have been well studied by serious labs. Some are anti-oxidants that will help to prevent mutations (and therefore cancer), some are co-enzymes that are necessary for metabolic activity. Think about iron in the hemoglobin (blood), for example. If you're lacking iron, you'll be anemic.",
"That being said, you usually can enough by eating a balanced diet with lots of fruits, vegetables, legumes, nuts, and a little meat. Except if you're pregnant and then you need some extra, especially folate which is necessary to lower the risk of malformation of the baby spinal cord. ",
"If you're not eating well, supplements can help, but would not be as good. You would be missing some other stuff like fibers. And variety in food is fun!",
"One last thing: That biophotonic scan to diagnose your general health and what vitamins you would be lacking? That's a scam."
] |
[
"When you train yourself to hold your breath longer, what exactly is it that you improve?"
] |
[
false
] | null |
[
"=======",
"Vital capacity (how much air your lungs can hold) is increased in competitive divers, but that may be misleading. Most competitive divers use a technique called \"lung packing\", in which they basically force more air into their lungs using their pharynx. This could cause changes in lung structure. Therefore it's not known if people who don't practice lung packing would also have increased vital capacity (AFAIK).",
"=======",
"Your brain is unique in its vascular needs for two reasons: First, it needs a lot of oxygen. It doesn't work well on anaerobic metabolism. Second, it's the only major organ completely encased in a rigid structure. If your leg needs more blood, more can go there and the leg will just expand. No problem. Not so with the brain...more blood there, and you get increased pressure, which is a Very Bad Thing.",
"That brings us to dynamic cerebral autoregulation (dCA). This is a mechanism by which your body keeps the blood pressure in your skull within reasonable limits. Enough blood for proper oxygenation, but not so much you squish your grey matter.",
"During breathold, you get a kind of compensation...more blood is allowed into the brain case. Vessels in the brain expand (allowing for greater volume in there), and vessels in the periphery constrict (increasing blood pressure and \"squeezing\" blood elsewhere). This is a reduction in the dCA mechanism.",
"People who train themselves in breathold diving can train themselves for greater reduction in dCA, allowing for more prolonged breath hold.",
"There is also an increased tolerance to the chemoreflex that gives \"air hunger\" in response to high CO2 in the blood. ",
"=======",
"In addition to the increased blood pressure, there is a reduction in heart rate with breathhold. This reduction is exaggerated in people that train to hold their breath longer.",
"=======",
"There are also effects in the spleen. It can act as a reservoir for red blood cells, and when it contracts, oxygenated RBCs are pushed out into the blood. This could possibly be trained, but AFAIK it has not been investigated. ",
"Spleens are bigger in competitive divers. However, this could be a physiologic adaptation to training (NBA players have well developed legs for jumping), or a pre-existing physical trait that makes better free divers (NBA players are tall)."
] |
[
"hi there ",
"/u/bloonail",
", could you please indicate your sources? i'm genuinely interested, but i would like to be confident about these facts in case i need to cite them in future. thanks."
] |
[
"hi there ",
"/u/bloonail",
", could you please indicate your sources? i'm genuinely interested, but i would like to be confident about these facts in case i need to cite them in future. thanks."
] |
[
"Would Earth be detectable from the perspective of Alpha Centauri with current exo-planet detection methods?"
] |
[
false
] |
Assuming a terrestrial planet in orbit around Alpha Centauri A with inhabitants that have identical detection methods to those we currently have. What would they find when they point their equipment at Sol?
|
[
"Depends on how you're looking.",
"Easiest way is the way the Kepler spacecraft uses, looking for dips in a star's light as a planet moves in front of it. I believe looking at Sol from Alpha Centauri, none of the planets move across the disc of the sun, so they wouldn't be detectable by this method.",
"The harder way is looking for wobbles in a star's light as a planet's gravity tugs the star back and forth during its orbit. I don't ",
" this technique is sensitive enough to detect Earth-sized planets ",
", but from Alpha Centauri you could probably detect Jupiter. Give it another 5-10 years and the answer might change."
] |
[
"What about our communications? We're leaking tons of signals that could be used to detect Earth."
] |
[
"We couldn't detect normal TV and radio transmissions from that distance. If we beamed a powerful signal right at Alpha Centauri with something like Arecibo, and there was another Arecibo over there listening to our solar system at the time the signal arrived, then it could be detected."
] |
[
"Is this accurate? Do we move in a forward motion in space?"
] |
[
false
] | null |
[
"It's not terrible. The scale of the planets is entirely wrong - they're much smaller in reality, but that's forgivable because it actually makes it possible to see what's going on. The periods of their orbits seem plausible too- Mercury looks to be whizzing around in the middle with the gas giants taking far far longer to complete an orbit. ",
"The sun does move through the galaxy, orbiting the galactic center. The angle looks about right too. We're inclined something like 60 degrees with respect to the plane of the galaxy. ",
"As for colliding with another solar system, the odds aren't very good. The solar system is sparse. Go give you a sense of distance, if the sun was a person standing in the endzone of a football field then the earth would be a marble in the other endzone. The moon would be a pencil eraser about 2 feet away. If we did have a close flyby with another star or system it's almost certain that nothing would collide. It's far more likely that the gravitational interactions would disrupt orbits, maybe stripping some planets from the solar system. ",
"As some extra reading, ",
"Phil Plait over at BadAstronomer",
" wrote a great debunking about some video that made a bunch of bogus claims about how the solar system goes around the galaxy. He does a great job of explaining how it actually all works. "
] |
[
"Thanks will read."
] |
[
"This is a list of other stars nearest to our own: ",
"https://en.wikipedia.org/wiki/List_of_nearest_stars_and_brown_dwarfs",
"The nearest one is about 4 light years and generally all stars in a certain region are moving in the same direction, so relative to each other they are moving at a small fraction of the speed of light, so even if one were on a collision course with us, a 4 light year gap would take a very long time to close."
] |
[
"Health concerns when using zinc as a catalyst. (Zinc oxide and you.)"
] |
[
false
] | null |
[
"Unfortunately this qualifies as asking for ",
"medical advice",
", which is not allowed under Reddit's user agreement. Sorry!"
] |
[
"I am seriously worried that you are working with chemicals yet appear to have no clue how to obtain safety information. ",
"Here is a ",
"material safety data sheet",
" for zinc oxide in powdered form. Read it. Do the same for every other chemical you work with."
] |
[
"I have amended the post to reflect an interest in chemical stability. Will this suffice?"
] |
[
"How do we take images of our own Milky Way Galaxy when we are INSIDE of the galaxy itself?"
] |
[
false
] |
[deleted]
|
[
"Any picture you will ever see of the Milky Way that looks like it was taken from the outside looking in, is either an artist's impression or actually a picture of another galaxy (albeit maybe a galaxy that was selected due to its similarity to the Milky Way). There are also plenty of real images of the galaxy which show the full 360 degree view taken from inside the plane (for example: ",
"https://asd.gsfc.nasa.gov/archive/mwmw/mmw_images.html#about",
"). These can be stitched together simply, much like the way a phone camera can take a panorama shot."
] |
[
"This is possible, but our knowledge of the specific locations of stars, nebulae, etc diminishes greatly as you cross to the opposite side of the galaxy. So unfortunately, we don't have the ability to map the galaxy in great detail across the entire surface"
] |
[
"Interesting. I had assumed the answer was going to be that they're projections based on what we can see from where we are now. A 3d panorama stitched together and then rotated so that we're looking at it from outside."
] |
[
"How do electrons move through a coil?"
] |
[
false
] |
I know that electricity running through a coil creates a magnetic field, because the charged particles moving in circles create a magnetic field from one end of the coil to the other. The question I am asking is "Why don't the electrons move straight through the coil, when the turns in the coil are wound tightly up next to one another?" To clarify: If the turns in a coil are wound tightly up to one another, what makes the electrons go around and aorund in the turns instead of just taking a "shortcut" thorugh the length of the , and not the length of the ?
|
[
"Insulation. Even if a coil is copper coloured, the cord has a thin layer of transulent insulation."
] |
[
"Specifically, coils are wound using ",
"magnet wire",
", which is coated with (usually multiple layers of) polymer film insulation. "
] |
[
"The magnetic field resulting from the acceleration of the electrons is something we can quantify, ( Michael Faraday ) but may never understand. ",
"I'm not sure what you mean by this. Both electromagnetism (which explains the magnetic field) and electronics (which explains the motion of electrons in the wire) are understood very thoroughly. Are you saying that we don't understand why moving electrons in the wire produce a magnetic field?"
] |
[
"Why are reptiles and amphibians grouped together in the field of herpetology?"
] |
[
false
] |
It's always seemed very arbitrary to me that reptiles and amphibians are grouped together when (as far as I know) they aren't particularly closely related. Aren't birds more closely related to reptiles than amphibians are?
|
[
"It's not just a word, it's professional societies, their conferences, and scientific journals that run herpetology. So in North America there is the CNAH, SSAR, Herpetologists League, ASIH and they publish journals like Journal of Herpetology, Copeia, Herpetological Monographs and meet every year all together with their ichthyologist friends at the Joint Meeting of Icthyologists and Herpetologists. Well, except this year, where there will be two meetings because of reasons.",
"OP, birds ",
" reptiles (there are other contortions you can do to accommodate phylogeny but this one is the best, IMO) mammals are more closely related to reptiles than amphibians are, and turtles are more closely related to birds than they are to snakes and lizards. But so what? There's no reason why researchers need to structure their field around monophyletic clades. The fact is, most researchers go to herp meetings but call themselves evolutionary ecologists, or conservation physiologists, or something. Mammalogy is monophyletic, but you don't really meet mammalogists either."
] |
[
"http://en.wikipedia.org/wiki/Herpetology",
"From the wiki basically it's an old term that just kinda stuck. Reptiles and amphibians when looked at broadly have some similarities that led to the thought of them being related and therefore grouped together, and once a term has persisted for so long it's kinda hard to get rid of it. "
] |
[
"There is a similar situation with Mycology. There are many things such as slime molds and Oomycetes which we used to think were fungi. Well, we got DNA sequences and turns out neither group are Fungi: the Oomycetes are more closely related to plants than Fungi and the slime molds fall out better with amoebas. They're still studied by Mycologist though."
] |
[
"How powerful would a laser have to be to penetrate Earth atmosphere? Specifically in relationship to whether or not it could blow up a spaceship too."
] |
[
false
] |
[deleted]
|
[
"It depends on the weather, your location, and the angle of the laser.",
"At sea level, at the equator, with an angle of 45 degrees into the sky, on a clear day, about 75% of the photons released in a laser escape into deep space.",
"So take however much power you need, multiply it by 1.33, and that's your answer. ",
"If you want to be able to shoot through clouds, or at a very low angle to the horizon, then you will need significantly more energy."
] |
[
"It depends on the wavelength of your laser. The middle graph ",
"here",
" seems to answer the question - for visual light, most of the laser would make it through (assuming your laser can stay coherent at those distances). Looks like less than 20% is scattered or absorbed.",
"Water vapour is a major component so clouds would definitely have an effect."
] |
[
"So how much heat would a laser need to generate to penetrate clouds, and how much energy would that require?"
] |
[
"What's the human body tolerance for sustained lateral acceleration?"
] |
[
false
] |
Hello reddit. I was wondering what the limit is for lateral acceleration for the human body. I'm interested in sustained acceleration, like from cornering at high speed, not in peak acceleration, like from a crash. I would also be interested in repeated short periods of acceleration, so, again, like a car driving around a circuit, but I understand this information might not be available. I've been looking around but there is much more research about vertical and longitudinal acceleration, which is understandable since that's more relevant for aircraft and spacecraft. So I'm having trouble finding what I want. Thanks in advance!
|
[
"Are you just interested in the force being applied to a different side of the body? There's a reason those sustained forces are applied to the back and not the side. You would need to put someone in a centrifuge sideways and intentionally injure them to find out."
] |
[
"You're right. That's probably why most of the research I found was from the 60s, not so many ethics questions when we're talking about the space race."
] |
[
"Testing this would be pretty unethical whether it's done on human or animal studies so hopefully the only real answer out there is that no one knows. I'd imagine it also matters a lot on age, risk factors, body habitus, safety equipment, etc."
] |
[
"Is it possible to die of \"old age\"? Absolute perfect health"
] |
[
false
] | null |
[
"Age alone does not kill you, but it does lead to ",
"senescence",
". This senescence probably causes you to become susceptible to ",
"age-related illnesses",
".",
"However, \"old age\" is not a cause of death.",
" There is always a biological reason. However, in many cases an autopsy to determine precise COD is not deemed necessary."
] |
[
"I think the question is better if simplified:",
"Can organic matter stay \"living\" forever if it is left uninfluenced from outside harmful variables.",
"I would assume it is impossible for a human being to survive the kind of sterile environment without outside contact in order to sustain itself in this manner. But in theory, I am curious if my above question is true."
] |
[
"Is it possible to die of \"old age\"? Absolute perfect health",
"Superficially \"perfect health\" still has problems: calcified and sclerotic arteries, decreasing tone from both sides of the autonomic nervous system, sporadic \"senior moments\" from the tail end of a gracefully decaying brain's lifespan.",
"Think about it this way: you get "
] |
[
"How exactly does a black hole's gravity create particle-antiparticle pairs in the form of Hawking radiation?"
] |
[
false
] |
So on the it says that this radiation is the "result of virtual particles being "boosted" by the black hole's gravitation into becoming real particles." Can anyone explain how gravity can do this?
|
[
"Unruh radiation is blackbody produced in accelerating reference frames. From a reference frame with significant acceleration, the vacuum is not empty: it contains a non-zero number of particles and antiparticles. One way of visualizing the Unruh effect is that the normal vacuum particle/antiparticle fluctuations are \"boosted\" by the acceleration into being real particle/antiparticle pairs. That \"soup\" of particles and antiparticles in the vacuum has temperature, which means it emits radiation.",
"According to the equivalence principle, gravitational fields and accelerating reference frames are the same. Imagine you're in a closed off box. You could feel a force - like gravity - from the inside, but it would be impossible to know whether the box is sitting on Earth, or if it's out in space accelerating at 9.8 m/s",
". There's no measurable way to distinguish the situations!",
"So, a significantly powerful gravitational field is like an accelerating region of spacetime, which thus produces Unruh radiation. In the case of a black hole, we call it Hawking radiation."
] |
[
"This is not correct, an antiparticle has positive mass and positive energy. An antiparticle falling into a black hole would increase its mass. In the virtual particle description of Hawking radiation, the in falling particle must have negative energy in order to reduce the mass of the black hole.",
"I believe this description is intended to be schematic and not a literal description of how the process occurs."
] |
[
"When an antiparticle collides with a particle, energy is conserved and must be transferred to the products of the reaction (typically photons). If this process were to occur inside a black hole the energy would still be trapped within the black hole, increasing its mass."
] |
[
"Are there any other useful gauge choices apart from the Lorentz and Coulomb Gauges?"
] |
[
false
] |
Gauge invariance allows a great amount of freedom regarding the choice of gauge used in EM theory, however all Griffiths and my EM II course only concern themselves with the Coulomb and Lorentz gauges. Are there any other gauges that are useful and practical in EM (or QED) and in what situations?
|
[
"I always like to mention this: it's actually Ludwig Lorenz, not Hendrik Lorentz, who developed the gauge condition in 1867. Griffiths even mentions this in a footnote (and Jackson consistently uses Lorenz). Since Lorentz was a giant in physics and electromagnetism, and since the Lorenz gauge is Lorentz invariant, people ended up misattributing the work to Lorentz. ",
"Now Lorenz is almost completely forgotten in physics history, which is too bad since he was a brilliant physicist who developed a lot of electromagnetism independently of Maxwell. I always try to encourage people to use \"Lorenz gauge\" to promote the guy.",
"To address the question, Landau gauge is used to solve Hall effect geometries in quantum mechanics, and I've seen axial and light-cone gauges, which can be useful if you have certain asymmetric situations."
] |
[
"The unitary gauge in which charge and current density are set to zero in the electroweak theory and spontaneous symmetry breaking is one example."
] |
[
"Interesting. Do you know why it's preferable to set charge to zero? I was under the impression that which W exchange boson mediates the interaction is dictated by charge conservation."
] |
[
"Why did we use MRNA?"
] |
[
false
] | null |
[
"Everything you claim here is wrong."
] |
[
"I got your mod message."
] |
[
"Yeah, I got your mod message"
] |
[
"When a fingertip regenerates after trauma, does the new fingerprint match the old one?"
] |
[
false
] | null |
[
"No. \nDepending on the type trauma there would be varying levels of scar tissue which would permanently alter the appearance of the fingerprint; even though the stem cells present near the fingertip can regenerate said fingertip, they can't prevent scarring from occuring. The fingerprint would remain similar, albeit for a scar at location of the trauma where the original fingertip was lost. While the scar may be tiny, it is still a scar, and therefore the new print will not match the old one.",
"Fingerprinting is actually quite an interesting area.\nThe film Men in Black shows Will Smith having his fingerprints erased through the burning of his fingers; this is actually possible. Another type of trauma for fingerprint erasure includes burning prints off with acid, which really does not sound enjoyable.",
"Anyway, I hope that answered your question for you!"
] |
[
"So if I used my fingerprint as a password, lets say for an iPhone, and I cut my finger there would be a possibility that I would never be able to access it again?"
] |
[
"You have bacteria living all over your body. The species vary from place to place. Your fingertip bacteria are different from those behind your knees, for example. You have around 20 types on your fingertips, and the combination is generally different for different people. In theory, they could take bacteria from something you touched and match it to you."
] |
[
"Do arteries unclog eventually? Or is plaque build up permanent?"
] |
[
false
] |
Is there anything in the body that breaks down the plaque?
|
[
"HDL participates in a process called ",
"reverse cholesterol transport",
" that can remove ",
" cholesterol from peripheral tissue. As qxrt points out, this might not remove the plaque itself."
] |
[
"HDL carries lipids back to the liver and can reduce the rate of the plaque-forming process through reduction of inflammation and sequestering of cholesterol, but once the actual plaque forms, it becomes calcified, and it's relatively permanent. I only say relatively since it's likely that there are some processes going on that reduce the plaque (since most biological systems are in a constant state of flux, with opposing forces balancing out to create homeostasis).",
"I'm personally not familiar with whether there's research to take advantage of any existing mechanisms of plaque breakdown, but current treatments involve either installing a bypass artery or busting open the artery, plaque and all, with a stent. There's no current treatment that removes the plaque itself. "
] |
[
"You're referring to an embolus, which can be caused by thrombosis, which is a blood clot that forms inside the blood vessels. A thrombus is composed of fibrin and platelets and other coagulation factors and is different from an atherosclerotic plaque. Risk factors for thrombosis include hypercoagulability (including the use of oral contraceptives, genetics, etc.), while atherosclerosis involves lipids, aging, etc."
] |
[
"What would happen to a stack of paper if compressed with an obscene amount of weight?"
] |
[
false
] |
Assume a simple stack of printer paper. What would happen if you were to apply an obscene amount of weight to the paper? I imagine it would undergo compression and likely become incredibly brittle, but past that, I have no idea what would happen.
|
[
"Wood fibres are hugely resistant to compression. Imagine how much pressure rests on the wood at the base of a redwood tree without damage. And wood fibres are not brittle under compression (except for very dry or damaged wood fibres).",
"Basically, the paper would flatten (as the air between layers was squeezed out and the pages forced together) but wouldn't change much because the wood fibres that comprise the paper would largely survive in their original laminar orientation. The pages would not bond with each other. Once you released the weight, it would look like a slightly flattened version of what you started with.",
"You need to add something to relax the wood fibres.",
"With a little water/steam, the fibre relax/reshape and compress paper makes a solid board that looks like cardboard but has properties closer to dense wood."
] |
[
" amount of compression",
"With an obscene enough amount of compression, the electrons in the atoms will merge with the nucleus and form ",
"neutronium",
" - a substance never yet seen on Earth. With even more obscene compression, the Pauli exclusion principles which prevents subatomic particles like electrons and neutrons from occupying the same space will be overcome, and you will have an even denser form of ",
"degenerate matter",
", such as quark matter. Increase the obscenity factor and you will eventually get an incredibly small black hole."
] |
[
" amount of compression",
"With an obscene enough amount of compression, the electrons in the atoms will merge with the nucleus and form ",
"neutronium",
" - a substance never yet seen on Earth. With even more obscene compression, the Pauli exclusion principles which prevents subatomic particles like electrons and neutrons from occupying the same space will be overcome, and you will have an even denser form of ",
"degenerate matter",
", such as quark matter. Increase the obscenity factor and you will eventually get an incredibly small black hole."
] |
[
"When developing a new measuring device more accurate than anything that existed before, how is it calibrated?"
] |
[
false
] |
[deleted]
|
[
"Determining accuracy is tricky, and essentially depends on testing your results via some well-established physical theory. ",
"Precision is what people usually talk about when they're developing new measuring devices, though, and that can be determined through statistical tests. Even a relatively imprecise instrument will give an average measurement close to the correct value (accuracy issues / systematic error notwithstanding), given a large enough data set, and the precision of the instrument can be evaluated by the variance of the data."
] |
[
"Accuracy: of a measurement system is the degree of closeness of measurements of a quantity to that quantity's actual (true) value",
"Precision: of a measurement system, also called reproducibility or repeatability, is the degree to which repeated measurements under unchanged conditions show the same results"
] |
[
"I'm not at all an expert in this area, but I once saw an interesting talk on metrology - did you know there are ",
"government bodies",
" whose role it is to determine calibration standards? I had no idea, despite taking measurements in nanometres for years... But anyway, I'll try to share what I know!",
"The simplest method of calibration involves taking a series of known samples and extrapolating a continuation of this series. This is called a ",
"calibration curve",
". There are a bunch of assumptions that go into an extrapolation like this, but if you can eliminate as many external factors as possible and take lots and lots and lots of measurements, you'll get a nice accurate calibration.",
"But in your question, you mention distance - so let's talk about that. So we can take an arbitrarily agreed standard and base calibrations upon that. The current definition of the standard unit of length, the metre, is ",
"\"the length of the path travelled by light in vacuum during a time interval of 1⁄299,792,458 of a second\"",
". Simple, right? We just take your device, and check that the distance is the same (mathematically) with the travel of light in a vacuum over that period of time... This calculation relies on someone having done, as mentioned before, many many many measurements under the same conditions and averaged the answer to reduce the error associated with the timer or other potential experimental errors.",
"There will always be some error associated with the calibrations, coming from a variety of sources, but as long as you can account for all of these and have some way of testing your device against agreed-upon standards, you'll be able to take measurements with an acceptable level of accuracy. ",
"Agreed-upon standards",
" are changed as new instruments and physical quantities are understood, so beware of that. Let me know if I need to be clearer on something or if I somehow missed the point of your question... Have a nice day!"
] |
[
"how powerful a laser would be needed to melt metal powder, eg aluminium or steel?"
] |
[
false
] | null |
[
"Are you looking for a theoretical minimum laser power? or do you want a practical answer?",
"If you want the theoretical answer, then I would highly suggest you amend your question to be \"What is the theoretical minimum laser power required to melt metal powders together?\" or something similar, and then resubmit.",
"For a practical answer, a lot of SLM processing has been done using laser powers in the 50-200W range",
"for things like laser engineered net shaping, which is a blown powder technique, I use laser powers in the 300-1000W+ range (when doing refractories). ",
"For steels and aluminum, you should be able to use powers in the 50-80W range. Do realize that you can get significant differences in properties depending on the laser powers and scan strategies used. "
] |
[
"Thank you very much for tge time you toom putting into your answer, i was looking at using a laser beem to melt powder togeather layer by layer. What sort of diffrences in properties could i expect from diffrent techniques?"
] |
[
"Depends heavily on the actual material. You might actually influence phase stability. For example, when I deposited a certain material, I could make it be pure fcc or pure bcc depending on my laser scanning speed.",
"Low powers might be sufficient to melt the particles together, but maybe not fully melt them. High laser powers might induce vaporization and you might get enhanced porosity in the part. ",
"This is very much a hot topic of research - looking at processing parameters and relating them to build quality"
] |
[
"What's the deal with Helicobacter pylori?"
] |
[
false
] |
H. pylori has been my favourite bacteria for a while, mostly because I love things that seem to defy an easy conclusion. My knowledge of it only extends about this far: H. pylori can cause ulcers. H. pylori produces a compound that can cause stomach cancer. There have been studies done showing a correlation between a lack of H. pylori (caused typically by antibiotic use) and increase in the chance of asthma and possibly obesity. However, this was all a few years ago. Have those early studies been disproved? Or is there more evidence lending weight to the statement that the presence of H. pylori could have some benefits? (If anyone does find the time to answer this, please feel free to go into excessive detail. I can read about bacteria and archaea for hours, they're my favourite.)
|
[
"Here's the best part about H. pylori. The guy who proved it caused ulcers won the Nobel, and no one believed him because it didn't cause ulcers in rats, so he drank a bunch of it himself and gave himself ulcers. Baller status of the scientific community.",
"It's very likely that it offers benefits, however the human system is entirely too complex to identify them easily. Your gut is full of microbes and without them you would die. With too many of them you also get sick. There are 10 bacterial cells in your body for every human one and every day the role of these bacteria is being more and more well understood."
] |
[
"There's even some evidence that eradicated h. pylori will increase platelet counts for those with ITP and other disorders."
] |
[
"no prob"
] |
[
"How do birds actually find worms in the ground?"
] |
[
false
] |
We had a hard rain here, and when I look out the window there are many blackbirds seemingly prodding into the ground at random places and 25% of the time pulling up a worm. How do they (or any bird hunting for a worm) know which spaces in the ground to pick? and furthermore once they have found a worm, how do they know? I assume the beak doesn't have nerve endings.
|
[
"The actual answer is that they can hear the worms. Birds use primarily visual or auditory cues to locate the subterranean prey, but perform best with both of those senses. When deprived of any vibratory input, their performance is unaffected. When they can't smell the food, they can still find it. But if their hearing is obscured with white noise their performance drops significantly. ",
"So they are listening for the worms. ",
"Source: ",
" (1997)",
" "
] |
[
"After a hard rain, worms will surface from the ground so they don't drown.",
"My guess is that birds are pecking at exposed worms or worms just peeking out of a wormhole.",
"Also, with flooded ground, the concentration of worms near the surface will be much higher than normal. Even taking random stabs is going to result in a much higher hit rate."
] |
[
"I have no clue about the factual accuracy of what I'm about to say, but I've heard that birds sometimes stamp the ground for a few minutes to imitate the feeling of rain underground to trick the worms into going near the surface. "
] |
[
"Can someone explain thermal conductivity units?"
] |
[
false
] |
I mostly understand thermal conductivity. What really confuses me, is the unit for it, watts per meter per kelvin (W/(m·K)). In general, derived units seem to make some kind of intuitive sense. One meter per second is a speed at which an object travels one meter in one second. One meter per second per second (1 m/s is a rate of acceleration of one m/s every second. An irradiance of 1 W/m is a watt of radiated energy falling on a square meter of area. Et cetera. All of these seem to make sense without further explanation. I've read articles on Wikipedia and elsewhere about thermal conductivity trying to wrap my head around "watts per meter per kelvin", and for whatever reason I can't figure out how a unit of power, a linear distance, and a unit of temperature combine to form a unit of thermal conductivity. Presumably the unit of temperature is intended as temperature differential. I'm okay with that. And watts are the amount of energy transferred through the material in question. But "meters" ? Why a linear distance? Why not a surface area, and a distance traveled through the material at a normal to that surface? For thermal conductivity, why the unit W/(m·K) ?
|
[
"The units are simplified which makes them hard to understand. These are the non-simplified units:",
"Thermal conductivity = (J*m)/(m^2*s*K)\n",
"Here is a sentence copy/pasted from wikipedia that explains it well:",
"It is defined as the quantity of heat, ΔQ, transmitted during time Δt through a thickness x, in a direction normal to a surface of area A, per unit area of A, due to a temperature difference ΔT, under steady state conditions and when the heat transfer is dependent only on the temperature gradient.",
"Wikipedia Source"
] |
[
"You could think of it as a diffusion distance of a watt per unit kelvin.",
"To put it in to more usable terms: a watt put into a \"good\" thermal conductor will distribute over a distance easily, while a watt put into \"poor\" thermal conductor will stay localized and not conduct outwards as easily."
] |
[
"Good dimensional analysis skills are key to figuring out how to solve problems that don't fit exactly in place with textbook examples. Even if you aren't sure of the exact equation, understanding the units, and what needs to cancel where is the first step to understanding a complex issue.",
"Solving the problem will give you a decent grade in the class. Understanding the background science, which includes why units appear they do, will give you actual skills that are useful as a scientist."
] |
[
"Will the curvature of my spoon's edge always be able to match the side of my yogurt cup so I get a clean scrape?"
] |
[
false
] | null |
[
"If the yogurt cup is a truncated cone (classic Yoplait cups come to mind), then all you need to scrape the sides is a straight edge. That is, you don't even need a spoon. A fork or knife will do just fine.",
"A more interesting question is \"what shape of yogurt cup allow for scraping of the sides with only a straight edge?\" In mathematical terms, you would have to be able to slide a line segment around ",
" the surface without distorting the line segment ",
" every point on the side of cup can be reached in this way. Such surfaces are called ",
"ruled surfaces",
". As the picture on Wikipedia shows, even a yogurt cup shaped like a hyperboloid would be acceptable. ",
"A sufficient condition for the surface to be ruled is that it have zero Gaussian curvature. (Curvature in this context means its extrinsic curvature, as a surface embedded in R",
".) This condition is not necessary, as seen in the case of the hyperboloid.",
"So why use a spoon then? Well, there's the obvious reason that it's easier to scoop out the interior of the cup with a utensil with higher surface area (i.e., yogurt just passes through the tines of a fork). But also not all yogurt cups or bowls are ruled surfaces. A typical cereal bowl, for instance, is more of an elliptical paraboloid or a hemisphere, both of which are not ruled surfaces. So to scrape the sides you need a utensil that itself is a curved surface. Of course, the spoon may not match the sides of the bowl exactly, but it likely approximates it well, or at least better than a fork or knife."
] |
[
"Yes, as long as the radius of curvature of the spoon (at some point on its edge) is larger than the cup's. When you tilt the spoon towards the vertical relative to the cup, it presents a smaller and smaller radius. At some point, it will match the local radius of the cup and you get maximum coverage. If you have a spoon the size of a penny, you'd never be able to contact the cup wall at more than one point, no matter how much you tilt it.",
"I'll leave the proofs to the experts, but this is as far as I can get on intuition and my knowledge of conics."
] |
[
"If your spoon is (a part of) an ellipse, then the ",
"curvature",
" of its edge is non-constant, varying from a maximum value (at the tip) to a minimum (on the sides). As long as the curvature of your cup is between these bounds, you will always be able to find a part of the spoon that ",
" matches the cup. Fortunately, the cup (if it is a plastic one, not a glass one...) is able to bend enough to make this match a bit wider than \"infinitesimal\", so that you can scrape all the yoghurt with a finite number of passes.",
"(To be more precise, there are three degrees of freedom to this problem: your spoon is tangent to the cup at the point where you are trying to eat, and then you can ",
"yaw/pitch/roll",
". I'm assuming that roll and pitch are fixed by the need to be able to catch the yummies, and you are only able to manipulate yaw. But as I wrote above, as long as you have one degree of freedom along which curvature varies enough, you are good).",
"This, however, leaves the problem of the bottom of the cup, which is where all the remaining yoghurt is always left."
] |
[
"People always say that the scissors never actually touch the paper ( atoms repelling and such ), so what would happen if two atoms actually did contact?"
] |
[
false
] |
The answer could be "Nothing at all". Just curious!
|
[
"In order to understand this you have to first understand that atoms do not have well defined boundaries. You may have learned that matter is made up of little \"particles\" like protons and electrons which form larger particles called atoms. In reality though, these things aren't really little hard balls. Particles do not have sharp boundaries.",
"Let's consider as an example the most basic atom which has one proton and one electron. This is the element ",
"Hydrogen",
". The electron in the hydrogen atom is not a little ball, but actually a diffuse cloud of matter. What I mean by this is that the electron is best thought of as having an area of influence where the strength of that influence decreases as you move away from its central point. The technical term for this area of influence is the \"wavefunction\" of the electron. Check ",
"here",
" for nice illustrations.",
"Since the effect of the electron decreases continuously and asymptotically to zero as you move away from its center, you can't really say that the electron has an outer edge. Therefore, when you talk about say two electrons \"colliding\" with one another, what's really happening is that their influence clouds are overlapping so much that they push strongly on one another. In this case, particles don't really ever \"touch\" in the usual sense. Instead they push more and more on one another as they get closer together. This push is the electric or ",
"\"Coulomb\"",
" force. When you sit on a chair this is the force at work. The electron clouds in your butt get close enough to the ones in the chair to push against one another.",
"For some particles, if you get them really close to one other then a whole bunch of other physical processes can happen in which the particles transform into other types of particles. If you push two atoms really close then these so called \"nuclear\" processes (so called because they involve transformations of the particles found in the nucleus of the atom, namely protons and neutrons) can frequently produce atoms of other types. Check out ",
"fusion",
" and ",
"fission",
"."
] |
[
"It depends on how you define \"contact.\" In our every day experience, we say objects contact each other when their electron's fields repel each other. That IS what contact is. ",
"If you want to talk about what happens when atoms overcome this repulsion, then you are talking about fusion. Inside of the sun and other stars atoms are forced together by powerful gravitational forces. This creates heavier elements and also releases some energy. They don't really \"touch\" rather than become a new, heavier element. "
] |
[
"Thank you for such a wonderful response. I've been trying to figure out how to explain things like this (should I ever need to, I doubt it though, I'm just a sucker for information). You did it wonderfully without being too complex."
] |
[
"Firing a gun in space; does rifling matter? Or could a smooth bore be just as effective?"
] |
[
false
] | null |
[
"Your cartridge is already air-tight - the powder contains its own oxidizer and does not require atmospheric oxygen to ignite."
] |
[
"There would be no difference. Riffling causes the bullet to spin, it acts like a gyroscope, giving it extra stability that keeps it from tumbling randomly and deviating from its intended target due to variable wind drag.",
"But there's no air in space, no wind drag, so whether a bullet tumbles or not, it will still follow the same path. ",
"And indeed when calculating the orbits of asteroids there's no need to take into account their rotation period."
] |
[
"The rifling would help to ensure that the bullet's trajectory when it leaves the muzzle is precisely in line with the barrel - and thus potentially increase accuracy.",
"With a smoothbore, there is a chance that the vector of the bullet is slightly off from the straight line and there will some deviation in aim. Probably a very small chance, but a chance. "
] |
[
"What’s the difference between clinical depression and regular unhappiness?"
] |
[
false
] | null |
[
"Clinical depression is characterized by a prolonged and enduring sense of dissatisfaction, unhappiness or feeling or similar low mood. It's beyond simply having a bad day. It's a pervasive experience, one that doesn't change like... Well, a mood. An important feature beyond the unhappiness is that patients often find that experiences that once brought them pleasure or happiness no longer do, or fail to rouse any interest in them.",
"More importantly, it's not someone CHOOSING to be sad. It's a physical thing. The brain is to a real extent caught in a a depressed state biochemically that can be very hard for people to get out of, willpower or no. To the extent that depression can present with physical symptoms of lethargy, tiredness, aches and pains and a lack of hunger or sex drive."
] |
[
"Depression isn't just being sad for fleeting periods of time. ",
"It does involve sadness, but also lack of motivation, fatigue, too much sleep or insomnia, weight gain or weight loss, lack of ability to find enjoyment, suicidal thoughts, feelings of worthlessness, often times anxiety, etc. To be clinically diagnosed, a lot of these symptoms must be present for at least 6 months I believe. "
] |
[
"2 weeks actually. You’d need at least 5 of the symptoms you mentioned to last for 2 weeks or more in order to be diagnosed "
] |
[
"Is this article on female/male brain differences accurate?"
] |
[
false
] |
The article: It makes a lot of claims about anatomical differences in male and female brains that I haven't seen sources for anywhere else. On a side note, how much is transgenderism related to these or other anatomical/biological differences between male and female brains? Paring it down: the differences, TL;DRed (the ones I'm more interested in are ): 1) Brain size: men have bigger brains and more processing power. Probably to take care of their bigger amount of muscles [ , is this related to hand-eye-coordenation and the amount of "APM" (actions per minute) a gamer can perform?] men lean to be more left-brain people and task oriented; women are more balanced and intuitive. 3) Relationships: women have better communication and emotional intelligence. Men have a harder time to pick emotional cues. men have a bigger inferior-parietal lobule (the math brains!) and perform better in standardized mathematical tests. Men have a different reaction to stress. [potentially better for competitive mental games?] 6) Language: Women have bigger language-related brain parts and use two hemispheres to communicate intead of one as men do. 7) Emotions: Women's deep lymbic system is bigger, thus they are better at getting in touch with themselves, communicating, understanding others but are also more prone to depression. Men are better at this. 9) Susceptibility to brain function disorders: Men are more likely to develop problems related to left hemisphere dominance, women are more likely to develop mood disorders.
|
[
"I'm a neuroscientist and I study sex differences in the brain. I can answer this but in order to do your question justice, can you pare it down a little bit? I don't really have the mental energy to address all 9 thoroughly and with citations -- or maybe I can take a few and someone else can jump in with the rest. "
] |
[
"Ok, I'll start with 2 and make new comments for the others as I get to them (if I get to them).",
"This statement is true for specific kinds of language processing:",
"During phonological tasks, brain activation in males is lateralized to the left inferior frontal gyrus regions; in females the pattern of activation is very different, engaging more diffuse neural systems that involve both the left and right inferior frontal gyrus. ",
"[Source]",
"But in spatial processing tasks, men show more activity than women in regions in the right hemisphere:",
"women showed less right-lateralized [cerebral blood flow] increase than men for the spatial task, where men tend to perform better than women ",
"[Source]",
"Memory for emotionally-arousing events is also strongly lateralized. Many studies have shown that in men, activity in the right amygdala is associated with emotional memory formation, but in women, activity in the left amygdala is associated with emotional memory formation ",
"1",
", ",
"2",
", ",
"3",
".",
"So I would say it is not really accurate to generalize that \"men are sharply left-brain dominant;\" the data suggest that men use their left hemisphere more for some tasks, and their right hemisphere more for other tasks.",
"I brought up language processing, spatial reasoning, and emotional memory because (to my knowledge) those are the 3 areas in which laterality differences have been consistently observed. Those don't really get at the rest of the statement in 2 though:",
"Even if the initial statement about laterality had been accurate, it would then be necessary to show that the left and right hemispheres are specifically associated with intuition, communication, social deftness, and being task-oriented. I do not think there is any evidence that either hemisphere is preferentially involved in any of those things except communication. In both sexes, verbal skills tend to be strongly left-hemisphere lateralized ",
"[source]",
" (although this is less true for people who are left-handed ",
"[source]",
").",
"So even if men were \"sharply left-brain dominant,\" that would actually undermine their claim that men are worse communicators, since language is largely a left-brain skill!"
] |
[
"Just jumping in to make one brief comment, which is that the way all 9 statements are phrased makes it sound as if ",
" men have the 9 differences compared to ",
" women. It's really important to keep in mind that every single one of the differences described is only apparent when you look at population averages. Some in fact are very subtle - I know that #5, for example, is almost never apparent if you look at a randomly selected man and woman - you have to sample a large population to detect a difference in stress physiology between the sexes. ",
"It's like the difference between these two statements:",
"(1) The average man is 5'9\" and the average woman is 5'4\".",
"(2) Men are 5'9\" and women are 5'4\". ",
"See how ",
" the second statement seems? How absurdly inaccurate it is? All 9 statements you said above are inaccurate in just that same way. (\"Spatial abilities - Men are better at this.\" No no no. ",
" men are better at this. But not all of them.)"
] |
[
"No fapping connection to muscle growth?"
] |
[
false
] | null |
[
"There was a single study that has not been replicated that showed testosterone levels rose up to around 147% of baseline value on day 7 of not touching your trouser snake.",
"This bitch",
" is the study from China that is hard as hell to access and nobody seems to ever speak of the full text; just the number in the abstract.",
"Given how testosterone fluctuates +/-20% or so of baseline value by just chilling at your computer, and probably more than that by looking at porn, and how ",
". I wouldn't give it too much of a thought.",
"Hell; the only other study I could find regarding testosterone and not taming the phallus dragon looked at how ejaculation affects the body when you haven't blasted a load for 3 weeks (note: neurologically its about the same as if you just blasted a load before heading into the lab) and when they took baseline readings, the group that didn't massage the meatpole had about 0.5nm more testosterone than control. This is a pathetically insignificant amount in regards to muscle building, and if I were to argue that testosterone went from 145.7% on day 7 and dropped to 102% on day 8 and maintained this low level, nobody could really prove me wrong since the study that noted a testosterone spike on day 7 stopped recording at that day. Nobody knows what the hell goes on between day 7 and 21, we just know that day 21 is pathetically small."
] |
[
"0.5nm more testosterone",
"That a typo?"
] |
[
"Yup"
] |
[
"Where are we on fusion power? How clean would it be? How long can we see fusion power in grid?"
] |
[
false
] |
According to wikipedia, On March 15, 2012, the NIF's array of 192 lasers fired a shaped pulse of energy that generated 411 trillion watts of peak power - 1,000 times more than whole of the United States uses at any one moment. [56] The total energy created as the pulse was generated, was calculated to be 2.03 million joules, making the NIF the world's first 2MJ ultraviolet laser – about 100 times more powerful than any other laser in existence.[57] "Mike Dunne, the National Ignition Facility’s director for laser fusion energy, is expecting the giant laser system to generate fusion with energy gain, or "burn", by the end of 2012" [58] But are we at all close to harnessing this power? Also, where are we at on Tokamak reactors? How come many of them are no longer operating. Note: I tried to search, but search doesn't really return any meaningful results.
|
[
"NIF has yet to reach ignition. That is to gain more power from the fuel than was used to generate the laser pulse. If NIF cannot reach this mark, it would represent an awesome laser experiment and materials shock wave physics testing platform but would not be suitable for a power source. Even if ignition were to be achieved, there are several significant challenges yet to overcome.",
"The fuel will need to be mass produced, we are talking about many thousands for sustained energy production. These capsules have to be manufactured to a very high precision and will be fired at a rate of ~80/s.",
"Energy will need to be captured from the chamber and converted into useful energy (i.e. electricity). This process will be relatively inefficient, due to Carnot efficiency limit, which in practice requires a significantly greater amount of energy to be produces before the power required by the laser shot is repaid.",
"The materials in the chamber will experience significantly hostile environments, a high rate, high radiation, high (and non constant) temperature profile makes the materials selection problem tricky. In practice we do not have much experience in this area of materials science (except in the Nuclear Weapons Programs) and therefore producing a commercially viable system, that is cost efficient to run, will require a fair bit more work.",
"While there are a few other problems I could list that imply that Fusion is a fair way off, let me be very clear, without Nuclear Fusion we are unlikely to support a growing population which is developing at a very fast rate. Nuclear Fission (and other alternative fuel strategies) will not cover the gap in the longer term. Without a stable energy source, that is easy to manage, we will have to realise a world where scarce resources continue to hamper our development. This may not affect you significantly in your lifetime, but I suspect it will affect the children who have been born today and will live until the end of this century.",
"In terms of realisable goals, I think that NIF is worth pursuing but I suspect that tokamak based designs are far more realisable as a commercial product. We are building the ITER reactor at present, which won't be a suitable power source but will let us iron out many of the bugs to design the first generation of DEMOnstration reactors that will realise commercial fusion power.",
"tl:dl Ignition - i.e. power in = power out, is still a fair way off with NIF. Even with ignition, we need to sort out how to commercialise such a device which includes looking at energy capture and materials design problems that have yet to be tackled properly. I think that fusion is vital for our planet and that tokamak based designs are more realistic as a first go for commercial viability.",
"p.s. I'm very sorry that there aren't more references, I'm not at work so I can't go and hunt down a few papers."
] |
[
"We cannot sustain fusion without enormous energy usage. We cannot produce any energy from fusion yet.",
"It will probably be a long time before it's used for commercial power production."
] |
[
"We are about ten years out. Same as last year. And the year before that. And the year before that."
] |
[
"Water freezing out of freezer"
] |
[
false
] |
[deleted]
|
[
"Related: What low temperature would you have to drink Vodka (or other spirits) at to cause physical injury to yourself? ",
"I heard a story about a soldier stationed in Korea who took a chug of vodka at -40C without thinking and ended up in the hospital for it. Wondering how true this would be and what a \"dangerous\" level would be. "
] |
[
"The process of lowering the temperature of a liquid or a gas below its freezing point without it becoming a solid is referred as supercooling also known as undercooling. The process of going from liquid to solid is exothermic. This means that as a liquid changes into solid, heat is released.",
"Water normally freezes at 0 degrees Celsius or 32 degrees Fahrenheit. The freezing and the cooking temperature of water can among others be influenced by increasing the air pressure. The higher the pressure is the lower the freezing temperature. There are some other factors that influence the freezing temperature like adding impurities. A great example is salt that is used to lower the freezing temperature of water.",
"If a liquid is cooled below its freezing point it will crystallize in the presence of a seed crystal or nucleus which a crystal structure can form around. A crystal or nucleus can be a dust particle for example. If the seed crystals or the nucleus aren't around the liquid won't go to a solid state. But there is a maximum temperature, this is -42oC / -44oF. If its cooled to this temperature the water will freeze, despite of any seed crystals or nucleus are arround. "
] |
[
"The internal heat generated by your body would melt the ice. You could theoretically choke to death on ice, but it would be very difficult."
] |
[
"How do people develop fetishes?"
] |
[
true
] |
It seems weird how many different things turn people on. I always wondered how people have so many different fetishes.
|
[
"There are 2 basic groups here. ",
" Looks like the jury is out on this idea, but we do know that neural crosstalk is real, and it is studied in several specialties, like pain management (",
"example paper",
"). The other type is an acquired fetish. This can come about in many ways, and there are several models trying to pick apart how it works. A couple common ideas are: ",
" (an object feels safe or good to you--generally during childhood--and you take that feeling with you into adulthood, where those feelings become sexually charged) and similarly an idea of ",
" (an object becomes associated with sex because the object is present during sexual experiences). "
] |
[
"Various neurologists pointed out that fetishism could be the result of neuronal cross links between neighboring regions in the human brain. For example, in 2002 Vilayanur S. Ramachandran stated that the region processing sensory input from the feet lies immediately next to the region processing sexual stimulation.",
"From the Wikipedia Article.",
"I wouldn't be claiming that congenital is a real thing, unless you have further evidence."
] |
[
"Several experts saying something ",
" is not evidence of anything."
] |
[
"Is it ever possible to experience the full effects of time in the Spacetime equation?"
] |
[
false
] |
After reading post it got me thinking about this question. If for example you are sitting at your desk right now, it seems that you're not moving at all, but in reality; the earth is spinning on it's axis, the earth is orbiting the sun, our solar system is orbiting our galaxy, and all galaxies are moving away or towards one another. So, essentially you are experiencing both effects of spacetime. Therefore, would it ever be possible to experience 100% time as photons experience 100% space?
|
[
"From your perspective, you are only traveling through time. So yes? It is an odd question.",
"By the way, you are always moving is some reference frame, and always standing still in another."
] |
[
"Nope, you would no more be standing still than you are now. There is no place or reference frame where you are only standing still or only moving. There is no such thing as absolute speed."
] |
[
"What he's saying is that you always have a velocity of zero in some frame, and a nonzero velocity in other frames, and no particular frame is objectively \"better\" (i.e. THIS FRAME IS THE UNIVERSE FRAME) than any other."
] |
[
"Do all planets rotate around the same plane/ axis ?"
] |
[
false
] |
This is hard for me to formulate but bare with me. So since outer space is a 3 dimensional space. Consider you're at the north pole of the sun looking to the sky, do all planets rotate at a single level as if they are aligned. is there even the slightest off possibilty that all planets align causing a solar system eclipse of some sorts ? Or do they rotate on different axis and planes?
|
[
"For a solar system we can calculate something called the ",
". This is the unique plane that passes through the centre of mass and is at right-angles to the angular momentum vector. It's a sort of weighted average of all the spins and orbits of all the planets (so bigger planets contribute more).",
"In our own solar system 98% of the angular momentum comes from the orbits of the four gas giants and those orbits, along with the orbits of the other four planets, are all within a few degrees of the invariable plane. But not exactly on it. The Sun's spin axis is itself a few degrees misaligned from the invariable plane, while the planets span the full range of axial tilt.",
"Smaller objects are on a much wider range of inclinations. For asteroids they still cluster around the invariable plane, just with a lot more variation than the planets, and retrograde asteroids are rare. Interactions with planets can kick asteroids into high-inclination orbits. Long-period comets show little tendency to a specific inclination; they originate from the outer solar system where orbital speeds are slow so a small nudge (perhaps from a passing star) can send a comet towards the sun at just about any angle.",
"When one planet appears to cross the sun as seen from another planet this is known as a ",
". Because the planetary orbits are not exactly aligned these aren't very common. From Earth, transits of Mercury occur once every 7 or 8 years. Transits of Venus occur in pairs with a few years between transits in a pair and then over a century before the next pair. In our solar system the relative sizes and distances of the planets mean that a transit is not a full eclipse - the transiting planet just looks like a small black dot on the Sun."
] |
[
"Relative to Earth Mercury's orbit is tilted by seven degrees, Mars's orbit is tilted by just under two degrees, ",
"etc.",
" They're all very close to being on the same plane but do not seem to have been placed by someone with OCD.",
"That's not luck. All the planets and the sun condensed from the same swirling cloud of gas. Friction and conservation of angular momentum encourage a collapsing gas cloud to spin, and for it to sort itself out so everything spins in the same direction. There are some very tilted orbits in the outer solar system but ",
" very few objects orbiting the sun \"backwards.\"",
"There are ",
"retrograde asteroids",
" but that's very very strange and not what orbits are supposed to look like."
] |
[
"Before exoplanets with highly eccentric orbits were observed, a polar orbit was deemed impossible. That was because of the accretion hypothesis.",
"It was more because we didn't really have much to go on besides the current snapshot of our own solar system and modeling complex systems with multiple bodies is difficult. It wasn't that anyone thought that objects ",
" migrate, it's just that there was no direct evidence or even good numerical simulations to back that up until recently. But it's been talked about for almost 50 years now. Which is pretty good since it wasn't until about 30 years ago that we really even had direct evidence of protoplanetary disks.",
"Retrograde orbits are proof that accretion may create planets, but solar systems evolve through other processes.",
"Which is fine but would stand in direct contradiction to your claim that:",
"We may as well toss the standard accretion model out the window.",
"The accretion model is still absolutely necessary. At best, your statement is ridiculous hyperbole.",
"Anyone reading your comments should take a moment to understand that this is certainly borne out of ",
"your complete inability to understand high school level science",
"."
] |
[
"Why do oil stains on paper appear clear, while water spots don't?"
] |
[
false
] |
I know that water and various non-polar substances reflect light differently, as in the instance of oil slicks reflecting 'rainbows' and lenses atop the surface of water...but I cannot explain why an oil stain on paper would be partially see-through while a water spot is hardly so. Anyone?
|
[
"Well, my daughter and I were interested in this so we ran an experiment with various fluids available to us here, just a moment ago. ",
"Here are the results. Now, if someone could explain the why's, that'd be awesome!\n",
"http://i.imgur.com/HJRp1mc.jpg",
" & ",
"http://i.imgur.com/I78HTDR.jpg",
"The first shows the page with the sun shining ",
" it. The second shows the sun shining ",
" it. "
] |
[
"Refractive index matching. The opacity of paper relies heavily on light scattering. Water doesn't match the refractive index of paper fibre, but oils are a lot closer."
] |
[
"Paper is made from wood pulp, which is basically cellulose; so this is a good refractive index reference, ",
"n = about 1.47",
" for paper. ",
"Oil has a refractive index that is ",
"about the same",
"Water is ",
"n=1.33",
"So from the refractive index matching part it certainly checks out [and is also the explanation that I have come across before while looking into this]"
] |
[
"How does alcohol affect vision?"
] |
[
false
] | null |
[
"It doesn't it affects the volume and composition of the fluid in your inner ear which regulates your equilibrioception.",
"This in turn affects your ability to determine which way is up and this makes you dizzy and your eyes rely on your equilibrioception to focus correctly.",
"If you look in a mirror at your eyes and tilt your head your eyes will automatically rotate in position aka you never truely see sideways.",
"When you lose equilibrioception you can't find which way is up and your eyes start to lose synchronicity which then makes them start to wander about and as a result you see double.",
"Some times blinking can reset your eye position which is why really drunk people blink heavily, in any case each eye is governed by your balance and when that is off whack they naturally wander about, when your eyes focus on two points equally you get double vision, you can correct for this by shutting one eye to some extent which may alleviate some resulting headaches as a portion of your headache may be from your eyes competing to focus while looking at multiple targets.",
"The same effects happen with vertigo and is why you can feel like the world is spinning when you lay down suffering from alcohol or vergito."
] |
[
"Great answer, I knew about the fluid but I didn’t know it affected the eyes.",
"Is this fluid a standard amount between people with different size? Or is this part of the reason that some people are affected faster from alcohol (by having less fluid or a different composition)?"
] |
[
"Multiple factors but all falls to blood alcohol percentage, the water in your ear is not like the water in the blood or brain it takes longer to dissipate so you may have sobered up slightly but still br dizzy or even sick later on.",
"Factors:",
"Body size is a big one ratio of alcohol to consume is greater to reach the percentage.",
"BMI can affect it too circulation restrictions and such",
"Food / Water intake",
"Liver / kidney function ",
"All sorts of things but mainly once you reach a certain Blood alcohol sweet spot you are going to have a bad time."
] |
[
"How would the earths orbit be effected by an increase in mass?"
] |
[
false
] |
The subject of near earth asteroid mining popped up in , and it got me wondering about the effects of mass on orbit distances. Will a change in mass cause a change to the speed of orbit or the distance at which it orbits. In my head I cant help thinking it would maintain its speed and gain momentum pushing the orbit further out. If this is the case, would that be a bad thing? Would it negate global warming? Would we have to set up some kind of mass exchange system? Every ton of metal in requires a ton of waste ejected out? Basically would the earth experience orbital changes, how significant would they be and would we need to counteract them?
|
[
"It depends on how the mass is added to the earth. If the earth just spontaneously gains a bunch of mass by magic, but maintains its speed, nothing will change. While the total momentum has gone up, so has the mass, so the specific angular momentum (angular momentum per unit mass) stays the same. In the same way, if asteroids were brought up to the same speed as the earth before being dropped off, you wouldn't have a change in orbit. If the asteroids were stationary, say if they were just chilling in the path of the earth and we were to hit them, they'd be adding mass but not momentum, and the orbit of the earth would change slightly. I'm too lazy to do the math right now, but I can say that to appreciably change the kinetic energy of the earth with asteroid impacts, you'd have to dump a LOT of kinetic energy, and a slight change in orbit would be the least of your worries, because you would be dead and probably also melted.",
"Of course, all of this is based on the approximation that the earth doesn't affect the sun at all. That's a good approximation until around the time the earth gets massive enough that the center of mass between the two bodies lies outside the sun. Just for dealing with asteroid mining, that's a fine approximation to make, since you could increase the mass of the earth by a factor of a few hundred it would make almost no difference. "
] |
[
"It depends on how the mass is added to the earth. If the earth just spontaneously gains a bunch of mass by magic, but maintains its speed, nothing will change.",
"In two body orbital mechanics, that would be true. In multi-body, it would shift the centre of mass of the solar system and could result in some significant changes... depending on the mass that is added, of course."
] |
[
"Sure, but again, a change of mass of that scale is ridiculously beyond anything you'll ever get from asteroid mining. In fact, the total mass of the asteroid belt is only around 0.1% that of earth. Also, the only planets that could possibly affect are Venus and Mercury, since from the point of view of everything outside of that, the center of mass of the system would not change. Edit: assuming the mass comes from the belt, that is. "
] |
[
"Do male enhancement products actually do anything? If so, what?"
] |
[
false
] | null |
[
"This is a question which can be answered with peer reviewed science and expertise, which is and remains the standard for askscience questions. Please stick to these sources for answering. "
] |
[
"Found a paper by Ted Manny and coworkers in 2011 with the title \"Penile Sclerosing Lipogranulomas and Disfigurement from Use of '1Super Extenze' among Laotian Immigrants\"",
"No link because you have to have a subscription to Journal of Sexual Medicine to see it and i dont feel like breaking any copyright laws. But here is a small excerpt from the paper. ",
"histologic findings consistent with sclerosing lipogranulomas were seen in specimens from affected subcutaneous and lymphatic tissue. '1Super Extenze' proved to be composed of mineral oil with tocopherol acetate (vitamin E). Conclusion. Injection of '1Super Extenze' into the penile shaft results in sclerosing lipogranulomas, which can cause severe sexual and urinary complications.",
"Did not see any other studies on Google Scholar sorry. No cool tag but im a researcher in tissue engineering and regenerative medicine. ",
"Edit 1: I did find this one article on Google Scholar about the scams in general, not peer reviewed but still interesting ",
"Clickly click",
" . In short, they are all scams. ",
"Edit 2: Putting my degrees to work, I would personally say there is no way an adult male could increase penis size with a pill or injection. Perhaps hyaluronic acid, linoleic acid, arachidonic acid, TGF-b, or other tissue growth factors could work but hyaluronic acid is temporary, linoleic acid and arachidonic acid work by inflammation and is also temporary, and TGF-b is the most promising but could cause disfigurement and systemic cancerous implications."
] |
[
"There was a study published in the British Journal of Urology that showed that a penis stretching device was able to increase the length by a third (32%) in men with below average penis size. ",
"http://www.livescience.com/3381-penile-extenders-work-doctors.html",
"This penis traction device was used for 6 hours a day for 6 months, so the doctors recruited \"highly motivated\" participants. Sounds like a lot of work, but for some pretty impressive results."
] |
[
"Can a routine blood test (CBC) detect a blood clot or pulmonary embolism?"
] |
[
false
] | null |
[
"I wish this was true but unfortunately not. Ddimer is used to help classify risk. A negative ddimer does not rule out a clot. In general ddimer should be used when a physicians suspicion is relatively low for the presence of a clot. If a physician thinks it’s unlikely to be a clot and has a negative ddimer then the patient is a very small chance of having a clot. Conversely if a physician has a high suspicion of a clot in a high risk patient then ddimer means nothing"
] |
[
"Not really, typically a D-dimer blood test is done to look for fragments of a clot as well as imaging of the areas where a clot is suspected. A CBC only shows the cells/components of the blood, it can identify a clotting disorder but it is not a good method of detecting clots."
] |
[
"This is correct. If a PE or clot is suspected a d- dinner test is run to rule it out. If it's negative there is no clot. If elevated, they will do further tests since it just indicates elevated clotting of any form. I.e. a bruise will elevate it etc. So only a negative will rule it out.",
"After an elevated d dimer they will usually run a CT scan with contrast."
] |
[
"Is Sigmund Freud's work valid? Does it stand up to more modern research? [Psychology]"
] |
[
false
] |
I ask because I hear mention of Freud around Reddit a lot, usually jokingly. But, is there any legitimacy in his research/conclusions?
|
[
"As a starting point, have a look at the ",
"legacy section of Wikipedia's Freud article",
". Your question has also been asked a lot, so ",
"there are quite a few answers on AskScience already",
".",
"When looking at contemporary psychological research, you're going to have a hard time finding any influence of Freud or other analytic thinkers on any aspect of the research being done now. The main reason is that his work was seriously flawed in terms of scientific technique or rigor (or even being science). He was interested in therapy and at the time therapy and psychiatry were more akin to philosophy than biology.",
"Some of his observations were correct, but some are just flat out wrong. A lot of his work is based on sexual development, and that was largely influenced by the times he lived in (Victorian society was not very open about sexuality). The oedipal complex is not that big a deal to developmental psychologists because sexual development doesn't follow Freud's thinking. Depressions is not hate directed inwards. Dreams are not some special symbols from the subconscious. And so on."
] |
[
"fear of spiders and snakes is there for a reason and nearly universal. A spider or a snake is just a symbol for the pain and death they can cause if treated without respect.",
"If fear of spiders and snakes is indeed prepared, then this is very little to do with treating them with respect and much more to do with them being predators at some point in human evolution. That being said, the evidence for the universality of snake/spider fear is not bulletproof. There are numerous societies where snakes and spiders are food and don't elicit fear responses.",
"Don't dismiss the symbols out of hand, they are there for a reason",
"Maybe. You're right in that I can't say that dreams definitely have no reason for being. But, it's proven very difficult to nail down a reason for us having dreams. My feeling is that this is good evidence against Freud's view, given how important he felt that dreams and their interpretation was. The disconnect between waking life and dreams is just too strong, in my opinion, for them to have the function Freud thought they did.",
"This may be true, however working with dreams can be very therapeutic.",
"I don't know enough about dream interpretation therapies to comment, just want to mention how many hundreds of different therapeutic techniques we've developed. I think people should engage whatever therapy helps them, but it'd be ideal if it was evidence-based practice."
] |
[
"Luckily there was an ",
"AskScience question exactly on this",
", so I don't have to waste any more time on Scholar today. Oh wait, I'm meant to be researching review articles. Back to Scholar!"
] |
[
"Humanity's dominant sense is vision - why then does a significant proportion of the population have poor eyesight?"
] |
[
false
] | null |
[
"The book \"Why we get sick\" by Nesse and Williams discusses this in one of the chapters. Natural selection selects for genes that increase an organism's ability to pass on their own genes (reproduce and make sure your offspring reproduce), regardless of whether or not the individual desires the trait associated with that gene. In humans, miscarriage occurs in a fairly high percentage of pregnancies, often without the mother ever knowing she was pregnant (This is why IVF clinics implant fairly large numbers (~7) of fertilized eggs). Nesse and Williams discuss that myopia (near sightedness) may decrease the percentage of pregnancies that result in miscarriages. So even though someone with myopia may not want myopia, the trait will be selected for if it means that person will have more offspring than a non-myopic person. Edit: Also, having myopia today is not as life threatening as it may have been for cavemen. If you live in New York you are unlikely to be eaten by a tiger regardless of how good your vision is!",
"Another example of this is Huntington's disease. ",
" (Edit: See Darkaardvark's comment) Huntington's symptoms tend to begin around age 40. Since many people reproduce before age 40, the debilitating effects of the disease do not decrease the ability to reproduce and the gene is not selected against.",
"Edit: More food for thought, if a hypothetical mutation appeared that caused exceptional vision, but also made the person sterile, it would never be passed on, no matter how desirable eagle eyes are."
] |
[
"optometrist here: one of the theories for the increase in myopia is that an increased amount of near-work increases myopia. so for instance, studying in school have been shown to make you more nearsighted. There has also been shown to be a genetic component for refractive error. Since glasses can correct for refractive error, poor uncorrected eye sight does not make you less likely to be able to reproduce so poor eye sight is still prominent in our society. "
] |
[
"I think it's a leap to say that Huntington's disease is kept around by some selective pressure. As you point out, a disease that only affects individuals after the time period where they would typically reproduce can not be selected against. But that doesn't imply any selective advantage in the mutation--just that it is not selected against. ",
"There may well be some linked traits to Huntington's that I don't know about that do tend to be selected for--an analogous example would be sickle-cell anemia, which continues to be prevalent (especially in Africa) because it is cross-linked with an immunity to malaria. But I don't know about any such 'side-benefit' of Huntington's. ",
"Your general point is well-made and correct as far as I know, however. "
] |
[
"Is it bad to eat entire sunflower seeds?"
] |
[
false
] |
I mean including the shell. If so, why?
|
[
"Aha, yes that what I was looking for. For some reason (not an expert) I had imagine the opposite, that the shells would act like fiber. Thanks for the link."
] |
[
"Aha, yes that what I was looking for. For some reason (not an expert) I had imagine the opposite, that the shells would act like fiber. Thanks for the link."
] |
[
"Every few years or so I'll forget that eating sunflower seeds with shells is a bad idea. I'll eat a whole bunch and then end up shitting razors the next day. There will be blood. "
] |
[
"If I try to lift up an object I cannot lift, where does all the energy go? My arms get tired from the exertion, but I haven't transferred any \"energy\" as I know it (kinetic/potential/chemical) so where does it go?"
] |
[
false
] |
[deleted]
|
[
"It becomes heat. ",
"The mechanics of muscle contraction are pretty hairy, but basically if the muscle contracts but cannot shorten some of the energy in the actinomyosin thingy has to be dissippated to compensate. This can become a vibration in the arm, or simply produce heat by the decomposition of high-energy phosphates.",
"(Usually, if it seems like energy is \"lost\" in something, it becomes heat.)"
] |
[
"The reason you don't notice the heat output is that thermodynamics operates on a whole different energy scale than you're used to: heat, under standard conditions on Earth, requires a shitload of energy.",
"To put this in perspective, imagine you heat a cold pint of beer from freezing to room temperature. A pint is about half a liter, and this is Budweiser, so the physical properties are identical to those of water. It starts at 0 C, and heats up to room temperature at 25 C. The specific heat of water (Budweiser) is about 4200, so heating half a liter, which weighs half a kilogram, requires: ",
"25 * 0.5 * 4200 = 52500 joules!",
"That's a lot of energy to heat one measly pint of beer! In fact, this is so much energy that if you could convert it to kinetic energy and throw the beer up in the air it would go (ignoring air resistance) higher than the top of Mount Everest -- ",
"The thing is you ",
" directly convert heat energy to kinetic energy. That's the Second Law of Thermodynamics. You can, however, turn kinetic energy into heat energy, which is what happens when you can't lift something.",
"But as you've seen, even the greatest exertion you're likely to muster won't heat your body significantly. If you pulled on a car for an hour, you might heat your arms by, say, one or two degrees. That's not to mention all of the heat getting carried away by the atmosphere; in fact while you're doing all of this work your body has to expend ",
" energy just to stay warm!",
"And that's why poor people can't afford to heat their houses. :p"
] |
[
"If the object is on a rigid surface and does not move no potential energy will be transferred to it. Work is done only when a force acts along a distance. The main source of energy loss here is in the mechanics of muscle contraction. ",
"Are you referring to the elasticity of seemingly rigid objects acting as a spring to allow small movement?"
] |
[
"Does the eye color gene follow simple Mendelian genetics?"
] |
[
false
] |
Briefly, my neuroscience teacher said this once, and I was wondering if it is true, or if there is ever a possibility where it doesn't follow? Thus, could a blue eyed person and a green eyed person make a brown eyed baby? Arent both blue eyes and green eyes recessive to brown, thus the parents would be homozygous recessive?
|
[
"It isn't simple Mendelian Genetics, because that would be 1 gene with 2 alleles (2 forms of the gene). There are many traits that are controlled by a single gene with 2 alleles. BTW, the alleles are located on separate chromosomes. You get 1 set of chromosomes from Mom, and the other set from Dad. This gives you 2 of each chromosome.",
"Simple Mendelian Genetics include: attached or detached earlobes, widow's peak, and cleft chin",
"Eye color is handled by many genes. There are at least 3 genes that contribute to eye color. ",
"http://www.athro.com/evo/inherit.html",
"There are also traits controlled by 1 gene, but with more than 2 alleles. The 4 kinds of blood type (A, B, AB, O) are controlled by 1 gene with 3 alleles. Both A and B are dominant over O, but neither is dominant over the other (codominance)."
] |
[
"http://en.wikipedia.org/wiki/Eye_color#Genetic_determination",
"\nIt's pretty complicated."
] |
[
"No, its not, eye color is polygenic, same as skin color, height, weight, gut morphology, eyelash length...etc..."
] |
[
"Which others diseases have we discovered to have a heterozygote advantage? (besides sickle-cell, tay-sachs, and cystic fibrosis)"
] |
[
false
] | null |
[
"That would be a decided disadvantage... I think he is asking about diseases where being a heterozygote carrier of a deleterious mutation is actually beneficial. Getting retinal cancer isnt beneficial"
] |
[
"Familial retinoblastoma."
] |
[
"Can you be more specific? Which disease is disadvantaged by Familial retinoblastoma?"
] |
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