text
stringlengths 24
30.8k
|
|---|
Scientists of reddit! Settle a bet for me. What affects the temperature of the seasons if it's not the tilt of the earth on its axis?
Cross post from askreddit, wasn't sure where I should put this. At stake in this bet: the very usefulness of Reddit. My friend thinks we are all sexless geeks. Prove him wrong by showing him how geeky you are! Whoever answers this question first (he's asking books, pshh) wins. Here's what I think I understand: The tilt of the earth on its axis of rotation makes the seasons, because of the angle at which sunlight hits the planet's surface. So the less sunlight the earth gets (shorter daylight duration + the more acute the angle at which it hits the earth's surface), the colder it is, right? But here's my question: The shortest day of the year, the winter solstice, comes in early December. It begins the winter season. If the thing I said above about sunlight were true, the winter solstice would come smack dab in the middle of winter--the coldest day, the least sunlight. So what is it that makes winter last until March, getting progressively colder until then, if the earth is getting progressively more sunlight during that time. Residual cold in the oceans? Please someone explain to me!
Check out what's called for the answer to your question. In a nutshell, it's the oceans and the rate at which heat radiates away versus stays. |
Do space launches account for the flight path of existing satellites?
As more satellites are launched into space I would imagine that there is an increased risk for collisions. Is there a map of current satellites as well as space junk?
To an extent yes. As for a map of space debris, this is publicly available at https://celestrak.com/ . Celestrak publishes the Two Line Element sets for everything that is observable to the ground (with only a few items missing such as a handful of spy satellites I believe). These TLEs give you the data needed to figure out where an object is at any point in time. They're only accurate for a short time though, and so the catalog is updated regularly (really anytime an object is observed). This can be every few hours for especially big things like the ISS, but may be days and sometimes weeks for new smaller objects. |
Are the effects of different carcinogens/mutagens cumulative?
I joke with people that I'm not overly cautious about lab safety (e.g. I don't freak out if I spill a drop of benzene on myself, though I do wash it off immediately) because I smoke cigarettes, so it's not going to be the benzene that kills me. Is that actually true, or are the effects cumulative/additive, assuming it's the same tissue (e.g. inhaling residual benzene fumes & cigarette smoke)? Does it depend on the type of DNA damage (like oxidative vs UV, and/or deletions/insertions vs DSBs)? Or does that not matter, because all of them can result in changes that can result in cancer?
Cancer is extremely complex. It is characterized by a number of different changes within the cell such as self-sufficiency of growth factors, evades apoptotic signals, immortality, able to metastasize, etc. Each of these characteristics are controlled by large pathways, and dozens of proteins. Therefore, there are a number of changes that have to occur for a cell to become cancerous. A single mutation is very unlikely to do this. For the most part, mutations tend to fall into either being silent or missense (change in amino acid of the protein product). These generally do not have a huge impact on the protein product (missense can, but it really depends on how different the new amino acid is from the original, and where the mutation occurred within the protein). Therefore, cells generally don't even notice these changes. Although, nonsense or frameshift mutations (which can occur from 1 nucleotide changes) can cause huge problems for a protein such as producing truncated/inactive forms, or overly long proteins due to the loss of stop codons from frameshifts. Even then, this is only one gene product that has been grossly changed. This isn't enough to push cells into a cancerous state, but definitely makes them a little more sensitive to it. |
This article seems highly sensationalized. It's about using quantum computing to break complex encryptions. Is this actually any threat?
No. It is true that quantum computers can do prime factorization in polynomial time ("quick"), something we have known since 1994 . However, we are nowhere near building a quantum computer powerful enough to do this. There are other cryptographic systems which are not easily broken by a quantum computer and research is being done into new systems which are resistant to quantum computers. Cryptography would evolve, like it has been doing for centuries. For more information see the wikipedia article on Post-quantum cryptography . The only thing that would treaten crypthography as a whole would be a proof that P= NP . |
What would happen if every mosquito on earth dropped dead right now?
This includes every mosquito egg, larva, etc from every mosquito species.
Depends on the region you are considering. In the arctic, which has very low species richness, you would have removed one of the key links in the very short food chain. Migratory song birds which feed of the adults would go hungry and probably fail to breed. Char and lake trout who feed off the larvae and nymphs would loose their main food source. These effects would then work up and down the food chain. INB4 "blackflies will take up that niche": Blackfly larvae could not substitute for mosquito as they live in biofilms on rocks in springs with strong current. Mosquito larvae colonize small stagnant pools and lakes and ponds with low currents. very different conditions. |
How come our muscles get tired even when no work is being done?
If for example there was a large heavy rock rolling down a hill, and someone were to hold it in equilibrium, afaik no work would be done in the act of just holding the rock in position. But something like that would still obviously cause the person's muscles to become fatigued. What's going on?
If we were a solid object we wouldn't be doing work, but the human body is made to be able to move. We could have been made like robots who could "lock into position" and so not do work when holding stationary, but the evolutionary solutions is muscles that contract, so that even if we are not moving on a large scale, on a microscopic scale work is being done, as chemical energy is converted to microscopic movement against a force, which is then ultimately converted into heat. Some of the chemical energy is converted to muscle tension (mechanical potential energy) but ultimately as that tension is released during muscle relaxation work is done on a microscopic scale as atoms move small distances against forces. |
Theoretically, could a person's head or brain be kept alive and conscious separated from the body?
It's never been done with humans, but monkeys, dogs, and rats have had their heads severed from their bodies and kept alive. ( source ). |
Is there a limit to calorie intake in a period of time?
Does the body have a limit of calories in can store from food consumed in a certain amount of time? What I mean is, if I eat within 1 hour say 50,000 worth of calories (say I'm eating high calorie nuts like cashews and pecans). After some time the food is digested and removed from my body. During this period, did my body intake 50,000 worth of calories? Is there a limit? is it dependent or something else?
If you were to consume 50,000 calories, the densest form you could eat it would be pure fat, which would be roughly 12 pounds of pure fat (9 calories per gram of fat). Your body would likely slow down your speed of motility of the fat from your stomach to your intestine so that there would be enough time for it to all be absorbed. If your body could slow down the rate enough, you would absorb all 50,000 calories of fat and likely store it (minus the calories it took to digest the fat). If your body cant slow down the rate of emptying enough, you would overwhelm the enzymes, and bile salts that emulsify and break down the fat, and some would just pass through into your colon. This second option is much more likely as you can have a greasy stool with a much lower amount of eaten fat. Also eating 12 pounds of fat in one sitting would be near impossible. |
How do we know there was a single common fish ancestor that got out of the water, and not several?
How do we know it was just one, and not several of them in different situations? That would explain the different evolutional trees occurring.
The premise isn't necessarily that we're descended from one single "Fish", but rather that we all evolved from one single "Something" at some point. We can look at shared features and shared DNA that carries from one ancestor to the next and we can measure the differences within and between groups. So we can see these points in time where a major split occurs: One family grew "lungs" and one or more did not. So we can see the ancestors of the ones that didn't and the one that did and compare similarities up until that split point. If your question is more "How do we know that two similar species didn't evolve separately, then interbreed", the answer is: We don't. In fact, recently we think cross-species mating and interspecies hybrids were a lot more common than early Darwin theory would suggest - Homo sapiens, for example, have a not insignificant quantity of Neanderthal DNA in their lineage. |
Does it take more energy to heat a house/apt by turning the thermostat off when you leave, or just turning it down slightly.
If it is better to turn the thermostat down slightly, then how much? In both cases, how come? Does the size or layout have an effect?
The purpose of the furnace is to replace heat lost through the walls and roof of the house. The rate of heat loss is proportional to the conductivity of the wall material, the area of wall, and the temperature difference. The first two of those you can do nothing about, but the smaller the temperature difference between inside and outside, the less heat will be lost. Thus it is always more energy efficient to turn the thermostat all the way down. Although it might not be as comfortable when you get home. |
Antibiotic Resistance - how does that work on the individual level?
To simplify my question, I always tried not to take antibiotics (or general medicinal drugs for that matter) unless I have to, under the notion that if i ever do need to take antibiotics, it will have a stronger effect on me, possibly helping me overcome health problems that would otherwise take longer to cure. So my question is, does avoiding antibiotics (or similar drugs) until absolutely necessary the smart thing to do? or should I just take them anyway whenever there is a slight need, since it actually doesn't matter?
You should take antibiotics only when prescribed by a doctor, but when prescribed, take the entire course as directed. You seem to have a common misconception - you don't become resistant to antibiotics, the bacteria that are infecting do. If you don't take them as directed, the chances of becoming resistant are higher, and that means it will become harder to treat. Likewise, using antibiotics when they're not indicated can drive resistance in other bacteria that get increased exposure. Again, follow your doctor's directions. You might want to read this recent piece about the misconception about antibiotic resistance: http://www.theatlantic.com/science/archive/2015/11/people-are-really-confused-about-antibiotic-resistant-infections/416118/ |
If all substances try to move towards the most stable state, why do we have substances that are not stable in the first place?
Some substances can be trapped in what is known as a "kinetically bound state". It's an energy state that isn't the lowest, but the substance stays there anyway. There is always an energetic cost to convert from one state to another, and sometimes it is just too high for it to happen. Diamonds are an example. Given enough time, they will spontaneously become lumps of coal, which has carbon atoms arranged in a lower energy configuration. But to do this, you will need to completely change the bonding of the carbon atoms involved -- and in this situation it is extremely hard to do. Is this helpful? |
This may sound stupid but do animals of the same species that have lived in different countries have the same "language"?
Not a stupid question, there's a lot of research going on in to that exact question. Here for example we see that the mating calls of cricket frogs are different depending on where they live, due to adaptation to environments with different acoustic qualities geographic variation in Animal communication systems I'm aware of a lot of other cases of populations with different ' regional accents' whales of the same species who sing in different frequencies, finches with different melodies to their songs, chimps with differing lengths of calls, even domestic cattle with different ways of saying 'moooo.' What would be really interesting to know is whether any animals capable of semantic representation, such as chimps or prairie dogs which can have a specific call to indicate a specific predator or prey species or individual member of the group have in-group calls not recognised by outsiders of the same species. |
Asteroid planned to 'hit' earth next year. How likely is this?
Taken from this article; How likely is that the impact will happen? Has this asteroid been in orbit of our solar system? Follow up: If this is a hoax, say that an asteroid this size will hit earth, what will the damage radius be?
The article is a hoax. Ignore it. DA14 is a -3.29 cumulative on the Palermo Scale . Anything under -2 is not considered something to be given serious impact consideration. In other words, not even worth mentioning. Answering your other question... Even if you assume the worst about the makeup (a stealthed iron core), it wouldn't be as bad as Tunguska, most likely. Some rough numbers: Your Inputs:
Distance from Impact: 100.00 km ( = 62.10 miles )
Projectile diameter: 44.00 meters ( = 144.00 feet )
Projectile Density: 8000 kg/m3
Impact Velocity: 7.82 km per second ( = 4.86 miles per second )
Impact Angle: 48 degrees
Target Density: 2500 kg/m3
Target Type: Sedimentary Rock Energy:
Energy before atmospheric entry: 1.09 x 1016 Joules = 2.61 MegaTons TNT
The average interval between impacts of this size somewhere on Earth during the last 4 billion years is 1.5 x 103years Major Global Changes:
The Earth is not strongly disturbed by the impact and loses negligible mass.
The impact does not make a noticeable change in the tilt of Earth's axis (< 5 hundreths of a degree).
The impact does not shift the Earth's orbit noticeably. Atmospheric Entry:
The projectile begins to breakup at an altitude of 1170 meters = 3850 ft
The projectile reaches the ground in a broken condition. The mass of projectile strikes the surface at velocity 7.46 km/s = 4.64 miles/s
The impact energy is 9.94 x 1015 Joules = 2.37 MegaTons.
The broken projectile fragments strike the ground in an ellipse of dimension 0.0675 km by 0.0502 km Crater Dimensions:
What does this mean? Crater shape is normal in spite of atmospheric crushing; fragments are not significantly dispersed.
Transient Crater Diameter: 908 meters ( = 2980 feet )
Transient Crater Depth: 321 meters ( = 1050 feet )
Final Crater Diameter: 1.14 km ( = 0.705 miles )
Final Crater Depth: 242 meters ( = 793 feet )
The crater formed is a simple crater
The floor of the crater is underlain by a lens of broken rock debris (breccia) with a maximum thickness of 112 meters ( = 368 feet ).
At this impact velocity ( < 12 km/s), little shock melting of the target occurs.
Thermal Radiation:
What does this mean? At this impact velocity ( < 15 km/s), little vaporization occurs; no fireball is created, therefore, there is no thermal radiation damage.
|
What is the largest an animal could possibly be?
I was reading about the largest organisms in the world on wikipedia and got to thinking. I know that on Earth, an organism's size peaks out because at a point they can't have enough muscle to keep themselves standing. Just making something bigger and bigger doesn't work, so no King Kong is going to happen here on Earth. But on a planet with lower gravity, or a different atmospheric makeup, could larger and larger animals be possible? Is there a point where, regardless of the environment the creature is in, it's not possible to be any bigger? That the creature would collapse under it's own gravity, or biological processes just would not function anymore?
There is a whole (contentious) field of study that kind of asks this question called allometry . Basically, it says that many things scale at very different rates. For example, if you increase the size of a sphere, the surface area increased at a rate of while volume increases at a rate of These scaling laws, if they're real (the contentious part), strongly affect a whole bunch of animal properties. For the purpose of your question, it limits size for a number of reasons (of which I'll just give a couple): since your mass increases at a much faster rate than your size, your skeletal structure (whatever that may be) reaches a limit where the skeletal integrity won't be able to support the mass. This is the "gravity" issue people are referring to. the rate of diffusion doesn't change as mass gets bigger, which means that oxygen diffusion through your body (which happens in all animals - even mammals at the facet of capillaries) will start to be ineffective as you get bigger. This be why larger animals have slower metabolisms - because they don't have enough oxygen to have fast metabolisms (physiologists, please correct me if I'm wrong - I'm going off memory of a couple of Brown papers I read four or five years ago). this one I'm going out on a limb, so please take it with a grain of salt: the speed of nervous reactions is not instantaneous, so even if you solved the other scaling issues, my guess is that a giant body would be very uncoordinated (literally). I suppose this could be solved with a decentralized nervous system, but I'm not sure. Fun question! |
How much sleep is really necessary for one to get through the day?
I tend to get only about six hours of sleep a night. With a coffee in the morning and possibly an energy drink in the afternoon I'm able to handle a full day of high school plus the commute to my school without getting too tired. How much sleep to we really need to function with a decent amount of energy?
Adolescents, children and young adults require more sleep than middle aged people do. A typical high school student requires 8.25 to 9.25 hours of sleep a night. Lack of sleep has negative effects on health and intellectual functioning. http://en.wikipedia.org/wiki/Sleep#Optimal_amount_in_humans |
How small could you compress the universe if the fundamental forces didn't exist?
The only thing holding atomic nuclei apart is electrostatic forces, right? (Ignoring kinetic energy for electrons and things). Is there a similar deal for quarks/leptons? If the 4 basic forces stopped working, could an atomic nuclei be condensed? Could a hadron? How about a quark, or a lepton? Could the whole universe be condensed to a point, or do things at that level actually touch each other in some way?
If the 4 basic forces stopped working, could an atomic nuclei be condensed? Could a hadron? How about a quark, or a lepton? No, not without a lot of energy at least. All quarks and leptons are fermions, and fermions cannot occupy the same state - it is called Pauli exclusion. If you want to start putting fermions in a well defined finite space - call it a box - then you can pack two into the lowest energy state, and two more into the next highest energy state, and so forth... The more fermions that you want to pack in the box, the more energy you need. The smaller that the box is, the bigger the difference between energy states and the more energy needed to pack a given number of fermions into the box. This is the case even for completely non-interacting fermions, with the fundamental forces completely turned off. In fact, on the order of half of the resistance of a common metal to being compressed comes from Pauli exclusion, not from electrostatic repulsion. EDIT: You absolutely need gravity to provide the energy needed to compress fermions to arbitrarily small volumes. |
Is the space-elevator just a "pipe-dream"? Why, or why not?
The material strength requirements are a bit unrealistic, they have to start imagining things like carbon nanotubes that are a hundred miles long, with no defects. Seems pretty pipe-dreamy to me. |
What is the ghosting i feel after a day on roller coasters?
today, i visited a theme park, and spent a good chunk of my time upside down, spinning, and falling. Every time i do this, that night, tonight included, i feel the exact same G-forces applied to me. pressure to my head, then pressure to my rear and feet. it washes. this "ghosting" starts as soon as i settle down for the night, and lasts for hours. oddly enough, it doesnt start until a few hours after leaving the park and being home. is it an inner ear thing? i would think my ear would have settled down after an hour or so of riding. is this common, and what the heck is going on?
Inner ear makes sense, you have small stones that sway when your head moves. The other is that all the swirling has created some current in your cerebrospinal fluid. maybe more or less of it gets reabsorbed when you jostle around and you're high or low. |
Does Alzheimers/Dementia affect muscle memory?
Sorry if this is a stupid question, but do memory loss diseases affect motor skills/muscle memory? Or is something like that lost when other memories are lost. Thanks
Hmm the answer here is dual. Technically yes, but not for the reason you'd expect. What people (and probably you as well) think of when they think of Alzheimer's is a memory disease. This is because Alzheimer is a neurodegenerative disease, and the hippocampus is among the first areas that get compromised.
Now the hippocampus is the area responsible for storing new memories and creating them and. So Alzheimer causes memory formation loss and subsequently memory retrieval by the degeneration of more and more brain space. However, this part of the brain is not responsible for learning motor skills or ''muscle memory''. In fact studies show that people with Alzheimer's not only can still ride a bike or whatever, but they can in fact also still new motor skills. Interestingly, they can do so without explicitly remembering learning the skill itself*. This is because motor skills (formation) and motor execution/planning are not skills that are dependent on the hippocampus, but rather cortical or striatal regions. HOWEVER Alzheimer's just a disease of the hippocampus. It's a neurodegenerative disease of the entire brain, it's just most apparent in the hippocampus. Because the entire brain is affected, you can indeed see mild motor problems in early-stage Alzheimer. Motor learning will eventually become compromised as well as motor execution* *. Eventually any skill will be near impossible to conduct or learn. So yes, muscle memory will eventually be affected. However, this process has nothing to do with the typical view of Alzheimer's being a memory disorder. * http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2039835/
* * http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3121966/ |
What exactly causes burns?
I understand that burns can be caused by a variety of different sources (radiation, chemical, electrical, friction, etc.), and it seems that most of these are in some way related to temperature extremes. So why do all these different sources cause similar injuries? Is there a similar underlying cause? If so, what is that cause?
In addition to heat, chemicals (specifically acids/bases) and radiation (including UV light) can cause protein denaturation leading to a burn. After the initial injury (heat/chemicals/etc) the body reacts by producing an inflammatory response which leads to blisters, swelling, and many other changes we associated with burns. |
If I have to wake up in 30 minutes, is it worth going to sleep now? At what point (if any) would it be better to just power through the night?
Studies suggest that 20 minute naps are ideal for a quick energy boost. If you go beyond that you have a high chance of waking up in a deeper sleep state and end up with something called 'sleep inertia', which is something that makes you feel groggy. Waking up in sleep stage 1 is ideal. Reference: https://en.wikipedia.org/wiki/Sleep#Stages |
What shape is the universe?
The universe is a sphere of radius 46.5 billion lightyears centered at Earth. What do I mean by the observable universe? Well, the universe is currently 13.8 billion years old. The furthest objects we can possibly see are ones whose light was emitted 13.8 billion years ago. But due to the expansion of the universe in that time, those objects are now even further away! After all, they've had 13.8 billion years to move away from us. If we could measure the distance to them now, we'd find that distance to be 46.5 billion lightyears. Beyond that 46.5 billion lightyear sphere, we don't know what the universe looks like. It might go on infinitely forever in every direction (infinite, unbounded). It might start repeating itself after a while and have identical copies of the same "unit cell" tessellated over and over again (finite, unbounded). It might just have a boundary and end somewhere (finite, bounded). We don't know, and have no way of knowing. Bonus fun fact: If the universe did repeat the same bit over and over, and the "unit cell" was smaller than our observable universe, we'd possibly be able to detect it by seeing the same object in multiple locations on the sky. Astronomers have carried out searches for such a repetition in the cosmic microwave background, and there appears to be no indication that we're in a repeating universe. |
Has there been a disease that was beneficial to humans?
It depends on how you want to interpret that question. Let's take a classic example: sickle cell anemia . Individuals who carry both alleles for sickle cell have the disease, which is serious. However, individuals that have only one allele for SCA are protected from malaria . So is the disease beneficial to humans? No, not if you have both alleles. But you might make the case that it is beneficial if you are an unaffected carrier. |
Is it feasible to make a nuclear powered steam train?
By using the heat of radioactive decay to boil the water. Or would it be more effective to use that energy to power a turbine that then powers an electric engine? How would one look? Obviously no tender needed for coal, but would it be heavier because of the shielding? What if it runs out of water? I'm picturing this massive black beast at the station, that leaks steam and hums gently due to the reactor. :P EDIT: Just to clarify. I just want to know if I can get a steam engine running by using radioactive decay as a heat source instead of burning coal.
It's not impossible, but it's probably unfeasible. There's patents and designs for all sorts of these things- nuclear powered space ships , submarines , planes , trains , (plantains?) etc etc. That last link about nuclear trains is something I found in the news- I'm not sure how reliable that source is or how likely it is to come through, but, as is tradition, if it sounds like mad science it's from Russia. The nuclear powered planes never got built though, for precisely the reason of weight and radiation shielding, and I expect a similar issue to arise if those Russians try to build that train. The difficulty is that nuclear power is expensive, especially building and deploying the reactor, even if you had a suitably scaled design that could fit in a locomotive (I'm not a nuclear engineer, so I'm not entirely sure how feasible this is). Nevertheless, I doubt you'll ever see widespread deployment of 'personal nuclear reactors' on the scale of trains and cars because they are dangerous when mishandled. Nuclear fuel and power generation is concentrated in a few very well guarded places - power plants, national labs, and military installations. An eager terrorist party would have a much easier time getting their hands on a nuclear car or nuclear train (if they existed) and making a mess with that material. Of course, it's a common misconception spurred by Hollywood that nuclear reactors can be detonated like bombs- nothing is further from the truth. But, if radioactive material were included in an explosion driven by conventional explosives it would make quite the mess. That's not to say that the radioactive material would enhance the explosion, but rather that it would spread two things: dangerous radioactive material, and panic. |
Can I train myself like a dog?
When you train a dog, every time he's successful, you can give him food, and he associates it with the success, so he gets better. Can I do the same with myself? Like, for instance, when I manage to play that guitar riff, I eat a M&M's. Will I get better that way?
It's also not the same scale of task - learning (or wanting to learn) a guitar riff is not the same as telling a dog to sit. If he were to get someone else to reward him with something small like a treat for doing very small tasks, it would be similar. Rewarding yourself is related to motivation; rewarding in classical conditioning requires someone else to do the rewarding, generally speaking. Also, motivation is incredibly related to learning and how receptive one is to new information. There are scores and scores of journal articles and books on the topic. Not all educators rely upon motivational theories as their underlying learning theory when teaching, but many do. |
Research has been done on the effect of gut microbiome on behaviour. Has any research been done on the effects of sharing elements of one's microbiome with a partner, through things like kissing and oral sex, might have on behaviour within the relationship? [medicine] [human body]
See title
We know that the microbiome does spread from person to person. In fact, a simple kiss can transfer thousands of bacteria. I can think of two effects this would exhibit on your health and behavior.
First, as two peoples' gut biomes align, they would start craving similar foods. As far as we know, the strongest behavioral effect a biome has on its host is the ability to manipulate what it eats. Ie. If we eat a lot of vegetables, the fiber loving bacteria in our gut will grow more dominant, and will cause us to crave after the type of foods the bacteria likes. In fact, those foods will start tasting better to us, since it has been shown that the bacteria can indirectly alter our brain chemistry. This is very real.
Second, people who live together and share similar microbiome profiles will show similar levels/types of oral decay and periodontal disease. This is relatively new research, but the thousands of bacteria that inhabit your mouth and form the plaque on your tooth surfaces play a large role in your oral risk factors to decay and perio, as well as dictating the microbiome profile in you gut. Theoretically, a skilled dentist could predict the state of your mouth by simply taking a sample of your oral bacteria. It's a little more complicated than this, and I'm not the expert to ask about this, but your microbiome has a much larger effect on your health and behavior than we give it credit for. |
Is sad music sad because we grew up associating it to sad movies? Or is it because the melody is objectively sad?
It's the dissonance. The pitches of minor chords are not in very symmetrical frequencies. This dissymmetry is somewhat unappealing to the ear, and is therefore associated negatively. |
Can characteristics of same plant species vary from one place of growing to another?
I'm just reading about some plant healing effects, how it's less effective if it was grown in Europe instead of Egypt, and I find this absurd.
Yes, plenty of plant attributes change depending on light availability, soil composition, local competition, weather, nutrient availability, water availability, etc. While every plant species is different, most are highly adaptable and can change in significant ways depending on environmental context. As a general example, a plant that grows under a lot of shade cover from other trees may grow to be very tall to get more sunlight, but may have smaller leaves to compensate for the stem energy allocation. On the flip side, if this plant grows in an area with no shade above it, it may grow to have a short stem with larger, broader leaves to maximize immediate photosynthesis. These attributes could then carry over to something like the 'healing effects' given in your example; because the plant allocated more energy to a certain structure during growth, that structure could have a different effect on our bodies if we ate it. tl;dr - Most plants can allocate energy towards different structures and functions to maximize their fitness given the environmental context. This changes the characteristics of full grown plants. |
Would a laser that produces light outside of the visible spectrum damage your eyes in the same way a typical colored laser would?
Yes, it can actually be more damaging because with a visible laser your blinking reflex will protect your eye after the first fraction of a second. |
The old 'travelling at the speed of light and turning the headlights on' chestnut
So someone posted an explanation to this problem here: . My question regarding it is here:
You can't travel at the speed of light, period. If you're travelling very close and you turn on the lights, the light appears to be going at the same speed for you, and someone at rest. This is one of the principles of relativity, that the speed of light is the same in all inertial frames. If you're travelling at 50% the speed of light relative to something, and you fire a missile forward at 50% the speed of light relative to yourself, it's not going the speed of light, it's going at 80% the speed of light. The actual formula for adding velocities v1 and v2 is v=(v1+v2)/(1-v1 x v2/c ). v=v1+v2 only works for things moving very slow. You can show this with a Taylor expansion. |
What does AskScience think of stem cell treatments for organ transplant recipients?
I'm interested to know what AskScience thinks of this study. My questions:
Is there really hope for stem cell treatments to aid in transplant patients? Most definitely there is. This is an active area of study and one that does show promise. There's a lot of unknown, and years of study ahead before this becomes common-place, but it's definitely something that is being examined. That said not bone marrow recipients are able to entirely avoid rejection drugs and the reasons for this are extremely complicated, but relate at least partially to different tissue markers. What's being done here is basically tantamount to providing a bone-marrow transplant as well as a kidney transplant. This will not be possible in all cases, and increases the risks of graft vs. host disease as well. There are many hurdles. Is this something that those in the medical field have dreamed of doing but never realized until now? I'd say no, we just haven't have the technology in place to perform some of these things until recently, and then of course it has to be proven in animal models before it's scaled up to human trials, at least typically. Is the study reputable? It's not really a study so much as a case-analysis of an experimental procedure. It worked in this specific circumstance well, that doesn't unfortunately prove very much. I also can't find the original notes to it anywhere, so it's tough to deeply examine. Is there any hope of one day using stem cells to actually repair damaged organs? We are studying the possibilities of self-grafts and cloning organs, but these technologies face considerable hurdles as well. |
Why do people feel stiff when it rains?
My muscles always feel tight when it rains and I've heard several other people complain that their bones ache. What causes this?
When it begins to rain and as it rains, air pressure rises. This rise in barometric pressure causes more strain to be put on the muscles and joints in order to support the body as it will weigh slightly more. People who have arthritis, sprained muscles, or another ailment of the sort will be able to feel these changes when a storm is approaching due to the rise in pressure placed on their bodies. My grandma can tell with near certanty when it is going to rain and how bad it will be from the increased pain she feels in her bones |
If you could somehow evenly apply an increase in the rate of neuronal action potentials across the entire brain, what effect would that have?
What effect would that have if you had a mild increase? moderate increase? severe increase? Would it be dangerous? Healthy? Would you 'use up' your brain faster (haha probably the least scientific way to describe this)? Would it 'fill up' your brain?
There is actually already a well studied way to apply an increase in the rate of neuronal action potentials across the entire brain. Electroconvulsive Therapy . But really at almost any level of intensity this would just be like giving someone a seizure. |
How early do you think a child should learn about SR, GR, and QM? How about calculus, topology, complex analysis? What do you think is the most important thing to teach to a middle-schooler?
They should learn about them when they're interested in them. The most important part in my development as a physicist was that my parents made sure to encourage my curiosity. When I was kid I liked to take apart electronics, and they let me. I wanted to learn to program, they let me. When I wanted to to learn to draw and paint, they let me. In my senior year I didn't win any science awards, I won the award for top art student. But after high school I chose science and now I'm in the last year of my PhD in theoretical physics. |
What is the Physical Consistency of the Surface of the Sun?
Yes, it's a big ball of plasma, but what is its surface like? If you had sufficient protection from the heat, radiation, and the like, would you be able to "stand" on it, like you could a solid? Or would it be more like a liquid that you could swim in? Or would you just fall through?
If you have a magical space suit that can resist the pressure, you'd eventually reach a point at which you're neutrally buoyant and float, but otherwise you'd be compressed too and just keep sinking. The density at the Sun's core is 150 times the density of water but it's still a plasma with no solidity to it since the particles are all moving too fast to bond to each other and hold each other in place as a solid. |
Why is Athlete's Heart considered a benign condition whereas Hypertrophic Cardiomyopathy is potentially dangerous?
More specifically, does anyone know what the underlying difference(s) are that would make the former 'benign', while the latter is considered the leading cause of sudden cardiac death, especially in athletes?
These are pretty good answers, but there's a central idea buried in there that I just wanted to state outright: Athletic conditioning gives you a heart that is slightly bigger, but much more efficient at pumping. Hypertrophic cardiomyopathy gives you a very big, floppy heart that is extremely inefficient at pumping blood. |
How can we really know the size of extra-solar planets?
So we've found 3 'Earth sized' planets recently. If we find these planets by the wobble of the star, or by the dimming of the star as they pass in front, how can we tell the difference between a larger than earth sized planet, and an earth sized planet with a moon? like for example could these be pairs of smaller binary planets? How do they account for this? Massive Edit: Thanks for the responses! It seems like the general attitude is that it wouldn't make a big difference to the measurements anyway. The reason I asked this is because I've heard that having a moon could be, or is, either essential or greatly beneficial, to it's capacity for harbouring life. When people announce 'earth sized' planets, where they could actually be ever-so slightly smaller but with a moon, the implications to the probability of life outside our own solar system are huge. I am making a game about travelling to other systems to find planets, it's all based on a procedural system generator. So the probability of moons and life is super important for that, and just interesting to me, I wouldn't be making it otherwise. My tutor was like 'that's going to be super tedious and boring if it's based on science'. But the more we find out about them, the more it seems extra solar planets in general, and even ones that could harbour life, aren't as rare as people assumed.
how can we tell the difference between a larger than earth sized planet, and an earth sized planet with a moon? Bear in mind that the amount of light blocked by a transiting planet in front of its parent star is a function of the radius , so it's not greatly affected by the additional presence of a moon. So for example: the Moon's radius is just about 1/4 of the Earth's radius. That means if we saw the Earth + Moon in transit, we'd see an extra (1/4) = 1/16, or an extra 6% dip in the brightness of the transit when compared to a transit of the Earth alone. If you run through the math, that would mean we'd estimate the Earth being just 3% larger than it actually is. That's still pretty close to the inherent error in the measurement, so it's really not going to greatly affect our final science result; you're talking about the difference between a planet with a size of 1.00 Earth-radius and 1.03 Earth-radius - it's still basically an Earth-sized planet. : Moons are small compared to their parent planet, and have an even smaller effect on the brightness dip of a transit, so it really wouldn't matter very much. to include your Massive Edit: The reason I asked this is because I've heard that having a moon could be, or is, either essential or greatly beneficial, to it's capacity for harbouring life. This is true. Some folks throw around the idea that having a moon might help with slightly suppressing the number of meteorite impacts, but that's really not the primary reason why a moon is beneficial for life...it's far more based on stabilization of the climate. Seasons are caused by the tilt of the rotational axis. Earth's axis is tilted 23 degrees, which gives us some seasons, but they're relatively mild compared to some other planets. Since our large Moon gives us a relatively constant tidal force over time, the absolute direction of our axis changes, but the actual amount of tilt stays pretty stable at 23 degrees...at most it varies between 22 degrees and 24 degrees over million-year timescales. Now, compare that with Mars. Since Mars has no large moon, the primary tidal forces are from the Sun and Jupiter, which are quite chaotic compared to our own Moon's steady tidal tugging. As a result, simulations have found that Mars' axial tilt has varied between a 0-degree axial tilt all the way to a 60 degree axial tilt. That means over million-year timescales, its climate has varied between no seasons to crazy intense seasons. That kind of erratic climate is really not conducive to life, and some have suggested it helped with the dessication of the planet's ancient oceans. : Having a moon stabilizes your seasons, which is good for life. : See the comment from /u/K04PB2B below. It would seem more recent calculations have suggested that a large moon may not be necessary for a planet to maintain habitability...which is good news for astrobiology. Obligatory hat tip to the orbital dynamicist dudes and dudettes out there. |
Would an exploding/imploding star create a shockwave?
I am aware that space is mostly empty and shockwaves would require matter to build up, but as a star expands during it's death would the matter being expelled create a shockwave, and could this shockwave push planetary bodies away from the star, creating a rogue planet? Or would they just be inevitably swallowed by the star?
Well as I understand it space is not a void, and there will be massive amounts of matter released during the explosion at rapid speeds. could this be enough to cause a shockwave? |
When measuring the mass of an electron (9.11*10^-31kg) is this the mass when the electron is at rest or when moving with relativistic velocity?
The modern definition of mass is a quantity which doesn't change with the speed of the particle. So the mass of the electron is the rest mass, which is the same no matter how fast it's moving. We can't determine particle masses from first principles. |
What happens if you throw an object during uniform circular motion?
If you were holding an object (say a ball) and were travelling in a uniform circle (say on a roundabout) what would happen if you threw the ball? I know that if you just let go of the ball, its force would be its centripetal force in the horizontal direction perpendicular to the circle (F=mrw ) and gravitational force in the vertical (F=mg due to such a small distance). If you physically propelled it instead of letting go, would this just add a horizontal force parallel to the circle, so that you just resolve the two with pythagoras? Or would you have to use some other calculation to resolve the net horizontal force? I think I'm right in thinking the vertical force would remain constant though.
The moment you let go of it, there is no centripetal force on the ball anymore. That was from you holding it the circular path. So from a top-down view (and neglecting drag), there are no longer any forces on the ball. It continues moving in a straight line at a tangent to where you released it. If you throw it instead, you're imparting an extra velocity to it in whatever direction, with respect to yourself. But there are still no forces on the ball from a top-down view once you let go.Add this velocity vector to the velocity vector of your travel around the circle. The vertical travel is just due to gravity and can be solved in isolation. Consider initial velocity, acceleration, time taken, solve for velocity at any point in time. |
Would it be possible/of any benefit to paint the inside of a swimming pool in a super hydrophobic coating?
I realise it's possible, but perhaps wildly impractical? Would the water behave differently to the point where you wouldn't want it for your backyard pool? If not, could there perhaps be benefits in such a treatment towards limiting the growth of algae or something similar? Thanks in advance, Science!
Superhydrophobic coatings are indeed useful for preventing biofilm formation in situations where you can't use chlorine, such as food processing, bioreactor fermentation, and high purity chemical synthesis. |
Would we ever be able to interact with alternate dimensions/universes according to the theory of Multiverse?
According to the Theory of Multiverse, there exists an infinite amounts of alternate scenarios in an infinite amount of different universes. Some people like to think of this as "Well, at least I got in some other universe", but I think it's scary because if we interact with these other universes, how do we know we're remaining in one universe and some super-civilization isn't doing multi-universal experiments on humans with wormholes, etc. beaming us to universes extremely similar to ours (but of course unnoticed to the subject). Basically the question is not whether we can, but if it is to interact with these other universes/dimensions?
According to the Theory of Multiverse, there exists an infinite amounts of alternate scenarios in an infinite amount of different universes. There is no "Theory of Multiverse". There are several things that are occasionally that, but nothing to which the term can properly apply. For details on the most common meaning of the phrase, see my comment in response to the question " Is multiverse an accepted theory or is it just an extreme hypothesis? " Your question appears to be about the implications of Everett's many-worlds interpretation of quantum mechanics (the second one I discuss in the above link). See palanoid's link to a proposed in-principle test. Note that these sorts of interactions don't necessarily provide for , let alone the transference of matter "between worlds" (a phrase that I'm almost certain doesn't actually make sense). You can read more about the Everett interpretation here . |
Is there an evolutionary trait that causes there to be a low percentage of natural leaders compared to those that follow?
I'm just curious as I can't imagine a world where everyone was a leader or a follower. It always seems like there is a natural flow to society with those who lead and those who fall in behind. Is there any reasoning for why this is? Evolutionary reasons or situational reasons?
Because an extraordinary trait is defined by the fact that it is not average. I do not agree with you, that some people are born leaders or something like that, but the above statement is true nonetheless. |
Can you have concussive force in space?
For example, if an explosion takes place say 20 meters from me on Earth that would cause massive internal trauma due to concussive force, will the effect be the same in the vaccuum of space? Not counting heat/shrapnel of course.
Not likely. What you're talking about is damage from the shockwave that propagates through the atmosphere after the explosion. Without an atmosphere, there's nothing to propagate the shock. You may be hit directly with the expanding gas from the explosion, but this will be very weak in most situations - the damage from an explosion is caused by the energy it adds to the air, not by the amount of gas it deposits. |
If the ratio of the modulus of elasticity to density of aluminum and steel are so similar, what goes in to the decision to use one over the other?
First, I will need to back up the title. I'm going to use numbers based on 4130 and 7075, because they are both relatively common high-strength alloys. Modulus of elasticity = 205 GPa, Density=7830kg/m ratio: 2.68*10 m / s (I don't know what this unit is. Keeping it to show calculations are consistent with each other) Modulus of elasticity = 71 GPa, Density = 2823kg/m ratio: 2.52*10 m / s Wouldn't this mean that a structural member made out of 4130 would actually be lighter than one from 7075 for the same stiffness? Obviously I'm missing something here, because the folks building airplanes didn't just pick aluminum because they felt like it. One thing that occurred to me when thinking about bike tubes is that the aluminum tube will be thicker than the steel, possibly making it more difficult to dent. Is that it? Edit: if this is bogus just let me know. I'm really trying to figure this out.
For airplanes Aluminium is easier to work with, because sheets of the right strength are thick enough. Steel sheets of sufficient thickness to have sufficient strength would be so thin that they are difficult to work with (plus there would probably be quit a lot of bending involved). For tubes, the stiffness does not increase linearly with wall thickness and radius so that by making a larger and thicker tube out of aluminium which weighs the same as an equivalent steel tube, you get a much more stable structure. Or a structure just as stable, but lighter. That is why its used in bikes. http://wiki.answers.com/Q/Why_is_aluminum_used_to_build_aircraft_instead_of_steel http://en.wikipedia.org/wiki/Aluminium_alloy |
Question on Relativity
I've got a bit stuck on this relativity question: How fast would you have to travel to get from the Earth to the Sun in one minute, assumiong the Earth is 8 light minutes from the Sun. I've been thinking about this for the last couple of days and just can't seem to get my head around it.
How fast would you have to travel to get from the Earth to the Sun in one minute, assumiong the Earth is 8 light minutes from the Sun. You would need to travel at 0.9923 times the speed of light. Of course, you will only reach the sun in 1 minute according to your watch. The people on Earth will see you moving in slow motion and your journey will take just over 8 minutes according to them. |
Do educational facilities ever BUY cadavers for educational purposes, or do they rely 100% on people to donate their bodies to science?
If they do, in what kinds of circumstances does that happen, and what on earth does the facility pay the family?
At universities near me the cadavers are essentially borrowed/rented, and are always donated, never bought. Universities can have them for four years before all remains are returned and cremated. Only in very special circumstances can body parts be kept as a permanent specimen. |
List of 26 things that did "not make sense" 4-8 years ago according to NewScientist. Current status?
I'm not sure about any of the others off the top of my head, but I know that the 'Bloop' has been considered solved. The answer: ice quakes . |
Why does wasabi have a really strong and spicy taste that lasts for a small amount of time compared to chillies which last for a long amount of time?
I recently felt this when I put too much wasabi on my sushi, it was spicy for about 30 seconds but then the sensation went away.
Wasabi, as with mustard and horseradish, has enzymes that break down compounds called glucosinolates that are present in these plants. The reaction produces isothiocynates, which are the 'hot' compounds you notice when eating those. The glucosinolates and the enzymes producing them are water-soluble, so drinking water will flush them away. Hot peppers on the other hand, derive their 'heat' from the presence of the compound capsaiscin , which is not very water-soluble (13 mg per liter of water), and so drinking water doesn't do much to remove it. Both these compounds bind to the heat receptors in your mouth (and if you're note careful, other parts too), specifically one called TRPV1 . It's entirely possible capsaicin binds more strongly to TRPV1 and causes a more long-lasting effect that way as well, but I don't know offhand if that's true or not (or whether it's even been studied). |
Were we taught to smile when we're happy or is do we smile for natural reasons? As in, what makes us smile?
While it's a combination of genetic and societal influences, smiling is largely thought of as a natural, innate response. We can observe smiling in blind infants (Freedman, 1964). If blind infants, who are unable to witness anyone smiling at all, smile when exposed to happy environments, we might be able to infer something about the "innateness" of this trait. Also, many physiological factors also suggest that it's a reflexive response. One fun study showed that the way your mouth sits can influence how you feel (Strack, Martin, & Stepper, 1988). For example, if you hold a pencil in your mouth, between your lips, it simulates a frown, and you will report more feelings of sadness, regardless of your previous internal states. However, if you hold the pencil between your teeth, simulating a smile, you will report more feelings of happiness. Kind of silly, but hey, it works! Your body responds to your facial cues in a way that would suggest smiling is a reflexive, physiological mechanism. Finally, studies have shown that smiling is universal. This is to say that regardless of geographical location, regardless of culture, smiles all mean the same thing. It's one of the few things that everybody has in common: you smile when you're happy. Other emotions/responses seem to be universal, such as that of fright, sadness, and anger. Paul Ekman's work has centered around a lot these "cultural constants", and if you're interested in the subject, I highly recommend seeking out some of his articles.
Freedman, D. G. (1964). Smiling in blind infants and the issue of innate vs. acquired. , 5(3‐4), 171-184. Strack, F., Martin, L. L., & Stepper, S. (1988). Inhibiting and facilitating conditions of the human smile: a nonobtrusive test of the facial feedback hypothesis. , 54(5), 768. Ekman, P., & Friesen, W. V. (1971). Constants across cultures in the face and emotion. , 17(2), 124. Edit: APA format for citations. :)
Also, smiling via emoticons are learned responses, not innate, like real smiles! |
Is there a human speed limit?
I always hear about people breaking records for non-powered travel (like running, swimming, etc.). Is there a limit to how fast a human can run? If so, what is it?
The limiting factor is the amount of force that muscles can apply over a given time. Going only off of this factor, the theoretical absolute maximum speed is around 19.3 ms or 43 miles per hour. This is obviously for short distances; for longer distances, cardiovascular and respiratory factors become the limits. Source This study also explores things like prosthetic leg extensions and finds that they may increase maximum speed. It's an interesting read if you have a few minutes |
According to metric expansion, is there "new" space being created between galaxies?
If space is expanding between galaxies, what are the properties of that space? When the distances increase, is space being "stretched" or is there "new" space being created in between them? As I understand it, the galaxies themselves aren't moving in the traditional sense of the word. Perhaps my question isn't quite clear, but I guess what I'm asking is, if there were a certain number of planck lengths between 2 galaxies, would that number be increasing as space expands, or do the lengths themselves get longer? If "new" space is being created, what is the process for that/where does it come from?
Space isn't really a "thing" that is being stretched. All that is happening is the distance between points is getting bigger. Space is also not divided into a number of planck-length "pixels". The planck length is important, and you do get some interesting physics happening below that length scale, but it is not actually an indivisible unit of space, except in some not very widely accepted theories. |
Is it true that a shooter absorbs an equal amount of force into his body as is being projected in the bullet?
There is a lot of confusion in the answers here about pressure, force, energy, and momentum. Working backwards through that list: Momentum is conserved, so both the shooter and the object hit by the bullet absorb the same amount of momentum. That means if you were floating in space and fired a bullet into someone with the same mass as you, you would both be pushed apart from each other and the change in velocity would be the same for both. Energy is also conserved, but as a scalar. The chemical energy in the gunpowder is converted into heat and kinetic energy, but that doesn't have to be shared with you and the bullet. In fact, because the bullet weighs less than you do (and less than the gun does), it receives much most of the kinetic energy after the bullet is fired. This also explains why the bullet can do a lot more damage when it hits something than recoil does to you. Force integrated over time is momentum. Since momentum is conserved, that means the integral of force is the same for you and the bullet (with opposite directions). But a high force experienced for a short time can have the same integral as a low force experienced for a long time. The gun acts like a spring so the force you experience is lower than the force the bullet experiences. This is the same reason that cars have crumple zones - an accident is much less dangerous if you spread out the force over a longer time. Pressure is force over area. This is one more reason a gun doesn't hurt you like a bullet does - the force is spread out over a larger area than on the bullet. This is also why a catcher's mitt protects the catcher's hand. So, momentum is conserved, but a shooter absorbs the momentum through a force spread out in time and area. That is why the shooter isn't hurt by firing the gun. |
What is the largest object that Humans can create/fashion that will have the exact same molecular makeup?
It's an entropy thing. An exactly perfect crystal has only one arrangement. It would be like flipping Avogadro's number worth of coins and getting all heads. Even if the coins are really unfair (analogous to a very low energy crystal state) some of them will come up tails. |
What is stopping light from being projected onto the moon from earth?
Specifically, is the ability to do this beyond us right now? Do we not have bright enough or focused enough lights? Is it possible to just colour the moon with light, even if there is no discernible image there? I'd think if it was possible to do it well, we'd be seeing a battle for corporate logos on the moon, so I guess it isn't.
Dammit I was about to post the same xkcd. Of course, we do shine lights on the moon, its just we don't get much light back. The only remaining continually operated part of the Apollo programme is a long running experiment that fires laser light at a reflector dish put their by astronauts and times the time it takes for the light to get back. Even with a laser, the light spreads out and is disrupted by the atmosphere and only one photons gets back for quadrillions sent out. (Incidentally the existence of the mirrors in the moon is one of the best explanations against conspiracy theorists who claim we never sent rockets to the moon). |
Since MERS has a high fatality rate (36%) and only about 2500 confirmed cases over a span of eight years, why hasn't it been contained (and basically eliminated) like SARS-CoV-1 was?
Unlike SARS (and SARS-CoV-2), MERS transmits very poorly in humans, usually only a few steps along a transmission chain, and it has not become established in human populations. All MERS transmission chains start with infection of a human by a camel. So the only way to eliminate MERS would be to eliminate it from camels. In camels, the virus doesn’t seem to cause any symptoms (or the symptoms are very mild and look like many other harmless conditions). So you can’t isolate and/or treat affected animals, or avoid them while they’re shedding. That leaves widespread vaccination of the camels as the main hope of eliminating the virus, and that is in fact what groups have been working toward. There are a number of candidate vaccines for camels that look quite promising ( Efficacy of an Adjuvanted Middle East Respiratory Syndrome Coronavirus Spike Protein Vaccine in Dromedary Camels and Alpacas ; Blocking transmission of Middle East respiratory syndrome coronavirus (MERS-CoV) in llamas by vaccination with a recombinant spike protein ), but since this was until lately a fairly low-profile disease, it hasn’t been heavily funded and has moved at a fairly traditional pace for vaccine development. |
Protein synthesis in chemistry?
If a certain protein is composed of a sequence of amino acids, can you simply combine said amino acids to create that protein? Is mixing amino acids a plausible way of creating a protein?
You can, up to a point! though it’s a bit more complex than just mixing amino acids together. The standard method of synthesising short peptide sequences - SPPS - works by fixing an amino acid to a resin surface, then successively adding the amino acids you want until the desired sequence is made. This only works efficiently for shortish sequences, fewer than 100 amino acids. For anything bigger or more sophisticated you need to use the same biological components that cells use, but this can also be done in a test tube. |
What gasses are inside a cavitation bubble? How does gasses from a liquid end up being gathered into a bubble format?
What gasses are inside a cavitation bubble? How does gasses from a liquid end up being gathered into a bubble format? I'm curious if it is possible to purposefully create cavitation bubbles and then harvest them into tanks so that you could extract air out of water.
Cavitation bubbles are made of the same substance as the surrounding fluid. That is, if you're generating them in the ocean, they'll be made out of water vapor. You know how water boils at a lower temperature at higher altitudes, so there are often different directions for stuff at sea level vs 10,000 ft? Well, cavitation occurs because the pressure drops so low that the fluid boils without any outside heat input - the boiling point becomes 2°C or whatever. |
If you sum these number patterns (picture in the description) with their palindrome number, the result will always be 1110. Why is that?
I was bored in math class, so I started typing some random numbers in my calculator. Then I realized that these numbers in this summed with the palindrome of that same number always results in 1110. Is there any reason for it to happen, or is it just coincidence? These are the possible results: 258+852=1110 456+654=1110 159+951=1110 357+753=1110
Two numbers across from each other on a calculator or phone grid will always sum to 10 because of the way they're laid out (and 5 is "across" from itself). By choosing only numbers that go through the center of the grid, you're making sure you only choose numbers that are across from each other. When you take the palindrome of these numbers, you're adding each number to the number across from it, which will give you 10 every time. To really see how this is happening, look below: 258 + 852 (2*100 + 5*10 + 8) + (8*100 + 5*10 + 2) (2+8)*100 + (5+5)*10 + (8+2) 10*100 + 10*10 + 10 1110 |
What happens if I use my 30-day disposable contacts beyond one month?
This is a medical question or sorts... But the FDA rates contacts at their "safe to wear" period. Beyond that, there is a increased risk of damaging your eyes due to any number of factors. The truth is that there's an organization that extensively tests these things for a reason: wear them for their proscribed time and not longer. |
Why can cracking a joint release muscle tension?
Regularly, I'll have muscle tension and/or pain in my back, shoulder, wrist, etc that seem to be resolved after cracking an affected joint. Just stretching the affected area isn't enough in these cases. Knowing that, fundamentally, cracking a joint is just creating a cavity between the bones (and hence stretching the muscles and ligaments), it's not clear to me why this should be.
To be straight, there is no answer backed with scientific evidence to answer this question of yours but there are many theories. I am a D.O. (osteopathic) medical student. One technique we do is called HVLA and involves "popping" or as we say gapping a restricted joint. The current running theory is that restricted tissues that limit mobility get congested and build up cytokines and stuff within the tissue. One major product built up is nitric oxide (NO) which is released by endothilial cells in response to inflammation in very small parts to only act locally in that area. By forcing your joint to move past its restrictive barrier into its anatomical barrier (the normal range of motion allowed before tearing a ligament, muscle or tendon) you force the nitric oxide bubble within all the inflammation to burst (popping noise) and achieve an overall relaxation response resulting in full range of motion being restored. |
Is the usable mathematics a limiting factor for study of Physics?
This is a very long post with a lot of questions: I recall a quote by Einstein saying that he could not proceed further after a point in GR with the general mathematical tools until he was able to use tensors in it. Is it that the more simpler concepts were too inadequate, or was it that it was almost unworkable with those simpler mathematical techniques? Looking at QM, Heisenberg initially worked with Matrices and Schrodinger waves, with the latter method simpler and more intuitive, but both later proved to be equivalent in their approach. Fermat claimed a very elegant proof of his last theorem, but didn't it take mathematics which were developed only recently(20th century) to prove it? And the proof is not elegant(100+ pages). Did the mathematics limit our idea or was it that only Fermat could prove it elegantly? My question being, would future theories rely more on using the most sophisticated mathematical ideas to create a complete model or is that the model be explained with more simpler tools , pointing towards an "equivalence"? And since mathematics is voluminous, would learning very complex models to be applied in physics be justified? Any additional info would be helpful too.
From the level of quantum mechanics that I have studied, almost every single form of Schrodinger's equation can be solved using perturbation theory. That's because in courses they only present you with problems that have known solutions, and are amenable to approximation methods like perturbation theory. By the end of the 2nd or 3rd year of QM and QFT you've seen basically everything that we know how to treat analytically. Basically, if there's a problem that can't be solved exactly by using analytical tools, then there is a method to solve it to many, many digits using intensive computational power. This is not true either. I work on approximation methods related to quantum spin systems, and this is a highly non-trivial problem. In fact, we have hardness results due to the rigorously proven computational complexity of quantum systems. This is the entire reason that quantum computing is interesting. If we could classically approximate, for example, the quantum amplitudes related to Shor's Factoring Algorithm, then there would be much less incentive to build a quantum factoring machine at all. The fact that we believe (on good evidence) that integer factoring is a hard computational problem is an example of what I mean by complexity theoretic evidence against quantum simulability. To take an example from another domain, quantum chromodynamics (QCD, the Quantum Field Theory which describes the strong force between quarks and gluons) is a strongly-coupled gauge theory which is very difficult to computationally simulate using a discretized lattice spacetime. "Strongly coupled" means that perturbation theory is not valid in the range of energies that describe e.g. nuclear physics, and "gauge theory" implies that there is an enormous redundancy in numerical descriptions caused by high degree of symmetry involved at every point in spacetime. Even a simple sounding calculation, like computing the mass of the proton from knowledge of it's constituent quarks, has only been possible in the last decade or so, and depends on a series of clever analytic transformations, neglecting all sorts of effects which by all rights should be important, and running on a supercomputer (none of this should take away from what an impressive accomplishment and test of the theory it is to calculate the proton mass). There are really no shortage of these kinds of examples, and they have important applications too. Some of our best descriptions of condensed matters systems, like high-temperature superconductors, are also described by highly non-linear quantum field theories. One of the most important near-term reasons for building quantum computers is the goal of doing scientific simulations that would be effectively impossible on classical computers of any conceivable size and speed. |
Ask Anything Wednesday - Economics, Political Science, Linguistics, Anthropology
Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...". Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists. Please only answer a posted question if you are an expert in the field. . In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for . If you would like to become a member of the AskScience panel, . Past AskAnythingWednesday posts . Ask away!
Taiwan and Costa Rica have an audit branch of government in addition to the three classic branches. What does it do and why do they have it? |
What is the difference between these equations involving Strangeness Conservation that makes one permissible and one not?
Why is Λ -> p + π permissible, but K + p -> n + π not? uds -> uud + d and s + uud -> udd + u Both involve a change of quark flavour - the s quark of the Λ and K both becoming down quarks - implying the Weak Interaction and hence Strangeness not necessarily being conserved. So what is different between the two interactions that means the second is a no-no? The two interactions have been pulled from different sources. The first is from Hyperphysics and the second is from a CGP textbook which claims it is not allowed. Admittedly the textbook does not even approach the idea that Strangeness is not always conserved... EDIT: got the sources mixed up.
The channel by which a strange quark decays into a down quark has additional byproducts, which show up in the decay channel of Λ that you mentioned, but not in the second reaction. The second section on this hyperphysics page shows the channels in which the various quarks can decay. There are 3 particles (technically, fields, but we're just going to treat them as particles) that facilitate the weak interaction: The electrically and flavor-neutral Z boson, and the W+ and W- bosons. The Z boson can't alter flavor, so it can't turn quarks into different quarks. The W± bosons can, and that's what leads to violations of flavor conservation, of which strangeness is one example. Strange quarks have -1/3 electric charge, and the W± bosons have ±1 electric charge. If a strange quark decayed into a W+ particle, it would have to also produce another particle with -4/3 charge; and no such elementary particle exists, so that can't happen (total electric charge is always conserved). On the other hand, a strange quark can decay into a W- and an up quark, which has +2/3 charge, because the total charge is -1/3 -> -1 + 2/3 = -1/3. The W- boson has a half life of about 10 seconds, so it practically instantly decays. W- bosons can decay into many different pairs of particles, such as any one of the leptons and their corresponding neutrino, or into d or s. This means that when a strange quark decays, it decay into an up quark, plus any one of those additional pairs of particles from the decay of the W- boson. The reason why the first one is allowed is because you start out with ud+s, and end up with ud + du , where the second term is the decay products of the strange quark (an up quark, plus a d pair). In the second example, you start with uud+s and end up with uud+d, indicating that the strange quark decayed into a down quark with no other products, which is impossible! |
Is there a foolproof way of drawing angles with relative precision without a protractor or compass?
I've always wondered this. Protractors are lovely, but sometimes you need to draw that 65° angle and you don't have one on you. It seems logical to me that using a ruler there should be some way that I am missing to be able to do this.
Folding paper can be handy. Fold a piece of paper diagonally from one corner for a 45º angle. Fold it in thirds for a 30º angle. Fold in half twice for a 22.5º angle. Fold in thirds, then in half for 15º, and so on. I use this to make reference angles for drawing from time to time. edit: If you do thirds, then half, then flatten it out, you have a piece of paper with a 90º corner and creases marking each 15º wedge. If you hold your ruler perpendicular to the centerline of each 15º wedge in turn, and subdivide each of these wedges into 15 subdivisions using the millimeter or 16th inch lines on your ruler, you can make yourself a pretty accurate protractor. It won't be perfect, but it'll be close enough to get you within a degree or so. |
How does the quantum tunneling effect limit development of micro processors and how do we overcome that?
The issue is not that the material is thin but rather that the distance between parts of different voltages (base and collector for example) is small enough that tunneling can occur through otherwise nonconductive material. The energy of the electrons is not the problem its the voltage gradient. Copper transistors would allow for smaller more efficient faster transistors if the technology to fabricate them existed but such technology would also make many other types of transistors possible and its extremely likely that copper would not be the optimal material. Metal oxide barriers can prevent tunneling between components but that will only help a little bit as it cant stop tunneling within transistors which is the main problem. 3D layouts allow for more transistors but makes thermal management harder so it is unlikely to be a solution to the problem. Graphene transistors can be made much smaller than silicon transistors without tunneling issues. I have no idea what you mean by "take advantage of the ease with which carbon atoms can be arranged on the nanometer scale." |
Apparently the sun's magnetic field is about to "flip." What causes this to occur and why does it do so every 11 years?
Why 11? Does it have something to do with the way the sun spins? The Solar System? Some type of Galactic process?
I'd like to elaborate in that we know a lot more than noott's post gives credit for. It is very hard to pin down exactly what we know though, with physics as complex as plasma physics in a body the size of a star we will never fully be able to recreate it and it is unlikely we will every analytically be able to point at an equation and say "this causes the magnetic field reversals". We have made a lot of progress in explaining the Sun's magnetic field though there is even more still to do. I'll give you a taste of the story so far though. The Sun's magnetic field comes from a physical process known as the Solar Dynamo, which is an example of an MHD dynamo. The sun is made of a conducting fluid, plasma, similar to the iron that makes up the Earth's core. A current in a conducting fluid produces a magnetic field, any conducting fluid you flow through a magnetic field will naturally produce currents that will reinforce the magnetic field. From this small starting current we can create the Sun's dipole, the general shape of the magnetic field, due to a giant ring of current under the surface going the entire way around the star. The region of high interest here is the Tachocline (border between convective and radiative regimes of the interior) where we think this current is generated due to the large change in rotation speed there (shear flows automatically = current). So yeh I'd say we know how the magnetic field got there. As for the solar cycle, that's trickier... ...unlike a solid body different parts of the Sun rotate at different rates, the equator rotates fastest and as you get nearer the poles it lags behind. This wouldn't mean anything if not for a neat law of plasma physics which is known as the "frozen in flux" theorem, which basically means where the conducting plasma goes, the magnetic field follows. Our fast rotating equatorial region drags our dipole field around and around, each time round the magnetic field becomes wound tighter and tighter, stronger and stronger. Magnetic fields resist being wound up and so this whole time energy is being stored up and it begins to leak out. This first manifests itself as active regions (and how those actually emerge from the interior is an entire posts worth itself), initally found nearer the poles when the dipole field is still dominant. As time passes and the magnetic field becomes more contorted, and these active regions form closer and closer to the equator. Around this time the magnetic field is very messed up. The field at the poles is shaky and the field nearer the equatorial regions is all over the place. Then a reversal happens. This is where my expertise is light, I have seen the talks and papers but can't say I understand them. This is further exacerbated by the fact that although the reversals are very recreatable, it is not reliable. It requires much tweaking by the modellers in models that are already not the full story (i.e. missing physics). TL;DR we do (mostly) know what is going on, how the field forms, how it gets twisted, how this leads to the sunpsot cycle and that this eventually causes a reversal but you are right there is more we need to find out! |
How do trains carrying liquid freight not have their cargo freeze in the winter?
I have to imagine they don't want whatever is in those tanks to freeze, but I can't figure out how they might prevent it...
Sometimes trains actually let the liquids freeze when transporting. Here's a fun fact: Liquid Na metal that is refined from the Downs process is directly put into ordinary railroad tank cars. That liquid sodium then freezes while it is inside the tank. When the car arrives at the destination, the entire car is heated up, most of the time with simple flames, until the Na re-melts. Then it is pumped or drained in liquid form into the delivery tank off the rail car. Pretty awesome. |
How does aging/curing meats avoid contamination from harmful bacteria such as c-botulinum?
Depends on the method. Dry aging for instance is usually done at colder temps, which halts bacterial growth. Most “curing” relies on salt to prevent the growth of harmful bacteria, meanwhile fermentation relies on either salt or lactic acid, or a combination of both. In all of these situations though it all boils down to “create an environment that isn’t hostile to humans, but is hostile to bad bacteria. |
What are the benefits of copper or aluminium layers in pans and pots?
What I think I understand are some copper clad frying pans I've seen that have sort of half cylinders of copper on their bottom transferring heat to a larger surface area of steel on the curve of the half cylinder of copper. What I don't understand are the very popular 3 ply steel pans that just seem to have a layer of aluminium sandwiched between steel. Is it textured at all? It seems like if it was flat there would be no surface area benefit, so the transfer would not improve.
Al and Cu have much higher thermal conductivities than steel, meaning they transfer heat faster than steel. However, they are not suitable for the daily abuse pots and pans see. They scratch easily, dent, oxidize, etc. So, the manufacturer compromises by using them in the core of the pot to do the bulk of the heat transfer while leaving steel to handle the rough stuff. Table of thermal conductivities below. http://www.engineeringtoolbox.com/thermal-conductivity-metals-d_858.html |
How does it happen that an entire volume of data can become corrupt when the writing of only a small portion of it is interrupted?
The other day, the electricity went out while I was saving a folder of word documents to a flash drive. When I powered it back up again, Windows told me that the drive was corrupt and needed a reformat. The flash drive is 16GB, and my documents were only a few megs. What happened that the entire drive became corrupt?
In your case it seems was damaged the File Allocation Table (FAT). This file system can be read and written by a wide range of devices, but it is very fragile because of how data is arranged logically. In most cases you can fix the problem with a specialized application, like chkdsk under Windows. If you are using it only on computers, you can format it with NTFS file system. This file system is more robust. |
Do our eyeballs grow after we are born?
I love how the guy asked his question on reddit, reddit searched google, google found a yahoo answers post, reddit copied and pasted it back on reddit and ended up wasting a lot more time than needed. But with that being said, I find a lot of interesting posts on reddit that I would have never thought about in a million years, such as this one. Interesting. Also, redditredditreddit. |
If a quantum wave function has 3 state would making a measurement on only 1 state collapse it?
for example if a particle is superpose in position A B and C with an amplitude of sqr(1/3) each, would testing if the particle is at C collapse the wave function assuming we find nothing or change it to 50% for A and B keeping it superposed.
Excellent question. I'm going to imagine this as a triple slit experiment. So basically the wave function is as predicted by QM. Now we put a detector beside one of the slits say the left slit, "collapsing" electrons that pass through this slit. These results are the same as a double slit through slit left and centre, and single slit on right. So basically it acts as two seperate experiments. The best way to think of wave function "collapse" is to imagine the "real" macroscopic world as being one big quantum mechanical system and collapse is jsut the particle becoming entangled with this system and since the system is so big that the particle can not become unentangled. |
Why didn't natural selection eliminate poor eyesight before glasses were invented?
My train of thought with this is that poor eyesight seems like it would've been a big enough hindrance to things like hunting and gathering and generally not running into stuff and dying back in those times that eventually people with poor eyesight wouldn't have been able to reproduce. Am I just confused on how poor eyesight works?
Most "poor eyesight" is heavily influenced by environment, not solely genetics. That is, you may inherit the tendency to become myopic, but you don't actually develop myopia unless you add in the environmental triggers: Even though the tendency to develop myopia may be inherited, its actual development may be affected by how a person uses his or her eyes. Individuals who spend considerable time reading, working at a computer, or doing other intense close visual work may be more likely to develop myopia. -- American Optometric Association In the days when hunting and gathering was important, most of the people weren't spending considerable time reading or working at computers, so even if they had a genetic predisposition, they wouldn't develop serious eyesight problems. (Alternatively, the people who had a genetic predisposition that didn't need environmental triggers -- or the people who had a genetic predisposition that was triggered by the components of a savannah environment -- did die, and those tendencies were not passed on.) |
Just as "red" in hundred meant "count", does the "ter" in close relatives (like father, mother, brother, sister) mean anything in Old(er) English?
Yes! Father, mother, and brother are derived almost unchanged from proto-Indo-European (PIE), where -ter is a kinship suffix. Sister is from PIE *swesor, probably from PIE roots *swe- "one's own" + *ser- "woman." If you like this sort of thing, etymonline.com is fantastic. |
Watching things at the speed of light
I read that the Pillars of Creation were destroyed about 6000 years ago, but due to the light speed limits we will not see the event for another 1000 years. If I travel towards the pillars at, let's say, 99% velocity of speed will I see the events fast-forwarded? And if away - slow-mo? Is it that simple or is there a catch to it? Does that mean that there's a natural fast-forward/ slow-mo limit?
If I travel towards the pillars at, let's say, 99% velocity of speed will I see the events fast-forwarded? And if away - slow-mo? Is it that simple or is there a catch to it? Does that mean that there's a natural fast-forward/ slow-mo limit? There is a distinction that can be very subtle here and many people - even those with degrees in physics - often miss. The distinction is between what you see and what is actually happening in your frame of reference. What you see is determined by the light that reaches you at any given time. When you fly towards the pillars at nearly the speed of light, or better understood as the pillars flying towards you, the pillars are time dilated - they are running in slow motion, and the destruction event happened millions of years ago. The space between you and the pillars is contracted to just a few light years or less, and all of the light which relays what happened to the pillars over all those millions of years since they were destroyed is scrunched into that space. So you will effectively see these events unfold in fast motion, even though the pillars are really going in slow motion. Additionally, the light will be blueshifted - i.e. it will appear as a higher frequency. There is no fast-forward limit. As you go get closer and closer to the speed of light, the space between you and the pillars continues to get smaller, and so you will see the destruction arbitrarily quickly. I have to think about the moving away case. |
If a billiard ball was fired into someone at close to the speed of light, would it vaporize him or leave a clean circular hole?
There is a fantastic explanation by an MIT professor depicting of the kinds of effects you might encounter with fractional C projectiles hitting another mass (in this case, a can of ravioli hitting a starship): http://www.mit.edu/people/daveg/Humor/ravioli_as_gas actually, let me just post the entire text for you.... What am I, the neighborhood blast physicist??? Well, maybe... :-) It all depends on speed of impact versus the speed of sound in the target
(what is called the Mach number, where Mach 1 means the speed of sound,
Mach 2 is twice the speed of sound, etc), and the speed of the ravioli
versus the speed of light in the target (which I'll call the Cerenkov
number, where Cerenkov 1 is the speed of light in anything; Cerenkov 1.3
is the speed of high-energy protons in a water-cooled reactor (that's why
you get that nifty blue glow), and you can get up to Cerenkov 2.4 using
diamonds and nuclear accellerators. In the late 40's people used to talk
about Cerenkov numbers, but they don't anymore. Pity.). Lastly, there's
the ravioli velocity expressed as a fraction of the speed of light in a
vacuum (that is, as a fraction of "c"). "C" velocities are always between
0 and 1. At low speeds (REAL low) the ravioli will simply flow over the surface,
yielding a space-cruiser with a distinctly Italian paint job. Faster (still well below speed-of-sound in the target) the metal of the
space-cruiser's skin will distort downward, making what we Boston drivers
call a "small dent". Faster still, you may have a "big dent" or maybe even a "big dent with a
hole in the middle", caused by the ravioli having enough energy to push
the dent through, stretching and thinning the hull metal till the metal
finally tears in the middle of the dent. Getting up past Mach 1 (say, 5000 feet/sec for steel), you start to get
punch-a-hole-shaped-like-the-object effects, because the metal is being
asked to move faster than the binding forces in the object can propagate
the "HEY! MOVE!" information. (After all, sound is just the binding
forces between atoms in a material moving the adjacent atoms -- and the
speed of sound is how fast the message to "move" can propagate.) From
this, we see that WileE Coyote often reached far-supersonic speeds because
he often punched silhouette-type holes in rocks, cliffs, trucks, etc. Around Mach 4 or so, another phenomenon starts -- compressive heating.
This is where the leading edge of the ravioli actually starts being heated
by compression (remember PV=nRT, the ideal gas law?) Well, ravioli isn't
a gas, but under enough pressure, ravioli behaves as a gas. It is
compressed at the instant of impact and gets hot -- very hot. Likewise,
the impact point on the hull is compressed and gets hot. Both turn to
gasses -- real gasses, glowing-white-hot gasses. The gasses expand
spherically, causing crater-like effects, including a raised rim and a
basically parabolic shape. In the center of the crater, some material is
vaporized, then there's a melt zone, then a larger "bent" zone, and the
raised rim is caused because the gas expansion bubble center point (the
bending force) is actually the hull plate. If the hull plate
isn't thick enough, then the gas-expansion bubble pushes through to the
other side, and you get a structural breach event (technically speaking,
a "big hole") in the side of the space-cruiser. Compressive heating really hits the stride up around 20,000 feet/sec (Mach
4 in steel, Mach 15 in air) and continues as a major factor all the way
up to the high fractional Cerenkov speeds, where nuclear forces begin to
take effect. Aside: the "re-entry friction heating" that spacecraft endure when the
reenter the atmosphere is NOT friction. It's really compressive heating
of the air in the path. As long as the spacecraft is faster than Mach 1,
the air can't know to get out of the way, so it bunches up in front of
the spacecraft. When you squeeze any gas, it gets hot. So, the glowing
"reentry gas" is really just squeezed air, which heats the spacecraft heat
shield by conduction and infrared. The hypersonic ravioli can be expected
to behave similarly. As we increase speed from the high Mach numbers (about 10 miles/sec) all
the way up to about 150,000 miles/sec, not much different happens except
that the amount of kinetic energy (which turns into compressive heat)
increases. This is a huge range of velocity, but it's uninteresting
velocity. At high fractional Cerenkov speeds, the ravioli is now beginning to travel
at relativistic velocities. Among other things, this means that the
ravioli is aging more slowly than usual, and the ravioli can looks
compressed in the direction of travel. But that's really not important
right now. As we pass Cerenkov 1.0 in the target, we get a new phenomenon -- Cerenkov
radiation. This is that distinctive blue glow seen around water-cooled
reactors. It's just (relatively) harmless light (harmless compared to
the other blast effects, that is). I mention it only because it's so
nifty... At around .9 c (Cerenkov 1.1) , the ravioli starts to perceptibly weigh
more. It's just a relativistic mass increase -- all the additional weight
is actually energy, available to do compressive heating upon impact. The
extra weight is converted to heat energy according to the equation E=mc
it looks like compressive heating but it's not. [Here's where I'm a little hazy on the numbers; I'm at work and
don't have time to rederive the Lorentz transformations.] At around .985 c (Cerenkov 1.2 or so), the ravioli now weighs twice what
it used to weigh. For a one pound can, that's two pounds... or about sixty
megatons of excess energy. All of it turns to heat on impact. Probably
very little is left of the space-cruiser. At around .998 c, the impacting ravioli begins to behave less like ravioli
and more like an extremely intense radiation beam. Protons in the water
of the ravioli begin to successfully penetrate the nuclei of the hull
metal. Thermonuclear interactions, such as hydrogen fusion, may take
place in the tomato sauce. At around .9998 c, the ravioli radiation beam is still wimpy as far as
nuclear accellerator energy is concerned, but because there is so much of
it, we can expect a truly powerful blast of mixed radiation coming out of
the impact site. Radiation, not mechanical blast, may become the largest
hazard to any surviving crew members. At around .9999999 c, the ravioli radiation may begin to produce
"interesting" nuclear particles and events (heavy, short-lived particles). At around .999999999999 c, the ravioli impact site may begin to resemble
conditions in the original "big bang"; equilibrium between matter and
energy; free pair production; antimatter and matter coexisting in
equilibrium with a very intense gamma-ray flux, etc.[1] Past that, who knows? It may be possible to generate quantum black holes
given a sufficiently high velocity can of ravioli. --Bill
Ninja edit - not sure if this "Bill" was a professor or not |
Do animals ever think of "why" something happens? If they can only think visually, do they ever reach that level of asking "why"?
I always wonder what my cat thinks me and a friend are doing when we're sitting on the couch talking. I wonder he thinks we're making sounds and looking at each other. But a recent discussion about animal thinking talked about how, without language, you can only think visually. People that didn't get taught language until they were well into their teens describe that period as very fuzzy and emotional, akin to what it was like being a baby. So, do they ever even to that level of questioning?
People that didn't get taught language until they were well into their teens describe that period as very fuzzy and emotional, akin to what it was like being a baby. What's your source on that? My impression is that the number of cases of this sort of thing happening that have been well documented is so small, and the conditions in each case so variable, that the results aren't generalizable (i.e. you can't really draw conclusions from them). Your question--whether dogs wonder why things happen--gets philosophical very quickly when you start to analyze it. By that I mean, it gets harder to give any sort of sensible scientific answer. What does it mean for someone to ask a question, if you ignore the linguistic form that marks questions in human speech? You might say "trying to gain a particular piece of information". Really, questions are just tools for trying to learn something (i.e. to create a model of "reality" in your brain, however crude). Does a dog try to gain information about the world? In a technical sense, of course! Get out a treat, and a dog will very clearly how to get you to give it to him. You might as well call that "asking himself the question: How can I get that treat?", if you're working with the definition above. But you might at this point say "Wait, sure, technically it's seeking information, but that's just instinct, not actual conscious questioning!" And that's where you'll say goodbye to science, and enter the realm of philosophy. You'll have to decide how to define consciousness, for starters, and, well, good luck with that. : As for whether, by the same logic as above, dogs ask "why" questions about things that don't directly concern their interests... that's a more difficult question. How would you recognize/measure that? Can you think of an experiment that would prove/disprove the hypothesis that dogs "wonder" why people are making sounds with their mouths all the time? I'm not sure I can. |
How does the flash from a camera "ruin" a painting?
In some museum galleries, they have signs that say "no flash photography" because it'll supposedly mess up the paintings over time. However, in other galleries flash is completely fine. Does it have to do with the type of paint or the age of the painting? What exactly happens?
It's not a single flash, I don't think, but the prospect of hundreds of strobing flashes every day---if they were exposed to sunlight, they would bleach and fade, and I'm positive the same would happen under enough flashes. |
What is the relationship (if any) of the electric field in EM radiation to the Force (perpendicual)/ Force (centripetal) and the electric field of a point charge?
In lecture today, I was told that E(rad) = kqa/(c r). Playing around with the equation I found another way to write this equation, however my professor quickly brushed this off as just a coincidence. I would like a second opinion. Here is what I found: given E(point charge) = kq/r , F(perpendicular) = ma(perpendicular), and when v=c F(centripetal) = mc /r, I saw that E(rad) = kqa/(c r) = E(point charge)F(perpendicular)/F(centripetal). Is there some reason behind this, or is it just like my professor said, a coincidence?
I'm not sure I understand your notation. An electromagnetic wave incident on a surface exerts a pressure that is equation to the average Poynting vector divided by c. The Poynting vector is proportional to the square of the electric field. Also, no charged object moves at the speed of light. |
Is there a way to tell if a product is made from BPA plastics over say, another plastic like ABS, if there are no recycling symbols given?
Asking because I have fake nails I glue onto my fingers, which means I’m in skin contact with plastic for weeks and through hot showers. I’ve heard BPA is a big issue in both these situations so I’m a bit concerned. Is there any way to test this at home? For example, through their reaction with alcohol or through testing their melting point?
You can’t tell on products like that unless the manufacturer tells you the material. You can ask them usually. I will say, the main way we’re exposed to these chemicals is through ingestion. I personally don’t think absorption through the nail would be very large. As a person who studies microplastics for my PhD, I wouldn’t be too worried about it |
What kind of unethical/illegal/immoral experiments would advance your field?
Being allowed to try any cancer treatment we can come up with (with plausible reason to think it would work) "just to see". but that's an easy/obvious one. |
I heard that after sex, men have a biological impulse to get away from the woman and women have the impulse to keep the man close. Is this true?
The real, honest answer, that you won't actually see much on reddit: Nobody knows. We don't know much about our behaviour and evolution and "Why do humans..". We can make guesses based on neurotransmitter levels. (Oxytocin especially in this case would be relevant). The statement "Humans have evolved to..." seems almost entirely irrelevant in todays human. Our behaviours are unpredictable and very largely based on enviromental factors like culture and parents. Off tangent. But I hate seeing people try to guess "why we evolved..." Like "Why did humans evolve to enjoy music so much" You will have countless postulations that go on patterns and seem plausible but in reality have to a scientific look at the question. The answer may actually be "We didn't.." or "no". Similar to your question. |
What is quantum tunneling? Under what conditions does it occur?
If we model an electron as a particle in a box, I understand that the box represents an orbital, its opaqueness models uncertainty, and the length of the box models the idea of different orbitals having discrete energy levels, sort of like standing waves of a string. How does quantum tunneling fit into this picture? BONUS: How do scanning tunneling electron microscopes work? How about atomic force microscopes? EDIT:Thanks for all the replies so far...I actually posted before searching the subreddit and your replies combined with some past questions about quantum tunneling have helped my understanding of the phenomenon. In particular, has been extremely insightful. Now I'm more curious as to why this is so. Mathematically or experimentally, how do we know that the probability distributions overlap at higher energy levels?
I only have a moment now, so let me answer what tunneling is, and leave the microscopy for another person or another time: In classical physics, we know that kinetic energy is always positive, and as a consequence, the total energy is always greater than the potential energy. That means it is impossible for an object to be in a region of space in which the potential energy is greater than the total energy; such a region is therefore classically inaccessible. In addition, classically, if you have two regions A and B in which the potential energy is less than the total energy separated by a region M in which the potential is greater than the total energy, because that middle region is inaccessible, an object in region A will never be able to get to region B, not because region B is intrinsically disallowed, but because the inaccessible region M is in the way. In quantum mechanics, it turns out that the classically inaccessible region M is no longer forbidden. Tunneling is the process by which an object that starts in region A can make it to region B; the region M decreases the probability that an object will make it from A to B, but it can and will happen. |
Why does sound travel farther on water?
For example, when I go fishing. I can hear a couple on a kayak at least 100 yards or so away, and still be able to make out what they're saying. While another person is only 20-30 feet down shore and I can't make out a word they're saying.
Two reasons: First, on the water there are much fewer objects to get in the way of the sound. Other than a few waves (and if you're fishing, I'm assuming there aren't many of those) there is nothing to block the sound getting to you, so you can hear it from further away. On the shore, you have rocks, trees, and other people that block the sound. Second, sound travels well through liquids (and solids), but it doesn't move from one medium to another (air -> water; air -> solid) very well, which means that your surroundings are not absorbing much of the sound either, which allows the vibrations to travel further. |
Would a plant housed in darkness with mirrors directing light at the leaves photosynthesise at the same rate as if it were outside?
Are the light waves reflected from a mirror identical to those hitting the mirror or is the mirror absorbing some of the energy? Does it depend on the mirror material (eg glass vs polished metal)? If so would this significantly impact a plant's capacity to grow under these conditions?
There is no such thing as a perfect mirror, so in some ways the answer is no. All mirrors transmit some percentage of light (transmit being the opposite of reflect), and it varies across the spectrum. That said a typical silver mirror reflects about 85-90% of visible spectrum light that hits it. Some specialized mirrors can reflect well upwards of 95%. So in practical terms the intensity of the light would be negligibly different. Using a parabolic mirror to focus light you could increase the intensity of the light hitting the plant beyond direct sunlight levels (and easily damage the plant). In terms of the "quality" of the light, the light reflecting off of a mirror isn't changed in any way. The mirror may reflect more or less light at certain frequencies, but there is nothing different about a photon of light that has reflected versus one that hasn't. Hope that helps. |
How does putting more metal stuff around it correct a ship's compass?
I visited a maritime museum over the weekend, and there was a part of the exhibit explaining that when ships started to be made of metal, it was found that it caused inaccuracies in the compasses when travelling east-west. This is corrected by a steel bar called a Flinders Bar, and maybe Kelvin's Balls - which are unmagnetised iron, all of which pretty much surround the compass. But how does this all work? Surely adding a lot more metal around a compass means it will be more attracted to that than to the earth's magnetic field?
The earth's magnetic field induces a magnetic field in the ship's metal, which alters the magnetic field seen by the compass. The point of the Flinders Bar is to exactly cancel the field generated in the ship's metal so that the total field seen by the compass is again the earth's field. |
Did Baumgartner ever actually break the speed of sound, measured at ambient air density, at any point in his descent?
The speed of sound in a gas depends on the composition of the gas and the ambient temperature. This relationship is c=sqrt(gamma * R * T) where c is the speed of sound, gamma is a thermodynamic property known as the ratio of specific heats, R is the gas constant for the gas, and T is the temperature. Gamma and R won't vary by much over the 39 km Baumgartner traveled, leaving only a temperature dependence. That's why the speed of sound varies with altitude. Mach number is always relative to local conditions, so when he was reported to have gone Mach 1.24, that means he was going 1.24 times the local speed of sound. And since temperature tends to decrease the higher up you go (although only to a point, then it starts increasing again, and then things get kind of silly ), the speed of sound tends to decrease. In short, relative to the local speed of sound (the only frame of reference that matters for aerodynamics), Baumgartner was supersonic. |
Is this a reasonable simulation of tension across a hanging rope?
Hi! I was debugging some game physics/kinematics and noticed something I found interesting: the tension across my hanging rope was equal across its entirety, which goes against one of the few things I remember from my physics classes a decade ago. However, the simulation seems to match most of the rope characteristics that I can think of having observed in real life (it's actually uncanny; I hate it), so I'm reexamining my understanding of physics. Attached is a screen grab; the red circles represent the tension at each point (the radius of each circle is equal to "tension", which is a variable in the engine with a magnitude and no real units). Is reasonably representative of what I would expect to see if I were to measure across a real rope with a... tension...ometer? Note: I haven't seen any posts like this, before, so I'm not sure if I'm allowed to do this; I notice that media posts are disabled, but I'm not sure if that means that they're not allowed, or if they're disabled to weed out low-effort spam. I'm assuming the latter (and also assuming that this isn't a low-effort question); please let me know if I'm wrong! Edit: suggested that the tension should be equal across the horizontal component, but I didn't even write code to that, let alone have it . So I wrote a little script to draw components of vectors (and to pass the direction component of the tension vector to the script) and !! Aaaaaahhhhhhhh I am BESIDE MYSELF RIGHT NOW HOW DOES CODE I WROTE KNOW MORE PHYSICS THAN I DO THIS IS AMAZING!!! I love all of you.
Tension is a vector. It has a magnitude and direction. The horizontal component of the tension should be equal everywhere. The vertical component will be max at the highest point and zero at the minimum point. This is assuming you have gravity. So, you probably have it right, but it would be easier to understand if you could separate out the two components of the tension vector. |
"An implication of Albert Einstein's theory of general relativity is that physical space itself is not Euclidean, and Euclidean space is a good approximation for it only where the gravitational field is weak." What does this mean?
Euclidean space is space described the Euclidean geometry, which is derived from a set of postulates originally published by the Greek mathematician Euclid. Euclidean geometry is geometry as you expect it in our every day life. Where the sum of the angles in a triangle is always 180 degrees, where two parallel lines will always be at constant distance from eachother, etc... If you change the basic axioms, however, you can come up with geometries with different properties. For example on a sphere, the sum of the angles in a triangle will be more than 180 degrees and two parallel lines will eventually converge. We call these geometries "curved", because when we visualize them, they appear that way. In contrast, plain old Euclidean geometry is called "flat". An important implication of the theory of relativity is that our physical space that we live in is not flat, but curved. Mass (and energy) cause spacetime to curve and this curvature is experienced by us as gravity. So in areas where gravity is weak, the curvature of spacetime is also rather small and it becomes reasonable to approximate it and say that it's flat, Euclidean space. This makes some calculations much simpler. For many purposes, we can make this approximation for the situation here on Earth. When civil engineers design a bridge or large building, they do not need to take into account the curvature of spacetime and they can simply assume that we live in a flat spacetime. However, when an astrophysicist models the behaviour of matter near a black hole, the curvature becomes very important. |
Can typical consumer Hydrogen Peroxide solution (3%) be turned into safe drinking water?
Heating water doesn't release oxygen from the oxygen atoms in H₂O. All it does is release any dissolved oxygen. This process does not involve the breaking of any chemical bonds. Hydrogen peroxide naturally decomposes into water and oxygen , and heat will increase the rate of decomposition. |
Which berry and fruit was the first in the world?
How did berries evolve? And where did they grow? I would like to learn all about this! (Posted this in , but mods told me to try instead, so here I am)
Fruits in the strictest botanical sense are produced by Flowering Plants, only. Fruits of flowering plants as we recognize them today, probably originated in the late cretaceous or the early paleocene, possibly after the K-T extinction event that killed most of the dinosaurs as well a large amounts of other life forms. Because fleshy fruits of course decompose very rapidly, there aren't many fossils of them and we can only compare to what we know about living families of plants, to fossils of leaves and stems. There are quite a few gymnosperms that use enlarged, oily or starchy seeds to encourage small animals to disperse them. Pine nuts for example. The idea being that while the majority will simply be eaten, some will be buried and forgotten about. This may have been the case with Cycads which are some of the most ancient woody plants and most primitive conifers. Modern cycads feature enlarged conspicuous seeds that may have been dispersed by ancient megafauna. Certain conifers such as those in the yew family, ginkgoes, and junipers produce specialized female cones with only a singe, or sometimes two seeds. The seeds are surrounded by a single, enlarged, fleshy scsle called an . While these may resemble fruits or berries produced by flowering they are in fact cones and are an example of Ginkgoes are represented by only a single species today, but were much more common in the mesozoic era first appearing around 290 M.y.a., it's likely that many of those featured fleshy arils like modem ginkgoes, and used various animals to help disperse their seeds. Likewise yews were quite common in the middle jurrasic and cretaceous period. |
Total Energy in the Universe?
Has anyone ever attempted to determine the sum of all the energy in the universe? Would it be expressible as a number of Joules? Is this even a meaningful question, considering that dark matter counterbalances the energy of matter (maybe my question is about the sum of the absolute values of all energy in the universe)?
Depends on what kind of energy you are talking about.
In general, cosmologists talk about the energy density of the universe (the ammount of energy per unit volume), because this is what actually matters in the evolution of the universe, not the actual total, this is because the total volume of the universe is not known and, depending on your cosmological model, is not always a meaningful concept (of course, one could measure the ammount of photon energy in the visible universe).
Edit: Now that I'm more awake, there's a paper that deals with exactly how energy is spread in the universe, http://arxiv.org/pdf/astro-ph/0406095v2.pdf .
A nice graphic of this: http://www.mpia.de/home/poessel/UT2012/cosmic_inventory.svg Now take notice, we know the how energy is spread in the universe, but we don't know the total, because we don't know the volume of the universe! Luckily, the universe seems to be isotropic and homogeneus, so we can mesure the energy coming from different sources, add them up and see what fraction of the energy is coming from which source. |
Is it true that my wife can't get pregnant when not in her fertile tone of the month?
I just got married last week. Someone in another thread mentioned natural family planning and the idea that it is impossible for a woman to get pregnant if she's not ovulating. Is this true?
Close. You can learn enough about her cycle to ensure she doesn't get pregnant, but the window is wider than just her partial week of ovulation. Sperm can fertilize an egg for about 3-5 days after it has been deposited. So pre ovulation sex can cause pregnancy. If you are serious about avoiding pregnancy through understanding her cycle, there are two outward signs I'm aware of that indicate ovulation. Body temperature, and the viscosity of her feminine fluid. For the temperature part, one should take their temperature every day, ideally right when waking at a regular time, and chart the increase that indicates ovulation. There is a bit more detail that an expert may know, but these are places to start. And I'm sure I'll get laughed out of the park for stating this~ but the catholic church, which is very anti contraception, has done a bit of research into this topic, and has classes on how to avoid pregnancy without using it by understanding her cycle. If you can get over the stigma of a church embracing science, then the title of their program you'd want to research is "natural family planning." |
What IS the placebo effect?
I don't understand it at all, any help?
Basically, sometimes people get better when you give them a fake treatment Its thought to be caused by a variety of reasons, the "power of positive thinking" , the relief of anxiety in knowing that youre now on a tablet for your condition, self delusion etc In testing drugs , you always divide up the patients , and give half of them a drug, and half a fake drug that is just a sugar pill which looks identical. This fake pill is a placebo. Time and time again, some people on the fake drug ( the placebo ) will get better. These people have experienced the placebo effect. In order for our new drug to actually be useful, it needs to be better than a placebo. It is very important to compare everything to a placebo, because if I brand some sugar pills and give them to patients with headache, you will see a few of them improve (even though its just sugar ), and I could claim that I have a treatment for headache. Which would of course be wrong. This is why if a treatment or drug trial isnt placebo controlled, you would be very VERY skeptical of any results. |
If the solar system travels thru a nebula or a big dense cloud of matter, can our solar system grow? Can Jupiter or the sun grow in size?
No. The solar wind creates a "bubble" of plasma that prevents gas and dust in the interstellar medium from touching planets or the sun. And that plasma doesn't touch most planets since it is deflected by their magnetic field. In the few cases when it does, like Mars, it actually takes away more atmospheric matter than it deposits. Actually the sun is traversing through a region of interstellar gas and dust (though not dense enough to call it a nebula). Even though density is very low, molecules actually collide with each other over very long times (at a much larger scale than a human lifetime). It is possible to define sound and speed of sound, even though it's not human hearable. The sun is travelling supersonic in that medium, so it creates a shockwave. Voyager 2 felt it with its magnetometer when it crossed the shockwave and entered interstellar medium, confirming scientific predictions. EDIT: corrected the "nebula" term. Thanks for the corrections. |
How do nations communicate with each other?
Formal day to day communication happens between embassies and (typically) state departement of the host country. They send very official hand delivered letters to each other (called Diplomatic Notes). They can also have meetings with government officials and ambassadors. Highest form of diplomatic contact are state visits were big bosses talk to each other. Bigger issues are settled in conferences and meetings between state heads during these visits and they ofthen end with signed agreements or statements. Usually they involve lots of negotiation beforehand between lower lever officials (it can take years). Of course there are informal phone discussions and emails whenever the need arisies. |
How exactly does cutting things work at the molecular/atomic level?
Sharp object cut things. I understand that. How does that work at the molecular/atomic level? Does it interfere with the covalent, ionic, metallic, or whatever other types of bonds the object being cut has? Can someone explain?
Check out this big thread on this topic. In short, it depends on what you're cutting. At the end of the day, you are disrupting intermolecular and/or chemical bonds when you physically separate something with a knife. |
Do large impacts cause nuclear reactions?
For example, in the impact that wiped out the dinosaurs, or the impact that created the moon, are the conditions during impact sufficient to cause nuclear reactions within the impact material?
I'm going to go ahead and say that I think it's not possible. The Chicxulub impactor (the one that we think killed the dinosaurs) was 10 km across, and going 20 km/s. A little Googling tells me people have done lots of simulations of what this might look like, and seem to believe that 10,000 K sounds like a reasonable upperbound for the peak temperature. This is also way way way smaller than temperatuers where thermonuclear fusion takes place. Think millions or even billions of Kelvin for that. |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.