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[
"What is the Greatest Degree of Convexity that Still Appears Flat to the Naked Eye?"
] |
[
false
] |
...assuming a highly polished surface, on a hand sized object, viewed at ordinary angles and lighting conditions? Edit: also assuming a glossy, and non textured surface. E.g.: small pane of opaque glass
|
[
"Is it textured or uniform? Glossy or matte?"
] |
[
"Ok, this is going to be a long answer. First, I should point out that the form of the answer might not be exactly what you are looking for because it's impossible to give a single number: the answer is going to depend on a lot of factors like (a) lighting conditions, (b) material properties, (c) distance to the observer, (d) size of the object, etc. ",
"Given these caveats, here is the ",
":",
"If you really mean a uniform perfectly glossy (mirrored) object -- we're actually pretty bad at recovering the 3D shape of such things reliably, and therefore their curvature.",
"If you are willing to allow other cues like shading and texture, then the range is basically set by our ",
"stereoacuity limits",
" and we are pretty good at this. The key reference is ",
"this",
" paper. It describes the smallest disparity curvature that we can discriminate from flat (0.2 min / deg",
" ) and the smallest difference in curvature we can tell apart between two surfaces (4-6% difference). Where disparity is the difference in the vergence angle needed to fixate on two points; the disparity gradient is the rate of change of disparity over visual angle, and disparity curvature is the rate of change of disparity gradient over visual angle -- second derivative of disparity. ",
"I'm going to take your answer at face value and assume that you really mean a glossy surface with no texture or shading cues to depth, so all we are dealing with is specularities. The visual system can exploit these to recover the 3D structure of an object. Blake and Bulthoff (",
"1990",
", ",
"1991",
") provide some of the math for this, but for a more recent and easily accessible treatment, I recommend ",
"Fleming, Torralba, and Adelson (2004)",
". They show that we can accurately recover the 3D structure of an object even from a 2D image if the only cue is specularity. ",
"In the real world case, however, we are dealing with a 3D object and the fact that we have two eyes provides disparity and depth information. Usually, disparity information is a very good cue to depth. For matte surfaces, the differences in positions of the texture on the surface indicate positions on the shape / serve as a cue to shape. For glossy surfaces, however, highlights and reflections ",
" appear on the surface of the shape, but instead appear either behind or in front of the surface. This means that the two cues provide conflicting information and, if these are the only cues to depth / shape, then observers regularly misperceive the shape, relying more heavily on the disparity cues than the specularity ones (",
"Murry, Welchman, Blake, and Fleming, 2013",
"). In other words, you do not correctly perceive the shape (and therefore the curvature) of truly glossy objects (although we are better for more complicated surfaces (i.e. not perfect spheres)).",
"All that being said, perhaps you actually meant not perfectly glossy and uniform surfaces, but more like something that we encounter in the real world (Koons sculptures aside) that does typically have some other cues like a little bit of texture and is somewhat matte. If you have shading and some edge information, for example, then the limits appear to be the same as ",
"stereoacuity",
" limits (",
"Bulthoff and Mallot, 1988",
"). If curvature is defined by binocular cues alone (e.g. ",
"random dot stereogram",
"), then observers are very good and can discriminate the direction of curvature reliably when the disparity curvature (second spatial derivative of disparity (see above)) is as little as 0.02 min / deg",
" (",
"Rogers and Cagenello, 1989",
"). In terms of curvature discrimination, observers are very good at this as well and the difference between two surface curvatures needs to be only about 4-6% (i.e. the Weber fraction). Similar results are obtained when using shading or texture as cues (but not disparity) (",
"Johnston and Passmore 1994",
". When both binocular and shading cues are available, it seems like we combine them optimally (",
"Lovell, Bloj, and Harris, 2011",
"). ",
"(There are other cues to depth and curvature like motion that I'm not considering here.)"
] |
[
"Uniform and glossy."
] |
[
"Why do we like the taste of some foods but not others?"
] |
[
false
] | null |
[
"Your sense of taste is a powerful survival tool. Sweet things and fatty things (generally) provoke pleasant reactions because they are full of sugar and fat, which is otherwise a fairly rare resource in nature!",
"Unpleasant tastes can be both innate and learned. Bitter flavors tend to be automatically offputting for kids because bitter is a fairly common flavor for substances poisonous to us in plants. Meanwhile we have something called taste aversion. Have uou ever eaten something, then been very ill (either due to the food or not!) And found that food now garners a very negative reaction for you? This is an evolutionary adaptation to teach us what foods we definitely SHOULDN'T eat again. ",
"In that last case though this is less an effect on your sense of taste and more a brain thing. Certainly you can get over your association if you really try, but taste is just one aspect of how you perceive a foods flavor!"
] |
[
"Some of it is hereditary. One extreme example is the chemical ",
"Phenylthiourea",
". So I'm sure other flavor chemicals may have similar variations. Evolution would favor us liking those that have the most energy. Like sugars and fats."
] |
[
"But what about people who have different tastes? E.G. People love olives or sardines vs. people hate them. Is this just natural variation within the evolutionary influence of sweet/fatty etc. etc. or is it more closely linked to something else?"
] |
[
"Sight and Color Questions"
] |
[
false
] |
[deleted]
|
[
"here",
"Edit: After rereading #2... All three types of cones would activate based on light at say 400nm. However, each would activate to a different extent. Our percept is the result of the proportion of activation for all three cones. So an animal that had the same small cone as us but different other cones would not have a comparable color perception."
] |
[
"thanks for the reply",
"As for 1a, could you explain how much difference variation could be? Is it possible for one person's cyan to be another person's pink, or is the variation less significant and more like cyan-turquoise?",
"And I'm nearly positive the answer is no, but is there anyway to use these peak wavelength numbers and show the variation in color? I mean using some formula or program to see how a difference of 4 in small and 8 in medium would alter the hue, luminance, etc. "
] |
[
"Since everyone's brain and eyes are different, no one gets the same signal or encoding from a particular light wavelength. There is NO absolute representation of color (or any percept, for that matter). It's different in everyone. However, it is possible to agree on a labeling (see 2). ",
"We could take two colors that you would call cyan and turquoise (0 and 1, respectively) and test for descriminability. For one person, two colors separated by 0.2 would look the same. Someone else might be able to descriminate 0.1. It's probably not alway uniform (0.1 closer to cyan, 0.2 closer to turquoise). Does that make sense?",
"Ignore the peak wavelength. It's just used for describing photoreceptors. ",
"They all respond to all wavelengths of visible light.",
". To investigate how the activation level of each type of photoreceptor contributes to a specific color, you have to control the impulses of individual photoreceptors. I don't exactly know anyone willing to volunteer have an electrodes at the end of needles injected into their eyes to test that ;) Also, what good what it do? On the other hand, experiments have been done on animals to directly ",
"record brain activation",
" for various stimuli (visible stuff). That's one of the ways that people have mapped out the visual cortex."
] |
[
"Is how rested you feel proportional to the amount of sleep cycles that you have had that night?"
] |
[
false
] | null |
[
"Disclaimer: I am not a professional. I am, however, a connoisseur of sleep (as well as not feeling rested); I have narcolepsy with cataplexy. A full night of sleep is generally marked by ",
"a sequence of sleep cycles that vary in length and \"depth\"",
" (i.e. which stages of non-REM or \"NREM\" sleep one reaches). As you can see from ",
"the wikipedia article on sleep",
" (I know, not the ",
" source, but I think it suffices in this case to state a basic point),",
"In humans, each sleep cycle lasts from 90 to 110 minutes on average,[13] and each stage may have a distinct physiological function. This can result in sleep that exhibits loss of consciousness but does not fulfill its physiological functions (i.e., one may still feel tired after apparently sufficient sleep).",
"This is precisely the problem that narcoleptics have, that of feeling tired after a \"sufficient\" number of hours of sleep; in fact, doctors use this feature in one of the tests for narcolepsy ",
"(the MSLT)",
". ",
"In my not-so-professional opinion, I think that how rested you feel when you wake up has to do with which stages of sleep you are achieving when you sleep (and the quantities thereof), what stage of sleep you awaken from (preferably light sleep, I think), how much sleep you got (and whether you have an overall sleep deficit), how many times you rouse during the night (as with sleep apnea, periodic limb movement disorder, REM sleep behavior disorder, etc.) ...",
"Sleep is much more complex than just the binary process we perceive of being either conscious or not, which is why ",
"sleep studies",
" measure so many different factors.",
"Also, for what it's worth, (though doctors are not infallible) ... before I was diagnosed with narcolepsy, several doctors over the years told me that I needed to sleep ",
" to be less tired/feel more rested. I was specifically told to cut out naps and not to engage in my \"marathon sleep sessions\" where I might sleep 12 or more consecutive hours in a night. This may be good sleep hygiene for healthy people. Unfortunately, it will not \"reset\" a person with narcolepsy in any way, shape, or form and so it was useless (and sometimes potentially harmful) advice to me. But it may be evidence that the amount of sleep cycles may actually at some point be inversely proportional to \"how rested you feel\" once you cross some line in the sand. Hopefully one of the experts can speak more to this point."
] |
[
"Rested in the sense of mental fatigue, general alertness, muscle fatigue?"
] |
[
"sigh"
] |
[
"Can individuals with complete hearing loss \"hear\" via bone conduction? E.G. Shower water hitting your body, resonating bass at concerts etc.?"
] |
[
false
] |
Theoretically I'd assume this makes sense, but are there conditions which inhibit this?
|
[
"Complete hearing loss does not come from the outer or middle ear - the ear canal, drum, or tiny bones. If you have a problem with these, surgeons can and do repairs and restore some, or sometimes even normal hearing.",
"Complete loss comes from damage to the inner ear, to the structures that convert vibrations to signal to send to the brain, or even damage to the brain itself. As the system that detects vibrations has failed, transmitting vibrations through bones won't do anything."
] |
[
"No. If the nerve is damaged (sensorineural hearing loss), they would not be able to hear at all from that side. This is opposed to conductive hearing loss (e.g. ear wax, ear bone disruption, ear drum injury) which you can rehabilitate with bone conduction devices.",
"Sometimes, if an individual has complete hearing loss on one side, they can put a bone anchored hearing aid on that side. It’s a little screw that goes into the skull and vibrates, transferring the sound via bone conduction to the opposite ear. It’s a way for people with single sided deafness to hear sounds from both sides."
] |
[
"So, yes, or no?"
] |
[
"Is there an isothermal DNA application method that can amplify sheared DNA that only has 70-100 base pairs?"
] |
[
false
] |
[deleted]
|
[
"Have you tried ",
"/r/labrats",
" or ",
"/r/biology",
"? This is a totally valid question for AskScience, I just want to make sure you get an answer and those two subreddits are great."
] |
[
"Have you looked into RPA (recombinase polymerase amplification). My lab has been having good luck with it recently. 100bp might be pushing it, since the technique requires longer than normal primers (~35bp on each end), but it runs very quickly and at 37C. The website for the company that makes it is ",
"here",
". You might also want to look into RT-NASBA (reverse transcriptase nucleic acid sequence based amplification). It can go down to ~100bp targets. Good Luck!"
] |
[
"I kind of figured that RPA targets would be too long for you, but it was worth a shot, since it's so easy to work with compared to the others."
] |
[
"Does increasing the volume on your iPod drain the battery any faster than having it on low volume? Will one type of speaker or headphone drain the battery any faster/slower than another?"
] |
[
false
] | null |
[
"This is incorrect. In typical iPod usage, the backlight turns off after a few minutes. Headphone volume can make a 10-20% difference in the power consumption (and thus, battery life).",
"Source: Me - I did power-consumption and battery life testing on the first few generations of the iPod."
] |
[
"The power consumption depends on your headphones' ",
"impedance",
"; the lower the impedance, the more current is drawn per volt of input signal, and the louder your music sounds (at a given volume setting).",
"Earbud-style headphones typically have an impedance of 16-32 ohms, and the output from an iPod's headphone jack is somewhere in the vicinity of 1-2 volts at full volume. Picking numbers in the middle of those ranges and applying ",
"Ohm's law",
" gives an estimate of ~100mW of power consumption. To put that in perspective, an iPhone 4 battery has about 5 Watt-hours of capacity, so if nothing except the headphones was powered, your battery would last around 50 hours.",
"Of course, when you're actually listening to music, the CPU and peripherals are also being powered -- and probably using a lot more than the headphones. Don't expect to get a huge boost in your battery life by turning down the volume, but I wouldn't be surprised if the effect is measurable under controlled conditions."
] |
[
"The amplifier on you iPod has a relatively low power consumption - much less than the back-light for the screen or the wi-fi. Therefore there won't be a noticeable difference between low or high volume"
] |
[
"Waking up naturally VS waking up via interruption (i.e. alarm clock). Are there any negative/positive long term side effects?"
] |
[
false
] |
Waking up naturally: I normally feel more refreshed when this happens - even if its a 6 or 7 or 9 hour sleep. Waking up via interruptions: Sometimes I feel more tired than before I went to bed. Anything bad/good about this?
|
[
"Your body has 4 phases of sleep elaborated here:\n",
"http://www.jetlog.com/uploads/pics/img_main_SleepStages_01_US.jpg",
". ",
"You want to wake up at the peaks of your cycle (Stage 1), also known as REM sleep, this is when your sleep is the lightest and when you dream. Naturally waking up ensures that you wake up during Stage 1, whereas an alarm clock always runs the risk of hitting you right when your in Stages 2-3. It is highly unlikely you will wake up from Stage 4 sleep even with an alarm; this is your deepest slumber and only happens during the first half of your cycle. Sleep amount has been tied to optimal body function; sleep quality is also similarly related. "
] |
[
"Stage 1 is not REM sleep. "
] |
[
"gj you ruined the placebo effect for him :/"
] |
[
"Dear /r/AskScience how come H20 has to be bonded for us to receive the benefits of hydration?"
] |
[
false
] | null |
[
"Because Oxygen has an electron config that leads it to bond, -2, it naturally links up with other Oxygen to form O2. In order to get O to show up on its own, you need to release it from its natural O2 state, which requires an input of energy. Some chemical reactions in the will produce oxygen radicals, or O-, but it will rapidly bond with carbon, hydrogen, or metals and is rarely found in that state."
] |
[
"H2O and separate H2 an O2 behave very differently. ",
"H2O is a solvent that rapidly dissolves various molecules and makes them available for chemical reactions. H2O is also a low energy and thus stable molecule, so it can take part in various chemical reactions without coming apart. ",
"H2 is a very light gas that rapidly escapes any open container, and is able to combust with air in a very wide range of concentrations.",
"O2 will spontaneously react with most metals and organic compounds, sometimes very violently. In high concentrations it is very poisoning to the human body. Normal oxygen levels in the air are around 20%, but at significantly higher concentrations can cause ",
"problems",
" such as severe vomiting, convulsions, amnesia, and persistent dazzle.",
"Basically, the separated gasses and water contain the same stuff, but are in different states. It is like a raw piece of chicken and a pile of flour/yeast/water, it is not the same as a McChicken burger, though they contain the same basic stuff."
] |
[
"Awesome answer! I just have one question though, what is the difference between O2 and O?"
] |
[
"Is the Earth's magnetic poles destined to switch?"
] |
[
false
] |
My physics teacher told my class that the Earth's magnetic poles are due to switch in the not so distant future, so north becomes south and south becomes north. Is this true?
|
[
"Yes. It happened many times in the past and it will happen again. But \"not so distance future\" is in geological terms. The time between reversals changes from 100,000 years to1,000,000 years and it takes hundreds of years for it to be completed once it started. Last reversal happened 750,000 years ago. "
] |
[
"what will the effects be? Will human technology be affected in any serious way, asides from compasses now pointing southwards?"
] |
[
"The magnetic field that we feel from the earth is very small so a variation in it won't do anything to us directly. As you might now, the origin is from the core and the field force drops at 1/r"
] |
[
"Do trees grow rings at the equator?"
] |
[
false
] |
And if so, do they correspond to one year of age like tree rings in other places? It seems like since there aren't traditional seasons at the equator, the trees either (a) wouldn't grow in a way that would form rings or (b) the rings would form at some other frequency.
|
[
"Equatorial hardwoods still have a growth cycle. ",
"While the sun may wobble north and south through the year, other factors, such as monsoon patterns, impose their own impact. ",
"Growth during wet season will leave different rings than growth during dry season, even if the sun is directly overhead during both seasons."
] |
[
"Many tropical trees do have rings, and many others don't (",
"example",
"). Tree rings are indicative of differentiated growth cycle (warm/cold or wet/dry) so many species that adapted to dry/wet cycle form rings. However many tropical trees with rings don't follow annual rings (false-rings) which makes it difficult to use tree-rings as an accurate tool to analyze age, past climate, etc.",
"There is a research effort to use isotopes in the wood that comes from water (H & O) to detect invisible rings in tropical trees. Atoms in water have different isotopic composition (i.e. slightly different atomic weight) depending on the season. So if tree uses water from a particular season for growth, the signature of the wood follows the seasonal precipitation, leaving a signal. Currently, the signal is too noisy (spoiler: trees don't only use water that just rained) but it shows some promising signals to be used for analysis of age as well as past climate and growth condition.",
"Here is an ",
"abstract",
" on the current status of tropical dendrochronology (study of tree rings) for a slightly more in depth."
] |
[
"I don't think that this is because of the latitude at which they grow. I grew up in Phoenix, AZ which is 34 degrees north, and we had palm trees, cacti, and yucca. We also had plenty of other trees that grew in rings."
] |
[
"If I eat a \"normal\" meal, then exercise, my body is flushed with insulin but my blood sugar remains normal. If my Type-1 diabetic girlfriend doses a normal amount of insulin for a meal, then exercises after the meal, she quickly becomes hypoglycemic. What's up?"
] |
[
false
] |
[deleted]
|
[
"I've got what I believe is the correct answer to you, which also describes why exercise (with appropriate insulin dosing) is supposed to have a positive effect on blood sugar in diabetics.",
"You sound like you know a bit about this, so I'll get right into it: What really allows sugar to enter cells (and leave the blood) is GLUT-4. In muscle cells, GLUT-4 is normally floating around within the cell, then when insulin binds to the exterior of the cell it signals for GLUT-4 to be transported to the membrane, where it basically is a tunnel for glucose to enter the cell. This is insulin-mediated glucose transport.",
"However, there are other ways to activate GLUT-4 translocation. AMPK is a molecule in muscle cells, which basically acts as an energy sensor. When you're using lots of ATP, AMPK becomes activated and starts all sorts of pathways that will bring energy to the cell, allowing it to meet workload demands. One of those pathways is to send GLUT-4 to the membrane & bring in sugar, just like insulin. Some people call this exercie-mediated glucose transport.",
"So if your girlfriend takes her normal dose of insulin, followed by a big dose of exercise (which has the same effect on GLUT-4), it's like a double-dose to her blood sugar.",
"I am not a diabetes expert, but I know that some people with type-1 diabetes also lose the ability to produce glucagon. Whether this is due to down-regulation of receptors (basically the same pathway as type-2 diabetes, but with glucagon) or due to the some process in the pancreas, I don't know. But given that your girlfriend experiences this dramatic drop in blood sugar with exercise, I would speculate that there may be some impairment in glucagon function as well."
] |
[
"I did not know about GLUT-4 and will have to read up on that, but sorry to nit pick: My original point was that I don't understand why the insulin produced by my pancreas along with a big dose of exercise for me after a meal does not crash my blood sugar.",
"If glucagon production is affected in Type-1 diabetics, then that would answer my question. I'll look it up when I have time."
] |
[
"Ahh, I see what you mean. Yeah, I suspect it's a case of glucagon being affected as well."
] |
[
"If heat is random motion of particles, and the faster you go, the more time dilatation you experience; do hotter things experience more time dilatation?"
] |
[
false
] |
How much slower is time as experienced by a human compared to something at absolute zero?
|
[
"yes (there's an effect) but no (it's negligible). we are talking ridiculous temperatures here, on the order of mc² = kT. at the point where temperature would contribute significantly to the total energy of the particle. at these temperatures a whole lot of other degrees of freedom then just particle motion are unlocked (atomic, nuclear or even more energetic). particles have rest mass of something like MeV (ie mc² is on the oder of mega eV) order while room temperature i think is something like meV scale (ie kT is on the order of milli eV = 10",
" mega eV) but i have no calculator accessible. the qualitative statement should still be good. ",
"i have a calculator now and mc² = kT give T ~ 10",
" k for a proton mass. divie that by a 1000 to be save you still have absolutely ridiculous temperatures of 10",
" k"
] |
[
"I'm not sure how hot stars get, but after looking up the hottest stars I can do some estimation and find that even then, the highest speeds are less than 1% the speed of light, and any time dilation effects from motion are still going to be small. There are definitely some stellar processes that have much higher speeds, like supernovae, and you'd definitely need to account for it there. The main effect would be that particles moving near lightspeed have a far higher energy/speed ratio than you'd expect without taking relativity into account. ",
"Much more important for everyday stars is gravitational time dilation, which is different because it actually does affect the rate of everything happening inside the star, including how long it takes for particles to collide. At the sun's surface you'd be 66 seconds behind after a year passes for someone far away. Larger stars have much stronger gravity and higher time dilation rates."
] |
[
"What about the particles of a star? Do their heat add enough time dilatation to need to be accounted for when calculating stuff about stars?"
] |
[
"Are there any theoretical Non-Carbon Based Organisms?"
] |
[
false
] |
In the scientific literature are there any non-Carbon based organisms that are complex in nature?
|
[
"Are there any theoretical Non-Carbon Based Organisms? ",
"In the scientific literature are there any non-Carbon based organisms that are complex in nature?",
"This seems to be two different questions.",
"Are there ",
" non-carbon-based organisms? Sure, you can draw chemical structures all day and imagine life forms based on, for example, siloxane chains.",
"Are there any \"non-carbon organisms that are complex in nature\" in the literature? No, because they've never been observed."
] |
[
"Are there theoretical non-carbon-based organisms? Sure, you can draw chemical structures all day and imagine life forms based on, for example, siloxane chains.",
"You can go further and propose string-based lifeforms in the hearts of stars, that paper got a lot of talk last year. \"Can Self-Replicating Species Flourish in the Interior of a Star?\"",
"Like you said, you can theorise all sorts of stuff."
] |
[
"In my second question I forgot to include theoretical... essentially was wondering if in scientific literature there are any theoretical models of non-carbon based organisms that are complex."
] |
[
"What were human sleeping patterns before working hours?"
] |
[
false
] | null |
[
"It is thought that people used to have segmented sleep. Some detail here:",
"http://www.bbc.com/news/magazine-16964783",
"The disappearance of cultural references to this type of sleeping pattern coincided with what the OP expected... somewhat. I've most often read people blame the shift on artificial light. However, I don't think anyone would doubt the correlation between prolific artificial light and a more regimented (institutional) system of working hours. But there is obviously a lot of common-cause here. Artificial lights were important for developing the work hours to begin with.",
"I don't know if our terminology is very good for this subject. It is, indeed, true that the term \"second sleep\" used to be used more often:",
"https://books.google.com/ngrams/graph?content=second+sleep&year_start=1800&year_end=2000&corpus=15&smoothing=3&share=&direct_url=t1%3B%2Csecond%20sleep%3B%2Cc0",
"But that isn't an extremely convincing trend. More scholarly people have actually read what was written, and believe there to be some cultural concept that changed, so I don't dismiss this entirely.",
"The idea is, more or less, that people would go to sleep when it became dark. After all, what do you have to do? But during the night, they would wake up after 4 hours or so. Maybe they fumbled around in the dark. Maybe they had sex. Maybe they ran around the forest naked.",
"It's also clear that latitude and seasons would have affected this pattern. During summer, the night closely approximates 8 hours in places, so the second sleep (the story goes) would be short or non-existent, only to come back in vogue during the winter months. Presumably, people near the equator would more consistently delve into the second sleep.",
"An anecdotal argument for this exists. Many people report waking up in the night (like they wouldn't normally do) during camping trips. I don't know if there's any substance to that."
] |
[
"None of the other great apes are nocturnal; we probably weren't either. Our eyes are not really adapted for night work.",
"Otherwise it becomes a question of energy conservation and what time of day is the best for hunting/fishing/foraging. That depends on the location.",
"It has been reported that some families would stay in bed 22 hours a day during winter."
] |
[
"This is a bit off. The human circadian rhythm is, on average, slightly longer than 24 hours and is entrained (re-synced) to the local environment by sunlight exposure. The suprachiasmatic nucleus is above the optic chiasm and so is well positioned to detect light exposure. It then triggers the pineal gland to release melatonin in darkness. All mammals, and perhaps other animals - I don't recall offhand, produce melatonin in darkness, even nocturnal animals. So melatonin is a timing hormone, not a sleep hormone. Compared to light, other zeitgebers (time-givers, things that entrain the circadian rhythm) are very weak and may be expressing their effects through light exposure (hunger drive you to awaken to find food and probably get exposure to sunlight during this time, which affects your circadian rhythm), and so they are not of great interest.",
"\"Literally\" waves of neurotransmitters throughout the brain.",
"This is \"literally\" incorrect. Neurotransmitters do not travel in \"waves.\" "
] |
[
"What would be a \"realistic\" reason for aliens to invade? Are there any natural substances common on earth that are rare on a galactic scale?"
] |
[
false
] | null |
[
"As others have said, raw resources like water, hydrogen, metals, and silicon are readily found throughout the universe so it's unlikely that they would come for those especially since interstellar travel would already take tremendous amounts of resources. They'd likely have self sufficient food, water, air and manufacturing production easily solved long before leaving. ",
"I don't really buy aliens attacking without provocation any time in the near future since we're many generations away from being able to attempt interstellar travel, let alone being able to threaten another planet. Maybe they've been attacked themselves and view any life as a potential existential threat or maybe they're thinking on such long time scales that we can hardly fathom what they would consider important.*",
"However, if their homeworld orbited a dying star or they faced a similar catastrophe then earth would be a mighty tempting target. Other redditors have posted illuminating discussions that explain why alien life might very well be more like us than not (regarding how unique and flexible water and carbon are and why other elements are not) so it wouldn't surprise me if an alien visit were to be by carbon and water based life. ",
"*I love the other theory about them wanting our biomass but that verges into sci-fi speculation, along with any other explanation based on them having entirely alien and unrelatable motivations. Sure, maybe they want to assimilate us or forceably evolve is into a more advanced species but we should focus on the reasons that make sense to us first. ",
"Edit 1: Comments on this post have been insightful and are well worth a read. Very good points were made that aliens could want to wipe out ",
" life they find to eliminate future threats, that intelligent life is what makes Earth so rare so they'd come to exploit that, and my personal favorite: that an alien race could have set out to a habitable planet with no malicious intentions and after tens of thousands of years they arrived and found it occupied. Without the prospect of a return trip and facing extinction they would simply take it by force since it's us or them. ",
"Edit 2: I want to clarify that my answer is based on a strict interpretation of the question - this is about an ",
" so I've downplayed things like them wanting to obliterate us from afar because we might become a threat or why they'd want to come peacefully. ",
"Side note edit: I personally feel that interstellar travel takes so long and consumes so many resources that the likelyhood of ",
" type of first contact is quite low. Moreover, a species advanced enough to make the trip probably doesn't really need anything that we have that they would have to take by force. Still an awesome discussion to have. ",
"I like to believe that peacefully seeking out alien life is the natural apex for a species that has fully developed itself and that is what could drive them to explore the stars. "
] |
[
"If they can live in Earth's ecosystem, then we have a whole planet sitting here ready to move in. (Even if they easily ",
" build space habitats or terraform hostile planets or whatever, why not take this one?)",
"Some people have postulated that biological materials (plants and animals) may be very valuable on their own. The extraterrestials have plenty of silicon and aluminum and iron wherever they go, but they don't have flamingos or llamas or beets. (They may have things that ",
" like flamingos, llamas, or beets, but those things will be biochemically different.)"
] |
[
"One of the most interesting ideas I’ve read about (posited by the author Iain M Banks) is one of alien tourism. The idea is that it is super rare to have a moon that’s the same size as the sun when you’re standing on the surface of a planet, and that the total solar eclipses we get would draw intelligent, curious alien species here to view them. "
] |
[
"If I blow into a straw that's in hot tea, does the tea cool down?"
] |
[
false
] |
[deleted]
|
[
"If the tea is warmer, yes. If the tea is cooler, most probably not.",
"Most probably because there could be evaporative cooling which I find unlikely given the high humidity of breaths."
] |
[
"If the breath temperature is lower than the tea temperature, yes, you will have heat transfer from the tea to the gas (breath), cooling the tea slightly. "
] |
[
"Yes, but I think it would be less effective than blowing on top. When you blow on the top of the liquid, you're removing a small layer of evaporated liquid. Evaporation carries away a bit of heat from the liquid, and you're blowing that away, leaving the remaining liquid to be cooler.",
"Or in simpler terms: the fastest molecules can break free of the liquid to swarm in a gaseous state above. You can then blow away the fastest molecules, leaving the slightly slower molecules behind, and the overall temperature of the liquid drops slightly."
] |
[
"If Earth's magnetic poles migrate, will the aurora migrate with them?"
] |
[
false
] |
If, for example, the magnetic north pole shifts so it's under Michigan, would the Midwest have aurora the way the Arctic does now?
|
[
"Yes - the charged particles from the Sun follow the Earth's magnetic field lines, which will converge wherever the pole is.",
"(I wonder if there's actually been any work on the position of the aurorae drifting with the pole's slow movement... To Google!)"
] |
[
"Yes! I learned about this in geology class last semester. In fact there will be up to 8 magnetic poles in the middle of the polar shift and auroras will cover the Earth. Cancer rates will increase too, as the Earth's magnetic field dies down while it's happening. "
] |
[
"Cancer rates will increase too, as the Earth's magnetic field dies down while it's happening. ",
"This has not been proven. It's actually very much debatable. The atmosphere may be able to block the additional radiation well enough that the difference wouldn't be significant.",
"From ",
"Wikipedia:",
"Statistical analysis shows no evidence for a correlation between reversals and extinctions.",
"Even if the magnetic field disappeared, the solar wind may induce a sufficient magnetic field in the Earth's ionosphere to shield the surface from energetic particles.",
"Higher cancer rates (and consequently mortality rates) are possible, but it's only a hypothesis. Nobody really knows for sure."
] |
[
"If every coulomb of charge that flows from a 1.5V battery transfer 1.5J of energy, how can a 2V battery transfer 2J per coulomb of charge if it’s the same amount of electrons in every coulomb?"
] |
[
false
] | null |
[
"Each electron has more energy."
] |
[
"Follow-up question!",
"How is the energy in the electron stored/portrayed? Is it moving faster? Prone to shake? Shake more? Can we see and define a difference between two electrons with different amount of energies?",
"Or is this just asking “what is energy?”..."
] |
[
"It's potential energy. If you imagine the electrons moving through the circuit as a ball rolling down a hill, at the negative terminal of the battery, the electrons are at the top of the hill. As they move around toward the positive terminal, they are rolling down the hill.",
"When you increase the voltage of the battery, you are making the hill higher, and giving the electrons more potential energy. So the same amount of electrons carry more energy."
] |
[
"If we can perform addition on two sound to get the sum of both, can we do the opposite?"
] |
[
false
] |
So, we know we can have background_music.mp3 and voice mixed into a song.mp3 - Then, can we subtract the background_music.mp3 from a song.mp3 to produce voice.mp3?
|
[
"Short answer is yes. It's much harder to do in practice, though, especially if you don't have the exact spectra/waveforms of the signals you're trying to \"subtract.\""
] |
[
"much like noise canceling works, right?"
] |
[
"I imagined to perform C - B = A you need C and B, but you are suggesting it can be done. What gives?"
] |
[
"Why are some chemical reactions irreversible?"
] |
[
false
] | null |
[
"Technically, there are none. It's just a matter of how complicated and energy-intensive it is to revert them.",
"For example, if you burn wood and capture all the gases and ash, you could use an organic machine that uses solar energy to turn CO2, water and minerals into cellulose structures (aka trees).",
"You have Sodium and Chlorine and mix them, you get Salt and a lot of heat and light, which are lost. Want to reverse it? you need even more energy to melt the NaCl (801C), then a lot of electricity to do electrolysis.",
"You can even \"uncook\" a hard boiled egg to some extent, or at least the non-kinetic part. It won't look like an egg anymore, but that's because its physical characteristics and not the chemical properties.",
"So you can revert anything, but in some instances it would take far more effort than it's worth."
] |
[
"The short, practical answer here is that irreversible reactions generate products that are significantly lower in energy than their starting materials. As with a lot of chemistry, the in-depth answer is a bit more complicated and not a black and white situation. ",
"A reaction is called spontaneous if it is favorable without any input energy. Spontaneity can be determined by calculating the free energy of reaction. The free energy of reaction is a way to tally up the energy needed to make all of the reactants, tally up all the energy needed to make the products, and looking at the difference. If the products have less energy than the reactants, the free energy is negative and the reaction is spontaneous. For example, the reaction of Hydrogen gas + Oxygen gas to give water, which has a free energy of -237 kJ/mol, is spontaneous. ",
"This doesn't mean that a balloon filled with H2 and O2 will automatically explode. A common way to conceptualize why is using something called a ",
"reaction coordinate",
", which is a diagram with two valleys and a hill in between. Picture two valleys: one valley on the left that's higher than the valley on the right and a hill in between. H2 and O2 start on the left valley (our reactants), but in order to become water, they first need to climb up the hill, but once they're over, they can fall down on their own to the right valley to become water. The energy needed to climb that hill is usually given in the form of a spark (although brief, are usually hundreds to thousands of degrees) or a flame (which is hundreds of degrees). The product (water) is in a deeper valley than H2 and O2, which means that the energy needed to get H2 and O2 over the hill is ",
" than the energy needed to get water back over the hill. ",
", if you're in a situation where you have a consistent energy supply to push water back over the hill, that's inherently more than enough energy to push the H2 and O2 that were just formed back over to become water!",
"In this H2 and O2 example, if you set it off and get water and the reaction is now 'done', it's actually at equilibrium. All chemical reactions are technically, although not practically, reversible. One of the useful equations for free energy (G) can actually give the calculated equilibrium distribution of the products, called the equilibrium constant: ∆G = RT ln K, where K is the equilibrium constant, R is the universal gas constant, and T is the temperature in Kelvin. Using -237 kJ/mol as the formation constant at STP, the equilibrium constant K is ~3 * 10",
" which indicates that the products are favored by a ",
" margin. The neat thing about equilibrium constants is that the ",
" of the forward to the reverse reactions is equal to K. This means that the forward reaction rate happens 3 * 10",
" times as frequently as the reverse! It is important to note though that this is a ratio of rates, which is unitless. If the forward rate was 1 per second, the reverse would be 1 per 3.6*10",
" seconds (which is over 10",
" years).",
"So in conclusion: all reactions are technically reversible, but many are pragmatically and practically irreversible."
] |
[
"To add a little context to what's being said in this comment: you can think of chemical reactions as molecules trying to reach equilibrium. So for many reactions, to make it go in the reverse direction, you can just increase the amount of product vs reagents. But remember things like heat, light, molecular structure, etc.. are also products and reagents of reactions. Thus, making something go in reverse isn't always easy."
] |
[
"If somebody gets a new organ and you check ~50 years later, will the organ still have the DNA of the donor?"
] |
[
false
] | null |
[
"It depends on the organ, and on what cells you look at. Some cells (monocytes, for exemple) are able to migrate inside tissues, and they would have the DNA of the host.",
"However, the huge majority of the cells would have the donor's DNA, yes."
] |
[
"That is the standard protocol, yes. However the man who designed the protocol now believes that it is possible to reduce the dosage to zero after several years. I'm not sure if a protocol has been designed around this, though. Anecdotally, I have met someone who did stop taking the drugs.",
"However I don't think this says anything directly about DNA. As I understand it, the immune system responds to surface proteins."
] |
[
"It all is about cell replacement. In a stable organ as cells wear out they'll get replaced by adult stem cells. When you transplant an organ you also bring with it the resident stem cell population, but stem cells are a bit uppity. It's a bit of an unsolved question, but it's possible that as the transplanted organ ages and cell replacement goes on that recipient stem cells will end up 'filling the gaps'. But the majority of the organ will still be of the donor's DNA, especially since there were all the local resident multipotent stem cells in the organ.",
"cf. the role of stem cells in tissue repair"
] |
[
"How is light created on the atomic level?"
] |
[
false
] |
Take for example, a lightbulb, it is completely dark until turned on. How do atoms work with light? Sorry if this is hard to understand, I am having a hard time putting my thoughts into words at the moment.
|
[
"The light that we see is the result of a change in energy levels of electrons in an atom. Electrons have very specific energy levels that they are able to occupy, but always try to return to their lowest level possible. In order to change energy levels, they need to absorb or release the exact amount of energy that makes up the difference. In the case of a light bulb, energy is added due to the electric current being passed through a filament with a relatively high resistance. This energy causes the electrons in the filament to move up any number of energy levels, and then when the electron \"falls\" back down to its ground state (lowest level) it releases the energy in the form of a photon.",
"Source: ",
"http://www.physicsoftheuniverse.com/topics_quantum_quanta.html",
"Edit: Added a source"
] |
[
"Wouldn't light in a filament be more a result of black body radiation caused by the resistance of it?"
] |
[
"Yes the atoms vibrate due to the high temp. The electrons accelerate and decelerate. This causes energy to be emitted as photons. Some electron accelerate or decelerate faster or slower than others giving a spectrum of wavelengths. You can divide the blackbody spectrum by their repective photon energys and get how many photons are emitted per their wavelength. "
] |
[
"Do the effects of PEDs affect the children of the athletes that take them?"
] |
[
false
] |
For example, take Lance Armstrong. If he had children while on EPO, testosterone and other PEDs would they reap the benefits as well and be "super children" for lack of a better term?
|
[
"Let's think about it this way. The only material passed from father to offspring is what is included in his sperm. Therefore, unless he does something to alter his sperm, nothing will be passed on. So for Lance, beyond having ultra awesome genes (let's face it, the guy was still a great athlete without PEDs, although a complete sack of shit), nothing should be passed on to this kid. Now, if the mother is on these drugs, there very well could be some sort of effect (not necessarily what you are thinking of)"
] |
[
"So would it be possible if someone like Marion Jones had a child while on PEDs the child would reap the benefits?",
"Also, since the use of testosterone and EPO allowed Lance to train and compete at inhumane levels would that sort of boost be passed on?"
] |
[
"Basically, what I am saying is that mother and offspring exchange blood, nutrients, etc, while the only thing the father provides is the DNA from his sperm. Effects of drugs, be it crack or HGH will be passed onto the child through the mother. I am in no position to comment on long term affects, but I can pretty much say that you won't develop a super human athlete by taking EPO, HGH, steroids, etc during pregnancy."
] |
[
"Where does the matter \"swallowed\" by black holes go?"
] |
[
false
] |
I've been told many different things, for example that the universe is like a table cloth and black holes are like dips in the cloth and that matter collects in the bottom making the dip larger. But what exactly is a black hole and what happens when matter falls into it?
|
[
"Worth pointing out that a black hole need not be a singularity. Any object dense enough can be a black hole. I read somewhere that singularities might be impossible with a theoretical maximum density for any matter. Only seen it mentioned once though, the current school of thought is that most black holes are singularities.",
"Also Hawking radiation has not been observed yet. It is pretty well understood and most scientists agree but no observations have confirmed the predictions. There is a hope that the LHC will create mini black holes as the smaller the black hole the faster the rate of Hawking radiation should be. A really tiny black hole should (contrary to original thought) \"shine\" really brightly for a fraction of a second before being destroyed. If this is seen then it would confirm Hawking's predictions."
] |
[
"We can't tell where matter entering a black hole goes because they have an event horizon. Once anything, even light, crosses this point, it's unable to escape the pull and is drawn into the black hole. This means that anything 'beyond' the event horizon is un-observable to us on the outside.",
"http://en.wikipedia.org/wiki/Event_horizon"
] |
[
"Matter is something like polysterene. Throw a huge brick in a bucket of paint thinner and watch it just WHOOOSH disappear. Matter is mostly hollow space and black holes are what's the matter do without all the hollow space inside the atoms. SQUISHHHH"
] |
[
"Where did all of the organic mass come from?"
] |
[
false
] |
The surface of the earth is teaming with life. Life is everywhere. And, we're living on a surface that is layers and layers, up to a mile, of previous living things. Oil is supposedly previously live creatures and is far below the surface. Limestone is huge amounts of formerly live organisms compacted over time by the layers above and the sea above. Where does all of this mass come from that we can pile hundreds of feet to a mile of organic matter across the surface of the earth. All of these components came from the primordial stew?
|
[
"There wasn't a carbon cycle before there was life. ",
"Yes there was, that's sort of the point I am making (although perhaps clumsily). Prior to the appearance of life (and keep in mind that our current understanding is that life appeared ",
" early, ",
"at least 3.8 billion years ago, and possibly earlier",
"), our planet had a perfectly sensible and functional carbon cycle, where inorganic carbon transited between various reservoirs (essentially the lithosphere, the atmosphere and the hydrosphere). Each of these mega-reservoirs has a bunch of sub-reservoirs (surface waters vs the deep ocean, for instance). ",
"If life had not emerged, there would still be carbon cycling between these reservoirs, essentially through inorganic processes. CO2 and possibly methane would be the main carbon species in the air and water, with dissolved carbonate also present in the water. And in rocks there is no shortage of ways carbon may be bound in minerals through purely inorganic processes as well.",
"The only difference in the cycle life has made, is that it has added one extra reservoir: the biosphere. This new reservoir also exchanges carbon with all of the others, and it has effects on the form and rates at which carbon fluxes occur (just like any other reservoir would), but in the end it is merely one extra reservoir among several, and not a particularly large one at that.",
"As to the original source of terrestrial carbon, it mostly originates from the degassing of the mantle, where immense volumes of carbon are trapped, and are slowly being released through volcanic activity to this very day. This is particularly well illustrated by one specific crisis our planet went through, the so-called ",
"\"Snowball-Earth\"",
" episode... This is a massive runaway glaciation we went through in the late Precambrian, where at least partial (but possibly complete) ice cover reached down to at least the tropics and possibly the equator. This, of course, did not do the biosphere any good, as the room left for photosynthesis became extremely limited, possibly being limited to seasonal occurrences in equatorial waters at the most. It may also have altogether stopped. As a result, the amount of carbon in the biosphere went down. Now, where things get interesting and relate to your question is how it ended. Since photosynthesis was close to nil and ice formed a barrier isolating the atmosphere from the oceans, whatever carbon finding its way to the atmosphere tended to stay there. So what happened is that ",
"volcanic activity kept adding CO2 to the atmosphere until an extreme runaway greenhouse effect installed itself and initiated a planetary meltdown",
". This is readily apparent from the carbon isotopes of the warm-water carbonate deposits topping the equatorial glacial deposits left by Snowball Earth. Ultimately, the CO2 emitted by volcanism finds its source in the mantle. And once the ice was gone, exchanges between the various reservoirs were able to resume, as did photosynthesis which went in overdrive and pumped that excess"
] |
[
"It helps to answer this kind of question to take a step back and view the ",
"carbon cycle (CC) as a whole",
". ",
"The CC essentially describes how carbon transits from one reservoir to the next. As you rightly point out, some of these reservoirs are organic, others are not.",
"One massive reservoir is the atmosphere, where it is stored in CO2. That reservoir equilibrates through gaseous exchange with the hydrosphere where CO2 dissolves. From these 2 reservoirs, organisms may convert CO2 into biomass through respiration, photosynthesis and other metabolic processes. Some of that goes into living tissue of immensely variable composition, some of that goes into somewhat inert skeletal components often made of carbonate. Both of these go back to the lithosphere where they may accumulate either as carbonate rocks or as hydrocarbons, and they may remain within that reservoir for very long times indeed.",
"Exchanges between reservoirs occur constantly.",
"So, one part of your answer is that the rate at which carbon transits from one reservoir to another may be immensely variable depending on which pair of reservoirs we consider. The lithosphere is the slow one, so carbon tends to accumulate there and that makes the lithospheric reservoir one of the huge ones."
] |
[
"I really love this response. Thanks. ",
"I guess what I'm still wrestling with is that there's enough new biomass created over time that the biosphere is now becoming part of the lithosphere. It's getting layered in. It seems that the biosphere is getting something for nothing - but, you've convinced me that it's an exchange. What one sphere gains is taken from another. "
] |
[
"In general, what type of information is obtained through spectroscopy?"
] |
[
false
] | null |
[
"You should check out the ",
"Wikipedia page",
" first. Spectroscopy is a ",
" broad term that encompasses many techniques, each of which can provide different information on the system being examined."
] |
[
"A ...spectrum. Essentially a range of electromagnetic energies that have been absorbed by the sample. Or in the case of mass spectroscopy, a breakdown of the atomic weights of the constituent atoms. In either case, the objective is to identify the material."
] |
[
"All those emissions or absorption lines tell you what the spacing between energy levels is. Every atom and molecule has a unique energy spacing structure which is like a fingerprint. If you see the same pattern, you can conclusively say that sample contains that atom or molecule, even if the structure is billions of light years away."
] |
[
"How do Google Maps and other GPS systems calculate distance between two points?"
] |
[
false
] |
Is it the birds eye distance or the actual distance a car would travel. For example: Looking at a right triangle, the length (birds eye) would be much different than the hypotenuse (actual distance). This would be significantly different when looking at distances between the bottom and peak of a mountain.
|
[
"Most GPS systems use graph-search algorithms for path-finding such as ",
"Djikstra's Algorithm",
" (in reality, the algorithms used by Google Maps, Bing Maps, etc. are considerably more complex and are likely trade secrets, but most of them, in concept, are very similar to Djikstra), where the route is a collection of data points with a recorded distance between two points. Traditionally, they don't calculate \"what's the distance between point X and point Y\", they have a table that says \"point X connects to points Y, Z, and K, and the distance between point X and these points is n\". This way they can factor in the length of curvy roads, etc.",
"So your question really becomes \"does the data source they're relying on for this data factor in changes in altitude\". I don't have a source to answer that question - my suspicion is yes."
] |
[
"Also, since Djikstra's algorithm runs slow when you have hundreds of thousands of data points, most of the paths are probably precompiled to simplify the process."
] |
[
"It depends on where you are and your GPS unit.",
"If you are in the wilderness, most nice GPS systems are pretty good about calculating elevation as well as x,y coordinates. For most distances you care about when using a GPS, it is trivial then to calculate a hypotenuse. In order to have elevation date, you need contact with at least four stallites. This is usually not a problem (you usually get more, so even additional accuracy).",
"For cities, distance is usually calculated through \"route\" data. In most mapping systems, there are features called ",
"\"routes\" (more info here)",
". Finding true distance from one point to another along a set of routes is quite trivial also - that data is stored implicitly within all route datasets I have ever seen. So assuming you have a correctly built route dataset for streets, and at least four satellites for traveling off-road, then you can get a pretty accurate surface distance between two points.",
"That being said, whether or not a GPS unit takes elevation into account when you input a destination and origin is entirely up to the GPS unit. Most I have worked with only calculate birds-eye-distances, at least by default. A more expensive GPS unit would certainly have both options."
] |
[
"When you are sick they tell you to cough up as much \"infected\" phlem as you can and get it out of your body, is coughing up and then swallowing it as effective?"
] |
[
false
] |
There are many situations where it is not feasible or socially acceptable to get rid of the phlem you just coughed up so people just swallow it, is getting it out of your lungs and into your stomach as effective as out of your body? does it just get stuck in your throat again when you try to swallow? Also, I realize phlem might not be the right word but you all know what I mean.
|
[
"Normal lung secretions are designed to end up in the stomach.",
"\nThey are tracked up through the bronchioles and bronchus by cilia (small rhythmically-flailing processes). They reach the oesophagus and are then swallowed. Any pathogens trapped in these mucous secretions are then destroyed in the highly acidic environment of the stomach.",
"\nAs long as there are no breaches in your GIT integrity you should be able to do the same with mucous containing a higher viral/bacterial load with little consequence. Acid plus a thick mucous wall protects you, and will effectively remove the \"infected\" phlegm from your body."
] |
[
"It is a dire fate indeed for an erstwhile fiercely pathogenic upper respiratory targeted microbe to end up surrounded by pepsin and hydrochloric acid, with nary an alveolus in sight :-O"
] |
[
"Though stomach acid will most likely kill bacterial/viral infection, high amounts of mucus in the intestinal tract will often cause diarrhea. "
] |
[
"Why is it so much easier to fall asleep in class than it is in my bed when I actually need to sleep?"
] |
[
false
] | null |
[
"This is a response directly to this statement and not the question as a whole, but I imagine that it's because, in class, you are trying to focus on a subject that you may find boring or uninteresting. When at home, your mind is free to wander and imagine whatever it is that you feel like. Internal stimuli can be just as powerful, if not more so, than external stimuli."
] |
[
"Genetics major. =)",
" By the way, I think this statement alone has made my entire week. Thank you."
] |
[
"I feel like that's the same reason you instantly wake up after the class you couldn't even keep your eyes open in. You've got stuff to do again, your brain is ready to think about a multitude of things. "
] |
[
"Have we come any closer to understanding the mind/body problem?"
] |
[
false
] | null |
[
"You should clarify which part of the mind-body problem you are referring to. Working theory is that the mind is a phenomenon that arises from processes in the brain. There are numerous brain damage cases that illustrate this effect. When the brain is damaged, the mind is altered.",
"It is a mistake to think of particles as \"dumb.\" They give rise to every intelligence and can take an infinite number of shapes. In a way, the particles \"know\" more than we do.",
"The mind is an amazing thing, but we are presumably not the only creatures that possess minds. It is safe to say that all creatures that possess a brain have a mind of some sort. The supporting evidence is that we have brains and minds that are tied together, and there is no contradictory evidence.",
"A large number of our inherited mental features existed long before man arrived on the scene. It is likely that pain, fear, frustration, and lust, to name a few, existed in animals long before the birth of the first man. The human mind is just able to make more detailed reactions to these strong emotions.",
"It is still unclear, however, exactly how particles bumping into each other really results in what we experience as our minds. There is not a clear way to draw the line between a physical process that gives rise to consciousness and one that doesn't. We assume that it can be attributed to the complexities of the living brain, but then again, complexity is everywhere."
] |
[
"It is safe to say that all creatures that possess a brain have a mind of some sort. The supporting evidence is that we have brains and minds that are tied together, and there is no contradictory evidence.",
"On the topic of consciousness, however, there is mounting evidence that neocortical areas near the system's inputs and outputs contribute less directly to conscious experience than neocortical areas at higher hierarchical levels (prefrontal cortex, posterior parietal cortex, inferior and medial temporal cortex), as well as paleocortical areas in the middle temporal lobe that look like seahorses. ",
"As just one example, if you test out a transcranial magnetic stimulator, you will place it over the cranium and attempt to use pulses to trigger contraction of the first dorsal interosseous muscle (a thumb twitch). This can be elicited easily in me, and in many others, and although the twitch clearly originates from the neocortical origin and uses the corticospinal pathways, I have no conscious knowledge of the twitch. I feel it just as though someone electrically stimulated the muscle through the skin. Not all cortical activity is consciousness, but some is.",
"Why is this important? Well, the proportion of the brain that is association neocortex is expanded dramatically in humans. If consciousness is biased strongly towards association cortical areas (and HUGE amounts of evidence now supports this), then the richness of the conscious experience of humans is not matched by other species. Even in a chimpanzee, it would be at most a third as rich, and in rodents consciousness would be but a tiny shadow of what humans experience. "
] |
[
"This is the correct answer. For anyone looking for more reading, the name of the problem is called the \"Hard Problem of Consciousness\"."
] |
[
"Schrödinger's cat... it seems like a ridiculous concept, can someone elaborate?"
] |
[
false
] |
[deleted]
|
[
"Other people have pointed out the implications of the thought experiment***, but it is worth pointing out the very reason why Schrodinger made the argument originally (although it comes from discussions with Einstein) which was to highlight some of the points you're making; the absurdity of extrapolating the quantum state to be an observer independent object to a macroscopic formulation. ",
"In his original paper, Schrodinger states",
"One can even set up quite ridiculous cases. A cat is penned up in a steel chamber...",
"See ",
"here",
" for a translation. ",
"Many people omit this sentence which is unfortunate since the experiment was originally devised to point out the ridiculousness of some aspects of quantum mechanics and now it has turned into something used to illustrate quantum weirdness as opposed to a criticism of the theory originally. ",
"***I've added a bit of an explanation further down the tree. "
] |
[
"Why is it assumed to be this way as oppose to just something definitive happening?",
"This is what Einstein would have said, as he refused to believe that nature was not deterministic. It turns out though, it's actually possible to prove mathematically that certain physical situations are impossible to explain deterministically. This is through something called Bell's inequalities, and how they relate to something called an \"entangled system\".",
"Say for example, you have two photons that become \"entangled\". This means that if you measure one to be in state <1>, you will always measure the other to be in state <-1>, and vice versa. No matter how far you separate the photons, even across the galaxy, the measurement of the state of one photon will always tell you the state of the other. There are two ways to explain this however:",
"Deterministic -- When the particles become entangled, one is assigned one state, the other is assigned the other, right away. So although you haven't measured what the states are yet, the photons have actually been assigned opposite states right away.",
"Probabilistic -- Both particles have a 50/50 chance of being either state <1> or state <-1>. As soon as you measure one, the wave function collapses and it must be one or the other. Once you know the state of one photon, you ",
" know the state of the other, as they cannot be the same. However, before you make a measurement, both particles are in a superposition of the two states, not one or the other.",
"Turns out, if you look at all the possible initial combinations in the deterministic situation, it doesn't match up with what we see in the lab. Only the probabilistic situation describes what we see experimentally. This was the nail in the coffin for deterministic physics."
] |
[
"I find that Wikipedia does a very good job",
".",
"Basically the idea is that if the quantum state is an observer independent fundamental object, then I should be able to write down the wavefunction of a cat, basically extrapolating the wave upwards from microscopic to a macroscopic. You need some quantum process, which is the purpose of the radioactive substance (interestingly enough when Einstein first suggested the experiment, he mentioned using TNT!) which is completely random to trigger releasing the poison which might kill the cat. Hence the system has some fundamental randomness to it, i.e. we don't know whether or not the radioactive substance will decay.",
"The original goes that if an atom decays, say with 50% for convenience (there are other things you could use instead, say the spin of an electron) if it decays then it triggers the poison and kills the cat. If it doesn't decay, the cat is alive. In quantum mechanics, we would write down the whole system as a superposition of decay and non-decay but this would also, logically, since we modelling the cat as quantum as well, would involve a dead cat and an alive cat. How you do this requires more knowledge of quantum theory which I'd rather not get into and the lectures above discuss it in the entire mathematical details, but just accept that it can be done and is entirely within the theory (although some might disagree about how to set-up the problem within the quantum framework depending on how you interpret quantum theory, which is the very point we're trying to illuminate). If our interpretation of quantum mechanics is correct, this means that we would have an alive and dead cat. The point is, this is absurd! ",
"Of course we could replace the cat with something else, say an inanimate object like a balloon and instead of radioactive decay triggering poison it triggers a needle that pops the balloon, then we would describe the balloon as being both popped and unpopped at the same time. Basically the cat is more gruesome. ",
"As for whether another person observes or not, then you run into different things, such as ",
"Wigner's friend",
". Basically Schrodinger was pointing out that if you have an observer independent phenomena then you can get very weird things. How these are resolved is the subject of textbooks and careers and the video lectures I linked to above get into all the gory details.",
"So overall, the whole idea of the thought experiment is to show crazy consequences of what happens when you interpret quantum mechanics a certain way. "
] |
[
"is there any animal who commits suicide?"
] |
[
false
] | null |
[
"Here",
" you will see how some penguins commit suicide by separating from the colony to wander aimlessly in the wilderness. It is not direct suicide, but suicide none-the-less."
] |
[
"There was that thing about the bear in China that killed its cubs then herself. Let me see if I can find it. ",
"Here's more info."
] |
[
"if you poison yourself before you are taken by other predators, mayby you won't be targeted by other predators?"
] |
[
"I want to learn more about statistics and probabilities. Where's a good place to start?"
] |
[
false
] | null |
[
"There are some good books that put stats and probability into real world everyday context. Just check out the non-fiction section of your local library. My favourite was \"Conned Again, Watson!: Cautionary Tales of Logic, Math, and Probability\""
] |
[
"I usually find it easier to use a book rather than wikipedia for learning, I used \"Mathematical Statistics and Data Analysis\" by J A Rice when I studied statistics. Using literature and doing the problems is usually a good start but as with everything you only get good when you practice your knowledge. Do you need statistic for a specific project? Try to apply the knowledge to that project. Otherwise why not make up a project."
] |
[
"if you have a 2% chance, then after 50 attempts you must be successful",
"With that sort of probems, i find it easier to calculate the opposite outcome: what are the odds to fail all 50 attempts ? It's 98% to the power of 50 = about 36%. If you have a 2% chance, then after 50 attempts your odds of success are only 64% (100-36)."
] |
[
"What does it take to domesticate an animal?"
] |
[
false
] |
I've been wondering about this question for some time now. Just thinking if certain types of animals should be easier to domesticate than others, and what would it take? for example, I know there were experiments to domesticate foxes, but there were difficulties. But what about a sloth? don't know if I'm allowed to ask another related question but I also wondered what would happen if dogs were bred selecting the smarter ones, creating a new race based on intellect, how 'smart' of a dog could we get?
|
[
"Domestication is very breed dependent",
". Take dogs and cats, for example. Dogs have an enormous range of size compared to cats, and many morphological changes in dog breeds have been recorded just in the ",
"last 100 years",
". Cats do have a range of features as well, but not nearly as broad a range as what we see in dogs. There are ",
"several proposals",
" for the source of this variation in dogs. It might be that dog breeders are more intense in selecting for new traits, or there might be genetic features in dogs that make it easier for alterations in the DNA to occur without producing an abundance of harmful mutations (such as repeated DNA segments that can be shortened or extended easily). ",
"Many ",
"animals have been domesticated",
", with dogs being one of the earliest, but we can't really say what makes some animals easier to domesticate than others. The horse and the zebra are closely related, but ",
"domesticating zebras has proved very difficult",
". Maybe animals need to have DNA that produces variation quickly, or maybe some wild features can't be bred out as easily as others. ",
"For your second question, there have been attempts to breed more intelligent dogs already. But we have different definitions of intelligence, and it isn't nearly as easy to measure intelligence as it is to measure size or coat type. If you keep breeding dogs for intelligence based on some standard metric, I'm sure you would see improvement with time. But we really have no idea how long it would take. "
] |
[
"The animals that would probably lend themselves best to this would be animals with a short breeding cycle, and animals that have been shown to have adaptable behaviours. ",
"Note that some animals are thought to have domesticated themselves. ",
"wiki link, sorry",
".",
"Do also remember that intellect is also thought to be environmental, not purely genetic."
] |
[
"It seems like your 1st question has been answered in depth already, but about the smart dogs; you could breed dogs to be the smartest creatures on the planet. The only limitations are time and physical impossibility.",
"How do you think humans got this smart? We didn't begin that way. If you could measure intelligence accurately in dogs, and you wanted to take the time, there is no law of biology or physics saying that they ",
" be extremely smart. Keep in mind that even with ruthlessly selective breeding, this might take millions of years."
] |
[
"What happens to my taste buds when I put a spoonful of hot food (hot soup, hot pizza, hot lava) into my mouth?"
] |
[
false
] | null |
[
"There are large concentrations of thermoreceptors in your tongue that detect the heat. That's how you can tell that food is hot.",
"As for your taste buds... well, under high temperature, their rate of degeneration accelerates. A good amount of lava would burn away your tongue, for instance."
] |
[
"A hot spoon of soup, or a sip of hot coffee will cause downstream signalling of your thermosensors, so you detect the heat, if it is too hot the downstream signalling will cause the sensitisation of itself and other receptors by phosphorylation. causing your tongue to be tingly and weird (your sensors are over firing because they are responding to stimulus they normally wouldn't)\nIn terms of your taste buds, i'm not so sure! Maybe they are de-sensitised by another mechanism?"
] |
[
"What's the feeling we get after burning our tongue? The crispy weird taste buds?"
] |
[
"Why do some people faint/vomit at the site of blood/severe injury and others not?"
] |
[
false
] |
I can watch operations on TV, I've seen people get deep, bloody cuts on faces, arms, legs and this doesn't bother me - but when I get a deep cut on my own body, I shut down. I sweat, feel nauseous and I generally start to feel faint and light-headed. What's going on here?
|
[
"This is semi-layman speculation, so please don't downvote me to hell for trying!",
"This is due to the ",
"vasovagal response",
". Essentially, when presented with a trigger such as a cut or injury or even seeing someone else get injured, a cascade of responses fire off.",
"On one end of the spectrum is the cardioinhibitory response, characterized by a drop in heart rate (negative chronotropic effect) and in contractility (negative inotropic effect) leading to a decrease in cardiac output that is significant enough to result in a loss of consciousness. It is thought that this response results primarily from enhancement in parasympathetic tone.\nOn the other end of the spectrum is the vasodepressor response, caused by a drop in blood pressure (to as low as 80/20) without much change in heart rate. This phenomenon occurs due to vasodilation, probably as a result of withdrawal of sympathetic nervous system tone.\nThe majority of people with vasovagal syncope have a mixed response somewhere between these two ends of the spectrum.",
"Everyone's different, so the sudden drop in heart rate/blood pressure affects some people more severely than others."
] |
[
"Correct! ",
"I would like to add that Vasovagal syncope can occur at any age, but is more common in those under 40. Also, in addition to nausea, vomiting can occur. "
] |
[
"Thanks!"
] |
[
"Which form of fusion power confinement is closest to producing net energy? Tokamaks, Inertial-Confinement, or something else entirely?"
] |
[
false
] |
I know that the two biggest players in fusion power are currently Inertial-Confinement Fusion and Tokamak Magnetic-Confinement Fusion. I'm curious, which of those is closer to producing viable commercial fusion power? I've heard that our best fusion efficiency so far has been JET, which has achieved a Q value of 0.7. As I understand it, that represents the total energy output divided by the total energy input. I know that that discounts the efficiency of the generator, so you need a Q >10 or so to have a net energy gain. I've also heard the somewhat-recent story about NIF reaching fusion breakeven, but I'm not sure what they mean by that, as the articles I've read on it were all non-scientific and did not actually explain what that means. Wikipedia tells me the actual gain from that experiment after accounting for the inefficiencies of the lasers (which I is Q) was actually only about 0.0077. From what I see, it appears that tokamaks are orders of magnitude more efficient than inertial-confinement fusion at the moment. Am I correct in that statement, or am I missing something? And is there any other reason that inertial-confinement is considered superior to magnetic-confinement for power generation, if not the pure efficiency?
|
[
"NIF recently was able to get enough fusion energy out of the capsule as it put in with the lasers. Of course this is not break even since the lasers are very inefficient. I think they are only 1% efficient and then you have the other inefficiencies along the way that generate that power. They are about an order of magnitude away for neutron yield from the point where alpha bootstrapping will occur. ",
"A big difference between ICF and Tokamaks is how easy it will be to extract energy for a future reactor. I believe Tokamaks would be easier for practical fusion. For ICF you are looking at injecting fuel pellets at 10 Hz into a chamber and have the accuracy to hit them with micron resolution with lots of lasers. This while making sure the old target debris is out of the way. ",
"Edit:spelling and added more"
] |
[
"Yeah, I was somewhat curious as to how ICF would produce continuous levels of power given the way they use fuel pellets.",
"What sort of efficiency do we get out of the plasma heating methods that tokamaks use?"
] |
[
"I am not as up to date on Tokamak efficiency. I only know about NIF stuff since I know people working on it. "
] |
[
"How is it possible that myopia (nearsightedness) has so far survived in the gene pool?"
] |
[
false
] |
How is it possible that myopia has not been eliminated from the gene pool? As far as I understand, it would give a major disadvantage to someone living in the wild: less able to find food, navigate around and avoid being eaten by tigers. I have myopia and I can't possibly imagine myself surviving in the woods or in a jungle without glasses. How could ancient people (100,000+ years) manage to survive with myopia? This has bugged me for quite some time.. Thanks!
|
[
"Ahhh... myopia isn't very well understood. There is believed to be a genetic and environmental cause involved in it's development",
"http://disease-reference.com/Myopia.htm",
"Makes reference to studies done on tribal native americans before introducing them to school and stuff like that. ",
"Studies done with Native American tribes found that before the introduction of widespread literacy, only the tribal records-keeper had myopia but none of the rest of the population. But after all children were taught to read, the percentage of children with myopia was approximately equal to that of the rest of America. The correlation can be explained by things like a tendency of people whose parents read a lot to read a lot themselves. \n",
"In taiwan we get the same phenomenon before students enerting university. Normal prevalence of myopia. After university a massive proportion of myopes.",
"So that's the environmental factors.",
"Then we have the genetic factors. A change to the length of a perfect sighted eye ball by 1.5mm will make it -6D myopic!!!!",
"The honest answer is we don't know. Some studies suggest that rigid contact lenses during adolescence will reduce the progression of myopia"
] |
[
"There are a lot of possibilities when conditions that seem to be detrimental stick around. One, as lwbannister posted, is that there's a large environmental component--that is, something about the modern world (possibly reading lots of small print close up) increases the incidence or exacerbates the severity. Another possibility is that an allele that contributes to the condition is either also beneficial in some circumstances (this is the case with sickle cell and malaria) when heterozygous (or even homozygous, in rare cases) or is linked to an allele of another gene that is beneficial and genetically hitches along for the ride."
] |
[
"This is probably the correct answer. When I first noticed I was having trouble seeing the board in high school while sitting in the back, biologically, I had been sexually mature for about five years. So I would have had more than enough time to reproduce before getting eaten by a lion, tiger or bear."
] |
[
"How can Methyl Propanoate be formed with ethanol as the only organic reactant?"
] |
[
false
] |
I can't think of any process that I've been taught that could result in it, Is there a way in which a methyl group can be taken from one molecule of ethanol and added on to another to form molecules of propanol and methanol?
|
[
"I wasn't aware that it could. What's the context?"
] |
[
"For ethanol to methanol you could: elimination reaction (forcing conditions), ozoneolysis, sodium borohydride. all of which can be completely inorganic."
] |
[
"It's this question I was emailed from RSC.org.",
"Though I've worked it out now, it included reactions with hydrogen cyanide and hydronium to from propanoic acid and fission of dehydrated, hydrolysed ethanol which was then reacted with hydroxide ions to form methanol.",
"I can go into more detail if you're interested in the mechanism."
] |
[
"What is the closest thing to a frictionless surface?"
] |
[
false
] | null |
[
"I don't know about frictionless surfaces, but superliquid/fluid substances come close. They are liquids which can ignore friction from surfaces when at extremely low temperatures (2K) or under extreme pressure. ",
"Here's a video of superliquid helium"
] |
[
"In particular, supppose I have a tube filled with superfluid liquid helium, and I find a way to give the helium an initial spin. Will it keep rotating",
"Is exactly what will happen. I attended a talk describing an experiment where they did that. But one caveat, you actually have to 'pin down' the motion of the normal helium in the mix. Otherwise it can drain energy and momentum from the superfluid helium. They use packed, fine, glass powder to do that. The superfliud helium could easily flow through the porosity, while normal helium was stopped. They used the gyro effect of the circularly flowing superfliud to measure any decay. They saw none in 6 hours of observation."
] |
[
"What exactly does \"ignore friction from surfaces when at extremely low temperatures\" entail? In particular, supppose I have a tube filled with superfluid liquid helium, and I find a way to give the helium an initial spin. Will it keep rotating (with adequate cooling, etc) indefinitely like a ",
"superconducting current in a loop",
"? Could I, in principle, make an analogous efficient superfluid kinetic energy storage?"
] |
[
"Can daily sunscreen use make you more vulnerable to the sun?"
] |
[
false
] |
It is to my understanding that UVA radiation is what triggers melanocytes to produce melanin. My skin is relatively tan naturally and growing up (Los Angeles) I rarely applied sunblock and never got burned. When I was 18 i started working outdoors for 9 hours at a time and noticed I began to develop sun burns; as a result, I did some googling and started applying sun block daily. Its been about a year now since I started applying daily sun block and it seems as if any day I don't apply it my skin burns. Growing up I could go hours and hours in the sun without being burnt and now I burn incredibly quickly. Is this a result of permanent damage done to my skin through the years or is this a result of my daily use of sunblock preventing melanocytes from producing the bodies natural sun block, melanin? tl;dr Does sunblock prevent melanin from forming, therefore, making you weaker to the sun when you do not apply sunblock
|
[
"Sunscreen doesn't make you more prone to burning, but being pale does. ",
"That said, as public service advertising has drilled in to me (Aussie) for as long as I can remember, \"tanning is skin cells in trauma, theres nothing healthy about a tan.\"",
"So while consistent sunscreen use can make you more pale, which means you are more likely to burn, being more tanned and tanning rather than burning is not at all better for you."
] |
[
"But for skin damage including cancer - no. That's a lifetime exposure risk, and is not related to burning.",
"Are you sure about this?",
"Here is a nice paper",
" on the relationship between severe sunburns and different types of skin cancer. They have a nice sample size: 87,166 women and 32,959 men.",
"I quickly glanced through their method and they seemed to control for amount of time spent in direct sunlight in the summer months, cumulative ultraviolet flux, and sunscreen use (among other things).",
"Their conclusion is that severe sunburns are associated with increased risk of melanoma, squamous cell carcinoma, and basal cell carcinoma in both male and female. Interestingly the risk is lower for women with all skin cancer types. Also sunburns on the trunk are associated more with skin cancer than sunburns on other parts of the body."
] |
[
"Not really. ",
"If you are pale, you are at risk of being burned, sure. Stay pale, maintain risk of burning when you forget to wear sunscreen. ",
"But for skin damage including cancer - no. That's a lifetime exposure risk, and is not related to burning. The melanin in your tan is not protecting you from skin cancer. "
] |
[
"Can things fall after a long time without being disrupted at all?"
] |
[
false
] |
[deleted]
|
[
"If something isn't falling now, but then is falling later, something had to make it fall. It won't necessarily take much: a light breeze, or some internal change in the structure of the object itself. For instance, stand a hardback book on end. It's held together by glue and stitching. Over time, the chemical properties of the glue can change in such a way that it's no longer sufficiently strong to keep the parts of the book in a physical arrangement that's stable against the pull of gravity, so the book might tip over.",
"But no, gravity doesn't \"take a while\" to \"notice\" things, like in the Wile E. Coyote cartoons."
] |
[
"It's almost certainly either a vibration or a rogue air current that's causing something to fall. It hasn't been \"falling\" for a few days, if that's what you are asking."
] |
[
"I thought I'd just add the idea of ",
"static friction",
" here.",
"As the other replies stated, some external factor would start the object moving. If a small gust of wind (or something similar) was able to overcome the static friction the object is likely to keep on sliding until it falls."
] |
[
"Negative pressure/space?"
] |
[
false
] |
Would it theoretically be possible to create negative space? Say you had a box made of diamond, attached to the most powerful machine on the earth that allowed the box to expand. If you created a vacuum in this box and then tried expanding the box, what would happen? Sorry if this is a dumb question, and I know you can't have negative pressure, but what if you tried???
|
[
"There would still be a vacuum. A true vacuum means that there is zero matter in the box. Even if you made the box bigger, there would still be zero matter, and thus still a vacuum."
] |
[
"I just feel the need to point out that diamond is hard in the sense it scratches everything else. You could easily shatter a piece of diamond with a hammer."
] |
[
"Something does change, though - if your machine could stretch the box, and there is an atmosphere outside the box, you would wind up with a box with more force pushing in on it. (The outside area of the box has increased, and the outside pressure is the same).",
"If you keep going with enough pressure and a weak enough material, eventually the box will implode."
] |
[
"Why do the helium balloons hit the deck when everything else is in freefall on the vomit comet?"
] |
[
false
] |
Whats going on with the balloons in from the vomit comet. As soon as the aircraft is in free fall causing everything else to float around the aircraft, the balloons seem to loose bouncy and do the opposite.
|
[
"This is one of my favorite physics demonstrations. The answer is buoyancy! It's the same reason a helium balloon in your car gets pushed ",
" when you accelerate and backwards when you brake.",
"Think about it in terms of the way gravity normally works. When the acceleration points down, the balloon goes up due to buoyancy. In the video, the acceleration points up, which wants to press the air against the roof. Thus the buoyancy of the helium exerts a force down."
] |
[
"You're right, nothing should move if the plane is in ",
" free fall. But any deviation is going to cause motion. I can't watch the video at work, but I'm guessing at some point the passengers of the plane float up due to slight negative g... the balloon should go down correspondingly."
] |
[
"It's partly right I think. If effective gravity went negative, this is indeed what would happen. Here's a zero g explanation:",
"The heavier air normally sits at the bottom, letting the lighter helium bob up top. These balloons are anchored with strings, which the buoyancy places under tension. If gravity suddenly disappears, the strings are still under tension, pulling the balloons downwards a little, giving them a downwards impulse. Once the force is gone (string no longer taut), the balloons continue their new motion towards the floor, only slowed by friction. "
] |
[
"Why do proline residues slow protein migration in SDS-PAGE?"
] |
[
false
] |
But, based on calculations from its amino acid residues, p53's mass is actually only 43.7 kDa. This difference is due to the high number of proline residues in the protein, which slows its migration on SDS-PAGE, thus making it appear heavier than it actually is.[7] This effect is observed with p53 from a variety of species, including humans, rodents, frogs, and fish. From . What is it about proline that does this? Is this only observed in p53? Thanks I'm advance.
|
[
"So polyacrylamide gels are basically long linear chains of a polymer which are cross linked. The cross linking between the linear chains takes something that is originally like two sticks standing next to each other and turns them into a ladder. And the entire gel isn't just one ladder, it's a massive field that's absolutely packed with them.",
"It isn't the weight of the object that limits how fast it can get from one end of the field to the other end, its how easily the object can get through the rungs of the ladders. It just so happens that how easily something can get through the holes tends to correlate pretty well with how much it weighs, but this isn't always the case. ",
"On a peptide bond you have the sp2 carbon from the carbonyl group of one amino acid linked to the nitrogen of the amine from another amino acid. The bond between these two atoms generally doesn't rotate because there is a resonance structure that can be formed and it gives the bond partial double bond character, and double bonds don't rotate. ",
"Then you have the aforementioned nitrogen also bonded to the sp3 carbon that has the group which makes the amino acid the amino acid that it is. But it's just a single bond and there isn't a resonance structure that is causing the bond to be unable to rotate. However, in proline the group loops back around and attaches back onto the nitrogen. If you attach something that can normally rotate to something that can't rotate from two different positions you remove the ability of that thing to rotate. The sp3 carbon of proline is attached twice to a nitrogen that can't rotate. ",
"It also has a funky angle which essentially equates to a kink in a chain that can't go away. The proline in and of itself isn't a big thing that makes it hard to get through the holes, but there's all of that other protein beyond the kink that has to get through the hole too and to some extent it's forced into a strange position that isn't easy to squeeze through the holes.",
"If you have a ton of kinks like this you can end up having a hard time getting through the rungs of the ladder, and though the molecule itself doesn't weigh as much as another molecule it will still have a harder time getting from one end of the field to the other. ",
"Again, the gel isn't separating the molecules by weight, it's separating them by how easily they get through the holes. The entire \"molecular mass based on migration distance through a polyacrylamide gel\" thing is only an approximation. It's usually a good one, but there are cases where it isn't. "
] |
[
"''It also has a funky angle which essentially equates to a kink in a chain that can't go away''. That's the important part right there. Most amino acids are fairly linear when you look at it, but think of proline as a rigid kink in your 3D structure. You find them in B-sandwich structures because they allow that ''folding'' effect. These kinks don't necessarily weigh down the protein more, but think of it as getting more easily tangled in the web that is polyacrylamide. "
] |
[
"as proline has the fixed angle as mentioned, the denatured protein will have a more extended \"random coil\" conformation and therefore have lower mobility in SDS-PAGE, thus appear to have higher MW."
] |
[
"The NTSB wants to lower the drunk driving BAC standard to .05: Is this change significant enough that it would change the ability of the brain to process information?"
] |
[
false
] |
Biologically, what is the difference between a BAC level of .05 and .08?
|
[
"Without doubt, there is an enormous difference in the cognitive effects of alcohol between 0.05% and 0.08% blood alcohol concentrations (BAC). Different cognitive tasks are sensitive to very different levels of alcohol; ",
"some are severely affected at levels as low as 0.02%, while others are relatively insensitive up to ~0.10%",
". ",
"There is a large literature showing increasingly poor performance with increasing BAC across the range 0.05-0.08%. To give a couple of examples, ",
"this study",
" found increasingly poor driving performance in drivers at approximately 0.015, 0.030, 0.045, and 0.060% BAC. Meanwhile, ",
"this study",
" found that several aspects of driving performance progressively declined for 0.00, 0.02, 0.05, 0.08, and 0.10% BAC.",
"In addition, it should be noted that most studies of the cognitive effects of alcohol are conducted during daytime. However, there is a significant interaction of alcohol with time awake, such that the same dose can create a much larger relative impairment after an extended time awake. For example, ",
"this study",
" found that 0.035% BAC produced significant impairments in simulated driving performance when participants had only 5 hours in bed the night before.",
"Empirical studies have found positive effects of reducing road alcohol limits to 0.05% in ",
"Europe",
" and ",
"other regions",
".",
"Since ",
"32% of the 30,000 fatal crashes in the US each year can be attributed to a driver with a BAC above 0.08%",
", even small reductions in risk could have an enormous positive impact on road fatalities. In fact, a fascinating recent study looked at all fatal crashes in the US from 1994-2008 and ",
"detected a significantly increased risk for drivers with 0.01% BAC compared to those with 0.00% BAC",
". The authors concluded:",
"The severity of life-threatening motor vehicle accidents increases significantly at blood alcohol concentrations (BACs) far lower than the current US limit of 0.08%. Lowering the legal limit could save lives, prevent serious injuries and reduce financial and social costs associated with motor vehicle accidents."
] |
[
"I'll assume you mean 0.05, since 0.5 is potentially lethal! :)",
"Countries with the 0.05 limit generally recommend the following upper limits: ",
"Two standard drinks in the first hour and then one standard drink per hour after that for men",
"One standard drink per hour for women",
"A standard drink here is defined as ~12.5 mL of alcohol. This is equivalent to ~100 mL of wine, ~300 mL of beer (depending on strength), or ~30 mL (one shot) of spirits.",
"Note that there are many other factors that can affect BAC, including body weight, percentage body fat, liver function, and food consumption. However, these are useful rules of thumb in most cases."
] |
[
"The most basic rule of thumb is that one standard drink, administered in bolus (i.e., at once), would raise your BAC 0.02%, and your body would eliminate about 0.02% per hour."
] |
[
"How would an isolated pile of neutrons behave?"
] |
[
false
] |
Neutrons are shot off in every direction during a fission reaction; is it possible to keep them separate once they have? The properties of isotopes seem to indicate neutrons in an atom don't have much of an effect on its chemical properties- Would a pile of loose neutrons have no response to magnetism? Would it behave like a fluid? What color would it be?
|
[
"They would decay to protons with a half life of around 10 minutes."
] |
[
"Would they just mostly pass through solid matter? "
] |
[
"Wouldn't they stick to the atom's nuclei of whatever container/table you rested them on - creating a bunch of strange extra-neutron-heavy isotopes?"
] |
[
"What year is this?"
] |
[
false
] |
[deleted]
|
[
"Just use ",
"Julian Days",
" and apply conversions from Julian Days to the various calendars, both current and historical.",
"What I am saying is other people recognized this problem and established the now-standard solution -- Julian Days."
] |
[
"How does this obvious suggestion merit a downvote?"
] |
[
"I've been looking around for any research that really gets in-depth with comparing the chronology of western culture and its calendars with tree rings and radiocarbon dating.",
"You don't really have to do that - tree rings and radiocarbon dating are hard to use to get to a precise year.",
"Although it might seem ironic, astrology provides a good method of precisely determining the accuracy of earlier calendars. Check out this ",
"horoscope",
" that Johannes Kepler prepared for General Wallenstein. It has the precise date of the General's birthday (Sept 24 1583) listed as well as the positions of all of the planets in the sky. ",
"The two wobbly lines on the left are for the constellation Aquarius, and the symbols for Jupiter and Saturn are shown there about 3 degrees apart.",
"With very precise models of planetary motion we can 'wind back the clock' and look at where all the planets were with extreme accuracy thousands of years ago.",
"You can go to the sky map at ",
"Fourmilab",
" and put in the Universal Time date '1583-09-24 0:00:00'. Then you will see that Jupiter and Saturn did indeed appear about 3 degrees apart in Aquarius. You can also look at the position of Mars and Venus and they are in the right place. The Sun and Mercury look a bit off - but that could be calculational error with Kepler's model as he is winding back the clock from 1608 to 1583 using renaissance models of planetary motion (probably Ptolemaic via the ",
"Alfonsine Tables",
". I could also be reading the horoscope wrong - I am not a Renaissance astrologer :)",
"People were doing this sort of thing all the way back to the Roman empire and before.",
"I don't think that this fully answers the question - but I think that it is cool."
] |
[
"In light of the recent growth of sightings of Tasmanian Tigers and possibility of a species coming back from what we thought was extinction... Has this happened with any other species in the last ~500 years?"
] |
[
false
] |
Question in title. Just curious if other species have rebounded that we are aware of. Thank you in advance. Edit: Really interesting answers by everyone so far. Thank you! Edit 2: Follow up question. What are the biological implications when a species that we thought was extinct, rebounds it's population? Is it just limited to things like focusing on changing what caused their extinction in the first place, like eradicating the rats in the "tree lobster" article? Edit 3: Holy cow ladies and gents. I never thought I would get this much feedback on my post. It's going to take me a bit to read through it. But I will. In the mean time, thank you again, from the bottom of my heart, for all your answers and feedback. Edit 4: Here are a couple links that led me to believe that the sightings had increased and were credible enough to be taken seriously by scientists. (copy/pasted from a buried comment) Here is a different which I read a couple days ago that prompted me to think that the number of sightings have increased recently. In the article they mention several recent sightings and the fact that there is a team of scientists taking action to further investigate the claims. More information on the scientists conducting the research can be found in a media release from James Cook University. Dr. Sandra Abell and professor Bill Laurence will be leading a team of scientists that will be placing 50 wildlife cameras out in strategic locations to try to catch a glimpse of the creature. This is part of an already existing study that they were conducting to monitor wildlife that had been modified to focus on the Tasmanian Tigers following the credible sighting reports.
|
[
"Black footed ferrets from the US and Canada were declared extinct in 1979 due to farmers poisoning prairie dogs, their food supply. Lo and behold, a farmer's dog brought home a dead one 2 years later and they became endangered instead!"
] |
[
"Yes, this happens quite often, although you will hear more news about animals like tigers since they are more popular. There is also the issue of deciding when to declare an animal extinct. Many birds are elusive and haven't been sighted in years. From a quick search here are some animals thought to be extinct but rediscovered:",
"Yangtze River dolphin ",
"http://www.npr.org/templates/story/story.php?storyId=14599250",
"\"Tree lobster\" ",
"http://www.npr.org/sections/krulwich/2012/02/24/147367644/six-legged-giant-finds-secret-hideaway-hides-for-80-years",
"imperial woodpecker ",
"http://www.npr.org/2011/12/23/144190097/searching-for-a-ghost-bird"
] |
[
"The tree lobster story was fascinating. Thanks for sharing!"
] |
[
"What's a career for PhD outside of academia like?"
] |
[
false
] |
I was reading thread hoping to find some descriptions of science careers outside of academia, but to little avail. My question is: What types of career's (in science, hopefully) are available to PhD holders outside of academia? I just finished my undergraduate in engineering and entering a graduate program in biomedical engineering come fall. However, academia has never attracted me; if anything, I feel quite the opposite, especially after reading . Thus it has been my plan to jump ship to industry after finishing my PhD; However it is my impression that this is the uncommon route for most people entering graduate school. Can anyone relate their stories of non-academia careers, and how or why?
|
[
"Not to be rude, but this is completely false. I know ",
" few (domestic) master's students in my graduate chemical engineering program--there's a good reason for that. Unless you already have a job, which is paying for your master's program, there is no reason to get that degree. You'd be competing for the same jobs that companies want to give to undergraduates, but asking for more money without more real experience, and as such you're at a competitive disadvantage. The people I know who left with masters ended up taking jobs at the undergrad entry level, on the same pay scale as those who went straight to work after graduating with their BS. That might say as much about the economy as anything else, but there it is.",
"In my department, I'd say that about a quarter of people end up in academic positions after their PhD, another quarter end up working for the government, and about half go into industry. Most of the industry folks are in R&D departments for oil companies, pharma companies, random consulting firms, or any number of other industries (this will vary a lot depending on where you are). I personally will likely end up working in industry after I graduate...the pay is about twice as much and I don't think I'd want to go the post-doc/tenure track route."
] |
[
"Still at the conference, so I can only drop short comments, right now a chemical engineer is talking, so I am doing this to keep from falling asleep. (sorry chemEs but reboiler calculations are super dull!) any how, don't believe that whole line about engineering phds not being worth anything in industry, it simply isn't true, I work with a bunch of them. The job is pretty stable, on occasion exciting, but font hold your breathe. The pace of research is much slower, but a lot more funded, so you spend a lot more time convincing people to let you work on a project, but once you have you get pretty much whatever you need. The research is easy, but very practically focused, you are not pushing frontiers but applying existing knowledge and refining it. The rewards are more financially, and the hours are predictable. I don't think about work outside of work, and I take vacations when I feel. My PhD advisor was in his office at 7 am on Sundays!"
] |
[
"I laid this out in my other comment, but I figured I'd give you an orange letter--In my ChemE department, about half of people end up in industry, a quarter in government, and a quarter in academia. There's absolutely nothing wrong with going into industry, and there are plenty of jobs in R&D and processing that they want PhD engineers for. I will probably end up there, because it will give me more freedom to decide ",
" I want to live, I'll get paid more, and I'd like to avoid the postdoc/tenure process. As for what your'e doing and what it's like, from what I understand it varies a lot by field and company."
] |
[
"Is there such a thing as a \"pure\" note?"
] |
[
false
] |
The same pitch has a different tone quality on different instruments. Is there anything that's considered to be a "pure" note, meaning it doesn't sound like any one thing and is just the pitch?
|
[
"To put it simply, no. We divide a note into \"pitch\" and \"timbre\". \"pitch\" is often simplified as being the frequency, but in reality it isn't necessarily all that related, there are a lot of things that can produce a pitch.",
"But the more fundamental problem is that, even we accept the frequency-based definition of pitch, what is a \"pure\" pitch? Is it is a pure tone, or an infinite harmonic complex with equal amplitudes across frequencies, or an infinite harmonic complex with equal energy across frequencies, or an infinite harmonic complex with equal loudness across frequencies? I can think of arguments in favor of all of these, and picking one as being \"pure\" is pretty arbitrary.",
"In the end, each way of producing a given pitch is going to result in a different timbre. You can define one timbre as being the \"pure\" one, but that will be your own definition."
] |
[
"The most important thing to understand is that almost every sound you hear is made up of many, many different frequencies. ",
"What makes a middle C a middle C is its \"fundamental frequency\", which for middle C is just over 261 Hz. Playing that note on a piano, or a guitar, or any other instrument will produce an oscillation at 261.625-etc. Hz. ",
"BUT!",
"Every instrument you play that note on will produce a ton of other oscillations too, many of them being harmonics (e.g. 2x that frequency, 4x that frequency, and so on) or different frequencies produced by other aspects of the instrument, or sounds produced by some part of the process by which the instrument produces the note (e.g. The sound of a guitar string hitting a fret). This mix of \"extra\" frequencies produces the sound you hear. Your brain can identify the fundamental frequency, and can tell that a middle C is the same basic note on a guitar or piano.",
"In our evolutionary past, pure tones would have been extremely uncommon. Virtually all sounds that aren't synthesized electronically are VERY complex mixes of different frequencies. Because sound identification is very important (was that a lion I just heard, or distant thunder?), we have evolved considerable ability to differentiate sounds on the basis of the mix of different frequencies in them, and that's why we can so easily tell instruments apart even when they play the same notes."
] |
[
"Playing that note on a piano, or a guitar, or any other instrument will produce an oscillation at 261.625-etc. Hz. ",
"That is not necessarily true. You can have \"middle C\" without any sound anywhere near 261 Hz. There are a number of ways to get sounds of a particular pitch without having any sound energy being at the fundamental frequency of that pitch."
] |
[
"What happens to circulation after a limb has been amputated?"
] |
[
false
] |
I know normally it would go in a circuit down to the end of the extremities and then back up to the heart and lungs to be for gas exchange, but what happens to circulation once that pathway is no longer there?
|
[
"This is generally correct (I say 'generally' because of the use of \"series\" which I will discuss later), but I think this might be above OP's level of understanding so I will elaborate. Blood typically flows through capillaries to get from arteries to veins, not directly from what you might think of as a normal artery to a normal vein. Capillaries are very very tiny (about one red blood cell in diameter) and numerous blood vessels that go through most of your body's tissues. This means that there are millions of passageways between arteries and veins forming a circuit. When Teedy was talking about blood flow branching, I think he meant to say many parallel circuits (There are circuits in series too! Your cardiovascular system is likely far more complex than any circuit board [I don't know too much about circuit boards]). The net effect of this is that there is blood flow along the lines of ",
"this diagram",
" to continue the circuit analogy. ",
"Let's pretend that leg is this very simple circuit, with the battery being the heart, R1 being capillaries in the upper thigh, R2 being capillaries in the lower thigh, and R3 the foot. If we perform a transfemoral amputation (above the knee) we will remove R2 and R3, but blood can still flow from artery to vein through R1 (the capillaries of the thigh). Closing the large vessels at the stump would be analogous to putting caps on the two horizontal wires that were cut. Because we have reduced the total cross-sectional area of the capillaries of the leg by amputating, we have increased the resistance of flow through the leg. Consequently, the flow to the leg will decrease.",
"I just read this ",
" *, I'm really tired, but I hope this helps, and if not, sorry about the minute."
] |
[
"You need to keep in mind that the body is a series circuit. This means that at every point blood flow is branching off to serve tissue. The arteries that feed the foot also feed the leg and so on. Basically, they anastamose or close large vessels at the stump, before sealing it. "
] |
[
"I totally meant parallel and screwed up my analogy.",
"I spent like, 10 seconds trying to remember which was which and didn't bother to google to confirm, so thank you sir!"
] |
[
"What's up with pubic hair?"
] |
[
false
] | null |
[
"Disclaimer: I summarize some research I've read below, but this is not my area of study.",
"As far as I know, it would be fair to say that the answer to this question isn't fully understood. The general outlines: it seems not to be the case that pubic hair was specifically evolved, but rather that it was selectively ",
" during the general shift towards hairlessness that was seen in the ape->human transition. Our predecessors seem to have had pervasive fur/hair, but we don't; instead, most of it was lost, but some was retained. Explaining why some of it was selectively retained would be easier if we understood the reasons for the overall transition to less hair, but those are not really solid.",
"One hypothesis is that humans evolved less hair/fur to avoid parasites that hair/fur hosts. In this theory, since humans were able to regulate their temperature with shelter, fire, and clothing, it became less necessary to have hair/fur, and beneficial to lose it in order to reduce parasite load. ",
"Here is a short paper (pdf)",
" arguing that position.",
"In that paper, they offer a fairly speculative hypothesis for why pubic hair would be retained, even though by the parasite hypothesis it should've been one of the first regions of hair to be selected against. The very general hypothesis is that it relates to sexual selection:",
"The retention of pubic hair poses a challenge for the ectoparasite hypothesis, as it provides a warm and humid environment favourable to ectoparasites — and indeed many specialize on these regions. An interesting possibility is that pubic areas may, owing to their warmth and humidity, be especially conducive to pheromonal signalling between the sexes. In support of this idea, the density of sweat glands in pubic regions is high (Stoddart 1990).",
"So what they're proposing here boils down to: hair/fur was selected against to reduce parasite load, but pubic hair was retained against that selective pressure, because it supports an important pheromonal signaling role in mating.",
"I think it's fair to say that this is a ",
" speculative hypothesis, though, not exactly a solid explanation. The authors themselves indicate that it is mostly interesting as a proposal for future research, rather than a conclusion."
] |
[
"While it may seem that humans have more hair around the pubis than other parts of the body, this is actually not true. We have approximately the same density of hair follicles over most of the surface of our skin except for the bottoms of our feet, palms, and the skin closely surrounding these two areas. I'm sure you've noticed the small, fuzzy hair that you can find on all other parts of your body like your forehead, the underside of your forearm, the sides of your torso; pretty much everywhere. Even though it is small and possibly looks colorless, this is still hair made out of the same stuff as your dark body hair! Humans actually have about 5 million hair follicles, with the same density of hair as our closest relative the chimpanzee, and about the same density as the other great apes.",
"What IS true about the hair around the pubis (and head hair, armpit hair, chest hair, leg hair, beard hair, etc.) is that it is ",
" hair. This means the hair has an extended and more vigorous growth period (hair turns on and off for growth, which is why your head hair doesn't grow to 100 meters long) compared to the tiny hairs. These mature hairs also likely produce a LOT more melanin (a brown pigment and the only pigment mammals make) that gives it a color range from blonde to nearly black, depending on how much melanin has been produced. So, since mature hair is thicker, longer, and darker you see it much more easily.",
"Hair usually matures at the onset of puberty, but can also mature at other times in life due to hormone responses, mutations, or other random activation causes (see ",
"Hypertrichosis",
", the possible explanation for werewolves). Even the hair on top of your head may not have been mature at birth, and only darkened after you were a few months old; it varies from person to person! It's easy to see how puberty causes maturation of hair in men, since facial hair darkens and forms a beard. Keep in mind, this facial hair didn't just poof into existence, it was already there as tiny little immature hairs (lots of people call it \"peach fuzz\").",
"The interesting question is WHY do we only have mature hair on certain parts of our bodies? There are dozens and dozens of hypotheses that address this question. I will list just a few:",
"Mature hair on the tops of our heads may be continually present just to protect us from sun exposure and prevent sunburns on our most exposed area. This hypothesis works for the head, but doesn't explain the rest of the body.",
"We used to have mature hair covering our bodies but lost maturity in most of it in order to cool our bodies more efficiently.",
"We used to have mature hair covering our bodies but lost maturity in most of it to cut down on the number of parasites that could cling to our fur.",
"We develop mature hair in order to hold onto our scents in areas of our body important to mating and pheromone production. (This may make sense if you look at the locations of ",
"Apocrine",
" sweat glands).",
"Remember, these are all hypotheses with varying degrees of evidence to support them. Other posts in this thread offer other hypotheses, but again these have varying degrees of evidence to support, so please take anyone's comments that sound matter-of-fact with a grain of salt.",
"Edit: I am an evolutionary biologist, although humans are not my area of study. Finding some old papers to link as sources where needed.",
"A couple sources: ",
"Schwartz & Rosenblum 1981",
", ",
"Shultz 1931"
] |
[
"What would happen to a person that comments the correct answer but lacks the expertise and source?",
"For example, I know of a suitable response for OP's question. However, I'm only regurgitating what I've learned from my experience as a biology student."
] |
[
"AskScience AMA Series: Colorado State University Unveils The First Human Clinical Study Measuring and Comparing the Absorption Rate of CBD Delivered Through Food & Supplement Product Formats, Ask Us Anything!"
] |
[
false
] | null |
[
"With no approved use for CBD outside of one medication used to treat intractable epilepsy, how is this kind of study beneficial - outside of marketing information for Caliper?",
"Is that the whole point? You can market your product based on absorption rate because you can't legally market it to treat any diseases or conditions?"
] |
[
"There certainly is a dearth of studies and a lot of claims being made about CBD. This is obviously a rapidly growing industry with a lot of interest. What options do you see to broadly establish trust and quality control? I appreciate that a study was conducted here, but I think people also are generally wary of industry-funded studies."
] |
[
"You list the ingredients for each of the Caliper offerings — does that matter to the final results? Can you isolate ingredients that are offering better absorption?"
] |
[
"Telomerase and cancer"
] |
[
false
] |
Why is telomerase necessary for cancer cells to divide?
|
[
"This is a bit of a complicated issue.",
"Technically, telomerase is not necessary for cancer cells to divide, any more than it is necessary for any of your other cells to divide. However, it is good for cells that need to divide a lot, so they can continue dividing.",
"When you replicate your DNA, the enzymes need to start somewhere on the strand; they can't just start at the very end. Because of this, you lose a tiny bit of DNA after each replication. This small amount of DNA is ideally part of the telomere. The telomere is basically unused DNA who's sole purpose is to get slowly lost. Think of it like cannon-fodder for DNA replication.",
"Once your telomeres run out, cells typically stop dividing through a host of complicated processes. However, if you have active telomerase, you can lengthen your telomeres, preventing the cell from stopping division.",
"Lots of cancer cells gain active telomerase. However, there are cells in your body that normally have it - stem cells.",
"Finally, you don't need telomerase to lengthen telomeres. There are other processes, particularly homologous recombination, by which telomeres can be lengthened. This is more complicated than the mechanism employed by telomerase."
] |
[
"I suspect that telemorase isn't absolutely required as fidelity on the chromsomal ends may not be short term issue for a tumour"
] |
[
"Active telomerase is ",
" a hallmark of cancer. There are many arrested and neutralized cancers that occur rather frequently in many organisms. Cancer is often a handful of mutations that occur and when those certain mutations occur together you get a virulent immortalized cell line."
] |
[
"What is the difference between sun burns and radiation burns from radioactive material?"
] |
[
false
] |
Both the sun and radioactive material are producing radiation. I'm curious: If I was near nuclear material, would I begin to exhibit the symptoms of a sunburn before the more serious issues occur? Likewise, if the solar radiation were magnified, could I suffer the same symptoms that one would experience when exposed to nuclear material?
|
[
"Yes, both are caused by DNA damage. The difference is that UV light that causes sunburn can't quite ionize and break DNA, but it can form ",
"thymine dimers",
" which prevent replication. UV light can't penetrate very far in the skin, so magnifying it won't get you anything but more sunburn. Ionizing radiation is generally lethal due to damage to the bone marrow or intestinal lining.",
"Ionizing radiation forms free radicals which react with DNA and break the bonds. Skin reddening is one of the first symptoms of acute radiation exposure. It takes quite a bit of radiation exposure for this to occur, though."
] |
[
"The danger from being very close to a nuclear reactor is actually from neutron radiation, which is difficult to shield against. It tends to thermalize in the presence of any thick chunk of water (i.e., your thighs), which increases its cross-section and causes it to react far more readily with other atoms. It's the same effect as the moderating material in a nuclear reactor has."
] |
[
"UV can trigger the growth of skin cancer. Gammas, neutrons, etc., go all the way through, and can start deep cancers. I don't think you can get bone/brain/liver cancer from UV. Maybe leukemias? Does UV make it into the capillary bed?",
"Odd trivia: some alpha-window geiger counters will respond to solar UV. They click madly, proving that sunlight is radioactive! :) If used outdoors, the thin window needs an opaque coating."
] |
[
"How can two different molecules exist in different states at the same temperature?"
] |
[
false
] |
If temperature is defined as the average kinetic energy of a system, how can one type of molecule exist as a solid and another as a gas at the same temperature, yet the latter is moving exponentially faster? Edit: How can two different molecules be considered the same temp. when one species is moving faster than the other? Edit 2: I don't think I worded this properly, so here is a longer explanation. So, like I said, temperature is defined as the average kinetic energy of a system. With that being said, how can one species of molecule that exists as a solid at temperature "X" be considered the same temperature as something that is a gas at temperature "X" when the species that is a gas is moving much much faster? I understand that different species exist in different states due to intermolecular forces (hydrogen bondering, van der vaals, etc.), but what I don't understand is how are they considered the same temperature? Is solid H2O vibrating just as fast as liquid ethanol is moving at 0°C?
|
[
"If temperature is defined as the average kinetic energy of a system",
"Because it's not, but it happens to be related to it for an ideal gas. (where the only form of energy/degree of freedom is kinetic motion) But real substances can store energy in intermolecular bonds (forming crystals and liquids), as vibrational and rotational energy of the atoms/molecules.",
"Water is a liquid at room temperature while O2 is a gas, because water has more of its energy stored in the intermolecular bonds of the liquid. O2 molecules don't stick together as much, and can't store that much energy there before they fly apart and become a gas.",
"The amount of energy is the same, but it's distributed differently among the things the molecules can do, because they're different molecules."
] |
[
"Temperature is ",
" defined as the average kinetic energy of the system. The definition is much more general, and is related to how much entropy a system will gain or lose when some energy is added or removed. Loosely speaking, for normal systems (forget exotic situations that can have negative/infinite temperature), if adding a unit energy increases your entropy a lot, then you have a low temperature. If adding a unit of energy increases your entropy by only a small amount, you are at a high temperature. (Formally, T=1/(dS/dU) where T=temp, S=entropy, U=energy, and d=partial differentiation operation).",
"Now, starting with very basic physical arguments, if you don't take into account quantum mechanics, it can be shown that a system's internal energy (not just its kinetic energy) is indeed proportional to temperature. This treatment, however, generally neglects the fact that the different particles that make up the system interact. It turns out that at high temperatures/low densities, this approximation is pretty good, and the resultant expressions accurately reflect measurements. However, these arguments normally break down at a \"critical temperature\", where the random fluctuations in density will occasionally yield local densities that would require the inclusion of particle interactions in the underlying theory. Phase change phenomena like condensation and melting arise from this effect.",
"Now, to answer your question. If I understand your question correctly, you are asking how one substance could be a gas at some temperature, whereas another substance is a liquid at that same temperature. As you mention, the differing intermolecular forces that are at play will dictate how important particle-particle interactions are, and thus determine the melting/condensation points. It's true that the gas molecules are moving faster and thus have a higher average kinetic energy, but the energy stored in the particle interactions is relatively low. In a liquid, on the other hand, a significant amount of energy is stored in the potentials of the interactions between molecules.",
"(Note: everything above is based on classical, i.e non-quantum arguments. The basic idea should survive the transition to a quantum treatment, however)."
] |
[
"When you talk about a phase change you need to consider the fact that these particles are interacting. In a non-interacting theory (i.e. ideal gas), the temperature is directly connected to the average kinetic energy of the gas molecules.",
"Now let's turn on an attractive interaction; temperature is no longer directly connected to average kinetic energy. At a low enough temperature, the system will condense and turn into the liquid phase. Usually one can create a toy model with an attraction (like van der waals) that can describe phase transitions. Now since every element has different properties due to the electronic structure (orbitals, number of protons etc.), the attraction between these atoms will be different. This discrepancy accounts for the different phase transition temperatures between different materials."
] |
[
"How far can germs crawl?"
] |
[
false
] |
If I pick up a piece of poop, and then use that hand to stir a pot with a metal spoon, will the poop germs get from the end of the spoon into the pot? Germs are really tiny so that's a long way to travel, and they can't build a chain of colonies on a metal spoon, right?
|
[
"Motility in bacteria is basically reserved to aqueous environments. They can use flagella to swim around in (as I'm sure is clear) very very very small amounts or layers of liquid. Helical bacteria have special structures that let them spin to move. Some bacteria make tiny amounts of gel that let them glide around when not in water. A large number of bacteria can't actually move on their own. What they rely on to \"move\" is replication. When bacteria divide they spread out in all 3 dimensions (but only so far up), so they move by basically making a big blob that spreads. It's why colonies form on agar plates when working with non-motile bacteria. (There's a special ",
"motility test",
" involving a stab down into a tube filled with agar, you see if the bacteria grow out from the stab or stay in the stab)",
"To your question. Bacteria in poop (notably E.coli) are highly motile. If there's poop or liquid or slime or something like that they can swim down the spoon. As to colonies on a metal spoon? Depends on what kind of metal the spoon is made out of. A lot of metals kill bacteria, which is why some faucets are basically always \"clean.\" ",
"Bacteria can travel pretty far if they're motile and in the right environment for it, and it's something you don't really think about a lot. ",
"Here's a plate of Proteus",
", which always makes this distinctive ripple pattern because of their motility. Even if they don't form this much of a lawn of growth you can still see ripples made in the agar of the plates after 1 day. Pretty neat stuff."
] |
[
"Copper is really really really really good at killing bacteria. Copper door handles and faucets are great. Silver too.",
"Basically all of the metals that are toxic to us are toxic to them, but unlike bacteria, we won't die from touching a copper doorknob."
] |
[
"TIL some metals kill bacteria.",
"Related to OP's question: Wash your fucking hands before touching a spoon."
] |
[
"Is it less carcinogenic to vaporize tobacco? What about marijuana?"
] |
[
false
] | null |
[
"Electronic cigarette expert here. If you're going to vaporize nicotine, you might as well not even bother with the leaf.",
"Nearly all of the carcinogens found in cigarettes are absent in electronic cigarettes. Ecig juice is comprised of propelyn glycol, vegetable glycerine, flavorant, and pharmaceutical grade organic nicotine derived from plants.",
"Nicotine in itself is surprisingly not very harmful at all. It is habit forming, but not as intensely as you'd think. It is the additives in tobacco leaf cigarettes that are carcinogenic, as well as the burning of organic material and intake of tar that creates additional carcinogenic effect. The additives are what get you hooked hard. The additives are designed to augment the addictive properties of the nicotine in a way that intensifies your need and cravings. The use of nicotine by itself is said to be on par with caffiene. It's a nervous system upper, but it's not dreadfully bad for you. Many e-cig users find that their cravings are much more tolerable and less often than traditional smokers for a few reasons.",
"Ecigs don't burn anything, they boil a liquid mix called juice or e-juice or e-liquid. When the liquid boils, it prodces a fine vapor, which acts as a vehicle for nicotine and flavor. It simulates the physical and checmical act of smoking, but has no tar, no ash, no carbon monoxide, and no carcinogenic additives. Unlike traditional cigs, where the tar is the vehicle for nicotine delivery, PG/VG vapor delivers its nicotine payload and pretty much immediately leaves your system. Cig tar lines your lungs and sticks in there, impeding lung function while delivering a stead ily dropping wave of nicotine. That's usually why cig cravings come on strong after a short while - you've lost that nicotine delivery and you need more NOW. When you vape juice, you get the nicotine now, and you're not getting any more once you're done vaping. What's in your system is carried out evenly and as a result, the cravings don't pound you. You just kind of taper into them. Many vapers even report being able to go many more hours without a vape than they used to with a cig. I can confirm this. Cravings are nothing anymore; I've even lowered my nicotine content in the juices I buy.",
"Propelyle glycol is the same substance used in fog machines, and has decades upon decades of reseach behind it proving absolutely no harm to humans as a vaporized mist, even under long periods of exposure. The worst it can do to you is dehydrate you as it is a dessicant. But that's about it. PG can actually help maintain a cleaner atmosphere as well, as some studies have shown. It is believe that the PG molecules actually attach and drop other contaminants, including pathogens, in the air. Studies have proven that the risk of communicable respiriroty infection are nearly eliminated in an environment that has some vaporized PG molecules in it (I can try to find the study if you are interested). ",
"Vegetable glycerine is similar in nature to PG, but there is not an awful lot of research on it yet. There was a recent WHO study done, asserting that ecig users that use pg and vg pose no health threats to themselves, as well as others near them. Both materials are, for all intents and purposes, benign at current levels of use.",
"Flavorants are an issue. Some cheap/bad ecig mfgs use some additives that pose serious health risks. Diacetyl is a known baddie - responsible for causing popcorn lung at factory-worker exposure levels, it's the buttery flavorant in popcorn. Eating it is fine, but vaporous exposure is pretty bad for your lungs. There are a few things to look out for, but most are pretty safe.",
"The nicotine is plant derived, so you're getting the same nicotine there as if you were actually smoking. No tar, no carbon monoxide, and comprised of materials that are, separately generally regarded as safe, ecigs are a much, much safer alternative than any other tobacco/nicotine replacement therapy. Sorry for the long winded response, but I wanted to cover every angle.",
"The same argument could be made for marijuana - vaporizing is just heating the payload to the point where the essential oils cook off into a vapor. Since you're not actually burning anything, yes, it is a safer alternative than inhaling smoke. "
] |
[
"There are way too many for me to list, but check the wikipedia page - it's pretty comprehensive. The only reason additives are there in the first place is to make tobacco more addictive by altering the way it and the additives interact with your brain chemistry. They don't put stuff like ammonia in cigs to make them taste better. Arguably, menthol is the only exception (flavor wise) here that I am aware of. I used to love a hardcore menthol smoke, and I still vape mostly mentholated juices.",
"http://en.wikipedia.org/wiki/List_of_additives_in_cigarettes"
] |
[
"What are the additives in cigarettes that makes a cigarette more addictive than nicotine alone?"
] |
[
"Salts can screen electric fields. Can they also screen magnetic fields such as in NMR?"
] |
[
false
] |
Recently I tried to perform a cpmg NMR experiment on a sample with a high salt concentration, about 2.2M. Unfortunately, the experiment didn't work. The technician said that the high salt effectively screened the magnetic field such that the pulse length necessary to pull the hydrogens out of alignment was longer than the decay timescale we were interested in. At first I took his explanation at face value because salts can screen electric fields but I've come to wonder if Maxwell's eqns also predict that salts can screen magnetic fields? Thanks.
|
[
"Conductive solutions (aka lossy samples) will be heated up by the RF pulses, meaning that instead of manipulating nuclear spin magnetic moments, you're using an NMR spectrometer as a really expensive water heater. Combined with the fact such samples make tuning the probe and calibrating pulse widths a nightmare, extremely salty samples need to be dealt with carefully.",
"Generally the simplest thing to try - if, say, you're working on a standard 5 mm high-resolution (liquids) probe - is to find an adapter so you can put in a smaller diameter sample (say, 2.5 mm) tube and see if that helps things. "
] |
[
"Interesting - we did have issues tuning the coil. I'm still wondering about the fundamental physics that causes these types of issues."
] |
[
"If the conductivity of the salt solution is high enough you could be having skin depth issues. What is the frequency content of your pulse?"
] |
[
"Is it possible to have loud enough bass to actually cook something, or even have an effect on temperature?"
] |
[
false
] |
This may seem like a REALLY dumb question, but here's my reasoning: Temperature is based off of molecule movement, and I'm wondering if bass can be turned up enough to get molecules to move really fast. I think it would be cool to cook a burger with a huge bass drop.
|
[
"I think it would be cool to cook a burger with a huge bass drop.",
"You need to put the energy into air and then have the burger absorb it. ",
"A loudspeaker has very low efficiency of putting power into the air. And a hamburger has low efficiency of absorbing sound. ",
"A good speaker will put 5% of the incoming energy into the air, and a hamburger is unlikely to absorb more than 1% of the energy that touches it and turn it into heat..",
"You can't focus all the energy form the speaker to the hamburger. Most will leak.",
"Let's say you have a good design and you can get 5% efficiency at the speaker, 10% from speaker to hamburger and 1% from hamburger surface to inside, then your overall effficiency is:",
"0.05 * 0.10 * 0.01 = 0.00005",
"Now suppose you have a nice amp that is putting 1kW RMS into your speaker. that means 1000W* 0.00005 is going into the hamburger. that's .05 watts.",
"A microwave is 1200 watts and puts maybe 25% of its energy into the burger => 300Watts.",
"The speaker system, even an extreme one as I have described, cannot raise the temperature of the burger by more than few degrees. "
] |
[
"Furthermore, bass frequencies are not absorbed well by burgers. I am honestly not that familiar with sound absorption spectra for most foods, but something a little higher frequency would probably work better."
] |
[
"I remember reading at a science museum that the energy released in in a year of continuous screaming is the same as the energy required to boil a cup of coffee. I'm without reference to this due to it not being an online article i can link to but i think it gives some idea as to how large the difference in energy is between heated food and sound."
] |
[
"If the universe is expanding, is the distance between my atoms increasing right now?"
] |
[
false
] |
The universe is expanding. (At an accelerating rate, so I hear.) Does that mean that the space between the atoms it my body (and on my table, and in the world) is currently increasing? (Also, how do I tag things as #physics?)
|
[
"Here",
" is a very similar recently asked question.",
"The answer is that the distance between your atoms ",
" be increasing if it weren't for the fact that the forces holding your atoms together, well, keep holding them together. It's like if you stretch out a spring -- the spring doesn't stay stretched out -- it springs back to its natural length.",
"Incidentally, even if the atoms weren't being held together, the expansion of space is so small on the distance scale of atoms that the atoms would separate at about 1/10",
" mm/s. In other words it would take well more than a trillion years for the atoms to separate by a millimeter. But again, long before that happens, the atoms \"fall back\" to their original separation due to the attractive force between them."
] |
[
"The force of dark energy, which is driving expansion, is very weak compared to the force of gravity. So objects like our galaxy, solar system, planet, you, me, etc, are not expanding because gravity is stronger and keeping those objects bound.",
"Expansion happens in deep space between distant large objects - where dark energy is stronger than gravity."
] |
[
"It would be clearer to say ",
"."
] |
[
"Do wild animals get dental cavities?"
] |
[
false
] |
Does not brushing lead to poorer dental hygiene in wild animals?
|
[
"Most wild animals certainly get cavities and other forms of periodonal disease, especially with age. That said, compared with people, rates are very low (below 10% in most cases). I guess its not surprising that the frequency of cavities changes with dietary mineral content and with increased sugar consumption - for example, in ",
"black bears",
", there is a higher incidence of cavities with changes in dietary selenium, and access to honey/berries.",
"As another example, ",
"Raccoons",
" get cavities less frequently than bears, but are 5x more likely to develop cavities if they live near people eating our garbage than if they live in the wild and forage.",
"Horses",
" have a lot of problems with cavities and gum disease. Equine dentistry is becoming quite the big thing. Here though, its more because of food being trapped between the teeth than diet - and also because horses have a complicated tooth pulp structure.",
"In the end...yes. Lack of brushing, and sugary/incomplete diets can cause cavities in wild animals. Not flossing too."
] |
[
"Oh. So dental problems are more related to sugar consumption than not cleaning teeth?"
] |
[
"Sugars don't act as acids. It's the lactic acid, the product of fermentation of carbonhydrates by bacteria(mostly streptococcus mutans, streptococcus sobrinus and lactobacilli)"
] |
[
"What was the name?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):"
] |
[
"Wait, the first question has been posted? It doesn't show up in my Posts... I have saved this one, but now I have no choice to access the other..."
] |
[
"As the submission page states, all submissions are placed in the spam filter for moderator review, so please be patient."
] |
[
"How is it we can use fusion in bombs but not for energy production?"
] |
[
false
] |
I have a pretty limited knowledge base on this subject so I'm asking anyone who'd care to answer. What's the disconnect between the fusion taking place in a and fusion being used as an energy source? I can speculate about several reasons: safety, lack of control, etc. but all would seem to apply to fission as well and we've managed to figure that one at. If I'm missing something big here feel free to call me out on it. Thanks in advance for your replies.
|
[
"I work on magnetic confinement fusion, so I can probably answer any question you have on this to any specified detail.",
"The general problem is that for a bomb you want to create a lot of energy very quickly. For a reactor, you want to generate a reasonable amount of energy very slowly and steadily. The way a fusion bomb works is that you heat up the core very quickly (with a fission bomb) and that heats up your fusing nuclei much faster than they can get out of the way. Note that the only way you can get things hot fast enough in a fusion bomb is with a fission bomb!",
"However, these difficulties are stopping people from trying to do this. The ",
"NIF",
" project is all about trying to make what is essentially small fusion bombs by using lasers instead of a fission bomb. 182 high energy lasers are focused on a tiny bead of deuterium-tritium mixture and heat it up incredibly quickly. They have successfully used this to create fusion in small amounts in NIF and other experiments, but they're still quite a ways to going to net energy gain.",
"The current main problems with ICF (inertial confinement fusion - or laser target fusion) seem currently to be the loading problem - getting the beads aligned to a fraction of a micron in less than a second; the cooling problem - getting the lasers to a pulse rate fast enough; and the energy generation problem - taking the output and converting it to electricity in an efficient manner; and the neutron damage problem - keeping focusing optics/lenses/mirrors from experience gross defects due to large neutron flux. Meanwhile ICF can be used to test out the effect of hydrogen bombs and some astrophysics. People working on ICF seem to think that the loading problem is actually the most difficult one.",
"Magnetic Confinement Fusion is an entirely different approach. Instead of heating things fast enough, the goal is to confine the hot nuclei with magnetic fields so that they stay around long enough to have a chance to fuse. This has its own different difficulties."
] |
[
"Fusion requires a tremendous amount of energy to start the process. You must push the positive nuclei together, and that requires a lot of energy to do so. Fission is an atom almost ready to break in two, and just needs one last neutron to do so. Much easier to initiate.",
"In addition, one can make a big block of fissile material. Fusile material tends to be a plasma. One must either circulate the plasma in a confinement vessel or create the plasma in such a way that it's rather confined to one small volume (rather than expanding outwards and slowing/stopping the fusion reaction). These are also very difficult challenges. Magnetic confinement of a plasma has a lot of turbulence problems that are not easily overcome. So-called \"inertial confinement,\" where we confine the plasma to a small volume as we create it is also fairly challenging (these are the big laser firing attempts)."
] |
[
"Fantastic answer.",
"Are you and your colleagues optimistic that the problems you listed are actually solvable? Or is there a fear in the field that both ICF and MCF are never going to work?"
] |
[
"Why are certain cancers more common than others?"
] |
[
false
] |
Lung Cancer, Breast Cancer, and Prostate Cancer rank among the most common cancers. Why are cancerous growths more common in these locations than in a place like your arm or brain?
|
[
"Oh this is a very interesting question. In short, there are more factors than I care to type out now. But to give you an idea I'll focus on two examples:",
"Every cell in your body accumulates mutations randomly across the genome during each cell division. One of the key driving events of cancer is some specific mutation (usually on a tumor suppressor or growth promoting gene). The mutation rate is constant so the fact that this specific mutation landed on this cancer causing position is random. ",
"So what does that mean for cancer frequency? ",
"Some cells in your body are terminally differentiated, so they don't divide often or at all (for example neurons). Other cells in your body are stem/progenitor cells, which continuously divide to produce new cells. The more a celltype divides, the more opportunities for a mutation to occur on a cancer driver gene. Blood cells divide a TON. this is the reason that leukemias and lympomas are so common. There are also lifelong stem cells in mammary tissue (breast cancer, most common for women) and intestinal tissue (colorectal cancer, 3rd most common).",
"Next, certain environmental factors can increase the mutation rate. UV exposure on the skin (melanoma, 6th most common). Toxins and sugars in your digestive tract (colorectal cancer, 3rd most common). Certain Viral infections and toxins in your urinary tract (bladder cancer 4th most common in men). And cigarette smoke and other mutagens in your airways (lung cancer 2nd most common, oral cancer 8th most common). ",
"The two most common cancers-prostate and breast cancer- are semi-environmental. We actually don't have a clear picture for why they are so common (to my knowledge). But we do know that both of these organs are very fat rich, and obesity is a risk factor for both. These are also organs that are highly sensitive to sex hormones. Androgens promote the growth and health of prostate cells, and estrogens promote the growth of mammary cells. Fat cells can produce estrogen, which will promote the growth of mammary cells. I believe there is some connection between androgens and fat in the prostate but I can't remember off hand. ",
"",
"tl;dr it all comes down to how often a tissue's cell divides, how exposed it is to environmental mutagens and carcinogens, and whether the local tissue environment supports tumor growth."
] |
[
"Lung cancer is statistically proven to be largely promoted by pollution and exposure to cigarette smoke. This explains the common nature of this particular tissue.",
"However, I’d avoid looking for a pattern, trying to create one, right? Cancer is a complex disease and there’s no reason each tissue should be equally as likely to develop cancer. That would be weird, not that there are differences."
] |
[
"Explaining it tissue by tissue is very hard and I don't know enough about these specific cancers to do it.",
"\nIn general, though, cancer is more likely to happen where there is a source of chronic inflammation or where the tissue is exposed to cancer-promoting elements (as mentioned in another comment, pollution, cigarettes, some compounds, etc.). ",
"Inflammation (and damage in general) forces cells to proliferate to repair the tissue. Now, this can mean thousands and thousands of cell divisions from the same small group of tissue staminal cells, which of course have a small chance to gather mutations per every division cycle. Pile them up for 40/50 years, and there you have a huge bunch of mutations in each of those cells. Some of them will repair the damage, some others will be removed by the immune system, but eventually, some others will develop in a tumoral mass. ",
"While what I just wrote stands especially for lung cancer, I do not know what's the exact reason why breast and prostate cancer are so common, I should definitely read something about them..."
] |
[
"When I make tea and stir in some sugar, I notice the sound of the spoon tinking against the side of the mug changes pitch. Why?"
] |
[
false
] |
Always wondered why this is happening.
|
[
"The addition of sugar changes the density of the medium (water) which changes the propagation velocity of the acoustic wave through it. A change in propagation velocity is manifested as a change in pitch, all else being equal. You can read this link: ",
"http://music.ece.drexel.edu/files/Navigation/K-12_education_initiatives/NSF_GK-12_Program/Activities/Density%20and%20Pitch%20Activity.pdf",
" for a very easy to understand explanation that is a bit more in depth."
] |
[
"this actually has a name"
] |
[
"This is an incomplete explanation. If you try it yourself, you'll notice that the pitch is strongly affected by stirring. I've done this experiment many times with hot chocolate, and the pitch while the liquid is rotating is typically around an octave lower than when it's stationary. The effect is easily reversible and repeatable."
] |
[
"How do we program highly complex cosmological simulation software?"
] |
[
false
] |
I was watching How The Universe Works on Netflix and they frequently show simulation models of galaxies colliding, dark matters influence on the shaping of of our universe, and many other highly complex simulations. I was wondering how do people design these programs to simulate this? These problems seem ridiculously complex. Does an astrophysicist sit in a room with a bunch of programmers telling them the math or do a bunch of astrophysicists get CS degrees and program it themselves. It seems like such a daunting task I was wondering if someone could shed light on this. Also, I apologize if this has been asked before, I tried the search function and could not find a question similar to this.
|
[
"Realize that ray-tracing, liquid simulation and a lot of things commonly done by computers is easily equally complex...",
"No idea how that specific program was done, but as a programmer, I've certainly had jobs where I basically had to bunker down for weeks with some complex textbook and convert all the formulas into programming instructions.",
"Once you have the equations written down, I wouldn't expect them to be too difficult to turn into code."
] |
[
"Sure, and most of that is structuring the code such that the formula's are nicely separated from the main code, so that the mathematician (or whoever) can review them without understanding much of the language or rest of the code.",
"You just send them a snippet and they can work out where the mistakes are or verify it is correct. If there is a missing term or missing absolute value or something, they just mark fixes and leave it to coders to implement.",
"I will say, the coders on these projects are not your run of the mill web developers... each would be a strong mathematician / physicist in their own right if they would have spent time on that instead of coding... they are all really smart capable people. "
] |
[
"A lot of scientists learn how to program out of necessity.",
"Whether or not collaboration happens with programmers usually depends on the complexity of the program relative to the scientist's programming skill and study scope/funding."
] |
[
"Why are we so sure that dark matter exist, rather than gravitational models being incomplete/incorrect?"
] |
[
false
] | null |
[
"See the astronomy FAQ."
] |
[
"No, the conclusion has not changed."
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"Your question is either commonly occurring or has been recently posted on ",
"/r/AskScience",
". It may also be answerable using a Google or Wikipedia search.",
"To check for previous similar posts, please use the subreddit search on the right, or Google site:reddit.com",
"/r/askscience",
" ",
"Also consider looking at ",
"our FAQ",
".",
"For more information regarding this and similar issues, please see our ",
"guidelines",
".",
"A good home for this question is our sister subreddit ",
"/r/AskScienceDiscussion",
". It might be too open-ended or speculative for ",
"/r/askscience",
". ",
"/r/AskScienceDiscussion",
" is also a better place for advice on education, book suggestions or general questions about working in STEM. Please feel free to repost there!",
"Please see our ",
"guidelines",
"."
] |
[
"About how far up would an average helium party balloon float if let go right after being filled?"
] |
[
false
] | null |
[
"Something I know! I'm not a scientist... or at least I'm a scientist on one specific topic: Balloons. But most people call me a balloon clown because I make animals and toys for kids while dressed up in a funny costume. ",
"Anyway, I usually deal with helium and often liek to send balloons into the sky with little notes into the sky hoping that a child finds them and let their imagination run wild. Sometimes when I release them I follow them with my telescope and so far I know they can reach a bit over 10 km. Other times I count how many seconds they rise from the ground to the top of a building whose height I know and then keep counting to see how much farther it goes... again I get about 10 km. So both my tests give the same result. But also keep in mind that the helium slows down a bit when it's in the sky because of wind and because the helium in the balloon begins to match the outside pressure...and that's when it gets bigger (cuz the air up there eventually gets as thin as helium is) and so there is no pressure to keep the balloon's rubber from expanding so it grows and explodes. Oh but I also have seen weather balloons go higher because they have stronger material than rubber... I would love to send my notes in one of those but they're pretty expensive!",
"Hope that helps and keep ballooning!"
] |
[
"It's just my take on the \"message in a bottle\" but with falling balloons for kids! I like to sparkle up the balloon and the note so that it catches people's eyes. And they are are on all type of topics just as long as they get the imagination going! I can give you some examples of the notes I have for my next launch:",
"\"I AM BABY ALIEN: XZIOIA9. I SEND BALLOON FROM MARS TO SHARE. PLEASE SEND NEW ONE BACK\"",
"\"Ever wonder what happens when you mix baking soda with vinegar? Ask your mom she knows the secret!\"",
"\"Hello! Looks like you got my message! I'm your imaginary friend! Please return my balloon to me when you can by closing your eyes and sending the coolest balloon you can imagine!\"",
"\"Remember that time you pretended your hand was a shooting gun? Well it was! You shot this balloon down!\"",
"\"My name is Jin Bao from China. My fortune cookie said that if I put this balloon in the air it will reach a special person. Please remember this.\"",
"\"Q. How do you know carrots are good for your eyes?\nA. Because you never see rabbits wearing glasses!\nNow eat more carrots!\"",
"\"Have you ever wondered how plants eat the sun when they don't have mouths to eat? Ask your dad to help you answer!\"",
"\"Q. Why did the sheep say \"moo\"?\nA. It was learning a new language!\nHow many words do you know in other languages?\"",
"\"SANTA CLAUSE'S BIRTHDAY TODAY\n MY PARTY IS ON TOP OF THE CLOUD BUT IF YOU WAVE TO ME YOU CAN KEEP MY BALLOON!\"",
"....yeah, kid's stuff. :)"
] |
[
"often liek to send balloons into the sky with little notes into the sky hoping that a child finds them and let their imagination run wild.",
"This is the most adorable thing I've heard all day. Has a child ever found one of your notes, to your knowledge? What kind of things do you put in them?"
] |
[
"Do other animals understand and comprehend photos/videos?"
] |
[
false
] | null |
[
"Some of them certainly do, but it's hard to say exactly how many just based on a lack of existing research. It's been clearly demonstrated that Rhesus monkeys pay attention and respond to videos of other monkeys in similar ways to how they would react to seeing them in real life (",
"Mosher et al. 2011",
"). Other work has showed that monkeys value even still images of other members of their species, and were willing to give up food to gain access to pictures of the faces of monkeys with high social status, or of female genitals (",
"Deaner et al. 2005",
"). Unsurprisingly, apes also certainly have ability to watch videos, and doing so together can apparently act as a bonding experience too (",
"Wolf and Tomasello 2019",
"). Finally, there's pretty good evidence that dogs can at least understand images to some extent, since they are capable of reliably identifying other dogs out of a pool of multiple animals even just from headshots (",
"Autier-Dérian et al. 2013",
"). So while I suppose there is room for debate on how much animals may be able to comprehend the ",
" of a video, it is clear that some mammals at least (and I would guess probably some birds too) can identify the ",
" of still and moving images when it is of interest to them."
] |
[
"Interesting!",
"A few questions if that's okay:",
"In Deaner (2005), I can understand, at least intuitively, the reasoning for trading food for the pornography, but I'm not sure I understand why they would trade good for individuals of social status. Unless I'm misunderstanding, are these same-sex individuals that have their photos taken?",
"In Autier-Dérian (2013), does (can?) this comprehension extend beyond headshots of other dogs? Can dogs understand pictures of, say, their owners?",
"I apologize if this is a silly question, but how are you differentiating subject matter from content in this context? ",
"Perhaps my biggest question is: ",
" do these animals understand photographs/videos? Is it neurologically similar to how human beings do these kinds of things? I'm not particularly familiar with the neurology of some of these animals, but is it accurate to say that birds have a different \"cranial makeup\"? Would they process these things differently than mammals?",
"I know you didn't mention it, but are you familiar with any research regarding cats? I'll be candid in saying that the origin of this question came to me in whether or not pets could understand things like family photos; the immediate extension of that was whether or not they could understand photos of themselves. From what I have seen, the large majority of cats/dogs pass the mirror test, but I'm curious if they can come to the same conclusion when it's not \"live feedback\"."
] |
[
"I know a cat will see a recognizable image in a TV. We once had a feral cat that because of his being born in a field, was deathly afraid of black birds, like crows. Well one day we were watching a nature documentary and when they showed a big black bird opening its wings, the cat went ballistic and tore around the house trying to hide. This first incident was with an old style CRT/raster scan TV. After we got a big screen LCD type TV, it happened again when the image of a black bird came on screen."
] |
[
"Are Pandas worth the conservation effort?"
] |
[
false
] |
It appears that these creatures get an unfair amount of coverage, attention and money for preservation when they aren't designed to survive as is. They don't want to reproduce and have a narrow diet spectrum. Why should they be preserved at such a cost, when that money could be diverted to other ecosystems that have a better shot at survival?
|
[
"Pandas are perfectly well designed to survive, and want very much to reproduce, when they are in their original habitat (large swaths of broadleaf forests of SE Asia). It's only in captivity, and when the forests get really fragmented, that they have problems. ",
"The bigger picture though is that panda conservation ends up helping a lot of other species too. What conservation biologists have learned over the years is that it's not always possible to divert money from popular species to less popular ones, and instead we've learned to leverage the interest in the popular animals (\"charismatic megafauna\") to save a ton of other species. ",
"First, you can use the popular animal for fund-raising and funnel the money to lots of other things. There is a term for these species - \"flagship species\" - i.e. a species that can get a lot of attention and draw public attention/laws/money to conservation efforts in general. WWF is a great example. The money they raise with their panda logo goes to all kinds of other projects too.",
"Secondly, flagship species also often turn out to be \"umbrella species\", meaning, species that can save their whole ecosystem. Most of the popular animals are large mammals, and large mammals almost always have large home ranges, so, to save a functioning population of a large mammal you typically have to save an enormous chunk of land and make sure the entire food chain is still operating and the whole ecosystem is in good shape. With pandas: yes, they have a narrow diet (bamboo), but the bamboo exists in a highly diverse broad-leaf forest that used to stretch through a lot of SE Asia and that supports a great number of other species. That ecosystem is actually very important and definitely deserves protection. Because of international pressure to save pandas, China now has a lot of preserves of these kinds of forests. (whether the preserves are effective is a different issue)",
"3rd reason, you end up learning a lot with that species that is directly applicable to related species. ",
"tl;dr - Pandas rock."
] |
[
"I don't think your question is really one science can answer, so please excuse my casual, non-scientific answer. ",
"My friend who worked at the san diego zoo told me many people go there primarily to see the pandas. In other words, free-market: people like pandas, so they are willing to pay more money to preserve them (zoos pay china millions of dollars to keep pandas, which is spent on the preservation of the species). It's not \"unfair\", it's not like that money is going to kill other endangered species; if it hadn't been spent to see pandas, it maybe would have been spent to see some killer whales at seaworld, or to play some putt-putt golf. "
] |
[
"From the WWF site \"That is one of the main reasons why they are so important: by mobilizing people to save the panda, we are actually helping preserve the rich biodiversity - plants, landscapes, other animals - that need to be there in order for the pandas to survive.\"",
"So they also said that the panda is a nearly universal symbol of conservation, so saving the panda is also a symbolic.",
"But I would love to hear if they are special in any way.",
"EDIT: ",
"Here's the source."
] |
[
"Since the earth is in constant orbit around the sun, how come we do not feel any effect from the centripetal acceleration?"
] |
[
false
] | null |
[
"We don't feel the centrifugal force due to the motion of the Earth around the sun because it's very small.",
"We don't even feel the centrifugal force from the Earth rotating about its own axis, which is much larger."
] |
[
"Good point. I hadn't thought about that. I guess then for the second question it is highly unlikely it would change anything?"
] |
[
"Correct."
] |
[
"How far ahead in the future can we (accurately) predict the weather?"
] |
[
false
] |
I had a teacher once say that any forecast ahead of 10 days was mostly just BS. How far ahead can meteorologists predict with 60% accuracy?
|
[
"Weather systems tend to be chaotic (Complexity Theory). This means that there may be sensitive dependence on initial conditions. At other times it means the system will behave in a predictable fashion for a period of time and even fairly hefty nudges won't make much difference.",
"When modelling weather one approach is to run your model multiple times with slight changes to the initial conditions. Sometimes the results vary tremendously - the system is sensitive to the starting conditions and small changes change the result significantly. Forecasting even a short time into the future in these conditions stands a good chance of being wrong.",
"At other times, the model (and weather) are stable under small changes. Predictions can often be made a considerable distance into the future with high confidence.",
"Obviously a complex (chaotic) system can change phases - be stable for a while and then become less easily predictable or vice versa.",
"As such, there can be times where a forecast may not be 60% accurate one day ahead. And others where the forecast can be accurate for an extended period of time (potentially months).",
"Maths POV answer - I am not a meteorologist."
] |
[
"Your teacher was right. Although forecasting has really gained accuracy in the past 50-60 years and we're able to see way more than we could before (using models, the most common being the MSL model, used by most newscasts. NEXRAD is also a popular choice (GOES satellite imaging is used as well)), it's still not as accurate as we'd like.",
"In short, with the technology we have now, we can accurately gauge precipitation up to 3 days in advance. As for temperature, we're able to see about 5 days in advance, and be accurate. When you see a 7, 8, or 10 day forecast, you're getting a load of bologna. ",
"I am currently in grad school going towards meteorology work, if this verifies anything for you. Oh, and I would suggest the next time you see a 10 day forecast, take the next 3 days (including the day you're experiencing, so up to 2 FULL days in the future after today) and take them as 'yep, that's going to happen.' As for temperature, you may look at the next 5 days (again, including the day you're experiencing) and take those 5 high temperatures and 4 overnight lows as being spot-on."
] |
[
"If this is so (and it sounds right), can a meteorologist tell us why forecasts don't come with accuracy ratings attached to them? "
] |
[
"How do changes in an entangled system propagate?"
] |
[
false
] |
[deleted]
|
[
"You and I live a mile apart. A thunderstorm rolls through, and at precisely nine o'clock, it starts to rain. It rains for a while, maybe with the occasional peal of thunder, then stops.",
"Later, I happen to run into you around town. \"Some thunderstorm, hm?\" I say, making conversation.",
"You are amazed. \"How did you know it was raining it my house?\"",
"\"Because it was raining at my house,\" I reply.",
"\"But how could two storms be synchronized in such a way that it rains at exactly the same instant in two places? How could the start-raining state change propagate instantaneously like that?\"",
"\"It didn't,\" I reply. \"We were both getting rained on by the same storm.\"",
"That's non-locality."
] |
[
"Well, another analogy might help further the point. ",
"Imagine there is a box that contains two marbles, one solid red and the other solid blue. You and I are hanging around and the dude that has the marble box asks, \"Hey, want a marble?\" ",
"Sure, why not. ",
"So, without us seeing, he puts the the two marbles into their own envelopes and gives us each one. Then he says not to open it until we go home. ",
"We part ways and each go home. Say you live across town from me. ",
"When I get home, I open my envelope. It's red. So that means yours is blue. I know because that's the only possible thing it could be. If you hadn't checked yours yet, and I wanted you to know your marble was blue, I'd still have to call you up in the normal way. So no instant communication. ",
"If you already opened your envelope and saw the blue marble, then you know mine's red. Again, just because it had to be. There's still no communication."
] |
[
"No."
] |
[
"Why is there an nth root symbol when you can just write it as an exponent?"
] |
[
false
] | null |
[
"The nth root of a (positive) number, A, is the positive root of the equation x",
"-A=0. The exponent A",
" is the evaluation of the exponential function of base A at the value 1/n. They are two different things, but it just so happens that you can show they are the same. But, if you care about the equation x",
"-A=0, you might choose to used the nth-root notation, if you care about the exponential function, you might prefer the exponential notation."
] |
[
"Defining ",
" roots in generality is a mess. Even in the complex numbers, most numbers have ",
" different ",
" roots. It's pretty much only in the nonnegative real numbers where you can say that a number has a unique nonnegative real ",
" root.",
"For example, in the quaternions, -1 has ",
" square roots. Not only that, they're uncountably infinite, and form a two-dimensional space inside the four-dimensional quaternions."
] |
[
"Are they guaranteed to be the same in any algebra, or is this something that is specific to the real numbers only? Does nsqrt(A) = A",
" still hold if A is a matrix or a quaternion, for example?"
] |
[
"How many senses do we have, I have heard there is more than the five children get taught"
] |
[
false
] |
I know there is more because if I spin in a chair and try to stand up one of my senses is screwed up but it ain't one of the main five. EDIT: Dammit bad grammar in the title, pls don't be too cruel
|
[
"Humans have more than five senses. Although definitions vary, the actual number ranges from 9 to more than 20. In addition to sight, smell, taste, touch, and hearing, which were the senses identified by Aristotle, humans can sense balance and acceleration (equilibrioception), pain (nociception), body and limb position (proprioception or kinesthetic sense), and relative temperature (thermoception). Other senses sometimes identified are the sense of time, itching, pressure, hunger, thirst, fullness of the stomach, need to urinate, need to defecate, and blood carbon dioxide levels. - Wikipedia"
] |
[
"Feeling of suffocation."
] |
[
"Smell touches your nose, light touches your optic nerve, etc. Touch is too broad."
] |
[
"How do we 'hear' memories, songs and voices in our head? Do the ears intervene somehow or does our brain reproduce sounds 'internally'?"
] |
[
false
] | null |
[
"The brain reproduces sounds internally. Although there are signals sent from the brain to the inner ear, these are used during active listening, not during imagination. You can stimulate parts of the brain and produce sensations of sight and sound without neurons in the eye or ear becoming active."
] |
[
"Yep. All conscious experience is the result of brain activity -- your sensors, whichever ones, ultimately activate neurons in your brain which are what cause the experience. If you somehow can stimulate them while bypassing the sensor, you'll have the same experience/sensation. Hallucinations are an example of experiences purely driven by brain activity with no external stimulation."
] |
[
"So, you mean that it's just brain signals somehow making us hear sounds? That's interesting. Thank you! "
] |
[
"Do deaf people still feel pain when they're exposed to really loud sounds?"
] |
[
false
] | null |
[
"The discovery of how we get pain from loud sounds is surprisingly recent--like 2015. There's a separate set of nerves that run from the hearing organs in the inner ear that seem to just be for reacting to sounds loud enough to cause hearing damage. We don't really understand how it works.",
"There are many, many causes of hearing loss. Any of the causes that don't damage these fibers or stop whatever process makes them fire would presumably leave this response intact. Hypersensitivity to sounds is actually a symptom associated with some kinds of hearing loss!"
] |
[
"We...don't know. Sorry! Might have something to do with the neurons in the ear becoming too sensitive and \"turning up the volume,\" but there's not too much hard evidence AFAIK.",
"https://www.karger.com/Article/Abstract/430459"
] |
[
"Thanks for the answer! That's really interesting"
] |
[
"Do photons accelerate??"
] |
[
false
] |
Had a doubt... When you switch on a light source, do the photons emitted accelerate to the speed of light or do they go from zero to c instantly??
|
[
"The photon is always traveling at the speed of light. When a photon is emitted, it is already traveling at the speed of light. ",
"An interesting addition to your question is that photons can be deflected by gravity. Even though it won't change their speed, strong gravitational potentials can bend the path of light, in effect like an acceleration. It's an effect called ",
"gravitational lensing",
", and it looks ",
"cool as shit",
"."
] |
[
"The energy of the light wave remains constant as it transitions between media. What changes is the velocity and wavelength. As an example, when light enters glass it slows down which on its own might imply energy loss, ",
" the wavelength of the light also decreases (recall that for light shorter wavelength = more energetic) so the total energy is conserved. When the light exits the other side the speed and wavelength both increase."
] |
[
"Follow up question. When light travels through a medium, like glass, it slows down. I've even heard some guys were able to slow down the light pulse to a walking speed. When light exits the other side, does it somehow pick up it's energy to speed back up again? It doesn't seem like it does, so how/why does it speed back up?"
] |
[
"Questions about High and Low Explosives?"
] |
[
false
] |
First, I am not trying to make an explosive device, I am purely curious as to the chemistry and how they explode. I understand that gunpowder is a low explosive, so it would need to be pressurized to make an explosion, so thats why it is good as a propellent for bullets. But I have some questions...
|
[
"Do high explosives, such as tnt or picric acid have to be contained or pressurized for them to explode or do they explode if they are just on a plate since the pressure and the explosion is so fast?",
"High explosives have a \"minimum critical diameter\" below which a detonation wave will not propagate. Confinement can decrease this diameter, but if you have enough high explosive that doesn't really matter.",
"Could the military add a high explosive to a low explosive (gunpowder), and make the gun powder a high explosive?",
"Yes but the purpose of gunpowder (and its modern equivalents) is to propel a projectile by burning. Detonation would destroy the gun. (Small amounts of high explosive such as nitroglycerin are added to modern smokeless powders to increase their energy, but the amounts added are below that required to make it a high explosive.)",
"How come you need a certain amount of a high explosive to explode a low or another high explosive? (This is super confusing because I would think if you took a high explosive like tnt and tried to set off another high explosive like anfo ig, but videos show it not working.)",
"Some high explosives are very insensitive and require a lot of energy to detonate. A more sensitive high explosive can be used to provide this energy.",
"Lastly, if the military were making warheads or missiles, would they use a high explosive to start the explosion, would the missile have a high, super sensitive explosive to then explode a low explosive? Or would this not work?",
"Modern warheads don't use low explosives. You're probably thinking of a \"primary explosive\" (a sensitive high explosive) being used to set off a \"secondary explosive\" (a less sensitive one)."
] |
[
"TNT is hard to detonate. Generally, a blasting cap is used. Usta be mercury fulminate, but maybe it's now lead azide. Same materials used in cartridge primers. Those are called \"primary explosives\", and turn a flame instantly into a detonation. ",
"Militaries filled shells with molten TNT, melted in steam-jacketed kettles. Sometimes ammonium nitrate is added to the TNT, since TNT is oxygen-poor, and NH4NO3 is slightly oxygen-rich."
] |
[
"HEs are specifically designed to not be shock sensitive (detonable by shock force e.g. dropping, throwing, impact in general) and therefore generally cannot be used to detonate one another. Most often electric fuses are used."
] |
[
"What are we processing when we see color? Frequency, or Wavelength?"
] |
[
false
] |
Lets take for example, a beam of red light, passing from air, through a glass block 1m wide (irrelevant) and out into air again at 90 degrees. We can see the beam clearly through all of this. From my understanding, because the light slowed down in the glass, but frequency remains constant, the wavelength must have changed to compensate, but I asked my Physics teacher (im in Australian Year 12 "senior year") and he said that the colour we will see in the glass will be the exact same as the colour in the air, because to humans, colour is a frequency property, I understand it a little using a Doppler effect analogy, but then why do we use wavelength so much to describe colour? Thanks all!
|
[
"From my understanding, because the light slowed down in the glass, but frequency remains constant, the wavelength must have changed to compensate,",
"No, light always travels at c, but when it passes through a medium other than a vacuum the atoms in the medium absorb and re-emit the photons which takes time and makes it seem like light has slowed down.",
"Furthermore, you cannot change the wavelength without changing the frequency and they're related by the equation f=c/λ. It doesn't really make sense to ask which one our eyes process because they're inseparable."
] |
[
"Because when it exits the glass it changes again to the exact same color it was, since the change is from air to glass and back to air, once it goes back to air and sends the photons to your eyes they are the same wavelength they were originally. ",
"Edit: Because the medium of the eye is unchanged (barring serious energy/disease) all light we perceive will always be passing through that last. "
] |
[
"That's not quite right. Although you are correct that there is an absorption and reemission process going on, the situation is a bit more complex, because photons are wavefunctions that represent excitations of the electromagnetic field, not billiard balls.",
"If you take a small resonator and inject some broadband microwave radiation, you'll find that the energy bouncing around inside is at a certain frequency: the resonant frequency of the cavity. You can predict this too: the resonant frequencies will be ones with wavelengths that are half-integer multiples of the cavity size.",
"If you now fill that resonance cavity with teflon and repeat the experiment, you'll find the resonance frequency has changed. So yes, the wavelength does appear to have changed.",
"Even though microscopically the individual photons may be at the same frequency, the delay process creates a phase shift. And some of these photons are absorbed and reemitted too, which introduces further delay and phase shift.",
"It turns out that if you take all these photons with all these phase shifts, they create an interference pattern in the field. If you calculate the interference pattern, at the macroscopic level it looks like a big wave. This macroscopic wave is propagating at a slower velocity, and with the wavelength that is a half-integer multiple of the resonator size."
] |
[
"If the US paid of every penny of its debt and the government made more mean income than they spent how would this effect the US and the world?"
] |
[
false
] | null |
[
"Such hypothetical / speculative / open-ended questions are better suited for our sister-sub ",
"/r/asksciencediscussion",
". Please post there instead."
] |
[
"I've been trying to 'correctly' post this for 10 minutes then you say it's the wrong sub"
] |
[
"I've been trying to 'correctly' post this for 10 minutes then you say it's the wrong sub"
] |
[
"how did we prove that all atoms have a gravity well if it's too tiny to measure?"
] |
[
false
] |
How do we know there isn't a little lump of "Gravitonium" at the center of each celestial body and that all the gravity we measure is a result of that un-seen object? What would it mean if we discovered that mass does NOT create a gravity well, it's merely affected by one?
|
[
"We can certainly measure the gravity of small bodies. The historical ",
"Cavendish Experiment",
" used torsion balance to measure the gravitational effect of a 158 kg lead ball.",
"That is certainly not the same as measuring the gravitational effect of single atoms, but it disproves your hypothesis of Gravitonium at the center of celestial bodies.",
"Experiments show, that there is correlation between mass and gravitational attraction. Thus it would make sense to create a theory that builds on the hypothesis that mass is a source of gravity.",
"\nHowever, our as of yet best theory of gravity (General Relativity) finds, that mass is not, in fact, the only source of gravity. GR proposes, that the ",
"stress-energy tensor",
" is the actual source of the gravitational field.",
"This would explain, why photons can be the source of gravity, despite the fact that they posses no mass. Since they posses energy, their stress-energy tensor can act as a source for gravity."
] |
[
"photons can be the source of gravity",
"Do you know if there have been observations of that? I know that they should but I didn't know if it had been observed or not"
] |
[
"The reverse effect (photons being affected by the gravitational force of large objects) is known as Gravitational Lensing."
] |
[
"How do we know that the age of meteorites correspond to the age of the earth?"
] |
[
false
] |
[deleted]
|
[
"Earth has never been directly dated (rocksinmyhead will come in here and post about an attempt using Lead to do it and that is a valiant effort). For now the best way to think about it is as follows:",
"Here is a brief history of our solar system",
"1) A long time ago a molecular cloud collapsed (probably from a super nova explosion). This cloud collapsed into a spinning disk",
"2) The inner material mostly collapse in to form the sun and the remnants forms the inner planets. The outer solar system is another story and irrelevant for now. ",
"3) About 4.56 billion years ago the first matter condensed out of the disk. This first matter is called Calcium Aluminum Inclusion (or CAI). Then other material starts to condense out as the temperature drops.",
"4) (Now we get to your question) These small objects initially the size of dust clump together and form ever larger objects (baseball, soccer ball, 10s of meters, 10s of kms, and then planetesimals). So the collisions that happen are ever more violent as time goes on. We know the timescale of formation for a planet the size of Earth is on the order of 10s of millions of years. These time scales come from a few independent sources including numerical models of accretion out of this initial disk and using hafnium and tungsten isotopes to calculate how quickly a core of a planet would form (a few million years).",
"5) A lot of other collisions and surface processes remelt the oldest rocks so they can't give ages",
"6) Hadean zircons form roughly 4 billion years ago in what is now western australia and canada.",
"So in short we have dates from these zircons that say its at least 4 billion years old. And then we have the earliest dates in the solar system which form an upper limit. This range is narrowed using formation models and other isotopic systems to study say core formation."
] |
[
"Now I feel obliged to post about Clair Patterson's dating of the Earth using lead isotopes... but will simply give the ",
"Wiki link",
". His age of 4.55 Ga is still our best estimate. However, to my mind the age of the Earth is the same as that of meteorites: 4.567 Ga."
] |
[
"Thanks for posting that I forgot who did it, I just remembered you posted it. About the age of meteorites though you should subtract idk 10 or 20Ma for formation time to get a nice age. Which gets you back to 4.55Ga which simply amazes me that his technique is so nicely on."
] |
[
"There's a petition in my town to legalize raising backyard chickens. I know this sort of thing is becoming more popular, but aren't there significant public health risks to raising chickens (or livestock) in populated areas? Are there any good studies about this?"
] |
[
false
] | null |
[
"Essentially what it says is that salmonella can be spread but you have to be directly in contact with the chickens' range, so if they are kept in a chicken run and a coup, the other areas outside of that won't have much salmonella contamination.",
"The salmonella is spread through chicken feces and can get on the chickens' bodies and spread to wherever the chicken walks (of course things can blow over in the wind so consider setbacks). Subsequently if touching areas where the chickens have been, wash your hands before sticking them in your mouth or rubbing your eyes.",
"So if you don't have chickens yourself, you will be fine."
] |
[
"This publication pretty much covers it. In summation: chickens can carry diseases like salmonella, however the risk is mainly to children, the elderly, and those with compromised immune systems. As far as the issues surrounding things like avian flu, most cities that allow backyard chickens only allow up to 3 or 4 chickens (and no roosters). By keeping the density low, the conditions that favor outbreaks of cross-species diseases are kept to a minimum and the overall cleanliness of the chicken yard is easier to maintain. The conditions that spawn bird flus tend to have much higher concentrations of animals, usually with several species of animals all living in close proximity (pigs, chickens, goats etc.), lack of vaccination, and poor sanitation. ",
"The reasons backyard chickens are banned in many cities usually has more to do with people's perception of the chickens being unsightly and bringing down property values. Other factors are the cultural association of chickens with poor immigrants, the worry of noise from roosters, the health hazards and the worry that people will not know to properly clean eggs before eating. ",
"I hope this helps! "
] |
[
"Yes, there are risks of bacterial/disease transmission. ",
"Here is an \"informative brochure\" type thing from the CDC."
] |
[
"When someone suffers from Acute Radiation Sickness they go through a \"latent\" stage where they feel well and healthy, despite potentiay lethal physiological damage. How is this?"
] |
[
false
] | null |
[
"If you get a sufficiently high exposure, it kills pretty much all of the bacterial fauna in your stomach and intestines, as well as your intestinal lining. Your digestive system just stops working. That manifests itself as rapid onset nausea, vomiting, and diarrhea. Once you're ah, empty, you feel better. No more barfing all over the place.",
"Unfortunately those cells aren't coming back anytime soon, and in the meantime much of your bone marrow might be dead, most of your white blood cells are dead, you might have severe organ damage. It's pretty much a matter of time. The train's already left the station, so to speak, and now you're just waiting for it to arrive."
] |
[
"Until the cells start to replicate or stop working, most of the damage won't be noticed by the body. A cell has enough proteins to keep functioning for a while. However once cell replication begins and cannot be completed, the cells begin to die without replacement, which leads to organ failure"
] |
[
"Unfortunately no, at least we don't know if any way to repair the damage. Acute radiation poisoning does severe damage to DNA which is what causes everything to stop working. CRISPR may be able to repair small sections of DNA in the future, but this sort of damage is too widespread and too random to be fixed by any type of technology we have"
] |
[
"What causes the graphite in nuclear reactor to become radioactive itself? Is it due to neutron radiation from the uranium fuel breaking apart the atoms of the graphite and causing them to become unstable?"
] |
[
false
] | null |
[
"Yes, the neutrons transmute nuclei within the graphite such that they are radioactive."
] |
[
"Interesting. Does that mean that the effectiveness of the graphite as a moderator decreases?"
] |
[
"Not significantly, because a tiny fraction of the nuclei inside the graphite get transmuted. The main effect is that the graphite can be lethally radioactive after being removed from the core."
] |
[
"[Mathematics] How would one construct this?"
] |
[
false
] | null |
[
"Not the right sub. "
] |
[
"Can you point me in the right direction? "
] |
[
"You could try ",
"/r/math",
" or a problem/riddle specific sub"
] |
[
"Does epigenetics contradict modern evolutionary synthesis? Why or why not?"
] |
[
false
] |
Many people have tried to argue with me that epigenetics somehow makes the importance of 'genetic frequency' redundant, because environmental factors influence genes in across lifetimes. I haven't read any expert arguments on the subject. Can someone who is well informed on this issue shed light on it? Is this a muddled topic or is there a clear scientific understanding of this issue?
|
[
"Even the enthusiasts of things like epigenetics and plasticity, who claim that we need an extended evolutionary synthesis, don't claim that gene frequencies are somehow rendered irrelevant. There's a good review paper ",
"here",
"(PDF) by Massimo Pigliucci, where he argues that we do indeed need a new synthesis. However, he specifically denies that gene frequencies are somehow now irrelevant:",
"Finally, the evidence if now becoming clear for the existence of a whole additional layer of inheritance at the epigenetic level (Jabolnka and Lamb 2005), which despite the quasi-Lamarckian memories it brings to mind, ",
" (p.2746)"
] |
[
"This is a great resource, thank you."
] |
[
"it's not that their irrelevant, it's that their effects are way over-interpreted, and there are so many vested interests in genetics that epigenetics has been sidelined for years. Until the biotech industry bubble pops, you won't hear about it. Read Jabolnka and Lamb, it's a great book."
] |
[
"I found a rock on the side of the road. Without using carbon dating, what is a reasonable estimate of the age of this rock?"
] |
[
false
] |
[deleted]
|
[
"If you have an approximate location, and you can approximate the type of rock, you can look at a geologic map of the area and come up with a fairly good idea of what it is and how old it is. If you have a piece of sandstone, a microscope, and a good idea of microbiology, you can look at the micro fossil assemblages (or even the macro fossil assemblages) and approximate a time based upon 'known' assemblages at particular times. ",
"If it is on the side of the road, however, it can come from anywhere. Many beginning, and even some professional geologists have been led astray from a random transported rock, or road grade that is far from any known road. "
] |
[
"Carbon dating wouldn't help, it only works back to around 60,000 years, and rocks don't always have high amounts of carbon.",
"You would need to use another form of ",
"radiometric dating",
"."
] |
[
"The oldest known rock is a gneiss from Canada that is about 4 billion years old. So, we can knock 500 million years from your estimate ;)"
] |
[
"Why did intelligence only evolve once?"
] |
[
false
] |
It is obvious that humans dominated the animal kingdom due to their intelligence, thus, making it a huge evolutionary advantage. So why didn't other species became intelligent?
|
[
"I would argue that intelligence is a continuum, not a single characteristic, and that many different animals have evolved to high levels of intelligence, relatively speaking. ",
"Humans might be at the top of this scale, however other animals, such as our primate cousins, cetaceans, and some birds certainly exhibit intelligent behavior that has evolved by natural selection. Compared to the nearly every other species of animal, a chimpanzee is incredibly intelligent.",
"As ",
"/u/Shiba-Shiba",
" pointed out, it might be that (starting from the dawn of life) intelligence, being an extremely complicated trait, has just taken a long time to come around, and we are the first ones to reach such a high level, and we've only been around for a few million years.",
"Perhaps if Earth had had a few less mass extinctions, some other species would have reached such a level first. Perhaps in a few million more years, the descendants of chimps, or dolphins, or some other current species, will catch up to us.",
"But then, if our descendents are still around in a few million years, how intelligent might they be?"
] |
[
"It is incorrect to claim that intelligence only evolved once. There are many intelligent species from different branches of the tree of life. Primates, dolphins, elephants, dogs, and even cephalopods are arguably intelligent to some extent. Humans certainly take that particular trait to an extreme, but so what? For any given trait you can think of, there must be one species on earth that is the most extreme example of that trait.",
"Humans are the species that takes intelligence to its furthest extent, but we are definitely NOT the only species in which intelligence has evolved. You are claiming that humanity is somehow qualitatively different from all other animals - that we have something that is not found even in the smallest quantity in other species. The data do not back up that assertion."
] |
[
"I would argue that intelligence is not by any means the single best evolutionary strategy. We're doing well, but so are plenty of other organisms. Intelligence is one survival strategy of many, and is only beneficial in that it results in higher reproductive and survival rates. Other species have evolved other ways to reproduce in large amounts and they're doing just as well as we are.",
"It would seem to me that our current dominance of the environment is pretty trivial to evolution. Ants, rats, and bacteria don't need to dominate their environments in order to thrive in them. We just stumbled on a successful strategy while those organisms found their own, equally good, strategies."
] |
[
"Why are clouds flat on the bottom?"
] |
[
false
] |
Not all are, but I'm assuming the ones that aren't are too high up to be flattened
|
[
"Clouds form at different temperatures, depending on the amount of water vapor the air contains. In most of the atmosphere, the temperature of the air decreases with altitude. (Temperature inversions, where the temperature of the air increases with altitude, are the exceptions.) So the bottom of the cloud is at the altitude where the air is at the temperature where the clouds can form. "
] |
[
"Most clouds have flat bottoms according to where the condensation level lies within the air column. The condensation level is the point at which air reaches saturation, and the temperature of the air matches the dewpoint temperature. As air gains altitude, rising through the air column (save temperature, surface, and nocturnal inversions), the temperature of the air decreases and gets more and more saturated (as each temperature has a different saturation point: lower temperatures can become saturated easily whereas higher temperatures require more moisture to become saturated). ",
"This is why you can have flat-bottomed clouds at any level. Fog, when it forms in valleys, can appear flat on the top and bottom (with its wispy, thin appearance when viewed from certain angles in certain conditions). ",
"Clouds don't form at different temperatures, per say--they form at different altitudes with flat bottoms according to where the condensation level lies within the air column which is dictated by moisture content in the air mass."
] |
[
"The other explanations are good but I'll chip in too. ",
"All clouds, except fog, are the result of air that rose, cooled down due to expansion, and condensed.",
"\nThe clouds with flat bottoms are called \"cumulus\" and they are a result of air that rose from the ground (",
"convection",
"), cooled down due to expansion (",
"gas law",
") and reached the ",
"condensation",
" point.",
"\nAs the cooling down is caused by expansion of the air only rather than interaction with the surrounding air (",
"adiabatic",
"), the condensation point is reached at a certain altitude. As the condensation altitude is pretty similar for a certain area it will cause a line under which moisture is still a gas and above which moisture is now water droplets (i.e. cloud). ",
"Example: dew point is 16C, temperature is 26C. The sun heats up the ground which heats the air in contact with it to 26C. As the hot air is on the surface and the air above is cooler it will start rising (convection). As it rises it doesn't mix with the surrounding air (adiabatic), it decompresses as the pressure drops with altitude according to gas laws and this makes the temperature drop, usually at around 1 deg for every 100m it rises (80~90m actually on a good summer day, called ",
"Dry Adiabatic Lapse Rate",
"). This means after rising 1000m (temp minus dew point divided by the cooling rate) it will reach the dew point and condense. All parcels of air will condense at similar altitudes unless you change temperature or moisture (so you can find lower condensation lines above a lake, for example). ",
"Source: paragliding pilot, we use this information to estimate the cloudbase for a given day and plan our distance flying. I'd be happy if anyone has any corrections to the above."
] |
[
"Why is it that portable chargers above a certain mAh cannot be brought on the plane?"
] |
[
false
] |
I was on a plane lately and they took away my 50000 mAh power bank :(
|
[
"Because it is a fire hazard. 50000 mAh for a 5V charger is about a million joules (250 watt-hours), i.e. if there was a short circuit such that the power bank dissipated its energy over the course of a minute (say), it would be putting out 15000 watts (the equivalent of 10 electric stovetop heating elements). A fire on an aircraft is one of a pilot's biggest fears because there is no escape from the toxic smoke and no way to land a plane from cruise altitude in less than 15 minutes or so even if the pilot's try to land as quickly as possible. This is why you always hear about not messing with the bathroom smoke detectors. Here are some notable examples of fatal commercial aircraft fires since 1980 or so: ",
"Saudia Flight 163",
", ",
"British Airtours Flight 28M",
", ",
"Nigeria Airways Flight 2120",
", ",
"Air Canada Flight 797",
", ",
"Aeroflot Flight 2306",
", ",
"South African Airways Flight 295",
", ",
"ValuJet Flight 592",
", ",
"Propair Flight 420",
", ",
"Swissair Flight 111",
", ",
"China Northern Airlines Flight 6136",
".",
"Note that ironically ",
"some newer aircraft use lithium ion power banks that have caught fire and lead to the temporary grounding of all 787 aircraft",
". "
] |
[
"Lithium ion battery chemistry in particular is dangerously volatile and there's a real chance that a broken or low-quality cell will spontaneously catch fire and burn ",
". There have been several incidents in the past years where a passenger's phone battery or a small power pack has started smoking or caught fire during a flight. Taking 50Ah worth of such volatile stuff with you on a plane would be playing with the life of everybody on the plane."
] |
[
"Thank you! I understand now"
] |
[
"Is there a specific equation or method to determine an element or compound's state of matter at a certain temperature and pressure?"
] |
[
false
] |
I know the states of matter and how they work. In organic chemistry my teacher often states something like, "this compound typically exists as a liquid." So I was wondering if this is just common knowledge for certain compounds, and if not, what way there is to determine its physical state besides forcing conditions upon it.
|
[
"Yes, there is. They're called ",
"phase diagrams",
". Essentially, people already did the tests you're talking about on a wide variety of materials for other people to use.",
"As for equations, you're looking for the ",
"Clausius-Clapeyron relation",
". It's a partial derivative of pressure and temperature."
] |
[
"But of course, the values of dP/dT are themselves estimates at best without using empirical observations."
] |
[
"The chemical potential of the different phases can give you a pretty good indicator of which phase should dominate at a given temperature and pressure, but getting these is not away so easy. "
] |
[
"Since the Sun is travelling around the Galactic Centre at 828,000 km/hr, if we travelled the opposite way the orbit is flowing, towards another star, would we get there faster than if we travelled to a star an equal distance away, but ahead of us in orbit?"
] |
[
false
] |
I apologize if I asked that in a confusing way. I can try and clarify if needed.
|
[
"Yes, but what about the star you're aiming for coming at you at (for the sake of argument) around 828,000km/hr?",
"It's not. It's also orbiting the galaxy at roughly the same speed as the sun, meaning that it's not moving toward or away from us. ",
"Think of it in terms of standing in the aisle on a bus. If you're standing in the center, with one of your friends in the very front of the bus, and another in the very back of the bus, can you reach one of them faster than the other? If you run at the friend in the back, is he moving toward you at 60 miles per hour just because the bus is moving that speed?"
] |
[
"No matter which direction you leave the solar system in, you start with the same velocity, relative to the galactic core, as the sun (slightly modified by the velocity of the Earth's orbit).",
"So it makes no difference if you travel forward or backward relative to the sun's galactic orbit. Either way, you'll have to accelerate/decelerate to the same exact degree if going the same distance."
] |
[
"Yes, but what about the star you're aiming for coming at you at (for the sake of argument) around 828,000km/hr?"
] |
[
"Is there a type of plant that can \"plug itself into\" another plant's root system?"
] |
[
false
] |
[deleted]
|
[
"Parasitic plants",
" do exists and they use their host's vascular system to obtain nutrients. The vascular system consists of xylem and phloem which transport nutrients and water throughout the plant. \"A parasitic plant is one that derives some or all of its sustenance from another plant. About 4,100 species in approximately 19 families of flowering plants are known. Parasitic plants have a modified root, the haustorium, that penetrates the host plant and connects to the xylem, phloem, or both.\" Common example would be ",
"Mistletoe",
".",
" Example: ",
"The Christmas Tree",
". Without knowing exactly which species are pictured in your image you cannot really tell if one is parasitic to another. That being said...more then likely it is not.",
"Mycorrhiza",
" \"is a symbiotic (generally mutualistic, but occasionally weakly pathogenic) association between a fungus and the roots of a vascular plant.\" Simply put the fungi help provide nutrients to the host tree and the tree provides the fungi a place to live. ",
"There are also ",
"epiphytes",
" grow on their hosts but to not use the host's vascular system. Epiphytes use hosts purely for structural support. "
] |
[
"Mycorrhiza from one root system can also fuse with the mycorrhiza of another root system. "
] |
[
"commercial cloning of japanese maples involves grafting the tree onto more aggressive trees root systems..."
] |
[
"Giant plate of stone on water."
] |
[
false
] |
Hey askscience, I had a flashback to an idea I had when I was washing the dishes as a kid. I'd always spin the floating dinner plates, make waves in the sink and make the plate sink eventually. Anyhow, I remember me one day wondering: "**If one would place an enormous dinner plate (i.e. a somewhat concave object made of stone; let's say 1 mile radius) in a giant pool of still water, would it still float like a dinner plate would in a sink full of water, or would the weight eventually become too high so it would sink? And would it make any difference if it were spinning or not? Thanks!
|
[
"Yep. Float just like a plate. ",
"What determines this is how much water is displaced. If you think of sitting a dinner plate in the water and then freezing the water and taking the plate out, you have a little concave area. If calculate the volume of the concavity it equals the weight of the plate. ",
"See ",
"Archimedes Principle",
"So as long as the plate can displace enough volume of water to weigh as much as itself without taking on water first... it would float."
] |
[
"Eureka! My kid self KNEW this!"
] |
[
"Same way a ship, built of heavy metal, loaded with cargo, manages to stay afloat. The weight of the water that it displaces weighs more than the weight of the ship. Two ways are available to increase this ability. Increase the size of subject vessel, or decrease it's weight."
] |
[
"In getting your daily water requirements, is it the same to chug 32oz twice (assuming you can keep it down) or to sip on 64oz throughout the whole day?"
] |
[
false
] | null |
[
"It would be better to sip it over the course of the day. When you ingest a large amount of water, your body will signal the kidneys to excrete the excess to regulate your blood pressure and balance out the concentration of fluids to solutes throughout your body. "
] |
[
"Its dangerous to drink more than a quart and a half of water in under an hour and a half or so... this depletes your body of its electrolytes and can lead to water toxicity"
] |
[
"It wouldn't lower your blood pressure, but the increased water content in your blood and intracellular fluid would dilute the concentration of solutes (like sodium or potassium) in your blood, which would cause chemoreceptors in your kidneys to allow more water to be filtered out to restore tonicity. ",
"If you had a sudden drop in blood pressure the reduced pressure on your arterial walls would cause your pituitary gland to release anti diuretic hormone to tell the kidneys to hold on to water and increase your blood pressure. It would also cause your blood vessels to constrict to increase pressure. "
] |
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