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[
"Does the Universe truncate?"
] |
[
false
] |
Einstein's Field Equation for general relativity involves pi. Pi is a transcendental number. It would be impossible for any computer to calculate the exact result of this equation, since pi is infinitely long. Yet the Universe manages to do it instantaneously, all the time. Does the Universe truncate its answers? How can it process things so quickly?
|
[
"The universe has no problem handling irrational numbers. Just because we cannot replicate them in our digital machines, does not mean they do not exist. "
] |
[
"You're assuming the universe is like a machine."
] |
[
"Equations and formulae describe the universe, not the other way around. It isn't \"impossible to calculate the exact result (of a number with pi in it)\" in reality because you can just leave pi in the answer. 2 pi is ",
" the number of radii that fit in the circumference of a circle in euclidean space. On computers, pi is approximated with rational numbers (decimals) because rationals are convenient to work with. We can make a rational number as close to the true value of pi as we desire.",
"We merely use decimals out of convenience, but the universe doesn't need to conform to our convention."
] |
[
"Why is space black?"
] |
[
false
] |
This might be the most stupid question ever, but I thought of this yesterday and, well, what the hell! What am I seeing when I see the black between celestial bodies? Why is space so black?
|
[
"It's not a dumb question at all! It's a rather famous paradox -- if the universe is infinite, why don't you see a star in every possible direction? This is known as Olbers' paradox:",
"http://en.wikipedia.org/wiki/Olbers%27_paradox"
] |
[
"Here's an explanation, and resolution, of Olbers' paradox:",
"http://www.universeadventure.org/big_bang/popups/conseq-dtrh-olbers.htm",
"Explaining exactly why the sky is black."
] |
[
"First, space is huge. The distance between light sources (stars, etc) is enormous.",
"Second, space is VERY dusty - you think ",
" have dust bunnies, the universe has you beat hands down. Dust obscures a lot of the light. This is the reason that looking up at our milky way galaxy does not look as impressive as one might expect - the dust is obscuring most of the light.",
"This is also why observatories observe the universe in many different wavelengths - some of the wavelengths allow us to see through the dust."
] |
[
"Biology - How do onions grow?"
] |
[
false
] |
Do onions add layers as they grow or do they start with all of their layers and they get thicker as they grow?
|
[
"Onions are just one variety of ",
"bulb",
", which means that the fleshy part that we eat is just a section of modified leaves attached directly to the diminished stem called the 'disk' or ",
"basal plate",
". ",
"Those fleshy scales grow sequentially as the bulb develops. The fleshy scales are produced based on a water/calorie feedback system, where thresholds of bioavailability will induce the plant to form more scales over its lifetime. Scales are consumed for calories during flowering and during drought or periods of calorie deficiency, so that the size of an onion and the number of layers at any given time is variable."
] |
[
"In our common onion cultivars the fleshy scales grow from the inside, pushing older layers outward. Much like the bark on a tree forming from the outer cambria, as the outer-most layer of cells expands the cellular integrity becomes compromised and it undergoes a conformational change. In the case of these onions, the layers pushed to the outside are gradually drained of their stored nutrients and left as a papery sheath of cell walls and sequestered compounds. These layers will continue to shed into the environment, just like our skin does, and regions of cells pushed sufficiently outward will integrate with the soil and be removed when the bulb is harvested.",
"So, yes, the outer layers keep dieing as new layers grow internally and the bulb expands. Because the rate of growth reaches a maximum just before flowering the original layers are typically looser and thinner than the inner-most layers at peak harvest, which contributes to the heterogeneously layered appearance of a mature onion."
] |
[
"So, all the leaves keep growing and the outer 1 or 2 die, then the outer layers keep dying?"
] |
[
"Can someone describe the phenomenon captured in this photograph of a lightning strike?"
] |
[
false
] |
[deleted]
|
[
"I believe this is actually a facility designed to study lightning. They fire off a rocket and facilitate a lightning strike through a conductive aerosol or liquid emitted by the rocket during its flight. ",
"{Edit}: A bit of background awesomeness:",
"*",
"Video",
"*",
"The photograph in question",
"*",
"Lightning Rocket: Wikipedia"
] |
[
"I know some of the experimental details of this experiment.",
"The facility is a tower which effectively a lightning rod. A rocket is fired from the top of the tower, with a conductive tether on it.",
"A high speed camera 1M FPS is focused on the tower, and used to capture lightning strikes. the image you show is several ms after the initial strike, you are observing several plasma streaks emanating from the wire (on the left) towards to lightning bolt, which has a higher potential than the ground wire.",
"Edit: Also this is not natural lightning. They are creating the strike from the tower from a series of high capacitance banks (base of the tether)"
] |
[
"It appears to be a ~5sec time exposure. The 'flames' aren't flames, theyre the motion-smeared lightning channel, captured while the shutter was open."
] |
[
"Regarding skin cancer, can it appear on parts of your body which hasn't been exposed to UV?"
] |
[
false
] |
[deleted]
|
[
"While it is possible to develop skin cancer from the natural accumulation of mutations or exposure to a carcinogen other than UV light, UV light is by far the most common cause of skin cancer. UV light exposure in one area will only affect the DNA of the cells that are exposed to it, and therefor can only create skin cancer in the region of UV exposure. So the simple answer is NO, it is not possible to develop skin cancer in an area of skin that is not exposed to UV light. However, the one exception would be development of a metastatic melanoma in a different region of skin. Melanocytes, the cells that produce melanin, the protein that causes skin pigmentation, are quite mobile. They therefore have a propensity to metastasize after tumorigenesis. Melanomas have a 65-70% chance of metastasizing to other areas of the skin, fat, and muscle."
] |
[
"Judging by the extremely thorough examination my bud just got from his dermatologist (spread them) I'd say yes. UV can penetrate light clothing, a white TShirt only has an SPF of ten.",
"edit* A quick google search of \"Skin Cancer where the Sun Don't Shine\" brought me to ",
"This article",
" which brings up two interesting points. The 2nd most fatal type of skin cancer behind melanoma is genital skin cancer, something to do with the HPV virus."
] |
[
"YES.",
"\nThere are three common types of skin cancer (Melanoma, Squamous cell carcinoma and basal cell carcinoma... won't include adnexal tumors and so). All of them are somehow associated with UV light exposure, but there are several other causes, especially for Squamous cell. \nYou can get SCC after burns, chronic infections that drain into the skin (think a bone abscess), industrial exposures, other forms of radiation and definitely HPV.",
"\nBSC is almost always related to chronic sun exposure and Melanoma to more acute exposures. Nonetheless it can appear spontaneousle (say, in your eyes or soles of your feet)"
] |
[
"Does the language you speak affect the shape of your palate?"
] |
[
false
] |
I was watching the TV show "Forever", and they were preforming an autopsy, when they said the speaker had a British accent due to the palate not being deformed by the hard definitive sounds of English (or something along those lines) does this have any roots in reality, or is it a plot mover?
|
[
"I don't believe there is any evidence to support that language affects palate morphology. However, vice versa it may be that morphology affected the development of (aspects of) languages.",
"For example, see these two paragraphs from a ",
"2015 conference paper by Moisik and Dediu",
":",
"It is an undeniable fact that human populations vary in certain systematic ways in their anatomy and physiology. This is true at both micro- and macroscopic levels, and advances in genetics will continue to elucidate the extent of these patterns of variation across populations. Early in the development of modern phonetic and phonological science, several proposals (e.g. ",
"[24]",
" and ",
"[2]",
") were made which held that some of the diversity observed in speech sound systems around the globe might be owing to systematic variation observed in the anatomy and physiology of the speakers of language, in addition to the other factors driving language change and diversification. These ideas were hastily dismissed as implausible, on the grounds that any human being can learn any human language.",
"It is an incontrovertible fact that normal variation of the human vocal tract does not preclude an individual from acquiring any spoken language. However, the hypothesis that human vocal tract morphology exerts a bias on the way we speak seems plausible, and the possibility that such biases might have expressions at the level of populations of speakers has never been satisfactorily ruled out. It also seems to have resulted in the unfortunate side- effect that details of vocal tract shape are rarely if ever correlated to production variables in phonetic research. A relatively recent return to the question of whether normal vocal tract variation can indeed exert such biases reflects the unresolved nature of the problem. Many examples exist for such research examining the individual level (e.g. ",
"[25]",
", ",
"[3]",
", and ",
"[18]",
"), and these are laden with implications for impacts at broader levels, with some researchers even suggesting it may be a driver of change of certain aspects of entire phonological systems (e.g. ",
"[1]",
", ",
"[5]",
", and ",
"[17]",
").",
"Of course, this wouldn't help you identify which language someone spoke while alive."
] |
[
"I do know that in Russia, it's considered a prominent and full-blown speech impediment if you can't properly roll your R's - like how \"speech impediment\" to Americans usually means someone who can't pronounce a rhotic R properly. Vladimir Lenin was one person who couldn't do it, and he has dozens of impersonators that overly exaggerate it for comic effect."
] |
[
"It is considered a speech impediment in every language which uses the roller R but is usually corrected by a speech language pathologist in childhood. It is the most common form of speech impedient in children, and it someone doesn't get it fixed and still speaks it like an adult, they should like a child. If someone wants to impersonate a child, they speak without rolling the R. The mayor of my town has a problem with rolling his R's and everyone mocks him for it behind his back..."
] |
[
"Can you tell me if there are really differences between male and female brains?"
] |
[
false
] |
Some say that male brains are more spatially aware and hence better at mathematics and driving cars, whilst female brains are better at emotional/linguistic construction and analysis. I heard that science can't actually classify brains as male and female however and that many people who are genetically of one gender actually have brains that conform to the suggested profile of the opposite gender. Is all this male brain/female brain a load of guff, or is there something in it?
|
[
"There is absolutely something in it. However, the waters are muddled a bit by experimental design. As it turns out, a woman's brain changes pretty dramatically depending on her cycle phase. Accordingly, unless you test your female subjects at the same cycle phase, it is tough to get clean results. Most studies so far have not tested females at the same phase, but enough have to see the difference. ",
"http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0014655",
"http://www2.cnrs.fr/en/797.htm",
"There's a bunch of psychological studies on woman's behavior during their cycle, but the long and short of it is that there are minimal sex-related brain differences near ovulation, and pretty significant changes around the end/beginning of the cycle. The monthly gray-matter fluctuations have been illustrated in video during lectures I have seen, and they are crazy-huge. ",
"Woman on the pill don't cycle as much (brain-wise), and are sort of in-between men's and women's brains. "
] |
[
"Yes, the ",
"sexually dimorphic nucleus",
" is a thing. It's part of the hypothalamus that's, among model mammals, quite a bit larger in males than in females, and appears to be involved in sexual behavior and preference. A corresponding region in the human brain is famously larger in heterosexual men, but smaller in homosexual men and heterosexual women. But don't get too excited; I remember reading somewhere it's about the size of a grain of rice (in humans).",
"At the end of that Wikipedia article is a brief mention of another sexually dimorphic brain region, also in the hypothalamus."
] |
[
"The monthly gray-matter fluctuations have been illustrated in video during lectures I have seen, and they are crazy-huge.",
"I'm very skeptical that gray matter volume is changing drastically on a times scale of weeks. The paper shows a concomitant decrease in CSF volume when GM volume increased, suggesting that this is a variation resulting from their tissue segmentation method, especially since only 8 female brains were scanned at 4 time points. The changes they're reporting in 1 week are on the order of what we see in longitudinal atrophy studies in 1 year. Changes in fluid balance are much more likely to be responsible for that dramatic an effect, rather than actual changes in brain structure."
] |
[
"Does wind affect the distance sound travels?"
] |
[
false
] | null |
[
"Wind represents a gradient in atmospheric pressure. Low pressure brings wind (attempt to balance) from high pressure. Sound is a wave disturbance (oscillating pressure gradient). So if there's a large wind, there's a large gradient in pressure that will absolutely affect sound propagation through the medium.."
] |
[
"You're forgetting that wind inherently mixes the air molecules around. Sound depends on one molecule linearly bouncing into the next molecule. And that happening over and over again, with a very large number of molecules, until the sound reaches your ears. ",
"A strong wind can literally blow the propagation of the sound wave away from your ears, so for practical purposes, wind can reduce the distance that you can hear something from. ",
"Also, wind means that air molecules are moving around at speed. Sound carries best in still air, because the wave propagates more cleanly. In moving air, the molecules are all moving at different speeds and directions. It's harder for a wave to maintain coherency at a distance if something like wind is happening. "
] |
[
"Sound is just a longitudinal wave in the air so yeah the motion of the air molecules will affect sound transmission. However, sound travels at like 300 m/s (in STP air, to one significant digit) so the effect is probably negligible unless the wind is very strong / gusty or the sound travels over a long distance (giving effects time to accumulate to become noticeable).",
"Imagine two cars driving near each other in still air - the relative motion of the air carries sound away and makes it harder to hear each other. The same would be true of two still cars in wind of the same speed. "
] |
[
"Imagining the Tenth Dimension: How much of this video is scientifically sound?"
] |
[
false
] |
's the video.
|
[
"The stuff up to three dimensions is pretty reasonable. The fourth dimension stuff gets iffy (although I hestitate to call it wrong), and the rest is just entirely nonsense."
] |
[
"He's actually talking out of his ass, it's not even a real scientific theory."
] |
[
"Actually, even the 3rd dimension stuff is pretty bad. They describe the 3rd dimension as the dimension in which curvature of a 2D surface is embedded. But you don't need to embed a manifold in higher dimensions for it to be curved. The best way to understand extra dimensions is as extra degrees of freedom. Read or watch some Brian Greene, he's pretty good at explaining it"
] |
[
"If a cell was as big as a basketball, how big would an atom be?"
] |
[
false
] |
I'm trying to understand the scale of us, to the cell, to the atom, especially the scale of the cell to both of them.
|
[
"As a rough approximation, assume an atomic diameter of about 1 Ångström for a hydrogen atom = 0.1nm.",
"A bacterial cell has an average diameter about 1 μm (I'm using ",
"S. aureus",
" because it's roughly spherical). If it were an animal cell it would be about 20 μm (using a ",
"Macrophage",
"). ",
"A basketball is about 250 mm diameter. ",
"So, compared to a bacterial cell, a hydrogen atom would be ",
"250 mm * 0.1 nm / 1000 nm = 0.025 mm = 25 μm\n",
"So, that atom would be a little smaller than the width of a human hair, or, conveniently, about the size 1-2 human cells.",
"If the basketball were a human cell, the math is ",
"250 mm * 0.1 nm / 20000 nm = 0.00125 mm = 1.25 μm\n",
"Or a little bigger than a size of a bacterium. ",
"All this will depend on what you define as the diameter of an atom, I'm using 2x the Bohr radius. It will also depend on what type of cell you're comparing to, size can change a lot between cell type and organism. "
] |
[
"Absolutely. And it assumes the atom is spherical, the cells are spherical, etc, etc. Back-of-the-envelope calculations are fun because you can make sweeping assumptions. :)"
] |
[
"Great answer.",
"All this will depend on what you define as the diameter of an atom",
"I think the atom you pick is more significant than the details of how you define your radius!",
"Hydrogen: 1 Ångström.\nCesium: 6 Ångströms.",
"; )"
] |
[
"The geoid and the centrifugal force"
] |
[
false
] |
It is commonly said that due to the centrifugal force the gravity at the equator feels a little bit weaker than at higher latitudes. I understand what the idea behind this is. The centrifugal force is proportional to the distance to the axis of rotation which gets smaller as you go towards the poles. So at the equator the centrifugal force is bigger and cancels a greater, though still a relatively small, bit of the force of gravity. Then we have the , or the reference shape of Earth. Now the Wikipedia article says that the geoid is the equipotential surface relative to the rotating Earth. The way I interpret this is that equipotential surface means that the force of gravity is the same everywhere on it. And since it mentions relative to the rotating Earth, I would assume that it takes the centrifugal force into account. Now if this is the case, then clearly the gravity should be the same, whether you are at the pole or at equator, when you are at sea level relative to the geoid. Is this right? In other words the often quoted fact that gravity is slightly smaller at the equator would not be true at all because it has been compensated for already in the definition of the geoid.
|
[
"Is the combined effect of gravity and centrifugal force the same everywhere on this surface?",
"Yes. If we were to ignore all the small-scale density-induced anomalies and only look at the major components of gravity as well as inertial forces due to the earth's rotation, then the value of ",
" at sea level (the geoid) will vary as such: ",
" = 9.80613 ( 1 - 0.0026325 cos 2L ) where L is the latitude in degrees",
"the 9.8 is solely due to the gravitational attraction while the second term is the correction due to the centrifugal force.",
"Thus ",
" is lower at the equator because the extra energy is coming from the rotational inertia"
] |
[
"When we say that gravity is weaker at the equator because of the centrifugal force, we imagine a perfect sphere. In other words, for a perfect rotating sphere, the geoid wouldn't be spherical.",
"Actually, the main reason the real geiod isn't spherical is because of the shape of the Earth, which is flattened at the poles."
] |
[
"So gravity really isn't weaker at the equator on the actual Earth then?",
"So if we assumed a perfectly spherical Earth, and of uniform density, then clearly the gravity would be a little less on the surface of Earth at the equator. But if geoid was defined as it is now, it wouldn't be spherical, it would go above surface at the poles, is that right? Or inside the surface? And then when you compare gravity on the geoid instead of the surface of Earth, at poles and at the equator, it would be the same everywhere?"
] |
[
"Why are the colours/brightness often slightly different in each eye?"
] |
[
false
] | null |
[
"I don't think this is what op means, I have the same thing, it's more a white balance issue. My left eye has warmer colors than my right eye on, most noticeable when looking at light objects. Sometimes I notice it when I have both eyes open, just like when using red/blue 3D specs but not as extreme of course. It's virtually no inconvenience during daily tasks. "
] |
[
"I suspect that the most likely answer is that when you close one eye, your pupil dilates as it would in a dark room. When you open that eye it takes a moment for the pupil to constrict again, meaning that more light is entering one eye than the other for a moment. This can be helpful when you have to turn on a light briefly late at night: close one eye while the light is on, and when you turn it back off only one eye will be \"night blind\".",
"The colour issue is similar. Within the eye there are two major sorts of ",
"light detecting cells",
". Rods are always on and detect gradations of light and dark, allowing you to see in the dark. Cones see colours, but are only active when it is bright enough. Depending on light conditions, your dilated pupil may allow more cones to fire than your constricted pupil.",
"That said, if what you are experiencing lasts longer than a few seconds after opening an eye, you may want to consult an optometrist."
] |
[
"Are you female by any chance? You may be seeing differences due to X chromosome mosaicism combined with heterozygosity of the M and/or L opsin genes. "
] |
[
"What is the most addicting chemical/substance known to man?"
] |
[
false
] | null |
[
"Meth is amazingly addictive. Just for a little comparison, an orgasm releases 800 to 1200 units of dopamine in the brain, while your first time smoking meth releases around 40,000 units and can last upwards of 24 hours. This causes you to chase the original high, but never reaching it. Your dopamine receptors get so burnt out from habitual use that you cannot feel pleasure for upwards of 7 years, outside of the flood meth gives you.",
"Now most abused substance, caffeine for sure.",
"Source: EMT (in training)"
] |
[
"yeah, you can die from alcohol withdrawals."
] |
[
"There's a such thing as a lethal withdrawal?"
] |
[
"Can someone describe the nuclear shell model?"
] |
[
false
] |
I stubmled upon and found it fascinating. I remember learning in school about the atomic shell model and how electrons occupied shells at different energy levels. Is this analogous to the electron shell model but with respect to atomic nucleons? Do nucleons have orbitals or energy levels they can transition into and out of, and what application might this have (such as electron energy level transitions usually produce spectral lines and can identify elements)?
|
[
"Is this analogous to the electron shell model but with respect to atomic nucleons?",
"Exactly.",
"Do nucleons have orbitals or energy levels they can transition into and out of, and what application might this have (such as electron energy level transitions usually produce spectral lines and can identify elements)?",
"Yes to all. Nuclear transitions produce gamma rays. So just like you can identify and element by its x-ray spectrum, you can identify individual nuclides (each isotope of each element) by their gamma ray spectra.",
"The nuclear shell model is exactly like the atomic shell model, except the interactions are more complicated, and much stronger. That means it’s computationally very difficult to model nuclear structure. But it’s conceptually identical to the atomic shell model."
] |
[
"Fascinating. As above so below. It seems to make sense to me that each layer is so similar but so much more complicated. "
] |
[
"The attractive interactions are also much shorter range, which is why the number of bound states is limited (and nuclei have a maximum size). ",
"Electron orbits are also only weakly spin dependent where as nuclear energy levels are extremely spin dependent. "
] |
[
"How is the human brain responsible for 20% of our daily energy consumption? What does it primarily use it for?"
] |
[
false
] |
I've had this question for a while and I was curious how our brain allocates its energy consumption. Also does this standard 20% represent an average of all humans? Does this average change if we had a long day of exams (SAT, MCAT, Finals Etc.) ? The reason I ask is because I was going over the concept of Long Term potentiation(LTP). It occurred to me that if the energy the brain uses is primarily for sending and receiving electrical impulses- would that energy requirement permanently increase for individuals who release more neurotransmitters and have more post-synaptic receptors, a.k.a. LPT? After a mentally draining day do we burn a significantly larger amount of calories? It seems crazy to me to think that the brain uses 20% of our daily energy needs since we're not strictly rebuilding it like we do muscles. Would it be accurate to say it's simply completing a number of tasks that require a lot of energy when added together? It would be super interested if anyone at could figure out the average energy requirement for 1 electrical impulse and use that to figure out the amount of energy required for an average person's day-to-day. Would it give us a reasonable comparison?
|
[
"What the brain primarily uses energy for is to pump ions across the membrane to re-establish the electrochemical gradient after action potentials and synaptic release.",
"There has been a lot of work on this area, and it would be very hard to summarize it in a reddit post. But I can show you the kind of estimates they do to work these numbers out.",
"To do some very rough math: During an action potential, a cell conducts about 1000 uA/cm",
" of sodium currents per membrane area for about 1 millisecond. Lets say an axon has a surface area of 0.1 cm",
" so that a total current of 100 uA [that seems high to me]. 100 uA for 1 millisecond is 0.1 uColoumbs of charge, which is 6 x 10",
" sodium ions [definitely seems high].",
"To pump 6 x 10",
" sodium ions back of the cell, the cell would use 2 x 10",
" ATP ions, and as you make about 38 ATP from every glucose, that means you need 5*10",
" molecules of glucose, which is 8 femtomoles, which weights about 1 picogram. If you have 100 billion neurons, each firing once every 10 seconds, over the course of the day that is 864000000000000 action potentials, using a total of 1 kilogram of glucose. Glucose has 4 calories per gram, which means this requires 4000 calories. Obviously, that is too high by about a factor of 10, but I'm actually surprised I got that close. I think my starting currents and areas were out (which I just came up with from my memory).",
"Action potentials only use about 1/3rd of the total energy use of the brain. 1/3rd is for synaptic release and 1/3rd is for house keeping. For what it's worth, releasing one vesicle of neurotransmitters uses about 70,000 ATP molecules.",
"Also, when you compare it to muscles, this 20% number comes from people at rest. Elite athletes might burn 6000 calories a day, rather than your 2000. Which means their brain only uses 7% of their calories. "
] |
[
"As trying not to think is actually thinking a specific thought/command to yourself, this would intuitively seem to be counterproductive. "
] |
[
"Lets say an axon has a surface area of 0.1 cm",
"I don't have any in-depth neurophysiology education, but this seems like the most likely place where you went too high. Wikipedia tells me the largest mammalian axons have a 10 micron (0.001 cm) radius. If the axon is a cylinder, then the area (not counting the ends) A = 2πrh. For your area of 0.1 cm",
", the length of the axon would be h = A/(2πr) = 0.1/(2π*(0.001)) = 16 cm!! And even longer if the axon was had a smaller-than-maximum radius. Surely most axons are shorter than that by at least a factor of 10 on average, especially in the brain, but you'd know that better than me."
] |
[
"Does gargling water reduce the risk of catching or spreading a viral infection such as influenza or rhinovirus?"
] |
[
false
] | null |
[
"This is borderline scientific, but then again the question is too. Japan's Ministry of Health has ",
"deemed gargling ineffective in the prevention of the flu."
] |
[
"As far as I know, the only medical/anti-disease use of gargling is to use Salt Water or other rinses to kill off an infection in your throat (ie, sore throat). Not my area of expertise, so I'm just posting what little I do know to keep your thread from being empty. :)"
] |
[
"As opposed to America where the location of the planets when you were born effect your love life and luck for the rest of your life.",
"The point is there are non-scientific folks everywhere, regardless of the nationality. At least we teach science in science class and don't spend time trying to sneak the Christian god in the back door."
] |
[
"What happens when you are \"seeing stars\"?"
] |
[
false
] |
To clarify, what I mean are those brightly glowing dots which swim around your field of vision for a moment after you've experienced some kind of shock, be it from getting hit in the face or jumping down from somewhere high.
|
[
"\"A ",
"Phosphene",
" is a phenomenon characterized by the experience of seeing light without light actually entering the eye.\"",
"Another quote from the Wiki article:",
"\"Phosphenes can be directly induced by mechanical, electrical, or magnetic stimulation of the retina or visual cortex as well as by random firing of cells in the visual system.\""
] |
[
"Great, but that doesn't answer the question at all."
] |
[
"Of course it does. Stimulation of the retina by mechanical means causes the brightly glowing dots.",
"Mechanical means in this context is the shock from getting hit in the face. This causes the nerve cells in your eyes to fire even without light."
] |
[
"Antibiotic resistant bacteria are becoming an issue, why isn't research being done on bacteriophages?"
] |
[
false
] |
In my high school biology class, my teacher spent a week teaching us about bacteriophages, viruses that target bacteria, and how they could potentially replace antibiotics as a way to treat bacterial infections. Whya hasn't money been put into research on this? Is it unsafe? Is there some reason that it isn't liked by the medical community?
|
[
"they will have to design a phage that can evade immune response",
"And this, is a ",
" bad idea..."
] |
[
"Not only that, but if it can evade the immune system it can easily share that information with other virues/bacteria via ",
"conjugation.",
"I'm sure we can all see why teaching bacteria and viruses how to hide from the immune system would be a bad idea."
] |
[
"As far as I know, bacteriophage research IS being done. But the main reasons they are not effective as therapy is they will induce an immune response themselves and will be quickly cleared by the immune system. Bacteriophage therapy would either need to be taken multiple times each day, OR they will have to design a phage that can evade immune response."
] |
[
"Can someone explain why AC current fluctuates from positive to negative?"
] |
[
false
] |
My CNSA professor tried to explain it to me, but I just don't know why the electricity would flow differently based on where the coil is in its rotation (From 0 degrees to 180 and around to 360.). It has something to do with magnetic fields. When I compared it to (The wheel rotating in a circle while the strut moves back and forth.) he said it was a good comparison, however that's mechanical and I can't wrap my head around a magnetic field doing that to an electric current. I think I'm right on the brink of understanding it, but I'm just not thinking about it the right way.
|
[
"http://www.ncert.nic.in/html/learning_basket/electricity/images/machines/ac_generator.jpg",
"From the above diagram of an AC generator you can see that the wires are always hooked up in the same \"direction\" because of the slip rings. As the coil spins in the magnets the \"direction\" of the current changes. Using the right hand rule you can figure out which direction the current is going for all rotations of the coil.",
"When the current is going \"backwards\" up the wires we can say that the current is negative."
] |
[
"I hope you get an answer because it's always been my understanding that transformers are useless in a DC circuit. If the electrons aren't sloshing back and forth there is no changing magnetic field to induce current in the other/secondary coil, so a transformer effectively breaks the circuit and nothing happens."
] |
[
"It's my novice understanding that AC is used because it's easier to step up the voltage via transformers. Higher voltage means the same amount of power can be transmitted using less current, according to the formula Power = Voltage x Current. Less current means less resistance in the lines and therefore less power lost as heat.",
"Someone please confirm or correct me if I'm wrong. "
] |
[
"How can basic geometric shapes be manufactured from primitive tools?"
] |
[
false
] |
I have been trying to think up a way one could make things like spheres, planar surfaces, cylindrical columns, or cubes with the natural raw materials/tools of the earth (gravity, rocks, water, fire, plants, etc). I'm having trouble thinking of a method that doesn't leave it up to subjective observation and adjustment. Any thoughts?
|
[
"Use strings or cables of some sort. If you want a plane, stretch a piece of string (maybe animal gut or woven from fur or reeds) over an arched stick, the stretched piece of string will be almost perfectly flat, and you can use it to help you judge the flatness of a surface you are carving. If you want a circle, again, use string, and fashion a primitive compass. It's just a start, but a pretty good one. After that, it's up to you."
] |
[
"Additionally: loop of string, two fixed points (tacks on a plane): ellipse.\nString hanging down with something heavy attached: straight line, use it to make something firm and straight, a plank, for instance.",
"With plank and string, you have a ruler and a compass. All of classical geometry is in your hands. Triangles, pentagons, hexagons, 8,10,12,15, 17-gons etc.",
"Measure 3, 4, 5 units on your string, form a right angled triangle. Right angles. Create a Cartesian grid, apply formulas. Create as many points as you wish and interpolate additional points.",
"(Create a Cartesian grid on the ground, raise spikes according to z=X",
"Y. You now have a parabolic shape.)"
] |
[
"Can you elaborate on your question a bit? I'm particularly unclear on what \"leave it up to subjective observation and adjustment\" means.",
"But just taking a stab, if you're suggesting that it's possible to construct geometrically perfect macroscopic objects with ",
" tools, primitive or not, you're mistaken. It isn't."
] |
[
"How is it that people who can't speak a word of English can sing in perfect or almost perfect English"
] |
[
false
] |
As title says. I have been wondering this for awhile.
|
[
"You learn it phonetically. ",
"I sing the non-english parts of this ",
"song",
" all the time. ",
"Don't have a clue what any of it means."
] |
[
"Yeah, I can sing most of Rammstein's songs but I only know like 10% of the German language "
] |
[
"Sure they can.",
" "
] |
[
"Does gravity have a range?"
] |
[
false
] |
This might be a stupid question, but I'm curious about the range of gravity. When we say we are in zero gravity are we actully that or is the gravity forces just so low, that they have no practical effect? If there is a max range, how far should I be from an object with the weight of 1, before it would have no effect on me? If there is no max range, will the object furthest away from each other in the universe eventually be pulled together?
|
[
"Falling but missing."
] |
[
"No, gravity affects any object, no matter the distance. But at some point, it will not be noticeable at all.",
"When talking about \"zero gravity\", you probably mean a space station or something. First, usually the term is \"micro gravity\", and second, there is quite a lot of gravity out there. The astronauts don't feel it because they are in free fall around the earth. You can do the same in an airplane (costs you something like five grand)."
] |
[
"Orbit is freefall. Their velocity perpendicular to the direction of Earth's gravitational pull is such that they move around the Earth at the same rate they are falling towards it."
] |
[
"Is it possible to isolate the particles of a virtual particle pair?"
] |
[
false
] | null |
[
"Virtual particles should not be considered to be \"real\" particles, but it's complicated. The most obvious reason is that they don't need to obey the energy-momentum relation,",
"which all \"real\" particles have to by definition. But we can say more: When say two particles interact, their interaction is a terribly complex thing to deal with which usually cannot be solved for exactly. But we have a technique, called perturbation theory, which pull out the most important behavior and gives us an infinite sum of understandable terms each one capturing some aspect of the full interaction.",
"An analogy would be summing frequency modes that make up a complicated wave, or using a Taylor series to describe some function. So let's say we scatter two electrons off each other, ",
"https://en.wikipedia.org/wiki/M%C3%B8ller_scattering",
"you'll often see Feynman diagrams like these. The two electrons exchange a virtual photon and bounce off.",
"In certain situations, this single Feynman diagram captures almost all of the interaction. But it's not the entire interaction. What about exchanging two virtual photons? That diagram is included too. What about a virtual photon which has a little e+e- pair which briefly shows up before collapsing back into a photon? In real life, this diagram should be added as well. So if we scatter electrons, and you insist that virtual particles exist, then you must acknowledge that ",
" virtual particles exist is indeterminant.",
"The point is that the full interaction sums across all possible diagrams and the hope of perturbation theory is that as the internal combinations of virtual particles becomes more complicated, they become less important. So even if we need to sum an infinite number of such interactions, only the first few are needed to get the gist of the effect. This isn't always true, and thus nonpertubative approaches might be needed and in those techniques, virtual particles never actually show up.",
"Now with all that said, there is a mechanism to \"promote\" a virtual particle to a real particle. The main ingredient to accomplishing this is allowing the virtual particle to actually travel a long distance in space. The farther the particle has to travel to complete the interaction, the more \"real\" it has to be... and the closer to,",
"being true it has to be. This is really easy to interpret using Feynman diagrams, all you have to do is cut the diagram in half such that virtual particle lines now must become external lines. External lines are the observable particles. Another way of thinking about this is drawing the virtual particle line to be really really long. This is effectively the same thing where now the almost real internal particle leaves the 1st interaction to become the incoming line of a 2nd interaction. A physical example of this is star light being absorbed by your eyes. That photon has had to propagate such an incredible distance that it is indistinguishable from a real particle (you can say it's energy uncertainty from Heisenberg's uncertainty principle is basically zero). But nobody talks this way, we just call such photons real.",
"A more technical example would be the production of charm or strange mesons from hadron collisions. Such mesons (quark-antiquark pairs) which have charm or strange quarks inside them can be produced by photon-nucleon scattering. But there's an issue: nucleons only have up and down quarks. How do we produce the J/psi meson which has a charm and anti-charm if the ingredients (a photon and a proton or neutron) don't have these quarks? In a sense, when we make particles like the J/psi, we are \"making real\" virtual quarks. A similar argument can be made for when a photon scatters off an atom and produces an electron-positron pair. The virtual pair has been \"made real.\" This kind of language can be used precisely because we're taking what otherwise would have been a Feynman diagram with internal virtual particles and chopping it up so the internal lines must now be outgoing particles which are real. So to answer your question explicitly: If you isolate a \"virtual particle\" it is no longer virtual, but a real particle."
] |
[
"In the original paper, nothing was said about virtual particles.",
"What you need to know is that particles are actually vibrations in quantum fields, and black holes cut off some ways of vibrating, so other vibrational modes that were originally cancelled out now aren't, which means there are now particles."
] |
[
"Thanks for your excellent answer"
] |
[
"How do we know the exact age of the earth?"
] |
[
false
] |
When i searched online i found that the method used to calculate the age was radiometric-dating, but then we should only know that the earth is as AT LEAST as old as the oldest rock that was dated. where did the upper bound on Earth's age come from?
|
[
"Meteorites. The idea is that dating primitive meteorites allows us to date the time that the solar nebula began to condense to form planets and other rocky objects, thus dating meteorites give us a date for planetary formation (and not just Earth, all the planets). There are myriads of write-ups on this topic written for lay audiences, a reasonably concise one is from the ",
"USGS",
". The ",
"wikipedia entry",
", specifically the ",
"modern radiometric dating section",
", gives a lot more info.",
"You'll see there that numerous different meteorites have been dated and that some individual meteorites have been dated multiple times by different techniques. The age range that we get from all of this (4.53-4.58 billion years) is quite consistent and also consistent with alternative methods (e.g. calculations based on lead-isotope ratios in ancient lead ore bodies)."
] |
[
"Thanks for the explanation and the links, so if i understand correctly, meteorites are the building blocks of earth and all the other planets in the solar system and by dating it, we get the upper bound on the age of earth "
] |
[
"Earth Sciences"
] |
[
"How efficient are solar cells, compared to biological systems that collect solar energy?"
] |
[
false
] |
I realize this is kind of a vague question. Want I want to know is if we can ever replace solar cells with some kind of biological system that collects sunlight in a way like the cytochrome-like proteins do. Could you convert the chemical energy into electrical energy that we can use/harness?
|
[
"We already do this with power plants that burn biomass. The plants grow in the sun and we burn the plants. The chemical energy is turned into heat which powers a rankine cycle which generates electricity."
] |
[
"Unfortunately this is using dead plants or soon to be be burnt to a crisp plants and generates some pollutants. I'm thinking more a long the lines of a living system that we could tap in to without killing the cells.",
"Or maybe even just stealing the type of machinery cells use to collect sunlight and bypassing the living cells altogether."
] |
[
"Meh, as long as you can create the machinery that makes a proton gradient from sunlight, turning this into useful electrical energy seems relatively straightforward and could probably be made extremely efficient (you're just talking about an electrochemical cell).",
"Also improving on the inefficiencies of plants seems like it would be possible - we could engineer better pigments, or use a wider range, we could engineer denser structures than a plant cell so that absorption is more efficient, etc."
] |
[
"What is stress?"
] |
[
false
] |
This word gets thrown around a lot. What counts as stress? What exactly goes on to your body or mind when you are stressed?
|
[
"stress is a response to insults that can be mental or physical. Whether it's pain, starvation, psychological distress etc. It's basically the body's response to these stimuli which can disrupt homeostasis.",
"basically stress in the body activates the flight or fight response and releases hormones like cortisol (aka stress hormone). The hypothalamus can recognize these \"insults\" and through the hypothalamic-pituitary-adrenal axis release stress hormones and other chemicals that can help the body to deal with stressful conditions"
] |
[
"Stress can be a difficult term to define, but physiological stress would be the body's response to any factor (\"stressor\") that threatens the health of the body or has an adverse effect on its functioning e.g. injury, disease, overwork, worry or sense of danger.",
"The initial registration and processing of stress starts in the brain. When the stressor first is registered, the perception activates the amygdala which is associated with emotional processing. ",
"The amygdala then activates the hypothalamus which is responsible for the regulation of the autonomic nervous system and certain hormones. The changes of the body during acute and chronic stress can be contributed to two major sources: The sympathetic nervous system and the hormone cortisol (often known as the \"stress hormone\") which is regulated by the HPA axis.",
"The hypothalamus activates the sympathetic nervous system which is responsible for the fight-or-flight response through the activation of the adrenal gland (which in turn secretes adrenalin) and by secreting noradrenalin directly to certain tissues. This main purpose of the physiological changes of the fight-and-flight response is to tap into the body's energy reserves and make them available for use to supply the body with an extra energy rush in order to combat (or outrun) the stress. The sympathethic nervous system would be considered the main component of acute stress.",
"If the stress persists, the hypothalamus activates the HPA axis by secreting corticotropin-releasing hormone (CRH) to the pituitary gland which in terms secretes adrenocorticotropic hormone (ACTH) to the adrenal gland which then increases the secretion of cortisol. Chronic elevated levels of cortisol induces a series of long term physiological and psychological changes of the body which people perceive as being \"stressed out\"."
] |
[
"Stress is your body's way of responding to any kind of demand. It can be caused by both good and bad experiences. When people feel stressed by something going on around them, their bodies react by releasing chemicals into the blood. These chemicals give people more energy and strength, which can be a good thing if their stress is caused by physical danger. But this can also be a bad thing, if their stress is in response to something emotional and there is no outlet for this extra energy and strength. This class will discuss different causes of stress, how stress affects you, the difference between 'good' or 'positive' stress and 'bad' or 'negative' stress, and some common facts about how stress affects people today."
] |
[
"Is the range of gravity infinite? Is the Earth technically (but insignificantly) helping slow the expansion of the Universe? Or does each object's.. \"well\" have a finite range of what it affects?"
] |
[
false
] | null |
[
"In short, there is no absolute limit. However due to relativity and laws of causation there actually is a limit given by the speed of light. That is to say if Earth magically doubled in mass in an instant(t=0) observers at varying distances from Earth would feel the increased gravity a some time t>0 depending on how far they are from Earth. Thus there is some distance limit on the effect of gravity if you include time. This concept is actually the basis for the ",
" explanation of ",
"Gravitational Waves",
" ",
"."
] |
[
"obviously the universe can't expand fast enough for an object at a finite distance from earth to move away from it at the speed of light",
"Nope, that's exactly what happens. The speed at which two objects are pulled apart by expansion is proportional",
" to their distance, so if they're far enough, it does exceed the speed of light. The laws of relativity limit to a constant the speed at which an object can move within the universe, which we call the speed of light, but they do not limit the expansion of the universe itself. And the effect is actually big enough that there are visible galaxies, right now, that are being moved away from us faster than light. Although obviously, the light that we see from them was sent so long ago that back then they were still close enough to us that they were still moving away slower than light.",
" proportional at a given time, but the factor is gradually increasing, which is the famous \"acceleration\" of the expansion, if my understanding is correct."
] |
[
"This leads to a question I've never thought of before: obviously the universe can't expand fast enough for an object at a finite distance from earth to move away from it at the speed of light, but will the furthest reaches of the universe eventually approach such speeds relative to us? Will that affect how we interact with those parts of the universe?",
"I'm imagining looking at spectral data coming from an object moving away from us near light speed. Do we lose information? Or is it just compressed into a smaller bit of the light spectrum, limited only by our ability to measure it? ",
"Edit: I seem to have been confused about the c speed limit - while nothing can travel through space faster than c, there isn't any relativistic reason space itself can't expand at a rate faster than c. Thanks for clarification guys! I definitely could use a cosmology course."
] |
[
"How do we know that planets like Jupiter are composed entirely of gas and not rocky planets with a thick atmosphere?"
] |
[
false
] |
It seems like no planetary survey missions have attempted to plunge into the gas giants and return more detailed information than is available by terrestrial/space astronomy or flybys with probes. Is there a possibility our understanding of gas giants is incomplete? Would a rocky core be a necessary "nucleus" for gathering gas and forming these planets to begin with?
|
[
"A quick search of \"gas giant cross-section\" shows that Jupiter and other gas giants are often depicted as having a solid rocky or iron core. That matches my half-remembered college classes. And here's a paper that models the formation of gas giants as solid cores which then attract gasses",
"http://www.researchgate.net/profile/Satoshi_Inaba/publication/222648354_Formation_of_gas_giant_planets_core_accretion_models_with_fragmentation_and_planetary_envelope/links/004635347c1aecf91e000000.pdf",
"So we don't really think that planets like Jupiter are composed entirely of gas. However, to call them rocky planets with a thick atmosphere doesn't truly capture their nature. Their cores only take up a small proportion of their total volume. We know ",
" has to be the case because we can measure the volume of the planet (by seeing its radius through a telescope) and the mass of a planet (by observing its gravitational pull), and from those two things we can get density. The densities of gas giants are far too low for them to be solid rock most of the way through. Saturn is less dense than water!"
] |
[
"There's also a ",
"Wikipedia article",
" on \"mini-Neptunes\" or \"gas dwarfs\", which would be closer to the idea of a \"rocky planet with thick atmosphere\". It doesn't appear that they have been thoroughly proven to exist yet, but there's several detected exoplanets with mass and density values that seem to be in the correct range. "
] |
[
"Europe \n ",
"Do you mean Europa?"
] |
[
"Why am I allowed to pour acids into water but I'm not allowed to pour water into acids?"
] |
[
false
] |
This is a rule in our chemistry laboratory.
|
[
"To add to AgentAsterisk, the exothermic reaction caused by adding the water can cause the water to boil immediately causing a sudden expansion of gas; naturally a sudden expansion of gas would at least splash acid everywhere."
] |
[
"To add to AgentAsterisk, the exothermic reaction caused by adding the water can cause the water to boil immediately causing a sudden expansion of gas; naturally a sudden expansion of gas would at least splash acid everywhere."
] |
[
"What I find concerning here is that the student either did not ask the teacher why, or the teacher answered “because that’s how we do it”."
] |
[
"Why do we see the milky way as having a black strip running through it?"
] |
[
false
] |
I saw image on and couldn't help but wonder: why does the milky way appear to have a black stripe across it? I mean, shouldn't we see the center as a glowing ball? Is there something in front of it (a gass cloud, something else) or does it have a peculiar shape that is not easy to spot at first? edit: is how i see it now: the galaxy shaped like a sombrero, with the center being the bright ball in the middle, and the outlined blue part is the "black strip" edit2: thank you all for all the replies! I appreciate all your insightful answers and discussions; for anyone looking for a tl;dr, here it is: For more beautiful pictures and a little background info on the photo, check the Last but not least, thanks again for the info, and for those of you who I left out - I'm sorry. I can only recommend to anyone who wants more info to read all the coments in this thread. I love this community! Edit3: There are so many answers and discussions, I couldn't possibly fit all of them in the TL;DR, but I'll do my best. Details on some of the things in the list can be found in the comments of the respective thread
|
[
"The Milky Way's spiral arms are filled with dust. Our solar system is in a spiral arm. As we look toward the center of the galaxy, our view is obscured by this dust."
] |
[
"JWST will do exactly that. Unfortunately, it probably won't actually be that pretty - most of the cool pictures of galaxies are cool because of all the gas and dust lanes have interesting structure. If you can look through the gas and dust to only see the stars, you'll generally just see a smooth distribution of starlight..."
] |
[
"Just imagine how sexy it would be to be able to see the center of our galaxy without all that garbage."
] |
[
"Can talking parrots have accents like us?"
] |
[
false
] | null |
[
"Yes and no. Not in the way you probably mean and not on their own. \"Talking\" parrots imitate the sounds they hear, including speech. If the speaker they imitate has an accent, the parrot also imitates that accent. They don't create their own accent.",
"However, wild living parrots can apparently have some kind of ",
"regional \"accents\" in their \"native\" calls",
"."
] |
[
"Parrots and other types of birds that can be taught to speak are really just adopting sounds of human speech as their \"calls\". They technically aren't communicating in the language they're producing, just very accurately reproducing it. Only rare cases, like A",
"lex, the African Grey parrot who died some time ago",
"), ever demonstrated true comprehension.",
"Anyway, talking birds will speak in whatever accent they hear. It's just a matter of how well they've learned to mimic the original speaker that determines how clear that accent is. ",
"As a matter of fact, I'd say ",
"Myna birds",
" and ravens are better mimics than parrots."
] |
[
"Thank you!"
] |
[
"Why do coniferous trees only seem to proliferate in mountainous or northern environments?"
] |
[
false
] |
I live in the Eastern United States. The only time I ever see conifers or "pine trees" is at Christmas or in the occasional wild grove or landscaping area. Yet out west in the Rockies, British Columbia, and everywhere in southern Alaska, conifer forests dominate, even at low elevations. Why is this? EDIT: Thanks for your responses! Although, let me be clear, I am fully aware that coniferous forests exist outside of the regions I provided; my Dad's family grew up near the Pine Barrens of New Jersey. All I was saying was that in Alpine environments and Northern regions, coniferous trees dominate.
|
[
"Conifers can grow just fine in temperate climates, but they'll usually get outcompeted by those faster-growing broad leafed deciduous tree like oak, maple, etc. But they have adaptations which allow them to do much better in colder climates than their broad-leafed competitors: their sap contains antifreeze like compounds; their small, wax-coated needles are less vulnerable to damage from cold weather, and can retain moisture well when liquid water is in short supply; since they don't have to drop their leaves, they can \"wake up\" from their winter slumber and start photosynthesizing before deciduous trees even start to bud."
] |
[
"This, however I will add a few facts.",
"Most of them are adapted for conditions with short summers and long winters, making the waxy coating (water loss resistant) and design of the needle (wind damage resistant) a benefit. Because these needles are hardy, they don't shed much and take a long time to break down. Meaning they had to adapt to poor soil conditions that are usually high in acidity. That's why they are good for Northern Climates and areas that are rocky/windy (mountains).",
"Deciduous trees go through bursts in a season, shedding their leaves in the winter. They take advantage of longer summers with their large leaves and excessive nutrient cycling.",
"Then you have trees that are a mix of the two, like the Bald Cypress. It's a coniferous tree that sheds its leaves before winter. Interesting!"
] |
[
"There's also the whole can of worms of disturbance regimes, fire regimes in particular. In many places the very high density pine dominated forrest you see in the temperate regions west aren't completely natural.",
"Before Europeans came many of ",
" the pondersosa pine",
" forrest in the west were actually more savannah or woodland like. Traditionally, small, low intensity fires would burn every few years and cut back the understory killing all the pine saplings and grasses but leaving only the larger more established pines alive. This resulted in really patchy forrest with a mixture grasses forbs and small shrubs below ",
"like this.",
"Now, following 200 years of fire suppression all those pine saplings that would've been killed by fires have been able to grow into big trees too resulting in the really high density forests you are used to seeing ",
"High Density Forrest.",
"\nNow throughout the western US instead having these small low intensity understory fires every 10 years we have these massive crown fires that destroy entire areas.",
"Also here's a good visual on the \n",
"effect of fire suppression",
"."
] |
[
"Why do clones die so quickly?"
] |
[
false
] |
For example Dolly, or that extinct Ibex goat that we tried bringing back. Why did they die so quickly?
|
[
"Dolly the sheep didn't die from cloning related complications, and she lived a long enough life to give birth to 6 lambs. Ultimately she died of lung cancer caused by Jaagsiekte sheep retrovirus (JSRV), a virus that was infecting the rest of her herd. She was euthanized due to the tumors in order to prevent her from suffering.",
"People often think that because her life was about half of the expected length that cloning must have been responsible, but it turns out she just had some bad luck and got sick. Was she more susceptible because she was cloned? Perhaps, but her non-cloned herd-mates didn't really fare any better, so I don't think so.",
"edit: typo"
] |
[
"Hmm, most clones don't make it until birth, and there are numerous explanations, largely depending on how the cloning was undertaken.",
"Typically, as with your examples, a process called ",
"somatic cell nuclear transfer",
" is undertaken. In short, cells are taken from adult animal, the nucleus containing the DNA is carefully scooped out, is then inserted into egg cells, which are finally induced to develop. The trouble is, the DNA you're inserting has already aged, often considerably. Take DNA from a 12-year old sheep and insert it into a sheep egg and you can be said to have a '12-year old sheep egg'. The years only continue piling on after that.",
"To get into the details, there are two major influencing factors (amongst others):",
"We're all reasonably familiar with the basics of DNA. A DNA sequence represents a string of 'letters', or nucleotides, which encodes information - information used by cellular machinery to make stuff. Simple enough. However, on top of this genetic code there lies a secondary layer of annotation, which helps inform the cell when/where/why etc. to use the genetic instructions. This is the epigenetic code.",
"Think of it a bit like a Word document; the main body of text is your genetic code, and let's say this doesn't really change. ",
"Epigenetics",
" is akin to someone reviewing your document, and writing comments, corrections, annotations on the side. And this higher level of annotation changes considerably throughout your lifespan; arguments going back and forth between different reviewers, suggestions written then hastily scribbled out, bits of text highlighted in different colours. A big ol' mess you now have to untangle.",
"A developing embryo reading this annotation is going to struggle interpreting how it should proceed with understanding the main body of the text. It will do some things a bit early, it will do things a bit late, it might not do some things at all. Extremely few cloned individuals make it to birth for this reason, and those that do often continue to express problematic phenomena such as gene dysregulation, over- or under-expression etc. etc. ever after.",
"This 'aint no recipe for a healthy animal.",
"DNA in cells is typically organised into structures called chromosomes. I mentioned above DNA sequences encode information? Well, that's not ",
" true. Only a small fraction of your DNA actually does - the rest can have a whole buncha' other 'non-coding' functions.",
"At the end of your chromosomes, you have a section of some of this non-coding DNA called a ",
". The purpose of this telomere is to act as a buffer during DNA replication, which happens every time your cell divides, in order to protect the rest of your DNA, including all the coding regions, from accidentally being chopped off. Every time your cell divides, a little bit of this telomere is removed instead, until eventually they no longer remain and your cell divisions could start cutting into important coding regions. This is bad.",
"Embryonic stem cells are capable of preventing this telomere degradation. So, y'know, normal embryos start development with a lovely long pair of telomeres. In a cloned individual, they can often start development with a severely shortened set; and they'll only be getting shorter. As such, many young cloned animals are disproportionately more likely to suffer premature cell line quiescence or self-destruction.",
"As with a dodgy epigenome, this 'aint exactly great for their health either.",
"More recent advances in cloning technology have meant we can better deal with the above considerations, and we've successfully and sequentially cloned, for example, several generations of mice without any telomere length loss. It tentatively looks like it kinda' depends on which tissue you got your original sample from. Likewise several epigenetic barriers that impede cloning processes are in the process of being overcome.",
"Cloning is slowly but surely becoming increasingly viable. Maybe we can try again with the ",
"Pyrenean ibex",
", who knows?",
" ",
" ",
" ",
" ",
" ",
" ",
" To clarify, this was intended as a broad explanation for the difficulties rearing cloned animals to adulthood historically and ",
"; none of this was written with respect to, nor applied to, Dolly herself, beyond perhaps the tangential fact she was the lucky 1 in 277 attempts that successfully navigated the challenge of epigenetic reprogramming to reach birth. Until, of course, she was unlucky. RIP, gal."
] |
[
"Her offspring is doing just fine! Four of them have lived to be 7-9 years old or 60-70 in human years. Proof that clones can live a normal healthy life. ",
"-Source-"
] |
[
"How many plants/trees would it take to sustain one average person's O2 needs and vice versa?"
] |
[
false
] |
As an example, Sandy from Spongebob Squarepants lives in a dome with a tree... How much foliage would actually be required to keep a healthy O2 level?
|
[
"Here an ANL scientist answers the question: How many plants are needed to make enough oxygen for one person for one hour? We are experimenting with Anacharis plants.",
" Check out the link, but the end result is: \"these are round figures, let us just say that between 300 to 400 plants are needed to produce enough oxygen to keep a person alive in an hour.\" I didn't think it would be so large!",
"Also, if you know the number of plants are needed to produce enough oxygen to replenish the O2 consumed by the average person then you know the answer to the second question you ask. "
] |
[
"That link isn't quite correct in the assumptions. Not 100% of oxygen we breathe in is converted to CO2. Humans actually only use 5-7% of the 21% oxygen we inhale, exhaling a mixture that contains ~14-16% oxygen. This reduces the number of plants one needs by a factor of four, so closer to 80-100."
] |
[
"By vice versa, I meant CO2 from the person to the greenery"
] |
[
"What is meant by the following statement which appeared in a physics article yesterday regarding the diphoton hangover? \"The absence of new particles almost certainly means that the laws of physics are not natural in the way physicists long assumed they are.\" [link in comments]"
] |
[
false
] |
I have an engineering degree level of physics understanding and am not religious so there is no need to address concerns regarding physics possibly being "unnatural".
|
[
"The article does explain what this means, in the \"Missing Pieces\" section. But I'll give it a go too.",
"The miracle of physics is that in everyday life we don't need to understand how Nature behaves at energies much higher or distances much smaller than we're interested in. So to study fluid dynamics you generally don't need to know that the fluid is made up of atoms, and to study chemistry you typically don't need to understand that protons and neutrons are made up of quarks. The way physicists say this is to call these sorts of theories ",
" (or often effective field theories, or EFTs). This means that they're not a fundamental description of Nature, but at certain energy scales they're valid to good approximation. Then, when you go to higher energies, the effective theory loses its validity and you need to understand some different, more fundamental physics in order to make heads or tails of things.",
"This isn't to say, though, that effective theories lose all knowledge of the fundamental theories from which they descend. The higher-energy theory leaves its imprint in the ",
" of the effective theory. In particle physics, an effective theory typically comes from ignoring all the types of particles heavier than some cutoff mass M. Then, roughly speaking, the effective theory is valid when you're considering energies E < Mc",
", since then you'll never excite those heavy particles in any physical process. But those heavy particles do contribute a background of sorts, especially since quantum mechanics tells us that ",
" of mass M can show up in interactions. So if you change the properties of those heavy particles, you'll change the free parameters of the effective theory as well.",
"Which heavy particles are we ignoring? That's speculative, but at the very least there should be new physics at the Planck scale, where our current theory of gravity (itself an effective field theory) breaks down, suggesting there should be new particles with masses around the Planck mass.",
"So how do the heavy particles influence the free parameters? Roughly speaking they try to drive those parameters up to their own mass. I'll give you a simple example with the Higgs. The Higgs has a \"bare\" mass, which is a number you're free to put in your equations. But the Higgs also should couple to heavier particles (if it doesn't, we'd need to explain why), and some of its interactions with those heavier particles can mimic a Higgs mass. You can think of it as the Higgs having to \"swim\" through a sea of heavy particles, increasing the mass we measure. That mimicked mass would end up being similar to the mass of the heavy particles.",
"The naturalness problem is then why the Higgs is so much lighter than the Planck mass - about 10",
" times lighter, to be precise! There are a few possibilities. One is that the bare mass just so happens to almost, but not exactly, cancel out the mass it gains from coupling to heavier particles. That would be really bizarre, though: it would require cancellation out to about 17 decimal places! There's nothing to say this is impossible, but if we see a 17-decimal-place coincidence, it would obviously cry out for a better explanation. A popular alternative is supersymmetry, in which these heavier particles come in pairs, and each member of the pair makes an opposite contribution to the Higgs mass (e.g., for every particle increasing the Higgs mass by M, there's another particle ",
" it by M), so the bare mass (which is a free parameter) is the physical mass. Unfortunately, SUSY doesn't seem to be doing so well right now, and that's what's causing a lot of angst. There are a whole bunch of other solutions too, although we're getting to the point where I can't really comment intelligently on many of them!"
] |
[
"I love this response because I know very little about the field and you have explained it to the point that I understand. Thank you for this. :)"
] |
[
"Thanks, that made my day! :)"
] |
[
"Is drinking artificially sweetened, carbonated water, in any way, less healthy than plain tap water for daily hydration needs?"
] |
[
false
] |
Is there any reason why someone might want to avoid drinking products like Fruition, which is just artificially sweetened and flavored, carbonated water, as a substitute for plain water? Does the body have to "work harder" to extract the water or are there any health hazards associated with the extraction of the CO2 from the water, e.g., kidney stones, etc?
|
[
"The body couldn't work harder, since water is absorbed passively as far as I know. But since sugar/carbohydrates bind water (as do electrolytes and alcohol and many other things), you won't get as much hydration from sugary (or salty or alcoholic) water than from the same amount of pure water.",
"I can't imagine carbonation having any significance. Your stomach acid is far more acidic than carbonic acid, meaning virtually all the dissolved CO2 will turn to gas and escape out your esophagus once it reaches your stomach. (and indeed, carbonated drinks tend to induce burping). ",
"Not that I'd expect it to matter even if it wasn't, since your body is full of CO2 and carbonic acid anyway; interconverting the two is one of the main ways your body regulates its pH."
] |
[
"Great, thanks. That's what I was hoping would be the case."
] |
[
"Coke is artificially sweetened, carbonated water. Why wouldn't you drink that?"
] |
[
"How is it that I sometimes see the most spectacular pictures of the milky way, but when I am i a desolate area I never see anything remotely like it?"
] |
[
false
] | null |
[
"Aloha from the Big Island of Hawaii where I am currently sitting in one of the worlds largest optical/IR astronomical observatories.",
"First, as you have already pointed out - long exposure times are used to get the detail we need. The other day we were observing Messier 15 and the exposure times were on the order of 130 seconds. Other objects (fainter and further away) may have exposure times in the hours.",
"Second, lots of the pictures you see are composites of different wavelengths (IR, Optical, XRay, Radio, etc) and colored to make the different frequencies more obvious to the eye.",
"Third, dust... the universe is FULL of dust and most of it obscures our ability to observe. Again, filters, time, and different frequencies are employed to see through that dust.",
"Forth, light pollution. On our island we have specially colored street lights that the observatories filter out of their images (though that is no longer as important as it used to be). Also, our mountain, at 13,976 ft is VERY high - where as most of the towns are at sea level. ",
"Finally, we are isolated from land in all directions by more than 2000 miles of pacific ocean (though the lights from Honolulu/Oahu can be detected by the instruments). ",
"Basically put - come here to the summit and look at the milky way and you will be amazed."
] |
[
"You will never see it as clear as in that picture. As someone who frequently does night photography, cameras will not only show details better, but will also render colors more vividly as humans don't have good low light color perception. ",
"Also, that picture is heavily edited. It would look quite diffrent in person."
] |
[
"You may be in the wrong hemisphere. The southern hemisphere gets a much clearer shot at the milky way than the northern, as the south pole points at the center of the galaxy, where you get those nice dense-looking clusters, and the north pole points away from it. "
] |
[
"Why does the equilibrium constant change only when temperature changes?"
] |
[
false
] |
[deleted]
|
[
"You have two reactions, one going A -> B, and the other going B -> A. The more A there is, the faster reaction 1 goes. The more B there is, the faster reaction 2 goes. This reaches a point where 1 is happening as fast as 2, so there is no net change in amounts of A and B. The equilibrium constant is the ratio of the two rate constants and can be used to find the equilibrium concentrations. The idea of trying to reverse any changes simply arises from the fact that in these reactions, an increase in A encourages the reaction which gets rid of A. ",
"The reaction rate constants may change in different ways due to temperature, so the ratio (Keq) may change. "
] |
[
"When you change the temperature you change the relative stability of the products and the reactants. The thing is though the relative stability does not change equally. As temperature goes up the product stability might increase at a slower rate than the reactant stability and as a result the equilibrium will shift toward the reactant side because that product becomes increasingly more stable."
] |
[
"Partial pressures are another way of talking about concentrations for the gas phase. There's no magical reason why the pressure has to stay constant (you could pump inert gases into the container and raise the total pressure), but if you increase the partial pressure of a reactant, the reaction rate for getting rid of it will also increase. "
] |
[
"Why don't meadows have bushes/trees like the land that typically surrounds them?"
] |
[
false
] | null |
[
"There are several causes for lack of trees. ",
"The meadow may just be in an early successional state where trees haven't grown back yet. This would be due to a disturbance like a fire or landslide that killed the trees that had been there previously.",
"The meadow could be growing in a location where the environmental conditions don't support tree growth but do support grasses. There could be a lack of water, the soil maybe very shallow, or the wind might be too extreme for trees.",
"It's also possible for grazing animals to keep growth low, so only plants that can come back from the roots like grasses will persist over time."
] |
[
"A biologist friend of mine loves to point at the boundary between trees and grassland and say “see that? That’s a war zone.”",
"Trees evolve inhospitable toxins in their leaves that they drop on the ground below, and ally themselves with fungi in the ground that make it hard for grass to grow. Similarly, grasses evolve abilities to break down the toxins and have their own alliances with fungi. It’s an evolutionary arms race for territory, and the boundary between trees and meadows is the front line. ",
"At least that’s the narrative explanation. I’m sure there’s a lot more to it than that."
] |
[
"This is supporting what you've said, but there's an interesting case in the Allegheny National Forest. ",
"Prior to the NF being created, the area had been clear-cut from a ~300 year old forest (the 300-year-old forest had grown back after a major wildfire). Once the national forest was created and they started managing tree growth there, they discovered that there were sections where the forests didn't grow back. ",
"The problem was the water table: once the trees were gone, the water table rose in these areas, and made them inhospitable to trees. The meadows have been gradually getting smaller as the trees at the edges make headway against the water, but it's a century-scale process."
] |
[
"What makes stainless steel \"food grade\"?"
] |
[
false
] |
Maybe some simple questions, but what makes stainless steel so good for food processing? Is it possible to do something to an old stainless piece of equipment to make it "food grade" again? What if the equipment was previously used in medical/hazmat/industrial settings? Does that matter? I see from "The most widely used austenite steel is the 304, also known as 18/8 for its composition of 18% chromium and 8% nickel." What makes that particular ratio of metals great for working with food? Why is 304 stainless steel better for food grade applications than other stainless steel?
|
[
"Food plant mechanic here. 316 is typically used where direct contact with food is required. Incidental contact areas like machine frames are typically made from 304 or 308 because it is cheaper. 316 is incredibly stable and corrosion resistant. 304 is similar, but not of the same quality. Some minor corrosion can occur. ",
"I also use it to make fountains and artwork that is exposed to chlorine. 304 will dissolve in such environments."
] |
[
"I assume it is because 316 SS costs more to manufacture. "
] |
[
"You can use whatever stainless you want. The worst that could happen is that you will get a little corrosion (rust) with a less corrosion-resistant steel. Fortunately, a little rust never hurt anyone. Cast iron rusts like crazy, and has been used safely in cookware for centuries."
] |
[
"Why doesnt AIDS burn itself out?"
] |
[
false
] |
[deleted]
|
[
"First, you need to make the distinction between AIDS and HIV. HIV is the virus that causes AIDS. AIDS is the state of immune deficiency caused by the HIV virus. People can be HIV positive for years or a lifetime and never developed AIDS, which is defined as having fewer than 500 CD4 cells per microliter of blood. Once a person's CD4 count drops that low, if it continue to drop, a person will die of opportunistic infection LONG before their CD4 count reaches 0."
] |
[
"What the other answers missed is that HIV-1 does ",
" do that, i.e. run out of cells to infect. When this happens in late stage disease the virus can undergo what's called a tropic switch. ",
"Almost all HIV-1 infections start out using the CCR5 coreceptor to infect T cells. But CCR5 is only found on a fraction of T cells, so HIV cannot efficiently adsorb (not absorb) to most T cells. ",
"As the virus runs out of cells to infect it can sometimes switch to using CXCR4 coreceptor to infect T cells. This coreceptor is on the majority of T cells, but CXCR4 HIV-1 is a better target for the immune system and also very inefficient in infecting new hosts. CXCR4 virus is therefore associated with later-stage disease. "
] |
[
"state of immune efficiency",
"You mean deficiency?"
] |
[
"How similar is mitochondrial DNA across species compared to the actual DNA of the species?"
] |
[
false
] |
I know that nearly all eukaryotes contain mitochondria in their cells, and that similar species share large portions of their genetic code, so this made me wonder - how similar is the DNA of mitochondria across species? Is the DNA of my mitochondria closer to chimpanzee's mitochondria than my DNA is to a chimpanzee? How close is my mtDNA to single celled organisms? Thanks.
|
[
"Mitochondrial DNA (mtDNA) contains some of the genes that are necessary for the oxidative phosphorylation that occurs inside mitochondria (genes such as ATP synthase, NAPH dehydrogenase, among some others). Since these genes are important for any organism that relies on oxidative phosphorylation (the process of slowly moving electrons to molecular oxygen and harnessing the energy to make ATP), then one would expect there to be a certain degree of similarity in the mtDNA across species. ",
"However, the mutation rate of mtDNA is higher than the mutation rate of nuclear DNA, which means that even within a certain species there is a lot of variation. This is medically relevant for humans in the form of mitochondrial diseases. People who have mutations in their mtDNA sequence have lower energy than most people. The brain and muscle are most severely affected. One specific example is Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (",
"MELAS",
"). These diseases are inherited through the maternal germ line, as is all mitochondrial DNA. Mendelian inheritance does not apply to mitochondrial DNA, which is why we can use mtDNA to trace lineages back in time from mother to mother. ",
"Finally, the mtDNA sequence within one organism can differ from cell to cell, and even from mitochondria to mitochondria. Once again, this is due to the higher than average mutation rate in mtDNA. This is called somatic mosaicism and is commonly found in other genetic disorders. An embryo that gets a mtDNA mutation in tissues that go on to form the brain or muscle will be worse off than an embryo that has the same mutation that is localized to the skin or other low-energy tissues. ",
"Source: I am a first year medical student at a US school and we just learned about mitochondrial genetics."
] |
[
"At this point is pretty much a fact. "
] |
[
"Er, chloroplasts, as well as all other plastids."
] |
[
"Voyager 1 is about to be the first man-made object to leave our solar system. Couldn't we just send a probe out orthogonal to the plane of our solar system in order to enter interstellar space faster? Why haven't we done this?"
] |
[
false
] |
Just wondered about this after reading the other thread about Voyager I. Thanks.
|
[
"One of the advantages of flying within the solar system is the possibility of gravity assists. These allow a spacecraft to speed up without spending too much fuel. If we wanted to launch a probe orthogonal to the plane of the solar system, it would have to rely on its own propulsion only.\n",
"Brief description of gravity assists included on Voyager mission page"
] |
[
"Ah that makes sense. After posting I also realized that we probably wouldn't want to waste the opportunity for close fly-bys/observations of most of the other planets in the solar system on the way out."
] |
[
"I had a similar question from that same thread.",
"Could we not attach a rocket to the probe, and circle it around our planet to pick up speed by gravity, then fire up the rocket to break out of orbit and continue into space, with the rocket still burning giving it more propulsion, and I assume that it would maintain it's speed unless it hit something or other circumstances affect it? e.g gravity from a meteor, so if it were going faster than Voyager 1, with a similar radioactive fuel system to power the instruments, would it not last longer, and be able to send more data about our solar system back to Earth and travel further into interstellar space?"
] |
[
"Why are there complex secure deletion algorithms with multiple passes when I can simply write 1's or 0's to my data?"
] |
[
false
] | null |
[
"To answer this, it is necessary to make a distinction between the abstract service which a computer presents to its users (which is digital in nature) from the physical implementation (which is analogue).",
"So far as the abstract machine is concerned, once you have overwritten it with zeros then the data is irrecoverable. There are a few caveats to that statement. In particular:",
"However provided the software or firmware doesn't get in your way, at a digital level zeroed is zeroed.",
"The physical implementation is a different matter entirely because bits are represented by a voltage, charge or flux that (to a reasonable approximation) can take a continuum of values. Overwriting with a zero only needs to take that physical quantity above or below a particular threshold to make it into a one or a zero, and in many cases the physical value after zeroing will depend to some extent on the value it had before it was zeroed.",
"That's not to say that recovering data under these circumstances is necessarily going to be easy, but if you overwrite with random data a few times before zeroing then you can make it much more difficult."
] |
[
"Solid state drives typically store data as a charge on a floating gate, and do suffer from data remanence.",
"However, as I indicated above, there is a bigger problem if you try to zero it because there will usually be a storage controller between you and the flash chip, and the controller is likely to implement wear levelling.",
"This is generally a good thing, because it allows you to use an ordinary filesystem on the drive without having to worry the fact that it is an SSD (otherwise you'd need an MTD-aware filesystem like JFFS2). However it does mean that each time you write to a given logical block number, it is likely to be mapped to a different physical location on the flash chip.",
"This makes reliable erasure of the drive as a whole very challenging, and selective overwriting pretty much impossible through ordinary write operations."
] |
[
"From what I remember Secure erase is to completely remove any of the original bias. Normally the device only reduces the charge to below threshold but doesn't completely discharge it. This means that it can still be read with the right equipment. ",
"This sort of thing is used on all types of memory and even some displays to remove image retention."
] |
[
"What was the most powerful volcano ever known to mankind?"
] |
[
false
] | null |
[
"Mason et al, 2004",
" provide a review of the largest explosive volcanic eruptions, their ultimate goal is to understand the frequency of eruptions of different size (it is worth noting, this compilation focuses on explosive eruptions, so thinks like ",
"Calderas",
", as opposed to systems like ",
"Large Igneous Provinces",
" which produce much large volumes of lava, but are not explosive generally). In their compilation (and more generally within volcanology), they classify size principally by the amount of material ejected as opposed to total energy released (partially because the amount of ejected material is a more direct / less biased measure as we can go and physically estimate this volume for ancient volcanoes). Within this framework, the eruption of the ",
"Fish Canyon Tuff",
", erupted from the ",
"La Garita Caldera",
" ~28 million years ago, was the largest explosive eruption on Earth. ",
"Now, to compare this to energy release, we'll use the estimate they provide in Mason et al, specifically that for a rhyolitic eruption, the amount of energy released is 1-1.2 MJ/kg of erupted rock (they go through the details of how they arrive at this conversion on page 744). The mass of the Fish Canyon Tuff is 1.8 x 10",
" kg (from table 2 in Mason, using the adjusted mass) so applying the conversion (and using a middle value of 1.1 MJ/kg) would imply an energy release of 1.98 x 10",
" MJ. So, how does that stack up to nuclear explosions? ",
"Little boy",
" released 6.3 x 10",
" MJ of energy, ",
"Fat Man",
" released 8.8 x 10",
" MJ of energy, and the ",
"Tsar Bomba",
" released 2.4 x 10",
" MJ of energy. So, for those keeping track at home, this would mean that the eruption of the Fish Canyon Tuff represented approximately the equivalent energy of exploding 3.14 x 10",
" Little Boys, 2.25 X 10",
" Fat Mans, or 8.25 x 10",
" Tsar Bombas.",
"If you want to restrict this to eruptions that occurred while humans existed, the next one on the list (the eruption of ",
"Toba",
") occurred around 74,000 years ago. The conversions for that are 1.2 x 10",
" Little Boys, 8.63 X 10",
" Fat Mans, or 3.16 x 10",
" Tsar Bombas."
] |
[
"If you're looking for recorded history, you probably want to look at ",
"Krakatoa",
".",
"Some highlights:",
"Ships as far away as South Africa rocked as tsunamis hit them, and the bodies of victims were found floating in the ocean for months after the event. ",
"In the year following the eruption, average Northern Hemisphere summer ",
"temperatures fell",
" by 0.4 °C (0.72 °F)."
] |
[
"Even something like a small hurricane generally releases more energy than a nuclear weapon! Nature is real crazy.",
"https://earthobservatory.nasa.gov/features/Hurricanes"
] |
[
"Why does fire change colour with certain chemicals inside it?"
] |
[
false
] | null |
[
"The color represents electron transitions between orbitals on the vaporized material (i.e., the fuel, the combustion byproduct etc.) Different materials have different energy levels for their electrons. The transition between these levels produces unique wavelengths of light. Taken in aggregate, these are the colors you see in the flame. "
] |
[
"Is \"different energy levels\"a fancy way of saying hotter or colder? I have always thought the color was indicative of the amount of heat. I.e. Blue flame hotter than yellow flame. "
] |
[
"Imagine the atom as a roundabout (or traffic circle, whatever) with multiple lanes that the cars can never leave. There are different amounts of cars in each lane and they go at different speeds. When some cars decide to go faster, they have to use more energy and move to a more outside lane. Eventually they can't keep this speed up and move back to their original lane. To do this, they put their blinker on. ",
"In this metaphor the cars are electrons and the roundabout is the electron cloud. The electron cloud is divided up into levels, with the lowest energy electrons in the center near the nucleus and the highest on the outside. When electrons get more energy, like through heat from a fire, they get excited (yes that's the technical term) and jump up to another energy level. They eventually release this energy as a photon of light and move back down to their previous energy level. Depending on the type of atom, the photon is moving at different speeds, creating different colors of light. ",
"At different speeds, the wavelength of light (as light can be described as both a particle and a wave, I know it's weird) looks different to us. Red is the slowest and violet is the fastest. That's why most regular fires are red and orange, they have the least amount of energy. Blue fire is extremely hot and has a lot more energy. ",
"This is grossly oversimplified, mostly about the energy levels because we don't use that model anymore, but the theory behind it is the same. I hope this helped! If you have any questions about anything just ask! "
] |
[
"Special relativity from multiple simultaneous perspectives?"
] |
[
false
] |
: Due to special relativity, if one atomic clock is on a space-craft moving very quickly (closer to the speed of light I suppose), and another atomic clock is on the planet standing still, the time on both of them will appear different. : How does this reconcile with multiple points of view of the same phenomenon? For example, if there are three points of perspective, A, B, and C. If each point of perspective watches the space-craft travel from a different vantage point, and then they all compare their notes to the actual data on the atomic clock from the space-craft, what will happen? Assume perspective A is at a fixed point behind the space-craft, perspective B is at a fixed point in front of the space-craft, and perspective C is at a fixed point to the side of the space craft. Once the space-craft is done traveling, wouldn't they all have different experiences due to the space-craft moving in different directions relative to the direction/speed of light? Due to the varied viewing angles, the light should behave differently and have a slightly different perceived speed from each vantage point, shouldn't it? For example, wouldn't the clock on the space-craft be faster than the clock at one vantage point, but slower than another? Yet if all the three vantage points were fixed relative to each other, how could they reconcile their data?
|
[
"In order to explain time dilation, let me fist explain what it is ",
". A popular, but entirely wrong notion of time dilation states, that time passes slower the faster you move. A quick examination of this claim, however, reveals that it cannot be true. There is no absolute velocity, so velocity only makes sense with respect to a frame of reference. That means, velocity only makes sense if we state relative to what we are measuring. Thus, if this version of time dilation were true, time on your spaceship would magically speed up and slow down depending on the frame of reference you measure your spaceship's velocity against. Thus, the statement that the rate at which time passes depends on your velocity (relative to an arbitrary frame of reference) cannot be true. ",
"Thus, ",
"Now, let's get started with actual time dilation: ",
"To understand how time dilation can happen, let's consider the following thought experiment:",
"A clock is any object that does an action periodically. As such, a light beam bouncing off two mirrors can be considered a clock, with each period of the photon bouncing up and down again being one tick. ",
"Let's now consider a train with such a clock in one of the compartments, as seen ",
"here",
".",
"Imagine a person in a resting train with a flashlight. They shine the beam of the flashlight to the ceiling of the carriage and time how long it takes to return to them. Very simply it is just the distance the light travels (twice the height of the carriage (d)) divided by the speed of light (c). Someone on the embankment by the train will also agree with the measurement of the time that the light beam takes to get back to the person with the torch after reflecting from the mirror.\nThey will both say that the time (t) is 2d/c.",
"Now consider what happens as the train moves at a constant speed along the track.\nThe person in the train still considers that the light has gone from the torch, straight across the carriage and returned to them. It has still traveled a distance of 2d and if the speed of light is c the time (t) it has taken is 2d/c. ",
"However to the person on the embankment this is not the case.\nFor them, the train has been moving during a tick of the clock, and the photon has to travel a longer distance accordingly. Instead of a straight vertical path up and down, the photon now follows a triangular path, like ",
"this",
". As we know, the beams of a triangle are longer than the straight line, so the photon now has to travel a longer path.",
"\nNow in classical physics, pre relativity, we would now say that since the light beam has moved further in the same time it must be moving faster, in other words we have to \"add\" the speed of the train to the speed of the light. ",
"But the theory of relativity does not allow us to do this. It says that the speed of light is constant. Thus, the photon will take longer to reach its destination from the point of view of the observer on the embankment. Hence we know that it takes the photon longer to complete this journey from the point of view of the observer on the embankment than it does from the point of view of an observer resting in the train. And we know that the time it takes the photon to complete its journey up and down again corresponds to one tick of a clock. Thus, it follows logically that the observer on the embankment sees clocks on the moving train as ticking slower than someone resting in the train. Which is exactly what special relativity is all about. ",
"The first thing we need to know for the twin paradox is, that acceleration ",
" absolute (or, in physics jargon, Lorentz invariant). That is, ship A accelerating away from ship B ",
" to ship B accelerating away from ship A in the opposite direction. A way to get an intuitive understanding for this fact is, by remembering that we can feel acceleration. ",
"We further need to know that one of the central claims in special relativity is, that all inertial (that is, un-accelerated) frames of reference are equally valid to describe a phenomenon. That is, the laws of physics are the same in all frames of reference that are not being accelerated. This is called the equivalence principle. ",
"Consider an inertial frame of reference I and another inertial frame of reference I' that moves at a constant velocity v relative to I. Time dilation states, that an observer O resting in I will measure clocks resting in I' as ticking slower than their own clocks. ",
"According to the equivalence principle, the same statement has to be true for an observer O' resting in I' as well, since they are both in inertial frames of reference. Thus, the observer O' resting in I' sees clocks resting in I as ticking slower than their own. ",
" ",
"\"But wait\", you might interject at this point, \"what about the ",
"twin paradox",
". The twin making a trip to space ages less than the twin remaining on earth. Doesn't that contradict what you are saying?\"",
"While that seems true on the first glance, this is actually not a contradiction. In order for the twin paradox to work, the twin traveling in the space ship has to return to earth. In order to do that, he has to change direction at some point. This change in direction implies acceleration, and acceleration breaks the symmetry of the problem. Remember, that we stated that all ",
" (un-acclerated) frames of reference are equal. By accelerating, the space traveling twin breaks the symmetry of the equivalence principle, thus leading to the observable difference in passed time."
] |
[
"The two observers would not agree about the distance traveled due to length contraction."
] |
[
"That's actually the core point of special relativity - that events do happen at different times and in different locations from different frames of reference. For instance, when a space-craft is moving quickly away from Earth, Earth sees the clocks on the space-craft as ticking more slowly. But from the space-craft's point of view, it's Earth that's quickly moving away from the space-craft, so they see the Earth's clocks as ticking more slowly.",
"Note that you end up finding contradictions if you ",
" consider time dilation. However there is another term - a \"break in simultaneity\" term - that is also important. Including this factor makes everything add up and remove any real contradictions. This is part of what resolves the twin's paradox. Although the Earth and the space-craft both see each other as time-dilated, if the space-craft turns around to return to Earth, the \"break in simultaneity\" term starts to come into play, and makes sure that they both agree that the space-craft returns at the same point in space-time, and both agree that the clock on the space-craft has ticked less."
] |
[
"Is it possible to edit the contents of a hard drive without using a computer?"
] |
[
false
] |
Like, is there any way a person could change, add or delete files with relative precision on a hard drive without going through any kind of system? I'm not talking about microwaving a hard drive and destroying everything. I'm wondering if selective, relatively specific changes can be made to digital storage devices without using software. If they can, is that change detectable or recorded in any sense?
|
[
"This would not be practically possible for multiple reasons.",
"Even if you somehow had a way of physically making the kind of physical changes with the incredible precision that a software-assisted hardware is able to do when storing information, a person would still have to know how a file (or anything meaningful to you and me) should be encoded \"in ones and zeros\" for an operating system. This is so complex and the amount low-level information that is stored in a hard drive would make this impossible in the sense I believe you mean in your question.",
"Here is an approachable article",
" about the history of storage media in computing. You can kinda start to see in a visual way the evolution from something that is tangible and usable by a human towards something that needs specialised hardware and software to be used. You can easily imagine that people familiar with punch cards could \"edit\" them on the fly without needing a specialised encoder (maybe for changing some value or fixing \"typos\"), but the complexity quickly gets out of hand as you progress to more advanced storage media and more general-purpose computing."
] |
[
"The real problem is the scale of the storage devices. Suppose you sit down to read through the contents of a modest 500 GB hard drive at 200 bytes per minute, which is probably a pretty fast pace for someone reading and trying to understand binary opcodes.",
"You finish in 4,756 years. The human brain is an amazing machine but it's not a SATA controller. "
] |
[
"As far as I can tell, the answer would be \"maybe\". ",
"As in, it's physically possible in a way. But that would require four things: one, a custom-made machine capable of accurately targeting the individual bits on the hard disk drive, with the hand-operated controls to trigger specific bits. (So, for all intents and purpose, a hand-controlled disk and arm controller). Two, the knowledge of the \"alignment\" of the disk - or, in a way, the \"map\" of where each file is saved on the physical disk. Three, the knowledge of the data structure that's on the hard disk drive so that it can be edited properly. And four, a non-intrusive indexing so that the human operator can know exactly where he's at. ",
"So, basically: With absolutely no electronics, it's like trying to hand-punch an old software punch cards (the ones you inserted in computers to be read) on cards that have a worn out grid that you can't see anymore. Also the holes need like to be, right next to each other. And you need to operate the hand punch with BBQ tongs. Or alternatively, it's like throwing a one-inch square dart into a 1.001 inch square hole, in a glass pane, at 400ft, with an overhead pitch that was done with your non-dominant hand. Repeatedly. Also you can't see the hole. ",
"With non-computing electronics? It's actually PROBABLY possible. I'm far from being an expert, but it might be possible to build a device that safely houses the disk, detects the bits and sectors, and has buttons to go next/previous bit, and switch it to 1 and 0. It's still, of course, extremely slow - let's take for example this text file I have here. It's a small text file - only shows up as 1kB in size, because it only has 205 characters in it. That's one kilobyte of data according to Windows (probably rounded up, but let's ignore that for the sake of this). One kilobyte is 1024 bytes. One byte is 8 bits. So, to recreate that small text file, it is 8192 characters. Assuming you're a prodigy and can set 10 bits per second, it's still 819 seconds - just about 14 minutes. And god forbid you try anything larger...",
"So, TL;DR: Is it possible? There's nothing saying it isn't, so it is almost certain to be possible - especially on older hard drives, as in I can see it happening on an old RAMAC 305, if human accuracy allows it. It's just not exactly practical. "
] |
[
"Does the diffusion of different substances in a solution depend on the other substances?"
] |
[
false
] |
I am studying cellular biology; specifically, diffusion involving cellular membranes. Thanks!
|
[
"Diffusion expert here about to embarrass myself while sleepy. The answer to your question is yes, always. However, often the effect of solutes on each other is so small that there is no harm in ignoring it.",
"To determine whether you can ignore the effect of different solutes on each other, you need to understand the ways in which they might meaningfully interact and the calculate, measure, or estimate the probability of such an interaction event occurring to a particular solute atom/molecule. A not very instructive example calculation follows.",
"The simplest example I can think of where these interactions might matter is sodium ions interacting with each other in water (this is just one species, not two, but the basic principal is the same). These ions will repel each other electrostatically because of their opposite charges, but because water is a polar solvent water molecules near each ion screen this effect by orienting themselves in a way that tends to reduce the overall electric field. The result is that the ions have to get pretty close to each other to interact. The distance that is \"close enough to interact\" is known as the ",
"Debye length",
". In the case of water it's about 0.3 nanometers. Taking that length as a radius and making a sphere we get a volume of about 10",
" liters. This means we'd need a concentration of 10",
" ions per liter (this is about a 15 Molar solution) before all ions were interacting with at least one other ion most of the time. The concentration we'd need to have some ions interacting with at least one other ion some of the time is a bit lower and depends on how fast ions are moving and rearranging in the solution. However, as the amount of sodium increases the screening length decreases, so the required concentration would actually be a somewhat higher. This result lands in the gray area where I'd want to do a more thorough calculation or measurement to see if interactions are going to matter. However, you can see that the key parameter is the distance over which an interaction could happen. The next step in the calculation is to consider the strength of an interaction relative to the thermal motion of the ions to see what fraction of interactions matter. I'd rather sleep though."
] |
[
"In a multicomponent mixture diffusivity is defined by the pair component-mixture, which ends up depending on its composition. For example in a ternary mixture involving components A, B and C, the instead of diffusivity D_AB you define D_A-MIX which is the diffusivity of A in the mixture of A, B, C."
] |
[
"This isn't true.",
"Diffusion is the movement of dissolved components in solution along concentration gradients (from high concentration to low concentration).",
"Even if (in your example) A had affinity to B, B would still be subject to the same principles guiding diffusion, that being the concentration gradient.",
"The case when this would not be true is across cell membrane which selectively allows 'some' or specific dissolved constituents across, but not others."
] |
[
"How easy or plausible is it to transfer location/schools once you have entered a PhD program at one?"
] |
[
false
] |
So I'm 21 and a male, in the US. This past month has been my first month in a Graduate program for biochemistry and biophysics. While I'm still questioning my decision to go to grad school, I am unhappy due to the location of the program. I shot myself in the foot in choosing to move halfway across the nation for this, as I got into a prestigious program pretty much exactly where I want to be now. I am still unsure why I chose the school I did, but I think it was on a whim, honestly. I feel as though I'd be more into the idea of grad school at the other location, as that's the biggest thing weighing on my mind right now. I simply don't feel as though I can commit 5-6 years of my life to this location. This is very hard to deal with, and I have already considered many things, including dropping out altogether and moving to go work for a couple years, trying to stick it out until I can leave with a Master's, and of course, transferring programs and locations. So Reddit, I ask you, how many of you that have a PhD is something scientific transferred graduate school programs or know someone that did? How did it work? Why did you, he, or she do it? What was the end result? edit: wording
|
[
"People do it, infrequently. But essentially you're applying to a new program all over again. Find an advisor at the school you want to work at, and talk to them specifically.",
"Edit to add: If you're questioning being in grad school at all, leave and don't come back until you're sure. No one needs a grad student who isn't committed."
] |
[
"Do you have your own funding? It's far easier to talk to a new advisor when you can say that they won't have to pay your salary. If someone agrees to take you, it's much easier to get into a department.",
"If you don't have your own funding, it will be a bit more difficult but still manageable. You need to re-apply all over again. Also make sure to tell your current advisor what is going on: I have seen this go bad when the student didn't come clean, and burnt bridges and angry past advisors are never good things in Science."
] |
[
"I know you may not know the answer to this question, but will that not scar my record, such that grad schools in the future may look down upon me for leaving once?",
"This is a legitimate fear of mine... "
] |
[
"How does the \"Doppler effect\" work for an accelerating source?"
] |
[
false
] |
I came across and am trying to imagine what it would look like for an accelerating object, like a jet. How would the shock front of an object with a constant and/or non-constant acceleration behave?
|
[
"A stationary source, like a radio sitting on a table, will sound normal. A radio moving toward you will have its sound waves appear closer to one another, like in the gif you linked to. This sound wave compression gives the radio music a higher frequency, which we percieve as a higher pitch.",
"If you mounted a radio on a car which is initially standing still, it will sound normal to you. If you gradually accelerate the car to a sufficient speed going toward you, you'll hear the music gradually getting a higher and higher pitch. Similarly, if you accelerate the car away from you, the radio gets a lower and lower pitch because the sound waves appear stretched out (like on the left side of your gif).",
"Basically, an accelerating sound source will sound similar to a car honking its horn as it passes by you. The pitch of the sound will change as the sound source accelerates toward and away from you. In fact, this is exactly what happens when a car passes by. When the car is moving toward you, it sounds high pitched because its sound waves are compressed. When it's next to you, the car is neither moving toward or away from you, making it sound normal. When it has passed you and is moving away from you, its pitch is lower. All the points in between cause a gradual change in the pitch of the car."
] |
[
"The difference between the two scenarios is that the first (car moving straight toward you) involves you standing on the path of the car. The second (the one in the diagram) involves you standing off to the side of the road.",
"If you're standing in the middle of the road, and a car moves toward you, you'll hear it at a high pitch. If the car reaches you and you miraculously don't die (the car passes through you), its pitch will instantaneously switch to a low frequency (since the car is now moving away from you).",
"In the second scenario, where you're standing on the side of the road, this pitch change is more gradual. The car's pitch starts off high and gradually changes to low as it passes by you. That's because ",
" changes according to the angle between you and the car. In the first scenario, the angle between you and the car is initially 180 degrees and then instantly changes to 0 degrees when the car passes you. In the second scenario, the angle between you and the car changes gradually, making the change in doppler frequency gradual."
] |
[
"That's the difference I was trying to explain (badly, apparently). A sound source that's moving at a constant speed (or at rest) will have a constant pitch to a listener. A car that's honking its horn and moving straight toward you will have a high pitch that doesn't change (because its speed doesn't change). If a car starts at rest and accelerates toward you, it will start at a medium pitch and increase as the car accelerates. The pitch will change gradually, just like the speed of the car changes gradually.",
"As for \"car driving by you\" example, I drew a ",
"highly scientific diagram",
" to help illustrate. The point marked ",
" is you, standing on the side of the road. The car, marked ",
" travels along the road in a straight line, with a constant velocity (",
"). This means the car is ",
" accelerating, so its pitch shouldn't change. But it still does, we know this to be true in real life. When a car drives by quickly we hear its pitch change.",
"You can break down the velocity of the car (",
") into two components: ",
" and ",
". ",
" represents the ",
" of the car relative to ",
". Basically, this speed determines whether the car is moving towards or away from you. ",
" determines the pitch you hear from the sound the car gives off. ",
" is the ",
" of the car relative to you. This speed has no effect on the pitch you hear from the car.",
"Looking back at the ",
"diagram",
" again, you'll notice that ",
" changes over time. ",
" is a component of a velocity which changes over time, so we could loosely say that ",
" \"accelerates\" as the car moves to the right. You might also notice that ",
" starts pointing toward you (producing a high pitch) and becomes 0 when the car is right in front of you (pitch sounds normal, as if the car were standing still) and lastly starts pointing away from you (lowering the pitch of the car). If you string it all together, you end up with the classic \"",
"\" sound a car makes when it drives by. The pitch starts high and gradually becomes lower."
] |
[
"Why is the spectrum of an incandescent lightbulb the way it is?"
] |
[
false
] | null |
[
"It’s not half of a Bell curve, it’s a black-body curve. That’s approximately the spectrum of any thermal radiator at equilibrium."
] |
[
"oh ok, thanks. Do you know why it looks that way?"
] |
[
"You can find derivations of Planck’s law online. It’s a little much to summarize in a Reddit comment, however."
] |
[
"What are the advantages and downsides of an Ion Propulsion system over conventional spacecraft propulsion systems, like liquid fuel?"
] |
[
false
] | null |
[
"There are several things that are interesting with ion thrusters and electric propulsion systems for spacecraft in general. ",
"The most obvious one is that they can accelerate propellant to much higher speed. This means that the certain quantity of propellant will generate more impulse. Impulse is the thrust time the duration of thrust. 1 kg of propellant in a liquid fuel engine can push with 1 kg force for around 450s maximum, for a ion thruster you can push with 1 kg force for up to 5000 seconds. So it's pretty obvious that ion thruster need a lot less \"fuel\" to accelerate a spacecraft than liquid engines. In practice that means you can make the spacecraft lighter and either use a smaller and cheaper rocket or share a rocket with another spacecraft. ",
"However accelerating propellant to higher speed requires a lot more energy. Each time you double the speed you have to quadruple the energy input. Liquid rocket engines are already Incredible powerful systems producing megawatts to gigawatts of energy. For an ion thruster you have to get that energy somewhere and in space that means (for now) solar power. While it's pretty great because you don't run out of it, the power is pretty small. Big satellites today only generate about 20kW of energy which is about 25 hp. So combining low energy input and very energy hungry ion thrusters you get a super low thrust. The result is that you need to keep you engine on for weeks and months at a time to get anywhere. This is an issue because you spend a lot of time just going somewhere and not performing your mission. All this time wasted is time where the spacecraft has to endure radiation and has chances of breaking. It also doesn't make money when it's in transit. Moreover those slower transits are usually less efficient than big burst of thrust for short periods of time.",
"Those kind of long and complicated trajectories are also a lot harder to calculate and you need mission planners who really know what they are doing to work on those.",
"There are also system level considerations. Electric propulsion systems usually use non-toxic propellants which means it is less dangerous (and less expensive) to fill the reservoirs. This is somewhat negated by a lot of ion thrusters using expensive xenon gas. This is why a lot of people try to not use xenon anymore. ",
"Ion thrusters also don't necessarily make sense if you don't already have a payload that needs a lot of energy. Adding large solar panels just for a thruster doesn't always make economic sense.",
"As with all engineering problems this is a tradeoff you have to do carefully. That said nowadays electric propulsion systems represent the majority of propulsion systems installed on new spacecraft. People used to be very intimidated by the complexity and think ion thrusters were mostly expensive laboratory toys. Over the past few years we have seen a lot of companies doing \"plug and play\" systems that makes ion thrusters a lot more accessible."
] |
[
"Yep, xenon production is a dozen tons a year. Starlink probably has in the order of 10 to 20 kg (I haven't done the math) so they would definitely have a supply issue so no surprise there. Krypton is nearly as good and much more abundant so it makes sense if you are developing a thruster from the ground up like they did. Alternative to xenon are super popular right now."
] |
[
"Would would to solar panels sail effect be stronger than the ion thrusters?",
"Nah, solar pressure is way way below the thrust you get from an ion thruster. This is why they are used all the time and solar sails have been only done for very limited experiments so far.",
"Also are radioisotope generators used for the power source? And how scalable would that be?",
"You could but they are not great. They weight a lot and produce very small amounts of power. They only get better than solar panels around Jupiter and beyond and there is just not that many missions that have gone (or are planned) that far out."
] |
[
"If we are running out of oil, how can gas prices be going down?"
] |
[
false
] | null |
[
"The short answer is time frame. We are running out of oil, but not for hundreds of years. So what is driving prices down is that we are pumping more oil out of the ground than is being used and competing companies and countries have decided not to stop pumping it out in an effort to break one or the other. So what you have is a situation where today's glut outweighs next century's famine. "
] |
[
"The good ole' supply demand rule in effect. You don't want to pay a lot for something you have huge quantities of. ",
"OPEC",
" don't want to put a lid on supply (how much is produced) due to the increased energy production through other sources (e.g. renewables and shale gas). This means that oil producing and exporting countries will have to increase their output of oil to earn the same income (since prices are falling). This exacerbates the situation. More oil to keep national income stable -> lower prices because the supply increases. Eventually, someone's gotta give. It's a pretty classic game of chicken, I'd dare say. ",
"edit: Oil is running out, but not for quite a long time. It doesn't affect the current oil prices at all. "
] |
[
"Pretty much more supply than demand, causing a surplus of oil in the market of oil, which causes a fall in price because businesses are trying to get rid of their excess oil that cannot be sold at the previous price."
] |
[
"People in the 1500's used mercury as a cure for syphilis. How did they obtain it? How and why did they decide that mercury was the answer?"
] |
[
false
] |
My source text is Bill Bryson's "At Home." Among many other topics, his book covers venereal diseases and their purported cures. Mercury has been mentioned as a cure for other general maladies as well. Why mercury? How did they obtain it? Why was it considered to be a miraculous cure, when it would seem to exacerbate their existing problems? Bryson indicates mercury would cure some symptoms. How and why? Bryson's quote: "Treatments for syphilis were severe. In the early days a lead solution was injected into the bladder via the urethra. Then mercury became the drug of choice and remained so right up to the twentieth century and the invention of the first antibiotics. Mercury produced all kinds of toxic symptoms – bones grew spongy, teeth fell out – but there was no alternative. ‘A night with Venus and a lifetime with Mercury’ was the axiom of the day. Yet the mercury didn’t actually cure the disease but merely moderated the worst of the symptoms while inflicting others."
|
[
"To get Mercury you just have to find some Cinnabar (red rock) and heat it up."
] |
[
"Why use mercury?\nBecause it was a strange material that was unlike many others. They thought it had some essence of life to it. People did a lot of things back then that we look back and consider very odd or ill-advised. Similarly, 400 years from now, people will look back and shake their heads at the stuff our people do now (banal tv talent shows, video games, etc.)"
] |
[
"Why use mercury?\nBecause it was a strange material that was unlike many others. They thought it had some essence of life to it. People did a lot of things back then that we look back and consider very odd or ill-advised. Similarly, 400 years from now, people will look back and shake their heads at the stuff our people do now (banal tv talent shows, video games, etc.)"
] |
[
"How is continental drift measured so precisely?"
] |
[
false
] |
A drift of, say, 2cm/year requires an extremely accurate measurement. Googling tells me that laser-equipped satellites are used. But wouldn't atmospheric distortion and slowing of the beam cause errors greater than what is required to measure such slow motions? Not to mention determining the satellite position so accurately.
|
[
"The first measurements of continental drift were actually made by radio astronomers using ",
"very long baseline interferometry",
"."
] |
[
"Many times we use GPS sensors to give absolute data in the current day, such as for ",
"the Basin and Range Province",
" (PDF warning!). However, there is one point that a lot of people get confused about: These readings are for the ",
". ",
"This means that if you look at the GPS and satellite slip components for the Pontide mountain range in Turkey, you will come to a very different conclusion than what is happening if you don't take into account the undercompensation of the orogenic root in response to rapid building, thus creating a mountain range that is essentially sinking. "
] |
[
"This is incorrect.",
"\n",
"Error Propagation in Addition and Subtraction",
"\nOr a more generalized look:",
"\n",
"Propagation of Uncertainty"
] |
[
"How can scientists tell how old light is?"
] |
[
false
] |
I've heard numerous claims of 'the light has been traveling x long to get to us'. But for something on the order of billions of light years away, I'm pretty sure you can't use parallax to measure how far away the light source is....furthermore, it is my understanding that because of expansion, a lot of stars were not as far away when they emitted the light as they are now, which in my mind would throw off any 'distance' calculations. So, how can they tell how 'old' light is?
|
[
"For these kind of distances the most popular way is to use a particular type of super novae. The progenitor system of these SN is usually a white dwarf and a larger companion. The white dwarf sucks in matter from the companion star until it reaches some critical limit and then goes super nova. This happen always at the same mass threshold, thus they always explode with roughly the same luminosity (there are a few caveats, but they are fixable and it all works pretty well). Thus, by identifying these specific SN via spectrum analysis, we know how far away they must be by measuring their apparent luminosity as seen from earth. These measurements have to be interpreted and a specific cosmological model, which also allows us to use these SN as a means to probe the expansion history of the universe."
] |
[
"Don't mix up Doppler shift and cosmological redshift."
] |
[
"Don't mix up Doppler shift and cosmological redshift."
] |
[
"Would quantum computers be better at predicting the weather accurately?"
] |
[
false
] |
Umm yeah the title pretty much says it all, if quantum computers became a thing would they be way better at predicting the weather than what we have now?
|
[
"I am under the impression that weather forecasting runs up against turbulence rather quickly. In that case, I think it's difficult/currently impossible to create accurate models generally which is a necessary precursor to creating algorithms to run said models.",
"But about quantum computers, they are not able to solve any problems that normal computers cannot. However, they can solve some problems much more quickly than normal computers. So unless the problem for weather prediction comes down to efficiency, quantum computers won't be much help."
] |
[
"This. While computational power is of course a problem with any model, the primary problem is the improvement of the model, not necessarily the computer. If the models used to predict weather improve, then the accuracy will be better, regardless of what it runs on.",
"The possible speed improvement of quantum computers may of course make it more convenient to apply these models, but the source of accuracy (or lack of accuracy) is in the models, not what they run on. We could apply the current weather prediction models we have using nothing but pen and paper. Weather forecasts would suck just as badly as they do now, only more slowly."
] |
[
"The real problem with weather predicting is that Earth is inherently a chaotic system (chaos here coming from chaos theory). The nutshell of chaos theory is that while the system behaves deterministically (ie if you know the current state exactly you can predict state of the system in 5 minutes), small uncertainties in knowledge of current state will result in huge uncertainties later on (so called butterfly effect). Since we cannot know the exact state of the system at the current time, no matter what our computational capabilities are, sonner or later our predictions will diverge wildly from the reality."
] |
[
"How do human vocal cords hit such low notes when strings and wind instruments have to be many, many times larger to do the same? Put another way, why are there no tiny bass instruments?"
] |
[
false
] | null |
[
"The difference between our vocal chords and string/wind instruments is that our vocal chords physically vibrate at the particular frequency through muscular tension, while strings and winds produce a longitudinal wave along their entire length that vibrates at the particular frequency. So for a string/wind instrument, a lower frequency requires a longer resonator. But a voice requires merely that the folds vibrate more slowly. To be sure, even with voices there is some dependence on length of the resonator: adult male voices are deeper than child and female voices in general; but this is the basic idea."
] |
[
"A speaker, or a pair of headphones is an example of how a smaller device can produce bass notes via vibration "
] |
[
"I think you have misrepresented the problem.",
"While the vocal cords themselves may be \"tiny\" (arguable) the human voice is composed (hah) of far more than merely the vocal cords.",
"After the sound is generated by air moving over the vocal cords, the resulting vibrations have their resonances and volume derived from other parts of the body, notably the chest, throat, mouth and sinus areas.",
"You could argue the whole of the human instrument competes with a cello for size.",
"That's like marveling that the reed in a clarinet or saxophone generates such a range and volume of sound, because wow, it's so small."
] |
[
"AskScience AMA Series: We're the New Horizons mission team that conducted the farthest spacecraft flyby in history - four billion miles from Earth. Ask us anything!"
] |
[
false
] |
On New Year's 2019 NASA's New Horizons flew past a small Kuiper Belt object named Arrokoth, four billion miles from Earth, in a vast region home to the icy, rocky remnants of solar system formation. Our team has new results from that flyby, and we're excited to share what we've learned about the origins of planetary building blocks like Arrokoth. We're also happy to address other parts of our epic voyage to the planetary frontier, including our historic flyby of Pluto in July 2015. Team members answering your questions include: We'll sign on at 3pm EST (20 UT). Ask us anything!
|
[
"How far in the distance/future have you plotted the course, such as including other objects gravitational effects, etc?",
"Or is this insignificant past Pluto on this scale?"
] |
[
"We do plot our course for years in advance! We do that with complete models of the gravity of the Sun and planets. - SAS"
] |
[
"Dwarf planets are planets too! --Bill McK."
] |
[
"How come mosquitos do not spread blood borne diseases like HIV and Hep C?"
] |
[
false
] | null |
[
"Mosquitos do not inject blood when they bite. Just saliva. So for most blood borne viruses like HIV, the virus can not replicate in the mosquitos digestive system, and never makes it into its saliva. ",
"Malaria on the other hand is essentially designed for transmission by mosquitos. it grows and reproduces in the mosquitos digestive system and move into the mosquitos salivary system to be injected the next time it feeds. "
] |
[
"So theoretically could hiv adapt to take advantage of mosquitos or is it outside the abilities of a virus"
] |
[
"Surely the mosquito mouthpiece will have bacteria and viruses on it ? Sharing a needle can transfer AIDS, how come a mosquito needle can't ? "
] |
[
"If glaciers hold approx. 70% of the worlds freshwater, and the glaciers are melting. Does all freshwater retreat to the ocean and is lost forever?"
] |
[
false
] | null |
[
"Well no, not in the way you describe it. It's true that the freshwater of the glaciers is lost for consumption, as it becomes salty, but most of the earth's glaciers aren't used for freshwater production (some of them are in a very tiny amount). So it wouldn't have an influence on the current freshwater production. ",
"The actual problem is, that in many regions we already have a scarcity of fresh water, so losing all the fresh water is a painful waste if you see it in that way. ",
"Does all freshwater retreat to the ocean and is lost forever? ",
"The water indeed enters mostly into the oceans, as the vast majority of glaciers is surrounded by them ( Greenland, northern Canada, Antarctica) or directly floats on the sea (north polar cap, antarctican ice shelfs). Only very few and comparatively small glaciers are on land that's not surrounded by water (Himalayan ice caps for example). ",
"However this water isn't lost forever, as it (at least partly) enters the water cycle. Also, we can extract fresh water from seawater, so \"losing it forever\" wouldn't be the correct term. But that would be very energy expensive. ",
"Losing all fresh water on earth is not possible, because of the water cycle. Seawater evaporates under the heat of the sun, mostly in the tropical areas and condenses and rains out in colder areas. This surface water then returns to the oceans via ground, rivers etc and can be used as fresh water by living beings. After that, the cycle starts over again. "
] |
[
"Two questions: If all the glaciers melted for whatever reason, would the oceans salinity be affected and if so how would the human race be affected? 2. Mars' ocean evaporated (so some scientists say), why couldn't ours? Granted, it wouldn't be overnight...."
] |
[
"Two questions: If all the glaciers melted for whatever reason, would the oceans salinity be affected",
"Yes, but not strongly, see this ",
"picture of water distribution on earth",
". Most water already is saltwater and almost one third of freshwater is not bound in glaciers or ice caps. ",
"Humans would be strongly influenced when all ice would melt, but mostly by the dramatical climatic change. Differences in temperature and salinity drive ocean currents which could then cease. Local climates could actually cool down, for example when the gulf stream cases, which is working because it is exchanging hot water from the equator and cold water from the north pole. If the temperature difference is to small due to global warming, then it could cease to exist, causing icy winters in europe and result in crop failure. ",
"That's only one example. Similar things can happen pretty much everywhere. We don't know exactly what would happen, but a complete meltdown would most likely be catastraphic in tearms of global weather change. Not to think of the raising level of seawater. It would raise by more than 55 meters, flooding any coastal city you know today. That would be an desaster, but is probably not going to happen in the near future. ",
"Mars' ocean evaporated (so some scientists say), why couldn't ours? Granted, it wouldn't be overnight....",
"Sure it could, but what would cause the evaporation and where would the water go? To evaporate water, you need sufficient heat. There is no source of heat to do that in the near future. The sun isn't sufficient enough in its current age to completely evaporate earth's oceans and we don#t know any asteroid or comet that is likely to hit earth that is sufficient to do so either. ",
"But let's suppose there was and Asteroid that could, all the water would go into the atmosphere and finally rain out again, after earth cooled down enough. An event like on Mars is not gonna happen, because earth currently has a magnetic field and strong gravity. Mars never had strong gravity, so its atmosphere extended much higher and without a sufficient magnetic field it could be eroded much easier by the solar wind. The water was literally blown into space, rather than raining back like on earth. Another thing is, that water could been split by high energy UV radiation, and with a thick atmosphere in the higher regions and the low gravity the hydrogen could easily escape mars. None of these circumstances you can find on earth. ",
"Additionally, not all water seems to have escaped, there are glaciers underground that remained there. "
] |
[
"Are we using energy when we think? If so how much?"
] |
[
false
] |
I was in a lecture the other day after a poor night's sleep and came across a pretty basic math problem that I could usually do in my head. I started working it out and then 3 seconds later decided I couldn't be bothered, which made me wonder, do we use up energy when we think hard enough just like we use energy when doing physical work? Why else would I be so opposed to working a problem in my head?
|
[
"I have unsuccessfully tried to find a source on any actual numbers when this question comes up on the subreddit every couple of months. Do you have any primary literature for that ~100 Calorie measurement?"
] |
[
"I have unsuccessfully tried to find a source on any actual numbers when this question comes up on the subreddit every couple of months. Do you have any primary literature for that ~100 Calorie measurement?"
] |
[
"Yes, but you have to have low blood glucose for quite a while before your brain resorts to utilizing ketones as a source of energy. Glucose is far and away the brains preferred metabolite."
] |
[
"If I was to attach a dynamo to the exhaust pipe of my car, how much electricity in theory would it generate?"
] |
[
false
] |
Lets say I have an average diesel engine car (if you need figures just pick any old car as example) and I was going 70mph how much electricity would I generate if I put some sort of dynamo on the back of the exhaust pipe? I'm just curious as to why no one has specifically made use of the energy that is being wasted by it just releasing it all. I don't have a clue how you would go about calculating it unfortunately and or if it would even be safe to obstruct it in some way. Thanks!
|
[
"Yup. First law of thermodynamics - there ain't no such thing as a free lunch. Any power generated from that dynamo would be coming from the engine anyway, so you're better off not having it. You can't consider the exhaust to be an unlimited source of moving air - you are combusting the engine to create that air, and any energy you can gain from it is taken away from the combustion."
] |
[
"I imagine that the backpressure put on the engine would diminish the engine's power more than the dynamo would produce?"
] |
[
"TANSTAAFL, unless you could harness the waste heat to run a stirling engine... but that was not his question."
] |
[
"Of all the nuclear tests completed on American soil, in the Nevada desert, what were the effects on citizens living nearby and why have we not experienced a fallout type scenario with so many tests making the entire region uninhabitable?"
] |
[
false
] | null |
[
"Difference between a blast delivered by a device, and a meltdown of a nuclear pile (far more material than a bomb, slower release)."
] |
[
"Pardon my ignorance, but how come people can live in those places after that, but Chernobyl is uninhabitable?"
] |
[
"Pardon my ignorance, but how come people can live in those places after that, but Chernobyl is uninhabitable?"
] |
[
"If you were to put a pipe down the the deepest part of the ocean that reached up to the atmosphere, would the water move up it due to the pressure and if so depending on the radius of the pipe how high could it go?"
] |
[
false
] |
[deleted]
|
[
"The pressure in the ocean depths is caused by the weight of the water above it. If you put an empty pipe down to the bottom of the ocean and opened it, water would be forced up the pipe until the weight of the water in the pipe balanced the force from the pressure at the bottom of the pipe. Not coincidentally, the level at which this balance occurs would be sea level."
] |
[
"You mean if the pipe were evacuated (made to be a vacuum) and if it were to go all the way up to space? Yes -- it actually would go a bit higher. About 30 feet higher. This is another take on the question: \"how long can you make a straw before it stops working?\"",
"The limit for any straw is about 30 feet, due to the weight of water.",
"A vacuum can lift a column of water about 30 feet high, but no higher. This comes down to how much atmosphere is above the evacuated pipe/straw and what the atmospheric pressure is. Straws only work because the sucking motion causes a decrease in pressure within the straw and the pressure of the atmosphere pushes up the fluid into the straw to balance out the pressure. ",
"It turns out for any size straw that is evacuated, a column of 30 feet of water perfectly balances out the 14psi pressure at sea level. By the same token, about 30 feet underwater the pressure is 2 atmospheres (1 from the atmosphere and another 1 from the 30 feet of water)."
] |
[
"Would the lack of pressure in the upper atmosphere/space suck it up higher?"
] |
[
"Want to build a real BMO (from Adventure Time) and want to know his actual size (x-post from AskReddit)"
] |
[
false
] |
[deleted]
|
[
"Thats not really what this sub is for guy. Can't you do this yourself anyways?"
] |
[
"BMO has no size, animation models exist solely through comparison to each other. You're asking for a guestimation based on screenshots to a show with a surreal bent that doesn't even have consistent sizing anyways. Your try is just as good.. as for the sub issue, AskScience is for ",
" not ",
" but I wouldn't care to argue that if your question actually had an answer. Make him as big or small as you see him as."
] |
[
"Why not? Is this not science related? I'm trying to engineer a BMO and I suck big time at math, so I thought lets ask the science guys."
] |
[
"[Light] Why is the angle of incidence the same as the angle of reflection? Why is it not twice, or half?"
] |
[
false
] |
I know this is quite abstract, and maybe it's impossible to know, but is there some reason it had to be that way?
|
[
"There's a derivation ",
"here",
". Both the law of reflection and Snell's law of refraction come from considering the boundary conditions on the electric field across the interface of two materials."
] |
[
"Fermats principle",
"https://en.wikipedia.org/wiki/Fermat%27s_principle",
"Essentially shows that light will travel the path that occupies the least time. For 2 points the shortest distance will be a straight line. In the case of a reflecting surface, that results in having the angle of incidence equal to the angle of reflection."
] |
[
"This is unfortunately an incomplete explanation, as it is entirely conceivable that (a) if the total momentum of the EM field is to be conserved, it is only the sum total of the incident, reflected, ",
" refracted waves which must be zero, giving you an extra degree of freedom to make your angle of reflection whatever you'd like; and (b) even in the case where there is no refraction, the total momentum of the EM field could change as the wave can impart momentum to the surface in the form of radiation pressure. \"The component of momentum of light parallel to the mirror is constant and the component perpendicular is flipped\" is a statement of the conclusion, not an argument supporting it."
] |
[
"How are instincts stored in the brain? The same as memories?"
] |
[
false
] |
Instincts, such as an infant sucking on a nipple, must have some sort of mechanism. Where is it location, and what does it look like?
|
[
"We know much of what we consider \"instincts\" in neonate creatures in nature are stored in DNA. The process of DNA->expression of a trait/protein is well known, however how this process results in the behaviors of instincts, we have pretty much no clue. In fact, it may be better to not think of instincts as a direct thought mechanism, but instead as reflexes. Many creatures in nature have complicated instincts such as covering up their tracks, that they seemingly do not have the true thought process to understand what they're doing. It's very possible they don't know why, they just do it, like a reflex. "
] |
[
"Two of the best examples I know:",
"http://www.nature.com/nature/journal/v493/n7432/full/nature11816.html",
"http://www.pnas.org/content/89/13/5981.short"
] |
[
"Thank you, I was having a hard time finding anything."
] |
[
"Water solubility of caffeine, or, if I use a tea bag a second time has it become mostly decaffeinated?"
] |
[
false
] |
So I find that I can get two cups of tea out of a tea bag (which I'm sure infuriates tea purists). I like to avoid caffeine near bead time, so I was wondering whether a second steeping of a tea bag would produce a mostly decaffeinated tea. So what do you think? Does most of the caffeine dissolve on the first steep? What I've learned today: Thanks all for the answers!
|
[
"I do the same thing, so I got curious about the exact numbers. Fortunately some researchers actually looked at this question systematically in ",
"this paper",
". The key result is summarized in ",
"this table",
", where they looked at the fraction of caffeine extracted after different types of tea were steeped for 5 minutes in boiling water three times in a row. The results show some variation from one tea to another, but on average close to 70% of the caffeine was extracted in the first steep and less than 25% on the second steep. ",
"As expected, bag tea is especially quick to lose its caffeine since its leaves have been smashed apart, giving them a larger surface area. For your purpose this type of tea would be the best candidate. For example for Lipton black tea, only 18% of the caffeine was extracted on the second steep. On the other hand, if you ever want go get more caffeine out of the second or third steep, loose leaf tea has the clear advantage there."
] |
[
"It should also be noted that the solubility of caffeine massively increases with temperature. That is to say that, in hot water, the majority of caffeine will dissolve pretty quickly. "
] |
[
"Which works out, since black leaf tea, which contains the most caffeine is properly steeped at near boiling. While white leaf, which has little caffeine is best steeped closer to 170 f. "
] |
[
"How do nutritionists know that something has zero calories?"
] |
[
false
] |
I know that a single calorie is the energy it takes to raise one CC of water one degree Celsius - (right?) - But how is it determined that something like sucralose has no calories? EDIT: I meant sucralose.
|
[
"There is an instrument called a bomb calorimeter. Its just a relatively closed system that is filled with pure oxygen so that you can burn stuff. After you are done burning stuff you see how much energy went into raising the temperature of the water around the sample. "
] |
[
"Wouldn't really work for something like sucralose. Sucralose is still an organic molecule and can burn and give positive calories in a bomb calorimeter, your body just doesn't have the capability of metabolizing it at all."
] |
[
"Sucrose (table sugar) has a pretty big caloric value. Are you sure you didn't mean sucralose? Like bitter_twin_farmer said, caloric value can be found with bomb calorimetry. But, you also have to take into account whether you body has the machinery to digest something like sucralose to get any valuable energy out."
] |
[
"Were fruits smaller in the past?"
] |
[
false
] |
I spent today watching some older films from over seventy years ago from the forties and before. When they show fruit trees or someone picking fruit the apples, oranges, lemons look so tiny compared to what I'm used to. Is this screen optical illusions or were the fruits smaller seventy years ago compared to now? If so, what caused them to grow bigger?
|
[
"there are a lot of things that science claims that have proven are in fact just theories and evolution is one of them.",
"You don't understand what a scientific theory is."
] |
[
"There are two explanations to this;",
"1 - Varieties of fruit vary hugely and the cinematographers may have chosen to film smaller varieties for various aesthetic reasons.",
"2 - We have been selectively breeding fruits bigger for thousands of years to improve the yield of crop from a single plant. This has has dramatically altered the size and shape of many fruits to better fit what consumers want and in the last 100 years we have accelerated this process even further with more breeding methods. This is even true of hen eggs which due to consumer demand have dramatically increased in size over the last 50 years."
] |
[
"Theory is something that science \"thinks\" happened and then writes in history/gography books as proven facts and to be honest im sick of this shit."
] |
[
"Could antimatter destroy a black hole?"
] |
[
false
] |
Since black holes are made of matter, could a large enough quantity of antimatter sent into a black hole destroy, or at least destabilize, a black hole?
|
[
"No. Antimatter still has positive mass it just has the opposite charge as it's normal matter partner. So antimatter that falls into a black hole will increase the total mass of the system. ",
"So why won't the matter-antimatter annihilation cause the mass inside the black hole to disappear? First to assume that annihilation can happen we have to make certain assumptions that somehow the initial matter that fell into the black hole will retain some kind of individual identity. We need this because a positron and say a down quark won't annihilate. Only only an particle and ",
" anti-particle. ",
"For the sake of argument lets assume this is somehow true so an infilling positron could find an electron at the singularity to annihilate with and it does so. We've not actually changed anything about the \"mass\" of the black hole. Yes we've eliminated the electron and positron, but in their place we've created two new photons with the exact same energy as those two particles had. These photons will continue to contribute to the gravity well as if they were still particles. ",
"This would still work since unlike the two particles photons always move at c, except at this point we're within the event horizon of the black hole, and the photons will therefore be unable to escape. ",
"So at the end of the whole thing we've still got the original electron's energy in the black hole and the added positron's energy is also bound within the gravitational well thus we have increased the energy of the black hole. "
] |
[
"To build on this, all of the mass-energy from the particle annihilation is still contained in the black hole and will not escape until it is emitted via Hawking radiation."
] |
[
"No. Whether a black hole gets its mass from matter or antimatter makes absolutely no difference; both increase the mass of a black hole. "
] |
[
"Question regarding Wasps/stinging insects: How did the biology of a stinging insect evolve correctly to produce a formula that would effectively hurt or \"sting\" its victim?"
] |
[
false
] | null |
[
"I'm not the best person to answer this but I googled the evolution of bee stings and found this. Perhaps someone else could run with this or elaborate on it: ",
"\"The bee's stinger evolved originally for inter-bee combat between members of different hives, and the barbs evolved later as an anti-mammal defense: a barbed stinger can still penetrate the chitinous plates of another bee's exoskeleton and retract safely.\"",
"Source: ",
"http://www.sciencedaily.com/articles/b/bee_sting.htm"
] |
[
"I'm not sure it makes sense to give evolution purpose like that (the quotes). Features don't evolve 'for' anything."
] |
[
"What you are describing is the idea of the Red Queen hypothesis, and to my knowledge, is still how many people think of things like this. No matter how far \"ahead\" a species get, it's always being \"one upped\" by another species."
] |
[
"What substances can reflect other parts of the electromagnetic spectrum?"
] |
[
false
] |
I know a mirror will reflect most of the visible spectrum; as well as some heat in the infrared. I guess what I want to know is do different types of substance reflect different parts of the electromagnetic spectrum?
|
[
"Yes, the frequency-dependence of a material's reflectivity is typically quite complicated. ",
" reflect some portions of the electromagnetic spectrum to some extent, and transmit or absorb more in other portions. For instance, take a look at this ",
"reflectance spectrum of grass",
", soil, and water. Even air has portions of the spectrum where it is much less transparent (mostly because of the water vapor in the air). For instance, air tends to be quite opaque in the terahertz. If you are designing a terahertz laser and you want the laser beam to travel a reasonable distance through air, you have to try to design the frequency to be in one of the spectral windows (the range of frequencies where air has higher transmission and lower absorption/reflection). For this reason, before our lab could design a terahertz laser, a colleague of mine had to ",
"make detailed measurements of air's terahertz transmission spectrum",
"."
] |
[
"Metals are generally good reflectors of EM radiation, at least up to X-ray scales. The reason is that they conduct, so when the radiation hits the metal, charge moves around in the metal to counteract whatever forces the wave is applying. That motion of charge then itself creates a wave of identical frequency to the incident wave, so it has the appearance of reflection.",
"It's trickier than just making a blanket statement of \"metals block EM,\" but that's at least the surface-level idea. To reflect/block radio waves, for instance, you really need something like steel-reinforced concrete."
] |
[
"Thanks for your great answer. My question came about thinking of home insulation and foil barriers. As long as they don't touch other surfaces (conduction) when built into a wall they behave (in the dark) as a reflector keeping heat in the house. I started to wonder if something actually needs to appear \"shinny\" to reflect in the infrared."
] |
[
"Why do atoms \"want\" to get full outer electron shells when bonding?"
] |
[
false
] |
A hydrogen atom on its own is stable, and has no overall charge. The same goes for oxygen. So why would they bond to form water, which has the exact same charge? Also what causes chemical bonds to have specific angles?
|
[
"Good question! Understanding this behaviour requires that you first understand that a reaction can be considered as a number of individual processes. When you combine chlorine and sodium to make table salt, the sodium atom loses an electron, the chlorine atom gains one and the resultant ions bond due to their charge (this description is accurate to a first approximation).",
"Removing electrons from atoms takes energy. Adding electrons to neutral atoms releases energy, but adding electrons to already-negative ions typically takes energy. Forming the resultant bond between the atoms releases energy. So, let's add this all up.",
"Sodium has a single electron in its outer shell. The energy cost of removing this, combined with the energy gain of creating Cl",
" and then the salt NaCl yields a large negative number for the overall energy change because the bond that's formed is quite strong. That is, the overall process is favoured and the reaction happens. You may ask: if the bond is quite strong, why not form two of them (i.e. NaCl",
") and get twice the energy out from bonding?",
"Removing a second electron from sodium is much tougher. It's at a lower energy level, much closer to the nucleus and more tightly bound. It turns out that the energy gain from a second bond doesn't make up for the extra energy required to remove a second electron. Similarly, for magnesium, which does form two bonds, this is because magnesium has two electrons in its outer shell which are comparatively easy to remove.",
"So, it's not so much that an element wants to form a particular number of bonds. Elements will form as many bonds as they can (because bond formation releases energy) until the energetics become unfavourable. Sometimes, if you have particularly reactive compounds, you can exceed the traditional \"correct\" number of bonds because the reactive compound releases sufficient energy in the reaction.",
"Bond angles are caused by the electrons in bonds repelling each other. If you have methane, a tetrahedral molecule, you end up with the bonds at an angle of about 109 degrees because that maximises the distance between bonds. However, lone pairs that aren't involved in bonding exert higher repulsion than bond pairs. So, in water, oxygen has two lone pairs which squeeze the bond pairs closer together to an angle of about 104 degrees. Read up on \"VSEPR\" for more about this."
] |
[
"I remember one of my lecturers telling me there was nothing special about a full shell, and that it is just where energy minima tend to be.",
"One of the reasons for this is shielding of the nuclear charge:\n",
"http://en.m.wikipedia.org/wiki/Effective_nuclear_charge",
"\nElectrons in inner shells shield the outer electrons from the nucleus's charge I.e some of the protons' attraction to the outer electrons is blocked by the inner electrons. As you go across a row of the periodic table, all elements have the same number of inner electrons, and therefore the same amount of shielding, but more protons and therefore a higher nuclear charge. This means the outer electrons of the elements on the right hand of the table experience a larger \"effective nuclear charge\" than the ones on the left. \nWhen a left and a right element are mixed together, for example lithium and fluorine, one of lithium's electrons will be pulled off and into fluorine (who has a much higher effective nuclear charge)'s last remaining space it its second shell. \nWith a now complete second shell, any more electrons pulled off by fluorine would have to sit in the third shell, which has two shells of shielding in between it and the nucleus, causing it to experience a much lower effective nuclear charge - lower than it would experience staying in orbit around the lithium atom meaning fluorine stays as F-, and the second Li goes off to find an F."
] |
[
"So, is this why some reactions cause exothermic reactions, and some cause endothermic reactions?"
] |
[
"Why and how is Carbon such a good element for forming life and are there other-element based lifeforms possible?"
] |
[
false
] |
I read an article in which Stephen Hawking said that Carbon has the richest chemistry possible. I have not studied chemistry beyond high school, and I sometimes think that ok, there should be other elements that are in the same "column" in the periodic table, and should behave similarly. Are we to believe that if we find life off earth, it would be carbon based, or is there a realistic possibility that it may be other-element based. I'd love if AskScience answered this. :)
|
[
"Short answer: Because there is more carbon that any other 4 covalent bond element like Si Ga Sn Lb,and it forms a large range of molecules ",
"long answer\nCarbon is a very good element for life as it can have up to 4 covalent bonds.",
"This means that carbon can form a range crazy range of molecules due to the possibilities of 4 bonds",
"From diamonds and graphite with just carbon having fun properties future uses in computing ",
"To complex hydrocarbons which we get from crude oil which we crack to get alkenes often ethene which is used as the base of many polymers and plastics by breaking the double bond to combine huge numbers of monomers together to form large long polymers. we can even break hydrogen and replace them on the h2c-ch2 ethene to get f2c-cf2 which is the monomer which we polymerize to produce Teflon or replace one hydrogen with a benzene ring to get strene and much much more.",
"We also get hydrocarbons used in organisms ethanol and glucose to name the which are produced and consumed in metabolic processes.\nEthanol in anaerobic (no O2) process in bacteria which this process is commonly called fermentation.\nThe glucose is used in respiration and produced in photosynthesis from Co2 and water, creating a path way to produce chemical energy from sun light rather than feeding on chemicals often produced by others means see (deep sea sulphur vents) and in doing so caused the worlds greatest pollution event and change organism across the world so greatly that life had to addapt to o2 rich enviroment which lead to the adoption of respiration using o2 to break apart this glucose.",
"So simply due to 4 bonds which are readily reacted and be in vast amounts in area leads a range of molecules which a range of properties for different arrangements very often. "
] |
[
"Silicon also works, and is key in certain animals, like echinoderms, but silicon has the disadvantage that it forms crystal matrices instead of carbon chains. Great for laying a starfish skeleton but less useful in other metabolic processes. "
] |
[
"on this planet with these conditions, yes. other planets, or even clouds of gas in space, have different conditions which might be ideal for silicon based life. we just dont know yet"
] |
[
"What would happen if we placed an object orbiting around a black hole such that in the closest point of the orbit, the object is inside the Schwaszschild radius?"
] |
[
false
] |
Assume that we initially place the object outside of that radius, but as it follows an elliptic orbit, it enters that radius while orbiting. Would it outspeed light? Would it be able to not fall inside the black hole?
|
[
"If something enters the Schwarzschild radius, it's not coming back out again."
] |
[
"There are no elliptical orbits with that description in a Schwarzschild geometry."
] |
[
"There's nothing special about an orbit that would make it escape a black hole. Putting something on an orbit entails giving it the appropriately orbital velocity to match the trajectory you want, which in this case, would be insufficient to keep it outside the Schwarzschild radius.",
"EDIT: It's a depressing commentary on our popular culture that Chrome wants to spellcheck Schwarzschild to Schwarzkopf."
] |
[
"Ask Anything Wednesday - Physics, Astronomy, Earth and Planetary Science"
] |
[
false
] |
Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...". Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists. Please only answer a posted question if you are an expert in the field. . In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for . If you would like to become a member of the AskScience panel, . Past AskAnythingWednesday posts . Ask away!
|
[
"How much heat does the earth receive from stars other than the sun? Say, as a percentage of the sun's heat."
] |
[
"Exo planets = planets not a part of the solar system.",
"Rogue planets = planets not orbiting ",
" star",
"Rouge planets = planets that are red"
] |
[
"What are the most likely candidates for dark matter at the moment? "
] |
[
"Wildlife biologists: Prospects of an anole in northern Virginia?"
] |
[
false
] |
So, my 19- and 21-year old roommates adopted a ringneck snake they found in the wild. Tonight they came home with an anole that is bigger in circumference than the snake and has been sitting at the top of the aquarium all night. It is raining now pretty badly but if it stops I am thinking about taking the anole outside. Is it probably going to die once the summer is over, and if so, would this still be a good idea at all? It is probably biased of me to think this but the snake doesn't seem too unhappy in captivity and I feel like if it could just eat crickets why feed it an anole? Another kinda irrelevant question: My roommates also have two red-eared sliders in an aquarium that I have been thinking about talking to them about releasing. What's your opinion on releasing these turtles into a wetland they didn't originate from?
|
[
"Please do not release animals to the wild. Ever. For any reason. Animals from the pet trade can harbor disease that can threaten entire populations. If they do make it they may harbor genetic differences that can negatively affect local populations. As you suggested, the individual will also be likely not to make it. Find someone who will adopt these animals or take them back to a pet store. Releasing captive animals is a threat to native wildlife also because introduced species can outcompete natives. "
] |
[
"If you get another snake and then teach both snakes how to golf, you could get anole in one."
] |
[
"Also, ",
" take animals out of the wild to try and take care of them. Its a bad bad idea."
] |
[
"Is \"anti-gravity\" physically possible? What about artificial gravity in space?"
] |
[
false
] | null |
[
"It is worth noting to your last point that according to the ",
"Equivalence Principle",
" acceleration can be indistinguishable from gravity."
] |
[
"The gravitational force as we know it acts in one way; as a force directing towards a mass. To oppose this we would require negative mass. Which as far as we know does not exist. To add to that statement, anti-matter ",
" to have positive mass according to CERN, sorry I don't have a link but they did experiments on anti-hydrogen to test this. Anti-matter is the only candidate, as far as I am aware, to potentially have negative mass but it is expected to behave like regular matter in the gravitational sense. ",
"As for ",
"artificial gravity",
". Not in the sci-fi sense as far as what I have seen, as in you flip a switch and suddenly the floor 'produces' gravity. Having a rotating disk in space could, in theory, produce an appropriate acceleration to mimic Earth gravity. "
] |
[
"As far as we can tell, the only thing that creates gravity is tons and tons of pure mass. Furthermore, it appears that all gravitational forces are purely attractive. So anti-gravity is not physically possible by any means."
] |
[
"What is at the centre of the moon/other planets in our solar system?"
] |
[
false
] |
Is the moon just a big rock? Do planets like Mars have molten iron at their core like Earth? What is at the centre of gas giants like Saturn, does the pressure cause the gases to react in any interesting ways?
|
[
"Most bodies orbiting the Sun have cores, for the most part they are made out of the densest materials found on that body (usually iron or silicates). For gas giants it gets a bit wired since they have no clear surface. They just increase in pressure gradually as you go deeper. For example on Jupiter at one point you get metallic hydrogen and from there on there is probably a small dense molten core."
] |
[
"You say Jupiter probably has a small dense molten core, but can you define small? Are we talking the size of a few miles wide, or more along the lines of a few Earths? I would think that Jupiter caught a lot of debris, from not only asteroids, but failed planets and moons over the last 4.5 billion years or so. Even if the planets and moons were torn apart upon entry, which I'm certain they would have been, wouldn't they settle in the middle of the planet?"
] |
[
"I expect the inner core to be between the size of Europa to the size of the Earth."
] |
[
"If the divergence of the magnetic field is zero, does that mean it always exists but its B is 0 sometimes?"
] |
[
false
] |
In E&M we went over the divergence of a magnetic field being zero while it has a curl. This brings me to my question: if the divergence of the magnetic field is zero, does this mean that there will always exist a magnetic field around a charged particle whose strength is zero when it is stationary? This seems to make sense to me since the field does not diverge from the source but it responds to changes in the particle's velocity.
|
[
"Divergence means this: If you draw any surface, is there more outward flux of the field than inward through the surface? For any electrically charged object, Gauss's law says that -- regardless of the shape of any surface you would draw around it -- the net flux of that field (out minus in) is proportional to that charge inside it. ",
"This statement for magnetic fields is this: it doesn't matter ",
" is inside the surface, the net flux (out minus in) of magnetic field through the surface is always going to be zero. This doesn't mean that the B field is zero. It just means that as much of the field is inward-pointing as it is outward-pointing."
] |
[
"The assumption is that if there were a magnetic monopole, then there would a law equivalent to Gauss' law, where the divergence is proportional to the \"magnetic charge\" of that monopole. So in a sense, the zero-divergence law for magnetism is saying that, as far as anyone can tell, there is no magnetic monopole."
] |
[
"The divergence is basically saying what happens to the field as you follow it. Because there are no magnetic charges, as you follow magnetic field lines they stay constant, so the divergence is zero. The curl tells you what happens as you move perpendicular to the field.",
"An electric charge monopole (which I think is what you're talking about) has no magnetic field in its rest frame, although in a frame where it is moving there is a magnetic field. This is a source of fine structure in atomic spectra.",
"There are also situations where the magnetic field is zero but the magnetic vector potential is nonzero, like outside a solenoid."
] |
[
"AskScience AMA Series: We are statisticians in cancer research, sports analytics, data journalism, and more, here to answer your questions about how statistics opens doors for exciting careers. Ask us anything!"
] |
[
false
] |
Statistics isn't what you think it is! With a career in statistics, the science of learning from data, you can change the world, have fun, satisfy curiosity and make a good salary. Demand for statisticians is on the rise, and careers in statistics are consistently on best jobs lists. Best of all, statistics applies to just about any field, so you can apply it to a wide range of personal passions. Just ask our real-life statisticians to learn more about the opportunities! The include: We will be available at noot ET (16 UT), ask us anything! Username: ThisIsStatisticsASA
|
[
"Are any of you at all worried about the huge output of data science \"boot camps\"?",
"It seems to me that an exceeding number of people come out \"knowing\" how to do statistics, meaning they can use code to test data but without having a deeper understanding of the limitations of using statistical approaches to describe the world around them.",
"Any thought on the value and risk of building a society where we are arming people with statistical testing without giving them the purchase of the theoretical or even ethical way to use these techniques?"
] |
[
"what are some unexpected/unconventional jobs you can get as a statistician? What stat related uni courses would you recommend that are most useful even for other majors?"
] |
[
"excellent question. I have found that most students (especially those who are taking it bc it's required) have very very low expectations (due to fear or bad rep that the class gets) so the silver lining to this is that you have no where to go but up!!",
"I have found that spending the first two weeks going through really interesting/provovative examples of real-life scenarios i.e. Alf Landon vs FDR election sampling issue or the conviction of Sally Clark works very well. I pick a few health headlines where the stats have been seriously misused and then ask them to bring some in.",
"Yes, those two weeks take away from maybe being able to get into multiple regression or something else at the end of the semester- but I have found it worth it to get them engaged and excited.",
"-LV"
] |
[
"Do trees create less oxygen in the winter after their leaves fall off?"
] |
[
false
] | null |
[
"Generally, yes. Photosynthesis, of which oxygen is a byproduct, happens in the chloroplasts. ",
"The vast majority of the chloroplasts are in the leaves, so a deciduous trees ability to produce oxygen is drastically reduced after shedding its leaves."
] |
[
"Here ya go.\n",
"https://www.jpl.nasa.gov/videos/watching-earth-breathe-the-seasonal-vegetation-cycle-and-carbon-dioxide"
] |
[
"That said, I'll mention it just in case, that's not an issue at all if you were thinking of the \"stock\" of available oxygen.",
"A few months after that Avengers movie with the Thanos snap, there was this interesting reddit discussion, in which \"what would happen if that snap also wiped half of the oxygen-producing plants and plankton\" was asked. And the fascinating answer is that the atmosphere contains centuries of oxygen in stock before a risk to run out is even foreseeable. So, we're cool ;)"
] |
[
"What is the mechanism for how alcohol affects your body?"
] |
[
false
] |
So I just did a quick google search to find the biochemistry behind the ingestion of alcohol, but my search has yielded diddily-squat. I know most recreational alcohol has many species of alcohol but the highest concentration of ethanol. My main question: What happens to ethanol once it enters the body and begins to be metabolized? Addition Questions: What neurotransmitters are affected? What causes the decrease in inhibitions? How is the alcohol metabolized? What does ethanol turn into? What happens to metabolized alcohol, is it flushed out in the urine? Thanks in advance reddit! I know you're smart.
|
[
"Your main question about alcohol metabolism is fairly well understood, it is oxidized to acetaldeyde then to acetic acid and excreted. The question about its neurological effects is actually a very good question because its on the cutting edge of research and really isn't well understood. ",
"Old textbooks, as well as new ones, will say that ethanol increases the fluidity of the plasma membrane, altering the activity of numerous neurons, but that's a little hand-wavey and the concentrations don't work right. Alcohols are now thought to act on many specific targets, most notably recent research points to members of a class of ion channels called GABA receptors (also possibly glycine and acethylcholine receptors). GABA, which stands for gamma-aminobutyric acid, is an inhibitory neurotransmitter that increases chloride current in GABA channels (it also binds other receptors, but the channel seems to be the important one in this case.) Ethanol ",
" this inhibition of the central nervous system by these channels, leading to altered function in many of the target neurons including, as you might know, glutamatergic cells that control motor function. Mood and decision making are also impacted by the overall depression of higher level consciousness, though I'm not an expert on the specific pathways involved. Other drugs , like barbituates or benzodiazipines (Valium), also increase the activity at these channels for use as anti-anxiety drugs. However, the activity isn't quite the same as ethanol (though they're all pretty addictive) because ethanol is much less specific.",
"Interesting paper on nailing down the specifics",
"Helping identify GABA channels as ethanol targets"
] |
[
"No problem, I really enjoy communicating science; its a big interest of mine. GABA channels are only one of the channels controlling chloride entry, sorry, I should have been a bit more clear on this point. Chlorine is usually at higher concentration outside of the cell, when it is allowed to flow in, the inside of the cell becomes a bit more negative since chlorine is negative (the cell usually rests at ~-65-75 millivolts, more chlorine makes this more negative). Usually, neuron \"firing\" is a depolarization, i.e. it becomes more positive, often with a flood of sodium or calcium into the cell, the increased chlorine suppresses this activity. ",
"So, to summarize, the GABA channels modify the activity of neurons by making them more negative and harder to activate (and yes, for ethanol we're focusing on the brain right now). Glutamatergic neurons release glutamate, the main neurotransmitter in the brain which mainly activates \"firing\" (by activating glutamate-activated cation channels like the AMPA receptor and to a lesser extent NMDA receptor). These cells are really the kind of \"workhorse\" of the brain, they're the processor and most other cell types modify their behavior (this is a real oversimplification, but it in a sense conveys the idea). So they fire maybe not more slowly but at a slower rate, and their activity is suppressed. Its okay when regulatory parts of your brain are trying to fine-tune your motor centers to let you pick up chopsticks with fine-motion and not throw them at the ceiling (a control sadly lost in many neurodegenerative diseases), then GABAs activity adds that fine counter-balance and level of control. A ton of Jager bombs during your graduation party however, takes this to a higher level, suppressing more than this sophisticated push-pull mechanism and depressing the entire system. "
] |
[
"Awesome! Great answer!",
"So the GABA channels control the flux of chlorine into and out of a cell? What kind of cells are talking about? Are we talking about neurons in the brain? So what exactly does GABA inhibit? The conformational change of the GABA ion channels to close, and not allowing chloride to flow? ",
"So does this influx of chrloide into the glutamatergic cells (which are neurons found in a certain area in the brain?) cause the cells not to function properly? What does that mean for a brain cell, to not function properly? Does it mean the brains cells fire synpases much more slowly? If so, why?",
"Thanks again for the fantastic response! I'm sorry to bombard you with questions that are not directly related to the OP."
] |
[
"Could someone please help me identify this mineral for my son? He is planning to take it to school for show and tell."
] |
[
false
] | null |
[
"It looks like ",
"bismuth",
". "
] |
[
"Technically, ",
" is the heaviest non-radioactive element; Bismuth is radioactive. However, it's so ridiculously stable that it's completely safe.",
"The half-life of the longest lived (and most commonly found) isotope is around 2x10",
" years, which is roughly 1.4 billion times the current age of the universe."
] |
[
"HOLY SHIT ITS BISMUTH!"
] |
[
"[Physics] Why do EM waves that reflect off a surface at very small angles polarize parallel to the surface?"
] |
[
false
] |
Preferebly with a nice metaphor to help a friend of mine understand
|
[
"When light encounters a boundary between two media with different indices of refraction, some will be refracted and some will be reflected. This is modeled by the Fresnel equations (which, I think gives the real scientific answer to your question ",
"https://en.wikipedia.org/wiki/Fresnel_equations",
")",
"I think that link provides all the answers you're looking for, but I'm pretty sure you're looking for a more \"EL15\" explanation too. First and foremost, you must have a good sense of visualizing things in three dimensions. There are lots of drawings of this phenomenon scattered around the internet, but I don't believe I have seen one that is appropriately modeled in 3D, making it hard to understand exactly WHAT is going on in the reflection/refraction process.",
"Visualize a ray of light coming straight toward the surface and then reflecting. Now, visualize the incoming light as being entirely unpolarized. So, along your light ray, imagine straight arrows extending perpendicular to your light ray, in all directions. (like this ",
"https://cnx.org/resources/98c42b0feabbfb691eec9cb507391dcbfef72a1a/Figure_28_08_04a.jpg",
", but make sure you have a good sense of how this picture looks in 3D)",
"Now visualize this ray making contact with the boundary of the two surfaces. As the ray makes contact, some of the EM represented by those arrows will be entering the medium before others do. These are the EM waves which are most likely to be transmitted into the medium (basically I think this occurs because part of the wave is already on the other side of the boundary before its other part gets there)",
"However, some of those arrows will not touch the surface until the entire length of the double sided arrow arrives at the boundary. (these waves are the ones polarized in the plane of the material) This makes the light unlikely to enter the medium.",
"For an analogy, imagine you take a random assortment of U.S. coins (pennies, dimes, nickels, quarters) and throw it at a screen completely saturated with nickel-sized holes. The smaller coins are more likely to make it through the screen, and the quarters will never make it through the screen. Your barrage of random coins is now \"polarized\". If everything but the quarters made it through, then it's completely polarized. But if you still have some leftover nickles, dimes, and pennies due to bad luck, then it's partially polarized."
] |
[
"Ohhhhhhhhhhh, I read the question completely wrong. ",
"/u/tbu720",
" gave a better response and I could have given a better one than I did if I had read it correctly. I read it as the wave reflects in almost the same angle it was incident in."
] |
[
"The situation is when light hits a surface nearly parallel to the surface, far from the normal. There's a critical angle below which the reflected light will be polarized parallel to the surface. I forgot the name of the effect however."
] |
[
"Do blind people have the same circadian rhythm?"
] |
[
false
] |
[deleted]
|
[
"I cannot speak to it in detail but I know some people who are blind have trouble with their sleep wake cycle. Its called non 24",
"https://en.m.wikipedia.org/wiki/Non-24-hour_sleep%E2%80%93wake_disorder"
] |
[
"I have answered this ",
"before",
", so I'll quote it here. ",
"[It's] a little complicated. First, we'll assume you mean totally blind, as even a little bit of sight (remember that legal blindness includes a range of low-acuity vision) will at least be able to tell light from dark. As long as the retina is able to convey light information to the suprachiasmatic nucleus in the brain, the circadian pacemaker (and thus the body's daily biorhythms) can be entrained to the 24-hour clock.",
"Circadian timing and biorhythms are entrained largely by solar cues, but there are other cues which entrain separate oscillators (e.g., food cues, which is one reason why you get hungry around the same times every day even with shifts in food intake). In lieu of entrainment, circadian rhythms will \"free-run\" without solar cues, even in non-blind individuals. This free-running clock is slightly longer than 24 hours (somewhere between 24 and 25 hours), which does create a problem in many (from what I've read, about half of) blind people who suffer from insomnia or other sleep/wake disturbances as their circadian clock gets more and more out of sync with daily time. Essentially, these people end up with life-long \"jet lag\". It has been suggested that daily administration of melatonin (at the same time each day) assists in entraining the clock and relieving sleep issues.",
"For a sample source, including some of the above results with melatonin, see: Sack, R. L., et al. (2000). Entrainment of free-running circadian rhythms by melatonin in blind people. New England Journal of Medicine, 343, 1070-1077."
] |
[
"this question interested me so I did a little research.. found this: ",
"The following is an abstract of a paper, \"Circadian rhythm abnormalities in totally blind people: incidence and clinical significance\", by Sack, R.L., Lewy, A.J., Keith, LD, and Nakagawa, H, 1992.",
"\"When people are completely isolated from environmental time cues, their circadian rhythms free run with a nearly 24-h cycle, generated by an internal body clock. Free-running temperature, cortisol, and melatonin rhythms have also been described in totally blind people, even though they were living in normal society and had access to abundant time cues; thus an intact visual system may be essential for synchronization of the circadian system. However, because of the small numbers of subjects studied, the incidence and clinical significance of circadian rhythm abnormalities among the blind has remained uncertain. In this study, plasma melatonin (n = 20), cortisol (n = 4), and sleep propensity (n = 1) were measured in serial samples taken from totally blind subjects for 24 h. Most totally blind subjects had circadian rhythm abnormalities. In about half of the subjects, the rhythms were free-running. Some blind subjects suffered recurrent insomnia and daytime sleepiness that were maximal when the internal rhythms were out of phase with the preferred sleep times. The high incidence of abnormal circadian rhythms in blind people underscores the importance of the light-dark cycle as an important environmental synchronizer for the human circadian system\"."
] |
[
"What makes hydrocarbons so efficient at storing energy?"
] |
[
false
] | null |
[
"They burn to carbon dioxide and water, and those reactions release a good deal of energy. There are plenty of other chemical structures that release energy in their reactions, but many of these are dangerously reactive (explosives, for example).",
"Carbon-carbon bonds, though, are stable in long chains (unlike many other elements), and substances like oil and gasoline are full of long-chain carbon compounds. In terms of energy release per unit weight, hydrocarbons are very good performers, especially for compounds that are stable on storage."
] |
[
"It's more the bonds that are being formed. Carbon dioxide and water, energetically, are quite a bit downhill from say, octane. Forming the two C=O double bonds is especially favorable, and the other thing that helps is that it's a gas. That means more entropy in the system when the reaction goes to products, and both of those (enthalpy of bond breaking and bond making / change in entropy) are factors in how energetic a reaction is."
] |
[
"Forgive me if this is getting too specific, but what exactly about the bonds in hydrocarbons make them release so much energy when broken? "
] |
[
"What plants have gone extinct along with animals over the years?"
] |
[
false
] |
So, I was reading about and I was wondering about quotes such as "17% of all families, 50% of all genera[6] and 75% of all species became extinct". Initially I assumed that only applied to dinosaurs and other types of animals and insects. However, did it also apply to plants, specifically fruits and vegetables? Do we have any information about the type of natural vegetation found that long ago? We can find fossils of walking dinosaurs and flying birds, but what about fruits and vegetables? Were there all types of completely unknown fruits and veggies back then that died off during a flood basalt event or something similar, so now we'll never get to try them?
|
[
"Well, I'm not a scientist, but Wikipedia's ",
"entry",
" on paleobotany seems fairly thorough, and it links to a list of ",
"extinct plants",
"."
] |
[
"That's awesome to know, and I promise I'll check those links when I'm not somewhere that blocks them."
] |
[
"That's awesome to know, and I promise I'll check those links when I'm not somewhere that blocks them."
] |
[
"Blood in stool sample, which kind of doctor should I go see?"
] |
[
false
] | null |
[
"Hi, we are sorry to hear about your symptoms. We don’t provide medical advice on this subreddit, all we can do is recommend you see a medical professional. If you have a general practitioner, that would probably be the most affordable option. The specialist who would deal with this is a gastroenterologist. ",
"Here",
" is some guidance on finding resources while uninsured."
] |
[
"You are amazing, thanks for your help"
] |
[
"Thanks, I really appreciate the info"
] |
[
"Ask Anything Wednesday - Biology, Chemistry, Neuroscience, Medicine, Psychology"
] |
[
false
] |
Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...". Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists. Please only answer a posted question if you are an expert in the field. . In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for . If you would like to become a member of the AskScience panel, . Past AskAnythingWednesday posts . Ask away!
|
[
"What are some possible experiments to support or refute the ",
"OrchOR",
" theory? I'm trying to think of something that shows any sort of information transfer along microtubules, and perhaps relating it to phosphorylation states of the tubulin and associated proteins. ",
"This paper",
" seems like a good example of the sort of data needed to be gathered to make progress in this theory. "
] |
[
"I think you may be confusing eye damage with evolution. While I'm not sure if constantly wearing coloured lenses would even cause a change, it's the ",
"intensity",
" of the light that causes damage, not the colour itself. Causes of colourblindness are genetic, or due to drugs/physical damage. ",
"On top of this, there is no selection pressure to drive the evolution. If wearing coloured lenses doesn't improve your chance for procreation, no new trait will be favoured above the old one(s), and individuals do not evolve, only populations. The most I could see happening by wearing glasses in this manner would be a reduction in sensitivity of your cones to certain wavelengths of colour, possibly leading to atrophy of some cone cells, but I would consider that highly unlikely. An MD would probably know more, but I don't see a viable path for evolution here, and even if there were, it could take thousands of years before any new trait emerged."
] |
[
"Neuroscientists: what scanning technologies are on the horizon? Is there soon to be a major increase in scanning resolution so that we can learn more about cognition?"
] |
[
"How does this occur? (Gif in text below). I know it's a prominence/flare but why is it spinning and circular?"
] |
[
false
] |
It appears to be almost the same size as earth. It appears to be spinning very rapidly and also appears to be a perfect globe. Why's it round? Where's the magnetic effects? How does it spin? It appears to be outside the corona, heat much?
|
[
"It looks a heck of a lot like a closed loop of magnetic field lines with some hot plasma trapped on it. The plasma will follow the field lines in a circle, and accelerating (circular motion) a charged particle (plasma) in a magnetic field can cause an emission of light - ",
"cyclotron radiation",
". These sorts of solar structures are usually associated with twisted magnetic fields which often contain closed loops.",
"Total (educated) guess here."
] |
[
"I'm trying to find a good graphic to illustrate it but I can't find any really good single ones so I'll link a couple of different ones. The basic idea is that, as different parts of the Sun rotate at different speeds (it's not a solid surface), the lines connecting those different parts get twisted up and wrapped around each other. ",
"This image tries to show that",
". If they get twisted tightly enough, lines can 'reconnect' to each other, like if you took a string in a knot, cut it in places, then took the cut ends that didn't match up and tied them together. This can turn what was once a knot of a single piece of string and turn it into a knot of many individual loops of string. When some self-contained ball of string is pushed to the surface it gets blown away and becomes a coronal mass ejection. ",
"This image",
" tries to show that progression, where in the last panel the field lines are about to reconnect and form closed loops in the places where they're very close together, which will make a free 'glob' that will be a coronal mass ejection. ",
"Here's the same thing viewing from the side",
". ",
"Here's one that tries to show the moment of reconnection",
", ",
"and here's another",
" that tries to show the whole progression."
] |
[
"Thanks, I'm still not getting how it actually forms the loop. Especially so far from the surface. There doesn't appear to be any reason. I understand the plasma can form a closed loop, although I've never seen it until now"
] |
[
"How can an alt-azimuth telescope align itself with only one star?"
] |
[
false
] |
I don't know much about astronomy, so I'll do my best to explain my question better. I own a Celestron telescope (Nexstar 90GT) that has a computerized panel to help find stars and track them as they move across the sky. The mount that the telescope is on can swivel in two directions; altitude and azimuth. When I power on the telescope, it will ask for some alignment information and give me a choice on what alignment method I want to use. One of the options is a one-star alignment. It's not very accurate, but it's good enough if you just want to quickly set up the telescope. The first thing it will ask is for the current time, timezone, date, and whether you use daylight savings. Then you simply select one of the stars on a short list and center it to complete the alignment. After that, you can use the telescope. You can ask it to go to another star and it will orient itself to within a few degrees or so of the other star. It will also track stars as they move across the sky. I'm curious how the telescope can know where all the other stars are given only the date, time, timezone, and location of one object in the sky. My intuition tells me that it would need at least two stars to determine the orientation of the sky around it before it can begin to make estimates of where other celestial objects are or to track the rotation of the earth. It boggles my mind. Unfortunately I haven't found much online about it (probably don't know the right astronomy terms to search). In my googling I learned about one-star polar alignment which, if I understand correctly, requires an equatorial telescope mount which my telescope does not have. Any explanation would be much appreciated. As a computer science student, if you could point me towards whatever algorithm and/or equations the computer is using to do this, I would certainly love to get hands on with some of the math.
|
[
"The telescope has a mathematical model of the Earth's rotation and orbit built in. Based on the time and date, the telescope knows the position and orientation of the Earth with respect to all the stars in the sky. Now all that's left to do is to find the orientation of the telescope with respect to the Earth. Specifically, it needs to know how the vertical axis of your telescope is oriented with respect to the Earth's spin axis.",
"It takes two angles to describe that orientation. If your telescope is level, they're just your latitude and longitude; if it's not, they'll be slightly different but it doesn't matter.",
"Anyway, you point your telescope at the star, and the position of your altitude and azimuth motors provide two data points to let the computer calculate the two unknown orientation angles.",
"The main reason this works is that while you'd think you'd need to know both the telescope's position on the Earth ",
" its orientation at that position -- four unknown angles -- those two things are redundant. If you flipped your telescope upside down so its feet were in the air before aligning it, it would think it was on the other side of the Earth, but it would still point correctly."
] |
[
"I see some ambiguity left. We know the time, so we know the point of Earth directly underneath the star. The telescope measures the star to be 70 degrees above the horizon. That narrows down the telescope position to a ring at the surface, and the orientation is a similar ring. If you want to go to a different star its' not unambiguous in which direction the telescope should go. For some position that star might be directly overhead, for another position it's 50 degrees above the horizon.",
"If the telescope can track the motion of that single star for long enough to detect the rotation of Earth then this ambiguity can be resolved."
] |
[
"Then how does it work? Unless it has GPS or a compass, one of them would remove the ambiguity."
] |
[
"Do wings on a spacecraft do anything while in space?"
] |
[
false
] | null |
[
"Short answer: ",
"Slightly longer answer: Wings do nothing at all significant while in high orbit. In a low orbit yes, you can get tiny amounts of lift as demonstrated by the ",
"GOCE",
" satellite but you're actually still in the (extreme upper) atmosphere at the 160km altitude GOCE was used at. It also didn't stay up there for all that long and needed an ion engine to counteract the atmospheric drag it experienced. You may be interested to know that the International Space Station experiences small amounts of drag too, and this necessitates little orbital boosts from time to time to keep it up there. At 370 km it's still not totally free of atmosphere's influence.",
"The particle density in deep (interplanetary) space is something on the order of ",
"5 atoms",
" per cubic centimetre at the radius of Earth's orbit, and this can generate no significant force at all on a spacecraft even with very large wings.",
"Solar sails are a slightly different approach and they use charged particles emanating from the sun, but they do generate a thrust force using naturally occurring particles in deep space so they have a little in common with wings. To achieve this they must have a huge area and the spacecraft's mass must be very low. Attitude control in the same way as a wing using control surfaces is not possible, and the force exerted on them is purely in an antisolar direction. Think of them like a parachute in a wind tunnel - they're not much like wings, they just carry the spacecraft away from the source of the gas, and even then acceleration is lethargic."
] |
[
"If you mount your reaction control system on your wing tips you may benefit from a more efficient production of torque, but I am not sure on the specifics."
] |
[
"This is correct, and you can think of it like a lever. The further you are from the center of mass, the more efficient it is. Think of putting a reaction nozzle in the center of mass. The spacecraft won't rotate if you fire it (it will accelerate slightly in the opposite direction though--a translational maneuver). As you move the nozzle outwards to the side, less of the energy pushes the \"far\" side, and more of it the \"near\" side, so the spaceship rotates. Ignoring the engineering considerations and just treating it as an abstract lever, the force becomes 100% rotational at infinite distance. Practically, it's good to put the nozzle as far from the center of mass as possible while still making the plumbing reasonable."
] |
[
"Are there mosquitos on atolls (islets, skerries, and cays) in the middle of the ocean? If so how do they even reproduce"
] |
[
false
] |
Mosquitos have to have standing fresh water right?
|
[
"True and fair, and a lot more detailed.",
"There are probably more places than just Antarctica where there's no suitable habitat or did source, or to which to mosquitoes haven't made it yet, or survived for long of they have made it there.",
"Mostly, it rains on these islands, so at least briefly there are fresh water opportunities, and brackish water makings. And where people and animals and sometimes debris make it, mosquitoes are likely to also have tried."
] |
[
"There is fresh water on those locations. It only takes two of the right kind of mosquito in the right place and time, and mood, to reproduce.",
"Yes, there are mosquitoes there.",
"Everywhere, I believe, except Antarctica. I’ve been to islands in the middle of the Pacific and have seen mosquitoes, but not to Antarctica. I recall hearing that on a documentary."
] |
[
"almost correct. there are islands with no mosquitoes other than the continent of Antartica. Iceland is a good example. With regards to non-human-colonized islands probably the majority of them have no mosquitoes (dispersal is a rare event).\nAlso note that a lot of mosquito species dont need “fresh water” per se but can survive and develop in semi-saline (think marsh waters) systems (e.g aedes taeniorhynchus, culex spp. and even aedes aegypti to some extent) .",
"With regards to how they get established within these islands, most commonly it is humans that carry mosquito eggs (tribe would be Aedini for these colonists) in these novel environments (think importing plants, tires, ships, cargo, etc.). Mosquitoes (insects in general) don’t suffer from inbreeding nearly as much as mammals do (Most islands have been colonized by a single introduction—-e.g bermuda) and are quite resilient to environmental catastrophes (hurricanes mostly in this context). "
] |
[
"How does sharpness work? If I had a blade that was impossibly sharp, could it cut through rocks like they were butter?"
] |
[
false
] |
Also, can sharpness be so sharp that the weight of the blade is enough to cut? ie A knife cutting through a table because its weight is enough force applied to cut.
|
[
"I see people giving you great theoretical answers with great science behind them, so I won't belabor the technical point they've already brought up and I'll move straight into the practical meat of the answer.",
"Short answer, no. This is because we don't have a material to make knives out of that would stand up to the rock. When making a knife, one considers its use when selecting not just shape and material, but what type of edge to put on it. The 'sharpest' edges are usually obtained by using a triangular blade profile with concave sides, sort of like a capitol letter V where the sides bulge inward. Think of a straight razor for shaving. In this sort of edge there is no profile change from spine to edge, just a smooth curve all the way down. This produces an extremely fine edge which cuts through things like hair, paper, skin, fabric etc... As though they're not there.",
"However, every time it makes a cut, a little material is worn away, and the edge is damaged a little. This is why extremely sharp blades have to be sharpened often to retain their keeness. The finer the edge, the more suseptable to damage it becomes. Think of two steel rods, one an inch thick and the other 3/32nd of an inch thick. Which is easier to bend? Edges are the same way.",
"Source: I'm a blacksmith who makes knives.",
" No, because the edge would become too fragile to cut before it obtained the desired sharpness. "
] |
[
"...except that the force/unit area also applies to the knife edge, which needs to be strong enough (and tough enough, which is a different issue) to withstand the applied stress."
] |
[
"I can't answer your main question, but I can answer your second question. Yes, a blade can be sharp enough that the weight of the blade alone is enough to cut things.",
"\"Cutting\" is applying force over area. If you have a barrel sitting on the ground, the weight of the barrel times the acceleration (gravity) determines how much force is distributed over the area of the barrel. Now, take 3 nails, and put them on the bottom of the barrel. Now, the entire force of the barrel is split over those 3 nails. If this hypothetical barrel was sitting on something soft, like swiss cheese, it is fairly likely that the pre-nail barrel would rest on the surface and that the nail barrel would sink in.",
"Now, imagine instead of the nails, you had a knife. The knife cuts through materials by applying force over area. The two ways to increase the cutting power are to apply more force or have the force applied across less area. As such, you can imagine that with a sufficiently small surface area (particularly sharp blade) the force of the weight of the knife times gravity should be able to cut."
] |
[
"How did omicron get *50*mutations? Would this happen in one host or would 1 or 2 mutations happen in one person and that transmitted just a bit better than delta?"
] |
[
false
] |
In other words….you’ve got the delta variant, which I assume is the variant omicron has fifty different mutations from? (Or is it 50 compared to the original?) Anyhow, person A has Delta. Does delta gain 50 mutations in person A, and so it transmits more and got to person B? Or does it develop 1-2 mutations reproducing in A, and go to B and mutate a few ways, then C? How many mutations can occur in an individual host? And, how many mutations would omicron need to become another variant that’s being tracked by authorities as a new thing? I’d assume just one if that one meant it travelled more successfully than omicron? Finally, let’s say we think of It like vehicles. Is this more like the Ford E350 where it can a bus or fire truck or ambulance or FedEx depending on what back you put on, but the core truck is the same? Or is more like a Toyota where each model broke off from another model by becoming roomier or sportier or fancier?
|
[
"A nit: omicron didn’t descend from delta, it’s a separate strain that developed, but wasn’t widely present in populations where testing occurs, about a year ago.",
"https://www.npr.org/sections/goatsandsoda/2021/12/01/1055803031/the-mystery-of-where-omicron-came-from-and-why-it-matters",
"I’m pretty sure the 50 count is relative to the original strain."
] |
[
"The latest hypothesis is it came from mice.. lots of unvaccinated animal reservoirs out there just brewing up variants.. White tail deer population is rife with corona virus ( same one we have)",
"Deer have Covid ",
"Mice have Covid ",
"all kinds of animals are Covid reservoirs ",
"Especially when you ‘humanize’ their lungs..."
] |
[
"A mutation is simply a mistake. When the DNA is copied, a mistake is made in that copy. That's all a mutation is. The copy mechanism for DNA is VERY good but you also can get 10,000 copies of a virus from a single cell. So, while mutations are on the rarer side (once every 10,000-10,000,000 copies), the numbers that we're dealing with here are huge also. It could be as often as once or twice per cell in your body that's infected.",
"Of course, a virus would have to mutate a couple times, then go infect another cell, and mutate a couple more times, then go infect another cell... the first 10,000 aren't going to have compounding mutations because they were created at the same time. So what we look at is generations. I couldn't find a number but I'm guessing there are a couple hundred generations in a typical cold or COVID infected human... might be something you can research.",
"But remember, those mutations are just mistakes. Some mutations have no effect on the virus at all. Some make that particular virus unable to survive. Some make the virus more or less deadly. Some make the virus more or less transmissible. The 50 mutations the scientists are talking about are 50 useful mutations that make Omicron less deadly, more transmissible, and better able to avoid vaccines.",
"The fact that only about half of everyone is vaccinated makes natural selection favor mutations that resist the vaccine. People with the vaccine get the virus in their airways, and the mucous in their head. The vaccine prevents it from getting into the blood and lungs and causing the really severe issues but being in the airways is bad enough. There, any mutations susceptible to the virus are killed but mutations that are more resistant are allowed to thrive. Those viruses can then go on to infect others and make more generations that are resistant. But those people wouldn't be infected in the first place if the unvaxxed and the unmasked would stop allowing it to spread so much. As one scientist put it, \"If I were the devil and I wanted to make a vaccine busting variant, I couldn't ask for a better experiment than having half the world's population vaccinated and the other half not.\""
] |
[
"What mammal is least related to all other mammals?"
] |
[
false
] |
That might have been a bad way of phrasing the question but basically you know how all animals have a closest living relative and that broader group will be closely related to a similar broader group so on and so forth but what mammal or even group of mammals is the most distant from all other living groups
|
[
"It's a little unclear exactly what you're asking, but the earliest branching event in the mammal tree of life is between monotremes (platypuses and echidnas) and all other mammals. This split occurred somewhere around 200 million years ago. However, the separation between platypuses and echidnas themselves is much more recent, perhaps as late as ~30 million years ago (",
"Phillips et al. 2009",
"). Since there is only one species of platypus, this is probably the biggest divergence you can find within mammals, as any other groups that are potentially on long branches will still consist of clusters of several species. E.g. pangolins, as mentioned in other comments, consist of 8-10 species that are clearly nested within the mammal phylogeny as the ",
"sister group to Carnivora",
" despite their appearance."
] |
[
"This is the current best guess based on phylogenetic data",
"So the first branching separates the monotremes from the rest. Monotremes include echidnas and platypuses. They have fur and largely resemble other animals, but still lay eggs, a carryover from our more repitlian past.",
"Then the next branching separates the marsupials from the placental mammals. Marsupials include the kangaroos, wombats, and so on that have external pouches (aka marsupium) where the young offspring continue to develop (marsupial give birth to much more underdeveloped offspring). ",
"Placental mammals have a placenta, where the young can develop to a much more mature extent before being born. The phylogeny within placental mammals gets more diverse and complex, and afaik is still under a lot of review, so I won't go too much into it."
] |
[
"You might want to add this ",
"phylogeny which is easier to read"
] |
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