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|---|---|---|---|---|---|
[
"Why is it a lightbulb can light up a room more than a fireplace, but the fireplace radiates a lot more thermal energy? . Or atleast so it feels like."
] |
[
false
] |
Question is basically in the title. I just wondered since thermal radiation is basically electromagnetic waves right? Or am i missing something? And shouldnt the intensity light=intensity of heat.. Only thing i could think of would be that the fireplace maybe is radiating a lot of its heat in the invisible spectrum? Just to make no confusion, since many answered this part. I meant that the radiating part of heat alone is stronger from a fireplace than a lightbulb. I know that the fireplace for obvious reasons will transfer also a lot of heat through convection/conduction too that a lightbulb won't do as much of because for one it's smaller. Some did answer what I was looking for though, specially thanks to them and thanks to everyone else who answered :)
|
[
"Radiation of thermal energy (as opposed to conduction of thermal energy) ",
" light, so when you say a fire feels very warm, it's because it ",
" producing lots of light, just not in the visible spectrum. ",
"Light bulbs were specifically designed to use materials that produce most of their radiation in the visible spectrum, for energy efficiency."
] |
[
"I was going to downvote you for the ridiculous '100% or more efficient' bit, but it turns out that these LEDs absorb heat from their surroundings to produce the extra light, so if you are only considering the electrical input and not the heat input this is technically correct. Interesting!"
] |
[
"Not true. LEDs are capable of producing 100% or more efficient optical light emission. ",
"Source"
] |
[
"Does a car run more efficiently on a full tank vs. a half-full tank?"
] |
[
false
] |
if not, is there a point where driving is less efficient? ex. 1/4 of a tank or almost empty
|
[
"The less gas in the tank the less the mass you have to lug around meaning it is always more efficient to carry less. That being said a full tank of gas weighs about 100lbs while a car weighs 4,000lbs so the difference in efficient is quite small. About 1% at a 1/2 tank assuming 20mpg."
] |
[
"In modern cars the fuel flow is tightly controlled. Pressure from the tank should have no influence on the fuel injection system. (Much) Older carburettors might be more susceptible to the feed pressure although where the sweet point is would depend on the particular car."
] |
[
"If I remember correctly it is the fumes the gas gives off that is the combustible part of the gas not the liquid itself therefore as long as you have a large volume of the fumes the amount of actually liquid doesn't matter."
] |
[
"What is our current progress behind Stem Cell research and what would its immediate uses be?"
] |
[
false
] |
I'm curious to how close we are to using stem cells for applications in which they would apply to. From the little that I do know about about them I recall that we produce them from cloned fetuses and genetically engineering them (not sure about this one). I only remember that they have the potential to regrow parts of the human body, would things like healing scars, regrowing teeth and limbs be possible? I have no idea what the most up to date information is on it, are we close?
|
[
"Stem cell research has boomed over the last few decades, resulting in a large amount of possibilities for cures in human bodies. Stem cells are found in their best conditions in embryos, and growing these stem cells in controlled conditions can result in beating hearts, functioning lungs (when placed into a human body of course) and other organs which are perfectly capable of being used in transplants. There are only two reasons scientists are not allowed to use embryos for stem cell research and medical research - one being that they have been banned by most governments because of the ability for people to live much longer lives which cound result in malnutrition from a sky-high population - and two being that it costs a lot of money to control the conditions which are needed to 'grow' these stem cells, which means the cost for the transplant would be much higher than one taken from a willing donor."
] |
[
"What is big right now is the use of 3D printing to \"print\" out new organs using a scaffold and the appropriate cells and growth media. I imagine we'll see huge strides in the next 10-15 years.",
"One of the major problems with stem cells is that certain individuals are not comfortable with human embryonic stem (hES) cells, or more specifically, how they are obtained. Back in the early 2000's about 33 hES cell lines were approved for research from ~day 6 post fertilization embryos. Only 11 are really usable, and to be honest, there are 3 cell lines that people tend to stick to. In the United States, Obama allowed for more use of more cell lines, but I've noticed people like to stay with cell lines that are well known and work well for them. ANYWAYS, a lot of focus has switched to induced pluripotent stem cells; problem with this is that they are not that reliable, turn into tumors, and net gain is minimal. But each day brings us a step closer!",
"If there were fewer politics involved, we'd be figuring out a lot more about diseases and organ growth a lot faster. Also, government grant funding is getting ridiculously low, but maybe a lab in the private sector will yield faster results.",
"But seriously, the 3D printing thing is going to get amazing."
] |
[
"That's intriguing that you could live much longer with the use of them and that governments would look down upon that. Almost seems reminiscent of that movie The Island. I suppose with increasing research and experience with stem cells the cost for growing the cells will become more reasonable."
] |
[
"Why and how can Parrots and a few other birds talk?..and is there any animals that talk that the common person doesn't know about?"
] |
[
false
] |
My main point is to get a good understanding of how a bird learned to talk through the evolutionary timeline and why?
|
[
"That's a bad example. Lyrebirds are fantastic mimics with zero understanding. ",
"However, many other species don't act that way. So for example, African Grey Parrots will use words from humans but won't generally try to imitate sounds around them unless they are actively from living creatures. so an African Grey may try to imitate a dog's bark or a cat's meow but won't generally imitate an alarm clock. There's a large body of evidence showing that African Greys are engaging in actual communication. The most famous is of course ",
"Alex",
" who was extensively studied by Irene Pepperberg and her lab group. There are documented cases of Alex telling other birds \"speak better!\" when they fail to pronounce terms. Alex was able to recognize colors, shapes, and count to small numbers. There's some (limited) evidence that Alex and other African Greys will coin words. The studies have all been carefully controlled so it is very clear that this isn't due to a Clever Hahns type result or anything similar. Subsequent work indicates that other African Greys in controlled conditions have capabilities near Alex's level. "
] |
[
"Corvids are considered some of the most intelligent birds on the planet.",
"Studies on magpies show that they possess self awareness, and many people speculate crows and ravens (cousins of magpies) possess the same cognitive behavior. There have been multiple studies on the intelligence of Crows and Ravens. Most notably in Japan where crows were found to drop nuts on the road to have the shells cracked open by passing cars, waiting for the light to turn red and then swooping down to pick up ",
"their meals.",
"I personally witnessed a large group of ravens in Fort McMurray, Canada working together to get into a large garbage bin. One raven would fly hold the lid open, while the others would get food. They would take turns so that everyone could get their fair share. Just like these crows do with a ",
"small garbage bin.",
"Talking Raven ",
"http://youtu.be/yFXU7o0fYII",
"Ruby the Talking Crow ",
"http://youtu.be/cgTCoTD3BWI",
"Terry the Talking Raven ",
"http://www.youtube.com/watch?v=-ZyBNWVD70w",
"Julian the Talking Raven ",
"http://www.youtube.com/watch?v=39Mk445CyME&playnext=1&list=PLF0BEB61D5874D88B",
"A Raven saying Nevermore and Waka Waka ",
"http://www.youtube.com/watch?v=rIX_6TBeph0",
"Snowboarding Crow ",
"http://www.youtube.com/watch?v=YP9RnDp_tms",
"Study on crow intelligence TED talk posted on Reddit some time ago.\nRemoved link due to the study being inaccurate. Here is the NY times link explaining the misinformation of the ",
"Crow Vending Machine",
"The Bait-Fishing Crow ",
"http://www.youtube.com/watch?v=y_8hPcnGeCI",
"Study on crows intelligence solving puzzles. In the last video the crow creates a tool to solve the puzzle. ",
"http://www.youtube.com/watch?v=SzEdi074SuQ",
" ",
"http://www.youtube.com/watch?v=M52ZVtmPE9g",
" ",
"http://www.youtube.com/watch?v=TtmLVP0HvDg",
" ",
"Talk on crows and ravens given by John Marzluff, he has conducted studies on Crow's being able to recognize human faces. Also they were able to determine that crows are able to pass this knowledge on to their children and other crows.",
"http://www.youtube.com/watch?v=XNuQURJJBlE&playnext=1&list=PL7E63F84DDB9E8D03",
" ",
"http://www.nytimes.com/2008/08/26/science/26crow.html",
"Crow Playing with ball and dog",
"Crow and Cat love",
"I don't know this woman and in no way affiliated, ",
"but her raven sings an aria and imitates her.",
" She has some radical Raven and Crow merchandise in the cafepress links in her video."
] |
[
"By talk do you mean repeat human sounds? Lots of animals talk, just not in English. Animal communication encompasses visual, chemical, auditory, and vibrational signals. In most birds, vocalizations like song and calls convey information, and in some species (e.g. mockingbirds, starlings, lyrebirds) females prefer males who have more complex 'vocabularies', or the largest repertoire of calls. This shows to the female that the male is healthy enough and smart enough to be a worthy mate. ",
"The actual mechanism by which parrots make complex sounds that sound human has much to do with the shape and complexity of their syrinx (the vocal organ of birds, equivalent to our larynx)."
] |
[
"Can the black and white TV static create a picture momentarily through randomness?"
] |
[
false
] | null |
[
"Hi PsychSpace thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"'mathematics'"
] |
[
"'Mathematics'"
] |
[
"Why does hot water freeze faster than cold water?"
] |
[
false
] | null |
[
"Out of the box, hot water does not freeze faster than cold water:",
"The cold water froze about 10 or 15 minutes faster than the hot water, and there was no detectable difference between the boiled water and the other kind. Another old wives’ tale thus emphatically bites the dust. Science marches on.",
"--",
"Which freezes faster, hot water or cold water?",
"However, there are conditions in which ",
" water freezes faster than cold water.",
"Then there is the strange Mpemba effect, named after a Tanzanian student who discovered that a hot ice cream mix freezes faster than a cold mix in cookery classes in the early 1960s. (In fact, the effect has been noted by many scientists throughout history including Aristotle, Francis Bacon and René Descartes.)",
"The Mpemba effect is the observation that warm water freezes more quickly than cold water. ",
"--",
"Why Hot Water Freezes Faster Than Cold—Physicists Solve the Mpemba Effect",
"Hydrogen bonding may be important:",
"O:H-O Bond Anomalous Relaxation Resolving Mpemba Paradox",
"Different Ways of Hydrogen Bonding in Water - Why Does Warm Water Freeze Faster than Cold Water?",
"The ",
"hydrogen bonding explanation",
" seems to be the most recent explanation, but that's not a guarantee that it's correct, of course. Some other explanations:",
"--",
"Does Hot Water Really Freeze Faster Than Cold Water?"
] |
[
"Absolutely not unusual. Our scientific knowledge is vast but the Universe is far vaster, so our knowledge is actually remarkably thin almost everywhere. There are innumerable commonplace phenomena that you only need to dig into a few steps to find a mystery that is currently unanswered by science (like, for example, ",
"how dominoes fall",
")."
] |
[
"I’m so shocked at the fact that we don’t know. I mean, us humans don’t know everything leading to the unknown mysteries. ",
"The idea of this question is so simple, but scientifically so complicated. ",
"Thanks for the responses. I’ve been thinking on this question for weeks beyond end. I’m so glad humanity has a platform such as Reddit. "
] |
[
"Is there a scientific explanation for a beer gut? Are they even real, or the result of being inactive?"
] |
[
false
] | null |
[
"Beer contains a high amount of calories. That is really why beer became popular. Back in the old days it was a good way to store cereal and grain crops to keep them from spoiling while maintaining the nutritional value. Many of the variations in styles of beers can be attributed to what grew well in particular areas. Given the amount of calories per serving and knowing how much some people drink it adds up quick. Consider that a regular beer on average has about 150 calories... If you kill a six pack you just consumed almost half of your daily caloric intake. If you do that on a regular basis and are not an active person (burning more calories than you take in) it will get stored."
] |
[
"At least according to this study, no causal link between beer consumption and abdominal obesity, at least not as opposed to consumption of wine/liquor. ",
"http://www.nature.com/ejcn/journal/v57/n10/full/1601678a.html",
"BBC news article about said study.",
"http://news.bbc.co.uk/2/hi/health/3175488.stm"
] |
[
"Yes. It's important to note that alcoholic beverages contain a lot of calories, both in the sweeteners used to combat alcohol's bitter taste (sugar is 4 calories per gram) but also the alcohol itself. Alcohol contains almost as many calories as fat (7 calories per gram versus 9 calories per gram). 4 oz of vodka is about 114 grams. At 40% alcohol by volume that's 320 calories from the alcohol content alone. Margaritas are intensely sugared and a a single serving of that can carry 500 calories or more."
] |
[
"What are the velocities of the arms of the milky way?"
] |
[
false
] |
[deleted]
|
[
"Something that you need to consider here is that the arms do not spin like a pin wheel. Rather the stars orbit the center of the galaxy independently of the arms. The arms are like compression waves in a traffic jam. Measuring the speed of the stars will not tell you the speed that the traffic jam is moving. "
] |
[
"The arms and the orbit of the stars aren't the same thing, basically. It's not a group of stars spinning around in the arm like a pinwheel, the 'arm' is a wave moving through the disc of the galaxy, bunching stars up locally.",
"There are animations on the wikipedia page that should help. ",
"https://en.m.wikipedia.org/wiki/Density_wave_theory"
] |
[
"The arms of a spiral galaxy aren't really \"objects\" though so I'm not sure it's even meaningful to assign them a speed. They are areas of higher stellar density caused by the cumulative motion of individual stars around the galactic core (and up and down through the galactic disc). Put another way galactic arms are an emergent property of stellar motion somewhat similar to a traffic wave."
] |
[
"What are the differences between comets, asteroids, meteors, and meteorites?"
] |
[
false
] |
Seriously? Is it the size, what they're made of, what? Please, science, enlighten me!
|
[
"Asteroids are from the ",
"Asteroid Belt",
", located between Mars and Jupiter. Asteroids are mostly rocky. Some asteroids have migrated from the Asteroid Belt region. If an asteroid is in near-Earth space, they're called a Near Earth Asteroid. If it moved to the region between Jupiter and Neptune, it would be called a ",
"centaur",
".",
"Comets",
": There are some who will only call an object a comet if it has a tail (or if it will produce a tail once it gets close enough to the Sun). Others will call something a comet if it's icy enough to have a tail were it close enough to the Sun, regardless of whether its orbit gets close to the Sun. Comets (those whose orbits will bring them close enough to the Sun that they will develop a tail) have highly ",
"eccentric orbits",
" with relatively large ",
"semi-major axes",
" (",
"or equivalently, orbital periods",
"). Using the later definition, 'comet' would include objects currently on stereotypically comet-like orbits as well as objects in the ",
"Kuiper Belt",
", ",
"Oort Cloud",
", and the vast majority of centaurs.",
"The main difference between asteroids and comets is composition: asteroids are mostly rocky (possibly with some ice), comets have a lot of ice. The outliers are the ",
"Main Belt comets",
", which have orbits within the Main Asteroid Belt, but which have been observed to have comet-like activity.",
"Since I've used the term a couple times, I should also define ",
"centaur",
": A centaur is an object whose orbit lies in the region of the giant planets (Jupiter to Neptune). Centaur orbits are not stable for long periods of time, they are transients. Most centaurs come from the Kuiper Belt.",
"A meteor is an object that hits Earth (where my use of 'Earth' here includes Earth's atmosphere). ",
"Meteorites",
" are the solid pieces that are left after an impact. Not all meteors lead to meteorites: a meteor could totally disintegrate in the atmosphere. These terms are independent of the origin or composition of the object that impacts Earth.",
"On size: some asteroids (and comets) are large enough to be considered ",
"dwarf planets",
". Examples include ",
"Ceres",
", ",
"Pluto",
", and ",
"Eris",
".",
"Edit: See also the 321science videos ",
"Asteroids vs Comets",
" and ",
"The Long and Short of Comet Periods",
"."
] |
[
"I agree with you except for the last part. You say pluto and eris are astroids (or comets) that are big enough to be dwarf planets but aren't pluto and eris kuiper belt objects and not astroids?"
] |
[
"You're right, they definitely aren't asteroids. Some people will call Eris and Pluto comets, which is why I put them in that list meaning for them to be understood as part of the '(and comets)'."
] |
[
"O.k., I've heard this a thousand times, that burr grinding will make a better cup of coffee because the grounds are more uniform. Does this really matter in a French press application if there is just as much total surface area touching the hot water?"
] |
[
false
] | null |
[
"If coffee is over-exposed to hot water, the water extracts bitter compounds from the grounds. The more finely ground the coffee is the less time it takes to extract the bitter compounds, and the faster your coffee turns bitter. The coarser the coffee is the longer it takes to extract the desirable coffee flavor.",
"If you have an uneven grind, the odds are you'll end up with small grounds that release the bitter compounds long before the good coffee flavor has been extracted from most of the grounds. With a large enough amount of grounds, you could always just brew it for less time, but most of the coffee would be wasted then.",
"As a matter of practical experience it's basically impossible to brew a pot of coffee using a blade grinder that doesn't have a detectable bitter edge to it without making it far too weak."
] |
[
"The reason I asked in the first place is that I've just not found that to be true. ",
"I do pour out all the coffee after pressing into a separate container; I don't find that any slurry is making it more bitter as it sits. Perhaps because it's not in an insulated container and gets too cool to make a difference, or maybe very little slurry gets into the finished coffee...I don't know much about partical theory in liquid...maybe the bigger grounds stay on top?."
] |
[
"I already wrote a brief answer but deleted it once I started having second thoughts.",
"My initial answer was that yes, uniformity matters greatly because each ground dissolves individually. If you have a mixture of ground sizes, the finer grounds will produce overextracted coffee by the time the larger grounds are at their optimal yield. ",
"/u/NoLemurs",
" seems to have raised this same point while I was typing.",
"The fact that a finer grind results in speedier extraction is not in any dispute, so I think we can set up the original question another way: if you mix overextracted coffee (smaller particles) and underextracted coffee (larger particles), will you end up with good coffee? Most people would probably intuitively say no fucking way, but I realize that I can't convincingly explain why this should be so.",
" Now I can. See ",
"my analysis here",
"."
] |
[
"Will hot tap water contain more minerals or chemicals than cold tap water?"
] |
[
false
] |
I've heard from someone that warm tap water will collect minerals or chemicals from the pipes that cold water will not or it will carry more of them. I've googled it a little and people are saying it has to do with solvency of the particles in the water or that hot water has been in the pipe longer. Others say that it is/was actually leaching lead from the solder used before 1988. What it boils down to is this, is this an old wives tale or is there some evidence to support using cold water over hot water from the tap? Are there more minerals in hot water versus tap? Is/was it just an issue with lead, but people continue it even though lead isnt in solder any more? Is there something I'm missing entirely that supports (or refutes) this? Thank you, scientists, for your help! Edit: thanks again for the help. I was hoping for more of a comparison as well. For example, all tap water travels through X amount of pipe, before some of it goes into the hot water heater. Where ever this water is coming from, wouldnt it also be sitting in some tank or pipes or w/e. Is the difference from sitting in the water heater, or being heated up and then going through pipes significant when compared to cold tap water?
|
[
"Most hot water tanks have a sacrificial anode made of magnesium or aluminum. The anode is designed to purposely corrode and prevent rust in the rest of the tank. So yes, water coming from a hot-water tank will contain a higher mineral content then cold water. That is my understanding of why things like coffee makers recommend using cold water instead of hot tap water. "
] |
[
"Do these minerals have any ill effects when ingested in higher quantities? My grandmother always freaked out when I used hot water from the tap to mix my daughter's bottles - is there a legitimate concern there?"
] |
[
"In both thermodynamic and kinetic terms, hot water is able to dissolve more things at a faster rate than cold water."
] |
[
"Is the Earth's gravity lessened by it's spinning?"
] |
[
false
] |
[deleted]
|
[
"The momentum granted to you by the spinning of the Earth does have a tendency to move you away from the Earth, and without gravity it would certainly fling you into space. With the effect of gravity, it has the effect of slightly resisting gravity.",
"But the spinning of the Earth creates more than a centrifugal force on you. The rotational momentum of a body as massive as the Earth causes it to have enormous kinetic energy, as angular momentum is a kind of stored energy, which, given the mass and the speed of rotation of the Earth, ",
". The fact that Earth is spinning actually makes it a fuckload heavier and more gravitationally attractive."
] |
[
"A small additional note - those 2 trillion kilograms may seem a lot to us, but compared to the mass of whole Earth (~6*10",
" kg) it isn't much. Those 2*10",
" kg are just a ",
" of Earth's mass."
] |
[
"I wish you hadn't said that, I wanted to make it sound like a big deal."
] |
[
"Why does hydrogen not exist naturally as a metal?"
] |
[
false
] |
Lithium with only 2 extra protons is a solid at room temperature (and is a metal). Why could hydrogen protons not be connected in a lattice with shared electrons bonding them (like a metal)?
|
[
"Such a state is theorized to exist, possibly in great amounts in Jupiter and Saturn. It requires extreme pressure like what is found in Jupiter and Saturn, and is a liquid. Actual observation is disputed. ",
"http://en.wikipedia.org/wiki/Metallic_hydrogen"
] |
[
"When you're talking at an atomic scale 2 more protons is a decent amount of weight and it's not just protons there are also neutrons which is why Lithium has almost 7 times the atomic weight of hydrogen. Basing the ability to be solid at room temperature on weight/proton content would also disregard other elements such as oxygen, any of the noble gases etc. ",
"The reason for the pressure is due to the ability of the atoms to form bonds with one another. Hydrogen in it's natural state is H2 or dihydrogen, this bond of H-H is extremely strong but as a result the attraction of H2 to other H2, the force necessary for closer bonds and more \"solid\" phases is near non-existent requiring either/both high pressure and Low temperature. Low temperature meaning less than 20K which is damn near close to no temperature at all. Essentially due to it's bonding nature with itself it cannot create the lattice structure necessary under the conditions of room temperature and 1atm."
] |
[
"Makes sense. How come Lithium doesn't bond with itself given that it also has only one electron in its outer shell?"
] |
[
"Why does steam come off of my water container?"
] |
[
false
] |
I drink my water out of a metal bottle thingy. When I put extra cold water in it from the sink it appears that steam is coming off of it. A) anyone else experience this? and b) what is it?
|
[
"A) Yep",
"B) It should happen when you open your freezer on a humid day. It's just water vapor in the air getting cold enough to condense into little water droplets that look like wisps of steam."
] |
[
"It is analogous to what happens to your breath in cold days. Moisture in your breath condenses down because of the colder air outside cools down the air you just expelled. ",
"In your water thingie you're probably seeing convection currents but I guess you probably live in a very humid place. "
] |
[
"Thanks! That was bugging me"
] |
[
"[Q] Can a strong immune system in a female negativly affect chances to become pregnant?"
] |
[
false
] |
.
|
[
"Semen contains chemicals that suppress the immune system.\nSperm are treated as non-self by the body\nhere is an abstract on the topic; the article is not free.\n",
"http://humrep.oxfordjournals.org/content/10/7/1686"
] |
[
"Most definitely, both in the stages of becoming pregnant, and in the stages of pregnancy itself. Although I wouldn't use the term 'strong' immune system, as it's a bit of a misnomer, there are immune complications that can affect chances of becoming pregnant. ",
"Leaving auto-immune diseases aside, as they affect all facets of life, a complication that is often overlooked is semen allergy. Some women are allergic to proteins present in their partner's, a condition called ",
"Hypersensetivity to Human Semen (HHS)",
". It can cause complications ranging from slight irritation to full-blown anaphylaxis. So you could definitely see this as negatively affecting chances to become pregnant.",
"Not directly on your question, but another common immune issue with pregnancy is what is known as ",
"Rhesus factor incompatibility",
". Basically, if a woman has rhesus factors that are incompatible with her partner, if the baby inherit's her partner's trait the body can have an immune reaction to the fetus. This is generally not an issue until a woman's 2nd or 3rd pregnancy, as it takes multiple exposures to incompatible Rh antigens to build up enough antibodies to cause a problem, and can be treated using a limited immune suppression regime close to birth",
"Hope I've answered your question!"
] |
[
"That's a great source, thank you!"
] |
[
"At what point along the evolutionary track did humans become sentient? What makes a species sentient?"
] |
[
false
] |
What differentiates homo sapiens from homo neanderthalensis in terms of intelligence? What about their common ancestor, homo heidelbergensis? What are the prerequisites for sentience, for example clothing or hunting techniques?
|
[
"There is no way of exactly knowing if an animal has ",
"theory of mind",
" yet we can try to find out by using carefully constructed behavioural tests as well as including observational data on day to day behaviours of individuals. One example might be ",
"the mirror test",
": \"to determine whether an animal possesses the ability to recognize itself in a mirror. It is the primary indicator of self-awareness in non-human animals and marks entrance to the mirror stage by human children in developmental psychology.\" However, the mirror test is biased in that it really only works for animals whose primary sense is vision. The previous wiki page provides a good starting point but I would also recommend other books by a number of scientists such as ",
"Age of Empathy",
" or \"Our Inner Ape\" by Frans de Waal, \"The Moral Lives of Animals\" by Peterson. More specifically books like ",
"Primate origins of human cognition and behaviour",
" or ",
"Animal Wise",
": where the author \"explores how this rapidly evolving, controversial field has only recently overturned old notions about why animals behave as they do. She probes the moral and ethical dilemmas of recognizing that even “lesser animals” have cognitive abilities such as memory, feelings, personality, and self-awareness–traits that many in the twentieth century felt were unique to human beings.\n By standing behaviorism on its head, Morell brings the world of nature brilliantly alive in a nuanced, deeply felt appreciation of the human-animal bond, and she shares her admiration for the men and women who have simultaneously chipped away at what we think makes us distinctive while offering a glimpse of where our own abilities come from.\"",
"First, it may be highly controversial to say this even here on ",
"r/askscience",
" but humans are not the only animal on this planet to have theory of mind. Other animals can approximate the mental states of other individuals within their groups and can also understand the difference between the self and others. This effects how we view animals in a profound way, no longer is there a clear and defining \"us\" vs. \"them\". I can go into more detail but these previous books do a way better job of thoroughly exploring the subject from a laymans point of view. Consequently, humans seem to acquire these abilities sometime around 18 months of age. I also know that there is extensive literature on theory of mind in humans with autism, although I am not familiar with the details of this literature. ",
"What are the prerequisites for sentience, for example clothing or hunting techniques?",
"There is no one single \"recipe\" for having or acquiring theory of mind. I can tell you it has little to nothing to do with anything you see that is modern around you (i.e. cars, clothing, tools or hunting). This is because people (or groups of people) and other animals without these things still have theory of mind. Even oral or written language as we know it today is not likely a necessary precursor to theory of mind. We can still have complex thought or processing without the need for complex language. Does oral or written language enable us to communicate in a more efficient way? Yes. I still don't think you can equate the two - perhaps (human) language requires complex thought, but complex thought does not require language. Many scientists hypothesize that \"theory of mind must have preceded language use, based on evidence of use of the following characteristics: intentional communication, repairing failed communication, teaching, intentional persuasion, intentional deception, building shared plans and goals, intentional sharing of focus or topic, and pretending.\" - all of these precede language and we see many of them expressed in animals, especially within the primate order. So first cognition then language.",
"However, animals that do have theory of mind tend to be highly social. Being social requires a lot of brain power in the sense that you have to be able to keep track of a number of individuals and your relationship to them. Long lived species need to keep track of these relationships through time. You also need to keep track of others relationship to other members of your group and you need to keep track of \"outsiders\" and \"insiders\". This stuff gets pretty complex. In order to navigate a complex social environment being able to tell yourself apart from others and even one individual from another is pretty critical.",
"What differentiates homo sapiens from homo neanderthalensis in terms of intelligence?",
"First I would ask you to define intelligence. It's not so easy, so what I can do is explain the differences in behaviour based on what we have found in the archeolgical record:",
"Neanderthals were able to use tools, well tools had been used by Hominins for millions of years by the time Neanderthals evolved and tool use isn't even unique to our lineage. But I digress, the tools used by neanderthals remained relatively consistent in design and use for their entire existence (from about 600,000 years ago to 24,000 years ago). On the other hand, human tool cultures were much more varied and were adapted to new environments. So humans have been described as better [tool] innovators than neanderthals. ",
"We lived in many different kinds of habitats and moved around a lot where as Neanderthals stuck to Europe. Therefore we have come to the conclusion that humans were better able to change our behaviour in order to survive in a variety of environments (tropics to temperate, deserts to alpine). We also had long-distance trade whereas neanderthal populations seemed pretty isolated from one another. Another indication that human oral communication may have been fast out-pacing the oral communication abilities of neanderthals (if they had them at all - some think that gestures played an important role in pre-language hominids, including early humans, in that they used gestures rather than words to communicate.) ",
"Neanderthals had jewellery, buried their dead, and probably made cave art etc. So they had some pretty complex cultures. But around 50,000 years ago human cultural activities exploded. There are statues, symbolic art, more complex burials etc. indicating a shift in our collective behaviour. This is known as ",
"behavioural modernity",
": \"It is the point at which Homo sapiens began to demonstrate an ability to use complex symbolic thought and express cultural creativity. These developments are often thought to be associated with the origin of [modern] language...One theory holds that behavioral modernity occurred as a sudden event some 50 kya possibly as a result of a major genetic mutation or as a result of a biological reorganization of the brain that led to the emergence of modern human natural languages\".",
"The control of fire and cooking date back between 500,000 and 1.2 million years with H. erectus. Fire is not unique to humans (Homo sapiens) or neanderthals."
] |
[
"What an amazing response! Thanks so much!"
] |
[
"Just a clarification: ",
" are \"the group consisting of all modern and extinct Great Apes (that is, modern humans, chimpanzees, bonobos gorillas and orang-utans plus all their immediate ancestors).\" The last common ancestor for all these species (i.e. what would have been considered the first \"great ape\" lived some 10 millions of years ago (sorry I forget the exact number). ",
" are \"the group consisting of modern humans, extinct human species and all our immediate ancestors (including members of the genera Homo, Australopithecus, Paranthropus and Ardipithecus).\" This group dates back about 6 million years ago. ",
"So the group you are interested in are the hominins, not hominids. Sorry if I previously mixed them up by typing in the wrong letter, which a single letter difference who can blame me?",
"The homo genus has been around about 2-3 million years and ",
" is generally considered to be the first member of the Homo genus, although this is sometimes debated and this species is placed with the Australopithecines. In general species distinctions are not set in stone within the hominin line. However, for the purposes of this discussion Neandertals and humans remain distinct species from previous Homo species.",
"Do you have any insight into interspecies relationships between humans and Neanderthals?",
"A little, well actually not a whole lot",
". We know that the range of overlap was small and that humans and neanderthals maintained distinct parts of their ranges. We don't know much about trade between the two groups but considering that neanderthal sites are not associated with human tools or artifacts suggest that trade was infrequent or non-exsistant. For example, Neanderthal spears were heavy and not well suited for throwing. Neanderthal skeletons tend to have a lot of injuries and some suggest that this stems from their hunting technique which was limited by their close-combat tools, so their were more likely to be injured by the prey animal. On the other hand, human spears were better for throwing and we could injure prey at a distance reducing risk for ourselves. Some might say there is a clear advantage to the throwing spear, so why wouldn't the Neanderthals adopt it where ranges overlapped? - A lack of trade? In-ability to communicate with humans? I don't know any recent papers which point in one direction or another, but there is something to be said for a lack of evidence for cultural transmission between the two groups. Moreover, just because a neanderthal site and a human site were found in proximity to each other does not mean they occupied that area at the same time, so we have to be careful about how we date sites and interpret the artifacts we find there. ",
"Humans did interbreed with neanderthals and about 1-5% neanderthal DNA is found in some human populations. A few things to think about regarding these findings:",
"A very small number of interbreeding events can account for the 1-5%",
"Gene flow was in 1 direction, neanderthals don't have human DNA. There could be many reasons for this. Perhaps neanderthal-female and human-male hybrids were unable to come to term, infertile or did not survive into adulthood. Perhaps neanderthal females killed hybrids because of cultural reasons. We can't really know fore sure.",
"We don't know under what context these interactions occurred. Were they hostile? rapes? was there mutual consent? ",
"In general, when two species occupy the same niche in the same area one typically outcompetes the other. We know that the neanderthal population was in decline and receeding in some areas before they encountered humans due to climate change. But where humans and neanderthals overlap it is more likely that they competed with one another over resources than worked cooperatively. \"Neanderthals were a separate species from modern humans, and became extinct (because of climate change or interaction with humans) and were replaced by modern humans moving into their habitat beginning around 80,000 years ago. Competition with humans probably contributed to Neanderthal extinction. Jared Diamond has suggested a scenario of violent conflict and displacement.\" So one researcher at least seems to argue for violent conflicts between the two species. "
] |
[
"Is their a theoretical limit to how big a supermassive black hole can be?"
] |
[
false
] |
I was reading article about attempts to measure the actual radius of black holes. It got me thinking...is there a limit to exactly how big a black whole could be? Could one, assuming it ate enough matter, become as big as entire solar systems or larger? If not, what would happen once it reached some limit? edit: and yes I know I used the wrong 'there' in the the title.
|
[
"Currently, there is no theoretical limit on how large a Black Hole could be. If it ate up a billion galaxies worth of matter, it wouldn't have any stability issues. ",
"If this got you thinking, read ",
"this",
". "
] |
[
"There's no limit as far as we know."
] |
[
"Depending on your definition, the universe has some properties of a black hole."
] |
[
"If capsaicin attacks our taste buds directly, what about spicy foods make us physically hot or sweat when eating them?"
] |
[
false
] |
[deleted]
|
[
"What do you mean \"attacks our taste buds directly\"?",
"You don't get physically hot from capsaicin. IT binds to and activates the TRPV1 heat receptor. Your brain just thinks you're hot. (This has been asked and answered many times before)"
] |
[
"Self recycled answer:",
"Capsaicin acts by by turning on the ",
"TRPV1 receptor",
". This receptor is sensitive to heat and several other chemical stimuli, but is not limited to the tongue. TRPV1 is present in the entire central nervous system. The trick to alleviateing the burning sensation (Remember that the receptor is sensitive to heat, so your nerves interpret this signal as \"hot\".) Is to present the active chemical, capsaicin, with a solution that it has a reater affinity for than the TRPV1 receptor. Milk and apparently ",
"10% sugar water solutions",
" are both effective at this task."
] |
[
"I'm not so sure about sugar water, but milk certainly works. Capsaicin is hydrophobic and doesn't get washed away well with water. Milk (specifically caseins in the milk) has a detergent effect on capsaicin. "
] |
[
"What else could the amount of energy that a human uses be used for?"
] |
[
false
] |
I.E. would the amount of energy used by a single person be enough to power a computer, a car for a day - and similarly how many peoples energy would you need to power something like a boat, an office block or a nation?
|
[
"Assuming 2000 Calories for daily intake:\n The energy would be equivalent to 1/16 the combustion energy of a gallon of gasoline. Which would drive my truck about 1 mile. "
] |
[
"Really? downvoted for an on-topic joke that isn't an anecdote, layman speculation, meme or medical advice?",
"Agent Smith must have an account on Reddit ..."
] |
[
"Or the matrix for about .0005 seconds."
] |
[
"How do denatured proteins in cooked food get absorbed and \"used\" in the body?"
] |
[
false
] |
What I mean is: Proteins are essential components in the body for building all kind of things like building enzymes....I also know that proteins denature at high temperature and that this process is irreversible as you destroy the disulfide bond between the amino-acids. So if you cook your food for example an egg you are destroying the proteins conformation. How can it still be used in the body? Does the body regenerate the aminoacids for usage?
|
[
"You already solved it - proteins are made from amino acids. Denaturing a protein just changes the conformation (shape) irreversibly. Your body would do that when you eat it. You need 22(?) essential amino acids in your diet that your body can't produce. Your body breaks down those amino acid chains and reconfigures them as needed.",
"EDIT - 22 total amino acids in human nutrition. 9 essential ones that cannot be synthesized from others. Thanks to ",
"/u/n00bz0rd"
] |
[
"There are 8 that cannot be synthesized by the human body: ",
"isoleucine",
"leucine",
"lysine",
"threonine",
"tryptophan",
"phenylalanine",
"valine",
"*methionine",
"There are 2 which can be synthesized, but studies have suggested insufficient productions (especially in infants):",
"*arginine ",
"*histidine ",
"1: Fundamentals of Anatomy and Physiology; Martini, Frederick H.",
"2: ",
"http://www.sciencedirect.com/science/article/pii/S0955286304000701",
"3: ",
"http://www.mayoclinic.org/drugs-supplements/arginine/dosing/hrb-20058733",
"4: ",
"http://pediatrics.aappublications.org/content/31/5/786"
] |
[
"There are only 8 or 9 \"essential\" amino acids for humans. The rest of them can usually be made by the body when necessary."
] |
[
"Why do clouds stay in \"puffs\" rather than just diffusing out all over the sky?"
] |
[
false
] |
Specifically nice big well defined clouds - what is keeping the water vapor or temperature difference from just equalizing?
|
[
"I'm a meteorologist. Hopefully I haven't screwed this up but I'm a bit out of practice since I spend most of my time at work looking at satellite pictures, radar, and weather models. Not on the science.",
"I believe the simplest answer is that in these clouds, the rate at which water vapor mixes out of a cloud through turbulence is equal to or less than the rate water vapor is injected into it, through moist air entering it from below, then cooling and condensing. Unless it isn't, in which case it dissipates. This doesn't take into account rain, which also obviously robs a cloud of its moisture.",
"Now why moist air is injected from below into a cloud makes for a much, much longer answer. It's a huge chunk of the material I had to learn for my degree and for my job training.",
"One reason air may rise from the ground is because the airmass in that area has become unstable. This happens when the rate the atmosphere cools with height exceeds a certain rate. In a dry atmosphere this is about 10 degrees Celsius per kilometer. When you have these conditions an air parcel rising from the ground will cool more slowly than the surrounding air cools with height, meaning it becomes warmer and less dense than the surrounding air, meaning it will continue to want to rise. ",
"Now, when one parcel of air rises, physics dictates that another parcel of air has to swoop in from somewhere to take it's place. So the atmosphere mixes, with some parcels moving upwards and others downward. Parcels will tend to move upwards in areas where the surface heats the most (more or less), and where the atmosphere will want to tend to become unstable first/the most. These preferentially heated areas are where cumulus clouds, the puffy ones, will form and sustain themselves.",
"Interestingly, when water condenses, heat is released, warming the air around it and making it less dense. This can cause a vicious cycle where air will become even more unstable and want to rise even further, which can allow for cumulonimbus, aka thunderstorms, to develop. It tends not to happen though, since the atmosphere is usually too stable at some layer of the atmosphere. Where the atmosphere is stable, a parcel rising will cool faster than the surrounding air cools, making it want to sink back to where it came from.",
"Another way for clouds to form is when one warm, less dense airmass moves overtop of a cold denser airmass. This happens along the warm front and these form nimbostratus, altostratus, cirrostratus and cirrus clouds. ",
"There's other types of clouds too. Orographic clouds, where air is forced upwards over a mountain. About six or seven different kinds of fog which involve the air near the surface cooling and condensing in some way."
] |
[
"Hi. You did teach me something about clouds and I am very thankful for that. "
] |
[
"Do you have any source of that? It almost seems like it would make sense, but I'm doubting it. I would think that the water molecules are too spread out in water vapor. It feels like an effect due to \"water tension\"/\"airborne tensions\" would be negligable or nonexistent. ",
"Edit: Wow... ",
"/u/Pyreload",
" completely changed his comment and answer. What I was replying to was that (I'm paraphrasing) he said that the clouds stayed together due to some \"airborne tension\" similar to how water beads up on tables (\"water tension\")."
] |
[
"Genetic diversity between dog breeds?"
] |
[
false
] |
[deleted]
|
[
"There is so much to unpack in that question (of what makes a species) that I don’t think I can really do it justice, because there are entire areas of biology devoted ONLY to that question. So I’ll tackle the easy one: Yes, presuming that the physics of inserting tab A into slot B didn’t get in the way, a Great Dane and a Chihuahua are perfectly capable of interbreeding. If you’re really interested in what makes a dog a dog vs a wolf, I would suggest picking up a copy of “The Domestic Dog” by James Serpell. It is an absolutely fascinating dive into the inner workings of the domestic dog, extensively (and I mean there are so many footnoted citations on the first page alone) researched and sourced. It is a somewhat chewy read (ie, this isn’t your typical beach murder mystery), but you will come away with a really great appreciation for these tame predators we share our lives with.",
"This is what Serpell offers as an introduction to the chapter addressing your question:",
"“After more than a century of argument and discussion, it is now generally agreed that the single progenitor of all domestic dogs, ancient and modern, was the grey wolf , Canis lupus , but when and where domestication first took place is still much argued about. Was the wolf domesticated in one part of the world or in many regions over its huge range covering the Northern Hemisphere, and what exactly constitutes a domestic dog? The word “ domestic ” means simply “ of the home, ” so any tamed animal may be said to be domestic, but if the term is to be used as a scientific descriptive it must have a biological definition, and there must be a clear separation between a wild species and its domestic derivative. A domestic dog is not a tamed wolf but is it a separate species? ",
"”To paraphrase the most frequently used definition (see e.g. Lawrence, 1995 , p. 551): a species is a population of animals that breeds freely and produces fertile offspring. If the hybrid offspring are infertile then the parents are separate species, for example the horse and the donkey. However, many animals that are normally considered to be separate species will interbreed with fertile offspring, as will all the wild species of the genus Canis , these being the wolf, coyote, and the several species of jackal. A more useful definition is the biological species concept which states that, “ species are groups of interbreeding natural populations that are reproductively isolated from other such groups ” (Mayr, 1966 , p. 19). Using this definition, all fully domesticated animals can be classified as separate species from their wild progenitors, from which they are reproductively isolated. The dog is no longer a tamed wolf but, as a result of selective breeding under human control, it has evolved into a new species, named by Linnaeus, Canis familiaris , which by further reproductive isolation and under the influence of both natural and artificial selection produces new breeds (Clutton-Brock, 2012 ).”"
] |
[
"What makes two breeds different is a collection of phenotypical traits. There are genes that control the appearance of the hair, the color of the hair, the shape of the head, the set of the ears, and so on. Different breeds have different collections of genes, and they have been bred so that they ONLY have that collection of genes, which is why when you breed two dogs of the same breed, you get more dogs of that breed. ",
"The domestic dog genome is pretty elastic, and that’s why you see such great variation of phenotype, but they’re still all the same species, and they can all interbreed freely with each other. The only difference between a Great Dane and a Chihuahua is that of phenotype."
] |
[
"The only difference between a Great Dane and a Chihuahua is that of phenotype.",
"",
"I have a different question. A German shepherd and a Eurasian wolf look much more similar to each other than Great Dane and Chihuahua do. Also the former pair can interbreed and I am not sure about the later. How do we decide that Great Dane and Chihuahua are one species and Eurasian and North Americon wolves are another single species?"
] |
[
"Why do immune reactions take place in the lymph nodes closest to the site of infection?"
] |
[
false
] |
From what I learned in high school, every B cell in every lymph node is entirely unique since the structure of the surface receptors is randomly generated, causing each B cell to recognise a different antigen. However, whenever there is an infection in the body, it always seems like the closest lymph nodes are the ones active, eg. under the jaw during a cold, or under the armpit after a vaccine. Wouldn’t there be just as much chance that the B cell able to identify your sore throat antigens lives in a lymph node further from the site of infection like the groin, ect.? Does the B cell travel to a closer lymph node once activated? Or are there many different B cells that can recognise an antigen to varying degrees, and the closest ones mount the fastest immune response, even if a B cell further away could do a better job?
|
[
"Your body has dendritic cells in basically every tissue, so when an infection happens the dendritic cell will mature and lose its adhesion to the tissue. After that it will follow a chemokine trail to the nearest lymp node where it will present the antigen to mature B and T cells in the lymph node. Your lymp nodes also monitor the lymph for antigens, so the closest ones to the infection site will get the most of them and will react the most due to the higher concentration"
] |
[
"The last sentence you wrote is essentially correct. The b cell that gets activated first, regardless of affinity, is the one that gets clonally replicated. Those clones have some randomization of their antigen matching site -> the ones that bind better get selected for future cloning -> ad infinitum until infection is clear.",
"Also, there are memory b cells of previous infections. Infections tend to be geographic; standard respiratory infections, hand infections, foot infections, etc. So those cells are already there for clonal proliferation."
] |
[
"In addition to the other answers, antigen naive (i.e. never-before activated) B and T cells circulate constantly between lymph nodes and blood. This maximises the chances of B and T cells finding their antigen and responding, even if the antigen is only found in those lymph nodes nearest to the infection."
] |
[
"It is said that the universe has no end, and is ever-expanding. But, assuming that we had a way to travel to (and possibly even beyond) the \"edge\" of the universe faster than it was expanding, what would we expect to be there? What would it look like? What would it even feel like?"
] |
[
false
] | null |
[
"This question can be found in our FAQ, along with others you may find interesting. Please take a look and let us know if you have any follow up questions. "
] |
[
"This exact question? Not to be rude, but I can't find it. "
] |
[
"You're asking what the universe is expanding into. There's a section on the ",
"expansion of the universe",
", including ",
"this post",
". "
] |
[
"How do quantum dots (>20nm) absorve and release vidible light (<400nm) if they are smaller than the visible light wavelength?"
] |
[
false
] |
Actually as I'm writing this question I also don't understand how we see materials, we do obviously see them but the atoms are smaller than the wavelength we see, so what is happening? Can atoms emit wavelengths bigger than their size? How? Or do we just see the cristaline structure of a bunch of atoms?
|
[
"Part of this answer is simple: the wavelength of radiation an object can emit is in no way limited by their size. Let's take a simple analogy, imagine you are standing on the short of a still lake with stick in your hand. If you tap the water periodically, you can create ripples that will radiate outward. You can control the rate of the ripples by how quickly you tap. If you tap slowly enough, then the wavelength can be much larger than your physical body.",
"In the same ways microscopic objects can radiate waves with a wavelength much larger or shorter than their characteristic dimension. Just in this case, the medium is not water, but the electromagnetic field and the stick is the light-matter interaction that transfers energy from the absorber/emitter to the EM field. Quantum dots are not really special in this sense. Even molecules and individual atoms, which are even smaller can emit visible light. Hell, even elementary particles which have no well-defined physical bounds and can be thought of as point particles such as electrons can emit visible radiation. For example the ",
"blue halo",
" in nuclear reactors comes from ",
" electrons that were accelerated to high speeds. ",
"Now there is a caveat to the discussion above, which is that by and large it is more efficient to transfer energy to and from a given field when the receiver matches the physical dimensions of the wavelength of the radiation. So to take your example, individual quantum dots are actually much better at sloshing up a fraction of incident light than a molecule. We would say that its absorption cross-section is higher. Nevertheless, in the grand scheme of things it still absorbs relatively little light. If you wanted to maximize absorption, you could use something like an optical antenna. Such a structure, in analogy with regular antennas would be closer in physical dimensions to the wavelength of the radiation to maximize energy transfer in both directions, ",
"as illustrated here",
".",
"edit: fixed the bit about Cherenkov radiation per mfb's comment"
] |
[
"I also don't understand how we see materials, we do obviously see them but the atoms are smaller than the wavelength we see",
"But you don't see the individual atoms, you see a material consisting of billions of billions of atoms. A material does ",
" behave just like a large pile of atoms, virtually all properties of a material are emergent, i.e. they are not present in individual atoms.",
"What you see is determined by the optical properties of the material, which are usually only indirectly related to the properties of atoms. For example, a piece of aluminium will look reflective because it is a metal, i.e. it conducts electricity. An individual atom cannot physically behave as a metal."
] |
[
"For example the blue halo in nuclear reactors comes from accelerating electrons. ",
"Their acceleration is not the relevant point. To emit Cherenkov radiation they just have to move faster than the speed of light in this medium. Sure, they lose some energy doing so, which changes their speed, but that's not the reason Cherenkov radiation is emitted."
] |
[
"Is there a sequence of moves that can be applied to a Rubik's Cube that results in iterating the cube through every possible state exactly once?"
] |
[
false
] | null |
[
"No. Take two moves, a and b, that don't commute, that is, doing a then b results in a different state than doing b then a. For example, twists of two adjacent faces. Now say that your magic move, g, done m times, results in a, and done n times, results in b. Now ab=(g",
")(g",
")=g",
"=g",
"=(g",
")(g",
")=ba, a contradiction."
] |
[
"It always fucks with me when someone solves a problem using group theory. It's so simple and yet I have zero intuition for it."
] |
[
"The second one is called Hamiltonian circuit and if you ask google about that, it says that yes, it exists, ",
"for example",
"."
] |
[
"Do small things (such as flies) view the movement of larger things (such as humans) as \"slower\" than we perceive it?"
] |
[
false
] |
I was thinking about how in movies and whatnot you will have something massive swing its fist and it will seem "slower" than a normal fist swing because of the relative distance it covers (for you it covers a large distance, for the massive thing it covers a short distance). Does this relative difference make the perception of the speed of the object any faster or slower?
|
[
"They can move across a landscape quicker than the speed of light in the same way a shadow can move quicker than the speed of light. Here is a wikipedia article with references: ",
"Faster-than-light: Light spots and shadows"
] |
[
"Hundreds of experiments with cockroaches reveal they suck at bullet time.I'm sure someone else will time how long it takes a survival impulse to travel to an insect's legs and make their tiny muscles do things for their size that would make them superheroes; and who knows how a lack of a consciousness would make them perceive the flow of time relative to us? ",
"But the effect is limited, at best. ",
"Besides, the \"big but slow\" thing in Hollywood is done for dramatic purposes so you can take in the size/destruction, and pretend that the squishies stand a chance against the giant robot. If we ignore all the stresses on metal or flesh that make anything humanoid from this planet at that size too fragile to do anything more than try to crawl a few feet, and likely destroy itself in the process, there's no reason at all that fighting a giant wouldn't be like playing in traffic, if every car and truck was determined to take you out and and didn't need to worry about a turning radius. ",
"That's before you consider that unlike in Hollywood, deadly space lasers would probably move at the speed of light. "
] |
[
"I'm sorry I have to shut you down like this, but deadly space lasers are beams of light in the first place, and can't go any faster than it's own speed. Sorry again!",
"Just wanted to clear it up in case some poor redditor didn't already know this."
] |
[
"Why do humans have different eye colors? Were they ever an evolutionary advantage?"
] |
[
false
] |
To my knowledge eye color doesn't affect your vision, and the only role I can imagine it plays in selection is an aesthetic one. Or is it perhaps desirable eye colors are linked to other desirable traits?
|
[
"A bit off-topic:",
"You should take a step away from the idea that evolution only 'creates' something because it would be advantageous to the species. Evolution is much more chaotic than you may think. Things just happen more or less by accident (mutation), and if these mutated species somehow survive (even if this new mutated trait doesn't serve any purpose - but also doesn't hinder them) they just keep it and it shows up every once in a while."
] |
[
"There is some material on blue eyes in Cochran and Harpendings ",
"The 10,000 year explosion",
". I'll try to summarize:",
"\n75% of eye color variation in Europe is caused by a single allele of the OCA2 gene. It's a very new allele, only between 10,000-6000 years old, so it must have a strong selective advantage. However, OCA2 is not an \"eye color gene\" but rather an important gene in the melanin pathway: Albinism is caused by two broken copies. ",
"Cochran and Harpending suggests that the advantage is not in blue eyes per se, but rather in reducing the function of OCA2: Reduced-function variants that causes albinism in homozygotes (but does not affect eye color in heterozygotes) are pretty common in southern africa, among the Navajo and in some parts of latin america. Since albinism isn't exactly advantageous, especially not in sunny regions, this points towards a ",
"heterozygote advantage",
". I haven't seen any speculation on what the advantage might be"
] |
[
"Further, why is it that only those of European descent (read: white people) have shades of eye colour different than dark brown? I've read that blue, green and grey eyes originate from Northern Europe, but that's about it."
] |
[
"Is neural activity affected by quantum uncertainty? Or are neurons too big for that?"
] |
[
false
] |
As far as I know, things are pretty much predictable at our level--you can predict a bullet's trajectory, whereas it seems you can't really predict a photon's. However, if it turns out that neural activity occurs on a small enough scale that things like quantum tunneling come into play, then perhaps our minds will never be predictable.
|
[
"We don't know. People have argued on both sides, and there isn't any evidence supporting quantum implications in neural activity in a major way. ",
"My opinion, as someone educated in QM, is that it's very likely no. The brain is too warm and the molecules too big for quantum behaviour to be a dominant part of the process I think. The heat means that the mean momentum of these chemicals is significantly larger than the uncertainty in their momentum by their approximate size. This is a good way of approximating quantum effects, is the product of your length scale and momentum scale on the order of the quantum of action (planck's constant)"
] |
[
"This is just a technical point, but it is often missed by people who have not heard of chaos before. A chaotic system is ",
" unpredictable in the strict sense of the word, since it is deterministic. It is just very difficult to guess the behaviour of a chaotic system for one set of initial conditions based on the known behaviour of the same system for another set of initial conditions."
] |
[
"(Computational condensed matter researcher here). As current theory goes, decoherence starts around mesoscale, unless you're pretty close to 0 K (",
"http://www.nature.com/news/2010/100317/full/news.2010.130.html",
"). Due to blood flow, the brain should be at a higher temperature than the rest of the body, in excess of 310 K. Neurons are (relatively) quite large, and thus (probably) aren't affected by quantum effects at normal temperatures. However, to answer the last bit of your question, the physical basis of consciousness, if it does in fact exist, is still unknown, and in any case unpredictability in the human sense and unmeasurability in the physical sense are two different and generally unrelated things"
] |
[
"Do satellites, like the Hubble Telescope, get dirty?"
] |
[
false
] |
I just saw a question asking about the remaining lifespan of the Hubble Space Telescope, and I was wondering if there is anything in space that causes satellites to get dirty, or rust, or otherwise deteriorate.
|
[
"Yes.",
"The space environment is pretty nasty. Atomic Oxygen, UV Radiation, Meteoroids/Orbital Debris all cause pretty severe surface degradation.",
"Here's a video explaining the effects of atomic oxygen ",
"https://youtu.be/bjyv7bK9X74",
"Here's a video explaining the effects of radiation on spacecraft ",
"https://youtu.be/lL5JnfWA6CY",
"And here's a video explaining the effects of charged particles ",
"https://youtu.be/GITtlkx2-Tw",
"And here's a comprehensive NASA guide on the environmental effects of space ",
"https://www.nasa.gov/sites/default/files/files/NP-2015-03-015-JSC_Space_Environment-ISS-Mini-Book-2015-508.pdf",
"Edit: and here's a good picture of the Russian Service Module on the ISS, that has been exposed to space for a long time. Look closely and you can see how dirty the once white surfaces are now. ",
"http://iss.jaxa.jp/spacerad/images/img_dos01_e.jpg"
] |
[
"This is one reason Gold is used in Satellites. It Reflects radiation and does not corrode. ",
"If you see a Satellite that looks like it is wrapped in a gold Mylar Blanket that is not gold it is a Polymer called Kapton with an aluminum backing which is a different type of Mylar Blanket and is an MLI, Multi Layer Insulation which also keeps the sat safe from degrading."
] |
[
"Surface degradation isn't really the same thing as being dirty though. Dirt can be cleaned, in principle. Degradation is irreversible without replacing degraded parts."
] |
[
"There's still time to start a project for the first Reddit Science Fair, hosted by AskScience!"
] |
[
false
] |
To all those forty thousand redditors who have joined AskScience since this was posted... You remember science fairs... a bunch of kids do science experiments, and present the results. It's the same thing here, except on Reddit, hosted by ! The Reddit admins have agreed to donate some awesome prizes, and AskScience will give you some sweet flair on our subreddit. Create and run an experiment by November 28th at 11:59 PM! This fair is all about , not . Make sure you're answering a question, and make sure you remember to hypothesize. Plan your experiment and complete it, making sure to spend no more than $40 US. After your experiment is done, write it up! Tell us what you did, what you learned, and what your conclusion is. Make sure you sum up the whole project in a one-paragraph abstract, too! Then post it to , again by November 28th at 11:59 PM. Make sure you do it before the deadline. After some judging-time, we'll make a post with some awesome prizes! Keep an eye out, because the AskScience panelists will be doing weekly workshops on Doing Science The Scientific Way (things like coming up with questions, making graphs, looking at data). These workshops will be at . ** and to keep up-to-date with the latest AskScience Fair developments!* Creativity! DIY materials! Testable ideas! Graphs! Pictures! Analysis! Friends or family! (Teams are ok, and so's doing it by yourself!) There's no age limit. There's no subject limit , but here are some things that aren't ok: Experiments with humans without their written consent aren't ok. Experiments that threaten community safety are not ok. No experiments with DEA-controlled substances or potentially hazardous biological agents. Unless you need to ask us about whether an experiment is ok, there's no need to tell us what your experiment's going to be. If you need help, feel free to post on . There are quite a few AskScience panelists who've volunteered to help out with questions. AskScience panelists are not eligible to compete. Judges are AskScience panelists who have agreed to help out on a volunteer basis. . While things you have lying around don't count as part of your $40 budget, keep in mind that following the spirit of the budget rule (intended to keep everyone on a level playing field) is a factor in scoring. Be creative! Judges might want some proof that you've stayed inside the cost limit. Keep your receipts. Projects need to be posted as threads on before to be considered. No late submissions. Your project must be developed for THIS contest, not something you've been working on for 4 months already. Give us anything you want in terms of format (link to a picture, link to a PDF, link to a Google document, link to the past), but it must include an "abstract" at the beginning telling us briefly what you did and found. An abstract is a short paragraph or two summarizing the main points or important ideas presented in your project. Try to avoid long youtube videos. In fact, try and avoid presenting your project in youtube format at all, unless you feel it really adds something. : When the deadline's passed, the projects will be randomly assigned to three judges each. That way it's not the same panel dealing with each project, and there won't be as much effect from individual scoring styles. Judges will be volunteer AskScience panelists. Each project will be scored by the scoring rubric, and the top three projects by score will receive prizes. Each judge will score projects to a maximum of 100 points, awarded as follows: Judges may post or PM questions to the entrants if they'd like further clarification. In addition to the top three projects by score, there'll be a few . These are: Judges' Choice: Presented to a particularly creative or all-around well-executed project that might not have made it to the top three. Best Research Question: Presented to the project with a really well-formed and creative research question. Best DIY Spirit: Presented to the project that best sticks to the spirit of the $40 limit - the "Doing The Most With The Least" award. Most Inventive Methods: Presented for ingenious investigative methods. Most Rigorous: Presented for best following the ideals of scientific rigor. Best Analysis: Presented for particularly fine analysis of data. Best Presentation: Awarded for excellent, clear, and impressive presentation of the experiment and results.
|
[
"Narf! I don't know if the top of your head would be the best platform for launching pumpkins, Brain. Poit!"
] |
[
"Tis the season for pumpkin launchers! There has to be an experiment in that somewhere!"
] |
[
"Closer to 50k now, I think."
] |
[
"What actually happens when I change the radio station in my car? How does my antenna know when I switch from 88.5 Newstalk radio to Oldies 101.1? Bonus points: why are FM stations odd numbers?"
] |
[
false
] | null |
[
"The antenna picks up the whole FM band. It gets amplified, then it gets combined with a variable Local Oscillator in a non-linear mixer which outputs the difference between the two signals to create an intermediate frequency at (typically) 10.7 MHz. So for 88.5 MHz the LO is 99.2 MHz. For 100.1 it is 110.8. That's how tuning is done. The 10.7 MHz is called the Intermediate Frequency. The IF is further amplified and filtered. This conversion to IF is known as the superheterodyne process. ",
"The frequencies all end in odd numbers because the channels are 200 kHz wide and the band starts at 88.0. So the center frequency of the lowest channel is 88.0+0.2/2=88.1. Each successive channel is 0.2 higher."
] |
[
"Inside the radio is an electronic circuit that resonates in a certain narrow frequency range. A signal recieved from the antenna at the resonant frequency is strengthened by resonating, even before any other amplification, whereas other frequencies do not resonate.",
"An ",
" is a simple example of a resonant circuit. It's just an inductor and a capacitor connected in parallel, and will naturally oscillate at a certain frequency like a weight bouncing on a spring, current and voltage flow back and forth between the two components. Changing the capacitance or (less often) the inductance will change the resonant frequency.",
"Real radios often use different, more complex circuits, but the idea is the same. On a radio with analogue controls the tuning knob is often directly connected to a variable capacitor.",
"Some types of antenna ",
" resonate. For an antenna it's desirable if it resonates well across the entire frequency band of interest, for example the 87 to 108 MHz used by FM radio, and then the circuits in the radio are tuned to resonate for a particular station in the band. Strong signals however can be recieved with a non-resonant antenna.",
"The range of frequencies used for a particular service, and the exact frequencies within that range, are a matter of local laws. The radio \"spectrum\" spans from a few Hz to hundreds of GHz, with different general frequency ranges having different pros and cons, and the spectrum needs to be divided up between broadcast TV and radio, air traffic control, police, ham radio, mobile phones, wifi, and many more. There are three broad regions - Europe Africa and the former USSR, the rest of Asia and Australia, and the Americas - with roughly agreed frequency allocations in each region, but nations can of course make their own laws.",
"FM stations being odd multiples of 0.1 MHz is North American practice, but in Europe even multiples are used as well and some countries even use ##.#5 frequencies. BBC West Midlands transmits on 95.6 for example.",
"A radio signal always has a certain ",
". For FM radio, for example Newstalk transmitting on nominally 88.5 MHz will have a signal that ranges from 88.4 to 88.6. Stations with centre frequencies too close together will have their signals overlap and interfere with each other."
] |
[
"The spectrum is divided into various bands. Avoiding interference is the main reason for spectrum regulation. I don't know why they chose 88-108 MHz for FM, but it was big enough to provide for 50 stations in each metropolitan area, but low enough for inexpensive receivers which all used vacuum tubes."
] |
[
"Won't landfills become fossil fuels in the future?"
] |
[
false
] |
Obviously assuming they are met with the same geologic phenomena that created existing fossil fuels. Essentially they are big piles of organic waste and plastic, which are already hydrocarbons. I guess I'm just curious as to what a future geologist would find when studying an area that was a landfill.
|
[
"There are organic and inorganic components, but the organic components do end up degrading. \"True\" fossil fuels usually require ",
"significant heat and pressure to form",
", but methane does get produced by bacteria breaking down organic material, and plenty of landfills capture this methane to burn or sell. ",
"The EPA page has a fair amount about capture and use of ",
"landfill gas",
"."
] |
[
"It’s a possibility but many of the conditions needed to make fossil fuels in the first place are no longer around. Coal cane from trees that died before bacteria or fungus existed to eat it, so it just piled up. Oil is created differently but I assume nowadays the process is no longer viable naturally. "
] |
[
"I didn't consider dams, but we are thinking on different time scales here, thousands of years from now yeah, there will still be a pretty big visible impact from what people have done so far. But millions of years from now? Rivers by their nature are ever changing, buildings will break down, radioactivity will decay, mines will collapse and be filled by geologic shifts or glacial movements. There was a series on the history channel back when they had stuff other than reality tv called life after people, it posed the question of what would happen the world if humans just disappeared. I was thinking about that show and it prompted the idea for this thread."
] |
[
"If weight is the measured effect of gravity on an object, and gravity is stronger the closer to the object’s center of mass the measuring object is, do objects high in the atmosphere weigh less than those on the ground, from a physics standpoint?"
] |
[
false
] | null |
[
"Yes, but the difference isn't very big. The radius of the Earth is about 6400 km (depending on where on Earth you measure). So if you're 10 km high in the atmosphere (the cruising altitude for long haul commercial aircraft), you're only 0.15% further away from the center of mass.",
"Since gravity is proportional to the square of the distance, that means there's a difference of about 0.31%. On a fairly average adult male of 80 kg, that's about a quater of a kg difference. This difference is certainly measurable, but it's also well within daily fluctuations of ones weight (a drink, a meal or a bathroom break could cause differences of similar magnitude)."
] |
[
"Provided the scales are calibrated well enough to reach the desired level of accuracy, yes. About a quarter of a kilogram for an 80 kg person."
] |
[
"So I weigh myself on a scale at the airport and directly as soon as we reach cruising speed, there will be difference??"
] |
[
"How do epidural shots work?"
] |
[
false
] |
I know that they block nerves but could anyone provide a more in depth explanation? (i currently am doing my first anatomy course in University and I've done a couple pharmacology course but this question didn't cross my mind until recently) Also, additional questions! What sort of receptors does it act on? What nerves do they block? what do the nerves usually innervate?? what sort of chemical is contained in an epidural shot?? how likely is someone to die/suffer an injury from an innaccurate / excess dose?
|
[
"I’m currently in anesthesia school and have been trained on epidurals. ",
"Some minor corrections to your comment.",
"Epidurals do not pierce the dura mater. They are EPI (above) durals. The needle pierces through the supraspinous ligament then the interspinous ligament then the ligament of flavum. The epidural space lies between the ligament of flavum and the dura mater of the spinal cord. If you pierce the dura you will deliver anesthetic directly to the subarachnoid space and that is called a subarachnoid block (SAB) aka a spinal block. ",
"Epidural injections usually consist of a local anesthetic such as lidocaine, bupivacaine, or ropivacaine. Often times narcotics such as morphine or fentanyl are added to increase the analgesic effect of the injection. ",
"Epidurals almost always utilize a catheter so that a continuous infusion of anesthetic can be infused into this space. This provides a longer nerve block than a spinal block that is a one time dose. Spinals can last about 1-3 hours. While epidurals can last as long as the catheter is kept in place and has medications infusing. ",
"The epidural infusion slowly diffuses across the dura mater to reach the nerves of the spinal cord where the local anesthetic takes action",
"Local anesthetics like bupivacaine work by blocking sodium channels on the nerve. When sodium channels are blocked, the nerve cannot depolarize and transmit impulses. There are different types of nerves that transverse the spinal cord. Some are for pain transmission, some are for sensory, and some are for motor movement.",
"Analgesics like morphine and fentanyl block opioid receptors in various places (I.e. dorsal horn) of the spinal cord so that pain transmission cannot be passed along to the brain for interpretation."
] |
[
"Here’s a very general layout (not a med professional, but have taken anatomy)",
"Your brain has 3 membranes surrounding it. \nThe Pia-Mater (soft mother) is right against the grey & white matter (grey matter “thinks”, white matter “conducts”).\nArachnoid membrane (called that because it has the blood vessels in it and looks like a spiderweb).\nand the Dura-Mater (tough or hard mother) is the outermost thick layer which also extends to cover the entire spinal cord (I can’t recall if the Pia-Mater and arachnoid do, they might though)",
"The term nerve block doesn’t mean it “closes” the nerve (not like a valve or bending a hose at least), but it stops signals from moving through it with a strong anesthetic.",
"An epidural shot uses a needle to pierce the Dura-Mater, going between vertebra, and put anesthetic right onto the spinal cord, thereby stopping/weakening any signals from below that point on the body. ",
"Epidurals are generally only used to numb the lower parts of the body because the higher on the spine it goes the higher chances are something will go wrong.",
"I do not know if epidurals always use the same anesthetic, but I do know that they are almost exclusively used for pain management. And I don’t know exactly what sort of transmitters are blocked but the receptors that send pain signals are called novice profs.",
"Epidurals are fairly safe procedures (when done by trained professionals, obviously) but problems can occur if the needle goes too deep, is misplaced, or some such."
] |
[
"Wow, thank you so much for that detailed response! Really appreciate it! :)"
] |
[
"Can you make a waterproof Shear-Thickening Fluid?"
] |
[
false
] |
Ok, as many of you are probably aware, the military uses a shear thickening fluid on kevlar to create pierce-proof body armor. They use Silica Nanopowder (or Calcium carbonate nanopowder) dissolved in Polyethylene Glycol, then they dilute it with ethanol, and soak the kevlar in it. Then they bake the kevlar to make the ethanol evaporate, leaving the Shear Thickening Fluid behind, between all of the fibers of the kevlar. Well, my question is this: Can you make a waterproof shear-thickening fluid that would do the same? I was considering using Polydimethylsiloxane silicone fluid that has dissolved calcium bicarbonate in it, and then try using Boric Acid to create the solidity needed? (This would be a variation of Silly Putty) And then maybe dilute it in pentane, dip a shirt in and bake the pentane out? Would this work? Is there a better waterproof liquid + calcium carbonate nanopowder that would make a better, or stronger Shear-Thickening fluid than the one I presented? Any help in this endeavor would be appreciated!
|
[
"You might want to try asking this question at ",
"r/AskScienceDiscussion",
" instead, since it's more of an exploratory question. I doubt anyone can tell you the answer to this simply because nobody's tried it before!",
"With that being said, a few things to consider: kevlar is already very strong even without the shear thickening fluid connecting it's fibers, so unless your shirt is made from something extremely strong it's not going to perform the same way. Second: ethanol or some other more aggressive organic solvent (like MEK) might be a better idea than pentane, since that won't disperse a particle of calcium carbonate very well.",
"Good luck!"
] |
[
"Two questions: how hydrophilic is the current kevlar armor, and why is it this way? ",
"I recommend you look into why a hydrophilic solvents are used before you consider alternatives. Changing the solvent you soak your kevlar could affect a lot of things (swelling the fibers, for example). Not saying an answer doesn't exist, but you'll have to consider it.",
"Also, if you're going to bake out your \"waterproof liquid\" how is it going to bestow waterproofing on your body armor? My guess is that your intent is for the PDMS to act as the hydrophobic agent, which may very well work. Something to think about: it's very doable to chemically modify silica so that it is very hydrophobic. This may be more compatible with existing manufacturing procedures. "
] |
[
"I think the problem with this process would be that the desired nanostructure that makes the coating what it is would not work. This is purely off the top of my head but i believe you will have trouble with the nanopowder actually setting into the fibers. Also possibly the carbonate reacting with weak acids in rain. - Current Nanotechnology student, not an authority."
] |
[
"With all the issues that chemical batteries have, why aren't capacitors used to replace standard batteries?"
] |
[
false
] | null |
[
"Is there something I am missing?",
"Yes. While capacitors have high power density, they have very low energy density, which is what you want in your batteries. In a water-electricity analogy: batteries would be like a swimming pool, and capacitors would be like a big bucket. Sure, you can dump the bucket out all at once, but then it's done. There's no water left. But with the swimming pool you can keep siphoning the water off and the water level hardly drops at all. Sure, you can't dump as much water out all at once like the capacitor/bucket, but you have a lot more stored in total."
] |
[
"I see, so the watthours of capacitors suck?"
] |
[
"That's correct. Capacitor energy is usually measured in Joules, which is = 1/3600 Wh. A large capacitor you might find in a flash camera can only hold around 5 Joules. "
] |
[
"Could sea creatures that live at great depths survive at 1 atm?"
] |
[
false
] |
Do they have higher internal pressure to counter the external pressure on their bodies? If so, would this cause then to swell and possibly “lyse” at the surface?
|
[
"That's actually the way many deep sea specimens are collected. If they are slowly acclimated to the decreasing pressure they can be brought to the surface alive. Live deep-sea squids and octopi caught by the Monterey Bay Aquarium Research Institute have been exhibited at the Monterey Bay Aquarium for short periods of time. They survive for a little while, but often die after a short period of time. However, their deaths could be caused by any number of stressors. Deep-sea environments are not the best understood, so it could be anything from differences pressure, nutrients, or temperature that kill them at surface level."
] |
[
"Many deep sea organisms can not tolerate 1 atm. Take for instance the blob fish:",
"https://i.imgur.com/pOMKdLl.jpg",
"This is in fact a somewhat normal looking deep sea fish whose tissues swell and lose structural integrity when they are brought up to the surface. This is a fairly common outcome for many attempts to bring deep sea organisms to the surface. This is by no means a universal problem and some organisms are adapted to allow for marked changes in pressure: sperm whales, colossal and giant squid all appear to tolerate quite marked changes in depth and pressure.",
"With regards internal and external pressure. The interior of deep sea organisms is at equilibrium with their surroundings so they experience no net pressure differential. They don't have an interior that is \"pushing out\" to resist the forces of water. Such a differential only manifests when they are brought up to the surface.",
"Contrast this to the sperm whale which dives from the surface to significant depths, they do have to maintain positive, internal pressure, while they dive. And even as well adapted as they are, sperm whales are not immune to problems which arise with large changes to pressure, and many show tell tale signs of having experienced The Bends",
"http://www.whoi.edu/oceanus/feature/even-sperm-whales-get-the-bends"
] |
[
"Suppose such animals are brought up slowly, similar to divers who decompress after being at great depths. Could they survive? "
] |
[
"If hurricanes in the northern and southern hemisphere spin different directions, what happens if one crosses the equator?"
] |
[
false
] |
Does it slowly change direction? Or does it die out, or continue in its old direction?
|
[
"They essentially can't cross the equator. Hurricanes rotate due to the Coriolis effect; the lack of such the closer you get to the equator means a tropical cyclone couldn't form at the equator, and would most likely die long before they reached it. Since records began, no tropical cyclone (nor a discernible remnant of one) have tracked across the equator. But there have been exceptional storms, like Typhoon Vamei, which formed very close to the equator, so it is hypothetically possible that a high pressure ridge could shunt a northern tropical cyclone south or a southern tropical cyclone north, and past the equator.",
"Nine times out of ten it'd die out before it reached the equator, and that'd be the end of it. If it was moving fast, it might retain its circulation essentially due to momentum for a very short while after crossing the equator, but would inevitably dissipate. It is conceivable, although even more extremely unlikely, that a tropical cyclone crossing the equator, after having degenerated (either just before crossing, or shortly after), would reenter favourable conditions further away from the equator and the open wave could develop a circulation once more (which would be in a different direction), thereby becoming a tropical cyclone. This would be a slow process, and operationally they would be considered two different storms."
] |
[
"Hurricanes can't ",
"cross the equator",
".",
"Essentially, within about 5 degrees of the equator the Coriolis effect essentially disappears. A hurricane forms because the rising hot air imparts a spin on the storm's motion. The spin creates the powerful winds and can helps absorb energy from the ocean's surface.",
"Near the equator the C. effect becomes negligible, even on the scale of a hurricane. The hot air just rises, but doesn't impart a spin. The storm basically just builds up and then fizzles away without forming a hurricane. Without the C. effect you don't get the tight central low-pressure eye, so you never get a real hurricane, just a boring storm.",
"In addition, the C. effect also tends to pull systems away from the equator. If you watch the paths of hurricanes, they virtually always go straight or turn away from the equator. For the next hurricane that hits the US, watch and it will almost certainly turn northward as it approaches the US. ",
"So basically, a hurricane can't form or survive near the equator. Because of that, a hurricane will never cross the equator. ",
"In the virtual simulation it did cross the equator, the hurricane would quickly fall apart. The loss of the C. effect acting on it would cause it to quickly dissipate, resulting in a tropical storm, but not a hurricane.",
"Edit: ",
"Here's",
" a great visualization showing that hurricanes always turn north in the northern hemisphere. You can see the paths always take the hurricane away from the equator. As they get far enough north they catch the 'Westerly Tradewinds' and turn back toward Europe. Usually, they get over cold waters and start to disintegrate that that point."
] |
[
"To be technical and nitpicky, it's less that hurricanes can't physically cross the equator so much as that it's very unlikely. But hurricanes can and do form and survive near the equator; Typhoon Vamei in 2001 is a great example.",
"Also the poleward movement of tropical cyclones is due to the beta-effect, positioning of subtropical high pressure ridges and generally inevitable interaction with upper tropospheric troughs, not the Coriolis effect."
] |
[
"Why does the speed of light squared have anything to do with the equivalence of mass and energy?"
] |
[
false
] |
[deleted]
|
[
"Just to make it clear to the OP, when we say \"speed of light\" we really mean \"the universal speed limit of spacetime\". Light really has nothing to do with relativity aside from light happening to have no mass, it playing a historical role in the discovery of relativity, and it being an easy way to teach relativity. If photons had mass, there would still be a universal speed limit, and it would not be the speed of light as light would, in such a case, travel slower than the universal speed limit.",
"With that said, in the specific equation E=mc",
" the c is really a units fudge factor. In natural units, the equation is just E = m. Natural units are not a gimmick but are central to the concepts of Special Relativity. In special relativity, a bit of time in one inertial frame can appear as a bit of space in another reference frame, so that space and time should really have the same unit. While it may seem weird to measure time in units of space (such as meters), that is exactly what Special Relativity is telling us to do. "
] |
[
"Just to make it clear to the OP, when we say \"speed of light\" we really mean \"the universal speed limit of spacetime\". Light really has nothing to do with relativity aside from light happening to have no mass, it playing a historical role in the discovery of relativity, and it being an easy way to teach relativity. If photons had mass, there would still be a universal speed limit, and it would not be the speed of light as light would, in such a case, travel slower than the universal speed limit.",
"With that said, in the specific equation E=mc",
" the c is really a units fudge factor. In natural units, the equation is just E = m. Natural units are not a gimmick but are central to the concepts of Special Relativity. In special relativity, a bit of time in one inertial frame can appear as a bit of space in another reference frame, so that space and time should really have the same unit. While it may seem weird to measure time in units of space (such as meters), that is exactly what Special Relativity is telling us to do. "
] |
[
"In terms of units of measure, the unit for energy is equal to the unit of mass, multiplied by the unit for speed, squared. What we call \"energy\" is just mass, times speed squared - and this is true everywhere, not just in relativity.",
"1 Joule = 1 kg * 1 (m/s)",
"For example, the kinetic energy of any moving object, in classic physics, is:",
"Ek = m * v",
" / 2",
"(the mass of the object, times the speed of motion of that object, squared, and then divide everything by 2)",
"For example, the kinetic energy of a car that weighs 2 tons, moving at 100 km/h (highway speed) is:",
"2 tons * (100 km/h)",
" / 2 = 0.7 MJ (megajoule), or the energy released by the explosion of 170 grams of TNT.",
"http://www.wolframalpha.com/input/?i=2+tons+*+%28100+km%2Fh%29%5E2+%2F+2",
"In other words, a car hitting head-on a stony mountain side at 100 km/h is like an apple-sized chunk of TNT going off, in terms of energy. Sounds about right, in terms of destruction.",
"Relativity is just a particular twist on this more general rule. Whenever you multiply mass, by speed squared, you always get an energy, as shown above.",
"Einstein simply demonstrated that there is an energy equivalent to the mass of any object - and the particular speed that binds them is speed of light, that's all."
] |
[
"Do all animals have distinct tissues?"
] |
[
false
] |
This question came up in my biology class, and I thought it was a tad vague. I would argue that they do not all have distinct tissues (granted a large majority of them do). If I understand correctly, porifera lack "true" tissues. If they do not have "true" tissues, is it fair to say that they would refute the notion that all animals have distinct tissues? I very well could be over-thinking this question. Thanks for the help!
|
[
"Porifera do lack tissues, although they do have several different cell types. The different cell types do not organize into specific tissues, however."
] |
[
"I am pretty sure mesohyl isn't a tissue. It's more of a matrix made up of collagen and other fibres. Porifera have specialized cells with flagella and what not but true tissues are endo-, ecto- and meso- derm. Some animals with true tissue lack a mesoderm but all animals with true tissue have endo- and ecto- derm."
] |
[
"I am pretty sure mesohyl isn't a tissue. It's more of a matrix made up of collagen and other fibres. Porifera have specialized cells with flagella and what not but true tissues are endo-, ecto- and meso- derm. Some animals with true tissue lack a mesoderm but all animals with true tissue have endo- and ecto- derm."
] |
[
"Why does smoking increase your risk of getting cancer in so many different areas of the body, not just your lungs?"
] |
[
false
] | null |
[
"Literature has definitely established a dose-response relationship between smoking cigarettes and lung cancers. This can also be said regarding cancers of the mouth and throat (as the cells are also directly exposed to the carcinogenic chemicals). While I am not well-versed in the literature relating the risk of smoking to other forms of cancer (and am not going to pretend like I am), whenever a malignant neoplasm (cancer) exists in one part of the body, it has the ability to spread (metastasize). Often times, the malignant cancer cells enter lymphatic vessels and accumulate within the lymph nodes (can result in lymphoma). These cancer cells can also spread to other tissues via the blood circulation. ",
"Sorry if this doesn't answer your question. Like I said, I am not well versed in the literature. "
] |
[
"Finally, a question I can answer. The lungs are composed of alveoli, small sacs with super-thin absorptive cells that facilitate gas exchange. The lungs are also HIGHLY vascularized, and the carcinogens themselves can enter through the lungs and travel through the bloodstream to virtually any target in the human body. "
] |
[
"The jury is still out on coffee. Working out doesn't because it has both things that would increase cancer and things that decrease it."
] |
[
"Isn't SETI pretty much useless if aliens are using some kind of digital transmission?"
] |
[
false
] |
Or am I understanding this wrong?
|
[
"Here is the basic premise of SETI:",
"Listening is better than not listening.",
"No matter how many resources we put into SETI, no matter how broadly we search, you can construct all kinds of scenarios SETI won't find the aliens. But that does mean we can't make some reasonable assumptions about what an alien transmission might look like, and look for that. Even if we are wrong, we can (and have) learn much from the effort."
] |
[
"No. If they were transmitting \"1\" at 110 MHz and \"0\" at \"90\" MHz then we could detect periodic spikes at 90 and 100 MHz."
] |
[
"relevant?"
] |
[
"What is the mass of the universe and how is it calculated?"
] |
[
false
] | null |
[
"The mass of the universe is only a meaningful question if you restrict it to the observable universe, or some other reasonable subset of the universe. You then have to define what you mean by mass - baryonic mass? (i.e, regular matter), matter mass? (regular matter + dark matter), total energy? (regular mater + dark matter + dark energy).",
"In any case, it is pretty straightforward to estimate.",
"Radius of observable universe = R ~ 47 billion light years",
"Volume of observable universe = V ~ 4pi/3R",
"Mass of observable universe = density of quantity * V",
"Density of baryonic matter ~ .05 * critical density",
"Density of dark matter ~ .25 * critical density",
"Density of dark energy ~ .7 * critical density",
"Where the critical density is given by roughly 10",
" kg/m"
] |
[
"Depends where your head is.",
"First, we need a cosmological model of our universe. Let's assume, three things. The universe is homogeneous (the same everywhere), isotropic (the same in all directions), and is governed on large scales by general relativity. Then what we get is the ",
"FRW model",
", and the expansion of the universe is governed by the ",
"Friedmann equations",
". These equations tell you everything you need to know about the universe, but first there are a few parameters in your model that you will need to measure: The Hubble constant (H_0), which tells us the current day expansion rate, the fraction of the energy in matter (ΩM), the fraction of the energy in dark energy (ΩΛ), and the fraction of the universe in curvature energy (ΛK). Given these we can compute anything we want to know about the universe. For example, the critical density of the universe is ",
"this",
", and the radius of the observable universe is ",
"this",
". How we measures all these parameters is a whole other bag of worms."
] |
[
"The amount of mass in the universe is calculated by how it affects (ie slows down) the expansion of space which is measured by the speed with which galaxies are receding from us. If there was a lot of mass in the universe the expansion would slow down and ultimately reverse (\"big crunch\") as gravity wins the cosmic tug of war. If there is \"just enough\" mass around, gravity and expansion would balance each other and the universe would come to a standstill. This years Nobel in physics was given to the discovery that in fact the universal expansion is accelerating, implying that there is way too little mass in the universe ",
"What's actually measured when looking at the rate of the expansion is the density of the universe with respect to the \"critical\" value where the expansion is perfectly balanced by gravity. Mass can then be inferred by multiplying by the size (volume) of the universe. The critical density is around 1e-28 kg/m3. Assuming the radius of the universe is 14 giga light years (1e26m) the mass is estimated to be at least 1e50 kg. In fact this is a lower limit since the radius of the universe is greater than 14Giga light years. "
] |
[
"If time slows down around a black hole then does the person falling in see a vastly sped-up outside universe before succumbing to tidal forces? How far does this go - seeing non local stars move around and disappear? Heat death of the universe?"
] |
[
false
] | null |
[
"Yes, pretty much so.",
"Perhaps the most surprising fact is that you don't need a black hole to see time outside speeding up. This effect has been demonstrated right here on the surface of earth.",
"The ",
"Mössbauer effect",
" has been used to measure gravitational redshift and it's one of the proofs of Einstein's general relativity theory. Rudolf Mössbauer got the 1961 Nobel Prize in physics for that. The Feynman Lectures on Physics has a good explanation on how this works."
] |
[
"GPS wouldn't work if we didn't account for the fact that time flows faster in space than on the earth."
] |
[
"It's both, but the time dilation due to gravity is more important. Time on the satellites is slower by 7 microseconds per day due to special relativity (their relative speed), and faster by 45.9 microseconds per day due to general relativity (the Earth's gravity)."
] |
[
"What is the air inside a bell pepper composed of?"
] |
[
false
] | null |
[
"Copied from an earlier question: source ",
"/u/danby",
" ",
"For peppers, The air in the void mostly has the same composition as the atmosphere and the air got there largely by diffusion through the fruit's tissues as the fruit (and the space) grew bigger.\nWith regards peppers; wild peppers are small and fairly packed with seeds, so there isn't a lot of space inside them at all. What space there is is present because, unlike their close relatives the potato and tomato they don't fill the cavity of their fruits with a liquid or gel. I'm not sure it is understood why chilli fruits don't also have a gel filling the fruit's interior but I would hazard a guess that it is likely to do with the fact that capsaicin (the spicy chemical) is not (very) water soluble.\nComing back to the larger sweet or bell peppers, these have large interior spaces because humans bred these peppers to have large fruits with lots of flesh and clearly the mutations which were cultivated for these traits did not also increase the size of the seeds by the same proportion.",
"https://www.reddit.com/r/askscience/comments/1ue4i9/the_air_inside_some_fruits_for_example_peppers",
"So I'm being original, here's what I get from it.\nThe air inside a pepper is the same as the air outside the pepper. Kinda how water from the ground becomes the water in the fruit, the air around the plant diffuses into the air inside the gaps. "
] |
[
"So ant man could theoretically live inside a pepper? Would it convert his CO2 to O2 within the pepper void so he could treat it as a diving bell?"
] |
[
"No idea what all the crazy talk is here but there are small holes near the stem so air can flow freely. Seriously put a pepper under water and give it a gentle squeeze. "
] |
[
"Is the radiation from a microwave oven considered a photon?"
] |
[
false
] | null |
[
"It's a stream of photons, yes. If the average photon has an energy of about 1.65-2.00 electronvolts (eV, a unit of energy) we call it \"red light\", if it's 2.75-3.26 eV we call it \"violet light\", if it's got 0.000001 eV to 0.001 eV we call it \"microwave\". There is no difference beyond that, \"microwaves\" are just light of much lower energy than visible."
] |
[
"A classical light wave is not a photon. It's a coherent state with indefinite number of photons. You can't say exactly how many photons there are, it's in a superposition of different photon numbers. The probability distribution for the number of photons is a Poisson distribution. So you can talk about the average number of photons. In the limit where the mean of the Poisson distribution becomes large, it behaves like a Gaussian distribution with the same mean, and with variance equal to the mean. So the relative fluctuations in the number of photons goes like sqrt(N)/N = 1/sqrt(N). For large N, the relative fluctuations are small."
] |
[
"What do you mean? Because the wavelength of a microwave is on the order of centimeters? As ",
"/u/RobusEtCeleritas",
" pointed out, a classical EM plane-wave like so:",
"https://en.wikipedia.org/wiki/File:Electromagneticwave3Dfromside.gif",
"is not made of a single photon. In fact, if you have a microwave that operates at 2.45 GHz then each photon has 0.00001 eV (or 10 ueV or micro-eV). Conversely, it probably runs at 1000 Watts, which if we assume for simplicity (we're just considering ballparked orders of size here), that it 100% turns that into microwave light, then 1000 Watts is 1000 Joules/second is 6250000000000000000000 (6.25e21) eV/s. That means it's \"making\" 6.25e26 or 625 trillion TRILLION microwave photons a second on average.",
"In fact a classical EM wave like the one above is actually, what is called, a \"coherent state\":",
"https://en.wikipedia.org/wiki/Coherent_states#Coherent_states_in_quantum_optics",
"which is to say that when light is most like its classical description, it is least like its quantum description of a fixed number of photons. In fact in a coherent state the photon number is in essence undefined."
] |
[
"Would it be possible or even beneficial to flood the Sahara?"
] |
[
false
] |
I was reading about some theories in th 1800s and 1900s to flood a part of the Sahara which, if i understood correctly, would turn Northern Algeria, Tunisia, and the lands north of the Atlas Mountains into islands and cover a relatively depopulated area into a sea. The water's evaporation would make the rest of the sahara more humid and improve agriculture. Until recently i would have dismissed this as either impossible or disastrous until someone told me that terraforming Mars to make it habitable was scientifically possible. If its possible to create conditions for plant life on Mars along with large bodies of water is it possible to reduce the Sahara and make it green here on earth? edit: What's with the downvotes? Are you afraid of a little intellectual curiosity? Nobody's saying it's a good idea or an idea that should be petitioned for and implemented. This is just a feasibility study. It'd be interesting if there happens to be an expert at who is an expert in meterology, large scale engineering, ecology, any field really. I'm curious if anyone's got an idea, it seems some do. You can downvote a wrong answer not a wrong question.
|
[
"Perhaps possible, with enough $, time and resources, but I think it is worth revisiting why the Sahara exists where it does. ",
"Global circulation atmospheric circulation is complex, but looking at a satellite image of Africa, one can observe large bands of arid desert roughly centered on the Tropic of Cancer and Capricorn, which roughly correspond to the 30 degree of latitude circulation cells described by Hadley Cells (",
"http://en.wikipedia.org/wiki/Hadley_cell",
"). Solar radiation heats the equatorial area, air rises and produces rain in the process. The rising warm (and now drier) air will move north and south on each side of the equator, descending around 30 deg north and south. As it descends this low moisture air warms. Of course this pattern is influenced by land masses and ocean, but is a pretty good indicator of why we observe deserts, rain forest and temperate areas across the earth. ",
"Even if we were to irrigate the sahara with a significant portion of the world's freshwater, the climate in the area wouldn't change. Salt would be a big problem in the sahara, since there is little surface water and no seasonal floods. Even in fresh water, there are trace amounts of salt. If we irrigate with fresh water on the surface and that water evaporates, over time, we will increase the salt saturation in the soil. We would need to be able to flush this salt out of the system somehow to prevent this accumulation. Maybe the water comes from the distillation of seawater, from some system that requires immense amounts of energy. This would produce very pure water without appreciable salt, but would require a huge battery of power plants. "
] |
[
"Never knew about that, so I went looking. Found this about ",
"flooding the Qattara Depression",
" near Cairo.",
"And then there's ",
"this paper about Saharan paleo mega lakes",
". ",
"Lake Megachad",
" once had a surface area of 361,000 km",
" , compared to Lake Superior at 82,100 km",
" ."
] |
[
"I would tend to agree. The amount of money and resources necessary to sustain this project would be exhaustive. The effects that we as humans could have in this region directly would likely not be enough to counteract the global circulation and tendencies to keep the region dry."
] |
[
"Do any animals respond to music in ways similar to how humans do, such as rhythmic foot-tapping (paw tapping?), etc"
] |
[
false
] | null |
[
"This is not very rigorous, but an example of animal response to music can be read in ",
"this",
" discovery article. The jist of it is that most animals will not have a reaction to music at all unless it's tailored to their ears, though some will be calmed by certain types of music. Many farmers believe that cows will relax and ",
"produce more milk",
" when classical music is played in the barn at milking time, but there are so many other factors involved that I think more testing needs to be done before one can say conclusively. Many animals will mimic human movements (when there is music present or not) as they are usually rewarded for such behavior, such as the adorable ",
"Juno",
". It's hard to say wether or not he is influenced by the music, however. In conclusion, they may respond by being calmed, but likely most animals will have no response at all, and any dancing or movement is probably a learned behavior."
] |
[
"Actually, yes it is, it's just not statistically significant. It's a data point. But taken in aggregate,",
"Schachner and her colleagues next studied thousands of YouTube videos showing animals dancing. The researchers checked to see which species had rhythm and could align their movements to musical beats. They identified 14 parrot species and an Asian elephant that appear to have this ability.",
"Source: ",
"http://dsc.discovery.com/news/2009/04/30/dancing-birds-rhythm.html",
"(I take your point however. It's just that the way ",
"/r/askscience",
" defines \"scientific\" is more narrow than the way scientists define the word. All science starts with observation. ",
"/r/askscience",
" is about published results. So yeah, I get it.)"
] |
[
"Actually, yes it is, it's just not statistically significant. It's a data point. But taken in aggregate,",
"Schachner and her colleagues next studied thousands of YouTube videos showing animals dancing. The researchers checked to see which species had rhythm and could align their movements to musical beats. They identified 14 parrot species and an Asian elephant that appear to have this ability.",
"Source: ",
"http://dsc.discovery.com/news/2009/04/30/dancing-birds-rhythm.html",
"(I take your point however. It's just that the way ",
"/r/askscience",
" defines \"scientific\" is more narrow than the way scientists define the word. All science starts with observation. ",
"/r/askscience",
" is about published results. So yeah, I get it.)"
] |
[
"Could a beam from a flashlight cause motionless smoke to move in a 0g vacuum?"
] |
[
false
] | null |
[
"Hi DronesForYou thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"'Physics'"
] |
[
"Physics"
] |
[
"Why do several citrus fruits have pre-made slices?"
] |
[
false
] |
I know it's a common question, but I haven't seen the answer yet.
|
[
"Pictures and discussion on attempting to eat wild oranges",
". ",
"Like most plants in grocery stores, oranges have been changed massively by selective breeding. Wild relatives are harder to separate and are often so acidic that they're capable of causing chemical burns - not to mention uglier and seedier. ",
"Hesperidiums are modified berries. Individual orange segments are called carpels, and are like swollen flower petals. I'm not sure why they always have segments but I've found oranges where one carpal was bad but the rest were fine - I think it's about compartmentalizing failures."
] |
[
"I'm a biology undergrad taking a Taxonomy of Flowering plants course so I can explain it in rather layman's terms. The type of fruit that come with \"pre-made slices\" are called hesperidium which includes the Rutaceae family(citrus fruits). What's happening is that during development of the fruit, ovules(immature seeds) attach to a placenta that runs from the top to the bottom of the fruit(axial placentation), and further compartmentalize themselves into two or more locules(pre-made slices)."
] |
[
"What was the evolutionary pressure for the slices? They seem incredibly useful for human-like hands."
] |
[
"AskScience AMA series: Geochemistry and Early Earth"
] |
[
false
] |
Today I am here to (attempt to) answer any questions you may have about early Earth, lunar history (particularly the late heavy bombardment), 9 million volt accelerators or mass spectrometers that can make precision measurements on something smaller than the width of a human hair. I am a PhD student in Geochemistry and I mostly work on early Earth (older than 4 billion year old zircons), lunar samples, and developing mass spectrometers. I have experience working in an accelerator mass spectrometry lab (with a 9 million volt accelerator). I also spend a lot of my time dealing with various radiometric dating techniques. So come ask me anything!
|
[
"There are several reasons but the strongest is: No one was around to watch it happen.",
"All we can do today is collect samples from Earth, Moon, and other bodies in the solar system (including meteorites) and compare them. What we know is Earth and Moon are identical in many isotope systems that have been measured (including O and Ti) and these isotope systems tend to vary around the solar system (from looking at meteorites). This observation suggests that Earth and Moon have a similar origin, perhaps are even made of the same material. From this however, all you can do is model likely scenarios that observe the laws of physics and currently there are 3 main contenders. ",
"However, Moon and Earth being so similar isotopically but different in elemental composition (Moon is depleted in volatile elements) brings up its own set of questions including how can you lose volatile elements but NOT fractionate their isotopes. I think this is probably the big question that will need answering from the chemical side of things going forward. ",
"The chief difficulty remains though in that we don't have adequate samples (heck adequate samples may not exist) and that chemical information is difficult to use to constrain a dynamical model."
] |
[
"So the first contender is two approximately equal mass bodies (1/2 earth mass) merged and then in that collision a moon formed. My gut suggests that this is unlikely and if you shift the mass ratio too far one way or another you end up with a moon that is not the same composition as Earth. The saving grace to this one is it lines up quite well with our current accretion models for Earth which suggest that the last stage was dominated by a few very large impacts. However, those models also should be taken with a grain of salt.",
"The second contender is that a small body hit a really fast spinning Earth and this caused some of Earth be launched out to form a moon. This one seems most likely although the evidence for it objectively isn't better than the other two. We suspect impacts happened quite frequently in the early solar system and so seems plausible.",
"The third contender is that a large object had a glancing collision with Earth and then went on it's merry way. My gut issue with this one is where is the large object? I suppose arguing it went into the sun is a cheap way out here but I'm not totally convinced.",
"Finally, it would help if we had a precise age of the moon and there weren't disagreements by 10s of millions of years."
] |
[
"That is a great question and the answer is it depends on the transition. For example between the Hadean and Archean there is no real transition or boundary, people even dispute when it is at the 100 million year level. It is not at all clear that there is a meaningful distinction between the Hadean and Archean (though the geological record for the Hadean is very poor). For other geologic divisions things like the appearance of a fossil is used to define the start of that period and the accuracy of the ages gets much better. For example the start of the Cambrian is known to ~1 million years. Actually looking at the timescale of the changes is another matter because it is entirely possible that a lot of the observed spread is simply because we cannot get precise enough ages. For example if we date something to the million year level or even the 50,000 year level that is quite good geologically speaking but still much longer than the written historical record.",
"For the Hadean/Archean transition the two lines of thought go it should be at ~4 billion years ago because the rock record goes back that far or it should be at ~3.8 billion years ago based on analyses of Hadean zircons. "
] |
[
"Is it true that there is only \"one\" actual photon/particle that exists?"
] |
[
false
] |
The question will seem a little odd but bare with me. I'm reading a book which, to enhance story line, mentions feynmans integral formulation and explains how a particle, say, a photo will take every possible path through space-time to go from A to B. It then goes on to say "there is only one photon in the entire universe, and that photon, spread across all of creation in a vast probabilistic smear, that one photon is responsible for all the light we see." I understand that particles will undergo all possibilities and will only show one when observed but i assumed that there were still a number of particles, not one expressing itself in many different outcomes. I was just curious if through some quantum science-y thing this actually was true and how. The book is "How to live in a science frictional universe" if anyone was wondering. Edit: Have to apologies for the bad english, writing isn't my strong point.
|
[
"No. That's a ",
" melange of the path integral maths formalism and the principle of indistinguishability.",
"The path integral formalism is just a way of doing maths. The technical details won't be helpful here, but you can think of it as being an application of Lagrangian mechanics to quantum physics, with an emphasis on Lorentz invariance. In other words, instead of focusing on the Hamiltonian, which varies in different frames of reference, the Dirac/Feynman formalism focuses on the Lagrangian. Each individual possible trajectory — for very liberal definitions of \"possible\" — has associated with it an amplitude that's given by, if I remember this correctly, something like ",
" with an ℏ in there somewhere, where ",
" is the action, or integral of the Lagrangian over time. Sum up all those terms, and you get the overall probability amplitude picture between those two events. Because some trajectories are separated from others by a pure phase, their contributions cancel out, which is mathematically equivalent to destructive interference in the wavefunction. What you're left with is only those trajectories along which the action is stationary.",
"Put more simply, it's an application of the principle of least action to quantum mechanics. It doesn't mean particles ",
" split into pieces and move along every possible trajectory any more than the calculus of variations in classical mechanics really means particles constantly try out little wiggles before deciding that nope, their action really is minimized along this one particular trajectory.",
"The principle of indistinguishability is even simpler. It just says that if you have two particles of the same kind in a box, the state of the box is a linear superposition of states corresponding to \"particle A and particle B\" and \"particle B and particle A.\" In other words, you can't attach little \"Hello my name is\" stickers to the lapels of each particle and keep track of which of them is which. In truth, not only is it impossible to tell which particle is which, but it is in fact meaningless to distinguish between them, because in superposition their discrete identities are wholly lost.",
"Does that mean there's only one electron? Of ",
" not. Chemistry would have a hell of a hard time if there could only be one electron at any given instant! All it means is that every electron is exactly the same as every other electron. Quantum field theory is consistent with this, because it treats electrons as states of the electron fermion field. So you ",
" without being too imprecise, say that electrons are all indistinguishable because they're all part of the same field. (And the same applies to other fermions and to bosons as well.)"
] |
[
"Chemistry would have a hell of a hard time if there could only be one electron at any given instant!",
"I think he means ",
"this",
". Of course this is not true either, but in the early days seemed possible. From what i read this was supported by the existence of positrons which are mathematically viewed to \"travel backwards in time\" electrons.",
"If this would be true you would need an equal amount of electrons and positrons, which, from what i know, is not the case."
] |
[
"You may have ruined the book for me but damn i feel a lot more educated.",
"Cheers and upboat for you."
] |
[
"Neptune hasn't \"cleared its neighborhood\" since Pluto regularly enters it. Doesn't that technically make Neptune not a planet according to the official definition by the IAU?"
] |
[
false
] | null |
[
"Clearing the neighborshood doesn't mean there's nothing else in it's orbit - by such a definition, Earth wouldn't be a planet, since there are asteroids which cross Earth's orbit. So we need a less draconian definition.",
"One approach is to divide the mass of an object by the mass of everything else in that orbital region. For Earth, this value is above a million - meaning Earth is a million times more massive than everything else in it's orbit. For Neptune, it's above ten thousand. Pluto's value is 0.077. So you can see, Pluto is definitely not the dominant influence in ot's region of space, the way the planets are.",
"You can read more here."
] |
[
"Kupier belt objects are within Pluto's \"neighborhood\", their mass is significant when compared to Pluto causing it to fail that criteria."
] |
[
"The orbits of Pluto and Neptune don't actually cross. Pluto's orbit is highly tilted so they will miss eachother and they're in a 2:3 orbital resonance.",
"Lots more details and pictures on Wikipedia"
] |
[
"Does tanning really age you?"
] |
[
false
] |
Or is it just that it damages your skin?
|
[
"Age is a constant thing... you'll never be older than 20 or 30 or whatever actual age you are. ",
"But you can APPEAR older than your actual age if you damage your skin, abuse your body, etc. ",
"If you're asking if the changes from a tanning bed are reversible, they aren't. Once the damage is done, it's permanent. Temporary fixes can improve texture and tone (moisturizers and Botox), but they don't last very long. For youthful skin, the best bet is to stay away from tanning beds and use sunblock. "
] |
[
"UV rays break down components of your skin like collagen and connective tissue, leading to earlier wrinkles and a dried-out, leathery appearance. ",
"The UV rays can also break down the DNA in the basal layers of your skin, potentially leading to skin cancers. "
] |
[
"The dried-out, leathery appearance: is that aging or just damage?"
] |
[
"If Chimp and Human DNA are so identical, why can't they produce a hybrid offspring similar to mules and zebroids?"
] |
[
false
] |
[deleted]
|
[
"Infertility is a result of the specific genetic differences between two species, not a result of the overall %genetic difference, much less the placement into same or different genera. As for why humans and chimps can't produce hybrid offspring, well, one crazy russian guy did some research back in the first half of the 20th century, but I don't think you can say that the idea has ever been extensively tested. It's possible that it could happen. You can write the grant application for that one.",
"Craziest hybrid animal...well there's the wholphin. That animal's parents aren't even in the same genus! Lots of plants will cross-fertilize with anything, as well."
] |
[
"Horses and donkeys also have differing chromosome numbers."
] |
[
"Horses and donkeys also have differing chromosome numbers."
] |
[
"Radiometric Dating: How do we know the parent:daughter isotope ratio was initially 100:0?"
] |
[
false
] |
A few simple questions about radiometric dating: I would gladly take articles about the last two questions with open arms if people could point me in the right direction. Thank you.
|
[
"Firstly, it's really important to distinguish between ",
" dating (which is what you're referring to) and ",
" dating. Radiocarbon dating is just one technique in a whole suite of radiometric techniques, which all work in slightly different ways and are appropriate for different timescales (e.g. radiocarbon dating is only effective for the past ~50,000 years) and materials. Radiocarbon dating is therefore generally unsuitable for dating rocks, since 50,000 years is not enough time for most consolidated rocks to form, and only very specific sedimentary rocks have enough organic carbon anyway. Your question (3) is therefore not really answerable since radiometric techniques that are applicable to rocks work in a very different way to radiocarbon dating, with different assumptions (they tend to use multiple isotopic ratios so that you do not directly need to know the original ratios).",
"To answer the question though, in radiocarbon dating, what you actually measure is the ratio of the parent isotope (",
"C) to a ",
" isotope of carbon, (",
"C). Because this ratio is extremely small (in all cases, ",
"C is much more common than ",
"C), we often write this ratio using the δ",
"C format, which basically tells you how much ",
"C you have compared to a standard reference ratio, where positive values mean you have an excess of ",
"C and negative values mean you have depleted ",
"C.",
"The key principle of radiocarbon dating, as you probably know, is that the radioactive isotope ",
"C is constantly being produced in the atmosphere through the decay of ",
"N induced by cosmic rays. ",
"C is radioactive however (with a half-life of 5730 years) which means as soon as ",
"C is created, it starts decaying at a known rate. We measure δ",
"C rather than just the concentration of ",
"C because ",
"C is nonradiogenic (i.e. it is not formed by the decay of any radioisotopes) and is nonradioactive, so its abundance is fixed over time. Under a simplified model, anything actively taking in carbon (i.e. anything that obtains its carbon from the atmosphere or living organisms) is constantly exchanging with this atmospheric reservoir of carbon, and therefore its δ",
"C is equal to that of the atmosphere. Once the organism dies and is no longer actively exchanging with the atmosphere, it is no longer in equilibrium with the atmospheric δ",
"C, so the radioactive decay of ",
"C results in the exponential decay of its δ",
"C. The deficit of the measured δ",
"C of organic matter versus the 'equilibrium' atmospheric δ",
"C (known as Δ",
"C) is therefore directly related to its age. Unfortunately, as you guessed, this simplified model is not entirely accurate, because fractionation effects during photosynthesis and disequilibria between atmospheric and marine reservoirs means that the δ",
"C of biosphere/marine reservoirs is ",
" exactly equal to that of the atmosphere. So in answer to your question (2), we are aware that the δ",
"C of organisms is not exactly equal to that of the atmosphere, and this is a known (experimentally measurable) effect and I would recommend reading a review such as ",
"Trumbore 2009",
" for more information (or for information about atmosphere-marine equilibria, let me know and I can send you some papers). Nevertheless, this is an effect that you can quantify and account for.",
"The bigger issue with radiocarbon dating is that, whilst ",
"C is constantly being formed in the atmosphere, it is ",
" formed at a constant rate and as such, the δ",
"C of the atmosphere changes over time. This is the main uncertainty in radiocarbon dating (at least for the terrestrial biosphere) and it is why good estimates of formation rates of ",
"C over time are absolutely fundamental to obtaining accurate radiocarbon dates. Other radiogenic isotopes formed through cosmic ray interactions in the atmosphere, as well as Δ",
"C measurements from archives with known dates (e.g. tree rings) are used to understand how ",
"C formation rates changed over time. Once you understand that, you can produce transfer functions that convert your 'measured' Δ",
"C age to an 'actual' Δ",
"C age. ",
"Reimer ",
" 2013",
" would be the paper to read for that.",
"Hope this helps!"
] |
[
"Going to piggyback off this, just to add a little bit to this excellent answer in regards to other radiometric dating techniques that are appropriate for rocks. ",
"In regards to the no preexisting daughter product (i.e. no inheritance) assumption, the answer depends on the radiometric system in question. For some systems, we both (1) have good reasons to make this assumption but importantly (2) we have methods to test this assumption every time a measurement is made. Let's take the example of a very common geochronologic method, U-Pb dating of the mineral zircon. We typically assume that there is no daughter product (Pb) in a zircon when it crystallizes from a melt and this is usually a safe assumption because, as a mineral, zircon has a specific ",
"crystal lattice structure",
" such that uranium atoms are the right size to be able to substitute for some zirconium atoms in the ZrSiO4 zircon structure, but lead atoms are not the right size so they would be excluded when the zircon is forming. Even though this is usually a safe assumption, we always test this assumption when dating a zircon by exploiting the fact that both U238 and U235 substitute into zircon and decay to different isotopes of lead, Pb206 and Pb207, respectively. We can compare the ratios of these two parent and daughter products and the ages we would calculate from them to determine if these systems are ",
"concordant, i.e. give the same answer",
" (here is a ",
"paper",
" also discussing the use and analysis of concordant ages). There are a variety of influences that can cause ages to be discordant (with the presence of initial Pb being one of them), and very often we can correct for these, e.g. for more details on that, check out section 4.10.13 of this ",
"chapter on U-Pb dating (pdf)",
". The exact methodologies and tests for initial daughter product for other geochronologic systems vary and I'm definitely not going to go through them all here as there are ",
"a lot of them",
", but suffice to say, part of a radiometric technique being useful and adopted is the ability to assess whether the assumptions necessary to interpret the age are met.",
"It is also worth noting, that there are specific strategies for using geochronologic systems that are specifically designed to be used when the assumption of no initial daughter product is violated (or likely to be violated), specifically ",
"isochron methods",
". In isochron dating (which isn't specific to a particular mineral or decay chain), you do not have to know the initial ratio of daughter to parent (or assume that there is no daughter product in the mineral/rock to start with), but instead you must assume that a population of minerals (or rocks if speaking of whole-rock methods) that you are dating have the same history, e.g. assuming that all the zircons you removed from a sample of rock crystallized at about the same time. Using isochron methods, you actually end up calculating the initial ratios of daughter to parent in the samples as part of the analysis."
] |
[
"The other comment covers radiocarbon dating pretty well, so I'll just drop a few comments of my own:",
"In some cases the daughter isotope is a different element from the parent isotope, and so the two will have different chemical properties. This means that certain minerals can form with only the parent isotope at the start, but once they solidify any daughter isotopes that are produced are trapped in place. Potassium-argon dating is a good example, as argon is a gas and so escapes from liquid magma, but is trapped once it solidifies. Uranium-lead dating also operates under this principle when zircons are used, as these are observed to form with uranium but not lead.",
"But in some cases a mineral does form with some of the daughter isotopes present, and we don't know the initial ratio. However, often in those cases there will be a daughter isotope present and then another isotope of the same element that is not produced by decay of the parent isotope, and there will different initial mixes of the parent isotope, daughter isotope, and non-daughter isotope in different parts of a given mineral. Assuming that nothing has changed these ratios except for radioactive decay, measuring their current values in different parts of the mineral can allow you to determine the initial overall ratio. I won't go into the algebra here but you can ",
"look it over",
" if you like."
] |
[
"How does Electro-Convulsiveshock Therapy work? How does it cure things like depression?"
] |
[
false
] |
As I'm currently looking down the ECT barrel due to what my psychiatrist called "treatment-resistant depression," I was wondering how exactly it does what it does. Unsure if this post will get disqualified due to rule 1, but I'm looking for all the chemistry/biology, maybe even a little psychology behind it. I've heard the whole "it restarts the brain" thing, but I want to know the entire process behind it.
|
[
"The exact mechanism by which ECT works is not fully known. If we knew that research would probably try to find alternate ways to accomplish the same thing that don’t require anaesthesia. There are some things we do know though:",
"The hippocampus and amygdala are parts of the brain involved in many processes including those related to emotion. ECT has been shown to increase the volume of these areas. This is known pretty much for certain but how it happens is less well known. Recently a protein called Narp has been suggested to be part of this process. ",
"There is a way to test if mice are depressed used in research called the ‘forced swim test’. Basically if put into water a depressed mouse will spend more time floating and less time swimming than a non-depressed one. Researchers took two groups of mice, one which has Narp and one which doesn’t and gave them both ECT. They found that the mice which don’t have Narp floated longer (indicating depression) than those without. This suggests that Narp involved in the mechanism through which ECT works because without it the mice stay depressed.",
"Using various staining methods the structural changes in the brain were also studied. This found that both groups of mice showed an increase in the number of neurones (compared to the control). BUT the mice which had Narp had far more dendrites on these neurones. These are the part that connect to other cells and allow for communication. This is thought to be at least part of how ECT can alleviate depression."
] |
[
"ECT has been around for almost a century, Psychedelic-assisted treatments are barely starting in this last few decades. So the difference in \"amount of studies\" is a red herring.",
"It's not a red herring. There are strict standards for medical procedures and the research required for it to be considered efficacious. This is why there are phases to clinical trials. Only one treatment of the \"psychedelic\" variety--psychotherapy with MDMA for PTSD--has reached phase III. If it's a red herring to adhere to reasonable quality standards of evidence to inform clinical practice, then I guess the field of medicine as a whole is founded upon a red herring model.",
"in my opinion it should only be used as a last resort when nothing else is available or likely to work",
"This is often the case. This underlines the seriousness of suggesting that someone reconsiders ECT. ",
"On the other hand, psychedelic phase 2 studies are already shown that these are nearly as effective or even more effective than ECT.",
"They don't \"show\" it, phase II isn't sufficient quality evidence. Phase II is only to assess whether there is an effect as well as safety, but not effectiveness, e.g. 'proof of concept' and 'dose-finding'. 80% of phase II studies end without a subsequent phase III. Compared to the amount of research on ECT, the studies on these interventions are abysmal and can't be meaninfully compared. Promising, sure! There are lots of promising interventions out there, but many fail to fulfill their promise.",
"In my opinion doctors that propose ECT as a first step",
"But what about this specific person to whom you provide this advice? ",
"And regarding a \"kick\", how else would you describe intentionally putting the brain into a full blown epileptic seizure for a few minutes? That it's done under anesthesia and the person is neither aware of it nor in danger from it (as most motor functions are inhibited), does not make it any less of a seizure. And this is repeated several times over a period of weeks.",
"It's quite simply not an explanation of how ECT works. It's just a metaphor, but this is ",
"r/askscience",
" so I would assume OP wanted an actual explanation and not one that is made up."
] |
[
"ECT has been around for almost a century, Psychedelic-assisted treatments are barely starting in this last few decades. So the difference in \"amount of studies\" is a red herring.",
"It's not a red herring. There are strict standards for medical procedures and the research required for it to be considered efficacious. This is why there are phases to clinical trials. Only one treatment of the \"psychedelic\" variety--psychotherapy with MDMA for PTSD--has reached phase III. If it's a red herring to adhere to reasonable quality standards of evidence to inform clinical practice, then I guess the field of medicine as a whole is founded upon a red herring model.",
"in my opinion it should only be used as a last resort when nothing else is available or likely to work",
"This is often the case. This underlines the seriousness of suggesting that someone reconsiders ECT. ",
"On the other hand, psychedelic phase 2 studies are already shown that these are nearly as effective or even more effective than ECT.",
"They don't \"show\" it, phase II isn't sufficient quality evidence. Phase II is only to assess whether there is an effect as well as safety, but not effectiveness, e.g. 'proof of concept' and 'dose-finding'. 80% of phase II studies end without a subsequent phase III. Compared to the amount of research on ECT, the studies on these interventions are abysmal and can't be meaninfully compared. Promising, sure! There are lots of promising interventions out there, but many fail to fulfill their promise.",
"In my opinion doctors that propose ECT as a first step",
"But what about this specific person to whom you provide this advice? ",
"And regarding a \"kick\", how else would you describe intentionally putting the brain into a full blown epileptic seizure for a few minutes? That it's done under anesthesia and the person is neither aware of it nor in danger from it (as most motor functions are inhibited), does not make it any less of a seizure. And this is repeated several times over a period of weeks.",
"It's quite simply not an explanation of how ECT works. It's just a metaphor, but this is ",
"r/askscience",
" so I would assume OP wanted an actual explanation and not one that is made up."
] |
[
"If someone wore glasses that made everything you see shades of red/blue, how would they perceive the world if it was removed after 50 years?"
] |
[
false
] | null |
[
"It is a misconception that we have one cone that detects red color, one that detects blue color and one that detects green. It is true that each type of cone is ",
" sensitive to the wavelengths of light that correspond to those colors but for almost all colors at least two cones are going to activate.",
"For red and blue glasses we can assume that the wavelengths seen would all be between 420 and 480 nm for the blue tinted lens and around 600-650 nm for the red tinted lens. 420-480 nm wavelengths would activate mostly the S-cones but 600-650 nm would activate the L-cones the most but also significantly the M-cones.",
"I'm not sure if there would be a significant change in the number of each type of cones (for both eyes all three types would be activated to some extent) but I'd rather think that changes would occur in the brain areas that process color information (the occipital lobe and temporal lobe mostly). Neuro-plasticity would allow for specialization (which could happen separately for each eye) but since the integration of processing for visual information from each eye starts pretty early in the neural pathway, it's hard for me to speculate in a meaningful way about the consequences.",
"Sorry I can't give you a better answer. Also English is my second language, hopefully my comment is clear enough.",
"Source: Bachelor's degree in neuropsychology"
] |
[
"Is this speculation or do you have something to back up your claims?"
] |
[
"Is this speculation or do you have something to back up your claims?"
] |
[
"How does compressing air lead to no temperature change theoretically?"
] |
[
false
] | null |
[
"In a ",
" compressing air ",
" lead to a temperature change. If you compress the air relatively slowly, though, you can let heat escape and the temperature equalize with the environment, keeping the gas temperature constant. Expansion and compression ",
" be adiabatic (no heat transfer), but don't have to be. "
] |
[
"I understand that the temperature can equalize while it is in the compressor tank. But excluding all external factors and just looking at this in terms of pressure, volume and temperature why is it that when I reduce the volume of a gas by half and increase the pressure by a factor of 2 the temperature stays exactly the same? At least according to the combined gas equation, and the values I have used."
] |
[
"If you aren't allowing heat transfer, then that's not what happens. If you reduce the volume by a factor of 2, in an adiabatic compression, then the pressure will go up by MORE than a factor of 2 because the temperature will go up too. You've got one constraint and 2 dependent variables, you can't predict the end state exactly from that equation alone, there are many states that satisfy that constraint. Only by allowing heat transfer to lock T into place can you say what the end pressure will be with that equation (and then you're really still using 2 equations: the one you listed and T=const.) ",
"EDIT: This plot shows the different paths for isothermal/adiabatic compression/expansion: ",
"https://i.stack.imgur.com/ttkqM.jpg"
] |
[
"How closely related are cherries and plums?"
] |
[
false
] |
I was eating cherries today and several of them looked like miniature plums I have eaten in the past. I know they are related, but how closely? When did the plants diverge and become separate enough evolutionary to identify or did they evolve separately from two different species? I would assume that being in the same genus they share a common ancestor.
|
[
"Here's",
" a recent article on the molecular phylogeny (i.e. \"evolutionary history\") of ",
". "
] |
[
"Cherries and plums are from the same genus, ",
".",
"In the way scientific classification works, it's likely that they came from a common ancestor and diverged due to different evolutionary pressures - whether it be from different geographical areas (allopatric speciation) or whatnot. ",
"If two different organisms have similar traits, but are in different taxa (kingdoms/phyla/classes/orders/families/genus/species) it can be from similar environmental factors, and similar adaptation strategies led to similar structures."
] |
[
"Almonds, peaches, plums and apricots seem to be one clade, and the cherries (sweet, sour, bird, laurel) a separate clade, within the prunus genus. So plums and cherries would not share a common ancestor (directly)."
] |
[
"Is body fat percentage correlated with how long someone can endure starvation before death?"
] |
[
false
] |
Let's say two people wash up on a deserted island. One with 7% body fat and one with 32% body fat. They have access to a reliable water source however there is no food on the island. Would the individual with a higher body fat percentage be able to survive through starvation longer than the other? Logically I would assume that because there is more energy stored and available for use they would survive longer, however I've not seen any meaningful data supporting that notion.
|
[
"Largely, yes, more body fat would enable you to live longer without eating.",
"",
"The answer is more complicated than that. The human body needs many nutrients and minerals to function properly which do not occur in body fat, and both people would become vitamin deficient at roughly the same rate. Such deficiencies can be fatal.",
"",
"If your question involved a supply crate of complete multi vitamins which both people could take indefinitely, then the person with more body fat would live longer.",
"",
"It's said that a pound of body fat is roughly 3500 calories. Depending on the physical activity of your victims, the number of calories they'd need per day would be different. A normal healthy person might need around 2000 but in such a situation, daily use could be closer to 1200 or lower, if they were very sedentary. Let's take 1200 because it's roughly 1/3 of the calories in a pound of fat. This would mean a pound of your fat alone could support you for about 3 days (don't do this in practice, it would be incredibly dangerous, and your body would begin to consume your muscle tissue for proteins as well, but we'll not count that).",
"",
"If we take a 32% body fat man who weighs 200 lb, we can say that his body contains 64 lb of fat. We could say the 7% body fat man might weigh closer to 150 lb and have ~10 lb of body fat. By the above estimates, the 32% man could last for 180+ days while the other man might last a month. In practice, I don't believe many people have ever lasted longer than a month without food, but again they rarely have access to multi vitamins.",
"",
"I don't know if there's enough data to accurately answer your question, but in general, body fat will let you survive longer."
] |
[
"Wow thank you for the response! Sorry for the late reply, I was busy the last few days and haven't had a chance to look at the post. Seeing the Math really put that in perspective. Also I can't imagine how much it would suck to have to take multivitamins on an empty stomach every single day. "
] |
[
"There is a case of Angus Barbieri, who fasted 382 days and lost 125 kg in process.",
"He was supervised by a doctor and regular check ups were done. He was getting the vitamins, potassium, sodium and yeast.",
"The case is also well documented in medical literature.",
"Here is the ",
"link",
" and ",
"medical journal article",
"."
] |
[
"What molecular properties determine a material's heat capacity?"
] |
[
false
] | null |
[
"If by \"material\" you mean a solid, then this is an incredibly complex question. In a nutshell, the specific heat of a thing (solid or otherwise) is determined by the number of places energy \"can go\" or \"be put\". In a mono-atomic gas, this is easy, 3 places: kinetic energy (i.e. motion) in the x direction, in the y direction and in the z direction. For a gas of diatomic molecules it's actually 7 for already some somewhat complex reasons (3 for linear motion as before, two rotational axis with the third one not counting due to the point nature of particles, and 2: one potential one kinetic for the compression of the \"spring\" that is the bond attaching them). So even at gas of the simplest possible molecules it gets complex.",
"In a solid, you can have all forms of new EFFECTIVE degrees of freedom originate. For example, in a solid you have a regular array of atoms, these atoms can be displaced from their preferred position. This can actually happen collectively over the whole material:",
"https://upload.wikimedia.org/wikipedia/commons/9/9b/1D_normal_modes_%28280_kB%29.gif",
"https://upload.wikimedia.org/wikipedia/commons/2/27/Lattice_wave.svg",
"This is sound, or quantum mechanically \"phonons\". However, not any type of pressure wave/phonon can exist in any solid. Rather the symmetry of the crystal lattice, like these examples:",
"http://www.substech.com/dokuwiki/lib/exe/fetch.php?w=&h=&cache=cache&media=crystal_lattice.png",
", only allow certain types of phonons to exist. Here's all the places energy can go into phonons for Germanium (a very simple material), the x-axis is \"momentum\" and the y-axis is energy. Effectively a line LA means, the material WILL absorb energy if it has this energy and momentum by creating a Longitudinal Acoustic phonon:",
"http://i.stack.imgur.com/btejb.gif",
"Here's one for a slightly more complicated material:",
"http://www.esrf.eu/files/live/sites/www/files/UsersAndScience/Publications/Highlights/2007/HRRS/fig-14.jpg",
"It's complex. And that's JUST where energy can go into phonons.",
"Thus, the point is, the types of atoms, the symmetry in which they are regularly arranged, their own electron number and the type of bonding between them, the spins of the outer-most electrons, etc. ALL can play together within a solid to make new EFFECTIVE excitations (phonons, plasmons, polaritons, quasi-electrons, spinons, magnons, etc.) and each one of these is a place where you can put energy and each one has different rules for what lumps of energy they can and will accept and under what conditions.",
"So the answer is, a LOT of things."
] |
[
"Ironically, even though the underlying principles are very complex, for many crystalline elements near room temperature, the heat capacity is approximately constant at 25 J/K/mole."
] |
[
"Well for \"regular\" materials there's always some level approximation you can utilize. For phonons for example you can use the Debye or Einstein models, but you can crash a google server with violations of expectations from the Debye model."
] |
[
"Tomorrow in Europe there is a solar eclipse. So is the moon today anywhere near the sun, in the sky, as sort of an almost-eclipse?"
] |
[
false
] | null |
[
"Yes, if we can call that an \"almost-eclipse\". We actually have a new Moon (or we're close to it). The eclipse will happen after about 14h (it's 19:50 in Central Europe at the time of writing this comment). The Moon moves 12º per day on the sky, so right now it must be nearly 6º west of the Sun. It must have set approx. 30 minutes before the Sun did.",
"Over the next 14h the Moon will traverse these 6º until it crosses in front of the Sun.",
"The angular diameter (i.e. apparent size) of the Moon in the sky is just 0.5º, so I wouldn't call this an \"almost-eclipse\". But the idea behind the term is still correct, right now the Moon is close to the Sun as seen from Earth."
] |
[
"It is pretty much as close as it is on every orbit a day before a new moon; the only difference is that usually new moons miss the sun a bit (passing either \"over\" or \"under\" the sun) so they don't cause an eclipse."
] |
[
"Yep! In fact, the moon gets very close in the sky to the sun every month, at new moon. Usually it is a little north or south, but when the orbits line up nicely, you get an eclipse."
] |
[
"How dangerous is alpha-Methyltryptamine?"
] |
[
false
] |
[deleted]
|
[
"Had to poke around some articles.\nOnly found one I could really use (Clinical toxicology [1556-3650] Hill yr:2011 vol:49 iss:8 pg:705 -719)\nBasically, there isnt enough research to know what the long term effects of this drug are specifically, but because of it's similarity to other drugs some inferences can be made. It was developed in the 60s as an anti-depressant and then for some reason the project was scrapped.\nThere is overdose risk for the drug, and at the very least he should be aware of the lethal dose, which it seems, is not entirely known (upper dose limit is around 60.mg but based on what little research exists, 60. mg may be dangerously high, 30 mg is probably the realistic max dose a person should take). The threshold dose for smoking the drug is far lower and so is likely far more dangerous.\nAgain, there doesn't seem to be any research on long-term effects because the drug is so rare. If you live in the United States, this is also a class 1 drug that carries a federal charge.\nBased on the primary activity of the drug, it acts as a serotonin agonist, meaning over the long-term it may interfere with this particular chemical system in his brain similar to the way MDMA effects serotonin circuits in the brain.\nIt also acts as a serotonin, dopamine and norepinephrine releaser and reuptake inhibitor, leading to large influx of chemicals in the brain.\nIf he does this drug, he absolutely should not take SSRI inhibitors (a class of anti-depressants). The combination will lead to serious health issues and may be extremely dangerous.\nIf he has a family history of mental illness, or personal history of mental illness, it seems likely this drug could trigger psychosis due to it's chemical similarity to LSD and MDMA.\nIf he has any health problems at all, or is on any medication, he should immediately stop doing this drug, as the effects of interactions are completely unknown.",
"Generally, it is not the greatest idea to be putting chemicals into your body that have not been thoroughly researched. Absolutely do not mix this drug with other stimulants, serotonin agonists, dopamine agonists or MAOI class drugs (basically any other synthetic or pharma drugs) since it is hard to predict what the outcome would be."
] |
[
"Good place to start is here:\n",
"http://www.erowid.org/chemicals/amt/amt.shtml"
] |
[
"Thank you very much. That's very useful."
] |
[
"Can you die from drinking from a long enough straw?"
] |
[
false
] | null |
[
"Physics"
] |
[
"Physics"
] |
[
"No."
] |
[
"Why didn't NASA plan the trip to Pluto to arrive in the prehelion, wouldn't that be a quicker trip?"
] |
[
false
] | null |
[
"Pluto takes 248 years to orbit the Sun, it was at last at it's closest point to the Sun (perihelion) in 1989, since we missed that opportunity, we would have had wait till 2237 to launch New Horizons, the next perihelion. That's too long."
] |
[
"It also implies that it's currently not very far from it's perihelion. There would be very little to be gained by waiting until 2237."
] |
[
"Perihelion was in 1989. It took 25 years from the initial proposals for a Pluto mission in 1990 for NASA to get this mission there in 2015 after numerous changes and an outright cancellation in 2000. They would have had to have started planning in 1964. ",
"NASA is also not in full control of its budget. Congress has to fund them the missions. Selection committees have to prioritize based on return, risk, feasibility and even preferences of the people involved. Astrobiologists for instance have little interest in Pluto while planetary geologists have less use for the ISS. Going back to 1964 a mission to Pluto, and Pluto alone, would have been deemed a very high risk, low return and probably infeasible with the existing technology in lack of miniaturization and size of rockets required to deliver such a probe. It would not have gotten past stage 1 of a mission approval. Even closer to perihelion, say 1980 the space program still had higher priorities. Even as late of the mid 90s the proposed Pluto mission was canceled because it was not practical with the technology and funding available."
] |
[
"How do scientists know how long the events after the Big Bang took?"
] |
[
false
] |
[deleted]
|
[
"We could reconstruct the evolution of the scale factor (how exactly the Universe expanded in time) by exploiting the Friedmann equations and measurements for the relevant parameters (Hubble's constant, deceleration parameter, density parameters etc) at the present time. Integrating the Friedmann equations back in time gives the scale factor from the Big Bang to today. One indeed finds a Big Bang at a certain point in the past. This approach only touches on the present era and the matter dominated era, which lasts basically for most of the history of the Universe.",
"Then one zooms in on the Big Bang and studies the thing more closely, in particular in the radiation-dominated era. Assuming the degrees of freedom are known (that is, which fundamental particles exist and what their mass and spin is), then we know how stuff behaves at a specific temperature, for example which species of particles are 'active' or where there are phase transitions. ",
"Then it's possible, though involved, to integrate for the scale factor and the temperature simultaneously and so know the time (since the big bang) when any given temperature was reached.",
"Obviously this fails for times so early that the temperature wanders out of the range of known physics.",
"These estimates are relatively precise in terms of relative error. So on the time of an event happening 3 minutes after the BB you might have an error of a few seconds. On longer estimates, you have a larger absolute error.",
"Also, how do they theorize that everything in existence today came from a single, subatomic point?",
"They most definitely never did, it's a popscience misconception. "
] |
[
"I hear the big bang means that it all started out from a point",
"that's wrong. What happened is pretty subtle. Not mysterious, just really unintuitive.",
"Basically the point is that the Universe is in ",
", not the content. It's not that spacetime is inert and galaxies are flinging out from an explosion point. Space itself is getting larger as time passes (in certain coordinates), which is equivalent to spacetime being curved in a certain way.",
"There is a special class of observers called comoving. This are the observers that at any time see the Universe on a large scale as being isotropic and uniform (i.e., they see the CMBR as isotropic). This class of observers define comoving coordinates on spacetime, including a \"universal\" time called cosmological time (it's just the time measured by one of them holding a clock). Two of these comoving observers, along with a chain of comoving observers inbetween, are able to measure the proper distance between them, that is literally the length of the arc connecting them at fixed cosmological time.",
"When people say that the Universe is expanding, they formally mean: that distance is not a constant, it increases with time. These proper distances are proportional to the overall 'size' of the Universe, the scale factor a(t).",
"When people say that there was a Big bang (in the context of classical GR), they mean that there was a time in the past when a(t) was zero. That is, all comoving observer came to be (going back in time) close together in terms of proper distance. However, they don't go towards a specific point in space, all of space just gets smaller. ",
"this",
" is a diagram of spacetime near the BB using as coordinates cosmological time and ",
" (not comoving coordinates). The fact that they seem to converge to a point is an artifact of choosing an arbitrary galaxy. Starting from another galaxy, they will seem to converge to that one.",
"The problem about \"reverse-tracing\" the positions of comoving observers is that positions are not vectors. You cannot confront positions at different times. Positions are given as values in a certain coordinate system, which is first of all arbitrary, and do not form the component of an object you can treat as vectors - it's pretty different from Newtonian mechanics where not only space is affine euclidean space, but also given an inertial frame you can confront positions at different times, sum subtract and divide them. Curved spacetime is immensely trickier instead. If you still insist and try to do this tracing in comoving coordinates (literally tracing the values of the position coordinates), you get something surprising. Since comoving coordinates are adapted to them, comoving observers always stay at a fixed comoving position. They don't get closer in terms of comoving distances.",
"this",
" is a diagram in conformal coordinates, which are related to comoving coordinates. Note how the observers do not seem to get closer. The big bang singularity is now an horizontal line, i.e. an instant in time which happens, pictorially speaking, everywhere in the Universe at the same time."
] |
[
"They most definitely never did, it's a popscience misconception.",
"Can you elaborate a bit on this? I hear the big bang means that it all started out from a point, but from what I've read the movement of the stars can't be reverse-traced back into a single point.",
"Just how big an area is a \"point\" that the entire universe originated from?"
] |
[
"Why do all the bubbles in a pint of beer tend to originate from specific points in the glass?"
] |
[
false
] |
After pouring a cold one, all the air bubbles that float through the glass seem to keep "spawning" from particular points wishing the class container. Why does this happen?
|
[
"Beer is carbonated so when it's made in a brewery they shove more carbon dioxide into the solution than would normally be able to dissolve at normal atmospheric pressures. This causes the solution to be supersaturated with CO2 once the beer is poured or opened. The CO2 in solution wants to find a way out so it does this thing called nucleation which is just a fancy word describing energetically favorable spots or areas for the carbon dioxide to come out of solution. So those specific points on the glass where bubbles are forming are just better nucleation points based on how the glass is shaped."
] |
[
"Bubbles may originate from small scratches or faults in the glass surface, but more commonly, they're produced by small sediment particles, either in the beer or adhering to the surface of the glass. ",
"This is more common with beers brewed with added wheat which can lend cloudiness and thicker head due to the much higher protein content in wheat. ",
"Different companies may allow settlement and filter their beers in different ways, adding varying levels of solids to the product. I've heard of adding additional malt sugars and yeast upon bottling to encourage in-bottle fermentation in a way similar to champagne production. The purpose of this would be for extra head and alcohol content.",
"For various reasons, it's much more difficult for new bubbles to form, than for gas to be evolved around existing surfaces in the container, such as small solid particles. These may have a large surface area despite their small size."
] |
[
"I also think that once a bubble forms, the disturbance it creates enhances more bubble formation.",
"A similar but 'opposite' reaction is found in supersaturated salt water, like that found in brine holes in Death Valley, out in the Devil's Golf Course. The surface if the water is perfectly smooth, the color yellow. Drop in a grain of sand and the disturbed surface enables the formation of salt crystals. The crystals grow until they're too heavy. When they sink, the surface is again disturbed and a new crystal begins to form. ",
"Our field geology class sat in the hot sun, waiting for the crystals to stop forming, for an hour. Pity we didn't have any beers."
] |
[
"Why does this calorie math not check out?"
] |
[
false
] | null |
[
"A food \"Calorie\" is 1000 thermodynamic \"calories,\" or a kilocalorie."
] |
[
"That is assuming perfect efficiency.",
"Humans turn chemical calories into mechanical work at about 20% efficiency.",
"The mechanical work -> electricity is ~40%.",
"An electric kettle (most efficient way to heat water) ~70% efficient.",
"That's around 300 kcal, which is on the order of 20-30 minutes of exercise, so that seems like a reasonable approximation."
] |
[
"The most common mistake with things like this, is that a dietary calorie is actually 1000 calories, enough to heat a ",
" of water by 1 degree Celsius."
] |
[
"How can digital numbers control path of electricity? (i.e. computers, microcontrollers...)"
] |
[
false
] |
For instance you can program a microcontroller to have power at a certain port. How can a line of code affect path of eletricity? Thank you for answers.
|
[
"With ",
"transistors!",
" They are clever little circuits that let one electrical current turn on or off another one. That line of code is really just a set of electrical activity in some electrical switches, that flip other electrical switches, that flip other ones, and so on. ",
"Transistors in computers work on ",
"Boolean algebra",
", which is a kind of logic of ones and zeroes. Using boolean algebra, you can design a set of transistors that compute any kind of function you like, so long as its made up of ones and zeros. "
] |
[
"There is a very nice book about these basics, called ",
"CODE",
" by C. Petzold. He starts from very basic concepts and thus it can be understood by laymen. "
] |
[
"I will second this. I believe that CODE is the single best book written on computers and computer science for laypeople. "
] |
[
"Why is the integral of 1/x = ln(x)+C?"
] |
[
false
] |
I mean I get that you cannot integrate it normaly as in: x-1 --> (x0 )/0 because you obviously cannot divide by zero. So why does this just happen to equal ln(x)?
|
[
"First of all, you mean to ask why the ",
" of 1/x is ln(x) + C. An ",
" is a limit of Riemann sums, i.e., a single number, and it has various interpretations: area, volume, probability, etc. The fundamental theorem of calculus simply provides a link between integrals and antiderivatives. But the two objects are not the same thing.",
"Many introductory textbooks simply define ln(x) to be an antiderivative of 1/x, and that's that. So the answer to your question is \"because it is\". A better way of defining ln(x) from first principles, at least in real analysis, is that g(x) = ln(x) is the inverse function of f(x) = e",
". The immediate question is then whether these two definitions are equivalent. They are.",
"Consider the function y = g(x) = ln(x). By definition, e",
" = x. Now use implicit differentiation (w.r.t. ",
") to find that",
"e",
" (dy/dx) = 1",
"Solve for (dy/dx) to get",
"dy/dx = 1/e",
"But note that e",
" = x, so we get",
"dy/dx = 1/x",
"Voila. If we define ln(x) to be the inverse of e",
", we still get that its derivative is 1/x. (By a similar method, you can show that if we define ln(x) to be a function whose derivative is 1/x, then ln(x) is just the inverse function of e",
".)"
] |
[
"Nice man! Thank you. I did not even know about the term antiderivative because my maths teacher only uses \"integral\"",
"That is unfortunate and quite common actually. We happen to use the same symbol ∫ for antiderivatives and integrals, and the fundamental theorem only further blurs the distinction. So teachers should make the distinction clear, otherwise students just get the impression that if \"∫\" comes with no limits, then you have to put \"+C\" at the end or you get points off."
] |
[
"Nice man! Thank you. I did not even know about the term antiderivative because my maths teacher only uses \"integral\". This makes sense to me so thanks for explaining!"
] |
[
"Are there studies that tested placebos on babies?"
] |
[
false
] |
Or people young enough to not know that medicine is supposed to be good for you?
|
[
"AFAIR both babies and animals are susceptible to placebo effects. It is a common alt-med trope to claim that they aren't, but this sort of argument forgets (at least) two things:",
"Babies and animals may not have a concept of medicine, but they ",
" realize that they receive attention and that somebody cares about them, and that can already make a difference - or at least decrease stress.",
"Because babies and animals can't directly tell us that they're feeling better now, the success of an intervention will usually be estimated by whoever is treating (or caring for) them. This is a tremendous source of bias: You ",
" that you did something to them and you ",
" a change, hopefully for the better. Confirmation bias will then do the rest."
] |
[
" \nI just read through a couple pages of a PubMed search on placebo and infant. They seem to use them relatively often. From the handful of abstracts I peeked at it looks like placebo is being used as having \"no effect\". "
] |
[
"That's why good studies are double-blind."
] |
[
"Do kidneys adjust to water intake or is there a sweet spot?"
] |
[
false
] | null |
[
"Hello,",
"We can approve this if you edit out all of the personal details.",
"Best."
] |
[
"I have no idea what personal details you're referring to. There's no age, gender, name, location, etc. Can you clarify?"
] |
[
"The whole question is about ",
" water drinking habits, and how it will affect ",
" body. The question can’t be specific to you."
] |
[
"When passing the event horizon of a black hole there are no paths leading away from the center, but are there longer or shorter paths towards the center?"
] |
[
false
] | null |
[
"Yes there are, depending on your angular momentum."
] |
[
"Is there any way to elaborate on that? I only have a loose Newtonian grasp of physics."
] |
[
"Well, you can go straight towards the center, or curve around and spiral in."
] |
[
"How can a relatively small river like the Virgin River cut a 2000 foot deep Canyon (Zion) while an enormous river like the Mississippi doesn't cut a canyon at all?"
] |
[
false
] | null |
[
"Because a canyon requires flow over rock and a significant elevation drop over the distance of at least the length of the canyon. The Zion canyon is cut into rock by a river constantly flowing over it with the vertical drop of 2000 feet.",
"The Mississippi River has only about an 800 foot elevation drop from its headwaters in Minnesota to the Gulf of Mexico, and it largely flows over soft mud which fills itself in as well as is carried out to sea forming the river delta and shoals in the Gulf of Mexico",
"If you have the elevation drop, but softer material, it results in valleys more than canyon formations"
] |
[
"There are various factors involved in erosion, but I think the most important one here is that the Virgin River starts in the mountains, and so can gain a lot of energy from gravity which can be used to erode sediment. The Mississippi starts pretty low, so it can't gain much energy, and can't cut too deeply until it's almost in equilibrium with the sea it's flowing into. In fact, the source of the Mississippi is less than 1500 feet above sea level, so it simply can't cut that deep. It's also cutting through loose sediment rather than solid rock, so the banks will just fall into the river if it cuts in much."
] |
[
"There is also the essential factor that the whole Colorado Plateau area has been uplifted due to tectonic forces over the past few million years. This is the reason why you get such spectacularly deep canyons - the vertical drop of rivers from source to mouth is maintained despite constant the downward erosive forces. "
] |
[
"What state are dissolved molecules in?"
] |
[
false
] |
Would the dissolved molecules count as a liquid or does it matter on the starting phase. For example if gas is dissolved in water does that gas stay in gas phase?
|
[
"The entire solution is the same phase--the phase doesn't describe each component, but rather the whole thing. In your example, a gas dissolved in water is a liquid. You can also have solid solutions (e.g. a metal alloy) or gaseous solutions."
] |
[
"a gas dissolved in water is a liquid.",
"No. No no no. No.",
"Things that are dissolved are in the dissolved \"phase.\"",
"Its not a phase like solid/liquid/gas. Those phases are distinct ways of organizing matter. A solution of carbon dioxide in water is a liquid, yes, but the carbon dioxide is NOT a liquid."
] |
[
"In a water molecule, the oxygen has a slight negative charge and the hydrogens have a slight positive charge. When salt dissolves in water, the slight negative charge on the oxygen is attracted to the positively charged sodium ions and likewise with the hydrogens and the negatively charged chloride ions. So in the end the ions get surrounded by water molecules and they drift apart."
] |
[
"Do humans have any special physiological defenses against fire/high heat?"
] |
[
false
] |
[deleted]
|
[
"Not likely. That kind of defense would come from a population regularly plagued by fires generation after generation. It’s easier to just move to a place that’s not constantly on fire. Although I say that living in California, so take it with a grain of salt."
] |
[
"Our defence is management and avoidance, so we don't need a physical one."
] |
[
"What do you mean by high heat?",
"If you mean high environmental heat, like in a desert, then humans have very good physiological defences: they can sweat, all over, and have little hair on most of their body so the sweat can evaporate well. Humans are very good at cooling themselves compared to most other animals. This also means they do not overheat when performing sustained activity and enable them to have longer endurance than almost any other animal. The oldest known form of human hunting is endurance hunting: chase the animal until it is exhausted and can't move, then come in close and kill it. Humans can do this because they can sweat, and most other animals cannot sweat effectively. ",
"If you mean heat like the burning flame of a wood fire or similar, then human defences are mostly from their tool using and cognitive abilities. They can make protective clothing from materials in their environment. For example, wet leather is quite fire resistant. Wool is fire retardant - it does not burn well, unless greasy in which case the grease burns. The usual human reaction to fire is to move away, to extinguish it using their tools and handling abilities, or to hide from it. Knowing which to do and how to do it is part of human cognitive skills."
] |
[
"Has anyone ever actually physically performed the double slit electron experiment where the electron is both a particle and a wave or is it just a thought experiment that is backed up by the math?"
] |
[
false
] | null |
[
"This has absolutely been done, many times. You can read about various such experiments ",
"here",
". ",
"You can even see video of the data collection of a recent such experiment ",
"here",
"."
] |
[
"While I agree with the facts in your post, to be fair to op, physics has quite a bit of untestable currently or perhaps untestable ever ideas that are supported by math. I'm thinking of Hawking's argument about blackholes storing information at the event horizon or string theory in general."
] |
[
"Nice thanks for the links."
] |
[
"Guilin Karst is a famous example of limestone mountains. Do limestone mountains occur elsewhere in the world? If not, why not?"
] |
[
false
] |
Google says that limestone occurs under marine water, but I've never heard of limestone mountains anywhere else? Am I misunderstanding?
|
[
"There are numerous examples of mountains comprised primarily of the marine minerals limestone (CaCO₃) and dolomite (CaMg(CO₃)₂).",
"Some examples:"
] |
[
"As mentioned in this thread, there are a variety of mountain ranges that have significant amounts of limestone within them. For collisional mountain ranges (e.g., Himalaya, Alps, etc), limestone is pretty common because the formation of the mountain range itself represents the closure of an ocean basin, first through subduction and then through collision once all of the oceanic crust is subducted. There is often some amount of carbonate (i.e., limestone) present within the ocean basin before it is closed and some of this carbonate will be scraped off and incorporated into the mountain range as it grows.",
"Now, specific to what you're asking about though are ",
"karst",
" features. Karst, broadly, is topography formed from the dissolution/collapse of limestone, not generally from deformation/faulting/etc of limestone as in collisional mountain ranges . There are a variety of different topographies that develop in karst landscapes, the Guilin Karst is a form typically called Kegelkarst. There are examples of Kegelkarst in a variety of tropical areas with limestone."
] |
[
"Thank you for the examples!"
] |
[
"How do they use CED-13 mRNA to trigger the change to increased longevity in a cell?"
] |
[
false
] |
Specifically; how do they use CED-13 instead of EGL-1 or what is the process to switch from EGL-1 to CED-13 triggering? Can I, as a human, activately promote the change of using the CED-13 as a trigger? I have no formal study in biology (just a mild interest) so if you could make it fairly simple that would be great. (sorry I don't have full text only the summary)
|
[
"You, as a human, do not have the CED-13 gene and its mRNA would probably have no effect in your cells given that it is a C. elegans gene. This is a nematode worm, which i spent many years studying (they are awesome). Had a look on worm base and couldn't find a direct mammalian homologue. One reason why I changed organism is because of the immense difficulty in drawing reasonable comparisons between these animals and vertebrates, especially when it comes to physiology. The male c. elegans literally only has 1031 somatic cells, what keeps it alive and functioning is just so different from a mammal with all our complicated organs, hormone systems and other crazy stuff we have going on. There have been loads of studies in mammals linking mitochondrial function and ageing, but how everything fits together is still a long way off. Studies like this will slowly add to the general knowledge of how everything works, but don't go injecting yourself with any CED-13 just yet. Tried to find you a nice review which doesn't need institutional access which might give you some more answers about the function of mitochondria and ROS in ",
"ageing.",
" "
] |
[
"In answer to your first question. They are describing a pathway that uses many components of the intrinsic apoptosis pathway, which is shown on the left hand side of the figure, activated by mtROS and CED-13 which leads to increased levels of longevity. There is no switch between EGL-1 and CED-13, they are activated in different circumstances. EGL-1 mediated programmed cell death is very important for normal development of C. elegans"
] |
[
"Okay, this was a bit tough to wrap my head around. Definitely in over my head with this stuff. So the study is more about observation of the pathway than changing the the pathway by adding or replacing genes? Or am I way off?"
] |
[
"Why can't electricity be economically generated from the heat energy in the air?"
] |
[
false
] |
It seems that all the energy we need is all around us, without needing to resort to fossil fuels, wind, hydroelectric or nuclear power. Shouldn't it be possible to concentrate heat energy from the air enough to boil water / turn a turbine and generate electricity? If the temperature of millions or billions of cubic feet of air were lowered, even by a degree or two, isn't that a lot of energy that can be used to generate electricity? Even if it's pretty inefficient to do so, it doesn't really matter if the energy is essentially free and doesn't need to be mined, drilled or transported. Is it simply that energy required to extract heat from the air exceeds the energy that could be generated? If so, how close are we to closing this efficiency gap? My understanding is that stirling engines can generate rotational force with a temperature differential of only a few degrees. Perhaps this is a starting point, with the cooler earth used as a large heat sink. Can this be deployed en masse? Is a heat differential strictly required? Thanks! Edit: spelling
|
[
"Try this",
". a Hilsch vortex tube. It separates the fast moving(hot) molecules in the air from the slow(cold) molecules. "
] |
[
"Have you studied thermodynamics yet? To get energy into a useful form you generally have to have a ",
"heat source and a heat sink",
". See the ",
"disadvantages",
" for Stirling engines.",
"Even if it's pretty inefficient to do so, it doesn't really matter if the energy is essentially free and doesn't need to be mined, drilled or transported.",
"You have to consider the materials costs to design a heat engine. If it's not economically feasible it's generally not worth it to make."
] |
[
"Right.. there's no overunity here. All air has fast moving molecules and slow moving molecules, mixed. It uses centrifugal force to separate the denser cold air from the hot air. hot air comes out one end, and cold air out the other. You have to supply it with compressed air for it to do its thing. "
] |
[
"How much of a body could a person survive without?"
] |
[
false
] |
I have read that (for example), a severed head would be unable to survive even if bloodflow and nutrients were provided to it. But a person with no limbs can otherwise be healthy, and people can survive with only one kidney, lung, part of their liver, etc. How much of your body is the minimum amount needed to sustain "life"?
|
[
"White blood cells do not cross the blood brain barrier anyways. Immune functions in the brain are performed by permanently resident microglia cells. But otherwise, you are right, obviously you would need some exchange system to provide the brain with O2 and glucose. "
] |
[
"You also need something to circulate blood and filter waste products.",
"At this point, it's no longer really surviving with just a head; it's surviving with a head connected to some minimally-sufficient body -- just that the body is artificial instead of natural."
] |
[
"Follow up: why can't we sustain just a head?"
] |
[
"Could a habitable moon potentially orbit a gas giant?"
] |
[
false
] | null |
[
"Yes, of course. However, in our solar system, the gas giants are outside of the habitable zone, and no extrasolar satellites have yet been detected, so at present, this is only science fiction. But conceptually, as long as the moon has an atmosphere, water, a stable orbit, happy temperatures, lacks excessive volcanism (could be an issue - see ",
"Io",
"), etc., then yes, that would be suitable for human life."
] |
[
"Depends what you mean by habitable. Jupiter's moon Europa is currently thought to be about the most likely place to find life in our solar system. Ice with water underneath, heated by Jupiter's gravitational forces etc."
] |
[
"Well, in billions of years when the sun goes into the red giant phase Europa might just become a nice place to live."
] |
[
"How does the human body anticipate how much force to use when lifting/pulling/pushing an object, and why are our bodies often momentarily confused when something weighs less than we had expected?"
] |
[
false
] | null |
[
"Your brain uses memory as a way to anticipate the effort required in these situations. There is a book called ",
"On Intelligence by Jeff Hawkins",
" that discusses this. You've opened thousands of doors, lifted thousands of objects. Your brain remembers how it felt to engage in that activity. So when you approach a door, your brain sees what type of door it is and anticipates how much effort will be required to open it. Sometimes your brain gets it wrong.",
"edit: a word"
] |
[
"Awesome, i figured this was a pretty stupid question but thanks for your reply!"
] |
[
"I work with people after injuries some injuries correlate with that momentary misjudgment- like when you expect another step and it's not there, the muscle length is wrong to accept your weight and adjust the joint position, so you pull muscles, ligaments or fracture bones. "
] |
[
"Where can I begin learning the history of particle physics and cosmology?"
] |
[
false
] |
[deleted]
|
[
"I think ",
"A Short History of Nearly Everything",
" might be what you are looking for.",
"Not sure it will 100% meet your needs but a great book nonetheless and worth a read."
] |
[
"You could try Coughlan's ",
" ",
"Don't have a recommendation for cosmology. :-("
] |
[
"This looks interesting, I will check it out. Thanks alot."
] |
[
"How big would the sun appear to the Voyager 1 at the distance it's at now?"
] |
[
false
] | null |
[
"It would appear about the same ",
" as the diameter of a human hair, held at arm's length. ",
"http://www.wolframalpha.com/input/?i=%28diameter+of+sun%29+%2F+18%2C534%2C175%2C964+km+*+1+m"
] |
[
"In terms of luminosity it's about 1 watt per square meter, still brighter than the moon appears on Earth."
] |
[
"An interesting question! I'm going to do a little rounding to make the math slightly easier.",
"Voyager 1 is 18500000000km from the Sun. The sun is 1391000km in diameter. The angular diameter of the sun is 2xarctan(1391000/(2x18500000000))= 15.509 arcseconds. The human eye's angular resolution is about 1 arcminute. Anything smaller than that is either imperceivable or appears as a single point (if it is bright enough). Therefore, to the human eye, the sun would appear to be a single point of light (the size of any other star in the sky). It would be the brightest point of light in the sky, though.",
"Edit: replaced the asterisks with x's because Reddit's formatting messed the math up."
] |
[
"Why don't the mirrors, crossbars, supports, etc. in a reflecting telescope block some of the image?"
] |
[
false
] |
I've always wondered this about telescope designs that place a mirror in the path of the incoming light (e.g. the ). Doesn't the mirror (and whatever is being used to hold it in the middle of the telescope) block some of the incoming light from reaching the viewpiece? Would this show up as a black space on the observed image, or is there some way of compensating for it?
|
[
"They do block some of the incoming light, so the image is dimmer than it would be without them. Telescope manufacturers try to minimize the light loss to such obstructions.",
"You don't see a black space because the part of the optics that is unblocked is capable of showing a full image. This is easy to see if you take a convex or parabolic mirror and cut a hole in its center. The remaining part of the mirror is still capable of bringing parallel light rays to a focus, it's just that rays that would have fallen on the missing part of the mirror now go straight through, so the overall image is dimmer."
] |
[
"The reason is that the image is out of focus ",
". Think about how a pinhole camera works. The entire view is obstructed except for a very tiny hole. How is it possible for the entire image to fit through that tiny hole? It's out of focus when it passes the hole. The light rays passing the hole are traveling in different directions.",
"In the telescope, before the image is created, the light rays are not parallel, just like in a pin hole camera. If you block some of those rays, it's no big deal because there is plenty of room for other rays to go past -- the blocked rays can't contribute to the image any more, so the image is more dim, but you can still see the entire image. It's the ",
" of those light rays that determine their final position in the final image, not just their location in the telescope. Position only becomes critically important as the rays converge at the final focus point. The closer you are to a focus plane when you block the light rays, the more shadow-like the blockage will become.",
"Incidentally, this is how the aperture on an SLR camera works. The aperture in an SLR lens is located at the plane containing the convergence point for \"straight\" light rays. (Well, they're not really straight. Maybe it's better to think of it as the rays that following the path that the rays in a pin-hole camera would take. I just can't think of a easy way to explain this right now.) Light rays that do not need to be \"bent\" are always in focus, just like in a pinhole camera. The extent to which the aperture is closed determines how far away from that convergence point light rays can be before they are excluded from the image. A nearly closed aperture (f/22) excludes nearly all light rays that do not pass through the convergence point, resulting in a pinhole-camera sharp, but dim, image. A fully open aperture (f/1.4) permits all available light rays through, resulting in a bright image that includes potentially out of focus rays. An interesting aside is that a focused image of a flat object (a painting, for example) taken with ",
"a more open aperture is sharper than that same image at a more closed aperture",
" due to quantum diffraction effects when the light passes the closed aperture."
] |
[
"Not a black space,",
" but the obstructions are visible in photographs."
] |
[
"Why is it so much easier to balance on a bicycle when moving than sitting still?"
] |
[
false
] | null |
[
"I can't believe all the confusion surrounding bicycle dynamics.",
"To my ",
" dismay, it has even been the subject of at least one PhD dissertation.",
"The reason for this confusion seems to happen when the rider's active steering input is neglected as a causative factor. Jeez.",
"To clarify the forces involved, let's do a thought-experiment:",
"Consider a bicycle going around a corner or around in a circle:",
"As you may know, such turns are always accompanied by a tilted ",
" toward the inside of the turn. At the same time, there is centrifugal force that pulls the opposite way; toward the ",
" of the turn.",
"To answer your question, the forward momentum is the source that powers centrifugal force when it is needed, by going into a turn. While you turn, the bike resists because its mass wants to continue forward instead. (Newton's 2nd law of motion)",
"The rider's job, whether she's conscious of it or not, is to balance (A) The right amount of leaning with ... (B) The right amount of centrifugal force. ",
"All this in the context of the forward velocity. Because greater forward velocity has an increasing effect on the amount of centrifugal force that comes from a given turn radius the rider is applying.",
"This is accomplished by \"steering into the turn\" until the turn is sharp enough to counteract the falling tendency with outward-directed centrifugal force.",
"The two forces are almost never in perfect balance for long, causing the rider to travel in a wavy path.",
"I hope this helps. ",
"Edit to Add: Gyroscopic effects are ",
" what hold the bike up. Get rid of that idea now. All the gyroscopic effects do is to help the bicycle (feebly) steer itself into a turn a bit when the bike is in the ",
". You can see this happen by launching a pilotless bicycle and watching it turn into its fall as it falls over, every single time."
] |
[
"You can further confirm how neglible gyroscopic forces are and how important steering correction is with two experiments.\n1) If you build a bike with tiny, lightweight wheels, like those found on a razer scooter, it can still be easily ridden despite the almost non-existent gyroscope effect.\n2) If you tighten the steering column of a bicycle untile the handlebars are difficult to turn the bike will be impossible to ride, even in a straight line, no matter how fast the wheels spin."
] |
[
"The reason for this confusion seems to happen when the rider's active steering input is neglected as a causative factor. Jeez.",
"You can see this happen by launching a pilotless bicycle and watching it turn into its fall as it falls over, every single time.",
"You can also see that a riderless bicycle in motion doesn't fall over as fast as a stationary one, so it's obvious there are other factors other than rider correction at play here. Ignoring that just to avoid \"chagrin\" is basically crossing out a lot of complex dynamics, covering your ears and saying \"la la la this is so simple\"."
] |
[
"Why can we control voluntary muscles but not involuntary muscles?"
] |
[
false
] |
In other words, what is different between the two that allows us to control one but not the other?
|
[
"There are several different types of nervous innervation. Your autonomic nervous system which controls involuntary function has General Visceral Afferent (sensory, send impulses to CNS) and General Visceral Efferent (motor, send impulses away from CNS) fibers (there are special fibers as well). Somatic Efferents are more commonly associated with voluntary skeletal muscle innervation.",
"From a logical standpoint, there just isn't any sense to need to actively control all those functions. You don't need to worry about what's going on with visceral innervation of your parotid salivary gland from the Glossopharyngeal nerve, which is cranial nerve number 9, because your body takes care of it. And yes, I know you said muscle, but there are a lot of other body functions that are subject to involuntary innervation. What about controlling your diaphragm to breathe; what about when you're asleep? It would be ludicrously impractical (and perhaps not even feasible) to have voluntary control over all body functions.",
"Smooth muscle also has a slightly different physiological mechanism of contraction that makes use of some slightly different proteins.",
"Cardicac muscle is even a bit more unique. It has structures known as purkinje fibers that carry electrical conduction throughout the heart; that and some slight physiological differences in the mode of contraction allow for the heart to have automaticity. That means that cardiac cells have the ability to depolarize spontaneously and without nervous system input. Smooth muscle has a much lesser ability to do this as well.",
"Skeletal muscle (voluntary) has no automaticity. Each myofiber must be innervated by a nerve and will not contract without nervous stimulation. "
] |
[
"Happy to elaborate!",
"First, a basic explanation of muscle contraction via a change in membrane potential. Each cell has a standard resting membrane potential at which activity is static. Ligand gated channels (and other mechanisms) have some influence on membrane potential, but voltage gated ion channels are the key players here. ",
"To offer a very simplistic model of a muscle contraction:",
"Nerve impulse arrives",
"Sodium channels open which leads to large depolarization in the cell",
"Subsequent depolarization causes Calcium release from the \nsarcoplasmic reticulum",
"Calcium ultimately leads to muscle contraction through some other physiological steps",
"So, once a depolarization happens, that should ultimately lead to a muscle contraction. ",
"So again, this is put very simply. The pacemaking cells in the heart have a special ability to cause a slow increase of the membrane potential of the cell until the threshold potential is reached that is necessary to allow the opening of voltage-gated ion channels and lead to a depolarization, which leads to muscle contraction. Because of the unique ability of this so named, funny current, the heart can beat successfully without constant nervous system input. "
] |
[
"Thanks for the great answer! If you could explain what you mean by \"cardiac cells have the ability to depolarize spontaneously and without nervous system input\" I would be very thankful."
] |
[
"\"Neutron moderator\" materials slow down fast neutrons so they can successfully interact with radioactive materials to continue the fission chain reaction. How exactly do \"neutron moderators\" slow down the neutrons? Thanks."
] |
[
false
] |
[deleted]
|
[
"Graphite has a decent mass match to the neutrons, can tolerate fairly large amounts of damage to the lattice before losing strength, has few possibilities for activation (nuclei capturing an incident neutron instead of scattering it, leading to radioactive by-products), and is fairly easy to manufacture. Light nuclei exchange momentum more efficiently than heavy nuclei and tend to have fewer paths to activation, so they are favored over, say, copper or lead; some light materials like lithium-6 and boron-10 tend to capture incident neutrons, so they are unattractive as a moderator in a reactor, where neutron economy is paramount. ",
"A variety of materials could in principle be used for moderation. Lithium-7 compounds (fluorides, hydrides, etc.), beryllium, and water (heavy or light) are other options, each posing their own set of engineering plusses and minuses. (Lithium-7 hydride is typically a relatively low-density powder, e.g., which is rather hard to work with compared with graphite.)"
] |
[
"The wiki article on this is actually really good: ",
"http://en.wikipedia.org/wiki/Neutron_moderator",
"The basic idea is that hot (i.e fast moving) neutrons will elastically collide with a bunch of cold moderator nuclei. Overall, the temperature and therefore speed of the neutrons will drop, by transferring the heat into the moderator.",
"To be maximally effective, you want the moderator to have about the same mass as neutrons. To understand this, consider a neutron bouncing off an infinitely heavy nucleus --- the neutron would leave with the same speed as before, resulting in no net energy transfer. In practice, you also need to balance the chemistry and engineering requirements."
] |
[
"Not being a nuclear engineer, I cannot give insight into the engineering trade-offs. However, a quick perusal of ",
"http://en.wikipedia.org/wiki/Neutron_moderator#Materials_used",
" suggests that there are lots of choices, graphite being only one or even a minority (esp. after Windscale)."
] |
[
"Why do all the planets in our solar system lie approximately in a plane?"
] |
[
false
] | null |
[
"All the planets have an inclination (orbit tilt) within a few degrees of each other. ",
"Mercury is the most tilted",
" relative to Earth at 7 degrees.",
"They also all circle the sun in the same direction in orbits which are approximately circles. ",
"This is because it all condensed from the same ",
"protoplanetary disk",
" of dust and gas swirling around the still-forming sun.",
"Now you might wonder why a protoplanetary disk is flat, and why it spins. The answer is collisions make it impossible to be any other shape for long. Disks where everything spins in the same direction minimize fast collisions, and an average tilt will be aggressively negotiated from initial randomness. Nonconformists will be pulverized, homogenized, and allowed to fall into the sun if necessary until orbital consensus is reached, just like politics. ",
"The outer solar system is not as flat because there were never enough collisions to force it to be flat. You will notice in the first link and other orbit tables that smaller and more distant objects often have extreme tilts."
] |
[
"Basically the planets and our sun formed from a single spinning cloud of matter. Everything formed perpendicular to the axis of the spin and collapsed to planets and the sun due to gravity and fluctuations in the density of the cloud."
] |
[
"Essentially the same reason our planets are on similar planes is the same reason Saturn has rings, right?"
] |
[
"Why can't Helium freeze?"
] |
[
false
] |
If you drag the temperature scale to 0 Kelvin, every element except Helium becomes solid. Helium, for some reason, stays liquid... I'd imagine every element should be completely solid at absolute zero.
|
[
"You have been misled by the idea that temperature is a measure of energy. While this is approximately true at high temperatures, it is not correct at low temperatures. Temperature is actually a measure of entropy (actually, its derivative).",
"At very low temperatures, quantum mechanical effects become important, and even at absolute zero (0 K), the particles have energy, known as zero point motion. In helium, this zero point motion is large enough to prevent the atoms from sticking together as a solid - it remains a liquid."
] |
[
"Internal energy."
] |
[
"Yes.",
" Above roughly 3.2 MPa Helium-3 becomes solid at high pressure. For Helium-4 it will become solid above ~2.5 MPa."
] |
[
"How do we know we’ve discovered a new species of human based on a single fossil, and not just a really ugly dude?"
] |
[
false
] |
This claims they’ve discovered a new species of human, which is awesome, but since the claim is based off a single fossil, how do we know that it wasn’t just one person with some sort of genetic defect?
|
[
"I'll start by saying that we actually don't know if this is a new human species or not. The authors who found this fossil argue that it is because:",
"\"A combination of primitive and derived features in the Harbin cranium establishes a good set of diagnostic features that were used to define a new Homo species.\" via Shao et al: ",
"https://www.cell.com/the-innovation/fulltext/S2666-6758(21)00056-4",
", published yesterday.",
"Basically, there are certain features that tend to be specifically diagnostic of species difference when we look at hominids. Things like brain size, face length, brow size, tooth differences, cheek bone size, etc. The reason we look at these things is because they tend to be variable between species, but fairly consistent within species. And, even in cases where one or more of these traits is variable (e.g., a baby born with microcephaly), all the concomitant traits probably won't change much. For example, the authors note that this fossil has a mix of features that are commonly seen in more human-like hominids, and those more common in \"primitive\" hominids:",
"Like humans:",
"\"large cranial capacity, short face, and small check bones\"",
"More \"primitive:\"",
"\"low vault, strong browridges, large molars, and alveolar prognathism\" via Ni et al: ",
"https://www.cell.com/the-innovation/fulltext/S2666-6758(21)00055-2",
", published yesterday.",
"Because this combination of traits isn't known in any other hominid, and because it doesn't seem to showcase signs of any known disease or deformity, it's unlikely (although never impossible) that this is just, like, some guy who looked real weird. ",
"Still, the leap that this is a brand new species just from one skull is problematic. First of all, there are known species of hominid that have unknown skull structures. The article you linked to mentions Devisovans as an example of this. They are a close relative species of ours, and some people of east Asian descent have their DNA in their genomes! We only know they exist because we sequenced the DNA of some non-skull bones, so we have no idea what their heads would have looked like. That means it's possible that this is just a skull of a species we already knew about. Even if this is the case, that's still a really cool find! ",
"I should also mention that even if this is a species we already knew about, it's almost certainly not ",
", as the time and place it was found doesn't match up with human migration. Present evidence suggests that modern humans probably didn't make it to East Asia until about ",
"50,000 years ago",
", and this individual lived in present day China over 146,000 years ago."
] |
[
"Thank you!! This was such a clear explanation. You have to think of course the authors are gonna be biased and want it to be a new species so always great to have a neutral perspective."
] |
[
"That article repeats the ",
" of the team that found the skull \"",
"\", but also puts it into the context of other old human remains discovered in the region.",
"Dragon Man joins a number of early human remains uncovered in China that have proven difficult to categorise. These include remains from Dali, Jinniushan, Hualongdong and the Xiahe jawbone from the Tibetan Plateau. ",
"There has been a fierce debate about whether these remains represent primitive examples of Homo sapiens, Neanderthals, a human group called the Denisovans, or something else entirely.",
"So it's one piece of pretty interesting evidence, the hard part is determining where it fits in the human evolution story and it's offshoots, predecessors and extinct or assimilated competitors etcetera. Because yeah, it's just one skull."
] |
[
"If the speed of light(C) is the universal speed limit, what would happen to the end of a pole sticking out of the Earth, whose radius is so long its circular velocity exceeds C?"
] |
[
false
] |
I've taken Calc 3 and University Physics, and this question popped into my head while using the restroom.
|
[
"The pole would bend.",
"This would only be a problem if the pole were infinitely rigid, but as you can imagine, that's not possible. The pole is made up of atoms, bonded together electromagnetically, and those interactions are all restricted by the speed of light limit. In reality any speed it reached would be far smaller than c, if it were made out of a normal material."
] |
[
"Sure. The problem is \"perfectly rigid\" isn't physically possible, so you can't really say what physics would predict in that case. But there's probably some limit in which that's what happens."
] |
[
"I like your thought process but unfortunately most of the answers you wrote aren't really correct. The bending that occurs due to super relativistic effects don't put extra pressure on the material because it's space 'bending' not the material. So if it was perfectly strong it would just bend forever in a spiral becoming infinitely long and infinitely thin. Also a space elevator wouldn't bend and this isn't the reason why we don't have one."
] |
[
"What ultimately causes death with Alzheimer's Disease?"
] |
[
false
] |
Assuming a person with Alzheimer's had some incredible caregivers and survives all of the safety challenges and also has all of their basic needs met, what ultimately causes death? Even assuming "everything that can be done" is done (e.g. someone who has progressed to the point they lose the response to eat goes on "tube feeding") what will ultimately cause death? Do organs eventually shut down?
|
[
"Usually aspirational pneumonia. Alzheimer's patients tend to have worsening impulse control issues, and as a result they may swallow or vomit in a way that fails to protect their airway, which leads to aspirational pneumonia, respiratory failure, and then death. Even when they have a gastric tube (i.e., a \"feeding tube\" that allows for continued enteral feedings), they still not cough or otherwise protect their airway from vomit or oropharyngeal secretions that would lead to pneumonia.",
"Other causes of death do exist for Alzheimer's patients, such as trauma, sepsis, non-aspirational pneumonia, etc. and can be related back to their Alzheimer's. However, it is key to remember that patients typically die because of something secondary to their Alzheimer's, not necessarily the Alzheimer's itself. "
] |
[
"thank you!"
] |
[
"Most Alzheimer's disease die from infections secondary to aspiration"
] |
[
"Why do we use uranium as the primary atom in nuclear reactions?"
] |
[
false
] | null |
[
"Because it's relatively plentiful and it's big and unstable enough to undergo the necessary decays to generate power."
] |
[
"The only fissile atoms are",
"(from wikipedia)",
"Fissile means the material is ",
" of critical mass and maintaining the nuclear reaction w/out an outside neutron source.",
"Notice, only U-235 is naturally occurring AND fissile. Plutonium and uranium-233 both require being bred through neutron capture (i.e. in a nuclear reactor). You HAD to start at U-235 to even make the other materials. And you don't have to do any special reprocessing in order to use U-235, just enrichment (unless you use a heavy water reactor with can run on natural uranium).",
"It makes logical sense that we started at U-235. The only reason we havent gotten away from it is we don't do reprocessing in the US, and those other types of reactors and designs are not licensed yet."
] |
[
"I assume you mean electrical power. Electrical power is generated from a working fluid which is cooling the nuclear fuel. So, yes, you would. In fact, in commercial power plants towards the end of their core life, much of the fission reactions taking place are from plutonium, which was bred from Uranium 238 initially in the core."
] |
[
"If we can't see the whole universe and are continuously seeing more of it, does that mean the universe expanded faster than the speed of light?"
] |
[
false
] |
We talk about the edge of the "observable universe" and how its continuously growing further as light from sources further away finally reaches us. If we can't see the whole universe and are continuously seeing more of it, does that mean the universe expanded much faster than the speed of light following the big bang?
|
[
"Here is a very relevant ",
"article."
] |
[
"You can use ",
"Hubble's constant",
" to calculate that the matter at the edge of the universe (radius ~46 billion light years) is moving away from us at more than 3 times the speed of light. ",
"Calculation",
"."
] |
[
"Here is an article concerning many of the popular misconceptions of the big bang and the expanding universe theory: ",
"Lineweaver Paper"
] |
[
"Using molecular vibration to degrade molecules?"
] |
[
false
] |
Hi Reddit, I was wondering if it is possible to use the molecular vibration of a molecule to help i'ts degradation. Let's say i have a salt, and i know the exact IR band at which light is absorbed at the ionic bond. Could i make an IR lamp with a bandpass filter and excite the molecules enough to cause increased dissociation? Does it make sense that if the molecule is in an exicted state, especially at the ion bond, it would dissociate faster or easier? Or would any dissociation just be becuase of the increase in energy of the molecule due to the temperature increase of absorbing tha IR radiation? Thanks.
|
[
"I don’t think salts are IR active... typically IR spectroscopy takes advantage of the polarity differences of covelent bonds. Since salts have ionic bonds they wouldn’t be affected by it. This is assuming you’re using a non-organic salt, like NaCl, rather than NaNO3, of which the NO3- would be active.",
"That being said, light can totally be used to break apart molecules, things get bleached by the sun all the time. And it’s not only color, certain plastics will degrade due to uv exposure as well. I’m not sure how well IR light would work, it’s much weaker, but since any excited state is less stable than the ground state it could make things a little more unstable, and more prone to degratation."
] |
[
"There is IR activity for some salts, but it tends to be pretty minimal to non-existent for many of the single atom salts often with defects/impurities causing the absorption. ",
"Which is why we use salt plates as a surface to take IR measurements for organic samples. Because they transparent in the IR region."
] |
[
"Yes, \"it is possible to use the molecular vibration of a molecule to help its degradation.” But as ",
" points out: ",
"I don’t think salts are IR active.",
"Simple salts do not absorb in the infrared range, and in fact they are ",
" transparent in the IR that ",
"salt plates",
" are used to hold the sample, when taking an infrared spectrum of an unknown.",
"Photochemistry initiated by ultraviolet light is well known:",
"things get bleached by the sun all the time. And it’s not only color, certain plastics will degrade due to uv exposure as well.",
"But the absorbance of UV light excites an ",
", not a molecular vibration. ",
"The infrared range is the right range to use to excite covalent bond stretching vibrations. And yes, you can use this to cause a specific bond to vibrate faster, leading to the bond breaking. With any complexity to the molecule, however, there are overlapping absorbances and rapid redistribution of vibrational energy, so exciting the vibration you want until the bond dissociates can be problematic. But with an IR laser at the right frequency, it's possible. It's even practical, for instance, to do chemical vapor deposition by ",
"decomposing disiloxane in the gas phase with an IR laser",
" to split it into H2SiO (which then deposits on the surface), and lose silane and hydrogen."
] |
[
"Ask Science: do any hair restoration things actually work?"
] |
[
true
] | null |
[
"what kind of dr did you see? a dermatologist? or just your general Dr?",
"It seems like from what I'm reading online that propecia is the way to go"
] |
[
"what kind of dr did you see? a dermatologist? or just your general Dr?",
"It seems like from what I'm reading online that propecia is the way to go"
] |
[
"did you feel any hormonal effects? libido etc"
] |
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