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[
"Do noise canceling headphones protect your hearing?"
] |
[
false
] |
I was on my flight home today and I had a thought: do noise canceling headphones actually make things quieter, like an in-ear monitors with a custom fit mold do? Do noise canceling headphones have this same effect? Or do they just fake your ears into thinking things are actually quieter?
|
[
"Noise-cancelling headphones use a microphone to detect outside noise and then create another signal to cause destructive interference. While one might think that two sound waves could only trick the ear into making things quieter, interference is actually a property of all waves. When one sound wave is at its crest at your ear drum, and another sound wave is at it's trough, they will cancel each other out, providing they have the same frequency. This destructive interference is the same exact thing as the resultant wave. If the interference works properly, the sound that you hear should be exactly the same as if there were no outside sound at all. However, noise-cancelling headphones can't always work perfectly so the noise is really only reduced."
] |
[
"Ear plugs, as non-vacuum matter, can still conduct sound. Even with a perfect plug without a passage of air to conduct sound around the plug, there is still some sound going through it.",
"Therefore, the effect of an earplug and noise-cancelling headphones are different. I'd say it depends on how well some types of sound are conducted through the plug vs. processed and cancelled by the headphones."
] |
[
"I was wondering if when they emit the opposite wave if that sound still affected your ear in anyway, or if its like the sound disappears. I'll check out the article. "
] |
[
"Do stars have anything like an Atmosphere?"
] |
[
false
] |
I've always assumed that stars are a swirly twirly ball of gas more like atmosphere than surface. But it occurred to me that the sun might possibly have significantly different layers of density. Is there anything like an atmosphere in regards to stars?
|
[
"Here",
" is a nice summary of the structure of the sun.\nTo quickly answer your question, the ",
"corona",
" of a star could be considered something akin to an atmosphere."
] |
[
"The Sun (and all stars) definitely have an internal structure. See ",
"this",
" page. ",
"This",
" section in the wiki page does an excellent job in explaining the different layers, including it's 'outer' atmosphere."
] |
[
"thank you!"
] |
[
"What's that smell coming out of my nose?"
] |
[
false
] |
I occasionally catch a whiff of a very sharp scent coming out of my nose (I think it originates in my lungs). I've smelt it on the breath of one other dude too, but it's an unmistakeable sharp smell. Is this the smell of one of the products of respiration, or what is it? edit: I don't have halitosis. I brush and scrape my tongue twice and floss once every day
|
[
"I'm pretty sure carbon dioxide is an odorless gas."
] |
[
"Not Safe For Life.",
"Worse than NSFW. Not safe for sanity."
] |
[
"Unless you're really sick, it's not from your lungs. Your mouth is filled with a myriad of different kinds of bacteria so it's impossible to answer this (for me). Maybe some other supastar will come along, but I'm reasonably confident of my answer. "
] |
[
"Rotate a 3D lens on a laptop screen and at certain angles it goes opaque. Why does this happen? [GIF provided]"
] |
[
false
] |
Rotate the lens from a pair of 3D cinema glasses on a screen, and at a specific angle (and the opposite angle) it completely darkens. Gif: I know it's got something to do with , but with only 1 lens, why would this happen? Thanks!
|
[
"I want to add to the discussion that most 3D glasses aren't simply linear polarization filters, but ",
"quarter wave plates on linear filters",
", essentially making ",
" polarization filters. This means that if you flip your lens over, it won't block the screen light in the same way."
] |
[
"LCD screens consists of two polarizing filters with a layer of liquid crystals inbetween. The first filter creates a linearly polarized light source. The layer of crystals either does nothing (if there is no voltage across the pixel), or turns the polarization direction of the light 90 degrees. The second filter is 90 degrees to the first, so if the crystals are inactive it will block out the light, leaving a black pixel, while if the crystal is active it will do nothing (leaving a bright pixel).",
"So the light coming out from the LCD screen is always polarized, and you can block it with an additional filter like you show.",
"Incidentally, a cute hack is to remove the second polarization filter from the screen, ",
"like this",
". Then the screen will appear white, but become readable if you look at it through polarized sunglasses!"
] |
[
"Yes I noticed this, if you flip it the other way it seems to have a blue/yellow tint, depending on the angle.",
"pic: ",
"http://imgur.com/a7z1L0a"
] |
[
"How does the annihilation of antimatter and matter upon impact cause both particles to disappear?"
] |
[
false
] |
[deleted]
|
[
"In classical approximations, conservation of mass is definitely a thing, and is probably discussed in most introductory physics courses. However, in relativistic or quantum regimes, mass and energy become interchangeable and exchangeable (think Einstein’s famous E=mc",
" ). Conservation of mass is no longer valid, since resting particles carry their own energy simply by existing. But conservation of energy is always valid. So, once the matter/antimatter pair annihilate and disappear, we’ll see light emitted with a total energy equal to the sum of all their energy - including the energy from their mass."
] |
[
"There is no such law as the law of conservation of mass. It is approximately true for non-relativistic systems. What has to be satisfied is the conservation of energy and momentum, plus other charges. In physics everything that is not forbidden is compulsory :) So, converting two electrons into one photon (a particle of light) is forbidden, while into two photons is perfectly allowed."
] |
[
"Trivial, but I believe there should be a plus sign between the two terms in the first equation."
] |
[
"Why does the browser on my smartphone take so much longer to load than the browser on my laptop."
] |
[
false
] |
I have a powerful smartphone (GS3) and a rather outdated laptop. When I load a webpage (almost any webpage) on my laptop it loads almost instantly, but if I load the same webpage on my phone it takes 3-4 seconds. The thing is- I run my computers internet over 3G! The websites I load on my computer are actually being routed through my phone. At 2.8ghz, my Computer is a lot faster... but browsers are surely not especially memory intensive. I've tried several: Chrome, Firefox, Opera, and they all run a lot more slowly on the phone. Why is this?
|
[
"The processor in your phone is not nearly as capable as the one in your computer. A browser is a relatively complicated bit of software - it has to take a html input and translate it into a complicated page format, while simultaneously placing and rendering image files, as well as (often) a lot of back-end security checks and handshakes. ",
"For reference, GHz is not a reliable way of estimating processor capability - even for home computing it's been meaningless for about 15 years. Using floating point operations per second (FLOPS) as a measure, most smartphones are capable of several hundred megaFLOPS. By comparison a modern home desktop might be looking at about 100 ",
"FLOPS. So 3 orders of magnitude difference in processing power."
] |
[
"Thankyou. This us exactly what I was looking for. ",
"I'd be interested to know why we don't benchmark in flops when buying a computer. "
] |
[
"Even FLOPS are not necessarily particularly meaningful in terms of performance. There's a lot of inter-relating factors, not least of which are the software you're interested in running in the first place."
] |
[
"If you were in a swimming pool on the Moon or Mars - Would you float higher, lower or the same?"
] |
[
false
] | null |
[
"The same. Buoyancy is dependent solely on the relative densities between the objects in question. Thus, you will float in water when you have displaced the same mass of water as you have. Masses and densities are not dependent upon gravity. "
] |
[
"This quote, and my explanation are not in conflict. ",
"An object floats when it displaces an equal amount of mass of water that the object has. Since an object and the water is in the same gravitational field, the object and the displaced water will also weigh the same. The weight of the water you displace is equal to the force the water places on the object floating in it. "
] |
[
"The ",
" of the water varies in exactly the same way as does the ",
" of the object (the product of local gravity and mass), so in effect it is displacement of equal masses."
] |
[
"Would ultrasound imaging find surveillance devices in drywall?"
] |
[
false
] |
If so, what's the cheapest type of device that would be likely to pick up a device, say, the size of a fish hook? Of course, there are better tools for the job, but I want something that's: 1) super cheap (you can rent medical equipment, but security equipment) 2) able to detect devices that have been remotely shut off 3) able to detect devices made of mostly non-metallic components Hiring a PI is an option, but I'm assuming even the best equipment will fail to find deactived devices in a one-pass sweep (that's why there's a monitor mode on the high-end devices). Would something like the Ultrasound Sonicator 710 work, or is that even an imaging device? Update: Just posted some related questions on a private investigator forum, and received this . Oh yeah, my real name isn't Oliver North.
|
[
"Ultrasound probably wouldn't work for looking past drywall. I'm guessing you would be looking for a device that is in the air behind the drywall and between the wooden frames of the wall? The air gap would destroy your signal. Ultrasound works by reflection of high-frequency sound off of material boundaries/interfaces, and the air wouldn't carry the sound well enough. This is why they put that goop on the transducer when a woman gets her uterus imaged.",
"If you were looking for something embedded in the drywall itself (not in the air behind the drywall) then ultrasound might work. But you would need to do a lot of work in understanding what ultrasounds look like, and what type of image you would be looking for to find your surveillance device.",
"I'd say your best bet would be to find a device that could look for whatever signal the surveillance device uses to send its data."
] |
[
"I have no knowledge on these devices, but I would have assumed that an ultrasound was developed to work within a specific set of frequencies - ones that are specifically picked to work well when travelling through human tissue and liquids - and to then reflect off just the right amount.",
"I would be seriously surprised if an ultrasound would see anything inside a drywall."
] |
[
"I would have thought that all the goop they use on the thing is there really to ensure that the sound is transmitted through into the body rather than just to make the scanner slide around the body easier. If they didn't need all that stuff, why not just do it througha T-Shirt or whatever without all the need for gels and gunk?",
"I agree that the concept would work, I just don't think that a medical ultrasound would function on a drywall."
] |
[
"How long did the Challenger Astronauts survive?"
] |
[
false
] |
I worked for a startup once that had an airforce pilot as one of the investors (he came from a wealthy family). He had done extensive training with NASA and was on the short list to go on a shuttle mission. He once told me that in the astronaut training, at one point they play the audio recording from the Challenger command module as it descended to the ocean. Contrary to popular belief, the astronauts were all still alive, and they can be heard on the recording. Supposedly, the ones with the military background remained remarkably calm, while Christa McAuliffe, on the other hand, was understandably freaking out. One astronaut even expresses that his only regret was that he never actually made it into space. When the recording ended, everyone in the room was in tears. Does anyone know whether a) this would even be possible, given the violence of how the Shuttle came apart, and b) whether there is any truth to this? Has anyone else ever heard this?
|
[
"Wikipedia",
" has about all the info you're likely to get",
"At least some of the astronauts were likely alive and briefly conscious after the breakup, as three of the four Personal Egress Air Packs (PEAPs) on the flight deck were found to have been activated. Investigators found their remaining unused air supply roughly consistent with the expected consumption during the 2 minute 45 second post-breakup trajectory.",
"While analyzing the wreckage, investigators discovered that several electrical system switches on Pilot Mike Smith's right-hand panel had been moved from their usual launch positions. These switches were protected with lever locks that required them to be pulled outward against a spring force before they could be moved to a new position. Later tests established that neither force of the explosion nor the impact with the ocean could have moved them, indicating that Smith made the switch changes, presumably in a futile attempt to restore electrical power to the cockpit after the crew cabin detached from the rest of the orbiter.[18]",
"Whether the astronauts remained conscious long after the breakup is unknown, and largely depends on whether the detached crew cabin maintained pressure integrity. If it did not, the time of useful consciousness at that altitude is just a few seconds; the PEAPs supplied only unpressurized air, and hence would not have helped the crew to retain consciousness. The cabin hit the ocean surface at roughly 207 mph (333 km/h), with an estimated deceleration at impact of well over 200 g, far beyond the structural limits of the crew compartment or crew survivability levels.[13]"
] |
[
" ",
"http://www.snopes.com/horrors/gruesome/challenger.asp"
] |
[
"And surely the voice recorder onboard was at least as well-designed as aircraft black boxes, which easily survive much higher G impacts than this one, and which have been recovered from the ocean floor.",
"The snopes article (And the original rumour) contains question of a personal recorder, not a Flight Data Recorder. The odds of NASA using a personal recorder for each suit is very small, since in the event of an incident, they would be unretrievable, or destroyed. Do they carry an FDR on the shuttles? Not that I can find any information on. It seems likely that shuttles would not fall under the same regulations and require one as well.",
"Furthermore, a tape could possibly have been recorded on the ground, although I doubt transmissions were still working from the command module to NASA.",
"Downlink was lost upon disintegration. This is confirmed.",
"And as for there being leaks... well, I heard about this back in 1995. So, consider that a leak. I'm curious as to whether anyone else has heard about it from a credible source. The source I heard it from was definitely in the astronaut program.",
"The transcript itself (Which started the initial rumor),was found to be falsified. Because of this, no information in that article can be considered accurate. This includes the first hand accounts you are considering to be leaks.",
"You claim your source was indeed in the astronaut program with NASA. I can not prove or deny this. However, you claim that he said he heard a secret tape during training. One that conveniently matches up to the rumours the rest of us heard. Since this is directly related to his profession, he/she is more than likely familiar with it as well. This could very well be the passing on of more rumour. He is not what I would consider a reliable source.",
"Finally, I doubt a secret recording is given to program trainers to play for the program trainees. If the information was available at this level, it would be available to the public as well."
] |
[
"Is the Planck Length the smallest measurable length, or is it the smallest something can be? In the latter case, how is it not theoretically possible to, say, halve this lengths?"
] |
[
false
] | null |
[
"See the FAQ. The Planck unit system has nothing to do with \"the smallest possible X\"."
] |
[
"All I would want to write about this, I've written ",
"here",
"."
] |
[
"Thank you "
] |
[
"What is the difference between an electrochemical gradient and an electrical current?"
] |
[
false
] |
How do they behave differently? Are they under vastly different physical constraints? This question comes from trying to figure out how the action potential works within neurons when it "hops" over the myelin sheaths during saltatory conduction. I forgot to add that this is a cross-post from
|
[
"They are two separate things. Electric current is simply the flow of charged particles. An electrochemical gradient is a combination of a gradient due to a chemical concentration difference between two concentrations of charged particles (ions) and the electric potential that is induced what you have two different amounts of charged particles. And so the ion gradient that is created across a neuron's membrane creates this electrochemical gradient which in essence creates a \"force\" for ions to travel a certain way. When you open ion channels in neurons, a current is generated because ions will travel down their electrochemical gradients. "
] |
[
"The action potential depolarization will propagate down through the cytoplasm of the axon until the next unmyelinated node of Ranvier, where ion channels there regenerate the action potential."
] |
[
"So how does the current go over the top of the myelin sheaths which have no ion channels? This discussion came up when talking to an friend who is in electrical engineering. He says that the distance that the current would have to go when hopping over is too far for electrons to travel, since a current needs \"direct\" contact to continue. I hope I'm making sense here."
] |
[
"How does our brain filter lots of conversations so that we almost always notice when our name is said?"
] |
[
false
] |
For example, when you're standing in a crowded room with a bunch of conversations, you won't usually notice what other people are saying, but if they mention your name, you tend to hear it. This seems like it would be useful for a number of reasons, but I'd like to know more about how our brain accomplishes this.
|
[
"What you're asking about is the ",
"cocktail party effect",
", which was used for quite a while to guide ",
"attention research",
". Have a read through both of those links, they should give you your answer. If you have any more questions, feel free to ask."
] |
[
"We have an attentional matrix - dedicated brain pathways to focus and attention -- always scanning all the various sensory inputs to see what is relevant to 1) our survival, and 2) our cognitive interests.\n",
"http://www.ncbi.nlm.nih.gov/pubmed/18025955",
"\n",
"http://brainblogger.com/2013/08/22/what-you-hear-affects-what-you-see/",
"\n",
"http://brainblogger.com/2013/07/07/boosting-cognitive-performance-by-chewing/"
] |
[
"put simply, the brain responds to stimuli based on the priority of said stimuli. when you hear your name in a conversation, outside of the one you are having, your attention shifts due to cognitive interest in possibilities that may occur from this new stimulant."
] |
[
"If an asteroid passed through the 36,000km satellite oribtal plane, would it sweep through destroying satellites or is it likely to just pass through and not touch anything? How densely filled is this satellite region?"
] |
[
false
] |
article got me thinking. If it was passing a bit closer to Earth, would it be putting lots of satellites at risk?
|
[
"Let's do some maths!",
"Google says that there are 402 satellites in geostationary orbit at the moment, and if we assume they are evenly spread around the world; that gives us one satellite every 36000km x 2 x pi / 402 = 562 km (350 miles). ",
"Now think about a town which is about that distance away from where you are - that's a lot of space between satellites for an asteroid to pass through without hitting anything. "
] |
[
"A minor detail: The 36,000 km are measured from the surface of Earth, to get the radius you have to add 6,000 km to get 42,000 km."
] |
[
"Here's something to keep in mind which I think is a pretty good example of how empty space is:",
"If you flew through the asteroid belt in a spaceship, you'd likely never know it. The asteroids inside are often millions of kilometers apart, and only collide regularly on geologic timescales. Hollywood has lied to you big time, the only place where chunks of matter are orbiting that close together is in planetary rings, which are only on the order of 10 meters thick, and mostly filled with sand and dust-like particles."
] |
[
"Do babies get hungry when they smell food they have never eaten yet?"
] |
[
false
] |
I have a couple of 9 month old twins who have just recently started eating basic stuff. Last night we went to pick up a pizza for dinner. Driving back, with my wife carrying the pizza box on her lap and the twins in the back seat, the amazing smell just filled the car, and I had all sorts of thoughts about what I'd do to the pizza when we got home. But what about the babies? Would their brains interpret that smell as delicious food if they've never had pizza? I imagine I had the reaction I had because I knew it was a pizza and my brain could do its thing based on that info. How would that work for the babies?
|
[
"\" I imagine I had the reaction I had because I knew it was a pizza and my brain could do its thing based on that info\"\nwell, actually it doesn't work that way, or not entierly.",
"\"But what about the babies? Would their brains interpret that smell as delicious food if they've never had pizza\"\neven if you had never eaten something you still could tell that it is delicious or not based on the smell and other factors.\nbecause humans are pre-disposed whit over millions of olfactory receptor caused by our genes.\nso when we inhale the air Each aroma sets off a signal made by the receptors that travels along the olfactory nerve to the olfactory bulb.The olfactory bulb sits underneath the front of your brain. Signals from the bulb tell your brain what reeks.\nso they know that a pizza is good.",
"https://www.livescience.com/10457-smell.html",
" <--- source"
] |
[
"This is an excellent question and I'm going to try to answer it in two parts - how the smell affects you and then how it affects an infant. If I don't answer you fully, let me know.",
"First up, what is happening to you (or any other adult) when you smell something strongly? It is well-established that smell is heavily connected to the limbic system. This connection is why smells so often link to memories and moods. In fact, diminished sense of smell is commonly seen in patients with depression.",
" Foods like pizza are often associated with memories and special occasions (birthday parties, holidays, dates, and so on). Not to mention tasting good.",
"In line with your guess, this all adds up to your excitement when you smell pizza. For you, the smell shoots into your limbic system and stimulates a positive mood and may evoke some memories of other pizza nights. You know you like the taste and you enjoyed pizza last time you got it, so you look forward to having it again. However, this is all based on past experience and learned associations, so none of this could be happening in the brains of your twins. What is the smell of pizza doing to them?",
"Some of a baby's reactions to food are pretty hard-wired. Just like babies prefer the face of their caregiver, they have a natural predilection for high-sugar foods.",
" In addition, they start developing food preferences prenatally. It has been shown that foods consumed by the mother (especially during the third trimester) can affect the baby's taste preferences after birth.",
" Also, in the breastfeeding phase, the composition of the mother's milk has been shown to affect a child's tastes.",
" Given this information, if a baby has already realized that a particular smell is associated with something it likes (a specific taste/high sugar/high sodium...) then that smell may evoke an anticipatory response in the baby.",
"However, you specifically mentioned that your twins have never had pizza. There's no way for them to connect the smell of pizza to any taste or biological craving. They may realize that the other people in the car (you and your wife) seem happy, but they may or may not draw a connection with the pizza. Does this mean that the particular smell of pizza would do nothing to them at first? Not quite. While some foods smell quite bland, pizza does not. As with so many hot/cooked meals, pizza has a distinctly \"food\" smell. Even if an animal has never had a particular food before, if it smells food, there's a bodily reaction.",
"Digestion of food is broken into several phases, and phase one is \"cephalic.\" In the cephalic phase, the smell and sight of food (before it even enters the mouth) provokes an increase in saliva and stomach enzymes. Think of it as a preparatory step so that your body is ready to consume the coming meal. If you're familiar with Pavlov, one of his lesser-known experiments was to show the cephalic phase in dogs. This is what your twins' bodies would be doing. They don't yet have any associations with pizza, (although they're beginning to build them now), but they do have the \"incoming food\" response built in like all other mammals. ",
"TL;DR The babies would be starting to develop associations between the smell of pizza and its taste and significance. They would also have the biological response of initiating the cephalic phase of digestion upon smelling food.",
"Croy et al., (2014), Olfaction as a marker for depression in humans, ",
"Bloomfield et al., (2017), Smell and Taste in the Preterm Infant, ",
"Beauchamp and Mennella, (2011), Flavor Perception in Human Infants: Development and Functional Significance, "
] |
[
"Awesome. Thanks for the reply and the article! "
] |
[
"How low cortisol affects on your mood?"
] |
[
false
] |
I'm currently on the process of investigating on why I have trouble producing cortisol, but due to me getting infeccted by covid-19, this had been postponed, so I wanted to know why even though I have trouble producing the stress hormone I am so stressed. I have generalized anxiety and recently I have been really angry about some stuff, not like angry enough to break material items but a standing anger, since last Friday, and before that I already was experiencing an easyness to be bothered by silly things like specific noises. Is this normal? Wasn't I supposed to be more chill due to my lack of cortisol?
|
[
"It would be more accurate to consider cortisol ",
" with stress rather ",
" it. In fact, it would be more accurate to say cortisol level is raised ",
" stress. The hormone does a lot of things, but on the whole, it helps your body to deal with stress better. This include raising blood sugar level, pumping more energy to your body, and regulating the immune system and inflammation, among other things.",
"That’d why, either too low or too high levels can lead to worse stress, because it means your body is handling stress inappropriately."
] |
[
"It’s a pretty general term, basically, it’s anything that throws your body off from its normal state. This can be anything from an injury, an infection, other illnesses, to mental stresses, which could be described as external situation that makes you feel you have to do something in response, something which could be difficult, something you need to ",
" for.",
"From there, it’s the stress response, how your body reacts to stress, that could harm you if it’s overblown or sustained over excessively long period. There’s a lot of things in stress response, but basically it’s the body stepping up metabolism, using up more energy, minimizing the function of certain parts of the body (the digestive system, urinary system, etc.) and of course, the change in mood and thought processes. Cortisol is just a part of this response, it being low (or absent) doesn’t stop the many other pathways, so it’s not that you won’t get a stress response at all, you get an imbalanced one. It’s like when a big rush job comes in at a workplace so everyone scrambles to do it, but one guy with a rather important duty is absent: it doesn’t make the job any easier. Being unable to complete the response, in many ways, lead to more stress for the body."
] |
[
"What is stress then? How does it harm us if cortisol is not present?"
] |
[
"Are human bodily fluids lethal to any plants/animals/organisms?"
] |
[
false
] |
A lot of plants and animals that have their own defense mechanisms like venom or other bodily fluids. Do humans have any bodily fluids that are lethal to other plants or animals?
|
[
"Saliva",
" has a number of antimicrobial factors, including antibodies and enzymes."
] |
[
"No, it would not kill every plant you urinated on. It can kill certain species, but not every single one since you can only urinate so much and it would have to be extremely concentrated with certain toxins present to be acidic enough to kill every plant, but then it would end up killing you if it was that concentrated. ",
"Still, don't pee on any flowers or in any gardens!"
] |
[
"No, it would not kill every plant you urinated on. It can kill certain species, but not every single one since you can only urinate so much and it would have to be extremely concentrated with certain toxins present to be acidic enough to kill every plant, but then it would end up killing you if it was that concentrated. ",
"Still, don't pee on any flowers or in any gardens!"
] |
[
"What are the effects of strong magnetic field on a human body?"
] |
[
false
] |
[deleted]
|
[
"You can actually see a bit of a demonstration of this on Earth. If you have a tattoo, especially one with red ink, you have to be careful about getting an MRI scan. The rapidly fluctuating magnetic fields (which are usually about 0.5-3 T) can induce current loops within the iron-rich ink, which can cause burns. Note that in this case it is the change in magnetic field, not the magnetic field itself, that causes problems, but rapidly rotating neutron stars and magnetars (which rotate more slowly but have a more powerful magnetic fields) could certainly have this same effect. ",
"Could someone please explain what would happen if we got dangerously close (within 10 000km?) to a very powerful magnetic field (up to 1 trillion gauss)?",
"You would die. A trillion Gauss is within an order of magnitude of the quantum electrodynamic field strength of B",
"=m",
"c",
"/he, which is about 4e13 Gauss. (And in fact, magnetars can have field strengths of up to 1e15 Gauss!) At these field strengths, ",
"strange effects occur",
": electrons process around fields at nearly the speed of light even in their ground energy states, atoms interacts as if they were thin cylinders, photons can split and recombine readily, and of course the chemistry of life as we know it would not function.",
"Would our senses pick up the magnetic field getting stronger as we approach a magnetar?",
"Some patients getting MRI scans report ",
"experiencing vertigo",
", and magnetic fields can induce currents in ion-rich nerve endings (MRI scans operate just below this stimulation threshold), so it's entirely likely that, sometime before being torn apart at a molecular level, you would sense the presence of strong magnetic fields."
] |
[
"The rapidly fluctuating magnetic fields (which are usually about 0.5-3 T) can induce current loops within the iron-rich ink, which can cause burns.",
"Most medical MRIs have a static magnetic field in that range (1.5T and 3T being most common; some research scanners go higher), but this main field doesn't oscillate or cause burns. The RF pulses that are necessary to form images can cause burns if you have some sort of electrical conductor on you (e.g., metallic inks).",
"Basically the way MRI works, is you go and lay down in a very strong giant magnet that's typically always on. Modern MRIs are made with superconducting magnets and so the current powering the main field is always on (absent undergoing maintenance or a quench or something). Note if you had swallowed a metal fragment that responds to magnetization, the greatest danger to you of it being dislodged would not be when the MRI starts taking images; the metal fragment would be ripped out of you as you approach the entry of the tunnel. Fiction often gets this wrong (e.g., this ",
"black mirror",
") episode). (The force is proportional to the gradient of the magnetic field which will be greatest near the entrance/exit of the MRI tunnel).",
"The purpose of the main field is to align the spins of the protons in the hydrogen atoms in your body (typically in water molecules) along this strong magnetic field. In reality it's only like 1 in a million that's more aligned than not aligned, but this is very noticeable effect when you have two times Avogadro number of protons per 18 grams of water in your body. This creates net polarization vectors that precess along the strong magnetic field at the Larmor frequency (42.578 MHz per Tesla).",
"There are two separate ideas behind MRI. First, you excite these net polarization vectors (comprised of many protons) by pumping in radio frequency (RF) pulses at the Larmor frequency of hydrogen. These RF pulses flip the net polarization vectors to flip to be aligned at a different angle (e.g., if 0 degrees is aligned with the B-field; typical pulse sequences would be 90 degrees or 180 degrees) and then the net polarization will gradually decay back to being aligned. As the polarization vectors decay they emit a radiation that is detectable. ",
"Second, in addition to the main magnetic field and the RF pulses, you also have gradient magnetic fields. These gradient fields allow you to select a slice. E.g., if the main field 1.5T is in the z-direction, you create one gradient in the z-direction so it varies from say 1.55T to 1.45T across your body, so the RF pulse only excites the narrow slice in the z-direction body where the Larmor frequency is right. Next while the magnetization vector is decaying you turn on relatively small gradients in the x direction (before starting to sample the decay of the polarization vectors) and then turn them on in the y-direction while sampling the polarization vectors. Doing it in this method allows you to effectively take various samples of the Fourier transform of that 2-d slice of your body, so you can just Fourier transform it back to reconstruct that 2-d image (and then construct a 3-d image by repeating the process). (I should add that most MRI doesn't just normally weight based on the proton density as described by this process, but tries to be sensitive to various properties of tissues and different decay mechanisms by having different pulse sequences of how they excite and then measure the pulses, but this is getting long).",
"But anyways my nitpick was all about it's not the MRI magnet that causes heating, it's the RF pulses that are designed to excite the protons in your body (which if you have conductors in your body, they act as receivers and can take too much of the RF pulse's energy in one small place). (Granted an RF pulse is an oscillating electromagnetic field, so you weren't entirely wrong)."
] |
[
"Thank you for this awesome answer! ",
"Could you elaborate just how a human would die? I imagine we would \"dissipate\" in a way? I always wondered what would happen to the molecular bonds. Lastly, I'd appreciate it if you could recommend a book on the topic of pulsars for someone with a firm grasp of mathematics and a relatively good one on physics (maybe via PM). "
] |
[
"If a pregnant woman gets sick, does the baby do so as well?"
] |
[
false
] |
If a pregnant woman gets, say, a cold...does the baby get the same cold? How does any given illness affect a fetus?
|
[
"Although you say HIV, I IIRC it's only transferred at birth, not during the pregnancy. There are some pretty effective barriers to help protect the baby, not only from pathogens but from the mothers immune system."
] |
[
"It depends on the illness I think. Not all your illnesses are because of pathogens in your blood, so they most likely won't affect the baby (I think cold doesn't for that reason, please correct me if I'm wrong).",
"But there are some very bad illnesses which if the mother gets can totally screw up the baby. Obviously HIV comes to the top, but there are other infections that are scary too, and one old-school test which looks for the most important ones is the ",
"TORCH panel",
". ",
"Even the blood compartments between mother and baby are separated by multi-layered barriers in the placenta that should act as barriers for pathogens too, but I don't know how effective they are against most diseases."
] |
[
"You're correct. And even still those barriers are deliberately leaky when it comes to some things. Mother's immune cells can't pass the placenta, but mother's antibodies can! (some types, at least.)"
] |
[
"AskScience, I suck at physics. Is it possible to calculate how long it takes for matter to change phases?"
] |
[
false
] | null |
[
"Great idea! It seems like a reasonable approximation, but it might be off because the heat loss will be quicker for hotter objects. If you focus on the temperature change closer to the boiling point (instead of the whole range from 20C to 100C) you might get a better approximation."
] |
[
"Yes. But you need to know a lot of information to do so.",
"Also, in your question you say \"reduce the mass of the liquid to the mass I want.\" I think that you are mixing up science terms."
] |
[
"No, latent heat is how much energy it takes the water to change phase.",
"The amount of heat you're putting in needs to be calculated from the flow of heat from the hot plate to the water, which depends on the thermal conductivity of the container.",
"You also need to figure out how much heat you're losing at the same time (you're heating up the air at the same time)."
] |
[
"Auditory and Visual Hallucinations?"
] |
[
false
] | null |
[
"Sorry but this falls under medical advice. Since this is against the reddit TOS I have removed it. Please speak to a doctor as it is the best course of action."
] |
[
"I just wanted a discussion on this topic. I'm an artist, and this is common. I wanted people to discuss the science and spiritual aspects. I just been getting the same thing though. 'Go see a doctor.'"
] |
[
"If you made the question more general and removed you as the subject that would be better. If it was a general question that didn't relate to you on a personal level the question wouldn't be medical advice."
] |
[
"Why do I feel tired throughout the day and then get a \"second wind\" at night?"
] |
[
false
] | null |
[
"If I'm not mistaken, I believe the cycling of the body temperature is correlated with it. At the time when you feel the most tired (the afternoon -- when people take ciesta), your body temperature is the highest.",
"http://en.wikipedia.org/wiki/Circadian_rhythm"
] |
[
"This is right. Transcriptional control of our clock genes (those that control, essentially, the many functions of our circadian clock) occurs in a cyclical fashion that is different for many of us. The interplay between two factors is what usually defines our personal rhythm: sleep-wake cycle and core body temperature/plasma melatonin concentration."
] |
[
"How long have you sustained this sleep schedule? If you went to bed at 3 AM for a year or more, it's gonna take a good while to fully adjust to this sleep schedule. The ideas of day and night people are not fully supported by sleep studies, and should not effect you to the point that it is. If it's been a while since you've developed this sleep schedule, it's probably best to give your body time to get fully on track.",
"If this is not the case, you may just not be getting as much sleep as you need. How old are you? This is also important. I remember seeing a study posted on ",
"/r/science",
" about how studies are starting to show that teens may have a natural cycle from 1-9 and how schools should perhaps be adjusting to this. If you are a busy young adult, you may simply need more than 7 to 8 hours. Maybe you're just not enthralled by the things you do in the daytime."
] |
[
"Can bacteria grow on soap?"
] |
[
false
] |
Most likely we wont find any bacteria on "anti-bacterial" soap but what about regular bars of soap we use in the shower?
|
[
"Definitely. Soap's function is not generally to kill or even remove bacteria from your body,though, but rather to make insoluble oils, fats, and greases water soluble.",
"The vast majority of bacteria you come in contact with either have zero effect on your overall well-being or are helpful (sometimes even vital) to your health.",
"It is said that there are more individual bacteria living in and on you than your body has cells."
] |
[
"It is estimated that 500 to 1000 species of bacteria live in the human gut and a roughly similar number on the skin. Bacterial cells are much smaller than human cells, and there are at least ten times as many bacteria as human cells in the body (approximately 10",
" versus 10",
" The mass of microorganisms are estimated to account for 1-3% total body mass. Though members of the flora are found on all surfaces exposed to the environment (on the skin and eyes, in the mouth, nose, small intestine), the vast majority of bacteria live in the large intestine.",
"http://en.wikipedia.org/wiki/Human_microbiome#Bacteria",
"I'm sorry to link to a Wikipedia page, but you might as well check out the sources yourself."
] |
[
"its not really necessary to cite such widely known facts. Every piece of shit that comes out of your anus has billions of bacteria. There are Staphilococcus aureus living in your nose and god knows what living in your bellybutton. The bulk of your commensal flora (as it is called) is in the gut of course, where it digests the food you eat, helps your immune system develop, and occupies the space that pathogenic bacteria would othewise seize. Among other things. "
] |
[
"Is a certain Sleep position considered healthier or beneficial?"
] |
[
false
] |
Back, side or front? Or does it matter? I was always told that sleeping on your right side helped with stomach aches. Is this true? Any longitudinal studies or research about sleep positions would be appreciated!
|
[
"This is really dependent on situation. As another poster commented, sleeping on your left can help with acid reflux. Additionally though:",
"Pregnant women are advised to sleep on their left side to prevent supine hypotensive syndrome. ",
"Obstructive sleep apnea can be exacerbated by sleeping on one's back.",
"Those with congestive heart failure or other respiratory issues oftentimes need to sleep with their head elevated."
] |
[
"Sleeping on your left side has been shown to help with conditions like acid reflux. A couple of references ",
"here",
" and ",
"here",
"."
] |
[
"An elevated head position is typically of benefit for patients with OSA as well."
] |
[
"Why electrons in atoms are not emitting energy?"
] |
[
false
] |
They are charged particles, so if they are experiencing acceleration they should, and any way they are moving around the atom they will experience it, even if they're in their lowest energy states. I understand that in quantum physics, due to Schroedinger equation, electrons' locations are static fields of probability around the nucleus and so are their charges, but that seems to only take into account their wave properies, completely neglecting the fact that they are also particles. So shouldn't there be some some explanation in the classical sense also?
|
[
"electrons should be able to have lower energies than the minimum",
"Then it wouldn't be the actual 'minimum', would it? But semantics aside, it's ",
" impossible for an electron to have a lower energy than its ground state, the Variational Theorem. ",
"the lowest state [..] is just minimal amount of energy that keeps the electron stable in the potential field of the nucleus increased by amount required by Heisenbergs uncertainty principal",
"I don't know where you got this from. The uncertainty principle doesn't really work by dictating that something must have a minimal amount of energy. What it and the Schrödinger equation say is that you will have a higher kinetic energy if a particle is more localized around some spot in space (more 'particle-like' if you want), and lower kinetic energy if it's more spread out (more 'wave like')",
"But with the attraction from the nucleus, spreading the electron out more (and thus farther away from the nucleus), will increase its potential energy. But minimizing the potential energy by having the electron concentrated to a small region near the nucleus results in a higher kinetic energy. ",
"The ground state is the one that minimizes the total energy. This is provable because the possible energy states form a complete set of orthnormal functions. Meaning that any electron-distribution you care to think of can be expressed as a superposition of these states. But a superposition of the ground state and higher energy states results in an energy that is always higher or equal to than the ground state energy, and equal if and only if the electron distribution is equal to that of the ground state.",
"'Zero' would be higher energy. The way it's normally defined, an electron has zero energy when stationary at an infinite separation from the nucleus. Bound states have negative energies.",
"There does not exist any classical theory that can explain how electrons behave in atoms. Such a theory cannot exist because then there is no uncertainty principle, and no reason why electrons should not minimize their potential energy by being at the nucleus, and their kinetic energy by being stationary. Which obviously does not happen. Quantum mechanics dictates that that scenario ",
" happen."
] |
[
"..., so if they are experiencing acceleration ...",
"Yes, ",
". They are not. That's the reason they do not radiate.",
"More broadly, classical radiation such as the kind generate by an accelerating charge is proportional to the square of the acceleration. The expectation value of the electron's position is constant (this is a feature of all energy eigenstates, and the reason they are also called ",
"). Related to this is the fact that an atom in its ground state has no classical dipole moment, and no way to generate one in a transition to a lower state of energy (because no lower state exists). ",
"It seems odd, since there is generally a nonzero probability to find the electron throughout the atom. But no classical acceleration is at work, i.e., the second derivative of the expectation value of position is zero.",
"You might wonder what's different about an atom in (say, just for concreteness) its ",
". You know that decays, and emits radiation. What is different about it? The answer is subtle (and beautiful): the atom in its excited state is ",
" in an eigenstate of the coulomb Hamiltonian (from the nucleus). It's in an eigenstate of the ",
" Hamiltonian of the system. The total Hamiltonian includes the electromagnetic field. The true energy eigenstates are ",
" of atomic states. That excited state I mentioned is really a super position of (mostly) the excited state plus a little bit of the ground state. This superposition state does possess a dipole moment, and hence radiates when the atom falls down to the ground state.",
"Your question is what kept the pressure on to find a better atomic theory than the Bohr model.",
"Edit: it's-its stuff"
] |
[
"I agree that it's unintuitive, because of what we know about classical systems. If a classical particle (say a little ball) had the same probability distribution, we would interpret that to mean that the ball was moving around the center of force, experiencing acceleration, and spending equal time in every little chunk of space surrounding the center. ",
"That is what early physicists thought too. But that model doesn't fit experimental data (the lack of radiation in the ground state being one such fact). When a model is invalidated by experiment, it must be thrown out.",
"The simplest model that does fit the data, is quantum mechanics. If you evaluate the expression for classical position (basically take the QM 'weighted average' of the position operator) you get the position of the center of force, and it has no time dependence.",
"Somehow, there is a probability for the electron to be found (almost) anywhere around the nucleus, and yet it is ",
".",
"For me personally, this just underscores how different physical reality is on the atomic scale. I constantly remind myself that I cannot apply classical imagery when I think about atoms and particles."
] |
[
"Does every chemical reaction emit a sound?"
] |
[
false
] |
There are several reactions/experiments known for making certain sounds, but are other (or just specific) reactions actually silent or does every chemical reaction emit a measurable sound?
|
[
"Sound is basically vibration. Vibrations that result from some source of displacement. In an abstract sense, even molecular movements like an enzyme changing its conformation create 'sound' in that when the energy resulting in the physical change is released and some of it is displaced outwardly to the environment in the form of mechanical/kinetic 'sound' waves."
] |
[
"Im guessing you're referring to things like the barking dog experiment. ",
"In general reactions, unless they're very exothermic and fast (ie explosions and combustion), tend to be pretty dull. In order to make a sound you need to move a lot of air, and this is generally accomplished by by rapidly heating it. Some very large scale examples of this are things like the recent Tianjin disaster or the PEPCON explosion. These are examples of many ton scale chemical reactions gone very very wrong.",
"In chemistry labs reactions tend to occur on the order of minutes to hours, so even if they are exothermic they amount of energy released is spread out over a long time.",
"In biological systems on the other hand you may have thousands and thousands of reactions going at any given moment but they're all on very small scale so once again the amount of energy released isn't enough to cause any sound."
] |
[
"No chemical reactions emit any particular sound in-themselves."
] |
[
"How valid is the framework behind the Drake Equation?"
] |
[
false
] | null |
[
"It's really not very subtle or arcane; it's just how fractions are multiplied."
] |
[
"Right, but then are the variables chosen accurate in providing the probablity of life out there?"
] |
[
"Yes, unless life can form independently of planets."
] |
[
"how is Thiomersal degraded? also, what is the mechanism of mercury toxicity?"
] |
[
false
] |
after some arguing with my father (a psychiatrist) about the possibility of vaccines that can potentially contribute to mental diseases like autism (he thinks they contribute, i don't), he pointed me in the direction of Thiomersal, a preservative in vaccines, which is apparently based on mercury. my question is this: how is this compound metabolized, if at all? my second question is this: how exactly does mercury cause toxicity? i have an extensive biology background, so get technical!
|
[
"Thiomersal is metabolised into ethylmercury which is excreted about ",
"six times faster",
" than ",
"mercury which is found in fish. If you were to look at say, the 2009 pandemic flu vaccine that contained 25 ug of mercury which would cause less exposure than eating a can of tuna. ",
" ",
" ",
"in the US",
" or most of the world since the FDA (I think) took it out as a precaution when given toxicity data that was based on methylmercury (which is more toxic). Also thiomersal was ",
" used in the MMR which was involved in the ",
"fake",
" autism scare.",
"All mercury is ",
"toxic",
" in the same way, the issue is how it gets into the system and how long it stays there. For instance elemental mercury is less toxic than organic mercury, ethylmercury is less toxic than methylmercury which is less toxic than dimethylmercury.",
"There is loads of epidemiological data to support that vaccines ",
" contribute to autism and autism rates should have gone down when they took thiomersal out of childhood vaccines."
] |
[
"Wasn't Thimerosal cut from the ",
"grand majority",
" of vaccines? There are very trace amounts, at best. It's more dangerous to eat a can of tuna because it contains more mercury ",
" you might slice yourself on the lid. "
] |
[
"Mercury is toxic because it binds very strongly to the thiol groups in the active sites of enzymes which not surprisingly throws a wrench into the works if there's enough Mercury around. In the human body it is metabolized to the EthylMercury cation. Thiomersal is a Mercury based preservative that is used in some but not all vaccines. There is absolutely no evidence that the level of Mercury present in any vaccine is capable of causing harm. Furthermore, Thiomersal was removed from vaccines meant for children long ago so even if Thiomersal could cause autism (which there is no evidence of) it can't because it isn't being used in childhood vaccines anyway,"
] |
[
"Why do mushrooms grow in a circle?"
] |
[
false
] |
I have noticed several circles of mushrooms in my field. What causes it?
|
[
"\"Subsequent generations of fungi grow only outwards, because the parent generations have depleted their local nitrogen levels.\"",
"From ",
"Wikipedia",
"."
] |
[
"Potentially something to do with the pattern of spore dispersal? Combined with other factors such as localised nitrogen and other nutrient depletion it might lead to that pattern. "
] |
[
"These are called fairy rings. The mushrooms you see are all most likely part of the same fungal thallus (body) that started from a single spore in the middle. Each year the ",
"mycelium",
", composed of threadlike ",
"hyphae",
" expand outwards.. When the fungus sends up ",
"fruiting bodies",
" they are all roughly the same distance from where the colony began from that single spore."
] |
[
"If conciousness is not a continued stream, why do I always feel like I am waking up in the same body everyday?"
] |
[
false
] | null |
[
"I don't understand what the potentially discrete nature of consciousness has to do with other bodies..."
] |
[
"Ill expand. In the transhuman subreddit I read people claiming that if an exact copy of your brain was uploaded, your copy would still be \"you\". They claimed that becuase there is no soul, and the concious mind is just a product of the physical brain (things I believe to be true) that your copy would also have your consiousness. ",
"I just don't see how I could feel like I am in two places at once. They insisted that I just didn't understand that I am a product of my brain, and like a mathamatical equation, if I am copied my conciousness will carry over. Again, I dont see how its possible to carry on with two simultaneous points of view though.",
"Then I started reading some buddhist philosophy that said all conciousness is the same being, which I also dont' agree with becuase if someone in china breaks their leg, I dont feel their pain. "
] |
[
"Yeah we don't have any empirical evidence for any of the buddhist stuff. As for uploading or copying consciousness, we don't have any way of doing that so we don't know what will happen. Most neuroscientists are physical realists though meaning that they believe that consciousness is the result of physical processes in the brain. "
] |
[
"\"Back in the 80s, all those scientists told us we were about to enter another ice age. now they say the earth is heating up instead. they don't know what they're talking about, so I don't believe any of this global warming business.\""
] |
[
false
] |
A family member recently told me he refused to believe in global warming because when he was a kid, he was taught that scientists believed the earth was in the middle of entering another ice age. I was completely thrown off, and had no good response. Reddit, can you help fill me in on what in the world he's talking about? He can be a very reasonable guy, but is stuck in this mindset based off something he heard decades ago. I'd love some help clearing up the facts so he can get on board with modern science.
|
[
"This tracks back to a myth that there was broad scientific belief in the 1970s that the earth was due to enter another ice age. It stemmed from a few studies about the specific timing of ice age cycles. The findings got picked up by the popular press and published in ",
"Newsweek and National Geographic",
". I doubt (m)any kids were actually taught this because it was not the type of thing that would have been in any textbooks. Compared to the 1970s, the whole idea gets lots more press today thanks to George Will and Rush Limbaugh. There are probably lots of ditto-heads who will swear it's what they were taught in grade school.",
"The attention given to global cooling in the 1970s arose from scientific discoveries at the time. Prior to the 1970s, scientists knew that there had been past glacial cycles but the exact timing of the glaciations was not well known. In the 1960s and 70s, technology and resources enabled drilling long ice cores on Greenland and Antarctica. Analysis of isotopes in the ice showed a clear record of the Milankovitch time scales in the past glaciation/interglaciation. Also, what the ice cores revealed was that, in the absence of other effects, the earth was due to enter an ice age in the next few hundred years. A few scientists pointed this out and then the press jumped on it. It is true that in the absence of industrialization, we would be heading back into an ice age in the next centuries, but that natural glacial/interglacial variation is going to be swamped by anthropogenic changes to the earth's radiation balance. ",
"edit: grammar/spelling"
] |
[
"That's fairly impressive. The idea that humans would be capable of completely up-ending something as big as the planet's ice age cycles/radiation balance (I like the second term better, thanks). ",
"I'm planning on sitting down with him soon and walking through what scientists know today. I plan to start with ",
"Nasa's big article on it",
". Are there any other really great articles I should be aware of as well?"
] |
[
"This whole site is good: ",
"http://www.skepticalscience.com/ice-age-predictions-in-1970s.htm"
] |
[
"What's the difference between a hydrogen ion and a regular proton?"
] |
[
false
] | null |
[
"A ",
"H",
" ion is the same thing as a proton."
] |
[
"While H+ technically means a proton, in chemistry, a proton generally cannot exist as a 'free' proton due to high charge density. Hence, it tends to bond with solvents which most commonly is water to form H3O+ which chemists just shorthand write as H+."
] |
[
"I remember being confused about various things ”exchanging protons” in highschool chemistry. It sounded like nuclear reactions which I knew didn’t happen in chemistry. Took me a while to realize they were talking about H",
" ions!"
] |
[
"If the fastest that neurons can oscillate at is a few hundred Hz, then how can we hear and process sound frequencies up to ~20,000Hz?"
] |
[
false
] | null |
[
"Frequency is translated not by how fast a neuron fires, but by which neuron fires.",
"Within the ear, the cells that detect sound waves are called hair cells; different hair cells get triggered by different frequencies of sound."
] |
[
"To expand a little, the cochlea is sort of snail shell shaped, and if you were to unroll it, you can see that it starts out pretty wide and gets narrower. This makes it so that different parts of it resonate at different acoustic frequencies. There is an animation somewhere that plays a melody, and you can watch the different parts of an unrolled cochlea vibrate in response to the different pitches."
] |
[
"That's like asking \"how can we see so many colors if all neurons are gray?\"",
"The properties of neurons are not relevant here, because information is encoded. The cochlea contains hair cells of different lengths. Long hairs detect low frequencies, short hairs detect high frequencies. These cells then transmit information (using glutamate) to post-synaptic neurons. The signal is transmitted to the temporal lobe, where there's a ",
"tonotopic map",
" (literally a physical map of sounds imprinted on the brain).",
"The signal transmission will produce oscillations (brain waves), but these oscillations do not transmit information themselves. Their function is unknown. In fact, they may be epiphenomena without any function."
] |
[
"Do you think there are any concepts in math (& science) that can not possibly be represented visually?"
] |
[
false
] | null |
[
"As far as physics goes, basically all of them. The language of physics is maths, not pictures. To the extent we use pictures at all — Feynman diagrams are what I'm talking about here — they are purely a tool used to facilitate the writing of equations."
] |
[
"What precisely do you mean by \"represented visually\"? Visual representations understandable without context are inherently Euclidean in less than 3 dimensions; anything which is not this (and the ",
" majority of math and science is not) cannot be fully represented visually. I don't think that's what you're asking though?"
] |
[
"I think he's talking about stuff like hypercubes. Things which are very difficult to illustrate, even in a layman-like way."
] |
[
"Is our moon relatively large, average or small, given the size of our planet, and the sizes of moons we've been able to observe orbiting other planets?"
] |
[
false
] |
I've always wondered this, and watching a couple of shows recently on the formation and theoretical origins, it just stands out to me that our moon is fairly large in comparison to Earth. Is this the case?
|
[
"Our moon is rather large on the scale of moons we have knowledge about. ",
"Actually our moon is the 5th biggest moon in the solar system. ",
"http://en.wikipedia.org/wiki/Moon",
"Edit: missed the \"5th\""
] |
[
"This is not correct. Our Moon is substantially less large than ",
"other moons in the solar system",
". However, it is the biggest ",
" to the size of the planet about which it orbits."
] |
[
"oops, i missed the 5th in my sentence.. that changes things quite a bit. Thanks for the heads up. "
] |
[
"Why do astrophysicists think that black holes have singularities? Wouldn't it be more likely that there's just a volume of ultra-dense matter?"
] |
[
false
] | null |
[
"GR predicts singularities. That being said, most physicists would agree that GR is a classical theory which is expected to break down at small scales. So many, if not most, physicists probably don't believe that singularities really exist."
] |
[
"Neat, is there any difference from an outsider’s perspective whether or not there’s an actual singularity or not? Does it change anything about what we know about black holes?"
] |
[
"Physical singularities (as opposed to coordinate singularities) are present in any set of coordinates. So all observers agree that there's a singularity there, according to GR."
] |
[
"What causes the discomfort of not breathing? Lack of oxygen or lack of air?"
] |
[
false
] |
If our bodies was constantly given fresh blood filled with oxygen, would we still experience the discomfort of holding our breath? Is the uncomfortableness directly linked to oxygen content in the body or is it a defense mechanism created by our bodies to prevent not breathing?
|
[
"When you hold your breath CO2 will start to accumulate in your blood. The CO2 will react with water creating HCO3- en H+. This will lower the pH of your blood. There are several receptors in your system (Chemoreceptors) who will detect the lower pH, this will make them overwrite the impulses given by you to stop breathing en make you breath again (so it is impossible to kill yourself by simply stop breathing, a reflex will prevent this). The accumulated CO2 however needs to be dispended. This is an important function of the lungs, since you would bypass the longs, the accumulated CO2 would not the be able to leave the body fast enough and cause the receptors to react to the lowering pH and cause a discomfort of not breathing. If you would use a system to also dispense the CO2 without usage of the lungs it would not cause a discomfort. This can be done by a cardiopulmonary bypass (",
"http://en.wikipedia.org/wiki/Cardiopulmonary_bypass",
"). "
] |
[
"CO",
" + H",
"O ⇌ H",
"CO",
" ⇌ HCO",
" + H",
"The pKa of the carbonic acid (H",
"CO",
") formed from the aqueous CO",
" is such that at physiological pH, it acts as an acid. It donates a H",
" to solution (lower pH) and the bicarbonate is merely the resulting conjugate base."
] |
[
"It's important to know that breathing is largely regulated by CO2, not oxygen. For example, you can trick your body into thinking that you don't have to breathe by hyperventilating (breathing in and out very rapidly) and getting rid of a lot of CO2. You can do this if you're snorkeling, but you then run the risk of not coming up at an appropriate time and passing out from a lack of oxygen before you make enough CO2 for your brain to notice.",
"Here's a ",
"Wiki link",
" if you want."
] |
[
"Is everything always in equilibrium?"
] |
[
false
] |
[deleted]
|
[
"This is one of those times where the answer is a simple \"no.\""
] |
[
"If everything was in equilibrium nothing would happen. The second law of thermodynamics implies this will eventually occur - ",
"http://en.wikipedia.org/wiki/Heat_death_of_the_universe"
] |
[
"This question could mean a number of different things. From a chemical perspective, no. Given enough time, things try to reach equilibrium, but they are not always in equilibrium. Think of putting ice in a cup in the summer. Equilibrium is reached when the ice has melted and is at the same temperature as the environment. But first it has to go through the process of melting. "
] |
[
"Can someone explain linkage disequilibrium to me?"
] |
[
false
] |
I am in grad school for bio-engineering. It's a long story, but out of curiosity I decided to take this obscenely intense genetics class. I'm trying to wrap my head around linkage disequilibrium, but can't really grasp the concept.
|
[
"It's basically a measurement of the extent to which alleles at different loci associate with each other. If the two alleles do not associate in any way, the frequency of all the possible haplotypes should be based solely on the frequency of each allele (this is the expected distribution). If they do associate, however, (i.e. having one allele makes having another more likely), then there will be a deviation from the expected distribution, and this deviation is the linkage disequilibrium."
] |
[
"In my opinion linkage disequilibrium is just another in a long line of awfully named biological phenomena.",
"First, linkage is a term that describes the physical connection of two genes on a chromosome. Because chromosomes segregate independently during meiosis, genes located on different chromosomes will be ",
". For instance, if genes A and B are on different chromosomes and the genotype of the individual is AaBb, then the possibility of forming any of the four possible gametes is the same. However, if A and B are located on the same chromosome and one copy of the chromosome contains A and b and the other contains a and B, then the only two possible gametes ",
" be Ab and aB. This is because the chromosome would segregate as a whole and the alleles that are encoded together on the same physical chromosome should segregate together. However, because of recombination (DNA swapping) between homologous chromosomes, genes can be swapped back and forth with some frequency. So even though a and B are linked together normally, some amount of chromosomes will contain AB and ab if there was swapping in between the two genes.",
"If you assume two genes are linked when you do a cross, you can calculated expected frequencies of offspring genotype. Linkage disequilibrium is a term that describes how different the observed vs. expected genotype ratios are under this assumption. Usually, the physical distance intervening two genes is related to the magnitude of the linkage disequilibrium.",
"Make sense? What school you at?"
] |
[
"Thanks for your help! I'm just trying to calculate LOD values for haplotypes, it's just sort of confusing despite hours of googling and reading journals.",
"I'm at univ of utah. Everyone said it was a mistake to take courses outside of engineering for a grade. Im now panicking in this Molecular Biology class where everyone has had years of biochem. I have learned my lesson..."
] |
[
"Where does the energy from sound go?"
] |
[
false
] |
I know it's a fairly simple question, but what is the final resting place of sound?
|
[
"The same as all other energy- heat. Heat is basically the final version of all forms of energy. "
] |
[
"What is sound? It's a wave travelling through a medium (typucally, through air). As it travels, depending on the period and amlitude of the oscillations, we perceive different sounds. ",
"During the compressions, atoms are hitting each other more frequently than normal, so eventually all the extra translational energy will turn into internal energy (aka, heat) of the air. ",
"TL;DR Heat. "
] |
[
"so if a sound is loud enough will you actually feel a temperature change? If so, how loud of a sound would be needed?"
] |
[
"Could the Kessler Effect be observable from earth?"
] |
[
false
] |
What might it look like? Would it require a telescope?
|
[
"It would not be observable to the naked eye.",
"Some satellites are visible to the naked eye as dots though most are very dim. The ISS may appear as a very bright and very fast moving dot, there are websites like ",
"heavens-above.com",
" that can predict when it will be visible in your area.",
"But if you're asking about Kessler effect we're talking about ",
" resulting from impacts. (Okay, there isn't a precise definition of the term, but it usually refers to Kessler's 1978 paper predicting that each collision will produce hundreds of fragments, leading to further collisions, leading to an exponential growth of the debris population.) Most fragments will be just a few cm across, definitely not visible to the naked eye.",
"Telescopes can see them, as well as radars and laser ranging stations. There are Space Surveillance and Tracking (SST) systems designed to monitor the situation, one of them is ",
"EUSST",
". The main purpose of this is to predict collisions, eventually performing avoidance manœuvres; and to predict uncontrolled atmospheric entry of large objects whose pieces could survive the \"burn-up\" effect and pose danger on the ground.",
"Also, note that SST systems can only see the larger fragments. Smaller ones may be ",
" visible to the sensor network but most of them will have too few observations to be identified or have their orbits determined. EUSST aims at cataloging 20% of objects 7cm across or larger in Low Earth Orbit. AFAIR other systems plan to get down to 1cm but I'm not expecting this to be a large percentage of them.",
"Smaller fragments are definitely not visible and still pose danger to spacecraft. For this reason ",
"MMOD shields",
" are still needed. The scary part of the story is intermediate sizes, too small to track and avoid but too large to resist with shields."
] |
[
"Could it lead to something like a never ending slow meteor shower as pieces re-enter?"
] |
[
"Worth noting that the worst debris situation right now is at altitudes between 600km and 1000km. It might take decades or probably even a century before the lower fragments' orbits decay low enough to reenter the atmosphere. There will be lots of further collisions in the meantime.",
"It's really hard to predict how much their number will have grown by then, how small the remaining fragments will be, or how frequently they will reenter (especially considering that those at 600km decay exponentially faster than the higher ones). We can only be sure that the smaller fragments will reenter first due to the square-cube law, and these are the less likely ones to produce a visible burn-up."
] |
[
"For any set of points on a graph, is there a polynomial that passes through each point?"
] |
[
false
] |
I was thinking about Brithey Spears rock solid hit "Hit Me Baby (One More Time)", and if it could be described with a mathematical polynomial. It is 210 seconds long. In 16-bit, 44,1KHz audio that means 9261000 points, one at each step of the x-axis, where y would be a vaule from -2 /2 to 2 /2. Is there hypothetically a polynomial that passes through each of these points? Can we estimate how many parameters it would have?
|
[
"For every finite set: Yes. In general you need a degree one less than the number of points N - sometimes you can get away with lower degrees of course. A polynomial of degree N-1 has N free parameters, you get a system of N equations for all N points, which leads to a unique solution as long as the x-values of all N points are all different. If you go to higher orders the solution is not unique any more.",
"These polynomials go through the given points by construction, but they tend to blow up immediately outside the \"fitted\" range, often with some oscillations starting towards the end already. They are a mathematical solution that is rarely useful in practice."
] |
[
"Yes, these are the Lagrange polynomials. You can always fit a polynomial to any finite set of points.",
"https://en.wikipedia.org/wiki/Lagrange_polynomial"
] |
[
"One interesting use of this is for ",
"-of-",
" secret sharing schemes. Let's say you want to distribute your secret will, backup password, or something to friends in case you die / are captured by the mob / whatever. Or the nuclear launch codes can only be accessed by a quorum of leaders, etc. You can set up a system so that you give out pieces to 10 friends, any 7 of which can reconstruct your password. Your password is the value of a 6th-order polynomial at X=0, and you give out the value of the polynomial at a variety of other X-values. Any 7 people can get together and find the polynomial based on their data points, then evaluate it at X=0 and get the password. But if you only have 6 data points, you have zero information about the password, it could be anything.",
"(Of course in practice you use polynomials over finite fields instead of real numbers; it makes the math a lot more tractable. The classic XOR-based one-time-pad is mathematically equivalent to a 2-of-",
" polynomial sharing scheme.) This technique was published by Adi Shamir, the S in \"RSA\", back in 1979."
] |
[
"[OPTIC] Why does every measurement of a system that contains coupling/transmission is approximated through a lorentzian function?"
] |
[
false
] |
I often read that something in the field of optic gets measured and then gets least-square fitted by a lorentzian functionl. I think it was always with coupling/transmission etc. hence the question, since I didn't find any source and everything that I found just stated that they did it.
|
[
"The reason Lorentzians pop up quite a bit in optics is that they describe the behavior of what is called a Lorentz oscillator. The basic idea is that to a first approximation you can treat an electron-bound to a nucleus as a simple vibrating spring. When if you stretch (or squeeze) the spring, there is a force that tries to restore it that goes as F = -k(x-x0), where x0 is the equilibrium position and k is the spring constant. At this point we have a simple harmonic oscillator. But to get the full Lorentz picture we need to go to a driven damped harmonic oscillator. For that we need two additional pieces: ",
"Next you drive this oscillator by applying an electric field. To make things especially easy, let's say that the field is a simple periodic function like: E=cos(wt).",
"By driving the oscillator with this field you are putting energy into it. However, let's say that the oscillator can also get rid of some of this energy in some fashion (e.g. by radiating it away). That is the damping that goes into the equation.",
"When you put everything back together, you get the following equation for the motion of the oscillator:",
"m*d",
"x/dt",
" = F",
" + F",
" + F",
"When you solve this equation, you will get a real (e') and an imaginary part (e''), which when plotted will ",
"look like this",
". It turns out that e'' is described by a Lorentzian function, centered around a frequency wo (the resonant frequency) and having a width determined by the damping. Because e'' is the imaginary part of the refractive index, it also determines the absorption lineshape you observe for a a simple resonance. For this reason, Lorentzian pop up all over the place where a system is well describe by this bare boens model."
] |
[
"It is generally true for any driven, damped, harmonic oscillator, as these are what is described by the model (equation) above. (E.g. not necessarily optical.) See the Wikipedia page on Harmonic_oscillator.",
"Note that small oscillations can almost always be approximated by a harmonic oscillation; note that almost any oscillator is damped, especially as the amplitude of the motion increases a lot, which happens when any oscillator is driven with a (near-)resonant frequency. (Otherwise, the amplitude would go to infinity, since its energy increases by the driving force, but no energy is lost without damping.)",
"To answer your first question: the transmission of a waveguide is wavelength dependent. It accepts light at a resonant frequency, but rejects light at different frequencies. In other words: a driving force (incoming light) drives the modes of the system (I.e. increasing the amplitude [\"amount\"] of the light inside) while some light leaks out (I.e. decreasing the amplitude, or damping). Et voilà: a driven, damped, harmonic oscillator."
] |
[
"But why can we describe a system containing of two waveguides and a ring resonator like that?",
"Is it generelly true for absorption around a resonance?",
"Is there a simple System that doesn't follow this model?"
] |
[
"Refrigerator with a vacuum or inert gas?"
] |
[
false
] |
I was reading recently that the reason we need to keep foods covered in the fridge is that the flow of oxygen promotes the growth of harmful bacteria. Was just wondering if it might be feasible to have a fridge that maintained an interior vacuum or else an atmosphere with an inert gas? Anyone have any thoughts on advantages/disadvantages/implementation issues?
|
[
"In a vacuum, liquid water simultaneously boils and freezes solid. This could potentially cause some foods to explode. ",
"In areas that were exposed to enough radiant heat or light (assuming the wall of the vacuum container were above 0 degrees C.), the remaining frozen water would slowly sublimate, converting directly from a solid into a gas like dry ice does. ",
"Over time foods would become completely dessicated. In other words, freeze dried. Such foods would last decades. ",
"Note: However certain vitamins break down over time, particularly vitamin C and folic acid. The absence of oxygen delays, but cannot prevent this. If you're relying on dried or otherwise preserved foods for more than 6-9 months, scurvy becomes an issue.",
"Purging with an inert gas like nitrogen or argon prevents some harmful bacteria, but encourages the growth of others. Most notably ",
" which is the third most common cause of food poisoning. A lack of oxygen is actually necessary for it's growth. Other bacteria that commonly cause food poisoning are slowed down but not in any way stopped by low-oxygen conditions. For example ",
" and ",
" species, or certain strains of "
] |
[
"On the plus side, it would be a fully functional freeze drier. They use lowered pressure to speed up sublimation, but freeze it first so nothing explodes or boils."
] |
[
"Good answer! Thanks for satisfying my random curiosity :)"
] |
[
"What causes dark circles under eyes?"
] |
[
false
] |
I’ve always been really curious what the actual physiology of dark circles is but every way I’ve ever tried to look it up just tells me that dark circles are caused by lack of sleep.
|
[
"Cortisol. When you become excessively tired your body releases cortisol to try to amplify sugar in the blood. Two side effects happen, blood volume increases and some vessels dilate (others constrict). The vessels under the eyes engorge which results in the bluish tint increasing (like when you see veins under the skin) and the areas adjacent to the eyes swell causing “bags above and under the eyes” which make shadows. The end result is the tissue appears darker."
] |
[
"The skin near you eyes is very thin, therefore the capillaries are prone to mistreatment. Therefore the skin under your eyes is easily susceptible to being bruised and overused creating the dark circles that indicate lack of sleep. Your eyebrows however are very tough which prevents the darkness from traveling upwards in bruise-form."
] |
[
"Depends on the conditions and how tired someone is, when they ate last....that kind of stuff. Cortisol and ACTH have weird effects on skin pigment because they can also control melanin production. So patients with Addisons can end up with hyperpigmentation. The eye thing is always more pronounced when tired because the skin there is so thin."
] |
[
"I want to make a cryostat less sensible to vibrations with attaching it to rubber bands. How do I find the optimal spring constant for damping these vibrations?"
] |
[
false
] | null |
[
"\"I will also add a damping pad\"",
"You may need to take account of this in your calculations. This is effectively another spring underneath your mass."
] |
[
"I thought of that to.\nTo be honest, I've worked in this lab for just one week and I've never had any other experiences. So this is all very new to me. I was said to find rubber bands which optimize the damping. That's all."
] |
[
"I may be missing something here but I think elastic bands are the wrong approach (and in my tired half asleep state) it seems like they couldn't really work as they would act as harmonic oscillators and only reduce oscillation a tiny amount.",
"There's ",
"some more info on damping here",
". I suggest you ",
"buy a vibration damper",
" (using the relevant equations I linked to, to find the correct type)."
] |
[
"Why can or can't I move differentials around an equation?"
] |
[
false
] |
I am currently working towards a bachelor's in mechanical engineering and I was wondering about calculus differentials. Quite often in class, we move them around freely and a professor will say something along the lines of "If you are a mathematics major, this probably makes you cringe. Technically you can't move differentials around but we can in this field." (physics or engineering) So basically my question is why is it that you cannot technically move them around, yet I do it all the time when solving problems?
|
[
"You ",
" move them around because the objects you are working with, dx's and df's and such, are vectors not numbers (technically, families of vectors). You can add vectors together and you can multiply them by scalars, but you can't divide them or multiply two of them together. In multiple integration dxdy does not stand for dx times dy, it stands for the ",
"outer product",
" of dx and dy, which is not multiplication but a process a little too abstract for a calc 3 class.",
"It seems like you ",
" divide and cancel them out due to the Chain Rule. Technically, df/dx is ",
" df divided by dx, but just the derivative of f(x) with respect to x. But we write it this way because the Chain Rule suggestive this way, and easier to use. In particular, the vector df is equal to the scalar multiplication f'(x)dx, or (df/dx)dx, due to the Chain Rule. Additionally, composition looks like a cancelling out of these things: (df/dx)(dx/dy) = df/dy. You're not ",
" cancelling anything out, you're just invoking the Chain Rule, which is just written suggestively with this notation.",
"This is also why you can't do all this hand-wavy stuff with partial differentials, because the Chain Rule is more complicated there so this kind of arithmetic isn't going to work."
] |
[
"You totally can. Well you can't because you haven't justified it, but it can be justified fully. A common way that it is formalized is used by people who study geometry, or differential equations, through something called a 'differential form', which requires concepts from vector calculus. There is a quick and dirty approach for ODE though (that again is completely justified).",
"Suppose you have a seperable differential equation",
"dy/dx = f(x) / g(y)",
"Then dy/dx g(y) = f(x)",
"We can then integrate both sides with respect to dx",
"int dy/dx g(y) dx = int f(x) dx + C",
"We'd like to rewrite the left hand side as int g(y) dy, and we can do that using the fundamental theorem of calculus (given that g(y) and y(x) satisfy the appropriate assumption), and in fact we don't need to do that much work really. We've already seen this in Calculus 1 (or 2 depending on your university), this is done exactly through integration by substitution!"
] |
[
"Thought they would mention them in the article, but the ideas are similar enough for these purposes, I'll edit the post."
] |
[
"How Exactly Does Prion Disease Kill?"
] |
[
false
] |
My friends and I were talking about cannibalism the other day and Kuru came up. I've looked around and haven't found anything that plainly states how exactly the disease kills. Same with Mad Cow. I know prion disease is the prion converting normal proteins into prions but why exactly is that lethal? What does that do?
|
[
"For kuru, and Creuztfeldt-Jakob disease, the reshaped prion proteins form aggregates in the nervous system. Disrupting whatever native function it had (that we still are not certain of). And damaging the cells, resulting in the spongiform pathology that is characteristic of it."
] |
[
"Prions are misfolded proteins. All cases that I know of in mammals are neurological. Prions are also infectious. \nThe problem arises when they transmit their misfolded shape to other normal functioning proteins (their mechanism isn’t for sure, but I’m sure you can find mechanism theories on Wikipedia). These misfolded proteins eventually aggregate and form amyloids. These amyloids inhibit proper protein functioning. And when the proteins (that are replicating over and over) in your brain stop working, you die. Hope that helps !"
] |
[
"Prion disease has somewhat of a domino effect.",
"\nOnce prions are introduced into the system, they can trigger misfolding in similar proteins. This will cause a buildup of plaques and leave the person with proteins that aren’t able to carry out their intended role which is never a good thing. ",
"We still don’t know a lot about prion diseases and how exactly they work though so information is limited. ",
"We do know that a membrane associated protein PrP",
" (it’s exact function is unknown, as far as I know) is transformed into PrP",
" this isoform is what will cause transmissible spongiform encephalopathy. \nThis is essentially the development of holes and shrinkage in the brain that will lead to death."
] |
[
"How does taking creatine improve your cognitive performance?"
] |
[
false
] | null |
[
"Read here",
", scroll down to the neurology section. With a normal diet and without any pathological condition, your body gets/generates enough creatine for brain use and a dietary surplus is not taken up into the brain. As to how it works, I think the relevant section is:",
"Creatine, through its ability to act as an energy reserve, attenuates neuron death induced by the MPTP toxin that can produce Parkinson's Disease-like effects in research animals,[273] reduces glutamate-induced excitotoxicity,[274] and preserves growth rate of neurons during exposure to corticosteroids (like cortisol) which can reduce neuron growth rates.[275] Creatine appears to exert these protective effects by acting as an energy resevoir, and prolonging the time it takes to deplete levels of ATP in the cell (which precede neuronal death).[273][274]"
] |
[
"It is made from amino acids, it's primarily used for energy, particularly for muscle energy, I'm not 100% sure it helps overly much for the brain, but I guess if it did it would be due to the extra energy to keep concentration."
] |
[
"it doesnt."
] |
[
"Does Jupiter have a solid core of anything or is it truly just a large ball of gas?"
] |
[
false
] | null |
[
"So first off...",
"is it truly just a large ball of gas?",
"We know for sure that this is not true. At the pressures and temperature in the interior of Jupiter, hydrogen turns into a liquid metal. In fact, by mass, Jupiter is ",
" liquid metallic hydrogen. It's also the only thing that can explain Jupiter's incredibly strong magnetic field.",
"Now, to address your original question...",
"Does Jupiter have a solid core of anything",
"This is a major question in the field right now, and one of the primary mission goals of the Juno spacecraft. There's still a lot of questions whether the liquid metallic hydrogen forms a mantle surrounding a solid core. Based on what we think we know about how giant planets form, though, we're pretty sure there's needs to be a core...or at least there used to be one.",
"Jupiter formed out past the \"snow line\" - the distance from the Sun where it's cold enough that water is stable as ice. This is important, because if you're a growing proto-planet, you can grow a lot faster out past the snow line using both ice and rock, rather than the planets that formed inside the snow line which formed from just rock alone. You need to hit a mass of about 5 to 10 Earth-masses before you have sufficient gravity to start holding on to hydrogen gas.",
"Our current hypothesis is that Jupiter's core is somewhere around 10 - 30 Earth-masses (compared to a total mass of 318 Earth-masses), and it's made of rock and exotic ices. Note that even though the temperatures are very high at the center of Jupiter, the pressure is so extreme that water will be solid, forming unusual crystal arrangements of ice.",
"Now there is a vocal minority of scientists who believe that Jupiter has no core at all. Some think it's because it formed from gas collapse instead of the more commonly-accepted core accretion theory outlined above. In the gas collapse scenario, the collective self-gravity of an extra-dense clump of hydrogen gas in the protoplanetary disk collapsed in on itself to form the planet. However, most of our models indicate there just wasn't enough time for that collapse to happen before the Sun ignited and blew all the gas away.",
"A few others think Jupiter used to have a core, but no longer. Again, surrounding this hypothesized rocky icy core is a massive mantle of liquid metallic hydrogen. Thing is, most of our models indicate that liquid metallic hydrogen is a very good solvent (we've only been able to produce metallic hydrogen in the lab pretty recently and only for a split-second, so most of our assumptions about the stuff come from computer simulations). If it turns out to be a good enough solvent, then it could actually have dissolved a 20 Earth-mass rocky icy core over the lifetime of the Solar System.",
": Probably. It's definitely ",
" just a ball of gas, though, as it's mostly liquid metal."
] |
[
"It probably wouldn't be too useful of an experiment. Our current weapons would have to be dramatically redesigned to even hope to survive the pressure deep into Jupiter's atmosphere. One could always just drop a large, subcritcal sphere of fissionable material into the atmosphere that is designed to compress to a critical density at a certain level, but even then it would be unlikely to generate enough power to \"excavate\" a hole for us to investigate, and there would be little to no control over what that bomb would generate. Where a nuke might be useful is in generating a signal for seismic tomography, but even this depends on a planet wide network of detectors located deep enough that they're in a liquid...which would be hard for all sorts of reasons.",
"Besides, the \"experiment\" has already been done. The G-fragment of Shoemaker-Levy 9 generated something like a couple thousand gigatons when it impacted Jupiter. The resulting disturbance illuminated a wee bit about the atmosphere but it barely scratched the surface. Jupiter is just that huge.",
"Lastly, while ethics may not seem to be a huge issue when dealing with a horrifying orb of radiation and mystery like Jupiter, it bears reminding that horrible things have been done in the name of science. If it seems overly squeamish to consider the consequences of a seemingly harmless experiment, the same justification of \"harmlessness in light of the greater good\" has been used to green light incredible atrocities. Scientific ethics should always be considered, even when nuking Jupiter. "
] |
[
"Hi, forgive the ignorance but wouldn't it seem more likely that Jupiter had a solid core? With Jupiters strong gravity it would have caused many asteroids to fall in and slowly sink to the centre causing a build up. "
] |
[
"Will a person who moves to a place located on a higher altitude become taller?"
] |
[
false
] |
Astronauts living on ISS become taller from the low gravity. Is there a measureable difference in height for people moving from for example sea-level to 4000m above the ocean?
|
[
"You are confusing low gravity with microgravity. If you were at the same height as the ISS and not noving, you would experience gravity similarly as on earth and fall towards the earth just the same. The change would be negligable. The reason people grow taller in space is because the space station is orbiting fast\\sideways enough to miss the earth when falling down, which causes the feeling of weightlessness. At this point the spine and the cushioning between them effectively don't have gravity affecting them, which causes expansion of the spine. "
] |
[
"When in orbit, a person in a spacecraft experiences 'zero gravity' because their spacecraft accelerates exactly as much as they do. Therefore, they go from an apparent gravitational acceleration of 9.81 m/s",
" to 0 m/s",
"When moving up 4000m, a person still experiences significant gravity from earth. Assuming g=9.81 m/s",
" and a spherical earth, gravity at 4000m above the surface is 9.7977 m/s",
" - so 99.87% of surface gravity. The difference here is negligible.",
"I can't speak to the biological side of this specifically, but from a physics perspective, there should be no significant difference when moving from 0m above sea level to 4000m above sea level."
] |
[
"An astronaut can grow up to 3percent height in space - from a reduction of gravity from 9.81 to 0m/s. Factoring an effect of 0.13% of it, it would give you an effect of 0.0039%. Taking an average height to be - say 170cm, it would give you a result of 0.00663cm growth - a negligible difference. It would probably take you a near infinitely large sample size to be able to find the minuscule amount of increase, assuming the differences in people generally. It is not a meaningful experiment.",
"You would probably find the same difference if you measure 2 groups of random people in the exact same location."
] |
[
"What is faster the speed of light or the expansion of the universe, and why?"
] |
[
false
] | null |
[
"They are not directly comparable - the speed of light is a measurement with units of <distance per time>. The expansion of the universe is a measurement with units of <distance per time per distance>.",
"So comparing one to the other is sort of like comparing a car's speed to a car's acceleration. The value you measure for the expansion of the universe depends on the distance you are looking at. If you are looking at something one megaparsec away (about 31 quintillion kilometers), the expansion of the universe will be about 70 kilometers per second. Vastly less than the speed of light. If you look at something two megaparsecs away, the expansion will be about 140 kilometers per second. And so on. At large enough distances, that value will exceed the speed of light, so there are distant parts of the universe that we will never get to observe (assuming the expansion doesn't slow down)."
] |
[
"Speed of light is essentially the speed of massless particle. It just so happens that the most visible massless particles in the universe are photons. This is the reason why \"speed of light\" is a universal limit and you can't exceed it. It's the speed of massless matter moving through space. ",
"The expansion of the universe is a different metric and the measure of the change in different between gravitationally unbound objects. The actual space changes so it's not really \"speed\" but more like a change in the topography of the universe, for lack of a better term. ",
"To really know the answer, you need to know what causes the expansion of the universe since it's upper limits will most likely be determined by that and people are not quite sure what really cases the universe expansion."
] |
[
"Also to add, when imagining the expansion of the universe, don’t imagine an edge speeding outwards. It’s not expanding into anything. It’s space itself which is expanding. Imagine yourself on the surface of a balloon covered in dots. When the balloon expands, the space between the dots expands. \nThe speed of light is essentially the fastest speed at which information can travel. So galaxies that are far apart can be receding at faster than light speed, but no information is able to pass between them. The logical conclusion to this is that eventually, in the distant future, everything around us will be travelling so fast away from us that all we see is a dark sky. No trace of anything else. It would look like we were alone in a void."
] |
[
"How are tectonic fault lines locations deduced and to what accuracy are they known?"
] |
[
false
] |
I was looking at maps of the San Andreas fault line and I don't understand what the line on maps represent. Is it meant to estimate the tectonic plate boundaries and if so what does it mean, is the place where one plate submerges under the other? What's the process from earthquake data to creating this line?
|
[
"Faults",
", in the upper portions of the crust where rocks behave like brittle materials (i.e. where they break), are discrete planes representing a discontinuity across which displacement has occurred (i.e. rocks have moved past each other along the fault). In many cases, these can be incredibly clear as they have obviously ",
"disrupted and moved packages of rocks",
". The line on a map representing a fault is tracing out the intersection of the fault plane with the surface of the Earth. Faults are identified and mapped as part of making a ",
"geologic map",
", which is a special kind of map showing the type and age of rocks exposed at the surface of the Earth. Generally speaking, earthquakes are not useful in mapping out faults at the surface (we'll return to this later), instead careful observations in the field noting changes in the type and orientation of rocks tell a geologist that there is fault. Sometimes faults are exposed, i.e. ",
"as a clear planar discontinuity",
" that offsets rocks. Other times, they may only be located approximately because of incomplete exposure (e.g. imagine walking a long a path where rocks are intermittently exposed and you notice after walking through a vegetated area that the rocks have changed type and orientation, you may have crossed a fault and you can approximately locate the fault between the two outcrops of different type and orientation of rocks).",
"There are different types of faults, we classify them based on the way the ",
"two sides of the fault moves",
" with respect to each other. The San Andreas is a strike-slip fault, meaning that movement is dominantly horizontal so neither plate is submerging under another at this type of boundary (one side moves under/over another along dip-slip faults).",
"Earthquakes are a key part of creating/growing faults. Faults are just fractures, and their growth can be reasonably well described (at a simple level at least) with basic ",
"fracture mechanics",
". Earthquakes represent discrete events in which movement occurs along a portion of a fault plane, and in some cases, in which the fault grows at its edges (e.g. ",
"crack propagation",
"). Earthquakes may help us to understand the geometry of the faults at depth, but they don't usually help us in terms of mapping them at surface. The exception would be faults that are not well exposed at the surface and experience an earthquake and the portion of the fault that ruptures intersects the surface. In this case, the deformation of the material at the surface may help us locate the fault.",
"Finally, as for accuracy/precision, it really depends on the map and the area in question. I discussed the exposure aspect a bit above. In some places, where exposure is not complete, locations of faults may be approximate. Faults also don't always intersect the surface, but they may still deform the surface through features like ",
"fault propagation folds",
", so we can interpret their presence but their location will not be precise or accurate, and we may only know their location within 100s of meters to kilometers. In other cases, you may be able to place your finger directly on the fault plane so the accuracy will be high (assuming you're a decent mapper and know how to locate yourself and features on a map and thus accurately place yourself on the map) and the precision will depend totally on the map. Maps have inherent precision limits because of scale, e.g. a 1:100,000 scale map means that 1 mm on the map equals 100,000 mm in the real world (or 100 meters). This means that if you have a single line on the map that is 1 mm wide, this represents a 100 meter wide area in the real world, so there will always be some uncertainty in the fault location on the map. This is an exercise we make all beginner geologic mapping students go through to realize that the placement (and thickness) of their lines on a map are important."
] |
[
"I just want to thank you for taking the time to write this detailed answer"
] |
[
"This is an amazingly clear answer. Thank you!"
] |
[
"What causes a headache?"
] |
[
false
] |
[deleted]
|
[
"The brain is lined by a protective covering kown as the meninges. Since the brain doesn't have any sensory innervation itself, the meninges have all the sensory information associated with pain. Basically, whenever the meninges are irritated, this can cause a headache. There are a wide variety of things that can irritate the meninges. Everything from a brain tumor, to just simply fatigue. Sometimes changes in blood flow to the brain and cerebrospinal fluid can also cause that meningeal irritation, which will result in a headache. I hope that answers your question. In summary, anything that irritates the meninges will cause a headache.",
"This pathophysiology has some good information: ",
"http://en.wikipedia.org/wiki/Headache#Pathophysiology"
] |
[
"Thank you for the quick response. I had actually had done a DANCON March for 22km earlier so that may have caused it. Keep up the good work. "
] |
[
"Why do I get a headache during caffeine withdrawal? "
] |
[
"Does \"letting the flavors blend\" actually work? And if so, what's going on?"
] |
[
false
] |
Lots of recipes for salads, coleslaw, or soups say to leave it in the fridge for a few hours so that "the flavors can blend together". But surely, between my mixing and the turbulent blending of the air before reaching my nose, everything I can taste/smell should be blended already, even if I eat it right away. Are people deluding themselves, or is there something else going on here?
|
[
"think of it more as infusing than blending. If you drank tea a few seconds after adding water, it would be very, very weak and the longer you let it sit it gets stronger. With something like salad dressing, it takes a bit of time for the flavour of herbs and spices to infuse through the oil."
] |
[
"I'm 99% sure it was an article in America's Test Kitchen where they answered this exact question. However my Google-Fu is lacking as I cannot find it any where online for free. (A couple of hits for \"food chemical reaction\" came up on Amazon but that's it. ATK is also behind a paywall.)",
"However in their article they created a number of dishes and did a thorough chemical analysis on them the day of. They then correctly stored the dishes and the for the next two days did the same analysis on the dishes. Their testing did indeed show that as the dishes sat they developed additional chemical compounds not found in the first test. Giving credence to the 'letting flavors blend' way of thinking in cooking. I remember that the first 24 hours had more additions to the dishes than the next 24 hours did.",
"If someone can find that research you'll know it's the same one as I'm referring to here because I also remember being surprised by their finding that for a standard Chili recipe, letting it sit to develop more flavor had almost no appreciable additions to the chemical analysis and almost none in taste according to their tasters."
] |
[
"It definitely works. You are allowing time for a few things. Depending on what the ingredients are, there may be chemical reactions occurring. Acids and bases may be reacting for instance.",
"Also, flavors will mix together. Take a sauce for example. For simplicity, take something like olive oil. Now add chunks of garlic to it. Even if you vigorously shake, stir and mix, the aromatic compounds and flavors from the garlic will not fully intermix with the oil until some time is given. You could taste the plain olive oil with no garlic chunks in it and taste that the flavors have not blended. A day or two later, the oil will be infused with the garlic flavor much more. You could strain the garlic out and still have the flavor in the oil.",
"So when you let the \"flavors blend\" you are allowing time for all of this to occur. It creates a richer, more complex flavor profile. Especially if the ingredients are in larger pieces. Chunks of garlic, onions, herb leaves, etc. You want the flavors to infuse throughout the concoction. So if you got a bite without any garlic chunks or onion pieces in it, you'd still be able to taste them."
] |
[
"How does a tunnel boring machine navigate?"
] |
[
false
] |
I've been looking at some videos and progress with the new light rail tunnels in and around Seattle, and it got me wondering how the heck they manage to bore through solid rock for miles and pop out exactly where they mean to. Most of the techniques traditionally used for navigation (GPS, cell radio triangulation, magnetic fields, stars, lasers, barometric pressure, etc.) would all seem to be completely useless underground in solid rock. How do you get a machine like that to maintain a straight and level path, when do you tell it to turn, and how do you make it line up with it's exit?
|
[
"You are saying \"can surveying really be that precise?\" The answer is yes. Even traditional surveying can. With the aid of lasers and/or modern optics, it gets even a bit easier."
] |
[
"I understand the basic principles of surveying, I guess the thing that gets me is seeing a machine break through a solid hillside, dead-centered inside of a metal ring that's already installed to complete the tube. I can understand boring straight through a hill, I know that's been done for a long time, but digging a hole miles from the start and placing the end point within (inches?) of where the machine comes out seems unreal to me. Do they use sonar as well?"
] |
[
"People have been making straight lines without the technologies you mentioned for thousands of years. The techniques for doing so fall under the umbrella of ",
"surveying",
".",
"To figure out which direction the straight line needs to go in, they use one of ",
"these",
". It basically measures the effect of the earth's rotation on a gyroscope, and uses that measurement to find orientation underground."
] |
[
"Would it be possible for the universe to stop expanding and begin shrinking?"
] |
[
false
] |
I read a post on askreddit or something that said something along the lines of, "There could have been a universe before ours that that stopped expanding and started shrinking into one very smell point that then exploded which was the Big Bang." Is there any real reason the universe would all of a sudden start shrinking?
|
[
"Absolutely; this is the idea behind the ",
"big crunch",
". Evidence suggests, however, that our universe doesn't have enough matter for its gravity to overpower dark energy which is currently making out universe expand at a growing rate. The fate of this universe seems to be one where it will continue to expand."
] |
[
"That's dark energy, which is easy to get confused with dark matter. Dark matter is a theorised form (or forms) of matter that accounts for the fact that, in various scenarios, certain effects can be seen that appear to be the result of matter, but lack an observable material cause (this is observed with galaxies, which frequently behave in ways that require them to be much more massive than they appear)."
] |
[
"For the most part, yes; that's correct. ",
"There are a number of observable phenomena which shouldn't, according to our measurements of perceptible matter, be possible. The only thing you've left out of your statement is the possibility for there to be no \"missing matter\" but instead that our understanding of gravitational attraction with respect to astrophysics is incomplete or inaccurate. "
] |
[
"Does dark matter contribute to the mass of a black hole?"
] |
[
false
] | null |
[
"Yes certainly some dark matter would be gravitationally captured by black holes and some would fall in. Note that it doesn't really matter what fell into a black hole other than its mass and charge and spin, so the properties of a black hole with mass that came from dark matter may be identical to a black hole none of whose mass came from dark matter."
] |
[
"First Disclaimers:\n1. I am an absolute layman.\n2. Almost nothing is known about dark matter except that it appears to exist. Anything stated about how it acts is necessarily speculative since we do not know how it fits into our theoretical frameworks (if at all).",
"However, I do believe that this question can be answered tentatively with a Yes.\nDark matter has only been observed on a galactic scale. We see a much greater gravitational effect than baryonic (regular) matter can account for. Therefore Baryons and Dark matter interact with gravity (i.e. they have mass). Since we cannot see it or run into it, baryons and dark mater do not interact electro-magnetically. One of the primary hypotheses of what dark matter is WIMPs (Weakly Interactive Massive Particles). The closest thing we have found to a WIMP is a neutrino.",
"So, since Dark Matter is thought to be made up of particles with mass (no matter how exotic) such matter will interact gravitationally with a black hole and under the right circumstances fall into one (just like neutrinos or even light which has no mass). Once in the black hole there is no reason I know of that dark matter wouldn't continue to have mass and add to the total mass of the black hole.\nOf course the nature of dark matter and even the interiors of black holes are not fully understood. We do not know for certain dark matter is made up of particles, which if untrue would negate the above answer. All bets are off I'm afraid. However, given what is known, I believe the above is the intuitive answer."
] |
[
"Hello, Im late to this one, but think I can answer it as dark matter is my area.",
"The answer is yes, if we assume dark matter to exist, then it would certainly contribute the mass of a black hole. There is no way to prove this, of course, as we can't detect it yet, but we do know that dark matter is affected gravitationally. It is also expected to congregate to some extent inside suns and planets, as well as black holes. The primary problem with the former two is that it would need to interact with the matter inside the planet to deposit enough energy to be captured, something not needed for black holes.",
"The fraction of mass that it will contribute will vary depending on the position of the black hole in its respective galaxy or even galaxy cluster. Since the distribution of dark matter is galaxies is not thought to be uniform (for gravitational reasons), one would expect dark matter to contribute more to a black hole in the centre of a galaxy, than on the edges.",
"Does this change anything? No, not really. Other than the spin, and charge of the black hole, the primary effect is gravitational. It would not matter (see what I did there) if it obtained it mass through cake or dark matter, so long as the mass was the same.",
"If you have any more questions, don't hesitate to ask."
] |
[
"How does external stimuli contribute to evolution?"
] |
[
false
] | null |
[
"How does the DNA know that it needs to create red and white spots to mimic a ladybug, when the input of information is visual by nature?",
"It doesn't work like that at all. The DNA mutates all over the place, into mostly bad stuff that doesn't stick around long. The good stuff that persists ends up in the case of camouflage looking very much like the environment, because that is what works."
] |
[
"DNA codes for some protein that dertermines the pattern on the back of the ladybug. In each generation of ladybug there will be a variety of patterns, because the copy mechanism for DNA is not perfect or there might have been mutating agents like radiation or toxins. This results in mutations of the DNA sequenze and thus in the protein that makes the pattern.Then Natural selection happens i.e. the ladybugs that have patterns which are easily seen by predators die and don't get to reproduce, so their unfavourable version of the DNA sequenze won't be passed on to the next generation. "
] |
[
"that makes perfect sense...now I'm facepalming, duh, of course, it determines success by which variations live and die. \nHow did I somehow overlook the basic tenent of evolution. Survival of the Fittest (and lucky!) is the vehicle.",
"Thank you! "
] |
[
"Why do higher elevations have lower temperatures?"
] |
[
false
] |
This is probably a simple question with a simple answer but I want to know if my hypothesis is correct. My hypothesis is that at higher elevations there is more wind travel (for a multitude of reasons) therefore cooling by convection. Is this the reason, or is there something I'm not considering (maybe air density)? This is something I was truly puzzled by as a kid with the train of logic "We're closer to the sun, why isn't it hotter?".
|
[
"The air at lower altitudes has to hold up all the air above it, which means it has to have a higher pressure. According to the universal gas law if a gas wants to have high pressure it has to get denser or a higher temperature or both. "
] |
[
"Earths atmosphere is kinda weird in that at sea level its one temperature, then it will decrease, then increase, decrease again, and finally increase on up. ",
"Seriously, here's a chart.",
" I cannot remember exactly why, but if I recall its due to the light getting absorbed at the layers of atmosphere. ",
"This explains better than I do, and with a picture",
", but the gist of it is certain wavelengths get absorbed and heat up the air. Once its absorbed that layer heats (and transfers heat, but not at the speed of light..) and that wavelength is gone. The thermosphere gets warmer as it absorbs a lot of the wavelengths between UV and X-ray. The mesophere doesn't really absorb much (leading to it being cooler than the thermosphere) and the Stratopshere with its ozone absorbs the rest of the gamma radiation as well as some IR. A lot makes it to the surface and heats the ground up. Then you have a lot of factors influencing the local temperature. Elevation does, but not even close to the effects of latitude and ocean currents. Look at Denver's Highs and compare that to places of the same latitude, you'll notice they're not that far apart. "
] |
[
"By this theory high altitude over Kansas or Nebraska would be warmer."
] |
[
"Whatever happened to string theory?"
] |
[
false
] |
I remember there was a bit of hullabaloo over string theory not all that long ago. It seems as if it's fallen out of favor among the learned majority. I don't claim to understand how it actually works, I only have the obfuscated pop-sci definitions to work with. What the hell was string theory all about, anyway? What happened to it? Has the whole M-Theory/Theory of Everything tomfoolery been dismissed, or is there still some "final theory" hocus-pocus bouncing around among the scientific community?
|
[
"They're still working on it. Pop sci journalism is the worst metric for discerning what people are actually working on. Or for anything, for that matter."
] |
[
"I'm not sure what this \"learned majority\" you're talking about is, but string theory is still very much an active area of research, and by far the most popular and, imho, most promising approach to quantum gravity. It's a very technical subject, having strong interactions with modern mathematics, and so it's difficult to convey progress in the field to the general population (even to those who are scientifically inclined). As far as experimental predictions, it does make a few, and there's even a longshot the LHC could find evidence of strings. But the main problem is that quantum gravity manifests itself at the planck scale, which is still orders of magnitude away from what we can probe. So pretty much any theory of quantum gravity will have the same problem."
] |
[
"Well, new papers are put on ",
"arXiv",
" every day. arXiv is a preprint database (so the papers posted to it have not necessarily been peer reviewed yet, and a lot of researchers with various levels of competence can upload to it) and is the main outlet for particle physics papers today. ",
"hep-th",
" is the category that includes string theory papers.",
"Not all of the papers on there are string theory, though. String theory ones will generally be the ones with the words \"string,\" \"brane,\" or \"de Sitter.\" That being said, there are usually at least a few string theory papers put out there each day.",
"This is the only measure of \"advances\" I can give you, because unlike most pop sci fodder - experimental/laboratory achievements - theoretical advances aren't necessarily known to be advances until some experiment comes along and proves them right."
] |
[
"If you were on the moon and traveling consistently towards the setting sun i.e. between night/day. Could you find a comfortable ambient temperature? Could you survive with just oxygen?"
] |
[
false
] |
[deleted]
|
[
"First of all, the moon has effectively no atmosphere. Therefore, aside from gravity, standing on the moon is the same as sitting out in interplanetary space. Both are effectively a vacuum, so there is no \"ambient temperature\". ",
"If you were standing on the moon without a space suit (and somehow managed to cancel out the effects of no air pressure), you would get dangerously hot if you were in the sunlight and eventually get dangerously cold if you were standing in a shadow. Earth's atmosphere has a way of blocking, scattering, and mixing up the light and subsequent heat from sun. With no atmosphere, there is no mixing agent."
] |
[
"One of the many layers of the spacesuit is a temperature control layer, it runs cool water around the suit to maintain the desired temperature, while an insulating layer keeps the astronaut warm enough. The suit is designed to reflect a lot of the radiant heat to minimize overheating, heat radiates off the suit slowly so sudden cooling isn't a concern."
] |
[
"Ok so Im confused. What then protects astronauts from the spontaneous freezing/heating up?"
] |
[
"Is ice harder than concrete?"
] |
[
false
] |
I tried googling it and found that some old solid ice mass is harder, but what about an ice rink? How come a fall that's comparable to what I sustain skateboarding hurts so much more when I'm ice skating?
|
[
"Two parts here:",
"There are different herdnesses of most objects. Mineral content in water will affect hardness as well as temperature. In general though, ice will rate somewhere around 1.5 Mohs. On he same scale, youd like concrete to be in he 5-7 Mohs range. So, yes, in general concrte is harder than ice.",
"It probably hurts more because your limbs are cold. "
] |
[
"In general though, ice will rate somewhere around 1.5 Mohs. On he same scale, youd like concrete to be in he 5-7 Mohs range.",
"As you note though, ice's hardness changes with temperature. At around -80 C (-112 F, far colder than where anyone is going to skate), ice reaches a hardness of 6 on the Mohs scale, roughly the same as concrete."
] |
[
"It depends on the ice and the concrete. There are variables that affect each, such as trapped air, impurities in the ice, uniformity of the aggregate, etc.",
"There is a type of aerated concrete that was being developed for use at the end of airport runways that would intentionally crush under the weight of a plane in order to stop them in case of an emergency landing.",
"There is also a type of ice made with cellulose, called Pykrete, that is potentially stronger than the kind if concrete used in highway construction."
] |
[
"Would all intelligent life in the universe evolve using the same visible light spectrum as us to see? Is our slice of the spectrum innately superior for vision?"
] |
[
false
] | null |
[
"I'd say it's the most effective general range - yes, some creatures go a bit higher or lower than humans, but it's pretty close.",
"Visible light is pretty good at going a good distance through the atmosphere without diffusing too much. It's passive - ambient light is used and we don't have to project anything and reveal our presence to a predator. The wavelength is small enough that the sensory organs don't have to be particularly large.",
"I'd say given A) the spectrum of the light given off by the Sun and B) the atmosphere of Earth that it was more or less inevitable HERE.",
"Elsewhere? Tell me what the most abundant wavelength of light is that reaches the creatures in question, with a high enough frequency to allow for small eyes... I'd suspect it'd be near our range, but maybe not identical."
] |
[
"I would like to clarify that visible light is the part of the spectrum where the sun outputs most of its light. If we tried to develop eyes that saw infrared or the ultraviolet then everything would be dimmer, because there is less of that light coming from the sun. The atmosphere is equally important because it cuts down the other wavelengths."
] |
[
"Plenty of animals don't see the same spectrum that we do. Lots of birds of prey see UV light (helps them track prey, and many have patterns on their feathers that can only be seen in UV light). Of course dogs see a different spectrum, as do cats (why some people mistakenly think that they are \"colorblind\"). Based on this, I don't think the visible light spectrum is necessarily better for all species."
] |
[
"Is it really bad for your health to eat in front of a computer?"
] |
[
false
] |
I've heard this more than once in my life, but can't recall hearing a plausible explanation. That is, one with the actual medical facts.
|
[
"Scientifically, no. There is absolutely no reason to think it would be.",
"But also scientifically speaking, i really doubt anyone has ever done a study on it.",
"It is unhealthy to eat a lot while sitting on your butt a lot in front of a computer a lot all day long. Easy to see why the myth could emerge. But there is no reason to believe it. If you are overweight, eat less and sit in front of the computer less. But eat in front of the computer all you want."
] |
[
"I remember being told not to eat at a computer in the early 90's. They just didn't want us getting food in the keyboard."
] |
[
"It doesn't have anything do with the computer, but more to do with your emotions towards eating. We sit at computers a lot, and if you connect food with the computer you ",
" find yourself eating more than you should for your diet. If you train yourself to think \"I should not eat in front of my computer,\" you are less likely to sit down at the computer and feel emotionally hungry.",
"I know that when I get bored and I'm at my computer I almost immediately want food for no reason in particular. There is some truth behind it, but its due to controlled eating habits rather than the computer specifically."
] |
[
"What causes Amino Acids to \"fold\" into proteins?"
] |
[
false
] | null |
[
"The amino acid sequence of a protein is going to ultimately determine how it is going to fold, and the folding is stabilized by several factors. The biggest factor driving protein folding is hydrophobic interactions. ",
"If you're unfamiliar with this, its basically the same idea as when you add oil to water, they dont mix and the oil will move together. This is because although the entropy of the oil is going to be decreased by being near each other, the overall entropy of the system is increased by the water molecules being moved away form the hydrophobic oil. ",
"This same principle drives the folding of proteins. There are several amino acids that have big bulky hydrophobic groups that water wants to push away from and forces themselves to be near each other. Once folded the protein's folded form is further stabilized by other interactions such as di-sulfide bonds, electrostatic interactions between polar side chain groups, hydrogen bonds, and van der waals interactions. "
] |
[
"There's nothing that says it has to be in its ",
" stable structure. Just a local minimum that's low enough in energy that the other structures with lower energy are adiabatically inaccessible; you can't reach them without adding more energy first. The particular local minimum that is reached is affected by the synthesis process, by chaperones, etc. The structure is not determined by the amino acids alone, without regard for how the folding process actually occurs. ",
"An example of why that's so is that 'silent' mutations (change to the codon but not the amino acid), can lead to changes in the structure."
] |
[
"There's nothing that says it has to be in its ",
" stable structure. Just a local minimum that's low enough in energy that the other structures with lower energy are adiabatically inaccessible; you can't reach them without adding more energy first. The particular local minimum that is reached is affected by the synthesis process, by chaperones, etc. The structure is not determined by the amino acids alone, without regard for how the folding process actually occurs. ",
"An example of why that's so is that 'silent' mutations (change to the codon but not the amino acid), can lead to changes in the structure."
] |
[
"How does pixel size on image sensor influence image quality?"
] |
[
false
] |
Some smartphone manufacturers decided to advertising bigger pixel size as an advantage. Is it really? Let assume two sensors with the same pixel count, but one sensor has bigger pixels (and has thus a higher area). I would expect bigger pixel size to induce poor sensitivity and poor spatial resolution. The image would be too dark in low light condition (but maybe less noisy) thus requiring bigger aperture and/or longer shots. But they are advertised as being able to capture more light thanks to their bigger area, but this doesn't seems to be a valid argument taking the lens into account. i.e.: if pixels are smaller, a focusing lens will concentrate more light on the smaller area, thus increasing sensitivity (thanks to smaller capacity). Am I missing something or is it truly false advertisement? Do scientific imaging tools prefer bigger sensors to smaller sensors (at a given pixel count)? For me the actual good criteria is "active" ratio: maximizing the ratio of the sensor that is actually sensitive to light vs. the area of the sensor receiving light. Maybe bigger pixels means that the inter-pixel space is smaller compared to the size of the pixels.
|
[
"What you call \"active ratio\" is called the ",
", and it is true that larger pixels will generally allow for larger fill factor.",
"Ignoring any differences in fill factor (and quantum efficiency), the performance of large vs. small pixels depends on how you do the comparison.",
"You can get equivalent spatial resolution if you match the optical magnification to the pixel dimensions. If you compare sensitivity at the same spatial resolution (and assuming the same numerical aperture, etc.), then the two pixels will collect the same amount of light and perform in a similar way.",
"However, in smart phone cameras, the pixel elements are so small (1-3 µm) that the spatial resolution is limited by the optics (the width of the point-spread function — or for ideal optics, the width of the Airy disk), not by the pixel dimensions. Thus, a large-pixel sensor and a small-pixel sensor can use the ",
" lens magnification, ",
" loss in the effective spatial resolution.",
"Under these conditions (same optics for both sensors), then of course the larger pixel will collect more light (all other factors being equal).",
"For high-speed imaging (which uses extremely short exposure time, therefore significantly cutting down on the number of photons that are captured by the sensor), cameras typically have sensors with very large pixel elements (20-30 µm).",
"I would expect bigger pixel size to induce ",
" and poor spatial resolution. The image would be ",
" in low light condition (but maybe less noisy)",
"Your intuition about the effect on sensitivity and image brightness is inaccurate. As explained above, with larger pixel size, the image will either be the same brightness as an image from a sensor with smaller pixels (if magnifications are equivalent), or ",
" (if the same lens is used). The amount of noise typically scales with the square-root of brightness, so the larger pixels will have either equivalent or reduced noise compared to the smaller pixels."
] |
[
"Thanks for the explanation.",
"My reasoning for bigger pixel sizes having poorer sensitivity is because they have a bigger capacity. i.e.: needs a bigger amount of photon to provide the same voltage. For high-speed imaging I guess they use the fact that the fill factor on those sensors with large pixel elements is better. But I might be wrong."
] |
[
"Actually, the ability to convert a photon to an electron (voltage) is what is called the ",
", which is not correlated with pixel size.",
"You may be thinking of ",
", which is the maximum amount of charge (electrons) that a pixel can collect before it saturates (or even cause charge to leak into neighboring pixels, a process called \"blooming\"). Full-well capacity is typically larger in larger pixels, but this is generally a good thing, because it increases the dynamic range of the sensor.",
"Typically, the gain of the analog-to-digital converter (ADC) would be set so that the maximum pixel brightness would correspond to the full-well capacity. So, all else being equal, it is in fact true that you would require more light to reach, say, a 50% gray-level in a large-pixel camera vs. a small-pixel camera. However, all else is ",
" equal: sensors with better dynamic range (i.e. the larger sensor) would normally be paired with an ADC that has a higher bit-depth, so that the numerical value of the pixel output would be equal or higher in the large-pixel camera. Alternatively, for equal bit-depth, the ADC gain can be adjusted to get equal or better performance for the large-pixel sensor.",
"I think you will find ",
"this page on the ClarkVision.com website",
" of interest. You will see that practically all performance measures have better results for larger pixels (higher pixel pitch)."
] |
[
"In a car, if I'm in 2nd gear at 3000 rpm, do I consume more or less fuel than in 5th gear at 3000 rpm?"
] |
[
false
] | null |
[
" You are correct. ",
" Think about it this way. When you are driving down a hill, you can remove your foot from the gas pedal, and easily maintain your speed and RPM while using VERY little fuel (if you have one of those fuel efficiency meters, it would say something like 99 MPG or more). Conversely, if you are driving ",
" but going ",
", you will obviously have to depress the gas pedal, probably significantly so. Your speed has not changed, your RPM has not changed, but you are now consuming orders of magnitude more fuel (your fuel efficiency gage will probably drop from 99+ to less than 20 or even single digits).",
"This is because fuel consumption is more a function of loading than it is RPM.",
"Edit for addendum:",
"It is a common misconception that fuel consumption increases linearly (or approximately linearly) with engine RPM. This is also not true. Given a constant engine loading, the ",
"specific fuel consumption is highest at the extreme ends of the RPM range",
". Specific Fuel Consumption actually lowers with increasing RPMs at the low end of the RPM range, until an optimum RPM is reached (depends on engine), and then increases again. For my 2004 Toyota Corolla the optimum range is 2000-3000 RPM, whereby the engine produces the most power for a given amount of fuel consumed. If I drove the car at lower than optimum RPMs (say 1000-2000), I would actually consume ",
" fuel even though the RPMs are lower, because the ignition system has to provide far more fuel per stroke to output the required power demanded."
] |
[
" You are correct. ",
" Think about it this way. When you are driving down a hill, you can remove your foot from the gas pedal, and easily maintain your speed and RPM while using VERY little fuel (if you have one of those fuel efficiency meters, it would say something like 99 MPG or more). Conversely, if you are driving ",
" but going ",
", you will obviously have to depress the gas pedal, probably significantly so. Your speed has not changed, your RPM has not changed, but you are now consuming orders of magnitude more fuel (your fuel efficiency gage will probably drop from 99+ to less than 20 or even single digits).",
"This is because fuel consumption is more a function of loading than it is RPM.",
"Edit for addendum:",
"It is a common misconception that fuel consumption increases linearly (or approximately linearly) with engine RPM. This is also not true. Given a constant engine loading, the ",
"specific fuel consumption is highest at the extreme ends of the RPM range",
". Specific Fuel Consumption actually lowers with increasing RPMs at the low end of the RPM range, until an optimum RPM is reached (depends on engine), and then increases again. For my 2004 Toyota Corolla the optimum range is 2000-3000 RPM, whereby the engine produces the most power for a given amount of fuel consumed. If I drove the car at lower than optimum RPMs (say 1000-2000), I would actually consume ",
" fuel even though the RPMs are lower, because the ignition system has to provide far more fuel per stroke to output the required power demanded."
] |
[
" you will use less fuel in 2nd gear but the mileage will be worse. The engine is less efficient at lower loads (load is lower in 2nd because vehicle is going slower). So physically the fuel used is lower. ",
" because you are not traveling very fast the MPG is actually worse, even though the engine is consuming lower fuel (the vehicle ends up consuming more fuel per unit distance). So don't drive in 2nd gear if you want better MPG. Read the below for more detail.",
"Detailed comments:",
"This depends the reference frae you define efficiency (miles or gallons). I assume that you mean in MPG (convolution of both miles and gallons), this obviously depends on miles, which depends on speed. In 5th gear the gearing is lower, so so for a given engine speed this means a faster vehicle speed. Faster vehicle speed means higher road load (aerodynamic losses, kinetic energy etc...). This means more load that the engine must provide, which means more energy.",
"The second factor (gallons) depends only on engine efficiency, which depend on load (which is set by vehicle speed). Higher load typically means higher engine efficiency.",
"Here",
" is what I mean about fuel consumption of the engine per unit load (brake specific fuel consumption contours). This is just mass of fuel per unit load. So a large bsfc items a smaller load can be lower (less fuel) than a higher load and lower bsfc(more efficient but but higher load). When the engine load is higher (vertical axis in cited figure) the fuel consumed reduces per unit output (lower number mean less fuel per unit power, i.e., more efficient). So long story short its complicated and specific to the engine and car. But ",
" using your conditions the engine will physically consume less fuel in 2nd gear because the load is lower. But in terms of distance traveled the vehicle is much less efficient at transporting itself (and you) thus MPG is worse because in terms of per unit distance the efficiency is low (bsfc is higher and speed lower)."
] |
[
"The structural determination of any molecule via a single instrument?"
] |
[
false
] |
I have a significant physics and chemistry background, but this isn't my subfield. I assume a mass spec/NMR setup provides enough information to determine the structure of many molecules, but has a setup been developed that allows a scientist to introduce ANY molecule and then pop out a formula, diagram, etc. for this molecule?
|
[
"Well, x-ray crystallography will do it, in general. ",
"I don't think you could make a setup that could do this for literally ANY molecule/substance, or at least it would be prohibitively complex. ",
"For straightforward, stable organic molecules, it would not be prohibitively difficult in principle to create an automated system that acquires the NMR and mass spec of an unknown sample. Whether this exists in practice I am not certain. Certainly high-throughput automated instruments for each of those individually exists.",
"I am not aware of a widely available program for automated structure determination from NMR spectra, although certainly it is a problem which is being worked on. The closest thing would be to use automated NMR prediction based on a guess for the structure and compare that to the actual structure. In any case, I believe NMR analysis is primarily done manually at this point even in high-throughput labs. "
] |
[
"Mass spectrometrist here.",
"There's some pretty cool stuff happening in the realm of mass analyzers that allow for traditional mass measurements (i.e. compound X weighs Y) in tandem with elucidating structural information. If you're looking for purely structural information, look into a mass spectrometer that is equipped with an ion trap. This will allow you to systematically break compound X into fragments at different energies, showing you what bonds are most stable and what exactly is attached to what. With an ion trap, you can do this multiple times (find X, break it into Y. now find Y break it into Z, etc) in order to yield information on both identity as well as connectivity. Look for the protein chemists, they'll most than likely have access to one of these.",
"If you're looking for information about molecular geometry look at a mass spectrometer with ion mobility spectrometry-mass spectrometry. The latter portion (mass spectrometry) gives basic mass measurements information but, the ion mobility spectrometry portion can give you information on a collisional cross section (i.e. how your ion is shaped). The field of ion mobility spectrometry is rather new, so only a few commercial instruments are equipped with them. ",
"The benefit of using MS is that it's much more sensitive than NMR and can be easily automated. The downside -- Your compound needs to be ionizable."
] |
[
"One ",
" conceivably use NMR alone to determine structure. There is a plethora of experiments one can do do gain bonding and spatial information, so it certainly goes beyond the simple NMR spectra one might think of.",
"However, like ",
"spinningspinning suggested",
", no instrument can accept ",
" type of sample."
] |
[
"How do you mass produce an antiserum?"
] |
[
false
] | null |
[
"You can't - to do so would be equivalent to farming people like they do in the movie Daybreakers. This is because antiserum is defined as the blood serum of naturally immune individuals.",
"You can, however, do something that would approximate the same effect. It is possible to extract and isolate the B-cells responsible for producing the inhibitory antibodies, expand them, and harvest the antibodies they produce. You can also sequence their genome to identify the variable regions of the antibody and make synthetic antibodies artificially. In both cases, you can then transfuse the antibodies and it would, for all intents and purposes, mimic transfusion of antiserum."
] |
[
"Nope, you are absolutely correct. If you have the sequence of the variable region of the antibody, you can express ",
"scFv",
" (single chain antibody variable fragments) in E.coli and have it secrete into the periplasm for purification. The scFv behaves exactly like each arm of the antibody and is perfectly functional. You can also even engineer entire antibodies to be made in E. coli, but that is trickier.",
"Source: I have personally done this in my research project. I sequenced B-cell hybridomas, synthesized scFvs with the variable light chain connected to the variable heavy, and expressed it in E. coli with the PAK400 vector with the pelB signal sequence directing to the periplasm."
] |
[
"Nope, you are absolutely correct. If you have the sequence of the variable region of the antibody, you can express ",
"scFv",
" (single chain antibody variable fragments) in E.coli and have it secrete into the periplasm for purification. The scFv behaves exactly like each arm of the antibody and is perfectly functional. You can also even engineer entire antibodies to be made in E. coli, but that is trickier.",
"Source: I have personally done this in my research project. I sequenced B-cell hybridomas, synthesized scFvs with the variable light chain connected to the variable heavy, and expressed it in E. coli with the PAK400 vector with the pelB signal sequence directing to the periplasm."
] |
[
"How exactly do physicists predict masses of yet unobserved particles?"
] |
[
false
] |
What does it mean, when a mass of a newly observed particle fits/doesn't fit the Standard Model? Is it more about algebra? calculus? statistics?
|
[
"Conservation of mass, energy, spin, etc. Often a simple case of addition.",
"Scientists look at the resultants of a given interaction, and if any property is not conserved, they posit a new particle to allow the given quantities to be conserved. "
] |
[
"The \"Standard Model\" is a description of all theoretical fundamental particles.",
"It organizes them so that they follow certain patterns like ",
"this.",
"It predicts how different particles react based on their properties and what properties a particle will have based on its other properties."
] |
[
"For the particles listed in the table in that link, there is no way of predicting or calculating the mass (that we know of, though a lot of people are looking). However, you can calculate the mass of composite particles built up from combinations of those. For example, if you know the mass of a neutron, which is made of two down quarks and an up quark (udd), you can get a rough prediction of the mass of the neutral lambda baryon (uds) by adding the mass difference between the down quark and strange quark."
] |
[
"Is pharmagenetic testing proven by the scientific community, or is it hogwash? It’s a genetic test to see which drugs (anti-depressants) work better depending on each individuals genes."
] |
[
false
] | null |
[
"It’s not a gimmick. It’s part of personalized medicine. In the past a doctor may try different prescriptions to see which one works best. Now there are tools to cut to the chase. It’s common in a variety of therapeutics, but the one I am most familiar with is chemotherapy. If there was a time limit on your life, you wouldn’t want to waste time trying to find the chemo that might work, right? You’d want the treatment best suited to you, which they have figured out through numerous, well-supported genetic epidemiology and pharmacogenomics research. "
] |
[
"The lab I worked for used to do it, we focused on 2 branches of testing, one to help those on antipsychotics and ensure they were getting the best medicine, and one to help athletes mostly in combat sports, to ensure that their supplements are all effective. It definitely isn’t fake, it does work, and there’s some pretty good science behind it "
] |
[
"Could this expand the list of drugs already known that have a laundry list of side effects yet not for X individual?"
] |
[
"Do electromagnets still have north and south poles? How is polarity in an electromagnet determined/changed?"
] |
[
false
] | null |
[
"Yes, they still have poles. The convention is the same: magnetic field lines point away from North poles and towards South poles.",
"You’ll often find electromagnets (superconducting or normal-conducting) with iron cores, and the iron is often shaped to create the desired shape of the magnetic field. These pieces of iron are often referred to as the “poles” of the magnet.",
"Here",
" is an example of a quadrupole magnet. You can see the coils where electric current runs through. Inside the red protrusions is probably some kind of high-permittivity metal. Those are the “pole tips”. In this case, they’re shaped like hyperbolae to create a quadrupole field near the central axis.",
"Not all electromagnets have these. "
] |
[
"The polarity is determined by the direction of current flow in the coil. Reversing the current reverses the poles. The ",
"right hand rule",
" is used to determine what direction of current is needed to make one specific pole north.",
"When wrapping the right hand around the solenoid with the fingers in the direction of the conventional current, the thumb points in the direction of the magnetic north pole."
] |
[
"Follow up question, does the conventional north pole of an electromagnet have the same expected interaction with the north pole of a conventional magnet? Would they still repel each other or is there other things to consider? "
] |
[
"How is it so that several (all?) mammals grow and lose a set of \"baby teeth\" before growing their final dentition? Why stop at two sets when other vertebrates such as sharks regenerate their teeth constantly?"
] |
[
false
] | null |
[
"There are a handful of mammal species that constantly replace lost teeth, but most don't. On the flip side, quite a few non-mammals continuously replace lost teeth. ",
"There's two factors that seem to be at play in mammal tooth growth patterns. First, early mammals were probably relatively short-lived little shrewlike insect - eating things like",
"this",
". You don't need to constantly replace teeth if you aren't wearing them out. ",
"But on the flip side, not constantly replacing teeth allows mammals to do things with their teeth that other groups can't. Even mammal ancestors like cynodonts were starting to get distinctive canines. Mammals take this further with an array of highly specialized teeth rather than just one or a few kinds of teeth like you see in other groups. And those teeth lock together in precise ways allowing mammals to process food effectively. Our jaws are simpler than the reptilian norm because some of the jawbones have been incorporated into the inner ear, but despite that our precision swiss army teeth let us eat efficiently and effectively. It's hard to have that kind of interlocking if teeth are constantly being shoved around as they get replaced"
] |
[
"Evo devo guy here. This is basically the answer the tooth researchers I know tend to favor. There is some mechanistic trade-off between the development of specialized teeth and the ability to re-initiate tooth development later in life. ",
"I tend to think \"its a waste of energy\" (mentioned by other posters) is unlikely to be a major factor. Its not a huge expense to produce more teeth, especially in large, long-lived mammals like apes."
] |
[
"Evolutionary developmental biology (informally, evo-devo) is a field of biological research that compares the developmental processes of different organisms to infer the ancestral relationships between them and how developmental processes evolved.",
"https://en.wikipedia.org/wiki/Evolutionary_developmental_biology"
] |
[
"If a large object (e.g. car) was dropped in the middle of the ocean, what kind of waves would we see when they reach land?"
] |
[
false
] |
So my understanding about ocean waves is that they are mainly created by wind blowing out in the middle ocean in a certain direction, they keep traveling while building up, and eventually they reach land. Please correct me if I'm wrong. My question is if wind blowing out at sea can create some pretty big waves, what if a heavy object (car?) was dropped from say 30 feet into the ocean a few miles off of shore? Would the waves created keep carrying make some massive breaking waves on shore or will they die out without wind?
|
[
"I think to answer this question simply, you would have to paint an ideal scenario. The atmosphere is completely still and there are no thermal gradients or ocean currents. You drop a specific car at a specific height. If someone can model this that would be great.",
"In a real scenario there is not quantitative answer since the energy of that wave will interact with a whole wave field before it reaches any land observer. I suppose with enough computing power and an exact observer time and location, it would be possible to answer this question, but not with any conventional calculation efforts. "
] |
[
"Bear in mind that waves would expand from your hypothetical car splash radially, so however much energy the car's hitting the water imparted would be spread out in ever expanding circles. So in the time the (ideally) circular wavefront had proceeded say 10 times farther out, that energy would also be spread round a circle of 10 times the circumference. So before it reached any very great distance it'd be pretty well attenuated. And this even without considering drag, heat, and other dissipating factors. "
] |
[
"I'm not an expert in fluid dynamics, but I'm just going to guess that the volume if the ocean is just way too large for a car. \nIf you think about it, tsunamis, which sometimes aren't even that big, are caused by entire plate shifts under the ocean. "
] |
[
"Will secondary light colors (CMY) reflect *all* of the primary colors (RGB) in it completely, or only some?"
] |
[
false
] |
For example, I know that if I shine red light onto a red backdrop, of the red should be reflected and colors are absorbed in the background. But if I shine a red light onto a magenta or yellow background, will of that red light be reflected and will it appear just as bright red to me as it did on the red backdrop? As in, will it have the same contrast level? In other words, will yellow pigments, for example, reflect reds and greens completely, or only a portion of the green and red light?
|
[
"In reality, the way pigments work is such that they do not absorb and reflect perfectly. ",
"If you assume that you have ideal surfaces, a yellow surface will absorb all blue light and reflect all red and green light. A magenta surface will absorb all green light, and a cyan surface absorbs all red light. "
] |
[
"Thanks. That is what i was thinking, but i couldn't find a straight answer."
] |
[
"There are two kinds of colour that our eyes see. A pure spectral line has a single wavelength, which if it isn't red green or blue will stimulate more than one cone in the retina, and our brains interpret the mixed signal and assume it is that colour. So yellow light stimulates both red and green cones, as the cones each have a spread of colours they see.",
"Mixed colours, say red and green stimulate the same cones and our brains again interpret it as yellow.",
"With coloured surfaces, if they truly only reflect one wavelength, say yellow, then the eye will see it as yellow under white light. But it will not reflect any red or green light at all.",
"Very few materials have such pure colour reflectance, but some pigments will look noticably different under sunlight or filament bulbs than they do under fluorescent lamps (which sometimes only emit a few spectral lines that mix to look white). This is why food outlets often use halogen bulbs on salad vegetables, as the food looks less fresh under fluorescent light due to the complex pigments in food."
] |
[
"The moon rotates around its own axis at the same speed as its rotation around earth, which is why we don't see the \"dark side\". Is this purely coincidental or not?"
] |
[
false
] |
I'm sure there's a logical explanation I'm not seeing, or is my interpretationof "dark side wrong? (Thank you all for your many responses!)
|
[
"Before answering your question, I'd just like to point out that there is no permanently dark side of the moon. There is a far side of the moon, which never faces the earth, ",
"but it experiences a normal cycle of sunlight as the moon goes around.",
" During a full moon (as observed by humans), the far side of the moon is unlit. During a new moon, when the moon is between the earth and the sun, the far side is fully lit but unobservable from the earth.",
"As for your question, the moon's orbital period and rotational period are the same because tidal forces between orbiting bodies tend to make these numbers the same. Tidal forces slightly deform the earth and moon in their orbits, which produce small torques on each other, which act to bring these periods together.",
"Smaller objects become tidally locked more easily, such as moons (like the earth's), or planets like Mercury which are locked in a 3/2 resonance around the sun. ",
"The moon is also acting to slow the earth's rotation, moving farther out in its orbit in the process. Eventually, many many billions of years from now (longer than the lifetime of the sun), the earth's rotation will become fixed as well, as the same side of the earth will always face the moon, as they all orbit and rotate at the same rate. Because the earth is so massive compared to the moon this will take a long time, but there are examples of this in the solar system- the Pluto-Charon system is 'doubly' tidally locked. ",
"So it's not just a coincidence, it's downright common!"
] |
[
"Thank you for taking the time to reply! Fascinating!"
] |
[
"As has been answered, it's not a coincidence. What is a coincidence is the fact that the sun is 400x the size of the moon, but also 400x as far away from the Earth as the moon, making the sun and moon appear to be approximately the same size in the sky."
] |
[
"Why do vaccines use mRNA? Why not just put the viral protein into the lipid nanoparticles instead?"
] |
[
false
] |
In the case of mRNA COVID vaccines, my understanding is they work by shutting mRNA into cells using lipid nanoparticles. Ribosomes then turn those mRNA instructions into a spike protein. Why don't vaccines just put the spike protein into the lipid nanoparticles instead? Wouldn't that trigger the same immune response? Why go to the extra trouble to get our own cells to synthesize the protein?
|
[
"In the process of translation within cells, where mRNA is translated into polypeptide chains (proteins), many copies of each protein are made simultaneously from a single copy of an mRNA. So, while a nanoparticle with a hundred copies of a protein would introduce just a hundred copies of that protein proteins, a nanoparticle with a hundred copies of an mRNA could produce many thousands of copies of the same protein. ",
"Also, although mRNA can be less stable in general than protein, mRNA doesn’t require any special folding or special cellular context for production, so mRNA is usually vastly easier and cheaper to make in a lab."
] |
[
"If you use mRNA, each molecule of mRNA will be translated by the cell to many copies of the protein, so you get an amplification effect. The mRNA also gets recognized by pattern-recognition receptors that activate the innate immune system, which is necessary to start up the adaptive immune system. Protein in itself does not have that effect, so such vaccines would require addition of a separate substance (called an adjuvant).",
"But perhaps the biggest reason is that designing, or re-designing, the vaccine is extremely quick with mRNA. You can literally design a whole new vaccine within a week or two. Protein or subunit vaccines are slower to develop."
] |
[
"Vaccines that use protein exist. For COVID-19 that’s Nuvaxovid. It’s a perfectly workable solution. But mRNA offers certain benefits, two of which are:",
"First is manufacturability. To mass produce very pure protein is hard. It is typically done by transfecting some cells with DNA of the protein to produce, then have these cells churn out the protein. However, the protein is not the only thing that’s made. So there is a need to purify the output from the cells. That’s laborious. There are many methods for this, and many cancer drugs nowadays are proteins produced like this. But when you want both volume and speed (as we want in a global pandemic), protein manufacturing is at a disadvantage against RNA, which is easier to synthesize in pure form. So speed of testing and ease of production means mRNA is very competitive when those features are highly beneficial.",
"Second, there is another complication that protein shape depends on context. For example, a certain protein subunit of HIV (gp120) was tested as a vaccine, but proved useless. The reason most likely is that gp120 by itself has a slightly different 3D shape than gp120 when part of the virus. So antibodies against the isolated protein failed to work against HIV. The nice thing with mRNA or DNA vaccines is that the protein that is expressed by the cell is within the human cell context, like presented on the lipid cell surface. If that’s a factor in COVID I don’t know, but as a general matter it could be useful to efficacy, though of course it might not be.",
"It’s worth noting that mRNA may be tougher to store and transport than more traditional forms of vaccine. It’s also a new form of vaccine so a more cautious person may rationally avoid it. So protein based vaccines are not to be disregarded."
] |
[
"At some point in the past, was the cosmic background radiation red shifted into the visible light spectrum?"
] |
[
false
] |
If we hypothetically existed during this time, would the entire universe illuminate a certain color? Blue first then very slowly becoming redder and redder until it was no longer in the visible light spectrum? Would the light be blindingly bright? Also I understand that the change from the blue side of the spectrum to red side would not occur during the lifetime of a human.
|
[
"The CMBR originates from the recombination era - a time around 380,000 years after the Big Bang. At this time, it had a temperature of around 2600 degC, so the light would be roughly similar in colour to that from a tungsten filament light bulb. It looks bright yellow, though well over half of the radiation spectrum is already in the infrared.",
"It wouldn't quite be as bright or as hot as being on the surface of the Sun, but the effect on a human would be basically the same: you'd be instantly vaporised.",
"The radiation is redshifted as the Universe expands, in exactly the way that a hot object cools: from yellow to orange to red. In a darkened room, the human eye can make out the red glow of an object down to 400 degC. The radiation would have cooled to this temperature about three million years after recombination.",
"From that point on, you can think of space as being dark."
] |
[
"It is thermal radiation, so it would never have been green. It would have changed in colour in exactly the same way as a hot glowing object changes as it cools."
] |
[
"\"green\" is a pretty narrow range of wavelengths. A star's emission can peak in green wavelengths (in fact, the Sun does), but blackbody radiation is a broader spectrum than what we see as \"green\", and our definition of colors is defined over so narrow a space that a star that peaks in green wavelengths just looks white, containing roughly equal parts blue, green, and red light. A blackbody spectrum peaked at green is close to flat over the range of visible light. ",
"I've heard astronomers argue over the color of the sun in part because of this. Some say white, some yellow, etc. I maintain that it's yellow because that's canon in the Superman universe. It all comes down to what your exact definition of each color is. The best description of the color of the Sun is that it's ",
"this",
" color. "
] |
[
"What's the distance between atoms in a solid?"
] |
[
false
] |
Just wondering how close together atoms are together in a solid item or molecule. I know that electrons are far from the nucleus but say i have two atoms next to each other, are the nuclei seperated by the electrons or are the electrons just kind of interlocked and the nuclei next to eachother?
|
[
"Atoms are surrounded by electrons, yes, but only the outermost electrons participate in bonding.",
"Therefore yes, there is a \"wall\" of electrons between the nuclei of two atoms that are close to each other. (Meaning every electron that DOES NOT participate in bonding is still \"AROUND\" the individual atoms.)",
"Most bond lengths (the distance between adjacent nuclei) are on the order of 100-250 picometers. (10",
" meters) The radius of the nucleus of an atom is about 1-10 femptometers (10",
" meters).",
"So if the question you are asking is \"how far apart are the electron clouds\" the answer is 0 because they literally overlap.",
"If you're asking how far apart the NUCLEI are, the answer is 100-250 picometers. ",
"It's worth noting that while you may THINK the nuclei make the \"solid\" part of matter, that really isn't true. Things appear and feel solid to us because of electron-electron repulsion. It's the electrons that make things \"solid.\" The electrons in the atoms of our fingers don't want to get close to the electrons in the table that we're touching, so there is a \"force\" created there that pushes back when they get close."
] |
[
"This isn't a question that can be answered directly like \"atoms are 1 Angstrom apart\" because atoms are not balls. You can talk about the density or the average center to center distance for an atom, but in a solid, there is no empty space between the atoms. They are in contact.",
"Rather than trying to retype it all, ",
"Professor Philip Moriarty has a 12 minuet video all about this in \"Do Atoms Touch\""
] |
[
"They are in contact, but we can give distances between their centers which is physically meaningful."
] |
[
"Is turning old paper into mulch and spreading it around trees better or worse than sending it to be recycled?"
] |
[
false
] |
In villages the people take old paper, put it in a bucket and leave it outside on rainy days. When it rains the paper turns into mulch. The villagers then take that and spread it around trees, mixing it with the dead leaf mulch. They believe it helps the compost, and judging from the quality of the trees and fruit they bear i can't say it has any visible negative effects. Is such a treatment better or worse than giving them away for recycling? I heard that unlike aluminum, where it's actually very profitable to recycle it, and glass, where it's marginally profitable, paper actually requires more energy to be properly recycled. Is that true?
|
[
"There is absolutely no bleach in paper after production is finished. Additionally, paper does not use chlorine bleach(which, by the way, is harmless after the reaction completes - saying bleach is bad because it contains Chlorine is like saying salt is bad because it contains Chlorine) they use hydrogen peroxide to bleach the pulp. "
] |
[
"Not a direct answer to your question, but this mulching not be good practice as ",
"a whole load of chemicals",
" are used in the process of making the paper. Whether these will get into anything that you subsequently grow in the soil and eat and whether they are harmful to health I do not know."
] |
[
"Newspapers use very safe inks (soybean oil and carbon black) and can be ",
"safely composted",
". This is potentially even a good idea because compost tends to run nitrogen-heavy and carbon-poor without sawdust or paper or something.",
"The brightly-colored latex-rich glossy advertisements once contained lead, chromium, PCBs and cadmium in the inks. This was supposed to be phased out many years ago, at least in the United States. "
] |
[
"Do black holes ever die?"
] |
[
false
] |
And if so, why and how?
|
[
"Ok. I'm seeing a lot of answers that are just missing the point so I'll say this straight.",
"Yes, Black Holes and Hawking Radiation are both Hypothetical. But per those hypotheses...",
"A black hole while being a region of the universe that no \"thing\" can escape from, Emits radiation on it's own at a temperature that is lower the larger the black hole gets (for stellar mass black holes, the predicted temperature is much lower than that of the cosmic background, so are unobservable). So , when black holes stop accreting matter and light, they slowly lose mass to hawking radiation, slowly increasing the mass loss rate as the size shrinks.",
"Thus a black hole will evaporate in a finite amount of time. This time is much longer than the age of the universe for astronomical black holes (stellar mass and larger), but for smaller ones that (which we have even less proof for) would emit a measurable amount of radiation.",
"This",
" should get you up to speed on black holes (except for the hawking radiation bits)"
] |
[
"It's not total mass but density that determines if there is a region in which gravity is so great light cannot escape. In theory you can make microscopic black holes, but they would evaporate very quickly. There was [a silly debunked fringe] concern that firing up the LHC would create a black hole that instead of evaporating quickly would swallow mass and begin to feed until it swallowed the planet.",
"EDIT: language on LHC statement."
] |
[
"It's not total mass but density that determines if there is a region in which gravity is so great light cannot escape. In theory you can make microscopic black holes, but they would evaporate very quickly. There was [a silly debunked fringe] concern that firing up the LHC would create a black hole that instead of evaporating quickly would swallow mass and begin to feed until it swallowed the planet.",
"EDIT: language on LHC statement."
] |
[
"Can life develop without a nearby star as an energy source?"
] |
[
false
] | null |
[
"I think this is only one answer, but the habitable zone doesn't necessarily have to be based within that very specific area around a star.",
"For example, there are geological processes that can create heat, or energy that life could develop with. Europa, a moon of Jupiter, has this going on as it is pulled against Jupiter and other moons. (I think, I'm not an expert I just watch a lot of shows about the Universe)"
] |
[
"This is just a creative, theoretical idea I read about.",
"A couple of scientists at ",
"Fermilab",
", Dan Hooper and Jason Steffen, calculated that \"the dark matter that lies at the heart of the galaxy could heat an alien world enough to make it habitable.\"",
"There was an article about it in NewScientist (4/9-4/15 2011) - ",
"\" that states: \"While WIMPs (weakly interacting massive particles) tend to pass through planets, they will occasionally slam into atoms, losing energy and speed. If they lose enough energy, they could become trapped by the planet's gravity and settle in its core, where they are likely to hit other trapped dark matter particles and annihilate.\" (Dark matter is believed to be made of WIMPs)",
"(From article) It is estimated that the amount of dark matter that lies inside the earth would produce ~1 megawatt. We absorb approximately 100 billion megawatts from the sun, so you can see a planet would need to be much closer to the center of our galaxy (about 26,000 light years closer) or another area where the concentration of dark matter is much more dense in order for it to be heated enough.",
"It's important to state that there is much less known about dark matter than known, so hypotheses based around it may (are likely to) become more or less true as science becomes more confident with its characteristics. Nonetheless, the concept that life could develop, somehow, on these potentially heated, starless planets, even trillions of years from now, is kind of awesome."
] |
[
"Dorian Abbot and Eric Switzer say they've calculated that rocky planets with a mass similar to that of Earth could stay warm enough to keep water liquid under thick, insulating ice sheets for more than a billion years.",
"Link"
] |
[
"How does scientist know the molecular structures of chemical compounds?"
] |
[
false
] | null |
[
"There are a lot of different analysis methods which give you information about a molecule, the most important ones are:",
"Mass spectronomy",
" gives you information about the mass of a molecule and possible even the exact number of different atoms",
"Elemental analysis",
": gives you information about the ratio of certain atoms in your molecule",
"Infrared spectroscopy",
": gives you information about certain structures in your compound",
"Nuclear magnetic resonance",
": gives you information about the \"neighbourhood\" of atoms, with that information you can build up fragments and figure out how they are connected",
"X-ray crystallography",
": the best method but only works on crystals. Gives you the actual structure.",
"Most of the time it's a combination of many of these methods and also important to add is that you need pure material for some, purification is done usually by ",
"chromatography",
", distillation or crystallization.",
"Also: sometimes you cannot analyse the excact molecule so you have to do ",
"derivatization",
", so you do a transformation and look at the product and then you can determine how the moelcule looked like.",
"And a last point: in most cases it's very difficult to determine the structures if you have ",
"enantiomers",
" (molecuels which act like mirror images to each other) since most techniques cannot differentiate between these two",
"Edit: mixed up X-ray techniques, thanks to CrambleSquash for the hint"
] |
[
"^ this is the correct answer. Structure determination almost always involves multiple complimentary techniques, and a good chemist will know (or at least appreciate) them all. "
] |
[
"I think you mean X-ray Crystalography? Though I might be wrong, but that matches your desciption better than the link.",
"X-ray crystalography works using diffraction - when light goes through a gap of a similar width to its wavelength, it will spread out, like a knew source of light... the end effect is, if you have multiple slits, you get strange interferance patterns ",
"http://en.wikipedia.org/wiki/Diffraction#Single-slit_diffraction",
". In a material, if you can get the wavelength of the light to be similar to the gap beween atoms then the light will diffract as it travels through it. This diffraction follows strict mathematical laws, which means if you look at the diffraction pattern you get when you fire x-rays through a material, its structure can be determined. This is very easy to do with crystaline materials like metals and diamond, but for molecules you can't just put your solution into the machine. Instead you have to grow a crystal of your molecule, which is possibly easier said than done, though is possible!"
] |
[
"Can you measure mass without acceleration?"
] |
[
false
] |
A kilogram is a measure of mass. On earth we weigh it with a scale, and in space we might try to accelerate an object and see how much force it takes. If for whatever reason we couldn't accelerate it, is there a way to measure it's mass? Also, now that I think about it, does this mean a person would technically be however many kilograms on earth or Mars, because if the definition?
|
[
"It's an interesting question, I think you cannot directly measure mass without somehow using acceleration (even indirectly), as mass is a \"measure of inertia\" so to speak, and you can only measure inertia accelerating the object. (EDIT: I was thinking Newtonianly only!!)",
"If you know some properties of the material though, you could indirectly get the mass from there.",
"For example, knowing the density, you could get the mass by measuring volume.",
"Knowing the specific heat you could measure the change of temperature after applying a known amount of energy.",
"Edit: oh, here's one theoretical, cheating and not actually practical way (I think): if you cannot accelerate the object, but you can use something else's acceleration, you could place other known mass object nearby and measure the acceleration of the other object towards the one you want to measure, then calculate the mass. This is however using acceleration.",
"One other theoretical way (speculating here) would be to measure the deflection of a light beam passing close to the object, calculating its mass from the space-time curve it caused."
] |
[
"1) take a large amount of antimatter, place it in a box ",
"2) ",
" place the object of unknown mass in the box (safety goggles are a must!)",
"3) examine the damage done to the solar system, use this to extrapolate the amount of energy released",
"4) simply convert that energy to mass using e=mc"
] |
[
"force=mass*velocity",
"No. Force=mass x acceleration. Mass x velocity is momentum.",
"This may have been a careless mistake, but in case it wasn't I felt the need to point it out. "
] |
[
"Why do toxicology tests take so long?"
] |
[
false
] |
I hear it in news stories constantly. People who have killed themselves, violent offenders like the Miami face eater, et cetera. The toxicology report will take two weeks, three weeks, four weeks. Is it a matter of the lab being backed up with tests, or is their an actual test that takes weeks to conduct? I always thought drug tests were just an analysis of the emission spectrums of whatever drug they are looking for.
|
[
"Imnunoassay development scientist here. One correction, immunoassays do not test for antibodies in the blood against toxins or drugs, they use antibodies in the assay to bind the molecule of interest itself. ",
"Think of it this way, testing for antibodies to a substance suspected of causing death in a person is pointless, because antibodies take weeks to develop, and persist for years, so are useless to determine if a person overdosed today."
] |
[
"Cool, never thought I'd come across an immunoassay developer. What types (as in RIA/EMIT/CLIA/etc) do you develop? Or do you primarily develop the antibodies? Oh, and I've wondered why it seems like surface plasmon resonance has less adoption in clinical labs than I'd otherwise expect- it seems like it would be simpler, being label free, no? Or am I missing some huge problem? Thanks!"
] |
[
"In addition, it is not likely that a single lab could test for all of these chemicals because doing such would require an enormous facility with a large number of different machines and specialized technicians. Thus it's easier for there to be numerous specialized labs that may be required for testing.",
"This is not so much the problem as obtaining samples that maintain accuracy and are not destroyed via testing is. Because of the sheer volume of metabolites, we need different draw tubes for a lot of different tests, and even then, the blood volume we use to test is typically good for a specific number of analyses, as we quite often employ destructive testing. This means multiple samples of multiple types, which exponentially increases what must be analyzed."
] |
[
"What's the estimated amount of time for distant galaxies to start disappearing due to the expansion of the universe?"
] |
[
false
] |
And would this be definitive proof of an unavoidable "big rip"?
|
[
"100 billion years"
] |
[
"For about the next 2.7 billion years, more and more galaxies will become visible as the light from them reaches us. After that, it will all start to slowly go dark as everything else is too far away for the light to EVER reach us, and the visible universes red shift into obscurity.",
"edit: said universes when I mean galaxies"
] |
[
"more and more universes will become visible ",
"I would love to see a source for this one."
] |
[
"AskScience AMA Series: We are working to build precise atomic clocks that could fit inside your smartphone. Ask Us Anything!"
] |
[
false
] |
Atomic clocks are among the most precise scientific instruments ever made, and play an important role in advanced navigation, secure communication, and radar technology. Kyriakos Porfyrakis and Edward Laird of the University of Oxford are working on building a hyperprecise atomic clock that could fit on a chip inside a smartphone. They begin with a nitrogen atom, which resonates at a particular frequency and acts as a very precise reference point by which to track time. Since nitrogen is highly reactive, they have to trap the nitrogen atom inside of an endohedral fullerene-a sort of atomic cage made out of 60 carbon atoms-in their lab. To do it, they used a process called ion implantation. This process produces a molecule called N@C_60 that can easily be collected and stored (they even sell it for £200 million per gram). But before they could put the molecule in a clock, they also had to figure out how to cancel out magnetic fields from the surrounding environment that could disrupt the energy level of the nitrogen atom within. Earlier this year, they developed a way to shield the nitrogen atom from external magnetic fields by applying a steady magnetic field that would cancel out any effects. They recently wrote about their work for IEEE Spectrum ( ). They'll be here starting 12 PM ET (17 UT). You can ask them about GPS, atomic clocks, nanomaterials, or anything else!
|
[
"The main advantage of timekeeping technology for smartphones is that any stable clock is also a precise frequency reference. In smartphones, the advantages are mainly for radio communication and for navigation via the global positioning system (GPS).\nImagine that your smartphone is trying to download a document over airport wifi at the same time as thousands of other people. To prevent the signals interfering, it has to keep precisely tuned to the frequency of the transmitter. Present-day smartphones have quartz crystal clocks to provide the reference frequency they need. A more accurate clock could let more phones use the same network, and keep track of weaker signals.\nFor GPS, all the users are downloading the same signal, so the problem is different. The challenge here is that the signal is extremely weak - roughly equivalent to one light bulb illuminating an entire continent. A stable clock lets the user look for this tiny signal in the narrowest possible frequency range, where it is most likely to be found."
] |
[
"Why? What benefit would this serve my phone?"
] |
[
"isn't it easier to just sync smartphones to a single atomic clock for daily reference?"
] |
[
"What makes Cancer so difficult to find a cure for? How far have we gotten and how far have we yet to go to find one?"
] |
[
false
] |
[deleted]
|
[
"Cancer by itself is a misleading term. It is not a single disease, but rather a group of diseases resulting from the consequence of a derangement of the cell cycle. In a normal cell there are phases of growth, each tightly regulated by biochemical feedback mechanisms. When that regulation breaks down and the growth and division of a cell is unregulated, cancer develops. ",
"The ways the cell cycle is regulated are many and some systems are redundant. Some cancers develop from a loss-of-function mutation of a regulatory gene/protein, while some cancers develop from a gain-of-function mutation in a growth promoting gene/protein. ",
"Additionally, using cancer as a blanket term is not accurate because the type of primary tissue also affects the characteristics of the cancer. Lung cancer behaves differently from lymphoma, and from pancreatic, and from renal, and from colon etc. Even within a specific tissue type, there are different types of cancers. Lung cancer can be small cell, large cell, adenocarcinoma, squamous cell, or even mixed. Each type of each tissue has certain biochemical characteristics which may be useful as a target for therapy, however not all lung adenocarcinomas (for example) will have the same abnormalities. ",
"Finally, we have the difficulty of treatment. Cancer therapies are aimed at walking the fine line between killing the exceptionally hardy cancer cells while not killing the patient. A cure for cancer isn't a cure if it kills the patient too. Therapies are varied, and targeted to the specific cancer's characteristics. Some modalities are hormonal, such as in hormone receptor positive breast cancer; some modalities disrupt cell division, such as in the rapidly dividing small cell lung cancer; some modalities are immunological, such as in emerging therapies for leukemia and lymphoma. Sometimes, if caught early, the cancer is just resected surgically. ",
"Modern practice is aimed at best practice for prevention. Colonoscopy for colon cancer screening has showed great progress in reducing colon cancer deaths, recent guidelines have recommended chest CT in certain smoking populations for early detection of lung cancer. Yearly mammograms are controversial in regards to breast cancer screening, but I still personally believe they are worthwhile. Pap smears and the HPV vaccine also are starting to have an effect on cervical cancer rates. Again, it all comes down to the specific type of cancer.",
"Some cancers cause symptoms so late in the disease that its often too late once they're found (pancreatic). Some cancers are so indolent that even with early screening and detection it doesn't make much difference when you find them (prostate). Context is everything.",
"I know this probably isn't the answer you were looking for, but it's important to define your terms. A 'cure for cancer' is a statement that doesn't make much sense in a medical or scientific context. What we can do is try to find more effective and tolerable therapies for cancer types, and to work to determine what sort of screening methods give us the most bang for our buck, both medically and economically. "
] |
[
"To add on to baloo's very thorough answer, this is why whenever you hear someone talk about a conspiracy to hide a \"cure for cancer\" or some such thing, you can know they have no idea what they're talking about. There can be no single treatment that can cure all forms of cancer, since cancer isn't a single thing that can be treated a particular way."
] |
[
"People have explained why it's hard to find a cure for \"cancer\". What seems to be poorly appreciated is how much improvement there has been in the past 30-40 years. ",
"Treatment of childhood cancers in particular has improved enormously. Cancers that were nearly death sentences 40 years ago are often nearly 100% curable now, and there's been improvement across the board.. ",
"Over the past 50 years, great strides have been made in diagnosis, treatment, and survival of childhood cancer. In the 1960s the probability of survival for a child with cancer was less than 25%, whereas today it may exceed 80%. ",
"--",
"Pediatric Cancers in the New Millennium: Dramatic Progress, New Challenges",
"For cancers of adults, the differences are not as dramatic, but the trends are still much better than many seem to realize. ",
"Age-specific cancer mortality rates have been steadily declining in the United States since the early 1950s, beginning with children and young adults and now including all age groups. During the second half of the 20th century, each successive decade of births from 1925 to 1995 experienced a lower risk of cancer death than its predecessor at virtually every age for which such a comparison can be made. A major decline in cancer mortality has been occurring in the United States for the past 50 years, affecting birth cohorts born as long as 80 years ago. Excepting lung cancer, much of this decline has occurred despite relatively stable cancer incidence. These findings suggest that improvements in cancer detection, treatment, and/or prevention have reduced the risk of cancer death across the life span for individuals born in the last three quarters of the 20th century.",
"--",
"The Decline in U.S. Cancer Mortality in People Born since 1925",
"From 1989 to 2015, breast cancer death rates decreased by 39%, which translates to 322,600 averted breast cancer deaths in the United States. During 2006 to 2015, death rates decreased in all racial/ethnic groups, including AI/ANs.",
"--",
"Breast cancer statistics, 2017, racial disparity in mortality by state"
] |
[
"If you could get to the centre of a black hole, would you just freeze in time?"
] |
[
false
] |
Or do you exit out of a white hole or something?
|
[
"Here",
" is RobotRollCall's comment on that topic which you might enjoy reading.",
"Also, BH questions come up fairly regularly here, so there is a wealth of knowledge on the topic in the ",
"/r/AskScience",
" ",
"search archive",
". "
] |
[
"you hit the surface and were pancaked into a roughly \"you\" shaped smear",
"Years of cartoons have allowed me to picture that image perfectly."
] |
[
"Very informative post from someone obviously much more informed than I am. And also eloquent. thank you kindly!"
] |
[
"Is the idea that women synchronise their periods a myth?"
] |
[
false
] |
I was having a conversation with a couple of girl friends yesterday who were saying how when they go back home they often synch their periods to their family members, I have always assumed that this phenomenon is a myth because I cannot think of a single productive reason why it would happen. Is there any science behind it?
|
[
"There is conflicting evidence. McClintock was a psychologist back in the 60's and 70's. She did a study back then which suggested synchronization but subsequent studies with lesbian couples conflict with her findings. As for the science behind it, I'd assume pheromones. "
] |
[
"Just to clarify - the last \"famous\" McClintock study related to this was in 1998 - wherein she exposed participants to swabs from the secretions (underarm if I recall) of other women over several weeks.",
"According to the study, \"It is likely that menstrual synchrony is part of a larger phenomenon of social influence on human ovulatory cycles similar to the chemosensory influences of female mouse reproductive physiology and behaviour\""
] |
[
"Do Women Who Live Together Menstruate Together?",
" (Scientific American)",
"McClintock is still actively researching the area. The most important questions, she says, are exploring the underlying mechanisms behind variation in the social effects on ovulation: Why do some women not respond? Why are some phases of the menstrual cycle more sensitive to external stimuli?",
"\"I completely agree with Jeff [Schank]. There are no perfectly lock-phased cycles that are sustained over 20 cycles; that is very rare. But given what I know about the causes of menstrual synchrony means I expect it to be rare,\" she says. \"So the fact that it is rare doesn't mean that it doesn't exist.\"",
"But until the relevant pheromones and their biochemical receptor pathways are better described, the current bulk of evidence suggests that popular notions of menstrual synchrony are more college town myth than dorm room reality."
] |
[
"If light is photons, what happens to a photon after it's spent its energy?"
] |
[
false
] |
Not sure if I'm understanding this correctly, here goes. When a candle shines in a dark room, we see a halo of light, surrounded by darkness. The photons that leave the candle are traveling outward from it in all directions, as far as I understand. What actually happens to the photon when it travels from its 'lit' state to its 'dark' state? Does it just disappear? Does it become something different? Thanks for any input!
|
[
"It sounds like the energy changes its label.. ",
"I like the way you put it. ",
"what does it become if no longer a photon? ",
"It stops existing. Just like the flame of the candle stops being a flame when someone blows it out. ",
"In some sense, the photon is a representation of an interaction, rather than merely a thing unto itself. And that interaction has ceased. "
] |
[
"Yes, it disappears. Its energy continues to exist, but the photon is gone. "
] |
[
"Imagine throwing a ball straight upwards. The ball slows down, and at one instance actually stops. Where did the kinetic energy go? It became gravitational potential.",
"Same thing with photons. When it is absorbed by an electron (for example), the electron gains energy."
] |
[
"Why did scientists like Slotin and Daghlian do their criticality experiments manually?"
] |
[
false
] |
I was reading about the , and I was wondering why the two scientists involved ever attempted to do their experiments manually? Maybe I'm just being a wimp, but I would think of anyone on the planet, Slotin and Daghlian would know best how dangerous that was. I understand that a remote system for doing these experiments was built after the second incident. Is there a reason this wasn't developed and used earlier?
|
[
"From what I read, during the war, time was the problem. They didn't have time to engineer a remote automated system to do it. By the time of Slotin's accident, May 21, 1946, there was no reason to do it manually. The war was over almost a year and the cold war had not yet begun. They said Slotin was just a daredevil, and liked showing off doing that.",
"https://en.wikipedia.org/wiki/Demon_core",
"Under Slotin's unapproved protocol, the only thing preventing this was the blade of a standard straight screwdriver, manipulated by the scientist's other hand. Slotin, who was given to bravado, became the local expert, performing the test on almost a dozen occasions, often in his trademark blue jeans and cowboy boots, in front of a roomful of observers. Enrico Fermi reportedly told Slotin and others they would be \"dead within a year\" if they continued performing it.[12] Scientists referred to this flirting with the possibility of a nuclear chain reaction as \"tickling the dragon's tail\", based on a remark by physicist Richard Feynman, who compared the experiments to \"tickling the tail of a sleeping dragon\".[13][14]",
"Daghlian's accident was just as the war ended. So time would have forced the tricky manual test. They were getting ready for a third bomb for Japan.",
"The next bomb of the implosion type had been scheduled to be ready for delivery on the target on the first good weather after August 24th, 1945. We have gained 4 days in manufacture and expect to ship the final components from New Mexico on August 12th or 13th. Providing there are no unforeseen difficulties in manufacture, in transportation to the theatre or after arrival in the theatre, the bomb should be ready for delivery on the first suitable weather after August 17th or 18th.[3]",
"Marshall added an annotation, \"It is not to be released on Japan without express authority from the President\", as President Harry S. Truman was waiting to see the effects of the first two attacks.[3] On August 13, the third bomb was scheduled. It was anticipated that it would be ready by August 16 to be dropped on August 19.[3] This was pre-empted by Japan's surrender on August 15, 1945, while preparations were still being made for it to be couriered to Kirtland Field. The third core remained at Los Alamos.[5]",
"On August 21, 1945, the plutonium core produced a burst of neutron radiation that led to physicist Harry Daghlian's death. Daghlian made a mistake while performing neutron reflector experiments on the core. He was working alone; a security guard, Private Robert J. Hemmerly, was seated at a desk 10 to 12 feet (3 to 4 m) away.[8] The core was placed within a stack of neutron-reflective tungsten carbide bricks and the addition of each brick moved the assembly closer to criticality. While attempting to stack another brick around the assembly, Daghlian accidentally dropped it onto the core and thereby caused the core to go well into supercriticality, a self-sustaining critical chain reaction. He quickly moved the brick off the assembly, but received a fatal dose of radiation. He died 25 days later from acute radiation poisoning.[9]"
] |
[
"The surrender of Japan was significantly more drawn out than the surrender of Germany.",
"The Japanese broadcast their surrender on the 15th but intermittent conflict occurred for several days afterwards. The last American serviceman to die in action was killed on the 18th. American troops would not land in Japan until the 28th."
] |
[
"You might find this serie of articles interesting too:\n",
"http://blogs.sciencemag.org/pipeline/?s=things+I+won%27t+work+with",
"this has many example of chemists taking unnecessary risks, as well as a long long list of terrifying experimental setups. Some people just seem prone to risk taking, even when they should know better."
] |
[
"If angiosperms (flower bearing plants) are so much more efficient than gymnosperms (non-flower bearing plants) at long distance dispersal and sexual reproduction, how come gymnosperms still exist everywhere?"
] |
[
false
] | null |
[
"to build on ",
"u/juandh",
"'s comment, you might take the analogy:",
"If priuses are more gas-efficient than other cars, why doesn't everyone drive a prius?",
"A pretty crude way to phrase the question, but it does give you insight into the same phenomenon. Efficiency certainly won't eliminate those that are less efficient, if there's a particular niche that they can occupy. We still have fish around that haven't changed much in 100's of millions of years, simply because they exist in a niche that hasn't changed much, and no other species has come along and out competed them.",
"A Prius won't replace a pickup truck anytime soon, regardless of how efficient it is."
] |
[
"An evolutionary disadvantage does not automatically lead to extinction. One species, genus, whatever may not be as evolutionarily fit as another, yet it may still manage to survive and even thrive.",
"There may also be certain trade-offs of a trait, meaning that no one species is dominant in every environment."
] |
[
"You also have to think of the angiosperms in the context of the ecosystem. If the fruit tree is on a cliff, who's going to eat the fruit to spread the seed? ",
"If the animals that the angiosperm requires to make the seed dispersal don't traverse the rugged cliff side, how would the seed get there in the first place? ",
"And then, do the animals that eat the fruit even want to live there? If the target pollinators aren't there, the flower won't have the chance to be pollinated in the first place, so that the fruit will never form.",
"Yes, angiosperms have advantages, but they require a more complex ecosystem to take advantage of that. So, no, the flowering plants won't necessarily dominate even after a mass extinction because they have to wait for the ecosystem to recover sufficiently to cary their seeds back and then cary on the reproductive cycle. "
] |
[
"so what if scientist figure out there was or/is life on mars?"
] |
[
false
] | null |
[
"Some things are interesting in their own right without leading on to anything else. Knowledge for the sake of knowledge.",
"However, at the moment we have only one data point for the existence of life in the universe. Life on Mars would be evidence that Earth isn't a fluke and suggest a greater chance of finding further life in the Universe.",
"There is still a chance that Life on Mars and on Earth had a common single initiation. The nature of life found on Mars would also be significant. If we can show that life arose spontaneously on at least two separate occasions that would be a huge boost for our expectation of the distribution of life through the Galaxy and beyond.",
"How the life is structured (if discernible) will also be interesting - does it use DNA? does it use the same bases and amino acids as Earth life. Does it have the same chirality as life on Earth?"
] |
[
"Treatid is correct. How the life is structured will mean so much to us. If it uses DNA then there is a good chance that it might be related to life on earth. If it happens to be the left-handed, double-stranded helix formation that our DNA is then we'd have to seriously reconsider the origins of life here on earth. We would start to consider exogenesis more closely. Would that mean that life came to earth on an asteroid? How old is life then? Where did this life originate? Did it evolve to become complex somewhere else? Is the extraterrestrial life that we search for similar to our idea of life and is it intelligent? And if life exists on Mars can we use this knowledge to help terraform Mars for any reason? Did an asteroid possibly collide with earth and send bits flying all the way to Mars along with a few ancient organisms (believe it or not it's possible)? Get the idea?"
] |
[
"ahh that is interesting. Now i am excited lol. I hope they do find something...",
"On that note, how big does an asteroid have to be, to make pieces fly from earth to mars!....Assuming for discussion purposes, lets say that did happen. Wouldn't the organism die during the travel through space??"
] |
[
"How do satellites focus on different obejects?"
] |
[
false
] |
Do they use thrusters to change/keep the view?
|
[
"If you're talking about the stereotypical spy satellite with cameras, the satellite itself usually doesn't move other than to stabilize or correct its orbit. The camera is gimbaled, allowing it to tilt and swivel. So it can track the focal point on the earth, and at the altitude it's at a simple 1° tilt can move the focus many miles on the surface of the earth.",
"TL;DR it's safer, cheaper, and smarter to just move the camera than it is to move the whole satellite."
] |
[
"Oh if you're talking about looking out from a planet that's a whole different story, but no they don't often change the orbit of satellites. See, holding a satellite in one stationary point would take an enormous amount of fuel while maintaining an orbit costs little to no fuel at all.",
"It's important to remember satellites are not outside of the Earth's gravitational pull. Rather they are far enough away and moving fast enough that they essentially fall at the same rate the earth moves out from under them. So orbiting objects need to maintain a certain amount of speed to stay in orbit. Meaning slowing down an object to hold it stationary would certainly bring it crashing back down to earth."
] |
[
"It's extremely expensive to use thrusters to \"retask\" a satellite because they have a very limited amount of fuel. It's not to say it never happens, but it would have to be something very important.",
"In general, they just try to have enough satellites whizzing around orbiting the Earth that one is likely to pass somewhere overhead of whatever it is that you want to look it, soon enough. It only takes about 90 minutes for something low orbit to completely circle the Earth, so that's less crazy than it sounds. Something in a polar orbit will be going in circles north-south over the poles, and the Earth turns under it every 24 hours. So it gets a decent look at the whole globe pretty much every day. Just not for very long, and not necessarily from a good angle."
] |
[
"Is it possible to make it all the way around the crossbar on a swing set?"
] |
[
false
] | null |
[
"on ",
"one of these",
", yes!"
] |
[
"Ah! Now the distinction here is that the arms are rigid. The rider can use them to keep herself at a constant radius. On a normal swing set, the arms are chains (usually), and will collapse at above horizontal. "
] |
[
"If you mean by having a person push or 'pumping' with your legs on a traditional (chain or rope, nonrigid) swing, no. When you get to a point close to horizontal chains, you'll notice the swing skips a bit at the peak. You come out of the seat for a second while you change direction. That skip costs you some of your precious momentum, more than you can add by pumping your legs in one swing, or by having someone push. ",
"If we are allowed to accelerate the swing some other way, you can get it all the way around.",
"If the support is rigid, you won't skip, and you can get it all the way around with just 'pumping' (and holding on while you're upside down.)"
] |
[
"Is mRNA stored in our cells? Do we have a reserve if lets say RNA polymerase II stops working?"
] |
[
false
] | null |
[
"No. The levels of a specific mRNA are tightly regulated, on the side of its synthesis as well as on the side of its degradation. There are no stores of \"excess\" mRNA, it's constantly dynamically regulated to the necessary amount."
] |
[
"Well could u help me determine the reason for why alfa-amanitin has a ”slow death”?"
] |
[
"It's not a total inhibitor. It just slows down the RNA polymerase II. See for example ",
"Rudd, 1996",
". It thus takes a while until things fully get out of whack."
] |
[
"Do Freud's teachings/ideas have any relevance anymore? If not, why are we still being taught them?"
] |
[
false
] | null |
[
"TL;DR No, it's better considered as history and not current science, and it's still taught because 1) Intro Psych professors don't like updating their courses 2) there's a legacy of psychoanalysis that's still influencing practice, especially in the APA.",
"Here's the longer story. First, we should separate Freud's ideas about development and the etiology of disorder from how disorder should be treated. I'm just going to focus on what he said about treatment because his treatment ideas are still influencing people today, while no one is seriously testing his hypotheses about the origins of personality, development or disorder.",
"First, Psychoanalysis have historically been resistant to studying their treatments empirically, as opposed to other \"schools\" of treatments. As it turns out, the very first meta-analyses showed that giving someone any treatment tends to be better than no treatment ",
"2",
" (This isn't the first, but it's a 20 year followup to the first showing basically the same thing). ",
"This is what Bruce Wampold has argued for, the \"common factors\" model, that it's more about therapist characteristics than about specific psychotherapies ",
"3",
"But there's a problem with that. It's called \"science\"! And that science has shown in hundreds of RCTs comparing specific treatments for specific disorders not just to waitlist controls but to \"treatment by experts\" or \"treatment as usual\" (which means treatment in the community\" and has established MANY superior, empirically validated treatments to the typical treatment that one might receive in the community.",
"And when you look at these lists, it is rare that any kind of psychodynamic treatment appears on the list ",
"4",
". In fact, hyponotherapy appears almost as often (2 times) as dynamic therapies do (3 times) on the list in [4]",
"Now, this may be because Psychodynamic people aren't good at getting their therapy studied. But if you want to claim that a therapy you are doing is supported by a scientific evidence, you really need to do the science. And they don't seem to be doing it. "
] |
[
"Only one of those studies in that meta-analysis you cited was an RCT, and most of their measures are pre-post measures. Entirely susceptible to regression to the mean, historical effects or any number of other problems. This is the problem with psychoanalysis, the quality of the research is shockingly poor relative to the prevalence of the method in the community."
] |
[
"I am not a scientist, but I do work in the fields of English/Philosophy/History, and can give you a perspective from the \"liberal arts\" side. I hope that I am forgiven as I do not mean to intrude upon the science sphere, but I think I have some information relevant to the OP's question.",
"Though most scientists and professional psychologist have discredited/discarded Freud, as others have pointed out, there is a peculiar fascination with him in the liberal arts. Literary Theorist still cling to him as able to answer some of the deeper questions and insights of literature. It is still very popular to do psychoanalytic/Freudian readings in literature, of using the Oedipus/Elektra complex to explain character's actions, or of studying his relationship between creative writing, \"phantasy\", and day-dreaming. As you can tell, this mostly is focused in the English/Literature departments, though a few in philosophy will discuss him as well.",
"One of the most influential reasons that Freud is still around in the Liberal Arts has to do with ",
"Lacan",
", a French philosopher/literary theorist and Freudian who reintroduced and made popular the insights of Freud in regards to philosophy, aesthetics, and literature. Though he has marked differences from Freud (his followers calling themselves Lacanians instead of Freudians), he draws upon Freud to make some major analyses, though at times he misrepresented or obfuscated his views. Nevertheless, the post-modern \"hype machine\" has meant that Freud is now more taught in English classrooms than in Psychology classrooms.",
"As an aside, I am neither a Freudian nor do I really understand ",
" there is such a fascination with him. I would love to see a response from somebody who maybe has the answer as to how science could discredit a large part of his theories while the liberal arts embrace them."
] |
[
"What are the units after integrating dx/x?"
] |
[
false
] |
Hello all, An interesting issue came up: I have the following differential equation: dF/dm == F/(k T) Now F has units J/cm m has units J, and k T has units of J, so the original problem satisfies dimensional analysis. But what about when you integrate? You get ln(F) = m/(k T), but that is dimensionally inconsistent! Where did the units inside the log go? If it's something like ln(F)+C then does any C work or is it arbitrary? and if C is arbitrary, then what's the significance of the equation? I feel like I'm missing something fundamental about the calculus...
|
[
"Taking a dimensionless number to the power of something with dimension is non-sensical.",
"Taking ",
" quantity to the power of a dimensioned quantity is non-sensical."
] |
[
"What you're missing here is that dF has the same dimensions as F. In other words, the differential of a quantity has the same dimensions as the quantity itself.",
"Think of this in terms of length ",
". ",
" is just a difference between two lengths, x(n+delta)-x(n), so it still has dimensions of length.",
"With that in mind, hopefully it should be clear that the integral of (dF/F) is actually dimensionless. ",
"Also, aside from the basic dimensional analysis in calculus, it's worth noting that a logarithm of something has to yield something dimensionless. Recall the definition x=log(y) is equivalent to y=e",
" . e is clearly a dimensionless number. Taking a dimensionless number to the power of something with dimension is non-sensical. ",
"This stackexchange answer explains why pretty well, I think."
] |
[
"Right. I agree with everything you've said.",
"But, in wolfram language: Int[F",
" F] evaluates to Log[F]. If F has units of, say, J/cm",
" then the integral is indeed dimensionless, but evaluates to something that is the log of a dimensioned quantity. The problem here isn't that Log[F] needs dimensions. It's that F has dimensions.",
"The resolution is something like log[F]+C as being the resolution such that if C represents then -Log[<thing with same units as F>], one obtains a dimensionless solution.",
"I think what I've forgotten is that you need an initial or boundary condition in differential equations such that the parameter space of this C variable reduces to a point. I guess I answered my own question... Bah."
] |
[
"If earth's mountains are formed by shifting tectonic plates, are mountains on Mars formed by the same process?"
] |
[
false
] | null |
[
"Here's a great video from a NASA employee",
" that outlines the various processes that form mountains on Mars. In short, no, there is no evidence for plate tectonics on mars. The mountains are caused by impact events, and occasionally by volcanism--which can occur without a plate tectonic system, similar to Hawaii or Yellowstone (hotspots). Like ",
"/u/Gila_Monster",
" mentioned, Olympus Mons is a huge volcano."
] |
[
"I find it really troubling An Yin says \"the evidence is quite clear\". Not that his evidence isn't important to consider, but he has no business (IMO) proclaiming it with such a degree of certainty. It just reeks of overzealous self-promotion without any acknowledgement of the complexity of the issue that others have put ",
" of work into. ",
"I have seen at least 4 or 5 theories for Valles Marineris and surrounding geomorphology on Mars. The current scientific \"consensus\" is that no theory fully explains all the geomorphology in the region. As far as I can tell, An Yin is just about the only person pushing this idea of plate tectonics strongly (EDIT: actually, thinking about it, I know of one more - although he at least accepts there is a lot of uncertainty involved).",
"It's really cool to see Yin adding this story to the debate (not that it hasn't been tried before), but all current \"evidence\" for plate tectonics on Mars can be fully explained, and explained easier, with other theories. Until something far more substantial comes along, it really shouldn't be passed around as any especially compelling evidence."
] |
[
"In short, no, there is no evidence for plate tectonics on Mars.",
"Might I draw your attention to ",
"this",
" image and ",
"this",
" article from 2012 regarding evidence for tectonic activity on ancient Mars. I'm having difficulty locating the original paper to which the article refers, but to quote An Yin, professor of Earth and Space Sciences at UCLA and the lead author of said paper: ",
"\"I saw that the idea that it is just a big crack that opened up is incorrect. It is really a plate boundary, with horizontal motion. That is kind of shocking, but the evidence is quite clear.",
"Edit: ",
"link",
" to the paper in question. "
] |
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