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Wednesday, October 30, 2019

How many molecules of a substance is required to define the physical state of that substance (solid, liquid, gas, plasma)?

How many molecules of a substance is required to define the physical state of that substance (solid, liquid, gas, plasma)?


How many molecules of a substance is required to define the physical state of that substance (solid, liquid, gas, plasma)?

Posted: 29 Oct 2019 05:47 PM PDT

Edit: Thank you, everyone! This seemingly small thought experiment has sparked a wonderful conversation and spurred my interest even more.

submitted by /u/BuditzMagee
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Can someone explain the spontaneity of time symmetry breaking in the Lukin and Monroe time crystal experiments?

Posted: 29 Oct 2019 03:35 PM PDT

As I understand it: In both experiments, there was a drive (lasers in Monroe's, microwave pulses in Lukin's) that causes a change in spin state of a system (Monroe: a chain of ytterbium ions; Lukin: defects in a diamond). In both cases, the spin states of these systems revert back to their original state. However, the drives were periodically applied, and the resulting spin state oscillation did not match the periodicity of the drive, but oscillated at 1/2 or 1/3 the frequency.

(I may have misunderstood this - I'm a biologist, not a physicist. Please correct me if so).

What I don't understand is - if the periodicity of these systems is a result of the periodicity of the drive, and not a product of the systems themselves under specific conditions, why is this spontaneous breaking of time symmetry?

submitted by /u/crashlanding87
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Why are Neutron Stars magnetic?

Posted: 30 Oct 2019 03:19 AM PDT

As the title states, why do Neutron stars not only have a magnetic field, but are some of the most magnetic objects in the universe? Given that they are comprised of mostly neutrons, which I understand to be electrically neutral, I can't see how they generate their magnetic fields. Even if say they're a slew of protons and electron in a given neutron star, combined with its rapid spin, I can feasibly see it generating a magnetic field, but the most powerful?

submitted by /u/MagicsMan
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Does the brain make a sound?

Posted: 29 Oct 2019 05:37 PM PDT

Obviously the friction in the blood vessels with the blood would make some noise, but do the neurons make any sound when firing?

submitted by /u/HawkerPublic
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How can freezing water break matter?

Posted: 29 Oct 2019 01:38 PM PDT

I'm not sure how to put it exactly so here is a simple, "ideal" scenario:

If I put a bottle of water in a room and start removing heat from the room, the water will first lose its sensible heat until it gets to 0 C.

Then, the water will give up its latent heat and start freezing. Since ice is less dense than liquid water, it will start to expend in volume as well.

But if my bottle is closed, the ice will build pressure inside it until it breaks. The ice will do "work" on the bottle.

My question is: how could the formation of ice break the bottle if the water is already giving up energy as heat? Is there a force known as "work energy of crystal formation" that would explain it? How could it be explained on an atomic level?

Thank you for considering this. I couldn't find a satisfying answer by myself.

submitted by /u/smaug88
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How do asexual organisms get the genetic variation necessary for evolution?

Posted: 29 Oct 2019 07:46 PM PDT

If asexual reproduction produces a clone or exact copy of the original cell or the parent organism, when or how do mutations happen? For example, can mutation happen in cellular fission? and if so, is it then incorrect to say that the result of fission are two or more cells identical to the original one? Thanks.

submitted by /u/Jacaranda123456
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What is an ecological niche?

Posted: 29 Oct 2019 02:10 PM PDT

If the entropic heat death of the universe happens, will the temperature of the universe be 0 °K?

Posted: 29 Oct 2019 04:44 PM PDT

Colleague and I couldn't figure this out during our lunch walk. Help us out Reddit!

submitted by /u/PaulOnPlants
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What happens to foreign particles in the human body?

Posted: 29 Oct 2019 07:41 PM PDT

What I mean here is what happens to dirt, pollen, microbes and other fine particles that presumably get stuck in our mucus or lungs when we breathe in? I would think it can't just stay because death would come fast.

submitted by /u/DAMONTHEGREAT
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How do teeth know how long they must get?

Posted: 29 Oct 2019 12:23 PM PDT

They're made from the same material as hair and nails, but they keep on growing, so why not teeth?

Reason I ask is because I just got braces and when I saw the simulation, I noticed that even my askew teeth will be the correct length after moving. How can this be?

submitted by /u/Coffeecat3
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Is there a place to find annotated transcripts, or a source explaining the audio/transcripts of things like the apollo or gemini missions?

Posted: 29 Oct 2019 05:29 PM PDT

I've been listening to the gemini audios because im super interested in this stuff and plan on majoring in aerospace engineering, but I am not at all a pilot, and being 17 years old I have nothing but self studied knowledge on the topic. I'd really like to listen to the audios and know what the heck is going on lol. Thank you for any response in advance.

(also I don't browse this sub very often I was hoping it was the right place, I also hope this was the right flair)

edit- typo

submitted by /u/Lefty517
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Does it take more energy to heat objects at higher temperatures?

Posted: 29 Oct 2019 03:01 PM PDT

For example I have a pan at 35 degrees and a pot at 70 degrees. Would it take more energy to increase the temperature of the pan from 35 to 40, than it would the pot from 70 to 75?

Basically I'm measuring changes in temperature and trying to figure out if starting at the same ambient temperature would matter or not if the ambient temperatures are fairly similar.

submitted by /u/Daruii
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How do DHT-Inhibitors like the ones seen in some hair loss treatments (Azelaic acid) affect the body's overall DHT and testosterone levels?

Posted: 29 Oct 2019 10:27 PM PDT

Is the inhibition of DHT only topical? Will it only reduce DHT in the scalp skin area? Could this have any affect on lowering athletic performance from a reduced levels of DHT?

I realize this is a very specific question, but I was not able to easily find it after searching through google. Hope somebody has an answer preferably with a solid source. Thanks!

submitted by /u/MemeLovar
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Are there problems that are more efficient using recursion?

Posted: 29 Oct 2019 03:27 PM PDT

Thanks to computerphile I know that there are certain problems like the Ackermann function which have to be computed using recursion.

However for other problems it seems like using recursion has greater complexity e.g calculating the Fibonacci sequence recursively repeats a lot of work whereas just iterating through values of n is less complex.

Are there any problems which can be solved without using recursion but recursion reduces the complexity?

submitted by /u/Quoggle
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Why do computers make a whine when powering up?

Posted: 29 Oct 2019 09:24 PM PDT

Does NASA have a way to track Rovers and Astronauts on the surface of the moon or Mars accurately?

Posted: 29 Oct 2019 02:53 PM PDT

Since GPS isn't a thing on the moon what alternative methods of tracking do we use?

submitted by /u/Izera
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Since birds are dinosaurs, are birds reptiles?

Posted: 29 Oct 2019 09:23 AM PDT

What will the continents look like in a few million years? Does anyone have a picture of what scientists think the world would look like?

Posted: 29 Oct 2019 09:38 AM PDT

How are the generic names of drugs determined? Is it based on the structure of the molecule, its effect, both, neither? Are there any hard rules?

Posted: 29 Oct 2019 11:39 AM PDT

How radioative are undetinated nuclear weponsq2?

Posted: 29 Oct 2019 12:19 PM PDT

Little boy contained 64 kg (141 lb) of enriched uranium. Supposedly(specifics are hard to find) more modern weapons use 2 to 4 kg(4.5 to 9 lbs.) of Plutonium How much radiation would that actually give off in an undetonated state? Do they put shielding in the bomb?

Edit: Apologies for the horrendous title my phone spazzed out :(

submitted by /u/Lilmriq
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How does a molecule "decide" to emit a photon?

Posted: 29 Oct 2019 09:30 PM PDT

I was reading this article about CO2 absorbing infrared radiation and it had this line in it:

The energy from the photon causes the CO2 molecule to vibrate. Some time later, the molecule gives up this extra energy by emitting another infrared photon.

I haven't really been able to find any good info on why it's "some time later" though. What causes the CO2 to eventually re-emit a photon?

submitted by /u/Dest123
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If terrestrial plants get the majority of their mass from the carbon dioxide in the air, where do aquatic plants get their mass from?

Posted: 29 Oct 2019 01:16 PM PDT

Tuesday, October 29, 2019

Proxima Centauri, the closest star to the Sun is 4.85 billion years old, the Sun is 4.6 billion years old. If the sun will die in around 5 billion years, Proxima Centauri would be already dead by then or close to it?

Proxima Centauri, the closest star to the Sun is 4.85 billion years old, the Sun is 4.6 billion years old. If the sun will die in around 5 billion years, Proxima Centauri would be already dead by then or close to it?


Proxima Centauri, the closest star to the Sun is 4.85 billion years old, the Sun is 4.6 billion years old. If the sun will die in around 5 billion years, Proxima Centauri would be already dead by then or close to it?

Posted: 28 Oct 2019 04:24 PM PDT

Can gravity set up concentration gradients in a solution?

Posted: 29 Oct 2019 08:17 AM PDT

If we take a perfectly mixed salt solution and leave it at rest indefinitely so the only mixing process is molecular diffusion, will the solution remain perfectly mixed or will the force of gravity set up a (small) vertical concentration gradient?

submitted by /u/Chlorophilia
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How are nuclear arms/weapons safely created and stored to prevent accidents related to arming and detonations?

Posted: 28 Oct 2019 09:28 AM PDT

How do we know that nuclear arms in storage silos/warehouses are 'safe' in storage? Is there a near-zero% chance for them to accidentally go off?

Thinking of every aspect of humanity and how, somewhere along the lines of bureaucracy, there's a human being slacking/messing up - doesn't that also apply for nuclear development of weapons?

While citizens can do nothing to help or prevent; are nuclear bombs and arms just 'safe' with their creation/storage methods to disallow accidents that could annihilate the world many times over?

submitted by /u/redditor080917
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Why is equipartition of energy expected in the modes of a resonant cavity? And why this should model a solid radiator?

Posted: 28 Oct 2019 06:57 PM PDT

I think the answer for this may be straightforward, but I don't see anywhere that explains this from the scratch:

A large resonant cavity with a small hole is used to approximate an ideal black body.

I understand the conditions for the modes inside the cavity. But there are two points that aren't clear to me:

1) I don't understand why it was considered that the energy should be equipartitioned between those modes. Because I don't see a reason why they couldn't be independent.

At least not if it was ideally reflecting body inside. In that case, just like in ideal vibrating stings, there could be no exchange of energy between the modes and the spectrum of the light inside it would be just like the spectrum of the light entering it.

I think the story has to do with the body not being perfectly reflecting and being in equilibrium with the modes inside the cavity. But even then: Why couldn't it just stay in equilibrium with the modes that has already being formed by the light that entered the cavity? Is the equipartition being mediated by the material portion of the cavity?

2) Why exactly does particular solution serves as a model for entirely solid radiators? Does this EM field modes exist inside opaque materials?

submitted by /u/guferr
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If trees get 95% of their mass from Carbon do Fruits and vegetables also mostly carbon?

Posted: 28 Oct 2019 02:28 PM PDT

A video from Veritasium recently stated trees get most of their mass from carbon. So do Fruits, vegetables, seeds, leaves also get most of their mass from carbon? I'm sure it's more water than the stalks/trunks.

submitted by /u/Duches5
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Why are microplastics bad, and why should I care about them?

Posted: 28 Oct 2019 05:41 PM PDT

When smartphone batteries lose some of their capacity over the years, do they take the same time to charge?

Posted: 28 Oct 2019 12:10 PM PDT

Alpha particles are released from nuclei because of how stable they are. Fe has the highest binding energy per nucleon, so why aren't Fe nuclei emitted radioactively?

Posted: 28 Oct 2019 03:15 PM PDT

That is to say, He's binding energy per nucleon is much higher than other similarly sized nuclei, making it low energy and thus energetically favorable to release alpha particles. Further, they can quantum tunnel, making it possible for their release. Why can't Fe, the most stable nucleus on a per-nucleon basis, be emitted in a manner similar to alpha decay? Is it just unlikely because it has an enormous coulomb barrier?

Binding energy per nucleon curve: http://clay6.com/mpaimg/p2.jpg

submitted by /u/OPDidntDeliver
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Was earth ever completely covered in trees?

Posted: 28 Oct 2019 02:29 PM PDT

The kid I babysit was wondering if the earth was once covered in forests; I just want to get the right answer for him. :) thanks!

submitted by /u/keepswitchingnames
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Are plastic jerrycans for diesel formulated differently than plastic jerrycans for gasoline?

Posted: 28 Oct 2019 10:43 AM PDT

Do all observers agree on the velocity of the Hubble flow at a given position?

Posted: 28 Oct 2019 05:58 PM PDT

I understand that the Milky Way is moving something like 600 km/s relative to the local Hubble flow. I suppose this means there must be some velocity at our position and time that is at rest relative to the Hubble flow. My question is: will observers moving near the speed of light agree and will distant observers agree?

More broadly: for a given position and instant, is there a velocity that is at rest relative to the Hubble flow that all observers and frames and reference can agree on?

submitted by /u/Zenodox
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Do bears look forward to hibernating?

Posted: 28 Oct 2019 08:42 AM PDT

Why do lasers have such low wall plug efficiency?

Posted: 28 Oct 2019 08:54 AM PDT

It seems that laser efficiency can range from a few percent to ~60%, but most seem to be on the lower end of the spectrum.

Where do these large inefficiencies come from, and how are lasers made more efficient?

submitted by /u/zaeran
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Are audiobooks ‘cheating’? Do we get same benefits as reading?

Posted: 28 Oct 2019 09:19 AM PDT

I always feel bad listening to an audiobook because I was taught that it was 'cheating' and that reading was far better in terms of learning vocabulary, retaining information and general learning. Is this true?

submitted by /u/Richydd
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Are there seasons along the equator?

Posted: 28 Oct 2019 03:40 PM PDT

Or does the weather remain overall consistent from month to month every year?

submitted by /u/yourgrandmasgrandma
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Does hormonal birth control stop implantation of fertilized eggs? What about the copper IUD?

Posted: 28 Oct 2019 11:47 AM PDT

I've heard an argument that birth control is "bad" (I understand this is a value judgment, not a scientific assessment) because it can prevent the implantation of a fertilized egg. However, upon researching this claim, I can't seem to find conclusive evidence one way or the other.

Some people seem to think it could happen, some people think it doesn't, and others think it needs to be researched more. A relatively recent NYT article says that hormonal birth control does not seem to prevent implantation but that a copper IUD does. Is there any update on this research? Or more scientific papers I could read about it?

Thanks!

submitted by /u/citadel72
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As permafrost melts, revealing ice age animals, is the bacteria in their bodies a danger to humans?

Posted: 28 Oct 2019 07:54 AM PDT

Or would water molecules (if any) that froze inside them destroy the genetic material making them inert? If it could be a danger, how dangerous?

submitted by /u/Aardvark_Astronaut
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What does respiratory depression mean, exactly?

Posted: 28 Oct 2019 08:26 AM PDT

I know that opioids reduce the sensitivity to CO2 in the medulla oblongata. But does respiratory depression mean that you just cannot breathe or that you ‚forget' to breathe while you're unconscious or sleeping? Because the phrenic nerve itself is not affected by opioid agonists, I think. Or am I not getting something? Thank you

submitted by /u/trashcanhanson
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Can Plants Self-Sustain Indefinitely?

Posted: 28 Oct 2019 08:03 AM PDT

I've seen a thing about a guy having a plant in a sealed vase for more than 40 years and he hasn't watered it in 40 years because it creates a self-sustaining ecosystem. Does this mean that, theoretically, in perfect conditions a plant could survive for an indefinite period of time?

submitted by /u/Classy_Maggot
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Monday, October 28, 2019

Why don't plants get sunburned or genetic damage/cancer being out in the sun all day?

Why don't plants get sunburned or genetic damage/cancer being out in the sun all day?


Why don't plants get sunburned or genetic damage/cancer being out in the sun all day?

Posted: 27 Oct 2019 05:17 PM PDT

When UV-B radiation and other solar radiation hits plants like trees or grass, why does it not cause genetic damage to the plants DNA?

submitted by /u/handouras
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How would the low thermal output of Chernobyl's reactor #4 on the night of the Chernobyl disaster have contributed to the reactor core's instability?

Posted: 27 Oct 2019 04:07 PM PDT

I am currently reading the book Midnight in Chernobyl, and I am mostly clear on the sequence of errors that led to the Chernobyl disaster. But one detail I am not clear on is why a low thermal output (200mw), in itself, would make an accident more likely. The book states that the thermal output of the reactor during the backup power test was meant to be between 700 and 1000mw, but one of the people supervising the test insisted that the reactor's thermal output be brought down to 200mw. The book speculates that this person insisted on the lower thermal output because he assumed it would be safer, and to my (layman's) mind, this seems to make sense.

As it happened, due to operator error, the thermal output of the reactor dropped to around 30mw, leading to xenon poisoning in the reactor. To bring the reactor back up to 200mw, virtually all of the control rods in the reactor were manually removed and numerous automatic failsafes were overridden. Supposing instead that the reactor was gradually brought down from its normal operating level to 200mw, could something still have gone wrong owing only to the low thermal output?

submitted by /u/BaggageClaim2007
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How violent/rapid was the separation of Pangaea?

Posted: 27 Oct 2019 01:04 PM PDT

Hi all,

I am wondering how the first few moments would have played out when Pangaea broke up.

Was there an almighty quake followed by a dramatic split? Or was it a small split of just a few centimetres that accelerated slowly?

Would there have been a point where there was literally a few centimetres separating the continents?

Thank you

submitted by /u/Bamonk
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Are fingerprint mutations (such as a random patch of dots instead of lines) common?

Posted: 27 Oct 2019 11:00 AM PDT

My left index finger has this mutation and I was curious to know if it was common or not. I can try to post pictures if anybody is interested.

E: Here's a couple pictures. Sorry for poor photo and skin quality.

submitted by /u/EyeAmWeToddDid
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Why, in layman terms, was the black body problem so important in quantum physics?

Posted: 27 Oct 2019 01:06 PM PDT

I am reading about it, but I cannot make sense out of it. Why quantization was so controversial? What was the problem really?

I know high school physics, so not so layman.

submitted by /u/RabidSpectre
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Is a great circle route really a straight line, or does your heading constantly change?

Posted: 28 Oct 2019 02:02 AM PDT

u/YMK1234 argues that a great circle is really a straight line. I am arguing that, except in the case of traveling on a meridian of longitude or on the equator, your heading constantly changes when traveling along a great circle.

From my basic understanding, a non-Euclidean mathematician might be best to answer?

submitted by /u/jbsailor_
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Can individuals with complete hearing loss "hear" via bone conduction? E.G. Shower water hitting your body, resonating bass at concerts etc.?

Posted: 28 Oct 2019 12:24 AM PDT

Theoretically I'd assume this makes sense, but are there conditions which inhibit this?

submitted by /u/lukedaviesor
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What is keeping the inner layers of the Earth hot?

Posted: 27 Oct 2019 07:35 AM PDT

What exactly is keeping magma in the mantle hot, shouldn't it have cooled after millions of years?

submitted by /u/SneakyFudge
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Why is uranium the unique element used in nuclear fission and hydrogen for nuclear fusion?

Posted: 27 Oct 2019 05:48 PM PDT

Since nuclear fission generates radioactive residue in cause of uranium use, why can't we use other element? The same question for nuclear fusion with hydrogen, could we use other elements?

submitted by /u/thearcher182
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How long do Pacific salmon live after spawning?

Posted: 27 Oct 2019 12:24 PM PDT

I couldn't find much data on how long salmon live after spawning, although I read somewhere that females will guard their redds for 1-2 weeks before dying. What happens to the males as they undergo senescence? Do they swim back towards the ocean as they deteriorate?

Bonus q: I read that the male giant octopus lives for a few months after reproduction, out of a total lifespan of 3-5 years. Is there another animal that spends a higher % of its time in programmed senescence?

submitted by /u/Duvark
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How did they determine the identity of Abu Bakr Al-Baghdadi so quickly?

Posted: 27 Oct 2019 08:06 AM PDT

As you've probably heard they've killed the ISIS leader. And according to Trump, their lab. unit had a positive identification after 15 min. How is that possible to do on-site? I could imagine them having some quick blood tests, specific for him, but I would still wonder how would the know with what to compare? And I would believe that DNA testing takes way longer and again they would need a sample of his DNA from before, which I imagine they didn't have.

submitted by /u/bledin2
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Why do Cpu’s and Gpu’s and other electronics preform better at lower temperatures?

Posted: 27 Oct 2019 10:08 PM PDT

Normally i would lean towards some thing being hotter preforms better like: matter heating up = particles moving faster. So why do electronics get bogged down by heat, and some out preforming at temperatures lower than ambient temps?

submitted by /u/Laidan22
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What happens to the extra skin when you lose a significant amount of weight?

Posted: 27 Oct 2019 09:04 AM PDT

What happens to the extra skin if someone loses enough weight to significantly change their body shape?Does it get broken down somehow? Does is just kind of hang there?

submitted by /u/padct
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Do Nocturnal Predators Often Hunt/Eat Sleeping Prey?

Posted: 27 Oct 2019 04:30 PM PDT

It seems to me that it'd be significantly easier for nocturnal predators to just find diurnal prey animals that are asleep and kill those instead of hunting down nocturnal ones that are awake. Are sleeping animals that much harder to find, or is this just something that you don't usually hear about?

submitted by /u/Daedalus_27
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Why are some earthquakes only felt by those hundreds of kilometres from the epicentre?

Posted: 27 Oct 2019 11:21 AM PDT

Today in New Zealand there was a magnitude 5.0 earthquake near Tauranga. This is a felt report where people can voluntarily submit the level of shaking they felt marked by squares. You can see the epicentre just south of Tauranga (near the top of the map) which is a relatively large city by NZ standards. However, the closest people who felt anything were 300km south east, and some were even over 500 km south from the event. This isn't hugely common but this definitely isn't the first time I've noticed it either. Why would the people in the first 100km radius not feel anything at all whereas those 300km south do? And why does nobody north feel anything at all?

submitted by /u/TypicalPakeha
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Why do dead whales explode?

Posted: 27 Oct 2019 10:23 AM PDT

I heard that dead whales explode, But how?

submitted by /u/chance8407
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How exactly do we know what causes food poisoning?

Posted: 27 Oct 2019 04:12 PM PDT

So it's common knowledge that certain bacteria and parasites can cause food poisoning. On the bacteria side, we have E coli., salmonella, and campylobacter. In terms of parasites, we have trichinosis and roundworms in fish like nematodes. However, how exactly do we know these pathogens are causing the symptoms of food poisoning? To my knowledge, we all have these bacteria in our intestines at any given time and are perfectly healthy and fine (well at least E-coli., not sure about the other two). What is the mechanism of action for "food poisoning"? How doe these bacteria cause it. What tests do we have to prove this? Do they simply take stool samples after someone has been sick?

submitted by /u/ZosoGG
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What type of fossils are most likely buried underneath the Antarctic ice shelf?

Posted: 27 Oct 2019 03:59 PM PDT

Are there any 2 species alive today that share a common ancestor species, which is also alive today?

Posted: 27 Oct 2019 11:05 AM PDT

Why does stretching your muscles feel good?

Posted: 27 Oct 2019 06:01 AM PDT

Is effective nuclear charge always going to be the same as the number of valence electrons?

Posted: 27 Oct 2019 10:42 AM PDT

In my chemistry class we are using Zeff (Z effective) to find the effective nuclear charge of a valence electron of a given atom. Since I am using the atomic number - valence electrons = core electrons, and atomic number - core electrons = effective nuclear charge, I am always getting the same for valence electrons and effective nuclear charge. Am I doing this correctly?

submitted by /u/vikingwarrior604
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What makes certain fruits and vegetables rich in particular compounds?

Posted: 27 Oct 2019 01:52 AM PDT

For example, why does bell pepper contain almost ten times more vitamin c than banana, but five times less carbohydrates? Is vitamin c somehow necessary for bell pepper to exist?

submitted by /u/toriyamaru
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Why do things “go stale.” I know it’s caused by exposure to air but what actually happens chemically?

Posted: 27 Oct 2019 12:35 AM PDT