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Monday, February 6, 2017

By guessing the rate of the Expansion of the universe, do we know how big the unobservable universe is?

By guessing the rate of the Expansion of the universe, do we know how big the unobservable universe is?

By guessing the rate of the Expansion of the universe, do we know how big the unobservable universe is?

Posted: 06 Feb 2017 04:29 AM PST

So we are closer in size to the observable universe than the plank lentgh, but what about the unobservable universe.

submitted by /u/dtagliaferri
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What is the physical setup used for the production of thermal neutrons used to create the 'Rio Red' grapefruit strain?

Posted: 06 Feb 2017 06:29 AM PST

I was reading about red grapefruit and how they were created through radiation mutagenesis. In particularly the Rio Red commonly used is cited as having been the product of thermal neutron irradiation of plant tissues in the 1980s in Rio (the city). None of the biology articles talk about the physics of the setup. Given no nuclear reactors in Rio how would this be done?

My first guess is a strong natural alpha emitter with beryllium and surrounded by a hydrogen plastic moderator. (ref). Or maybe just a Californium-252 neutron source with plastic moderator. But that's the point, I don't know which or what.

Hensz's actual papers about the 'Rio Red' and many others cite Caldecott et al 1954 but none of them have detail. I've spent about ~45 minutes searching for the early 1950s protocol papers on the subject by Caldecott but there's nothing but abstracts online.

Does anyone in the field know about the actual setup used by plant biologists for thermal neutron mutagenesis?

submitted by /u/superkuh
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What causes the difference between kinetic and static friction?

Posted: 06 Feb 2017 06:24 AM PST

Hola physicists (and everyone else),

I was wondering (out of the blue) why moving objects once they are in motion is easier than the initial movement.

Can't recall any physics teacher actually discussing it.

submitted by /u/AVeryLazy
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If Concentration of hydrogen on sun is 1.1%, then what's the rest?

Posted: 06 Feb 2017 04:30 AM PST

In string theory-Brane cosmology: Is the collision of two branes considered to be the cause of the big bang?

Posted: 05 Feb 2017 02:22 PM PST

A follow up question: How many other ways can branes interact with one another?

submitted by /u/elder--wand
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Why does enthalpy of atomization *increases* down the group in transition elements?

Posted: 06 Feb 2017 03:16 AM PST

Also whats up with the anomalous enthalpy of atomization of Tc, Mn?

submitted by /u/loremusipsumus
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My paper grocery bag says "This 100% recyclable bag made from 100% recycled paper" could this process be repeated ad infinitum?

Posted: 05 Feb 2017 01:19 PM PST

Would there be material lost everytime? Or a limit to the number of times the material could be used? Same question about plastic or metal recyclables.

submitted by /u/djz7c
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Do the oceans get saltier over time? Has this had any biological impact?

Posted: 05 Feb 2017 02:03 PM PST

From what I know ocean salt comes from land deposits, so there's a constant influx of salt into the ocean. But from evaporation no salt leaves. It seems to me that this would imply an increase in salt concentrations.

submitted by /u/FrancisNarwhalBacon
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why is it important to autoclave the medium soon after preparing it or to keep it refrigerated until it can be sterilized?

Posted: 05 Feb 2017 06:05 PM PST

When we are preparing medium, bacteria can contaminate it quickly because it is nutrient rich. Autoclaving the medium can sterilize it quite effectively. However, what problem can occur with the medium if we were to prepare it on one day, leave it on the bench at room temperature and then autoclave it two days later? (In other words, why is it important to autoclave the medium soon after preparing it or to keep it refrigerated until it can be sterilized?

submitted by /u/elizabethbrooks
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Does a superconductor truly have 0 Ω resistance, or is it only arbitrarily close?

Posted: 05 Feb 2017 07:50 AM PST

A true-zero resistance would, to my understanding, cause problems with implementing Ohm's Law. Additionally, I believe there is still a non-negligible degree of Joule heating, which leads me to think that the resistance of the material is some fraction above true zero.

submitted by /u/Shapoopy178
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How far away from the nucleus does 100% of the electron cloud extend?

Posted: 05 Feb 2017 01:08 PM PST

The electron cloud is usually defined as the volume where between 90 and 97% of the electron resides. Using modeling software you can alter the parameter to see the cloud expand to 99% or 99.99%. Is there some portion (1X10-100000ish) of the cloud existing a meter away from the nucleus? How about a lightyear away? Can we use this for ftl communication somehow? Does quantum nature or the Plank length act as a limit to this idea? I've tried looking through physical chemistry and quantum physics literature before, but it was too far out of my field and I gave up.

submitted by /u/trackmaster400
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How do stars generate elements "heavier" than lead?

Posted: 05 Feb 2017 10:04 AM PST

I know that all of the natural occurring elements are formed in the fusion reactions within stars. As I understand it (correct me if I am wrong), during the life cycle of early stars (the first generation after the Big Bang), as they burned through hydrogen and helium, their cores eventually became made of of large quantities of lead, making nuclear reactions impossible. The stars blow up, scattering their contents into space where that stuff is used in the formation of new stars, planets and all the other matter in the Universe.

That accounts for all of our elements up to lead on the periodic table. Is it correct that some of the heavier (from Lithium to lead) elements that become part of new (second generation and beyond) stars are "fused" in the nuclear reactions in the star into elements beyond lead? Is there an established understanding of how the fusion of heavier elements (those heavier than H and He) are fused within a star? For example, do we know that lithium will only undergo fusion with certain other elements, or is it totally random?

Thanks!

edit -- I wrote lead when I meant iron.

submitted by /u/Anticipator1234
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Why does the US launch rockets in Alaska?

Posted: 05 Feb 2017 08:30 AM PST

I get that they could launch over the Pacific so they don't fly over people, but doesn't the equator have an easier time due to the faster rotation of earth? Is it for longitudinal orbits? Thanks.

submitted by /u/pepperyourangus37
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Can a parasite change a human's genome?

Posted: 05 Feb 2017 12:26 PM PST

I'm writing a science-fiction novel, and I'm wondering if it would be possible for a parasite to take over a body and change it completely. I don't need to know whether or not a parasite exists that does this, but if, hypothetically, it's possible. And if it is possible, how would it go about changing human DNA?

submitted by /u/jninja117
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What chemically defines an element as a metal?

Posted: 05 Feb 2017 10:33 AM PST

How can alkenes be diastereomers and have diastereotopic protons?

Posted: 05 Feb 2017 03:19 PM PST

I thought diastereomers have to have chiral centers right? If you take a look at the diastereotopic example in the mastering organic chemistry website then it shows that the alkenes are diastereomers, but they dont have any chiral centers. http://www.masterorganicchemistry.com/2012/04/17/homotopic-enantiotopic-diastereotopic/

Also as an additional question, can alkenes have enantiomers or enantiomeric protons?

submitted by /u/zakil44
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Besides solar are there any industrial scale means of generating electricity other than turning a turbine?

Posted: 05 Feb 2017 01:36 PM PST

Nuclear, coal, gas, wind and solar thermal generation all heat water to create steam to drive a turbine. Are there any other ways of generating on a meaningful scale? Also has turbine technology peaked or are we likely to see more watts per volumetric unit of steam as technology advances?

submitted by /u/peepsandpoops
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Is it true that stars orbit the galactic center at the same speed, regardless of their distance from it? Is this still thought to be an effect of dark matter? How would dark matter need to be dispersed to create the result we observe?

Posted: 05 Feb 2017 09:43 AM PST

How does a dipole in a electric field or a bar pendulum in a gravitational have a torque acting on them if Coulomb force and Gravitational forces are central forces and angular momentum is a conversed quantity? How does the torque come about?

Posted: 05 Feb 2017 12:15 PM PST
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Sunday, February 5, 2017

Are humans closer in relative size to the planck length or the entire observable universe?

Are humans closer in relative size to the planck length or the entire observable universe?

Are humans closer in relative size to the planck length or the entire observable universe?

Posted: 05 Feb 2017 05:11 AM PST

When you boil water, does it ever get hotter than 100°C in the pot?

Posted: 05 Feb 2017 06:01 AM PST

Is there a theoretical limit to the number of chemical elements that could exist in the universe?

Posted: 04 Feb 2017 03:13 PM PST

Why isn't nuclear physics considered to be chemistry?

Posted: 04 Feb 2017 05:13 PM PST

Why is time measured in with 60 seconds/minutes and not 100?

Posted: 05 Feb 2017 07:29 AM PST

Why are hours, minutes and seconds as long as they are?

Posted: 05 Feb 2017 06:00 AM PST

We all know why a day is as long as it is, but what made some dudes decide that it should be split up into exactly 24 hours? And what made them decide to split every hour into 60 minutes and then every minute into 60 seconds?

submitted by /u/Doodinator
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Why does solar output fluctuate?

Posted: 04 Feb 2017 02:59 PM PST

I have been reading about prehistoric climate change and it seems that changing solar forcing has often been a very important factor. What causes these various increases and decreases in solar radiation?

submitted by /u/BrotherDaaway
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Does Precession of the Earth Affect Climate?

Posted: 04 Feb 2017 04:42 PM PST

Since the Earth goes through a gyroscopic wobble that has a 2600 year period does this at all create climatic shifts or cycles that we could notice? I'd be curious if there are trends that people have recorded or noticed because of this other than just what stars are in what point of the sky.

submitted by /u/23Udon
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Do we have models of natural endothermic nuclear fusion?

Posted: 05 Feb 2017 06:25 AM PST

I seen charts explaining how different isotopes decay and into which isotopes, and also different fusion reactions (for example how carbon is created via triple-alpha process.) And it seems like we have very accurate knowledge how all of that works.

But what I have not seen is how elements heavier than nickel are created in a supernova. Are there even theories on how exactly this happened or is it predicted to be compleatly chaotic?

What im looking for is like for example:

12 C + 68 Zn + Energy = 80 Kr

And how big portion of 80 Kr we find in nature is created via this example process (that I dont know if it exist)?

submitted by /u/empire314
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Are stars the only natural nuclear fusion users in the universe?

Posted: 04 Feb 2017 10:13 AM PST

What speed is room temperature?

Posted: 05 Feb 2017 05:50 AM PST

As we all know, temperature is the average speed of particles. The higher the temperature, the higher that speed. If I understand correctly, that speed is not dependent upon the particle. 25° would be the same speed if we're talking about an iron lattice, or NaCl.

Well then, what is the speed of particles that's called 25°?

Also, 2 more related questions: is -273 theoretically a speed of 0? (I know that it can't actually be reached) If the temperature was infinity (again, theoretically), would the speed be Lightspeed?

submitted by /u/lirannl
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Why does wetting my finger causing it to have more friction?

Posted: 05 Feb 2017 03:08 AM PST

When turning a page on a book for example

submitted by /u/Staviao
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What's the limiting factor behind slug and snail size? Why don't we see land slugs and snails larger than 1 kg in weight?

Posted: 05 Feb 2017 02:33 AM PST

I know insects are limited by factors relating to their tracheal system but slugs and snails have lung that are functionally similar to terrestrial vertebrates. Is it because they're too soft and squishy?

submitted by /u/rendelnep
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Is Albinism more prevalent in communities with lower melanin levels?

Posted: 05 Feb 2017 01:37 AM PST

My question is whether communities that have lower melanin levels, e.g. Nordic populations, have a higher level of albinism than communities in the tropics, which have selected much higher melanin levels. I suppose my question boils down to whether the mutation of albinism is truly random, or whether it is in fact beneficial to survival and thus is more likely in areas in which low melanin is a benefit.

submitted by /u/crombopmikhail
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How does a computer know when a "word" starts and finishes in binary ?

Posted: 04 Feb 2017 07:16 PM PST

Let's take the binary string 11011100001

How does the computer know if it is only one word (command), or two "1101" and "1100001", or three...

submitted by /u/milanonabil
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Why is the radiation from Chernobyl and Fukushima so intense, when Uranium has a half life of billions of years? Shouldn't it be minimal?

Posted: 04 Feb 2017 10:18 AM PST

If space is a vacuum, how can it smell?

Posted: 05 Feb 2017 01:55 AM PST

Chris Hadfield said space smells like brimstone. How can a smell exist if space has no particles?

submitted by /u/Drake_Heisenberg
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Do Singularities "evaporate" or is the only thing that does disappear over time the Event Horizon?

Posted: 04 Feb 2017 03:54 PM PST

I've been piecing together information based on an idea and I reached a stumbling point based on several videos and various written information on the topic. In them, the people explaining it seem to state that the Singularity and the Event Horizon of a Black Hole are separate in terms of what occurs in the normal lifetime of the object, but then they go on to it as a collective object and that the "Black Hole" itself evaporates overtime.

I've seen the evaporation described as the Event Horizon being a curved line with one particle on one side and another particle on the other, with one entering the Singularity and the other escaping as an X-ray or similar type of escaping "object" as the evaporation effect. Wouldn't that mean that the Singularity itself is still intact with all the matter it's collected over time in whatever location it's currently at, because while some particles are being expelled other particles are being collected inside the Singularity. Or does the Singularity eventually actually have to burn through the matter that's been collected when it's no longer able to collect more, so eventually it'll convert all of its captured matter into radiation and the Singularity itself dissipates as well?

My confusion stems from the fact that no one seems to give a clear answer to that. At the point they discuss the "evaporation" of the Black Hole they refer to it as a collective unit where as before they made a point to differentiate between the Singularity itself and the actual Event Horizon surrounding it. Is it just because we don't fully understand the mechanics behind it, so when it "evaporates", as Hawking and his team discovered, that's where our knowledge ends because we can't actually mathematically predict what happens so we just assume they both disappear when it's not known?

submitted by /u/Ashendal
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Is the electron transport chain made entirely of proteins?

Posted: 04 Feb 2017 12:22 PM PST

Are all the molecules in the chain proteins?

Wikipedia states "An electron transport chain (ETC) is a series of compounds"

and goes on to say...

"The molecules of the chain include peptides, enzymes (which are proteins or protein complexes), and others"

What does it mean by "others"? Are all the "others" proteins too?

submitted by /u/Deproc
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What was central and south-eastern South America like during the last glacial period?

Posted: 04 Feb 2017 06:11 AM PST

Is it safe to assume that it regularly snowed in what is now central Brazil? What about the Atlantic Forest, how did it do? Were there temperate forests?

submitted by /u/SagaCult
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Saturday, February 4, 2017

Do NSAIDs (Paracetamol, etc...) slow down recovery from infections?

Do NSAIDs (Paracetamol, etc...) slow down recovery from infections?

Do NSAIDs (Paracetamol, etc...) slow down recovery from infections?

Posted: 04 Feb 2017 04:39 AM PST

NSAIDs (paracetamol, ibuprofen and others) can be used to reduce fever and inflammation. But as I understood it, fever and inflammation are mechanisms the body uses to boost the effectiveness of the immune system. Does the use of NSAIDs therefore reduce the effectiveness of the immune system in combatting an infection? If so, has this effect been quantified (e.g. "on average recovery time for infection X is Y% longer with a daily dose of Z")?

And is there any effect when NSAIDs are used when there is no infection (wounds, headaches, etc...)?

submitted by /u/Rannasha
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How can I estimate radiation exposure to x-rays in my practice?

Posted: 04 Feb 2017 12:57 AM PST

I'm a veterinarian that has to do a lot of x-rays, and usually the owners hold the animals. Most owners have no clue (I still get asked daily if they have to turn off their mobiles), but some are interested in knowing more about risks. I know that holding an animal for x-ray just once results in very little exposure to radiation, but just how little? Knowing the kV and mAs and the distance from the main focus, can I provide a good enough estimate of exposure? Thank you!

submitted by /u/firstcaress
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Why can our brain automatically calculate how fast we need to throw a football to a running receiver, but it takes thinking and time when we do it on paper?

Posted: 02 Feb 2017 06:09 PM PST

I was playing some catch the other day with a friend of mine. He would run off down the field, and I would throw the ball, and 90% of the time it was an accurate throw to him. The other 10% was due to wind difference, so I would adjust the throw and make it to him. All of that is done automatically in our brains, and it works pretty fast.

Now, why is it that when we see the same situation, but on paper, it takes time to calculate all of that information. Is it because our brains see the actual numbers compared to real world events that are happening right there? Or shouldn't our brain be able to pick that information and automatically translate it, as if it were happening right there?

Edit: fixed wording. But man, this blew up, and got a lot of great responses for this. Initially had it marked as physics, but I see it got changed to psychology. Very interesting. Thanks for all that took time, and made the explanation better for me!

submitted by /u/maxxxl
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How is actual sleep different from "sleeping" via anesthesia?

Posted: 03 Feb 2017 01:02 PM PST

What goes on in squirrel nests?

Posted: 04 Feb 2017 07:01 AM PST

A bit of context. I live in Eastern Canada, and grey squirrels (Sciurus carolinensis) are everywhere. They build conspicuous "nests" made of twigs and leaves, up in the canopy of trees.

Naïvely, I accepted what I was told as a child, namely that those are where squirrels retire to hibernate for the winter...

But here's the thing: not only do the nests seem a bit too small and flimsy to shelter the squirrels in any meaningful way in -30°C weather and winter winds, but the critters are scampering outside all winter long. So they manifestly don't hibernate. What exactly do squirrels actually do with those structures?

submitted by /u/Gargatua13013
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Why does the ISS need to "re-boost" in order to stay in orbit?

Posted: 03 Feb 2017 08:05 PM PST

The main common justification for this re-boosting I've heard is that since it is in low orbit, it is constantly falling a little bit and if it was farther away from earth it wouldn't need this. However, I just took my first physics course and we learned the equation for Centripetal Force is mv2/r, so from my understanding of this equation, why doesn't it just speed up in general in order to maintain a constant orbit.

submitted by /u/Tman1677
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Has a particle physics result that reached 3-sigma subsequently not reached 5-sigma and been abandoned?

Posted: 03 Feb 2017 08:22 AM PST

Famously, the higgs boson result was confirmed when the chances that the higgs finding was not real was no more than 1 in a very large number (5-sigma). Recent news articles on CP violation have reached 3-sigma. Has there been a promising result that got to 3 or 4 sigma, only to never get to 5-sigma significance?

submitted by /u/PrivateFrank
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What is the weak nuclear force?

Posted: 03 Feb 2017 02:59 PM PST

Whenever i hear about the 4 fundamental forces, i always hear 3 of them explained very to fairly well, and then we get to the weak nuclear force and whoever is explaining mumbles something about radiation and quickly moves on.

So, reddit, what is the weak nuclear force, and what does it do?

submitted by /u/bizzehdee
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What are the surface properties of a cooling dwarf star?

Posted: 03 Feb 2017 04:09 PM PST

when a star (like ours) dies it expands and collapses again

after collapsing it should still be pretty hot but its not heavy enough to become a black hole so it will become a dwarf star the dwarf star should be pretty hot and dense but heat keeps radiating away so my question is: when it cools down (after a long time) it should become cooler, so what would the surface of that dwarf star be like if the surface had ~200°C (solid? liquid?)

and if it cooled down even more to about 20°C could you just walk on it or will it never be solid in any way

submitted by /u/Taetares
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Is it purely coincidence that the human sleep cycle roughly matches the day and night cycle of Earth or is it the time of day that determined our sleep habits?

Posted: 03 Feb 2017 08:26 PM PST

For example, if days lasted 48 hours on Earth instead of 24 hours, would humans have adapted to stay awake for all the daylight hours and sleep for twice as long or do humans biologically need around 8 hours of sleep to function regardless of the amount of sunlight?

submitted by /u/airsabe
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Is the Earth the only other place in the solar system (other than the Sun) where nuclear reactions have taken place (fusion *or* fission)?

Posted: 03 Feb 2017 09:48 PM PST

Effects of environmental determinism on colour perception/discrimination/terms?

Posted: 03 Feb 2017 06:38 PM PST

I know there has been a lot of research on colour term universality vs linguistic relativity, but does anybody know of much research on environmental determinism or other forms of determinism (e.g. lifestyle) on colour perception, discrimination, number of basic colour terms in language, etc.?

Berlin & Kay (1969:15-17) speculate a little about why industrialised societies seem to have more colour terms but it's all very speculative and it's not based on anything empirical. Has anybody does any research on these sorts of topics since then?

Thanks for your help!

submitted by /u/l33t_sas
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If you put an object that was perfectly red in a room with absolutely no red wavelengths, what colour would it be?

Posted: 03 Feb 2017 07:30 PM PST

Asking because I know objects are certain colours because of the light they reflect. So if there were no wavelengths of that colour to reflect, but there was still visible light to illuminate it, what would you see?

submitted by /u/RubberyBannana
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What keeps neutrons in the nucleus of an atom?

Posted: 03 Feb 2017 03:39 PM PST

They have no charge so what force keeps the neutrons in the nucleus?

submitted by /u/morseerman
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[Physics] What happens to neutrons that are ejected from nuclei through various processes (fission, knocked out by high energy photons, etc)?

Posted: 03 Feb 2017 12:41 PM PST

Do they just float around in space or do they attach themselves to existing atomic nuclei? Is there a significant amount of exclusively neutron material in our universe that simply exists unbonded to an proton? I don't think I've ever heard of neutrons existing by themselves outside of special cases like a neutron star (exclude these cases), so it made me curious.

submitted by /u/kentuckyk1d
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Stabilization of N- and C-terminus in amino acids?

Posted: 03 Feb 2017 09:15 PM PST

My professor stated that an amino acid like glutamic acid will lower the pKa of one of the COOH groups to dissociate its proton, while the other COOH group while increase its pKa to prevent dissociation (which would cause repulsion due to like charges).

I can't seem to find this anywhere in my textbook or online. Can anybody confirm if this is correct, and if so, what effects does this have on amino acids on a larger scale?

submitted by /u/blackphonecover
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Can paper products be used to sequester carbon?

Posted: 03 Feb 2017 12:39 PM PST

With concerns about CO2 emissions and talks about deforestation releasing sequestered carbon, I'm curious about factory farms and their ability to sequester carbon. Trees essentially turn air into wood, wood which is pulped up into paper, paper that is then thrown away or recycled.

I'm wondering if subsidizing paper products to increase the number of factory farms could have any signifant impact on the amount of CO2 in the atmosphere.

submitted by /u/therationalpi
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Since electron energy levels are discrete, why are absorption spectra continuous?

Posted: 03 Feb 2017 01:51 PM PST

It's pretty standard in intro-level chemistry or physics to talk about absorption/emission spectra that have discrete lines like this, where each line corresponds to an electronic transition. Pretty simple. But I've found that absorption curves (like this) come up more often, and I can't figure out how the continuous peaked curve corresponds with the quantum image.

I've been under the impression that absorption curves are also produced by electronic transitions, so I don't quite get what the difference between the two is, and under which conditions each would be produced. All I can really say is that I've done tons of spectroscopy tests that produced curves, and never whatever type of test is necessary to produce the discrete spectra.

I'm guessing it has something to do with the thermal energy of the individual atoms and molecules, which is variable in a sample and thus produces slightly different transition energies for each molecule?

I'm also pretty sure I'm conflating at least a couple concepts here.

Thanks

submitted by /u/newappeal
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Are there any animals that build upon the tools/structures/techniques they utilize from generation to generation?

Posted: 03 Feb 2017 11:31 AM PST

Similar to humans in that we learn and adapt from those who came before us. Is a beaver dam more structurally sound today than it would have been 400 years ago? Is a happy face spiderweb stronger through geometric design today than in the past? Do animals use better materials for their tools now than they did 50 generations ago?

submitted by /u/MrAloha808
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I have many questions about melanocytes; Does melanocyte distribution affect skin-tone evenness, and if so, what affects the distribution of melanocytes? Do darker-skinned people have more melanocytes, or just make more melanin? etc.

Posted: 03 Feb 2017 11:13 AM PST

What I (think that I) know:

I know that melanin is a skin pigment that determines how dark or tan a person is, and that it's production is somewhat determined by genetics combined with UV exposure. From my understanding, things like freckles, age spots, melasma, and general uneven skin tone are all caused by an uneven distribution of melanin in the skin. It is also my understanding that treatments (such as hydroquinone) aimed at improving the evenness of skin tone - or even just overall lightness - often work by targeting melanin production and somehow inhibiting or reducing the amount of melanin produced by cells, whereas other treatments (like lasers and IPL and chemical peels) destroy or break apart or burn-off the melanin. I've even heard of a drug (Melanotan) that increases melanin production to make someone more tan. And finally, I've learned that melanin is produced by certain cells called melanocytes, and that treatments aimed at changing pigmentation often are targeting the action of these cells, and that melanoma is specifically cancer of these cells.

What I don't get:

Where my understanding falters, is in why melanin is produced more in one spot of skin than another, or more in one person than another, and how that is determined by melanocytes. Do people with darker skin have more melanocytes, or just produce more melanin with the ones they have? Why would a melanocyte two inches over from another, with the same amount of UV light exposed to it, produce a big blob of melanin (an age spot or freckle) whereas the other didn't? Or is the case that the melanocytes aren't evenly distributed themselves - in which case, why does that happen? And related to that, if melanocytes aren't distributed evenly, why don't skin care treatments target the cells themselves, instead of their action? Is it possible to target and destroy melanocytes like the procedures that destroy hair follicles for permanent hair removal? Or is there a way to grow or even transplant more melanocytes where they are lacking (like how hair follicles are moved to treat male-pattern baldness)? And if melanocytes are moved with a skin graft (like in a burn patient) - do those melanocytes act the same as they always did, or do they change based on new factors (like host genes)? Would skin donated by a tan person stay tan if transplanted to a less-tan person, or would it fade over time? Even more curious to me, is what about melanoma in relation to melanin and melanocytes distribution? I've heard that people who are tan have less likelihood of getting it - but wouldn't they either have less melanocytes, or less active ones? Wouldn't they be at a lower risk of their melanocytes growing and dividing out of control, then? Or are they at greater risk for melanoma in the same way that they are at greater risk for other melanin-related pigmentation changes like age spots, and if that's the case, would it decrease someones cancer risk if they could get more melanocytes and/or produce more melanin (or more evenly)?

That's a lot of questions, I know - but I appreciate any responses!

submitted by /u/waitwuh
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If I stretch a metal bar, it becomes thinner at one point, and then suddenly it snaps. What is the molecular-level reason why it doesn't keep becoming thinner and thinner?

Posted: 03 Feb 2017 07:08 AM PST

Eg see here https://www.youtube.com/watch?v=fnkSLZKxlRk

I understand the material stretch curve and elastic-inelastic deformation, but what "changes" between the regime where the material is stretching in inelastic deformation and the regime where it just suddenly snaps?

submitted by /u/esbio
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Why do I see the dark part of a crescent moon?

Posted: 03 Feb 2017 05:37 PM PST

When it's a crescent moon I can obviously see the crescent made of the sun's light reflected off the moon. But I also can make out the dark disc of the unlit remainder of the moon. Why is that? My guess would be that the dark part is fractionally lit enough for me to differentiate it from the light reflecting off the atmosphere but I'd like to be sure.

submitted by /u/CorporalCalamity
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