Recent comments in /f/askscience

rdrast t1_jdb236e wrote

Reply to comment by flyfruit__ in What happens when we die? by darsenalmex11

Yes, the autonomic system, keeping heart and lungs working can still keep running, even if the cerebral cortex is completely gone.

The autonomic system is deep in the brain, and is the ladt to go, normally.

ETA: at the point there is no higher brain function (stimulus to light, sound, pain) "You" are essentially dead, but the body can continue to function, since a basic thing is to keep going.

The autonomic systems really will keep going, provided oxygen and food.

Sometimes for years.

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Shirkie01 t1_jdaxzfb wrote

Reply to comment by Dorigoon in Do we know where is the center of big bang located presently in reference to earth? by MagnetCarter

The answer to "where did the Big Bang happen" is always "exactly where you are", no matter where you are. This is because it's not an event that happened in the universe, it is the universe.

Unfortunately I can't find the GIF with the expanding red dots that made it clearer, but the idea is that there is no preferred reference frame and thus no location that's "more important" than any other.

This image might help. Picture A is the location of galaxies at some given time, while Picture B is the location of galaxies at some future time. Pictures C and D show that the galaxies appear to be moving away from "here", wherever "here" might be, and the galaxies farther away from "here" appear to be moving faster.

https://allthatsinteresting.com/wordpress/wp-content/uploads/2013/03/big-bang-dots.jpg

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SweetStrawberry4U t1_jdawsll wrote

Reply to What happens when we die? by darsenalmex11

Life is a multi-constituted process, and so is Death. Several aspects that actually make Life livable, Die similarly.

https://youtu.be/LVlFJPOGyWE

In short, it takes anywhere between 2 hours to 14 days, for Life to end, and therefore Death to 'occur'. Constitutes, involuntary and voluntary systems, Immunity, buoyancy of the spine, temperature regulation etc.

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lizardweenie t1_jdapyy8 wrote

Reply to comment by Dr-Luemmler in Can a single atom be determined to be in any particular phase of matter? by Zalack

I just thought of a reasonable thought experiment that might clarify your confusion:

Say you have a bath of non interacting hydrogen atoms (consider for a moment, only electronic excitation), and we are able to measure the state of each atom.

Say we measure this bath and find that f_0 fraction are in the ground electronic state E0, and f_1 are in the first excited state E1. We could then infer a temperature by comparing these populations to a Boltzmann distribution, which tells us the relative probability of finding an atom in a state at a given energy (for a given temperature). In this case temperature is a well defined and meaningful concept.

Now say instead that we have a single hydrogen atom, we measure its state, and we find that it's in the first excited state. What then is the temperature? If we try to infer a temperature from this, (using a Boltzmann distribution), we get -inf. Say instead we measure it, and it's in E0. In this case, our inferred temperature will be 0. So for this single atom system, any temperature that we try measure can only give two values, (0, or negative infinity). In this system, clearly temperature isn't behaving how we would like it to.

This troublesome result points to a larger problem with the question: asking "what is the probability distribution for state occupation" doesn't really work well for the example: the atom was measured and determined to be in state E1, its probability distribution is a delta function, which is an inherently non-thermal distribution.

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lizardweenie t1_jdamc26 wrote

Reply to comment by Dr-Luemmler in Can a single atom be determined to be in any particular phase of matter? by Zalack

No worries, you're not being rude. As for references, this a matter of basic definitions so I'd recommend some good textbooks, depending on your background.

I'd say that Chandler's book is pretty good: (I used it at the beginning of my PhD) http://pcossgroup.xmu.edu.cn/old/users/xlu/group/courses/apc/imsm_chandler.pdf

If you're looking for a different perspective, I've heard good things about Reichl: "A Modern Course in Statistical Physics"

Fun fact about this statement: > the amount of "accessible" states need to increase with increasing temperature to hold the first formula

This need not be the case. In certain scenarios, you can actually obtain negative temperatures which are perfectly valid. https://en.wikipedia.org/wiki/Negative_temperature

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