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Entropy explained, with sheep (2016)

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Re: Entropy explained, with sheep (2016)

#21

Post by keenmaster »

AnimalMuppet wrote: post #18
keenmaster wrote: post #17

Earlier quoted context omitted.

Where did those particles come from? Is there any scientific theory for the beginning of the beginning? A friend who studied physics told me that there's no reason that matter/energy couldn't have just existed forever. I don't find that explanation satisfying. If "entropy always increases" is a universal rule, then there must have been a time where it went from zero to non-zero. If "matter cannot be created or destro…

No. In a forever-existing universe, as you go back in time, entropy could asymtotically approach zero (or some other limit) without ever actually reaching it. It doesn't have to be zero at some point in the past. In fact, if it is zero at some point in the past, then what happened before that? Did it not increase before that point, or was it less than zero before that point?

I get your point about the asymptote, but I should have clarified: I was synthesizing two rules, "entropy always increases" and "matter cannot be created or destroyed"

Beyond that, metaphysically, how does something increase without having an origin? "Everything just always was" seems to conveniently handwave away a very important line of inquiry. This line of inquiry might be uncomfortably close to religious thought, but that shouldn't be a reason to terminate it.

As time goes on, we are able to explain more and more things scientifically, and yet, arbitrarily, we are supposed to be satisfied with "energy and matter were just always there, any other explanation is arbitrarily religious" without a sense of irony. That belief is held onto with religious conviction, sometimes used to dismiss alternate ideas with religious fervor, and backed with a religious rather than scientific standard of evidence.

Here's a premise for a (maybe horrible) book idea: God manipulates the minds of top scientists so that they do not definitively prove his existence, which would ruin the point of his simulation. Each time they get close, he finds an idiosyncratic way to make them forget about it or dismiss the idea. The people who discover God's tricks get brownie points in the afterlife. The people who discover God's tricks but try to publicize them, hence ruining the illusion, get...taken care of. Perhaps you can say the entropy of their body would increase.

Re: Entropy explained, with sheep (2016)

#22

Post by wolco »

keenmaster wrote: post #17
selim_tiotoys wrote: post #10

Earlier quoted context omitted.

There is a fantastic book by Leonard Susskind [0] that tackles this questions. His answer - rooted in string theory - is based on a "landscape of possibilities" and we happen to be in the place where all elementary particles (more specifically the Higgs) had the right energy configuration. [0] The cosmic Landscape: https://www.amazon.com/Cosmic-Landscape-String-Illusion-Inte...

Where did those particles come from? Is there any scientific theory for the beginning of the beginning? A friend who studied physics told me that there's no reason that matter/energy couldn't have just existed forever. I don't find that explanation satisfying. If "entropy always increases" is a universal rule, then there must have been a time where it went from zero to non-zero. If "matter cannot be created or destro…

Don't black holes decrease entropy?

Re: Entropy explained, with sheep (2016)

#23

Post by keenmaster »

wolco wrote: post #22
keenmaster wrote: post #17

Earlier quoted context omitted.

Where did those particles come from? Is there any scientific theory for the beginning of the beginning? A friend who studied physics told me that there's no reason that matter/energy couldn't have just existed forever. I don't find that explanation satisfying. If "entropy always increases" is a universal rule, then there must have been a time where it went from zero to non-zero. If "matter cannot be created or destro…

Don't black holes decrease entropy?

Apparently black holes can die. Entropy can decrease in a subsystem so long as the subsystem is drawing energy away from a larger system. https://en.wikipedia.org/wiki/Hawking_radiation

Re: Entropy explained, with sheep (2016)

#24

Post by novaRom »

jbay808 wrote: post #13
keenmaster wrote: post #5

Great explanation. What are the top theories for why the universe began in a low entropy state? The mere fact of that seems to contradict our current understanding of entropy. That implies that there is something very fundamental about the universe which we don't understand.

> The mere fact of that seems to contradict our current understanding of entropy What part of our understanding does it contradict? The second law of thermodynamics says that entropy increases with time; this seems entirely consistent with a low-entropy past. One explanation for why the universe began in a low entropy state is that that state has a very low description length. (This is a bit of a truism, since descri…

Your reasoning is strange. Actually, higher entropy is what we may call "of lower complexity" requiring ever-shorter description length.

Re: Entropy explained, with sheep (2016)

#25

Post by 0134340 »

keenmaster wrote: post #17
selim_tiotoys wrote: post #10

Earlier quoted context omitted.

There is a fantastic book by Leonard Susskind [0] that tackles this questions. His answer - rooted in string theory - is based on a "landscape of possibilities" and we happen to be in the place where all elementary particles (more specifically the Higgs) had the right energy configuration. [0] The cosmic Landscape: https://www.amazon.com/Cosmic-Landscape-String-Illusion-Inte...

Where did those particles come from? Is there any scientific theory for the beginning of the beginning? A friend who studied physics told me that there's no reason that matter/energy couldn't have just existed forever. I don't find that explanation satisfying. If "entropy always increases" is a universal rule, then there must have been a time where it went from zero to non-zero. If "matter cannot be created or destro…

>then there must have been a time where it went from zero to non-zero.

Take a step towards the door. On the next step, take half that step. Keep taking half the step as before and you'll never get to the door. Perhaps the multi/universe is so infinite that there's no end or beginning as we know it. You can fill in the blank with deities, anthropomorphic or what have you, but that's where science ends and religion begins.

Re: Entropy explained, with sheep (2016)

#26

Post by jbay808 »

PaulDavisThe1st wrote: post #14
jbay808 wrote: post #8

Earlier quoted context omitted.

This is a very good question. Yes, time reversal would also reverse the process of our perception and memory, so we would experience time "moving forward" even if time were "moving" backward. We would experience entropy increasing even if entropy were "decreasing with time". (And it's perfectly valid to call the past "+t" and the future "-t"; the laws of physics don't care; if you do that, you'll see that entropy dec…

Entropy decreasing is not equivalent to time reversal. [Edit: to expand a bit: time reversal requires that some previous macrostate is achieved again. Entropy decreasing merely requires that the system enters any macrostate represented by less microstates than the current one. Put in more simple terms, the ice cube could reform but in a different shape. Entropy would have decreased, but it would not "look like" time…

This is true! I oversimplified a bit, because it's much easier to concretely discuss that scenario and its consequences, and it's more important from a philosophical perspective. Just like it's much easier to catch ice cubes forming on film by rewinding a tape than to run the camera waiting for spontaneous entropy decrease.

Nonetheless, if the entropy of the whole universe were to consistently decrease for a sufficient time, even along a different route than time reversal, you should gradually start to notice that it's easier to form predictions or "memories" of the future than to remember the past, due to Landauer's principle. Before long, you should go back to considering the future to be the state of higher entropy.

Re: Entropy explained, with sheep (2016)

#27

Post by foota »

andrewflnr wrote: post #16

So one thing I've never understood is how you can "count" microstates, or bits required to describe them, when the relevant physical parameters all seem to be real numbers. For instance, a gas of N atoms is described by 6N real numbers (3d position and velocity) regardless of how hot it is. The article talks about quanta of energy, but that seems like a simplification at best: a given interaction might be quantized,…

IANAP but there's two different things that come to mind.

Even if the number of states were infinite, as long as there's a reasonable probability distribution you can know you can integrate over the probabilities that have some property vs another (say: solid vs not).

Secondly, energy is quantized (on a very very very small level) in reality. Ymmv though, I tried googling this and read some stuff about waves being quantized and particles not and about how it depends on what system you're looking at and I had to drop out of quantum physics when I took it :-)

Re: Entropy explained, with sheep (2016)

#28

Post by jbay808 »

novaRom wrote: post #24
jbay808 wrote: post #13

Earlier quoted context omitted.

> The mere fact of that seems to contradict our current understanding of entropy What part of our understanding does it contradict? The second law of thermodynamics says that entropy increases with time; this seems entirely consistent with a low-entropy past. One explanation for why the universe began in a low entropy state is that that state has a very low description length. (This is a bit of a truism, since descri…

Your reasoning is strange. Actually, higher entropy is what we may call "of lower complexity" requiring ever-shorter description length.

A higher entropy state has a longer description length.

For example, let's say I have a magic electron microscope that can scan and record the exact position and velocity of each particle in some 1-cubic-micron volume, to within Heisenberg uncertainty limits and some finite digitization precision.

If my sample is a 1-cubic-micron volume of flawless monocrystalline silicon at 0 Kelvin, I can 'zip' my recording and transmit that description in a much shorter sentence (in fact, I just sent it to you!) than if my sample is a cubic micron of room-temperature saltwater (whose macrostate I just described, but whose microstate I did not).

Re: Entropy explained, with sheep (2016)

#29

Post by jbay808 »

keenmaster wrote: post #17
selim_tiotoys wrote: post #10

Earlier quoted context omitted.

There is a fantastic book by Leonard Susskind [0] that tackles this questions. His answer - rooted in string theory - is based on a "landscape of possibilities" and we happen to be in the place where all elementary particles (more specifically the Higgs) had the right energy configuration. [0] The cosmic Landscape: https://www.amazon.com/Cosmic-Landscape-String-Illusion-Inte...

Where did those particles come from? Is there any scientific theory for the beginning of the beginning? A friend who studied physics told me that there's no reason that matter/energy couldn't have just existed forever. I don't find that explanation satisfying. If "entropy always increases" is a universal rule, then there must have been a time where it went from zero to non-zero. If "matter cannot be created or destro…

You might enjoy Julian Barbour's theory of timeless physics, as described in his book "the End of Time".

Re: Entropy explained, with sheep (2016)

#30

Post by PaulDavisThe1st »

jbay808 wrote: post #26
PaulDavisThe1st wrote: post #14

Earlier quoted context omitted.

Entropy decreasing is not equivalent to time reversal. [Edit: to expand a bit: time reversal requires that some previous macrostate is achieved again. Entropy decreasing merely requires that the system enters any macrostate represented by less microstates than the current one. Put in more simple terms, the ice cube could reform but in a different shape. Entropy would have decreased, but it would not "look like" time…

This is true! I oversimplified a bit, because it's much easier to concretely discuss that scenario and its consequences, and it's more important from a philosophical perspective. Just like it's much easier to catch ice cubes forming on film by rewinding a tape than to run the camera waiting for spontaneous entropy decrease. Nonetheless, if the entropy of the whole universe were to consistently decrease for a sufficie…

I think you're priviledging microstates. There are plenty of entropy decreases that are possible without the ice cube reforming. They're (extremely) unlikely of course, but somewhat less unlikely than the new, singular microstate you're asserting is somehow "less of a coincidence". It's vastly more likely (for example) that 1% of the particle velocities reverse than all of them doing so, and that could (depending ...) still lead to a decrease in the entropy of the system (but not a reformed ice cube).

I don't see how a long term entropy decrease that does not follow the time reversal route could be easier to form predictions in. There are many possible higher entropy states for the water than the water sitting in the glass, and if the universe enjoyed random entropy decreases, I see no reason why it would tend to pick certain macrostates over others.

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