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What is entropy? A measure of just how little we know

quantamagazine.org

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Re: What is entropy? A measure of just how little we know

#41

Post by Serenade »

daoboy wrote: post #20

The interactive graphic that tries to show entropy is subjective doesn't sit right for me. They fail to properly define the macrostate of the system under consideration, then show two different observed entropies for two different macrostates (Colors for Alice and Shapes for Bob). That doesn't show entropy is subjective, it shows that defining the system is subjective. The same two macrostates would still have the sa…

Thank you for articulating what was bothering me about this.

I couldn't quite put my finger on it, but you're right. They are confusing defining the system with defining the entropy of a system and then saying it's the entropy that is subjective. That isn't the case at all. Entropy is just a measurement.

Re: What is entropy? A measure of just how little we know

#42

Post by FrustratedMonky »

api wrote: post #36
amelius wrote: post #35

Makes sense. If we knew the theory of everything and the initial conditions of the universe, then we could just compute the next episode of a series instead of streaming it.

Not necessarily. A theory of everything does not imply either the computability of a future state or determinism. Even if our ToE is deterministic the universe may be computationally irreducible, meaning it cannot be computed accurately at lower resolution in all cases. Note that such a universe could contain within it regions that are computationally reducible, just not the whole and not all regions. I would expect…

"cannot be computed accurately at lower resolution"

The Map is not the Territory.

Our universe is the lowest resolution. So to compute the next instant in our Universe, would need another entire Universe.

We could be the computation occurring.

Re: What is entropy? A measure of just how little we know

#43

Post by plank »

mojomark wrote: post #39
plank wrote: post #26

Interesting to read this, 27 years after my PhD* (theoretical physics), in which I did compare the view WITH and the view WITHOUT ‘unknowns’ causing entropy as a driver. * My PhD was about how to treat a (quantum mechanical) system inside a cavity: a cavity with one perfect mirror and one 99.999999% perfect mirror. The (one dimensional) universe was made whole by another perfect mirror at the other side of the non-pe…

I read you're comment with interest, but ultimately I can't understand the point being made because I don't know what kind of mirror you're referring to (optical?), I don't know what 'l' or 'L' represent (lateral spacing of mirrors?, vacuum energy desnities?), and the last sentence I think maybe the word 'how' should be deleted?

Answers to your questions: 1): all the way to the left, a mirror with a reflectivity|r| of 1 (or a 100%). In the middle an |r| of slightly below 1. Yes, optical, system with photons (a and a^dagger with [a,a^dagger]=1). 2) distance between mirrors 1 and 2: l. Distance mirror 2 and 3:L. (Later taking the limit L/l ==>> infinity) 3) the how is actually correct, I guess the word behaves is missing twice: .... how .... behaves and a .... behaves.

Re: What is entropy? A measure of just how little we know

#45

Post by api »

FrustratedMonky wrote: post #42
api wrote: post #36

Earlier quoted context omitted.

Not necessarily. A theory of everything does not imply either the computability of a future state or determinism. Even if our ToE is deterministic the universe may be computationally irreducible, meaning it cannot be computed accurately at lower resolution in all cases. Note that such a universe could contain within it regions that are computationally reducible, just not the whole and not all regions. I would expect…

"cannot be computed accurately at lower resolution" The Map is not the Territory. Our universe is the lowest resolution. So to compute the next instant in our Universe, would need another entire Universe. We could be the computation occurring.

That’s what I meant, but perhaps did not describe well.

Re: What is entropy? A measure of just how little we know

#46

Post by guerrilla »

LudwigNagasena wrote: post #38
guerrilla wrote: post #8

Earlier quoted context omitted.

> mundane observation What makes an observation mundane? I think what you said is insightful and demonstrates intelligence. I don't think it's at all obvious to the masses of students that have poured over introductory physics textbooks. In fact, it seems to me that often entropy is taught poorly and that very few people understood it well but that we are beginning to correct that. I point to the heaps of popsci maga…

Maybe if you opened only introductory physics textbooks then it’s not mundane; but If you opened introductory information theory textbooks, statistical textbooks, introductions to Bayesian probability theory, articles about MaxEnt thermodynamics including articles by E.T. Jaynes, then it’s a quite mundane observation.

So, what you're saying is, not very mundane at all and, in fact, that it's specialized knowledge requiring advanced education. ;)

Re: What is entropy? A measure of just how little we know

#47

Post by FrustratedMonky »

api wrote: post #45
FrustratedMonky wrote: post #42

Earlier quoted context omitted.

"cannot be computed accurately at lower resolution" The Map is not the Territory. Our universe is the lowest resolution. So to compute the next instant in our Universe, would need another entire Universe. We could be the computation occurring.

That’s what I meant, but perhaps did not describe well.

Sorry, I was really just re-stating it, to see if I was grasping the point.

Re: What is entropy? A measure of just how little we know

#48

Post by Trasmatta »

noiv wrote: post #44

What about the efficiency to remove entropy? Is there a threshold our combined efforts called science cannot surpass? Do we need Frank Herbert’s spice to progress?

A localized reduction of entropy will always result in an increase of entropy in the larger system.

It doesn't matter how efficient your process is, the entropy of the surrounding system will ALWAYS increase as the result of the work needed to effect a localized reduction.

Re: What is entropy? A measure of just how little we know

#49

Post by markisus »

kergonath wrote: post #31
kqr wrote: post #2

> As physicists have worked to unite seemingly disparate fields over the past century, they have cast entropy in a new light — turning the microscope back on the seer and shifting the notion of disorder to one of ignorance. Entropy is seen not as a property intrinsic to a system but as one that’s relative to an observer who interacts with that system. Maybe I have the benefit of giant shoulders, but this seems like a…

> Maybe I have the benefit of giant shoulders, but this seems like a fairly mundane observation. It is not mundane, and it is also not right, at least for entropy in Physics and Thermodynamics. > High-entropy states are those macrostates which have many corresponding microstates. That is how you deduce entropy form a given model. But entropy is also something that we can get from experimental measurements. In this ca…

Maybe the experimental apparatus is not objective. The quantities we choose to measure are dictated by our psychological and physiological limitations. The volume of a container is not objectively defined. An organism which lives at a faster time scale will see the walls of the container vibrating and oscillating. You must convince the organism to average these measurements over a certain time scale. This averaging throws away information. This is the same with other thermodynamic quantities.

Re: What is entropy? A measure of just how little we know

#50

Post by rcxdude »

niemandhier wrote: post #6
pndy wrote: post #3

http://www.thelastquestion.net/ - in case someone missed it somehow

Wow. When did we take the turn from sci-fi like that to the ever dystopian laments we read today.

It's pretty cyclical, there's older sci-fi that's more dystopian and still older sci-fi then that which is optimistic. (and of course, the trends are only trends)
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