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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

#61

Post by kergonath »

markisus wrote: post #49
kergonath wrote: post #31

Earlier quoted context omitted.

> 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 t…

> The quantities we choose to measure are dictated by our psychological and physiological limitations.

No. The enthalpy changes measured by a calorimeter are not dependent on our psychological limitations.

> The volume of a container is not objectively defined.

Yes, it is, for any reasonable definition of "objective". We know how to measure lengths, we know how they change when we use different frames of reference so there is no situation in which a volume is subjective.

> An organism which lives at a faster time scale will see the walls of the container vibrating and oscillating.

This does not matter. We defined a time scale from periodic physical phenomena, and then we know how time changes depending on the frame of reference. There is no subjectivity in this, whatever is doing the measurement has no role in it. Time does not depend on how you feel. It’s Physics, not Psychology.

> This is the same with other thermodynamic quantities.

No, it’s really not. You seem to know just enough vocabulary to be dangerous and I encourage you to read an introductory Physics textbook.

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

#62

Post by bee_rider »

ziofill wrote: post #56

Very nice article. There’s an alternative way of thinking of the Gibbs paradox, which is to attach labels to the particles. This naturally makes them distinguishable and increases the total number of possible configurations, and with it the maximum value of the entropy.

Attaching labels to the particles would make them fundamentally different types of particles, right? So it doesn’t seem that surprising that a system with different types of particles would be different.

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

#63

Post by IIAOPSW »

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?

The imperfect mirror means that epsilon% of the time the light goes through to a much larger "back room" whereas (1-epsilon)% of the time the light just reflects like normal. The point being made is that this is an extension of an ordinary ideal cavity to include unavoidable (but weak) interaction with the much larger system outside of it (aka the whole universe). It just so happens the much larger external system is also being modeled as a simple 1d cavity.

In other words, entropy is equivalent to bits of information needed to specify the complete state of the system leaking outside of the confines of where those bits are being observed by an experiment (eg tunneling through an imperfect mirror).

Entropy is an accounting tool to keep track of how many bits are missing, and how far this ignorance has percolated into what you can safely predict about the system.

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

#64

Post by kergonath »

LudwigNagasena wrote: post #40
kergonath wrote: post #31

Earlier quoted context omitted.

> 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…

> It is not mundane, and it is also not right, at least for entropy in Physics and Thermodynamics. Articles about MaxEnt thermodynamics by E.T. Jaynes where he talks about the “anthropomorphic” nature of entropy date back to 1960s. How is that not right in physics?

By the look of it, it is another misguided attempt to apply information theory concepts to thermodynamics. Entropy as information is seductive because that way we think we can understand it better, and it looks like it works. But we need to be careful because even though we can get useful insights from it (like Hawking radiation) it’s easy to reach unphysical conclusions.

> How is that not right in physics?

Why would it be right? Was it used to make predictions that were subsequently verified?

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

#65

Post by pixl97 »

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.

I mean they had dystopian sci-fi back then too...

Technology changes, yet people remain ever the assholes.

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

#66

Post by pessimizer »

pndy wrote: post #18
srean wrote: post #12

Earlier quoted context omitted.

For all who haven't, please read the other two as well. Last Answer Nightfall

Gotta mention that Nightfall exists as both Asimov's short story and a novel he co-wrote with Robert Silverberg nearly 50 years later

And that the short story is the important one.

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

#67

Post by [deleted] »

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.

[deleted]

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

#68

Post by zV62drdTw6CM »

Happy to see the article being discussed here! I was responsible for the technical implementation of the interactives. If you are interested in the source code, you can find it here: https://github.com/jnsprnw/mip-entropy It’s built in Svelte 5 with Tailwind.

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

#69

Post by kgwgk »

kergonath wrote: post #64
LudwigNagasena wrote: post #40

Earlier quoted context omitted.

> It is not mundane, and it is also not right, at least for entropy in Physics and Thermodynamics. Articles about MaxEnt thermodynamics by E.T. Jaynes where he talks about the “anthropomorphic” nature of entropy date back to 1960s. How is that not right in physics?

By the look of it, it is another misguided attempt to apply information theory concepts to thermodynamics. Entropy as information is seductive because that way we think we can understand it better, and it looks like it works. But we need to be careful because even though we can get useful insights from it (like Hawking radiation) it’s easy to reach unphysical conclusions. > How is that not right in physics? Why would…

That misguided attempt has resulted in full graduate courses and textbooks. Maybe one look is not all that it takes to fully assess its worthiness.

https://www.amazon.com/Microphysics-Macrophysics-Application...

https://arxiv.org/pdf/cond-mat/0501322

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

#70

Post by [deleted] »

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…

[deleted]
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