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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

#81

Post by johnea »

But consider the "monkeycide paradox". If we start a nuclear war, and kill every single primate on the planet, does the universe cease to exist? Does time start running in reverse? Maybe time would go back to before we nuked everyone out of existence, and life would be like one of those endless time loop anime? Will matter start spewing out of black holes instead of going in because there was no monkey there to watch it? Would it be enough if a dog observed the universe? (they're "like our family" after all) or a squid? What about a yeast cell?

Obviously this is hyperbole 8-) but I think the point is clear. If anyone really believes that the existence of primate life on our little planet "observing the universe" is what makes all physical processes advance, they have some serious issues of overcharged ego.

Of course a theory doesn't have to be completely correct to be useful. Old ideas of heat as a fluid have been supplanted, but they still helped design working systems in their time. Modern ideas of quantum mechanics, as incomplete as they are, still model a concept of "tunneling" that's sufficiently accurate to make semiconductors work.

Or, you can just run with the Rovelli quote from the article: “What they’re telling me is bullshit” 8-)

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

#82

Post by johnea »

openrisk wrote: post #14

Is there a specific name for the art and craft of presenting a topic online (as a web page) using a flow of text interspersed with interactive activities? Whatever the name of this approach, quantamagazine is definitely good at it!

I'm pretty sure this is called "writing"

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

#83

Post by gligorot »

kqr wrote: post #78
zV62drdTw6CM wrote: post #76

Earlier quoted context omitted.

First, when I joined the project, it wasn’t clear how it would be published. Svelte, which outputs compiled JavaScript, can fit into many CMS workflows that newspapers/publishers use. I believe Svelte was developed by Rich Harris at the NY Times for this very reason. We ended up using iFrames, so other frameworks like React could have been used. Second, Svelte is very well suited for these small interactives because…

> We ended up using iFrames, so other frameworks like React could have been used. Wait, wasn't one of the original selling points of React that it could be embedded piecewise to enhance interactivity of the parts of pages that needed it? It should certainly not need a separate page!

It’s a PITA to extract a stateful react component to a standalone piece of code that can be inserted in a random place (in another page, served via API etc.). Not sure about Svelte, but achieving this in React was unexpectedly hard/impossible in our use case.

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

#84

Post by [deleted] »

IIAOPSW wrote: post #63
mojomark wrote: post #39

Earlier quoted context omitted.

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…

[deleted]

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

#85

Post by mike_ivanov »

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…

Interesting. Could you share a link to your thesis?

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

#87

Post by codethief »

kqr wrote: post #78
zV62drdTw6CM wrote: post #76

Earlier quoted context omitted.

First, when I joined the project, it wasn’t clear how it would be published. Svelte, which outputs compiled JavaScript, can fit into many CMS workflows that newspapers/publishers use. I believe Svelte was developed by Rich Harris at the NY Times for this very reason. We ended up using iFrames, so other frameworks like React could have been used. Second, Svelte is very well suited for these small interactives because…

> We ended up using iFrames, so other frameworks like React could have been used. Wait, wasn't one of the original selling points of React that it could be embedded piecewise to enhance interactivity of the parts of pages that needed it? It should certainly not need a separate page!

It doesn't.

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

#88

Post by TexanFeller »

Entropy got a lot more exciting to me after hearing Sean Carroll talk about it. He has a foundational/philosophical bent and likes to point out that there are competing definitions of entropy set on different philosophical foundations, one of them seemingly observer dependent:

- https://youtu.be/x9COqqqsFtc?si=cQkfV5IpLC039Cl5

- https://youtu.be/XJ14ZO-e9NY?si=xi8idD5JmQbT5zxN

Leonard Susskind has lots of great talks and books about quantum information and calculating the entropy of black holes which led to a lot of wild new hypotheses.

Stephen Wolfram gave a long talk about the history of the concept of entropy which was pretty good: https://www.youtube.com/live/ocOHxPs1LQ0?si=zvQNsj_FEGbTX2R3

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

#89

Post by Jerrrry »

Computers are finite ergo the largest number any computer can compute is all ones in binary.

That's it's Busy Beaver number, but think how easy all ones in binary is to compress from an information theory standpoint.

So the most entrophic state would be the one state requiring the most compression.

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

#90

Post by kergonath »

whatshisface wrote: post #79
kergonath wrote: post #61

Earlier quoted context omitted.

> 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…

The enthalpy changes measured by a calorimeter are dependent on the design of the calorimeter, which could have been a different piece of equipment. In a sense, that makes it dependent on the definition of enthalpy. If you introduced a new bit of macro information to the definition of an ensemble, you'd divide the number of microstates by some factor. That's the micro level equivalent of macroscopic entropy being und…

> The enthalpy changes measured by a calorimeter are dependent on the design of the calorimeter, which could have been a different piece of equipment.

Right, but that is true of anything. Measuring devices need to be calibrated and maintained properly. It does not make something like a distance subjective, just because someone is measuring it in cm and someone else in km.

> If you introduced a new bit of macro information to the definition of an ensemble, you'd divide the number of microstates by some factor. That's the micro level equivalent of macroscopic entropy being undefined up to an additive constant.

It would change the entropy of your model. An ensemble in statistical Physics is not a physical object. It is a mental construct and a tool to calculate properties. An actual material would have whatever entropy it wants to have regardless of any assumptions we make. You would just find that the entropy of the material would match the entropy of one of the models better than the other one. If you change your mind and re-run the experiment, you’d still find the same entropy. This happens e.g. if we assume that the experiment is at a constant volume while it is actually under constant pressure, or the other way around.

> In a sense, that makes it dependent on the definition of enthalpy.

Not really. A joule is a joule, a kelvin is a kelvin, and the basic laws of thermodynamics are some of the most well tested in all of science. The entropy of a bunch of atoms is not more dependent on arbitrary definitions than the energy levels of the atoms.

> The measurables don't tell you S, they only tell you dS.

That’s true in itself, the laws of Thermodynamics are invariant if we add a constant term to the entropy. But it does not mean that entropy is subjective: two observers agreeing that the thing they are observing has an entropy of 0 at 0 K will always measure the same entropy in the same conditions. And it does not mean that actual entropy is dependent on specific assumptions about the state of the thing.

This is also true of energy, and electromagnetic potentials (and potentials in general). This is unrelated to entropy being something special or subjective.

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