Comment by ludwik

Comment by ludwik 10 hours ago

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> there are far more ways for a system to be disordered than ordered

I'm a complete layman when it comes to physics, so forgive me if this is naive — but aren't "ordered" and "disordered" concepts tied to human perception or cognition? It always seemed to me that we call something "ordered" when we can find a pattern in it, and "disordered" when we can't. Different people or cultures might be able to recognize patterns in different states. So while I agree that "there are more ways for a system to be disordered than ordered," I would have thought that's a property of how humans perceive the world, not necessarily a fundamental truth about the universe

mr_mitm 9 hours ago

You only hear these terms in layman explanations. Physics has precise definitions for these things. When we say "ordered", we mean that a particular macrostate has only few possible microstates.

Check this Wikipedia article for a quick overview: https://en.wikipedia.org/wiki/Microstate_(statistical_mechan...

Details can be found in any textbook on statistical mechanics.

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  • Gravityloss 7 hours ago

    Exactly. The coin flipping example is a very nice way to put it. It works since the coins are interchangeable, you just count the number of heads or tails.

    If the coins were of different color and you took that into account, then it wouldn't work.

    It's not intuitive to me what gravity has to do with entropy though, as it's classically just a force and completely reversible (unlike entropy)? Ie if you saw a video of undisturbed objects only affected by gravity, you couldn't tell if the video was reversed.

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    • floxy an hour ago

      > Ie if you saw a video of undisturbed objects only affected by gravity, you couldn't tell if the video was reversed.

      How does that work with things like black holes? If you saw an apple spiral out of a black hole, wouldn't you suspect that you were watching a reversed video? Even if you take account the gravitational waves?

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      • immibis 6 minutes ago

        That's the question of why time only goes forwards. It seems to be that the universe started in an extremely low-entropy state. It will go towards high entropy. In a high entropy state (e.g. heat death, or a static black hole), there's no meaningful difference between going forwards or backwards in time - if you reverse all the velocities of the particles, they still just whizz around randomly (in the heat death case) or the black hole stays a black hole.

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      • kgwgk an hour ago

        If you saw a comet coming from the sun, or a meteorite coming from the moon, etc. you would also find that suspicious.

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hackinthebochs 10 hours ago

Think minimum description length. Low entropy states require fewer terms to fully describe than high entropy states. This is an objective property of the system.

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  • sat_solver 9 hours ago

    You're thinking of information entropy, which is not the same concept as entropy in physics. An ice cube in a warm room can be described using a minimum description length as "ice cube in a warm room" (or a crystal structure inside a fluid space), but if you wait until the heat death of the universe, you just have "a warm room" (a smooth fluid space), which will have an even shorter mdl. Von Neuman should never have repurposed the term entropy from physics. Entropy confuses a lot of people, including me.

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  • zmgsabst 8 hours ago

    “Number of terms” is a human language construct.

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    • hackinthebochs 8 hours ago

      No, it's a representation construct, i.e. how to describe some system in a given basis. The basis can be mathematical. Fourier coefficients for example.

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      • zmgsabst 6 hours ago

        Mathematics is a human language. It being a formal language doesn’t change that.

        Further, it’s not objective: you’re choosing the basis which causes the complexity, but any particular structure can be made simple in some basis.

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  • amelius 10 hours ago

    In a deterministic system you can just use the time as a way to describe a state, if you started from a known state.

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