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Is gravity just entropy rising? Long-shot idea gets another look

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Re: Is gravity just entropy rising? Long-shot idea gets another look

#291

Post by cryptonector »

raattgift wrote: post #264
cryptonector wrote: post #135

Earlier quoted context omitted.

You have it backwards. The lowest entropy state of the universe would be if there were no attractive forces, only repellent forces, as then all particles would be forced into something of an expanding lattice, but with all particles equidistant from all nearest neighbors (of the same type). It is gravity which disrupts this and causes clumping, and that _increases_ entropy. I know it's confusing because normally one…

If everything must be constrained to the lattice points, yes. However, empty space has high Boltzmann entropy: you can cut a patch of empty space from here and swap it for the same volume of empty space from there, and the two coarse grain macrostates will be indistinguishable. Expanding de Sitter quasi-vacuum has tremendous growth in entropy. Gibbons and Hawking gives this (for 3+1d de Sitter) as a quarter of the ho…

Oh, and by the way, entropy is the evolution of a system given the forces in it. So yes, in a universe with only repellent forces at first it would have low entropy (like ours did) and then as the particles get forced into an ever emptier lattice the universe would have more entropy. It's the forces -attractive or repellent- that make the system evolutions possible that lead to higher entropy over time.

Re: Is gravity just entropy rising? Long-shot idea gets another look

#292

Post by antonvs »

ajkjk wrote: post #269
antonvs wrote: post #185

Earlier quoted context omitted.

You’re glossing over an important point: your knowledge of the future state of the system is “heads or tails”. One of the things entropy tells us how a system is likely to evolve in future. But looking at this another way, entropy actually helps dictate how it will evolve in future. And we can prove that mathematically.

What are you talking about? Entropy doesn't tell us that at all. Entropy tells us how much data is encodes between two ways of describing a value. It has nothing to do with time at all.

You're confusing two different perspectives on entropy without understanding either properly. In physics, which is what's being discussed, entropy is certainly closely related to time.

Re: Is gravity just entropy rising? Long-shot idea gets another look

#293

Post by Ma8ee »

fc417fc802 wrote: post #290
Ma8ee wrote: post #281

Earlier quoted context omitted.

The existence of a rock is definitely a physical property, and thus is the number of rocks in a collection a physical property, at least as much as temperature is it for a gas.

Numbers aren't "existence" they're a property of an abstract set. The observer draws a fairly arbitrary mental line around a cluster of objects. Whether the set numbers two, three, or four cannot be determined by observing one of the rocks in isolation. Fundamental physical properties don't depend on other members of an arbitrary set as determined by an observer. > at least as much as temperature is But here I've bee…

Why would you need to observe anything in isolation for it to be a physical property? This is the proposition that I find absurd. It’s like saying that a hydrogen atom isn’t really a hydrogen atom, but just an arbitrary set of nucleons.

Re: Is gravity just entropy rising? Long-shot idea gets another look

#294

Post by nathan_compton »

quantadev wrote: post #288
nathan_compton wrote: post #286

Earlier quoted context omitted.

I'm not trying to disprove what you are saying, I'm just providing some context. Although, point of fact, I think its a weird framing, since even GR, which you seem to be talking about, casts gravity as reciprocal with matter. As the old saying goes: spacetime tells matter how to move, matter tells spacetime how to bend. If that isn't an interaction, I don't know what is. But, that aside, the idea that gravity is spa…

Shape of space simply means the "Metric Tensor", and saying it's the sum total of what General Relativity is describing isn't some "bold" or "weird" framing (your words); it's both complete and correct.

It isn't so simple, even in GR:

https://plato.stanford.edu/entries/spacetime-holearg/

Re: Is gravity just entropy rising? Long-shot idea gets another look

#295

Post by quantadev »

nathan_compton wrote: post #294
quantadev wrote: post #288

Earlier quoted context omitted.

Shape of space simply means the "Metric Tensor", and saying it's the sum total of what General Relativity is describing isn't some "bold" or "weird" framing (your words); it's both complete and correct.

It isn't so simple, even in GR: https://plato.stanford.edu/entries/spacetime-holearg/

Thanks for the link. I'm not even saying GR isn't emergent from something else. All I'm saying is that it contains the sum total of what is currently the proven mathematics governing gravity.

I myself have many 'unproven' things about Physics, that I believe, with a high degree of probability (near certainty). Dig thru my past posts for lots of them. For example, I believe Minkowski Space is indeed itself emergent. I think our entire universe exists on the "surface" of a 3D Event Horizon (manifold). I don't believe in the Big Bang, because our reality 'formed' not from a singularity (exploding out), but like a Black Hole (falling in). So I'm open to lots of ideas, but just pointing out the what we currently know as General Relativity, isn't even that complex, and is just about a shape (curvature/tensor) at every point in spacetime. It's all we've "proven".

Re: Is gravity just entropy rising? Long-shot idea gets another look

#296

Post by heyjamesknight »

cwharris wrote: post #128
heyjamesknight wrote: post #106

Earlier quoted context omitted.

Entropy isn't a force. It doesn't "favor" anything. Its a property of statistics, information, and distributions. Also why does this have that particular ChatGPT social media post rhythm to it? Please, Lord, tell me we haven't reached the point where people are writing HN comments w/ AI.

You’re right. the cadence is written by ChatGPT. I’m pretty terrible at keeping my thoughts cohesive, so I often use it as a post processor. I’ll try not to do that. Because you had the decency to respond, I’ll spent some more time thinking about this and see if I can come up with a more well rounded response that incorporates more of the traditional language of physics. But to your point about entropy not being a “f…

Words have meanings. You can look them up and learn them.

If you're not willing to do that, then you should probably not try to participate in a technical discussion where the meaning of words is arguably paramount.

Re: Is gravity just entropy rising? Long-shot idea gets another look

#297

Post by Quarrel »

enriquto wrote: post #38
Quarrel wrote: post #20

Earlier quoted context omitted.

It does, but because you have to divide the energy change by c^2, it is really really hard to detect it, and mostly overwhelmed by other effects of the heating/cooling.

why do the units matter here? Under this theory, will a body at absolute zero have no observable mass? No attractive field around it, no inertia if you try to move it.

I'm only now seeing this a week later, but for E = mc^2, m is the rest mass.

rest mass = all the energies of the mass, not just its thermal energy. So, as it approaches 0 kelvin the thermal energy approaches 0 and the mass approaches its minimal possible energy (its kinetic energy approaches zero), but even at absolute zero, it still has the rest-mass of its fundamental particles (electrons, neutrons and protons) which have mass inherently. In practice, the scale of the mass of the particles massively outweighs the scale of the thermal mass, so while strictly true, it mostly doesn't matter.

So, because the scaling factor is stupid stupid large, changing temperature from anything to absolute zero does lower the mass, which does lower the gravity, but it just doesn't matter.

Re: Is gravity just entropy rising? Long-shot idea gets another look

#298

Post by heyjamesknight »

cwharris wrote: post #166
echelon wrote: post #129

Earlier quoted context omitted.

Because it has emdashes and ellipses that Chrome, Firefox, Mac, Linux, and Android text input controls do not natively produce. I don't know about iPhone. If you see these artifacts, it was authored in some other software (be it an editor or LLM) and pasted over.

I like how people are recognizing "OH THIS IS TOKEN OUTPUT", and that's like... the only thing you can come up with to refute the argument? Like not the actual content or meaning of the text, which I chose to post, but the mere fact that it wasn't typed in to a keyboard directly in a hacker news text box, but rather pasted after using a tool to refine the verbiage. Honestly? Great test for most posts. We live in a wo…

I come to HN because the caliber of poster here is above and beyond what you can find basically anywhere on the web.

If we wanted to debate ChatGPT, we can go do that on our own.

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