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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

#251

Post by potamic »

hellohello2 wrote: post #186
abetusk wrote: post #160

Entropic gravity is like the "brazil nut effect" [0] [1]. The idea is that if you shake a glass full of different sized nuts, the large ones will rise to the top. From what I understand, this is because larger objects have more mass, moving slower when shaked, so as the larger (brazil nuts) don't move as much relative to the smaller ones (peanuts), and because of gravity, there's a cavity left under the brazil nut wh…

Not a physicist either but this passage from the Feynman lectures seem related to what you are describing: https://www.feynmanlectures.caltech.edu/I_07.html "Many mechanisms for gravitation have been suggested. It is interesting to consider one of these, which many people have thought of from time to time. At first, one is quite excited and happy when he “discovers” it, but he soon finds that it is not correct. It wa…

> earth, in moving around the sun, would impinge on more particles which are coming from its forward side than from its hind side

Would this be true if the speed of particles is constant in all frames of reference?

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

#253

Post by raattgift »

klodolph wrote: post #243
forgotoldacc wrote: post #241

Earlier quoted context omitted.

This sounds really dumb, so forgive me. But one thing that's always felt weird to me about gravity is how we consider things to be one body. Like yes, when we look at earth from incredibly far away, it's a pale blue dot. But all those oceans on it are flowing and separate from the solid ground underneath. Those large boulders on earth that would have their own (tiny) gravitational pull on their own in space are just…

There’s a bit of math you can do where you calculate the gravitational effect of standing on a sphere. You can redistribute the mass within the sphere and it won’t affect the gravitational pull, assuming it’s radially symmetrical. One of those unintuitive results. It probably only works in classical gravity but it’s still neat.

The bit of math is the Shell Theorem https://en.wikipedia.org/wiki/Shell_theorem>.

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

#254

Post by Gravityloss »

kgwgk wrote: post #240
Gravityloss wrote: post #221

Earlier quoted context omitted.

Comets are in elliptical orbits around the sun so literally half the time they're traveling away from the sun.

Sometimes they don’t make it: https://en.wikipedia.org/wiki/Sungrazing_comet https://www.space.com/8478-comet-collision-sun-captured-3.ht...

Yea and those happen when other forces than gravity come into play. When matter starts colliding.

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

#255

Post by killerstorm »

jstanley wrote: post #34
killerstorm wrote: post #32

Earlier quoted context omitted.

Isn't that how equations get solved? Pretty much anything known entered through such placeholder, it's just that equations could be connected more easily. It's not like Higgs field is something you can directly observe

Maybe, (I don't know), but it's easy to accidentally come up with a theory of "mysterious stuff" that appears to explain something, but neither constrains your expectation nor provides predictions. Phlogiston is the classic example. https://www.lesswrong.com/posts/RgkqLqkg8vLhsYpfh/fake-causa...

I'm pretty sure physicists are aware that "dark matter" hypothesis is nowhere as solid as theory of electromagnetism.

It's still useful to denote the area of study.

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

#256

Post by klodolph »

Agentlien wrote: post #247
klodolph wrote: post #243

Earlier quoted context omitted.

There’s a bit of math you can do where you calculate the gravitational effect of standing on a sphere. You can redistribute the mass within the sphere and it won’t affect the gravitational pull, assuming it’s radially symmetrical. One of those unintuitive results. It probably only works in classical gravity but it’s still neat.

That actually sounds really intuitive to me. If you start with a uniform mass and then redistribute mass symmetrically it makes sense that the change in the two sides would cancel out.

It works for some types of symmetry but not others!

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

#257

Post by Agentlien »

klodolph wrote: post #256
Agentlien wrote: post #247

Earlier quoted context omitted.

That actually sounds really intuitive to me. If you start with a uniform mass and then redistribute mass symmetrically it makes sense that the change in the two sides would cancel out.

It works for some types of symmetry but not others!

Interesting! Now, that sounds like a more unintuitive result to me. Can you give examples of symmetries for which it doesn't work?

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

#258

Post by kgwgk »

Gravityloss wrote: post #254
kgwgk wrote: post #240

Earlier quoted context omitted.

Sometimes they don’t make it: https://en.wikipedia.org/wiki/Sungrazing_comet https://www.space.com/8478-comet-collision-sun-captured-3.ht...

Yea and those happen when other forces than gravity come into play. When matter starts colliding.

Every object has been subject to forces other gravity at some point.

And the point is that sometimes comets do indeed fall into the Sun. If you object to people calling that a comet that’s fine - we can use whatever name you want.

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

#260

Post by throwawaymaths »

cantor_S_drug wrote: post #134
pif wrote: post #40

As an experimental physicist, I refuse to get excited about a new theory until the proponent gets to an observable phenomenon that can fix the question.

Sometimes I wonder, imagine if our physics never allowed for Blackholes to exist. How would we know to stress test our theories? Blackholes are like standard candles in cosmology which allows us to make theoretical progress.

we dont know much about black holes, and there are theories which dont allow for proper black holes but do allow for objects that look like black holes in the limit (but e.g. don't produce Hawking radiation)
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