High School Understanding Entropy & Universe Expansion: A Beginner's Guide

[Keith Wright]

This is my first post and I need to preface my question by saying I have no physics background, so I'm genuinely asking for help in understanding.

A thought occurred to me about the continuing expansion and acceleration of the universe and I'm asking for your help in understanding where my thinking may be flawed. Because It seems odd that entropy doesn't slow the universe's expansion,
I began thinking why. Is it possible that the black hole at the center of our galaxy is causing the earth, our solar system, and all local systems to move faster as we draw closer to the center? And as a result, we perceive that the universe is speeding up and away, relative to our own "time slowing"?

 

[Nugatory]

Because It seems odd that entropy doesn't slow the universe's expansion

Entropy is not a force that can push or pull on something, so it can't speed things up or slow them down.

Is it possible that the black hole at the center of our galaxy is causing the earth, our solar system, and all local systems to move faster as we draw closer to the center? And as a result, we perceive that the universe is speeding up and away, relative to our own "time slowing"?

No and no. The solar system isn't being drawn closer to that black hole, it's more like the planets orbiting the sun without being pulled into the sun.

 

[BvU]

No

And:
Helo Keith,

Do some searching PF and perhaps get a background that way ...

 

[pervect]

While there are some interesting papers that suggest there could be a relation between entropy and gravity, it's not a common view, though it is published in a peer reviewed paper. Looking through the wiki article on "entropic gravity", I find https://arxiv.org/abs/1001.0785

The relationship to the title of this thread is that entropy may be related to gravity, and gravity is most likely related to the slowing down of the expansion of the universe, thus entropy may be related to the slowing down of the universal expansion.

This theory is outside the scope of General relativity, though according to the author of the paper, the approach eventually winds up with the Einstein field equations, which is the mathematical heart of General relativity.

However, our sun (and by extension the solar system) is orbiting the center of the galaxy, rather than falling into it, so the above paper probably has little to do with the OP's personal theory.

T

 

[Vanadium 50]

Because It seems odd that entropy doesn't slow the universe's expansion,

You don't need to go to exotic situations: an object in motion remains in motion. Entropy doesn't change that.

 

[PeterDonis]

gravity is most likely related to the slowing down of the expansion of the universe

But the expansion isn't slowing down now, and hasn't been for the past few billion years. If the Verlinde model in the paper you referenced, or something like it, is correct, it would have to explain accelerated expansion as well as decelerated expansion. Whatever that explanation is, it isn't going to be as simple as "entropy slows the universe's expansion".

 

[pervect]

Gravity tends to slow the expansion down. Dark energy , aka the cosmological constant, aka quintessence, causes the expansion to accelerate. I assume one can add dark energy to the Verlin model in the same way as one can add it to General relativity but I don't really understand the Verlin model that well, I could be mistaken.

 

[PeterDonis]

Gravity tends to slow the expansion down.

I would say "matter and radiation", not "gravity" here. "Gravity" here has to mean "spacetime curvature", and dark energy causes spacetime curvature just like matter and radiation do; the difference is the kind of spacetime curvature it causes. So the effects of dark energy are "gravity" just as much as the effects of matter and radiation are.