I Gravity of a Baseball-Sized Universe: Reach to Infinity?

[Pjpic]

When the observable universe was the size of a baseball, did its gravity (field?) extend to (as opposed to towards) infinity?

 

[PeterDonis]

The question can't really be answered as you ask it, because it includes the term "gravity field", which is not a good way to look at how the matter and energy in the universe affects its dynamics. Matter and energy is everywhere in the universe; it's not as though our observable universe is somehow different from the other parts. And the dynamics of the universe as a whole is determined by the matter and energy in the universe as a whole; there's no boundary line drawn around the observable universe that separates its effect from the effect of the rest.

 

[Vanadium 50]

The whole question assumes there is something outside of the universe we can use as a test mass. There isn't.

 

[BRIAN VORHIES]

Can the question be stated in this way?
Earlier in the expansion of the universe, when there was less empty space between matter, was the influence of gravity greater than it is now? I.e. did time pass at a slower rate, did entropy happen at a slower rate?
It seems to me that, being within the universe, we wouldn't be able to measure a difference. But if we could hold the past universe in our left hand, and the present in our right, and watched. Would disorder be increasing more slowly in the past, than it is in the present?

 

[PeterDonis]

Can the question be stated in this way?
Earlier in the expansion of the universe, when there was less empty space between matter, was the influence of gravity greater than it is now?

Still not answerable because "influence of gravity" isn't a good way of looking at it. As Vanadium50 has pointed out, there is no "outside reference" you can use to measure the "influence of gravity" of the universe.

did time pass at a slower rate, did entropy happen at a slower rate?

How would you make the comparison? The fact that there is no "outside reference" means there's no way to compare "rate of time flow" long ago to "rate of time flow" now.

It seems to me that, being within the universe, we wouldn't be able to measure a difference.

Correct.

if we could hold the past universe in our left hand, and the present in our right, and watched

There is no way to do this, so the question is not meaningful.

 

[BRIAN VORHIES]

Can't the answer be extrapolated mathematically? If time moves more slowly at sea level than it does on a mountain top, couldn't it be assumed that time would move more slowly at any given point in the universe, if the distance between every given point was decreased? If every stellar object in the universe was closer to Earth by half, wouldn't the force of gravity between me and every stellar object increase by 4? Slowing time?

 

[PeterDonis]

Can't the answer be extrapolated mathematically?

Answer to what?

If time moves more slowly at sea level than it does on a mountain top

Which has nothing whatever to do with comparing the early universe to now. They are two different scenarios that are modeled by two different solutions to the Einstein Field Equation. You can't just wave your hands and say "well, they look sort of the same". They aren't.

 

[PeterDonis]

The OP question has been sufficiently addressed. Thread closed.