13 votes
Accepted

Will a light come back within finite years?

We don't know if the universe is finite or infinite. John Rennie's answer alludes to this in the latter parts- it is either infinite (and has always been infinite) or finite (but without an edge, so ...
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  • 16.6k
12 votes
Accepted

What happens when the universe runs out of fuel?

Then star formation ceases and the universe goes dark. At this stage of the universe's evolution, there'll still be plenty of hydrogen, they just don't form stars. In theory you can create hydrogen ...
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  • 16.2k
8 votes

What happens when the universe runs out of fuel?

Star formation will die out long before all the hydrogen runs out. Much of it will be trapped in very low mass stars and lots more will be in the very sparse intergalactic medium (where $\sim 50$% of ...
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  • 110k
5 votes

What happens when the universe runs out of fuel?

Well, fate of the universe has a lot of possible scenarios, from which periodical expansion/contraction is very unlikely, because universe expands in an accelerated fashion, and it doesn't looks that ...
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5 votes

Space-time continuum expansion

But when we have an infinite number of points, changing the length between them simply does not make any sense. It absolutely does make sense. Infinite sets need care. Many of the ideas that work for ...
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3 votes

Space-time continuum expansion

An infinite number of points is not a definite number. Don't think of it like a normal number. No matter how small a distance you make between two any points there is always an infinite number of ...
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2 votes

Will a light come back within finite years?

Well, the two answers are not talking about the same thing. What Javier was describing is what the asker was inquiring about in their question: a "finite but unbounded" periodic universe. ...
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2 votes

Hubble expansion rate and reaction rates

This is a question that puzzled me once. This is simply a misleading statement. For now, a more satisfying one would be: Once the interaction rate drop to $\Gamma\approx H$, the neutrino, for instance,...
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1 vote

What is there at a point the universe hasn't expanded past yet?

If the universe is constantly expanding that means that there is a point the univese [sic] hasn't expanded past... Your premise is not necessarily correct. with that what would be past that point? ...
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  • 7,006
1 vote
Accepted

If I moved in a straight line forever, would I hit something?

No. The question is a bit vague, but I try to answer it in spirit. Remember Olbers' paradox, which asks why the sky is dark at night. In an infinitely large, infinitely old universe, one should see ...
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  • 4,322
1 vote

About a hypothetical universe

You have the hubble constant, but you have to integrate that to get the cosmological parameter: $$\begin{align} \frac{\dot a}{a} &= - \sqrt{\beta}\tan \left(\sqrt{\beta}t\right)\\ \ln a &= \ln ...
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1 vote

Are there any mathematically conceivable arrangements of an indeterministic universe that are not physically possible?

The answer to your first question depends on what you mean by "mathematically conceivable". If your definition of "mathematically conceivable" is wide enough then, yes, there will ...
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1 vote

What is meant when it is said that the universe is homogeneous and isotropic?

Most of modern cosmology is based on the Cosmological Principle, which states that the spatial distribution of matter in the Universe is homogeneous and isotropic when viewed at a sufficiently large ...
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