Can a true vacuum exist if gravitons cannot be shielded?

[Mohd Abdullah]

I think, only the observable Universe can be said as finite but unbounded. So, infinite Universe (that's it, if an imaginary object keep moving straight forever it will never return to its starting point) is more likely than the finite yet unbounded Universe.

Sometimes, if I want to show that space is indeed "something" rather than "nothing", I will make an assumption by imagining a lone object without anything else. So, hypothetically this lone object would be fully static because motion is relative. But as these terms, "static" and "motion" are both relational concepts, then in reality we can't really say that this hypothetical lone object is static. But nevermind, for the sake of this imaginary assumption, the lone object would be static. This is sometimes begging the question, why makes this lone object to remains stationary in its position?

 

[PeterDonis]

I think, only the observable Universe can be said as finite but unbounded.

This is not correct. Our observable universe is finite because the age of the universe is finite, so light has only had a finite time to get to us from distant parts of the universe. But it is not "unbounded" in the sense in which that term is normally used--it is not a 3-sphere. It's an ordinary 3-volume that is part of something larger--we just don't know whether the something larger is an infinite space or a finite but unbounded space like a 3-sphere.

infinite Universe (that's it, if an imaginary object keep moving straight forever it will never return to its starting point) is more likely than the finite yet unbounded Universe.

This is true, but not for the reason you give. It's true because the model in which the universe is spatially infinite (and spatially flat) is the best fit to the data we have.

The rest of your post is personal speculation.

 

[PeterDonis]

This topic has been sufficiently discussed. Thread closed.