We Know The Extent Of The Sun, What Is The Extent Of Space Time?

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Offline Titanscape

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We know the extent of the sun at four times the distance to Pluto, but what is the extent of the universe's space time?

If we draw back and look at the universe, it would be a spot like a single star, how far is the reach of the four dimensions, beyond the matter?

Or is space time infinite? Taking into account space curvature, although I do not understand it that well.

I suppose we could theorize a place so far from the universe that we see it beginning?

Looking at black holes, could it possibly be that the whole universe will become one and end space, time and matter completely?


Offline LeeE

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The universe is generally considered to be unbounded, which is to say that there are no potential limits on it's size, either in space or in time.  The observeable universe appears to be finite in both time and space in so far as it has only existed since the Big Bang, giving a finite duration, and because of special relativity and expansion, is therefore finite in size, being about 14 billion years old and about 93 billion light years across (the discrepancy between 14 billion years of age and 46 billion light years radius is due to the expansion of the universe).

Spacetime was created at the Big Bang, and so it too would appear to be finite except that being unbounded, is not limited in time or space and so is potentially infinite - we just haven't lived infinitely long yet, by which time both time and space would be infinite.

In theory, we can see the beginning of the universe if we look in any direction.  If the universe is about 14 billion years old and we look at 'stars' that are 46 billion light years away, we are looking at the beginning of the universe.  Or at least, very nearly.  One of the early phases of the Big Bang was opaque to photons so we can't actually see further back past then.  This phase wasn't opaque to gravity waves, however, so it would be possible to study this phase if we had suitable instruments.

The universe could have been either 'open' or 'closed'.  If it were 'closed' then it would have eventually stopped expanding and then collapsed back in on itself but observations indicate that it is 'open'
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Offline turnipsock

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The Hubble did a thing called Deep Field that actually looked back in time. The JWST will probably do the same thing when its up and running.


Four dimensions! What about the rest?
Beeswax: Natures petrol tank sealant.

When things are in 3D, is it always the same three dimensions?