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Topic: physics question... speed of light
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Erstwhile
rabble-rouser
Babbler # 4845
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posted 12 June 2008 06:53 AM
quote:
Originally posted by PB66:
There is no "edge" of the universe. The common analogy is to say that the universe is like the surface of a balloon. It has a finite width around, but there's no edge.
quote:
Originally posted by Fidel:
If we could push a sharp pencil through the fold, the tip might come out at the far end of the universe, or some such.
....or pop the balloon! 
You mad fools! You'll kill us all, with your pointy sticks pokin' at the space-time continuum!
From: Deepest Darkest Saskabush | Registered: Jan 2004
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PB66
rabble-rouser
Babbler # 14465
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posted 13 June 2008 12:20 AM
quote:
Originally posted by Fidel:
There are theorists who suggest that black holes must contain a single point of infinite density where known laws of physics no longer apply, an "edge" of the space-time continuum. An object entering the black hole would be squeezed out of existence. Some say that a spaceship's free-fall trajectory toward the black hole, but not close enough to be drawn into it, could be a one-way time machine.
Oops, yes, Fidel is quite right. Deep within a black hole, it is expected there will be singularities, according to classical relativity. Either space-time will simply end, or quantum effects will become important, which might remove the singularities. It's not really known what happens with the singularities in relativity, and, more generally, properly combining quantum effects and relativity remains one of the biggest problems in physics. There was a lot of research done on this sort of thing in the '70's, but not much progress was made, and researchers have put this aside to work on problems which can be solved. I was thinking the question was about what it meant for the universe to be expanding. In that case, we imagine the universe to be some-what like a three-dimensional version of the surface of a balloon. It has a total length around, but no edge. If the balloon is inflated, that length around increases, but for imaginary two-dimensional people living on the balloon (or for us in the three-dimensional universe), it cannot be seen where that expansion is occuring.
From: the far left | Registered: Aug 2007
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