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Q & A: universal expansion

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Most recent answer: 12/15/2010
Q:
Soon after the big bang, as the universe is expanding at some speed < c, would not light travel beyond the bounds of the expanding universe?
- Andy
Chicago, IL
A:
 Nice question, but it makes some assumptions that do not fit with our best understanding of the behavior of our universe. We do not think it has any "bounds". Whether that's because it wraps around on itself on some very large scale or simply extends infinitely far, we don't know.

When you assign a velocity to the expansion, that must refer to the expansion of two particular objects, as seen by each other. Pick another two objects, nearer or farther from each other, and you get a different velocity.

It is true, however, that light and other things can travel away from us (as seen in a standard us-centered reference frame) and get beyond our horizon, so that they can never be seen again by us. I think that's the process to which you were referring.

Mike W.


(published on 12/15/2010)

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