Special & General Relativity Questions and Answers
If the universe is finite, can gravity waves have already traveled completely around the universe and back?
No, because there has not been enough time in the last 15 billion years for them to circumnavigate the amount of 3-d space now available. Like any other information traveling at the speed of light in such a cosmological 'model', the signal will make one complete trip around the universe just as the universe enters its 'Big Crunch' state. When such a closed universe is at its turnaround point, the signal will have gone exactly 1/2 way around and we will see exactly 1/2 of all the space that eventually came out of the Big Bang.
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All answers are provided by Dr. Sten Odenwald (Raytheon STX) for the NASA Astronomy Cafe, part of the NASA Education and Public Outreach program.