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#### SpeedFreek

##### Guest

yevaud":1teviq8z said:It's along the same idea that if one were to keep heading for the "edge" of the universe, one would end up on the other side of the universe, which, as we know today, is absurd.

Sorry I'm late! The notion is only "absurd" due to the rate of the expansion of the universe precluding the detection of such a topology if the fundamental domain of the universe is larger than a certain size. Of course, it is absurd to think we might be able to traverse the whole universe as we cannot beat the rate of expansion, but topologically it is probably the most likely scenario unless the universe is infinite in extent.

http://arxiv.org/abs/astro-ph/0604616

Extending the WMAP Bound on the Size of the Universe - 2006

What is the shape of space? While this question may have once seemed more philosophical than scientific, modern cosmology has the chance to answer it using the oldest observable light in the Universe, the Cosmic Microwave Background radiation (CMB). NASA’s Wilkinson Microwave Anisotropy Probe (WMAP) has made a detailed map of the CMB sky which has been used to provide answers to many age-old questions about the nature of the Universe.

While it is certainly possible that the Universe extends infinitely in each spatial direction, many physicists and philosophers are uncomfortable with the notion of a universe that is infinite in extent. It is possible instead that our three dimensional Universe has a finite volume without having an edge, just as the two dimensional surface of the Earth is finite but has no edge. In such a universe, it is possible that a straight path in one direction could eventually lead back to where it started. For a short enough closed path, we expect to be able to detect an observational signature revealing the specific topology of our Universe.

It seems however, that we cannot find a short enough closed path. This does not necessarily mean the universe is infinte, it might just mean the universe is too large to have such a closed path, so the question is still very much an open one.

In simple terms, there are real problems like the ones Gödel describes if the universe has a boundary, so the universe is either infinite, or if it is finite it "wraps around" on itself topologically such that there is no boundary. So a straight line either goes on for ever, or comes back to where it started, or passes back through regions it has already traversed but on a different path (like a line drawn at an angle around a torus, for instance), but it never reaches an edge.