http://en.wikipedia.org/wiki/Observable_universe wrote:
If the universe is finite but unbounded, it is also possible that the universe is smaller than the observable universe. In this case, what we take to be very distant galaxies may actually be duplicate images of nearby galaxies, formed by light that has circumnavigated the universe. It is difficult to test this hypothesis experimentally because different images of a galaxy would show different eras in its history, and consequently might appear quite different. Vaudrevange et al.: [12] claims to establish a lower bound of 26 gigaparsecs (85 billion light-years) on the diameter of the whole universe, meaning the smallest possible diameter for the whole universe would be 98.5% of the diameter of the last scattering surface (since this is only a lower bound, the paper leaves open the possibility that the whole universe is much larger, even infinite). This value is based on matching-circle analysis of the WMAP 7 year data; this approach has been disputed.[13]