Can one hear the shape of the Universe?
  It is shown that the recent observations of NASA's explorer mission "Wilkinson Microwave Anisotropy Probe" (WMAP) hint that our Universe may possess a non-trivial topology. As an example we discuss the Picard space which is stretched out into an infinitely long horn but with finite volume. 
R. Aurich, S. Lustig, F. Steiner and H. Then