Cosmic rays could find proof of extra dimensions by detecting tiny black holes.The Pierre Auger Observatory, currently being constructed in Argentina to study cosmic rays, could examine the structure of spacetime itself, say physicists in the United States.

If, as some suspect, the Universe contains invisible, extra dimensions, then cosmic rays that hit the atmosphere will produce tiny black holes. These black holes should be numerous enough for the observatory to detect, say Jonathan Feng and Alfred Shapere of the Massachusetts Institute of Technology in Cambridge, Massachusetts.