| time travel can become theoretically possible only for observers but not as participants. By participants, i mean able to alter the course of history if traveling back in time. As an observer, all one has to do is to catch a photon and extract all information about the past and the future. To overtake the speeding photon, one needs superluminal speed. For an idea of just how fast a photon is: in just one second it reaches the moon. |