THE WORLD AS A HOLOGRAM

According to 't Hooft the combination of quantum mechanics and gravity requires the three-dimensional world to be an image of data that can be stored on a two-dimensional projection much like a holographic imag e. The two-dimensional description only requires one discrete degree o f freedom per Planck area and yet it is rich enough to describe all th ree-dimensional phenomena. After outlining 't Hooft's proposal we give a preliminary informal description of how it may be implemented. One finds a basic requirement that particles must grow in size as their mo menta are increased far above the Planck scale. The consequences for h igh-energy particle collisions are described. The phenomenon of partic le growth with momentum was previously discussed in the context of str ing theory and was related to information spreading near black hole ho rizons. The considerations of this paper indicate that the effect is m uch more rapid at all but the earliest times. In fact the rate of spre ading is found to saturate the bound from causality. Finally we consid er string theory as a possible realization of 't Hooft's idea. The lig ht front lattice string model of Klebanov and Susskind is reviewed and its similarities with the holographic theory are demonstrated. The ag reement between the two requires unproven but plausible assumptions ab out the nonperturbative behavior of string theory. Very similar ideas to those in this paper have long been held by Charles Thorn. (C) 1995 American Institute of Physics.