Braneworlds, Presentism, the Arrow of Time, and the “Now” Problem

Abstract: For millennia physicists and philosophers have debated the nature and properties of time, including the “arrow of time” and the nature of the “now” moment, but so far there is no consensus theoretical agreement on these matters. However the recent development of string theory and M- or Brane theory has provided us with novel theoretical concepts that were not available to earlier theorists, concepts that may have a direct bearing on problems of the nature of time. These new string or brane theories showed that general relativity and quantum mechanics can be unified in an eleven-dimensional space-time, a realization that could produce an even greater revolution in our concepts of space and time than the one produced by relativity theory in the last century. And brane theorists have suggested a “braneworld” model in which the universe is a 3-brane that moves along a time axis. In such a braneworld the local “now” moments could be defined as the intersection of each spatial point in the brane with that time axis. Further, the motion of the brane itself in the time direction could provide the necessary asymmetry in time that is required to produce an “arrow of time.” Such temporal asymmetry is not found in any of the fundamental physical laws that operate inside the brane, but the motion of the brane itself does not necessarily depend on the physical laws that operate inside the brane. Resolution of the problems of the “now” moment and the “arrow of time” may force us to think “outside the brane.”