To the ordinary human it is obvious that there is a clear distinction between the spatial dimensions in which one can go either way and the temporal dimension in which one seems only to move forward. But the uniqueness of time is also rooted in the standard presentation of general relativity in which the metric of space-time is locally Lorentzian i.e. η_ij = diag (1,−1,−1,−1).  This is presented as an independent axiom of the theory, which can not be deduced. In this talk I will claim otherwise. I will show that the existence of time should not be enforced on the gravitational theory of general relativity but rather should be deduced from it. The method of choice is linear stability analysis of flat space-times. Hence, the distinction between space and time can be explained on a physical basis for the first time.

1. Asher Yahalom "The Geometrical Meaning of Time" [“The Linear Stability of Lorentzian Space-Time” Los-Alamos Archives - gr-qc/0602034, gr-qc/0611124] Foundations of Physics http://dx.doi.org/10.1007/s10701-008-9215-3 Volume 38, Number 6, Pages 489-497 (June 2008).

2. Asher Yahalom "The Gravitational Origin of the Distinction between Space and Time" International Journal of Modern Physics D, Vol. 18, Issue: 14, pp. 2155-2158 (2009). DOI: 10.1142/S0218271809016090

3.  Asher Yahalom "Gravity and the Complexity of Coordinates in Fisher Information" accepted for publication by the International Journal of Modern Physics D (2010).