The big bang as a higher-dimensional shock wave
  We give an exact solution of the five-dimensional field equations which describes a shock wave moving in time and the extra (Kaluza-Klein) coordinate. The matter in four-dimensional spacetime is a cosmology with good physical properties. The solution suggests to us that the 4D big bang was a 5D shock wave. 
P. S. Wesson (1), H. Liu (2), S. S. Seahra (1) ((1) University of   Waterloo, Canada (2) Dalian University of Technology, China)