We have all laughed at those fragments of film run backwards, where broken vases miraculously reassemble themselves, or sprinters reverse at full speed into their starting blocks. In the everyday world these things could never happen - time's arrow only points forwards. Hitherto, the laws of fundamental physics have seemed to be reversible: a film of elementary particle behaviour run backwards is indistinguishable from the same film run forwards. A particle sprinter could apparently run full-speed backwards as well as forwards.
06 Nov 1998