Release Message:  A man inventing a time machine using Dirac's theories of negative energy travels to the 1960s and discovers he can participate in the past, but not change it. Written by Geoffrey A. Landis

Description:  The affecting story of a scientist seesawing inescapably through time, this brilliant work effectively deconstructs most time-travel stories that came before. Winner of the 1989 Nebula Award for best short story. A man inventing a time machine using Dirac's theories of negative energy travels to the 1960s and discovers he can participate in the past, but not change it (Nebula Award 1989).