Short Story #2: “Ripples in the Dirac Sea” — Geoffrey Landis (1988)
A scientist invents a time machine and discovers — too late — that he cannot change the past. Nor can he prevent his impending death, after he finds himself trapped in a burning highrise. Unable to stop the fire, he uses the moments he has left to repeatedly jump back in time and live in the past, finding solace with a pair of doomed hippies in Haight-Ashbury at the height of the ’60s.
As much an exploration of dealing with grief and learning to let go as a thoughtful theory of how time travel might work, “Ripples” won the Nebula Award for Best Short Story. You can dive in and read it here: http://diracsea.net/ripples-in-the-dirac-sea/