Time War — Lin Carter

John Lux was an electronic scientist, a level-headed industrialist, an ordinary twentieth-century man -- at least he thought he was an ordinary man...until he discovered he could teleport himself!
...Until he discovered that forces 200,000 years beyond his time were trying to destroy him! Until he discovered that civilization of the future was being pampered into extinction in a kindergarten world -- and he was the only man in all eternity who could save it!