1905 Albert Einstein publishes the special theory of relativity; time dilation predicted

1908 Einstein conjectures that gravity slows time

1915 Einstein's general theory of relativity published

1916 Karl Schwarzschild presents the first black hole/wormhole solution of general relativity

1916 Ludwig Flamm discovers wormhole character of Schwarzschild's solution.

1917 Einstein proposes a cosmic repulsion force-the first conjecture about antigravity

1934 Black holes from collapsing stars predicted

1935 Einstein-Rosen bridge (wormhole) discussed

1937 W.J. Van Stockum discovers the first solution of Einstein's equations with time loops

1948 Kurt Godel's rotating universe found to incorporate time travel

1948 The Casmir effect discovered: negative-energy quantum states first discussed

1957 John Wheeler conjectures existence of wormholes

1957 Hugh Everett III proposes the many-universes, or parallel-realities, interpretation of quantum mechanics

1963 Doctor Who begins on BBC television

1963 Roy Kerr discovers that spinning black holes could contain time loops

1974 Cygnus X-1, the first serious contender for a black hole, discovered by X-ray satellite

1976 Frank Tipler shows time travel possible near infinite ratting cylinders

1977 Spinning black holes as gateways to other universes discussed

1985 The movie Back to the Future released

1985 Carl Sagan writes Contact

1989 Kip Thorpe initiates study of wormhole time machines

1990 Stephen Hawking proposes the chronology projection conjecture

1991 J. Richard Gott III proposes cosmic-string time machine

1999 Michael Crichton's book Timeline published