Caltech Science Question of the Month: Time Travel
Answered by: Kip Thorne, Feynman Professor of Theoretical Physics
PASADENA—This is a new monthly feature produced by the Caltech Media Relations Office, in collaboration with Caltech's faculty, to answer commonly asked or particularly intriguing questions about science and the natural world.
Question: What would really happen if you tried to travel back in time, to before the date of your own birth, to change your parents' destiny?
Answer: The laws of quantum fields in curved space-time (QFCST for short) report to us that, no matter what method I might think of to make a time machine, at the moment I activate the machine, an intense beam of radiation (vacuum fluctuations of quantum fields) will fry the machine and probably fry me as well. Unfortunately, just before the machine is fully destroyed, the laws of QFCST fail and are replaced by the laws of quantum gravity, which we don't understand at all well. Quantum gravity holds clutched tightly to its breast the secret of the ultimate fates both of the time machine and of my parents—along with the secrets of the origin of the universe, the nature of the singularity at the core of a black hole, and the final fate of an evaporating black hole. If I must speculate, I would guess that quantum gravity does not change the story reported by the laws of QFCST: the time machine and I would both get fried for trying to tamper with history.
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