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Gravity Probe B

Testing Einstein's Universe

Special & General Relativity Questions and Answers

Is time linear, or could there be other dimensions to it as for space?

Time must be exactly one dimensional, otherwise we would find past, present and future twisted around like a complicated Gordian knot with 'loops' that violate the universally observed rule that you can never revisit your past. Strange things DO happen to time in the quantum world, however. Mathematically, an anti-matter version of an electron traveling from time T1 to a future time T2 is exactly equivalent to a real matter electron traveling BACK IN TIME from T2 to T1. It is not, however, possible to use this mirror symmetry to transmit information from a future moment T2 to a past moment T1. Also, because of Heisenberg's Uncertainty Principle, electrons can actually travel back in time for short periods of time because we are prohibited from making a detailed measurement of their energy at a specific instant in time.

An entertaining book by Ouspensky called Tertium Organum published at the turn of the century speculated about this and other things, but he was primarily a mystic/philosopher and didn't know much physics. Still, he did imagine some of the problems associated with multi-dimensional time and it is an amusing little book to read if you like that sort of speculation.

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All answers are provided by Dr. Sten Odenwald (Raytheon STX) for the NASA Astronomy Cafe, part of the NASA Education and Public Outreach program.