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Gravity Probe B

Testing Einstein's Universe

Special & General Relativity Questions and Answers

Does time stop when you travel at the speed of light?

Since no matter can ever travel at exactly the speed of light, you are asking a hypothetical question. We know from experiment that the half-lives of unstable particles such as muons are prolonged in OUR reference frame by an amount predicted from their speeds by special relativity. So, by simple extrapolation, we expect that for particles moving at nearly the speed of light, their times are greatly increased so that 1 minute of their time might be weeks or months or even longer in our rest frame. So, time does 'stop' at relativistic speeds, but you have to get to practically the speed of light itself to get the most extreme situation.

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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.