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Gravity Probe B

Testing Einstein's Universe

Special & General Relativity Questions and Answers

If you travel fast in space will you REALLY come back younger than the friends you left behind?

Well...a zillion experiments with accelerated sub-atomic particles, and with clocks carried in jet planes, confirms that you and the clock moving with you will age more slowly than a clock at rest. But for the kinds of speeds we can travel, the amount of time is measured in minute fractions of a second. For sub-atomic particles, we can accelerate them to 99.9999 percent the speed of light and see some real major things happen as their lifetimes become many times longer than what they should be if they were not traveling so fast. The effect seems to be real enough.

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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.