Special & General Relativity Questions and Answers
Why does the 'Twin Paradox' exist as a physical phenomenon?
Because it is an experimental fact of life for us. We can see this effect in the impossibly long lifetimes of decaying muons than, at 95 percent the speed of light, live in our reference frame, much longer than they ought to in their own moving reference frame. In the case of the muon, it is in the same accelerated frame of reference as we are, so it is not 'acceleration' that is the problem. Presumably, for interstellar travelers, they, like the muons, will return a younger age than those of us who stayed behind. Of course it will be a LONG LONG time before this will ever be put to the test!
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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.