A thought experiment in which one twin (A) travels into space
at nearly the speed of light and returns to find she has aged
less than her sibling (B) who has remained on Earth. This result
is paradoxical because of the seemingly symmetric roles played
by A and B in the story. In fact, A returns younger than B because
only A travels in a non-inertial (accelerating) reference frame.
From Bs point of view, A experiences time dilation, but
from As point of view the distance traveled is shortened
because of length contraction.
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