Making Light:  Tracking Nielsen Haydens in their habitat ::: August 16, 2004, 03:19 PM

Xopher:

  Andy, I meant the person who stays on Earth is also predicted to
  be older than the one who flies at a significant fraction of C.
  Relative to the frame of reference of the one who flies off, the
  Earthbound twin is moving at a significant fraction of C.  It's
  called the Twins Paradox because each twin ages more (and less)
  rapidly with respect to the other.

  Now, if I misunderstand that, I'm ready to be corrected.  But that's
  how I had it explained to me....

I think the disconnect is that Andy was describing relativity without
mentioning the twin paradox, and you're describing the twin paradox.

  ... Mere one-sided time dilation doesn't strike me as paradoxical,
  or is my sensibility just too post-Einstein to see it as such?

I agree that the idea that two equally valid reference frames can
disagree on which frame is time-dilated seems paradoxical.  I guess
that's why Heinlein got it wrong in Time for the Stars, if I remember
right.  Though I don't how it should have worked, except possibly that
it shouldn't have worked.  Nor ansibles neither.  They're just weird
scifi ideas, ginned up to make plots more interesting than "They left
and we never heard from them again."