4 ms·

But optimize this by not running too close to c (or is it the contrary ? My restrained relativity courses are rusty)

• kaybe 9y ago
  In your reference frame nothing will be different, so it really depends on whether you want to loose weight for yourself or for others.
  • ssfsa 9y ago
    Except he had to accelerate to speed and back, so only our reference frame matters.