Last night I was watching a youtube video about twin paradox. It still continues to baffle me :).

In that video, the speaker conceptualizes a clock that measures time by reflections of light. If we consider speed of light as reference to our time measurement, I guess it is natural to expect that our time measurements will be warped if we are traveling at speeds comparable to that of light.

I was wondering, what if if we measure time with something else as reference? Say, a digital clock, assuming it works under such extreme speed/acceleration... So, my questions:

  1. Would our time measurements then be still warped?
  2. I think, even if the measured times indeed gets warped, is it not just the perceived time for the traveling twin? Logically, the twins have lived for the same amount of time (as measured from a digital clock on earth) and should have grown/aged similar. Why would the twin who stayed back on earth be aged more?

I might be totally wrong, but I would appreciate if somebody helps me understand where I went wrong.

Thanks for your time.

  • $\begingroup$ This is no more puzzling than the sum of the two legs of a triangle being longer than the third. The travelling twin makes a triangle is space time, going out then coming back, and the time along the two legs adds to less than the time along the third leg. $\endgroup$
    – Ron Maimon
    Commented Jul 13, 2012 at 20:15

2 Answers 2


Yes,the time measurement still shows dilation. since if a mirror clock and conventional clock in the spacecraft agree with each other on the ground but not when in flight,the disagreement between then could be used to find the speed of the spacecraft independently of any outside frame of reference-which contradicts the fact that all motion is relative


The type of clock you use makes no difference. It's common to use a clock that measures light using a light beam because it's conceptually simple, but whether you use a digital clock, one with a spring or one with a pendulum you'll get the same result.

I don't want to go into the twin paradox here because it's been discussed to death over the years, not least on this site. I'll just say the effect is quite real. It's not down to some sort of mathematical trick but instead it's a fundamental property of spacetime: specifically the invariance of the proper time.

If there are aspects of the twin paradox (NB it's not a paradox) that you don't understand post a more specific question here and I'm sure there'll be lots of answers. Have a search of the site first though to make sure your question hasn't already been answered.


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