Tags: 1.21, according, distance, lightyear., long, planet, reach, spaceship, TAKE

3 Responses to “Q&A: The distance to Planet X is 1.21 light-year. How long does it take a spaceship to reach X, according to the pi”

1. Brats says:

   November 3, 2011 at 06:42

   First we have to find the distance in the pilot’s frame. The distance will shrink with a factor of gamma where gamma is
   1/sqrt(1 + v^2/c^2)
   = 1/sqrt(1 + 0.73^2)
   = 0.807

   so the distance in the pilot’s frame is 0.807*1.21
   = 0.977 light years

   now divide this by his speed
   0.977/0.73c
   = 1.34 years

   so according to pilot, it will take 1.34 light years

   Reply
2. rhsaunders says:

   November 3, 2011 at 07:18

   First response is not correct. The speed is high enough that Einsteinian mechanics must be used to get the correct answer. Second response is on the right track; the only obvious error is the use of the term “light years” in the final answer; it should be simply “years”.

   Reply
3. Bekki B says:

   November 3, 2011 at 07:22

   To an external observer, the time is
   t = 1.21 c-years / 0.73c

   To the pilot, this is reduced by dividing by a time dilation factor gamma (the second answerer got a sign wrong in his calculation of gamma, which is never less than 1, and then tried to make up for it by multiplying instead of dividing the distance by it)

   gamma = 1 / sqrt (1 – (v/c)^2)
   = 1/sqrt (1 – 0.730^2)

   Pilot time = sqrt(1 – 0.730^2)* 1.21 / 0.73 years

   Reply