1. The problem statement, all variables and given/known data The premise of the Planet of the Apes movies and book is that hibernating astronauts travel far into Earth's future, to a time when human civilization has been replaced by an ape civilization. Considering only special relativity, determine how far into Earth's future the astronauts would travel if they slept for 105 years while traveling relative to Earth with a speed of 0.9900c, first outward from Earth and back again. 2. Relevant equations I think delta t = Y*delta t0 where Y = 1/[1-(v/c)^2]^1/2 3. The attempt at a solution I used the above equations (delta t0 = 105 y, v = 0.99c) and got 744.3253. Then I multiplied this by 2 and got 1488.651 y which is the wrong answer. Thanks for your help!