# Special Relativity - Twins sending light pulses

by jinksys
Tags: light, pulses, relativity, sending, special, twins
 P: 123 1. The problem statement, all variables and given/known data Twin A is on earth. Twin B is aboard a spacecraft that leaves earth toward a start 12LY away at 0.6c. Both twins send light pulses every year according to their clocks. How many pulses does A send and receive and how many does send and receive if B makes a round trip to the star and back? 2. Relevant equations 3. The attempt at a solution For twin A I need to know how long it takes B to complete the round trip. time = d/r = 24LY/0.6c = 40 years Twin a would send 39 pulses since B would arrive at year 40. For twin B, the universe is moving past him at 0.6c so I need to compute the length of the trip according to his point of reference. L = $$L_{0}$$$$\sqrt{1 - 0.6^2}$$ = 9.6LY t = d/r = 18.6LY/0.6c = 32 years Twin b would send 31 pulses since b would arrive at year 32.