b.) The Twin Paradox On their 215 birthday, Peter leaves his twin brother Paul behind on a freely falling spaceship and departs at a constant relative speed of - 33 (in geometric units), for a free fall of 7 years of his proper time (that is, time as he experiences t). Then he turns around and returns symmetrically in another 7 years. When he returns, he is 35 years old. How old is Paul? Using the figure below, Paul's age is equal to 21 2(ox), where or is the length (in years) of the line segment connecting the points o and z. You'll need the following hyperbolic trig identities: