Energetic proton Cosmic ray primary protons with energy up to 1020 eV (almost 10 J) have been detected. Our galaxy has a diameter of about 105 light years. (a) How long does it take the proton to traverse the galaxy, in its own rest frame (proper time)? (1 eV = 1.6 × 10-19 J, Mp = 1.67 × 10-27 kg.) What is the proper time for a photon to traverse our galaxy? (b) Compare the proton's energy to the kinetic energy of a baseball, mass = 145 g, traveling at 100 miles/hour.