Special Relativity URGENT! 1. The problem statement, all variables and given/known data The galaxy is about 10^5 light years across and the most energetic cosmic rays known have energies of the order of 10^19 eV. How long would it take a proton with this energy to cross the Galaxy as measured in the rest frame of (i) the galaxy (ii) the proton 2. Relevant equations 3. The attempt at a solution So I've done (i) and got the right answer (10^5 years) since to the best accuracy of my calculator, the particle is travelling at the speed of light.... For part (ii) I want to use lorentz transform, but i can't seem to get my calculator to take the accuracy.. basically: ct' = gamma(ct-Bx) where B is v rel.. now i found gamma to be (1.06699... x 10^10) which means B is root(1 - 8.798...x10^-21) now on my calculator this gives a value of B of 1, which obviously means t' = 0...The actual answer gives t' as just over 4 minutes... I'm wondering if there is another way to work out t'..how can i compute it to get the answer required!? THANKS :) !