Hey Friends, In Einstein's special relativity I find "Twin Paradox", where Dick and Jack, two twins . one of them went to space at a speed of 0.80c to a star 20 light year away (where c is the speed of light) and other remains on earth. When Jane returned to earth his age was 50 but who stayed in earth, Dick, his age was 70. I find a formula there : √1 - v2/c2 My question is how is it find and why Jane was younger than Dick ?? Thank you..