"I studied relativistic physics my entire life. One thing emerged over and over - can't change the past. Can't do it. Whatever happened, happened. All right? But then I finally realized... I had been spending so much time focused on the constants, I forgot about the variables. Do you know what the variables in these equations are, Jack? Us. We're the variables. People. We think. We reason. We make choices. We have free will. We can change our destiny."