What happens if you go back in time, but end up changing your life course? What if you kill your parents or grandparents? Wouldn't that change your life forever, or make your life not exist at all? But then how would you go back in time to change your life if it didn't exist at all? This is the grandfather paradox. It has been featured in movies such as Terminator and Back to the Future, but physicists debate the reality and extent of this paradox.
Some physicists claim the solution to this paradox lies in the existence of a multiverse. String theory, which connects the theories of quantum mechanics and general relativity, stipulates that we are part of a two dimensional membrane in space, and that there is a significant possibility that other membranes with other universes exist. Then, if you went back in time and killed one of your parents, you could still exist, just in a parallel universe.
Another way physicists solve the grandfather paradox is with self consistency. This uses probabilities to "close the causative loop". So, you could be born with a one half probability of killing your grandfather, which would mean that your grandfather has a one half probability of being killed. Because no outcome is guaranteed, this is enough to escape the grandfather paradox while satisfying the laws of quantum mechanics.
Some physicists claim the solution to this paradox lies in the existence of a multiverse. String theory, which connects the theories of quantum mechanics and general relativity, stipulates that we are part of a two dimensional membrane in space, and that there is a significant possibility that other membranes with other universes exist. Then, if you went back in time and killed one of your parents, you could still exist, just in a parallel universe.
Another way physicists solve the grandfather paradox is with self consistency. This uses probabilities to "close the causative loop". So, you could be born with a one half probability of killing your grandfather, which would mean that your grandfather has a one half probability of being killed. Because no outcome is guaranteed, this is enough to escape the grandfather paradox while satisfying the laws of quantum mechanics.