Some solutions to the equations of Einstein’s general theory of relativity lead to situations in which space-time curves back on itself, theoretically allowing travellers to loop back in time and meet younger versions of themselves. Because such time travel sets up paradoxes, many researchers suspect that some physical constraints must make time travel impossible. Now, physicists Daniel Greenberger of the City University of New York and Karl Svozil of the Vienna University of Technology in Austria have shown that the most basic features of quantum theory may ensure that time travellers could never alter the past, even if they are able to go back in time.
I don’t know much of anything about quantum physics, but I always just kind of liked to think that if you could go back in time, obviously you wouldn’t be able to change anything. If you went back in time and killed your parents, you would never be born, so duh… you can’t do it! Now there is some model of quantum mechanics that might explain this, but I’m not going to pretend to understand it.