Posthuman Blues

No paradox for time travellers

"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."

Finding this story headlining at The Anomalist came as something of a synchronicity, since I just finished reading a chapter about the quest to avoid causality violation in Jenny Randles' "Breaking the Time Barrier." The article indicates that waves sent into the past will self-destruct, ensuring causality, but what about physical objects?

So far the best "explanation" I've heard is the "principle of least action," which allows for time travel but requires infinite energy in order to change something that would threaten the time traveler's own (future) existence. Maybe.

Then there's the Many Worlds take, in which you can endlessly "violate" causality because you're not even in the same universe you came from and, presumably, anything goes; you're just a blip in the quantum ocean, one of potential trillions of doppelgangers.