One of the big arguments against time travel is the ease with which a paradox can arise. The most commonly used example is the “grandfather paradox” where a time traveller goes back in time, kills his (or her) grandfather, negating their own existence which means the murder could not have happened.
Back to the Future-like slow fades out of existence notwithstanding, this particular paradox illustrates the complexities of time travel. The post-selected model of time travel, however, forbids these paradoxes outright.
By going back and outlawing any events that would later prove paradoxical in the future, this theory gets rid of the uncomfortable idea that a time traveler could prevent his own existence. “In our version of time travel, paradoxical situations are censored,” Lloyd says.
Recently, scientists developed a series of experiments using photons to test this post-selected model. Although there was no time traveling involved, the experimenters placed the photons into quantum situations similar to those that might be experienced in time travel.
As the photons got closer and closer to being in self-inconsistent, paradoxical situations, the experiment succeeded with less and less frequency, the team found, hinting that true time travel might work the same way.
What does this mean in regards to the grandfather paradox? It means strange things would happen:
For instance, a bullet-maker would be inordinately more likely to produce a defective bullet if that very bullet was going to be used later to kill a time traveler’s grandfather, or the gun would misfire, or “some little quantum fluctuation has to whisk the bullet away at the last moment,” Lloyd says. In this version of time travel, the grandfather, he says, is “a tough guy to kill.”
To read the full Wired article, check it out here