The grandfather paradox states that if a time traveler were to go back in time, he could accidentally prevent his grandparents from meeting, and thus prevent his own birth.
Special relativity posits that space and time are aspects of the same thing, known as the space-time continuum, and that time can slow down or speed up, depending on how fast you are moving, relative to something else.
Gravity can also bend time, and Einstein’s theory of general relativity suggests that it would be possible to travel backwards in time by following a space-time path, i.e. a closed timeline curve that returns to the starting point in space, but arrives at an earlier time.
“The question of time travel features at the interface between two of our most successful yet incompatible physical theories – Einstein’s general relativity and quantum mechanics. Einstein’s theory describes the world at the very large scale of stars and galaxies, while quantum mechanics is an excellent description of the world at the very small scale of atoms and molecules.” said Martin Ringbauer, a PhD student at UQ’s School of Mathematics and Physics and a lead author of the paper.
Simulating time travel The scientists simulated the behavior of two photons interacting with each other in two different cases.
“The properties of quantum particles are ‘fuzzy’ or uncertain to start with, so this gives them enough wiggle room to avoid inconsistent time travel situations,” said co-author Professor Timothy Ralph.
Although it has been possible to simulate time travel with tiny quantum particles, the same might not be possible for larger particles or atoms, which are groups of particles.