"Scientists from the University of Queensland, Australia, have used single particles of light (photons) to simulate quantum particles traveling through time. They showed that one photon can pass through a wormhole and then interact with its older self. Their findings were published in Nature Communications.
The source of this time travel conundrum comes from what are called "closed time-like curves" (CTC). CTCs are used to simulate extremely powerful gravitational fields, like the ones produced by a spinning black hole, and could, theoretically (based on Einstein's theory of general relativity), warp the fabric of existence so that space-time bends back on itself – thus creating a CTC, almost like a path that could be used to travel back in time.