Scientific American reports that the researchers used single particles of light (photons) to simulate quantum particles traveling through time. They have, in effect, shown that one photon can pass through a wormhole and then interact with its older self. Their findings were published in Nature Communications.
"Closed timelike curves" (CTC) are the source of the time travel conundrum. CTCs are used to simulate extremely powerful gravitational fields, like the ones produced by a spinning black hole. Theoretically, they could (based on Einstein's theory of general relativity), warp the fabric of existence so that spacetime bends back on itself - thus creating a CTC, almost like a path that could be used to travel back in time.
Many physicists reportedly find CTCs "abhorrent, because any macroscopic object traveling through one would inevitably create paradoxes where cause and effect break down." But others disagree with this assessment.
In 1991, physicist David Deutsch showed that these paradoxes (created by CTCs) could be avoided at the quantum scale because of the weird behavior of these fundamental particles that make up "matter". At the quantum scale, these particles do not follow the rules that govern classical mechanics but behave in strange and unexpected ways that really shouldn't even be possible, reports Collective Evolution.