Scientists from the University of Queensland, Australia, have used single particles of light (photons) to simulate quantum particles travelling 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 timelike 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 spacetime bends back on itself – thus creating a CTC, almost like a path that could be used to travel back in time.
According to Scientific American, many physicists find CTCs “abhorrent, because any macroscopic object traveling through one would inevitably create paradoxes where cause and effect break down.” Others disagree with this assessment, however; in 1991, physicist David Deutsch showed that these paradoxes (created by CTCs) could be avoided at the quantum scale because of the weird behaviour of these fundamental particles that make up what we call matter.
It’s well known that 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.
Welcome to the world of Quantum physics, where pioneering Physicist Niels Bohr once said, “if quantum mechanics hasn’t profoundly shocked you, you haven’t understood it yet.”
“We choose to examine a phenomenon which is impossible, absolutely impossible, to explain in any classical way, and which has in it the heart of quantum mechanics. In reality, it contains the only mystery.” – Richard Feynman, a Nobel laureate of the twentieth century (Radin, Dean. Entangled Minds: Extrasensory Experiences In A Quantum Reality. New York, Paraview Pocket Books, 2006.)
In the quantum world, paradoxes that we don’t understand are common findings, but this should not deter people from taking this science seriously. Even Einstein didn’t believe a lot of quantum theory, but I’d like to think that if he were alive today, he would definitely be having some fun, given all of the recent breakthroughs.
“It’s intriguing that you’ve got general relativity predicting these paradoxes, but then you consider them in quantum mechanical terms and the paradoxes go away.” – University of Queensland physicist Tim Ralph (source)
Tim Ralph (quoted above) and his PhD student Martin Ringbauer simulated a Deutsch’s model of CTCs, according to Scientific American, “testing and confirming many aspects of the two-decades-old theory.” Although it’s just a mathematical simulation, the researchers (and their team/colleagues) emphasize that their model is mathematically equivalent to a single photon traveling through a CTC. Nothing has actually been sent back through time though; to do that, scientists would have to find a real CTC, which has yet to happen as far as we know. Of course, there always remains the possibility that black budgetscience has.
Think in terms of the ‘grandfather paradox,’ a hypothetical scenario where someone uses a CTC to travel back through time to cause harm to their grandfather, thus preventing their later birth. Now imagine a particle going back in time to flip a switch on the particle-generating machine that created it – this is a possibility that these physicists say they have shown through their simulation.