Fittingly, for a year that many of us would like to fast-forward past or, alternatively, rewind and start different, 2020 has ushered in a massive shift in time travel discourse. Time travel into the past, once thought to be theoretically impossible, became theoretically possible thanks to advanced math and simulations.

Retiring the Grandfather Paradox

Thus far, assumptions about time travel into the past have included the “grandfather paradox,” wherein one’s ability to alter the course of events culminating in their own origin (like killing a progenitor or ancestor) meant traveling into the past involved a poenial internal contradiction. Whether stepping on a butterfly or distracting your mother from your dad’s courtship, the classical assumption has been that if you alter the causal arrow’s path, you could cease to exist. An ordered universe couldn’t allow that to happen.

As it turns out, the universe is more elastic than previously thought. Researchers at the physics program at University of Queensland, longtime leaders in time travel research, produced a paper explaining mathematically what we can also explain through narrative analysis: if you go back in time and “try and stop patient zero from becoming infected with Covid-19,” something else will happen to result in the same outcome. For example, you may get the virus yourself, or someone else would. Ultimately, something will happen that’s “close enough [to what did happen] so that the time traveler would still exist and would still be motivated to go back in time.”

Queensland scientist Fabio Costa explained this concept earlier this year, though not in easily accessible terminology. His paper’s abstract explains that “complex dynamics is possible in the presence of CTCs [closed-time-like-curves], compatible with free choice of local operations and free of inconsistencies.” Another member of the Queensland team explains, “Einstein’s theory of general relativity predicts the existence of time loops or time travel,” and this suggests that “space-time can potentially adapt itself to avoid paradoxes.”

This is a huge development as, up until now, the paradox (and not the mechanics) seemed to rule out backwards-directed time travel altogether. We are still left wondering why, if it’s possible, we haven’t yet been visited by travelers from the future (perhaps we have), but that’s a question for another time.

Professor Mallett’s Time Machine

The Queensland work suggests that Einstein’s “time loops” contain the seeds of backwards time travel. University of Connecticut physicist Ron Mallett not only agrees, but has built an experimental device to test the theory. Fascinated with H.G. Wells and haunted by the death of his father, Professor Mallett takes, as a starting point, Einstein’s observation that “the stronger gravity is, the more time will slow down.” Gravity isn’t so much a “force” as a bending of space by large objects. If space can be bent, Mallett reasons, it can also be twisted. In other words, wormholes, wherein one can travel both into the past and back to the future, are possible. The scientist and his time machine can be found here.

Time Travel Simulators Are A Thing

University of Queensland researchers have been at this for a while. A few years ago, they constructed a time travel simulator that “simulated the behavior of a single photon traveling back in time and interacting with an older version of itself.” This provides more concrete evidence that reality will stretch to fit our time travel scenarios. This is the advantage of quantum mechanics over classical physics. One article compares quantum time travel to classical time travel by using the examples of the Avengers: Endgame and the Back to the Future movies. The latter series “represents time travel through classical physics,” where Marty’s alteration of events threatens to erase his own existence, while “Endgame is a model of quantum time travel,” where characters can manipulate events and it’s obvious that timelines are alterable.

It’s a long way from theory to practice, but it’s nice to know that we won’t be incurring any paradoxes when we finally decide to go back in time and warn people about Covid-19.