In 1992, Stephen Hawking presented the “chronology protection conjecture,” essentially stating that you can never go back in time. As comedian Dara Ó Briain noted in an interview with Hawking, the assertion “ruined the Terminator movies.”

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BBC/Rain Media Entertainment/Joseph Berry

The BBC interview contained an eye-opening, somewhat disappointing, assertion from Stephen Hawking, whose work on black holes led to worldwide recognition as an authority in theoretical physics. Briain asked whether black holes might allow for time travel at some point in the future.

“If you jump in a black hole,” the renowned physicist responded, “you will meet an unpleasant fate. It will be little consolation that your mass energy will be recycled as hydrogen radiation.”

Pushing Past Complicated Concepts

While Hawking can scientifically articulate why time travel—particularly traveling back in time—is impossible, the A Brief History of Time author has also used the scientific method to prove that time travel can’t happen. To that end, he devised a simple, but brilliant, experiment.

In 2009, Hawking hosted “a reception for time travelers,” but he only sent out the invitation after the event. Sadly, no time travelers joined the acclaimed scientist at his reception.

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Into The Universe

“I sat there a long time, but no one came,” Hawking told Michael Venables in an interview for Ars Technica.

Still, Hawking notes that the invitation stands.

“I’m hoping copies of [the invitation] in one form or another will survive for many thousands of years,” Hawking said. “Maybe one day someone living in the future will find the information and use a wormhole time machine to come back to my party, proving that time travel will, one day, be possible.”

An Assertion Up for Debate?

In Hawking’s 2015 interview with Ó Briain, the comedian pressed the physicist about whether a person might be able to send particles of light back in time to send a message to himself. Hawking stood firm.

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BBC

“You can’t send a message back in time,” the theoretical physicist insisted.

The comedian joked that if he could, he would have sent himself a message “not to ask that stupid question.”

Lee Billings, writing for the Scientific American summarizes Hawking’s perspective:

Hawking and many other physicists find [a theoretical framework for time-travel called “closed timelike curves”] abhorrent, because any macroscopic object traveling through one would inevitably create paradoxes where cause and effect break down.

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In the same Scientific American article, Billings sites theorist David Deutsch, who noted “that the paradoxes created by closed timelike curves could be avoided at the quantum scale because of the behavior of fundamental particles, which follow only the fuzzy rules of probability rather than strict determinism.”

In other words, since quantum mechanics can demonstrate that the probability of particles being able to go back in time is greater than zero, scientists must acknowledge that time travel technically could happen.

Recent Advances Open New Possibilities

While no one—as far as we know—has figured out how to join Hawking at his 2009 time travelers’ party, Chinese scientists have figured out how to teleport particles into outer space, which may lead to additional research into the feasibility of time travel. There is, of course, a caveat.

“Though this feat is called quantum teleportation,” explains the Carl Sagan-inspired website, Cosmos, “no actual teleportation of objects occurs. It’s a way of transmitting information about a particle; while it sounds exotic, it is routinely used in laboratories on Earth.”

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iStock

This new achievement has put us on a path towards a “quantum internet,” dramatically improving processing and communication speed. It’s also possible that quantum teleportation techniques, when applied to the theory of closed timelike curves, could change the way we think about time travel.

With that said, don’t expect the Terminator franchise to veer into scientific reality anytime soon. Humanity is in the earliest phases of developing this quantum technology, which only sends the smallest slivers of information. We’re a far away from using this technology to move anything through space and time—especially a dinner party guest.