Time loop: is it possible to return to the past

Could the famous “murdered grandfather paradox” described by Rene Barzhavel in 1943 become a reality?

On June 28, 2009, world renowned physicist Stephen Hawking threw a party at Cambridge University with balloons, snacks and champagne. However, no one came to her, because Hawking sent out invitations only after the party was over. It was, in his words, “a ceremonial reception for time travelers” – thus the physicist wanted to reinforce his long-standing hypothesis that time travel is impossible.

But Hawking could be wrong. In theory, there are no direct prohibitions on travel to the past. This trick could be made possible on the basis of Einstein’s general theory of relativity, which describes gravity as the curvature of space and time in energy and matter. An extremely powerful gravitational field, formed, for example, by a rotating black hole, can deform matter so that space will be curved “inside out.” This would create a so-called closed time-like curve – a cycle that would actually be time travel.

Hawking and many other physicists consider the closed timelike curve to be absurd, because the time travel of any macroscopic object inevitably creates paradoxes that break causation.

But recently, a physicist from the University of Queensland (Australia) Tim Ralph and his graduate student Martin Ringbauer tried to investigate the “murdered grandfather paradox” from the point of view of quantum mechanics.

The essence of the paradox is to go back in time and kill your own grandfather, thereby preventing your own birth. According to the hypothesis that the past cannot be changed in any way, the grandfather must have already survived the attempted murder, or the time traveler thus creates an alternative timeline in which he will never be born.

From the point of view of quantum mechanics, if a person is presented as a fundamental particle, then its a priori deterministic emission does not exist – there is only a probability distribution. That is, a person with equal probability both would commit a murder and would give his grandfather a chance to be saved – and this is enough to close the curve and avoid the paradox, Australian researchers note.

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