The loop of time: is it possible to return to the past?

June 28, 2009, the world famous 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 end of the party. It was, in his words, a “solemn reception for time travelers” - thereby the physicist wanted to reinforce his long-held hypothesis that time travel is impossible.

But Hawking could be wrong. Theoretically, there are no direct prohibitions on traveling to the past. This trick may become possible based on 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 time-like curve absurd, because time travel of any macroscopic object inevitably creates paradoxes that break the causal relationship.

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

The essence of the paradox is to return to the past 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 should have survived the attempted murder, or the time traveler thereby creates an alternative time line in which he will never be born.

From the point of view of quantum mechanics, if one imagines a person as a fundamental particle, then its a priori determined emission does not exist - there is only a probability distribution. That is, a person with equal probability would have committed the murder, and would have given his grandfather a chance of salvation - and this is enough to close the curve and avoid the paradox, Australian researchers note.

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