Time loops may not be forbidden by physics after all

Physicists find that causal loops, where two events separated in time influence each other in paradoxical ways, are allowed in many theoretical universes, some of which share features with our own

Physics 5 July 2022

Illustration of a clock in a spiral

In certain universes, achieving a time loop is possible without breaking physics


A causal loop is a classic time travel conundrum. If you send information to the past – say, you give Albert Einstein the formula E=mc ² before he theorises it himself, then he publishes it and you go on to find it in a textbook – you would create a situation in which the information has no true origin.

A new analysis shows that this type of causal loop is possible in more theoretical universes than had previously been expected.

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