Quantum Time Travel Paradox Solved: Study

If a person travels back in time and kills her own mother, well that’s pretty sinister—but it also creates for her an existential paradox. How does she exist if her mother doesn’t give birth to her?

Quantum computing theory was plagued by a similar paradox. It could be used to solve very complex mathematical problems, but to do so could seriously mess with time.

An international team of scientists has developed a way, however, for quantum computing to use time travel without breaking causality. They published their study Nov. 24 in the journal Quantum Information.

The key is using open timelike curves (OTCs) instead of closed timelike curves (CTCs). Both are time-loops, which are made possible within Albert Einstein’s General Relativity theory by traveling through wormholes.

The CTCs create causal paradoxes, similar to the woman killing her mother in the past. This happens because an object entering a wormhole can interact with causal factors in its own past. But, in the case of OTCs, the object cannot interact with those factors.

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“[It] is completely isolated from anything that can affect its own causal past during the time-traveling process,” the study states. “This naturally occurs, for example, in instances where the wormhole mouths are spatially separated.” [See a diagram here]

So how does this help solve complex equations?

Foundational constraints of quantum theory are broken. For example, “the uncertainty principle can be violated, and arbitrary unknown quantum states can be cloned to any fixed fidelity,” the study explains. Scientists are able to bend the rules that make solving some equations seemingly impossible, thus making the solutions possible.

Before the recent findings, it was thought that this rule-bending brought with it the paradox of broken causality.

With OTCs, however, the study explains: “The time-traveling particle has the potential to break causality, [but] its complete isolation ensures that causality never actually breaks.” The rules can still be bent to solve the equations, but the paradox of broken causality is avoided.

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