Quantum mechanics is a robust, empirically successful theory that enables powerful technologies. Understanding its implications for the nature of reality and experience remains difficult, and some conceptual problems persist despite a century of work. The non-intuitive character of quantum physics fosters misunderstandings. No experiment has yet sent quantum particles back in time. Time-travel proposals invoke hypothetical quantum 'time loops' — spacetime twists that could permit systems to exit earlier than they entered, possibly via tunnels in spacetime. Recent proposals use quantum teleportation of qubits with entangled pairs to transfer states without moving carriers; standard teleportation succeeds at most one-quarter of the time unless corrected, and some approaches suggest discarding failed cases to keep only successful outcomes.
Quantum mechanics is unquestionably a robust and successful theory - so far, all its predictions have held, and scientists can build powerful technologies based on it. Yet, understanding what it tells us about the nature of reality and how we experience it has proven tricky. Physicists and philosophers have been grappling with it for a century, ironing out some of the early ambiguities, but some conceptual problems remain.
The idea relies on exploiting quantum 'time loops' - hypothetical twists in space-time that allow a particle, or anything else, to come out of the loop at an earlier time than when it went in. These loops could exist in the Universe, for example through tunnels in the fabric of space-time. A century of quantum physics The recent proposals were based on quantum teleportation of qubits, in which the state of a qubit is transported from one location to another, without physically moving between them.
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