Posts tagged QM

So much for classical objects and time travel. But what would happen if a quantum particle entered a closed time-like curve? In the early 90s, the physicist David Deutsch showed that not only is this possible but that it can only happen in a way that does not allow superluminal signalling. So quantum mechanics plays havoc with causality but in a way that is consistent with relativity and so prevents grandfather-type paradoxes. Deutsch’s result has extraordinary implications. It implies that closed time-like curves can be used to solve NP-complete problems in polynomial time and to violate Heisenberg’s uncertainty principle.

via https://medium.com/the-physics-arxiv-blog/the-quantum-experiment-that-simulates-a-time-machine–185a7cc9bd11

As with so much else in quantum mechanics, this concept of retrocausality is limited in scope. Only in certain circumstances can we see the future influence the past. Although individual particle processes can move backward or forward in time, the universe as a whole is skewed in the forward direction, because its past endpoint was highly ordered, and its future endpoint is highly disordered. Our mortality is this asymmetry in microcosm.

http://nautil.us/issue/9/time/the-quantum-mechanics-of-fate