https://www.livescience.com/63182-quantum-computer-reverse-arrow-time.html
A new technique for quantum computing could bust open our whole model of how time moves in the universe.
A new paper, published July 18 in the journal Physical Review X [ https://journals.aps.org/prx/abstract/10.1103/PhysRevX.8.031013 ], opens the door to the possibility that the arrow pf time is an artifact of classical-style computation — something that's only appeared to us to be the case because of our limited tools.
A team of researchers found that in certain circumstances causal asymmetry disappears inside quantum computers.
In this paper, the researchers looked at physical systems that had a goldilocks' level of disorder and randomness — not too little, and not too much.
They tried to figure out those systems' pasts and futures using theoretical quantum computers (no physical computers involved). Not only did these models of quantum computers use less memory than the classical computer models, she said, they were able to run in either direction through time without using up extra memory. In other words, the quantum models had no causal asymmetry
"While classically, it might be impossible for the process to go in one of the directions [through time]," said Jayne Thompson, of the National University of Singapore, "our results show that 'quantum mechanically,' the process can go in either direction using very little memory."
And if that's true inside a quantum computer, that's true in the universe, she said.
Quantum physics is the study of the strange probabilistic behaviors of very small particles — all the very small particles in the universe. And if quantum physics is true for all the pieces that make up the universe, it's true for the universe itself, even if some of its weirder effects aren't always obvious to us. So if a quantum computer can operate without causal asymmetry, then so can the universe.
Thompson added that the research doesn't prove that there isn't any causal asymmetry anywhere in the universe. She and her colleagues showed there is no asymmetry in a handful of systems. But it's possible, she said, that there are some very bare-bones quantum models where some causal asymmetry emerges.
(Score: 5, Informative) by requerdanos on Wednesday August 08 2018, @12:50AM (1 child)
Specifically, time moves from "now" to "later" in intervals of time whose length is h (Max Planck's constant).
Well, not so fast. Quantum theories describe the behavior of very, very tiny things on very, very tiny scales. Something with more mass than, say, an atom, has a quantum wavelength shorter than itself, rendering quantum phenomena essentially inoperable and handing the object or item off to classical physics for handling. So while the tiny things that quantum theory does apply to do technically exist "in the universe", it doesn't follow that things "in the universe" will behave according to the predictions of quantum mechanics. Anything above a certain very, very small size doesn't.
(Score: 0) by Anonymous Coward on Wednesday August 08 2018, @04:05AM
bah. Entropy.
so if this system is zero entropy. then wow, it breaks thermodynamics. that'd be a big deal.