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: 1) by khallow on Wednesday August 08 2018, @03:28AM
The point of trying is to get rid of yet another need to invoke the anthropic principle to explain why the universe looks the way it does. A priors that just are - significantly constrain our ability to explain the universe and do science. Not all instances of the anthropic principle are equally crippling. Starting on a planet with a moon, which was instrumental to the development of a habitable environment for us, doesn't preclude us from studying potential environments which are not planets with moons. But starting in a universe with a time arrow and a particular distribution of matter and anti-matter, does preclude us from studying universes with different such states (unless there is a more encompassing physical reality of which we are currently unaware connecting us to those universes that we can somehow observe sufficiently well through the connection).
The thing is, you will get a time arrow from any embedding or representation of a classical computational system in a time-agnostic QM system. From the viewpoint of that classical computation system, you have the time arrow because the system has memory - it doesn't remember the future. That time asymmetry of the observer is all one needs. Needless to say, our brains have the classical computation system and the time arrow. Thus, we have an explanation right there for why there's a time arrow. Technically, that's good enough, but it leaves the door wide open to whether there's other such systems in incompatible universes which exist in some sense (perhaps they could be observable by a time-agnostic quantum mechanical system), but which we will never observe because of our inherent physical limitations.