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Physicists reverse time using quantum computer
Researchers from the Moscow Institute of Physics and Technology teamed up with colleagues from the U.S. and Switzerland and returned the state of a quantum computer a fraction of a second into the past. They also calculated the probability that an electron in empty interstellar space will spontaneously travel back into its recent past. The study is published in Scientific Reports.
"This is one in a series of papers on the possibility of violating the second law of thermodynamics. That law is closely related to the notion of the arrow of time that posits the one-way direction of time from the past to the future," said the study's lead author Gordey Lesovik, who heads the Laboratory of the Physics of Quantum Information Technology at MIPT.
"We began by describing a so-called local perpetual motion machine of the second kind. Then, in December, we published a paper that discusses the violation of the second law via a device called a Maxwell's demon," Lesovik said. "The most recent paper approaches the same problem from a third angle: We have artificially created a state that evolves in a direction opposite to that of the thermodynamic arrow of time."
(Score: 2) by hendrikboom on Tuesday March 19 2019, @01:17AM (3 children)
The direction of time is an emergent statistical phenomenon.
Feynman diagrams are time-invariant. You can run them forwards, backwards, left-to-right, down-to-up, and they are all just as valid.
It's no surprise that a quantum event in a quantum computer doesn't care about the direction of time.
But there's not enough statistical behaviour to trigger entropy as a direction in time.
Rivelli's book on quantum gravity says, if you fine there's a direction in space-time where entropy increases, you can choose to call it time. But you need enough effective randomness for entropy to be meaningful.
(Score: 2) by acid andy on Tuesday March 19 2019, @02:46AM
Is this anything more than a linguistic issue though? In the sense that it just doesn't deserve to be called time because that word ceases to be a useful label due to it lacking the properties we normally ascribe to time? If so that doesn't necessarily mean it really ceases to be time in a physical sense. It strikes me as sounding a bit like the question as to whether a tree falls in a forest if no-one is there to hear it. I don't know.
DISCLAIMER: I am AINQP and AINQP Is No Quantum Physicist!
Master of the science of the art of the science of art.
(Score: 0) by Anonymous Coward on Tuesday March 19 2019, @06:33AM (1 child)
what do you find so confusing about this?
time has a given direction. for some reason in most basic phenomena the equations are invariant to time reversals.
but the universe is not a basic phenomenon. the moment you introduce complexity, you lose statistical time invariance.
the probability of observing a closed system with decreasing entropy is practically zero for macroscopic systems.
but Poincare's theorem says this will happen, and it has been observed for small enough systems.
time does not emerge from complexity, it's direction is just made evident by our imperfect measurements. and once you introduce quantum effects, there are inherent stochastic effects that serve to spread out probability distributions, again making time's direction evident.
(Score: 0) by Anonymous Coward on Tuesday March 19 2019, @10:46PM
Yeah man, what's so difficult about that? Geez!