Paradox, Solved: Thermodynamics and Quantum Mechanics CAN Be True at the Same Time
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Quantum mechanics and classical physics don’t always get along, and can sometimes form apparent paradoxes where observed quantum behavior violates well-established physical laws.
In quantum mechanics, it’s possible to revert particles to previous states (aka time reversal) while also preserving information, but the Laws of Thermodynamics suggest that this is impossible.
Scientists from the University of Twente in the Netherlands untangled this paradox using photons and optical chips.
The properties of quantum mechanics have long puzzled physicists—even Albert Einstein once described quantum entanglement as “spooky action at a distance.” That’s because quantum mechanics, at least at a glance, seems to frequently flout the laws of classical physics (specifically Isaac Newton’s Laws of Thermodynamics) and regularly creates pesky paradoxes that suggest we’re still missing a piece of the puzzle.
One of these paradoxes involves time reversal. In quantum mechanics, it’s possible to reverse particles to a prior state while still retaining information. However, the laws of thermodynamics state that time has a direction and information is inevitably lost.
So, how can both these things be true at once?
Scientists from the University of Twente in the Netherlands untangled this paradox using photons and optical chips, and discovered that Newton’s laws still held up even in this quantum environment. The results were published in the journal Nature Communications earlier this month.
“One of the core questions of quantum physics is how to reconcile the unitary evolution of quantum states, which is information-preserving and time-reversible, with evolution following the second law of thermodynamics, which, in general, is neither,” the paper reads. “We have experimentally shown that a pure quantum state in a closed environment can locally behave like a thermal state because of entanglement with the other modes.”
The team made use of optical chips with channels that allowed photons to pass through. At the beginning of the experiment, the team knew exactly how many photons were in the channels, but lost count as they shifted position (which was a good and planned thing).
“When we looked at the individual channels, they obeyed the laws of thermodynamics and built up disorder,” says co-author Jegler Renema in a press release. “Based on measurements on one channel, we didn’t know how many photons were still in that channel, but the overall system was consistent with quantum mechanics.” That’s because these various channels—or subsystems—became entangled, thus preserving “missing information” in the entangled subsystem.
This work, along with previous theoretical and experimental solutions, just shows how the frontiers of scientific understanding can seem “spooky” at first, but slowly solving these seemingly impossible paradoxes brings us one step closer to that ever-elusive Theory of Everything.
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