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How Maxwell’s Demon Continues to Startle Scientists [Entropy]
https://www.quantamagazine.org ^ | APRIL 22, 2021 | Jonathan O'Callaghan

Posted on 04/29/2021 10:38:11 AM PDT by Red Badger

The thorny thought experiment has been turned into a real experiment — one that physicists use to probe the physics of information

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It took physicists 115 years to tame Maxwell’s Demon.

The universe bets on disorder. Imagine, for example, dropping a thimbleful of red dye into a swimming pool. All of those dye molecules are going to slowly spread throughout the water. Physicists quantify this tendency to spread by counting the number of possible ways the dye molecules can be arranged. There’s one possible state where the molecules are crowded into the thimble. There’s another where, say, the molecules settle in a tidy clump at the pool’s bottom. But there are uncountable billions of permutations where the molecules spread out in different ways throughout the water. If the universe chooses from all the possible states at random, you can bet that it’s going to end up with one of the vast set of disordered possibilities.

Seen in this way, the inexorable rise in entropy, or disorder, as quantified by the second law of thermodynamics, takes on an almost mathematical certainty. So of course physicists are constantly trying to break it.

One almost did. A thought experiment devised by the Scottish physicist James Clerk Maxwell in 1867 stumped scientists for 115 years. And even after a solution was found, physicists have continued to use “Maxwell’s demon” to push the laws of the universe to their limits.

In the thought experiment, Maxwell imagined splitting a room full of gas into two compartments by erecting a wall with a small door. Like all gases, this one is made of individual particles. The average speed of the particles corresponds to the temperature of the gas — faster is hotter. But at any given time, some particles will be moving more slowly than others.

What if, suggested Maxwell, a tiny imaginary creature — a demon, as it was later called — sat at the door. Every time it saw a fast-moving particle approaching from the left-hand side, it opened the door and let it into the right-hand compartment. And every time a slow-moving particle approached from the right, the demon let it into the left-hand compartment.

After a while, the left-hand compartment would be full of slow, cold particles, and the right-hand compartment would grow hot. This isolated system would seem to grow more orderly, not less, because two distinguishable compartments have more order than two identical compartments. Maxwell had created a system that appeared to defy the rise of entropy, and thus the laws of the universe.

“He tried to prove a system where the entropy would decrease,” said Laia Delgado Callico, a physicist at King’s College London. “It’s a paradox.”

Two advances would be crucial to solving Maxwell’s demon. The first was by the American mathematician Claude Shannon, regarded as the founder of information theory. In 1948, Shannon showed that the information content of a message could be quantified with what he called the information entropy. “In the 19th century, no one knew about information,” said Takahiro Sagawa, a physicist at the University of Tokyo. “The modern understanding of Maxwell’s demon was established by Shannon’s work.”

The second vital piece of the puzzle was the principle of erasure. In 1961, the German American physicist Rolf Landauer showed that any logically irreversible computation, such as the erasing of information from a memory, would result in a minimal nonzero amount of work converted into heat dumped into the environment, and a corresponding rise in entropy. Landauer’s erasure principle provided a tantalizing link between information and thermodynamics. “Information is physical,” he later proclaimed.

In 1982, the American physicist Charles Bennett put the pieces of the puzzle together. He realized that Maxwell’s demon was at core an information-processing machine: It needed to record and store information about individual particles in order to decide when to open and close the door. Periodically it would need to erase this information. According to Landauer’s erasure principle, the rise in entropy from the erasure would more than compensate for the decrease in entropy caused by the sorting of the particles. “You need to pay,” said Gonzalo Manzano, a physicist at the Institute for Quantum Optics and Quantum Information in Vienna. The demon’s need to make room for more information inexorably led to a net increase in disorder.

Then in the 21st century, with the thought experiment solved, the real experiments began. “The most important development is we can now realize Maxwell’s demon in laboratories,” said Sagawa.

In 2007 scientists used a light-powered gate to demonstrate the idea of Maxwell’s demon in action; in 2010, another team devised a way to use the energy produced by the demon’s information to coax a bead uphill; and in 2016 scientists applied the idea of Maxwell’s demon to two compartments containing not gas, but light.

“We switched the roles of matter and light,” said Vlatko Vedral, a physicist at the University of Oxford and one of the study’s co-authors. The researchers were ultimately able to charge a very small battery.

Others wondered if there might be less demanding ways to use information to extract useful work from a similar system. And research published in February in Physical Review Letters seems to have found a way to do so. The work makes the demon into a gambler.

The team, led by Manzano, wondered if there was a way to implement something like Maxwell’s demon but without the information requirements. They imagined a two-compartment system with a door, as before. But in this case, the door would open and close on its own. Sometimes particles would randomly separate themselves into hotter and colder compartments. The demon could only watch this process and decide when to turn the system off. In theory this process could create a small temperature imbalance, and therefore a useful heat engine, if the demon was smart about when to end the experiment and lock any temperature imbalance in place, much as a smart gambler on a hot streak knows when to leave the table. “You can either play all night on the roulette table, or you can stop if you win $100,” said Édgar Roldán, a physicist at the International Center for Theoretical Physics in Italy who was a co-author on the study. “We’re saying we don’t need such a complicated device as Maxwell’s demon to extract work in the second law. We can be more relaxed.” The researchers then implemented such a gambling demon in a nanoelectronic device, to show it was possible.

Ideas like this could prove useful in designing more efficient thermal systems, like refrigerators, or even in developing more advanced computer chips, which may be approaching a fundamental limit dictated by Landauer’s principle.

For the time being, though, our laws of the universe are safe, even when placed under the greatest scrutiny. What has changed is our understanding of information in the universe, and with it our appreciation of Maxwell’s demon, first a troublesome paradox, and now an invaluable concept — one that has helped to illuminate the remarkable link between the physical world and information.


TOPICS: Astronomy; History; Science; Weird Stuff
KEYWORDS: 1867; astronomy; disorder; electricuniverse; entropy; ftl; jamesclerkmaxwell; maxwellsdemon; maxwellsilverdemon; physics; science; stringtheory; wboopi
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1 posted on 04/29/2021 10:38:11 AM PDT by Red Badger
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To: SunkenCiv

Pingy!....................


2 posted on 04/29/2021 10:38:30 AM PDT by Red Badger ("We've always been at war with Climate Change, Winston."..............................)
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To: Red Badger

.


3 posted on 04/29/2021 10:41:26 AM PDT by sauropod (Chance favors the prepared mind.)
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To: Red Badger

O’Callaghan is a political genius!

“After a while, the left-hand compartment would be full of slow, cold particles...” And there’s where the word “demon” comes into play.


4 posted on 04/29/2021 10:46:35 AM PDT by sanjuanbob (Do NOT buy Chinese Products)
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To: All
The researchers then implemented such a gambling demon in a nanoelectronic device, to show it was possible.

The demon is now rehabbing in a secure Gamblers Anonymous facility and retaining a lawyer because he was forced into a gambling detail, which he did NOT volunteer for, and as a result suffers gambling addiction. He, his name is kept confidential, is seeking compensation for kidnapping, mental cruelty and miscellaneous damages.

5 posted on 04/29/2021 10:48:31 AM PDT by BipolarBob (Jeffrey Epsteins last words "I am not committing suicide".)
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To: BipolarBob

Thermodynamics: It’s not just a good idea, it’s the law.


6 posted on 04/29/2021 10:54:04 AM PDT by The Antiyuppie (When small men cast long shadows, then it is very late in the day.)
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To: Red Badger

Maxwell’s demon retired to a nursing home a long time ago - you can easily recognize him - he’s the one with Schrodinger’s cat in his lap (or not).


7 posted on 04/29/2021 10:54:23 AM PDT by Stosh
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To: Red Badger

Unmixing Color Machine (Ultra Laminar Reversible Flow) - Smarter Every Day 217

https://m.youtube.com/watch?v=j2_dJY_mIys


8 posted on 04/29/2021 10:59:30 AM PDT by ADemocratNoMore (The Fourth Estate is now the Fifth Column)
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To: Red Badger

Alaska and space are not the final frontiers. Quantum mechanics is. Just because it’s spooky is no reason not to study it.


9 posted on 04/29/2021 11:00:44 AM PDT by BipolarBob (Jeffrey Epsteins last words "I am not committing suicide".)
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To: ADemocratNoMore

Let me know when they can unscramble an egg....................


10 posted on 04/29/2021 11:07:17 AM PDT by Red Badger ("We've always been at war with Climate Change, Winston."..............................)
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To: Red Badger

The 2nd Law of Thermodynamics and the Law of Conservation of Energy prove an intelligent orderly creator of the universe. Personality and civil/moral law proves a personal God


11 posted on 04/29/2021 11:11:50 AM PDT by Jan_Sobieski (Sanctification)
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To: Jan_Sobieski

The mere existence of anything proves the existence of God................


12 posted on 04/29/2021 11:16:34 AM PDT by Red Badger ("We've always been at war with Climate Change, Winston."..............................)
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To: Red Badger

re: “The universe bets on disorder. Imagine, for example, dropping a thimbleful of red dye into a swimming pool. All of those dye molecules ... But there are uncountable billions of permutations ... If the universe chooses from all the possible states at random, you can bet that it’s going to end up with one of the vast set of disordered possibilities.”

And yet - nature DOES organize.

I give you 1) Animal life and 2) storm structures (notably, tornadic thunderstorms and hurricanes).


13 posted on 04/29/2021 11:22:24 AM PDT by _Jim (Save babies)
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To: Red Badger

This is why thought experiments are interspersed but are not proof


14 posted on 04/29/2021 11:30:31 AM PDT by Nifster (I see puppy dogs in the clouds)
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To: BipolarBob

re: “Quantum mechanics is.”

100 yr old ideas/idealogy BADLY in need of a re-write.

“Steven Weinberg on What’s the matter with quantum mechanics?”

https://youtu.be/3nnLbRaxtCE?t=227


15 posted on 04/29/2021 11:30:39 AM PDT by _Jim (Save babies)
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To: Red Badger
LOL...I once attended a lecture by one of the world's greatest interpreters of the physical and metaphysical aspects of the universe.


Professor Irwin Corey..Genius

The good prof explained in great detail that it was necessary to enact Newton's third law in order to keep humanity from continually falling on its ass.

16 posted on 04/29/2021 11:46:20 AM PDT by PerConPat (A politician is an animal which can sit on a fence and yet keep both ears to the ground - Mencken)
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To: Red Badger

Japanese physicists have demonstrated the equivalence of information and energy. So the Trinity surfaces again. Matter, Energy, Information.

https://physicsworld.com/a/information-converted-to-energy/

https://amazon.com/Astrophysics-Cosmology-Gravity-Like-Fields-Dr%C3%B6scher/dp/3000506241/ref=sr_1_1?dchild=1&keywords=gravity-like+fields&qid=1619721907&s=books&sr=1-1


17 posted on 04/29/2021 11:47:02 AM PDT by SubMareener (Save us from Quarterly Freepathons! Become a MONTHLY DONOR)
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To: SubMareener

That explains why I get fatter when I read a lot..................


18 posted on 04/29/2021 11:48:52 AM PDT by Red Badger ("We've always been at war with Climate Change, Winston."..............................)
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To: Red Badger

It’s Elvislution - the entire universe is tending to the perfection of Elvis.


19 posted on 04/29/2021 11:49:47 AM PDT by Psalm 73 ("You'll never hear surf music again" - J. Hendrix)
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To: Red Badger

“He realized that Maxwell’s demon was at core an information-processing machine: It needed to record and store information about individual particles in order to decide when to open and close the door.”

Seems like there’s a flaw in this logic, since the “demon” could simply be a cleverly-designed valve, which would involve no information processing in the traditional sense, but would still accomplish the same purpose.


20 posted on 04/29/2021 11:59:24 AM PDT by Boogieman
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