Skip to comments.Natural selection acts on the quantum world
Posted on 12/23/2004 8:31:39 AM PST by PatrickHenry
Objective reality may owe its existence to a 'darwinian' process that advertises certain quantum states.
A team of US physicists has proved a theorem that explains how our objective, common reality emerges from the subtle and sensitive quantum world.
If, as quantum mechanics says, observing the world tends to change it, how is it that we can agree on anything at all? Why doesn't each person leave a slightly different version of the world for the next person to find?
Because, say the researchers, certain special states of a system are promoted above others by a quantum form of natural selection, which they call quantum darwinism. Information about these states proliferates and gets imprinted on the environment. So observers coming along and looking at the environment in order to get a picture of the world tend to see the same 'preferred' states.
If it wasn't for quantum darwinism, the researchers suggest in Physical Review Letters [Ollivier H., Poulin D. & Zurek W. H. Phys. Rev. Lett., 93. 220401], the world would be very unpredictable: different people might see very different versions of it. Life itself would then be hard to conduct, because we would not be able to obtain reliable information about our surroundings... it would typically conflict with what others were experiencing.
The difficulty arises because directly finding out something about a quantum system by making a measurement inevitably disturbs it. "After a measurement," say Wojciech Zurek and his colleagues at Los Alamos National Laboratory in New Mexico, "the state will be what the observer finds out it is, but not, in general, what it was before."
Because, as Zurek says, "the Universe is quantum to the core," this property seems to undermine the notion of an objective reality. In this type of situation, every tourist who gazed at Buckingham Palace would change the arrangement of the building's windows, say, merely by the act of looking, so that subsequent tourists would see something slightly different.
Yet that clearly isn't what happens. This sensitivity to observation at the quantum level (which Albert Einstein famously compared to God constructing the quantum world by throwing dice to decide its state) seems to go away at the everyday, macroscopic level. "God plays dice on a quantum level quite willingly," says Zurek, "but, somehow, when the bets become macroscopic he is more reluctant to gamble." How does that happen?
The Los Alamos team define a property of a system as 'objective', if that property is simultaneously evident to many observers who can find out about it without knowing exactly what they are looking for and without agreeing in advance how they'll look for it.
Physicists agree that the macroscopic or classical world (which seems to have a single, 'objective' state) emerges from the quantum world of many possible states through a phenomenon called decoherence, according to which interactions between the quantum states of the system of interest and its environment serve to 'collapse' those states into a single outcome. But this process of decoherence still isn't fully understood.
"Decoherence selects out of the quantum 'mush' states that are stable, that can withstand the scrutiny of the environment without getting perturbed," says Zurek. These special states are called 'pointer states', and although they are still quantum states, they turn out to look like classical ones. For example, objects in pointer states seem to occupy a well-defined position, rather than being smeared out in space.
The traditional approach to decoherence, says Zurek, was based on the idea that the perturbation of a quantum system by the environment eliminates all but the stable pointer states, which an observer can then probe directly. But he and his colleagues point out that we typically find out about a system indirectly, that is, we look at the system's effect on some small part of its environment. For example, when we look at a tree, in effect we measure the effect of the leaves and branches on the visible sunlight that is bouncing off them.
But it was not obvious that this kind of indirect measurement would reveal the robust, decoherence-resistant pointer states. If it does not, the robustness of these states won't help you to construct an objective reality.
Now, Zurek and colleagues have proved a mathematical theorem that shows the pointer states do actually coincide with the states probed by indirect measurements of a system's environment. "The environment is modified so that it contains an imprint of the pointer state," he says.
All together now
Yet this process alone, which the researchers call 'environment-induced superselection' or einselection [Zurek W. H. Arxiv, Preprint, link at footnote 2 in original article], isn't enough to guarantee an objective reality. It is not sufficient for a pointer state merely to make its imprint on the environment: there must be many such imprints, so that many different observers can see the same thing.
Happily, this tends to happen automatically, because each individual's observation is based on only a tiny part of the environmental imprint. For example, we're never in danger of 'using up' all the photons bouncing off a tree, no matter how many people we assemble to look at it.
This multiplicity of imprints of the pointer states happens precisely because those states are robust: making one imprint does not preclude making another. This is a Darwin-like selection process. "One might say that pointer states are most 'fit'," says Zurek. "They survive monitoring by the environment to leave 'descendants' that inherit their properties."
"Our work shows that the environment is not just finding out the state of the system and keeping it to itself", he adds. "Rather, it is advertising it throughout the environment, so that many observers can find it out simultaneously and independently."
I donno. I just post the stuff. Maybe one of the smart guys around here can help.
This is quantum natural selection, not quantum evolution. As someone who questions macro-evolution, I have no problem with the ideas put forth in this article.
Metaphysical paraconformities ping. (aka quantum fun-house mirror)
My understanding is different. Decoherence is interaction with the environment destroying entanglement - in effect, the environment "factors" an entangled quantum state into independent parts. It does not explain how a mixed state "collapses" to a single outcome.
Whoever wrote this apparently has been spending too much time with my sister or has fallen into a Mixmaster at some point in his life.
This whole mess is B.S.; rather like comparing a telescope to a fishing net.
... or in the back of the Biltmore Garage, especially if his name is Nathan.
What is waving? Particles are pieces of what?
I followed the link, and my beeber was STUNED!
"All your conspiracy are belong to us."
Where do they come UP with this stuff??
On second thought, maybe I don't really want to know...
Cheers and Merry Christmas!
One need not use the game sequence number as Parrondo's version does.
There some evidence that muscle contractions use a mechanism simlilar to Astumians.
It's also interesting that there are two commentaries (one Polish and one in something like "Physics Today") that review these games but get the math wrong.
Detroit is snowed in today. (Amazing how Runyon ties into so much scientific discussion.)
What does this have to do with YEC?
Careful, they take this stuff seriously. You might hurt the purposeless feelings of some soulless, will-less evolutionist in his imaginary world who is particularly lonely this time of year.
Waving? Visualize sawdust floating on a lake with waves moving across the surface, that's a rough analogy. In a sense the sawdust particles and waves are ONE. Now with ElectroMagnetic waves, from radio(long)to gamma(short)wavelengths it's like the(localized)particles are rotating in a circle as they move in a linear direction. Now change the floating sawdust to corks tied together on a string vertically at one foot spacings going down in the water(with some anchor weight at the bottom of the string). As you see, the top cork goes through the largest circular motion as the crest/trough passes by. The next one down(1 ft lower)a slightly smaller radius, the third cork(2 ft down)still a smaller radius, and so on down to where there is virtually no detectable circular motion at all. Now, this is just the opposite to EM wavelengths : shorter=higher energy. Getting tossed around in a boat on the LONG wavelengths of surface water waves in a storm is definitely more energy than being way under the waves in a submarine, yes? This then is the difference between EM waves, which govern bosons(photons of light)and DeBroglie's matter waves which govern fermions(electrons/protons/neutrons/etc):shorter waveLENGTH=higher bose energy and lower fermi energy. Ok then, get laid back and think about WAVES, WAVES, WAVES over the christmas to New Years holidays, then we can discuss PARTICLES.
Frankly, none of this sounds Darwinian at all. I suppose they just thought "quantum Darwinism" sounded catchy.
If you assemble enough people, those in the back won't be able to see the tree ...
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