Posted on 04/19/2007 5:36:46 PM PDT by LibWhacker
Quantum mechanics just got even stranger.
There's only one way to describe the experiment performed by physicist Anton Zeilinger and his colleagues: it's unreal, dude.
Measuring the quantum properties of pairs of light particles (photons) pumped out by a laser has convinced Zeilinger that "we have to give up the idea of realism to a far greater extent than most physicists believe today."
By realism, he means the idea that objects have specific features and properties —that a ball is red, that a book contains the works of Shakespeare, or that an electron has a particular spin.
For everyday objects, such realism isn't a problem. But for objects governed by the laws of quantum mechanics, like photons and electrons, it may make no sense to think of them as having well defined characteristics. Instead, what we see may depend on how we look.
This notion has been around ever since the advent of quantum mechanics in the early twentieth century. The theory seemed to show that, in the quantum world, objects are defined only fuzzily, so that all we can do is work out the probability that they have particular characteristics — such as being located in a specific place or having a specific energy.
Allied to this assault on reality was the apparent prediction of what Albert Einstein, one of the chief architects of quantum theory, called 'spooky action at a distance'. Quantum theory suggests that disturbing one particle can instantaneously determine the properties of a particle with which it is 'entangled', no matter how far away it is. This would violate the usual rule of locality: that local behaviour is governed by local events.
Einstein could not believe that the world was really so indeterminate. He supposed that a deeper level of reality had yet to be uncovered — so-called 'hidden variables' that specified an object's properties precisely and in strictly local terms.
Failed test
In the 1960s the Irish physicist John Bell showed how to put locality and realism to the test. He deduced that if both ideas applied to the quantum world, then two particular quantities calculated from measurements made on a pair of entangled photons would be equal to one another. If so, there would be nothing 'spooky' about entanglement after all.
Experiments were done to test his prediction in the ensuing two decades, and results showed that Bell's equality was violated. Thus, either realism or locality, or possibly both of these ideas, do not apply in the quantum world.
But which is it? That's what Zeilinger, based at the University of Vienna in Austria, and his colleagues tried to find out.
They came up with a similar test to Bell's, to see whether quantum mechanics obeys realism but not locality. Again the experiment involves comparing two quantities calculated from measurements on entangled photons, to see if they are equal. But whereas in Bell's test these quantities are derived from the so-called 'linear' polarization of the photons — crudely, whether their electromagnetic fields oscillate in one direction or the other — Zeilinger's experiment looks at a different sort of polarization, called elliptical polarization.
Like Bell's, Zeilinger's equality proved false. This doesn't rule out all possible non-local realistic models, but it does exclude an important subset of them. Specifically, it shows that if you have a group of photons that all have independent polarizations, then you can't ascribe specific polarizations to each. It's rather like saying that you know there are particular numbers of blue, white and silver cars in a car park — but it is meaningless even to imagine saying which ones are which.
Truly weird
If the quantum world is not realistic in this sense, then how does it behave? Zeilinger says that some of the alternative non-realist possibilities are truly weird. For example, it may make no sense to imagine what would happen if we had made a different measurement from the one we chose to make. "We do this all the time in daily life," says Zeilinger — for example, imagining what would have happened if you had tried to cross the road when a truck was coming. If the world around us behaved in the same way as a quantum system, then it would be meaningless even to imagine that alternative situation, because there would be no way of defining what you mean by the road, the truck, or even you.
Another possibility is that in a non-realistic quantum world present actions can affect the past, as though choosing to read a letter or not could determine what it says.
Zeilinger hopes that his work will stimulate others to test such possibilities. "Our paper is not the end of the road," he says. "But we have a little more evidence that the world is really strange."
Before painting them, Picasso liked to get his models shiftfaced.
That would in the world of teenagers when ‘the party principle’ is engaged ;)
One can say the same for classical mechanics. Say you have a isolated system with zero angular momentum, and it separates into two systems S1 and S2. You measure the angular momentum of S1 and it turns out to be L. Surprise surprise! S2's angular momentum is now -L! How did S2 know it's angular momentum had to be -L?! S1 must have magically transmitted information to S2! Or maybe S1 and S2 are mysteriously entangled! But in general people know better than to talk this way.
In a similar vein, some insist that 'Santa Claus can materialize out of the vaccuum' and 'pterosaurs can suddenly poof into existence and snatch your kids away' are implications of quantum mechanics.
Are you sure these guys aren't working on climate modeling rather than QM?
Let’s hope they are really, really small ones.
That way I can put up one of them sticky fly ribbon thingies.
funny! I read it.
Sure, its's an intellectually delectably absurd image, but in what way would it be untrue? The point was that any random process would eventually, given infinite time, come up with every string of letters written by mankind up till now.
Only an agenda driven fool believes purpose is supplant-able with random chaos.
Sorry, but I cannot for the life of me see in this example any agenda. Maybe because I understand that it's true, and it didn't matter what 'works' were chosen to illustrate the point.
By the way, although I guess my choice of the phenomenon of flying monkeys made it sound as if I were being derisive I meant it literally, and I confess to no agenda.
< }B^)
“... any random process would eventually, given infinite time, come up with every string of letters written by mankind up till now.” I don’t particularly agree with that assertion ... random process, even with infinite time to generate patterns, will not necessarily create the particular pattern that is the entirety of the Shakespearean Sonnets. Why? Because even random processing, over infinite time, loses randomness to fall into patterns with deadend value thus derailing the generation of continuing randomness. But the fairy tale sounds nice if you want to believe in the ‘divinity’ of randomness.
You are correct, sir!
I would only add that many of the familiar properties of everyday objects are pure manifestations of the quantum. My favorite example is metal, aluminum foil to be specific. What a strange sort of cloth! Classical physics offers no explanation whatsoever of its properties, only a phenomenological description. When you look at a shiny piece of metal, you’re staring straight into the depths of the Fermi sea.
Einstein was declaring that God’s creation had laws that govern it’s appearance and behavior, that reality was predictable and that observable phenomena was not random. The idea that God did not intervene in the course of events, except in the good deeds of righteous men. The scientific method used as a way to know reality is based on this assumption. You imply an unknowable, random universe.
The universe would pass into cold death too ...
More like, the Sun would live and die a billion times.
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