Skip to comments.Physicists bid farewell to reality?
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.
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.
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."
in a quantum sense
Reality isnt all its cracked up to be anyway
that was unreal man ...like a deja vu thing
A recent article to be published in Foundations of Physics involves laser light experiments which indicate that light consists of waves and particles, presumably very fast particles of some sort and waves which those particles create as they travel through some sort of a medium.
Albert Einstein is considered one of the greatest natural philosopher in history. Most people are familiar with his famous statement dismissing quantum physics uncertainty principle:
"God does not play dice with the universe."
However, most people do not know that he made the statement to his colleague and friendly rival, Niels Bohr, who made the less famous reply:
"Albert, stop telling God what to do."
I tend to agree with Bohr, and with God, of course.
I also tend to use this quote when dealing with many televangelists, most Imams and Mullahs and just about anyone prattling on about man made global warming.
Dang, all this time I was sure my Z car is gold. This shakes that all up. I can’t be sure it’s gold, or if it’s even a car.
Must be supernatural ;0)
I'll vote with Einstein; the only problem is that he's dead and we don't have a replacement for him.
...or charm - but what color is it?
Thanks for the ping. Thanks for the ping to the GB Probe thread as well. Too bad the stuck on stupid types got there first. (Why I did not post on it)
I believe its mauve
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