Quantum Trickery: Testing Einstein's Strangest Theory

[bascule]

http://www.nytimes.com/2005/12/27/science/27eins.html?pagewanted=1&incamp=article_popular

 

Einstein said there would be days like this.

 

This fall scientists announced that they had put a half dozen beryllium atoms into a "cat state."

 

No, they were not sprawled along a sunny windowsill. To a physicist, a "cat state" is the condition of being two diametrically opposed conditions at once, like black and white, up and down, or dead and alive.

 

These atoms were each spinning clockwise and counterclockwise at the same time. Moreover, like miniature Rockettes they were all doing whatever it was they were doing together, in perfect synchrony. Should one of them realize, like the cartoon character who runs off a cliff and doesn't fall until he looks down, that it is in a metaphysically untenable situation and decide to spin only one way, the rest would instantly fall in line, whether they were across a test tube or across the galaxy.

 

The idea that measuring the properties of one particle could instantaneously change the properties of another one (or a whole bunch) far away is strange to say the least - almost as strange as the notion of particles spinning in two directions at once. The team that pulled off the beryllium feat, led by Dietrich Leibfried at the National Institute of Standards and Technology, in Boulder, Colo., hailed it as another step toward computers that would use quantum magic to perform calculations.

 

But it also served as another demonstration of how weird the world really is according to the rules, known as quantum mechanics.

 

The joke is on Albert Einstein, who, back in 1935, dreamed up this trick of synchronized atoms - "spooky action at a distance," as he called it - as an example of the absurdity of quantum mechanics.

 

"No reasonable definition of reality could be expected to permit this," he, Boris Podolsky and Nathan Rosen wrote in a paper in 1935.

 

Today that paper, written when Einstein was a relatively ancient 56 years old, is the most cited of Einstein's papers. But far from demolishing quantum theory, that paper wound up as the cornerstone for the new field of quantum information.

 

Nary a week goes by that does not bring news of another feat of quantum trickery once only dreamed of in thought experiments: particles (or at least all their properties) being teleported across the room in a microscopic version of Star Trek beaming; electrical "cat" currents that circle a loop in opposite directions at the same time; more and more particles farther and farther apart bound together in Einstein's spooky embrace now known as "entanglement." At the University of California, Santa Barbara, researchers are planning an experiment in which a small mirror will be in two places at once.

 

Niels Bohr, the Danish philosopher king of quantum theory, dismissed any attempts to lift the quantum veil as meaningless, saying that science was about the results of experiments, not ultimate reality. But now that quantum weirdness is not confined to thought experiments, physicists have begun arguing again about what this weirdness means, whether the theory needs changing, and whether in fact there is any problem.

 

This fall two Nobel laureates, Anthony Leggett of the University of Illinois and Norman Ramsay of Harvard argued in front of several hundred scientists at a conference in Berkeley about whether, in effect, physicists were justified in trying to change quantum theory, the most successful theory in the history of science. Dr. Leggett said yes; Dr. Ramsay said no.

 

It has been, as Max Tegmark, a cosmologist at the Massachusetts Institute of Technology, noted, "a 75-year war." It is typical in reporting on this subject to bounce from one expert to another, each one shaking his or her head about how the other one just doesn't get it. "It's a kind of funny situation," N. David Mermin of Cornell, who has called Einstein's spooky action "the closest thing we have to magic," said, referring to the recent results. "These are extremely difficult experiments that confirm elementary features of quantum mechanics." It would be more spectacular news, he said, if they had come out wrong.

 

Anton Zeilinger of the University of Vienna said that he thought, "The world is not as real as we think.

 

"My personal opinion is that the world is even weirder than what quantum physics tells us," he added.

 

(cont'd)

[gagsrcool]

Hi,

 

I think you mean the EPR experiments. Very interesting one. Sort of almost disproved Relativity.

 

gagsrcool

[5614]

Einstein made his EPR Paradox many many years ago saying that QM could not be correct due to the "cat state" or the ability of an atom to be in superposition (two states at once).

 

Einstein died before Bell came up the the answer to the EPR Paradox, the solution was called the Bell Theorem or Bell Inequality.

 

EPR Paradox: http://en.wikipedia.org/wiki/EPR_paradox

The solution (Bell's Theorem): http://en.wikipedia.org/wiki/Bell's_theorem

I liked this explanation of the whole thing: http://atschool.eduweb.co.uk/rmext04/92andwed/pf_quant.html#Q30

[Kedas]

Any chance that all particles in the universe are entangled we just don't know which with which.

And how to disprove something like this?