That's because for a lot of things in quantum physics (and baseball), exactly what happened in the past can be as much of a mystery as the what will happen in the future. The future, though, may be literally telling us what is happening now, according to a real trailblazer in the admittedly spooky world of quantum physics "One remarkable thing about quantum physics is that so many of the fundamental arguments are still with us today," says physicist Yakir Aharanov of Chapman University in Orange, Calif. Aharanov, in Washington D.C. to collect a National Medal of Science this past week, stopped by USA TODAY to talk about his latest work, plumbing the "deep questions" of modern physics. Aharanov received the medal partly for his first foray into this arena of quantum physics in 1959, working with the physicist David Bohm, to describe what is now called the "Aharanov Bohm" effect. They showed that charged particles can have their trajectories, momentum and other characteristics affected by an electromagnetic field, even when the field is completely shielded from the particle. This sort of "spooky action at a distance," that Einsteincomplained about in quantum mechanics — how can something affect something else without apparent connection — is one of those weird and disturbing (and completely, true, this is how stuff works on the quantum level) things about modern physics that has disturbed people for decades. "Anyone who is not shocked by quantum theory has not understood it," Danish physicist Niels Bohr said. "Einstein complained nature is being capricious," Aharanov says. "But nature is not being capricious. Nature is trying to tell us something, I think, about the way we think about the future." Consider one of the simplest experiments that initially surprised physicists, the double-slit experiment. Physicists could fire tiny electrons from a hot wire towards a screen with two slits, and a second screen lined with electron detectors. Close the left slit, open both and then close the right one, and add up how many electrons smack into any one position on the second screen, for a minute each. What happens? The first surprise is that the number of electrons recorded from when both slits are open won't equal the number you would get from adding the electrons that pass separately through the right and left slits. The second surprise is that when both slits are open, there are points on the second screen where fewer electrons land than when just one is open. They actually land in an interference pattern indicating that electrons separated by slits are somehow interacting. "Somehow each electron knows that both slits are open," writes the physicist Sandu Popescu of the United Kingdom's University of Bristol in a March Nature Physics article. "But how does an electron passing through one slit know if the other slit is open or not?" Quantum mechanics explains this by throwing away certainty, and saying on the atomic, or sub-atomic level, objects behave in ways determined purely by their probability of arriving somewhere else, suggesting in a real sense that a particle behaves as if following paths through both slits and then "reincarnates," in Popescu's words, as an undivided particle when it strikes the second screen. Because the electron has been effectively in two places at once as it traveled through the two slits, the electrons could interfere with each other. "It is one of the great mysteries of physics," Popescu concludes. The Aharanov Bohm effect further scrambles the picture. Stick a shielded electromagnet in between the slits and the electrons fly through the slits differently than they would otherwise, even though the electrons are shielded from the magnetic field. Well, that's just spooky. But physicists can calculate the impact of these spooky effects on the odds of the electrons ending up in their various places, and chalk it all up to quantum weirdness, if they like. A number of experiments even take advantage of such effects for "quantum cryptography" experiments that transmit secure messages across great distances. But in the November Physics Today, Aharanov and colleagues lay out a new way of looking at quantum weirdness. Pointing to a series of experimental successes based on their predictions in amplifying the intrinsic magnetism, or "spin," of atomic particles, they suggest, "the physicists' notion of time needs to be revisited." What is really happening in the double-slit experiment, they say, and really wherever atomic particles are interacting with each other (that is to say, everywhere), is not that the two electrons are in two places at once. Instead, time is running both forward, from the electron leaving the wire, and backward, from its final location on the second screen. Where time meets, running backwards and forwards, determines which slit the electron chooses. The future is affecting the past, all the time, on the quantum level. (Sadly our brains don't work on the quantum level, although I really don't want to know what I will look like in another 10 years.) Thinking about quantum effects this way doesn't change the outcome of past experiments. But it allows physicists to effectively select the future they want their particles to have, within limits, amplifying the results for a desired outcome. A 2008 Science magazine report, for example, used this future selecting technique, called"weak measurement," to amplify the deflection of a laser path by a factor of 10,000. Who cares? Well, the next revolution in electronics is expected to be in "spintronics," using the intrinsic magnetism of atoms to store information and energy much more efficiently than "electronic" devices. If you want your spintronic ear-bud phone to pick up your calls, amplification might come in handy. "Weak measurement" is the second advance that President Obama mentioned when presenting Aharanov with his medal last week. One of Aharanov's former students, Jonathan Oppenheim of the United Kingdom's University of Cambridge, has a study in the current Science magazine looking at the limits of "spooky action at a distance," in quantum mechanics. Aharanov says physicists have only started to plumb the possibilities of taking advantage of these so-called "non-local" effects. "I really believe we are close to a second revolution in physics as big as the one a century ago," he says. "I feel we are only beginning to free existing quantum theory and to do so, we must think of time in another way." The key to the future is the future, in other words, and it is coming towards us fast.
Future holds key to quantum physics Posted 1d ago | Comments 23 | Recommend 2 E-mail | Save | Print | Reprints & Permissions | 
EnlargeBy J. Scott Applewhite, AP President Obama stands with Yakir Aharonov, a professor at Chapman University in California recognized for his work in quantum mechanics, during a ceremony for recipients of the National Medal of Science and the National Medal of Technology and Innovation, the highest honors bestowed by the United States government on scientists, engineers, and inventors, at the White House on November 17.
If Yogi Berra had pursued a career in quantum physics instead of baseball, you could imagine him saying something like, "It's tough to make predictions, especially about the future."By Dan Vergano, USA TODAY
Monday, 22 November 2010
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