13 July 2014

Are we on the verge of a new quantum revolution?

When faced with the bizarre nature of quantum indeterminism, Einstein was convinced that there was something wrong with the equations, quipping "God does not play dice". But the mathematics couldn't be denied, and the idea that nature is fundamentally probabilistic became ingrained in quantum mechanics. The bizarre, counter-intuitive implications of this have vexed physicists and philosophers for nearly a century.

If the hype is to be believed, the stage may be set for a paradigm shift. There's an article from Wired that's been making the rounds recently which describes researchers in fluid dynamics being able to create quantum-like effects in classical systems, such as the interference pattern in the famous double-slit experiment:
In a groundbreaking experiment, the Paris researchers used the droplet setup to demonstrate single- and double-slit interference. They discovered that when a droplet bounces toward a pair of openings in a damlike barrier, it passes through only one slit or the other, while the pilot wave passes through both. Repeated trials show that the overlapping wavefronts of the pilot wave steer the droplets to certain places and never to locations in between — an apparent replication of the interference pattern in the quantum double-slit experiment that Feynman described as “impossible … to explain in any classical way.” And just as measuring the trajectories of particles seems to “collapse” their simultaneous realities, disturbing the pilot wave in the bouncing-droplet experiment destroys the interference pattern.

Droplets can also seem to “tunnel” through barriers, orbit each other in stable “bound states,” and exhibit properties analogous to quantum spin and electromagnetic attraction. When confined to circular areas called corrals, they form concentric rings analogous to the standing waves generated by electrons in quantum corrals. They even annihilate with subsurface bubbles, an effect reminiscent of the mutual destruction of matter and antimatter particles.
In each test, the droplet wends a chaotic path that, over time, builds up the same statistical distribution in the fluid system as that expected of particles at the quantum scale. But rather than resulting from indefiniteness or a lack of reality, these quantum-like effects are driven, according to the researchers, by “path memory.” Every bounce of the droplet leaves a mark in the form of ripples, and these ripples chaotically but deterministically influence the droplet’s future bounces and lead to quantum-like statistical outcomes. The more path memory a given fluid exhibits — that is, the less its ripples dissipate — the crisper and more quantum-like the statistics become.

According to the article, pilot-wave theory is nothing new — but it's had a rough history. Nonetheless, some researchers think it could potentially revolutionize quantum mechanics. Quantum physicists, though, seem less enthusiastic. The biggest pitfall is that the pilot-wave theory adds assumptions without yielding new or more accurate calculations, and the potential of pilot-wave theory remains conjectural.

It's easy to overlook the fact that the standard model of quantum mechanics is the single most successful theory in the history of science. The degree of accuracy with which it can predict reality is unprecedented — Richard Feynman famously remarked that it's like predicting the width of the United States to the accuracy of the breadth of a human hair. The idea that there is a superfluid-like substrate underlying reality currently lies somewhere in the realm of conjecture analogous to string theory and its Planck-scale, 1-dimensional vibrating strings. It's a theory that could show its hand as physicists are able to probe deeper and deeper scales, but no one's about to rewrite the most successful scientific model in history anytime soon.

And really, that's the most intriguing possibility with pilot-wave theory. It doesn't stand a chance of rewriting quantum mechanics as we know it, but it could someday provide a means of understanding quantum gravity and advancing the long-coveted unification of quantum mechanics with general relativity.  For now, though, it's just hype, and the researchers have a long, long road ahead.

Read the full article on Wired here:
http://www.wired.com/2014/06/the-new-quantum-reality/

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