Friday, August 29, 2008

Spooked

The word everyone uses is "spooky." What they are talking about is entanglement, the spooky heart of quantum mechanics. You create a pair of subatomic particles, photons say, and send them on their separate ways. The particles seem to know what is happening to each other on their separate journeys. An activity performed on one particle can instantaneously change the properties of the other particle, no matter how far apart. And -- this is the kicker -- apparently instantaneously. Their fates are "entangled."

In the latest test of entanglement (reported in the August 14 issue of Nature), physicists entangled photon pairs using a source in Geneva, Switzerland, then passed them through fiber-optical cables of exactly equal length to receiving stations in the villages of Jussy and Satigny, which lie respectively east and west of Lake Geneva, 18 kilometers apart. "Here, the photons' entanglement was checked by an identical pair of interferometers. As they had travelled identical distances, the photons would have reached the interferometers simultaneously, as best as modern optics and electronics allows."

The effect does not seem to diminish with distance. Eighteen thousand kilometers? Eighteen milllion kilometers? Acrosss the universe? Instantaneous action-at-a-distance? The new experiments in Switzerland suggest that "any signal passing between the entangled photons is, if not instantaneous, travelling at least ten thousand times faster than light." Is the universe itself entangled at the subatomic level from a big bang source? And what, pray, would it mean if this were so?

I'm being somewhat whimsical about an entangled universe, but clearly nature is trying to tell us something with the quantum entanglement experiments, but no one knows quite what. Einstein and Schrodinger, two of the founders of quantum mechanics, admitted to being baffled by entanglement, an effect that seems to violate our common notions of physical causality. Spooky? Oh, yes, spooky, indeed.