Phun with Physics

John Cramer is a Seattle science fiction author and columnist who practices what he preaches at the University of Washington His most recent experiment is an interesting one. From the Seattle P-I:

Going for a blast into the real past
If the experiment works, a signal could be received before it's sent.

If his experiment with splitting photons actually works, says University of Washington physicist John Cramer, the next step will be to test for quantum "retrocausality."

That's science talk for saying he hopes to find evidence of a photon going backward in time.

"It doesn't seem like it should work, but on the other hand, I can't see what would prevent it from working," Cramer said. "If it does work, you could receive the signal 50 microseconds before you send it."

Uh, huh ... what? Wait a minute. What is that supposed to mean?

Roughly put, Cramer is talking about the subatomic equivalent of arriving at the train station before you've left home, of winning the lottery before you've bought the ticket, of graduating from high school before you've been born -- or something like that.

"It probably won't work," he said again carefully, peering through his large glasses as if to determine his audience's mental capacity for digesting the information. Cramer, an accomplished experimental physicist who also writes science fiction, knows this sounds more like a made-for-TV script on the Sci Fi Channel than serious scientific research.

"But even if it doesn't work, we should be able to learn something new about quantum mechanics by trying it," he said. What he and UW colleague Warren Nagourney plan to try soon is an experiment aimed at resolving some niggling contradictions in one of the most fundamental branches of physics known as quantum mechanics, or quantum theory.

A brief background:

One of the paradoxes of interest to Cramer is known as "entanglement." It's also known as the Einstein-Podolsky-Rosen paradox, named for the three scientists who described its apparent absurdity as an argument against quantum theory.

Basically, the idea is that interacting, or entangled, subatomic particles such as two photons -- the fundamental units of light -- can affect each other no matter how far apart in time or space.

And what John is looking at:

"If you do a measurement on one, it has an immediate effect on the other even if they are separated by light years across the universe," Cramer said. If one of the entangled photon's trajectory tilts up, the other one, no matter how distant, will tilt down to compensate.

Einstein ridiculed the idea as "spooky action at a distance." Quantum mechanics must be wrong, the father of relativity contended, because that behavior requires some kind of "signal" passing between the two particles at a speed faster than light.

This is where going backward in time comes in. If the entanglement happens (and the experimental evidence, at this point, says it does), Cramer contends it implies retrocausality. Instead of cause and effect, the effect comes before the cause. The simplest, least paradoxical explanation for that, he says, is that some kind of signal or communication occurs between the two photons in reverse time.

It's all incredibly counterintuitive, Cramer acknowledged.

The article has a lot more detail about the experiment and includes this wonderful quote:

"I thought it would get shot down, but people got excited by it," Cramer said. "People tell me it can't work, but nobody seems to be able to explain why it won't."

This sounds really plausible -- entanglement has been observed in other experiments and although I am not a Physicist (I leave that to my Dad), I cannot see anything wrong with John's theory...