University of Washington physicist (and science-fiction author) John Cramer is moving forward with his experiment in backward causality, thanks in part to tens of thousands of dollars in contributions sent in by his fans. Although Cramer emphasizes that his lab is looking at "nonlocal quantum communication" rather than backward time travel per se, the gadgetry he's assembling could settle a controversy surrounding a seemingly faster-than-light effect that Albert Einstein thought was downright spooky.
Boiled down to its basics, the experiment involves splitting laser light into two beams, so that characteristics of one beam are reflected in the other beam as well. That's an example of what physicists call quantum entanglement. Specifically, Cramer has been planning to fiddle with one of the entangled laser beams such that it takes on the property of waves or particles. If one beam behaves like particles, the entangled photons of light in the other beam should behave like particles, too.
So what happens when the beams go their separate ways, and you conduct a wave-vs.-particle measurement on one beam? When someone else checks the other beam, the same measurement should yield the same result. In fact, you could visualize using the wave-vs.-particle toggle as a means for communicating information, sort of like Morse code. Theoretically, you could check one beam to receive a message instantaneously from whoever is fiddling with the other beam - even if you're separated from the receiver by millions of light-years.
That's what Einstein considered "spooky action at a distance." Such an effect could send information faster than light beams could travel, running counter to special relativity - and thus Einstein thought the effect was impossible to achieve. However, the evidence is mounting that quantum entanglement actually happens.
Cramer planned to start out by testing this kind of communication through quantum entanglement - that's the "nonlocal communication" part of the experiment. If that worked, Cramer would go even further: He would send one of the entangled beams (call it Signal A) through a circuitous detour - say, a few miles of fiber-optic cable - then fiddle with it when it came out of the cable. If the principles behind nonlocal communication held true, the evidence of that fiddling should be detected at a corresponding place in the other entangled beam (call it Signal B).
Now brace yourself for the backward-causality part: Because Signal B followed a shorter route to its detector, the fiddling in Signal A could theoretically show up in Signal B before Cramer actually fiddles with Signal A. It would be as if Cramer's actions had an effect that worked backward in time.
If Cramer detected that effect, the findings would raise the kinds of paradoxes you might see in science-fiction novels or "The Twilight Zone." What if you detected a signal from the future, but then decided not to send the signal? (That's called the "bilking paradox"). What if you received the text of a best-selling manuscript from yourself in the future, had it published, then saved a copy so you could send it to yourself in the past? (Cramer calls that the "immaculate conception paradox.")
"Perhaps the fact that there are such paradoxes is nature's way of telling us that our experiment isn't going to work," Cramer said.
Nevertheless, Cramer is anxious to find out whether it might work - and if not, why not. He suggested the framework for the experiment a year ago, and no one could come up with a reason why it should fail. Except for the money problem. ...
For months, Cramer struggled to find the funding he needed to buy the equipment for the experiment, to no avail. Then an article about his plight came out in the Seattle Post-Intelligencer - and within weeks, thousands of dollars flowed in from foundations and private donors who, for one reason or another, wanted to find out what kind of answers Cramer could come up with.
Cramer said the fund now amounts to $40,000, and now that he's back from a tour of duty at the Relativistic Heavy Ion Collider, he's moving forward with the laser experiment. "If that laser holds out, then I think we're in pretty good shape," he told me today.
He's hoping to complete the experiment by September, when the equipment he's using will have to be moved someplace else to make room for remodeling. "It would be very nice if we could finish up by the 15th of September, but I don't know if we'll be able to do that or not," he said.
Cramer is grateful for all the donations, but he admitted that he's "a little uncomfortable" about the way things have gone so far. Usually, physicists work in obscurity, get some funding, conduct an experiment, publish the results - and only then does the publicity come, if the results are spectacular enough. The way Cramer sees it, there's been a heck of a lot of publicity already about an experiment that has yet to be done.
"We seem to be doing it sort of backwards, in a sense," he said. Then, realizing that he's been talking about backward causality, he added with a chuckle that "it may be relevant to the experiment we're trying to do."
Cramer, who is the author of two science-fiction novels and a regular columnist for Analog magazine, said the experiment represents "a rare opportunity to push the envelope of quantum mechanics." No matter how it turns out, the results will be put to good use, he said.
"If this experiment we're doing works, then I will follow up and push it as hard as possible. And if it doesn't work, I will write a science-fiction novel where it does work," he said. "It's a win-win situation."
Feel free to add your thoughts about backward causality and time travel in the comments section below, or visit our discussion board. And if you've already come up with a solution for backward time travel, fill me in on the secret ... yesterday.
Update for 8:52 p.m. ET Jan. 9, 2008: Here's an example of future developments affecting past postings: It turns out that Cramer was given more time to do his backward-time experiment, and as of early January he was still setting up the apparatus.
Update for 11:50 a.m. ET May 21, 2009: Another example of Internet time travel ... Cramer is gearing up for "phase 3" of the experiment, but still no results.