A Physicist Explains How to Send Messages Back in Time

Time is both space and money, which is why it's financially viable to lay a $300 million fiber optic line under the North Atlantic Ocean—at least for high-speed, high-frequency trading firms who are going to be paying big bucks for the privilege of a five millisecond edge when sending data between North America and London.

Trading firms aren't the only ones looking to cut out latency. NASA communicates with its Mars rovers with a 20-minute delay. There's a lot to be gained, financially, and scientifically by cutting that down—and I found someone who thinks he knows how to cut it out entirely. Actually, what John Cramer told me was that you could make the sending operation happen "before or after" the receiving operation.

Cramer is a professor of physics at the University of Washington, and he's also one the biggest proponents of seeing just what we can do with quantum nonlocality. If those words don't add up to much, stick with me here. They didn't mean much to me when I called up Cramer either.

When I spoke to him, he had just gotten back from a NASA conference at Arizona State University, where they were discussing ideas from science fiction that NASA could adapt to their own uses. Cramer told me about how, in his own science fiction writing—the books Twister (not the movie) and Einstein's Bridge—he had anticipated digital cameras with internal memory and a type of remote presence, not that he takes credit for their invention or inspiration or anything. It's just the path from science fiction to science reality is well-worn. With that in mind, I asked him to explain to me how the future could one day call backwards. He explained it as if it were the simplest thing in the world.

MOTHERBOARD: You’ve got a long-term project that has a really improbable sound to it: retrocausality. How would you explain that to a layperson?

Cramer: First of all you have to understand the difference between normal, Newtonian mechanics and quantum mechanics. In quantum mechanics there’s something called the uncertainty principle. There’s a lot of things that are definite in the way that Newton looked at things, that are indefinite in quantum mechanics—energy and momentum and position and so forth can be not-well specified in a quantum mechanical wave function.

In a quantum mechanical system, you can divide it into two pieces—for example an atom that’s two photons can be split to go in opposite directions—then there is a connection between the two pieces because the properties are unspecified because of the uncertainty principle, yet conservation laws still tie them together. If you make an measurement on one of the pieces it affects the possibilities of measurement of the other piece. This is called quantum nonlocality.

Albert Einstein and two of his colleagues, Boris Podolsky and Nathan Rosen, published a paper in 1935 in which they pointed out that this kind of thing was going on in quantum mechanics, and they considered it a curious flaw. Einstein in a letter called it “spooky actions at a distance” and he thought this was a showstopper, that it must indicate that quantum mechanics is wrong.

In the late 1970s and 1980s, the technology evolved to the point where people could actually go into the laboratory and test to see whether quantum nonlocality was a real thing or some problem with the formulas. Rather to the surprise of the people who were doing the work, it turned out that quantum mechanics is right and quantum nonlocality is there. There are these non-local correlations between two separated parts of a system and they look like nature is communicating between the parts faster than light and backwards through time or whatever you want to call it.

The question has been, from the beginning of when this phenomenon was discovered, whether it can be used to communicate between one individual and another via “nature’s private telephone line”—you could use for you own purposes. A while back I came across some work that had been done in a PhD thesis at the University of Maryland Baltimore Country that seemed to indicate that one could use quantum nonlocality for communication by breaking up a system into two pieces, and if you caused one of the photons going one way to behave like a particle then the other is forced to behave like a particle. If you force it to behave like a wave the other photon behaves like a wave also.

At a meeting I was at, I proposed this as sort of a paradox, and I thought someone would point out the obvious problem with it, but everyone seemed to think it was interesting idea and proposed that I do the experiment. So rather left-handedly I got roped into doing the experiment.

There’s been an ongoing history of this in which various things have been tried and there’s a lot of problems with noise in the system and so forth. The recent breakthrough that I found while visiting a laboratory in Vienna and found that they had already done a lot of work that was unpublished that was related to what I was interested in. The system they were using turns out to be really easy to analyze mathematically. You can see what’s going mathematically much easier than what I was doing.

Two results come out of this: A) What I wanted to do wouldn’t have worked, according to these mathematics but B) I found a sort of work-around that would indicate that there’s a way to use it for communications. It’s sort of a twist on what had been done before. I’m now in a situation when I have a pretty convincing mathematical model showing the way of doing nonlocal communication that needs to be tested experimentally.

When you say “communication” do you just mean between the two split parts of the system?

Well, basically what happens is you have photons going one way across the table and photons going the other way across the table, and when you do something to photons on the left, something changes on the right side of the table. The usual way of saying it is to picture two people, Bob and Alice, each receiving these photons. The question is, can Alice do something in measure to her photon that creates a signal that Bob can receive on his end of the system. They might be on the other side of the side, they might be light years apart. It doesn’t really matter quantum mechanically how far apart they are. The question is whether you can do the communication.

If nonlocal communication were possible it changes all the rules that we know about for communication, because the signal is sent whenever Alice does the measurement and is received whenever Bob does the measurement.

And by putting in extra distance with time delays or coils of fiber optics, you can delay either of these. You can make the sending operation happen before or after the receiving operation, so in principle you could send messages backwards through time. There may be reasons you can’t send messages backwards in time, but if you can’t, if you can communicate nonlocally otherwise, it opens other interesting possibilities.

As you’re driving down the road, you can see cable companies putting up fiber optics and wiring tunnels that are typically 10 kilometers long. And so it takes about 50 microseconds for light to go 10 kilometers. If you could borrow one of those spools and put it in your laboratory, you could send the signal through the spool of cable you’d receive the message before it's sent by 50 microseconds, for example.

It’s an interesting question whether that would do anything. It’s worth noting that Goldman Sachs has spent a very large amount of money moving their electronic stock trading options into the same building with the New York Stock Exchange so that they can shave a few seconds off the delay time while doing their trading. That implies that there might be a lot of value in being able to do this trick with 50 microseconds.

I guess if computer aids the trading that 50 microseconds all of a sudden matters a great deal.

Right. The first step isn’t doing something like that; it’s doing something on one side of the table and watching what happens on the other, and that’s what I’ve been doing.

Are you going to work with this team in Vienna or are you on your own?

The easiest thing would be to, since they’ve already done something similar and if the hardware is still around, the easiest thing to do would be to ask them to do it. But so far I haven’t been able to convince them that it’s worth doing, because they have a lot of other irons in the fire.

Option A is to set up and do it at the University of Washington, if I can get funding for it. If the Viennese decide they’re interested, it’d be easier to do it in Vienna, but I’d like to do it either way. At present the plan is to do it at the University of Washington.

Want do you want to do in the next experiment?

The first thing you have to do is to set up a laser driven device that sends the laser beam into a nonlinear crystal and produces a pair of polarization entangled photons. The first thing is building a device that’s well documented in the literature to be a very efficient source of pairs of entangled photons. After you do this, you set up an interferometer for each of these photons, that’s not very hard thing to do. And you need to arrange for a situation where interferometer can be monitored electronically, so if you change one end of the interferometer and look for a change in the interference pattern you measure in the other one.

That’s basically what you have to do. It’s something that’s fairly routine quantum optics. All the pieces have already been done and well-documented it’s just a matter of putting them together in a way that’s different from what’s been done in the past.

Can you think of other examples of how this becomes tech?

One of the things NASA might be interested in is if you had a relay station on Mars that generated pairs of entangled photons. If one of them went to a Mars rover and one went to the Earth along with all the video feeds of what’s coming in on the rover and they were wired to a steering device—a joystick or something—you could put on a virtual reality helmet and drive around on Mars in real-time with no time delays. Or exploring the planets becomes something you do in virtual reality.