“I’d take it in and get it fixed.”
“Damn straight. However, we can’t take the universe in and get it fixed, obvious as the need might be. Now it so happens that the only way we know what’s happening with subatomic particles is to bounce other subatomic particles off of them, and subatomic particle behavior is quantized—it can only take on certain values, like that five-speed speedometer. Therefore when we bounce one particle off another one to find out what’s going on, we don’t get a single answer—we get a distribution of probabilities. Sort of the way you’d take a guess at what your car was doing—’Well, probably ten percent chance it’s between 10 and 26, seventy percent it’s between 26 and 110, and twenty percent it’s more than 110, so I’m probably okay on the highway.’ No matter how exactly we bounce the particle or measure its behavior after the collision, we don’t get a precise picture, but a set of bets, probabilities assigned to possibilities. Still with me?”
“This is worlds easier when I’m not drunk.”
“I bet. Okay, now here’s the tricky part: there’s no difference between a measurement and any other interaction with the universe. Any physical process that depends on that particle will act as if all the possibilities were happening at once, with that mix of probabilities. Unless you do something for which the particle must be in exactly one state—and if you do that, then it will ‘collapse’ into that single state.”
“Pretend I understand you and give me an example.”
“Ever hear of Schrödinger’s cat?”
“Why would I want to shred anybody’s cat?”
I ignored that. “Schrödinger suggested a thought experiment, trying to get at how weird the problem is. He said, suppose you put a cat in a box so that you can’t observe the cat, and inside there’s a bottle of poison gas, which has a fifty percent chance of releasing the gas, based on some quantum event it’s going to observe. Then since the unobserved quantum state is 50 percent one way and 50 percent the other, until you open the box, the cat must be 50 percent alive and 50 percent dead.”
“Sounds like something a German would think of doing.”
“He didn’t do it. He just pointed it out as an example of how hard that is to understand in ordinary life. Naturally, when you open the box, since the cat has to be either alive or dead, what you find is either a live cat or a dead one, and that tells you how the quantum event came out. But up till then the box should behave as if it had a 50 percent alive cat—whatever that means— inside it.
“Now, one of the greatest arguments in all of science, still going on after 150 years, is about what that means. The Copenhagen Interpretation, which most physicists buy, is that it’s all just a computational device, and that it’s just that we don’t know how to really understand our own equations—all we know is that they work. The Aphysical Interpretation is that somehow there’s a ‘real’ world that ours is only a shadow of, and the probability distributions somehow reflect an underlying unified reality that we can’t perceive. And the Many Worlds Interpretation says that every time a quantum event happens, the universe splits into multiple worlds, enough so that across all those worlds, each event happens all the possible ways. When a Copenhagen interpretation guy opens the box, he finds the cat alive and says, ‘The calculations showed a 50 percent chance that this would happen.’ The Aphysical guy opens it and says, ‘This live shadow cat reflects the state of the real cat.’ And the Many Worlds guy says, ‘Aha! I am in the universe that got the live cat; in some other universe at this moment someone is recognizing that he is in the universe with the dead cat.’ And the really clever trick, so far in the history of physics, is that all these are just interpretations. The experiment doesn’t go one bit differently from one interpretation to another; the only thing that changes is the meaning we read into the event. At least up till now; we might be conducting, somehow, a giant experiment that’s showing that Many Worlds has, let us say, a certain edge.”
Her jaw dropped. “So if Many Worlds is right, then there could be an infinite number of universes with divergent pasts out there? And maybe what’s happening is that things are crossing the fence, or whatever it is, between the universes?”
I nodded. “That’s what I mean. But there’s a lot of what is going on that doesn’t seem to fit that theory. Why should that make it impossible to phone America? Supposing that you and I are meeting different versions of each other—Lyle Prime flew you to Saigon, and Helen Prime rescued me in the shooting at the Curious Monkey—why don’t we ever run into ourselves? And why do the crossings over only seem to happen now and then, and why don’t we all just have multiple pasts until someone asks us a question?”
“Prove we don’t.”
“All right, I’m thinking of a past event. I’m not thinking of a distribution of them. Is any part of your past a distribution of events?”
She thought hard for a moment. “As far as I can tell, no.”
“See? It doesn’t fit with what I’d expect. Let’s go to lunch and try to get away from all this for a while; by the time we get back we should have results from our survey.”
Since we were trying not to talk shop, there was practically nothing to talk about; wedding plans seemed hopelessly indefinite, managing the apartment together required practically no consultation (since we were both neat minimalists), and the weather was perfect as it tended to be at this time of year. We ate, we looked out the window, and we read the paper to each other (learning mainly that the world was proceeding about as always—I can’t recall a single surprising thing). By one-thirty, when it was time to return to the office, we were looking forward to it.
The results were about as much of a nonresult as you could get; we had a few hundred responses, and the “I don’t knows” for each item, plus the disagreements, were generally uncorrected with address, time of response, domain, or anything else. “Some of the answers correlate,” Helen said, “but that kind of figures. Hardly anyone has Mickey Mouse being a Disney character and a newspaper character named after a brand of chewing gum; nobody has Teddy Roosevelt assassinated by German agents in 1916 and being Secretary of War during World War Two. Which just tells us that most people live in a locally consistent world. Not the most informative thing I’ve ever seen, eh?”
I shrugged. “Well, there’s one implication in the whole thing. If the addresses and domains aren’t correlated with the histories, then what that tells us is that people are distributing across the various pasts without any regard for geography, which kind of implies that the rate of crossing over is uniform around the world. Which lends support to the idea that somehow or other people have begun to drift between the Many Worlds.”
“People, objects, phone calls, and e-mail at least,” Helen said. “I wonder what else is? And here’s a question for you. Suppose Schrödinger teaches the cat to flip a coin and push a lever based on the outcome, and then he puts the kitty in the box with a setup so that one lever releases poison gas. How come the cat isn’t half alive and half dead from doing that, just as if he used a subatomic experiment? Schrödinger has no way of knowing which way the coin flip came out from the outside. But I’m sure the cat is either alive or dead, no other way about it. What difference does using a subatomic gadget make?”
“Great question,” I said. “In fact—”
The phone rang, Helen picked it up, said hello, mouthed “Iphwin” at me. “Yes,” she said. “Of course we’ll be happy to do that, sir, but I was wondering why you think that we—oh, my god. Well, I see. Okay. We’ll get right down to the apartment, pack a bag, and get ready to go. Yes, sir, of course. Thanks and good-bye.”