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What I want to do next is present a bunch of examples of consciousness as a persistent object. I don't think they lead anywhere, I just like them.

Branching doesn't have to be accidental, as with teleportation, it can also be intentional … which brings me to a favorite story of mine, Permutation City. In it, a nondestructive scanning process is used to create copies, but the copies are information objects rather than physical ones. I like the following passage because I think it really captures what branching would feel like.

Maria opened her eyes. She'd just recalled the first thing she'd meant to do on waking. Every scanner was programmed to recognize—in real time, before all the arduous data processing that followed—the magnetic resonance spectrum of four or five special dyes, which could be used for alignment and identification. The scanning technician had obligingly loaned her a “number three” marker pen—and instructed the scanner to blind itself to that particular dye.

She pulled her hands out from under the sheets. Her left palm still read: YOU ARE NOT THE COPY.

Of course, branching would also feel like this.

Maria woke from dreamless sleep, clearheaded, tranquil. She opened her eyes and looked around. The bed, the room, were unfamiliar; both were large and luxurious.


She suddenly remembered the Landau Clinic. Chatting with the technicians. Borrowing the marker pen. The tour of the recovery rooms. The anesthetist asking her to count.

She pulled her hands out from beneath the sheet. Her left palm was blank; the comforting message she'd written there was gone.

The marker pen is a great touch, not least because it reminds me of the result code in a Unix process fork. How does that work? One process calls the function fork (or some equivalent); at that moment, the state of the process is copied (or some equivalent); then the two processes both execute, and the way they tell themselves apart is that they see different results from the function call.

Once you have an information object that's conscious, you can do all kinds of interesting things. You (the object) can make another copy of yourself.

Peer closed his eyes. When I see my original, sitting on the porch, I'll know who I am, and accept it.


Peer felt no change. He opened his eyes. His newly made twin stood on the ground where the interface window had been, staring at him, wide-eyed.

You can make lots of other copies. You can back yourself up. And you can be paused and unpaused, because the agent of growth is computation rather than physics. That last thought leads right to the main theme of the book, but I'm not going to say any more about that, because I don't think I can do it justice. I will mention, though, that I found a similar theme in The Story of a Brain.

An artificial intelligence would be able to do the same kinds of things, but, strangely, I've never seen a story take advantage of the fact.

A different kind of branching occurs whenever there are alternatives. If you're stuck in traffic, say, you can imagine a world in which you chose an alternate route, and that hypothetical world is like a branch of the real one. The alternatives don't have to be the result of conscious choice, they can arise from inanimate objects, from a throw of the dice; and they don't have to be a discrete set, either. Whether you place your foot a millimeter this way or that as you walk, or whether you arrive somewhere a second earlier or a second later (as in Sliding Doors), everything creates alternatives.

And, surprise surprise, language is reasonably well adapted to discussing such alternatives. Why, there's even a special verb form, the subjunctive, just for indicating that a situation is hypothetical! By the way, not all hypothetical situations arise from alternatives. I can imagine what it would be like if I could fly, but I can't see any way that such a situation could actually arise. In any case, I have to amend what I said earlier. We do know how to talk about multiple branches … as long as the object that's branching is the whole world, and as long as only one branch is real.

If more than one branch is real, suddenly we're back talking about science fiction, specifically, about parallel universes. Just as with teleportation, the idea of parallel universes has a long history, which I haven't bothered to investigate. But, I have taken five minutes and thought of a couple of relevant stories that I like. The Game of Blood and Dust is an old favorite about alternatives, short and to the point; and Terraplane is a classic parallel-universe story. That's not even close to an exhaustive list, but it will do.

Actually, there's a distinction I should make here. The idea behind the name “parallel universe” is that the other universe should run parallel to our own. A branch doesn't do that—it may run parallel, in some sense, but if you follow it backward, you find that it terminates at the branch point. So, I suppose I should have said “alternate universe”. The problem is, that phrase has a more specific meaning. An alternate-universe story is one set entirely in a single alternate universe, without any of the cool travel-between-universes stuff. There are a lot of such stories, but they're too close to historical fiction for my taste.

Now, here's an interesting thing. If you live in a universe governed by classical mechanics, it doesn't make any sense to talk about alternate universes actually existing, because classical mechanics is deterministic. The state of the universe at any instant uniquely determines the state of universe at all future (and past) times; there can be no branching. You can still usefully talk and think about hypothetical situations, but that's only because you have incomplete knowledge.

If, on the other hand, you live in a universe governed by quantum mechanics, it does make sense to talk about alternate universes existing. In fact, there are several equivalent formulations of quantum mechanics, and in one of them, the many-worlds formulation, alternate universes actually do exist! The alternate universes don't interact with ours, of course—otherwise the formulations wouldn't be equivalent—but that doesn't mean we can't enjoy thinking about them.

Greg Egan, who wrote Permutation City as well as two of the short stories mentioned later, also wrote an excellent novel about quantum mechanics and alternate universes, Quarantine.



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@ September (2002)