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> Objects and Identity
Examples of merging are much harder to come by, and in fact I only know of two. One is in Permutation City. It is too complicated to explain here, but if you read the book (as you should), you can recognize the example by the fact that it contains the following two sentences.
Once, preparing to be scanned, he'd had two futures.
I know several examples of having multiple instances, but before I start talking about them, I ought to point out that having multiple instances is not as simple for a conscious physical object as it is for (say) a can of green beans. A can of green beans doesn't change a lot over time, so it's easy for us to ignore the facts that some cans are older than others, and that they're all gradually going bad, and say, look, they're all identical instances. A conscious object, however, does change a lot, so when we talk about instances, we have to be careful to specify which versions the instances belong to.
I already cited identical twins and clones as examples of having multiple instances. They aren't perfect examples, of course, but they're close enough to be interesting. So, let's suppose we have a pair of identical twins, and that they're truly identical—two identical instances of a single abstract object. The abstract object develops through a series of versions, and for each version, there are two instances, existing at the same moment in time.
Now suppose we have some clones, or, rather, an original and a clone, and that they're truly identical. They're not identical at the same moment in time, of course, because the original is older, but perhaps the clone at age one is identical to the original at age one. In that case, the abstract object still develops through a series of versions, and each version still has two instances, but now the corresponding instances exist at different moments in time.
There are a few points worth noting, here.
The problem with both those examples is that the instances aren't really identical, just similar. To have true identical instances, you'd need to have identical environments for them to exist in, and that's difficult or impossible to arrange. (But, see Closer for a good attempt.)
The stories Learning to Be Me and Where Am I? take a different approach. Instead of the whole physical object, they try to duplicate only the consciousness, or mind. Minds, you see, are intangible, so it's easy for us to imagine identical minds having different physical representations; once we've done that, all that's necessary for two minds to be identical is that they start in the same state and receive the same input.
(The novel Rogue Moon takes the same approach, but deserves special mention because there's also teleportation involved. I won't spoil it by saying any more.)
How could two minds receive the same input? The following (disjointed) excerpts from Where Am I? indicate one method.
I was shown around the life-support lab in Houston and saw the sparkling new vat in which my brain would be placed, …:
Once we've decided to focus on the mind rather than the body, all kinds of other possibilities open up. In the above, the computer duplicate could be backed up, and the resulting instance wouldn't develop over time. (The same idea of being backed up appears in Beyond Rejection, and, I think, in at least one other story I've seen somewhere.) Other duplicates could be made to run with different inputs; the abstract object would branch, but the resulting instances would still be instances of the object. And so on.
@ September (2002)