You think that this is impossible.
But, the book insists, it is perfectly imaginable, and hence possible in principle..
You wonder whether the book has in mind reincarnation of the transmigration of souls, but, anticipating the wonder, the book acknowledges that while reincarnation is one interesting idea, the details of how this might happen are always left in the dark, and there are other more interesting ways it might happen. What if your brain were to be transplanted into a new body, which it could then control? Wouldn’t you think of that as switching bodies? There would be vast technical problems, of course, but, given our purposes, we can ignore them.
It does seem then (doesn’t it?) that if your brain were transplanted into another body, you would go with it. But, are you a brain? Try on two sentences, and see which one sounds more like the truth to you:
I have a brain.
I am a brain.
Sometimes we talk about smart people being brains, but we don’t mean it literally. We mean they have good brains. You have a good brain, but who or what, then, is the you that has the brain? Once again, if you have a brain, could you trade it in for another? How could anyone detach you from your brain in a brain switch, if you are always go with your brain in a body switch? Impossible? Maybe not, as we shall see. After all, if you have recently returned from Mars, you left your old brain behind, didn’t you?
So suppose we agree that you have a brain. Have you ever stopped to ask yourself how you know you have a brain? You’ve never seen it, have you? You can’t see it, even in a mirror, and you can’t feel it. But of course you do know you have a brain. You know it because you know that you’re a human being and all human beings have brains. You’ve read it in books and been told it by people you trust. All people have livers too, and strangely enough what you know about your own brain is rather like what you know about your own liver. You trust what you’ve read in books. For many centuries people didn’t know what their livers were for. It took science to discover the answer. People haven’t always known what their brains were for either. Aristotle is said to have thought that the brain was an organ for cooling the blood—and of course it does cool your blood quite efficiently in the course of its operations. Suppose our livers had been in our skulls and our brains were snuggled into our ribcages. As we looked out at the world and listened, do you think we might have found it plausible that we thought with our livers? Your thinking seems to happen behind your eyes and between your ears—but that is because that’s where your brain is, or is that because you locate yourself, roughly, at the place you see from? Isn’t it in fact just as mind-boggling to try to imagine how we could think with our brains—those soft grayish cauliflower shaped things—as to imagine how we could think with our livers—those soft reddish brown liver shaped things?
The idea that what you are is not simply a living body (or a living brain) but also a soul or spirit seems to many people to be unscientific, in spite of its ancient tradition. “Souls,” they might want to say, “have no place in science and could never fit into the scientific world view. Science teaches us that there are no such things as souls. We don’t believe in leprechauns and ghosts any more, thanks to science, and the suspect idea of a soul inhabiting a body—the ‘ghost in the machine’—will itself soon give up the ghost.” But not all versions of the idea that you are something distinct from your purely physical body are so vulnerable to ridicule and refutation. Some versions, as we shall see, actually flourish in the garden of science.
Our world is filled with things that are neither mysterious and ghostly nor simply constructed out of the building blocks of physics. Do you believe in voices? How about haircuts? Are their such things? What are they? What, in the language of the physicist, is a hole—not an exotic black hole, but just a hole in a piece of cheese, for instance? Is it a physical thing? What is a symphony? Where in space and time does “The Star Spangled banner” exist? Is it nothing but some ink trails on some paper in the Library of Congress? Destroy that paper and the anthem would still exist. Latin still exists, but it is no longer a living language. The language of the cave people of France no longer exists at all. The game of bridge is less than a hundred years old. What sort of thing is it? It is not animal, vegetable or mineral.
These things are not physical objects with mass, or a chemical composition, but are not purely abstract objects either—objects like the number π, which is immutable and cannot be located in space and time. These things have birthplaces and histories. They can change and things can happen to them. They can move about—much the same way a species, a disease, or an epidemic can. We must not suppose that science teaches us that every thing anyone would ever want to take seriously is identifiable as a collection of particles moving about in space and time. Some people may think it is just common sense (or just good scientific thinking) to suppose you are nothing but a particular living, physical organism—a moving around of atoms—but in fact this idea exhibits a lack of scientific imagination, not hard-headed sophistication. One doesn’t have to believe in ghosts to believe in selves that have an identity that transcends any particular living body.
You are Sarah’s mother, after all. But is Sarah’s mother you? Did she die on Mars, or was she moved back to Earth? It seems to you she returned to Earth—and of course it seemed to her before she stepped into the teleporter that she would return to Earth. Was she right? Maybe, but what would you say about the results of using the new, improved Teleclone Mark V? Thanks to the miracles of noninvasive CAT-scanning techniques, it obtains its blueprint without destroying the original. Sarah’s mother still might decide to push the button and step into the chamber—for Sarah’s sake, and in order to get the full story of her tragedy back to earth in the words of an eloquent spokeswoman—but she would also expect to step out of the chamber and find herself still on Mars. Could someone—some one—literally be in two places at once? Not for long, in any case, but soon the two would accumulate different memories, and different lives. They would be as distinct as any two people could be.
What makes you you, and what are your boundaries? Part of the answer seems obvious—you are a centre of consciousness. But what in the world is consciousness? Consciousness is both the most obvious and the most mysterious feature of our minds. On the one hand, what could be more certain or manifest to each of us that that he or she is a subject of experience, an enjoyer of perceptions and sensations, a sufferer of pain, and entertainer of ideas, and a conscious deliberator? On the other hand, what in the world can consciousness be? How can living physical bodies in the physical world produce such a phenomenon? Science has revealed the secrets of many initially mysterious natural phenomena—magnetism, or photosynthesis or digestion are in principle equally accessible to any observer with the right apparatus, but any particular case of consciousness seems to have a favored or privileged observer, whose access of any others—no matter what apparatus they may have. For his reason and others, so far there is no good theory of consciousness. There is not even agreement about what a theory of consciousness would be like. Some have gone so far as to deny that there is any real thing for the term “consciousness” to name.