Let us consider an interesting thought experiment, which may perhaps seem fanciful and irrelevant, but which technology may make very relevant in several decades.
Let us imagine a machine called Scan and Duplicate, that works on an atomic level. The machine scans the atoms in a person's body, from the tip of your toes to the top of your head. As it is scanning, the machine produces an exact duplicate of what it is scanning. The only problem is that in order to do this exact reading of the state of all atoms in your body, the machine must destroy each part of your body that it scans.
So as the machine scans your body from your toes to the top of your head, each layer of your body is destroyed: first your feet, then your shins, then your knees, then your thighs, then your thorax, and finally your head. But as each part of your body is destroyed, a duplicate body is being assembled next to yours.
Finally at the end of this process, your body is a charred, blackened mess, like a chicken that was left in the oven at 500 degrees for three hours. A blanket is placed over this burnt body, and the body is wheeled to the incinerator. However, the newly created body awakens and it claims to be you.
“Well, that all went very well,” says the freshly assembled person, and that person goes on living the rest of your life, remembering everything in your memory.
Now my question is: is this newly constructed person you? Or did you die when this operation is done, and is the surviving person merely a copy of you?
When I posed this question to my family, I got different answers from different family members. My answer is: the newly assembled person is not you, but is merely a copy of you. If this operation were to be done, you would die during the operation. There would be a newly created person that would act just like you, but it would merely be a copy of you; it would not be you.
This thought experiment is relevant because of a technological possibility that has been widely discussed: the possibility of uploading a human mind into a computer or robot.
Some technological enthusiasts imagine that in several decades we will be able to create computers or robots that have all of the capabilities of the human brain, with a great deal of additional memory and processing power. Such enthusiasts imagine that we might be able to scan a person's brain and transfer a person's consciousness to a robot body or a computer. Such a technique has been promoted as a way of achieving immortality through technology.
There are two types of mind uploading that can be imagined: destructive uploading (in which the original brain of the person is destroyed) and non-destructive uploading (in which the original brain and body of the person is preserved).
Let us imagine non-destructive uploading to a robot body that resembles your body. Your mind is copied to a robot body, and now two people are walking around with your memories and personality.
In this case, it is fairly obvious that the newly created mind (with all your same memories) would not really be you. Because in this case, your original body and mind would be preserved. So the real you would be the original you, not the new entity that looked like you and had your personality.
What is a little less obvious, but still something very likely, is that even in the case of destructive uploading the newly created entity would not be you. If your body is destroyed at the same time that a new biological or robot entity is created with all your memories and personality, it would really mean that you had died, even though a newly created person would continue to act like you and remember what you had remembered. If a doctor performed such an operation, he would actually be guilty of murder.
You might argue that it would not be murder for the doctor to perform such an operation, because even though your original body had been destroyed, there would be a new life, so the net number of living persons would be unchanged. But we don't exonerate someone for killing just because he created a new life at the same time he ended another life. “I impregnated my wife at the time of the murder” is not a successful defense in court against a charge of murder.
Because of considerations such as these, you should take no comfort in stories about the possibility of mind uploading. Mind uploading wouldn't really extend your lifespan; at best it would mean additional years for someone or something that was a copy of you. If you want to entertain the prospect of living far beyond the human lifespan, you can consider possibilities such as biological life extension or replacing your body below the neck with a robot body or the possibility that near death experiences suggest a chance of spiritual immortality. I don't believe mind uploading is going to save anyone from the Grim Reaper.
For an excellent blog post considering other problems with the idea of mind uploading, check the blog post here.