As a thought experiment, suppose that clinical immortality were possible, in which through advanced life support machinery or similar, the bodily functions of a comatose human could be kept running in perpetuity. Is it good news to keep a vegetative human's heart pumping for aeons? According to the vast majority of ethicists, "Not at all," since unending biological functioning is not what is at issue in immortality. Ultimately, what one desires is some sort of permanent preservation of personal identity, not just unceasing metabolic integrity. 

This brings up the philosophical issue of the meaning of consciousness. As another thought experiment, suppose a surgeon replaces part of a man's brain with a pacemaker (this is actually done to treat Parkinson's). After this procedure is done, the patient comes out of his anesthesia feeling like the same person.

For the intentions of this experiment, suppose that doctors already fully understand the brain and are able to successfully move sections of the brain's neural network and memories onto hardware where they can perfectly emulate the "architecture" of the brain. Over a period of time, suppose that the individual has many more operations with the intent of gradually replacing parts of his brain with computer hardware. Eventually, the man has a brain made entirely out of computer parts. The man comes out claiming that he is the same person as before. He has the same memories and acts the same. 

Now suppose that instead of replacing parts of his brain with hardware, he copies the entire brain onto hardware. The computerized version of this man's brain acts the same way, and claims that it is the same man who underwent the procedure. The original man is still alive, however. Are the machine and the man the same person? Are they somehow linked in consciousness? These are the types of situations that illustrate the lack of knowledge concerning the meaning of consciousness that we as a civilization currently possess.