One of the more exciting and controversial approaches to immortality is "uploading" -- the transfer of the human mind from the human brain/body into a different substrate, such as a digital computer system or a robot.
We don't know exactly how to do this yet, but it seems likely we'll figure it out during the next few decades ... at worst during this century.
Even if it turns out that the brain/body's functions can't be emulated effectively by a digital computer, uploading should still be perfectly possible -- one would just need to create the right sort of computer, such as a quantum computer or a quantum-gravity computer, or whatever.
Yes, it's conceivable that physics somehow prohibits us from copying the details of a mind out of a brain so it can be projected into some other substrate -- but based on all we know about science, that seems extremely unlikely.
The philosophical questions raised by uploading have been debated ad nauseum within the futurist community, to the extent that discussion of the issue is forbidden on some futurist email lists (due to the repetitive nature of the discussions).
The Cosmist perspective is simple: based on everything we know today, it seems extremely likely that the uploaded version of Bob Jones is "the same mind as" Bob Jones, in the same sense that Bob Jones at 4:15 PM on a certain day is "the same mind" as Bob Jones at 4:14 PM on that day.
The patterns comprising Bob Jones's mind in its human-brain/body version, would also be there in its uploaded, computer-substrate version. So from the point of view of Third, it's all the same Bob Jones.
And, from the point of view of First, it's all one big, small moment of experience.
Worries about continuity of self and mind would seem to be assuaged by uploading scenarios in which the biological brain is transferred into a digital simulation one neuron at a time. And then, perhaps the digitally simulated brain is gradually, slowly transformed into something less and less resemblant of a legacy human brain.
What About Weaker Forms of Uploading?
More controversial are weaker forms of uploading, such as creating a computer-based mind that emulates Bob Jones based on information gathered from things he wrote, videos of him moving around and speaking, and so forth.
One question is whether such weak-uploads could be created with sufficient fidelity to capture the "essence" of the individual's mind and self. My guess is yes, but we don't know enough to say for sure.
Another question is about continuity of self: when Bob's weak-upload first gets up and running, it won't necessarily feel like a continuation of Bob's previous thought-stream. The "continuity" aspect of growth exists only weakly here ... this is less a growth of existing patterns, than a replacement of prior patterns with new, highly similar ones. Consequently this seems to be an inferior form of uploading -- but still, quite an interesting one.
Does Human Mind Make Sense Without Human Body?
The mind is tied to the body, more closely than some (especially modern computer geeks) want to recognize. Mind emerges from body as well as brain.
This raises the question of whether some the commonly envisioned forms of uploading even make sense, experientially. Perhaps putting a human mind in a PC is intrinsically senseless, because that mind would very rapidly drift into a wholly nonhuman state of being due to its radically nonhuman embodiment.
In this case, the key to making uploading work psychologically would be to upload the mind into a receptacle that shared the key experiential features of the human body, but lacked its more problematic issues -- like its rapid rate of decay!
One nice thing about uploading is that it can potentially be tried over and over, with the same mind being placed into a vast number of different substrates with different properties. In this way a single stream of awareness could diverge into several different streams emerging from different substrates. And why not?