[darkmighty]

Even if we had a "permanent" energy source, we have only a finite number of atoms. So one day we would actually also be guaranteed to cycle our thoughts.

http://en.wikipedia.org/wiki/Poincar%C3%A9_recurrence_theore...

So for me true immortality is not only about unbounded time but also unbounded size, neither of which seems achievable.

For all purposes of regular human condition though, an approximation is good enough.