If even the new consciousness isn't able to know, then what does "same" mean and what part of that definition aren't you satisfying? More acutely, why should you care about satisfying it?
This is an interesting question because as-is, I don't think anyone can really understand what it means to be someone else. For this purpose, I can say my consciousness is something that exists currently and has memories from before, but there is no way to verify that the memories were recorded by the same consciousness. There could have been a different person that no longer exists.
Perhaps a good alternate angle is to consider the “copy” (rather than “replacement”) proposition someone else mentioned: let's say a perfect copy of you could be made (i.e. the entirety of a consciousness is somehow material). Are the two consciousnesses linked somehow? Or are they completely separate despite thinking exactly alike, having the same memories &c.? If they are separate, what happens if the original is killed? Then, the next logical step is to ask how that is different from a consciousness transplant.
It's wild stuff. Or seems like it to a thus-far (presumed) single consciousness.
If you make an exact copy of me at time t, then until the original and the copy part ways and have distinct thoughts and experiences, they're both just me_t, one no more so than the other. At t+1, me_t doesn't exist any more; this is true regardless of how many copies of me_t once existed.
It means you think you just spent $500m on your 'upload' when in reality you just committed some elaborate suicide, launching some other (very similar) chap into immortality.
This isn't responsive. You've only answered my question to the extent of defining "same" as the opposite of "other", which is not a lot of progress. So again, what makes this "other" chap "other", and why should anyone care about satisfying that criterion?
Since the process isn't necessarily destructive to the 'original', both entities could subsequently exist simultaneously and lead separate lives. They're now two separate individuals, with an identical memory up to a certain moment. The original will never experience what it is like to be the reproduction after that point, and the reproduction will never know what it is like to be the original after they were branched. It doesn't make the reproduction any less 'legitimate' as a consciousness, but they're definitely not the same.
It'd be another thing entirely if you could join the 'threads' back together, though. Imagine forking yourself into 12 different entities, each living a separate life for 100 years, then reintegrating.
