> how do you transfer the "you" into the new brain?

Yeah this is the big question: what constitutes as "you"?

Your body? You can lose a limb or parts of your brain and still remain "you". Your memories? they are constantly re-forming with people forgetting things and new memories being made. Your way of thinking? Neurons are extremely long lived cells.

Unless you believe in souls (which many religions do), the experience of "you" is entirely defined by the matter of your body and maybe your surroundings.

Let's assume we can build machines that can fully emulate human minds. Let's assume this emulation is good enough to also emulate the self-ness experience we are interested in.

Your question was (and the question of LoSboccacc), that if you have this technology, can you somehow transfer the self-ness so that the real, legitimate, "you" gets there, and not a copy? How do you know it's really you?

I'd argue that consciousness and self-ness is weirder than humans usually experience it: it can do more things than you'd think.

Let's take Bob, someone born in the simulation, that is, he has spent his entire life being simulated in silicon. For all purposes, his self-ness is the only true legitimate one. There is no difference in legitimacy between his simulation and a human in flesh and blood. That's just a simple conclusion of the basic assumption that there are machines that can do this.

Now if we have such a machine, then it runs some kind of program that can at least store Bob's state as a finite set of bytes. Whether it's a petabyte (less likely) or a yottabyte (maybe) is less relevant, what's more important is that it's a set of bytes.

Now you can do interesting things with this data. What happens if you pause the emulation, save the data to disk, and then decide to either a) stop the emulation and load it from the saved state or b) delete the saved copy and resume the emulation. In both scenarios a and b you'd resume with the same state for Bob as in a) you load the same data you just stored and in b) you just create a disk backup and delete it. Nothing would really change. It would be the same Bob afterwards in both scenarios.

In the next experiment, you save it to disk, turn off the emulating computer for a day, then turn it on, loading the disk again? It would be the same Bob, right?

Let's combine the two experiments. Let's pause the emulation, save the data to disk, and then decide whether to either a) turn off the computer for a day or b) resume the emulation and run it for a day. After the day concluded we power cycle the computer and load the data we stored to disk yesterday. Now my argument is that it's still the same Bob in both scenarios. Scenario a) is our second experiment. As for scenario b), at the point of the pausing, we haven't decided yet about whether to choose a) or b). So clearly, the Bob stored on disk must be the legitimate one, otherwise a) would end up "killing" Bob. So it follows that in scenario b) it's the same Bob as well.

Next I'd argue that whether there is a decision or not isn't really relevant for which data is being stored. It'd be the same Bob if you always chose b). In the fourth experiment, you'd just always go with b).

If we apply this thought experiment to the boundary between emulated and incarnated minds, the conclusion to be drawn is that the cloud copy is always [1] legitimate, whether the original host dies during the copy, after the copy, or not at all.

This conclusion is a bit humbling and it's understandable that people are critical, in fact I'm myself. But I believe this is just because the way we experience life on earth as separate individuals and consciousnesses, simply because our bodies are made like that. Our perception of what a consciousness is is blinded by the fact that each human starts with a blank set of memories and has their own way of deciding things, own skills etc. But once we get the ability to copy entire brains, those new experiences with consciousnesses in our society will fold the perceptions of individuals. Of course there will always be people who still believe in souls, and maybe there are in fact souls we just don't have the detection technology for. But 100 years ago people were superstitious of being photographed as they'd think you are stealing their soul. Maybe in 100 years we'll think that the old kind of thinking about consciousness is the same kind of superstition.

I'd say it's an artifact of our self-preservation drive. Of course it's very important to quality control whether the simulation is really doing what's promised.

To conclude, I think it's much easier to believe in life after death if you've seen your friends and family do it before your own eyes. Even Thomas ended up believing!

Uhh the comment has gotten a bit longer than I anticipated.

[1]: Note that this opens the question: can you just make any kind of copy and call it legitimate? Of course not. Consciousnesses are even weirder. The transition between legitimate and illegitimate is fluid. I'd consider someone who had a stroke and can't talk or walk any more as a weakly legitimate copy of the person pre-stroke. My argument assumes legitimate copies, but of course people can have different opinions/standards on what constitutes a legitimate copy. The question will become especially interesting if billionaires will get access to different copying methods than poor people.