alt Hacker News> But let's say they do. Identical brains, identical inputs = identical qualia. What differentiates both consciousnesses?
I'll start with this, because it should help with the other item. We know there are two identical consciousnesses exactly because they are separate in spacetime. That is, while I can send the same input to both and get the same mind, that's not the interesting thing. The interesting thing is that I also can send different inputs, and then I'll get different minds. If it really were a single consciousness, that would be impossible. For example, you can't feed me both pure redness and pure greenness at the same time, so I am a single consciousness.
Here is where we get back to the first item: if we accepted that qualia are not localized in spacetime, we'd have to accept that there is no difference between me experiencing redness and you experiencing redness. Even if you consider that your qualia are separate from my own because of our different contexts, that still doesn't fully help: perhaps two different beings on two different planets happen to lead identical lives up to some point when a meteorite hits one of the planets and gravely injures one of their bodies. Would you say that there was a single consciousness that both bodies shared, but that it suddenly split once the meteorite hit?
Now, that is a valid position to take, in some sense. But then that means that consciousness is not continuous in any way, in your view. The day the meteorite hit planet A is not special in any way for planet B. So, if the single consciousness that planet A and planet B shared stopped that day, only to give rise to two different consciousnesses, that means that this same phenomenon must happen every day, and in fact at every instant of time. So, we now must accept that any feeling of time passing must be a pure illusion, since my consciousness now is a completely different consciousness than then one that experienced the previous minute. While this is a self-consistent definition, it's much more alien than the alternative - where we would accept that consciousness is tied in spacetime to its substrate.
> Would you say that there was a single consciousness that both bodies shared, but that it suddenly split once the meteorite hit?
I agree, this is super weird. In a sense this seems to be the difference between viewing consciousness from the first person vs the third person. But until we understand how (if at all) matter generates felt experience the latter view can not, by definition, be about consciousness itself.
I guess this kind of perspective commits one to viewing first person experience in the way we understand abstract concepts - it is nonsensical to ask what the difference between this "1" here and that other "1" over there is. Well, you can say, they are at different positions and written in different materials etc, but those are not properties of the concept "1" anymore.
So yes, coming back to the thought experiment, one of the consequences of that would have to be that both bodies share the same consciousness and the moment something diverges the consciousnesses do too.
The point about time is interesting, and also directly related to AI. If at some point machines become conscious (leaving aside the question if that's possible at all and how we would know without solving the aforementioned hard problem), they would presumably have to generate quanta at discrete steps. But is that so strange? The nothingness in between would not be felt (kind of like going to sleep and waking up "the next moment").
But maybe this idea can be applied to dynamical continuous systems as well, like the brain.
(Btw this conversation was super interesting, thank you!)