alt Hacker News> Qualia exist "outside" spacetime, e.g. redness doesn't have a position in spacetime.
I'm sensing redness here and now, so the sensation of redness exists very clearly tied to a particular point in spacetime. In what sense is the qualia of redness not firmly anchored in spacetime? Of course, you could talk about the concept redness, like the concept Pi, but even then, these concepts exist in the mind of a human thinking about them, still tied to a particular location in spacetime.
> If consciousness is purely physical, then how can two identical systems (identical brains with identical sensory input) giving rise by definition to the same qualia not literally be the same consciousness?
The two brains don't receive the same sensory inputs, nothing in the experiment says they do. From the second right after the duplicate is created, their sensory inputs diverge, and so they become separate consciousnesses with the same history. They are interchangeable initially, if you gave the same sensory inputs to either of them, they would have the same output (even internally). But, they are not identical: giving some sensory input to one of them will not create any effect directly in the other one.
> I'm sensing redness here and now, so the sensation of redness exists very clearly tied to a particular point in spacetime. In what sense is the qualia of redness not firmly anchored in spacetime? Of course, you could talk about the concept redness, like the concept Pi, but even then, these concepts exist in the mind of a human thinking about them, still tied to a particular location in spacetime.
But qualia are inherently subjective. You can correlate brain activity (which exists at a position in spacetime) to subjective experience, but that experience is not related to spacetime.
Said otherwise: imagine you are in the Matrix at a coffee shop and sense redness, but your brain is actually in a vat somewhere being fed fake sensory input. "Where" is the redness? You would clearly say that it arises in your brain in the coffee shop. Imagine then the vat is moved (so its position in spacetime changes), your brain is rolled back to its previous state, and then fed the same sensory input again. Where is the redness now?
You can't differentiate the two sensations of redness based on the actual position of the brain in spacetime. For all intents and purposes, they are the same. Qualia only depend on the internal brain state at a point in time and on the sensory input. Spacetime is nowhere to be found in that equation.
> The two brains don't receive the same sensory inputs
But let's say they do. Identical brains, identical inputs = identical qualia. What differentiates both consciousnesses?