There's a long-running philosophical argument about the conceivability of otherwise-normal people who are not conscious, aka "philosophical zombies". This has spawned a shorter-running (only fifteen years!) rationalist sub-argument on the topic. The last time I checked its status was this post, which says:

1. Both Yudkowsky and Chalmers agree that humans possess "qualia".

2. Chalmers argues that a superintelligent being which somewhow knew the positions of all particles in a large region of the Universe would need to be told as an additional fact that any humans (or other minds possessing qualia) in this region of space possess qualia – it could not deduce this from mere perfect physical knowledge of their constituent particles. Therefore, qualia are in some sense extra-physical.

3. Yudkowsky argues that such a being would notice that humans discuss at length the fact that they possess qualia, and their internal narratives also represent this fact. It is extraordinarily improbable that beings would behave in this manner if they did not actually possess qualia. Therefore an omniscient being would conclude that it is extremely likely that humans possess qualia. Therefore, qualia are not extra-physical.

I want to re-open this (sorry!) by disagreeing with the bolded sentence. I think beings would talk about qualia - the "mysterious redness of red" and all that - even if we start by assuming they don't have it. I realize this is a surprising claim, but that's why it's interesting enough to re-open the argument over1.

https://www.astralcodexten.com/p/p-zombies-would-report-qualia