>Could you explain this?

I'm not intending to say anything particularly deep. If we could exhaustively list the features of a "conscious observer", every feature except for qualia (the qualitative experience) could be cashed out as some kind of information processing (e.g. knowledge of one's own mental states). And so when it comes to explaining consciousness, the difficulty isn't the observer part, but the qualitative experience part.

>In biological terms, fine. In physical terms, impossible.

But if biology is just physics, then it should be possible in principle. We should encourage people to bring their particular expertise to the problem instead of taking our own conceptions so seriously to the point of actively discouraging ideas that don't fit. I'm happy Tegmark seems immune to charges of being a crackpot.

If consciousness is a physical thing, how can you be so convinced that it is impossible to talk about it in physical terms? Couldn't the difficulty be due to a deficiency in our current explanatory power, as opposed to something more fundamental? What evidence do you have to support that biological talk (about consciousness, or otherwise) is necessarily irreducible to physical talk?

These questions are very interesting and very hard, and dismissing honest attempts to grapple with them rigorously, wrong as they may turn out to be, seems rash to me.