Tipler would simply deny that such an AI would be able to anything for Searlian reasons. You can't prove that an AIXI-style AI will ever work, and it's presumably part of Tipler's argument that it won't work, so simply asserting that it will work is sort of pointless.
The AIXI proofs seem pretty adequate to me. They may not be useful, but that's different from not working.
More to the point, nothing in Tipler's paper gave me the impression he had so much as heard of AIXI, and it's not clear to me that he does accept Searlian reasons - what is that, by the way? It can't be Chinese room stuff since Tipler has been gung ho on uploading for decades now.
The AIXI proofs seem pretty adequate to me. They may not be useful, but that's different from not working.
It's really not obvious that if you run an AIXI-like AI it will actually do anything other than self-destruct, no matter how much juice you give it. There have been various papers on this theme recently and it's a common LW meme ("AIXI drops an anvil on its head").
By "Searlian reasons" I mean something like emphasizing the difference between syntax and semantics and the difficulty of the grounding problem as representative of thi...
...has finally been published.
Contents:
The issue consists of responses to Chalmers (2010). Future volumes will contain additional articles from Shulman & Bostrom, Igor Aleksander, Richard Brown, Ray Kurzweil, Pamela McCorduck, Chris Nunn, Arkady Plotnitsky, Jesse Prinz, Susan Schneider, Murray Shanahan, Burt Voorhees, and a response from Chalmers.
McDermott's chapter should be supplemented with this, which he says he didn't have space for in his JCS article.