Anders Sandberg, <email@example.com>, writes:
> The problem of shrinking horizons posed in the Krass and Starkman
> paper (incidentally, our Nick Bostrom has written a paper with
> Circkovic on the problem too, gr-qc/9906042) is not dealt with by
> Tiper or (to my knowledge) Tegmark. If the expansion of the universe
> is accelerating (as current data seems to suggest), then horizons will
> creep inwards and limit the mass-volume intelligence can use,
> eventually squeezing it out altogther.
Tipler is not dealing with the expanding-universe case so any problems relating to horizons in that scenario would not apply for him. He is working with the Big Crunch model and although there are some issues with horizons he assumes/calculates them away.
Frank Tipler and David Deutsch both take an aggressive and (to me) puzzling approach to these issues. They claim on philosophical grounds that the universe MUST be such that life can exist (and grow) forever. Therefore if we are right about eternal life being impossible in an open universe, we must be wrong about the universe being open. So one of the predictions of Tipler's theory is that current astronomical opinion is wrong, and the universe will turn out to be closed.