THOMAS AQUINAS may never have actually wondered how many angels can dance on the head of a pin, but his tortured musings about metaphysical issues associated with the non-corporeality of angels (and the related issue of whether there is excrement in heaven) stretched the limits of reasonable rational inquiry so far that later scholars invented the phrase to mock him.
My thoughts turned to Aquinas last week as I sat through a lengthy seminar on the subject of Boltzmann brains. The speaker decided his ruminations were so important that he needed 90 minutes rather than the customary hour. To my surprise, many in the room seemed to agree with him.
He goes on to explain what this is all about:
The problem is that statistical arguments suggest that in long-lived universes, far more Boltzmann-brain consciousnesses will develop than intelligences like our own, which have evolved over billions of years. That would mean we are far from typical, so anthropic explanations of our universe fall by the wayside.
Some theorists have therefore tried to develop constraints that would force all inflating universes like our own to decay well before Boltzmann brains can infect them. The bad news here is that in this case our universe must be unstable, and heading for a catastrophic end. But at least anthropic arguments from string theory would not be undermined. You can decide for yourself which you would prefer.
and to conclude:
If debating angels dancing on pins marked the intellectual low point of medieval theology, then we may similarly question the merits of debating problems that require hand-waving arguments involving unknown quantities that differ by billions and billions of orders of magnitude. Let’s focus on other issues, at least until better theories come along.
Update: At Lubos Motl’s blog, there’s a comment from Krauss noting that the title was chosen by an editor, not by him, and that he agreed that it was misleading, since the piece was not specifically about string theory.