I certainly didn't intend to suggest that an infinite number of theoretical layers might be necessary to explain nature (though I suppose I can't rule it out).

I certainly didn't intend to suggest that an infinite number of theoretical layers might be necessary to explain nature (though I suppose I can't rule it out). Everything in my comment was meant to be compatible with (to take one example) the possibility that some particular well-defined refinement of string theory turns out to be the ultimate theory of nature, and only variations in local conditions are unpredictable. (This is meant in much the same way that the well established laws of gravitation, electromagnetism, and nuclear physics will give rise to very diverse solar systems.) There are interesting questions in many multiverse models about the history and origin of the universe, and I've seen people express concerns about the possibility of "infinite history" in much the same words you've used here. But that's a different issue than Smolin's notion of infinitely many layers of theory being needed to keep the cosmic machinery running. Personally, I'm not overly bothered by the notion of space and time existing forever in both directions, with new bubbles of interesting reality occasionally spawning themselves from the remnants of the old ones at random after uncounted eons of darkness. I don't know why that structure might exist rather than something else (or why there is something rather than nothing), but positing a "first cause" wouldn't make me any more satisfied (and would raise additional questions). I think modern math and science are more comfortable with the possibility of infinity than folks used to be, and that our notion of a "cause" is rather different. (When I think of "causality", all I think about are light cones and Cauchy problems: http://en.wikipedia.org/wiki/Cauchy_problem http://en.wikipedia.org/wiki/Cauchy_problem .)