Paul Davies is an excellent speaker. I thought he would have made a good wake-up talk, now he's talking to me to sleep. I am equally impressed as depressed that one could take a transcript of his talk and just publish it - no *oohms*, no *aahs* no inflation of Okay's, Right's or other glitches. That's depressing because my stuttering will likely never get anywhere close to that.
Either way, Paul started his talk with the question of whether in our search for fundamental laws we might always find an even more fundamental theory - nicely summarized in the explanation that our world rests on the back of an elephant, who stands on the back of a turtle, and if you wonder what the turtle is standing on - well, it's turtles all the way down. (See Wikipedia for full story.) Translate into: if we look closer into the microscopic features of nature, we might have to refine our theories over and over again.
Alternatively, there might be a fundamental theory, a final "Superturtle", so Paul suggests, to hold the tower of turtles. It seems to me quite a substantial fraction of theoretical physicists today believes in the existence of the Superturtle. Though one might ask whether it is even possible for us to decide between turtles all the way down and the final Superturtle, given that we lack experimental evidence for even the next turtle. See also my earlier post Will Physics turn into Philosophy?
Last week, I attended a conference on Emergent Gravity. The idea behind these approaches is roughly that the laws of nature we currently use and the ingredients of our present theories, including space and time itself, are not fundamental, but "emerge" from a potentially completely different microscopic description.
The following four pictures might give you a very sketchy analogy of emergence. Depending on the level you "zoom" in you will be able to recognize different patterns, and you might chose different ways to describe what you see. Similarly in nature, depending on the level we "zoom" in, different variables might be useful to describe what we see. (If you get lost in the multiphoto, the zoom is onto the upper right corner.)
[Click here for a large version of the last picture, about 2MB. I meant add a the link to where I downloaded it, but I can't find it, sorry.]
The phenomenon that a different resolution of structures makes other variables more appropriate is familiar from an abundance of examples. You wouldn't describe cells with the standard model or particle physics - not because it doesn't apply, but because that description would be essentially useless and utterly inappropriate. The cell is better characterized by other variables, as might be the in- and output of certain chemicals. Likewise, it isn't of much use to describe human behavior by considering all cells humans are made of. Effective theories in physics are an especially strict notion of making sense of resolving structures only to a limited precision, in which case the ingredients of your theory might change. (See also my post on Emergence and Reductionism.)
Anyway, given the nature of this conference on the Multiverse, I think the question to ask here is instead whether it's turtles all the way up? If we consider the universe at larger and larger scales - possibly beyond what we can observe, would there be emergent laws connecting these universes? Emerging Multiverse-superlaws determining how we are embedded in the ensemble of universes that we might be part of? And is is possible for us at all to say something about these turtles?
(Aside: Min 37 - James Hartle's commentary on Max Tegmark's Mathematical Universe. He is criticising Max' use of the word 'exist'. I totally agree with Jim, that's exactly my criticism, see my post on The Mathematical Universe.)