Hi Marc,
You've done a remarkable job here. The scope of the essay is amazing; you touch on every idea I've ever come across on cosmic foundations and give us an insightful assessment in each case, and it's wonderfully readable. Unfortunately, the ideas you settle on are hard for me to appreciate philosophically.
First, the notion of a Maxiverse of all possible abstract structures doesn't seem relevant to me, because our universe is the opposite of abstract. It evidently instantiates many different kinds of mathematical structures, at many levels. But as I wrote in a comment to Cristi Stoica's fine essay, while mathematical abstraction lets us make explicit the general patterns in the way things operate, it's the unique instances of these patterns that constitute our empirical universe.
In a previous FQXi essay, I tried to make clear that there's even an essentially non-mathematical aspect in the language of physical equations. A quantity of energy is different from a quantity of momentum, or mass or electric charge. The fact that all the dozens of distinct observable parameters in physics can be represented by abstract symbols in equations doesn't make physics equivalent to pure mathematics.
My own interpretation of the fine-tuning of our fundamental physics is that it serves specifically to support the possibility of measurement. Gravity and electromagnetism and nuclear physics all help make possible the existence of stable material structures, without which there would be no "clocks and measuring rods," nor any way to measure any physical parameter. Without the finely-tuned cooperation of all these different mathematical structures, the universe would indeed be "nothing" - nothing observable or physically determinable.
In my current essay, I describe measurement as a form of random natural selection, creating new facts that help set up other situations in which new facts can become determinate. But my point here is that however the so-called "collapse" occurs, the particular result of a quantum measurement is not mathematically determined. To me, this seems to make the concrete facts established by accidental events more basic than the mathematical structures that arise from their statistics.
So that's one issue I have with your argument. The other is that I don't like treating "consciousness" in the old Cartesian fashion, imagining it as somehow emerging separately from the material universe... or even co-emerging with it. There is no doubt something that transcends materiality in human consciousness, but as my essay shows, I think it can be understood well enough through evolutionary processes. And again, I don't think the concept of "abstract structure" captures what's essential to the uniqueness of each person's mind, any more than it does what's essential to our unique universe.
But though I disagree with your philosophical preferences, I admit that the scheme of co-emergence is an ingenious and imaginative solution to a "hard" problem you've considered carefully from many angles - so it ranks high above the general trend of speculation in these contest essays.
I think you came closest to the truth at the beginning, with the idea of a "strange loop" approach to foundations, as an alternative to "straight chain" explanation. This captures the recursive character that I take as the key to foundational processes in physics, as well as in biology and the human mind... none of which seem to be built on a "self-evident, rock-bottom" kind of foundation.
Also at the end, you make a nice statement - "It is as if physics is trying to tell us that the world arises out of the point of view of single observers, even if they do in the end form a community that observes a single unified reality." This also relates to my discussion of human consciousness. If I may quote myself: "Each human consciousness evolves its own universe... I emphasize this, because unless we recognize how isolated we are, in our own minds, we can't appreciate what our communication software does, or how remarkably it works."
Thanks for an excellent and well thought-out contribution -
Conrad