Davies, Paul

Paul is a theoretical physicist, cosmologist, astrobiologist, author and broadcaster. He is College Professor at Arizona State University, where he founded BEYOND: The Center for Fundamental Concepts in Science. A Templeton Prize winner (1995), he is the author of many books on the Big Questions including The Mind of God, God and the New Physics, The Cosmic Blueprint, Are We Alone?, The Fifth Miracle, The Last Three Minutes, About Time, How to Build a Time Machine, The Re-Emergence of Emergence (with Philip Clayton); and The Goldilocks Enigma: Why is the Universe Just Right for life? In the latter (Goldilocks), Paul describes all possible explanations of existence—brute fact, unique laws, intelligent design, life principle, self-explaining universe, fake universe—and concludes that all of them are “either ridiculous or hopelessly inadequate,” though he ultimately opts for a ?self-creating, self-explaining, self-understanding universe-with-observers, entailing backward causation and teleology”). Following are excerpts from Paul’s address, “The Problem of What Exists.”  “The puzzle of why the universe consists of the things it does is one of the oldest problems of philosophy. Given the seemingly limitless possibilities available, why is it the case that atoms, stars, clouds, crystals, etc. are “chosen” to exist in profusion in preference to, say, pulsating green jelly or pentagonal chain mail? A related question is why the entities that do exist conform to the particular physical laws that they do as opposed to any other set of laws one might care to imagine. Physicists have mostly ignored this problem, content to accept the observed physical systems and their specific laws as “given,” and preferring to concentrate on the job of elucidating them. Notable exceptions were Einstein, who famously remarked that he wanted to know whether “God had any choice” in the nature of his creation, and Wheeler, whose rhetorical question “How come existence?” provided the basis for a series of speculative papers. Recently, however, theoretical physicists and cosmologists have been giving increasing attention to the problem of “what exists.” In part this stems from the growing interest in unification, especially string/M theory, and the concomitant sharp disagreements about uniqueness. Meanwhile, the popularity of multiverse cosmological models has prompted a dramatic reappraisal of the very concept physical existence. Once one embarks on the slippery multiverse slope, it is unclear just how far from the familiar universe we observe one must be prepared to go in considering members of an all-embracing ensemble. The “standard” multiverse model based on the string theory landscape and eternal inflation, its 10500 instantiations notwithstanding, is actually highly restrictive, containing a long list of prerequisites, all of which could be challenged or relaxed in a generalized version of the multiverse. I have considered in a speculative vein some possible generalizations—alternatives to quantum mechanics, departures from integer space dimensionality and non-Platonic laws of physics—and asked whether there exist any anthropic constraints on these generalizations. The ultimate goal of this agenda is either to discover anthropic explanations for the list of prerequisites A - K, or to establish which of these prerequisites is not necessary for life and observers, and which might therefore require a deeper level of explanation. Tegmark has suggested a total multiverse in which “anything goes.” However, his extreme position has few advocates. Moreover, it is not without its own problems. We may thus separate universes into two sets: those that really exist and those that could have existed but in fact do not. The former set consists of universes that are both logically possible and physically instantiated, the latter consists of universes that are mere contenders for reality but do not actually exist. We may then ask where the all-important selection rule comes from, and why that rule applies rather than some other. Stephen Hawking has addressed this issue and expressed it poetically: “Something must breathe fire into the equations,” he says, to promote a merely-possible but non-existent universe into the Real Thing. What is this fire? Who or what breathes it? Who or what gets to choose what exists and what doesn’t? Thus, in all but the most extreme versions of a multiverse theory (i.e. super-Tegmark sets of all possible universes of all possible categorization qualities), we are still left with the fundamental problem of existence: the mysterious process whereby the existent is divided from the possible-but-nonexistent. Clearly, invoking a multiverse does not solve that problem: it merely shifts it up one level from the realm of universes to the realm of selection rules. The resulting meta-problem—which equations are “fired up” and which remain “un-ignited” would seem to be at least as hard as the problem in pre-multiverse days of explaining why a single, unique universe exists.