What does it mean to say that the principle of relativity is itself emergent? And from what would it emerge? Are laws really laws, in the strong sense we understand historically and definitionally? Or are laws, even what we call natural laws, situational or contextual? Moreover, if nature actually were itself evolutionary and emergent in its processes, then wouldn’t such laws be eo ipso also evolutionary and emergent? Furthermore, does this mean that what we consider to be the two main pillars of scientific reasoning, namely the repeatability of the experiment and the predictive power of the hypothesis, are nothing more than local occurrences? Are they simply artifacts of the current regional ontology (or cosmology)?
If this is the case, what is the relation between the restlessness of quantum theory, the possibly emergent nature of relativity, and religion or religious experience? And what effect does this have on our understanding of classical mechanics? Moreover, does such thinking smack of what some might call special creation in the broadest sense?
Read on to explore some of these dilemmas in the abstract of Robert Laughlin’s talk at the symposium held in honor of the 90th year of John Archibald Wheeler. Laughlin is on the Program Oversight Committee for this event and won a Nobel Prize in Physics in 1998.
Like many other physicists born in the 1950s I learned general relativity from Prof. John Wheeler’s book and was inspired in my own career by his willingness to generate deep questions by pushing incomplete physical theories to their limits. I found myself disagreeing with his answers much of the time, but nonetheless developed tremendous respect for his priorities and eventually adopted many them as my own. I have been a committed Wheelerian for a long time, and gratefully acknowledge its positive influence on everything I have done in physics that matters.
My views on the great unsolved physics questions at the core of this symposium—quantum measurement, the emergence of the correspondence limit through decoherence, spontaneous ordering, hierarchies of laws—are strongly influenced by my life in condensed matter physics, a discipline that forces theoretical ideas to immediate and brutal experimental test by virtue of its low cost. Anyone subjected to this long enough eventually develops the habit of thinking experimentally, of evaluing a theoretical idea on the basis of what one could measure in a given situation and little else. This is considered overly conservative in many circles, but I disagree. I think it is theoretical physics operating at peak performance in its proper role as the interpretive and predictive partner of experimental science. In this environment one gains a healthy respect for the natural world’s ability to surprise and a healthy DISrespect for the belief that all things can be calculated from first principles. This is not to suggest that the fundamental laws are wrong, but only that they are sometimes not very relevant. Superfluidity is a simple case in point. We know from experiment that the properties of superfluids are exact and universal, but we also know that proving this starting from quantum mechanics is impossible. At some point in the logical path from microscopics we have to invoke the principle of superfluid broken symmetry—which is to say postulate the superfluidity. This is especially noticeable near the crystallization pressure of liquid helium-4 where first-principles computation has enormous difficulty predicting whether the helium-4 is a superfluid or a quantum solid, much less the spectroscopic properties of either. Yet we know from experiment that the low-energy properties of the liquid and solid phases on either side of this transition are universal and completely characterized by their mass densities and sound speeds.
I plan to talk about the black hole horizon paradox and the incompatibility of relativity and quantum mechanics. This is obviously a great problem in the Wheelerian pantheon and something of great interest to all of us, particularly in light of recent advances in string theory. However, what I have to say is largely orthogonal to string theory. I have become increasingly convinced that the essence of the problem is not microscopic at all but collective, and that studying microscopic models of the vacuum maybe the wrong thing to do EVEN IF THE MODELS ARE RIGHT. I think black hole formation is a quantum phase transition. For this to make sense it is necessary for the principle of relativity itself to be emergent. I will argue that this is the case, that it is the correct resolution of the quantum gravity conundrum, and that experiments capable of demonstrating the breakdown of relativity at high energy scales (e.g. the propagation of super-energetic cosmic rays) constitute the key test.