Large Cosmic Lessons in Physics
I once asked John Wheeler what he regarded as his greatest contribution to science. He thought for a moment and then answered “Mutability!” Wheeler was referring to his concept of Law Without Law, which he sometimes expressed by saying that there is no law except for the law that there is no law. More colorfully, he would sometimes avow everything comes out of higgledy-piggledy.
Scientists seem to divide into two camps on the status of the laws of physics. On the one hand are those (myself included) who believe that there is a really-existing mathematical order in nature, and that we might one day establish the bottom level laws in which all of physics is grounded. By this I mean what Steven Weinberg and others refer to as a final theory. Theorists who work on unification, such as string theory or M theory, normally assume that there exists a truly fundamental law or set of laws out there, though the so-called laws we find in current textbooks remain tentative and provisional. These theorists usually suppose that the search for the final law or theory is a completable program. Indeed, Stephen Hawking famously lectured on the topic that the end of theoretical physics might already be in sight. Those in this camp see physics as a logical progression, inexorably homing in on a final set of laws via a series of ever-better approximations to truth. Implied in this philosophy is that the universe is, at rock bottom, both rational and comprehensible, as opposed to arbitrary or absurd.
Other scientists, and many non-scientists, hold a very different view. They maintain that theoretical physics is just model building carried out largely for the satisfaction of physicists, and successful only in their terms, rather than in some absolute sense of approaching truth. To be sure, the models get more complex, elaborate, and useful, but there is said to be no objective progress; i.e. the models aren’t actually converging on anything definitive out there. According to this view, humans invent laws and attach names to them, but these laws simply represent a convenient way for us to think about the world and order experimental data. In other words, the laws of physics are our laws, not Nature’s.
Some evidence for the latter position comes from high-energy particle physics and cosmology. What were previously seen as sacrosanct laws have often turned out to be violated or transcended under extreme physical conditions. For example, the conservation of baryon number was widely regarded as an inviolable law of physics 30 years ago. Today, most theorists suppose that baryon number can change at high energy, and did indeed change in the hot big bang. It is tempting to believe that as the physical conditions become more and more extreme, so one by one our cherished laws fall away, until at the end point there is … Nothing? Just higgledy-piggledy?
The successive transcendence of laws with increasing energy was an idea pioneered by John Wheeler, and now seems to be an accepted principle, though it is too soon to say whether familiar laws merely get replaced by others as the energy rises, or whether lawfulness in general becomes replaced by lawlessness, as Wheeler suggests. More shocking, however, is the possibility that cherished laws might be transcended even at relatively low energy. Joao Magueijo, a theoretical physicist at Imperial College London, has been closely involved in astronomical observations that claim just that. Along with John Barrow, John Webb, and others, he has assembled evidence that the fine structure constant of quantum electrodynamics might actually not be a constant at all, but a parameter that varies over cosmological timescales. A synopsis of his paper follows. If Magueijo is right, it will most definitely put the cat among the pigeons. If we can’t rely on the basic constants of nature behaving themselves, then what happens to electrodynamics, or the theory of relativity? If things go wrong even at that level, where do we begin to rebuild physical theory? Well, this Internet forum might be a goodplace to start.
A number of surprising observations made at the threshold of the 21st century have left cosmologists confused and other physicists in doubt over the reliability of cosmology. For instance it has been found that the cosmological expansion appears to be accelerating. This is contrary to common sense, as it implies that on large scales gravity is repulsive. Another upheaval resulted from the high redshift mapping of the fine structure constant. Evidence was found for a time dependence of this supposed constant of Nature. Yet another puzzle was the observation of rare very high energy cosmic rays. Standard kinematic calculations, based on special relativity, predict a cut off well below the observed energies, so this may perhaps represent the first experimental mishap of special relativity.
These three surprises are not alone and prompt several questions. Is the Universe trying to tell us something radical about the foundations of physics? Or are astronomers merely trying to irritate the conservative physicist? It could well be that the strange observations emerging from the new cosmology are correct, and that they provide a unique window into dramatically novel physics. Is the Universe trying to give us a physics lesson?
It would be surprising if we already knew everything there is to know about physics. Indeed we expect that current theories must break down in the very early universe, or at very high energies. However no one knows to what extent our little concepts are inadequate in these extreme situations—the damage caused could be unimaginable. Perhaps Lorentz invariance is broken, energy is not conserved, and the time translational invariance of physics itself is lost. The constants of nature could be lawless dynamical variables, and the observed stability of physics nothing but a sign of old age. We argue in favor of these extreme possibilities, speculating over just how bizzare the new physics might be.
One dramatic possibility is that the speed of light is a dynamic variable. If so we may indeed expect the above phenomena to be true. In addition, it could be that near black holes the speed of light congeals to zero, preventing observers from approaching the “singularity” and invalidating most current black hole theories. It might also be true that in the vicinity of cosmic strings the speed of light is much higher, allowing for high-speed travel without the annoyances associated with time dilation effects. Yet another possibility is that time variations in c cause the energy stored in the cosmological constant to be converted into normal matter. This process might even account for the creation of the Universe. Or perhaps something even more unpalatable to the unimaginative physicist is behind our existence.
The amazing possibility remains that these radically new phenomena may also manifest themselves here and now, not just in the very early Universe. Maybe we have only recently started to look hard enough. Crazy as all of these ideas might be, some may already make contact with observations, unlike more conventional approaches to unification and quantization of gravity. For this reason I will argue that these off-the-mainstream cosmic lessons may provide the much sought after observational inspiration for such longstanding unsolved problems as the quantization of gravity.