What if the laws of physics as we know them are just accidents, the products of cosmic happenstance?
Science proceeds from the assumption that the universe is ordered in a rational and intelligible manner. The most refined expression of the rational order in nature is encompassed in the laws of physics.
But what are these ultimate laws and where do they come from? Such questions are often dismissed as being pointless or even unscientific. As the cosmologist Sean Carroll has written, “There is a chain of explanations concerning things that happen in the universe, which ultimately reaches to the fundamental laws of nature and stops… at the end of the day the laws are what they are… And that’s okay. I’m happy to take the universe just as we find it.” Conventionally, the job of the scientist is to simply assume the laws and get on with the job of applying them to real problems. But in recent years physicists have been excited by the prospect of unifying laws from different branches of the subject into a sort of final super-law, and this has encouraged speculation about the nature of the laws themselves.
There has long been a tacit assumption that the laws of physics were somehow imprinted on the universe at the outset, and have remained immutable thereafter. Physical processes, however violent or complex, are thought to have absolutely no effect on the laws. There is thus a curious asymmetry: Physical processes depend on laws but the laws do not depend on physical processes. Although this statement cannot be proved, it is widely accepted.
There is, however, a subtlety. Physicists have discovered that the laws of physics familiar in the laboratory may change form at very high temperatures, such as the ultra-hot environment of the Big Bang. As the universe expanded and cooled, various “effective laws” crystallized out from the fundamental underlying laws, sometimes manifesting random features. It is the high-temperature versions of the laws, not their ordinary, lab-tested descendants, that are regarded as truly fundamental. The laws of physics as we know them may just be “frozen accidents.”
Consider an analogy: There is a “law” that says compass needles point north. They do so because when Earth first cooled, it established a local magnetic field. The currently “effective law” of compass needles is valid enough, but it is not fundamental. Rather, it is a derived part of a larger set of electromagnetic laws that are fundamental and apply throughout the universe.
If the Big Bang were replayed, the low-temperature laws that emerged next time could be different. In fact, many cosmologists now think the Big Bang that created our universe was but one of an infinity of bangs scattered throughout space and time, each spawning a universe with low-temperature laws different from those in the universe next door. Nevertheless, the underlying high-temperature laws would still be the same for all these myriad universes. It is those deeper, universal, ultimate, laws that are taken to be immutable. From now on, when I refer to laws, it is this ultimate set I have in mind.
What is the origin of these laws? Why do they have the form that they do, as opposed to a limitless number of other forms? When I was a student it was thought that the Big Bang was not just the origin of matter and energy, but of space and time too. Anything that came before the bang, or triggered it, was regarded as beyond the scope of science. Then in the 1980s, a number of cosmologists, notably James Hartle and Stephen Hawking, attempted to explain the Big Bang (including the origin of time) in terms of the laws of quantum gravity. For this type of explanation to succeed, the laws need to be transcendent: That is, they must exist in the absence of the universe—even in the absence of space and time.
Where, then, do these laws exist? Perhaps they occupy some abstract Platonic mathematical realm. Or maybe they live in the multiverse—a cosmic menagerie in which our universe is just one of many, each born in its own big bang. In this currently fashionable picture, the hot explosion that gave rise to our universe was not the ultimate origin of space and time, but just one spectacular event in an infinite and eternal space and time. The ultimate laws predate our universe because they already existed in the multiverse from which our universe sprang.
But this maneuver merely shifts the mystery of the cosmic birth back one logical step from the Big Bang explosion to the laws that govern that explosion. The origin and form of those laws remain unexplained. One just has to accept them as “given.”
Furthermore, the laws are assumed to be fixed and immutable. Experiments support that assumption—no one has ever caught the laws of physics changing before his or her eyes—but we can only test the form of the laws to limited precision. Suppose the laws—even the ultimate high-temperature laws—evolve with time? What if they depend, perhaps in a subtle way, on the physical states of the universe, so that states and laws are coupled and can co-evolve? Such ideas are scientific heresy: The immutability of the laws has been at the foundation of physics since the time of Newton. But that does not make it sacrosanct.
Trying to explain the origin of the amazing laws of physics may lie beyond the scientific enterprise, and at the end of the day we may just have to accept them as an unexplained mystery. But before we dismiss the origin of the laws as an unscientific question, some further thought seems worth a shot.
Editor’s picks for further reading
Discover: Is the Search for Immutable Laws of Nature a Wild Goose Chase?
Astrophysicist Adam Frank on the physicists who are challenging the idea that a single set of laws can describe the universe at all times.
Information and the Nature of Reality: From Physics to Metaphysics
In this book of essays, scientists, theologians and philosophers discuss information as the fundamental “stuff” of the universe.
Perimeter Institute: Laws of Nature: Their Nature and Knowability
In this series of talks, physicists, philosophers, and mathematicians explore ideas on the nature of physical laws.