LEE SMOLIN is a theoretical physicist at the Perimeter Institute of Theoretical Physics in Waterloo, Ontario. He is the author, most recently, of The Trouble with Physics: The Rise of String Theory, the Fall of a Science, and What Comes Next.
The revolutions made by Einstein and Darwin are closely related, and their combination will increasingly come to define how we see our worlds—physical, biological, and social.
Before Einstein, the properties of elementary particles were understood as being defined against an absolute, eternally fixed background. This way of doing science had been introduced by Newton. His method was to posit the existence of an absolute and eternal background structure against which the properties of things were defined. Particles have properties defined not with respect to one another but each with respect only to the absolute background of space and time. Einstein’s great achievement was to realize successfully the contrary idea, called relationalism, according to which the world is a network of relationships that evolve in time. There is no absolute background, and the properties of something are defined only in terms of its participation in this network of relations.
Before Darwin, species were thought of as eternal categories, defined a priori; after Darwin, species were understood to be relational categories—that is, defined in terms of their relationship with the network of interactions making up the biosphere. Darwin’s great contribution was to understand that there is a process—natural selection—that can act on relational properties, leading to the birth of genuine novelty by creating networks of relationships that are increasingly structured and complex.
Seeing Darwin in the light of Einstein, we understand that all the properties a species has in modern biology are relational. There is no absolute background in biology.
Seeing Einstein in the light of Darwin suggests that natural selection could act not only on living things but on the properties defining the various species of elementary particles.
At first, physicists thought that the only relational properties an elementary particle might have were its position and motion in space and time. The other properties, like mass and charge, were thought of in the old framework, defined by a background of absolute law. The standard model of particle physics taught us that some of those properties, like mass, are only the consequence of a particle’s interactions with other fields. The mass of a particle is determined environmentally, by the phase of the other fields it interacts with.
I don’t know which model of quantum gravity is right, but all the leading candidates—string theory, loop quantum gravity, and others—teach us that all properties of elementary particles may be relational and environmental. In different possible universes, there may be different combinations of elementary particles and forces; indeed, all that used to be thought of as fundamental—the elementary particles and space itself—are increasingly seen, in models of quantum gravity, as emergent from an even more elementary network of relations.
The basic method of science after Einstein seems to be to identify something in your theory that is playing the role of an absolute background—that is needed to define the laws that govern objects in your theory—and understand it more deeply as a contingent property which itself evolves subject to law.
For example, before Einstein the geometry of space was thought of as specified absolutely as part of the laws of nature. After Einstein, we understand that geometry is contingent and dynamical, which means it evolves subject to law. Einstein’s move can even be applied to aspects of what were thought to be the laws of nature, so that even those aspects turn out to evolve in time.
The basic method of science after Darwin seems to be to identify some property once thought to be absolute and defined a priori and recognize that it can be understood because it has evolved by a process of, or a process akin to, natural selection. This has revolutionized biology and is in the process of doing the same to the social sciences.
These two methods are closely related. Einstein emphasizes the relational aspect of all properties described by science, while Darwin proposes that ultimately the law governing the evolution of everything else—including perhaps what were once seen to be laws—is natural selection.
Should Darwin’s method be applied even to the laws of physics? Recent developments in elementary-particle physics give us little alternative, if we are to have a rational understanding of the laws that govern our universe. I am referring here to the realization that string theory gives us not a unique set of particles and forces but an infinite list out of which one came to be selected for our universe. We physicists have now to understand Darwin’s lesson: The only way to understand how one out of a vast number of choices was made, which favors improbable structure, is that it is the result of evolution by natural selection.
Can this work? I showed that it might in 1992, in a theory of cosmological natural selection. This remains the only theory so far proposed of how our laws came to be selected that makes falsifiable predictions.
The idea that laws of nature evolved by natural selection is nothing new; it was anticipated by the philosopher Charles Sanders Peirce, who wrote in 1891:
To suppose universal laws of nature capable of being apprehended by the mind and yet having no reason for their special forms, but standing inexplicable and irrational, is hardly a justifiable position. Uniformities are precisely the sort of facts that need to be accounted for. Law is par excellence the thing that wants a reason. Now the only possible way of accounting for the laws of nature, and for uniformity in general, is to suppose them results of evolution.
This idea remains dangerous, not only for what it has achieved but for what it implies for the future. For its implications have yet to be absorbed or understood, even by those who have come to believe this is the only way forward for science. For example, must there always be a deeper law, or meta-law, that governs the physical mechanisms by which a law evolves? And what about the fact that laws of physics are expressed in mathematics, which is usually thought of as encoding eternal truths? Can mathematics itself come to be seen as time-bound rather than as transcendent and eternal platonic truth?
I believe we will achieve clarity on these and other scary implications of the idea that all the regularities we observe, including those we have got used to calling laws, are the result of evolution by natural selection. And I believe that once this is achieved, Einstein and Darwin will be understood as partners in the greatest revolution yet in science, a revolution that taught us that the world in which we are embedded is nothing but an ever-evolving network of relationships.