LAWRENCE M. KRAUSS is Ambrose Swasey Professor of Physics and Astronomy and director of the Center for Education and Research in Cosmology and Astrophysics at Case Western Reserve University. He is the author, most recently, of Hiding in the Mirror: The Mysterious Allure of Extra Dimensions, from Plato to String Theory and Beyond.
Science has progressed for four hundred years by ultimately explaining observed phenomena in terms of fundamental theories that are rigid. Even minor deviations from the predicted behavior are not allowed by a theory; if such deviations are observed, these provide evidence that the theory must be modified, usually being replaced by a yet more comprehensive theory that fixes a wider range of phenomena.
The ultimate goal of physics, as it is often described, is to have a “theory of everything,” in which all the fundamental laws that describe nature can neatly be written down on the front of a T-shirt (even if the T-shirt can exist only in ten dimensions). However, with the recognition that the dominant energy in the universe resides in empty space—something so peculiar that it appears very difficult to understand within the context of any theoretical ideas we now possess—more physicists have been exploring the idea that perhaps physics is an “environmental science,” that the laws of physics we observe are mere accidents of our circumstances, and that there could exist an infinite number of different universes with different laws of physics.
This would be true even if there were some candidate for a fundamental mathematical-physical theory. For example, as in an idea currently in vogue related to string theory, perhaps the fundamental theory allows an infinite number of different “ground state” solutions, each of which describes a different possible universe with a consistent set of physical laws and physical dimensions.
It may be that the only way to understand why the laws of nature we observe in our universe are the way they are is to understand that if they were any different, life could not have arisen in our universe and we would thus not be here to observe them.
This is one version of the infamous anthropic principle. But things could actually be worse: It’s equally likely that many different combinations of laws would allow life to form, and that it’s a pure accident that the constants of nature result in the combinations we experience in our universe. Or it could be that the mathematical formalism is so complex that the ground states of the theory—the set of possible states that might describe our universe—might not be determinable.
The end of “fundamental” theoretical physics (the search for fundamental microphysical laws—there will still be lots of work for physicists who investigate the host of complex phenomena at larger scales) might very well occur not with a theory of everything but with the recognition that all so-called fundamental theories that describe nature are purely phenomenological—that is, derivable from observational phenomena—and don’t reflect any underlying grand mathematical structure of the universe which would allow a basic understanding of why the universe is the way it is.