Lee Smolin aims to breathe new life into cosmology by borrowing concepts from biology, notably natural selection. Ayala Ochert reports
When cosmologist Lee Smolin turned to biology for inspiration and developed his Darwinian view of cosmology, he admits that "it seemed like a very desperate step". Physicists like to think that theirs is the most fundamental of sciences, biology ranking several rungs further down the scientific pecking order. But, according to Smolin, these are desperate times for physics. "Rather than thinking that the revolution (in physics) was made with quantum physics and relativity, and that there are just a few bits to tidy up, I think we're in the midst of something quite large and we have quite a way to go."
Based at the Center for Gravitational Physics at Pennsylvania State University, Smolin is a key protagonist in the search for a so-called "theory of everything". Such an explanation would embrace two fundamentally incompatible theories - quantum theory, a description of matter at the atomic scale, and Einstein's theory of relativity, which describes the structure of the universe at much larger scales. A fusion of the two into a theory of quantum gravity would be a suitable contender for the title of "theory of everything". But Smolin's assertion that physics may be experiencing some form of crisis could come as a shock for those seduced by physicist Steven Weinberg's Dreams of a Final Theory into thinking that a grand synthesis is just around the corner.
The job of cosmology, according to Smolin, does not end with the creation of an all-encompassing mathematical formula that can be printed on a T-shirt - it has to come up with a "real explanation". His new book, The Life of the Cosmos - which gives an example of what a "real explanation" might look like - has been dubbed "the most important science book of 1997".
Cosmological natural selection, Smolin's big idea, makes a clean break from Newtonian tradition by conceding that events during the history of the universe may have shaped the very laws of physics. This strikes at the cornerstone of Newton's vision of a world governed by universal, unchanging laws. Originally bound, like other physicists, to the "Platonic notion that there is at the root of things some permanent, transcendent reality that is (their) task to discover", Smolin found this clean break a bitter pill to swallow. "It (the Platonic notion) was why I went into physics," he confesses.
The test-beds for any theory of quantum gravity are black holes, since neither quantum theory nor relativity can adequately explain them. At the centre of a black hole, where matter and light are sucked to a single point of infinite density, relativity theory would say that time "ends". Accordingly, the Big Bang is the moment when time "began", and this convergence of physical descriptions has not escaped the notice of cosmologists, Smolin among them.
Worried by the conceptual problem of a beginning or an end to time, he wondered whether our Big Bang might also be a black hole in another universe and that, instead of time ending or beginning, there might be a "bounce" thanks to some as yet unknown quantum phenomenon.
According to cosmological natural selection, "time branches like a tree, so that each black hole is a bud that leads to a new universe of moments". But the lethal blow to the Newtonian worldview is the liberation of the laws of physics: at each "bounce" Smolin suggests these laws could mutate. From this small change in the laws that govern matter, the mass of an electron in a fledgling universe might differ slightly from the mass of an electron in its parent universe. "It is obviously a pretty wild hypothesis," says Smolin, "but what has given me the courage to bring it forth is that colleagues I respect have taken the idea seriously and have helped me to test the idea."
The idea could help cosmologists out of a corner: their most promising attempts at a unified theory all run into the same problem. They cannot predict the values of the fundamental constants, such as the mass of the electron, its charge and the strength of gravitational attraction. Any value seems to do for each trial theory. That would not matter but that the existence of stars and galaxies apparently depends on these "magic numbers" having precisely the values they do. Alter them a fraction and the universe could be very different, and almost certainly inhospitable to life. This has been fodder for theologians, because it makes our existence seem improbable and, for the same reasons, it has made cosmologists uncomfortable.
Cosmological natural selection could help because it is a process through which the "right" numbers can be chosen. The values of the fundamental constants in any universe determine all its key features, including whether stars will appear, whether galaxies will form, and, most importantly, whether it will have lots of black holes, a few, or none at all. A universe that makes a million black holes will produce a million new universes out of each, and these baby universes, resembling their parent, will themselves produce around a million black holes, forming part of a "continually growing community of universes".
Universes with few black holes have few offspring, so eventually, sheer force of numbers would require that universes that produce lots of black holes - like our own - dominate. "It's a sign of being in this transitional state that people who work in fundamental physics and cosmology are willing to entertain ideas that seem at first sight pretty far out," says Smolin, but a crucial factor in the idea being taken seriously is what he calls its "testability". Thanks to cosmology's mathematical underpinning, what might otherwise sound like wild speculation can be turned into concrete astronomical predictions. "I'm able to argue that if a neutron star is found with a mass larger than three times the mass of the sun then, by a certain chain of argument, the theory is refuted," says Smolin, "and I wouldn't terribly much mind if that happened."
Such a willingness to court defeat is regarded by cosmologists as an essential quality, because of the particular danger in cosmology of imaginations drifting unreined by reality. Stephen Hawking, with his idea that baby universes open out of black holes into something called "imaginary time", would make Smolin appear conservative. Despite their apparent similarities, Hawking and Smolin occupy separate corners in cosmology. "I personally believe that time is fundamental, and that when we get down to the fundamental quantum level, there will still be a notion of time and a notion of causality," says Smolin.
But, whereas Hawking can imagine time away through mathematical artfulness, and so sidestep the issue of origins, Smolin has no such option. A persistent criticism of cosmological natural selection is that it does not answer the question of where universes ultimately come from. He appeals to history for his defence: "I think that it's a quite legitimate strategy in science to push back our questions. For example, natural selection itself pushes back the question of the origin of life. That question couldn't be solved in the 19th century, but that doesn't mean that natural selection wasn't an important idea." The origin of life is also a central interest of Smolin's. According to the Newtonian view, which is only concerned with particles and laws, life is simply an historical accident. "This point of view has often been opposed because it seems to cheapen life, to make our existence meaningless," says Smolin. "(But) it is not just a question of ethics, or what makes us feel comfortable - this view is no longer working as science." The beauty of cosmological natural selection, on the other hand, is that the emergence of life is as natural a consequence of our universe as the galaxies it contains. "Life on the surface of a planet like ours or life anywhere else in the universe is possible because it uses the flow of energy through the system from some hot region to some cold region to organise itself," explains Smolin.
The history of ideas has played a key role in the development of Smolin's thinking, and he likens the revolution now in motion in physics with the Copernican revolution. But his respect for history and philosophy does not extend to many modern-day historians and philosophers. Smolin believes postmodernists have missed the intellectual boat, and scientists and artists have taken the helm. "(One finds) a rather gloomy and pessimistic mood when one is in the domains of (literary) criticism and the humanities, but when one hangs out among scientists and artists and social theorists one feels a very optimistic mood."