Pedro Ferreira ponders a vision of the Universe in which time is paramount.
Time Reborn: From the Crisis in Physics to the Future of the Universe
- Lee Smolin
Theoretical physicist Lee Smolin's recent books have been about crises in physics so catastrophic that physicists need to completely rethink their methods. In his 2006 book, The Trouble with Physics (Houghton Mifflin), he stated controversially that a cabal of researchers working on what he thought was a moribund theory of fundamental physics — string theory — was preventing a new generation of clever young thinkers from working on other, rival theories. Through his brilliant writing and articulate arguments, readers took him seriously. One string theorist told me that he struggled to convince non-physicists that he wasn't a charlatan after the publication of Smolin's book.
Now, in Time Reborn, Smolin attempts to chip away at basic theories of modern physics. He makes the case that by doing away with time, existing theories are missing a trick. He uses the orbits of planets in the Solar System as an example: each orbit is an ellipse existing in three dimensions. A planet will lie, at some moment, on a point along that track. But its motion can be described without knowing what happens at that particular moment, or at any other. Newtonian physics is essentially timeless.
According to Smolin, our picture of a timeless Universe stems from the assumption that all modern physics — quantum as well as classical — is predictive. How a system evolves is entirely encoded in the starting set of 'initial conditions' and their transformation according to the laws of physics. Evolution in time is secondary, a by-product of the theory. This bothers Smolin. A timeless view of reality is, he says repeatedly, incomplete (where do the initial conditions or laws come from?) and, simply, “wrong”. He believes that a better description of time lies at the heart of some of the big questions, such as the marriage of quantum physics and general relativity.
Smolin sketches an alternative path for modern physics. Inspired by the ideas of Brazilian philosopher and political theorist, Roberto Mangabeira Unger, who argues that social structures emerge without an underlying natural order or guiding principle, Smolin develops some of the ideas behind his first book, The Life of the Cosmos (Oxford University Press, 1997). In it, he argued that the Universe evolved through natural selection, mediated by the birth and death of black holes, to give us the physical laws and properties we measure today.
In his latest vision, time reigns supreme and is the backbone from which everything else emerges. Each state of the Universe pops up somewhere in time, from what the Universe is made of to what it does. A prime example is space, which — echoing some of the ideas put forward by different schools of quantum gravity — emerges not as a fundamental entity, but as a tapestry of connections between events happening over time. More importantly for Smolin, none of the laws or principles that we have discovered over the centuries constitute the bedrock of physics, nor are any perennial. On the contrary, they emerge in a somewhat unpredictable way from what is going on at each time. In this way, he says, his embryonic theory satisfies a “principle of explanatory closure” — there is no need to invoke any external laws or initial conditions.
It is a tall order, and if Smolin's theory is to work, then all the great experimental discoveries in physics — from elliptical planetary orbits to the Higgs boson — need to be incorporated. Hallowed theories such as quantum physics and relativity must be dismantled and some radically new way of explaining how the Universe evolves must come into play. Smolin shies away from actually telling us what that new way is, because he doesn't seem to know himself. All he can do is to explain how different his theory must be from everything we have done before.
To explain why anything can be predicted at all in such a lawless Universe, Smolin invokes reproducibility: if a physical process has happened in a certain way before, it will happen in the same way again. We can predict what will happen if we have some familiarity. But, Smolin notes, there will be situations that we have never seen before, in which it will be impossible to predict the outcome.
Writing a book is a well-worn way of presenting a provocative theory that is still in its infancy. Smolin, a respected physicist with a track record of best-sellers, has a privileged platform for promoting his ideas, similar to Arthur Eddington, Erwin Schrödinger or Fred Hoyle before him. Books can, however, feel reckless without the filter of the (albeit flawed) peer-review process.
Yet I enjoyed Time Reborn. Smolin is an excellent writer, a creative thinker and is ecumenical in the way he covers so many different branches of thought. Even as I mentally argued with this book, I kept on ploughing through to see how Smolin dealt with the objections. I would love to sit down with him over a drink and debate the ins and outs of his theory. And that is how this book should be read: as an account that makes you ask questions.
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Ferreira, P. Physics: Clockwork cosmos. Nature 496, 430–431 (2013). https://doi.org/10.1038/496430a