We tend to think of the laws of nature as fixed. They came into existence along with the universe, and have been the same ever since. But once you start asking why the laws of the universe are what they are, their invariance also comes into question. Lee Smolin is the type of theoretical physicist who likes asking such “why” questions. His inquiries have led him to believe that the laws of the universe have evolved from earlier forms, along the lines of natural selection.  In this in depth interview he offers an account of how he came to this view of the evolving universe and explains why physics needs to change its view of time. 

Lee Smolin is a rare breed of theoretical physicist. Whereas most physicists see themselves in the business of discovering what the laws of the universe are, Lee Smolin goes a step further: he wants to know why the laws of the universe are what they are.

“I believe in an aspirational form of Leibniz’s Principle of Sufficient Reason. When seeking knowledge, we should act on the assumption that the principle of sufficient reason is true, otherwise we are likely to give up too soon.”

The Principle of Sufficient Reason being the idea that there is a reason for why things are the way they are and Leibniz being a 17^th century rationalist philosopher. Lee Smolin is not like other physicists in another way: he draws inspiration from many different fields, including philosophy.

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Smolin admits that it might be the case that at some point our explanations simply run out and there are no further “why” questions we can ask.

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It’s perhaps hard to appreciate how unconventional this way of thinking about physics is. Leibniz was a key figure of early modern rationalist philosophy that held necessity to be the key concept that would unlock the mysteries of the universe – things are the way they are because they had to be this way, and reason could explain why that was. Modern science on the other hand for the most part has given up on this idea that the world is governed by rational necessity. Instead, contingency rules: the way things are is the way things are, we can’t really know why. For many scientists the question doesn’t even make sense. Smolin admits that it might be the case that at some point our explanations simply run out and there are no further “why” questions we can ask.

“Of course this might be the case, and it might not be.  The only way to find out is to try to see how far we can go.”

And Smolin is prepared to go a lot further in his questioning than most. Pushing the boundaries of explanation has led him to put forward some extraordinary theories, including the idea that the laws of the universe are not invariable across space and time, but are evolving. When asked to give an account of how he arrived at this theory he offers a kind of intellectual autobiography, and why he sees the issue of time as crucial to how we think about laws of nature.

Smolin came of age during the era when the main puzzle of theoretical physics was how to make Einstein’s General Relativity consistent with Quantum Mechanics. Time according to General Relativity was seen as a relational property – not as something absolute or external to the universe, as Newton had thought. This means that time becomes secondary, as Smolin says – a merely relational property between events in the universe, not something fundamental. Quantum mechanics, on the other hand, still seemed to depend on an absolute framework of time that wasn’t relational. This was one the key contradictions at the heart of physics at the time Smolin was still a physics student and laws of nature were seen as invariant – as time-independent.

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Smolin wasn’t satisfied with having just a description of how particles interact – he also wanted to know why. Why is the neutron slightly heavier than the proton?

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The second big issue playing on Smolin’s mind when he was a graduate student at Harvard came from particle physics. The Standard Model had just started going, and it seemed to be an immensely powerful tool for explaining the interactions of fundamental particles. But Smolin wasn’t satisfied with having just a description - even if it was a very good description - of how particles interact – he also wanted to know why. Why is the neutron slightly heavier than the proton? And why is the mass of the electron 1800 times smaller than that of the neutron?

“These near coincidences are very important for how the world turned out to be.” Smolin adds.

There was a group of cosmologists at the time who were also asking this question of why the universe seemed to be so perfectly tuned to allow for matter to be formed – all these constants, including the Cosmological Constant, had just the right values to allow life to eventually develop. Was this mere accident? Or was there a reason for it? Cosmologists like Martin Rees of Cambridge developed the idea of the Anthropic Principle that postulated the existence of many different universes in which these constants all had different values, leading to completely different outcomes. Life was possible in our universe because we got lucky – in other universes not only is life not possible, there are no atoms to begin with.

Smolin admits “this is a pretty cool idea” but he doesn’t think it’s really a scientific theory since it doesn’t make any predictions. But the puzzle it tried to tackle was a real one, and Smolin had a better idea for how to solve it. He thought to himself, where else do we find systems that are fine tuned for the emergence of complexity? Biology was to him the obvious answer. “I’m pretty good at stealing ideas from other fields. Everybody has a trick, and that’s mine” he says jokingly.

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This seemingly paradoxical balance of the cosmos is not a mere accident - there was a process behind it, akin to natural selection, that gave rise to it.

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That’s how Smolin came up with the idea of applying the principles of evolutionary biology to the universe as a whole. In the same way that in biology Darwinian evolution was able to explain the existence of perfectly developed organisms, with organs that work just the right way to keep them alive and functioning, the idea that the universe as a whole has been undergoing a process of evolution can explain the existence of this fine tuning of cosmological constants. This seemingly paradoxical balance of the cosmos is not a mere accident -  there was a process behind it, akin to natural selection, that gave rise to it. It’s an idea that he was surprised to find the American pragmatist philosopher Charles Peirce had also hinted at in the early 20^th century.

Putting forward this theory of the dynamically evolving universe led to the other central idea in Smolin’s work: a reassessment of the centrality of time. 

Smolin is always talking about his collaborators - many of them unconventional thinkers and eccentric in their own way - and how they’ve contributed to his work. Roberto Mangabeira Unger is one of them, a professor at Harvard’s Law School, a Brazilian politician, and a philosopher. Smolin credits Mangabeira with forcing him to come to terms with the contradiction he was seemingly committed to. On the one hand Quantum Gravity that Smolin was working on saw laws of nature as fundamental, and time as secondary, as emergent.  But “applying natural selection to cosmology we get the opposite: time becomes fundamental, and laws of nature evolve”, are emergent. This led to a collaboration between the two thinkers, and the publication of their book The Singular Universe and the Reality of Time. Smollin ended up espousing the view that time is fundamental, not secondary as General Relativity would have it, and space an emergent property of it. This was a view that Fotini Markopoulou, another collaborator of Smolin’s, also arrived at independently – a view that most theoretical physicists, including Carlo Rovelli, oppose (although Smolin thinks Rovelli is coming around to that view in his recent publications).

Both these theories, that the universe and its laws are changing, and that time is a fundamental property of the universe, whereas space derivative, pose several questions, questions that Smolin sees as invitations for further elaboration and investigation, rather than as objections.

One of the questions I was curious to find out more about was how Smolin thought of the evolution of the universe. What is the mechanism here, exactly?

Smolin has three possible answers to this question, all of them hypotheses, as he stresses to me, given that they aren’t capable of making predictions: “I’m not Darwin!” he says.

The most prominent hypothesis is that the universe gives birth to other universes through black holes. This, in itself, was not a new idea. Theoretical physicists John Wheeler and Bryce DeWitt first put forward this hypothesis before, but Smolin tweaked it to fit his view of a universe that evolves, almost along the lines of natural selection. Whereas Wheeler and DeWitt thought the new universe produced each time has random values of the cosmological constant and other key parameters, Smolin took a more Darwinian approach, proposing that each universe embodies very small changes to those cosmological values, allowing for a cumulative change and fine tuning, until we arrive at the universe we have today.

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How can the universe “learn” anything, and how does the universe remember what has happened in the past, and use it as a precedent to decide what will happen in the future?

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The question I immediately raise is whether this picture of an evolving set of universes, in which the laws of nature are not fixed, but are ever changing, requires us to postulate a kind of meta-law, a law that would dictate the way that this evolution can take place. So are we not back to where we started, the cosmos being dictated by some fixed meta-laws? Smolin is not happy with this solution, “you can’t solve this by just accepting that there are fixed laws, they’re just meta-laws” he says. But he also doesn’t really have a definitive answer either. It’s a question he takes seriously, however, and has spent much of his book with Roberto Mangabeira Unger tackling this issue.

Smolin has two other hypotheses for how the universe might be changing. One he calls The Autodidactic Universe, the self-learning universe, the other The Principle of Precedence - borrowing a concept from jurisprudence when thinking about laws seems quite clever, and in line with Smolin’s “trick” of stealing ideas from other disciplines. They each come with their own conceptual challenges – how can the universe “learn” anything, and how does the universe remember what has happened in the past, and use it as a precedent to decide what will happen in the future? Thinking of the universe in these terms seems to bend our concepts to breaking point, although admittedly things like machine learning, a technology that is very much real, does the same. If machines can “learn” from a trial-and-error process, why not the universe as a whole?  In fact, Smolin has collaborated with Microsoft computer scientist Jaron Lanier, to model how the universe might be understood as a giant machine learning process.

The other major challenge to Smolin’s theory is directed at his view that time is more fundamental than space. How is that even possible, I asked him. If time is some measure of change, how can there be change without space? Where is the change taking place?

Here Smolin brings up another collaborator, Julian Barbour, who he acknowledges as his mentor when it comes to the philosophy of fundamental physics. In work they did together they showed that it is indeed possible to do dynamics, the study of evolving quantities, without space. In order to do that, Smolin tells me, you need to think of time as playing a causal role itself – as creating new events from past ones. If we think of time this way, all we have to do is look back in time “coming at you from your past” and the causes that have made you, to see change.

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“I don’t claim to have complete ideas, but I believe I have done enough to show that these are things worth thinking about. I haven’t built a new paradigm yet, but I’m having a lot of fun in the process.”

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These are fascinating ideas that really capture the imagination, which goes some way to explain why Smolin, a theoretical physicist who is mostly in the business of publishing highly technical papers, impenetrable to the uninitiated, has acquired something of a cult status beyond the world of academia.  But even though his theories are these beautiful mosaics of ideas from physics, philosophy, biology, computer science, the question is, do they ultimately offer us answers to the puzzles they set out to tackle?  Smolin offers a humble self-diagnosis that captures both the joy of research, but also the hope of an enduring legacy:

“I don’t claim to have complete ideas, but I believe I have done enough to show that these are things worth thinking about. I haven’t built a new paradigm yet, but I’m having a lot of fun in the process.”