Lee Smolin was a founding faculty member of the Perimeter Institute in Waterloo, Canada. Smolin is a theoretical physicist and cosmologist who is best known as one of the contributors to the theory of loop quantum gravity, the major alternative to string theory, which Smolin criticized in his 2006 book The Trouble with Physics.

Smolin collaborated on the theory of loop quantum gravity (LQG) with Carlo Rovelli and others. LQG is an approach to the unification of quantum mechanics with general relativity which utilizes a reformulation of general relativity in the language of gauge field theories. LQG uses techniques from particle physics, particularly the expression of fields in terms of the dynamics of loops. With Rovelli he discovered the discreteness of areas and volumes and found their natural expression in terms of a discrete description of quantum geometry in terms of spin networks. In recent years he has focused on connecting LQG to phenomenology by developing implications for experimental tests of spacetime symmetries as well as investigating ways elementary particles and their interactions could emerge from spacetime geometry.

In his 2019 book, Einstein's Unfinished Revolution, Smolin says he accepts Einstein's idea that quantum mechanics is "incomplete," that it can be completed by adding "hidden variables," and that this would restore a "realistic" picture of nature.

Einstein and other realists believe that quantum mechanics gives us an incomplete description of nature, which is missing features necessary for a full understanding of the world. Einstein sometimes imagined that there were “hidden variables’’ which would complete the description of the world given by quantum theory. He believed that the full description, including those missing features, would be consistent with realism.

Thus, if you are a realist and a physicist, there is one overriding imperative, which is to go beyond quantum mechanics to discover those missing features and use that knowledge to construct a true theory of the atoms. This was Einstein’s unfinished mission, and it is mine.

Einstein's Unfinished Revolution, The Secret for What Lies Beyond the Quantum, p.xxi

Smolin describes his opponents, the anti-realists...

Some anti-realists believe that the properties we ascribe to atoms and elementary particles are not inherent in those objects, but are created only bv our interactions with them, and exist only at the time when we measure them. We can call these radical anti-realists. The most influential of these was Niels Bohr. He was the first to apply quantum theory to the atom, after which he became the leader and mentor to the next generation of quantum revolutionaries. His radical anti-realism colored much of how quantum theory came to be understood.

Another group of anti-realists believes that science, as a whole, does not deal in or talk about what is real in nature, but rather only ever talks about our knowledge of the world. In their view, the properties physics ascribes to an atom are not about that atom; they are instead only about the knowledge we have of the atom. These scientists can be called quantum epistemologists.

And then there are the operationalists, a group of anti-realists who are agnostic about whether there is a fundamental reality independent of us or not. Quantum mechanics, they argue, is not in any case about reality; it is rather a set of procedures for interrogating atoms. It is not about the atoms themselves; it is about what happens when atoms come into contact with the big devices we use to measure them. Heisenberg, the best of Bohr’s protégés, who invented the equations of quantum mechanics, was, at least partly, an operationalist.

In contrast to the disputes between radical anti-realists, quantum epistemologists, and operationalists, all realists share a similar perspective—we agree about the answer to both questions I posed above. But we differ on how we answer a third question: Does the natural world consist mainly of the kinds of objects that we see when we look around ourselves, and the things that constitute them? In other words, is what we see when we look around typical of the universe as a whole?

Those of us who say yes to this question can call ourselves simple or naive realists. I should alert the reader that I use the adjective “naive” to mean strong, fresh, uncomplicated. For me, a view is naive if it is not in need of sophisticated arguments or convoluted justifications. I would argue that a naive realist is, whenever possible, to be preferred.

Einstein's Unfinished Revolution, p.

Smolin's hypothesis of cosmological natural selection, also called the fecund universes theory, suggests that a process analogous to biological natural selection applies at the grandest of scales. Smolin published the idea in 1992 and summarized it in his 1997 book aimed at a lay audience called The Life of the Cosmos.

In his 1992 article "Did the universe evolve?", he wrote...

A mechanism for natural selection in cosmology

What I would like to propose is a theory of the evolution of the entire universe, including the parameters that govern its basic physics, via a mechanism of natural selection. Now, as in biology, an explanation by means of natural selection of the occurrence of a particular property must have two components: a random component, by which the parameters that determine this property change randomly, but slowly, over many, largely similar, systems and a selective component by which those systems with a particular property are, after some time, more likely to occur. As any physics in which the parameters of the standard model change must be new physics, the random mechanism proposed here is speculative. But the selective mechanism will be based on known physics. In fact the selective mechanism will simply be gravitational collapse. The mechanism is contained in the following two postulates concerning the physics near spacetime singularities.

Each finai singuiariy is fuiiowed by an initial singularity, which evolves into a universe which is spatially closed. An alternative hypothesis, which is equivalent as far as its consequences for the subject of this paper, is that instead of an ending in a final singularity, the interior of a black hole tunnels into a new spatially compact universe. We may note that this hypothesis has been advocated as a resolution for the problem of information loss in black hole evaporation and has also been discussed recently in connection with the baby universe scenario.

"Did the universe evolve?", Classical and Quantum Gravity (1992) v.9 pp.173-191

In The Life of the Cosmos, Smolin writes...

We have thus abstracted a formal representation of natural selection that applies equally well to both biology and to our cosmological hypothesis. Any conclusion that can be deduced from it then applies to both domains. Biologists have been using the picture of a fitness landscape since the 1930s. One can find it described in the writings of evolutionary theorists with views as diverse as those of Richard Dawkins and Stuart Kauffman. Biologists have made many studies of the behavior of populations in such landscapes, whose results confirm the conclusions I have drawn here.

It must also be stressed that at this formal level, concepts like “survival of the fittest” or “competition for resources” play no role. What matters is only that rate of reproduction varies strongly as we vary the possible genes. What is responsible for that variation, and what goes into the differential survival rates, is not relevant for how the basic mechanisms of natural selection work. It is, by the way, for this reason that there can be controversy among evolutionary theorists without there being any challenge to the basic theory of natural selection. What is being argued about is what the important determinants of survival rates are, not how or whether natural selection functions in nature.

The Life of the Cosmos, p.104

Of course, the principle of natural selection will be more difficult to apply in cosmology than it is in biology, as we have access to only one member of the collection. In biology we may study properties of the distribution of genes in a population. This may lead to conclusions about how evolution proceeded, such as the classifications of species by genetic distance or the discovery that we are all descendants of a single Eve. It is hard to see how cosmological analogs of these may be extracted from observations made only on one universe. For example, it is difficult to see how we will be able to tell whether there was a first universe, as I assumed earlier. But this will not prevent us from drawing some testable conclusions from the theory.

Thus, if this theory is right, the universe shares certain features with biological systems. In both cases there is a large collection of distinguishable individuals, the properties of each of which are specified by a set of parameters. In both cases, the configurations that would be realized for most values of these parameters are very uninteresting. In both cases one has the development of structures that are stable over time scales that are very long compared to the fundamental time scales of the elementary dynamical processes. In both cases what needs to be explained is why the parameters that are actually realized fall into these small sets that give us an interesting, highly structured world. And, if the theory I have proposed is right, the explanation in both cases is found in the statistics behind the principles of natural selection.

This is certainly right in biology, how likely is it that it applies as well to cosmology? In the following chapters we will examine this question, but for now I would like to emphasize some rather general reasons for taking it seriously. The key point, it seems to me, is how seriously we should take the observation that our universe is very highly structured, compared to universes with most other values of the parameters. Should we take this as some kind of cosmic coincidence, or should we see it as something that needs to be explained?

I would argue that there are not many options, if we restrict ourselves to an explanation that can be subject to experimental test and that stays within the usual framework of causal explanation. To quote Richard Dawkins, in The Blind Watchmaker, “The theory of evolution by cumulative natural selection is the only theory we know of that is, in principle, capable of explaining the existence of organized complexity. Even if the evidence did not favor it, it would still be the best theory available.”

The proposal I’ve made here may not hold up to test. But, once we begin to seek a scientific explanation for the values of the parameters that does not ignore the fact that the actual values produce a universe much more structured and complex than typical values, it may be difficult to ignore the possibility that cosmology must incorporate some mechanism analogous to natural selection.

The Life of the Cosmos, pp.105-108

Smolin describes the role of black holes as the species that undergoes variation and natural selection,

The basic prediction made by the theory is that the parameters in the laws of elementary particle physics are close to a value that maximizes the numbers of black holes made in our universe. It may seem at first sight that it is not possible to test this prediction. We do not have available a laboratory full of universes whose parameters could be set by tuning dials. But this is not the only way the theory might be tested. Even if we do not have access to these other universes, we ought to be able to deduce, from the physics and astronomy that we know, what the effect of a small change in the parameters would be. If there are cases in which we can do this well enough to be able to deduce whether the result would be a world with more or less black holes than our own universe, the prediction of the theory is testable.

In fact, there turn out to be many cases in which we can deduce that a change in the parameters would have a strong effect on the processes by which black holes are made. Given that there are at least twenty parameters in elementary particle physics and cosmology, this means that if the theory is wrong, it should be easy to refute it. As each parameter can be either increased of decreased, this gives us at least forty chances to contradict the theory. If the theory is wrong, we have no reason to expect that there is a relationship between the parameters and the numbers of black holes. It is then likely that as many changes should lead to decreases as lead to increases. On the other hand, were all forty changes to lead to decreases in the numbers of black holes, there would be little choice but to take the theory seriously, for the chances of this happening if the values of the parameters and the numbers of black holes have no relation to each other, is about one chance in 240, which is a huge number.

The Life of the Cosmos, p.108

Smolin concludes his The Life of the Cosmos with some very deep thoughts about different philosophers...

The Italian philosophers have what I think is an interesting way to refer to the transition taking place in the twentieth century in philosophy. They refer to what they call strong theory and weak theory. Strong theory is what philosophers aspired to do before this century, which was to discover by rational reflection and argument the absolute and complete truth about existence and elaborate these truths into complete philosophical systems. Weak theory is what philosophers have been doing since Wittgenstein and Gödel taught us the impossibility of doing this.

I would like to describe the same thing in different terms, borrowed from Milan Kundera. I would like to contrast the heaviness of the old and failed attempts at absolute knowledge with the lightness of the type of philosophy we are now aspiring to develop. Nietzsche also talked about heaviness, the heaviness of life yoked to the eternal return, weighed down by the impossibility of novelty. Nietzsche’s darkness and heaviness were exactly reflections of the weight of the heat death of the universe, carrying with it its implication that life has no permanent place in this world, so that any joy—indeed any change—was at best transient. Furthermore, Nietzsche was right to worry about the impossibility of novelty, because on the physics of his time it was indeed impossible to imagine how it might occur.

Even more than this, the old search for the absolute is heavy and it has weighed us down for long enough. It implies that there is a stopping point, a final destination; it reeks, really, of the Aristotelian belief in the meaningfulness of being at rest, of Newton’s absolute space, of hierarchy, in knowledge as well as in society, of stasis.

We have also had enough of the weight of utopianism, which comes of the idea that it is possible to arrive at a description of the ideal society by pure thought, indeed by the thought of one or a few solitary individuals. And, we have had enough of the weight of violence, and its justification in terms of any and all systems by which people can be made to believe in their special access to absolute knowledge.

Against this I would like to set the lightness of the new search for knowledge, which is based in the understanding that the world is a network of relations, that what was once thought to be absolute is always subject to evolution and renegotiation, that the complete truth about the world is not graspable as any single point of view, but only resides in the totality of several or many distinct views. We understand now that there is no meaning to being at rest, and hence no sense for stasis; this new understanding of knowledge might be said to be imbued with the freedom of the principle of inertia and grounded not in space but only in relations. And these develop not in absolute time but only in succession, in progression. Finally, this new view of the universe we aspire to will include a cosmology in which life has a proper and meaningful place in the world. That is, in the end the image I want to leave is that life is light, both because what we are is matter energized by the passage of photons through the biosphere and because what is essential in life is without weight, but only pattern, structure, information. And because the logic of life is continual change, continual motion, continual evolution.

Finally, the new view of the universe is light, in all its senses, because what Darwin has given us, and what we may aspire to generalize to the cosmos as a whole, is a way of thinking about the world which is scientific and mechanistic, but in which the occurrence of novelty—indeed, the perpetual birth of novelty—can be understood.

The old image of the Newtonian universe was as a clock: heavy, insistent, static; in this metaphor one feels both the iron hold of determinism and, behind it, the threat of the clock running down. Further, this was always a religious image as a clock requires a clockmaker, who constructed it and set it in motion. Against this, I would like to propose a new metaphor for the universe, also based on something constructed by human beings.

For reasons that I thought were quite irrelevant to its content I was drawn to finish this book here, in the greatest city of the planet, my first home. A few weeks ago I took a walk around, looking for a metaphor with which to end this book, a metaphor of a universe constructed, not by a clockmaker standing outside of it but by its elements in a process of evolution, of perhaps negotiation. All of a sudden I realized what I am doing here for, in its endless diversity and variety, what I love about the city is exactly the way it mirrors the image of the cosmos I have been struggling to bring into focus. The city is the model; it has been all around me, all the time.

Thus the metaphor of the universe we are trying now to imagine, which I would like to set against the picture of the universe as a clock, is an image of the universe as a city, as an endless negotiation, an endless construction of the new out of the old. No one made the city, there is no city-maker, as there is a clock-maker. If a city can make itself, without a maker, why can the same not be true of the universe?

Further, a city is a place where novelty may emerge without violence, where we might imagine a continual process of improvement without revolution, and in which we need respect nothing higher than ourselves, but are continually confronted with each other as the makers of our shared world. We all made it or no one did, we are of it, and to be of it and to be one of its makers is the same thing.

So there never was a God, no pilot who made the world by imposing order on chaos and who remains outside, watching and proscribing. And Nietzsche now also is dead. The eternal return, the eternal heat death, are no longer threats, they will never come, nor will heaven. The world will always be here, and it will always be different, more varied, more interesting, more alive, but still always the world in all its complexity and incompleteness. There is nothing behind it, no absolute or platonic world to transcend to. All there is of Nature is what is around us. All there is of Being is relations among real, sensible things. All we have of natural law is a world that has made itself. All we may expect of human law is what we can negotiate among ourselves, and what we take as our responsibility. All we may gain of knowledge must be drawn from what we can see with our own eyes and what others tell us they have seen with their eyes. All we may expect of justice is compassion. All we may look up to as judges are each other. All that is possible of utopia is what we make with our own hands. Pray let it be enough.

The Life of the Cosmos, pp. 297-300

In Smolin's theory a collapsing black hole causes the emergence of a new universe on the "other side", whose fundamental constant parameters (masses of elementary particles, Planck constant, elementary charge, and so forth) may differ slightly from those of the universe where the black hole collapsed. Each universe thus gives rise to as many new universes as it has black holes. The theory contains the evolutionary ideas of "reproduction" and "mutation" of universes, and so is formally analogous to models of population biology.

Alternatively, black holes play a role in cosmological natural selection by reshuffling only some matter affecting the distribution of elementary quark universes. The resulting population of universes can be represented as a distribution on a "fitness landscape" of parameters where the height of the landscape is proportional to the numbers of black holes that a universe with those parameters will have. Applying reasoning borrowed from the study of fitness landscapes in population biology, one can conclude that the population is dominated by universes whose parameters drive the production of black holes to a local peak in the landscape. This was the first use of the notion of a landscape of parameters in physics.

Leonard Susskind, who later promoted a similar string theory landscape, argued that, since Smolin's theory relies on information transfer from the parent universe to the baby universe through a black hole, it ultimately makes no sense as a theory of cosmological natural selection.

The idea that information transfer from the parent universe into the baby universe through a black hole is not conceivable, he says. Information that enters a black hole is irretrievably lost.

It is true that some thinkers like Stephen Hawking initially argued that no information that goes into a black hole can be lost, but later Hawking reversed his position. The current view is that no information can enter and later leave a back hole intact.

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