Risorse Bibliografiche

SMOLIN Lee, Time Reborn. From the Crisis in Physics to the Future of the Universe, Houghton Mifflin, Boston – New York 2013, pp. xxxi + 319.

fascicolo II, volume 23 (2014), pp. 361-364.

SMOLIN Lee, Time Reborn. From the Crisis in Physics to the Future of the Universe, Houghton Mifflin, Boston – New York 2013, pp. xxxi + 319.


Time Reborn is a must-read book. It shows how fragile our current physical understanding of nature is when confronted with deep philosophical issues. If only for that, the book is worth reading. But its author should be credited for a variety of reasons. First of all, for his emphasis on the reality of time. Time has always puzzled philosophers and Smolin succeeds in getting across the same message for physicists and cosmologists: «[O]n every scale, from an atom’s quantum state to the cosmos, and at every level of complexity, from a photon made in the early universe and winging its way toward us to human personalities and societies, the key is time and the future is open» (p. 271).

The book rightly points out the main drawbacks of the current most outstanding physical theories when dealing with time. For the reader interested in a quick summary, comparisons in pp. 248-249 are extremely useful for distinguishing among physical theories based on the so-called Newtonian paradigm and would-be physical theories for which time is not an emergent property of nature but a primary reality. However, Smolin’s criticism of the Newtonian paradigm runs throughout the book because of the latter’s sharp distinction between initial conditions and timeless dynamical law.

Relativity turns out to be affected by this shortcoming even more acutely. For relativity theory, the universe «is timeless in two senses: There is nothing corresponding to the experience of the present moment, and the deepest description is of the whole history of causal relations at once» (p. 58). Since any talk of motion in time could be translated into mathematical theorems about a timeless geometry, what is real is all the events of the universe taken together. The reality of the world consists in its history taken as one (cf. pp. 62-63). Even more sophisticated proposals for a quantum gravity theory, like loop quantum theory, fit into the Newtonian paradigm (cf. p. 180). In contrast, Smolin’s search for a scientific understanding of nature makes him claim that «space may be an illusion, but time must be real» (p. 192).

These critiques are not unmotivated. The author is well aware of the scientific method’s limits when it is applied to the whole of the universe (cf. p. 83). This is the fallacy of extending the “physics-in-a-box” method to a no-box situation. Physics always make an implicit division of reality into a subsystem, whose dynamic is to be studied, and an environment, whose physical influence is encapsulated in simplified boundary conditions. However, it is extremely doubtful that such a priori divisions can work for the whole universe’s dynamics.

Quite remarkably, Smolin closely adheres to epistemic criteria for picking out promising theories that extend beyond the Big Bang. His own theory of cosmological natural selection—for which black holes are fathers of new universes and black-hole abundance in a universe correlates well with its specific biofriendliness—does better than any multiverse theory. The latter merely provides a selection principle, while the former accounts for our world as a typical universe (cf. p. 131). Moreover, multiverse theories fall into the statistical fallacy of taking advantage of the freedom to arbitrarily choose a probability distribution that describes unobservable entities and thus cannot be checked independently (cf. p. 137). But in «a scientific argument, the universe cannot be presumed to be a single case of a more general class, because no assertion as to the characteristics of that class are testable» (p. 100).

Since we do not «observe any other universes, it is impossible to know which constants vary over the hypothetical multiverse» (p. 136). By contrast, «hypotheses based on the idea that the laws of nature evolve over time are more vulnerable to falsification than are timeless cosmological scenarios» (p. 139). In those cases, the choice of laws made in the most recent Big Bang would be explained in terms of events in its causal past; depicting a scenario that might well be checked experimentally (cf. p. 120). Only «in the case of sequential universes are there real predictions for doable experiments» (p. 238). Because of this, according to the author, the «hypothesis of the reality of time leads to a more scientific cosmology» (p. 241). However, no explanation is given of how fundamental physical constants change inside black holes in order to spawn new worlds. Nor does Smolin explain how the black hole curvature singularities—essentially different in nature from Big-Bang singularities—could geometrically match with a smooth, biofriendly universe.

Among the merits of Time Reborn, one must consider its way of dealing with thermodynamics and the special role assigned to gravity. The author acknowledges that the «initial conditions of our universe appear to have been finely tuned to produce a universe that is asymmetric in time» (p. 206). After 13.7 billion years, our universe is not in equilibrium and the solution that describes it is time-asymmetric (cf. p. 203). In other words, we «know that our universe was not produced by random choice» (p. 209) because mere statistics is not an explanation of the second law of thermodynamics. Smolin refers to the so-called «Boltzmann brain paradox» (p. 212) showing that evolution is statistically more expensive than the random emergence of brains, supposing that the former were a sheer fluctuation of a universe in equilibrium. But the allusion to the “infinite Boltzmannian tragedy” is less clear: if space is infinite, anything that might happen is happening an infinite number of times right now (cf. pp. 228-229), which need not be the case in a non-ergodic universe.

On the other hand, there is the anti-thermodynamic nature of gravity, which makes the emergence of structures in the world possible. The symmetry-breaking mechanisms operating at the very beginning of the universe allow for the appropriate onset of gravity and the conglomeration of matter into stars and galaxies, contrasting with the perfect symmetry of equilibrium achieved by heat-death—a “boring” universe. For Smolin, there is a three-fold explanation for our “interesting” universe: (i) the principle of driven self-organization; (ii) the fine tuning of fundamental laws; and (iii) the anti-thermodynamic nature of gravity (cf. p. 226). Thus, his deep stance becomes crystal-clear: «Within a metaphysical framework in which time and the flow of moments from the past to the future are real, it is perfectly natural to have time-asymmetric laws governing a time-asymmetric universe» (p. 209).

From the point of view of physics, Time Reborn occasionally ventures bizarre statements when attempting to specify how laws evolve with time. Smolin suggests a “principle of precedence” that allows for a small degree of freedom in the evolution of novel states and patterns their repeated occurrences (cf. p. 146). He seems to ignore the standard quantum mechanics interpretation when he claims that quantum mechanics is time-reversible (cf. p. 52) and he favors Julian Barbour’s theory of the universe as a “heap of frozen moments” (cf. pp. 85-88). Nevertheless, I will deal only with philosophical criticisms in the remainder of this review.

Smolin’s thought is marked by a univocal concept of reason and logos. In his own words, «logic is not the mirror of causality» (p. 246). Fair enough; many philosophers would agree with that claim. However, he treats the difficult relationship between logic and physical causality in a dialectic fashion, according to his identification of logic and reason with purely scientific reason. This opposition between logical thought and physical time ultimately leads him to assume that if one accepts a timeless absolute, time becomes an illusion. One might wonder why mathematics and time, or the absolute and time, cannot be both real. Ontological pluralism is not an option for Smolin; the legitimate epistemological monism of scientific method turns into ontological monism in his case. Some corollaries of this position, together with his preferences for a flowing time, are that «time cannot have a beginning» (p. 71) and that to «learn to live with our planet, we have to rid ourselves of the vestiges of this old yearning for elevation from it» (p. 257).

However, over the course of the book, philosophical problems emerge from Smolin’s stance—problems that he himself acknowledges. One of the main messages of Time Reborn could be summarized as follows: «Facts about the world need to be explained, and a fact most in need of explanation is why particular laws are observed to hold in our universe» (p. 119), and «to make laws explicable, we must consider them as much a part of the world as the particles they act on» (p. 121). But, as Smolin is well aware, we cannot evade the so-called “meta-laws dilemma” (cf. pp. 243-245): the existence of a timeless law describing how laws evolve in sequential or parallel universes. Even if quantum mechanics is in the end our best theory for the physical universe—a theory «in which you can make probabilistic predictions of how systems behave, but in which those systems have as much freedom from determinism as any physical system described by probabilities can have» (p. 150)—there remains a core of timeless probabilistic laws.

Finally, it is necessary to consider some of Smolin’s metaphysical views. Within the author’s line of reasoning the possibility of an Absolute Creator of a time-developing creation is unthinkable: «The universe simply is—or better yet, happens (…). Why it is, why there is something rather than nothing, is probably not a question that has an answer (…). The universe itself has no relation to anything outside it. The question of why it exists rather than not is beyond the scope of the principle of sufficient reason» (p. 246). «Why is there something rather than nothing? I can’t imagine anything that would serve as an answer to this question, let alone an answer supported by evidence. Even religion fails here, for if the answer is ‘God’, there was something—God, that is—to begin with. Or, if time has no beginning, do all causes recede into the infinite past? These are real questions, but if they have answers, those are likely to forever remain outside science. Then there are questions that science cannot answer now but that are so closely meaningful that sometime in the future, it is hoped, science will evolve language, concepts, and experimental techniques to address them» (pp. 265-266). He considers himself committed to the ethics of science, which prevents him from taking another route to reliable knowledge (cf. p. 266). Does this mean that experimental methods of physical science are the only worthy means of inquiry? If so, his position turns out to be without foundations.

At least in Time Reborn’s final paragraphs, Smolin somewhat distances himself from the view of scientism and acknowledges the pertinence of the metaphysical questions: «Some advocates of science insist that questions science cannot answer are meaningless, but I find this unconvincing—and unattractively narrow-minded» (p. 267). To sum up, in a sort of act of faith, he holds to a would-be scientific methodology that will eventually have full potential to answer these questions. But need that be so? Smolin’s honesty regarding the current limits of scientific knowledge is reflected in his comments on the problem of qualia and consciousness, which «seems unanswerable by science because it’s an aspect of the world that is not encompassed when we describe all the physical interactions among particles. It’s in the domain of questions about what the world really is, not how it can be modeled or represented» (p. 269). If only for such moments of candor, the reader is encouraged to join Smolin in his somewhat unbalanced but nevertheless authentic search for the truth.