Carlos Rovelli’s “Reality Is Not What It Seems”

C.P. Snow’s “Two Cultures”

Back in 1959, the influential British scholar C. P. Snow gave a lecture entitled The two cultures and the scientific revolution. In this discourse Snow warned of a widening divide between the scientific world on one hand and the humanities on the other: “This polarization is a sheer loss to us all.” Snow wrote,

A good many times I have been present at gatherings of people who, by the standards of the traditional culture, are thought highly educated and who have with considerable gusto been expressing their incredulity at the illiteracy of scientists. Once or twice I have been provoked and have asked the company how many of them could describe the Second Law of Thermodynamics. The response was cold: it was also negative. Yet I was asking something which is about the scientific equivalent of: “Have you read a work of Shakespeare’s?”

I now believe that if I had asked an even simpler question — such as, What do you mean by mass, or acceleration, which is the scientific equivalent of saying, “Can you read?” — not more than one in ten of the highly educated would have felt that I was speaking the same language. So the great edifice of modern physics goes up, and the majority of the cleverest people in the western world have about as much insight into it as their neolithic ancestors would have had.

So what can be done to bridge this unfortunate and destructive divide? One hopeful sign of progress is that more and more accomplished scientists and mathematicians are taking up the challenge to communicate the excitement of their field to the wider public.

Many of us remember Carl Sagan’s Cosmos TV series, which introduced modern science in general and planetary science in particular to a wide audience in a very appealing format, first broadcast on the U.S. Public Broadcasting Service in 1980. More recently, Neil DeGrasse Tyson narrated a new version of Cosmos, which has been similarly successful.

In the general arena of mathematics, physics, cosmology and astronomy, perhaps the most successful recent expositions are Brian Greene’s books The Elegant Universe and The Fabric of the Cosmos, which again were developed into a relatively successful TV series that reached millions. Others with a background in this general arena, who have written successfully for the larger public, include John Barrow, Paul Davies, Alan Guth, Lee Smolin, Leonard Susskind, Lisa Randall and Max Tegmark.

Carlos Rovelli’s “Reality Is Not What It Seems”

The latest entry in this genre is Carlos Rovelli’s Reality Is Not What It Seems: The Journey to Quantum Gravity. In this book, Rovelli attempts to lay the philosophical and historical foundations for recent research in physics in general, and loop quantum gravity in particular.

Rovelli starts by telling of the ancient Greek scholar Leucippus and his disciple Democritus, who was later described by the Roman scholar Seneca as “the most subtle of the Ancients.” Democritus, who lived about 450 BCE, was one of the first to argue that there had to be “atoms” that comprise all material things. Democritus observed that matter could not be continuous and infinitely divisible, because (as Aristotle later reported the argument) no matter how many of these presumably infinitely small pieces were woven together they would still have no extension.

With the development of modern chemistry in the 18th and 19th century, most scientists were convinced that atoms had to be real, but some still demurred, citing the lack of definitive evidence. In 1897, for example, Ernst Mach declared, “I do not believe that atoms exist!” The first definitive proof of the “atomic hypothesis” was provided by an obscure, rebellious 25-year-old working at the Swiss patent office, namely Albert Einstein. Einstein developed a theory to explain Brownian motion, and was able to calculate the size of atoms and molecules for the first time.

Rovelli then recounts how physicists fretted in the late 19th century over a nagging discrepancy between Newton’s laws of motion and the laws of electromagnetic fields, as discovered by Faraday and mathematized by Maxwell. Maxwell’s theory led to the derivation of the speed of electromagnetic waves, but with respect to what? Again it was Einstein, who in 1905 showed that by abandoning the notion of absolute time, the two theories could be brought into agreement (except for gravitation, which had to wait for his general theory of relativity in 1915).

In another reference to ancient philosophy and literature, Rovelli points out that in Dante, in his Inferno, appears to have comprehended the basic notion that the space around us is a 3-sphere, as deduced by Einstein.

Rovelli moves on to more modern physics, including the fundamentally discrete nature of all things, e.g., Einstein’s finding that light consists of discrete quanta, and the development of quantum mechanics in the 20th century by Niels Bohr, Werner Heisenberg, Paul Dirac and others. Rovelli then turns his attention to the lingering problem of how to reconcile the laws of quantum mechanics, which govern the very small with remarkable precision, with those of general relativity, which govern the large-scale structure of space-time.

Here Rovelli again hearkens back to Democritus and argues that the fabric of space-time must itself be granular, and in fact given by a networked grid — a “spin network.” These are the “atoms” of space and time, and in fact it follows that our perception of time flowing uniformly forward is but an illusion at the macro scale. Rovelli also points out how loop quantum gravity also suggests that the Big Bang might be a misnomer — our universe may have arisen in a “Big Bounce” from an earlier universe.

Rovelli finally addresses the question of empirical confirmation. He acknowledges that definitive tests of loop quantum gravity are still lacking, but he points out that supersymmetry, which is thought to be an underpinning of string theory (the other, better known theory of quantum gravity), has suffered severe setbacks, because not one of the hypothesized supersymmetric particles has appeared in the latest experiments at the Large Hadron Collider.

All of this is described in a very lucid manner — Rovelli and his translators clearly have a remarkable talent for this type of exposition. And their exposition is accompanied rather effectively with numerous graphics to illustrate the increasingly subtle concepts that are presented.

In spite of the maxim that every equation will halve book sales, Rovelli doesn’t demur, and inserts, here and there, the real equations of the theories he is discussing, as much for their beauty as anything else. These include the equations of general relativity and also the equations of loop quantum gravity, confirming that observation that if a theory can’t be summarized by equations that fit on a T-shirt, then something must be wrong.

Commentary on Rovelli’s book

Rovelli’s book was reviewed by physicist Lisa Randall in the New York Times. Randall complimented Rovelli on his attempt to bring recent research in physics to a broader audience, but she faulted him on certain details. For example, she noted that Rovelli had given the ratio of the size of universe (the largest dimension) to the Planck scale (the smallest dimension) as 10120, whereas the actual ratio is 1060. In a response, Rovelli acknowledges the error, although he points out that in loop quantum gravity, it is most natural to compare areas, where the ratio is 10120.

Secondly, Randall criticized Rovelli for presenting a theory (in the context of the Big Bounce) that “isn’t sufficiently well developed to do the necessary calculations to establish such a claim.” That is a valid criticism, but oddly this same general criticism could be leveled at Randall’s own recent book Dark Matter and the Dinosaurs.

Perhaps the most significant criticism is Randall’s observation that perhaps Rovelli has tried too hard to connect modern physics to the writings of the ancients: “Ideas about relativity or gravity in ancient times weren’t the same as Einstein’s theory.” The present blogger has to agree with this general assessment — it is easy to over-romanticize the past.


In spite of these flaws, Rovelli has written a marvelous book, definitely one to place on your stack (or your iPad or Kindle) for summer reading. The present blogger looks forward to additional works by this talented writer.

[This appeared on the Math Scholar blog.]

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