Book Review: Reality Is Not What It Seems: The Journey To Quantum Gravity by Carlo Rovelli

In 2014, theoretical physicist Carlo Rovelli wrote a popular science book called Reality Is Not What It Seems: The Journey To Quantum Gravity in his native tongue, Italian. In the same year he wrote a much shorter book — a pamphlet, really — called Seven Brief Lessons on Physics. The shorter book was the first to be published in English, beating its older sibling by a year. In that time span, Seven Brief Lessons on Physics became an international bestseller and today remains the author’s best known book.

I find this to be a shame because Seven Brief Lessons on Physics is a distillation of its predecessor, and it is beyond me why anyone would wish to distill Reality Is Not What It Seems. I am positively enamored with what Rovelli has done in this book.

I expected Rovelli to share interesting stories about scientific discoveries and dazzling explanations of quantum mechanics. These are indeed the general makeup of the book, but there are many unexpected elements as well, and it is to these delightful unexpected elements that I dedicate this review.

The first surprise that I’ll discuss is Rovelli’s tone, which carries less ego than I have come to expect from popular science authors. From there I’ll give a brief description of the book itself as imagined by its author.

Next I will spend some time unpacking the first chapter of the book, which tells how science got its start in ancient Greece. I will use this a starting point to discuss the two major unexpected elements of this book. First, that Rovelli is a kindred spirit of the Romantic poets. Second, that he tells the history of science from a unifying perspective, by which I mean he highlights commonalities wherever possible — across theories, scientists, and ways of thinking.

Finally, I aim to show that while Rovelli’s humble tone, Romantic ideals, and unifying perspective are initially surprising, they are a natural fit for his chosen topic.

With these ideas explained, let’s turn to the text.

From the onset, Rovelli’s tone is grounded and self-aware:

We are obsessed with ourselves. We study our history, our psychology, our philosophy, our gods. Much of our knowledge revolves around ourselves, as if we were the most important thing in the universe. I think I like physics because it opens a window through which we can see further. It gives me the sense of fresh air entering the house.

There is a lot of ego in science and a lot of ego in writing, but there is very little ego in this book. Rovelli is a co-founder of the theory of loop quantum gravity, the primary alternative to string theory. As an acclaimed scientist he may be expected to ham things up a bit in his book, especially the chapters about his own research, but he does not. He is passionate and opinionated but not egotistical. Fresh air indeed.

What is the book actually about? Rovelli does a nice job of summarizing it so I’ll defer to him:

This book gives an account of the current state of the search for our new image of the world, as I understand it today. It is the reply I would give to a colleague and friend asking me, “So, what do you think is the true nature of things?” as we walk along the shore on a long midsummer’s evening.

This is how Rovelli writes: simply but elegantly. Our so-called walk along the shore begins near an actual shore: the eastern shore of the Aegean Sea, in the ancient Greek city of Miletus. A well trafficked hub of the Mediterranean, Miletus was a melting pot of ideas. In the fifth century BCE it played host to an “immense revolution in thought” begun by Thales, Anaximander, and Hacataeus:

The Milesians understand that by shrewdly using observation and reason, rather than searching for answers in fantasy, ancient myths, or religion — and above all by using critical thought in a discriminating way — it is possible to repeatedly correct our worldview and to discover new aspects of reality that are hidden to the common view. It is possible to discover the new.

What new things did the Milesians discover? They discovered that “Earth floats in the sky and the sky continues beneath Earth”; “that animals and plants evolve and adapt to changes in the environment, and that man must have evolved from other animals”; and that “the entire universe is made up of a boundless space in which innumerable atoms run.”

Rovelli explains that it was the Milesians’ novel way of thinking, more than the the ideas that they came up with, that marked a breakthrough in man’s ability to understand the world. In this way of thinking, “the disciple is no longer obliged to respect and share the ideas of the master but is free to build on those ideas without being afraid to discard or criticize the part that can be improved.” Rovelli calls this “the dawn of a new era.”

While Rovelli lauds the brilliance of individual thinkers, he underscores that the Milesians’ greatest accomplishment was learning to think together. In doing so they laid the groundwork for scientific thought and simultaneously paved the way for modern government. “Through discussion, it is possible to reach the best decisions for the community,” Rovelli writes; “through discussion, it is possible to understand the world.” The moral of story is that people progress when they work together. Rovelli’s unifying perspective stems from this very moral: if scientific accomplishments are made when people work as a collective, then credit for the accomplishments should be paid to the collective and not to the individual.

By Rovelli’s account, fifth-century Miletus was a special place because of the unity that emerged there. People learned to think together without thinking the same, and this enlightenment gave way to other forms of unity. Circa 450 BCE a man named Leucippus left Miletus and founded his own school in Greece where he took up a disciple named Democritus. Democritus would to come to offer a particularly inspired vision of the unity inherent in all things, which Rovelli summarizes as follows:

There is no finality, no purpose, in this endless dance of atoms. We, just like the rest of the natural world, are one of the many products of this infinite dance — the product, that is, of an accidental combination. Nature continues to experiment with forms and structures; and we, like the animals, are the products of a selection that is random and accidental, over the course of eons of time.

Rovelli harbors a certain fondness for Democritus and the other ancient Greeks for their ability to live naturally — that is, to view themselves as a part of nature. This is where Rovelli’s perspective turns Romantic. In the eighteenth century, an artistic and intellectual movement known as Romanticism began in Europe. Romanticism is in general characterized by emotion and the pursuit of beauty, but two specific features of the movement pertain closely to Rovelli’s chapter on ancient Greece: the glorification of the past and the love of nature.

These two ideas were often combined. That is, Romantic thinkers glorified ancient Greece because there man was united with nature. Novalis, a Romantic poet, wrote in Novices of Sais that

to those earlier men, everything seemed human, familiar, and companionable, there was freshness and originality in all their perceptions, each one of their utterances was a true product of nature, their ideas could not help but accord with the world around them and express it faithfully.

Rovelli’s’ view of the ancient Greeks strongly resembles Novalis’, as both authors are convinced of the ancients’ ability to understand the natural world around them while understanding their place within it. Some Romantics believed that the ancient Greeks were more closely united with the supernatural world as well. In A Defence of Poetry, Shelley wrote, “Of no other epoch in the history of our species have we records and fragments stamped so visibly with the image of the divinity in man.” Rovelli echoes these sentiments when he contrasts “the mind-set of the Middle ages” with that of Democritus:

The medieval cosmos so marvelously sung by Dante was interpreted on the basis of a hierarchical organization of European society: a spherical cosmic structure with Earth at its center; the irreducible separation between Earth and heavens; finalistic and metaphorical explanations of natural phenomena; fear of God, fear of death; little attention to nature […]

There is none of this in the world of Democritus as sung by Lucretius. There is no fear of the gods; no ends or purposes in the world; no cosmic hierarchy; no distinction between Earth and heavens. There is a deep love of nature, a serene immersion within it; a recognition that we are profoundly part of it; that men, women, animals, plants, and clouds are organic threads of a marvelous whole, without hierarchies. There is a feeling of deep universalism […]

Rovelli shares the Romantics’ view of the ancient Greeks and there are even moments when his language is indistinguishable from that of the poets. In his poem Childe Harold’s Pilgrimage, Lord Byron called the Acropolis of Athens “[t]he dome of Thought, the palace of the Soul.” For Rovelli, Miletus was a place that “radiat[ed] its thought and spirit.”

People tend to associate Romanticism with positive connotations, but in reality the movement wasn’t all sunshine and rainbows. The Romantics weren’t celebrating the current state of things but mourning man’s departure from nature, which occurred sometime after the “Golden Age” of ancient Greece. There is a strong sense of permanent loss, with which Rovelli can certainly relate:

I often think that the loss of the works of Democritus in their entirety is the greatest intellectual tragedy to ensue from the collapse of the old classical civilization. […]

We have been left with all of Aristotle, by way of which Western thought reconstructed itself, and nothing by Democritus. Perhaps if all the works of Democritus had survived, and nothing of Aristotle’s, the intellectual history of our society would have been better.…

Many more parallels can be drawn between Rovelli and the Romantic poets but I hope the point has been sufficiently made: the Romantic ideal of unity is alive and well in Rovelli.

This brings us to the other aforementioned idea — that Rovelli writes with a unifying perspective. I want to illustrate this theme of unity in three topics: unity of scientific theories, unity of scientists, and unity of thought. I’ll begin with unity of scientific theories.

After the chapter on ancient Greece Rovelli takes us to seventeenth-century England to visit “the greatest scientist of all time,” Isaac Newton. Rovelli recalls a simple thought experiment that Newton performed: calculating how long it would take for a very small moon to orbit the Earth. Using the experimental findings of Kepler and Galileo, Newton discovered that the hypothetical moon’s acceleration would equal the acceleration of falling objects on Earth. This simple idea, Rovelli declares, spawned “[a]n immense vision”:

Suddenly, after millennia, there is no longer separation between the heavens and Earth; there is no “natural level” for things, as Aristotle presumed; there is no center to the world; things let free no longer seek their natural place but move straight, forever.

Newton unified multiple observations into a single theory — that gravity on Earth is the same as gravity elsewhere — and used this theory to create the first coherent picture of the world, which Rovelli illustrates in the following diagram:

This diagram evolves as our journey continues. After Newton we visit Michael Faraday and James Clerk Maxwell, who demonstrated that electricity, light, and magnetism are all, to quote Wikipedia, “different manifestations of the same phenomenon”: electromagnetic radiation. Their discovery results in a redrawing of the diagram:

Faraday and Maxwell’s discovery divides Newton’s concept of particles into two separate ingredients: fields and particles. Despite this being a division, it has been called “the second great unification in physics (the first being Newton’s unification of terrestrial and celestial mechanics).”

We are just getting started. After Faraday and Maxwell’s great unification, Einstein contributes two of his own. First, that space and time are the same thing — they “fuse together in a single concept of spacetime.” Second, that “Newton’s space is the gravitational field.” As the diagram shows, our understanding of world gets simpler and simpler:

By now it seems inherent that the diagram will eventually converge to only one ingredient, and indeed this is exactly what happens when we catch up with modernity:

Covariant quantum fields are “[f]ields that live on themselves, without the need of a spacetime to serve as a substratum, as a support, and which are capable by themselves of generating spacetime.” (Rovelli actually does a nice job of explaining this idea, however opaque it may seem out of context.) With this ultimate single ingredient, the diagram is complete — at least for now — and its message clear: great strides in understanding occur through unifications.

Behind the unification of ingredients is another form of unification. Breakthroughs occur when scientists combine their ideas with the learnings of others. Rovelli writes, “we develop our conceptual schema for understanding the world by exploring new ideas, but also by building on the powerful intuitions of giant figures of the past.” This brings us to the second type of unity: unity of scientists.

Reality Is Not What It Seems is practically a love letter to Rovelli’s personal heroes. Every discovery is marked by adoration of the scientists behind it. We have already heard him call Newton “the greatest scientist of all time,” but he showers many others with accolades, too. James Clerk Maxwell was “one of the greatest mathematicians of the [nineteenth] century.” Michael Faraday “[wrote] one of the best books of physics ever written.” And don’t get him started on Democritus. The point is, it’s easy to get caught up in all this greatness and make the mistake of believing that these geniuses had their breakthroughs in a vacuum. Rovelli vehemently dismantles this fallacy by illustrating that every breakthrough is the result of building off of — and sometimes rewriting — others’ ideas.

Examples abound. Newton discovered that the force of gravity on Earth is the same as the force of gravity that governs celestial bodies by “stud[ying] in depth the results of Galileo and Kepler and […] combining them.” The theory of relativity came about because Einstein tried to tackle two problems at once: “First, how can we describe the gravitational field? Second, what is Newton’s space?”

As cheesy as it sounds, teamwork is the true force behind scientific discoveries. Sometimes teamwork happens across the span of centuries or even millennia, as was the case with Democritus, Einstein, and Newton’s contributions. Other times, teamwork happens in the more literal sense: between multiple people working on the same problem at the same time. Rovelli points out that “Einstein was no great mathematician” and that “he needed help” from mathematicians to formally construct the theory of general relativity. Likewise, when the physicist John Wheeler struggled to describe the concept of quantum space, he got help from a colleague named Bryce DeWitt. The two worked so closely together that once they had produced a suitable equation, they disagreed on who should get the credit for it:

For a long time, DeWitt called it “Wheeler’s equation,” while Wheeler called it “DeWitt’s equation.” Everyone else just calls it the “Wheeler-DeWitt equation.”

But where there’s teamwork there’s competition, and Rovelli harbors no illusions that scientists sometimes make a fuss about whose name gets put on what. This was certainly the case when Einstein was working on his theory of general relativity. A mathematician named David Hilbert attended one of Einstein’s lectures and “understood that Einstein was in the process of making a major discovery,” so he tried to beat him to the chase. After Einstein won, “a degree of tension between Hilbert and Einstein did develop,” but “the two gave a truly wonderful example of wisdom, clearing the field of all negative tension.” In an act of friendship, Einstein wrote Hilbert a letter stating, “It is a pity if companions such as we are, who have managed to forge a path aside from the pettiness of this world, could find anything other than joy in each other’s company.” Hilbert and Einstein went head-to-head for the glory of having derived “the most beautiful of equations” and were still able to patch things up. Sometimes competition gives way to reconciliation.

Even when it doesn’t and disputes go unsettled, the field of science puts itself back together again. It is self-healing and self-corrective and thus the best way forward, according to Rovelli. Reflecting on the cooperative yet competitive nature of science research, he writes,

The sociology of science has shed light on the complexity of the process of scientific understanding; like any other human endeavor, this process is beset by irrationality, intersects with the game of power, and is affected by every sort of social and cultural influence. Nevertheless, despite all this, and in opposition to the exaggerations of a few postmodernists, cultural relativists, and the like, none of this diminishes the practical and theoretical efficacy of scientific thinking. […] Science is the best strategy if we value reliability.

Science is reliable because, in the end, “we can check whether a theory is right or wrong.” Exposing his philosophical side, Rovelli declares, “This is what distinguishes science from other kinds of thinking, where deciding who is right and who is wrong is usually a much thornier question, sometimes even devoid of meaning.”

This is neither Rovelli’s first or last time picking on religion in the book, and it brings us to the third type of unity: unity of thought.

Rovelli has legitimate beef with religious thinking. All but one of Democritus’ works were destroyed as a result of the “edicts of Emperor Theodosius, which in 390–391 declared that Christianity was to be the only and obligatory religion of the empire.” The poet Lucretius, many of whose poems were inspired by Democritus, had a similar run-in with religious authority over a millennium later. “The Catholic Church attempted to stop Lucretius” in 1516 and in 1551 “but it was too late.” One gets the sense that Rovelli would give his right hand to read the complete works of Democritus, so why shouldn’t he be enflamed by Christianity’s repeated destruction of Democritus’ ideas? By that same token, shouldn’t one of the world’s leading scientists be concerned that his entire field may one day be erased by, say, an emperor’s edict?

Religion is a frequent target for Rovelli because it is a system of belief that suppresses reason and curiosity. “There is always someone who has the presumption to be the depository of Truth,” writes Rovelli. Religion is undemocratic; no one is allowed to question those at the top because those at the top already have “The Truth.” “The curiosity to learn, to discover, to look over the next hill, the desire to taste the apple: these are the things that make us human,” he declares. Religion, already in possession of all the answers it needs, would rather leave the apple untasted.

Most of Rovelli’s references to religion are veiled, but in the last chapter he finally confronts it and discusses its relationship with science:

The search for knowledge is not nourished by certainty: it is nourished by a radical distrust in certainty.

This means not giving credence to those who say they are in possession of the truth. For this reason, science and religion frequently find themselves on a collision course. Not because science pretends to know ultimate answers, but precisely for the opposite reason: because the scientific spirit distrusts whoever claims to be the one having ultimate answers or privileged access to Truth. This distrust is found to be disturbing in some religious quarters. It is not science that is disturbed by religion: there are certain religions that are disturbed by scientific thinking.

Rovelli’s brief argument against religion, if it can even be labeled as such, concludes with an olive branch: “I don’t criticize those who prefer to believe in this: we are all free to believe in whatever we want.” It is the kind of unifying statement we should come to expect from Rovelli.

Still, while Rovelli may not be “disturbed by religion,” he does have a better belief system in mind: one in which everyone has the ability to openly question and disprove each other, and in which everyone can be endlessly curious. “For my part,” he writes, “I prefer to look our ignorance in the face, accept it, and seek to look just a bit further: to try to understand that which we are able to understand.” This is the unity of thought that he wishes for mankind: for people to think together without thinking the same, like the Milesians did nearly three millennia ago. This is a Romantic outlook and it is fundamentally scientific. It was the Romantics, after all, who believed that man’s “salvation” would come “through the contemplation of nature.”

There are many elements of Reality Is Not What It Seems that seem unexpected. Its author is a leading theoretical physicist and a modern Romantic. It summarizes the most important scientific discoveries of the past three millennia and frequently alludes to works by Lucretius, Dante, Shakespeare, and many others. It reads like a history of science and like a treatise on the importance of unity at the theoretical, social, and philosophical levels. For some, the union of these disparate topics may seem contradictory. But for Carlo Rovelli, it is only natural.