Reality is Not What it Seems: The Journey to Quantum Gravity by Carlo Rovelli
My rating: 4 of 5 stars

"The only truly infinite thing is our ignorance."

I love reading works by Carlo Rovelli, one of the world's top physicists, and - in my view - the best ever popularizer of modern physics. Statements like the one I used in the epigraph, about human infinite ignorance, resonate with me. I teach mathematics at a university, I have quite an extensive exposure to classical physics, yet my ignorance about modern physics is certainly limitless. (By the way, there is no better way to understand the vastness of one's ignorance than being a professor.)

While I will not rate this book by Dr. Rovelli as a masterpiece like Seven Brief Lessons on Physics , it is still a great read and I have learned a lot from it - not only about my lack of knowledge. The author begins with a story about Anaximander of Miletus (450 BCE) whose work contributed to the foundations of Western science and philosophy.

"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."

Progressing through time, we read about Democritus, then through Copernicus, Newton, Faraday, Maxwell, we follow the evolution of human models of reality. Then come Einstein, Heisenberg, Bohr, Dirac - fathers of the modern physics - and we arrive at the "two pillars of twentieth-century physics - general relativity and quantum mechanics." General relativity is "a simple and coherent vision of gravity, space, and time." Quantum mechanics unveils the three aspects of reality: "granularity, indeterminism, and relationality."

Part Three, Quantum Space and Relational Time is to me the most fascinating part of the book. General relativity and quantum mechanics, "the two jewels that the twentieth century has left us," seem to contradict each other. "They cannot both be true, at least not in their present forms." Chapters 5 through 7 provide an introduction to the loop quantum gravity theory in whose development the author has played one of the key roles.

"[...] the world described by the theory is far from the one we are familiar with. There is no longer space that "contains" the world, and no longer time "during the course of which" events occur."

Part Four, Beyond Space and Time, discusses such aspects of cosmology as Big Bang and black holes. I found the chapter Information the most illuminating. Information is defined as the number of possible alternatives, connections to Boltzmann's statistical mechanics are shown, and the author presents yet another crucial idea - thermal time and its connection with the concept of irreversibility. The author's succinct summary is stunning:

"Time is an effect of our overlooking the physical microstates of things. Time is the information we don't have. Time is our ignorance."

I absolutely love the powerful final chapter, Mystery, with its convincing argument why nothing but science can be reliable:

"The answers given by science [...] are not reliable because they are definitive. They are reliable because they are not definitive.

This is the most powerful argument I have ever heard against all kinds of mumbo-jumbo that ignores science, which is particularly important in the times of a pandemic.

The author provides two fascinating historical vignettes: the first about a "race" to formalize Einstein's theory between David Hilbert, one of the most famous mathematicians in history, and Albert Einstein. The other vignette is about a little known Belgian priest, Georges Lemaître, who showed that both Einstein in his skepticism about the expansion of the universe as well as pope Pius XII in his declaration that the Big Bang confirms the account of Creation given in Genesis were wrong.

Fascinating read!

Four-and-a-quarter stars.

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