I was listening to the On Being podcast where Krista Tippett was interviewing Carlo Rovelli. Rovelli is an Italian physicist working with the Quantum Gravity research group at Centre de Physique Theorique in Marseille, France.
As soon as the episode was over, I went over to Amazon and ordered the book he had been talking of – Seven Brief Lessons on Physics. This is an English translation of Rovelli’s Sette brevi lezioni di fisica written in 2014. The book was translated into English by Simon Carnell and Eric Segre in 2015.
In his discussion, I felt that there were still parts of Physics that I would like to explore and read up more on. Although the book does not have footnotes that would help me to learn more. It is an intense book packed with information. I read this book between March 17, 2020 and finished it on May 26, 2020. The book is 79 pages long.
The first lesson of the book explores Einstein’s theory of general relativity published in 1915. But, before we get there we have to realise that in one of his three papers written in 1905, Einstein suggested that time is not the same for everyone. The Theory of General Relativity suggests that gravity is the curvature of space.
In the second lesson, Rovelli deals with Quantum Mechanics. In 1900, Max Planck conducted an experiment to measure the electric field in a hot box. For calculations, he considered energy to be lumps of energy that he called quanta. While the results agreed, it disagreed with what was known till then about Energy.
In 1905, one of the three papers that Einstein submitted showed that Planck’s view of the world is true. He showed that light is made of similar packets, called photons. This paper birthed the field of Quantum Physics. The rest of the second lesson explores how Niels Bohr and Werner Heisenberg flesh out the field of Quantum Physics with Einstein objecting and rejecting the results that the field proposed.
The 1905 introduction to the paper begins with “It seems to me that..”. Rovelli suggests that genius hesitates and great scientists doubt till the end.
The third lesson is a chapter filled with diagrams. The reason why is explained beautifully by Rovelli, thus:
This lesson is made up mostly of simple drawings. The reason for this is that before experiments, measurements, mathematics and rigorous deductions, science is above all about visions. Science begins with a vision. Scientific thought is fed by the capacity to ‘see’ things differently than they have previously been seen.
Carlo Rovelli, Seven Brief Lesssons in Physics, Third Lesson, pp 21-22, 2015, translated into English by Simon Carnell and Eric Segre
The diagrams refer to how our view of our world changed from Earth below to sky above to us being in an ordinary solar system in an ordinary galaxy. The diagrams describe the structure of our universe.
The fourth lesson talks about particles. It goes into the development of quantum physics and then ends up discussing the various issues related to the Standard Model. The Model is a series of equations that has “never been taken entirely seriously by physicists” and seem to them “piecemeal and patched together”. The Model when applied directly leads to nonsensical predictions. A process called re-normalization is used to make them sensible. One of its limitation is an inability to explain dark matter. However, this Model provides the best answers to the phenomena we witness in the universe.
The fourth lesson also introduces an important concept. It introduces us to a “world of happenings, not things”. He explains:
The nature of these particles, and the way they move, is described by quantum mechanics. These particles do not have a pebble-like reality but are rather the ‘quanta’ of corresponding fields, just as photons are ‘quanta’ of the electromagnetic field.
Carlo Rovelli, Seven Brief Lesssons in Physics, Fourth Lesson, pp 30, 2015, translated into English by Simon Carnell and Eric Segre
The fifth lesson introduces us to a conundrum in the world of physics. General Relativity is our best theory that explains things at the cosmic scale and which led to the development of fields like Cosmology and Astrophysics. Quantum Mechanics provides our best theory that explains things at the quantum scale and led to the development of fields like atomic physics, nuclear physics, physics of condensed matter, etc. However both these fields do not agree with each other.
Many theories are being postulated to try and bring these two laws together and fit them together. The author himself is part of such an effort called Loop Quantum Theory. He is part of one of several groups trying to integrate the two theories.
The sixth lesson deals with concepts of heat that I was not aware of. The nature of time is dependent on nature of heat.
The difference between past and future only exists when there is heat. The fundamental phenomenon that distinguishes the future from the past is the fact that heat passes from things that are hotter to things that are colder.
Carlo Rovelli, Seven Brief Lesssons in Physics, Fourth Lesson, pp 51, 2015, translated into English by Simon Carnell and Eric Segre
He then says that the answer to why heat flows from hot bodies to clod bodies is very simple. It is just probability. The rest of the chapter flows from probability towards the concept of the heat of black holes. This still unanswered question brings together the field of quantum mechanics, general relativity and thermal science.
The book is a lot of information to take in about 79 pages. Even writing this review of the book took me more than a week. I don’t think I have done justice to the book. But, writing more would have become the equivalent to just writing the book here. What I have sought to do here is to try and build an outline of the book and introduce you to the mysteries that pulled me towards reading the book.
This is a book that provides a simple, deep understanding of the Physics of the twentieth century. It helps you understand where we stand and throws a light on where we are headed.
Parallel Spirals 
