This booklet has been given to me as a gift; I will always be grateful for it. Rovelli’s Seven Brief Lessons on Physics is an essay on the major revolutions in Physics during the XX century, from Einstein’s “Theory of Relativity” to the open questions about the Universe’s architecture, elementary particles, quantum gravity and time and mind’s nature. The language is accessible for everyone, creative and almost poetic, revealing the passion and dedication behind Rovelli’s writing. For me that I am ignorant of physics, this book was a splendid revelation, giving me the chance to pleasantly learn something about a difficult subject.
In this article, I will try to summarize Rovelli’s lessons into short paragraphs, for you to have an idea of the book’s contents. However, it is worth reading all of it, to get that sense of magic and wonder that physics can instill in the common reader. Although more suitable for the inexperienced, I believe that Rovelli’s writing would be pleasurable even for students of physics, for sharing that sense of amazement felt during the discovery of the Universe and the laws regulating it.
- First Lesson: The most beautiful of theories. The first lesson is dedicated to Albert Einstein’s ‘Theory of Relativity’ or ‘Special relativity’, this appeared for the first time on the scientific paper Annalen der Physik, Zurich, in 1905. This theory clarifies why Time does not flow for everyone equally; for Einstein, it was necessary a studying period of the 10 years for finding the definitive solution in 1915. Rovelli defines Einstein’s theory a masterpiece because, once it is fully understood, it is shockingly simple. Indeed, Einstein’s genial idea stands in thinking of Space as the gravitational field; contrarily, Newton believed that gravity was mysteriously scattered in the Universe. Thus, Space becomes a “material” part of the world, an entity that curls, bends, sags and twists; we are no longer contained in a rigid box, but we are actually immersed in an enormous flexible mollusc. Planets rotate around the Sun; things fall because of the bending Space. This bends where there is matter. Einstein’s vision is the ‘curved space’, his equation the expression for it. Within this equation, there were predictions that, one by one, revealed to be true: the bending of Space around stars (verified by mathematics in 1919), the bending of Time, the black holes, Space’s extension and expansion (verified in 1930), the origin of the Universe with the Big Bang (verified through observations of the cosmic microwave background radiation) and the rippling of Space with gravitational waves (of which effects are visible on binary stars in accord with the theory’s previsions). All these ideas are the results of a splendid elementary intuition: Space and the gravitational field are the same things.
- Second lesson: The Quanta. The two most important physics’ theories of the 20th century, Einstein’s relativity and the quantum physics, are sharply different from each other. However, both teach us how nature’s structure is much thinner of what we think. Generally, Quantum physics is believed to be born in 1900. Max Planck calculated the electric field within a hot box; for doing this, he imagined that the field’s energy is distributed in ‘quantum’, small energetic packs. Although the results confirmed the calculus, Planck’s idea was in contrast with others modern theories which considered energy like something always changing; instead, he measured it in small blocks. However, Planck himself did not fully understand his own calculation’s efficacy. It was Albert Einstein to comprehend the reality of these small “energetic pockets”, by showing that light is made of particles, today called “photons”. It was Einstein’s work on the discontinuity of light into Space to create the basis for quantum physics; moreover, it is the theory that won him the Nobel prize. Nonetheless, during the passing of time, Einstein outdistanced himself from quantum physics’ development. Indeed, it was Niels Bohr to continue in the study of quantum physics, introducing the concept of “quantum leap”. In 1925, the theory’s equations came to light, obtaining a great success and replacing Newton’s mechanics. Thanks to this theory, everything was easily calculated; for instance, Mendeleev’s “Periodic Table of Elements” is easily explained by quantum physics, this solving the nature of the table itself. The whole Chemistry emerges from this simple equation. W. Heisenberg was the first to write quantum physics’ equations; he imagined that electrons exist only when interacting with something else. For describing this idea, an abstract mathematical function that lives just in abstract mathematical spaces was employed; moreover, the quantum leaps happen arbitrarily, thus rendering possible to calculate just their probability. At this point in Physics’s studies, everything seemed chaotic and casual; even Einstein, the creative genius, was against this possibility, him believing in a sort of objectivity of the Cosmos. However, he recognised Heisenberg’s merits in understanding something fundamental about the world. They both continued to discuss their different ideas through essays, lectures and articles, recognizing each others’ observations and conclusions, often developing ideas by new responses. However, their doubts remain unresolved today, as the quantum physics’ core. Indeed, even if it is used for all contemporary technology, quantum physics’ equations are still a mystery, a great intuition about nature’s works.
- Third lesson: The architecture of the cosmos. In the second half of the XX century, physicists applied the two mentioned theories to all nature, from the Universe’s macrocosm to particles’ microcosm. In the third chapter Rovelli briefly retraces historical visions of the Universe, from Anaximander to modern days. In the 30s, thanks to astronomers’ measurements, we understood that even our Galaxy is small dust grain among billions of others galaxies within a huge cloud that expands in the Universe infinitely. Moreover, Space is not flat but curved; its weave is moved from waves that, when particularly rough, create black holes. Nowadays, we also know that the Cosmos originally emerged from a dense and hot cloud, the Big Bang. Other questions, such as the presence of more Universes, still remain unanswered.
- Fourth lesson: Particles. Light and things move within the Universe; the things we see are made of atoms, the light of photons. Atoms have a nucleus and electrons, the nucleus contains neutrons and protons. The American physicist Murray Gell-Mann has called neutrons and protons’ sub-particles “quarks”, a senseless name taken from J.Joyce’s Finnegans Wake; quarks are kept together by gluons. Electrons, quarks, photons and gluons are the components moving into Space, the ‘elementary particles’ of physics. All these particles’ nature and movements are described in quantum physics. Nothing is empty in Space, particles are created and destroyed quickly in a short-range of time. Quantum physics and experiments on particles have taught us that the Universe is an ever-changing reality, made of ephemeral entities that born and die continuously. The theory of particles developed during the 40s, 50s and 60s, until the creation of a new theory, “the standard model of elementary particles”; although it is the best modern theory describing the nature of things, it is full of contradictions and doubts that make it debatable (the existence of the inexplicable dark matter, the theory’s equations’ renormalization, etc). For now, we “only” know that matter is made of elementary particles that vibrate and fluctuate between existence and death, they come together and disappear for creating the Universe’s history, from cosmic rays to grains of sand.
- Fifth lesson: Grains of Space. Nowadays, both Quantum physics and the Theory of relativity are taught at University; however, they cannot co-exist because they contradict each other. The problem is that both theories work very well and it is difficult, for now, to create a coherent vision of the Universe. Groups of physicists from all around the world are working to solve this dilemma, the field of study is called “Quantum Gravity”. The research is mostly focused on the “Loop Quantum Gravity”, this trying to combine general relativity with quantum mechanics, both theories rewritten for making them compatible. The central prediction of this theory is to affirm that Space is not continuous and divisible, but made of atoms of Space, these even smaller than the smallest of atom’s nucleus. The atoms of Space are called “loop” (rings) that are not isolated but ringed between each other, creating a web of relations that shape the Space’s weave. These atoms of Space are nowhere, because are themselves Space. Moreover, this theory implies the absence of Time, giving the fact that ordinary processes are no longer subjected to ordinary successions of moments: every process happens independently but cooperatively with others, while everything follows its own rhythm. The Time’s flow is internal to the Universe, born from the relation of quantum events that are themselves the source of Time. The “Loop Quantum Theory” would be a change from our familiar perception of things, because of the absence of parameters such as Time and Space. One way to see and prove this theory is through the observation of Black holes, these formed from collapsed stars. The hypothetical final stage of a star’s life, where the pressure generated from quantum fluctuations balances the matter’s weight, is called “Planck star”; this is not stable but, once it is compressed to a maximum, it bounces and starts to expand once again. This process is fast while happening in a Planck star, while it is very slow when seen from the outside. Physicists are still studying this phenomenon. Another consequence of the Loop Quantum Gravity concerns the beginning of Universe: we could find that the Big Bang was generated by a Big Bounce, implying that our Universe was born from a precedent one, this once collapsed and afterwards bounced and expanded again. Studies made from the 20th century onwards point to ideas that are completely different from our instinctive intuitions on the Matter, Space and Time. Loop Quantum Gravity is an attempt to decipher these clues and look a little far beyond.
- Sixth lesson: Probability, Time and the heat of Black holes. Until the second half of the 19th century, physics tried to understand the ‘heat’ as a sort of fluids, but this proved wrong. Boltzmann and Maxwell sensed that a warm substance reached its state by the faster movement of atoms, in contradiction with the atoms’ slow pace in a cold substance. Moreover, they claimed that the difference between past and future existed only when there is heat, this moving from warmer to colder things. For completing this idea, Boltzmann included the notion of ‘probability’, claiming that the heat goes from warmer to colder things just for a certain amount of probability and not for an absolute law. Including probability for explaining physics was considered absurd at first, but universally recognized later in time. From Boltzmann onwards, ‘probability’ will be clarified by statistical physics; one of this subject’s trophies was to comprehend the probabilistic origin of heat and temperature’s behaviour, called as ‘thermodynamics’. During the XX century, thermodynamics and statistical mechanics were applied to electromagnetic fields and quantum phenomenon; however, their relation to the expansion of space was difficult to conciliate. Moreover, we still don’t have equations that describe the thermal vibrations of a spacetime heat. Questions lead us back to the same problem: what is Time’s flow? Albert Einstein would have said: “Just a stubborn illusion”. However, we all perceive a changing time in our everyday life. Time’s flow emerges in physics not by explaining the state of things, but rather in the fields of thermodynamics and statistics. This could be the key to the mystery of Time: the ‘present’ does not exist, but the microscopic interactions of the Universe create temporary phenomena for a system that interacts with billions of variables. Our memory and consciousness are built on these statistical events that change in time. It is not clear and a lot remains to be understood. Stephen Hawking, by using quantum mechanics, was able to demonstrate that black holes are always “hot”, thanks to proved mathematical calculations. Understanding the heat within black holes will actually decipher the flow of Time…
- Ourselves. Rovelli concludes the book by including us, the human race, within the discourse of modern physics. ‘What are we?’ is the question that Rovelli wisely eludes to answer for its difficulty. He goes back in time, reflecting on our origins, contemporary results and progresses, wondering how a Neanderthal man would have looked to a modern individual flying on planes. Rovelli also critically reflects on the environmental disaster we have created, observing that, while we will witness the end of our society, the Universe and the Earth will go on undisturbed. He meditates on the effective existence of liberty, considering the fact that life runs just according to necessity… Brilliantly enough, he finishes with some Lucretius’s verses that exalts that beauty of the Universe and our wonder at its perfection. Evidently, we are still learning and the Unknown shines in front and within us in its mystery and beauty.
Although it cannot be considered a literary piece, I wanted to include this Rovelli’s book on my blog because it gave me the opportunity to wave in the world of physics, although my being completely ignorant of it. His language is poignant, full of wonder and passion for the narrated subject. His style is fluent and decisive, demonstrating a profound competency on the subject. A truly great small book, a spaceship for anyone who looks at the world with wonder, astonishment and thankfulness.
Let’s always look at the stars!
See you soon,
P.S. Just for the occasion, I copy here the link for one of the best scenes of the NatGeo’s series Genius dedicated to A. Einstein. Enjoy the great Geoffrey Rush in his performance!