In Seven Brief Lessons on Physics, Helgoland & The Order of Time, Carlo Rovelli, a top theoretical physicist and co-author of the quantum loop gravity theory, explains Einstein’s general theory of relativity and quantum theory, and covers a multitude of other topics in this mind-expanding series of books.
Seven Brief Lessons on Physics
The Order of Time
Book Review: Three books by Carlo ROVELLI:
(1) Seven Brief Lessons on Physics (2016)
(2) Helgoland (2021)
(3) The Order of Time (2018)
The books are referred to as (1), (2), and (3) in the review.
Brushes, already immersed in paints, already dissolved…
Yes! Coming to terms with aging
Is as difficult as with coming-of-age.
The aging onlookers move along with the young crowd
Dispassionately unengaged, as if in a museum hall,
Looking with mindless arrogance – as if on petrified debris –
On the unimaginable golden-ripe treasures of modernity.
Leonid Martynov, What can you convince the aging of?
Blessed be old wine and good bread from the oven,
And the woman who makes us ecstatic after tormenting us in our desire.
But what is it for us when rosy Aurora colours the enchanted chilled sky,
Filled with silence and unearthly peace?
What can one do with an immortal poem?
One can’t eat it, or drink it, or even kiss it …
Nikolai Gumilev, The Sixth Sense
Carlo Rovelli, a top theoretical physicist and co-author of the quantum loop gravity theory, explains the two grandest “golden-ripe” intellectual pillars of modernity:
- Einstein’s general theory of relativity (“the most beautiful of theories… that describes a colorful and amazing world where universes explode, space collapses into bottomless holes, time sags” (1), and
- Quantum theory (QTh), which opened the way to most of the technological marvels of our information-revolution era (computers, transistors, internet, etc, etc). QTh possesses remarkable predictive powers too.
However, Rovelli (2) stresses, “…science is not just about making predictions. It also provides us with a vision of reality, a conceptual framework for thinking about things.” As yet, though, QTh has failed to provide meaningful conceptual insights into “intimate grammar of our world.”
The two theories “couldn’t be more different from each other,” and a frantic yet unsuccessful global search is underway to converge both theories together with thermodynamics into a conceptual congruence.
The chapters begin with epigraphs. There are verses from Horace, Shakespeare, Dante, and many others. Narratives extending beyond the physics theme are Rovelli’s trademark – lucid, erudite, utterly enjoyable, suffused with broad cultural and philosophical references. Rovelli refers to and quotes ancient Greek, Chinese and Indian philosophers, Mozart, Kant, Proust, Mach, Lenin, Michelangelo, and many more. His powerful, encyclopedic, and artful appeal to the global culture, combined with his ability to make accessible the “intimate grammar” of reality to equation-illiterate readers like myself (for whom his books are an eye-opening gift) are perhaps his most engaging and inspiring accomplishments as a writer. It felt as if I had been awaiting this gift ‘forever’ (since my mid-teens – and now I’m a great-grandmother) and it has not failed my expectations.
What revelations has QTh yielded in its hundred-year history?
- That “the world is subtly discrete, not continuous... Granularity is the most characteristic feature of QTh… A minimum scale exists for all phenomena… Continuity is only a mathematical technique for approximating very finely grained things.” (3)
- That elementary particles of matter (electrons, quarks, photons and gluons) “…do not have a pebble-like reality but are rather the ‘quanta’ of corresponding fields… elementary excitations of a moving substratum… wavelets… [An] empty region of space in which there are no atoms, [still has] a minute swarming of these particles… There is no such thing as a real void… Where are these quanta of space? Nowhere. They are not in space because they are themselves the space. Space is created by the linking of these individual quanta of gravity… The world seems to be less about objects than about interactive relations.” (1)
- That (a) our world is indeterminate and probabilistic, and that (b) the real interpretation of our world is relational.
“The electron is concrete only in relation to the other physical objects it is interacting with…Between these interactions…the electron has no precise position, as if it were dispersed in a cloud of probability…we say that it is in a ‘superposition’ of positions…It is hard to take in the idea that an electron behaves in such a bizarre way. It is even more difficult to digest that this is also the way time and space behave. And yet, according to all the evidence, this is the way the quantum world works: the world that we inhabit.” (3)
“Einstein [showed] that gravity is carried by a field that is the very geometry of space and time… Spacetime is a physical object like an electron.” (2). “The physical substratum that determines duration and physical intervals – the gravitational field – …is also a quantum entity that does not have determined values until it interacts with something else. When it does, the durations are granular and determinate only for that something with which it interacts; they remain indeterminate for the rest of the universe…This, I believe, is the most radical discovery made by quantum mechanics.” (3) “Is it clear? No… [For instance], how the gravitational field behaves when it heats up is still an unresolved problem.” (1)
- That a quantum phenomenon [called entanglement: when the position, spin, momentum, and polarization are found correlated in two photons drifting light-years apart] “…embodies the radical interdependence of things.”(2)
“…The strangest of all strange quantum phenomena…it is also something general, which in a sense weaves the very structure of reality…How two entangled particles behave in the same way…without communicating at a distance?…The solution lies in remembering that properties exist only in relation to something else…The facts that are real with respect to an object are not necessarily so with respect to another…No universal set of facts exist…The joint properties of two objects exist only in relation to a third…Entanglement is…far from being a rare phenomenon…it is what happens, generically, in an interaction…considered in relation to a system external to it…The external perspective on the very relations that weave reality…Individual objects are the way in which they interact.” (2)
- That “…there is no difference between time past, present and future, between cause and effect…in the elementary laws that describe the mechanisms of the world.”(3).
“This [second law of thermodynamics] is the only basic law of physics that distinguishes the past from the future…None of the others do so…In the elementary equations of the world, the arrow of time appears only where there is heat. The link between time and heat is therefore fundamental: every time a difference is manifested between the past and the future, heat is involved.” (3)
“It is not impossible for a hot body to become hotter through contact with a colder one: it is just extremely improbable.”(1) This is the essence of the 2nd law of thermodynamics; this is called entropy and epitomizes disorder which only ever increases in the world.
But there is a critical ‘loophole’: entropy can and does decrease locally at the expense of further increase elsewhere related to this locality. This is how all life operates: life means order, organisation, decreased entropy – but at a cost elsewhere (consumed food and oxygen). “It is entropy, not energy, that drives the world.” (3)
Perhaps a good way to visualize it is the classical metaphor of Alexander Gurwitsch: a crystal ball dancing in a fountain’s upward spray. The ball’s entropy is low (it is ‘alive’) thanks to (and as long as) general entropy is increasing due to the energy spent pushing water up. The ball is shattered (disorder increases) the moment the upflow (oxygen supply) is cut off.
Summing up: “QTh describes the way in which one part of nature manifests itself to any other single part of nature…The discovery of QTh, I believe, is the discovery that the properties of any entity are nothing other than the way in which that entity influences others. It exists only through its interactions. QTh is the theory of how things influence each other. And this is the best description of nature that we have” (2)
“We are not entities, we are relations”. Historically, the idea that ‘entities’ are the foundation of reality has been doubted since antiquity. Rovelli offers a fascinating panorama of it in millennia worldwide: “I…propose the definition of being: that it is nothing if not action.” (Plato, 2) “The central thesis of Nagarjuna’s teaching [India, 2nd century CE] is simply that there is nothing that exists independently from something else [but] only in interdependence with something else.” (2)
“There is, of course, something bewildering about the vision of the world that emerges from QTh. We must abandon something that seemed most natural to us: the simple idea of a world made of things…To understand QTh, we need to modify the grammar of our understanding of reality, as when Anaximander understood that the true shape of the Earth changed the grammar of notions of what is ‘up’ and ‘down.’ Objects are described by variables that assume value when interacting, and this value is determined in relation to the objects in the interaction , not to others…This phantasmal world of quanta is our world.” (2)
What could be wished for from the author? QTh “…has never been found wrong” (2) by the language of mathematics and it seems so “absolute” that it is not always needing the support of predictive power. But why is that, why is mathematics such a “final-truth oracle”? How error-proof, how accurate, is it? “The ultimate fabric of reality really is mathematical” (Tegmark, Our Mathematical Universe, 2014). But not infallible: some equations (like the “fine theories” of SU(5) and of supersymmetry) seem to end up failing. And Eugene Wigner wrote: “The enormous usefulness of math in the natural sciences is something bordering on the mysterious, and…there is no rational explanation for it” (The unreasonable effectiveness of mathematics in the natural sciences, Lecture, May 11, 1959; Communications on Pure and Applied Mathematics 13: 1–14, 1960). Current comments on the role of mathematics in Nature would be welcome.