Relatività generale. Una semplice introduzione

by Carlo Rovelli, Pietropaolo Frisoni (Translator)

Formulata da Albert Einstein con qualche contributo da parte di amici e colleghi tra il 1907 e il 1917, la relatività generale è la teoria che oggi meglio descrive lo spazio, il tempo e la gravità. Con la chiarezza espositiva che lo ha reso celebre in tutto il mondo, Rovelli ne illustra i fondamenti fisici, filosofici e matematici, ne presenta la struttura formale, e ne deriva nel modo più semplice le sue stupefacenti predizioni - buchi neri, onde gravitazionali, espansione dell'universo, dilatazione del tempo... , senza trascurare alcune idee di base su come potrebbe essere estesa ai fenomeni quantistici. Per il lettore con formazione scientifica questo libro rappresenterà dunque una agile introduzione agli aspetti fondamentali della teoria, ma nel contempo lo scienziato e lo studente avanzato vi troveranno una discussione approfondita e originale della sua struttura concettuale.

Genres: Science, Physics, Nonfiction, Stem

163 pages, Paperback

First published January 1, 2021

About the author

Carlo Rovelli is an Italian theoretical physicist and writer who has worked in Italy and the USA, and currently works in France. His work is mainly in the field of quantum gravity, where he is among the founders of the loop quantum gravity theory. He has also worked in the history and philosophy of science. He collaborates regularly with several Italian newspapers, in particular the cultural supplements of Il Sole 24 Ore and La Repubblica.

Reviews

[Myat Thura Aung · Rating 5 out of 5]

For those who already had some technical exposure to the subject, Rovelli wouldn't let you down.
I myself gained a lot and will revisit the last chapters to fill in the gaps in my understanding, after mastering some necessary technical details.

[Miguel]

Don’t feel like rating this since this is like a mini textbook. I will say though, that I have never had as intuitive of a grasp of what the math in GR is trying to say about physics than after reading this book.

I think the geometrical background I have had in previous exposures was great, and were big mindfucks. However, I feel like this physical approach was a lot more inspiring, and aligned with why I am a physicist and not a mathematician.

Also helps that I’ve taken formally taken classes in Gravitation and Accretion Physics and Cosmology.

[Mark Moon · Rating 4 out of 5]

This book is nice and concise; it delivers on what the title promises.

[Aidan · Rating 2 out of 5]

If you’re a dummy like me you might struggle with this book. Thought I’d give it a try as I find General Relativity interesting, and loved other Carlo Rovelli books but this is very equation heavy and a bit too technical if you have limited knowledge of formulas and equations.

[Ken Rideout · Rating 4 out of 5]

A very math-y exposition. Honestly most of the math went over my head. I wish I had read this book when I was in grad school, but alas it was only published a few years ago. Despite the math being so explicit throughout, a dedicated and interested reader can get a lot out of this book in the way of a deeper understanding of General Relativity than the popular, math-free expositions out there. I will list some quotes I found pithy, insightful, or revelatory to me below
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"General Relativity is the field theory of the gravitational field just as Maxwell theory is the field theory of the electromagnetic field." (p.3)

"Galilean relativity is the discovery that 'to be at the same place' at different times is an ill-defined notion, while special relativity is the discovery that 'to happen at the same time' in different places is an equally ill-defied notion." (both require a reference object with respect to determine distance of time, respectively) p. 7

"It is sometimes stated that he Newtonian notions of space and time are instinctive and natural. They are not. Perhaps they are now familiar, after centuries of success of Newton's Physics.... But they are not natural, Before newton, the dominant understanding of space and time, both in common use and in the learned tradition, was the relational one." (p. 12)

"If you want to do great science, read philosophy." (p. 13)

"..the effect of gravity [is] to redefine the notion of inertial system." (p. 17)

"Newtonian space and time are nothing else than a particular configuration of the gravitational field." (p.18)

"The arbitrary coordinates used to coordinate a curved surface do not have the meaning of distances...[In developing his theory, Einstein's] conceptual difficulty was to separate the notion of coordinate from the notion of distance." (p.26)

"geometry is not a Kantian a priori, necessary to conceive the world: geometry is an epiphenomenon of the gravitational field" (p. 60)

"... many are confused by [the cosmological constant] and claim, mistakenly, that it represents "Dark Energy" (it is no more mysterious than the 20 or so other fundamental constants in physics) p. 62

"physical points are not defined by themselves. They are only defined by the solutions of the equations of motion, by the fields, by the positions of the particles, and by the geometry.... this is profoundly different from what happens in non-general relativistic physics, where we assume that physical spacetime points are well defied.... independently from the dynamical fields." (p. 70)

"[In classical physics time evolution means] the evolution of physical variable over time...in general relativity...relative evolution of the physical variables with respect to one another." (p. 72)

"Therefore, in general relativity, we can say that things fall towards a mass because mass slows down time in its vicinity." (p.81)

Gravitational waves do not cause particles to move, the particles move "with respect to one another" as the wave passes. This is confusing to us because we are confusing the coordinates of the objects with the distance between them (p. 88)

"So Einstein correctly guessed the existence of the cosmological force, which we now know really exists. But he didi t for the wrong reason: he thought this would result in a static universe, and that's not true. So he missed a most spectacular prediction of his own theory: the universe cannot be static at large scale. But he ended up introducing a correct improvement of his equations.
Formidable." (p.97)

"[because the cosmological constant is positive], gravity is attractive at small distance but becomes repulsive at large distances..This force (nots any mysterious 'quantum vacuum energy' or dark energy')is the reason the expansion of the universe is currently accelerating. " (p.119)

"[the time it will take for the tidal forces to tear you apart in a supermassive blackhole]... can last for hours. Therefore, a physicist can in principle enter the horizon and do all sorts of measurements and detections in the interior. It is true that she is most likely going to die soon, crushed in the small r region; but we all die anyway, even outside the horizon." (p. 131)

"One often reads that GR predicts a 'singularity' at the centre of the hole; whatever this means, this is not relevant for the natural world, because quantum mechanics becomes relevant and changes the picture before reaching such a hypothetical 'singularity.'" (p. 132)

"Einstein's everlasting insight [is]that spacetime geometry is a manifestation of a dynamical field... in this sense, space and time disappears from the conceptual structure of physics... crucially, the old relational notions of space and time maintain their sense entirely.. But there is no preferred clock in the theory nor any sense of localisation besides the relative adjacency of quanta of matter and the quanta of space." (p. 155)

[Alessandro Casaburo · Rating 3 out of 5]

E' difficile per me dare un voto a questo libro. Se da un lato la conoscenza della materia di Rovelli è fuori discussione - ma non ci voleva questo libro per capirlo - dall'altro il testo si pone a metà strada tra lo step successivo alla pura divulgazione scientifica e quello precedente ad un testo universitario. Il risultato è un testo che non fornisce gli strumenti per capirne il contenuto ma che è molto dettagliato in certi frangenti, sia nel formalismo matematico che nell'interpretazione fisica dei fatti accompagnata dalle equazioni. Il risultato è un libro che non si capisce se vuole essere una introduzione o un piccolo compendio. Peccato, perché quando, equazioni alla mano, la fisica viene spiegata, colpisce forte.

[Loïc FLOURY · Rating 5 out of 5]

At the beginning of the book, it goes into the mathematical foundations of General Relativity, more specifically the various geometries for example: Riemann geometry, Newtonian geometry, Cartan geometry, Lorentzienne geometry. It also covers the parameters of the coordinate points in the different curved spaces. The book also goes into geodesics and their parameters. Additionally the book goes over the Ricci tensor and scalar showing how they correlate with Einstein’s field equations.

The book was enjoyable overall, it covers various topics that correspond to the foundations of General Relativity. In my opinion, the book lacks some more in depth mathematical explanations (more visual for better understanding). The book could have benefited from a longer view of time dilatation and how a gravitational field affects it (ex. Black hole). Go over the foundations of Λ.

I strongly recommend this book to students who want to understand the foundations of general relativity and are comfortable with the mathematical and physical tools involved.

[Vinnie · Rating 5 out of 5]

Amazing introduction to general relativity! Having read this as a 2nd year undergraduate physics student, I feel like this book allowed me to grasp the concepts and ideas of general relativity in order to begin a more in depth study of the subject. The writing style feels quite casual, which is good if, like me, you intend to read this in order to just get a surface understanding of GR. However, a lot of the maths and technical bits are in there. Rovelli provides plenty of examples and a few exercises, along with asking the reader to prove things which are told to you, so there are plenty of chances to sink your teeth into the technical bits of GR (which I definitely will be trying on a second reading).

[Rachelle · Rating 4 out of 5]

Do I understand General Relativity? No. I just love how Carlo Rovelli writes with elegance.

[Giovanni Panciroli · Rating 4 out of 5]

Libro di una complessità decisamente superiore alle solite pubblicazioni divulgative di Rovelli. Nonostante questo non si perde troppo nella matematica e arriva subito al nocciolo degli argomenti. Una persona non addentrata nella fisica o che non possiede degli strumenti matematici che vadano oltre la quinta superiore potrebbe faticare a goderselo.