Che cos'è il tempo? Che cos'è lo spazio?

by Carlo Rovelli

English Text. Roma, 2006; paperback, pp. 70, cm 14x21.

Genres: Science, Physics, Nonfiction, Philosophy, History

63 pages, Paperback

First published January 1, 2004

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

[Anton · Rating 5 out of 5]

Utterly charming short biographical essay. Loved it!

[Old Man JP · Rating 5 out of 5]

I've said it before and I'll say it again. I absolutely love reading this sort of stuff but I simply do not have the mental capacity to actually understand it. I've read a couple of other Carlo Rovelli books and they've all left my mind spinning. An example of what he says is that if we combine general relativity with quantum mechanics it follows that since space is a field then space must have a granular structure, like the electromagnetic field which is the photon. In turn, the quanta of the gravitational field must be grains of space because the gravitational field is the physical space. Hence space must be described as clouds of probability of grains of space. When he talks about time he says since space does not exist in quantum gravity, only the gravitational field exists, which is made of probabilities of elementary quanta, or grains, then space is just the network of grains. So, if time and space form a single entity, the non-existence of space implies the non-existence of time. His conclusion is that time is an effect of our ignorance of the details of the world. Since I really don't understand what this means, I'm sure my summarizing of his ideas is not accurate but I think that's what I enjoy about reading this sort of thing, it forces me to try to grasp some meaning from it.

[Juxhin Deliu · Rating 2 out of 5]

Una breve presentazione del percorso scientifico e personale di Rovelli, in cui espone la sua teoria dei "loop", introduce alle due principali teorie fisiche (la relatività generale e la meccanica quantistica) e spiega come non esistano spazio e tempo come li conosciamo nel nostro senso assoluto, intramezzando le sue esperienze da ricercatore. Essenziale.

[Ardalan]

I own 3 of his other recent books and currently reading 2 of them and meanwhile out of curiosity opened this book which belongs to his earlier works and found the intro extremely captivating and promising. To the degree that It compelled me to put it into my list and to write a review for those few pages read! I suggest anyone reading this review to read that biographical introduction which is beyond mere physics and science in my idea and reveals a restless soul dreaming of making the world a better place to live and by this invitation I wish this could affect people to be a bit more of a dreamer and less of a conformist!
Full five stars!

[Andrew Paterson · Rating 5 out of 5]

Loop Quantum Gravity

I enjoyed this tremendously. It was a fascinating insight to the shift in thinking that has been required to propose an approach to quantising the gravitational field, in particular to think of spacetime as the gravitational field itself and to hypothesise that space and time at the microscopic level are nothing like how we understand them in daily life.

[MissFede · Rating 4 out of 5]

Un altro piccolo gioiello del professor Rovelli.

[Bruno · Rating 4 out of 5]

Carlo Rovelli est un chercheur globe trotteur. Très jeune, il s’est passionné pour les questions de temps et d’espace. Puis cette passion s’est renforcée au cours de ses voyages – d’Italie en France, en passant par l’Angleterre et les Etats-Unis – et de ses rencontres avec des physiciens. Sur fond de biographie, ce livre raconte l’évolution de ses pensées et de ses travaux concernant le temps et l’espace, en particulier dans le cadre de la théorie des boucles – concurrente de la théorie des cordes – qui reconsidère ces deux concepts et sur laquelle il a travaillé de nombreuses années. A la fin de l’ouvrage, Carlo Rovelli ouvre la réflexion sur la science dans le monde et sur son enseignement.

[Maurizio Codogno · Rating 2 out of 5]

In questo libretto davvero smilzo l'autore, fisico teorico e uno dei cosiddetti "cervelli all'estero", racconta le sue ricerche sulla natura dello spazio-tempo. Spero di non rovinare la sorpresa a nessuno se vi dico che secondo la sua "teoria dei loop" (da non confondersi con la più nota teoria delle stringhe) non esiste né spazio né tempo. Ciò detto, devo anche rassicurare il lettore allergico alla matematica: qui di formule e robacce del genere non ne troverà affatto; piuttosto leggerà una specie di rapida autobiografia dove qua e là si parla anche di fisica. Magari la cosa può anche interessare, ma di una divulgazione così all'acqua di rose non me ne faccio molto.

[Brian Boyce · Rating 2 out of 5]

I read the english translation of this and while it is a brief portrait of time and space it is like a sketch or line drawing and needs more content. But i enjoyed the brief glimpse.

[Barbara · Rating 2 out of 5]

12 euro per una chiacchierata (breve) tra amici... Il contenuto è piacevole ma non lo ricomprerei.

[Abhishek · Rating 4 out of 5]

Came across some really interesting ideas about spacetime.

[Chandler Collins · Rating 4 out of 5]

A great little book on the nature of space and time in which Rovelli concisely and clearly puts forward his argument for loop quantum gravity theory. The book is unique in that Rovelli interweaves his scientific findings with biographical accounts of his academic journey, as well as the provisional and ever-changing nature of scientific thinking. At times, this does make the book feel a bit disjointed, but this is no major weakness. The major strength of this book is the clarity with which the author explains Einstein’s general relativity theory, the findings of quantum theory, and the difficulty of integrating these two systems into a unified theory. I will simply quote Rovelli below on each of these points as I could not write it out any better:

“However, the two theories appear to be incompatible. They lead to two very different ways to describe the world. Quantum mechanics, in its present formulation, uses the old notions of space and time, which are contradicted by general relativity. General relativity, in turn, is formulated using the old notions of matter and energy, contradicted by quantum mechanics. We do not know how to merge the two into a unique consistent conceptual framework” (p. 12).

On space
“In the same way, Einstein understood that the fields don’t need to live on a fixed table-space, because they can live “on top of one another”. After Einstein’s discovery one no longer thinks of “fields in space” but of “fields on fields” (p. 17).

“Einstein discovered that Newton had made a mistake: table-space is not at all something that much different from the fields and the particles that move on top of it. On the contrary it is itself a field, just like the others” (p. 17).

“This is Einstein’s theory which is called general relativity. It is called “relativity” because in the theory there no longer exists an absolute location of things in space, but only the location of physical objects with respect to one another, that is “relative” to the one another” (p. 17).

“Concepts initially completely disconnected - space, the force of gravity, the fields - all become aspects of one simple entity: the gravitational field” (p. 17).

“If one now combines the basic ideas of general relativity and quantum mechanics, it follows immediately that since space is a field (the gravitational field) space must have a granular structure, as does the electromagnetic field. The quanta of the electromagnetic field are the photons. The quanta of the gravitational field must be “grains of space”, because the gravitational field is the physical space. The dynamics of these grains must be probabilistic. Hence space (i.e. the gravitational field) must be described as “clouds of probability of grains of space” (p. 19).

“From Aristotle to Descartes, space has been more often described as a relation and not as an entity. This means that space does not exist if there are no objects. Space is the relation between dynamical objects, like a marriage is a relation between two individuals: there is no marriage without the two individuals. More precisely, space is the relation of adjacency, namely of being in touch, between objects” (p. 29).

On space and time
“A novel image of the world is taking shape: a world without space and without time. The space where the world “inhabits” and the time “along which” things evolve might soon disappear from our fundamental description of the physical world, in the same manner in which notions such as “the centre of the universe” have disappeared in the past” (p. 48).

Rovelli is very humble concerning his own insights about loop quantum gravity and admits that he could very well be wrong. Rovelli wants to avoid certainty and dogmatism in his scientific method as he critically works toward a more accurate view of the world.

[Rafa Santos · Rating 5 out of 5]

The book exposes many of the ideas that Rovelli discusses in "Seven Brief Lessons in Physics" and "The Ordering of Time", which he wrote many years later. However it also contains something that I had been wondering about, but which Rovelli does not touch on in these later books, namely, an exposition of his views on string theory, the major alternative to the thesis he co-created in quantum gravity, loop gravity theory (though in "Seven Brief Lessons" he does demurely gloat that the existence of super-symmetric particles on which string theory depends had failed to encounter empirical support after relevant experiments were performed). That alone makes it worth reading this book even after I've finished those later, larger books. Explanations of his ideas are intertwined with endearing autobiographical glimpses where the author recounts his journey as a student and professor and his friendship with other exponents of physics. He also expands on his values as a citizen and gives his opinion on America as a European. One small warning I need to give, however, is that the English edition I read, which I understand to be a translation of the Italian original, is full of minor spelling and grammar errors, as if it had been made by some dedicated amateur with no editor support and then uploaded to the internet. Otherwise this was a grateful read.

[Peter Fox · Rating 4 out of 5]

Once upon a time writers were only meant to write captivating drama. Now, there is Carlo Rovelli writing captivating and intriguing quantum physics books. What makes them extra special, is the fact that you do no have to be one of the intellectually gifted to develop an understanding of what this talented man is explaining.

I have found each of his books difficult to stop reading and nearly impossible to leave for any of the good family reasons. He has made it onto one of my all time favourite authors list, and I enjoy his work as much as I have when reading Darwin, Kant and Rousseau.

Hopefully he will have a long life and even more of these compelling books for me to enjoy and cherish.

[Steven · Rating 4 out of 5]

Enjoyable pamphlet with some autobiography and cool exposition of space-time and loop quantum gravity. Rovelli is one of the originator of the theory where space consisted of indivisible unit called the quanta which is shaped like a little unit of field (eg. gravitational or electromagnetic). He theorized that time also has this kind of quanta, that time does not exist. What exists is relations between units of measurement.

[esplovago · Rating 4 out of 5]

Una piacevole chiaccherata sul tempo e sullo spazio, con un po' di excursus storici e filosofici.
Utile anche come introduzione concettuale e storica alla teoria della Loop Quantum Gravity (LQG) sviluppata da Rovelli assieme a Smolin e Ashtekar. Per proseguire (e iniziare) lo studio della LQG meglio rivolgersi al libro scritto da Rovelli assieme a Francesca Vidotto.

[M. V. · Rating 4 out of 5]

an "interview booklet" with interesting insights into space-time physics as studied by rovelli. it also provides nostalgic biographical references to rovelli's life, politics and personal philosophy. other of rovelli's work is more focussed on his research, but this is still an interesting, insight into the life + history of the scientist.

[M. Shane Tomblin · Rating 3 out of 5]

Disappointing

Arrogant, preachy fluff. I wish he had spent more time actually presenting something. If one is going to write a science popularization, at !east put a little substance in there. Brian Greene, anyone?

[JOHN ROBERTSON · Rating 5 out of 5]

A little piece of science love

He has a way of making science your own understanding, and questions. It''s like listening to and old college buddies speak his science speak to you because he knows you'll listen with anticipation because you're in this together.

[Luca Frasca · Rating 2 out of 5]

Lettura piacevole che si esaurisce in un'ora, focalizzata prevalentemente sul percorso biografico dell'autore. Manca qualsiasi approfondimento scientifico.
Sicuramente non uno degli scritti fondamentali di Rovelli.

[Reenah · Rating 2 out of 5]

Terrible translation! Also, it's more like a mini-autobiography.
But I liked Carlo Rovelli's thinking and his views of science. I'll definitely be reading one of his "real" books, in a good translation!

[Gabriel Edwards · Rating 3 out of 5]

Brief but worthwhile

One for fans of Carlo who'd like a brief recap of loop quantum gravity. Nothing new but an opportunity to reflect on earlier reading and to learn more of how the author came to be in Marseille.

[MDM · Rating 5 out of 5]

Ottimo libro, scorrevole e stimolante per tutti gli appassionati di fisica. Si legge velocemente ma contiene al suo interno temi che possono far riflettere una vita intera. Consigliato, soprattutto a giovani studenti e cervelli in fuga!

[Ivan · Rating 2 out of 5]

Piccolo libriccino da intermezzo... simpatico il racconto privato di Rovelli ed il suo muoversi nella fisica moderna, riguardo al tema però in pratica non dice nulla...

[Helio Winter · Rating 3 out of 5]

Harder to grasp than his other books. The best one -by a mile - still Reality Is Not What It Seems.

[Steen Ledet · Rating 4 out of 5]

Another good overview but frustratingly chatty.

[Rolande · Rating 5 out of 5]

I love Carlo Rovelli.

[Mihkel Ummelas · Rating 4 out of 5]

Rovelli comes across like a decent human being / scientist :).
Nice little intro into loop quantum gravity bundled with a short bio.

[Alessandro Piovaccari · Rating 4 out of 5]

Brilliant ideas, sometimes interweaved with some less interesting stuff out of topic stuff.

[Fernando Cignola · Rating 3 out of 5]

Rispetto agli altri libri che ho letto di Rovelli questo è uno (o due) gradini sotto. Gradevole comunque