Jump to ratings and reviews
Rate this book

Reality is Not What it Seems: The Journey to Quantum Gravity

Rate this book
From the best-selling author of Seven Brief Lessons on Physics comes a new book about the mind-bending nature of the universe

What are time and space made of? Where does matter come from? And what exactly is reality? Scientist Carlo Rovelli has spent his whole life exploring these questions and pushing the boundaries of what we know. Here he explains how our image of the world has changed throughout centuries. Fom Aristotle to Albert Einstein, Michael Faraday to the Higgs boson, he takes us on a wondrous journey to show us that beyond our ever-changing idea of reality is a whole new world that has yet to be discovered.

256 pages, Hardcover

First published January 1, 2014

Loading interface...
Loading interface...

About the author

Carlo Rovelli

43 books3,118 followers
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.

Ratings & Reviews

What do you think?
Rate this book

Friends & Following

Create a free account to discover what your friends think of this book!

Community Reviews

5 stars
6,262 (48%)
4 stars
4,943 (38%)
3 stars
1,484 (11%)
2 stars
191 (1%)
1 star
42 (<1%)
Displaying 1 - 30 of 1,446 reviews
Profile Image for Manny.
Author 30 books14k followers
August 12, 2017
Goodreads friends who know about physics told me that this book really does provide a comprehensible explanation of loop quantum gravity. I was a little sceptical, having already seen a couple of unsuccessful attempts, but now that I've read it I'm convinced. It does what it says on the box.

If loop quantum gravity (LQG) hasn't been on your radar, let me give you some background and explain why this is a big deal. Physics has for the last century rested on two basic theories, quantum mechanics and general relativity. Each of these is very successful at what it sets out to do (roughly, quantum mechanics explains atoms and relativity explains galaxies), but, embarrassingly, the two theories are incompatible. This hardly ever matters, which is why physicists have been able to get away with it. But when you're dealing with extreme situations - black holes, and the beginning of the universe - it matters a great deal. As you probably gathered if you watched Interstellar, physicists don't really understand what goes on inside black holes. They are even less certain about what happened right at the beginning of the universe.

The current situation is, to say the least, unsatisfactory, and physicists have been trying to find a way to stick the two theories together for nearly a century: that's what "quantum gravity" is. The leading contender over the last few decades has been string theory, which has achieved a high enough profile that almost everyone at least recognises the name. For a good while, string theorists tried to make out that they were the only approach worth mentioning. When Lee Smolin wrote Three Roads to Quantum Gravity at the end of the last century and gave equal billing to the alternative approach of LQG, there was angry muttering from some string theorists that he was being unrealistically partial to his pet idea.

Since then, however, LQG has made steady progress while string theory has run into problems. Most worryingly for the string theorists, none of the supersymmetric particles essential to the theory have been found by the LHC, our friendly local particle accelerator. That doesn't necessarily mean they aren't there; maybe they don't quite have the predicted properties and are harder to find than expected. But the old Feynman crack about string theorists making excuses rather than predictions is starting to sound unpleasantly apposite. Now LQG has taken another step forward in making itself respectable. This book does a great job of describing the ideas in simple, straightforward language and explaining their appeal. Non-experts - including, one assumes, some who control funding - will soon think that there's a real choice available. If I were a string theorist, I'd be feeling that someone had better start writing a reply.

I won't try and explain here how LQG works. As noted, the book does that very well, and is also fun to read. If you know a little quantum mechanics, my guess is that you'll find it surprisingly simple and intuitive: basically, it's just the way you'd expect to be able to combine quantum mechanics and gravity. I'm sure that there's a huge amount of complexity not visible under the surface, and if I'm suspicious it's because it seems just a bit too good to be true. But deep learning, a subject I know more about, was like this. The idea is super-simple, but it took ages to fix some annoying technical problems that held up progress; once they were solved, the whole field took off. It sounds like LQG could be headed in the same good direction.

Okay, I can't deny it: I'm interested. Where do I find a level 2 treatment with a few more equations, so I can look under the hood and kick the tires? I'm seriously thinking of buying.

(I also have a frivolous review here).

Update: the level 2 treatment is Covariant Loop Quantum Gravity: An Elementary Introduction to Quantum Gravity and Spinfoam Theory . It requires nontrivial knowledge of quantum mechanics and general relativity - but if you wanted more detail about the footnotes in Reality Is Not What It Seems, there's no doubt that it'll deliver. Available for free download here.
Profile Image for BlackOxford.
1,085 reviews68.4k followers
November 14, 2019
Making Space

Quantum Gravity is the closest thing in Physics to a coherent explanation of the origin and fate of the universe - how it began, how it works, how it evolves. Quantum Gravity also has a pretty fair shot to reconcile the apparent paradoxes and contradictions involved in and between the theories of General Relativity and Quantum Mechanics. Most recent scientific observations favour it over alternative theories as the way forward for Physics. But Quantum Gravity does fail to explain one important thing: meaning, including the meaning of the idea of Quantum Gravity.

According to the latest findings of empirical research in Quantum Mechanics, the fundamental constituents of the cosmos are fourteen or so 'quantum fields', the behaviour of which produces, more precisely constitutes, discrete particles of energy and matter. Despite the unintuitive character, and sometimes apparently paradoxical implications of Quantum Mechanics, every scientific test conceived and executed has confirmed its predictions. It is the biggest single scientific truth available at the moment.

Einstein's Theory of General Relativity states that Space and Time are not separate categories of existence but part of a composite Space-time. This may be tough to visualise but Quantum Mechanics makes the picture even less imaginable by portraying Space-time itself as a Quantum Field. Like other fields in Quantum Mechanics, it too is 'quantised', that is, composed of quanta, small indivisible bits. There is thus a smallest Space-time component which sets a definite lower limit not just on how small anything can be but also how densely compacted any material or energy can be. One implication, therefore, is that the mathematical horrors of General Relativity don't occur: the universe did not start as an infinitely dense 'point' at the Big Bang; nor do black holes consist of infinitely dense material.

At this point theoretical Physics starts to get properly spooky. Quantum Gravity considers Space, on its own, as a field. This field is theorised as composed of discrete 'threads', analogous to electromagnetic lines of force, which form 'nodes' when the threads intersect. The threads are conceived as 'loops' which then 'interweave' at the nodes. These nodes are the small, discrete bits of Quantum Space.

The most that can be said at this stage in scientific thought is that Space is somehow 'woven' by these discrete 'threads'. These are effectively, then, atoms of Space, upon which other quantum fields are somehow layered. Perhaps the most astounding aspect of the theory of Quantum Gravity is that Time disappears entirely as a basic component of the universe. Rather, Time is merely a manifestation of the underlying quantum gravitational field. Simple really!

In the world of Quantum Gravity, the principle of cause and effect no longer holds. Space, particles, quanta only exist when they interact. And they only interact probabilistically. Processes have starting points and end points. But a determinate connection between these points does not exist. Particles, quanta, fields interact but they do not cause 'future' states of particles, quanta, and fields because there is no determinate universal 'future'.

Therefore, there can be no sequence involving time. Time simply doesn't exist at the quantum level (happily perhaps because Special Relativity had already shown that time wasn't something anyone wanted to touch with a scientific barge pole). When the tortuously complex detail is put aside, it turns out the entire world is made of one 'Covariant Quantum Field', which includes Space as well as all the other fields of matter and energy layered onto it. Everything that happens in the universe emerges from this unified field.

Well not quite everything. The problem that Rovelli stays as far away from as he can is this: What the Covariant Quantum Field might not produce is Carlo Rovelli contemplating the Covariant Quantum Field. That is, nowhere in the theory is there an indication that anything like an idea, which is immaterial, can be produced. The only products of the field are material: space, energy or matter. None of these constitutes an idea. Nor do they collectively constitute the emotion that Rovelli clearly has about the Covariant Quantum Field. The issue is important to keep science from slipping into ideology, a pattern typical in modern science from Millsian economics to Darwinian biology to Nietzschean philosophy.

Rovelli implies that the Covariant Quantum Field does indeed generate ideas and emotions, at least indirectly, because it is the ultimate foundation of all that exists, including his brain and the readers'. There may be many rungs up the ladder from the field, to fundamental particle interactions, to non-quantum events, and ultimately to life, both human and otherwise. But the field, inevitably, is the ultimate source for all human behaviour, including human thought.

This argument would then include the thoughts of, say, Purpose and Success. Rovelli makes no attempt to explain the precise connections up the great chain of being from the 'sea foam' of the quantum fields to the grey matter of the human brain. But his implication is clear: We, our ideas, our actions, including the writing of a book about the Covariant Quantum Field are generated by the Covariant Quantum Field.

Although Rovelli's presentation is couched in terms of Quantum Gravity, it is precisely the same stand (and the same hubris) taken by generations of classical physicists who believed that the world ran exclusively on Newtonian laws - from atoms right up to professors of physics. It is called Reductionism: the claim that all of existence can be reduced to the laws, rules and observations of a single discipline. Judging by his incidental comments about the harmful effects of religion on science throughout the ages, it is immateriality that is his intended reductionist target. But this gets him into a bit of trouble. Ideas, in particular, don't fit easily into the theory. Any theory that claims universality ultimately has to deal with them.

Rovelli has his own intentions which are stated or implied in the book: to communicate facts and theories, to contribute to the prestige of his discipline, to express his poetic take on science, to establish science's superiority over other modes of inquiry. Finally, he is making a case that science is beneficial for the world; it is successful; it has value. None of these intentions are pure description. They are all ideas and they all involve what we commonly call purpose. And they all clearly have great emotional significance for Rovelli.

Where did these ideas, these purposes, and implicit criteria of success or value along with their emotional baggage come from? Who or what is responsible for them? How are they to be assimilated into political and social life? This book, according to the title, has a claim to defining reality. Any such claim needs more than mere disciplinary or even scientific justification. Physics cannot claim a privileged position. This is Scientism, the presumption the superiority of scientific authority in the description of the world.

One possibility is that Rovelli is being manipulated by Quantum Gravity to investigate itself, and the field is providing him the criteria for successful investigation at the same time. Unlikely as it is that the author would like such an interpretation, it's a logical possibility. Is there an alternative?

Could it be that purpose, intention, emotions are not a properties or implications of the field at all? Could it be that the Covariant Quantum Field has absolutely nothing to say about what is a criterion of better or worse, or of what constitutes success? To admit this possibility would mean that purpose and other ideas, like Quantum Gravity itself, are independent of the field. Such a possibility would require Rovelli's inclusion in the theory not merely as an observer who affects quantum results, but as an evaluator, a judge of the reasons for his inquiry in the first place, one who defines what a result is.

Purpose, for example, could well be what is called in Systems Theory an 'emergent property.' Such a property would not be a simple consequence of the behaviour of the field, neither logically nor physically. Emergent properties can't be predicted on the basis of the interactions in the field. Such an emergent property would fit with the random character of field interactions. But it would also 'transcend' these interactions. That is, some relations and interactions, like Purpose and Success, have the field as a necessary condition, but not as sufficient condition for their existence. Something else has to contribute.

Rovelli accepts the relativity involved in modern physics. But he doesn't like the relativity implied by differences in Purpose and Success, what might conveniently, if somewhat loosely, be called Politics, the process of the establishment of value. He considers particles but not people to be defined by their relationships. On the one hand he clearly detests religion for its dogmatic stance on truth and about what's important. On the other hand, he dislikes modern philosophy for its challenge to dogmatic claims to truth and about what's important. Only physical scientists, it seems for Rovelli, have the imaginative skill to understand the world and to express it adequately. This is not just a cosmology, it is a cosmological ideology.*

He is therefore ambiguous about what Quantum Gravity really means. He can only state rather tired cliches about the superiority of scientific method - science as exploring new ways of thinking; tireless scientific genius; religion, particularly monotheism, as an enemy to thought; philosophy as misleading nonsense. What he means by scientific method are the procedures and criteria he and his colleagues employ at the moment, whatever they are. But he doesn't want the philosophical arguments that justify his freedom applied generally. This he sees as 'relativism.' He wants the theory Quantum Gravity accepted by the public. But he doesn't want current theories to be taken literally, that is to be interpreted by non-scientists, as a description of the world. He wants us to rely on the experts to know what Quantum Gravity implies and to leave what it means alone.

In short, he wants power to realise his intentions. Ideologies are ideas that justify power. In this case, the power of physicists to establish the definition and boundaries of reality. Ideologies work by limiting the scope of what can be considered real and important, by prescribing what's valuable. The ideological import of the book is apparent in the title, and subtly confirmed in its content.

Is there space in Quantum Gravity for something else?


* An important clue to Rovelli's ideological intent is his inclusion of Shannon's Theory of Information to support the conjectures of Quantum Gravity. Written in 1948, this theory is hardly state of the art. However it does have a compatibility with Rovelli's point of view. It 'reduces' all of reality to bits of digital information. It is this theory which inspired the Beam Me Up Scottie of Star Trek as well as Neal Stephenson's Cryptonomicon. It is also an idealised description of the totalitarian state in which all individuals are the information stored about them. Theories of this sort are not simply descriptions of the world. They transform easily and almost invisibly from method to ideology. Shannon's theory for example played a large part in the influence of Cybernetics in the 20 years following WWII. Cybernetics as an ideology deflected public and scientific attention away fro the discussion of ends, purpose, to the discussion of means, mainly the technology of industrial efficiency and war. See GR review of Kurt Vonnegut's novel Player Piano.

Contrast Shannon's reductionist's theory of information with that a semiotic theory of information. In Semiotics the unit of analysis is called a 'sign'. A sign is something that can be interpreted as having a meaning, which is something other than itself, and which is therefore able to communicate information to the one interpreting or decoding the sign. In Semiotics, words are signs, behaviour is a sign, anything with a potential meaning is a sign. So the Covariant Quantum Field is a sign. In fact a person is also a sign. Defined as a sign, a person is not 'decomposed' into bits, but taken as an entire human entity. This entity can, in fact insists upon, being interpreted and interpreting. It is not constituted by anything other than itself. Like quantum particles, a sign is always relative to other signs but not subordinate. Unlike quantum particles, the human sign can love. Perhaps Professor Rovelli might consider this sign as an alternative reality.
Profile Image for Darwin8u.
1,599 reviews8,732 followers
August 25, 2017
"Before being technical, science is visionary."
- Carol Rovelli, Reality is Not What it Seems


(5 stars for poetry; 3 stars for precision)

When one discusses matters celestial or theoretical or cosmological it best translates when done in math or poetry. Rovelli has an amazing talent for singing the esoteric, theoretical language of Quantum Gravity. He finds meter with its loops and rhyme in the paradoxes. He is able to fluidly convert the edges of theoretical physics into a language that amateur scientists, the untrained, or even the casually curious can enjoy.

I'd write more today, but I'm heading tomorrow to a land where I can observe better the eclipse next week. May the sun shine, the clouds part, and the predictive abilities of cosmologists continue, at least for another week. I'll pick this review up again in a week+ with some notes and comments about the eclipse and the non-infinite universe.

**** (x) ****

Post eclipse Baily's beads. So, one of the people I met at the eclipse totality (she stayed at my sister-in-law's house in Rigby, Idaho) was Lisa Randall, Harvard professor of particle physics and dark matter expert. I teased her about how it must be tough to hear an Italian physicist proclaim the death of String Theory and that Loop Theory is where it is at. She sniffed and said he was a great writer, but she couldn't take seriously someone who got the basics of quantum mechanics and the date of the discovery of the Higgs particle wrong*. The many errors, and general sloppiness of physics in the book drove her nuts.

I can see Randall's point, but also still love the way that Rovelli translates, even with a certain looseness, Quantum Gravity and the history of physics for layman like myself. It highlights one of the tensions that have existed for years in science. Often, fame follows not just who is RIGHT, but who WRITES well.

As my NOW favorite LIVING theoretical physicist Lisa Randall suggests in her New York Times review :

"The beauty of physics lies in its precise statements, and that is what is essential to convey. Many readers won’t have the background required to distinguish fact from speculation. Words can turn equations into poetry, but elegant language shouldn’t come at the expense of understanding."

* On page 129 Rovelli says "A recent confirmation was the discovery of the Higgs particle, which caused a sensation in 2013." (4 July 2012 was the date of discovery; on December 10, 2013, Peter Higgs and François Englert were awarded Nobel prizes for predicting this discovery). Randall also told me she had an issue with the metaphors Rovelli used. "Metaphors are supposed to make things more clear, not more confusing."
Profile Image for Barbara.
1,396 reviews4,907 followers
May 31, 2023

3.5 stars

In this book Carlo Rovelli, a theoretical physicist, explains Loop Quantum Gravity (LQG) - a concept that merges Einstein's theory of general relativity with quantum mechanics.

Carlo Rovelli

The theory of LQG was developed over the past few decades by theoretical physicists using sophisticated mathematics.

Theoretical physicists, however, were hardly the first people to speculate about the nature of the universe. Rovelli's discussion starts with ancient philosophers like Anaximander, Plato, Socrates, and Archimedes - men who had surprisingly insightful notions about the world.





Humanity's understanding of the cosmos then advanced over the ages, with huge breakthroughs by Sir Isaac Newton and Albert Einstein, and important contributions by many others. Rovelli gives us a brief overview of the work of many great thinkers.

Sir Isaac Newton

Albert Einstein

[Note: We'd probably be much farther along if women had been allowed to contribute throughout history. LOL 😎]


LQG - being largely mathematical - is difficult to explain in plain English, but Rovelli does a creditable job conveying the general idea. I'll try to provide a VERY abbreviated explanation in this review, starting with general relativity and quantum mechanics.

The Theory of General Relativity posits that gravity results from the curvature of spacetime. For example, a planet bends space around itself, and a moon circles around a planet because it follows the curve of space (like a marble that rolls around a funnel). This explains the 'force of gravity' that prevents the moon from flying off into the galaxy.

Quantum Mechanics contends that the energy of a field is distributed in 'quanta', or packets of energy, like electrons in an electrical field. However the exact location of the quanta is unknowable because they exist in a haze of probability. That is, at any instant a quantum might show up at point A, or point B, or point C, etc....but some locations are more likely than others.

LQG combines these two concepts by trying to quantize space itself. In other words, LQG treats space like it comes in quanta or small chunks. The current idea is that space is a fabric of loops (closed filaments) and nodes woven together into geometrical assemblages called spin networks.

Filaments and Nodes

Spin networks are combined with time to produce spin foams. Thus, the universe is comprised of spin foams. [Rovelli mentions that this model doesn't explain dark matter, which we still don't understand. Get to work physicists!!!]

The components of spin networks are unimaginably small, having what is called a 'Planck length' of 1.6×10−35 meters. The size of the Planck length can be visualized as follows: "If a particle or dot about 0.1 mm in size (which is about the smallest the unaided human eye can see) were magnified in size to be as large as the universe, then inside that universe-sized dot, the Planck length would be roughly the size of an actual 0.1 mm dot.

LQG is useful because it tells us more about black holes and adds to our understanding of the origin of the universe (which could have been a 'big bounce' rather than a 'big bang').

Moreover, LQG eliminates pesky singularities in math and science (points at which an object's behavior is very bizarre and hard to explain).

"In the center of a black hole is a gravitational singularity, a one-dimensional point which contains a huge mass in an infinitely small space, where density and gravity become infinite and space-time curves infinitely, and where the laws of physics as we know them cease to operate."

Currently LQG is competing with String Theory to explain the universe, but that's a whole other book. 😊

I'm interested in theoretical physics so I enjoyed Rovelli's narrative. I'll admit, though, that I'm still not clear about everything the author says, which probably requires knowledge of the underlying math. Still, I'd recommend the book - which explains LQG a billion times more thoroughly than this review - to folks interested in the subject.

You can follow my reviews at https://reviewsbybarbsaffer.blogspot....
Profile Image for Bradley.
Author 5 books4,107 followers
June 1, 2018
I'll be honest and up front, I only wanted to read more into Loop Quantum Gravity.

Say what?!? Well, it's the leading contender against String theory. It doesn't try to mash together the main problem area of gravity with quantum mechanics, but rather extends quantum mechanics as a granular geometric equation into the macro realm of what we understand as special relativity.

In other words, Reality is finite, quantifiable, and can be extrapolated from the underpinnings of the general field of quantum mechanics.

If you know anything about the underlying basis of string theory, this idea is both flabbergasting and simplistic. And maybe, it's also correct.

I can't say for certain, and as far as I can tell, neither can the author. Most of the book gives us a survey of the underpinnings of reality physics from the conceptualization of the atom through Einstein's reformulation of heat energy on the equilibrium of those atoms in their environmental matrices. (E=MC squared)

Spin Foam is the name of the minimum Planck distance that forces atoms into discrete and quantifiable distances between each other. It's the reason why atoms don't just fall into singularities like black holes or crushed neutronium states under normal gravitic circumstances. It's not merely probability shells and energy levels, but quantum loops that behave like bubbles forcing certain distances... and therefore forcing Matter to behave the way it apparently behaves... making atomic structure.

The most interesting idea I'm getting from this is the idea of the Big Bounce. In other words, the cause of the great expansion once the Big Bang got lit. It reminds me a lot of how iron molecules make stars burp in the process of digesting (fusion) and cause a nova. Only we're dealing with a quantum state that coaxes atoms into creation through special wave functions behaving like granular notations. You know, like how light behaves like both a wave and a particle.

And beyond this... I'm completely lost. :)

I don't know the math but this book is pretty decent on the conceptual side. The basics are commonplace and I was mainly into it for the later weird stuff.

But all in all? Rovelli is a very, very good writer. Convincing. Clear.

It may not be the answer to the great question of our day and age, but he makes a very good case. :)
Profile Image for Manny.
Author 30 books14k followers
August 9, 2017
Enlightenment à la Rovelli (serves 2)

1. Divide the Dante into equal halves and fasten together with a good transdimensional adhesive to form a 3-sphere. Be careful not to get any glue in the primum mobile. Set aside to dry.

2. Stir the Lucretius, Galileo, Newton, Einstein and Heisenberg until thoroughly mixed. Add a little Anaximander to taste. Put in a warm place until it has risen.

3. Add the Feynman path integral and the lattice approximation to the spacetime. Whisk into a spin-foam using a quantised volume operator. Make sure the fields are covariant.

4. Pour the historical influences and the ἄπειρον into Canto XXXIII of the Paradiso. Squint at the mathematical footnotes so that you intuitively grasp the significance of the formulas without actually reading them. You may not get this right first time, but it is definitely worth the trouble. Wait for the enlightenment to take effect.

My girlfriend and I ordered this recently at the CERN cafeteria. I thought it was delicious, but in the interests of full disclosure I am forced to admit that my girlfriend was very disappointed. She said it tasted of penguin and she was sure the spoon used to serve it had previously been used for the Joël Dicker. I had no idea what she was talking about and ate her portion too.

(I also have a serious review here).
Profile Image for Max.
347 reviews338 followers
September 14, 2020
Rovelli crafts a unique presentation combining insight from the ancient Greeks, some Dante, a selective history of physics and his own quest for a theory of quantum gravity. He adds a little philosophy and even a few lines of poetry to challenging scientific concepts. Despite the trimmings, Rovelli is definitely writing for the science buff. For those that read popular physics books, there is little new in the historical section, but his selections help him make his point. He describes the incompatibility of general relativity and quantum mechanics as an entry into his ideas on quantum gravity. I had not read much about quantum gravity before. I had to take my time reading these sections and pause to think through what he was saying. After a while his arguments began to make sense and actually seemed quite logical. Undoubtedly some of it flew over my head; still I got some good takeaways and felt my time was well spent. My notes follow.

Rovelli gives snippets of the work of Newton, Faraday and Maxwell, Einstein, and Bohr, Heisenberg and Dirac to illustrate the progression of thought regarding the fundamental constituents of reality. Newton sees reality as space, time and particles. Faraday posits lines of force and Maxwell defines them mathematically adding fields to space, time and particles. In Special Relativity Einstein combines space and time into one entity spacetime so now we have spacetime, particles and fields. In General Relativity Einstein shows spacetime to be the gravitational field but not quantum. The work of Bohr, Heisenberg and Dirac reduces fields and particles to quantum fields so we are down to spacetime and quantum fields. Finally Rovelli goes on to argue that based on his ideas about quantum gravity spacetime is also a quantum field so there are only quantum fields.

Key quantum concepts to Rovelli are granularity, relationality and indeterminacy. Granularity: Nothing is continuous, everything is discrete. Nothing is smaller than the Planck scale. Thus unlike general relativity, infinities are eliminated. There are no singularities. Distances and volumes can’t be subdivided forever. Relationality: Only properties of objects that don’t change are inherent. All variables (position, momentum, energy) of objects are defined by interactions. Electrons only materialize when there is a collision. Rovelli says to think in terms of processes, not things. Indeterminacy: The specific values of the next interaction are not definite only probable.

Rovelli embraces Heisenberg’s matrix solution to quantum mechanics and sees Schrodinger’s wave function only as an aid to calculation, not reality. He also relies heavily on Dirac’s formulation of quantum mechanics holding that fields and particles are the same. He gives an example: “The electromagnetic waves are vibrations of Faraday’s lines, but also at a small scale swarms of photons. When they interact with something else, as in the photoelectric effect, they manifest themselves as particles…Photons are the ‘quanta’ of the electromagnetic field. But the electrons and all other particles of which the world is made are equally ‘quanta’ of fields!”

Granularity in quantum mechanics tells us that within any system there are a finite number of states, in other words a limit to the information within a system. But while everything is composed of discrete quanta, Rovelli clarifies “The world is not made up of tiny pebbles. It is a world of vibrations, a continuous fluctuation, a microscopic swarming of fleeting microevents.” It is the interaction or relation between these microevents that we see as particles. “There is no reality except the relations between physical systems. It isn’t things that enter into relations, but rather relations that ground into the notion of thing. The world of quantum mechanics is not a world of objects: it is a world of events. Things are built by the happening of elementary events.” Rovelli’s view of quantum mechanics is called the “relational interpretation”.

Rovelli turns to loop quantum gravity to reconcile the disparity between general relativity which doesn’t incorporate quantum fields and quantum mechanics which doesn’t take into account the curvature of spacetime. In quantum gravity space itself is quantized. Thus postulating gravitons proceeding through space doesn’t work. Loop quantum gravity is based on a solution by Lee Smolin and Ted Jacobson to the Wheeler-DeWitt equation that describes curved space. In loop quantum gravity the lines of the gravitational field are in loops that meet at nodes. The loops provide for spacetime’s curvature. The nodes are the quanta of the gravitational field. The volume of space arises from the nodes. The lines link the volumes together. Unlike other quanta such as photons which reside in space, nodes are not in space, they are space. In Rovelli’s words “At an extremely small scale, space is a fluctuating swarm of quanta of gravity, and together acting upon things…”

In this theory, time doesn’t exist as a continuous flow in which events occur. In Rovelli’s words “…the quanta of gravity do not evolve in time. Time just counts their interactions.” Time “…is born of the world, out of the relations of quantum events that are the world and themselves generate their own time.” “The space and time that we perceive in large scale are our blurred and approximate image…of the gravitational field.” “Fields that live on themelves, without the need of spacetime as a substratum, as a support, and which are capable by themselves of generating spacetime, are called ‘covariant quantum fields”. Rovelli holds that everything is made of these fields that simply lie “one on top of the other: fields on fields.”

Rovelli considers the effect of quantum gravity on cosmology, although he notes his ideas are exploratory. General relativity would have the universe come from an infinitely small and dense beginning, the Big Bang. In quantum gravity there is a limit to how small things can get. The equations of loop quantum gravity support the idea of the Big Bounce. If a universe collapsed it would proceed to the point where quantum repulsion took over and begin expanding. The same logic applies to black holes since there is no singularity in quantum gravity. The initial expansion would proceed very slowly since the intense gravitational force in a black hole slows time, but once it broke the event horizon there would be an explosion. Rovelli hopes we could detect such explosions in primordial black holes.

I find Rovelli’s ideas as palatable as the others I have read by theoretical physicists. Even though I have no way of knowing whose ideas, if any, will turn out to be important, I still enjoy reading these books. They send my mind wandering as I try to visualize the reality they describe. Although whether quantum gravity, string theory, wildly different quantum mechanics interpretations, it always seems like we are just peeling back another layer of the onion. Or as Rovelli puts it, “We are akin to small blind moles underground who know nothing about the world. But we continue to learn…”
Profile Image for India M. Clamp.
226 reviews
January 19, 2022
“Reality is Not What It Seems,” is pure prose told by Theoretical Physicist Carlo Rovelli. Utilizing advances in physics from Roman poet Lucretius, Greek philosophers delve into the enigma of what is existence. Here we turn toward a bright light in which gravity, energy, motion are substantive to chemistry, astrophysics and meteorology---all lumped together. Without knowledge of physics, full comprehension of the world is lacking. With common connections, this text bridges the gap between the scientist and the layman (who finds himself navigating the rough seas named reality).

"Sweetness is opinion, bitterness is opinion; heat, cold and color are opinion: in reality only atoms and a vacuum exist. Atoms...our life is a combination of atoms; the light we see is composed of atoms, which brings us images."
---Carlo Rovelli

Rovelli contends that poetry and science should be in a harmonious relationship adding "they are two tools to open our eyes to the complexity and beauty of the world.” Rovelli is compared to Primo Levi (Italian Scientist-writer) who agrees that science and poetry are quite compatible and are mutually attracted. The universe is made up of atoms and in their order we can find something quite revealing. Movement of the heavenly bodies interacting tells a story quite different than one we assume on faith lacking the freedom to ask questions. The physics of the interaction and benefits could be likened as being in proximity with an angelic force and thus being transformed or compromised by such. And such is dependent upon how one defines outcomes.
Profile Image for David Katzman.
Author 3 books475 followers
June 3, 2017
I've always thought that the generally accepted "solution" to Zeno's Paradox wasn't very acceptable. A curve approaching infinitely small = zero? But really, they aren't equal. You just kind of...round down? So imagine to my surprise, Rovelli supplies the most satisfying solution ever. Space...hold on...I have to pause dramatically, because this is just mindblowing...

Space is granular. That's right. Space itself is chunked just like light is made of photons. HOLY SHIT! That is why the hare can pass the turtle. There is no infinitely small. The Planck distance measures more than the smallest measurement possible, it measure the literal granules in spacetime. I'm stunned by the simplicity.

The first half of this book is a recap of the current experimentally demonstrated science of quantum physics, gravity, spacetime and particularly Einstein's theories. Rovelli is enlightening in this regard; he does an amazing job of making them comprehensible and further frames them in ways that I've never read before. Then Rovelli moves on to what he describes as untested theory around how gravity works and what it is. Although unproven, he was very convincing and the deductions logical.

One item that I found quite interesting was what Rovelli left out. He did not even once mention the multiverse theories that have grown from physicists trying to explain the meaning of the randomness in the Schrodinger Equation and the Copenhagan Interpretation. I thought he might have backhandedly slapped that approach when he said that those who focus on the solution to the equation are misguided.

If you have any interest at all in physics or the nature of the universe and reality, I highly recommend this book. I will likely read it again.
Profile Image for withdrawn.
263 reviews258 followers
June 21, 2018
“ ... let's look at the Earth, then you'll see there are things that stand still and things that will sooner or later come to a standstill, that is, at the moment they happen to be moving from one place to another, there is stoppage and delayed stoppage, there are two if we consider only the Earth and the way we see it, but if we take the realm of the invisible where, let's say, he says, neutrons and protons and electrons and hadrons and leptons and quarks and bosons and superpartners bicker and so on and so forth where the series endlessly continuable as time passes - because they too are only assembled out of something - well, no matter, the point that here we see motion, the interruption or stoppage of which, how shall I say deferred forever, so that we have stoppage and motion, but behind both, and pay attention now, he says, there is that elusive, unfathomable gigasystem that determines what is it going to be, stoppage or motion, and beyond the world there are other worlds, every world perfectly conceals another world, of course, although the whole thing can also be expressed by saying that any one world is only a gateway, a secret door to billions of worlds .... “
László Krasznahorkai (words of a drunk in Budapest) in The World Goes On

“Hold Infinity in the palm of your hand
And Eternity in an hour.” William Blake

When I was between the ages of 12 and 15, my family lived across the street from a cemetery. (No there are no extra-physical beings in this review.) On warm, summer, prairie evenings, I would wander over and lay down in the grass to watch the sky. (This was a time when I had rejected the totality of the human race. The peace of the cemetery was welcoming.) I saw a great deal, both above me and in my thoughts.

I recall the sparrow hawks circling overhead and then dropping from above at tremendous speeds to capture the unsuspecting insects that flew into the paths of the open jaws of the birds. And I waited each time for the swoosh of the wind through their wings as they pulled out of their seemingly inevitable meeting with the earth. I never lost the wonder of it.

And every night, the darkness came, or better, the light that pushed back the darkness came and I entered into a world of my imagination at its best. I lay trying to imagine those two greatest enigmas for me (having written off humanity) - infinity and eternity. I had not yet heard of William Blake, but I was delighted when I first read ‘Auguries of Innocence’ - despite its religious overtones.

I would lie there for hours watching the sky roll by and becoming entranced with my own thoughts. It was my childhood version of Zen. I was less concerned with finding an answer to my questioning and more taken by my state of mind. I realized that I could never really imagine a universe that stretched on infinitely - nor could I imagine one that had limits. What could be beyond the limits?

The same types of ideas arose around eternity. How could time stretch backwards and forwards without beginning or ending? And what did that all mean anyway? I lay there boggling my mind and thoroughly bewildering myself. Interestingly, it never occurred to me that science could help with this. In the early 1960s, we learned nothing beyond seventeenth century science, and not much of that. Until recently, I never tried to grasp anything about Quantum Physics. I’ve been more the poet than the scientist. Now I struggle with the most basic concepts. Carlo Rovelli is trying to help. He also wants to explain that he too has the heart of a poet. I’m not sure.

So, what would Rovelli make of my childhood reveries? Well, he would, and has, among many other things, explained to me that space and time, at least in my sense, do not do not ‘really’ exist. And, I suppose, that Blake had it wrong. There are particles and there are relationships between these particles but my concerns have been misplaced. Well, misplaced in any ultimate sense. I have immersed myself in enough Madhyamaka Buddhist thinking to be able to understand that I can distinguish ‘conventional’ stuff from ‘ultimate’ or ‘absolute’ stuff and that the absolute stuff is not only unknowable but is not reality. And of course, such ideas would seem at times to be where Rovelli and I part company. But then, maybe not. I do not even agree with his use of the word “reality”. His definition seems to meander.

Some quotes:

“And it is reliability that we need, not certainty. We don't have absolute certainty, and never will have unless accept blind belief. The most credible answers are the ones given by science, because science is the search for the most credible answers available, not for answers pretending to certainty.”

“ ... parts of an indispensable grammar for understanding the world. This grammar has evolved, and is still in the process.”

“water? A wave is not an object, in the sense that it is not made of matter that travels with it. The atoms of our body, as well flow in and away from us. We, like waves and like all objects, are events; we are processes, for a brief time monotonous. .... Quantum mechanics does not describe objects: it describes processes and events that are junction points between processes.”

“What makes a subject hard to understand - if it's something significant and important - is not that before you can understand it you need to be specially trained in abstruse matters, but the contrast between understanding the subject and what most people want to see. Because of this the very things [t]hat are most obvious may become the hardest of all to understand. What has to be overcome is a difficulty having to do with the will, rather than with the intellect. The reason there is so much "resistance of will" is because we wrongly assume that that which we are explaining resides in some foundation beyond us, be it God or the foundation of the physical world, namely,. particles. We need to see that we and our surroundings are the foundations, and we describe these, we do not explain them; just as we do not explain our consciousness; rather, we are conscious.”

I would like to agree with Rovelli on this last point, I really would, but I do not know that he has succeeded. He has not completely, in my case anyway, been able to convert his formulas and numbers into language that I can totally grasp. Too much of what he presents is in the form of metaphors, and until those metaphors become so deeply embedded in our daily speech, the are only metaphors. I don’t know that I can wait that long.

Where Rovelli has succeeded is in further eroding those metaphors of my past. I will no longer look at the night sky in search of limiting walls to the universe. I shall simply continue to wonder (perhaps in cemeteries at night). ... and read, of course.
Profile Image for Brian Clegg.
Author 204 books2,652 followers
December 14, 2016
I was no great fan of Carlo Rovelli's flowery, overpriced previous title, and the introduction to this book on loop quantum gravity has a similar style, but thankfully it settles down a little. However, there is still rather too much of the woffle, reverting to floral form on Lucretius and his atomist poem on nature. For those who remember How to be Topp, this is the Fotherington Thomas school of popular science - all 'Hullo clouds, hullo sky!'

We then get onto Galileo. At times, Rovelli's history of science goes wildly astray - he says, for example, that Galileo was the first experimenter - what of William Gilbert or the medieval optical experiments, for example? Similarly, Rovelli tells us that no one from Newton to Faraday tried to come up with an explanation for action at a distance - which just isn't true. Not only did Newton himself have an idea, there were plenty of mechanisms proposed. This isn't a matter of obscure history, you can read about it in Wikipedia. Best then to move on from mangled recounting of the past and get on to the more recent physics.

Here, in a gallop through special and general relativity and quantum theory we get far more rigour, though oddly it often comes in ways that aren't always obvious - for example we jump into to general relativity with the idea that spacetime is a field, without any of Einstein's far more accessible route using the equivalence principle. It fits better with the model that Rovelli is using, but it doesn't help the reader understand what he is talking about.

The last part of the book takes in what has been its goal all along - loop quantum gravity. In his opening, Rovelli remarks that a book (for the public) on loop quantum gravity didn't exist which is why he had to write it. This isn't true, there was Martin Bojowald's Once Before Time - but that failed singularly to explain the theory in a comprehensible way. This is where I hoped I could finally get the point of Rovelli's writing. I desperately want to see a good, accessible introduction to loop quantum gravity.The good news is that Rovelli on the topic reads a lot more smoothly than anything I've so far read - but he still fails to bring the topic to a level the general reader can get his or her head around. The book should have had an editor brave enough to keep sending it back until Rovelli had got there, but it clearly didn't happen.

You may gather I had problems with this book, but I have to congratulate Rovelli for trying. What was most frustrating was that if loop quantum gravity were as obvious to physicists and as complete as it's presented, it would be quantum gravity solved and no one would be bothering about string theory (which Rovelli only gives a passing mention to). Tick. Next problem? We know it's not really like that. Also, like many physicists seem to do, Rovelli either doesn't realise a model isn't the same as reality, or forgets to explain this to his readers. Even so, it is an interesting book despite its problems.
Profile Image for WarpDrive.
272 reviews406 followers
August 7, 2017
This is an introductory book to one of the most promising theories of “quantum gravity” currently attempting to merge quantum mechanics and general relativity: Loop Quantum Gravity (LQG), of which the author is one of the co-founders.

Loop quantum gravity posits that spacetime is essentially just a new field, conceptually not dissimilar to the other quantized fields postulated by Quantum Field Theory, and similarly characterized by features such as granularity, “probabilistic” behaviour and “indeterminacy”. Contrarily to the assumption of General Relativity (and as implicit in Quantum Field Theory too) that space is a continuum, the basic structure of space-time in LQG is assumed to be discrete, and subject to quantum fluctuations. Moreover, the locations of the single quanta of space are not defined with regard to something else, but only by the inter-relational links between them. The gravitational field is assumed indistinguishable to the geometry of spacetime (after all, in general relativity the same mathematical object, which is the metric tensor field, represents both gravity and the geometry of spacetime): space is created by the interaction of individual quanta of gravity.

This book is directed at the layman with only limited background in physics, and it does not get into any quantitative detail (do not expect to find here any mention of Lagrangians, Hilbert spaces or operator algebras), so it may be quite a disappointment to the more knowledgeable reader looking for some mathematical treatment of this theory. At least some sort of appendix with some decent mathematical detail would have been highly beneficial, in my opinion.
Moreover, the book does not get into any meaningful physics until page 50, as its first part is mainly dedicated to a brief history of physics starting with the Ionian Greek philosophers, reaching up to Newton; an history that does not add much to the book and it is also disseminated with platitudes and inaccuracies (such as the myth that the experimental method started with Galileo, that the Middle Ages were the “Dark Ages”, that there is a direct link connecting modern physics with the Ancient Greeks etc.).

Things do get better with chapters 3 and 4, when the author deals with special and general relativity, quantum mechanics and quantum field theory. The treatment is still at 30,000 feet altitude, and with an impressionistic style and approach, mind you, but the author at least manages to express the main concepts with great lucidity, elegance and conciseness. I also like the way the authors highlights the increasingly fundamental importance of relational and informational aspects in modern physics.

The author now leads us through the main concepts of loop quantum gravity, which is a very interesting theory, of which one of the most appealing features (at least to me) is that it tries to combine general relativity with quantum field theory in a rather conservative way: it does not require exotic new entities such as invisible extra dimensions or an infinite number of parallel universes, and it does not employ other hypotheses apart from those of GR and QFT, suitably rewritten to render them compatible.

It also naturally removes the re-normalization issues that characterize Quantum Field Theory (and very possibly any theory assuming a continuum of spacetime, I would like to add – think about the singularities in General Relativity), as it assumes a minimum length/volume of spacetime.
As an aside note, I must say, personally speaking, that I am still to be convinced that the need for renormalization is such a big, decisive issue: after all, QED is a fully renormalizable theory requiring only three counter-terms, and in more general terms, re-normalization is not that big evil as portrayed in some popular science: it is simply a procedure which allows us to sensibly calculate the effects of low energy physics, independently of how it may be possibly corrected at high energies (where for example there might be some heavy particles contributing to the diagrams and removing the divergencies apparent at lower energies). Renormalization is not an exercise in hiding infinities, but a process followed in order to identify any corrections necessary to an initially formulated Lagrangian, so to make it represent real life at “low energies”.

Anyway, loop quantum theory does appear very enticing in its postulating that everything is about fields, where all fields do not “live in spacetime” - fields live, so to speak, “one on top of the other : fields on fields”. Moreover, contrarily to what characterize other more exotic theories such as the Multiverse (theories that verge, in my eyes, perilously close to metaphysics), Loop Quantum Theory appears to be, at least in principle, open to empirical verification. I greatly appreciated that the author dedicates a whole chapter to this aspect (there is even some detail about the predicted statistical distribution of the fluctuations of the cosmic background radiation, and the predicted cosmic gravitational background radiation that might be identified by the future LISA experiment). This is absolutely fundamental – without at least the possibility for some experimental empirical support, no theory can be taken too seriously.

The only serious criticism that I have to make to the author's approach is that he verges on the disingenuous when he does not discuss potentially significant open issues with Loop Quantum Gravity (these are issues that are for example discussed by Penrose in his brilliant book “The Road to Reality”. Penrose is quite keen on this theory, and he does not hide his admiration for several aspects of Loop Quantum Gravity, but this does not prevent him from honestly highlighting the open issues of such theory).

To conclude, I also must say that I particularly enjoyed the positions that Rovelli has in relation to the epistemological role of science: “...science is affected by every sort of cultural and social influence. Nevertheless, despite all of this, and in opposition to the exaggerations of a few post-modernists, cultural relativists and the like, none of this diminishes the practical and theoretical efficacy of scientific thinking”. “Science is not reliable because it provides certainty. It is reliable because it provides us with the best answers we have at present. These answers are not reliable because they are definitive. They are reliable because they are not definitive”.

Overall, a pleasant enough book, not badly written, and informative (to a point), but in my personal view it represents a bit of a missed opportunity, as aimed too much at a very generic audience.
3 stars.
Profile Image for TS Chan.
719 reviews884 followers
August 14, 2018
For a topic as mind-bending as quantum physics, I marvel at Carlo Rovelli's ability to distill it down to something which normal folks like me can comprehend. To a certain extent, anyway.

The first part of the book which talked about the evolution of physics was well-written, concise and fairly easy to understand. Once he started to move into the realm of quantum gravity, the ideas and notions do get harder to grasp. Loop quantum gravity, spin networks and spin foam - the alternative to string theory - are almost beyond the reasonable imagination of humans who can only see and visualise matter on a macro level. Whoever said scientists have no imagination and creativity have no clue what they are talking about.

In referencing Dante's Paradiso, Rovelli writes:
I believe that this example demonstrates how great science and great poetry are both visionary, and may even arrive at the same intuitions. Our culture is foolish to keep science and poetry separated: they are two tools to open our eyes to the complexity and beauty of the world.

An intuitive representation of quantum gravity

I will need and want to revisit this book in the future once I've studied more on the subject and be able to compare string theory to loop quantum gravity. Similar to his other book, Seven Brief Lessons on Physics, this is a beautifully written book on a scientific theory that is one of the most difficult to understand. I will also be reading his latest book, The Order of Time, hopefully soon.

“To a wise man, the whole earth is open, because the true country of a virtuous soul is the entire universe.”
- Democritus
Profile Image for Manny.
Author 30 books14k followers
August 17, 2017
Does anyone know what "spinfoam" is in French? I was trying to describe this book to a francophone friend and couldn't find a translation.

The word comes across as sensible in English, but écume de spin sounded just plain weird to both of us. My friend was visibly unimpressed when I told her that that what the world was made of.
Profile Image for Jose Moa.
519 reviews68 followers
April 28, 2018
There are two main streams of research in joining quantum mechanis and general relativity,the string theory that is background dependant,the space-time,and the loop quantum gravity that is not backgroun dependant as it is a quantum theory of the space-time,in this sense ,for me, this is a more fundamental theory.
This is the first book I have read on loop quantum gravity and I have found it very clear ,accesible and easy to read in this difficult and technical subject,I also have found this theory beautiful and natural in the sense that it uses the same way to obtain a equation on the quantum dynamics of gravity as have used Schrödinger to obtain his equation on quantum dynamics of a particle,Schrodinger derived it from the classical mechanics equation of Hamilton-Jacobi and followig similar ways this theory derived it equation for the classic general relativity Hamilton-Jacobi equation of Wheeler-De Witt.
After a brief histhory and fundamental concepts of quantum mechanics and general relativity where Aristóteles is subtly criticed and Democritus praised the book tells that the solutins of quanticed Wheeler-De Witt equation are spin networks where in the knots is the quanticed space vales and the relations with the next quanticed space knots are in the links where the spin resides and can have multiple of 1/2,I have found this razonable as the spin,a quantum magnitude that has not classic analoge, is related with the matrix unitarian representation in complex spaces of the Lorentz group,the group of lorentz transformations,a generalization of the space rotations and time translations of the galilean group, of the space-time in Special Relativity.
In this theory the time dont appear in the equation,the time is relational,a ordered sucesión of events,macroscopically this order is given by the irreversibility the dynamics of the spin network is the spin foam and the quanta of gravity and space are the same in the new field named quantum covariant field.
So far this is only a beautiful theory,but for me have several positive points :
First-The Heisenberg incertidumbre principle for position momentun only give not absurd results if the space cant be shorter than Plancks length.
Second-As the space have a minimun size,the infinites in the quantum field theory dont any more exist as the perturbative serie is finite and renormalization trick is not needed.
Third-Inside the black hole the infinite density zero space point singularity dissapears.

In a editorial world full of rather fancy physics books as those of Brian Green,Lisa Randal and others,this is a honest and fresh air book that gives a realistic alternative point
As a anecdote,it seems that Greg Egan is a fan of this theory because in his novel Schids Lader the theory of everything is a quatum graph theory,the novel a really hard SF novel, begins textually so :
"In the beginning was a graph,more like a diamond than graphite.Every node in this graph was tetravalent :connected by four edges to four other nodes.The edges has not length or shape,the nodes no position ;the graph consisted only of the fact that some nodes were conected to others.This pattern of connections,repeated endessly,was all there was "¡The world, pure geometry!
Profile Image for Yegane.
15 reviews18 followers
August 15, 2021
ایکاش میشد کتابو بکوبونم تو دهن دبیر فیزیکا.
Profile Image for Charlene.
875 reviews525 followers
April 27, 2017
This book is a modern day, On the Nature of Things. Like Lucretius himself, Rovelli is a poet who, with his words, constructs beautiful images of the true nature of reality.

The key message in this book is that everything comes down to geometry and the geometry of space is much more interesting than we probably suppose. Energy has morphed into various shapes as it traveled from the radiation of the hot, dense, atom sized ball it was when it was young, to elements and forms seen in the cooler, expanding, vast universe of today. The laws of thermodynamics have ensured that various geometrical shapes occur and those geometrical shapes are forced to interact with other thermodynamically created geometrical shapes. What a symphony!

Rovelli detailed the most exquisitely beautiful history of how humans have come to understand the geometry of space itself, the matter that populates space, and how that geometry translates into motion of objects on Earth and in the universe at large. For example, Newton came to understand, and subsequently helped the rest of humanity understand, that because of Earth's shape and size, it would exert a strong gravitational pull on an apple and the apple would exert a small pull on Earth. Humanity could then finally understand how they would remain solidly planted to the ground if the earth were to rotate. It was perfectly reasonable before Newton to assume a human would fall off Earth if it spun upside down.

However, Newton himself could not understand the implication of his own theory. What physical material could do the action of pulling one object to another-- something Einstein later called "spooky action at a distance."? Without this substance, Newton could not understand how gravity could cause the large object to pull the smaller object physically toward it.

Michael Faraday was able to shed some light on this problem when he came to understand that the electric field and magnetic field were one in the same, the electromagnetic field, which can be thought of as lines in space that fill all of space, that attract elements toward each other. But, how then could this fully explain the gravitational pull of a large object like the sun pulling Earth toward it or a black hole pulling whole solar systems toward it?

(As an aside: I love all histories of Faraday. I cannot help but constantly play a voice inside my head that says, "Michael Faraday, May The Force be with you!" This is so stupid and has nothing to do with the actual force in the universe; and yet, I cannot help saying it in my head every time I read about Faraday.)

With his theories of special and general relativity, Einstein helped humanity understand how forms with large masses could pull smaller masses toward them. Einstein came to understand how spacetime itself was not just populated with Faraday's field lines; spacetime itself was warped by large objects. That is, large objects bend and stretch the fabric of spacetime such that nearby smaller objects have their spacetime bent too. The spacetime bends so the large object is always at the bottom of a hill and all the objects around it are higher up and fall toward it. The density of the object is what bends the spacetime and acts to lower the energy needed for other objects to fall toward it. (it really isn't that different from an enzyme in living systems). This is why Caleb Sharf (who was not mentioned in this book) called black holes "Gravity's Engines." They power the motion of the universe.

Rovelli argues that, like Faraday's field lines, gravity has its own lines. But, and this is the crucial but, gravity does not make up lines in space, gravitational lines *are* space. They construct the actual space upon which Faraday's lines can exist. John Wheeler's equations show that these gravitational lines close in on themselves. Thus, they are a loop; and thus, they are quantized loops of gravity. According to this theory, these quantized loops of gravity are what makeup spacetime itself.

These quantum loops of gravity have some important and fascinating implications. Since each loop is a specific quanta of space, it affects how we understand the singularity of the beginning of the universe or the singularity of black holes. General relativity tells us that gravity in a black hole will pull objects into it to smaller and smaller spaces, to a point of infinite density. But, and this is an important but, quantum gravity says that nothing can be condensed indefinitely. Things being pulled into a black hole can only be pulled in to a *finite* density. This is because *space itself* is quantized. Space itself can only get so small (the size of each loop of gravity). So, an object can only be condensed to the size of the smallest size of space itself (the loop).

I love the idea of each loop being a node in a web, but I would eventually like a more solid explanation of how that can be. I suspect that the universe works that way, but that is based on nothing except for the my love of networks. I need a little more convincing before I buy the whole argument, but I have to say, it is by far my favorite argument for how the universe works.

At the end, Rovelli eluded to Jeremy England's work on dissipation of energy in living systems (thermodynamically driven evolution, which is a continuation of Schrodinger's work) but didn't really do much other than gloss over it. Still, I was happy to see it included.
Profile Image for Alvand.
56 reviews6 followers
September 18, 2021
یک کتاب علمی خوب چه کتابی است؟ کتابی نیست که مفاهیم پیچیده و فرمول‌های عجیب غریب و سخت داشته باشد؛ بلکه کتابی است که به ساده‌ترین شکل ممکن بتواند این مفاهیم پیچیده را با فروتنی و عدم ادعا بیان کند. دقیقا این چیزی است که کارلو رووِلّی آن را در این کتاب به کار برده است.

"هدف علم این است که بفهمد جهان چگونه کار می‌کند، تصویری از جهان بسازد و آن را گسترش دهد و ساختاری مفهومی فراهم کند که از طریق آن بتوانیم به جهان بیاندیشیم."

تصویری که در این کتاب از جهان ارائه می‌شود از ابتدای اندیشه‌ی انسان در فیزیک یعنی از آناکسیمندر و اتم‌های دموکریتوس شروع می‌شود با گرانش نیوتن و میدان‌های فارادی و ماکسول و نسبیت‌های خاص و عام انیشتین ادامه می‌یابد تا در نهایت به تصویر زیبایی که مکانیک کوانتومی و گرانش کوانتومی از جهان نشان می‌دهند، ختم می‌شود.

چه لذتی بالاتر از لذت یادگیری و فهمیدن��

"به نظر من تلاش برای بیشتر دیدن و پیش رفتن یکی از شکوهمندترین چیزهایی است که به زندگی معنا می‌دهد. مانند عشق ورزیدن یا نگریستن به آسمان. کنجکاوی برای یادگیری، برای کشف، برای سردرآوردن از پشت تپه‌ی بعدی، میل به مزه کردن یک سیب، این‌هاست که از ما انسان می‌سازد. همانطور که اولیسِ دانته به همراهانش یادآور می‌شود، ما نه برای 《زندگی مانند حیوانات، که برای جستجوی فضیلت و دانش ساخته شده‌ایم》.
Profile Image for aPriL does feral sometimes .
1,932 reviews438 followers
July 17, 2017
I finished it, for which I deserve five stars. The author used great illustrations, for which he deserves five stars.

However, I think the author should have described certain quantum ideas, like 'spin networks' and loops with more illustrations and longer chapters and more words rooted in common everyday language - but on the other hand, my brain grasps liberal arts with ease while I flounder and drown in math conceptualizations, not to mention in solving higher-math equations. Maybe the author DID describe accurately those things.

The author has extensive notes, an annotated bibliography and an index. As far as I can tell, this is a fantastic book. The author certainly tried very very hard to make quantum mechanics understandable.
Profile Image for hayatem.
688 reviews169 followers
August 18, 2020
يساعدنا الكتاب على إعادة النظر للعالم، وطرق فهمنا له وبعين واسعة نافذة ، كذا إعادة اكتشاف فهمنا لطبيعة الأشياء من حولنا بعقل متسائل وناقد . كما يجعلنا نعي كثيير من الأمور العظيمة التي طالما ظننا بأنها يقيناً.

الكتاب يدور حول أعظم اكتشافات القرن العشرين: النظرية النسبية ل للعظيم آينشتاين و ميكانيكا الكم. مع التركيز على جوهري المحتوى الفيزيائي للاكتشافين.

الواقع ليس كما يبدو؛ الواقع هو انعكاس، وصورة لكل ما يدور في أذهاننا، باتساعها وضيقها بين فنية وأخرى، الواقع المرئي لا يتطابق معه بأي حال من الاحوال! ذلك أن الواقع مستقل في وجوده عن الوعي الإنساني.

رائع جداًً
Profile Image for Dan Graser.
Author 4 books105 followers
February 3, 2017
Given the audacity of several titles on string theory that have been published for the last decade or so, I can forgive the overly grandiose title here. A more appropriate title would be, "The Contextual Justification for Early Elements of the Theory of Loop Quantum Gravity as a Means of Linking Quantum Mechanics and General Relativity." If this is your first introduction to several modern concepts in physics then this is a 5 star book for you, those more familiar with the material can likely skip the entire first half and delve into his material on this competing theory (competing with the over-published string theory) linking quantum mechanics and general relativity, that being loop quantum gravity. Rovelli is a very passionate writer and only occasionally strays off into overly poetic language that confuses more than explains. A fun read and good introduction to a theory of which the general public is likely unaware.
Profile Image for Markus.
216 reviews70 followers
April 19, 2019
"Die Wirklichkeit, die nicht so ist, wie sie scheint"

Genau betrachtet implizieren diese Worte,
1. dass es eine Wirklichkeit gibt,
2. dass diese scheint (ein Bild im Betrachter hervorruft),
3. dass Bild und Wirklichkeit nicht übereinstimmen.

Man beachte, dass es sich hier um reine Annahmen handelt, die niemals überprüft werden können. Dazu müssten wir die Wirklichkeit zugleich beobachten und nicht_beobachten, ein typisches Paradoxon …. aber langsam, ich komme darauf zurück.

Meinen Wissensstand in Physik aufzufrischen und mich dann mit der Idee der Schleifenquantengravitation zumindest im Prinzip bekannt zu machen, ist Carlo Rovelli mit diesem Buch perfekt gelungen. Er versteht es, in klaren Worten das Wesentliche aus dem komplexen Stoff herauszuholen und für den interessierten Laien anschaulich und verständlich aufzubereiten. Die physikalischen Gegebenheiten stehen dabei nie für sich selbst, sondern werden in Beziehung zu Philosophie und in den Kontext eines historisch bedingten Weltverständnisses gesetzt. Rovelli überträgt seine Neugier an den Geheimnissen der Welt und seine Bewunderung der Schönheit der Physik mit oft überschwänglicher Begeisterung auf den Leser. Ein wirklich beachtenswertes, spannendes und faszinierendes Buch!

Die Geschichte beginnt in der Antike mit den Vätern des Atomismus Leukipp von Milet und Demokrit, die als erste die Idee vertraten, dass die Welt aus kleinsten unteilbaren Teilchen bestehen müsste. Nach der Dunkelheit des Mittelalters wird die Spur rasant wieder aufgenommen, Newton begründet das Gravitationsgesetz, Faraday und Maxwell erforschen die elektromagnetischen Felder. Ab diesem Zeitpunkt bestand die Welt aus Raum, Zeit, Teilchen und Feldern. Anfang des 20. Jahrhunderts erneuerte Einstein diese Sicht radikal, indem er Raum, Zeit und Gravitation als Einheit erkannte und das Konzept des Gravitationsfeldes als gekrümmte Raumzeit begründete. Die Welt besteht bis heute nur mehr aus Feldern und Teilchen. Bohr, Heisenberg und Dirac legten die Grundsteine der Teilchenphysik: Der Mikrokosmos ist granulär, indeterminiert und existiert nur in Form von Wechselwirkungen.

Beide Konzepte, Feld und Teilchen, sind in sich schlüssig, aber bis heute nicht unter einen Hut zu bringen. Die Quantengravitation ist der Versuch ihrer Zusammenführung. Unter zahlreichen Theorien und deren Varianten (siehe M-Theorie, Stringtheorie, Matrixtheorie, asymptotische Sicherheit, Supergravitation, usw., die im Buch nicht behandelt werden), ist die Loop- oder Schleifenquantengravitation ein vielversprechender Kandidat und Carlo Rovelli einer ihrer prominentesten Vertreter. Im zweiten Teil des Buches versucht er die sehr komplexen Vorstellungen dieser Annahme zu erklären und auf ein für unsereins halbwegs verständliches Niveau herunterzubrechen, was ihm auch sehr gut gelingt. Stark vereinfacht geht es darum, dass es Raum und Zeit als beliebig unterteilbare Kontinuitäten nicht gibt. Die Dinge befinden sich nicht "im" Raum, Ereignisse entwickeln sich nicht "in" der Zeit. Es gibt kein Raumzeitkontinuum, als leeres "Behältnis", in dem die Welt stattfindet. Die Raumzeit hat in der subatomaren Größenordnung eine gequantelte Struktur in Schleifenform, sogenannter Spinschaum, der aus einer Art Wolke aus Wahrscheinlichkeiten durch die Wechselwirkung der Teilchen permanent entsteht und vergeht: www.youtube.com/watch?v=SW7hmll8MKY

Bis jetzt sprechen gute Indizien für diese Hypothese, Beweise gibt es nicht, könnten aber durch exaktere Vermessung der Hintergrundstrahlung und schwarzer Löcher noch folgen. In diesem Fall müssten einige in der Wissenschaft gültige Annahmen revidiert werden. Der Urknall wäre nicht der absolute Anfang des Universums und schwarze Löcher wären keine ewig stabilen Objekte. Beide Annahmen setzen einen unbegrenzt teilbaren Raum voraus, der Ursprung des Urknalls genauso wie das Zentrum eines schwarzen Lochs sind laut Relativitätstheorie auf unendlich kleinen Raum verdichtete Materie/Energie. Auch der Begriff der Unendlichkeit wäre überflüssig, Mikro- sowie Makrokosmos wären relativ zu drei Naturkonstanten vermessbar, der Lichtgeschwindigkeit c, der Plank-Länge Lp und dem Plankschen Wirkungsquantum ħ als kleinste Informationseinheit.

Es ist außerordentlich spannend, wie Begriffe aus unserer unmittelbaren Welterfahrung in der Physik zunehmend verschwinden: oben und unten, kalt und warm, dann der 3-dimensionale Raum und jetzt noch die Zeit. Auch die Unendlichkeit könnte sich als Hirngespinst erweisen, dazu erfunden, Mysterien und Religionen zu unterfüttern oder unser Unverständnis mathematisch zu hintergehen.

Das vorletzte Kapitel behandelt die Erkenntnisse Claude Shannons und den Begriff der Information, der in der Quantenmechanik eine entscheidende Rolle spielt und den manche Forscher für den Schlüssel zum Weltverständnis halten. Anschließend bringt Rovelli den Begriff der thermodynamischen Zeit ein. Wenn ich das richtig interpretiere, gäbe es per se keine Zeit, sie wäre Surrogat eines Informationsgefälles - wir erzeugen selbst die Zeit, um unseren Mangel an Information zu kompensieren - der gleiche Mechanismus der die Wärme einer Tasse Tee an die Umgebung abgeben läßt.

Viele Quantenphysiker bezeichnen den Beobachter als konstituierend für die Wirklichkeit. Ich denke, es ist kein Zufall, dass die für die Quantenphysik essentielle Informationstheorie Shannons auch zur Kybernetik und in Folge zum Konstruktivismus und zur Systemtheorie geführt hat. Ein Zusammenhang ist jedenfalls nicht zu übersehen und die Vorstellung, dass die vermeintlichen Fundamente der Wirklichkeit Konstrukte des Beobachters sind, nicht mehr so abwegig. Auch in der Gehirnforschung gibt es dazu zahlreiche Hinweise.

Der von mir sehr geschätzte Physiker, radikale Konstruktivist und Kybernetiker Heinz v. Förster sagte "die Wirklichkeit, wie wir sie wahrnehmen, ist unsere Erfindung" und noch radikaler, dass "wir Teilchen nur erfinden, um eine Lücke in unserer Hypothese zu schließen".
Heinz von Förster - Teilchen sind Erfindungen

GR-Freund BlackOxford warnt in seiner Rezension des vorliegenden Buches vor einem Reduktionismus und weiter im Zusammenhang mit Shannon und der Kybernetik vor damit verbundenen totalitären Tendenzen. Ausnahmsweise teile ich hier seine Meinung überhaupt nicht. Aus der konstruktivistischen Perspektive Heinz v. Försters (wie auch Maturana, Varela, Watzlawick ...) ist das Gegenteil der Fall. Försters bekanntes Zitat "entscheide stets so, dass sich deine Möglichkeiten vermehren", ist im Sinn der Informationstheorie ein Bekenntnis zur Komplexität und klar antireduktionistisch.

Auch Rovelli weist auf die Bedeutung des Betrachters hin, wenn auch etwas abgeschwächt: Was wir über eine Sache wissen, hat nichts mit dem absoluten Zustand der Sache zutun. Was wir wissen, betrifft nur unsere Beziehung zwischen uns und der Sache. Alle Erscheinungen sind Wechselwirkungen zwischen einem Subjekt und einem Objekt.

Der Beobachter ist integraler Teil jeder Aussage über die Welt, auch wenn Bohr Einstein nicht überzeugen konnte, dass der Mond nur da ist, wenn man hinschaut.
Womit wir wieder beim Buchtitel wären. Es ist wohl anzunehmen, dass es eine Wirklichkeit gibt und zwar unabhängig von einem Beobachter. Doch wie sollen wir diese ohne Beobachter beobachten? Diese prinzipielle, elementare Unmöglichkeit zeigt, dass es auch Fragen gibt, die wir niemals beantworten können, genauso wie es nach Gödel in logischen Systemen immer Aussagen geben wird, die weder beweisbar noch widerlegbar sind.

Genau das gibt Rovelli in seinem Schlusswort auch zu bedenken. Wissenschaft behauptet nicht, die Wahrheit zu besitzen und kann sie auch nie besitzen: "Wir sollten keinem vertrauen, der behauptet, er halte die Wahrheit in Händen. [...] Wir brauchen Vertrauenswürdigkeit, keine Gewissheiten, denn echte Gewissheiten haben wir nicht und werden wir nie bekommen. Es sein denn, wir überantworten uns blind dem Glauben."
Profile Image for Britta Böhler.
Author 8 books1,911 followers
October 24, 2017
Although the subject - the journey from the Newtonian laws of motion to quantum physics - is fascinating, Rovelli's book is a not very succesful mix of very basic information (which is boring if you are the least bit familiar with the topic) and - not very well explained - difficult details and examples (which are incomprehensible if you are new to the topic).
Profile Image for kartik narayanan.
740 reviews205 followers
April 26, 2020
Reality is not what it seems is a good book on physics. But like the author himself mentioned, seven brief lessons on physics is a more concise and direct treatment of the topics covered in the book. I would agree and direct readers to 7 Brief instead of this one.
Profile Image for Atila Iamarino.
411 reviews4,384 followers
July 16, 2017
Rovelli defende uma outra interpretação da gravidade quântica que eu não conhecia, a Loop Theory. Em oposição às supercordas adotadas e explicadas pelo Sean Carroll em The Big Picture: On the Origins of Life, Meaning, and the Universe Itself. Ele faz um ótimo trabalho de chegar nesse ponto explicando o conceito de gravidade através da história, dando alguns insights que não tinha visto em outros livros. Mas não fica tão claro o que é conclusão científica e o que é especulação ou extrapolação sem suporte – o mesmo problema do livro do Sean Carroll.

Mesmo tendo lido sobre o trabalho do Newton em vários livros, como o ótimo Explicar o Mundo, Rovelli foi o primeiro a me dar os passos lógicos de Newton pensando sobre o que aconteceria se a Lua fosse menor e girasse mais próxima da Terra. Que foi o passo para entender que o "impulso da Lua" é a mesma aceleração gravitacional de objetos aqui na Terra. Nesse sentido, o livro é bem didático, embora ele faça a mesma comparação exagerada com os gregos de outros livros recentes – o The Evolution of Everything: How New Ideas Emerge não cansava de falar do De Rerum Natura também.

Achei bom para me familiarizar com a Loop Theory, sobre a qual nunca tinha lido. Mas se estiver atrás de explicações sobre o que compõe a matéria e como o universo funciona, ainda acho os livros da Lisa Randall mais acessíveis e eles saíram em português.
Profile Image for Robert.
817 reviews44 followers
September 12, 2021
OK, I give up because this is making me too angry.

The errors are multitudinous, egregious and recognisable by any physics final year undergrad worth the name. The final straw was the claim that "particles don't exist when they are not interacting." This notion is an obvious breach of conservation of energy and not supported by quantum theory, which states that insofar as conservation laws can be breached at all, there is a time limit. It's given by the famous Heisenberg Uncertainty Principle and put simply, it says that the more energy you want to "borrow" the less time you can do so for. The energy of entire particles is large in this context - they can't cease to exist for long periods. This is experimentally verified in accelerator experiments such as the Large Hadron Collider, where it's found that any time a particle emits another, or changes into one or more others, it takes a finite length of time - but a ridiculously short one. (Different for different types of event, btw.)

Anyway, I can't face any more of this right now; instead of pointing out every error and misconceptiion I'm just going to have to draw a line and say: DO NOT READ THIS BOOK: It's full of falsities and misleading bullshit.
Profile Image for Veronika Sebechlebská.
381 reviews129 followers
September 16, 2023
Tam, kde sa väčšina popularizátorov fyziky uchyľuje ku kuchynským analógiám, Rovelli využíva metaforický jazyk a básnické prirovnania, je to iné, pre niekoho asi osviežujúce, pre niekoho vyslovene otravné, mne osobne Rovelli prostredníctvom poézie umožňuje nahliadnuť tam, kam by som skrz obmedzenia intelektu nikdy nedovidela.

A inak vždy som bola veľkou fanúšičkou strunovej teórie, už len preto, že je to proste krásna predstava, ale teraz, po dvoch Rovelliho knihách som taká, že Loop Quantum Gravity ideeeeeeeeeeeš!!!!

Nesúrodé a s ničím nesúvisiace poznámky:

Čím bližšie zemi, tým väčšia gravitácia, čím väčšia gravitácia, tým väčšie spomalenie času. Je dokázané, že hodiny položené na podlahe idú pomalšie ako hodiny umiestnené na skrini, pri mori starnete pomalšie ako na horách
Čo konečne vysvetľuje, prečo mám tak často chuť zaliezť si niekam veľmi hlboko!

Na fundamentálnej úrovni čas neexistuje. Naše vnímanie chodu času je čisto aproximáciou, ktorá funguje na makroskopickej úrovni Vedia o tomto na daňovom??
Profile Image for Stefano Ottolenghi.
189 reviews92 followers
February 28, 2014
Questa è fisica. Questa è divulgazione. Questa è chiarezza. Rovelli sa di cosa parla e sa parlare, capace di riassumere la fisica dalla Grecia a oggi. Come vorrei fosse il mio insegnante.
Profile Image for Fran.
176 reviews6 followers
June 6, 2023
Tengo cierta debilidad por los libros divulgativos de física. Ya saben, aquellos que se dedican a explicar a los profanos en la materia la relatividad general o la mecánica cuántica —casi siempre lo mismo— de mil maneras distintas, algunos con comparaciones de lo más peregrinas, pero casi siempre entendibles. Asimov, Feynman, Hawking, Kaku y ahora Rovelli. Para torpes como yo, estos autores evitan el balbuceo de sobremesa cada vez que alguien menciona el tema.

¿Y qué diferencia a Carlo Rovelli del resto? Pues la clave la da él mismo: "Nuestra cultura, que separa ciencia y poesía, es necia, porque así no ve la complejidad y belleza del mundo que ambas revelan". Y punto.

De este modo, con un pie en la literatura y otro en la filosofía, el autor es capaz de explicar conceptualmente teorías muy complejas. El enfoque y las referencias bailan de un lado a otro a ojos del lector: de Demócrito pasa a Heisenberg; lo mismo cita a Platón que explica someramente una ecuación; relaciona a Dante con Einstein o se recrea contando la cautivadora historia de la física del siglo XX. Buen escritor.

Merece mucho la pena.
Displaying 1 - 30 of 1,446 reviews

Can't find what you're looking for?

Get help and learn more about the design.