Seven Brief Lessons on Physics

by Carlo Rovelli

Riverhead Books, New York, 2016

Carlo Rovelli is a theoretical physicist, the head of the "Quantum Gravity Group" at the Centre de Physique Théorique of Aix-Marseille University, and a "founder" of the loop quantum gravity theory. He is thus the real thing as a physicist; and this book is based on a series of popular articles he wrote about modern physics that were published in an Italian newspaper, Ile Sole 24 Ore, and then in a book Sette brevi lezioni di fisica [Adelphi Edizioni, Milan, 2015].

One might fear that the essays thus could be too dumbed down to be of interest -- although, unlike Stephen Hawking, who was told by his publisher that only one equation, E=mc2, would be allowed in A Brief History of Time, Rovelli actually gives us Einstein's general equation for gravity: , without however a whole lot of explanation [and not in quite this form; p.12]. But essays like this pose a revealing challenge to a physicist. He cannot hide behind jargon or the unexplained abstraction of equations. He must deal with the concepts involved in the physics, and this frequently raises philosophical issues that he might then choose to tackle, which enables us to judge his knowledge and acuity in philosophical matters. Thus, the final chapter of the book, "In Closing, Ourselves," which consists partially of a moralizing sermon about Global Warming, we learn that Rovelli is a materialist and a determinist, who warmly invokes Baruch Spinoza as his philosophical antecedent:

I am, as Spinoza maintained, my body and what happens in my brain and heart, with their immense and, for me, inextricable complexity. [p.75]

However, Rovelli has misunderstood and misrepresented Spinoza. Spinoza is not a materialist, and he did not "maintain" that I am my body and whatever goes on in it. Spatial extension, which was the essential property of Cartesian matter, for Spinoza is only one of an infinite number of attributes that belong to God, the only other one of which we are aware is the attribute of thought. Thus, thought and consciousness are equal to and independent from the essence of matter, while Rovelli clearly believes that consciousness is an epiphenomenon of matter, for which cognitive scientists and neurologists are busy trying to account. Rovelli seems confident that the reduction of consciousness to the brain and its derivation from matter will shortly be fully explained. Meanwhile, for all Rovelli's professed love of the "God intoxicated" philosopher, the physicist mentions God, even Spinoza's God, not even once. We are left with no more than "the mystery and the beauty of the world." And these features do not carry him to the Unseen, as they would for Plato.

Now, it is not unusual for Spinoza to be misinterpreted and misrepresented by the eager partisans of materialism and atheism. So we probably cannot blame Rovelli personally for getting this wrong. He's just repeating the sort of thing he would have heard. But what is curious about his book is that his materialism and determinism are of a sort that is subverted, by not philosophers, but by the very physics that he recounts here, chapter by chapter. He has subtly distorted or ignored features of the science in which he is himself presumably the expert. And it is not just because we peons cannot appreciate his lofty thoughts. He has left things out, things that are easily explained, as they often have been, in ordinary language. Key among the exclusions are any mention of Erwin Schrödinger, despite the fact that "Schrödinger's Cat" is something that has entered popular culture and that involves a fundamental question about the nature of quantum mechanics. But, it turns out, the Cat poses an awkward question for the reductionistic materialism and determinism that Rovelli prefers. His reason for avoiding it looks more defensive and dissimulating, if not dishonest, rather than a paternal regard for what the ignorant masses will be able to understand. The effect is either an intentional or an unconscious distortion, and it does show us where Rovelli's loyalties lie.

The "First Lesson, The Most Beautiful of Theories" (note that we are getting "lessons," lezioni) gets off to a good enough start, dealing with Einstein's General Relativity. Indeed, we get a big solid insight here, such as is sometimes lacking from other discussions about physics:

And it is at this point that an extraordinary idea occurred to him [i.e. Einstein], a stroke of pure genius: the gravitational field is not diffused through space; the gravitational field is that space itself. This is the idea of the general theory of relativity. Newton's "space," through which things move, and the "gravitational field" are one and the same thing.

It's a moment of enlightenment. A momentous simplification of the world:  space is no longer something distinct from matter -- it is one of the "material" components of the world. An entity that undulates, flexes, curves, twists. We are not contained within an invisible, rigid infrastructure: we are immersed in a gigantic, flexible snail shell. [p.8]

This is a profound intepretation of Einstein's insight. Its philosophical significance is in relation to debates about the nature of space. Thus, it has not at all been unsual for philosophers and physicists to maintain that Einstein's physics refuted the Newtonian (or Kantian) theory of space and vindicated that of Leibniz. However, Leibniz did not believe that space even existed, a feature of his theory that really seems to have escaped a physicist like Ernst Mach, and his apologists. While Rovelli does not get into these historical disputes about the metaphysics of space, his assertion constitutes an intepretation of Einstein that sharply contradicts Leibniz and that subverts interpretations of Einstein that follow in the tradition of Mach and others. As it happens, thinking as Rovelli does is not ususual. At a seminar on time given by Irwin C. Lieb (1925-1992) at the University of Texas, I was personally present at a talk by the great physicist E.C.G. Sudarshan, one of the originators of the idea of "tachyons," particles that travel faster than the velocity of light. Sudarshan said that Einstein's equations for space-time look like those of fluid mechanics:  Space-time seems to "flow" like water. This is consistent with Rovelli's view of the question here -- although later Rovelli will reject the idea that time "flows." We later learn, in the "Fifth Lesson, Grains of Space," that Rovelli's theory of quantum loop gravity depends on the quanticization of space itself. So he has some considerable intellectual investment in the reality of space. But we get no hint of him having any awareness of the misappropriation of Leibniz by several generations of Einstein interpreters.

However, the next chapter, "Second Lesson, Quanta," goes a long way to spoiling the achievement of the previous chapter. First of all, let me note how quantum mechanics subverts both materialism and determinism; and then we can see how Rovelli manages to avoid or distort his problems. Materalism takes a hit from quantum mechanics in two ways. The first is the "Copenhagen Interpretation" of Bohr, which is that nothing exists until it is observed and measured. Thus, nothing exists until it is part of our knowledge and consciousness. This is the anti-realism that Einstein hated and that leaves matter itself floating off in some sort of non-reality. It actually doesn't make a whole lot of sense. On the other hand, even if there is a reality out there, observing it radically alters its character. This also involves a principle from Bohr, "Complementarity," which is that phenomena can appear as waves or as particles, but not both at the same time, with the difference consisting of whether we are looking, or even whether we can infer what is there. Thus, the common explanation that our observation disturbs the phenomenon, collapsing the wave function and producing the distribution of particles, doesn't hold, since the wave function collapses even if we do not observe and disburb it, but only have knowledge by inference. In this way, consciousness plays the same priviledged metaphysical role whether we use the Copenhagen Interpretation or simply rely on Complementarity; and this gives to consciousness a place in reality that Einstein could not accept, although it had been featured in philosophy since Immanuel Kant.

In turn, determinism is subverted in quantum mechanics by role of indeterminacy, uncertainty, and randomness in the process. It is not uncommon for people to think that randomness all by itself posits free will, but this is not quite right. Indeterminacy allows for free will, but does not imply it. That calls for more metaphysics than any physicist, or most philosophers, have the gumption or the background to tackle. Indeed, there is considerable confusion about the relationship of purpose, meaning, and determinism in popular discourse. But Rovelli seems insensible of how the barn door has been left open by the theory that he describes himself.

We see Rovelli begin to go astray when he introduces Heisenberg:

The first to write the equations of the new theory, basing them on dizzying ideas, would be a young German of genius, Werner Heisenberg.

Heisenberg imagined that electrons do not always exist. They only exist when someone or something watches them, or better, when they are interacting with something else. They materialize in a place, with a calculable probability, when colliding with something else. The "quantum leaps" from one orbit to another are the only means they have of being "real": an electron is a set of jumps from one interaction to another. When nothing disturbs it, it is not in any place. It is not in a "place" at all. [p.17]

This is a curious passage indeed, and it shows us what Rovelli is trying to do. First of all, it is not clear to me that Heisenberg originated the "it doesn't exist" school of metaphysics here. I suspect that was Bohr's contribution, although it looks like Heisenberg would heartily agree. At the same time, what Heisenberg is the most famous for, the Uncertainty Principle, is not mentioned; but then Uncertainty does not need to be subsumed under the "it doesn't exist" school of metaphysics. If we cannot pin down the position and momentum of particles with precision at the same time, which is Heisenberg's Uncertainty, this implies a sort of mushiness in reality, in which squeezing one feature balloons another, but not that the particles don't exist. But then Rovelli clearly does not want to accept the implications of the real Copenhagen Interpretation. Thus, while he allows that electrons become real through some kind of interaction, he alters Bohr's principle, by saying that someone or "something" does the observing, or that observation is not necessary at all because electrons become real "when they are interacting with something else" -- perhaps not noticing that "something else" doesn't exist for (non-existent) electrons to interact with. This is not the physical system described by Bohr or, for that matter, by Heisenberg. Rovelli sneaks it in here, where the only purpose of the alteration is to eliminate the need for the "someone" and to restore something more like materialism. But it's wrong and, indeed, incoherent.

Bohr's Observer, and even the Observer's equipment, stand outside Bohr's anti-realism (which perhaps is why sometimes people write me to say that Bohr is really a Kantian). This is what makes Rovelli uncomfortable, since it concedes to consciousness or knowledge a reality denied to the external world. So Rovelli wants to substitute any kind of "interaction" between particles to produce the effect that Bohr attributed only to observation. But Rovelli has previously accepted that the particles don't exist before his intereactions, events that cannot, of course, take place between non-existent objects. Also, Rovelli's own example of this is misconceived. When electrons change orbits in "quantum leaps," they are not becoming particles and are not observed as such. They are transitioning from one wave function to another, while spinning off or absorbing a (wave) quanta of energy. We never see where the particle is. Indeed, if we target an electron in a atom and want to know where it is, we must break the atom, collapsing the wave function of the electron to produce it in a specific location, which removes it from the quantum state of being in an orbit of the atoms. We would not know this from Rovelli's account, which subsumes a phase transition to the function of Bohr's observation, which it certainly is not.

Indeed, we never hear of the wave function from Rovelli at all, which is why Schrödinger or Louis de Broglie are never mentioned. Since both de Broglie and Schrödinger believed in the physical reality of the wave function, even as de Broglie himself originated the idea that particles of matter, like electrons, can exist in wave form, this would give Rovelli a way of subverting Bohr's anti-realism. But that is not what Rovelli wants to do. He thinks that he can get anti-realism and materialism at the same time, which is a combination that doesn't make any sense. But he persists with it.

In quantum mechanics no object has a definite position, except when colliding headlong with something else. [p.18]

Here Rovelli has now totally forgotten the "someone" of Bohr's Observer; and he has also forgotten something that he actually has not bothered to mention, which is that Heisenberg's Uncertainty prevents an object from having a "definite position" unless we allow a corresponding degree of uncertainty in its momentum. Also, we have no idea that an object has been "colliding headlong with something else" unless we observe it, which brings back the Observer who Rovelli obviously wants to get rid of. But he can't get rid of it. Until we observe the collisions, the position of the particles, and the reality of the collisions, is undetermined. But Indeterminacy is a concept that we do not find in Rovelli's book.

Indeterminacy is summed in the wave function, whose equation was written by Schrödinger and that is now used in preference to the "matrix mechanics" developed by Heisenberg, although Paul Dirac demonstrated that they were mathemtically equivalent. But Heisenberg's matrices are obviously a mathematical technique whose physical meaning is unclear, while Schrödinger's equation, , was for something he believed to be a physical reality. Rovelli ignores all of this, having truthfully said that Heisenberg was "the first to write the equations of the new theory," but then leaving us with the impression that Heisenberg's equations are the ones that continue to be used, when they are not.

Having misrepresented the physics of Bohr and Heisenberg, Rovelli cannot avoid mentioning the feature that actually subverts his determinism:

...these interactive leaps with which each object passes from one place to another do not occur in a predictable way but largely at random. It is not possible to predict where an electron will reappear but only to calculate the probability that it will pop up here or there. The question of probability goes to the heart of physics, where everything had seemed to be regulated by firm laws that were universal and irrevocable. [p.18]

But Rovelli's phrase "interactive leaps" conceals a host of sins and assumptions. Electrons do not need an "interactive leap" to "pass from one place to another." A photon or electron that passes through the screen of Thomas Young's interference experiment appears to interact with itself on the other side, as through it passed through both slots, but then it doesn't if we determine, any whatever means, which slot it used. Thus, for the interference effect, the photon or electron must have an indeterminate location before we observe the effect. Rovelli gives us no clue about this, or that the probablity of where the photon or electron can occur is now calculated using Schrödinger's Equation for the wave function. At the same time, if the wave has a physical reality, then it can easily go through both slots, and the dilemma of where the electron actually is does not arise.

Einstein had two principal objections to quantum mechanics. One was the "God does not play dice" objection to the randomness of the collapse of the wave function. The other was the anti-realism of the Copenhagen Interpretation or of the Kantian dualism whereby consciousness determines, through observation, that the wave function collapses. Rovelli is correct that:

Einstein did not want to relent on what was for him the key issue:  that there was an objective reality independent of whoever interacts with whatever. [p.19]

But the irony of Rovelli putting the question this way is that he has attempted to dismiss the "whoever" from his own description of quantum mechanics, so that his version of Bohr's anti-realism means that non-existent objects somehow create themselves by their interaction, evidentaly whether we are around or not, which is actually more like what Einstein was looking for. Rovelli's own materialism and determinism, achieved by the neglect and distortion of Bohr and Schrödinger, is exactly what Einstein might have been happy with. Indeed, Spinoza's theory is often associated with Einstein, although it is not clear whether Einstein's view of Spinoza was as confused as Rovelli's since Einstein talked about God a lot, while Rovelli doesn't. No one need rebuke Rovelli, as Einstein was rebuked, not to be telling God what to do.

Rovelli's "Third Lesson, The Architecture of the Cosmos," does not contain the kinds of problems found in his treatment of quantum mechanics. He commendably credits Anaximander with visualizing the Earth as a finite body floating in space; but, no more than most historians or philosophers of science, does he explain that the problem with heliocentrism in ancient and mediaeval astronomy was the physics, not the astronomy -- a physics that was not corrected until Galileo. He gives short shrift to any questions of evidence for the astronomy of Copernicus. In fact, soon enough we get a postive error:

In the 1930s, however, precise measurements by astronomers of the nebulae -- small whitish clouds between the stars -- showed that the Galaxy itself is a speck of dust in a huge cloud of galaxies, which extends as far as the eye can see using even our most powerful telescopes. [pp.27-28]

However, this was determined in the 1920's, not the 1930's, by Edwin Hubble, whom Rovelli never mentions. So one wonders whether, as a physicist, Rovelli actually isn't all that familiar with this history. Also, Rovelli continues:

But this endless uniformity, in turn, is not what it seems. As I explained in the first lesson, space is not flat but curved. [p.29]

That's what everyone thought. Now, while space is locally curved, in Einstein's geometrical rendering of gravity, the universe as a whole appears to be flat and Euclidean. This is a conundrum for recent cosmology, where the largest scale geometry of the universe, and whether space is finite or infinite, has disappeared behind the horizon created by the early "inflation" of the universe, leaving observable space as an unknown fraction of even a finite universe. Rovelli perhaps doesn't need to explain this in his brief "lessons," but one also wonders how much the problem interests him.

He seems to have a bit more interest in the "Fourth Lesson, Particles," where we do have an informative and, I think, accurate presentation of the problems that currently exist in particle physics. Where Schrödinger was previously overlooked, now we do hear about Murray Gell-Mann and Paul Dirac, together with the mystery of "dark matter" and the failures of recent theories, like "supersymmetry." None of this runs afoul of the earlier confusion of wedding anti-realism and indeterminacy to Rovelli's materialism and determinism. But he will get back to it.

The "Fifth Lesson, Grains of Space," introduces us to some features of Rovelli's own theory, "quantum loop gravity." However, he never does explain how his quanticization of space, which seems like a promising idea, provides a better explanation for gravity than Einstein's geometry of curved space-time or the exchange of virtual particles in quantum mechanics. Instead, gravity has some relation to "atoms of space," which are "loops or rings" [p.43]. There is nothing intuitive about this as there is to Einstein's geometry or virtual particles. Whether it is explicable or not, Rovelli admits "there is as yet no experimental verification" for the theory.

But Rovelli likes the implications when we take the theory and return to cosmology with it. Since the "grainy" nature of space means that Black Holes and the Big Bang cannot involve singularities, i.e. the geometrical point into which Black Holes collapse or from which the Big Bang originates, Rovelli thinks that a collapsing universe would result in a "big bounce," leading to a new universe [p.48]. This is a little confusing. This "bounce" cannot happen with regular Black Holes, or it would be happening all over the place, and we would notice. And, with the current state of cosmology, it cannot happen to the universe as a whole, whose expansion is accelerating with no prospect of it ever collapsing. Rovelli has not mentioned the disturbing discovery that the expansion of the universe is accelerating -- something that has shaken up cosmology as much as anything else has since the (unmentioned) Edwin Hubble. Rovelli mentions "dark matter" [p.35] but not the "dark energy" that is the placeholder for whatever is actually driving the acceleration. So if a bouncing universe is the best that quantum loop gravity can do, its predictive power is a little underwhelming.

With the "Sixth Lesson, Probability, Time, and the Heat of Black Holes," we are back to problems with Rovelli's physics and metaphysics. Rovelli says, "The difference between past and future exists only when there is heat" [p.53]. I think that this is quite false. The feature of heat that Rovelli wants to use is actually a feature of entropy. Yet Rovelli even cites Ludwig Boltzmann himself, without mentioning entropy, despite "Boltzmann's Law" of entropy, , being engraved on Boltzmann's grave (although Boltzmann actually didn't write the Law himself). Rovelli asks, "What is heat?" [p.51], and we can answer that heat (Q) is energy (E) or, alternatively, heat is temperature (T) times entropy (S), so that the units of Boltzmann's Constant, which are for entropy (heat divided by temperature, Q/T) are Joules/Kelvins (J/K), i.e. energy divided by absolute temperature.

We learn nothing about this from Rovelli -- even though at one point he carelessly lumps together "heat and temperature" [p.56]. But, as with the missing Erwin Schrödinger, there is a method to his neglect. Heat is the energy that atoms or molecules have that cause them to vibrate and hit neighboring atoms and molecules. This is random (again) motion, and it alows Roselli to exult that the (unamed) Second Law of Thermodynamics works because "it is sheer chance" [p.53]. But this is where ignoring entropy serves Rovelli's purpose. Entropy is not just about chance, but about order and disorder. The glass that falls from the table and breaks may involve some heat (as the glass impacts the floor), but we cannot say that any amount of randomness or probability will reverse the sequence and allow the glass to miraculously reassemble and leap back onto the table. That doesn't happen for good physical reasons, which are that the process expends energy and does work. It cannot be reversed unless you put energy back into the system, which will mean a lot more energy that it took to break the glass in the first place. The extra energy will be needed to overcome the disorder, the increased entropy, of the result -- just as a Rubik's Cube is easily scrambled (by any fool) but only restored, for most of us, after great effort (and cheating). And, you know, even gluing the glass back together isn't going get something that looks like the original.

So why does Rovelli ignore these physical realities? He says, "The difference bewteen past and future exists only when there is heat" [p.53]. Of course, since heat is energy, then there will be a difference between past and future when there is energy, which is all the time. Similarly, if there is heat when there is entropy, and past and future are essential to entropy, then there will always be past and future also. So, actually, Rovelli wants to abolish time:

Physicists and philosophers have come to the conclusion that the idea of a present that is common to the whole universe is an illusion and that the universal "flow" of time is a generalization that doesn't work. When his great Italian friend Michele Besso died, Einstein wrote a moving letter to Michele's sister: "Michele has left this strange world a little before me. This means nothing. People like us, who believe in physics, know that the distinction made between past, present and future is nothing more than persistent, stubborn illusion." [p.60]

Einstein can be forgiven this flight of metaphysics. Carlo Rovelli cannot be. Rovelli should know, as Einstein did not, that the abolition of simultaneity in Special Relativity would be subverted by Bell's Theorem, which made it possible to test whether the collapse of the wave function in quantum mechanics was instantaneous and violated Special Relativity. It did. This ended, long after his death, Einstein's hope of refuting quantum mechanics through the Einstein-Podolsky-Rosen (EPR) Paradox. If Rovelli, or his other "physicists and philosophers," doesn't know this, his "lessons" about physics are going to be unreliable, and not just for the philosophy or metaphysics involved.

Rovelli is a little worried about Martin Heidegger and his followers for the central nature of time in their metaphysics [pp.60-61]. Of course, he is worried about the wrong thing. The evil influence of Heidegger is not becuase he believed in time but because he believed in, and belonged to, the National Socialist Party of Nazi Germany. Perhaps Rovelli wants to accuse anyone who believes in time of being a Nazi. On the other hand, what Rovelli says here shows how he can turn all the randomness of quantum mechanics and heat into a hard determinism:

Our memory and our consciousness are built on these statistical phenomena. For a hypthetically super-sensible being, there would be no "flowing" of time: the universe would be a single block of past, present, and future. But due to the limitations of our consciousness we perceive only a blurred vision of the world live in time. [p.62]

Of course if past, present, and future already exist frozen in "a single block," then all of physical history already exists and there never was either possibility or probability that things could happen any differently than they ever have or ever will. This is actually a doctrine stronger than determinism. Spinoza was a determinist, in that things unfold in time as the expression of the essence of God. Things happen the way they do, and can happen no other way, because it is, in effect, the Will of God. But Rovelli, who seems to think that time is essentially another dimension of space, existing simultaneously (despite Relativity), there is no unfolding in time at all. All time already exists; and this is what we should call "fatalism" rather than "determinism." As the Muslims say in Lawrence of Arabia [1962]:  "It is Written." Rovelli is a fatalist, as is the Einstein of the quote warmly endorsed by Rovelli.

So, despite apparently endorsing the Copenhagen Interpretation and the randomness in quantum mechanics and thermodynamics, Rovelli can take it all back in an instant and, with the non-existence of time, produce the materialism and determinism that apparently own his heart. Sub specie aeternitatis, we do not have indeterminacy, uncertainty, or statistics. All exists as it is, will be, and ever has been. The microscopic probabilities of quantum mechanics disappear, and Rovelli never does consider what we have become increasingly aware of as the uncertainties and indeterminacies of chaotic macroscopic systems like the weather or history. Chance does not remain in the lab.

The payoff of this is what we get in the last chapter, "In Closing, Ourselves," whose misuse of Spinoza I have already visited. But, this is not the only confusion in the chapter. We find Rovelli saying:

During the great period of German idealism, Schelling could think that man represented the summit of nature, the highest point where reality becomes conscious of itself. Today, from the point of view provided by our current knowledge of the natural world, this idea raises a smile. If we are special, we are only special in the way that everyone feels themselves to be, like every mother is for her child. Certainly not for the rest of nature. [p.67]

This raises from me, not a smile, but anger. The arrogance that Rovelli wants to atribute to Schelling, or to humanity (or mothers), is in fact his own arrogance, by which he fancies himself superior by knowing of our own insigificance. Now, one might say that Rovelli is doing no more than Socrates, whose advantage lay in the recognition of his own ignorance. Isn't Rovelli modestly just doing the same? No, because, not only did Socrates thus claim to have nothing to teach, but his approach to people was to assume that they did, which meant that they could teach him and he could learn from them. That this never worked out did not mean that Socrates did not openly give them a chance. We never get "lessons" from Socrates. The situation is very different with Rovelli. His superiority is because of what he knows, which is substantial, and about which he has already been writing a book -- something Socrates never did. But if Rovelli's confidence rests on his knowledge, he better get it right. And he doesn't. Again he forgets or neglects entropy. And quantum mechanics. Humanity is in fact at "the summit of nature" just because we manifestly embody the lowest entropy of which we are aware. Beavers build dams, but human beings build everything from pyramids to cell-phones, which nature is not otherwise just going to randomly generate through Brownian Motion. Rovelli is oblivious to this. Of course, he is not alone. Steven Jay Gould didn't like the idea that Evolution improves things, but then Gould had more excuse for that sort of thing than Rovelli does. Entropy is part of physics, not paleontology.

Rovelli also is not attentive to what he has said. Where else, I would ask him, has "reality become conscious of itself"? We have no clue; and it is especially troubling that no equivalent of I Love Lucy has been detected beaming from the other stars of the Galaxy, or beyond. Where is everybody? We don't know. In their absence, we are unique, for all our follies -- like the self-denigrating arrogance of "physicists and philosophers." But Rovelli, in a now venerable tradition, seems to derive some considerable pleasure, Schadenfreude, from telling us how insigificant we are:

...amid the infinite arabesques of forms that constitute reality, we are merely a flourish among innumerably many such flourishes. [p.68]

OK, like what? The Klingons? ET? Oh, they're imaginary. We don't know of any other such "flourishes" of literate, technological civilizations, or even of any other living things -- forget humans -- off the Earth. We are now beginning to spot a few Earth-like planets in nearby space, but no radio signals of the sort that we've been beaming out for about a century now. If such civilizations have been around the Galaxy for a few million years -- not much time geologically -- why haven't we picked up their signals? ET, phone Earth!

And again, as with Heidegger, Rovelli has chosen a bad philosopher as his target. The "great period of German idealism" was, as Schopenhauer thought, an age of absurdities and dishonesty; and Schelling was not someone who made any positive or durable contribution to the progress of philosophy. But it's not like we have been given any reason to rely on Rovelli's judgment about philosophers:

These conditions [i.e. that "our nature as subjects, and particular subjects, imposes upon experience"], nevertheless, are not, as Kant imagined, universal -- deducing from this (with obvious error) that the nature of Euclidean space and even of Newtonian mechanics must therefore be true a priori. They are a posteriori to the mental evolution of our species and are in continuous evolution. [p.68]

Now, Rovelli perhaps wanted to say that Kant deduced the "nature of space" as Euclidean; for if Euclidean space is not Euclidean, as Rovelli seems to say, one wonders what it would be. The nature of Euclidean space is true a priori. We just want to know if physical space is itself Euclidean; and, as I have already noted, Rovelli seems to have missed the development in cosmology that the large scale structure of space in the universe actually does seem to be Euclidean.

Now, Rovelli obviously relies on the common perception, the canard and even the myth, that Kant and Euclid were all refuted by the mere existence of non-Euclidean geometry. Among modern philosophers the insight is all but non-existent that Kant's theory of geometry predicts, rather than contradicts, the existence of non-Euclidean geometry. What is the more interesting question, and one that never gets asked, is not only why the Greeks (and Arabs, etc.) thought that space was Euclidean, when presumably it could have been anything, but why the modern unprejudiced student (or unprejudiced philosopher) finds features of non-Euclidean geometry incomprehensible. For, as it happens, in one of the most familiar forms of non-Euclidean geometry, extending a straight line indefinitely results in it closing on itself. I contend, boldly, that this line cannot be visualized as closed and straight at the same time. This fact can be evaded by resolutely determining not to visualize it.

Be that as it may, Rovelli is not attempting to offer a cogent critique of Immanuel Kant. And if he wants to argue that there is nothing a priori in science, that is not exactly what we find in his book. Instead, after the pro forma swipe at Kant, whose proof of the a priori truth of Newtonian mechanics I have failed to find in the Critique of Pure Reason, Rovelli gets down to the serious business of reducing consciousness to the physical brain, for which he thinks he has Spinoza as a willing accomplice:

Specific ideas on how the mathematical form of the structure [of the brain] can correspond to the subjective experience of consciousness are currently being discussed, not only by philosophers but also by neuroscientists. [p.71]

In other words, how can a mass of gray goo, whatever its "structure," imply the sensory qualia, interiority, and apperception of consciousness? A proper materialist and determinist will simply dismiss them, or redefine them in a way that will be the equivalent of dismissal -- like Rovelli does with free will:

When we say that we are free, and it's true that we can be, this means that how we behave is determined by what happens within us, within the brain, and not by external factors. To be free doesn't mean that our behavior is not determined by the laws of nature. It means that it is determined by the laws of nature in our brains. [p.73]

That makes me feel a whole lot better. But this redefinition of freedom as "free from external contraint" is called "soft determinism" and can be found in Thomas Hobbes or David Hume. I don't think Spinoza resorts to such sophistry. Determinism is determinism. And, of course, if the laws of nature involve a great deal of indeterminacy and chance (such as is denied, say, by Hume, or by the fatalism endorse by Rovelli himself), then the laws of nature are not going to specifically determine all outcomes even within our brains. Other things may be going on.

But the worst thing in all this, which is betrayed by Rovelli's misuse of Spinoza, is his failure to note the foundational place of consciousness in the very physics he has been telling us about. Rovelli says in the first chapter that "space is no longer something distinct from matter -- it is one of the 'material' components of the world" [p.8]. But by the same token, after considering the nature of quantum mechanics, Rovelli should have said, "consciousness is no longer something distinct from matter -- it is one of the 'material' components of the world." In other words, the very materialism of matter is compromised by the presence and role of consciousness, as this is presented by no less than Niels Bohr -- or Baruch Spinoza. And if the idea is that space is an underlying reality constituting matter, then we might consider that consciousness is the reality constituting space and matter.

So Rovelli probably ends on the right note, with a long quotation from the atoms-and-the-void Epicureanism of Lucretius, who, at least according to some, ended his happy life with suicide. This dismal doctrine was not very popular among the Greeks or the Romans, but it seems to provide fertile ground for varieties of modern nihilism. The sad thing is that a physicist like Rovelli should be at such pains to mutilate all the roots in modern physics from which more meaningful questions and insights could have grown.

There has been a review of Rovelli's book in the Wall Street Journal, "Hitching a Ride on a Light Beam," by Alan Hirshfeld [Apirl 23-24, 2016, C10], together with The Universe in Your Hand by Cristophe Galfard [Flatiron]. Dr. Hirshfeld is himself a professor of physics, at the University of Massachusetts Dartmouth. However, Dr. Hirshfeld does not note any of the problems in Seven Brief Lessons, and he includes a disturbing description,

If you pinpoint where a matter particle is, you can't know where it's going; if you know where it's going, you can't pinpoint where it is! Despite such confounding attributes, Mr. Rovelli points out, quantum physics has become a linchpin in some sectors of the high-tech marketplace...

Now, Carlo Rovelli can hardly point out anything in relation to Heisenberg's Uncertainty Principle because, as I have noted, he doesn't actually mention, explain, or discuss it at all. So what is disturbing about this passage is that it makes it look like Dr. Hirshfelt has not actually read Rovelli's book, or at least not read it very carefully. Perhaps he assumes it must talk about the Uncertainty Principle, even though it doesn't. Of course, as we have seen, Rovelli doesn't talk about it because he has a different agenda; and obviously, whatever reading he has done, Hirshfeld has not picked up on that. If he has detected where Rovelli was going, his review could have been a lot more interesting and informative; and we could have found out where Hirshfeld stands on the reality of time and the other metaphysical issues.

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