By Carlo Rovelli, Riverhead Books, May 8, 2018, 073521610X

Carol Rovelli studies quantum gravity and is a proponent of loop theory. The Order of Time describes Rovelli’s view of his work. I enjoyed it, and learned a bit about quantum physics.

There is one equation in the book, which is key: entropy never decreases. There are other equations in footnotes, which interested me at times and are too complex for me in general. You don’t need to read them, but you do need to understand that disorder increases, and that’s what matters. For adherents of loop theory, time does not exist at the microscopic level.

Time does exist in the world we can perceive, and Rovelli explains why it does. It’s interesting. Music is not a collection of tones, but a relationship of those notes. Time exists as a blur between the notes, but that’s what we hear. The blur between microscopic states is how we interact with the world.

Rovelli ties in a lot of biographical details to the subject of the book. Boltzman had bipolar disorder, and he “saw atoms and molecules frenziedly moving.” A month before Einstein dies, he writes, “the distinction between past, present and future is only a stubbornly persistent illusion.” He was writing to console the sister of Michele Besso, Einstein’s best friend, who has just died. Interesting, but there are too many of these details for my liking.

The “fight is still raging” over whether Rovelli’s view of the quantum gravity is more probable than other theories, which he doesn’t discuss in any detail. That bothered me, but I probably wouldn’t have been able to absorb the details.

I learned some facts, which kind of put things in perspective. Planck time is 10-44 seconds, which is the smallest unit of time. Planck length is around 10-33, which is the smallest length. Kind of interesting.

Rovelli mixes in lots of culture. He seems to be well-read and a fan of the philosophy of science. He uses quotes from the ancient Greeks and the Grateful Dead (below). Cute.

His writing is often over the top poetic. The sentences get too long. He also worships idols. He notes (in a footnoote) that he tends to single people out as being heroes of science, and that people have complained about this, because scientific discoveries are the work of many people. He does this over and over, which gets tiresome.

At then end equates time with suffering (a la Buddhism), and that he’ll be ready for death when it comes. That world view is a bit odd to me, because it conflicts with his criticism that we think too much about the future. It presumes death will be quick. If you die slowly with chronic pain, somebody may be ready to kill themselves and others may be seriously uncomfortable for a decade. Time plays a real factor in how we die, too, and his position seems too trite.

[k59] The rush of seconds, hours, years that hurls us toward life then drags us toward nothingness…. We inhabit time as fish live in water.

[k67] The nature of time is perhaps the greatest remaining mystery.

[k81] One after another, the characteristic features of time have proved to be approximations, mistakes determined by our perspective, just like the flatness of the Earth or the revolving of the sun.

[k108] Let’s begin with a simple fact: time passes faster in the mountains than it does at sea level.

[k119] The ability to understand something before it’s observed is at the heart of scientific thinking.

[k136] Where time passes uniformly, in interplanetary space, things do not fall. They float, without falling. Here on the surface of our planet, on the other hand, the movement of things inclines naturally toward where time passes more slowly, as when we run down the beach into the sea and the resistance of the water on our legs makes us fall headfirst into the waves.

[k147] I have an enduring passion for Anaximander, the Greek philosopher who lived twenty-six centuries ago and understood that the Earth floats in space, supported by nothing. We know of Anaximander’s thought from other writers. Only one small original fragment of his writings has survived–just one:

Things are transformed one into another according to necessity, 
and render justice to one another 
according to the order of time.

[k159] the whole of our physics, and science in general, is about how things develop “according to the order of time.”

[k171] Times are legion: a different one for every point in space. There is not one single time; there is a vast multitude of them.

[k173] Einstein has given us the equations that describe how proper times develop relative to each other.

[k182] Time has lost its first aspect or layer: its unity.

[k232] Sadi’s pamphlet finds its way into the hands of a fierce-eyed, austere Prussian professor called Rudolf Clausius. It is he who grasps the fundamental issue at stake, formulating a law that was destined to become famous: if nothing else around it changes, heat cannot pass from a cold body to a hot one.

[k236] This is the only basic law of physics that distinguishes the past from the future.

[k241] In the elementary equations of the world,13 the arrow of time appears only where there is heat.

[k247] The ball’s slowing down and coming to rest are due to friction, and friction produces heat. Only where there is heat is there a distinction between past and future. Thoughts, for instance, unfold from the past to the future, not vice versa–and, in fact, thinking produces heat in our heads….

[k258] Clausius’s entropy, indicated by the letter S, is a measurable and calculable quantity that increases or remains the same but never decreases, in an isolated process.

[k264] Forgive me for the equation–it’s the only one in the book. It is the equation for time’s arrow, and I could hardly refrain from including it in my book about time.

[k291] The growth of entropy is nothing other than the ubiquitous and familiar natural increase of disorder.

This is what Boltzmann understood.

[k294] It was a brilliant intuition, and a correct one. But does it clarify the difference between past and future? It does not. It just shifts the question. The question now becomes: why, in one of the two directions of time–the one we call past–were things more ordered?

[k310] The notion of “particularity” is born only at the moment we begin to see the universe in a blurred and approximate way.

Boltzmann has shown that entropy exists because we describe the world in a blurred fashion. He has demonstrated that entropy is precisely the quantity that counts how many are the different configurations that our blurred vision does not distinguish between.

[k324] It’s a conclusion that leaves us flabbergasted: is it really possible that a perception so vivid, basic, existential–my perception of the passage of time–depends on the fact that I cannot apprehend the world in all of its minute detail?

[k360] For everything that moves, time passes more slowly[.]

[k408] The notion of “the present” refers to things that are close to us, not to anything that is far away.

[k411] It depends on the precision with which we determine time. If by nanoseconds, the present is defined only over a few meters; if by milliseconds, it is defined over thousands of kilometers.

[k528] It is awkward to organize train timetables if each station marks time differently.

[k535] It can hardly be pure coincidence that, before gaining a university position, the young Einstein worked in the Swiss patent office, dealing specifically with patents relating to the synchronization of clocks at railway stations.

[k553] So if nothing changes, if nothing moves, does time therefore cease to pass?

Aristotle believed that it did.

[k555] Time is the measure of change: if nothing changes, there is no time.

[k585] It indicates time that is “absolute, true, and mathematical,” assumed by Newton to run independently of things that change or things that move.

[k597] In a still celebrated, furious counterblast, Leibniz defended the traditional thesis according to which time is only the order of events, arguing that there is no such thing as an autonomous time.

[k612] Aristotle was the first to discuss in depth and with acuity the meaning of “space,” or “place,” and to arrive at a precise definition: the place of a thing is what surrounds that thing.

[k617] For Newton, between two things there may also be “empty space.”

[k619] Newton imagines that things are situated in a “space” that continues to exist, empty, even when divested of things.

[k647] The synthesis between Aristotle’s time and Newton’s is the most valuable achievement made by Einstein. It is the crowning jewel of his thought.

The answer is that the time and space Newton had intuited the existence of, beyond tangible matter, do effectively exist. They are real.

[k653] Physicists call “fields” the substances that, to the best of our knowledge, constitute the weave of the physical reality of the world. Sometimes they may be given exotic names: the fields “of Dirac” are the fabric of which tables and stars are made.

[k655] But–here is the key point–there is also a “gravitational” field: it is the origin of the force of gravity, but it is also the texture that forms Newton’s space and time, the fabric on which the rest of the world is drawn.

[k666] But the field can also undulate, in what we call “gravitational waves.”

[k679] True and mathematical Newtonian time exists; it is a real entity; it is the gravitational field, the elastic sheet, the curved spacetime in the diagram.

[k691] Einstein writes the equations of the gravitational field in 1915, and barely a year later it is Einstein himself who observes that this cannot be the last word on the nature of time and space, because of the existence of quantum mechanics.

[k704] The discipline that studies these is called “quantum gravity,” and this is my own field of research.

[k707] My scientific life has been largely dedicated to contributing to the construction of a possible solution to the problem: loop quantum gravity, or loop theory. Not everyone is betting on this turning out to be the right solution. Friends who work on string theory, for instance, are following different paths, and the battle to establish who is right is still raging.

[k716] The three fundamental discoveries that quantum mechanics has led to are these: granularity, indeterminacy, and the relational aspect of physical variables. Each one of these demolishes further the little that was left of our idea of time.

[k724] Together, these determine the time to 10-44 seconds[.]

[k725] This is Planck time: at this extremely minuscule level, quantum effects on time become manifest.

[k729] The “quantization” of time implies that almost all values of time t do not exist.

[k732] In other words, a minimum interval of time exists. Below this, the notion of time does not exist–even in its most basic meaning.

[k735] The good Lord has not drawn the world with continuous lines: with a light hand, he has sketched it in dots, like the painter Georges Seurat.

[k742] In the thirteenth century, the great philosopher Maimonides writes: “Time is composed of atoms, that is to say of many parts that cannot be further subdivided, on account of their short duration.”

[k747] The spatial sister of Planck time is Planck length: the minimum limit below which the notion of length becomes meaningless. Planck length is around 10-33 centimeters[.]

[k758] Spacetime is a physical object like an electron. It, too, fluctuates. It, too, can be in a “superposition” of different configurations.

[k767] Indeterminacy is resolved when a quantity interacts with something else.

In the interaction, an electron materializes at a certain point. For example, it collides with a screen, is captured by a particle detector, or collides with a photon–thus acquiring a concrete position.

[k782] When it does, the durations are granular and determinate only for that something with which it interacts; they remain indeterminate for the rest of the universe.

[k794] So, after all this, what is left of time?

You got to deep-six your wristwatch, you got to try and understand, 
The time it seems to capture is just the movement of its hands...

Let’s enter the world without time.

[k809] None of the pieces that time has lost (singularity, direction, independence, the present, continuity) puts into question the fact that the world is a network of events.

[k817] The fundamental equations do not include a time variable, but they do include variables that change in relation to each other.

[k842] We cannot think of the physical world as if it were made of things, of entities. It simply doesn’t work.

[k843] What works instead is thinking about the world as a network of events.

[k874] Newton’s mechanics, Maxwell’s equations, quantum mechanics, and so on, tell us how events happen, not how things are.

[k880] It does not even form a four-dimensional geometry. It is a boundless and disorderly network of quantum events. The world is more like Naples than Singapore.

[k908] Twentieth-century physics shows, in a way that seems unequivocal to me, that our world is not described well by presentism: an objective global present does not exist. The most we can speak of is a present relative to a moving observer.

[k929] Change, what happens–this is not an illusion. What we have discovered is that it does not follow a global order.

[k941] To ask oneself in general “what exists” or “what is real” means only to ask how you would like to use a verb and an adjective. It’s a grammatical question, not a question about nature.

Nature, for its part, is what it is–and we discover it very gradually.

[k945] Grammar developed from our limited experience, before we became aware of its imprecision when it came to grasping the rich structure of the world.

[k949] The structure of reality is not the one that this grammar presupposes. We say that an event “is,” or “has been,” or “will be.” We do not have a grammar adapted to say that an event “has been” in relation to me but “is” in relation to you.

[k1014] There is nothing mysterious about the absence of time in the fundamental equation of quantum gravity. It is only the consequence of the fact that, at the fundamental level, no special variable exists.

[k1037] John [Wheeler] and Bryce [DeWitt] were my spiritual fathers. Thirsting, I found in their ideas fresh, clear water to drink.

NOTE: I find writing like this overly dramatic, and it is excessive in this book. This is also an example of how he idolizes other scientists.

[k1117] Everything in the world becomes blurred when seen close up.

[k1147] This observation opens up a new perspective: in an elementary physical system without any privileged variable that acts like “time”–where, in effect, all the variables are on the same level but we can have only a blurred vision of them described by macroscopic states. A generic macroscopic state determines a time.

[k1156] Time that is determined in this way by a macroscopic state is called “thermal time.”

[k1186] And it is this thermal and quantum time, I believe, that is the variable that we call “time” in our real universe, where a time variable does not exist at the fundamental level.

[k1191] Temporality is profoundly linked to blurring. The blurring is due to the fact that we are ignorant of the microscopic details of the world. The time of physics is, ultimately, the expression of our ignorance of the world. Time is ignorance.

[k1238] Speed is a property of an object with respect to another object. It is a relative quantity.

[k1242] The entropy of the world does not depend only on the configuration of the world; it also depends on the way in which we are blurring the world, and this depends on what the variables of the world are that we interact with. That is to say, on the variables with which our part of the world interacts.

The entropy of the world in the far past appears very low to us. But this might not reflect the exact state of the world: it might regard the subset of the world’s variables with which we, as physical systems, have interacted. It is with respect to the dramatic blurring produced by our interactions with the world, caused by the small set of macroscopic variables in terms of which we describe the world, that the entropy of the universe was low.

[k1283] it isn’t that apples grow where people drink cider, it is that people drink cider where apples grow. Put this way, there is no longer anything strange about it.

Similarly, in the boundless variety of the universe, it may happen that there are physical systems that interact with the rest of the world through those particular variables that define an initial low entropy. With regard to these systems, entropy is constantly increasing. There, and not elsewhere, there are the typical phenomena associated with the flowing of time: life is possible, together with evolution, thought, and our awareness of time passing. There, the apples grow that produce our cider: time. That sweet juice that contains all the ambrosia and all the gall of life.

[k1360] What makes the world go round are not sources of energy but sources of low entropy. Without low entropy, energy would dilute into uniform heat and the world would go to sleep in a state of thermal equilibrium–there would no longer be any distinction between past and future, and nothing would happen.

[k1421] Traces of the past exist, and not traces of the future, only because entropy was low in the past. There can be no other reason, since the only source of the difference between past and future is the low entropy of the past.

[k1571] When we listen to a hymn, the meaning of a sound is given by the ones that come before and after it. Music can occur only in time, but if we are always in the present moment, how is it possible to hear it? It is possible, Augustine observes, because our consciousness is based on memory and on anticipation. A hymn, a song, is in some way present in our minds in a unified form, held together by something–by that which we take time to be. And hence this is what time is: it is entirely in the present, in our minds, as memory and as anticipation.

[k1609] In the wake of Husserl, Martin Heidegger writes–as far as my love of the clarity and transparency of Galileo’s writing allows me to decipher the deliberate obscurity of Heidegger’s language–that “time temporalizes itself only to the extent that it is human.” For him also, time is the time of mankind, the time for doing, for that with which mankind is engaged. Even if, afterward, since he is interested in what being is for man (for “the entity that poses the problem of existence”), Heidegger ends up by identifying the internal consciousness of time as the horizon of being itself.

NOTE: Rovelli says Heidegger is obtuse, but I find Rovelli obtuse at times. These sentences could be simplified. He also goes on about philosphers thinking about time, which I’m not sure helps his argument about the order of time.

[k1637] We are stories, contained within the twenty complicated centimeters behind our eyes, lines drawn by traces left by the (re)mingling together of things in the world, and oriented toward predicting events in the future, toward the direction of increasing entropy, in a rather particular corner of this immense, chaotic universe.

[k1643] It is with respect to that physical system to which we belong–due to the peculiar way in which it interacts with the rest of the world, thanks to the fact that it allows traces and because we, as physical entities, consist of memory and anticipation–that the perspective of time opens up for us, like our small, lit clearing.

NOTE: I found this 60 word sentence unnecessarily complex. I read and reread and didn’t gain any more understanding.

[k1649] Buddha summed this up in a few maxims that millions of human beings have adopted as the foundations of their lives: birth is suffering, decline is suffering, illness is suffering, death is suffering, union with that which we hate is suffering, separation from that which we love is suffering, failure to obtain what we desire is suffering.

[k1653] We long for timelessness, we endure the passing of time: we suffer time. Time is suffering.

NOTE: This is his particular view based on his particular fears. I don’t know that it is a good argument in a book about quantum time.

[k1692] There is a present that is near to us, but nothing that is “present” in a far-off galaxy. The present is a localized rather than a global phenomenon.

[k1729] This is time for us: a multilayered, complex concept with multiple, distinct properties deriving from various different approximations.

[k1733] Many parts of this story are solid, others plausible, others still are guesses hazarded in an attempt at understanding the whole.

[k1759] Perhaps the emotion of time is precisely what time is for us.

[k1763] When we cannot formulate a problem with precision, it is often not because the problem is profound: it’s because the problem is false.

[k1782] I am afraid of frailty, and of the absence of love. But death does not alarm me.

[k1784] I love life, but life is also struggle, suffering, pain. I think of death as akin to a well-earned rest.

[k1793] Our fear of death seems to me to be an error of evolution.

[k1795] Natural selection has produced these big apes with hypertrophic frontal lobes, with an exaggerated ability to predict the future.

NOTE: Evolution doesn’t exaggerate. Characteristics like this evolve, because they have survival value.

[k1804] We are not, in the first place, reasoning beings.

[k1807] Reason arbitrates between instincts but uses the very same instincts as primary criteria in its arbitration.

[k1810] But what drives us is not reflecting on life: it is life itself.

[k1818] We are more complex than our mental faculties are capable of grasping.