On “The Order of Time” by Carlo Rovelli

Charley Knight
Sep 5, 2018 · 6 min read

If I told you the temperature is slightly different in two places, most likely you would agree. So too for time. Mass bends time; time goes slower in proximity to it. This is the first lesson Carlo Rovelli shares in his concise new book, The Order of Time (2018).

Einstein realized this before clocks sensitive enough to measure it were built, but it is true. Time moves slower at low elevations; on the floor versus the table top. We can easily confirm this now.

Physicists are beyond arguing that time is a uniform entity; that there is one true clock that tells the universal t. For physicists time is relative. What is important is the difference between times at different places. This is the theory of relativity.

In another concise book, Albert Einstein’s Ideas and Opinions, there is an essay about the flow of rivers. How water moves faster the further from the bank, and more importantly how there are spriralling lateral currents within the flow. Rivers meander as a result.

I know now Einstein was thinking about time, and the spiralling of galaxies, as he thought about how rivers flow.

When I first read it I was thinking about rivers. Twenty years later I can better understand how time flows, and how it is attracted to masses thanks to Carlo Rovelli and The Order of Time.

There is only one equation in this small book of phyics: The mind expanding ΔS ≥ 0 the change in entropy (S) is always greater than or equal to 0. No other equation has been pondered more by so many. Entropy (disorder) always increases or stays the same. This is the second law of Thermodynamics. How does it relate to time?

The equation relates to time because it suggests there is a before and after, and the before is always more ordered. Always more ordered in the past? Why?

Boltzman by way of Rovelli says it is sort of arbitrary. Because we perceive it to be that way. Because we cannot see the choas in the past, the many ways it may be disordered. The future is more disordered relative to the past. Don’t worry, I’m confused too.

The Order of Time is full of mind bending new rules. The next is that time depends on motion. The faster we move, the slower it goes. Einstein knew this before it could me measured. Now we can. It is true.

The next is a deconstruction of the meaning of now. There is no universal now. Anyone who has participated in a poor cell phone connection knows time delayed conversations suck. We live in the here and (my) now. But my now is relative, and only extends so far away from me. My mass and speed affect my now. If you have a similar mass and speed, maybe we can talk — now.

Clearly there is no universal now in the universe, since bodies (planets, etc.) have so many different masses and speeds. Each body (or mass) has its own future and present. This is not such a leap.

Rovelli shows these different realities as hourglass figures; two cones connected by a neck. The neck is the now, the base cone the past, the top cone the future (by convention). Each mass then has its own hourglass figure. Its own reality. If there is a space in the universe where only the future cones point for all masses — this is a blackhole! A place where there is no past.

In other words a blackhole is a unique orientation of the past and futures of masses, a space where there is no past.

How frustrated Einstein must have been, trying to reconcile time between train stations, with the full knowledge that it couldn’t be. Noon in Graz is quite different than noon in Tokyo or even Vienna. Why even try to reconcile these?

Rovelli concisely introduces two different hypotheses of time. One from Aristotle who believed time measured change; morning to night, winter to spring, young to old. And one from Newton who thought there was a universal background time that could not be measured, one that would go on even if the universe froze. Even if nothing changed.

Tell your students, tell your friends, in science the answer is usually both. So too in this case. Both Aristotle and Newton were right. It took Einstein to integrate them into one space-time continum. One where masses, speeds, and gravity warp time. It is not the same everywhere, yet marches on regardless of things.

In perhaps the most autobiographical part of The Order of Time, Rovelli reveals his fascination with Plank time and Planck length. These are the limits to quantizing time and space, respectively. 10^-44 time or 10^-33 space intervals seem to be where the idea of granuals, or units of time or space degrade or become useless. These units are just too small to be meaningful. Rovelli is still trying to figure out what happens in this space called quantum mechanics. He troubles himself about whether things still exist at those scales. He wonders like the Grateful Dead, does the time our watch keeps, “only capture the movement of its hands?”

“Noting is, things happen…change is ubiquitous.”

In the fundamental equation of quantum gravity, a time variable does not exist. It is not necessary. The movement of bodies is described in relation to other bodies. Time holds no privlidged position. Change is more important.

These changes are “events”, and events do not occur in isolation in the world of quantum mechanics. They are predictable (or probabilistic), and occur in an interrelated network, otherwise known as a ‘spin network’. These spin networks are the “loop” in the “loop theory.” There is even “spinfoam” in this quantum spacetime, it is found at the intersections between loops. Maybe this is why I don’t study phyics.

Rovelli says that what we need is not energy, but low entropy. The sun has low entropy. Plants feed on this low entropy. Likewise, animals feed on the ordered carbohydrates that plants make from this low entropy. Low entropy comes from even lower entropy, so we must consume it.

Towards the end of the book, Rovelli turns to some uncomfortable questions that emerge from this new perception of reality. If time is relative, and the process of atomizing time or objects can eventually render them meaningless — what am I?

Am I meaningless?

Rovelli gives us three anchors on which to couch our new reality of self. 1) Everything is relative to our point of view, 2) We are natural groupers. We order our world to make sense of it. We see ourselves in relation to others. We are an extension of this association, this ordering, this grouping. 3) We are defined by our memories. “Our present swarms with traces of our past. We are histories of ourselves, narratives” of our past.

Our brains are uniquely capable of preforming this ordering of events to create time. Past, present, future. To catch a ball, we must remember how other similar sized objects have behaved when similarly tossed. Placing our hand to catch it requires projecting into the future where the object will be. Like this example, we construct our realities, from our perspective, by ordering, through memory.

Time may only exist in our minds

Our persective is critical for making the world we inhabit, the time we live in. If that idea is scary, Rovelli suggests that is all time is. Its no more complicated than that. We created it. We must live with it. The alternative is… He suggests we should stop there. “If a question cannot be formulated into words, it may not be bacuase it is profound. It’s because the problem is false.” He suggests we should go back. Go back to, “serrenly emmersing ourselves in time…to savoring the clear intensity of every fleeting moment of our brief existence.”

It was about 20 years ago — actually more — that I read Einstein’s Ideas and Opinions. Around that time I also read Alan Lightman’s Einstein’s Dreams. A wonderful book about a fictional universe, where on subsequent days, life unfolds at a different pace, as if variables in Einstein’s own equations of special realativity are altered. Reading The Order of Time, helps to understand the universe we live in today. Our time. It is an exceptional book. Not quite as breif or easy to grasp as his Seven Brief Lessons in Physics, but perhaps more rewarding. Bravo!

Charley Knight

Written by

Professor of Evolution & Ecology, Cal Poly, San Luis Obispo, CA, USA

Welcome to a place where words matter. On Medium, smart voices and original ideas take center stage - with no ads in sight. Watch
Follow all the topics you care about, and we’ll deliver the best stories for you to your homepage and inbox. Explore
Get unlimited access to the best stories on Medium — and support writers while you’re at it. Just $5/month. Upgrade