The Order of Time by Carlo Rovelli
My rating: 4 of 5 stars

""Reality is often very different from what it seems. The Earth appears to be flat but is in fact spherical. The sun seems to revolve in the sky when it is really we who are spinning. Neither is the structure of time what it seems to be: it is different from this uniform, universal flowing."

It is not Carlo Rovelli's fault that I don't rate his The Order of Time (2017) as high as the absolutely outstanding Seven Brief Lessons on Physics . The reason may be that my amazement about finding an author who can write about contemporary physics in a convincing and accessible way has worn out a little. Also, naturally, there is some repetition between both books. Still, Order is a wonderful treatise on the nature of time from the viewpoint of cutting-edge physics.

I find the book amazingly readable; since it is also short, 211 small-format pages, I have devoured it in two short sittings. I love the verses that open each chapter: they come mainly from Horace's Odes, translated by Giulio Galetto

"The brief arc of our days,
O Sestius,
prevents us from launching
prolonged hopes. (I,4)

But back to physics. Dr. Rovelli tells us strange things full of wonder. As humans we are immersed in the stream of our perceived linear time, yet the universal "now" (i.e., the present) does not exist. The "speed at which time flows changes from place to place." The arrow of time appears only in connection with heat. "Spacetime is the gravitational field - and vice versa." Time is granular.

Dr. Rovelli, a world-famous physicist, is one of the main researchers in the field of quantum gravity. He has offered major contributions to the loop quantum gravity theory, which attempts to combine quantum mechanics and general relativity. I find Part II of the book, The World Without Time particularly fascinating. The author stresses that

"The world is not a collection of things, it is a collection of events.

Then he explains the basic tenets of the loop quantum gravity, which I am too hesitant to summarize because of my deep ignorance of contemporary physics. I am happy, though, to emphasize the connections of the theory with probability, which is the branch of mathematics that I love the most, and with the concept of entropy. In 1972 I was taking the thermodynamic course from Prof. Jerzy Rutkowski at the Warsaw Institute of Technology. I will never forget the professor running around the auditorium and yelling "Entropy is the spirit that governs the Universe." And now, almost 50 years later, I read in Dr. Rovelli's book:

"It is the growth of this entropy that powers the great story of the cosmos."

And to make things even more explicit:

"Traces of past exist, and not traces of the future, onlybecause entropy was low in the past. [...] the only source of the difference between past and future is the low entropy of the past."

As I tend to easily get into overly somber mood I will not write much about the last chapter, beautifully written The Sister of Sleep, about human impermanence and our fear of death.

An absolutely wonderful book!

Four-and-a-half stars.


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