By sheer coincidence I published the essay, “What is Time”, shortly before reading Carlo Rovelli’s book. Rather than writing additional commentary here, I put a pointer to that essay. While it does not address Rovelli directly (I hadn’t read him yet) it covers the points made in the review included below. But I do not want to discourage people from reading this excellent book. It is always good to understand the arguments of authors with which you (in this case I) happen to disagree. One cannot claim to be a well rounded philosopher without understanding what it is that those you disagree with are saying.

The Order of Time by Carlo Rovelli (2018) Amazon review

Like consciousness, time is a subject that no philosopher or physicist has ever managed to nail down completely. Thanks to their slippery character, being so close to us (the first one IS us) they are endless sources for fountains of speculation. In this book, Rovelli’s subject is time, but consciousness comes into this narrative as well.

Rovelli is a “time denier”. OK, that’s being a little unfair but not by much. What he denies is that there exists an independent, fundamental property or quality of the universe that is time. Of course the universe is full of movement and change, events unfolding into other events. His basic position is that time emerges into our perspective, our viewpoint, from these phenomena, but it is merely an illusion. The movement is real, the changing is real, but the time in which all of this seems to occur is nothing more than a manifestation of human (possibly animal) mind and the illusion, in turn, is supported by the entropy generated in the functioning of our brains.

The book (not long read) is divided into three parts. In the first Rovelli covers the various sub-disciplines of physics and their temporal implications (or lack thereof). He begins with classical physics (the equations work backwards in time), and moves on to General and Special Relativity, and quantum mechanics. Here he demonstrates that our simple intuition of a universal time flowing from past to future is untenable. Time, mind-independent time, if it exists at all, cannot be like that. In part two he further demolishes time. Not only is it not what we think, in and for physics, it doesn’t really exist at all; even the present is an illusion! In part three, he puts time back together for and in the perspective of an subjective viewpoint.

He argues it is the fact that we view the world from a perspective, that when we perceive the world we inevitably blur the details into a sort of summary or gestalt for our perspective, that causes time to appear to mind, The physics supporting that appearance comes down to thermodynamics. Human time, brain time, is “thermal time”. Certainly Rovelli thinks thermodynamics (in particular the 2nd law) is real, but while responsible for what consciousness perceives of time and so a real enough subjective experience, from the 3rd party perspective of physics, change is real, but time is a mirage.

This book is written for a lay audience. There is almost no math in it (what there is appears in footnotes), and it defends a view common to much of the physics and philosophy community. To be sure Rovelli differs a bit from some of his peers. He argues that relativistic “block time” is no more a “true portrait of objective time” than any other theory. In Rovelli’s view remember there is no such thing as “objective time”.

In 2015 a philosopher (Roberto Unger) and a physicist (Lee Smolin) wrote “The Singular Universe and the Reality of Time”. This book (reviewed by me on Amazon) makes precisely the opposite case from that of Rovelli. Of course they recognize what Relativity and quantum mechanics imply about time, but they maintain, nevertheless, that a notion (and reality) of objective, “universal time”, is more fundamental than any other phenomena of the universe, even more than space! Rovelli mentions this book in a footnote and admits that Unger and Smolin’s view “is defensible”, but he leaves it there and never addresses what is defensible about it.

The Unger/Smolin book goes against the grain of 95% of today’s physicists. Personally I agree with Smolin and Unger. The fact (thanks to limiting effect of the speed of light) that we cannot map our present to any present in a remote galaxy, or even the nearest star does not mean there is no present there, in fact everywhere. Something is happening, NOW, everywhere in the universe. We do not know what it is, but that does not mean the present isn’t real as Rovelli believes. Had Rovelli directly addressed Unger and Smolin I would have given this book another star. Had he not mentioned them at all, I would have taken another away.

In summary this is a decent and well written book advocating for a particular view of time (or no time) that I happen to think is wrong, but what do I know? It happens to be the dominant view in physics today. Rovelli is a well respected physicist and a good writer. Those of you interested in the subject will find this book valuable whether you agree with the author or not.