Having earlier read 'Seven Brief Lessons on Physics' by eminent physicist Rovelli, I had high hopes from 'The Order of Time'. Not only have those hopes been fulfilled, but Rovelli has gone much beyond. This book would be favoured by readers who like to be challenged.
Rovelli starts with the seemingly innocuous fact that "time passes faster in the mountains than it does at sea level", something empirically proven but perhaps not known to the majority of common people. He goes on to prove that this is true across the universe, well-proven a hundred years back by the curved space-time equations of Einstein (later revealed to be a gravitational field), who postulated that time slows down the closer one is to the source of greater gravity.
Next, Rovelli demolishes the idea that time is unidirectional, establishing that it's increasing entropy and a phenomenon called 'blurring' which gives the impression of time progressing, and that heat exchange is the only event which is unidirectional and thus giving rise to 'thermal time'. On the way, Rovelli puts paid to the concept of cause and effect, and even to past and future. (Did Einstein really write that "the distinction between past, present and future is only a stubbornly persistent illusion"? Rovelli provides the context for that famous saying in chapter 7).
Coming to the 'present', Rovelli next establishes that "the present of the universe does not exist", using the example of interstellar travel. What effect this has on genealogies is an interesting aside.
Ultimately, Rovelli says, 'The world is made of events, not things'. And as Aristotle said: 'Time is nothing other than the measurement of change' in those things. Along the way, Rovelli also refers to the concept of 'loop quantum gravity' which is one of the approaches in quantum theory on which he works.
And all this is explained by about the middle of the book. The rest of the chapters touch upon more complex, seemingly esoteric, concepts like 'indexicality'.
The range of sources across centuries accessed by Rovelli for this tome on time (though a slim volume at less than 200 pages) is mind-boggling, from Mahabharat to Ecclesiaste to the Greek philosopher Anaximander (the title of the book is from one of his writings) to the the Persian poet Shirazi to Aristotle to Newton and much beyond upto 20th century - reminds one of Carl Sagan's legendary 'Cosmos' which also had similar breadth of references.
This is not a book for casual reading. I usually read parts of 4-6 books on a typical day, but for this book I had to ensure complete peace and focus, else one may tend to lose the train of thoughts. But once the reader is able to focus, a rich harvest is assured.
