by Carlo Rovelli
‘Things are transformed one into another according to necessity, and render justice to one another according to the order of time.’ [Anaximander c. 570 BCE]
This delightful little book makes us look again at many of the concepts we take for granted. In childhood, we learn to think of reality as the things which surround us in the world – other people, dogs, cats, football teams and so on. We learn to tell the time on a clock or a watch without giving much thought to what ‘telling the time’ actually means. But this view of the world is mistaken. We think of past, present and future, and imagine we know what they are: the past is history – ours or that of the world; the present is the now -not only our ‘now’ but everyone else’s too; the future has yet to be written.
‘ ΔS = ≥0 ‘
Time, Carlo Rovelli tells us, is not what we think it is. The Order of Time explores a strange new reality in which time is stripped of all its everyday properties and dissolves into a kind of blurring of quantum particles, a mysterious world of heat, energy and entropy. There is no univeral ‘now’; the idea of a universal present is meaningless.
‘It simply makes no sense to ask which moment in the life of your sister on Proxima B corresponds to now. It’s like asking …. how much a musical note weighs.’
The first part of The Order of Time examines what modern physics has discovered about time. The theories of relativity (both general and special) and quantum mechanics are well tested, but what they say about time seems contrary to everything we think we observe in our limited world space. A man (or woman) who lives on top of mountain ages more quickly than a woman (or man) who lives at sea level. High speed travel keeps you young. The fundamental laws of physics ** do not distinguish between past and future. Rovelli introduces some of these ideas in a novel way, showing, for example, how light cones resemble genealogical trees upside down.
‘…. time and space are no longer containers or general forms of the world. There are only events and relations. It is the world without time of elementary physics.’
Part Two is trickier. Here the author goes on to talk of his specialist areas of research – quantum gravity and loop theory. But first we are required to grasp the idea that the world is a collection of events, not of things. Sometimes his thinking is deeply philosophical. He quotes Aristotle that ‘time is the measure of change.’ Indeed, he refers to Aristotle a lot; in Part One he pits him against Newton and tells us both were right – in a way. He likes Anaximander too; philosophy and mathematics have always been comfortable bedfellows.
‘We are histories of ourselves.’
When we reach Part Three, we are in even more blurred territory. Much of the remainder of the book is Rovelli’s own speculation. Philosophy begins to usurp science. Here, we need to grasp deeper mysteries, and concern ourselves with concepts such as quantum time and ‘particularity’. Rovelli doesn’t mention the Anthropic Principle as such but the idea is implicit in the discussion about perspective or point of view. I suppose the idea is something along these lines : we can’t truly be an impartial observer because we are part of the system we are observing.
The Order of Time ends, bizarrely, with a discussion about death.
I always enjoy reading books about physics, even if, sometimes, I have to read some chapters twice (or thrice?) This volume was no exception. It’s such a long time since I studied the subject formally!
NOTE ** except the one represented by the above equation – the only equation in the book.