In this small book filled with giant ideas, Carlo Rovelli gently teases apart everything we take for granted about the concept of time. That it travels in a linear direction from the past to the future, that it exists independent of us, that we are subjected to it and at its mercy. One would not expect a book on the physics of time to also be philosophical and spiritual but it very much is. As he notes, it is likely that humanity’s anxiety about time is what has spurred its studies and philosophies and religions.
Time, for us, is defined by a few essential elements. Each of these comes under scrutiny – the idea of time recorded by clocks, the concept of the ‘present’, the moment the we call ‘now’. He compares Aristotle’s and Newton’s definitions. Aristotle’s time is nothing other than the measurement of change while Newton holds that there is a time that passes even when nothing changes.
Rovelli now begins to take apart the basics. First, there is time’s unity. Two clocks at two different places read different times. So which clock has the ‘real time? It’s like comparing currencies but they only have values relative to each other. So time is relative between between two clocks, two persons, two places… and if every point has its own time, we now have not two times but an infinitude.
The concept of “now” is completely unravelled. What is ‘now’ for me on this planet means something different for the ‘now’ that you claim were you on a different planet. Time passes differently, light takes lightyears to reach from your point to mine – if I see your ‘now,’ I am actually seeing what happened perhaps a few years ago and the ‘now’ that I tried to claim simultaneously is in my ‘past.’ So time is not an objective entity that exists outside of us – it is relative between the two or countless entities that are experiencing it. “Time is a legion; a different one for every point in space.”
Next, he explains that it is heat that gives time its arrow of direction. “If nothing else around it changes, heat cannot pass from a cold body to a hot one.” He relates how Rudolf Clausius made this interpretation and described this irreversible loss of heat as ‘entropy,’ derived from the Greek word for transformation. So time is given its shape by entropy – the changing of state, the disintegration of an order. Yet, is this order inherent or something that we perceive? He uses the example of a pack of cards. We may claim it is ordered by colour (low entropy) – red and black. When shuffled, we have lost the order (high entropy). However, the order is lost only from our perceptive which claims that the colour gave its order. It is this perspective on the order that is called ‘particularity.’ If we looked at the suits or the numbers, in the other words, if we could perceive all the configurations, then as the shuffle occurs, there would be no change from past to present, but rather a change in configuration. So, at the minute level, time ceases to exist. The changes from past to future are simply a product of our ‘blurred’ vision.
If that makes your brain hurt, there’s more! Having rid us of our innocent comprehension of time, Rovelli now takes us into the sources of time. He sheds light on difficult theories ranging from time as a layer alongside electromagnetic and gravity, and also contemplates our mortal experiences and senses, enabling them to exist impossibly, side by side in our minds and hearts.
According to him, “we can think of the world as made of of things. Of substances. Of entities. Of something that is. Or we can think of it as made of events. Of happenings. Of processes.” “The difference between things and events is that things persist in time; events have a limited duration.” He uses the example of a stone. As a ‘thing’, we may know where it will be tomorrow but it may also be nothing more than a long event. Stones change, they are formed by chemistry and physics and may disintegrate to dust. Thus, the world is a ‘network of events.’
After entirely breaking down the concept of time, in the third and final section, he builds it back up. It comes down to what we see and know. Our perspective is everything. We may see ourselves as disintegrating faster than the world as a whole, or we may perceive change on a planetary scale as moving at a glacial pace but this is all from our perspective only; our ‘blurring.’ And so we have a point of view – our conception of the world divided into groupings – and then, we have memory. “We are histories of ourselves. Narratives.” “It is memory that solders together the processes, scattered across time, of which we are made.” He sums up, “In the elementary grammar of the world there is neither space nor time – only processes that transform physical quantities from one to another, from which it is possible to calculate probabilities and relations.” and notes that, “we human beings are an effect of this great history of the increase of entropy, held together by the memory that is enabled by these traces.”
We are time. This makes sense now.
From here, Rovelli swirls a rich tapestry of imagery, pulling us out into the universe of mysteries and magic and bringing us up close to moments of love, sunshine and mushrooms that dissolve our reality. It is an inspired closing that throws a warm blanket over our chilled skin after contemplating the dissolution of everything we took for granted.