The Order of Time

by Carlo Rovelli

It is Entropy, not Energy, that Drives the World

What makes the world go round are not sources of energy but sources of low entropy.

It isn’t true, as is sometimes stated, that life generates structures that are particularly ordered, or that locally diminish entropy: it is simply a process that degrades and consumes the low entropy of food; it is a self-structured disordering, no more and no less than in the rest of the universe.

Even the most banal phenomena are governed by the second law of thermodynamics. A stone falls to the ground. Why? One often reads that it’s because the stone places itself ‘in a state of lower energy’ that it ends up lower down. But why does the stone put itself into a state of lower energy? Why should it lose energy if energy is conserved? The answer is that when the stone hits the Earth, it warms it: its mechanical energy is transformed into heat. And there is no way back from there. If the second law of thermodynamics did not exist, if heat did not exist, if there existed no microscopic swarming, the stone would rebound perpetually; it would never land and be still. It is entropy, not energy, that keeps stones on the ground and the world turning.

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What causes events to happen in the world, what writes its history, is the irresistible mixing of all things, going from the few ordered configurations to the countless disordered ones. The entire universe is like a mountain that collapses in slow motion. Like a structure that very gradually crumbles.

From the most minute events to the more complex ones, it is this dance of ever-increasing entropy, nourished by the initial low entropy of the universe, that is the real dance of Shiva, the destroyer.

But memory, causes and effects, flow, the determined nature of the past and the indeterminacy of the future are nothing but names that we give to the consequences of a statistical fact: the improbability of a past state of the universe.

To a large extent, the brain is a mechanism for collecting memories of the past in order to use them continually to predict the future.

This being between past and future events is central to our mental structure. This, for us, is the ‘flow’ of time.

It is within my mind, then, that I measure time. I must not allow my mind to insist that time is something objective. When I measure time, I am measuring something in the present of my mind. Either this is time, or I have no idea what time is.

Augustine’s exposition of the idea is quite beautiful. It is based on our experience of music. When we listen to a hymn, the meaning of a sound is given by the ones that come before and after it. Music can occur only in time, but if we are always in the present moment, how is it possible to hear it? It is possible, Augustine observes, because our consciousness is based on memory and on anticipation. A hymn, a song, is in some way present in our minds in a unified form, held together by something – by that which we take time to be. And hence this is what time is: it is entirely in the present, in our minds, as memory and as anticipation.

in the moment that we hear a note the previous note is ‘retained’, then that one also becomes part of the retention – and so on, running them together in such a way that the present contains a continuous trace of the past, becoming gradually more blurred.

‘time temporalizes itself only to the extent that it is human’.

Buddha summed this up in a few maxims that millions of human beings have adopted as the foundations of their lives: birth is suffering, decline is suffering, illness is suffering, death is suffering, union with that which we hate is suffering, separation from that which we love is suffering, failure to obtain what we desire is suffering.19 It’s suffering because we must lose what we have and are attached to. Because everything that begins must end. What causes us to suffer is not in the past or the future: it is there, now, in our memory, in our expectations. We long for timelessness, we endure the passing of time: we suffer time. Time is suffering.

A present that is common throughout the whole universe does not exist

There is a present that is near to us, but nothing that is ‘present’ in a far-off galaxy. The present is a localized rather than a global phenomenon.

in order to escape from the anxiety time causes us that Parmenides wanted to deny its existence, that Plato imagined a world of ideas that exist outside of it, and that Hegel speaks of the moment in which the Spirit transcends temporality and knows itself in its plenitude. It is in order to escape this anxiety that we have imagined the existence of ‘eternity’, a strange world outside of time that we would like to be inhabited by gods, by a God or by immortal souls.fn1

And we begin to see that we are time. We are this space, this clearing opened by the traces of memory inside the connections between our neurons. We are memory. We are nostalgia. We are longing for a future that will not come. The clearing that is opened up in this way, by memory and by anticipation, is time: a source of anguish sometimes, but in the end a tremendous gift.

‘Every day countless people die, and yet those who remain live as if they were immortals.’1

where c is the speed of light, is the acceleration of Galileo and h is the height of the table.

‘The notion of “now” is nothing more than a certain relation between a certain observer and the rest of the universe.’

The choice is between forcing the description of the world so that it adapts to our intuition, or learning instead to adapt our intuition to what we have discovered about the world. I have few doubts that the second strategy is the most fruitful one.

Time is: ‘number of change, with regard to before and after’