#63: The Order of Time

There’s nothing like theoretical physics for making you feel that words are floating, untethered to any normal experience. Or to put it another way, that a self-supporting explanation for phenomena is being built without reference to anything verifiable on an everyday level.

This is at times how I felt on a first head-spinning reading of Rovelli’s The Order of Time, in which he tries to explain to ‘my dear, cultivated reader’, as he puts it, what time is in terms of physics. Why does time move from the past to the future? Does the present exist? Is time an objective ‘container’ for events which exists independently of them, or is it measurement of change, so that if nothing happens, time stops?

Well, here is my stab at a summary of the book’s answers to these questions:

Why does time move from the past to the future?

This is a tough question. Rovelli explains physicist Ludwig Boltzmann’s idea that the direction of time is due to our ‘blurred’ vision of microscopic events. If humans could ‘take into account all the details of the exact, microscopic state of the world’, the difference between past and future vanishes. What gives rise to our understanding of time passing is that the world is moving from a state of low to high entropy, meaning that disorder is increasing. One example of this is the sun, a source of low entropy when it emits photons, after which entropy increases when the earth emits 10 cold photons is in exchange for every one from the sun. This increasing disorder causes events to happen, and means traces of the past are found in the present. No? Me neither, well… maybe a little. This footnote from the book helps:

    The point is not that what happens to a cold teaspoon in a cup of hot tea depends on whether I have a blurred vision of it or not.… It just happens, regardless. The point is that the description in terms of heat, temperature and the passage of heat from tea to spoon is a blurred vision of what happens, and that it is only in this blurred vision that a startling difference between past and future appears.

Entropy itself is a result of our blurred vision, as is the ‘particularity’ of our universe which means that it is, extremely unusually, moving from a state of low to high entropy.

Does the present exist?

Rovelli thinks an ‘objective global present’ does not exist, since the most we can speak of, post-Einstein, is ‘a present relative to a moving observer’; time has been shown to be relative to qualities such as speed and proximity to an object. However, he acknowledges voices arguing for ‘a privileged time and a real present’.

Aristotle and Newton, p. 59

Is time an objective ‘container’ for events which exists without them, or is it measurement of change, so that if nothing happens, time stops?

Rovelli explains how the first view was that of Newton, the second of Aristotle. He brings in Einstein to create a synthesis of them: space-time is one field among many. (‘Fields’ are substances which ‘constitute the weave of the physical reality of the world’). Space-time is a field which exists independently of matter, but ‘stretches and jostles’ with other fields.

The 'curved' space-time field, p. 69

Connecting physics with other worldviews

Bravely, the book moves outside physics, into biology, philosophy and religion. Rovelli believes physics allows us to study time free of ‘the fog of emotion’, but he also celebrates our emotional need for time, its necessity for making us who we are through memory. Perception of time is also crucial for survival, since we have evolved neural structures that allow us to predict the future based on our understanding of the past. He also speculates that it is anxiety about time that caused Plato to imagine timeless, abstract ideas and philosophical constructs. A meditation on death comes at the end of the book. 

These departures from physics into different areas seem somewhat disconnected from the physics-based approach of the rest of the book, and less well-developed. For example, Rovelli thinks our sense of our identity comes from interaction with others, not introspection. But have not psychologists been studying this for decades? Perhaps these attempted connections with more human concerns exist to add interest to what could otherwise be a very dry book, or to clarify that physics coexists and is separate from other levels of understanding — psychological, biological, philosophical. How physics may, or may not, connect with these areas is something that, for me, awaits another book.

The Order of Time is published by Penguin.