My work has often involved an exploration of time, in particular, how we can best imagine a past moment as ‘now’. Recently I’ve been re-reading Carlo Rovelli’s ‘The Order of Time’ and have been particularly interested in entropy and the part it plays in the fact time always flows from the past towards the future.

But what is entropy and what has it got to do with time? Well, the answer is complex and would require a book to answer it properly. However, as a layman, and as far as I understand it, entropy is, at a very basic level, the measurement of how much atoms in a given substance are free to spread out, move and arrange themselves in random ways.

As ever, Professor Brian Cox describes it perfectly here:

The difference between past and future lies in this “natural disordering that leads to gradually less particular, less special structures” [Rovelli, The Order of Time]; structures like the piles of sand as opposed to the sandcastle.

One aspect of Rovelli’s book I took a while to grasp was the idea of ‘blurring’. Rovelli asks the question, why do phenomena that we observe around us in the cosmos begin in a state of lower entropy in the first place. He describes a pack of cards:

*“If the first twenty-six cards in a pack are all red and the next twenty-six are all black, we say that the configuration of the cards is particular; that it is ordered. This order is lost when the pack is shuffled. The initial ordered configuration is a configuration ‘of low entropy. But notice that it is particular if we look at the colour of the cards – red or black. It is particular because I am looking at the colour. Another configuration will be particular if the first twenty-six cards consist of only hearts and spades. Or if they are all odd numbers, or the twenty- six most creased cards in the pack, or exactly the same twenty-six of three days ago … Or if they share any other characteristic.*

*If we think about it carefully, every configuration is particular; every configuration is singular, if we look at all of its details, since every configuration always has something about it that characterises it in a unique way. Just as, for its mother, every child is particular and unique. It follows that the notion of certain configurations being more particular than others (twenty-six red cards followed by twenty-six black, for example) makes sense only if I limit myself to noticing only certain aspects of the cards (in this case, the colours). If I distinguish between all the cards, the configurations are all equivalent: none of them is more or less particular than others. The notion of ‘particularity’ is born only at the moment we begin to see the universe in a blurred and approximate way.*

*The notion of particularity, is born only at the moment we begin to see the universe in a blurred and approximate way. Boltzmann has shown that entropy exists because we describe the world in a blurred fashion. He has demonstrated that entropy is precisely the quantity that counts how many are the different configurations that our blurred vision does not distinguish between.”*

*The difference between past and future is deeply linked to this blurring. So, if I could take into account all the details of the exact, microscopic state of the world, would the characteristic aspects of the flowing of time disappear? Yes. If I observe the microscopic state of things, then the difference between past and future vanishes.*

*The future of the world, for instance, is determined by its present state – though neither more nor less than is the past. We often say that causes precede effects and yet, in the elementary grammar of things, there is no distinction between ’cause’ and ‘effect’.”*

It was this line which took me a while to grasp: “He has demonstrated that entropy is precisely the quantity that counts how many are the different configurations that our blurred vision does not distinguish between.”

If we think back to the sandcastle and the pile of sand we can imagine the number of different configurations of each and can easily imagine that the number of configurations for the castle are far, far fewer than of the pile of sand. The castle therefore has few configurations that our ‘blurred vision does not distinguish between’ (low entropy) as opposed to the sand pile (high entropy).

As far as I understand it then, our blurred view of the world equates to our recognition of things as things; objects with form, and it’s because of this that we experience the flow of time; the sandcastle collapsing on the beach and the castle falling slowly to ruin.

But what has this to do with my work?

See my next blog post to find out.