The Holi photograph and the idea of entropy
A photograph of a crowd, and how the idea of entropy can be recognised in it without getting lost in formulas.
A photograph of a Holi festival in India: hundreds, perhaps thousands of people, covered in coloured powder, all in motion and without any visible structure. At first sight it looks like chaos. On closer inspection there is a great deal of order in it, but of a different kind from the one we usually recognise.
Such an image calls to mind the notion of entropy, a term from physics that is sometimes misunderstood in mental health care. Entropy is not a synonym for "chaos" or "disorder", although it is occasionally used that way. It refers to something more precise, and it is worth pausing on that for a moment.
What, roughly, is entropy?
Entropy, as Boltzmann defined it in the nineteenth century, is a measure of the number of possible ways in which a system can be in a given state. That sounds abstract; an example may help.
Suppose you have a box containing twenty numbered balls, which you shake up. The state "all twenty balls lie in order, with number 1 in the top left corner" can be reached in exactly one way. The state "the balls lie in no particular order in the box" can be reached in a great many ways: billions of combinations that all look about equally untidy.
The ordered state has low entropy: there is one way. The disordered state has high entropy: there are very many ways. Shaking the box therefore almost always produces a state of high entropy. This is not because nature strives towards disorder, but simply because there are far more untidy configurations than tidy ones.
The Holi photograph
Back to the crowd: hundreds of people in motion, colourful and spontaneous. That state can come about in a great many ways; if a number of people change places, the picture hardly changes. In the terms of the example: high entropy.
A military parade is a different matter: the same people, but now in tight rows and in the same posture. That state can be reached in far fewer ways, and a small shift is immediately visible. Low entropy.
Both images have order and structure, but they involve different kinds of order. The parade has an order of fixed pattern, the crowd an order of freedom.
What this has to do with mental health care
In complexity science, entropy is used to say something about how rich and flexible a system is. A healthy human system seems to show a certain degree of entropy in its daily functioning: flexibility, variation, room for change. Not all days are the same, and no hour is exactly like the one before.
Some psychiatric presentations seem to go together with a decrease in that entropy. The system then becomes more rigid, more predictable and less varied. In severe depression, life sometimes runs along fixed patterns, with days that resemble one another and emotions that keep returning in the same forms. The entropy of the system then appears to have fallen.
In other presentations there seems rather to be too much entropy. In severe dissociation or psychosis the system can become so incoherent that hardly any repeatable pattern can be found. There, entropy seems unhealthily high.
Health probably lies somewhere in between: enough structure to be recognisable, enough freedom to be able to move.
A modest conclusion
Although the concept of entropy comes from thermodynamics, it also seems clinically useful, provided it is used with care. It does not explain everything, but it helps to formulate questions that would otherwise be hard to ask. Does a patient have enough dynamic room in her daily functioning? Is she moving along too narrow a path, or has her life become so incoherent that no recognisable pattern remains?
The Holi photograph shows that order does not always coincide with rigidity. Sometimes a rich, colourful mobility is in fact a healthy form of order. And when that mobility diminishes, or tips over into excess, there may be something to talk about together.