Petals and particles

Popular (and unpopular) science frequently relies on the use of metaphor in explanations. Metaphors have occasionally even been responsible for scientific discovery; in 1865 August Kekulé dreamt of a snake biting its own tale. He said this was the inspiration to his figuring out the structure of benzene.

The description of the expanding universe as a balloon being pumped up is ubiquitous in cosmology. But this ubiquity can be a problem; too often the metaphor ‘becomes’ the thing you are describing, and nothing is ever exactly the same as anything else. Any description of reality is limited in its accuracy by its reliance on words.

In quantum physics, light can either be thought of as particles or as waves, depending on how you observe it (the same is true of sub-atomic particles, i.e. they can equally well be thought of as sub-atomic waves). Thomas Young’s famous experiment at the beginning of the nineteenth century showed that light makes diffraction patterns when travelling through parallel slits. Diffraction is a property of waves. Conversely, Einstein’s early work showed that the photo-electric effect, in which light strikes a metal surface and liberates electrons, can only be explained if you treat light as a particle. So, clearly, our everyday concepts of ‘particles’ or ‘waves’, which are complementary, are inadequate to explain the true nature of light.

But physicists never let mere paradoxes stop them and this drawback was elevated to ‘the complementarity principle’ by Niels Bohr. He stated that something can be both one thing and its opposite, and that it didn’t matter, because physics can only be concerned with what you observe and not with the true underlying nature of reality. ‘There is nothing outside the experiment.’ (A nice counterpoint to Derrida’s ‘there is nothing outside the text’.) Different experiments show different aspects of reality, but there is no reason to suppose that you can have an experiment which shows all aspects.

The complementarity principle is an interesting riposte to those people who accuse scientists of having one-track minds, unable to see the subtleties inherent in reality. Keats claimed that Newton ‘unweaved the rainbow’ by explaining the physics behind this phenomenon. On the contrary, Newton deepens our perception of the rainbow through his description of light being diffracted by water droplets in the atmosphere.

Ezra Pound’s famous poem ‘In a Station of the Metro’ runs (in its entirety)
‘The apparition of these faces in the crowd;
Petals on a wet, black bough.’

The two images in this poem are so finely balanced that they mirror each other and it is never clear which is the metaphor and which is the reality. Dangerous for science, but prescient in its complementarity. Pound wrote this in 1913, when Bohr was developing his model of the atom.