In this Article, owing to errors in the production process, incorrect units were shown on the x axes of Fig. 1c and d. These values are dimensionless and therefore the x axes for Fig. 1c and d should have read ‘Total density, n 0 ’ and ‘Time, t’, respectively, instead of ‘Total density, n 0 (μm−3)’ and ‘Time, t (ms)’. In addition, in the main text, the statement ‘the fractal-like structures seen around t = 80 ms’ should have read ‘the fractal-like structures seen around t = 80 (in dimensionless units)’. These errors have been corrected online.