The Neuroscientist Jonathan Touboul does research on hipster-alike-neurons, i.e. "they fire when every neuron around them is quiet; or they fall silent when every neuron around them is chattering." (I myself was not aware of this definition of hipster and feel quite uncomfortable hip right now, but that will pass.) And he noticed some rather interesting similarities between societies involving hipsters in general and brains involving hipster neurons in particular:
But members of society do not have immediate knowledge of cultural trends. Neither do neurons immediately recognize what other neurons are up to.
So the important term here is: immediate. There is a delay - and due to the delay, there comes syncronizity in the reaction: This is why hipsters look all the same. Read more on the mathematics behind it on io9: A Mathematical Model Explains Why All Hipsters Look The Same. Or, with a broadend focus on entrepreneurs at NoStartupHipsters: What do Neurons, Hipsters and Entrepreneurs have in common?