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Pink Floyd’s famous album the Dark Side of the Moon has on its cover an illustration of a prism breaking white light into different colours. This iconic image is beautiful in its simplicity, attracting the attention of anyone curious about the nature of light. However, the image is also wrong. Light does not diffract on entry into a prism. It diffracts only on exit, as can be seen by careful observation of a real experiment.
This disconnect between Pink Floyd’s cover and the real nature of light is unfortunate in that it has installed a false idea of reality in a lot of people’s minds. Many students of physics go their entire lives assuming that diffraction happens both at the entry and at the exit of a prism. This in turn, leads to the assumption that light is a wave phenomenon. Snell’s Law is frequently sited. Yet, all of this is incorrect. Light does not behave like waves. It behaves like particles wrapped inside pilot waves.
This would have been a trivial matter if it wasn’t for the fact that the behaviour of light as it travels through a prism is the biggest mystery in optics. It’s at the heart of an age long debate over the true nature of light. The wide distribution and general acceptance of Pink Floyd’s cover as a correct representation of reality is therefore a big deal. It has confused an issue that is of great importance in physics.
A great deal of work has been done on optics, and much time has been wasted on the incorrect assumption that Pink Floyd was right. However, any text on optics can be immediately ignored if it uses illustrations in which light diffracts at both the entry and exit of a prism. Entire theories can be ignored as fiction. They answer questions that only exist in the minds of people but have no anchor in reality.
The damage done by Pink Floyd’s cover is so wide reaching that most school books on optics give the impression that light diffract on entry as well as exit through a prism. Many students of physics are not only exposed to an iconic image on a record album. They are also told at school that the image is factually correct. A very important debate on the nature of light has thus been thoroughly corrupted.