AKA: Extramission; The Theory With The Eye Beams
Theory born: 5th century BCE
Parent(s): Empedocles
Description: The goddess Aphrodite (apparently) made the human eye out of the four elements (earth, wind, fire and water). She lit the fire within the eye, causing it to emit beams that illuminated their surroundings and enabled them to be seen. The eye beams didn't work when it was night because something something interaction with sun rays something.
Despite its obvious problems, this theory persisted for hundreds of years by intertwining with intromission theory (the theory that light entered the eyes, rather than exiting them). Plato circa 400BCE, for example, suggested that both theories were true.
Theory death: Death began in approximately 1000CE
Cause of theory death: Alhazan (polymath, physicist, mathematician, astronomer; b. 965, d. 1040CE)
Alhazan's genius was in combining the Roman physician Galen's work on the eye with Aristotle's intromission theory of vision and Euclid's mathematical modelling of light rays. Although Euclid himself had been uneasy with emission theory back in 300BCE (how, he had wondered, can distant stars immediately be seen when opening the eyes when the light coming out of the eyes needs time to travel to them and back?), he still used emission theory in his work. However, that growing unease was recognised by increasing numbers of philosophers and scientists who accumulated contradictory evidence until the whole emissions theory collapsed under its weight. For example, mathematical modelling had shown the light rays could enter the eye and create an image; for another, and the anatomy of the eye clearly was orientated towards focusing incoming, rather than outgoing, rays.
Notable features: A 2002 study revealed that up to 50% of adults still believe this theory to be true.
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