The first known debates over the speed of light date back to ancient Greece. Empedocles was the first to theorize light has a finite speed. Other philosophers at the time did not believe light moved, or at least not at a finite speed. Aristotle argued "light is due to the presence of something, but it is not a movement." A popular argument was the "emission theory," which taught that light was emitted from the eyes, enabling vision. Heron of Alexandria, expanding on that theory, deduced the speed of light must be infinite, since distant objects, such as stars, are visible immediately after opening opening the eyes.
In 1021, the Islamic philosopher Alhazen, in his Book of Optics, dismissed the emission theory, and argued light moves from objects to the eye, enabling vision. This argument led him to join Empedocles in the finite speed argument.
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