Emergence of experimental method and physical optics

The use of empirical experiments in geometrical optics dates back to second century Roman Egypt, where Ptolemy carried out several experiments on reflection, refraction and binocular vision. However, he either discarded or rationalized any empirical data that did not support his Platonic paradigm. Experiments did not hold any importance at the time, and empirical evidence was thus seen as secondary to general theory. The incorrect emission theory of vision thus continued to dominate optics through to the 10th century.

The turn of the second millennium saw the development of an experimental method emphasizing the role of experimentation as a form of proof for scientific inquiry together with the development of physical optics where mathematics and geometry were combined with the philosophical field of physics. The Iraqi physicist, Ibn al-Haytham (Alhazen), is considered a central figure in this shift in physics from a philosophical activity to an experimental and mathematical one, and the shift in optics from a mathematical discipline to a physical and experimental one.

Due to his positivist approach, his Doubts Concerning Ptolemy insisted on scientific demonstration and criticized Ptolemy's confirmation bias and conjectural undemonstrated theories. His Book of Optics (1021) was the earliest successful attempt at unifying a mathematical discipline (geometrical optics) with the philosophical field of physics, to create the modern science of physical optics. An important part of this was the intromission theory of vision, which in order to prove, he developed an experimental method to test his hypothesis. He conducted various experiments to prove his intromission theory and other hypotheses on light and vision. The Book of Optics established experimentation as the norm of proof in optics, and gave optics a physico-mathematical conception at a much earlier date than the other mathematical disciplines. His On the Light of the Moon also attempted to combine mathematical astronomy with physics, a field now known as astrophysics, to formulate several astronomical hypotheses which he proved through experimentation.