Physics is a science that covers a very broad area of the material world, ranging from research on subatomic particles to the study of galaxies. In physics, what is most important is the composition and behavior of matter and all its fundamental laws. The most fascinating works on physics created by Islamic scientists concern a subfield of physics: optics.
This article discusses the contributions of Ibn al-Haytham.
Ibn al-Haytham: Youth
Ibn al-Haytham, more commonly known in Europe by his Latinized name « Alhazen, » was born in the city of Basra in 965 CE. He attended local schools and moved to Baghdad to pursue advanced studies in science, as many Arab scientists did at the time. However, he may have had some disagreements with the Fatimid caliph Al-Hakim bi-amr-Allah, which led to his being buried alive in 1011. He is believed to have remained buried alive for several years, until the caliph’s death in 1021.
He then moved to Spain to focus on science again. At the end of his life, he returned to his native Egypt, where he died in 1039.
Ibn al-Haytham and his « books on optics »
Ibn al-Haytham is primarily known for his work in optics, which did not go unnoticed in Europe. In his seven-part book, « Kitab al-Manazir, » he began with harsh criticisms of several past theories. One of these theories was the theory of vision.
He examined, in particular, what happens when someone is exposed to bright light. He discovered that light entering the eye from an external source has a certain influence on vision. To expand his knowledge, he began with a series of experiments in which he studied the relationship between light fraction and image distortion. He learned that the mathematical aspects of optics, specifically reflection and fraction, had to be correlated with knowledge of the anatomy of the eye. For this reason, he included a diagram of the eye with all its components in his book, as shown below:
In his book, Ibn al-Haytham elaborated on the fact that the light reaching the eye originates from the visible object. In the chronological book by David C. Lindberg (a recently deceased American historian), « Theories of Vision: From al-Kindi to Kepler, » the author provides Ibn al-Haytham’s definition of the theory of vision:
Light illuminates all visible objects and this light later reaches the surface of the eye, allowing humans to perceive the object in question.
Because Ibn al-Haytham clearly challenged the vision theory and supported his own hypotheses with evidence through his experiences, he was able to garner widespread appreciation in the West.
George Sarton, a Belgian-American historian of science, paid tribute to Ibn al-Haytham’s contribution to science in his book « History of Science »:
He, Ibn al-Haytham, was the greatest Islamic physicist and student of optics the world has ever known. Whether his successors live in England or Far Persia, they all draw from the same wellspring. He had a considerable influence on European thought, from Bacon to Kepler.
Ibn al-Haytham and his camera obscura
Ibn al-Haytham frequently used the term « al-Bayt al-Muthlim » in his experiments, which translates as « the dark chamber. » He also developed his camera obscura, a device that projects an image through a small hole. None of his predecessors (Aristotle, Euclid, or al-Kindi), like Ibn al-Haytham, studied the effects of light passing through a camera obscura and were able to prove that everything projected onto the screen originated from the other side of the hole.
With this, Ibn al-Haytham became the first to prove it through an experiment using a lamp with multiple light sources distributed and arranged over a large surface. He was also the first scientist to successfully project an image onto a screen using a camera obscura.
As such, Ibn al-Haytham was the first scientist in history to develop a functional camera.