Standing on the shoulders of giants…and yelling in their ears

Isaac Newton said he saw further because he stood on the shoulders of giants. He meant that all scholars build on work done by people who came before them. Among the many brilliant scholars whose shoulders Newton stood on were several from the Islamic world. In fact, Isaac Newton’s understanding of his actual ability to see and to comprehend the things he saw, was thanks in part to a man named Ḥasan Ibn al-Haytham. From 622 to 1258 CE, a golden age of science and learning spread across much of Afro-Eurasia. Islamic empires expanded and built schools and libraries. Hasan Ibn al-Haytham was part of that world

Our understanding of the Universe—of the stars that travel across the night sky—depends on our ability to see light. Scientists had to understand how light moves and how it reaches us before they could make the discoveries that we take for granted today. For example, one of the most important inventions for understanding our Universe was the telescope, which lets us see deep into space. But the telescope was only invented because people understood light and how we see it. The study of light is a science called optics.

Ibn al-Haytham’s most important book was The Book of Optics. This book explained how the human eye works and how we see objects, such as stars, that are very far away. After Ibn al-Haytham’s book was translated from Arabic into Latin, around 1200 CE, it sparked a revolution in optics in Europe. His knowledge provided the basis for many of the great scientific discoveries of later scholars such as Galileo, who greatly improved on the design of the first telescopes.

That’s impressive, but what makes Ibn al-Haytham special was how he approached science. He also stood on the shoulders of giants, but he didn’t just stand there. He learned from the knowledge of Greek authorities like Euclid, Aristotle, and Ptolemy, but he also challenged their ideas. To challenge the ancient ideas of these scholars, Ibn al-Haytham used the scientific method. The scientific method is the process of asking a question, developing a hypothesis (an assumption), and testing that hypothesis through rigorous experiments. Ibn al-Haytham used this method of scientific inquiry about 500 years before the method became the standard way to conduct investigations.

The Universe through a pinhole

Ibn al-Haytham was born in 965 CE in the city of Basra (in present-day Iraq). This part of the world was a center of science and learning at the time. In Basra, Ibn al-Haytham became famous for his mathematical ability. One night, sitting in a dark room, he noticed moonlight passing through a tiny hole in the wall. Where the light hit the wall on the other side of the room, an image of the Moon was projected. But it was upside down! Why? This question led Ibn al-Haytham to launch a series of experiments to verify a theory he had formed, based on his observation.

For his experiments, al-Haytham reproduced the effect he had seen in the moonlight by building a camera obscura and documenting his observations. These observations seemed to have certain patterns, and Ibn al-Haytham developed mathematical explanations for these patterns.

Camera obscura is a Latin phrase meaning “dark chamber.” When the light of the Moon passed through a small hole into Ibn al-Haytham’s dark room, it produced an effect that humans have known about and been experimenting with since at least the fourth century in ancient Greece and China. Ibn al-Haytham wanted to know why the projection produced an upside-down image. This effect helped him understand that light moves in straight lines. When light is reflected off an object, it travels in straight lines away from the object in all directions. So, for example, when that light reflecting from the top of an object hits a tiny opening, like the hole in Ibn al-Haytham’s room, it must travel in a straight line. It can only land at the bottom of the room. Likewise, light reflecting off the bottom of the object can only land at the top of the room. That’s why the Moon appeared upside down on his wall.

Before al-Haytham, people believed that human eyes could shoot rays of light outward in a cone, and that when these rays hit objects, we could see them. They believed this because it was claimed by several ancient Greek scholars. Ibn al-Haytham was suspicious of this idea and challenged it. This challenge was a big deal. At the time, people respected ancient scholars and their ideas, and many assumed them to be true. Although Ibn al-Haytham might have respected these ancient thinkers too, he wasn’t willing to accept their theories without testing them. He took the theories of Greek scholars like Euclid, Ptolemy, Galen, and Aristotle and combined them with newer ideas from Islamic thinkers. By challenging and improving on these ideas, he developed new theories about light and sight. He backed up his theories with repeated testing and verification, an aspect of the scientific method that scientists still practice today.

Changing how we see the way we see

Ibn al-Haytham’s big claim was that humans see things because rays of light reflect off objects in straight lines that then travel to our eyes, and then our brains. That’s probably something you’ve already learned, but without the work of Ibn al-Haytham, you might have been taught that we’re able to see because our eyes shoot beams of light!

At the time, and for centuries to come, Ibn al-Haytham’s ideas were revolutionary. His observations in that dark room helped him prove that the Moon appears bright to us because sunlight reflects off it. These observations led him to understand that our eyes are connected to our brain by optical nerves. Later scientists—like Newton—stood on al-Haytham’s shoulders as they developed innovations like telescopes, microscopes, cameras, and eyeglasses. Ibn al-Haytham’s dozens of books and experiments helped other scientists better understand how we perceive objects in the night sky. There’s even a crater on the Moon named after him.

Ibn al-Haytham encouraged others to use his rigorous process for proposing and then testing theories. He wrote:

The seeker after truth is not one who studies the writings of the ancients…and puts his trust in them, but rather the one who suspects his faith in them and questions what he gathers from them. . .Thus, the duty of the man who investigates the writings of scientists, if learning the truth is his goal, is to make himself an enemy of all that he reads, and, applying his mind to the core and margins of its content, attack it from every side..

In this quote, Ibn al-Haytham is urging other scientists to use the scientific method. In other words, we shouldn’t trust ancient ideas just because they’ve been around a long time. We should make ourselves “an enemy” of everything we read: always questioning, always testing. Thanks to the work of Ibn al-Haytham in the tenth and eleventh centuries, later scholars in the Islamic world and Europe—including Isaac Newton—were able to develop new theories about gravity and the movement of stars and planets.