Ibn al-Haytham: Testing is Believing

Among the astrophysicists and astronomers eager to scour these super-detailed views of the universe is Burçin Mutlu-Pakdil, Ph.D., who teaches at Dartmouth College. “My fascination with space was purely…” she pauses, looks up as though tracing the arc that has taken her from her 2009 bachelor’s degree in physics at Bilkent University in Ankara, Turkey, to her 2016 discovery, as a doctoral student at the University of Minnesota, of a new type of galaxy.

“There was this middle school assignment,” she says, face and hands animated, “which was ‘Write an essay about your ideal person.’” She asked her sister, “‘Who is the cleverest person in the world?’ ‘Probably Einstein. Check it out.’”

Mutlu-Pakdil did, and there she discovered the world of science and, specifically, “black holes [and] mysterious objects in space,” she says. Years later Mutlu-Pakdil was analyzing images of a galaxy some 359 million light years away from Earth. She and her team initially interpreted them as showing a rare, ringed formation known as a Hoag’s object, due to what seemed like a central ball of stars encircled by a fainter ring of stars. But when Mutlu-Pakdil filtered out some of the brightness at the center, she discovered a second, diffuse ring of stars that were redder, and hence older. Nothing else like this had ever been seen. Now officially catalogued as PGC1000714 and nicknamed the Burçin galaxy, this discovery hooked Mutlu-Pakdil on “extreme galaxies,” she says, “any extreme galaxy.”

She currently has focused her gaze on galaxies with just a few billion stars—far fewer than our Milky Way’s estimated 100 to 400 billion. “They are the smallest. They are the faintest. They are the oldest. They are the least chemically enriched systems. And they are the most dark-matter dominated.” Unlike her celestial namesake, these so-called dwarf galaxies are also the most common galaxy in the universe. Thanks to the Rubin Observatory’s telescope and camera, she hopes to “discover basically hundreds of these faint galaxies” that can shed light on, “ultimately, the nature of dark matter and galaxy formation.”

While Mutlu-Pakdil’s research questions and equipment would astonish scientists of old, to Nader El-Bizri, recipient of the 2014 Kuwait Prize for Arabic and Islamic Scientific Heritage, it seems clear that much would also feel familiar, particularly to Abu ‘Ali al-Hasan ibn al-Haytham, who is often known in the West as Alhazen. Born in 965 CE in Basra (now present-day Iraq), Ibn al-Haytham was a polymath who, says El-Bizri, studied physics through the lens of mathematics.

The Greeks, El-Bizri explains, had regarded physics and mathematics as distinct ways of studying reality: Physics described a dynamic, tangible world of movement and flux, whereas mathematics described an unchanging, abstract world. Along comes a generation looking for ways to merge these into a single science, and two aspects of Ibn al-Haytham’s work particularly stand out, says El-Bizri, who currently serves as dean of the College of Arts, Humanities, and Social Sciences at the University of Sharjah in the UAE: “the experimental method and the ‘geometrizing’ of the study of natural phenomena.”

This is what Ibn al-Haytham did in studying light. Though some before him had also believed that light traveled in straight lines, it was Ibn al-Haytham who first applied mathematics to explain how light rays actually behaved. As ingenious as this was, what truly sets Ibn al-Haytham apart is that he did not stop with assertion: He devised experiments to find out whether rays really did travel in straight lines and to observe how light behaved under varying conditions, thus testing theories about everything from rainbows to how light moves through different transparent mediums—refraction. Many of these experiments he detailed in his Kitab al-manazir (Book of Optics), completed sometime before his death in about 1040 CE. Within 200 years, a Latin translation began circulating in Europe under the title De aspectibus.

Ibn al-Haytham’s experiments ranged from the simple to the complex. In addition to observations about sunlight, firelight and other forms of light, he described testing the theory that light travels in straight lines by placing candles at various distinct locations in the same area, and when they all face a window that opens into a dark recess, and when there is a white wall or [other white] opaque body in the dark recess facing that window, the [individual] lights of those candles appear individually upon that body or wall according to the number of those candles; and each of those [spots of light] appears directly opposite one [particular] candle along a straight line passing through the window. Moreover, if one candle is shielded, only the light opposite that candle will be extinguished, but if the shielding body is lifted, the light will return. And this can be tried anytime.

In another experiment, Ibn al-Haytham built an enclosed space in which the only source of light was a small hole in one wall. Now heralded as the world’s first systematically recorded camera obscura (literally “dark room”), this innovative experiment led ultimately to the photographic camera. Ibn al-Haytham constructed his camera obscura to both confirm how light travels and deepen his understanding of how we see. He observed that the faint image of the scene outside on the wall opposite the hole was correct in all its details except that it was flipped upside down and backward—because light travels in straight lines. (See illustrations.)

This and other experiments bolstered Ibn al-Haytham’s theories about sight. In his time, the dominant theory was that we see because our eyes shoot out a beam that widens into a cone of light, somewhat like a superhero deploying X-ray vision. Ibn al-Haytham argued it was the other way around. Light, he postulated, travels into our eye through the pupil, just as it does through the pinhole in the wall. This is the physiological and physical aspect of sight, El-Bizri explains, adding that Ibn al-Haytham was the first to understand that vision is also cognitive.

“I do not simply see because of the light coming into my eyes and leaving an impression on the optic nerves and even touching my brain,” El-Bizri summarizes. Ibn al-Haytham, he says, argued that there is also “an investing of the faculties of imagination, memory, discernment, syllogism. I don’t see if my mental faculties are not engaged in determining the intended meaning behind what I see.”

Similarly, his work in such things as refraction proved crucial to our understanding of optics. If you stand in a swimming pool and look down, for example, the part of your legs that are under water appear stubby and distorted. If you place a drinking straw in a glass of water, from the side it looks severed at the waterline, as the top and bottom no longer align. Remove the straw from the water and the illusion disappears. The only thing that has changed is the medium through which you’re viewing the straw—air versus water. Although others had observed this phenomenon, Ibn al-Haytham crystallized it in mathematical formulas that by the 1200s CE helped scientists in Italy develop the first eyeglasses. His notes on experiments with refraction and reflection through convex and concave lenses helped Dutch scientists in the 1600s develop the telescope.

More broadly, Ibn al-Haytham’s work set the course for the field of science itself: The 13th-century-CE English empiricist Roger Bacon cited Ibn al-Haytham extensively and, as El-Bizri points out, the 17th-century Polish astronomer Johannes Hevelius chose to depict Ibn al-Haytham on the frontispiece of his 1647 book Selenographia, which provided the first attempts at mapping the moon.

In the centuries that followed, however, many scholars outside the Islamic world let Ibn al-Haytham’s contributions slip below the horizon as they focused on the likes of Bacon and his teacher, Robert Grosseteste, who pursued both science and theology to explain natural phenomena. Up to the 20th century, El-Bizri says, most Western historians of science attributed the experimental method to Grosseteste. But today, scholarly circles across the globe look increasingly to Ibn al-Haytham, including even the UK-based Ordered Universe Project, which focuses on Grosseteste’s legacy. Now, says El-Bizri, who is himself affiliated with the group, “they are fully convinced that whatever they have thought about Grosseteste is indicative of their not being aware of earlier approaches to experimentation. … They have now moved that milestone by two centuries to the work of Ibn al-Haytham.”

Though Ibn al-Haytham worked with candles and a hole in a wall, it might not take him long to appreciate the new instrument on Cerro Pachón—our generation’s newest pinhole through which we will observe, analyze and learn about our universe.