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Physics, optics and light

The father of modern science and optics, Ibn Al Haytham, seen here depicted on a 1962 Iraqi banknote.

The Hockney Falco thesis says Ibn Al Haytham's theories enabled Renaissance atmospheric perspective

Ibn Al Haytham's 11th century camera obscura greatly influenced Renaissance European optics

Ibn Al Haytham's studies of the eye gave the first modern understanding of lens, retina and optic nerve, as well as the mechanics of vision and perception

Ibn Al Haytham's studies of the eye gave the first modern understanding of lens, retina and optic nerve, as well as the mechanics of vision and perception

Sir Isaac Newton discovers gravity, possibly theorised by Ibn Al Haytham

Ibn Al Haytham's experiments laid much of the groundwork for other scientists in this field and enabled the European telescope and Leeuwenhoek's microscope, both still in use today


Although Al Kindi's unproven theory of relativity suggested an Arab and Muslim visionary willingness to go far beyond existing theories of time and space, it was not until the rise of another great thought centre, the Fatimid House of Knowledge in Cairo in the early 11th century, that Arab physics would really take off.

The popular Western misconception is that the Greeks founded modern physics, via theories of atoms and light. But on closer investigation, many of the early Greek theories of physics would prove to be only that - theory - unverified by experimentation.

The Greeks had an innate ambivalence about the experimental method that seems to go all the way back to Aristotle, Plato, and their followers. In fact, they believed that the senses were not to be trusted... that the highest form of analysis was reason, not the observation and collection of data, which would come through the imperfect lens of the human senses and perception.

This Greek disinclination to test and verify their admittedly fascinating theories resulted in some major scientific errors. At the very least, it calls into question the conventional Western view that they alone created the modern scientific method.

For example, the great Ptolemy had explained light and vision by saying that light was a ray that emanated from the eyeball and then travelled to the object being looked at, thus 'lighting it up' and making it visible. This theory was not tested for more than 800 years, although Al Razi had his doubts about that one, and also with some of the Roman physician Galen's explanations of the human body. Possibly, he was just so busy that he couldn't take the time necessary to prove his doubts.

But why would Arab Muslims show a greater inclination to use the experimental method to first dismantle some of the revered Greek theories... and then to create new explanations of matter and energy that were grounded in verifiable fact?

The Indian-Pakistani historian Mohammed Iqbal would later write:

"The general empirical attitude of the Qur'an... engendered in its followers a feeling of reverence for the actual, and ultimately made them the founders of modern science. It was a great point to awaken the empirical spirit in an age that renounced the visible as of no value in men's search after God."

This is a difficult fact for many modern readers to absorb: that the new-born Arab religious faith of Islam was once interpreted to support and encourage the development of the empirical scientific method.

Western historians also have trouble with that, because their own frame of reference is shaped by the early confrontation between traditional Christianity and the emergence of Western science.

European Christianity had a strong anti-intellectual tradition that survived until the late mediaeval period, and occasionally burst forth in the Renaissance, as during the heresy trial of Galileo Galilei. This struggle ended when Western science 'overthrew' the traditional Christian view of the physical world, beginning in the 18th century, and has remained dominant ever since. Ironically, some fundamentalists are still fighting the battle, particularly over Darwinism, creationism, and intelligent design.

So, many modern observers have a hard time accepting that early Islam could accept 1,200 years ago what modern Christianity still has trouble with. Admittedly, modern Islamic fundamentalists also share a parallel rejection of the empirical scientific method, preferring to go back to sacred text.

But to understand when and how the Arab empirical scientific method finally came into full flower, and really laid the foundation for the rise of modern Western science, it is necessary to go back to a world long vanished - to ancient Fatimid Cairo exactly 1,000 years ago.

One of the greatest thinkers and inventors of human history was an Iraqi Arab by the name of Ibn Al Haytham, and he had the good fortune to begin his career in a way that most people only dreamt of. He had been marked from childhood by his unique intelligence, and because of that he was given the best education of the caliphate, being groomed to work in the employ of the caliph and his imperial administration.

As a young man, Ibn Al Haytham was appointed governor of the port city of Basra and surrounding region. Although flattered by the honour and the responsibility of his job, over time he grew weary of the political, bureaucratic, and even theological duties of his position.

Like his contemporaries, Ibn Al Haytham was drawn to the rapidly developing fields of mathematics, astronomy, and physics. In particular he was fascinated by the mathematical implications of light and shadow, and during the interminable meetings and discussions as Governor, quite often his mind was wandering to the play of light and shadow in the room; the way the quality of daylight changed from dawn to noon to dusk.

This was what he wanted to do with his time: understand the physical world, not be a politician and a bureaucrat. Finally he could stand his work no longer, and after a long period of soul-searching, tendered his resignation to the caliph.

The community was stunned, his family mortified. This was unheard of. No one ever willingly gave up such a desired appointment. No one turned away the generosity of the caliph, which could be boundless.

The reason for Ibn Al Haytham's resignation was officially accepted, but it is likely that those around the caliph began to wonder if there was some darker motivation. It is likely that some began to speculate that Ibn Al Haytham had some deeper difference with the caliph, or with the very nature of the caliphate.

Ibn Al Haytham was no fool. He probably began to realise that his future in Iraq was growing increasingly limited. Historians do not agree on whether he was the first to approach the rival Fatimid ruler in Cairo, Al Hakim, or whether Al Hakim, hearing Ibn Al Haytham was unemployed, came to him with a job offer. But around 1006, Ibn Al Haytham accepted an offer of employment, and crossed the uneasy dividing line between Sunni Buyid Iraq and Shiite Fatimid-ruled Egypt.

Ibn Al Haytham would arrive in Cairo with a most daunting challenge. Though his real orientation was towards scientific research, he presented himself to Al Hakim as an engineer, with an almost impossible job description.

His challenge was to stop the annual flooding of the Nile, most likely by building a dam near Aswan. Initially, Ibn Al Haytham thought he could do it, because he needed a job, and because he sensed that the Fatimids might be more supportive of his inclination towards pure research.

But once he and his crew travelled upriver, he saw the impossibility of his task. Even the mighty Al Hakim did not have the resources to fund a dam at Aswan. In fact, it would be another 950 years before such a project could be undertaken.

Although we do not know for sure, multiple accounts say that Ibn Al Haytham chose to avoid almost certain imprisonment or even execution for his failure, by feigning insanity. Others say that he fled to Syria or other locales. Some stories say that he was placed under a form of house arrest for a decade.

Whatever the truth of these stories, Ibn Al Haytham dropped off the public map for that time, but found a special freedom in his obscurity. For the first time in his life, he was able to devote all his time to researching and understanding the properties of matter and light.

In the many years of work that followed, Ibn Al Haytham not only transformed himself from a brilliant student and amateur scientist into one of the greatest scientific thinkers of all time. He also laid the foundation for the rise of modern science.

By the time of his death around 1039, Ibn Al Haytham had taken the early intuitive statements by Jabir and Al Kindi of the experimental and empirical scientific method and transformed them into the basis of the coming scientific revolution in Europe. Historian Richard Powers writes that Ibn Al Haytham's achievement was the most influential idea of the last 1,000 years. Historian George Sarton says that Ibn Al Haytham was "not only the greatest Muslim physicist, but by all means the greatest of mediaeval times." The Biographic Dictionary of Scientists calls him "the greatest scientist of the Middle Ages" and says that his work was unsurpassed until the time of Johannes Kepler 600 years later. More recent historians have even found evidence that his work with optics and vision gradually helped revolutionise Renaissance art, enabling the introduction of perspective that was so critical to the rise of the techniques of realism that defined work by Michelangelo, Leonardo Da Vinci, and others.

Perhaps his greatest work, Book on Optics, was written during that long period of obscurity between 1011 and 1021. Ibn Al Haytham would finally overthrow Ptolemy's theory of light as a ray emitted by the eyeball. He would prove, using the scientific method, that light came from sources like the sun, candles, and mirrors and was reflected back to the eye.

Ibn Al Haytham's utter overthrow of Ptolemy on that count would also be paralleled by his increasing discomfort with Ptolemy's elaborate mathematical explanations of the visual errors created by mistakenly putting the Earth at the centre of the solar system. Had he had the time and energy to devote himself totally to this question, Ibn Al Haytham might have discovered the sun at the centre 500 years before Galileo and Copernicus.

But there were so many other misconceptions and areas of faulty knowledge that he had to work on; it was probably hard to choose which way to turn. He stayed with the basics of light, vision and the human eye, perhaps because he felt that if they were not properly understood; other questions could not be answered.

Using accounts of dissection, he would show how the eye really worked. He would explain the function of the lens, cornea, and retina. Implicit in this was the foundation for the later creation of eyeglasses, telescopes, and microscopes.

He would invent the first camera obscura in that period, credit for which was mistakenly given to Leonardo Da Vinci 500 years later.

When Ibn Al Haytham synthesised his studies of the human eyeball with those of the camera obscura, he not only combined anatomy with optics, he launched the field of modern physiological optics.

Ibn Al Haytham was also drawn to the mathematical implications of spherical and parabolic mirrors, which triggered flights of higher mathematical calculation that paved the way for later development of infinitesimal and integral calculus. Looking at the lyrical quality of twilight, he diligently deconstructed it into mathematical factors, and proved that twilight occurred only when the sun was 19 degrees below the horizon. This phenomenal breakthrough, which would be verified 1,000 years later with the use of telescopes, computation, and satellites, was matched by his accurate calculation of the depth of the Earth's atmosphere, also proven correct in the 20th century.

But massive as these contributions were, he also began to touch on aspects of gravity and the attraction of masses 600 years before Sir Isaac Newton formalised our modern understanding.

Ibn Al Haytham developed the concepts of inertia and of momentum, arguing that the celestial bodies were governed by the laws of physics - thus launching the field of astrophysics. He also described something he called "gravity at a distance".

Ibn Al Haytham proved for the first time that light travels in straight lines. In a related point, he was the first to state what later became known as Fermat's principle: that a beam of light travels between two points in the least amount of time possible.

He also theorised that light was a stream of particles rather than a disembodied energy. Amazingly, the debate between those who say light is a physical substance versus pure energy is still not resolved after 1,000 years.

Some modern historians have had a hard time reconciling Ibn Al Haytham's deeply-professed religious faith with his scientific scepticism and submission of all theories to rigorous testing. A thousand years ago, Ibn Al Haytham saw no such contradiction: for him, the questioning and empirical nature of Islam as shown in the Qur'an required Muslims to use the methods of investigation, testing and research to find scientific truth.

As he would write:

"I constantly sought knowledge and truth, and it became my belief that for gaining access to the effulgence and closeness to God, there is no better way than that of searching for truth and knowledge."

In his book Doubts about Ptolemy, he described his scientific approach:

"Therefore, the seeker after the truth is not one who studies the writings of the ancients and, following his natural disposition, puts his trust in them, but rather the one who suspects his faith in them and questions what he gathers from them, the one who submits to argument and demonstration, and not to the sayings of a human being whose nature is fraught with all kinds of imperfection and deficiency. 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. He should also suspect himself as he performs his critical examination of it, so that he may avoid falling into either prejudice or leniency."

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