Isaac Newton is, as most will agree, the greatest physicist of all time.


At the very least, he is the undisputed father of modern optics,* or so we are told at school where our textbooks abound with his famous experiments with lenses and prisms, his study of the nature of light and its reflection, and the refraction and decomposition of light into the colours of the rainbow.

Yet, the truth is rather greyer; and I feel it important to point out that, certainly in the field of optics, Newton himself stood on the shoulders of a giant who lived 700 years earlier.

For, without doubt, another great physicist, who is worthy of ranking up alongside Newton, is a scientist born in AD 965 in what is now Iraq who went by the name of al-Hassan Ibn al-Haytham.

Most people in the West will never have even heard of him.

As a physicist myself, I am quite in awe of this man's contribution to my field, but I was fortunate enough to have recently been given the opportunity to dig a little into his life and work through my recent filming of a three-part BBC Four series on medieval Islamic scientists.

Modern methods

Popular accounts of the history of science typically suggest that no major scientific advances took place in between the ancient Greeks and the European Renaissance.

But just because Western Europe languished in the Dark Ages, does not mean there was stagnation elsewhere. Indeed, the period between the 9th and 13th Centuries marked the Golden Age of Arabic science.

Great advances were made in mathematics, astronomy, medicine, physics, chemistry and philosophy. Among the many geniuses of that period Ibn al-Haytham stands taller than all the others.

Ibn al-Haytham is regarded as the father of the modern scientific method.

As commonly defined, this is the approach to investigating phenomena, acquiring new knowledge, or correcting and integrating previous knowledge, based on the gathering of data through observation and measurement, followed by the formulation and testing of hypotheses to explain the data.

This is how we do science today and is why I put my trust in the advances that have been made in science.

But it is often still claimed that the modern scientific method was not established until the early 17th Century by Francis Bacon and Rene Descartes.

There is no doubt in my mind, however, that Ibn al-Haytham arrived there first.

In fact, with his emphasis on experimental data and reproducibility of results, he is often referred to as the "world's first true scientist".

Understanding light

He was the first scientist to give a correct account of how we see objects.

He proved experimentally, for instance, that the so-called emission theory (which stated that light from our eyes shines upon the objects we see), which was believed by great thinkers such as Plato, Euclid and Ptolemy, was wrong and established the modern idea that we see because light enters our eyes.

What he also did that no other scientist had tried before was to use mathematics to describe and prove this process.

So he can be regarded as the very first theoretical physicist, too.

He is perhaps best known for his invention of the pinhole camera and should be credited with the discovery of the laws of refraction.

He also carried out the first experiments on the dispersion of light into its constituent colours and studied shadows, rainbows and eclipses; and by observing the way sunlight diffracted through the atmosphere, he was able to work out a rather good estimate for the height of the atmosphere, which he found to be around 100km.


In common with many modern scholars, Ibn-al Haytham badly needed the time and isolation to focus on writing his many treatises, including his great work on optics.

He was given an unwelcome opportunity, however, when he was imprisoned in Egypt between 1011 and 1021, having failed a task set him by a caliph in Cairo to help solve the problem of regulating the flooding of the Nile.

While still in Basra, Ibn al-Haytham had claimed that the Nile's autumn flood waters could be held by a system of dykes and canals, thereby preserved as reservoirs until the summer's droughts.

But on arrival in Cairo, he soon realised that his scheme was utterly impractical from an engineering perspective.

Yet rather than admit his mistake to the dangerous and murderous caliph, Ibn-al Haytham instead decided to feign madness as a way to escape punishment.

This promptly led to him being placed under house arrest, thereby granting him 10 years of seclusion in which to work.

Planetary motion

He was only released after the caliph's death. He returned to Iraq where he composed a further 100 works on a range of subjects in physics and mathematics.

While travelling through the Middle East during my filming, I interviewed an expert in Alexandria who showed me recently discovered work by Ibn al-Haytham on astronomy.

It seems he had developed what is called celestial mechanics, explaining the orbits of the planets, which was to lead to the eventual work of Europeans like Copernicus, Galileo, Kepler and Newton.

It is incredible that we are only now uncovering the debt that today's physicists owe to an Arab who lived 1,000 years ago.

Professor Jim Al-Khalili presents Science and Islam on BBC Four at 2100GMT on Monday 5, 12 & 19 January

Abu Ali al-Hasan ibn al-Hasan ibn al-Haytham (and known in Europe as Alhacen or Alhazen) was born in Basra in present-day Iraq. He probably died in Cairo, Egypt. During the Islamic Golden Age, Basra was a "key centre of learning", and he was educated there and in Baghdad, the capital of the Abbasid Caliphate, and the focus of the "high point of Islamic civilization". During his time in Iraq, he worked as a civil servant and read many theological and scientific books.

One account of his career has him summoned to Egypt by the mercurial Al-Hakim bi-Amr Allah, ruler of the Fatimid Caliphate, to regulate the flooding of the Nile, a task requiring an early attempt at building a dam at the present site of the Aswan Dam.After his field work made him aware of the impracticality of this scheme,and fearing the caliph's anger, he feigned madness. He was kept under house arrest from 1011 until al-Hakim's death in 1021. During this time, he wrote his influential Book of Optics.

Although there are stories that Ibn al-Haytham fled to Syria, ventured into Baghdad later in his life, or was even in Basra when he pretended to be insane, it is certain that he was in Egypt by 1038 at the latest.During his time in Cairo, he became associated with Al-Azhar University, as well the city's "House of Wisdom", known as Dar Al-Hekma (House of Knowledge), which was a library "second in importance" to Baghdad's House of Wisdom.[5] After his house arrest ended, he wrote scores of other treatises on physics, astronomy and mathematics. He later traveled to Islamic Spain. During this period, he had ample time for his scientific pursuits, which included optics, mathematics, physics, medicine, and the development of scientific methods; he left several outstanding books on these subjects.

Other works on physics

Ibn al-Haytham wrote several other treatises on optics. His Risala fi l-Daw’ (Treatise on Light) is a supplement to his Kitab al-Manazir (Book of Optics). The text contained further investigations on the properties of luminance and its radiant dispersion through various transparent and translucent media. He also carried out further examinations into anatomy of the eye and illusions in visual perception. He analyzed the camera obscura and pinhole camera, and investigated the meteorology of the rainbow and the density of the atmosphere. Various celestial phenomena (including the eclipse, twilight, and moonlight) were also examined by him. He also made investigations into refraction, catoptrics, dioptrics, spherical mirrors, and magnifying lenses.

In his treatise, Mizan al-Hikmah (Balance of Wisdom), Ibn al-Haytham discussed the density of the atmosphere and related it to altitude. He also studied atmospheric refraction. He discovered that the twilight only ceases or begins when the Sun is 19° below the horizon and attempted to measure the height of the atmosphere on that basis.

Astrophysics

In astrophysics and the celestial mechanics field of physics, Ibn al-Haytham, in his Epitome of Astronomy, discovered that the heavenly bodies "were accountable to the laws of physics".[81] Ibn al-Haytham's Mizan al-Hikmah (Balance of Wisdom) covered statics, astrophysics, and celestial mechanics. He discussed the theory of attraction between masses, and it seems that he was also aware of the magnitude of acceleration due to gravity at a distance.[30] His Maqala fi'l-qarastun is a treatise on centres of gravity. Little is known about the work, except for what is known through the later works of al-Khazini in the 12th century. In this treatise, Ibn al-Haytham formulated the theory that the heaviness of bodies varies with their distance from the centre of the Earth.

Another treatise, Maqala fi daw al-qamar (On the Light of the Moon), which he wrote some time before his famous Book of Optics, was the first successful attempt at combining mathematical astronomy with physics, and the earliest attempt at applying the experimental method to astronomy and astrophysics. He disproved the universally held opinion that the Moon reflects sunlight like a mirror and correctly concluded that it "emits light from those portions of its surface which the sun's light strikes." To prove that "light is emitted from every point of the Moon's illuminated surface," he built an "ingenious experimental device."According to Matthias Schramm, Ibn al-Haytham had formulated a clear conception of the relationship between an ideal mathematical model and the complex of observable phenomena; in particular, he was the first to make a systematic use of the method of varying the experimental conditions in a constant and uniform manner, in an experiment showing that the intensity of the light-spot formed by the projection of the moonlight through two small apertures onto a screen diminishes constantly as one of the apertures is gradually blocked up.

Mechanics

In the dynamics and kinematics fields of mechanics, Ibn al-Haytham's Risala fi’l-makan (Treatise on Place) discussed theories on the motion of a body. He maintained that a body moves perpetually unless an external force stops it or changes its direction of motion. This was similar to the concept of inertia, but was largely a hypotheses that was not verified by experimentation. The key breakthrough in classical mechanics, the introduction of frictional force, was eventually made centuries later by Galileo Galilei, and then formulated as Newton's first law of motion.

Also in his Treatise on Place, Ibn al-Haytham disagreed with Aristotle's view that nature abhors a void, and he thus used geometry to demonstrate that place (al-makan) is the imagined three-dimensional void between the inner surfaces of a containing body.

Ibn al-Haytham also discovered the concept of momentum (now part of Newton's second law of motion) around the same time as his contemporary, Avicenna (Ibn Sina).