The Arab Muslim scholar Abu Ali al Hasan ibn al-Haytham, known in the west as Alhacen
or Alhazen was born in 965 in the city of Basra in Southern Iraq, hence he is also
known as Al-Basri.1 He was educated in Basra and Baghdad, and died in Cairo, Egypt
in the year 1040.2
Many details of the life of Ibn al-Haytham have been lost over time. The stories related
to his life are often contradictory, depending on the historian relating them. Most
of the data on the biography of Ibn al-Haytham came from the writings of the thirteenth
century Muslim historian Ibn al-Qifti (1172–1248). Initially, Ibn al-Haytham was trained
for a civil service job and was appointed as a judge for Basra. Due to the presence
of various religious movements with diverse and conflicting views at that time, he
became disillusioned with religious studies and decided to dedicate his time and effort
for the study of science. His knowledge in mathematics and physics became legendary
and he was well known in Iraq, Syria and Egypt. He was invited by Al-Hakim bi-Amr
Allah, the Fatimid Caliph of Egypt to help in regulating the flow of the Nile during
the floods. Al-Hakim, a Shiite of the Ismaili sect, was known to be an eccentric ruler
who issued several arbitrary edicts and laws, prohibiting the consumption of certain
foods, preventing women from leaving their homes, killing all the dogs, and forcing
people to work during the night and rest by day. He was quite brutal and had killed
his tutors and ministers on a whim. When Ibn al-Haytham realized on his field work
along the Nile that his scheme to regulate the Nile’s water flow by building a dam
south of Aswan was impractical, he feared for his life. To avoid the potential of
the deadly wrath and anger of his temperamental and mentally unstable patron, he faked
insanity. He was stripped of his possessions and books, and was kept under house arrest
for about 10 years until the time of Al-Hakim’s death in 1021, when he was assassinated
in mysterious circumstances.
Original image, Diagram of the Eyes and Related Nerves, from Kitab al-Manazir (Book
of Optics) by Ibn al-Haytham, Istanbul, Eleventh Century.
Following his release from house arrest, he lived in a domed building (Qubbah) close
to the Azhar Mosque in Cairo, teaching mathematics and physics, writing science texts,
and making money by copying texts.3
During his period of incarceration, he wrote his influential “Kitab Al Manazer” or
the Book of Optic, in addition to several significant books and chapters on physics,
mathematics, engineering, astronomy, medicine, psychology, anatomy, visual perception
and ophthalmology. He wrote his introduction of the scientific methods.4
Ibn al-Haytham was a prolific author. He wrote more than 200 works on a wide range
of subjects, of which at least 96 of his scientific works are known, and approximately
50 of them have survived to date. Nearly half of his surviving works are on mathematics,
23 of them are on astronomy, and 14 of them are on optics, with a few on other areas
of science.5 Not all of his surviving works have yet been studied, but some of his
most important ones are described below. These include:
Kitab Al Manazer (Book of Optics)
Risalah fi al-Dawa’ (Treatise on Light)
Mizan al-Hikmah (Balance of Wisdom)
Maqalah fi al-Qarastun (Treatise on Centers of Gravity)
Risalah fi al-Makan (Treatise on the Place)
Al-Shukuk al Batlamyus (Doubts concerning Ptolemy)
On the Configuration of the World
The model of the Motion of the Seven Planets
Scientific Method
Elements of modern scientific methods are found in early Islamic philosophy, in particular,
using experiments to distinguish between competing scientific theories, and a general
belief that knowledge reveals nature honestly. Islamic philosophy developed in the
Middle Ages and was pivotal in scientific debates. The key figures for these debates
were scientists and philosophers. Ibn al-Haytham was quite influential in this regard.
An important observation in his book “Kitab Al Manazer” led him to propose that the
eyes receive light reflected from objects, rather than emanating light themselves,
contradicting contemporary beliefs, including those of Ptolemy and Euclid. The way
in which Ibn al-Haytham combined observations and rational arguments had a great influence
on Roger Bacon and Johnnes Kepler in particular. Bacon (1214–1296), a Franciscan friar
working under the tuition of Grosseteste, was inspired by the writings of Ibn al-Haytham,
who preserved and built upon Aristotle’s portrait of introduction.
Ibn al-Haytham developed rigorous experimental methods of controlled scientific testing
in order to verify theoretical hypotheses and substantiate inductive conjectures.
Ibn al-Haytham’s scientific method was very similar to the modern scientific method
and consisted of a repeating cycle of observation, hypothesis, experimentation, and
the need for independent verification.5,6
Gorini wrote the following on Ibn al-Haytham’s introduction of the scientific method:
“According to the majority of the historians, al-Haytham was the pioneer of the modern
scientific method. With his book, he changed the meaning of the term “optics”, and
established experiments as the norm of proof in the field. His investigations were
based not on abstract theories, but on experimental evidences. His experiments were
systematic and repeatable”.7
Physics and Optics
Ibn al-Haytham’s theory of light and vision is neither identical with nor directly
descendant from any one of the theories known to have previously existed in the antiquity
or in Islam. The first real appreciation of the action of a lens, in particular the
ability of a convex form to produce a magnified image of an object, appears to be
credited to Ibn al-Haytham.8,9 It was not until the late 13th century that spectacles
were invented, representing the first practical use of magnification in society.9,10
Ibn al-Haytham made a thorough examination of the passage of light through various
media and discovered the laws of refraction. He also carried out the first experiments
on the dispersion of light into its constituent colors. Ibn Al-Haytham’s seven volume
treatise on optics, Kitab al-Manazer (Book of Optics), which he wrote while incarcerated
between 1011 to 1021, which has been ranked alongside Isaac Newton’s Philosophiae
Naturalis Principia Mathematica as one of the most influential books ever written
in physics, drastically transformed the understanding of light and vision.8,9
Structure of the eye, by Ibn al-Haytham, from the Book of Optics.
He dealt at length with the theory of various physical phenomena like shadows, eclipses,
the rainbow, and speculated on the physical nature of light. He also attempted to
explain binocular vision, and gave a correct explanation of the apparent increase
in size of the sun and the moon when near the horizon. He is known for the earliest
use of the camera obscura and pinhole camera. 11 As stated above, he contradicted
Ptolemy’s and Euclid’s theory of vision that objects are seen by rays of light emanating
from the eyes; according to him the rays originate in the object of vision and not
in the eye. Through these extensive researches on optics, he has been considered as
the father of modern optics.
In addition to the Book of Optics, Ibn al-Haytham wrote a supplement entitled “Risala
fi l-Daw” (Treatise on Light). This supplement contained further investigations on
the properties of luminance and its radiant dispersion through various transparent
and translucent media. 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. His optical writings influenced many Western intellectuals
such as Roger Bacon, John Pecham, Witelo, and Johannes Kepler.11,12,13
Astronomy
While not counted among the greatest Arab astronomers, his works show that he had
mastered the techniques of Ptolemaic astronomy. Some of these works also reveal his
ability to solve the problems that received attention from Arab astronomers, such
as determining the Qiblah (direction of prayer). His critique of Ptolemaic planetary
models, as presented in the Almagest and Planetary Hypotheses, appears to have inspired
research that led to their replacement by non-Ptolemaic arrangements in the 13th century
Maragha and 14th century Damascus. This astronomical work was written between 1025–1028
“Al-Shukūk ‘alā Batlamyūs”, and then translated as Doubts concerning Ptolemy or Aporias
against Ptolemy.14 He considered that some of the mathematical devices Ptolemy introduced
into astronomy, especially the equant, failed to satisfy the physical requirement
of uniform circular motion.14
Astronomers of the European Renaissance were influenced by his work “On the Configuration
of the World”, where he continued to accept the physical reality of the geocentric
model of the universe, presenting a detailed description of the physical structure
of the celestial spheres: “The earth as a whole is a round sphere whose center is
the center of the world. It is stationary in its [the world’s] middle, fixed in it
and not moving in any direction nor moving with any of the varieties of motion, but
always at rest”.15
Ibn al-Haytham’s The Model of the Motions of Each of the Seven Planets, written in
1038, was an important book on astronomy. The surviving manuscript of this work has
only recently been discovered, with much of it still missing, hence the work has not
yet been published in modern times. His reform excluded cosmology, as he developed
a systematic study of celestial kinematics that was completely geometric. This in
turn led to innovative developments in infinitesimal geometry.16
Mathematics
In mathematics, Ibn al-Haytham built on the mathematical works of Euclid and Thabit
ibn Qurra, and went on to systemize infinitesimal calculus, conic sections, number
theory, and analytic geometry after linking algebra to geometry. His contribution
to mathematics was extensive. He developed analytical geometry by establishing linkage
between algebra and geometry. He studied the mechanics of motion of a body and was
the first to maintain that a body moves perpetually unless an external force stops
it or changes its direction of motion. This is strikingly similar to the first law
of motion described centuries later by Isaac Newton.
His work on catoptrics in Book V of the Book of Optics contains the important problem
known as Alhazen’s problem. It comprises drawing lines from two points in the plane
of a circle meeting at a point on the circumference and making equal angles with the
normal at that point. This leads to an equation of the fourth degree. This eventually
led Ibn al-Haytham to derive the earliest formula for the sum of fourth powers; and
by using an early proof by mathematical induction, he developed a method for determining
the general formula for the sum of any integral powers. This was fundamental to the
development of infinitesimal and integral calculus. 17
In geometry, Ibn al-Haytham developed analytical geometry by establishing the linkage
between algebra and geometry. Ibn al-Haytham also discovered a formula for adding
the first 100 natural numbers.
His contributions to number theory include his work on perfect numbers. In his Analysis
and Synthesis, Ibn al-Haytham was the first to realize that every even perfect number
is of the form 2
n
-1 (2
n
-1) where 2
n
-1 is prime, but he was not able to prove this result successfully. It was proved
later on in the 18th Century by Euler.17
Medicine and Psychology
Ibn al-Haytham was the first to describe accurately the various parts of the eye and
give a scientific explanation of the process of vision. In medicine and ophthalmology,
Ibn al-Haytham made important advances in eye surgery, and he studied and correctly
explained the process of sight and visual perception for the first time.18,19 He described
in detail the various parts of the eye and introduced the idea that objects are seen
by rays of light emanating from the objects and not the eyes, as was popularly believed.
“Sight perceives the light and color existing on the surface of the contemplated object.
Vision perceives necessarily all the objects through supposed straight lines that
spread themselves between the object and the central point of the sight”.10
Ibn al-Haytham is considered by some to be the founder of psychophysics and experimental
psychology, for his pioneering work on the psychology of visual perception.20
Philosophy
In philosophy, Ibn al-Haytham is considered a pioneer of phenomenology. He articulated
a relationship between the physical and observable world and that of intuition, psychology
and mental functions. His theories regarding knowledge and perception, linking the
domains of science and religion, led to a philosophy of existence based on the direct
observation of reality from the observer’s point of view. Much of his thought on phenomenology
was not further developed until the 20th century.21 In fact, he is well known to have
articulated a comprehensive theory of knowledge.22
Ibn al-Haytham is said to have been a supporter of the Asha’ri school of Islamic theology,
and opposed to the teachings of the Mu’tazili school, though he may have been a Mu’tazili
supporter himself at some point in his life.
Finally, Ibn al-Haytham left his impact on many scientific disciplines through his
genius insight, and novel and original observations. Without doubt, he is considered
as the pioneering father of modern optics.