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Without
question, the greatest name in physics
during the Arab/Islamic Empire was Ibn
al-Hay-tham, born in the city of Basra,
Iraq, in 965 A.D. By the time he
died in 1030, he had made major
contributions to optics, astronomy and
mathematics, some of which would not be
improved upon for six centuries.
Ibn al-Haytham's main field of interest
and the one to which he made his greatest
contributions, was the branch of physics
we call optics. Striking parallels exist
between his work and that of the
seventeenth century English physicist,
Isaac Newton, one of the greatest
scientists of all time.
One of Newton's major accomplishments was
his famous Law of Universal
Gravitation. The most significant
aspect of this theory is that it
considers gravitation to be universal;
that is, the same laws apply in the
heavens and throughout the universe as
apply on earth. This contradicts the idea
held from the time of Aristotle (384-322
B.C.) that there is a difference between
the laws governing events on earth and
those pertaining to celestial bodies.
Newton realized that the force that
causes an apple to fall from a tree is
the same force that holds the moon and
all the planets in their orbits and,
indeed, is the same as that which governs
the motion of the stars themselves.
If this idea were considered new in the
seventeenth century, it was certainly new
in the eleventh. Yet some of Ibn
al-Haytham's experiments showed that he,
too, believed that extraterrestial
phenomena obeyed the same laws as do
earthly ones.
Ibn al-Haytham evolved his theories of
optics through the study of light rays,
and his investigations revealed a number
of important properties:
that light travels
in a straight line; that every point of a
luminous object radiates light in every
direction; and that light weakens as it
travels from its source. He studied these
characteristics of light from a variety
of light sources, i.e. self~mitting (the
sun, fires and various lamps), and
reflecting (the moon and reflecting
bodies on earth).
This
seemingly trivial experiment is in fact
an early example of what is known as the
"scientific method." Ibn
al-Haytham designed an experiment to test
a hypothesis, namely, that light travels
in anamely, that light travels in a
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straight
line. His experiment was arranged to
avoid the possibility of the
experimenter's bias affecting the
conclusions. Today, it seems obvious that
light travels in straight lines, yet
there was a time when intelligent men
thought it obvious that the sun travels
around the earth. The most advanced and
sophisticated theory in modern physics,
the Theory of Relativity, is derived from
a refutation of ideas that are based on
our everyday experience. Performing
experiments to test and verify theories
is at the heart of all modern scientific
methods.
Ibn al-Haytham's
experiments have even greater
significance. By using the sun, the moon,
lamps, fires and a variety of other light
sources in his experiments, he was saying
that light is light, regardless of its
source. In this sense, he anticipated the
universal laws of seventeenth century
scientists.
We have described only the simplest of
Ibn alHaytham's experiments on the
properties of light rays, but there are
many others that were considerably more
sophisticated. Ibn al-Haytham foresaw the
works of later scientists not only in his
use of experimentation but in the use of
instrumentation:
devices
to help make measurements, the key to all
modern science. He designed and
constructed a variety of instruments,
pipes, sheets, cylinders, rulers and
plane, concave and convex mirrors in
order to conduct his tests.
In
addition to his studies of reflection, he
also studied refraction, a phenomenon in
which light rays bend when travelling
from one medium to another, such as from
air to water. The effect causes an object
to appear to be in a location other than
where it actually is,making him the first
scientist to test a property of
refraction that seems so obvious today.
He demonstrated that a ray of light
arriving perpendicular to the air-water
boundary was not bent at all and showed
that this was true for light passing
through not just two, but several media.
Clear parallels exist between his work
and that of Isaac Newton six centuries
later: both men studied the effects of
light passing through glass, and both
realized that the accepted ideas of their
day were wrong.
It is difficult to appreciate the degree
of intellect required by both these men
to overcome the
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