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24
The Science of Light
The importance of light is emphasized
in the First Book of Moses in
the Bible: “In the beginning, God
created the heaven and the earth.
And the earth was without form,
and void; and darkness was upon
the face of the deep. And the
Spirit of God moved upon the
face of the waters. And God said,
Let there be light: and there was
light. And God saw the light, that
it was good: and God divided the
light from the darkness.” Without
light life is impossible. Light plays
an important role in our lives.
And the question of the “nature
of light” is one that we have
always endeavored to answer.
Besides mechanics, optics would
seem to be the oldest field in which
scientific work has been conducted.
The Babylonians, on the basis of their
experience, were already applying
the law of the rectilinear propagation
of light around 5000 BC in the use of
astronomical instruments.
There is evidence of scientific
study in the field of optics in Greece
in the 6 th century BC: here the emphasis
was on explaining the effect
the visible object had on the eye. The
various schools developed ideas that
differed from each other to a greater
or lesser extent and were generally
rather imprecise.
The predominant theory in Ancient
Greece was the extramission
theory, which can presumably be
traced back to Pythagoras (570/560-
480 BC) and was later supported
in particular by Euclid (around 300
BC) and Ptolemaeus (around 100-
160 AD). The extramission theory
assumed that we are able to see as
a result of hot rays that emanate
from our eyes towards an object. The
resistance these rays meet with when
they reach the cold object causes
them to be sent back, enabling the
information they have gathered to
reach the eye. The ability of many animals
to see at night was put forward
in support of this theory.
Aristotle (384-322 BC), in particular,
had a different view. He believed
that light is not something physical
that moves between the object and
the eye, but rather that the process
of seeing is the result of the effect
the object has on the eye by means
of the medium between them (“the
transparent”).
In addition to the process of seeing
in itself, the Greeks also studied
the laws of geometric optics. It seems
that Plato (424-347 BC) was aware
of the law of reflection and he described
the reflection of concave and
cylindrical mirrors. The mention of
oars bending in water indicates that
the phenomenon of refraction was
also familiar. The playwright Aristophanes
(445-385 BC) described the
effect of burning glasses (glass lenses
or glass globes filled with water).
Ptolemaeus, who summarized the
entire optical knowledge of the ancient
world and systematically examined
the refraction of light, is perhaps
the most important optical scientist
of that time.
During the Middle Ages, Christianity
was not particularly open to
science. It was the Arabs who not
only collected and translated the ancient
writings but also made their
own scientific contributions. The
most important Arab scientist was
Abu Ali Al-Hasan Ibn Al-Haitham
(965-1040), also known as Alhazen,
Innovation 15, Carl Zeiss AG, 2005