Speed of Light in Ancient Greek Philosophy

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THE SPEED OF LIGHT
Cosmic Adventure 3.04
Iris – the goddess of light

Extraordinary speed
Most of us are familiar with the fact
that light travels at a tremendous
speed about 3⤬108 m. per second. It
can travel round the world eight
times in a second.
Compared with the speed of objects
observed in our daily lives, this
figure is indeed astronomical. That is
why for all practical purposes, the
speed of light is regarded as infinite.
However the ancient Greeks had a
different idea.
Seven and a half times round the
world in a second

Idea of Light in ancient Greek
The idea that light has a finite
speed has long existed in the mind
of the ancient Greeks. The nature
of light was truthfully depicted in
the great ancient epics of Iliad and
Odyssey as early as about the 9th
century BC. Homer was
traditionally regarded as the
author of both epics. It is widely
recognized that these Homeric
epics had become the foundation
of early Greek culture. Homer’s
idea on light was the contemporary
concept at the time. The blind poet Homer and his guide - Painting of
by William-Adolphe Bouguereau (1825–1905).

Iris – the Goddess of Light
In the Homeric poems, light was
personified by Iris, the goddess of
light and a messenger of the gods.
She carried messages around
Olympus, from gods to gods, and
from gods to men.
Iris appeared in ancient Greek vase
painting as a beautiful young woman with
golden wings to signify her fleetness. She is
often seen as a flying maiden carrying a
herald's wand (an kerykeion) in one hand,
and sometimes a water-pitcher (oinochoe
jug) in the other. The herald’s wand is the
precursor of the caduceus and the pitcher
contained nectar with which she served
Zeus and Hera.

Iris
The Goddess of Rainbow
In Greek mythology, Iris is also
regarded as the goddess of the
rainbow.
In the Homeric poems, Iris did not
appear as the goddess of the
rainbow, but the rainbow itself was
called iris (xi. 27, xvii. 547).
Iris is able to change shapes. When
she delivered messages to mortals,
she would usually assume the
appearance of a mortal known to the
message receiver.

Iris replaced by
Hermes
As Iris worked as the messenger
for the gods and men, she
needed great speed. However
Iris only appeared in the Iliad
and as figures on Greek vases. In
Odyssey and in Roman times,
she was replaced by Hermes.
But one thing was certain - the
idea that light has a finite speed
has long existed in the mind of
the ancient Greeks.

SPEED OF LIGHT
IN ANCIENT GREEK PHILOSOPHY

The Four Elements
The idea of light has a finite
speed was finally shed its
mythological shroud when it
was first supported with
philosophy by Empedocles of
Aragas (492-432 BC). He was
best known as the Greek
philosophers who advocated
the idea of the four classical
primary elements - earth, fire,
water and air.
Empedocles and his four cosmogonic elements

Finite Speed
Empedocles later found that sight
is not a simple issue and
postulated that the images in their
various colors from the world
outside the body were carried by
light from the objects to the eyes.
This light, according to him, was
also one form of the four
elements, that is, it is a kind of
matter in a specific form under
transportation.
Since all material objects took time
to travel from one place to
another, light should be no
exception.

Image in between
Aristotle (385-322 BC) thought
that if light took time to travel,
"any given time is divisible into
parts, so that we should assume a
time when the sun's ray was not
as yet seen but was still travelling
in the middle space ... before it
reaches the earth." De sensu and De
anima.
With finite speed, there are bound
to be images in between the
object and the observer. The
observer sees the image a
moment later. But this did not
appeal to Aristotle.

Aristotle
What Aristotle said did not mean that
he was supportive of Empedocles’
idea of light having a finite speed, he
was only expressing the unlikely
situation of having light in between
the object and the observer when
every vision was so instantaneous.
Aristotle was a strong advocate for
the infinite speed of light. He quoted
Empedocles simply for the purpose of
criticism. He often did this as his
favorite way of denouncing his
opponents while making way for his
arguments.

Plato - Infinite Speed
The second main idea of a
different nature about the speed
of light came from Plato (429–
347 BC) and was augmented by
Aristotle (384 – 322 BC).
Aristotle favored the idea of an
infinite speed - that light
traversed space in no time at all.
Once light was emitted from the
source, reached the receiver
instantly.
∞

Lucretius – Infinite Speed
Even if light was made up of
particles, these particles would travel
across space in not time. Lucretius
(ca.99-55 BC Roman poet), furthered
this idea in his epic philosophical
poem De Rerum Natura (On the
nature of the Universe - 55 BC):
“The light and heat of the sun are
composed of minute atoms. When
shoved off, they lose no time in
shooting right across the interspace
of air in the direction imparted by
the shove.”

Heron’s Night Vision
In the first century BC, Heron of Alexandria (c. 10-70 AD the greatest inventor and
experimenter of antiquity) believed in the theory that images could be seen because
light was emitted from the eye to the object. When the light bounced back to the
eye, vision was established.

Heron’s Infinite Speed
Infinite speed was evident to
Heron because when he closed
his eyes at night and opened
again, he could see the stars
immediately. This only meant
that light took no time in
travelling from his eyes to the
distant star and back.

Heron’s Night Vision
Heron thought in such a way
because he was already prejudiced
by the idea that light rays were
emitted only when he opened his
eyes in the first place; secondly he
did not realize that the light rays
from the stars were already there in
front of his eyes even before his
eyes were open. As soon as his
eyelids were lifted, the images of
the star entered immediately, giving
him the impression of an
instantaneous transfer of image.
Light already
there all the time

Heron’s Stone Throw
By pure reasoning, Heron further argued that one can find conviction in the analogy
of objects falling freely after release. When an object is thrown horizontally, it first
travels in a straight line and then drops to the ground (a, b, c). The harder is the
throw, the longer is its horizontal path. If the object is thrown with an infinite
velocity, it would keep on moving in a straight-line forever (d). Similarly, for light to
travel in a straight line, it must move with an infinite velocity.
Heron’s infinite stone throw

Pure Speculation
There were also other schools of
thinking on the speed of light.
However as a general practice,
these ancient Greek
philosophers did not bother to
verify their ideas by observation
or experiment, particularly on
the issue of light speed. They
just entertained themselves by
pure reasoning or intuitive
guesswork and did not bother to
go to the length of actually
measuring the speed of light.

Dominance of Infinite
Speed Theories
With Aristotle’s influence and
the support of many renown
philosophers, the idea that light
travels at an infinite speed
became the dominate theory
over two thousand years.
Although Galileo knew
something was not going right
with the idea, he also had no
way or instrument with enough
precision to to measure
tremendous speed of light.

Medieval Age
The Middle Ages in European
history lasted from the fall of the
western Roman Empire (circa A.D.
395) to the Renaissance in the
14th or 15th century. During this
period, the civilisation of the
Greeks and Romans were replaced
by barbarism. Most of the ancient
teachings and their records were
lost or destroyed. Fortunately
some of them were copied and
preserved and developed in the
Muslim countries. The ruins of Roman civilizations

Revival of Greek Learnings
From the thirteenth century onwards these
writings came to see the light again in Europe.
They were recovered as rare copies from
forgotten corners in the attic or store rooms.
Some of them were also brought back from the
Muslim countries and were translated in Latin.
After emerging from a thousand years of
darkness, the European civilisation was in a
badly retrograded shape. The ancient
knowledge and philosophies appeared so much
superior to theirs that they were treated with
almost superstitious reverence. The teaching of
Aristotle in particular became the guiding light
of the time.

Authority of
Aristotle’s Teachings
The weight of Aristotle's teachings
were later further enhanced by St.
Thomas Aquinas (1224-1274 B.C.)
who brought them in line with the
Bible, making them the answer
books to all scientific enquiries.
In the centuries to come Aristotle's
philosophy was regarded as the
ultimate truth throughout Europe.
When Aristotle said that light travels
at infinite speed, no one else would
have thought otherwise.

LIGHT SPEED IN RENAISSANCE

Infinite Speed of Light
Since the days of Greek cultural
revival, the idea of an infinite
speed of light was persistent and
influential mainly because of the
influence of Aristotle.
Even in the days of renaissance
in the16th century, the great
French philosopher and
mathematician René Descartes
(1596-1650 A.D.) was in favour
of such an infinite speed idea.

Instant Transmission
Descartes believed that space is
filled up with a stable fluid made
of microscopic spherical particles
(the Plenum), acting as a medium
for the propagation of light. The
light particles transmitting
motions in a straight line across
the medium instantly, “like a stick
transmits a push on one end to
the other end” In other words,
light is a kind of pressure
transmitted through a medium at
infinite velocity. . . . .
Descartes' Principia Philosophiae (Principles
of Philosophy) published in 1644.

Johannes Kepler
Johannes Kepler (1571-1630), the
renowned astronomer who
established the first two laws of
planetary motion, also put his faith
on an infinite velocity of light. He
believed that the speed of light was
infinite since empty space had no
obstacle to it.
In fact, most of philosophers of the
time were quite happy with the
ancient idea. So the idea of light
with an infinite speed remained
popular for a further 200 years
after Descartes.

THE WORLD OF INFINITE LIGHT SPEED

The Infinite Speed of Light
In the world before 1676,
the popular believe was
that light travelled at an
infinite speed. That is, light
is instantaneously
everywhere at once. What
one sees is what one gets.
In the picture, the moon
and the tower at the distant
hill is simultaneous with
the objects nearby.

Universe with Infinite
Light Speed
So whatever people saw in their
life were instantaneous what
they got. The entire universe
would have appeared to them
all at the same time.
The distant stars were there as
the castle close by were in front
of us simultaneous.

Classical Position of Objects in Motion
This was particularly so in daily life where objects are so close together, the delay
due to light speed was usually not taken into consideration. Things happens as they
were regardless how fast they moved.
𝑣𝑣

𝑑𝑑
Classical Position in Infinite Light Speed
The position of a moving object is simply: 𝑑𝑑 = 𝑣𝑣𝑣𝑣, without the slightest notion
that light actually took time to cross the space between them.
𝑣𝑣

Universe in Antiquity
The idea or the non-idea of infinite
speed prevailed in all religious
drawings and paintings.
The events in the heavens beyond
the clouds were perceived to be
happening at the same time as the
events happening on earth.
This is how light work – diligent
but unobtrusive. People didn’t
even notice that it is there, not
even border to argue if its speed is
finite or infinite.

ABCC
MEASUREMENT OF LIGHT SPEED
To be continued on: Cosmic Adventure 3.07

Speed of Light in Ancient Greek Philosophy

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Speed of Light in Ancient Greek Philosophy