Welcome to a brand new series where we will explore the origin of the Aether concept and
look at how this concept has developed over time and how this could offer an alternative
to our understanding of light and other electromagnetic phenomena as well as gravity. We have previously
covered the idea of a gravity aether in the gravity series here we will explore the light
aether. But we must start our journey at the beginning by exploring the very first mention
of the word Aether in a scientific context.
In order to start our journey we need to look back at the original concepts of light. The
earliest ideas of light can be traced back to the Greeks. Aristotle used the term matter
in a very different way to the way we use it today. His word for matter meant something
out of which something else could be made by imposing on it a further condition or structural
principle called form. Ordinary bodies he thought were made up of four elements, fire,
air, water and earth. He believed that each could be transmuted into the other and therefore
only different forms associated with a prime matter which was itself inaccessible to experience
When we examine their initial concept of light they defined it with the metaphysical notions
of potency and act. A transparent body has a potency for transmitting light but it does
not become actually transparent until light is passed through it and thereby brings the
transparency into action.
The next advancement in the ideas of the universe and what light is would take nearly 2000 years
and were made by Descartes. The age which preceded the birth of Descartes, and that
in which he lived, was marked by events which greatly altered the prevalent conception of
the world. The discovery of America, the circumnavigation of the globe, the invention of the telescope,
the overthrow of the Earth centric view.
One of the problems of natural philosophy was to account for the actions transmitted
between bodies not in contact with each other, like magnets, the moon and tides. Descartes
rejected that these were caused by occult influences and instead thought that these
must be explained through simple mechanical things like pressure and impact. This immediately
means that all objects must somehow be connected to each other. He rejected action at a distance.
This also meant that the space between the Earth and the moon could not be empty, indeed
the whole of space could not be void. He viewed that this space was occupied with normal matter
and also that the whole of the rest of the space must be filled with particles of a much
more subtle kind, which wherever press upon, or collide with each other. Space in Descates
view was a plenum, being occupied by a medium which, though imperceptible to the senses,
is capable of transmitting force, and exerting effects on material bodies immersed in it.
- the aether.
The aether had originally meant blue sky of the upper air and had been borrowed from the
Greek by Latin writers, from whom it was passed into French and English in the Middle Ages.
Descartes was therefore the first to bring the term Aether into science.
In his view, it was to be regarded as the main constituent of the universe, save for
that infinitesimal fraction of space which is occupied by ordinary matter. Now that probably
sounds familiar… right?
Descartes viewed that the Aether particles were constantly in motion. As space was completely
filled with these particles it would mean that the movement of a single particle of
aether would need to involve the motion of an entire closed chain of particles. The movement
of these closed chains constituted vortices, which he felt performed important functions
in his picture of the cosmos.
Descartes was the originator of the Mechanical Philosophy but he believed that it was not
necessary to match theory with observational evidence and experiment.
Huygens directly criticised Descartes for exactly this saying of Descates ‘ He puts
forward his conjectures as verities, almost as if they could be proved by his affirming
them as an oath. He ought to have presented his system of physics as an attempt to show
what might be anticipated as probable ub this science, when no principles but those of mechanics
were admitted: this would indeed have been praiseworthy’
The many defects of Descates method led to the rejection of almost all his theories in
less than a century.
The Cartesian philosophy
Matter in the cartesian philosophy is characterised not by impenetrability, or by any quality
recognisable by the senses, but simply by extension; extension constitutes matter, and
matter constitutes space. The basis of all things is a primitive, elementary, unique
type of matter, boundless in extent and infinitely divisible. In the process of evolution of
the universe three distinct forms of this matter have originated.
These are the luminous matter of the sun, the transparent matter of interplanetary space
and the dense opaque matter of the Earth.
He believed that the luminous matter of stars had been scraped off the other particles of
matter when they were rounded; they move at incredible speeds which means that when they
meet other bodies it is with such a force that this causes the other objects to be broken
up by it into smaller particles that are so numerous that they fill all the holes and
smaller spaces which exists around these bodies.
The matter of interplanetary space constitutes most of the rest of matter. The particles
are spherical, and are very small compared with the bodies we see on earth. Descarted
viewed that they did however have a finite magnitude.
The final type of matter is the dense opaque matter we are more familiar with. These are
much larger and heavier and are not moved as easily as the other two types.
According to Descartes the sun is the centre of an immense vortex formed of the first or
subtlest kind of matter. The vehicle of light is the second kind of matter, composed of
a closely packed assemblage of globules.
The globules of the second element and all of the first type are constantly straining
away from the centres around which they turn, owing to the centrifugal force of the vortices.
This means the globules are pressed in contact with each other and tend to move outwards.
It is the transmission of this pressure which constitutes light in Descates view. This means
that the action of light extends on all sides of the sun and stars, and travels instantaneously
to any distance.
Descartes supposed the diversities of the colour of light was due to the different ways
in which matter moves. In particular he thought the rotation rate directly related to the
colour of light with those that rotate the most rapidly being red and slowest blue. The
idea that colour was related to some aspect of the periodic time is an interesting foreshadowing
of a great discovery which was not established until much later.
As crude as Descartes theory was it did encompass a wide variety of phenomena and stimulated
the spirit of inquiry and in some degree prepared the way for the more accurate theories that
would come later.
The next noteworthy event in the theory of light came from Robert Hook and this is what
we will cover in the next episode.