JANUS 1 : Naissance de la cosmologie avec Platon, Aristote, Ptolémée, Copernic

This is a first video of a serie where I will try to explain
the main lines of the Janus model. In this first part we will examine the actual
model of concept, especially in cosmology. This is one of the best portrait we have
about the Greek Aristotle who lived in the third century BC and who was Alexander the great’s preceptor. Aristotle had created a model of the universe which werebased on experimental
findings that were undeniable for him. Here you can see Aristotle on the top of a wall where is holding a stone on one hand
and a feather on the other. Of course the stone falls faster than the feather. From there he concluded that heavy objects are more
sensitive to forces then light objects. That’s the first Aristote’s principe One day Aristotle was wandering around some docks when he had the idea to detach a boat and push it away. He observes immediately
vortexes behind the boat. Proof is when the boat stops the vortexes stop too. Hence: vortexes, forces, boat. So he states that if a object moves,
a force is acting on it. Aristotle lacks a concept which did not exist at his time. Here’s a second experiment. that we can easily do and make you understand deep concepts: extrêmement profond je vous suggère la
chose suivante vous allez dans un take a supermarket cart and fill
it with errants then push it away from
you. The cart rolls away. First observation: the air vortexes are not
making the cart move. It is momentum.
If you were able to live at aristotle’s time and be able to introduce that concept,
you would have Rock the science because the momentum
concept did not exist back then. Indeed at his time everyone thought
that an arrow could move in space because
of air vortexes pushing it. Third principle of aristotle’s physics there exists a relationship between objects
in the universe and geometry. Geometrical objects are circles,
lines, spheres. He classes objects on wether
they would be perishable or permanent
like astronomical objects. The limit being the orbit of the moon: everything under that limit would have a beginning and an end, mostly described by a line. Above the moon would be considered divine, and therefore best described by circles, as those objects have no beginning nor end. Since antiquity, some could
localise precisely planets in the sky, thanks to star constellations in the background. But it was obvious that Mars orbit
for example was not following aristotle’s principle stating it’s orbit should be Circular. Here is a drawing showing distribution
of the planetsa round the sun Earth goes around the sun in one year. But Mars goes around in 22 months. Hence the angular speed is slower. Here is a drawing where a yellow line
between Earth and Mars displays an apparent movement on the
background (whiteline). After some time laps, we can see the White Line being straight. But since the angular speed of Earth
is greater than Mars, it then displays an apparent movement backward. Moving along, the Earth passes in front and the apparent Mars position keeps moving back. That does not match aristotle’s principle
of circular movement. Five centuries later, Ptolemy knew about aristotle’s
works, and dogmae, and observed the apparent nonlinear
movements of the planets. Therefore he considers having planet
Earth moving in space. At all times, people were considering
all sorts of hypothesis even the craziest. So Ptolemy asked himself:
why would the Earth not be moving? There he falls on an impossibility: According to Aristotle if an object movesit
is because a force is acting on it. But since the Earth is hosting much
lighter objects on its surface, those should stay still while
the earth would be going away. Therefore Ptolemy abandons the idea of a moving Earth. This is a drawing that would illustrate Ptolemy’s idea where the Aristotle’s dogma of the circles is kept while explaining the nonlinear trajectories of a planet like Mars. Here again you can see Ptolemy’ circulatory trajectories for every planet that would explain the aberrant trajectories of those. One amazing thing about those theories was that they
were all elaborated in order to explain astrology, At this time Kings and Wars were dependent from planets Wars weddings and Alliances were done after
astrological themes and predictions. Astrology was the queen of science, and it was absolutely important to predict planets movements, eclipses etc… but since there is still some observations missing explanations they were adding more circles to explain
various phenomena. Sometimes up to 4 circles for improving precision There was no limit to stick to the observations. That theory held for 15th century until the story goes that the Spanish infant told his preceptor that if the mighty Lord had consulted him he would have advised to build a much simpler system. The main idea to retain here is that a false model can give Right results. Then, when with copernicus the sun got replaced at the centre of the system, people went again with hypotheses
that planets had Circular trajectories. But this time the results were inaccurate. Therefore those circular trajectories theories with the sun in the middle were mainly rejected at the time, When  Ptolemy’s circle theories
( with the sun not at the centre) were giving more accurate results. Hence the wrong model was giving right results and the
right model was giving wrong results. So let’s resume now, here we are Still in the geocentric model, aristotle’s model. Ptolemy’s model is almost the same except planets have little circles going along the orbits. This model shows the sun as a yellow sphere revolving
around the Earth along with other planets displayed in some kind of a Russian doll configuration,
evolving in an ultimate doll being the celestial sphere that revolves
around as well and beyond is just black.oir But in this model,
even though modified by Ptolemy he does not care about
the nature of the celestial objects what matters for him is their position in the sky because it holds a functional aspect,
a mechanic that would be explaining astrology. In the 13th century when one would go to the main university of middle age medicine in Salerno, Italy a doctor’s assistant would ask your date of birth in order to calculate the positions of the planets in the sky and map an astrological theme for you. Thus this former geocentric model has been used for 15 centuries successfully. Let’s not forget that during Let’s not forget that during
aristotle’s times, planets were considered as objects
floating in the sky, therefore light objects.. in comparison
to heavy objects. The goal here is not to retrace the history of astronomy but rather to explain what is a model. First we had a model based on the Earth seen as the centre, then the sun being at the centre, then Kepler comes and states that the orbits are not circles but ellipses. Here is a little story about Kepler
who tried to create a model to locate each planet according
to their distances from the sun… today we have an empiric law called
Bode’s law about planets distances ( which by the way I shall make a video about this subject and Souriau’s model in regard to distances) but for now let me grab a book… it is in this comic that I first went on illustrating
Kepler’s drawings about creation, and his model of solar system. This is Johannes Kepler, a man quite worried by the way… here are the principles of his model: he was stating that
one must use geometrical forms such as spheres etc, as well as those forms called Plato’s polyhedron, made out of 3D triangles, squares and pentagon. Here Kepler starts from the Sun
as the centre of the system, then he represents a sphere
on which Mercury is orbiting. Around this sphere he would place one of Plato’s polyhedron: the octahedron which is similar to 2 Pyramids stuck upside down together. Each of the faces of both pyramid being
tangent to the sphere of mercury’s orbit. Now Kepler is going to draw another sphere that is touching each summit of the octahedron. According to him if Mercury’s orbit is in the first sphere within the octahedron, Venus ‘ orbit is on the sphere
wrapping the octahedron. Now we shall integrate venus’ sphere into a new plato’s polyhedron: the icosaedron, made out of 20 equilateral
triangles. According to Kepler’s Model, each face of the icosaedron shall touch the new sphere. Then of course he would draw a third sphere that would touch each summit of the icosaedron. This new sphere will be then describing the Earth orbit. Here again the new Sphere will be placed in a new plato’s polyhedron which is the dodecaedron,
that is a 12 faces figure. Each face represent a pentagon, and each face is tangent to the sphere. Again he wood draw a fourth spear touching each summit of the polyhedron that will describe the orbit of
Mars. Again he would take that new sphere
and put it into another plato’ figure, this time it is a tetrahedron, with
four angles and four faces. Another sphere is drawn that is touching each of the four angles and is now describing the orbit of Jupiter. Again this sphere will be integrated in the last Plato’s polyhedron which is The Cube. Again one sphere is described touching each angle of The Cube, and we’ll be holding Saturn s orbit. All of this is quite precise and complicated and one may ask why Petit insisted on describing so precisely Kepler’s Model, since this is no longer a valid model.
Indeed, now we use Bode’s model which is more specific. Now we have more empiric Titus-Bode model, we will come back to it later. Just like everyone in Kepler’s times, people were trying to describe those divine objects and their movements, since divine was synonymous to plato’s polyhedrons. There was 6 geometrical figures in plato’s polyhedrons and there was 6 planets known so it was perfect and
convenient. Then he went on constructing an actual 3D model, but of course there was a 7th planet which was Uranus but not discovered at that time. What would have done Kepler’s
if he knew about Uranus since there are no more than five
regular polyhedron in mathematics? You cannot make any more regular polyhedron with an hexagon for example. Yet you can have polyhedron made out of various types of 2D figures such as pentagons and hexagons. One very good example here is one object that has been literally creating a religion, in the sense of linking people together,
and that gathered hundreds of millions of devotees.. and that is the Cult of the object call footballhedron. This is a polyhedron that is made out of 32 faces with half pentagons and half hexagons. Now coming back to Kepler’s Model, it is the perfect illustration of The Marriage of myths and science. And we shall see later that this is merely the beginning. But what we did successfully in the middle age with those polyhedron is the Beginnings of chemistry or at the time the so-called Alchemy. Each polyhedron was associated to a substance. For example the cube was standing for earth, the octahedron for the air, icosaedron for water and tetrahedron for fire. Then the fifth polyhedron, the dodecahedron was linked to the quintessence which is literally the fifth element. We shall see later that in advanced astronomical
research, this quintessence seems to focus interest again… as we shall see later on, the modern era is hosting again many of the old myths.. Examples being the black matter, black energies black holes etc .. All this black science that is on nowadays.. but before that we should be talking about Descartes, Newton, Einstein….

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