Over the previous four videos
we saw something growing :
what is the process that finally resulted from
all of these sequences of the history of science
well that's abstraction
Abstraction etymology means extracting out
we perceive a phenomenon
then we succeeded in extract something
Let's take an example of an abstraction approach
Here you could see Galilee
he observes pendulum movements
measuring beat frequency
as at this time clocks did not really exist
he did it by measuring time with his heart beats
So that's why he put the thumb
on the right wrist to measure period
And this observation it deduce that
the square of the period of this pendulum
vary as the pendulum length
There's a different way of expressing it :
period varies as the square root of the length
so obviously today we say that
period equals square root of
the ratio between the length and g
g = 9.81 meters per second * m²
the acceleration constant of gravity
Now be extremely careful in what follows
you have a scene with a observer
Galilee who observes is pendulum
In the speech balloon
there is the relation related to the phenomenon
Now observe what will follow
First I remove the pendulum, I remove the object
secondly I remove the observer
what's left of ?
It remains the formula  :
letters, symbols and signs
That is abstraction !
How could we explain the scientific game
it is a little bit a kind of dialogue, a round trip
with concrete that secretes the abstract
and pure abstract
that suddenly found an application in the real
Here your have example
 mentioned in the  previous videos
its a Danish using a very accurate aiming instrument
invented by a Portuguese
makes very accurate observations
giving him datas on planets trajectories's
and Kepler manages all this and 
identifies these trajectories to ellipses
And states that the sun occupies center
Area law, speed and so on.
And then Newton invent a force law that works
And give its trajectories and areas.
Wonderful...
The Newtonian formalism create
 elliptic planet's trajectories
But  we saw that the ellipses trajectories
of Earth, Venus and Mars and others
have very moderate eccentricities
So is there any trajectories 
with very strong eccentricities?
Halley find it with his comet
look at path he had calculated it
it is a beautiful ellipses ! Not a circle !
So when we see what this 
mathematical Newton formalism creates
We see three types of curves
there's ellipse, hyperbole that is not closed
and parabola that is an ellipse with infinite focus
we could summarize it by saying that a parabola
is an ellipse that went wrong !
So we could ask: is there any hyperbolic trajectories ?
yeah we have aperiodic comets
time to time a comet shows up
so immediately amateur and professional astronomers
captures data, calculate speed
plans its trajectory
distance at which it will pass near sun
possibly its hyperbolic trajectory
So we say this comet never come back
this is not a periodic comet
returning every 76 years as Halley comet
this comet is about to disappear
So here there's a happy marriage
we will see that this will not last eternally
between observations, formalism
between the Newtonian model, this how we must call it
and what we observe.
ellipses is not newton invention !
it existed since Greek then
Is that Greeks have hunches about  planets trajectories?
Not at all !
they were playing with sticks and twine
look at this installation in yellow
you take a table where you put two nails
add a string with a pencil and
you draw a beautiful ellipses
So ellipse, hyperbole, parabola
are geometric properties
Greeks were very interested in geometry
What it is curious
that suddenly we make mathematical, shapes, formalism
we write beautiful flies dung on a sheet
Does it makes sense? Well... not necessarily !
watch the misfortunes of Kepler
he takes plato's polyhedrons
he believed he could explain 
why the planets are locate at their places
So it does not work every time
Sometimes there terribles failures
The most heartbreaking contemporary failure
it's super-string
it is a whole bunch of guys who imagined
 that one can describe
all different particles with a
system of ropes in many dimensions
everybody rush on that
and that was the trend in the theoretical physics labs
At each recruitment
candidates had been asked if 
they were in the super-string movement
if you're in OK if not your out!
And with this policy of concentration
means on the string-theory, well for thirty forty years
these super ropes people knitted super socks !
and it gave a mountain of publications
I can mention the speech of a president of university
who received in France a symposium on super-string
He said : " altough this theory is never explained anything neither predicted anything
given the amount of publication on super-string
we note extreme vitality of this new discipline
right now in 2017
I think no one talks about it...
do not expect to find in papers
a great discovery of super-string
I believe that everyone understands that this is rubbish !
So sometimes it is not working
its  complicated and thick
we predicted we bells and whistles
and then it misfire stupidly
The string theory
I do not know if it will find a new renaissance
some people say it is so far ahead that
it is a theory which found that
application in 50 years
Well, back to our main topic
In principle, all these videos are
built around a central theme
which is cosmology
Nevertheless, I will nees to do a
small detour by quantum mechanics
to explain essential things
here's a little montage starting from a angling problem
you see a fishing float attached to the line
you pull the line like this and you
made circular wave which propagates
and then before this fishing float
you have a dam which has two slots
circular wave arrives at these two slots
and the water will rise in the two
slots alternately mount down
so that both forms will behave exactly
as if they were sources like as if they were
two fishing floats going up and down
they will create their own circular system
that go downstream
we must understand that the oscillations
of the two floats in slots that go up and down
are absolutely synchronous
acts as two sources
each one emitting their circular waves
interfering and those interférences will 
create chop in the basin
and what interests us is what will happen on the wall
who receives this waves
I represented the water level
on the wall which receives it
how does it work?
horizontal dotted line shows the calm water
then we see that there is a rise
and descent
and then there parts of the wall
where the water level oscillates
and others where it remains constant is without disturbance
with this experience
these two waves emitter
it creates a signal on the wall
here the green line represents the level
of the pool water when it is not disturbed
and then here I put green dots on the line
represent places where water level don't change
it is between these places that the water rises and falls
then it is not grasped these things
you could still go back and review the sequence
this is very important to understand
you should ask you:  what does he mean ?
we speak cosmology after
we do a small tour in Quantum mechanics
and then we have an Hydraulic experience
with waves on a water
well you figure this experience it was made
in 1800 by Thomas Young a english
he did it with light, on drawing you have
the layout with a light source two slots and then
on the screen what he see projected
is not two images but their rays
succession of light streaks
same thing with hydraulics
that suggests that the light is a wave
and wave it goes through the two slots and that at that time
these slots behave as light emitting phase, synchronous
there's interference
and we see on the screen the result of these interference
where succession of lines deposits its energy
its major light rays and in the contrary
when two light loads cancel you se dark stripes
we will not recount the history of physics and
science in the 18th 19th century
but this experience and several other
enshrines the idea that light
is a wave while Newton thought it was particular
it was not the only one
also because there was a kind of discussion
whether light was particles or light grains
or if I was a wave
the wave aspect  win after all
the appears electricity, magnetism
Faraday, Ampere
everyone makes fantastic experiences
Faraday and Ampere trying to make the equations
then equations you will see beautiful
it can be said that during all 18th century 19th
scientists  build a formalism
they invented great stuff
operators and other stuff
A real flies dung catalog !
like my wife says
and there is a extremely important characterl
James Maxwell was not the inventor of Coffee !
is an English that takes
equations that are scattered
which people tried to create
and he to pack them to extremely clever synthesis
and so here goes
maxwell with his set of equations
and his equations describing electromagnetism,
saw the letter e this is the electric field the letter
b its magnetic j electric current
and all that it works wonderfully
there is a kind of delta upside called
the  nabla operator
you have a weird D that is partial derived
this mathematic formalism is completely present-day
a mathematician  or 2017 physicist that read
Maxwell and he has the impression that is it in a college
so he wrote these equations who describe all electromagnetism
and more is what is fantastic is that
from these equations where
he shows that this system managed by these equations
creates waves and these waves
are  light waves
which means that light is an electromagnetic wave
So one could say with
these experiences such as Young
and other and the Maxwell's ones
the physical ended up in
here comes the little troublemaker
quantum mechanics  Devil
and  you say oh misery it will we
explain quantum mechanics
No!  There are lots of people on the net that do it well
even they're very lucky because
I remember the words of Richard Feldman
who was one with the most leading scientists in this field
and who said you might encounter
one day people who said I understand everything
on quantum mechanics and
I tell you they are the most perfect liars
because we includes me understand nothing of
some recipes works but that's all
Now we reached the epilogue of this fifth episode
We will understand why we detailed
Young experiment
why we raised the issue of quantum mechanics
This Young experiment we'll tray again in modern times
We replaces the Young source's by
the device that has the property of
emitting one photon at a time
then we were told that light
was wave
and we shown that it was also photons
you know I I've lived something pretty amazing
I am a non-practicing astronomer
I have not spent time behind a telescope
but one day of Marseilles people's were nice enough
to take me to their observatory
and my friend had interesting assembly
he looked a very distant galaxy
when you want to make very far galaxies image
in one observing night they gather
few thousands of photons
he show photons of a laptop screen
and put a sound system on it
so while we wait we hear one after the other
and it's like why it happens
So light comes in small packets like that so photons exists
so the  the common sensare then to this month
Common sense said if the device sends one photon at a time
it pass or left or right in the slots experiment
I won't have interference fringes
and yet we still have fringes
then the quanticien say it's a trick
"magical forces" paraphrasing Kipling
it is not worth looking at understand
the quantum mechanics said this or that...
what does it mean?
we enter with quantum mechanics
and the relativity and general
in the fly dung era
where understanding universe
is to take a paper writing x and y
sinus and cosine things and stuff
Its the only way
then in fact it's relaxing because when I'll take you
in special relativity and general relativity
you must just relax
saying I do not try to create a mental picture
And you will see everything going very well!
