good evening are we there yet
where are we today where in
are we in the knowledge of
world looking for this knowledge
of this understanding of this
explanation of the world is a great
adventure that lasts for more than two
millennia and that continues today
and the question is to know exactly
where we are and what we are
near the goal ie is what we
are close to understanding the world
so obviously understand the world
I think it’s a desire that existed
always and everywhere in all
civilizations but it happened
something in our civilization
let’s say in the fifth century before
jesus christ pretty much with
philosophers of nature who’s called
the Presocratics who wanted to approach
this question in a rational way
and that was new and this concern for
rationality that is to say to introduce
reasoning finally for
understand and explain how
works the world
well we can consider that this is the
beginning of science not really a
science as it is understood today
but at least the beginning of the research
scientist and so from the vth
century before BC during all
Greek antiquity for example and then
it’ll continue after in a way that
I will explain different schools of
philosophers of nature philosophers
as they are called it’s the name we
gave if you want to scientists
at the time have issued assumptions have
tried to build systems
explanation of the world
so what’s important is that they
have set up a kind of framework and
which is always the framework in which
we operate today a framework
which allows precisely 2
to address this issue of
knowledge of the world on the mode of
rationality
so this framework is what it is
to adopt broad principles of
great principles
for example it can be love and
hate condensation on the contrary
expansion the symmetry the harmony or the
chaos the chance it depends on the
philosophers it depends on the schools of
philosophy a few some of
his ideas work very well others do not
walk less well and then
they mix, we are
adopts one rejects them
and it gives different systems of the world
different explanations of the world to
the time
the second thing is to know from
what is the world made of
compose the world for example space
from the extended the concept of spaced not
really established among the Greeks
an extent therefore in which are going to
continue the phenomena for one
for example for Greek atomists
it’s empty
and then know in this framework what is this
that there is some matter and then
the material and well we will think that these
facts of fundamental elements then by
example for platon aristotle it’s going to be
four fundamental elements that are the
earth the water the air and the fire and everything
we see around us these are
combinations these four elements for
others called the atomists
greg down these are atoms that are
spread out in an unlimited empty space that
looks like what’s called today
elementary particles
so see there are several ways
to approach the world who are in
competition
and it will be that of Plato and Aristotle
which will prevail at the time not
because it’s better but for
lots of historical reasons that’s going
last about until the rebirth
and then there is a third point after
the principles after the content it’s the
laws and finally the laws they go
be expressed in a mathematical way
because very early in this story
in this development of this adventure
this cultural adventure to explain
the world we see the need
to use mathematics for
explain the world so that was said
since the fifth century before
jesus christ for example pythagoras everything
and number but also platon than the draw
enter here
geometer then we will have galilée the
world is written in mathematical language
and then newton that goes mathematized on
world that goes mathematized physics and
then stein steira and it goes on
still continues today so we have
a vision
we already have a forecast of the world or
rather a set of vision
competitors none of which works
really very well and that’s not all
no longer functional we have this already
in Greek antiquity
and then it’ll last for almost two
millennia where we will see that these
designs are questioned there are
competitions we show that some
stuff does not work other steps
finally and we end up at the xvi
century to the seventeenth century to the great
Newtonian revolution which is the
foundation of physics or finally if
you want and a really system that
will set up and who will
operate and this system is fine that’s
newton so who will set it up and
this is again the beginning of the
modern physics and also of
modern astrophysics low newton is going
resume all that but he will specify
ie he will say there is a frame
for the world and this framework is space
and the time
there is a content it’s particles
it’s matter made of particles
then also radiation waves
finally it also depends on the conceptions of
the time there is nothing bit of debate on
that question
and then all that and mathematized from a
very precise way and newton ago
a lot of math in this
foundation of physics and there are
laws laws that will be expressed
mathematically but all notions
Physical are represented by
mathematical notions so the laws are
mathematics and it’s going to work from a
extraordinary way it’s going very, very
well-marketed and in physics there are
always two aspects is the aspect
practice is what we today
allows satellites to be sent around
of land or probes that arises
on march or to make manufacturing
computers to make transistors
lasers all you want from
manufacture systems that allows
to implement intelligence
artificial good all this these results
basic research in physics
but there is also in physics
knowledge of the world how
the world works and so newton us
gives a frame of thought for the world
in the world and a space framework and the
time and then there is content
the particles for example that obey
to laws and it’s going very well on
a practical plan it works a little bit
less conceptually because
that this conception of the world
Newtonian she is not at all
perfect and suddenly in the twentieth century for
different reasons
it’s going to be challenged again on
is going to have a fundamental revolution
in physics that goes completely
swept the conceptual framework the framework of
Newtonian thinking to establish one
other in fact to establish another
it’s not quite true because it
will be two different and
competitor to know that in the twentieth century
there is not a scientific revolution
but there is a double revolution
scientist also from one side we
have the theories of relativity
general in the 1950s 1910 1915
until 1920 established essentially by
a single man who is albert einstein and
on the other side we have physics
quantum of which einstein is also a
founder but there are many others
protagonists as of irak freudiger
eisenberg edge and other names that
you may have already heard and his
two new frameworks of thought in
physics will give conceptions of the
completely new world and
completely different from the design
Newtonian and the problem is that these
two conceptions of the world are
different and they are even
incompatible go very quickly that
tells us for example the design the
general relativity
she tells us that we have to give up
some Newtonian notions it takes
abandon the notion of spaced the notion
of time it is necessary to replace them with a
notion of space-time which is something
something really different ie
sometimes we will hear that
space time is space and the
time simply no it’s some
something much more subtle than that and
which completely changes our perception
things that is, what we
let’s call the time that allows us to
we gather here to give us some
appointments and be on time at
go and well it’s kind
of illusion that nour and pencils that
works fine on our scale but
that does not work at all on the scale of
fundamental physics so the
general relativity we can say this is
a
I conceptual framework
the explanation of the conception of the world
Newtonian for the benefit of a new
will deny space and time and who will
replace his part a new notion
which is the time space in which the
material design made of
particles does not really change
if we look now at the other component
of this scientific revolution it’s up to
to say quantum physics is
completely different
the Newtonian frame is going to be also
rejected but we will keep the space and the
time and this is the material that we are going
change is the design of the
matter ie according to physics
quantum the material is not made of
small particles that can be located
which one can say they are there they
have some speed and everything but
it’s something a little blurry you
may have heard of this
which is called the uncertainty principle
and well the uncertainty of physics
quantum that’s ultimately what
expresses that the conception we have of
the material ie the contents of
the universe is no longer that of
newton
she is new so see on one side
general relativity on the other side
quantum physics rejects
completely forces us to reject the
Newtonian design replaces it with
a new design but the problem
it is that these two conceptions are not
not the same and they are even
antagonists
so if they are different but
they can not be both
true since they are contradictory
so is there one that is
true or neither of them
is not true and there is one that we do not
not yet know who would be the right one
so that’s what most people think
physicists and obviously this
design
he seeks everyone seeks
what is the good physical theory that
would go beyond general relativity
and beyond quantum physics that
would be a lot more unified a lot
more global that would allow us
to have a unique conception of the world
so you may have heard of
of string theory of gravity
quantum of other approaches that have
names a little barbaric called the
twister where noncommutative geometry
no matter ultimately
but that means we’re looking for people
theoretical physicists looking for a
new conception of the world today
so obviously always with the idea
that it will have to be expressed by
mathematics so probably with some
new mathematics
so today we are looking for a new
world design
we are looking for a new conception of
framework in which the phenomena are played out
maybe always space time but
a space time that is not the one
which we think today a
new conception of the material that
is probably a little fuzzy because the
quantum physics tells us that it has to
to be blurry and ultimately also
new laws that they express themselves without
doubt the new at the news level
formulas and new tools
mathematics and that’s the job of
theorists of theoretical physicists
today who founded physics
conceptual and so to answer the
starting question where are we
today
and here we are we are not
are not the end of the road physics
theoretical the fundamental physics it’s
an activity that continues there are heaps
of theoretical physicists who do that and
believe me it’s extremely interesting
and it’s a great pleasure
thank you
[Applause]
[Music]
”
Be First to Comment