speech is going to be substantially
different from the previous and yet
you will see that maybe you
find some similarities
it’s a bit of a surprise for me but
you will see I am specialized in
theoretical physics in physics
fundamental and I wondered in
how far does this discipline
talk about the reality of the world but of
the reality of the world what is it that
space time the material the
light the glide and so on and
notions that are finally achieved
in a rather difficult way with
experiences very observations
delicate and that’s why we talk
of fundamental physics because it
this is fundamental questions is
very difficult to tackle
and I wondered in what
measure this discipline could we
help and guide us in our life
personal in our lives of all
days and I arrived at several
answers and I chose one for
you talk about it tonight there are some
others there are others for example
unique and very interesting is
question the creativity of these
scientists who gave us
remarkable results like einstein
or newton galilée and many others and
it is extremely interesting
extremely rewarding and when we
questions the reasons for this
creativity
oh of course there is no miracle there is
no easy answers but
find some of the aspects that we
just heard but it’s another
that’s another aspect that I want
to evoke tonight is the lesson that I
would like to shoot it’s finally it
beware of our intuition there
to take back what was said all
on time
beware of our first impressions
so it’s not quite in the
hands
circumstances it’s not so much about
meetings with colleagues or
people we are brought to
to attend but be wary of
impressions in a general way
and when we want to understand what is
pass around us and for that
I had chosen an example that will be
drawn from the fundamental physics of the
general relativity which is a
theory of which of course you
have heard about it and you do not
know maybe not in all his
details and I tell you a few
words
I could have chosen another
branch of theoretical physics which
is called quantum physics which is
full of surprises but so
I chose tonight relativity
general and a more specific theme that
is that of temporal notions and you
go see that general relativity
sends us a message that is very
clear is that time does not exist and
yet time is something
that we handle every day that
allows us to find ourselves
give appointments that we
use without stop in our
practice in all aspects of our
life
and yet physics teaches us
that time does not exist and I would like
to make a precision that is also very
important because sometimes and me
even I just told you
relativity the theory the
general relativity tells us that
time does not exist but in fact it is
not quite that is it’s
very precise world observation
by physicists by their experience
by the observations that teaches us
that time does not exist and that’s
then general relativity by
the intermediate dalsh of einstein who in
was the creator it’s einstein who
by this theory gives us a
interpretation of the world that holds
account of this fact established that time
does not exist ie it is not the
general relativity or anything
what theory will you say
specifically time does not exist
but it is the observation of the world
experimentation on the world
the research that physicists do
practical and concrete way that we
says the world as we discover is
incompatible with the existence of time
and then general relativity
built by einstein will give us
a description of the world that takes in
account of this fact but who I repeat is
a fact of infective observations
of experience the time does not exist and
why I chose this topic if because
that obviously the existence of time that
is so much and so pervades our
music our lives is something
something we had the intuition
it’s something that seems to us
obvious time obviously exists on
want to say well no
the observation of the world itches
so to start before going back
in the subject of relativity
General
I just want to expose you a
result of very precise experiments
I could have chosen a lot but I
will give you one that is very
accurate that was accomplished there is
few years and that will illustrate the
does not exist time that you
will give one an experimentation if
you want concrete
so these are the most clocks
accurate than men and never
built these are atomic clocks
these are very atomic clocks
complicated very systems
complicated called in this case
particular optical fountains for
reasons that I will not go to you
explain here and these clocks are
extremely accurate ie if
you have a watch and your watch
do not go forward let’s say one second
delayed by one second in one year
good you’re going to be I think pretty
satisfied me I never have a watch
as precise good and well there the
clocks that I’m talking about you can
to be sure only about 13 billion
of years of existence of the universe they
do not advance or delay more
of a second
so this is the most accurate lose that
we never could build and it’s
even hard to imagine better
good then physicists have built
clocks like that and if you
leave one beside the other and
well they are perfectly
synchronized
when you put them on time you
obviously at the same time
and l always always indicates
the same hour as long as it stays one
next to each other but you take
one of these clocks and then you
bring it slowly to the floor at
above in the building you let it
a moment at the stage above and then
you bring it down and and when you
the down and well his indication
no longer coincides with the indication
the other clock while these are two
perfect clocks
so of course they will not be
shifted by one second of a minute
but a small fraction seconds but
that their precision makes it possible to measure
means what it means everything
simply that there is one thing that is
sure is that since both
clocks walk to perfection
and since it gives results
different if time is there
at least one of the two that does not give
the time they do not measure the time
and if you take 10 clock
different than you make them from
different routes in the building
again it’s something that
was achieved simply by ascending
the clock on the floor above
a few meters higher you will have
with 10 clock of the result
different with his clock without
different result and there is no
reason to think that they are one who
indicates the time and the other which
would indicate something else then we
could imagine several times ago
there is the time number in which indicates
the clock number one the time number 2
and but at that moment you go
to be forced to imagine that times
and has two
if you have 10 clock there are 10 if
everyone at his clock
how many 7 billion people
on earth there will be 7 billion time
different etc etc
there is no limit so it is
impossible to imagine that time and 7
billions of facets like that and
finally the only way to get
go out and that’s what do the
physicists and this has been confirmed by
from experience of other types that I have
no time to exhibit tonight but
finally the only coherent vision of the
world is to say time does exist
not so what measures a
clock and many a measurement clock
finally a duration is not at all
the same thing ie the clock
measure the time elapsed since the
when it is put on time
until we go to the lyre and
finally the message we have
according to this experience it is that
between two very specific moments and well
two clocks two people are going
measure go live will experience
different durations
the physicist paul langevin who was a
einstein’s friends in the years
1920 and who was one of the first to
to have understood the general relativity
imagined a little experience of
thought in this kind an experience of
two twins two twins who
obviously when he is born snes at the same
place and have the same age and then a
of the two twins going at one point
go on a trip to space and
find his twin brother and well
that they are the same age to the point of
departure let’s say the moment they
kiss before the twin
travelers board his ship
spatial and the moment of return when
to find each other well there was one who
lived for example 20 years and the other who
lived fifty years so they’ll get
find in the situation where his two
twins who obviously initially had
the same age well there is one who
will be 40 years old and the other 70 years
good it’s something that has never
been made for reasons
practical because it would be necessary
twin travelers to make a trip
very fast with a rocket that the
subject to an acceleration that
would be unsustainable
but if you want it’s a
transcription at our scale of this
experience clock was
realized and so the conclusion
again is that time does not
can not exist because each of the
two twins could say – the duration
that I lived is a measure of time
and as they are different he can
not be a single time for all the
world and that is the message of the
relativity and this relativity
where does it come from you know it’s
a creation of this son
an awesome guy named albert
einstein and to say two words good
albert einstein was born in 1889 and in
1879 pardon and in 1905
while Anne Stein was employed in
a patent office while he
had never been in universities
when he had never had contact
with faculty with teaching
university graduate he wrote
in this year 1905 three articles
who have all three in a way
different revolutionized physics
while it was not at all
professional researcher like there is
had already at the time and as there
still more today
so that’s one of the great mysteries
how this young man apart from
circuits could have three ideas too
awesome of course the historians the
psychologists everyone is interested
a lot to that but I will leave
side for tonight but among these three
articles there is one that we consider
as the foundation of physics
quantum another one that we consider
as a confirmation that we had
really needed at the time of what we
call the atomic hypothesis
that is, the design of the
matter that is made of atoms which
is our design today is the
third article founded this
theory of relativity
because einstein discovered this
fundamental thing that time does exist
not he did not discover in the way
which I indicated previously
because the experiences that I you
mentioned that they were made there
a few years ago was not at all
within the reach of the technology of
the time he discovered it from another
way by questions of
synchronicity I’m not going to you
expose here but have been analyzed
of course by the physicists we
explain me in relativity classes
which have also been analyzed by
historians because like einstein is
he came to all that good it’s
extremely interesting also
but what’s interesting is that
what einstein found out first
is that the notion of simultaneity
can not exist
so imagine that you have a friend a
colleague and cosmonauts and who
find on the planet march and you have
want to ask you the question at
the precise moment when I
what is my friend talking about?
to do on the planet march
at the precise moment when I speak good
you can ask him the question
have the soul is that if you ask me the
wanted question send a message by
example by radio the message 28 minutes
so after eight minutes he goes
receive the question what are you
doing it he ‘ll say I’m in
decapsulate a bottle of
beer
but when you go to receive the
answer eight minutes it will still be
elapsed so he will have largely bus to
beer and anyway you will not have
we will not have the answer of what he
did when you sent
the message
so there is a communication problem
how to synchronize how to know
what my colleague from planet mars
does at the moment I speak and einstein
realized that there was
a difficulty
so this difficulty he tried to
solve it
he tried to tell himself is what we
could imagine a procedure that goes
to be necessarily more complicated than this
exchange of signals that I just
to mention is what we could
imagine a procedure allowing me to
to know what my friend is doing right now
for example me I capsules a
bottle of beer
hey he imagined a process like that
on which everyone has put
okay and well I apply this process
which is a bit complicated but who is
quite feasible in practice and
I come to the conclusion
while I capsules my bottle
of beer my friend on march is also in
decapsulate his bottle of
beer the problem is that if my friend
on march is doing
exactly the same as me
and ask yourself what is
when he capsules his bottle
of beer he’ll find that I’m in
finishing the video is so
absolutely impossible to put
okay and there is no way on the
notion of simultaneity ie me
I will think that homo eats
my bottle
my boyfriend’s capsules his bottle him
he’ll think that by the time gilles
capsules his bottle
I have almost finished my beer
there is no way to get in
Okay
so it’s an impossibility of the
simultaneity and so it’s also a
impossibility of time because if the
time existed if for example we could
said
it is currently 20 hours in all
the universe
the notion of simultaneity it would
very well defined just say to
the other looks at your watch which indicates the
time if we indicated the time and say
me what you did at 8 pm and I
know what I did at 8 pm I
capsules and my good beer and in this
case we could agree
on an answer
so if you want the impossibility of
to agree on a response that
was found by einstein well which has
been confirmed in multiple ways
since tells us that not only does
notion of simultaneity does not exist
but the notion of time can not
to exist
on the other hand, the notion of duration exists
perfectly what a clock measures
again this is the duration that
has passed for this clock
accurate from when making
so the time is finally the fact that
for two clocks that live two
different stories
because we have a breastfeeding age at
above the durations do not coincide
it surprises us of course that we
prevents us from doing what we do
usually that is to say to say
takes all the durations that coincide
everything is to say it’s called the time
now if it’s hard and a
coincide more well we can more
call it the time in life
commonplace of course as the
differences that I’m talking about it’s
microseconds we do not care
completely
and so what we call time it
comes from the fact that all the durations that
we live for example between the moment
where we enter this room and the
moment we are going out we live
each of the different durations but
different than a fraction of a second
so everything happens as if it were the
same durations
so we’re going to say we all lived the same
duration it’s called the time and for
everyday
it works very well but we know
now we know it with physics
particles that go very quickly with
cosmic rays with
astrophysics with navigation
space with telecommunications
space with the GPS system thanks to
all that millions and millions of
every day we check that the
time does not exist and can not
to exist
so what consequences in life
everyday and I will end up there
good the first is that so as I
wanted to say you have to be wary of his
intuitions of our intuition that we
said balloting obviously that exists
beware of first impressions
and
also it means about ourselves
what are we ourselves
what is my friend cosmonauts
because I can not think of my
cosmonauts friend at the moment
because I do not know what he’s doing
at the moment and I have no
way to know it I have to think
to my friend cosmonauts as someone
who lives a story that lives a
history of his past with his present
with his future that describes a story
and myself who am I
if I want to define myself I’m not
only the one who speaks to you in this
moment I am the one who took the train
just now I’m alone incident
technical
it’s okay I’m the one who did
she travels a while ago who has
wrote a book that met so-and-so
or so- and- so I’m the one who’s going
resume the train tomorrow who will do
another trip so if I want to
to define myself I do not define myself
as I am for a moment at the moment
present
but I define what I call my
universe line ie the
continuity of all the events that
I lived from my birth to my death and
that’s me and if I want to know who
you are and well it is not enough to
you observe in this famous tenth of
second we were talking about previously
because I would have felt
biased but I have to know who
you are from the beginning it has to be that
I know your universe line
in other words you are not a
point in space at some point
but you are a line and this line
she is not in space but she
is in what is called space time
and so ultimately this message
fundamental that seems a message
relatively abstract of these theories
of relativity who tell us no
do not live in space and in the
time but by emptying something
more complicated what time space I
will not you and define today what
that it is that space time but
finally it applies also I think
to our everyday life and
maybe we need the hall and a
little against our intuition ie
than what exists to know myself
ourselves, but also
any object an object it’s not
something that is a given moment
in the
happens but it’s something that
is a story in space time and
so if we want to understand the reality
of the world
it’s better to speak in history that is
unfolding that unfolds not in the
time but in the space time because
the time if we want to be strict
there are more and so we are all
stories all the objects we
meet that we rub shoulders are
stories and so I think our
worldview as well in physics
fundamental needs to be inspired by physics
fundamental and say that we live
in a time space unlike
maybe to our intuition
thank you
[Applause]
”
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