Translator: John Tinneny
Reviewer: Peter Van de Ven This evening, I'll talk to you about one
of the biggest scientific scandals of the last hundred years at least. For you to understand
the extent of this scandal, I'll start by showing you three photos. Here's the first one. A picture of a black hole. A black hole is one of the most
fascinating objects in astrophysics, but maybe also one of the most worrying
and most terrifying in the universe. Everything that falls into it
is trapped there forever. Not even light can escape from it, therefore it appears
as black, dark and shady. Its existence had been predicted
by Einstein's theory in 1915, around 100 years ago. At first, nobody really believed in them, and today, we know that one exists in the centre
of nearly every galaxy in the universe. What is inside it nobody knows. Nobody has seen inside,
and I discourage you from going there. No current theory is able to explain what happens inside black holes. The second photo represents a phenomenon
which has no link to the previous one. The most enlightened minds
will have seen some small similarities, but this time, it concerns
a piece of dark matter. We call it dark matter
because we don't know what it is. We haven't found another name. We can't smell it, we can't see it. What we think we know is that it is found
in nearly all galaxies. How? By watching the way
in which galaxies rotate. Galaxies, today,
rotate so fast in the universe that they ought to break apart. Take a bowl of soup, spin it around on your table
faster and faster. You'll quickly see that you have something
that doesn't look very much like a galaxy, but the soup will break apart in some way. Similarly, we ought to observe
the same thing with galaxies. But we see that they prevail. They are there. So, physicists have theorised that a form of matter, dark matter,
exists in small amounts to stick elements of the galaxy together
thanks to gravitational interaction, and stop it from coming apart. This dark matter, today,
according to our calculations, supposedly represents 25%
of the contents of the universe. Third photo. The third photo, you are now major experts
on astronomy and cosmology, you will recognise here dark energy. (Laughter) Dark energy - we find a little of it
everywhere in the universe. Here in a galaxy cluster. And dark energy,
just like its friend dark matter, is called that way
because we don't know what it is. We can't see it, we can't smell it. Why do we think we know
that dark energy exists? Because 20 years ago, we noticed that the universe
was growing faster and faster. If the universe was a balloon, imagine that someone was blowing
into it harder and harder to make it grow faster and faster. In this image, this person
who breathes in the energy is exactly who we call "dark energy". Obviously, there's no one
at the end of the universe - or maybe there is,
but I haven't seen them yet - there is no one
who is pushing the universe, but today we see it
grow faster and faster, and so we suppose
that a form of energy exists that we call dark energy. According to our calculations, dark energy forms 70%
of the universe's contents. So, let's take stock. We're now at a point
where this is the model of the universe. The small white square up there
is what you know: galaxies, planets inside it, stars. We put black holes there as well,
knowing roughly what they are, though we don't really know
what is inside them. All the rest, 25%, is dark matter,
70% is dark energy, so as to arrive at a point
where we don't know what 95% is. I don't know if you know
about the resources and the energy used in order to understand
what happens in the universe. What are the resources? They are several thousands researchers who work hard for hundreds
upon thousands of hours, in labs, in observatories, who use the most powerful tools, the most sophisticated
that man has ever made: particle accelerators, gravitational wave detectors, satellites which we send into the sky to carry a lot of telescopes
and obtain images from the sky. All that, to arrive at the point where we don't know
what 95% of the universe is. (Laughter) What society would accept that ? Who would accept
the use of so many resources to get this result? So, we go to the researchers,
and we ask them, "What is happening here?" "I don't know. It's hard.
The universe is big ... We don't get it. It's not exactly like we are looking
for a needle in a haystack. It's the haystack we're looking for!" (Laughter) (Applause) Once we've assessed the situation,
we must try to move forward. I am a theoretical physicist. With my colleagues and collaborators
placed roughly all over the world, we work out theories
in order to try and perceive the nature and the existence
of dark energy. This evening, I'm more than a little proud to show you the results
and the fruit of our recent discoveries, and I am sure that you will join me
in seeing the secrets of dark energy and dark matter
in this equation behind me. Contain yourselves. It's true. (Laughter) It's crazy, all the things we can see
from this equation here. We see lots of things there. In my opinion, an equation like this isn't far off from being a masterpiece. Van Gogh, "Starry Night". For those that have
never seen this painting, I'll try to describe it. A tree in the darkness. In the background, a village beneath a slightly
tormented sky, Van Gogh style, stars and moonlight. If I begin to describe it to you, you will certainly be able
to visualise the painting and possibly understand
what Van Gogh meant with it. But if you go to a museum
and you see "Starry Night", what you feel will be much greater. It's kind of the same thing
with an equation. I show you an equation,
and I can try to put it into words, tell you what lies behind it,
what it means. If I am good enough,
you'll maybe see two or three things which will make you understand
the nature of dark energy. But if you were to read the equation
in the language of mathematics, if you were to visualise it, as it were, I guarantee you that the emotion and
intellectual satisfaction you'd feel would also be much greater. For this reason, certain physics equations
which you will have heard of - Einstein's equation
for the infinitely large, Schrödinger's equation
for the infinitely small - are considered
true masterpieces of physics. So our equation, frankly, I don't believe
that it has the beauty of Einstein's. And honestly, we still
aren't completely convinced that it will enlighten us
about dark energy. (Laughter) So, maybe we shouldn't overdo it. But in all seriousness,
at the start, when I prepared this talk, I said to myself, "No equations!" But I work with them every day, and I couldn't resist the temptation
to show you at least this one. I also said to myself, "Why speak to them
about dark energy and dark matter?" The only thing that we recognise are these beautiful images
I've shown you at the beginning. We are not sure what dark energy
and dark matter are; it's all hypotheses and doubts. So basically, maybe we can try to take a step back
from these questions, and maybe the right question to ask is, Why haven't we managed this
despite all the resources we're given, and why isn't this a scandal,
but, in fact, the opposite? So why haven't we managed this? The answer I can give you is clear. It's just because it's difficult.
It's darn difficult. (Laughter) So, we can't do it, but it's not because it's difficult or because the situation
seems absurd at first glance that we should lose motivation
and abandon the question, on the contrary. Here we deal with the theme
of this evening: the physicists' utopia. The physicists' utopia is where we believe
that we'll equip ourselves with tools which will allow us to respond
to every question that surrounds us. Frankly, it's one of the reasons
that I do physics, this desire to understand
everything which surrounds me. But at the same time,
we know that the more one knows, the more difficult it will be
to know more, because in the end, the questions which remain
are always the most difficult ones. And in this case,
we must ramp up our imaginations. We must find the most eccentric ideas, the most revolutionary ones, build even stronger, more sophisticated,
more powerful instruments to unearth the solution somewhere in between the infinitely large
and the infinitely small. These problems with dark energy
and dark matter are beautiful stories
that illustrate this fact. One hundred years ago,
when Einstein came up with his theory, we thought we had the tools
that would allow us to explore every nook
and cranny of the universe. And then, just like that,
dark energy and dark matter arrived! And now, we no longer know. The tool we thought would be able
to dig it all up no longer works. We can't make it tell us
what we want it to. But this isn't a bad thing,
because in the history of physics, we have loads of moments like this, where we thought we had theories -
for example in the 19th century - that would allow us to know everything
about the world, about you and me, about what existed in the past
and what will exist in the future. And what remained to clarify
were only small details here and there. And these small details
proved to be true cataclysms. The entire theory collapsed,
we had to rebuild it, and that's how we ended up with quantum mechanics
for the infinitely small and general relativity
for the infinitely large. I don't know if the problems
of dark matter or dark energy will lead to revolutions
as cataclysmic as this. What I do know is
we will do everything to get there. But we also know that we want to get closer
to a form of absolute truth. Scientific truth, the truth of every single day, is an asymptotic concept. The closer we get to it,
the more difficult it is to access. It's a bit like the paradox
of Achilles and the tortoise. Achilles, you all know,
is the figure from Greek mythology, and the tortoise is a tortoise ... (Laughter) Achilles leaves late in his race,
behind the tortoise. He is confident. After a certain point,
he gets the animal in his sights. He says to himself, "No problem." He advances and advances,
and every time, a distance remains, small, obviously,
smaller and smaller, surely, but a distance which is always there
in order for him to catch up. The more he advances,
the heavier his limbs are. The earth retreats like shifting sands. The story says that Achilles
will never catch up with the tortoise. And the physicist knows it. The scientist knows it. They know very well the feeling
of Achilles behind the tortoise, but they continue, they advance because they dream
of discovering new worlds. And in the end, in physics, science,
we advance in small steps. Sometimes, we make great leaps. Sometimes, we move backwards; maybe we back up to gain momentum. Other times, we advance and we find ourselves
facing a steep drop, maybe dark energy, an incommensurable problem. It seems that I can't get past it. (Laughter) In these cases,
I either jump into the public, or we try to build new roads, new bridges, that will allow us
to get to the other side. Often, history tells of these bridges
which were built by one man. We remember Einstein. Einstein practically made his own laws, new roads, which allowed us to explore,
literally and metaphorically, all the nooks and crannies
of the universe. We went far with Einstein's theory. But very often, the construction of a scientific bridge
is a collective effort. Someone comes and puts down a brick, or someone takes away a brick
which was broken and didn't work. Another will add cement. And finally, we end up with marvelous edifices. So maybe in one, ten,
twenty, thirty or a hundred years, one of you - in one hundred years -
will be there and will explain how they succeeded in constructing
a bridge towards the AIDS vaccine, towards solving the problem
of global warming, towards a solution for world poverty, towards the conquest of Mars, or someone who'll be there
to tell us what dark energy is. As physicist today, I owe it to the curiosity that lots of my teachers
and those around me have fed within me. Wanting to know and knowing
are an infinite source of inspiration, but that's not enough. You must also accept not knowing,
accept the limits of achievement. But this form of ignorance should not be a source
of frustration or bitterness. It should be a source of motivation. Okay, we know about 5% of the universe, but there is still 95% to explore! Let's go! TED is offering us lots of rockets. Let's fly off towards dark energy! Thank you. (Applause)
