Transcriber: Maria K. Reviewer: Denise RQ
Ladies and gentlemen, why are we here?
I don't mean here, today, specifically, but why are we here at the first place?
Why we are able to comprehend the fact that we are here.
And why is it that we live in a Universe that's so strangely, radically beautiful
in such a way that it supports conscient life in the first place?
So those are the biggest questions that humanity has always asked.
Today, thanks to recent advances in cosmology,
we might be on the brink of actually answering these questions,
for the first time, to understand
our place in the Universe or perhaps in the multiverse.
I had a series of beautiful slides which would have shown you
dark matter, dark energy,
and the way the entire of structure of the Universe is set up,
but unfortunately, we have a slight technical glitch today
so I can't show them to you;
but me, being Italian, I just wave my hands.
I am sure is going to be exactly the same.
In any case, dark matter and dark energy are invisible anyhow.
If we think back for a second to what our ancestors thought
about our place in the Universe,
everything was simple and easy for them.
Earth was at the center of the Universe,
the Sun, the Moon, the planets, the stars were all revolving all around us.
Easy, ordered; and wrong.
We now look back at these,
and we think this is a very primitive model for the Universe,
but actually it worked pretty well for thousands and thousands of years
until Galileo, in the 1600s, did a revolutionary thing.
He was the first man to do something completely new.
He took a telescope that he had put together himself
and turned it to the sky.
He saw the heavens in a completely new way
and understood that for example that Moon had craters on its surface.
It was not the perfect sphere that our ancestors thought.
He saw that Venus has got phases just like the Moon.
Therefore, there was something going on in the sky
for which the heavenly bodies were changing with time.
They were not immutable and forever the same.
He was the first person to discover the satellites
going around another planets but the Earth.
He discovered the four Galilean moons around Jupiter.
We now know that are many more moons going around Jupiter,
but he was the first to see them.
And after the Copernican revolution,
our place in the Universe was radically changed.
Earth was no longer at the center,
but the Sun was at the center of the Solar System
and Earth was but one of nine planets.
Eight now, because Pluto has been demoted to a minor planet;
eight planets going around the Sun.
In the last century or so,
our place in the Universe has been changing constantly,
and we found ourselves even more at the outskirts.
Not only we're not at the center of the Universe,
not only we're just a minor planet going around the Sun,
not only is our Solar System one spec of dust in the galaxy,
the Milky Way, that contains a 100 billion stars.
With recent technology, we've been able to map out the sky
to an unprecedented level of accuracy, precision, and depth.
With the Hubble Space Telescope, a flying telescope,
which is one of the best machines to look at the Universe that we have,
we can look at the sky in great detail.
If you look at a bit of the sky
- which is about the same size as the eye of a needle
held at arm's length; a tiny portion of the sky -
if you look at it through the Hubble Space Telescope,
you will see an incredible tapestry of galaxies.
About 5,000 galaxies fit into the eye of a needle.
Five thousand galaxies.
And each one of them has got a 100 billion stars just like the Sun,
and there are about 50 billion galaxies in the visible Universe,
so why are we here?
Why are we part of such a beautiful Universe
and yet, so apparently meaningless and lost
in all of this incredible, incredible Universe.
But there is actually more,
because it turns out all of this stuff that's out there
that we can now see with our telescopes and other instruments,
all of this stuff is actually itself only the tip of the iceberg.
Ninety-five percent of the Universe is actually dark, invisible,
and we have to find clever ways of actually bring it into the realm of light-
this invisible Universe.
All the stuff that I've been telling you about so far,
it's just really a tiny, tiny portion of what's out there.
Twenty five percent of the Universe is made of dark matter,
probably a new type of particle,
and 70% of the Universe is made of dark energy,
which is something really we don't know what it is.
We just call it dark energy
because it makes it sound as if we knew what we're talking about, but we don't.
So, what is this dark stuff out there,
and how do we know it's out there in the first place?
OK, so we have to step back for a second,
go back to Einstein and his idea about how the Universe is put together.
So Einstein was revolutionary in his thinking as we all know
because of one reason:
he was the first one to understand that space and time,
which we think about as being two separate entities, usually
- a clock ticks away at a regular rate,
a meter here is a meter on Jupiter, is a meter on the Andromeda Galaxy -
Einstein understood these two entities were not separate;
they were married together,
they were one single entity, which he called space-time.
Space-time is not immutable either, space-time is flexible, is malleable,
is changeable, and in fact, the shape of space-time
responds to the presence of matter in the Universe and vice versa.
The shape of space-time determines
the way matter and energy travel through the Universe.
So we think about the Moon:
for example, as going around the Earth in a curved orbit, for example,
because it's held by gravity as Newton thought as wrong.
Einstein says the presence of the Earth is changing the shape of space-time
in such a way that the shortest path, the straightest possible path
for the Moon to beyond is actually not a straight line.
It's a circle, it's the shape of space-time being changed
by the presence of the Earth's mass.
Gravity therefore, is geometry.
What does it tell us about the Universe?
The entire Universe is full of stuff.
And so, the way the Universe evolves with time,
the way it changes, and the way it expands with time
will depend on what is out there.
We now know, we have incredibly detailed proof
of the fact that the Universe started from a very dense,
very hot, very energetic beginning which we call The Big Bang.
Thirteen point seven billion years ago, it has been expanding ever since;
it is still expanding nowadays, but rather like the way an apple
that I throw upwards will at some point stop and then turn around and fall back
unless I give it enough speed
to leave the Earth and just get lost in space.
Well, rather like an apple that goes up and stops and comes back down,
the Universe started from a point,
it started, it expanded, it expanded, it expanded,
if there is enough gravity in the Universe,
if there is enough mass, enough stuff out there,
it will stop expanding, just turn around
and collapse back into The Big Crunch, the reverse version of The Big Bang.
Or it could go on and expand forever
slowing down as it does so but never quite turning around.
So you see that in a very general way understanding what's out there,
what is the mass in the Universe, and how much gravity there is,
what is the shape of space-time, if you like,
will enable us to understand what will be the destiny of all there is,
of the entire Universe.
There's another option there which I haven't talked about yet.
What if, instead of slowing down under the influence of gravity,
which is an attractive force which slows the Universe down,
what if we had something different, we had anti-gravity, dark energy,
something that instead of slowing the Universe down
makes it accelerating its expansion
so that the Universe will become bigger and bigger with time
and will become emptier and emptier with time?
That's a weird Universe to live in
and yet, it seems that this is precisely the Universe we happen to inhabit.
So things become even stranger
when you start thinking about what is this dark energy made of?
Dark matter is not a solved mystery yet,
but we're on our way of solving 25% of the Universe.
We think that dark matter is a new type of particle
beyond the type of particles that we know about,
and we're trying to catch this particle by producing it in the lab.
For example, at CERN,
The Large Hadron Collider will restart later this year,
and we'll try to catch, to produce some dark matter
and measure it in the lab.
Then we will know what is 25% of the Universe made of.
But what is this anti-gravity?
What is this dark energy which I told you
is making the Universe fly apart faster and faster with time,
and it's actually acting as a sort of anti-gravity?
And how do we know it's out there in the first place if we can't see it?
The way that we can tell the Universe is very special and very different,
is by looking at explosions of distant stars called supernovae.
Supernovae explosions are beautiful to see
and just picture them in your mind's eye because they're not here with me today,
but beautiful explosions are not different from a night table light.
In other words, they are pretty much the same throughout the Universe
and so if I take a night table,
and put it here a meter away and measure how bright it appears,
I'm going to get a certain reading.
If I put it ten meters away, it's going to look fainter to me.
And because it's the same night table by measuring how bright it appears,
I can work out how distant it is.
That's exactly the same way
we use supernovae explosions in the Universe
to measure distances in the cosmos to the furthest corners of the Universe.
What we find is the more distant supernovae are too faint.
Those are stars that look fainter than they should,
meaning that they have been expanded away
by an accelerated expansion of the Universe.
The Universe is growing bigger, faster with time,
and so we live in a Universe that's dominated
by this strange, repulsive force, all-pervasive force, dark energy.
Seventy percent of Universe is dark energy,
and we don't have the slightest clue as to what dark energy is.
But it gets worse,
because I'm a cosmologist, I am an astrophysicist,
so I'm interested in all these phenomena,
and I study them by using telescopes and satellites,
but I've got colleagues in particle physics,
who pretend that they understand the fundamental makeup of the Universe.
And they do, to great precision in some cases,
but except for this dark energy mystery,
because we can measure how much dark energy there is in the Universe,
and we can write it down on a piece of paper,
and then we can take this piece of paper and go with it
to our particle physics colleague and say,
"Well, now you go off and use the best tools,
the most advanced mathematical and physical concepts we have nowadays
to compute out of the first principles, out of our fundamental theories of reality
what do you think dark energy should be in the Universe?
How much dark energy should be out there?"
And then [inaudible], take some time, work it out on a piece of paper,
come back, and we'll compare numbers.
The two numbers, the one our theories predict should be out there,
and the one that we actually measured
thanks to our telescopes, and the supernovae explosions, and so on.
The two numbers are not quite the same.
They are different by a factor of 10 to the power 120,
so that's one with 120 zeros after it.
So it's, by no means, a small mistake.
So we truly don't understand this huge difference.
Completely wrong!
It's the most spectacular wrong prediction in the history of science ever.
That's our best theory of what the Universe is made of.
It gets weirder when you start to realize
that actually, of these 120 zeros, if you took out but one or two,
we wouldn't be here to talk about it today.
Because what happens is if dark energy was
only slightly, slightly, slightly different
from what it actually is,
the Universe would be expanding too fast. Galaxies would not form.
solar systems would not form, planets like Earth would not form,
and we would not be here to talk about it,
and so in this sense, it seems the Universe is a very special place.
It's finely-tuned, if not for us to be here,
then certainly finely-tuned for life to be here.
And so the question is: why?
Is there something very deep, very puzzling about this Universe
we do not understand?
Clearly there is.
The mystery deepens because we think
we understand the Universe very, very well on many other fronts.
For example, you might have heard a couple of weeks ago about
the BICEP telescope result.
It was all over the media if you follow science in the media.
You might have heard scientists have now discovered
the presence of gravitational waves in the Universe.
These are essentially little ripples in space-time
which have been left over for us to observe
by the very, very, very beginning of the Universe,
trillionth of a trillionth of a trillionth of a second
after the Big Bang,
and so nowadays, we can reconstruct our Universe
all the way to the very beginning,
except we don't understand why is it so special?
Why is this dark energy exactly what it is?
One possibility is actually there is more to the Universe than we think.
It could be that we live
not in a Universe but actually, in a multiverse.
The idea of the multiverse is we are in one bubble, a big bubble,
a huge bubble, all the stuff that I talked to you about.
It's all in our corner of the multiverse, but there are many, many other bubbles.
And each bubble is different.
Some bubbles will have dark energy, some won't.
Some will have stars, some won't.
Some will have galaxies, some won't. Some will have planets, some won't.
Some will have human beings and essentially, life,
and most won't to have that.
But we being here and observing the Universe all around us,
we are bound to be
in a corner of the multiverse that's supportive for life,
because we couldn't be anywhere else, clearly.
All the other corners of the multiverse are empty in the void of life
and clearly, we as essential life forms, we couldn't be in these other corners.
We have to be here.
So our Universe is not special in a sense.
It's just one of a huge collection of universes.
And how many of them are there out there?
Well, about 10 to the 500, we believe.
So how big is - being one out of 10 to the 500,
that's 10 with 500 zeroes,
it's rather like if you take 400 coins, and you flip them all at once -
fair coins - and they all land heads.
So that's the probability of us being here in this special place.
Strange, beautiful, and totally incomprehensible.
But perhaps, just perhaps, one day, we will be able to crack it.
Thank you.
(Applause)
Thank you, Roberto.