Transcriber: Emma Gon Reviewer: Shlomo Adam
I'd like you to imagine the scene.
I am giving a talk to room full of around 200 eminent astrophysicists.
But there has been a bit of a child care crisis.
Child number two is sat grumpily in the front row.
I am about to present a new result,
and still to this day, I don't know why,
he decided this was the time to jump up,
but he jumped up and he shouted out,
"My mommy doesn't know what she's talking about."
(Laughter)
For a four-year-old boy, he really is quite astute.
I specialize in observing the dark side of our Universe,
the stuff that we can't see or touch but that we know it is there,
because of the effects on the things that we can see,
like all of these galaxies in the Universe,
and all of the stars that are swirling around inside them.
These stars and galaxies
are made of the same chemicals that you and I are made up of,
but this type of matter
accounts for a very, very small fraction of our Universe,
less than 5%.
And to be honest with you,
we physicists don't understand the dark side.
We don't understand what makes up 95% of our universe
and this is one of the major challenges facing science today
because it is widely believed
that if we can understand the nature of the dark side of our Universe,
we're going to have to bring about some sort of revolution in physics
that will forever change our cosmic view.
So you see, to some extent, my son was right.
I don't always know what I am talking about.
But that's the beauty of science.
We have our theories,
but we are never going to be able to prove our theories,
so our job is to try and disprove them to get better theories,
to better understand the world around us.
So let me tell you about our best theories,
about the dark side of the Universe.
There are two dark entities:
dark matter and dark energy.
And these two dark siblings are currently fighting out
a cosmic battle of epic proportions
with the gravity of dark matter trying to pull everything together
and its evil sister, dark energy, undoing all that good work
by causing the expansion of our universe to get fast and faster each and every day.
Tºhis picture that you can see behind me
is the result that caused my son's abrupt outburst.
It is the widest map of dark matter that we've ever made,
and we made it by looking at the way
the dark matter's gravity bends the whole of space and time.
Imagine that you're looking up at the night sky,
this whole map here spans
about the size of your palm on the sky.
And what you can see
is that the dark matter in our Universe likes to clump together.
And we can go and look,
and what we find is that the galaxies that we can see
live inside these giant clumps of dark matter.
Indeed,
there is a giant clump of dark matter around our own Milky Way Galaxy
and all of the stars that are currently swirling around.
If we didn't have a giant clump of dark matter there,
then those stars would simply fly out into our Universe.
So we need dark matter to keep our own galaxy bound together.
If there is a giant clump of dark matter surrounding our own galaxy,
then we can conclude there must be some dark matter in this room.
So I'm hoping that you'll indulge me this afternoon
in a little TEDx science experiment
to see if we can catch an elusive particle of dark matter.
First of all, we're going to need to construct
our science experiment equipment.
So if you could be so kind as to put your thumb and finger together
to form your dark matter butterfly net.
Excellent! I can see all your dark matter butterfly nets.
And what we're going to do now
is try and catch an elusive particle of dark matter
and count together to five,
one, two, three, four, five.
Keep your dark matter butterfly net up,
if you managed to catch any dark matter particles.
Our theory about dark matter
is that the dark matter particles are what we call
a weakly interacting matter particle, or a WIMP.
They don't interact with the particles that we are made up of,
and that's why you didn't feel any of the dark matter particles
that were flying through your dark matter butterfly nets.
But in those five seconds, about a billion dark matter particles
flew through each and every one of your dark matter butterfly nets.
Indeed, in the time that it's taken for you to come into this auditorium,
sit down and listen to the talk so far,
there's probably been one direct collision
between the dark matter particle and a particle in your body.
Ouch!
But you don't feel them.
Particle physicists are currently building
giant dark matter butterfly nets deep under the ground
to try and catch one of these elusive particles.
And how successful they are,
it just depends on how much of WIMP these particles really are.
So, that is our theory about dark matter,
but what about the evil sister dark energy
that is causing the expansion of our universe
to get faster and faster each and every day?
In order to understand the simplest theory about dark energy,
we first of all we need to think about the physics of nothing.
There are wide volumes in our universe
where there is absolutely nothing,
no galaxies, no gas, a complete vacuum,
nothing there;
apart from a swarm of virtual particles
that can simply pop in and out of existence
and in doing so,
add energy into our universe that fuels its accelerated expansion.
And if you like, you can think of this as a perpetual motion machine
because the faster our universe expands, the more vacuum is created,
and the more opportunity there is
for these virtual particles to pop into existence,
thereby fueling further expansion.
And this beautiful, and simple, elegant theory has only one small problem
in that you can calculate exactly how much energy this would produce
and it's a one with 120 zeros after it bigger
than the energy that we currently measure.
That's the problem with that theory
and that's what is leading us to look at other theories.
It could be
that just as Einstein came along and looked at Newton's theory of gravity
--with the apple falling on his head and Einstein said:
"Hang on a minute, that's not right." --
and came up with his Theory of General Relativity,
it could be that we need some new bright spark
to come along, thinking in abundance,
and come up with a new theory of gravity
that explains the Universe as a whole.
In the next 10 years,
we're going to be launching a new telescope into outer space,
it's going to survey the whole sky
and produce dark matter maps of the whole of our universe.
And with this exquisite data set
we're going to be able to confront our theories about the dark universe.
I've got this feeling, that by the time I'll retire,
I'll look back at this TEDx talk,
and I'll think back to my son's comment and laugh about how right he was.
So I am quite sure our theories about the dark universe will have changed.
But that's the joy of thinking in abundance
and the beauty of science as a whole.
Thank you.
(Applause)