Dancing in the Dark: The End of Physics? Page #3

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you typically find among

experimentalists.

The fact is, though, that

though the hunt for dark matter has

so far proved to be the world's

least productive experiment,

the world's large telescopes are

providing increasing evidence that

the elusive WIMPs, whatever they

are, really are the dark matter.

This array forms one of the world's

largest telescopes.

In fact, its name is the VLT -

the Very Large Telescope.

We're in the Atacama Desert in Chile,

at the top of a big mountain at the

European Southern Observatory,

so there are four massive telescopes

that we use to stare

into deep space

and they give us

even more information

on the dark matter that

fills our universe.

The Very Large Telescope has

produced some staggering images,

but perhaps one of the most

compelling is this one.

This image shows a large

cluster of galaxies.

Such large objects can bend light

of the galaxies that are behind it.

We call this technique

gravitational lensing.

These arcs are distant galaxies

behind the cluster

that have been brightened

and stretched

as the light passes through

the cluster and gets bent.

And what's very interesting

is this technique

allows us to measure

the mass of the lens,

and when we do that

using these arcs,

we find the mass of the lens

is about 100 times more

than the light we see in this image.

But second of all,

and more importantly,

it tells us that the dark matter

that we can't see

is more distributed and acts as

a dark matter cloud of particles.

So this is conclusive evidence

of dark matter,

but it also is conclusive evidence

that that dark matter

must be more spread out than

the galaxies we see here,

and in fact it tells us it has to be

a cloud of dark matter particles,

not just individual objects

in the cluster.

So here's the thing.

Dark matter has to have mass.

Remember, that's the reason it has

to be there in the first place -

all those speeding stars.

And it seems that

it's not just matter we can't

see because it's not shining.

So it has to be some

kind of other stuff

that we can't see by definition.

And more than that, it has to be

some kind of material

that's capable of clumping together

in something like a gas.

And all this adds up to one thing -

we're looking for a new particle.

And when it comes to new particles,

there's really only one place

to come - Switzerland...

and France.

This place might look

like a third-rate

provincial technical college,

but if the hunt for dark matter

has taught us nothing else,

it has shown that a book should

never be judged by its cover.

And so it is with this place,

because beneath

the dismal architecture

lies the most exciting piece of

scientific apparatus ever created.

This is CERN, the world's

biggest physics lab,

home to the Large Hadron Collider,

the largest particle accelerator

on the planet.

It's here where scientists

investigate what stuff is made of...

by smashing it apart.

Protons are fired around its

27-kilometre-long circular tube

in opposite directions

at nearly the speed of light,

before being smashed together.

EXPLOSION:

Waiting to trawl through the debris

resulting from those collisions

are two-thirds of the world's

particle physicists.

One of them is Dave from Birmingham.

He is in charge of

one of the huge detectors

which record each

and every collision.

I have to admit, I come

down here a few times a week

and pretty much every time I come in,

my jaw still drops when

I see ATLAS in front of me.

I mean, it's incredible that

we built this detector

and that we're able to operate it.

So the whole detector itself

is about eight or nine storeys tall,

and so we're about

halfway up at the moment,

so four or five storeys

above the base of the detector.

The total weight of the detector

is about 7,000 tonnes,

which is about the same as

the weight of the Eiffel Tower.

While it might weigh the same,

the ATLAS detector

shares few other characteristics

with Paris's most famous flagpole.

Fitted with 100 million detectors,

it produces the equivalent

of a digital photograph

40 million times a second,

providing Dave and his team

with a permanent record

of the precise nature

of each particle's demise.

When the protons collide,

most of the time the particles

they produce... Nearly always

some new particles are created,

but they tend to be

low-mass particles so they tend

to be the familiar quarks,

the familiar hadrons, the protons,

the neutrons, pions,

which are also light hadrons.

But sometimes, very rarely,

you produce these much

more massive particles,

and that's where we're looking for.

So if we are producing

Higgs particles or we're producing

even more massive particles -

which would be ones

we don't know about,

they would be ones beyond

the standard model -

these are the guys that

we're really looking for.

The LHC has been switched off for

two years while it's been upgraded.

Now it's been switched on again

and will run at twice

the energy it did before.

It might be that more

new particles might emerge.

If they do, they could well be

the elusive WIMPs,

one of which could well be

the dark matter.

The idea is that we're looking for

imbalances of momentum in the event

that signify that there are

unobserved particles

going off with high energy

carried out of the detector.

So what you're actually seeing is

an absence of something?

What we're seeing is

an absence of something,

an imbalance of something, yes. It's

some particles that we can't observe

and we can infer that they're there

by looking at the rest of the event.

So that's beautiful, isn't it?

That you can find dark matter

which you can't by definition see

and you discover it by

not seeing it? Exactly, yes.

On the face of it,

this is an extraordinary,

not to say logically

contradictory idea,

that ordinary matter

smashes into itself

to produce invisible matter

that can't readily be detected

because it only interacts weakly

with the stuff that produced it

in the first place.

And yet this is precisely

what is being predicted

in another part of CERN

by theoretical physicists

like John Ellis.

My job as a theoretical physicist

is to try to understand

the structure of matter, what makes

up everything in the universe,

the stuff that we can see,

the stuff that we can't see.

It's the stuff we can't see

that is currently occupying

most of John's time.

So the astronomers tell us that

there are these dark matter particles

flying around us all the time,

between us as we speak.

But they've never detected

these things.

Now, we were going to try to

produce them at the LHC.

It sounds like a bold statement

but it's based on a very

conventional idea -

namely, that everything

we can see and can't see

has its origins at the point

of the Big Bang

when things were as hot

as it's possible to be.

And it's only in the LHC that,

at least in theory, energy levels

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