topical question.

BRADY: If I put my hand in front of the beam at the Large Hadron Collider,

(laughter)

what would happen to my hand?

PROF. BOWLEY: Don't know.

Don't know.

Don't know.

PROF. COPELAND: Not a good idea.

And wouldn't recommend it.

And in fact, of course you can't.

The beam is a hundred meters underground.

PROF. BOWLEY: Well I really don't know. I mean you've got these things coming together

and you would have thought it'd be extremely dangerous.

Somebody would yank you out of there before you could do that.

PROF. EAVES: I th...

gosh ...

um ...

I don't think you'd feel very much.

PROF. MERRIFIELD: That's a good question. "I don't know," is the answer.

Probably be very bad for you.

And they'd be very cross with you

as well, I can say.

PROF. MORIARTY: I don't know the total amount of energy that'd be distributed,

and I don't know the energy density

PROF. COPELAND: The beam is sending protons in one direction,

and of course there's a counter-beam going in the other direction.

These protons are going to have an energy of the order,

when it's reached its maximum,

of order of 7 tera electronvolts.

That's about the energy of a mosquito.

So it's not a lot, right? It's of one proton.

But the difference is this energy is like

concentrated into a volume a million million times smaller than the mosquito.

So it's like a really sharp pin prick.

But it's still only one proton.

Unfortunately there are

something like 3000 bunches

going around the beam

around the accelerator.

Each bunch has a hundred billion protons.

PROF. EAVES: But by the scale of energies that we notice, it wouldn't

it wouldn't be that noticeable.

I'd be ... interesting ... I'd ...

Would I put my hand in the beam?

I'm not sure about that.

PROF. MORIARTY: 'cause the other thing, 'cause I've worked at synchrotrons

And the real problem with,

if you're giving off synchrotron radiation

because you've got particles traveling very close to the speed of light,

if they're accelerating then you're giving off synchrotron radiation.

And synchrotron radiation is very nasty.

PROF. COPELAND: When they collide them together there are something like 600 million collisions

per second.

So there's a lot of collisions go on.

The total energy stored in the beam,

whereas the energy in the individual proton may not be very high,

the total energy stored in that beam is about

300

mega joules.

That's like the energy of an aircraft carrier moving at 11 knots.

So now

that beam is going to come around.

It's suddenly gonna hit your hand, or your body,

however,

whatever you put in. And it's got to deposit that energy.

So it's like being hit by a massive object.

And I don't think you'll survive very much.

BRADY: Because it's just hitting such a small space

won't it just drill the ultimate hole through your hand?

Why would it start affecting other parts of your body?

PROF. COPELAND: And that's where I...

that's why I was hesitating of course at the beginning,

'cause I don't really know

what will happen.

When they collide

they

the beam has a ranges from a width of about a millimeter,

down to a width of about

I think

um

like a fifth of a hair

hair's width, when they actually collide the beam.

So they're really narrow when they collide them.

When they're not being collided they're about a millimeter.

So they're going to come in and crash in here.

So I have thought maybe they'll just shoot through, but

but it seems to me that what's got to happen

is this energy is all got to be dumped.

because it's now hitting a lot of matter.

Normally it doesn't hit anything

it's a real, it's a

almost a total vacuum in in those things,

in the accelerator ring.

But now

there's this big high density region,

and so all these particles, it seems to me, will just

hit in there and just start

bombing out. So that's why

I thought it might be a bit more dramatic

than a little pinprick going straight through you.

PROF. EAVES: There's a vacuum there so that might have some unpleasant consequences

on the,

on my hand,

pressure

pressure change.

But I don't think it would have a huge effect.

BRADY: If there was a galaxy made completely out of antiparticles,

would it behave the same way as ours?

PROF. COPELAND: So the main thing that goes on in galaxies is gravitational

right? And gravity doesn't care whether you're a particle or an antiparticle,

gravity cares about the fact you've got a mass.

And so as far as gravity is concerned,

as far as forming this antigalaxy if you like,

I think that dynamics would be the same.

With regard to the actual interactions,

assuming that the antihydrogen can form,

for example that's an antielectron and an antiproton,

then I suppose the same basic processes can take place.

They will emit light when they interact with one another

because the light is just an emission of energy.

And as long as that's still taking place and energy is being lost

then you'll still have light.

PROF. MERRIFIELD: The reason we know the universe doesn't have such galaxies in it

is that actually even the empty space between galaxies isn't completely empty.

And so this galaxy would actually start interacting with its neighbors,

and of course when the matter comes into contact with the antimatter,

it would annihilate, there'd be a big burst of gamma rays.

And the fact that we don't see a very large gamma ray background in the entire universe

tells us that the universe isn't actually full of antimatter galaxies as well as matter galaxies.

BRADY: At the point when the universe came into existence

so did all the forces and physical constants

which affect the universe today.

However if the universe was to come into existence again,

like another Big Bang,

would we have all the same forces and the same physical constants?

PROF. MORIARTY: Ah, ok,

so this is the sort of multiverse idea, and the fact that we have

we've got a wide range of different universes with different physical constants.

PROF. COPELAND: Ooo, that's a good question.

um ...

uh ...

PROF. MERRIFIELD: That's a difficult question to answer,

'cause of course you can't do the experiment.

You know physicists like to do an experiment

and we're not allowed to make universes,

or at least we haven't figured out how to do it yet.

PROF. EAVES: The idea now is that

little bubble universes can

can pop up everywhere.

And it's thought that right in the early stages,

the fundamental constants can be different.

And the question then arises,

what would it be like living in a universe

where the fundamental constant were different,

where the mass of the electron is different,

or its charge,

or Planck's constant were different, and so on.

And this is a fascinating question.

PROF. MERRIFIELD: So it's not clear, there's even

there are theories that actually say that the universe didn't come into being as a single universe.

There's actually lots and lots of universes were created, a thing called the multiverse.

And in some of them the kind of the laws of physics work, and in some of them they don't.

And so the ones where the laws of physics work kind of thrive and take over.

And so it could be that there may be other universes out there

that have very different laws of physics

different values for physical constants and so on.

So it's ... but

but it's a sort of ...

again, it's sort of on the realms of philosophy rather than physics

because it's not something you can really do an experiment to test.

PROF. BOWLEY: (chuckles)

Would we get the same forces of physics?

Now that's

that's really beyond anybody's imagination.

PROF. MORIARTY: I think that the current understanding is,

in terms of a multiverse situation at least,

that there could be other universes with radically different physical constants.

PROF. BOWLEY: I mean Dirac said that God thought that

God created the universe with beautiful mathematics.

And you're asking the question,

if He does it again, or She does it again,

is it going to be the same mathematics,

or is He going to twist it around in some way?

So I really don't know the answer to that question.

I don't know that you could ever begin to answer that question.

PROF. COPELAND: What we can't explain, even with

within the context of string theory at the moment,

is the relative magnitude of those forces.

We still don't know why

gravity is so weak compared, say, to electromagnetism. We

we can measure it

and we can understand in terms of the the constants,

but we can't predict those constants.

And the electric charge, why it's got value it has.

The masses of the particles, why they have the values they have.

So until we can do that

and definitively say, this comes from

this is a unique solution that can have no other values,

then you can't say that if

if in a parallel universe it suddenly popped up

the universe popped up in it

that you would have all the same coupling.

PROF. EAVES: But it turns out that

that we have to be very careful about how many of these constants

that we could imagine turning around.

Because there are certain scenarios that if the constants were

very much different from what they are

we wouldn't be around to

to observe it.

So certain values of the constants

are just not conducive to life, or

and certainly not to intelligent life.

So for example,

gravity has to be extremely extremely weak.

BRADY: What would happen to the Earth

if one of the closest stars,

like Alpha Centauri is the example we were given,

went supernova,

would the earth be protected by its magnetic field?

DR. BAUER: Alpha Centauri won't go supernova.

(laughs)

If a close star went supernova, then there would be

radiation coming at all wavelengths.

But

turns out our atmosphere does a very good job of

deflecting that radiation.

I mean radiation comes from the Sun all the time

but we're not affected by right

by x rays, for instance.

MEGHAN GRAY: Well this is a common doomsday scenario right?

Supernova explosions are some of the biggest

most catastrophic events that we know of in the universe.

So it's very reasonable to say

"What would happen if one happened nearby?"

We know that the Sun will not go supernova.

It's not the right type of star,

it's not massive enough to go supernova.

But maybe there are some stars in our neighborhood that might.

We actually know that of the type of stars

that are likely to end their lives in a supernova,

there aren't that many that are that nearby.

So for something called a Type II supernova,

which is when a star just gets really massive and blows itself up,

one of the nearest candidates for that is actually the star Betelgeuse.