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  • Well this is a very interesting and deeper

  • 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