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 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.
It's a famous word, and it's also a famous star.
It's actually the shoulder of Orion,
one of the well known constellations.
It's very red, and we know that it's actually
probably nearing the end of its life.
Maybe not on the time scale of humans watching it,
but it could be thousands,
it could be just millions of years away.
DR. BAUER: Still, the main damage
we wouldn't get very much optical damage,
other than looking at it.
So
if a star supernovas it'll get very bright
and it could affect our eyes,
just as when you look at the Sun it will affect our eyes.
MEGHAN: But even then,
Betelgeuse, which is about 400 light-years away,
it's still too far away,
luckily, to probably cause us enough damage.
If it went it would be quite spectacular.
We would probably see it with the naked eye in the daytime.
That would be the visible light output.
We'd have to worry about something like gamma ray radiation,
but even then it's it's probably too far away,
thankfully, to do much damage.
BRADY: Do you have a favorite symbol and why?
PROF. COPELAND: Oh, my favorite symbol?
I don't know if we've done the favorite one yet.
But my favorite symbol at the moment is probably
lambda, the cosmological constant,
because it's this enigmatic quantity
which could actually be driving the acceleration of the universe today.
And no one knows why it's got the value it has.
We should do
we should do a video on it.
PROF. EAVES: Oh, the fine structure constant alpha,
1 over 137.0599, my favorite.
Look at our Sixty Symbols video on it,
on alpha.
MEGHAN: I quite like the symbol for infinity
because it's a cool concept.
It's a really hard thing to get your head around.
But also it's just a nice symbol.
And it kind of kind of packages
packages up what it means.
You know you've got this infinite loop
that just keeps  going round and round and round,
so it kind of does what it says on the tin.
PROF. MERRIFIELD: I guess my favorite symbol is a slightly unusual one
which is a symbol called upsilon.
Greek letter looks like a seagull,
and it's used by astronomers
to measure the mass-to-light ratio of things,
how much mass there is and how much light there is.
BRADY: And you've discussed it on Sixty Symbols.
PROF. MERRIFIELD: And we made a video, and
it's not one of the most popular ones I'm sad to relate, yes.
DR. BAUER: I think my favorite symbol is the infinity symbol.
I really like the concept of infinity.
Even though I think about it a lot, it just
blows my mind every time.
And I just like the little infinity,
can just kind of go on forever.
PROF. MORIARTY: So I guess aesthetically
or in terms of the background of the same,
but that's what the symbol actually means,
I guess those are two separate questions,
aesthetically either psi, the pitchfork one,
or big sigma, which is sort of this sort of
looks to me almost like a strange sort of Pac-Man type  thing.
In terms of what the symbol means and related to my work,
I guess it's gotta be Planck's constant.
Largely because Planck's constant is fundamentally embedded
in quantum mechanics, the study of small things.
PROF. BOWLEY: Well I've thought about this
and I will go for a "ket" ...
no, no for a "bra", because
Dirac invented this wonderful notation.
There's something like that which he called a "bra",
and something like that which he called a "ket",
and the two together made a bra-ket,
a bracket.
And he was really proud of it
because this word "bra" is in the English dictionary.
It is an actual word in English, and he invented it.
And he's proud of it.
He was proud of it because he was in the dictionary,
not realizing it had other connotations.
