Kind: captions
Language: en
the following is a conversation with
Harry Cliff a particle physicist at the
University of Cambridge working on the
Large Hadron Collider beauty experiment
that specializes in investigating the
slight differences between matter and
antimatter by studying a type of
particle called the beauty quark or B
quark in this way he's part of the group
of physicists who are searching for the
evidence of new particles that can
answer some of the biggest questions in
modern physics
he's also an exceptional communicator of
science with some of the clearest and
most captivating explanations of basic
concepts in particle physicists that
have ever heard so when I visit in
London I knew I had to talk to him and
we did this conversation at the Royal
Institute lecture theatre which has
hosted lectures for over two centuries
from some of the greatest scientists and
science communicators in history for
Michael Faraday to Carl Sagan this
conversation was recorded before the
outbreak of the pandemic for everyone
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support this podcast and now here's my
conversation with harry cliff
let's start with probably one of the
coolest things that human beings have
ever created the Large Hadron Collider
ohc what is it how does it work
okay so is essentially this gigantic 27
kilometer circumference particle
accelerators this big ring it's buried
100 100 meters underneath the surface in
the countryside just outside Geneva in
Switzerland and really what it's for
ultimately is to try to understand what
are the basic building blocks of the
universe so you can think of it in a way
as like a gigantic microscope and and
the analogy is actually fairly precise
so gigantic microscope effectively
except it's a microscope that looks at
the structure of the vacuum in order for
this kind of thing to study particles
which are microscopic entities it has to
be huge yes gigantic Waxhaw so what do
you mean by studying vacuum okay so I
mean so particle physics as a field is
kind of badly named in a way because
particles are not the fundamental
ingredients of the universe they're not
fundamental at all so the things that we
believe are the real building blocks of
the universe are objects invisible fluid
like objects called quantum fields so
these are fields like like the magnetic
field around a magnet that exists
everywhere in space they're always there
in fact actually it's funny they were in
the wrong institution because this is
where the idea of the field was
effectively invented by Michael Faraday
doing experiments with magnets and coils
of wire so he noticed that you know if
he was very famous experiment that he
did where he got a magnet and put it on
top of it a piece of paper and then
sprinkled iron filings and he found the
iron filings arrange themselves into
these kind of loops of which was
actually mapping out the invisible
influence of this magnetic field which
is a thing you know we've all
experienced we're all felt held a magnet
and or two poles the magnet and pushing
together and felt this thing this force
pushing back so these are real physical
objects and the the way we think of
particles in modern physics is that they
are essentially little vibrations little
ripples in these otherwise invisible
fields that are everywhere they fill the
whole universe you know I don't
apologist perhaps for the ridiculous
question are you comfortable with the
idea of the fundamental nature of our
reality being fields because to me
particles you know a bunch of different
building blocks makes more sense sort of
intellectually so visually like it's it
it seems to I seem to be able to
visualize that kind of idea easier yeah
are you comfortable psychologically with
the idea that the basic building block
is not a block but a field I think it's
um I think it's quite a magical idea I
find it quite appealing and it's well it
comes from a misunderstanding of what
particles are so like when you when we
do science at school and we draw a
picture of an atom you draw a like you
know nucleus with some protons or
neutrons these little spheres in the
middle and then you have some electrons
are like little flies flying around the
atom and that is a completely misleading
picture of what an atom is like it's
nothing like that the electron is not
like a little planet orbiting the atom
it's this spread out wibbly-wobbly
wave-like thing and we know we've known
that since you know the early 20th
century thanks to quantum mechanics so
when we carry on using this word
particle because sometimes when we do
experiments particles do behave like
they're little marbles or little bullets
you know so in the LHC when we collide
particles together you'll get you know
you'll get like hundreds of particles
will fly out through the detector and
they all take a trajectory and you can
see from the detector where they've gone
and they look like they're little
bullets so they behave that way um you
know a lot of the time but when you
really study them carefully you'll see
that they are not little spheres they
are these virial disturbances in in
these underlying fields so this is this
is really how we think nature is which
is surprising but also I think kind of
magic so here we are our bodies are
basically made up of like little knots
of energy in these invisible objects
that are all around us and what what is
the story of the vacuum when it comes to
LHC so what why did you mention the word
vacuum okay so if we just if we go back
to let us the physics we do know so
atoms are made of electrons which were
discovered 100 or so years ago and then
nucleus of the atom you have two other
types of particles there's an up
something called an up quark and a down
quark and those three particles make up
every atom in the universe so we think
of these as ripples in fields so there
is something called the electron field
and every electron in the universe is a
ripple moving about in this electron
field the electron field is all around
we can't see it but every electron in
our body is a little ripple in this
thing that's there all the time and the
quark feels the same so there's an up
quark field and an up quark isn't a
ripple in the up quark field and the
down quark is a little ripple in
something else called the down quark
field so these fields are always there
now there are potentially we know about
a certain number of fields in what we
call the standard model of particle
physics and the most recent one we
discovered was the Higgs field and the
way we discovered the Higgs field was to
make a little ripple in it so what the
LHC did it fired two protons into each
other very very hard with enough energy
that you could create a disturbance in
this Higgs field and that's what shows
up as what we call the Higgs boson so
this particle that everyone was going on
about eight or so years ago is proof
really the particle in itself is I mean
it's interesting but the things really
interesting is the field because it's
the the Higgs field that we believe is
the reason that electrons and quarks
have mass and it's that invisible field
that's always there that gives mass to
the particles the Higgs boson is just
our way of checking it's there basically
and so the Large Hadron Collider in
order to get that ripple in the Higgs
field you it requires a huge amount of
energy
yes opposes so that's why you need this
huge that's why size matters here so
maybe there's a million questions here
but let's backtrack why does size matter
in the context of a particle collider so
why does bigger allow you for higher
energy collisions right so the reason
well it is kind of simple really which
is that there are two types of particle
accelerator that you can build one is
circular which is like the LHC the other
is a great long line so the advantage of
a circular machine is that you can send
particles around a ring and you can give
them a kick every
and they go round so imagine you have a
is actually a bit of the LHC that's
about only 30 meters long where you have
a bunch of metal boxes which have
oscillating to million volt electric
fields inside them which are timed so
that when a proton goes through one of
these boxes the field it sees as it
approaches is attractive then as it
leaves the box it flips and becomes
repulsive and the proton gets attracted
then kicked out the other side so it
gets a bit faster so you send it but
then you send it back round again and
it's incredible like the timing of that
the synchronization that wait really
yeah yeah yeah yeah that's I think
there's going to be a multiplicative
effect on the questions I have is that
okay let me just take that attention for
a second how the orchestration of that
is that a fundamentally a hardware
problem or software a problem like what
how do you get that I mean I might so I
should first of all say I'm not an
engineer so the guys I did not build the
LHC so they're people much much better
at this stuff than I for sure but maybe
but from from your sort of intuition
from the the the echoes of what you
understand you heard of house design
what's your sense how what's the
engineering aspects that the
acceleration bit is not challenging okay
okay there is always challenges
everything but basically you have these
the beams that go around you like see
the beams of particles are divided into
little bunches so they're called their
bit like swarms of bees if you like and
there are around I think it's something
of the order 2000 bunches spaced around
the ring and they if you were if you're
a given point on the ring counting
bunches you get 40 million bunches
passing you every second so they come in
like you know just like cars going past
from a very fast motorway so you need to
have if you're a electric field that
you're using to accelerate the particles
that needs to be timed so that as a
bunch of protons arrives it's got the
right sign to attract them and then
flips at the right moment but I think
the the voltage in those boxes
oscillates at hundreds of megahertz so
the beams at like 40 megahertz but is
oscillating much more quickly than the
beam so and I think you know it's
difficult engineering but in principle
it's not you know a really serious
challenge the bigger problem this
probably engineers like screaming at
ureña probably yeah
what
okay so in terms of coming back to this
thing why is it so big well the reason
is you wanna get the particles through
that accelerating element over over
again so you want to bring them back
round that's why it's round the question
is why couldn't you make it smaller well
the basic answer is that these particles
are going unbelievably quickly so they
travel at 99.999999 1% of the speed of
light in the LHC and if you think about
say driving your car round a corner high
speed if you go fast you need a very you
need a lot of friction in the tires to
make sure you don't slide off the road
so the the limiting factor is the how
powerful a magnet can you make because
it's what we do is magnets are used to
bend the particles around the ring and
essentially the LHC when it was designed
was designed with the most powerful
magnets that could conceivably be built
at the time and so that's your kind of
limiting factors if you wanted to make
the machines smaller that means a
tighter bend you need to have a more
powerful magnet so it's this toss-up
between how strong your magnets versus
how big a tunnel can you afford the
bigger the tunnel the weaker the magnets
can be the smaller a tunnel the stronger
they've got to be okay so maybe can we
backtrack to the data model and say what
kind of particles there are period and
maybe the history of kind of assembling
that the standard model of physics and
then how that leads up to the hopes and
dreams and the accomplishments of the
Large Hadron Collider yeah sure okay so
for all the 20th century physics in like
five minutes
yeah please okay so okay the story
really begins properly end of the 19th
century the basic view of matter is that
matter is made of atoms and the atoms
are indestructible immutable little
spheres like the things we were talking
about they don't really exist and
there's you know one atom for every
chemical element as an atom for hydrogen
for helium for carbon photon etc and
they're all different
then in 1897 experiments done at the
Cavendish laboratory in Cambridge where
I am still where I'm based showed that
there are actually smaller particles
inside the atom which eventually became
known as electrons these are these
negatively charged things that go around
the outside a few years later and it's
Rutherford very famous nuclear physics
nuclear physics shows that the atom has
a tiny nugget in the center which we
call the nucleus which is a positively
charged object so then by in light
1910-11 we have this model of the atom
that we learn in school which is you've
got a nucleus electrons go round there
fast forward you know a few years the
nucleus people start doing experiments
with radioactivity where they use alpha
particles that are spat out of
radioactive elements as as bullets and
they fire them other atoms and by
banging things into each other they see
that they can knock bits out of the
nucleus so these things come out called
protons first of all which are
positively charged particles about 2,000
times heavier than the electron and then
10 years later more or less neutral
particle is discovered called the
neutron so those are the three basic
building blocks of atoms you have
protons and neutrons in the nucleus that
are stuck together by something called a
strong force the strong nuclear force
and you have electrons in orbit around
that held in by the electromagnetic
force which is one of the you know the
forces of nature that's sort of where we
get to by late 1932 more or less then
what happens is physics is nice and neat
in 1932 everything looks great got three
particles and all the atoms are made of
that's fine but then cloud chamber
experiments these are devices that can
be used to the first devices capable of
imaging subatomic particles so you can
see their tracks and they use to study
cosmic rays particles that come from
outer space and bang into the atmosphere
and in these experiments people start to
see a whole load of new particles so
they discover for one thing antimatter
which is a sort of a mirror image of the
particles so we discovered that there's
also as well as a negatively charged
electron there's something called a
positron which is a positively charged
version of the electron and there's an
antiproton which is negatively charged
and and then a whole load of other weird
particle start to get discovered and no
one really knows what they are this is
known as the zoo of particles are these
discoveries fundamentally first
theoretical discoveries or the
discoveries in an experiment so like
well yeah what was the process of
discovery for these early it's a mixture
I mean that the early stuff around the
atom is really experimentally driven
it's not based on some theory it's
exploration in the lab using equipment
so it's really people just figuring out
hands-on with the fenomena figuring out
what these things are the theory comes a
bit later that there is that's not
always the case so in the discovery of
the anti-electron the positron that was
predicted from quantum mechanics and
relativity by a very clever theoretical
physicist called Paul Dirac who was
probably the second brightest you know
physicist of the 20th century apart from
Einstein but isn't as well anywhere near
as well known so he predicted the
existence of the anti electron from
basically a combination of the theories
of quantum mechanics and relativity and
it was discovered about a year after he
made their prediction what happens when
an electron meets a positron they
annihilate each other so if you when you
bring a particle in its antiparticle
together they they react well they react
they just wipe each other out and they
turn their mass is turned into energy
usually in the form of photons so you'll
get light produced so when you have that
kind of situation why why does the
universe exists at all if there's matter
in any matter oh god now we're getting
into the really big questions so you
want to go there now
yeah that's me maybe let's go there
later that's because I mean that is a
very big question yeah let's let's take
it slow with the standard model so okay
so there's matter and antimatter in the
30s mmm
so what else so matter antimatter and
then a load of new particles start
turning up in these cosmic ray
experiments first of all and they don't
seem to be particles that make up atoms
there's something else they all mostly
interact with a strong nuclear force so
they're a bit like protons and neutrons
and by in the 1960s in America
particularly but also in Europe and
Russia scientist article particle
accelerators so these are the
forerunners of the LHC so big ring
shaped machines that were you know
hundreds of meters long which in those
days was enormous you never you know
most physics up until that point had
been done in labs in universities you
know with small bits of kit so this is a
big change and when these accelerators
are built they start to find they can
produce even more of these particles so
I don't know the exact numbers but by
around 1960 there are of order a hundred
of these things that have been
discovered and physicists are kind of
tearing the hair out because physics is
all about simplification and suddenly
what was simple as
come messy and complicated and everyone
sort of wants to understand what's going
on it's a quick kind of a side and the
probably really dumb question but how is
it possible to take something like a
like a photon or electron and be able to
control it enough like to be able to do
a controlled experiment where you
collide it against something else
yeah is that is that that seems like an
exceptionally difficult engineering
challenge because you mention vacuum to
so you basically want to remove every
other distraction and really focus on
this collision how difficult of an
engineering challenge is that just to
get a sense and it's very hard I mean in
the early days particularly when the
first accelerators are being built in
like 1932 Ernest Lawrence builds the
first what we call the cyclotron which
is like a little celery - this big or so
there's another widely they're big
there's a tiny little thing yeah I mean
so most of the first accelerators were
what we call fixed argot experiments so
you had a ring you accelerate particles
around the ring and then you fire them
out the side into some target so is eat
that makes the kind of the colliding bit
is relatively straightforward to use
fire it whatever it is you want to fire
it out the hard bit is the steering the
beams with the magnetic fields getting
you know strong enough electric fields
to accelerate them all that kind of
stuff
the first colliders where you have two
beams colliding head-on that comes later
and I don't think it's done until maybe
the 1980s
I'm not entirely sure but it takes is
much harder problem that's crazy because
yet it's like perfectly you had them to
hit each other I mean we're talking
about I mean what scale it takes what's
this this I mean the temporal thing is a
giant mess but the spatially like the
size mmm it's tiny well to give you a
sense so the LHC beams the
cross-sectional diameter is I think
around a dozen or so microns so you know
ten ten millionths of a meters then a
beam sorry just to clarify a beam
how many is it the bunches that you
mentioned yes multiple poles is just one
part oh no no the bunches contained say
a hundred billion protons each so a
bunch is not really one shape they're
actually quite long they're like 30
centimeters long but thinner than a
human hair so like very very narrow long
sort of object so those are the things
so what happens in the LHC is you steer
the beams so that they cross in the
middle of the detector so the basically
have these swarms of protons are flying
through each other and most of that you
have so you have 100 billion coming one
way 100 billion another way maybe 10 of
them will hit each other okay so this
okay that makes a lot more sense that's
nice so there you're trying to use sort
of it's like probabilistically you're
not you can't make a single particle
collide with a single oh yeah so that's
not an efficient way to do it you'd be
waiting a very long time to get anything
yeah so you you're basically right see
you're relying on probability to be that
some fraction of them are gonna collide
yeah and then you know which is it's
it's a it's a swarm of the same kind of
particle so it doesn't matter which ones
each other exactly I mean that that's
not to say it's not hard you've got a
one of the challenges to make the
collisions work is you have to squash
these beams to very very the basic their
narrower they are the better because the
higher the chances of them colliding if
you think about two flocks of birds
flying through each other
the birds are all far apart in the
flocks there's not much chance that
they'll collide if they're all flying
densely together and they very much more
likely to collide with each other so
that's the sort of problem it's tuning
those magnetic fields getting them angry
feels powerful not that you squash the
beams and focus them so that you get
enough collisions that's super cool do
you know how much software is involved
here I mean it's sort of I come in the
software world and it's fascinating this
seems like it's a software is buggy and
messy and so like you almost don't want
to rely on software too much like if you
do it has to be like low-level like
Fortran style programming do you know
how much software isn't a Large Hadron
Collider I mean it depends at which
level a lot I mean the whole thing is
obviously computer-controlled so I mean
I I don't know a huge amount about how
the software for the actual accelerator
works but you know I've been in the
control center so has CERN there's this
big control room which is like
bit like a NASA mission control with big
banks of you know desk where the engine
is sit and they monitor the LHC because
you obviously can't be in the tunnel
when it's running so everything's remote
I mean one sort of anecdote about the
sort of software side in 2008 when the
LHC first switched on they had this big
launch event and then you know big press
conference party to inaugurate the
machine and about ten days after that
they were doing some tests and the this
dramatic event happened where a huge
explosion basically took place in a
tunnel that destroyed were damaged badly
damaged about about half a kilometer of
the machine but the story is viewed the
engineers here in the control room that
day they'd one guy told me the story
about you know basically there's all
these screens they have in the control
room started going red so these alarms
like you know kind of in software going
off and then they assume that lists all
wrong with the software cuz there's no
way something this catastrophic could
have could have happened yeah but I mean
when I worked on one when I was a PhD
student one of my Jobs was to help to
maintain the software that's used to
control the detector that we work on and
that was it's relatively robust not so
you don't want it to be too fancy you
don't want to sort of fall over too
easily the more clever stuff comes when
you're talking about analyzing the data
and that's where they're sort of you
know are we jumping around too much do
we finish for the standard model we
didn't know we didn't hurry and start
talking mark works we haven't talked
about me yet got to the messy zoo of
particles go back there if it's okay
okay that's take us the rest of the
history of physics in the 20th century
okay sure
okay so circa 1960 you have this you
have these hundred or so particles it's
a bit like the periodic table all over
again so you've got like like having a
hundred elements sort of a bit like that
and people try to start to try to impose
some order so Murray Gelman he's a
theoretical physicist American from New
York he realizes that there are these
symmetries in these particles that if
you arrange them in certain ways that
they relate to each other and he uses
these symmetry principles to predict the
existence of particles that haven't been
discovered which are then discovered in
accelerators so this starts to suggest
there's not just random collections of
crap there's like you know actually some
order to this under
a little bit later in 1960 again it's
round the 1960s he proposes along with
another physicist called George Zweig
the these symmetries arise because just
like the patterns in the periodic table
arise because atoms are made of
electrons and protons that these
patterns are due to the fact that these
particles are made of smaller things and
they are called quarks so these are the
particles they're predicted from theory
for a long time no one really believes
they're real a lot of people think that
there are kind of theoretical
convenience that happen to fit the data
but there's no evidence no one's ever
seen a quark in any experiment and lots
of experiments are done to try to find
quarks just try to knock a quark out of
her so the idea if protons and neutrons
say made of quarks you should work to
knock a quark out and see the quark that
never happens and we still have never
actually managed to do that really no so
the way but the way that it's done in
the end is this machine that's built in
California at Stanford lab Stanford
Linear Accelerator which is essentially
a gigantic three kilometer long electron
gun fires electrons almost speed of
light at protons and when you do these
experiments what you find is a very high
energy the electrons bounce off small
hard objects inside the proton so it's a
bit like taking an x-ray of the proton
you're firing these very light
high-energy particles and they're
pinging off little things inside the
proton that are like ball bearings if
you like so you actually that way they
resolve that there are three things
inside the proton which are quarks the
quarks that governance why I could
predicted so that's really the evidence
that convinces people that these things
are real the fact that we've never seen
one in an experiment directly they're
always stuck inside other particles and
the reason for that is essentially to do
with the strong force the strong forces
the force holds quarks together and it's
so strongly it's impossible to actually
liberate a quark so if you try and pull
a quark out of a proton what actually
ends up happening is that the you kind
of create this that this spring-like
bond in the strong force we've imagined
two quarks that are held together by
very powerful spring you pull it pull
and pull more and more energy gets
stored in there
bond like stretching a spring and
eventually the tension gets so great the
spring snaps and the energy in that bond
gets turned into two new quarks that go
on the broken ends so you started with
two quarks to end up with four quarks
so you never actually get to take a
quark out you just end up making loads
of more quarks in the process so how do
we again forgive the dumb question how
do we know quarks are real then well eh
from these experiments where we can
scatter you fire electrons into the
protons they can burrow into the proton
and knock off and they can bounce off
these quarks so you can see from the
angles the electrons come Alice you can
infer you can infer that these things
are there the quark model can also be
used it has a lot of successes you can
use it to predict the existence of new
particles that hadn't been seen so and
basically there's lots of data basically
showing from you know when we fire
protons at each other at the LHC a lot
of quarks get knocked all over the place
and every time they try and escape from
say one of their protons they make a
whole jet of quarks that go flying off
it has bound up in other sorts of
particles made of quarks so they're all
the sort of the theoretical predictions
from the basic theory of the strong
force and the quarks all agrees with
what we are seeing experiments we've
just never seen a an actual quark on its
own because unfortunate it's impossible
to get them out on their own
so quarks these crazy smaller things
that are hard to imagine a real so what
else what else is part of the story here
so the other thing that's going on at
the time around the sixties it's an
attempt to understand the forces that
make these particles interact with each
other so you have the electromagnetic
force which is the force that was sort
of discovered to some extent in this
room or at least in this building so the
first what we call quantum field theory
of the electromagnetic force is
developed in the 1940s and 50s by
Fineman Richard Feynman amongst other
people julian schwinger tominaga who
come up with the first what we call a
quantum field theory of the
electromagnetic force and this is where
this description of which I gave you at
the beginning that particles are ripples
and fields well in this theory the
photon the particle of light is
described as
people in this quantum field called the
electromagnetic field and the attempt
then is made to try what can we come up
with a quantum field theory of the other
forces of the strong force and the weak
the other third the third force which we
haven't discussed which is the weak
force which is a nuclear force we don't
really experience it in our everyday
lives but it's responsible for
radioactive decay is the force that
allows you know in a radioactive atom to
turn into a different element for
example and there are a few we've
explicitly mentioned but so there's
technically four forces yes I guess
three of them were being in in the
standard model like the weak there's the
strong and the electromagnetic and then
there's gravity in this gravity which we
don't worry about that because maybe
maybe we bring that up at the end yeah
gravity so far we don't have a quantum
theory of and if you can solve that
problem you win a Nobel Prize well we're
gonna have to bring up the graviton at
some point I'm gonna ask you but let's
let's leave that to the side for now so
those three okay fine man a
electromagnetic force the the quantum
field yeah where does the weak force
come in so so yeah well first of I mean
the strong force a bit easiest the
strong force is a little bit like the
electromagnetic force it's a force that
binds things together so that's the
force that holds quarks together inside
the proton for example so a quantum
field theory of that force is discovered
in I think it's in the sixties and it
predicts the existence of new force
particles called gluons so gluons are a
bit like the photon the photon is the
particle of electromagnetism gluons are
the the particles of the strong force
and so there's there's just like there's
an electromagnetic field there's
something called a gluon field which is
also all around us but these part
there's some of these particles I guess
the force carriers or whatever they
carry that well it depends how you want
to think about it I mean really the
field the strong force field the gluon
field is the thing that binds the quarks
together the gluons are the little
ripples in that field so that like in
the same way that the photon is a ripple
in there in the electromagnetic field
but the thing that really does the
binding is the field I mean you may have
heard people talk about things like
verge as you've heard the phrase virtual
particle
so sometimes in some if you hear people
describing how forces are exchanged
between particles they quite often talk
about the idea that you know if you have
an electron and another electron say and
they're repelling each other through the
electro bratok electromagnetic force you
can think of that as if they're
exchanging photons so they're kind of
firing photons backwards and forwards
between each other and that causes them
to repel therefore time is then a
virtual particle yes that's what we call
a virtual particle in other words it's
not a real thing doesn't actually exist
so it's an artifact of the way theorists
do calculations so when they do
calculations in quantum field theory
rather than there's no one's discovered
a way of just treating the whole field
you have to break the field down into
simpler things so you can basically
treat the field as if it's made up of
lots of these virtual photons but
there's no experiment that you can do
that couldn't detect these particles
being exchanged what's really happening
in reality is the electromagnetic field
is warped by the charge of the electron
and that causes the force but the way we
do calculations involves parties let's
say it's a bit confusing but it is
really a mathematical technique it's not
something that corresponds to reality I
mean that's part I guess of the fireman
diagrams yes is this virtual product
okay that's right yeah some of these
have mass some of them don't mm-hmm is
that is that what what does that even
mean not to have mass and maybe you can
say well which one of them's have mass
or which don't okay so and why is mass
important or relevant in this cupboard
in this in this field view of the
universe
well there are only two particles in the
standard model that don't have mass
which are the photon and the gluons so
they are massless particles but the
electron the quarks and they're a bunch
of other particles I haven't discussed
there's something called a muon and a
Tau which are basically heavy versions
of the electron that are unstable you
can make them in accelerators but they
don't form atoms or anything they don't
exist for long enough but all the matter
particles there are twelve of them six
quarks and six what we call leptons
which includes the electron and it's too
heavy versions and three neutrinos all
of them have mass and so do this is the
critical bit so the weak force which is
the third of these
quantum forces which is one of the
hardest to understand the force
particles of that force have very large
masses and there are three of them
they're called the W plus the W minus
and the Z boson and they have masses of
between 80 and 90 times that of the the
protons they're very heavy learn wow
they're very heavy things they're what
the heaviest I guess they're not the
heaviest the heaviest particle is the
top quark which has a mass of about 175
ish protons so that's really massive we
don't know why is so massive but they're
coming back to the weak force so that
the the problem in the 60s and 70s was
that the reason that the electromagnetic
force is a force that we can experience
our everyday live so if we have a magnet
and a piece of metal you can hold it you
know a meter apart if it's powerful
laughs and you'll feel a force whereas
the weak force only is becomes apparent
when you basically have two particles
touching at the scale of a nucleus so if
you get two very short distances before
this force becomes manifest it's not
doesn't we don't get weak forces going
on in this room they don't notice them
and the reason for that is that the
particle well the the field that
transmits the weak force the particle
that's associated with that field has a
very large mass which means that the
field dies off very quickly says you
whereas an electric charge if you were
to look at the shape of the electric
field it would fall off with this you
know this one called the inverse square
law which is the idea that the force
halves every time you double the
distance no sorry it doesn't have it
quarters every time you see every time
you double the distance between say the
two particles whereas the weak force
kind of you move a little bit away from
the nucleus and just disappears the
reason for that is because these these
fields the particles that go with them
have a very large mass but the problem
that was that theorists faced in the
sixties was that if you tried to
introduce massive force fields the
theory who gave you nonsensical answers
so you'd end up with infinite results
for a lot of the calculations you tried
to do so the basically it turned it
seemed that quantum field theory was
incompatible with having massive
articles not just the force particles
actually but even the electron was a
problem so this is where the Higgs that
we sort of alluded to comes in and the
solution was to say okay well actually
all the particles in the standard model
of mass they have no mass so the quarks
the electron they don't have a mass
neither do these weak particles they
don't have mass either what happens is
they actually acquire mass through
another process they get it from
somewhere else they don't actually have
it intrinsically so this idea that was
introduced by what Peter Higgs is the
most famous but actually they're about
six people that come up with the idea
more or less at the same time is that
you introduce a new quantum field which
is another one of these invisible things
as everywhere and it's through the
interaction with this field that
particles get mass so you can think of
say an electron in the Higgs field it
kind of Higgs field kind of bunches
around the electron it sort of a drawn
towards the electron and that energy
that's stored in that field around the
electron is what we see as the mass of
the electron but if you could somehow
turn off the Higgs field then all the
particles in nature would become
massless and fly around at the speed of
light so this this idea of the Higgs
field allowed other people other
theorists to come up with a well it was
another a unit basically a unified
theory of the electromagnetic force on
the weak force so once you bring in the
Higgs field you can combine two of the
forces into one so it turns out the
electromagnetic force and the weak force
are just two aspects of the same
fundamental force and at the LHC we go
to high enough energies that you see
these two forces unifying effectively so
that so first of all it started as a
theoretical notion like this is just
something and then I mean wasn't the
Higgs called the god particle at some
point it was by a guy trying to sell
popular science books yeah yeah but by
me I am because when I was hearing it I
thought it would I mean that would solve
a lot of the you know file a lot of our
ideas of physics was Molloy's my notion
but maybe you can speak to that was is
as big of a leap is it as a god particle
is it a Jesus particle which which you
know what's the big contribution of
Higgs in terms of this unification power
yeah I mean to understand that I maybe
helps know the history a little bit so
when the what we call electroweak theory
was put together which is where you
unify electromagnetism with the weak
force and the Higgs is involved in all
of that so that theory which was written
in the mid-70s predicted the existence
of four new particles the w+ boson the
w- boson the z boson and the Higgs boson
so there were these four particles that
came with the theory that were predicted
by the theory in 1983-84
the W's and the z particles were
discovered an accelerator at CERN called
the super proton synchrotron which was a
seven kilometer particle collider so
three of the bits of this theory had
already been found so people are pretty
confident from the 80s that the Higgs
must exist because it was a part of this
family of particles that this
theoretical structure only works if the
Higgs is there so what then happens this
question right why is the LHC the size
it is yes well actually the tunnel that
the LHC is in was not built for the LHC
it was built from for a previous
accelerator called the large electron
positron Collider so that that was bit
began operation in the late 80s early
90s they basically did that's when they
dug the 27 kilometer tunnel they put as
accelerator into it the collider defiers
electrons and anti electrons at each
other electrons and positrons so the
purpose of that machine was well it was
actually to look for the Higgs that was
one of the things it was trying to do it
didn't man I didn't have enough energy
to do it in the end but the main thing
it was it studied the W and the Z
particles at very high precision so it
made loads of these things previously
can you make a few of them at the
previous accelerator you could study
these really really precisely and by
studying their properties you could
really test this electroweak theory that
had been invented in the seventies and
really make sure that it worked so
actually by 1999 when this machine
turned off people knew well okay you
never know until you until you find the
thing but people were really confident
electroweak theory was right and that
the Higgs almost the Higgs or something
very like the Higgs had to exist because
otherwise the whole thing doesn't work
it'd be really weird if you could
discover and these particles they all
behave exactly just theory tells you
they should but somehow this key piece
of the picture isn't it's not there so
in a way it depends how you look at it
the discovery of the Higgs on its own is
it's also a huge achievement in many
both experimenting and theoretically on
the other hand it's this it's like
having a jigsaw puzzle where every piece
has been filled in you've this beautiful
image there's one gap and you kind of
know that that piece must be there
something right so yeah so the discovery
in itself although it's important is not
so interesting it's a good confirmation
of the obvious yes at that point but
what makes it interesting is not that it
just completes the standard model which
is a theory that we've known had the
basic layout offs for 40 years or more
now it's that the Higgs actually is a is
a unique particle is very different to
any of the other particles in the
standard model and it's a theoretically
very troublesome particle there are a
lot of nasty things to do with the Higgs
but also opportunities so that we
basically don't really understand how
such an object can exist in the form
that it does so there are lots of
reasons for thinking that the Higgs must
come with a bunch of other particles or
that it's perhaps made of other things
so it's not a fundamental particle that
it's made of smaller things I can talk
about that if you like a bit that's
that's still an ocean so yeah so the
Higgs might not be a fundamental
particle there may be some in my oh man
so that that is an idea it's not you
know it's not been demonstrated to be
true but I mean there's all of these
ideas basically come from the fact that
it's a this is this is a problem
motivated a lot of development in
physics in the last 30 years or so and
there's this basic fact that the higgs
field which is this field that's
everywhere in the universe this is the
thing that gives mass to the particles
and the Higgs field is different from
ever all the other fields in that let's
say you take the electromagnetic field
which is you know if we actually were to
measure the electromagnetic field
we would measure all kinds of stuff
going on because there's light there's
gonna be microwaves and radio waves and
stuff but let's say we could go to a
really really remote part of empty space
and shield it and put a big box around
it and then measure the electromagnetic
field in that box the field would be
almost zero apart from some little
quantum fluctuations but basically it
goes to naught the Higgs field has a
value everywhere so it's a bit like the
hole it's like the entire of space has
got this energy stored in the Higgs
field which is not zero it's it's finite
it's got some it's a bit like having the
the temperature of space raised to you
know some background temperature and
it's that energy that gives mass to the
particles so the reason that electrons
and quarks have mass is through the
interaction with this energy that's
stored in the Higgs field now it turns
out that the precise value this energy
has has to be very carefully tuned if
you want a universe where interesting
stuff can happen so if you push the
higgs field down it has a tendency to
collapse to what there's a tenon if you
do you're sort of naive calculations
they're basically two possible likely
configurations for the Higgs field which
is either it's zero everywhere in which
case you have a universe which is just
particles with no mass that can't form
atoms and just fly by at the speed of
light or it explodes to an enormous
value what we call the Planck scale
which is the scale of quantum gravity
and at that point if the Hicksville was
that strong even an electron would
become so massive that it would collapse
into a black hole and then you have a
universe made of black holes and nothing
like us so it seems that the the
strength of the Higgs field is - it
could achieve the value that we see
requires what we call fine-tuning of the
laws of physics you have to fiddle
around with the other fields in the
standard model and their properties to
just get it to this right sort of
Goldilocks value that allows atoms to
exist this is deeply fishy people really
dislike this well yeah I guess well so
what would be a so - two explanations
one there's a god the design this
perfectly and two is there's an infinite
number of alternate universes and we'll
just happen to being the one in which
life is possible
yeah complexity so when you say I mean
life any kind of complexity that's not
either complete chaos or black holes
yeah yeah I mean how does that make you
feel what do you make that has such a
fascinating notion that this perfectly
tuned field that's the same everywhere
yeah is there what do you make of that
yeah well you make of that I mean yeah
you like that two of the possible
explanations yeah I mean well someone
you know some cosmic creator way yeah
let's fix that to be at the right level
that's more possibility I guess it's not
a scientifically test for one but you
know theoretically I guess it's possible
sorry to interrupt but there could also
be not a designer but could never be
just I guess I'm not sure what that
would be but as some kind of force that
that some kind of mechanism by which
this this this kind of field is enforced
in order to create complexity basic
basically forces that pull the universe
towards an interesting complexity I mean
yeah I mean I has those ideas I don't
really subscribe to them as I'm saying
it sounds really stupid no I mean yeah
and there are definitely people that
make those kind of arguments you know
there's ideas that I think it's Lise
Mullins idea one I think that you know
universes are born inside black holes
and so universe is that behaved like
Darwinian evolution of the universe
where universes give birth to other
universes and they've universes where
black holes can form are more likely to
give birth to more universes so you end
up with universes which have similar
laws I mean I don't whatever but why I
talked to dr. Lee recently understand
this podcast and he's he's a reminder to
me that the physics community has like
so many interesting characters yeah it's
fascinating yeah anyway so so I mean as
an experimentalist I tend to sort of
think these are interesting ideas but
they're not really testable so I tend
not to think about very much
so I mean going back to the science of
this there wasn't that there is an
explanation there is a possible solution
to this problem of the Higgs which
doesn't involve multiverses or creators
fiddling
about were the laws of physics if the
most popular solution was something
called supersymmetry which is a theory
which is in