we're going to talk about some freaky
stuff are we
yeah we're going to talk about shining
light through walls shining light
through walls yeah so there's a new type
of particle that you can introduce to
the standard model and you introduce it
because it solves some problems that
exist in the interactions that make
protons and neutrons so the strong
interactions so they're called axions
why that was that mean um so axion was
originally the name of a brand of
washing powder i think and the name was
given to the particle because they clean
up a mess that exists
in in the strong interaction what's this
mess in the first place what needs to be
cleaning up there's a
symmetry in the sector that shouldn't
exist so a symmetry between particles
and anti-particles that that actually we
don't expect from the theory what that
means is that there's one parameter one
number that tells you how whether this
if that number is zero the symmetry
exists if the number is non-zero then
the symmetry doesn't exist and what
you'd expect is for that number to be
large and for the symmetry to be
completely uh broken but what we see
when we do measurements is in fact that
there's symmetry's there so there's a
number that you have to tune to be
really really small
and that's that's kind of uncomfortable
from from building theories we don't
like having to make numbers really
really small if you had a particle
and
you flip it's charge and you you do a
reflection in space
um if this symmetry exists it tells you
that you should get back to the same
thing so flip the charge uh invert
everything do a mirror reflection of
everything physics should look the same
that's in fact what we see
um but the theory predicts that we
shouldn't see that but there should be
some differences when you when you do
this interchanging theory isn't quite
matching what happens in reality right
and you just invent a particle paper
over the cracks that seems that's
basically what we do in in physics that
doesn't seem right to me that seems
naughty that's that doesn't seem elegant
uh so so the idea the hope is actually
that it's a more elegant solution so
instead of having to have this one
number be really really small what this
new particle so this new particle
replaces that number that you have to
make really small and instead of just
deciding that it's small and that's the
end of the story you have a way of
explaining how it evolves to be small
just about anything they can do axion
can undo this particle is postulated
because the soul's a problem for you
what what would we know about it would
it have a mass would it have a charge
would it is it like a bit like like what
what if this particle exists
tell me about it yeah it exists it has a
mass that you don't know it has
interactions with all of the other
fields of the standard model and in fact
that's what makes it really interesting
because those interactions give rise to
some cool things that we can then go and
try and see if this particle
exists
can't we find it like would we not just
now go and test for it and break things
apart and
like has are people looking for it yeah
absolutely and in fact that's what this
light shining through walls stuff is
it's a way of trying to look for these
new particles because they interact with
photons so what can happen is as a
photon travels through a magnetic field
it can turn into an axiom
so the idea of the experiment that
people are doing there's one uh at a lab
in hamburg in germany at the moment that
they're building so the idea is you have
a big magnet
and you shine a laser beam through the
through the core of the magnet
and you put a wall in the middle so
laser on one end camera on the other
wall in the middle so you shouldn't be
seeing any light in the camera but if
these axions exist as the photons from
the laser beam travel through the
magnetic field they can turn into axions
and the axioms don't care about the wall
they very happily travel through the
wall and then if you're lucky the
reverse process happens on the other
side your axiom turns back into a photon
and that's what you see in your camera
the other side what you need is a really
strong really long magnet and then you
can try and find
fine axions the nice thing about this
experiment is there's there's no
background you
uh if if axions don't exist you expect
to see nothing so if you see something
that tells you an axiom is there as soon
as you see something you know there's an
accident you've got a limited number of
photons in your laser beam you know the
more photons you can put into your
magnet the
higher the chance that one of them turns
into an axiom
so that's the kind of
engineering challenge of doing this
getting as many photons uh inside your
magnetic field as you can turning up the
magnetic field strength it's not it's
not like photons are a scarce commodity
you just could shine the laser for years
and just wait for one to happen right um
and that's what people people are trying
to do in fact it's just it's just a case
of um getting the money building the kit
and and then leaving it to run basically
has this been built is this running or
not so the the the um so it's called the
alps experiment so the any light
particle search or axial light particles
such uh and a first iteration of it ran
a couple of years ago for particle
physics a cheap thing to do because
they've been able to
essentially cannibalize some old magnets
that used to be part of a particle
collider
and use those turn those into into an
axion search um so they did this kind of
as a proof of concept a couple of years
ago and now they're building a 100 meter
long detector to try and search for
accion so that should be coming that
should be turning on in a couple of
years
because you know so little about axions
you don't know how likely it is
that the photon is going to turn into an
axiom so it could have been very likely
and if we'd have been lucky the
experiment that already ran would have
seen it
uh we weren't that lucky so it's a lot
rarer than that so you have to sort of
just keep running your experiment with
more sensitivity