Hello, and welcome to the Physics World weekly
podcast. I'm Hamish Johnston.
In this episode, I'm joined by my colleagues
Margaret Harris and Matin Durrani to talk about
what's new in the world of physics.
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So first up, we've got Margaret who's going
to take us to Mars
and talk about the first observation
of an aurora
from the surface
of the red planet. Hi, Margaret.
Hi, Hamish.
So Margaret, can you
first remind us what an aurora is? I
mean, people have been seeing lots of them
here on Earth,
over the over the past few months. But
what what are people seeing?
Well, what you're seeing is the
manifestation
of an interaction between our planet's magnetosphere
and the solar wind. Okay. So what's the
magnetosphere?
The magnetosphere
is sort of an envelope that surrounds Earth,
and it's caused by the Earth being,
basically, a big gigantic magnet. So there's a
magnetic dynamo in the center of the Earth.
It's probably due to the fact that we
have a liquid iron core,
creating a magnetic field.
And so this is great. This is great
because it protects us from the solar wind,
which is a stream of charged particles
coming from the sun.
And when that stream of charged particles from
the sun slams into our planet's magnetosphere,
it it it produces the aurora borealis if
the if you're in the Northern Hemisphere and
or the aurora australis if you're down south.
Okay. And and so what what has been
seen on Mars? I think we when we
were first discussing this paper a few weeks
ago, we were really hoping that there was
going to be a fantastic
image of, you know, the classic
shimmering
red and green lights,
above the Martian surface.
Is that essentially
what
what what has been seen
on Mars?
Okay. Well, so first things, in order to
see something really
shimmering and gorgeous, you need a couple things.
One, you need a solar storm that's big
enough because not every time,
not every solar storm is big enough to
create the, you know, tremendous
sort of light show that we've been seeing
recently here on Earth because,
we're at a solar maximum, as in the
maximum of
So first off, the solar storm that produced
the aurora that was seen on Mars was
a really minor one. It may have turned
the sky just sort of, like, faintly greenish.
So that's hard to detect even for for
for the naked eye. It's hard even to
detect for cameras. And the other thing is
that this was seen on the surface of
Mars by the Perseverance rover.
And the Perseverance rover is a great little
instrument, but it's mostly designed to be looking
down.
It's designed to do geology on Mars and
to do all sorts of fantastic stuff associated
with, you know, trying to work out whether
life ever existed on Mars.
It's not really designed to look up.
And it's not designed to do observations in
the dark. You don't do much geology in
the dark.
So
the cameras there were not really optimized to
pick up, you know, a really fantastic aurora,
but they did pick up something. They picked
up the fact that the sky turned from
being its normal subdark color to being sort
of vaguely grayish green. And that's important because
we'd never seen an aurora from the surface
of another world before.
We'd seen auroras
from orbits
on all sorts of of planets in the
in the solar system, any any,
planet that has a magnetosphere,
which interestingly, Mars doesn't really have its magnetosphere
in the same sense that Earth does, but
it does have a weak magnetosphere.
It's called a hybrid magnetosphere
that's generated not by this in interior planetary
dynamo, but by some weakly, residually magnetic rocks,
I believe in its southern hemisphere,
and by just the fact that Mars is
a big object.
And so it tends to sort of warp
the solar wind into and the magnetic fields
that come from there sort of get warped
around it and kinda gathered around it like
a like a sort of gauzy summer shawl.
So it has this very, very weak magnetic
field. It's although it's not strong enough to
protect,
objects on the surface of Mars from intense
radiation, from the cosmic rays, and from the
solar wind, it is strong enough to produce
an aurora. And that's what Perseverance saw.
I see. And, I mean, it sounds to
me that this was was was this sort
of an accidental
or a serendipitous
observation that I don't know. They they just
happened to leave the cameras on at night
and, and and they caught this, you know,
this is sort of the equivalent of the
of the doorbell cam here on Earth or
or,
were they actually looking for it? Oh, they
were definitely looking for it. They were definitely
looking very hard for it. And the thing
is that, you know, Perseverance is a busy
little dude. You know? It can't just keep
its cameras looking up just in case there
might be an aurora up there. Mhmm. They
had to have some really good predictions
of
when this to first for actually, first, go
back a little bit. First, they had to
see the solar storm
that produced the aurora,
and then they had to, work with some
scientists at NASA's Goddard flight Space Flight Center
to,
understand when that aurora was gonna hit Mars.
It takes about three days, but they can
kinda predict it to within a few hours.
And then they had to make a decision,
like, is this aurora big enough that,
Perseverance is not very optimized for looking at
the sky cameras could see something. And then
they had to request time and Perseverance, get
it to stop doing whatever else it was
doing and to look up at the sky.
And then they had to be lucky, basically.
They had to
have all those things happen at just the
right time. And I think it took him
about,
I think it took him about four goes
before they managed to actually capture an aurora
on Mars. But this is important. It's the
first one to be done, and it's also
the first aurora to be seen
anywhere other than the Earth that's been measured
in visible
light wavelength rather than in UV light.
And that's important because visible light cameras are
a lot cheaper
than UV cameras.
So if we can do these observations with
nice cheap cameras,
then we should be able to do do
more of them, essentially.
Right. And, it is I mean, it does
seem to be a very good time here
on Earth to be to be out looking
for Aurora. I mean, I've seen reports
in North America where, you know, even this
time of year,
aurora have been spotted,
further south than forty five degrees north, which
is, you know, that's closer to the Equator
than the North Pole, which, you know, is
is pretty impressive. And I'm guessing that has
to do with some increased solar activity
at the time. So,
are
the the people who who use Perseverance,
are are they geared up for more observations?
And I'm guessing they're probably looking for time
when they know there's gonna be a big
solar storm,
that that to to turn
the the the rover's cam cameras skyward. Is
that is that the sort of thing that
that's going to be next
for, for people there?
I think they certainly want to do that.
Whether they'll be able to get time on
on perseverance is, you know, another question. It
it's as I said, it has lots of
other priorities.
But, definitely, this is probably gonna be hopefully
the first of many detections of aurora,
by robots that are
by robots that are exploring,
the surfaces and the atmospheres by the planets.
Oh, that's great. That's really interesting.
And staying in space, but sort of looking
into the far, far future,
you've also got an update for us about
the ultimate fate of the universe
and the news that it might
not be as long lived as previously expected.
And I think this has something to do
with white dwarf stars,
which are expected to persist
for an extraordinarily
long time.
And
when I say extraordinarily long, I think we're
talking about ten to the
thousands or even tens of thousands of years.
So so why are white dwarfs
important
when it comes to understanding the the future
of the universe?
Okay. So white dwarfs are lower mass stars
in the final stage of their lives. They
weren't massive enough to collapse into a neutron
star star or a black hole. They're just
kinda hanging out, gently glowing from the residual
heat. They're not doing any thermonuclear fusion or
anything exciting.
And that means that as long as they
don't get cannibalized by a companion star or
fall into a black hole or something weird
and, also, I should say, as long as
our universe doesn't undergo some sort of big
crunch, this is not this this story is
not to do with the sort of grand
scale cosmology. It's really about white dwarf stars,
the physics of white dwarf stars. So as
long as those things don't happen, they can
last a really long time.
But crucially, a really long time is not
the same thing as forever. There is a
few things that could make a white dwarf
star disappear.
So one of them is if protons decay.
Various theories predict that protons should decay,
but nobody's ever seen that happen, and it's
not for lack of trying. There were several
experiments looking for proton decay, I think, in
the nineteen eighties and nineteen nineties.
But the best we can say that if
if protons do decay,
they do it on a time scale that's
longer than our experiments so far have been
able to measure. Okay. That's proton decay.
The other way of making a white dwarf
star disappear is via process called piconuclear
fusion.
I had never heard of this before I
saw this story, but it's derived from the
Greek word pyknos, meaning dense.
So piconuclear
fusion is nuclear fusion that only happens in
extremely dense material
like you get inside a white dwarf star.
And it's kind of a complicated process, but,
essentially, what's happening is that the nuclei inside
white dwarfs are oscillating around their zero point
energy.
And sometimes these oscillations are actually enough to
allow them to fuse. There's some quantum tunneling
involved.
And if that happened to matter under normal
conditions,
like, stuff would be fusing all over the
place. But fortunately, that doesn't happen. It only
happens really in inside white dwarf stars, or
it's only important, let's say, inside white dwarf
stars.
And
the consequence of pyronuclear fusion is that it
turns the carbon and white dwarf star cores
into nickel, which then decays to, I think
it's iron 56. Don't quote me on that.
I think it's iron 56
by emitting a positron.
And once you've got that iron core, you've
no longer got a white dwarf star. You've
got a black dwarf star,
which is a theoretical object that's never before
been seen,
not just because it's dark, but because
the time required for that to happen
is actually longer than the lifetime of the
universe so far.
So even if it's possible, it hasn't happened
yet.
I see. And and so the idea here
is that the the end of the universe
that we're talking about is when all is
when these white dwarf stars go
that they don't produce any more light. They
go dark.
It's even weirder than that because so while
we're going out on a out on a
speculative limb here, turning carbon into iron leads
to a loss of electron degeneracy
pressure, which is what's keeping
the black door from collapsing in on itself.
And eventually I mean, we're talking very, very
eventually.
That will reduce the maximum mass
that the black dwarf star can have before
it collapses.
It's called the Chandrasekhar
limit.
Right. And so that will actually make the
black dwarf star unstable.
So this is the other process that could
cause otherwise stable white dwarf stars to disappear,
and it's it's really slow. It's you mentioned
it would take somewhere between ten to the
eleven hundred years
and ten to the thirty two thousand years
depending on the mass of the black dwarf.
So higher masses would be quicker because they
would reach the Chandrasekhar limit quicker.
Right. Okay. And that that is a very
long time. That is a very long time.
So those those are the so,
proton decay, if it happens, is actually relatively
quick. If you're if protons don't decay and
piconuclear fusion is your only mechanism, that's really,
really slow.
Right.
But there's some new research now,
where some physicists have looked at a process,
or a phenomenon called Hawking radiation.
And,
they've they've applied this to, white dwarf stars
in the in the far future, and and
they've come up with a a much, much,
much
shorter
lifetime. Still very long,
but much, much shorter. So so what is
Hawking radiation? How does it fit in to,
to the life's lifetime of, of these stars?
Okay. So if you've heard of Hawking radiation,
it's probably in the context of black holes
because that's where it was first formulated by
Stephen Hawking,
building on some ideas of another theorist called
Jacob Bekenstein.
The idea is that particle antiparticle pairs are
popping in and out of the quantum vacuum
all the time. They borrow energy from the
vacuum to to appear, and then they almost
immediately give it back again because they annihilate
and they disappear.
However,
if one half of that pair happens to
drop over a black hole's event horizon
in that brief period between coming into existence
and annihilating,
then it won't ever be able to recombine
with its partner, so it'll take away some
energy. And this is the mechanism by which
black holes radiate away their mass energy
and shrink
rather than continually growing.
But, obviously, a black hole is not the
same thing as a white dwarf.
But the kicker is that Hawking radiation doesn't
just happen to black holes.
A couple of years ago, the black hole
expert Heino Falke, quantum physicist Michael von Drac,
and mathematician Walter von Sudekum. Apologies. Their Dutch
names I don't know speak Dutch. So if
I pronounce those incorrectly, I'm very sorry. Don't
even try, Margaret. Don't even try. Try.
I'll do my best. I'll do my best.
So they worked out that this whole particle
falling over the event horizon scenario
is really just an extreme case of particles
not being able to annihilate because gravitational tidal
forces have pulled them far away from each
other.
And in principle,
that kind of
gravitational tidal force separation
can happen at least some of the time
in the vicinity of any object with a
gravitational field,
and that includes white dwarf stars. In fact,
it includes humans
because you and I, we also have a
gravitational field. It's very tiny, but it exists.
And
so
this trio worked out it would take a
white dwarf star around ten to the seventy
eight years
to dissipate via Hawking radiation,
which is it's a hell of a long
time, but it's a lot shorter than ten
to eleven to the eleven hundred years or
ten to the thirty two thousand years you
get with piconuclear fusion reactions.
And as a side note, they also calculated,
you know, somewhat tongue in cheek,
that if
Hawking radiation was the only process involved, you
know, you got rid of all of chemistry
and biology and all sort of various physical
events that could,
cause them interrupt this process,
then
it would take a human,
which is obviously less dense than a white
dwarf star,
around ten to the ninety years to
dissipate entirely via Hawking radiation.
Now I don't think that's there's gonna be
much of an interesting universe around in ten
to the ninety years. After all, we've just
shown that white dwarf stars, even white dwarf
stars, will have winked out of existence
in, ten to the seventy eight years. But
in principle,
that is how long a a a human
could or a human sized object made of
water, let's say, could, could last in the
universe.
And, of course, that that doesn't take into
consideration
these sort of cosmological
Oh, yeah. Issues Yeah. Yeah. About whether whether
the universe is going to keep on
keep on expanding or if it's going to
sort of bounce back or this is just
how long
stuff in the universe can actually
exist. Yeah. Exactly. Exactly. Yeah. Which is still
interesting to think about. I mean Oh, yeah.
Yeah. Yeah. Well, I mean, it is very
interesting because, you know, I'm guessing that by
doing these calculations on Hawking radiation,
they're, you know, sort of moving our knowledge
forward
of,
you know, the sort of the interplay between
quantum mechanics and,
and general relativity
Yeah. Which is always very interesting. Well, thanks,
Margaret. Thanks for coming on and talking about
about Aurora on Mars and the age of,
objects in the universe. And you can find,
both of those articles written by Margaret. They're
both written by you, Margaret. Is that right?
Yep. Yeah. Both articles written by Margaret about
these,
subjects on the Physics World website. Thanks.
Thanks, Hamish.
Now let's move from the future to the
past and an important
moment in physics history.
Matin, you'll soon be traveling to the German
island of Helgoland
for a hundredth anniversary
celebration.
What happened in Helgoland
back in 1925?
Well, it was in June 1925 that Werner
Heisenberg,
who at the time was a young postdoc
at the University of Gottingen,
he suffered from a really bad bout of
hay fever.
But he famously asked his supervisor, Max Born,
if he could go to this island for
two weeks to recover
from the allergies that he had because it's
an island in the North Sea.
I've looked on Google Maps. It's probably about,
an hour off the coast of Germany. And,
you know, it's very windswept,
and it's very isolated.
There's no trees in the sea, so no
pollen.
Exactly. Yeah. Yeah. So he went he went
there, and it was on this island in
June 1925 that
he,
had this,
amazing insights. His ideas that he'd been working
on came together, and he formulated
the ideas of quantum mechanics,
you know, proper mathematical framework for
all these weird quantum effects that people were
seeing.
And so, yeah, that was a hundred years
ago.
So a very famous moment in history of
physics that is being celebrated this year. That's
right. In the the international year the UN's
international year. UNESCO, is it? Yeah.
UNESCO, which is a UN agency,
the International Year of Quantum Science and Technology.
And and so this was matrix mechanics that
he came up with. This is this this
idea of, of,
representing,
reality in terms of,
vectors and and matrices and multiplying them together
and, and all that sort of stuff that
you learn, I suppose, as an undergraduate.
And,
and and that was a big deal, wasn't
it? Because before that, wasn't there the, I
mean, I might have the the lingo wrong,
but the old quantum mechanics where people didn't
really understand what was going on. They knew
that physics was really weird. And it was
only when Heisenberg sort of wrote down this
matrix mechanics that,
it all start started to make sense or
well, started to make sense. It still doesn't
make sense, does it? Quantum mechanics,
famously.
If you think you understand it, you don't.
But, yeah. So so a very, very exciting,
a very exciting,
time, 1925
in Helgoland. So Helgoland is it's an island.
It's off the the West Coast Of Germany,
so it's in the North Sea.
And,
so you're
you're going there, very exciting, to this conference,
that's been organized
in Helgoland
to commemorate this.
But you're starting in Hamburg, is that right?
Which I suppose is the nearest
big city to Helgoland. So what's going to
happen in Hamburg,
the the preconference event?
So on the Monday so it's the it's
quite soon, coming up soon. So it's Monday,
the,
June 9. There's a preconference
banquet dinner at a hotel in in Hamburg,
and there are three speakers talking about the
history of,
the subject. And one of them is actually
Phil Ball, Philip Ball, who's an old friend,
dare I say, Physics World. Listeners may remember
he's written quite a lot for us,
and, he's a bit of an expert in
the history of quantum mechanics.
And he's one of those unusual journalists who's
kind of reached almost, like, the status of
a knowledgeable expert in this area. He's at
that really a crossover between being a journalist,
science journalist, and the sort of experts on
this area. So he's doing one of the
talks at the conference dinner
on the Monday. And then the next day,
we get this ferry, which takes about four
hours to get. You go up the Elbe.
That's right. Yeah. Because Hamburg is actually a
long way from the sea. It is. It's
on a big river called the Elbe.
And then so you go out the Elbe,
and then do you turn right? Or does
it turn left? You turn
up up. I'm sure I'm sure the captain
will know which way to go to Helgoland.
So the Elbe, it's a Hamburg is a
seaport and very, you know, important for Germany,
but, it's quite a way
inland. And so you go up the Elbe
and then turn right, I think, as you
say, and then you get to Helgoland
after about four hours. Right. And and Helgoland
itself, we're we're talking about this yesterday.
And you said it's it's about the same
size as the Bristol suburb of Clifton,
which is not very big. It's not very
big. I think it's about there's about 1,500
people live on it. So suddenly, at this
conference, there are gonna be 300 physicists
turning up. So the population will increase by,
is that 20%?
And, yes, about one it's about 1.7 kilometers
long and maybe a kilometer wide. There's actually
a second island next to it,
so not very big.
These days, it's a kind of holiday resort,
and there are a lot of beach
villas and cottages and that sort of thing.
Right. So I suppose it hasn't changed much
because Heisenberg was on holiday there. So,
Well, there is that famous story that after
the second World War, the British ally and
the allies, they collected all their unexploded bombs
and put them on Helgoland. Oh, dear. Practically
blew the island up.
So that didn't do much for tourism. No.
So anything that is connected with where Heisenberg
stayed doesn't exist anymore. All the all the
housing was blown up. So there's no sort
of this is the room that Heisenberg stayed
in that you can see, I don't think.
Okay. Although there is a, a little
sculpture statue thing,
in honor of Heisenberg, so I'll make sure
I have a look at that. Oh, yeah.
I'll get some pictures. Definitely. Yeah. And and
one of the big worries about going is
accommodation.
And,
I I think am I right in thinking
that you've you've sort of got a somebody
probably canceled and you've got a last minute
booking,
so you're actually lucky enough to be able
to go out to Halgo Land,
where I'm guessing accommodation is pretty scarce. Yeah.
There was instructions for anyone who wanted to
go to, you might have to camp on
the beach.
I didn't really fancy doing that. And, luckily,
there is a
a, yeah, a place that I'll be staying
in, which is very, very fortunate. But, yeah,
all the hotels are booked
out, have been for quite some time,
like I say, with these 300 physicists turning
up. So, yeah, it should be, and then,
yeah, it's four days on the island. Yeah.
And then come back to Hamburg. So it's
a really unusual event,
and there are some, you know, big big
names going on. Am I am I right
in thinking speaking of big names that Bob
Kreese,
longtime
Physics World, contributor. Is he is he speaking
there? I know he's written about how Golang
Forest.
He no. He is not going, but there
are, some eminent people going, including I think
I've counted four
Nobel Prize winners,
and I think all the Nobel Prize winners
get must get tons of invitations, but there
are four on the list there. Mhmm.
Serge Haroche,
Anton Sailinger,
David Wineland, and Alan Aspect.
Wow. So so some pretty strong connections to
quantum physics there as well. Yeah. And then
the rest of the people is it is
a kind of who's who. I mentioned Phil
Ball. There's people like Charles Bennett who came
up with one of the algorithms.
Michelle Simmons from Australia,
Carla Ravelli,
Michelle Lukin who won the Yeah. Yeah. Our
favorite is on the podcast Exactly. Not too
long ago. Yeah. And there's also Elisa Krill
who's appearing in, Physics World.
Oh, that's right. Yeah. She's a philosopher. Yeah.
So so there will be a philosopher. It
won't be Bob. Yeah. Not him. Right. There'll
be a New York based philosopher.
That's what you need at every conference. Yeah.
Right. So, So, yeah, it's, you know, it's
a real who's who. And there's other people
like John Preskill Oh, right. Yeah. Sandhu Pippescu
from the University of Bristol, Janeway Pan is
invited,
Nicholas Guissaint
from Geneva,
Bill Unruh,
Canadian Yeah. Yeah. Person.
Peter Zola.
You know, if you're if you're into your
quantum physics, this list of people I'm just
looking at So it's a who's who, definitely.
Pretty, yeah, you know, some big big shots,
dare I say. Big big cheeses.
Right. Okay. Well, that's that's great. And, you
know, I mean, normally, I would say try
to make it try to go there, dear
listener, yourself, but I think unless you wanna
camp out on the beach.
And, and we have had some lovely weather
recently, but, you know, it is in the
North Sea,
Northern Germany, so it could be a bit
a bit chilly.
Right. And,
I mean, we have we have been doing
lots of coverage of the International Year of
Quantum Science and Technology
in physics world.
And, one thing that we've, that we've published
very recently is a,
a quantum briefing,
which is chock full of some fantastic articles
about,
quantum physics.
And it it has some flash fiction in
it as well. It's a short story by,
Kevlin Henney, who is a Bristol based, author
amongst many other things.
And he's he's looked at this famous voyage
that, Heisenberg made to Helgoland,
and he's come up with an alternative
universe in which,
Heisenberg didn't go there.
And, you know, I suppose in in the
spirit of the multiverse,
has written about that. So can can you
give us just a little preview of that
story? Obviously, we want people to go and
and read it. But, what what's Kevlin's premise
on that?
So so Kevlin is someone who is a
physicist by training but works in the IT
sector. And he was actually on our Physics
World Stories podcast, so you can find out
more from,
last month. But, yeah, he
is enjoys writing flash fiction, so he came
up with this idea. I can't remember who
it was, whether it was me or Tushner,
our colleague, or him. This idea of an
alternative universe where if Heisenberg hadn't been allowed
to go to Helgorand
and was had to stay in Gottingen,
would that great event of discovering quantum mechanics
have happened? So what he's he took took
the idea and he's written it as a
diary.
So on the left hand side, he's got
a diary, an imagined diary of what he'll
Heisenberg did in Helgoland
day by day. And on the right, he's
kind of written a parallel diary of him
staying at home and imagining him being frustrated
and not being able to go.
I did email Phil Ball and mention
this to him, and he did actually say
that he was interested in this idea of
what we've done, but actually, he slightly poured
cold water on it. He kind of thinks
even if Heisenberg had never gone to Helgoland,
he probably would have done this work anyway,
just not on Helgoland.
So it wasn't the magical
Well hole in free sea air
of Helgoland that Well, I think that's what
he was implying in the email that he
sent me that this would've it would've happened
anyway. It would've been maybe would've been somewhere
else or maybe a while later.
But, yeah, it's a great little idea that
he came up with of this. And so
we've imagined it as if as if Kevlin
Henney has discovered these notebooks. I mean, there
there are no notebooks, but we've we've
we've in the article, we've we've, laid it
out as if it's a notebook.
So it looks it looks quite realistic. It
looks quite fun. So so, yeah, a clever
little idea and, just a bit of fun,
to sort of twist
on old history, I think it's called.
So, yeah, keep an eye out for that.
Yeah. And and that is it's it's available
for reading. The the quantum briefing can be
found on the Physics World website, and I'll
put an a link to it, in the
notes for this podcast. It also, has an
article by Margaret, a feature length article by
Margaret
about the quantum Zeno effect,
which is,
a sort of a fascinating
quantum thing.
And that that's actually the first quantum briefing,
isn't it? There's there's gonna be a second
quantum briefing that's going to be Not not
quite a second we're gonna update this one
with some extra articles.
So this is a a digital magazine that
so it's quite ease well, relatively easy to
add in extra stuff. Right. Okay.
There there were there are some limited printed
copies in fact. We I'm gonna take a
hundred
in my suitcase. That's a hell go land.
So anyone anyone listening, you know, get your
hands on those. I'll be wandering around with
these boxes with my suitcase trundling around the
island, handing them out.
But yeah. And also, yeah, the before we
forget, there's the really great cover that we've
got for it,
which I know you were gonna come on
to, which is by
Tushner commissioned
Felicity Inkpen, who's a scientist and artist who
used to work So an artist called Inkpen.
What what's that called? Nominative
determinism?
I think so. Yeah. Mind me out that
wrong. Felicity. Yeah. It is a lovely it
is a lovely cover.
So what she's done is she
it's called the the the painting is called
Cubitt's
Duality.
So she it's a sort of, what she
did is she took a tank of water
and poured some colored dyes in and took
lots of photographs and inspired from those pictures.
She then painted an oil painting, and it
kind of meant to symbolize
wave particle duality.
And we did that for the cover because
I think we wanted something a bit different
that's special for us and not just the
usual
standard stock pictures that,
wouldn't perhaps have done the content justice. Yeah.
Yeah. No. It it it really looks nice.
Yeah. So, yeah, definitely look out for that.
And if you happen to be on Helgoland,
ask Matin for a for a copy.
Now, Hamish, before we finish,
you have been writing something quite interesting, a
research update about
neutrons
and, which obviously these are subatomic particles without
charge,
but using it in a very unusual way
to differentiate between counterfeit
and genuine antique
coins. So what are these coins, Hamish? Well,
they're, they're Korean coins from the early nineteenth
century.
And, you know, if you if you're sort
of familiar with old coins, they're that that
sort of classic
round coin with a square hole in the
middle of it. You know, you that seems
to be a common Didn't the Danish used
to have coins like that? Oh, maybe they
did. Maybe you'll find some on Helgoland Oh,
yeah.
Washing up on the beach. But the these
are from Korea.
And, yeah, some researchers
in Korea and also in The US
have used,
a a a sort of a a novel
technique using neutron scattering to tell the fake
ones from the real ones. Yeah.
And, well, how did they do that? Well,
the the the they used two techniques. But
the the technique that I found,
most interesting
is,
they used the presence of hydrogen
in the coins,
to tell the difference between,
an a genuine antique one and a sort
of a more modern fake one that has
just been
chemically treated to look old. So the fakes,
modern fakes pretending to look old. They weren't
fakes from the time. Yeah. Yeah. They're yeah.
They're modern fakes. They were people trying to
sort of, Exactly.
No. No. No. No. No. No. No. These
are modern fakes. I suppose these coins are
collectible.
And it's it's interest I I found it
interesting. I do have love for neutrons.
And I I found it interesting because it's
sort of a twist on how neutrons are
normally used
to study materials.
Usually, you take a a beam and you
scatter them from a sample, and the resulting
diffraction pattern tells you
about the structure of the sample. That's a
very straightforward
use of neutrons and Nobel prizes have been
won for developing,
those sort of techniques.
But the thing about hydrogen is that it's
a bad thing when it comes to neutrons.
Hydrogen messes up this process because the proton
that, you know, the nucleus within a hydrogen,
is a very good incoherent
scatterer of neutrons. And essentially, that means that,
if there's lots of hydrogen in your sample,
it blurs these patterns that you're looking for.
And,
in order to do neutron scattering experiments on
hydrogen rich samples,
researchers actually replace the hydrogen
with deuterium.
They call this deuteration.
And they do that because deuterium, which is,
a proton with a neutron, so helium hydrogen
two,
is not a good incoherent
scatterer. So in the world of neutrons, you
want to avoid hydrogen,
at all cost.
But in this new work, which was led
by Youngju Kim
and Daniel Hussey at, NIST, at the National
Institute of Standards and Technology, and
presence of hydrogen
in coins
was detected by, you know, sort of looking
for
this incoherent
scattering of neutrons.
So how did that work? I guess the
neutrons travel through the coins, do they? And
maybe the does the hydrogen block the neutrons
more than the,
the other ones? Yeah. That's exactly what happens.
Beauty of neutrons is that they can travel
through a lot of materials very easily.
And so,
the the the neutrons can travel through the
metal
of the coin very easily, but they're actually
blocked, as you say, by by hydrogen.
And this hydrogen is in inclusions
of hydrogen rich
materials that are created by corrosion.
And it turns out that because the real
coins are older,
they have much deeper corrosion
inclusions
than the fakes.
And though that much deeper corrosion
is what,
is revealed
by the, by the neutron experiment. So even
though the fakes have been corroded to look
old, they they don't have these deep inclusions
because that takes time.
And, Oh, I see. So they actually corrode
the fakes to make them look old, but
Exactly. The real the real stuff has deeper.
Has deeper deeper inclusions. Yeah. That's right. So
that Hang on. Now they know what to
do. So they're Well, yeah. That's the problem
is that if, you know, if you if
you make fake Korean coins
and you
read missed press releases or physics world, you're
you're you're on your way.
And Hang on. Is there a big market
for these fake coins? Is that Well, I
would imagine. I mean, you know, people do
like to collect coins.
So yeah.
Yeah. And and they they also used
another technique to look at at these coins,
and that's a a sophisticated
version of something called small angle scattering.
And small angle scattering is something that allows
you to look at
fairly big things
in a sample, so not the atomic structure,
but bigger structures
within a sample.
And what they did is they used the
small angle scattering
to look at tiny pores on the surfaces
of the coins. And these pores occur as
the coins age, you know, they they interact
with their environment.
Material is removed from the surface of the
coin.
And counterintuitively,
what they found is that the genuine
older coins
had smaller pores
than the fake coins. Fake coins had pores,
but the pores were much bigger.
Now you might not expect that to happen,
but
they believe the researchers believe that the reason
this happened is that
because the old coins have been buried actually,
I think in this case, they've been underwater
for a long time.
The the pores are produced, but then they
start to fill in
through other chemical processes.
And so the genuine
old coins
have,
have much smaller pores
than the new coins, which have been sort
of artificially
corroded or aged.
And so in in a sense, the neutrons
have revealed
two
signatures
of old coins.
And so now,
now these researchers are they're they're going back
and they're gonna look at a broader
sample of fake and real coins and and
and see if they can confirm this. But,
yeah, I thought this was a really interesting
use of neutron scattering.
You you I mean, you know, I I
I had the privilege of of working at
a a reactor where they did neutron scattering.
And, yeah, of course, you know, they were
looking at new magnetic materials and things like
that, but they're also very interested in,
you know, sort of industrial applications.
You know, they would look at bits of
a jet engine to look for
cracks
within the,
the turbine blades that are not evident from
the surface.
So, you know, neutron scattering is, you know,
there's lots of really interesting applications, and one
of them, I suppose, is
looking at, you know, antiquities and,
spotting fakes.
So yeah. But I was just trying to
imagine to to imagine if someone offers you
a fake Korean coin. You go, hang on
a minute. Let me just go down to
the, NIST in Colorado,
check check with these neutron people. Can can
I take my coin along to check it?
Yeah. Yeah. Yeah. Or or or will I
It's just in Maryland. Maryland. Or will I've
already bought it? And maybe I've already bought
it, and then I wasted my money. And
then I then I'm gonna be really disappointed
I'm gonna take it, and it works out
as Yeah. I mean, I think what these
researchers say in their papers that it's probably
more useful for people who do historical research.
Because,
you know, a lot of our understanding
of history comes from coins, and where coins
are found.
And so it'll allow,
historians
and I suppose archaeologists
to verify,
finds of coins and and and that sort
of thing. Yeah. So Do you know what?
I've been reminded of that feature we had.
Do you remember a few years ago about
studying Chinese porcelain
using optical microscopy to look for the inclusions
in the, glazing? Oh, right. Yeah. And that
again was for spotting fake fake Chinese vases,
which is a, you know, huge market for
that. Yeah.
Yeah. It is interesting. And I I suppose
at the end of the day, okay,
these counterfeiters,
they might know
that they need to put these inclusions in.
But unless they've got a neutral facility,
they won't know if they've done it properly.
So I suppose in principle, they could they
could improve their fakes.
But,
it it would be very difficult to, you
know, they might try to slip in a
research proposal
to, you know, to that mist reactor.
Hopefully, somebody would spot it.
Yeah. So that's neutrons and fake coins. And
you can find find out more about this
on the Physics World website. Just look for
the headline,
neutrons
differentiate
between real and fake antique coins. Thanks, Matin.
Thanks, Hamish.
I'm afraid that's all the time we have
for this week's podcast.
Thanks to Margaret Harris and Matin Durrani for
joining me today.
And a special thanks to our producer, Fred
Ailes.
We'll be back again next week.