(air whooshing) - Thank you Emma so much for
the invitation to come tonight. I'm really thrilled to be able to talk for the Royal Institution if not at. The Royal Institution as
much as I'd have liked to have been there, I'm
in my slippers right now and I've just had a cup of tea. So I'm hoping that you're doing the same as we go through about a
billion years of history. And we're going to be talking
about lots of mysteries. I'm going to be talking
to you tonight about lots and lots of big discoveries
and astrophysics. And one of the biggest
discoveries that famed my childhood when I
learned about it which was the Discovery of Tutankhamun's tomb. So here on the left you
can see Howard Carter and Lord Carnarvon and
they've just chipped away the first part of the tomb door that's not being opened for thousands of years. And as Howard Carter held up a candle to Lord Carnarvon and said what can you see? What can you see? And Howard Carter just simply
replied wonderful things, wonderful things and
everywhere the Glint of Gold she is a wonderful story
and finding out about our history understanding
these great discoveries was enough for me when I was a teenager and I'm still interested in it today. But my head was turned when I learned how much we didn't know about physics and then later how much we didn't know about the history of our universe. And so tonight I'm going
to be talking to you still about history, still
about where we come from to something we're
fascinated out by as humans we want to always look back always ask who we are, where we came from. And this starts even when we're children, just as my fascination
with Egyptology did. You are fascinated by
lots of different things when you are a child, you're
fascinated with archeology and history like I've just
said, uncovering the tombs. You're fascinated with dinosaurs,
dinosaurs are the best. And of course there's the
one that caught my eye, which is space, all three of these are like the Holy Triad of
children's passions, right? And so tonight we're
gonna be looking at this, we're gonna be blending space and history and sadly not dinosaurs,
though I am actually wearing dinosaur earrings, I've just
realized, so that's nice. So I want to start tonight properly off by talking about what is light. We're gonna be talking about
lights an awful lot tonight. We're going to be talking
about first light. So when the lights first
came on in the universe but we're also going to be talking about light as a diagnostic tool. So how can we use all the
different types of light to diagnose our universe as it were? There's lots of different types of light. The one with familiar with
is the optical wavelengths. So those are the wavelengths
of light currently entering your eye onto your retina, so that you can see me waving at you. There's lots of other
different types of light that we're used to, so for example, radio light, the radio
wavelengths of the spectra, because light is a spectrum and so it goes from very long wavelengths
to very short wavelengths. So with radio wavelengths, we
bounce them off the atmosphere of the universe, atmosphere
of the earth for example, and they'll bounce back down allowing us to cover really long
distances with our radio. There's the infrared
radio, infrared radiation, which we can use, for
example, to track criminals as they run away on some
American cop series or something. We can use UV light to
decorate ourselves nicely for when clubs used to
exist or for example, if you're watching CSI, they
can also be used to find gruesome discoveries of where
you can find the bodies. And then the last one we might
be familiar with for example, is x-rays, so when you
break your arm, for example, the doctor might first say oh
yeah that's definitely broken, using optical light to notice that it's at a completely wrong angle, but you'd be a bit worried if
they didn't also use x-rays to diagnose exactly how it's
broken, exactly how to fix it. And so with light acting
as a spectrum as it is, as I've just gone from small
wavelength to long wavelengths, we use the same kind of spectrum
to diagnose our universe. So here we've got Centaurus A, a galaxy, so you can kind of see fairly
big compared to the stars. But when we actually look
at it in radio waves, this galaxy is revealed to its true self. So we see these incredible
radio waves, radio lobes, injecting material out of
the central black hole. And if we just had an optical telescope we'd say, oh, well, that's about it. There's certainly no sign of a black hole the way we're looking at it now. But if we switch this radio telescope on at the same time then
suddenly what we can see is a great big sign
saying Black Hole Here. So using all of these
different wavelengths to find out different
things about our universe is what we do on a daily basis. These are very different types of light as you've probably noticed
from the different kinds of well, it's all the same
thing, it's all the same light, but they're all very
different wavelengths. But the one thing they
really have in common is that they're incredibly, incredibly fast. So the speed of light is
around 300 million meters per second, that's really, really fast, which means that when I wave at you, you don't really see any lag at all. So if I wave at you,
then hopefully you're sat on your sofa or your bean bag or whatever and you're waving back
because you can see it almost instantaneously,
but now let's imagine that we were actually on the moon. So on the moon, what would happen would be you would have a signal
going, so you would wave at your friend on the moon
and they would wave back and because it's only 1.3
seconds in light time away, you're quite happy with that,
your friends waving back and yeah, there we go,
little friend waving back, and so your friendship stays intact. But if we then go onto
the next slide, yep. Yeah, sorry, hang on, I
have to go to the next side, so it's gonna take me a
minute, now let's imagine that our friend was on the
moon on the Mars, sorry and if you've got the
same kind of signal going towards Mars then you
can wave at your friend, but it takes four minutes
for the light to actually get to them and another four
minutes for it to get back. And so by that time, you're pretty sad, because you think that your friend has just completely forgotten about you. Just left my Duplo person
somewhere though, okay. Now, oh dear, sorry, I've just gone on too far then, there we go. Okay and now you might've
heard the very QI-able fact that the light that we see from the sun is actually eight minutes old,
I've got a pretty giant sun here but I can't actually
fit it in the thing. But anyway, so light takes
about eight minutes to get to the sun and it takes about
eight minutes to get back, by which time you've just lost all hope that your friend's even seen you and the friendship's probably broken. Now, what this means is that because the light takes eight
minutes to get to us, we are seeing the sun eight minutes ago. So anything that happens on the sun, whether it's your friend waving, whether it's a solar flare,
whether it's a supernovae, we will only learn about
it eight minutes later. Now we can extend that
even to a larger scale. So let's say that we were going
to wave to our alien friends in a completely different
galaxy, a nearby galaxy. Now the light, because
this galaxy is so far away, the light would take an
incredible 2.5 million years to get to that galaxy and
another 2.5 million years for our friend to wave back, by which time we're not just really
sad, we're actually also really, really, really
dead which is a problem. Now this again is really
great because what it means is that we can look back in time. We can look back 2.5 million years ago and see Andromeda or
whatever nearby galaxy is, we can see our nearby galaxy as it was two and a half million years ago and also, equivalently our alien
is actually not waving, if they are observing us right
now, they're not observing us watching a boring institution lecture, they're actually observing the
earth 2.5 million years ago. So what they're seeing is one
of the first ancestral blocks of humanity, which is
pretty, pretty crazy, right? But this is exactly what
we're doing on a daily basis in astrophysics, the longer
light has taken to get to you, the further you are looking back in time. So we can really use this to fill out the timeline of our universe,
so here we've got a timeline of about 14 billion years because we think that give or take that's roughly how long the universe has been knocking around for. We know lots about our earth,
because we can just look out the window for start, we
can do lots of tests on it. So we can put that on, on our notice board and be pretty happy that
we know lots about it. As we go a little bit
further back in time, as I've said, a few
seconds away is the moon, about four minutes away is Mars in terms of light travel time,
but we can still find out a lot about them, in fact,
you know, there's plans to put boots on the moon, boots on Mars. So it will be that we're
even going to have humanity back on these structures
at some point soon. And then we've got the
closest galaxy to us, that's about 2.5 million
years away, Andromeda and even further, we can
look back even further, with incredible telescopes
and see galaxies for millions to even
billions of years old. And indeed the Hubble
Deep Field is a photograph which was taken by the
Hubble Space Telescope and what it did was it stared
at a tiny patch of the sky, about a 10th of the area of the moon, a patch of sky that big and
it stared at it for a while and what it found was deep as in very deep in light travel time, it found galaxies all over that patch of sky,
so just thousands of galaxies and I'll do a bit of a
larger image of that later, but the point is we can
really push back to about a billion years after the Big Bang, maybe 800 million, but
it's a bit contested, so a billion years after the Big Bang. And we can even jump
much further back now. So to go right to the start
of this universal timeline, we know quite a bit
about the Big Bang now, we've got a lot of theories
for a 100 years now, all about how the universe started as an infinitely dense
point and expanded out a huge amount to the
universe that we see today. And we've even managed
to measure the radiation from this Big Bang, which I'm going to go into a lot more in a minute. So my point here is, is that even though this is not remotely to
scale, the point I want you to take away is that we've managed to fill out huge chunks of our timeline and we can be really,
really smug about that, but there's a whole era missing of about a billion years in length and then we call this the
era of the First Stars. So if we look on a bit
of a prettier image here, it's kind of just saying the same thing, which is what happened here, what happened where the question marks are, we know that there was a Big Bang. We know that when we look around us now, there is incredible diversity,
incredible complexity in terms of structure, how on earth did we go from one to the other? And so let's have a
look here, there we go. As I've just mentioned we
believed that there is a Big Bang. Now the Big Bang, as I've
just mentioned to you, is this infinitely dense
point expanding out which is entirely preposterous. I say it very easily in
one sentence but actually to believe that there is
a Big Bang to understand why we believe there is a Big Bang is a whole different thing entirely. And so I'm to start
going into a little bit about the evidence for the Big Bang, because it is important because
if there isn't a Big Bang, if there isn't a start to
the universe as some people did believe a 100 years ago
they thought that the universe was infinite in time, infinite
in space and so forth, there wasn't the first of anything. So if I'm going to talk
to you about first light, the first baby steps of the
universe, the first stars, then there's not much point
in me doing it at all, if there wasn't a Big Bang, if there wasn't a first of everything. So the first thing I want to convince you of tonight is that there was a Big Bang. And the first piece of evidence
that we can give for this is how the surrounding
galaxies are moving. If you think back to the last
action movie that you watched, so probably starring Bruce
Willis and Arnold Schwarzenegger and Sylvester Sloan, I'm not sure, but imagine that there
is a gigantic explosion. Now, what you see is you see
the people, you see the debris, you see the buildings, you
see it all flying apart. You see them all moving
away from each other as they're blown away,
hopefully, not blown apart, blown away by these incredible explosions. And what we actually see
in the surrounding galaxies is a very similar thing,
so I'm still not sure if you can see my pointer,
but it doesn't matter. Hopefully you'll see the red
arrows here and the point is, that when we measure
how all of the galaxies around us are moving,
they're all moving away. And we can be pretty sure about this because how these first
galaxies are moving, we can find out by looking
at the light they emit. So here, what I'm showing you in the color is an Example Spectrum, we call it. So all of the different colors of light that a galaxy might give out, all of its stars give
out at the same time. And normally you would
expect this spectrum to be quite full, which means lots of lots and lots of color, so no gaps. And when you get gaps in your spectrum, as you can see here with the dark lines, we call those absorption
lines, what that tells you is that there was a
certain chemical element, so let's for argument's
sake call it calcium, for this demonstration,
if there's calcium present in that galaxy in large
amounts then that calcium likes to absorb wavelengths of very,
very specific wavelengths, specific to that element
and so what you'll find is you'll find absorption
lines and it's kind of like a barcode which tells you exactly what the ingredients are, so
we can look at this spectra on earth and we can tell that there is calcium present in that galaxy. Now, if the galaxy moves away from us, what happens is that we perceive the light from that galaxy to be
what we call red-shifted. We perceive those absorption lines to be moved up the spectrum
to the red wave so red-shifted and as well if the galaxy
is moving towards us, then what we do is we see
those absorption lines shifted to the blue end and we
know that's not where they are meant to be
because we can put calcium in a laboratory, we can chuck
a whole load of light at it, and we can figure out which photons, which wavelengths it prefers,
so this is a really cool way of figuring out what speed
and what direction et cetera, all of these different
galaxies are traveling at. And like I said, apart from
Andromeda, apart of Andromeda which is moving towards
us on a collision course, it's the vast majority of these galaxies we see moving away from us at
very, very, very high speeds, which is an indication that
a big explosion has happened. And you can't really
get a bigger explosion than the entire universe starting with an incredible inflation period. The second piece of
evidence for the Big Bang is the radiation that it leaves behind, so this has got a very
grand name, the cosmic, meaning all around us
kind of thing, big scales, microwave meaning microwave wavelengths, background meaning it's not
in your face and radiation. Okay, so as the universe is expanding, then the radiation of the Big Bang, it moves to longer and longer wavelengths. So this radiation is everywhere, this radiation is pervading
the whole universe and as it goes larger, it loses energy, it loses energy, it loses energy, until eventually that light
get shifted straight out of the visible wavelengths and
into something much longer, the microwave's for example,
the radio a little bit. And interestingly if you are old enough to have had an analog
television when you were young or even older then you will
know that when you used to tune the stations between
the different TV channels, you got a hissy kind of
static like and interestingly, a significant portion is small but there, a portion of that static
noise was actually from the cosmic microwave
background, good. I've just realized my
video wasn't on, sorry, so you couldn't see me gesticulating
wildly, but never mind. And what we can see with the telescope is not just the static on the television but you can actually see the
cosmic microwave background in full glory and full
color and so we have these space telescopes that have been for the last couple of decades really filling in this information. So the point I want you to take home is that we have seen this,
is that the Big Bang, there's more than that
in terms of evidence, but the two big pieces
for most astrophysicists is the movement of the
galaxies and the fact we can actually measure
the leftover radiation to exactly what is predicted
by Big Bang theory. And so even though the idea of a Big Bang is completely preposterous,
it's also completely acceptable and completely believed pretty much within mainstream astronomy,
so what that means for us, is that there were first
stars, that there were these first entities that
we want to find out about. But one question is a really
good question to have, that you might be too afraid to ask is, well, hang on, if there was a Big Bang, that's already completely ridiculous. So is it possible that the
first stars, the first galaxies, just popped out of that Big
Bang completely, fully formed? Is it that we don't really
need to find out how those entities got created
and how they formed, but actually that the first stars just went pop, out of the Big Bang? Well, we know from understanding
the physical mechanisms behind the Big Bang what was going on, we know that just after the Big Bang, it was incredibly incredibly hot. Incredibly, incredibly
violent and so you have all of these photons going all
around and basically messing up, building anything taller
than anything greater in size than a helium or hydrogen atom. So hydrogen atom is made of
just for example, one proton. So if we use it like
that and helium is made from two protons and two
neutrons and some electrons. And what I always imagine
is that if you are in a room of sugar-crazed toddlers
or a sugar-crazed toddler, then you can try and build a bigger tower, a bigger atom but it won't be too long until you get your little
friend coming along, and cracking it down into
its constituent parts. So while you might try
to build a taller tower and you might succeed sometimes, it's really not so long until eventually you're just left with your
basic building blocks. And that's exactly the
same in the early universe. Try as you might, you
might build up lithium, but you'll end up with just
hydrogen and just helium. And that's certainly not what
constitutes a first star. So we definitely need
to figure out how we got from a universe that was
just hydrogen, just helium, all the way up to where
you've got galaxies, you've got planets, you've
got carbon based life forms that breathe in oxygen, how
did we get to all of that? So hopefully I've convinced
you that there were first stars and now I will need to convince you about why we need to care
about the first stars. So we're missing around a billion years of our timeline which is a huge amount. And missing a billion years
of a 14-billion-year timeline is really equivalent
to missing for example, the day of your child's birth right up to their first day at school. So if you consider how much
stuff happens in that time, it's a really formative time
and if were to imagine a alien from Andromeda coming down
to see us and he wants to learn all about the human lifetime, so what happens in the
average human lifetime? So an average one, you start with a baby, you become a child, you possibly procreate and then you enter the autumn
and winter of your life. But if our alien flies
down to worth and only has limited time, limited
research funds, is really tired, then they might only take samples. They might only photograph, for example, certain humans in certain types and they might end up
with incomplete data, which is exactly what we're
looking at with the first stars. And it doesn't take too much imagination to think, well, okay, I
heard that person talking about where babies come from, so maybe that's actually
what's happening here. This model, it fits our data perfectly, excellent job done, time for a beer. And so our alien would
just float off happily back to Andromeda completely
unaware that they've made completely incorrect conclusions because of their missing data, because
of then incomplete data. And as I've said, we're missing about that first billion years of
life, which is equivalent to your first five, six years of childhood and it's no wonder that as
astrophysicists we're kind of quaking in our boots
about what's being missed. The next reason to care is because the first stars themselves
are extraordinary. So I study them because I love them, because I find them absolutely fascinating and because to hop back
to my Egyptological days, they are lost, so they are
something that we can't look up in our backyard, I can't walk next door and talk to an ancient Egyptian. It's just not possible anymore. And they're different, so this is our sun. This is an incredible image of our sun. You can see some solar
flares, you can see sunspots, we love our sun very much
for, for many, many reasons. And for the first star
here, I've had to kind of put an artist's impression
which was basically me, just going PowerPoint artists
effects and making it look a bit fuzzy because we
haven't got a single picture of a first star, they're not
around anymore or are they? We'll talk about that later but mostly they're not around anymore,
so we can't take pictures of them, but we know a lot about them because like I said, we
can do the kind of maths of what the chemical
cooling reactions were, how big a star could get,
how small a star could get. We can do all these calculations. So to the best of our
knowledge these first stars were about 100 times the mass of our sun. Some simulations even
think that they were up to a 1000 times the mass of our sun, which is a really, really huge amount. That's a really, really big difference and it's very difficult
to kind of imagine, but for the sake of the fun,
it's kind of the difference between a red squirrel and a great Panda. That's a huge difference in terms of mass and it's what we are looking
at with these first stars. And this analogy, stretched analogy, works even better because
like the great Panda which is on the verge of extinction, it's the same thing with our first stars. We think they are either extinct or on the verge of extinction, so definitely worth looking up. The reason we think that we can't see them around us anymore that they are extinct is if we look at the mass
lifetime relationships of stars. So if we have our first
star, they are really, really massive and really,
really massive stars guzzle through their hydrogen
that they are fusing. So all of the fuel that gives out the heat and the light they'd
cancel through that fuel at an incredible pace,
because they're just more gravity, more
contraction, more pressure. And so they will have a short
lifetime of say a million to probably near a 100 million years, which is really, really
short in terms of stars because stars like our sun,
they're like the friend that you take to a restaurant
and they just pick over a side salad, they are very leisurely, in terms of their consumption of hydrogen and so they will last
more like 10 billion years before they run out of
fuel and that's just about the lifetime of our sun, our
sun's nearing 9 billion years, of which it's halfway
through, which is good. Don't like to think about the
end of that half to be honest, but it's also the time that
Andromeda is due to collide, so we can't be sure how
much time we'll be around, but who knows maybe we'll
have managed to get some kind of extra galactic movement by them. So we think that these first
stars are extraordinary in themselves but also
because they're extinct. And more than that,
they're not just contained in themselves or are very
interesting to look at and then we move on to the
next thing in the museum, they actually changed
the universe in a way that no other star has managed to do, in quite such a dramatic
fashion and they're very, very different in that
they contain fewer metals and we category as
stars as astrophysicists in many many ways, because
we liked collecting things. And what we call these
first stars are metal-free. And that is because they formed out of gas that is just hydrogen and just helium. And so I'm just trying to, yeah, so you can see the hydrogen and the helium on this image here and every other element on this periodic table you
might be having PTSD hawing back to your chemistry lessons right now, from when you had to go,
hydrogen, methane buline. As astrophysicists, we're really used to rounding up absolutely
everything in our universe, because huge distances, huge timescales, we round everything up
and so we've rounded up the periodic table too because pretty much everything's hygiene and helium and then everything else,
we just call it metals. So sorry to any chemists that are present, but that's the way it
is and so if we go back to this lovely picture
here then what we're saying is that here we've got
an arrow talking about how the stars evolved over
the timeline of our universe. So we start off with
just hydrogen and helium. And so we call these stars, metal-free. These stars fuse the
the hydrogen and helium into slightly heavier elements
like lithium, beryllium, carbon, nitrogen, oxygen
and as they explode, they send all of these materials flying and then they can come
together when the gas is cooled down, they can come together and all that gas can come together, form a new star, but this time it's got a bit more metals in, so it's metal-poor. And then we go on to the
stage where our sun is at now, so the stage of our universe
where we're producing lots of kind of sunlight stars and they are what we call metal-rich,
so they've got lots of metals and it's actually still just
a small percentage compared to the hydrogen in the
star, but it's there and it's enough for us to categorize it. I'll just flick through
my lovely slides here. Yeah, okay, so as I've
said, you have the fusion, lots and lots of fusions,
heavier elements and boom. You manage to take all of
those heavier elements and seed the local universe, such that the gas is no longer primordial,
it's no longer pristine. It's no longer just hydrogen and helium, it's actually got carbon,
nitrogen and oxygen. And so early in the universe,
what we're looking at is as I've said, just
hydrogen, just helium, nothing very interesting
to look at at all. As I've mentioned before with the cosmic microwave background where
it was very early on, it was, you know, very bright,
you would have probably seen it as well as, yeah,
you would have seen it. As the universe cooled
down to say 500,000 years after the Big Bang then
everything was very dark. Everything was incredibly boring and so if you had your Tardis
and you went back in time and you saw it, you'd
be really, really bored because this is what you would see, is not my presentation broken. But somehow we get to the
point of seeing galaxies all around us, just like
this and as I promised, this is a slightly larger
version of the Hubble Deep Field. And this is on my kitchen
is on the big canvas on my kitchen wall because I just love it. I can stare at this for hours
because if you just look at some of these spirals
like on the right hand of the image you've got
this yellow gorgeous spiral, you've got really flat spirals
looked out from the edge on, you've got orange ellipticals,
every piece of light on here is galaxy, which apart
from the odd interloper star, but the vast majority are galaxies, which is just fascinating
to me, because this came from a postage stamp size, so
less than a 10th, what is it? I think it's, if you hold
out your thumb and you close your eye that's about
the the patch of the sky that's covered, even smaller
than that about a 10th of that that's covered by this kind of structure. And the only reason that
this can happen at all is because you have the
metals to form them. And it's only because of the
first stars that we created those metals and we
were able to then go on to forming galaxies and
planets and of course us, okay. So, hopefully I've now convinced you that there were first stars and hopefully I've also convinced you
that they were extraordinary and worth learning about and
what the aim of this game is of course is to go from a
rubbish artist's impression that I mocked up to an actual image, and actually learning
about that first star. So how can we do this? Well, we can start by
looking back in time. I'll take a drink for a moment, while you read that terribly
inspirational quote. I spent a long time at the start
of this talk convincing you that as astronomers we
can look back in time, which is a skill set you
have to have on your CV. And what that means is
that, of course if you are on Andromeda or a nearby
galaxy then you might see one of the ancestral branches of humanity. Now to turn that around
all we need to do then, is we need to tune into
light that has traveled so far to get to us
it's lost so much energy against the expansion of the universe, just like the cosmic microwave background, that it's shifted from
the shorter wavelengths into the longer wavelengths, if we tune into that wavelength just like
we tune into a radio station, then we might be able to
see the light from this era of the first stars and
that's what we're doing. And this is just as crazy and
just as real as for example, if I was interested in
ancient Egypt and the speed of light was much, much,
much, much, much, much slower, then we could just use clever optics to look back at Egypt from
where I am now and I would be able to see them building
the pyramids firsthand. So not a simulation, not what we think from their tombs and the writings, but actually see ancient
Egyptians building these pyramids. And that's what we're
doing, we are using the fact that light has a finite speed, how much energy it is,
how we can tune it in, we're using all of that to
actually see light from the era of the first stars to
actually see this era begin and how it progressed and ultimately how it ended and the
second stars came along. Now to do that, we can't unfortunately just use a handheld garden
telescope as you've seen here, we use something called a radio antenna. And that's because the light
has been red-shifted so much, you can see here, so I was
talking about red-shift, as which would go to
the longer wavelengths, so you're getting into
the longer wavelengths as it travels near the earth
and so that's no longer in the optical part of the spectrum, that's in the radio part of the spectrum. And so what we do is
we use radio telescopes and here's one I made earlier. So this is an artist impression
of on an amalgamation really of real antennas and the background of the the Milky Way and what are this is, is called the square kilometer array. So this is the second
big telescope in my life, we'll get onto the first in a minute, but it's very simple
technology in some ways, because as you can see this is basically what we call a Christmas tree antenna. I'm not just making that
up for the festive season, but it is because they look
roughly like Christmas trees and because we decorate them
accordingly every December. And the idea of this is that
we can put loads and loads of these antennas out and we can tune in to the right wavelengths that we know that this light from the
first stars is at the minute, because it's traveled so far to get to us and we can pick up that
radiation and we can learn things about the first stars, but
how do we actually do that? Well, what we're doing
when we're tuning in is we are taking the temperature
of those first stars. We're taking the temperature
of the surrounding gas at that time actually, this
is one way we can do it. One way can find the first stars. So on the top here, I've
got the age of the universe, going from the left, which is very young, and going all the way to the
right, which is present day. Now on the left what I want
you to see is that before the first stars came to
life then we've just got a universe of hydrogen,
of helium, of photons, and if we take the
temperature of that gas, then it's very, very cold,
there's nothing much heating up. You can't see anything,
so it's very, very cold. But what we can tune into
specifically is that, as I've got a picture here
between the blue thermometer and the red thermometer
is that we can tune into something called a
21 centimeter radiation and this is the radiation that is coming from the era of the first stars. What it is is that when you
have a complete hydrogen atom, so a proton and an electron,
then that very specific makeup can produce a photon which
travels off with a wavelength of exactly 21 centimeters,
which by the time it's reached us, by the
time it's been stretched, it's lost all his energy,
it's at wavelengths of nearer two meters which is
why we use radio telescopes, 'cause that's about the
right wavelength for radio. So now let's look at what happens when the first stars come to life. So you have all this hydrogen
pervading the universe. What happens is that this
hydrogen starts to come together. It comes together closer and
closer, closer through gravity, it gets pushed together by
constant gravitational pressure and then suddenly right at the
center, you get this fusion. You get these first stars turning on and it happens over here,
it happens over here, it happens over here, one by
one lighting up the universe. So like fireflies in the
nights, just coming on, like switching on the
ferry lights, if you will. But as these first stars
come on, they heat the rest of the hydrogen that hasn't become a star, so there's still lots of
hydrogen floating around, lots of clouds of
hydrogen and a bit helium and what these first stars do
is they heat this hydrogen. And what we measure when we measure this 21 centimeter radiation is we measure a jump in temperature and so
when we measure that jump, we know that the universe's,
the light from that time is coming from a time where the
first stars have come alive. And then as we go longer,
so longer from the age of the universe to let's
say a billion years after the Big Bang what
happens is not only do these first stars heat the hydrogen, but by now you've actually
got the second generation of stars and you've
got the first galaxies. And at this point, what
happens is something called ionization which I've got here between the red and
the empty thermometers. What happens is the photons
that are being emitted by these first stars and galaxies
and everything like that, It breaks apart this hydrogen,
it breaks it apart completely so that the proton and the
electron are completely split and so no 21 centimeter
radiation at all can be produced. And what this means is that
suddenly you can't measure any temperature of the hydrogen gas, because it's just not
emitting those photons anymore for you to pick up, so you
have an empty thermometer as it were, but that
still tells us something. So even measuring when we get
no reading of temperature, tells us when these first
galaxies have managed to ionize all of that gas, how big were they? How many there were to be able
to do it in that timeframe. Okay, so a bit more just to hammer home what it is we're actually observing. I've got the same
timeline here but in red, I'm kind of representing all
of the radiation that comes from this time and what
we would actually observe. So with these radio
telescopes, what we can do is we can build up a picture of all of that hydrogen across
an area of the sky. So we tune it in, we tune
into exactly the wavelength, so about two meters that we're expecting this first light signal or to come to. And what we observe at first
is we observe the light from what's called The Dark Ages, so it's dark for an obvious reason, as I've said because it is actually dark. The first stars haven't
come on, so what we see, is in our picture is we see
a completely full picture of hydrogen 'cause
there's tons of hydrogen, it's all held together, it's
potent electrons together, so there's lots of this 21
centimeter radiation, lovely. As we move on these first
stars start to ionize and heat their local
hydrogen and it's what we call a Swiss Cheese Model, so, again, here's one I made earlier and I was just telling
the producers this stinks. I didn't realize that I'm not gonna use this as a prop again, but yeah,
you get bubbles and we call this the Swiss Cheese
Model, put that over there. And as the first galaxies come
on and the second generation of stars start emitting
lots of ionizing radiation, so lots of these photons
not only do you get nice, kind of a nice clean
Swiss cheese-like bubbles when the first galaxies come on and the first black holes actually, you get huge amounts of radiation which makes very, very large,
very, very wispy bubbles which coalesce very quickly, which overlap and eventually, you really kind of get your empty thermometer,
so in the black here is an absence of 21 centimeter radiation. So you start to measure nothing at all. And what we can do with our
radio telescopes now is, we can reverse engineer
this, so what we are going to measure and what we are
measuring is this bottom row. So we are measuring all
of these images throughout about a billion year lifetime,
the first billion years of our universe, we're
building an actual home movie, and so not a simulation
but an actual movie of how this hydrogen is changing and while that might not seem
particularly impressive, compared to say the Hubble
Ultra Deep Field images where you've got all
these beautiful galaxies, I'm showing you some red
with some black holes in, which I get it, it's
underwhelming, but it's all about what we can infer from
this time and remember, we are talking 13 billion years ago, so give us a little bit of slack. So if we measure a complete
picture of hydrogen, then we can know that that
points back to The Dark Ages, that's when The Dark Ages are happening. As we go through our
movie, it's still full. It's still full, it's still full, oh, there's the first holes. It's the first kind of Swiss cheese we see and we start measuring
that upturn in temperature, which is before that and
that we call the Cosmic Dawn. And so from looking at these bubbles, how big they were, how many they were, we can really start to infer
what the first sources were, how many first stars,
how long did they live? When did the second population
of stars come around? When did the first
black holes come around? We can tell all of this actually, by just looking at these bubbles. So it might be low tech, it
might be low production value, but it's incredible in my mind anyway. And it's something we've
managed to do actually. So the first detection of the Cosmic Dawn or the end of The Dark Ages,
the start of the Cosmic Dawn, was tentatively made in February, 2018. I say tentatively because
it is yet to be validated by another experiment, so this is a really, really hard experiment and so to really believe the
result we need validation, but everything looks pretty good actually and what they measured was was
this change in temperature, which showed the first
stars had started and that was at about 180 million
years after the Big Bang. So we've got a marker,
we've got a timeline for when the pyramids
were built if you were. That was the Square Kilometer Array that I was talking to you about. That's being built in
the next couple of years and we'll go on to that a
little bit more in a minute, but the Low Frequency
Array in the Netherlands is the telescope which is is closest to my heart at the minute because it's the first telescope that I used and it's the one that I
continued to use today. And again, the technology
is a bit underwhelming if I'm honest, but you've
got the antennas here on the top right and then
about 48 of those are under all of these black tarpaulins
squares in the background. And I can't remember what
my t-shirt says but I feel like it might be fitting
for tonight, something like, Oh, well, nevermind a
translation, it appears everything in my life is spectacular going wrong or something like that, very
British problems, but anyway. So with the LOFAR, we've been observing for about 10 years now
and it is mostly based in the Netherlands but
it also stretches out to a lot of Europe, so we've
got stations in France, in Italy, in England and Wales, all of these different islands. So in all of these different places. And so by combining the signals from all of these different
times, we're able to tune into this 13, billion years ago. I said that we've been
observing for 10 years. So you might ask, well surely
you should have done it, by now, surely you should have
come up with something more than just the starting
point, at 190 million years, and the reason is that it's
really, really difficult, because when you might have
had this question already, but when you have this
light from the first stars weaving its way to you, it
gets to you at a wavelength about two meters, so we
tune in to a wavelenghth of about two meters, great. Problem is, is that a lot of
stuff, including mobile phones, solar panels, wind farms,
all of these things produce interference that is
at a wavelength of two meters. Tons of stuff in our galaxy produces stuff at this wavelength as
well, so it's like driving along your road and
tuning into lovely, calm, classical radio first stars when suddenly a pirate radio station comes
out of nowhere and it starts giving out very very
different kinds of noise. So let's say heavy death
metal or something like that and that's a problem and it
means that our first star signal is buried just act like archeologically, under about a signal of
around 10,000-ish times the size of the first star signal. So that's a huge, huge
problem to have to deal with, but it's not one without hope. This is what I do on a day job and the first star signal
is a different shape, just as if you were listening
to these two stations, you could still tell which part of which signal belonged to each station, because they're playing very
different kinds of music. And it's exactly the same
with what I do in this. Okay, so we've talked about LOFAR. I'll just be very brief
on Square Kilometer Array, but it's gonna be awesome,
whereas LOFAR's got about 3,500-ish antennas just
a couple of thousand anyway, with Square Kilometer Array, we're going to be building 512 stations,
so 130,000 antennas in total in the Western Australian desert, because it's really quiet there, which is what you need
for big radio experiments that are trying to listen into the early, very quiet signal from
the very first stars. And it is an incredible undertaking. It's such an incredible undertaking that the UK government was fighting to get to be one of the first to
actually donate money to it, which just shows you,
you know getting money out of our government is no easy thing, but they were jumping on this, okay, to give their amount of money in and it's because it's driving innovation. So this is one of my reasons
to care about astronomy, if you don't care about
astronomy and it's that, for example, the fiber optic
cable that's where we need to connect all of these antennas
together could wrap around the earth twice and so
that's a huge amount. And we're driving innovation now because these fiber optic cables
cannot move data quick enough for us, we have to delete data sadly, on the fly as it as it's happening, because we can't store it all. We're filling about 35,000 DVDs a day, a million laptops for you anyway and it's a huge amount of data. That's overloading computing chips, it's heating them up, so
we're driving innovation in how to cool these computer chips. So there's a huge amount of investment in this next generation telescope, the Square Kilometer Array, like I said, it's turning on in a few years. We'll probably get the
first real science results, probably in more like
five years, six years, maybe even a bit longer than that, but that's not too long to wait, but while we wait them
are another couple of ways that we can look at these first stars and I will spend a bit
of time on them now. So stellar archeology
is one of my favorites. Sorry I'm just using this to track which slide I'm on, there we go. Stella archeology is
one of my favorite areas for obvious reasons
just because of the name and what stellar archeology
is is not looking back to the birth of these first
stars, but actually kind of looking at the artifacts
that got left behind. Now, you might say, well, hang on, how did anything get left behind? Because what you've
said is that they lived very, very short lifetimes of a million to a 100 million years and
that's absolutely true, we think that most of the
first stars were very massive and so lived very, very short lifetimes, but we also think because
of lots of simulations now that these first stars were
born with sibling stars and we think these sibling stars
were probably a few of them and they're probably much
lower mass, such low mass, about 80% the size of our
sun that they would have had the lifetime or will have a lifetime of about 13 billion years which
gives them just enough time to still be around today
in our local Milky Way. The problem is that these first stars were pristine in nature, so as I've said, is like hanging your
beautiful white, dazz white and washing out into your London backyard. It starts off really lovely itself, so really metal-free, unpolluted,
but it is not too long until everything looks a bit rubbish and it's the same with the first stars. So whereas they start
metal-free, they start pristine. Their outer layers very
quickly can accrete metals. They can get polluted by
their local surroundings and that happens for 13 billion years. So stellar archeology is
about looking in our backyard, looking at all these different
stars and figuring out which ones are actually first
stars under all that gunk. And you might look at the wrong one a lot, but you also might now and
then get the right one. And the problem is is that these stars are really, really well
camouflaged so this only needs to be shown like twice so
we can move on already. But the point is that, you
know, they look almost exactly the same as every other
star and the reason I talk a lot about Egyptology at the same time is that there's so many
parallels to be drawn, because it's not often mentioned
that when Howard Carter found the tomb of Tutankhamun, he didn't just stumble across it. What happened actually was that
he bought the permit to dig there from another fellow,
Lord Carnarvon paid for it and he spent five years
gridding up the entire site and going square by square
by square to the point where even Lord Carnarvon was saying, that's it, I'm cutting
you off, you've had enough of my money, you've
found absolutely nothing, at which point after five
years, Howard Carter says, look just one more, dig,
one more dig and I'm done. Guess what you find,
which is crazy, but true. So at the point he finds, you know, the biggest archeological
discovery in history and is rich beyond his wildest dreams at which point Lord Carnarvon, presumably forgave him pretty quickly. And this is what we're going
to do with our first stars. So it's about looking
at the entire Milky Way, which is about 250 billion
stars plus or minus a 100 billion, that's how many
they are we can't count them. And it's about looking at
each of the stars in our grid or the ones we think are most likely to be metal-free, how do you know that? That's another thing that
we're struggling with really and you look at the light
that's being emitted by those stars and as I said
before, if you have metals, like carbon, iron, calcium
present in your star for example, you will get absorption
lines in your spectrum. So you will get dark lines
pertaining to those elements. And so what we want to
do is we want to find a metal free star where
we can't really observe those absorption lines
at all or we only observe the tiniest, the faintest
gray of a line if you will, that we could attribute only to pollution. It's hard though because when
you have 250 billion stars to get through you can spend an awful lot of time looking up the wrong ones. And this is a field that
is incredibly interesting. It's incredibly challenging, but I think on the same time scale, as, you know, building the Square Kilometer Array, we're constantly pushing further down. We found even what we think to be a second generation star
which is a star so old that we think it formed
only from one supernovae. What's a supernovae you ask? So supernovae is the third and final thing that I really want to
talk to you about tonight, because it's the third and
final way that we can look at this era of the first stars. Now, as I've mentioned, unfortunately, we can't see the light from
the first stars themselves because it's just too
faint, we can't pick up that signal optically,
but if these stars explode in what are some of the
brightest explosions in our universe which is a
certain type of supernovae, so supernovae just means the
whole star explodes basically, we do have the option or the
possibility rather of being able to observe this light
with a big space telescope. And so that's what the American certainly are going to try and do,
it's not the only reason or by far the most important reason that they have built this telescope, but what are they going
to do is they're going to launch a rocket and they're going to do what I call an origami space telescope, where over an agonizing month it folds out it's five sun shields, just
like your dining table, if it's got leaves on
it, it unfolds each leaf to make a mirror, which is quite frankly, as I write in the book, just terrifies me, because this has cost $9 billion, $9 billion so far to build and the idea that it might not unfold
correctly over that month, I mean, I should say that, you know, they've tested it so
much that the probability of anything going wrong
is just minuscule now, but still I'm a worrier
and it would worry me. Yeah, if we can just, thank you very much. Yeah, $9 billion, so you
might be sat there going, we're in the middle of a
global pandemic, $9 billion? Well obviously there's
$9 billion has been spent over a very long time 'cause it takes a very long time to think
up these experiments. But as one astrophysicist
is quoted as saying, and I'm not sure it's true, but anyway, the overlaying message is, he said that "That's only what Americans
spend on potato chips annually." So actually $9 billion you have to set in the context and $9 billion, it's fostered huge collaboration. You need expertise from around the world. You're creating new technologies
like the folding out the sunshield, nobody's done that before. Nobody could do that before
and it has applications in defense, in military and all sorts. Fiber optic cables all of these things that are coming from the
Square Kilometer Array. But just for the science,
you know, I won't apologize for saying that I want to do all of this not to create better fiber
optic cable, but because we can. We can look back in time, 13 billion years and observe these first stars
forming, we can observe them. Now we can observe them, their
artifacts and we can observe their deaths as well using the supernovae. And the aim of the game is of course, to go from we can detect the first stars to we have detected the first stars. And I really do believe that's going to be in the next decade which is
why I wrote a book really, to pass on my excitement
and I've touched on a lot of the subjects here but
there's a lot more in there. And at the end of it all,
it's incredible science which I just love and
it's incredible discovery, so wonderful things,
wonderful things all around. And thank you so much for
your attention and yeah, there's my book, it's really pretty. So think about buying
it for your loved ones or for yourself, thank you. (audience claps)
