(dramatic music) (audience applauding) - Thank you very much. It is a historic place. Thank you very much for coming
to this wonderful place. It is an amazing time
in astronomy right now, because of the launch of the
James Webb Space Telescope. So, how many people watched the launch of James Webb on Christmas Day? Look at that, very impressive. Did it spoil your Christmas lunch? It nearly did mine,
because I was so nervous about all the things that I knew might go wrong on that launch. But the good news is that
James Webb's performance is actually better than the specification and its lifetime is gonna
be 15 years, not five years. So, we're gonna have
fantastic opportunities with James Webb. Now, this deep image, which was first released to the
public in July of last year, the first scientific image that was released at a press
conference hosted by Joe Biden. And what you see is an eight-hour exposure with this fantastic new telescope. There is a bright star here
in the center of the field, but that's not really of interest. What is of interest is all
of these white objects, which are galaxies that are
physically at the same distance. We call that a cluster of galaxies. They're gravitationally
bound to one another, and even that's not the most
exciting thing in this image. What's really exciting are
the objects that are red and distorted and magnified
by this cluster of galaxies. This is a phenomenon that was predicted by Einstein over 100 years ago. It's called gravitational lensing. It's similar, but not
identical, to optical lensing in the sense that this is a huge, this cluster of galaxies, is like a huge telephoto lens in space. And James Webb is peering through it and using that as an additional telescope, a sort of free telescope, if you like, to look at the distant universe. These objects in red are much further away than the cluster of galaxies
in the foreground here. Now, Joe Biden introduced this image. I think it's fair to say he didn't completely grasp the physics of what was going on in this image, but you know, he had many other things on his mind at the time. When we look out in space
with a powerful telescope, we look back in time. Astronomers are time travelers. You're familiar with, you know, the layers of rock in the Grand Canyon, and you know that as you go further down, you're going back in history, is very similar concept
when we look out in space. The further we look, the further back we're
looking back in time, because the speed of light is finite. The Sun is eight light minutes away. If the Sun were to mysteriously disappear we wouldn't know for
just over eight minutes. That's the light travel time
from the Sun to the Earth. The nearest star is just
over four light years away, but the situation is
completely transformed when we use a powerful
telescope like Hubble or the telescopes that
I use on the ground. We're looking back not millions of years, not even a billion years,
but over 13 billion years. Now, the universe itself is we
think 13.8 billion years old. So, that's about three times
the age of the solar system. And we're looking back
then over 13 billion years to when the universe was less
than 10% of its present age. So, the challenge and the excitement, is to try to piece together the history of the universe
via direct observations. And obviously, to do that we need to know how far back we're looking. You see, when we look at this picture, not all of these galaxies
are at the same distance. Some of them are very nearby, some of them are very far away. How do we know how far we're looking? And that's obviously, very
important as a timestamp for determining the
history of the universe. We don't live long enough to
witness any galaxy evolve. So, it's a statistical question. It's a little bit like if you
didn't know the human lifetime and you are only on the
Earth for a few minutes. You might piece together
a human story from a baby that you saw to a teenager
doing something terrible to, you know, an adult being sensible and to an old age person like
me walking down the street. So, you'd piece together
the lifetime of a human by looking statistically
at the population. And that's what we have
to do with galaxies. This is the only equation in the talk, and it is in fact the
only equation in my book. What we're looking at
here is the way in which we can determine how
far back we're looking. Now, you probably know that
the universe is expanding. You've probably heard of the Big Bang and you probably think the Big Bang was some kind of big explosion. And you know, matter was
sent hurling into space. That's not the correct view. Galaxies are not projectiles expanding into pre-existing space. They are actually sitting on
space that is itself expanding. This was the realization that Einstein and many others made in the 1920s, that the solutions of Einstein's equation permitted space itself to be stretching not a static material. So, here's a galaxy here
far away, and we are here. And this blue light ray
is beginning its journey from that galaxy to a
telescope on the Earth. And it's such a long distance and it takes that light
ray so long to reach us that during that time space has stretched. And so, by the time it reaches us, not only has space stretched, but the light ray itself has stretched from being a blue light
ray to a red light ray. And if you've heard the world red shift, that's what red shift is. Now, that's physically
somewhat different from, you know, the ambulance that goes past you and you hear it's siren and you notice the change in frequency. You know the frequency
changes in which sense, depending on whether the ambulance is coming towards you or away from you. That effect is physically
happening in the universe too. Galaxies may have very small motions, which can give them that
so-called doppler effect, but this effect of the
expansion of the universe is quite different and
happens on very large scales. So, what we need to do is
to measure this red shift. So, how do we do that? Well, we have to study the galaxy, the light signal that
we get from the galaxy, and find some characteristic
property of it. For instance, the
fingerprints of hydrogen, or carbon, or oxygen, that's contained in the radiation that the galaxy emits. And if we know in the laboratory what that radiation looks like at rest, then we can measure the shift and how far those fingerprints
have been shifted. And that gives us the red shift. And it's a very fundamental quantity, because it is the factor by which the universe has expanded since
the light left that object. So, every time we measure that red shift, it tells us how much
smaller the universe was when the light left that object. And we can convert that red shift into what we call a lookback time. If the red shift is zero,
the object is nearby, and we're witnessing
it more or less today, at least on cosmological timescales. If the red shift is high, then the universe has
expanded a huge amount since the light left that galaxy. Therefore we are looking at that object when the universe was very young. So, astronomers like
the word lookback time, because it is a very, very useful concept. It's a timestamp, and each
galaxy in that original picture will have a different red shift. So, the technology to measure
this red shift is fundamental to the observational astronomer. So Hubble, which I'm sure you've heard of, Hubble Space Telescope, has now been in operation since 1990. It's still there. It's not at all eclipsed by James Webb. It's still doing fantastic work. And the combination of
ground-based telescopes, which have measured these red shifts and beautiful images from Hubble have given us the first
glimpse of how galaxies evolve. So, broadly speaking today,
there are two types of galaxies. Over here you'll see what we
call an elliptical galaxy. It's a ball of stars. The stars are all more
or less the same color, and it's a very simple structure. This kind of galaxy down here is very similar to the Milky Way. It's a spiral galaxy. It has a nucleus and it has
spiral arms that are quite blue. If we go back to when the universe was only 5 billion years old, these are the kind of
pictures that Hubble delivers. Their red shifts, if you're interested, are listed up here. They're determined from
ground-based telescopes. So, these two objects
here look pretty similar to that elliptical galaxy suggesting that elliptical galaxies formed quite a long time ago. These galaxies resemble a spiral galaxy. They have a nucleus, but
they're not quite as beautiful, they're not as elegant, which suggest is that they're still in a sort of more primitive form. These galaxies here are what
we call irregular galaxies. They're not symmetric. There are irregular galaxies today, but it looks like when we go back in time, there are many, many more of them. Now, let's go to when the universe was only one to two billion years old. And you can see things
really change quite markedly. The galaxies are not symmetric. They have multiple components
as if they're still coalescing and they're physically small as well. So, what you see in this
picture is very similar to that story I told you about the alien that comes and lands on the
Earth for a few minutes. You see the evolution not
of an individual galaxy, but you see a sort of
overall population change from small multi-component objects that are irregular to
the gradual formation of the beautiful galaxies
that we see today. So, this story so far has taken
about 20 years of research with the Hubble Space Telescope and these red shifts measured from giant ground-based telescopes in Hawaii and Chile and other places. But I want you now to contemplate going even further back in time to this concept of Cosmic Dawn. So obviously, this is a
schematic illustration. Time is running from left to right. Here's the Big Bang
13.8 billion years ago. Now, what happened in the Big Bang is it was dense and very, very hot. All of the material was broken into its constituent particles. There were no atoms, no molecules. It was a gas that physicists would say is completely ionized. And there was radiation, because
the gas was very, very hot. And as the universe expanded, it cooled, and about 370,000 years
after the Big Bang, the temperature went down sufficient that the electron and the proton combined to form the hydrogen
atom for the first time. So, we have this period which is dark, where there are hydrogen
gas clouds in space. And this is sometimes
referred to as the dark ages. Now, astronomers are very
fond of the adjective dark. You've probably heard of dark matter. You may have heard of dark energy. We now have dark ages. It's very useful to have
these mysterious terms. It's very good for raising grants money, you know, to continue doing the research. So, these gas clouds of hydrogen collapse under their gravity. They have mass, so they collapse
eventually under gravity, and as they collapse, they get hot. Just like when you pump a bicycle tire and you compress the gas,
the bicycle tire heats up. The temperature goes up and up and eventually, nuclear
ignition is ignited. And that's of course, that
fusion hydrogen to helium is how the Sun is shining. And so, the universe is for the first time bathed in starlight. And that moment we rather
euphemistically call Cosmic Dawn. The time when the universe
is first bathed in starlight. We don't know if it's a dramatic event, you know, suddenly it was
dark and then it was light, or whether it's a process that takes tens of millions of years. And the excitement, and
the story in my book, is that we've reached the point where we hope to witness
this event directly. Now, why is this important? Well, you know, the fusion
that occurs in stars, hydrogen to helium, helium to carbon, oxygen, nitrogen, silicon, iron, is responsible for all the chemistry that we see around us today. The universe at the time of the Big Bang was primarily only hydrogen
and helium after 370,000 years. So, everything that you see around us, everything in this room,
everything in your body, the iron in your blood,
the calcium in your bones, was synthesized in stars. So, this moment when
starlight first emerged is in a sense the birth
of everything that we see. It's a milestone just as
important as the Big Bang itself. So, I have a movie here, which
I have to physically start. It's a regrettable fact
that we live in a world with theoretical astronomers. They have no need for
telescopes or observations that all they need is a powerful computer. And here's a simulation of Cosmic Dawn by one of my theoretical
colleagues, Harley Katz, who's at Oxford University. And what you see here, time is running. This is real time in millions
of years since the Big Bang. And what you see is purple
filamentary clouds of hydrogen collapsing and forming stars
whose lives are so short, tens of millions of years, that
they explode as supernovae. And all the nuclear products that have been synthesized in those stars are then pollutants
that go back into space and then form the next
generation of stars. It's a little bit like college soup. You know, it's basically,
refreshing the intergalactic gas and the interstellar gas in galaxies and leading up to the
chemistry that we see today. So, I like this figure very much, because it sort of mirrors
my own personal career. I was an undergraduate
also in UCL in the 1960s. And what this is, is
the most distant object. Its red shift and the age of the universe when it is being observed as a
function of publication date. And what you see is that
when I was a student, the most distant galaxy was way down here with a red shift less than one being seen a few billion years ago. But then somehow through technology, we've looked so far back in time that we're now measuring
objects at red shifts of 11, when the universe was a
mere 500 million years. That's something like six
or 7% of its present age. And I use this slide a lot. It was produced by one of my
colleagues at Imperial College. But in the space of just a
few months with James Webb, this figure is out of date. That's the progress that we make through new technology and new facilities. So, the big questions that we face today and the theme of the talk is, you know, when did this thing happen? When did this Cosmic Dawn occur? Was it gradual? Was it sudden? And most importantly, can we
witness this event directly? Will we wake up one day
with news from James Webb that we have found an object
emerging from darkness so that we know exactly
when this whole story of all the chemistry in the universe and our presence in it began. So, back to when I was a
boy in Wales, North Wales, I went into the library and picked up this book
written by Patrick Moore. How many people remember
Patrick Moore's programs? Yeah, you see, you are all enthusiasts. And this book, which
I read when I was six, is about a boy and a girl who go to visit their eccentric uncle called Richard by chance. And he basically, has a telescope and he introduces these children to the delights of the night sky. And you know, I was inspired by this book. I realized that there's
a universe up there, you know, that you look up and there's things to discover there. And from that point on, I was hooked. And years later I appeared on his program. You'll remember that "Sky at Night" is was the longest-running program. It was still running of course, but it was the longest-running program with the same presenter in world history. And here's Patrick, and I told him about this
book, and he gave me, when I got home a few days later, I got a copy signed by him of his, what it seemed to be his personal copy. So, it's an adventure
exploring this universe. That curve I showed
you about progressively going to more distant
objects is an adventure that begins with the mighty
Palomar telescope in California, which was first commissioned in 1948 and is still doing great work. It travels to Australia,
where then Prince Charles opened the Anglo-Australian Telescope. A collaboration between
the UK and Australia, which meant astronomers like me had to go all the way to Australia
several times a year just to use a big telescope. The UK then exploited the wonderful skies in the Canary Islands and built the William Herschel Telescope, which is still doing well. And then I emigrated to the United States and used the twin Keck Telescopes
on the summit of Hawaii before returning to Europe and using the European
southern observatories, large, very large telescope. Now, of course, those were
ground-based telescopes. All of those telescopes are very powerful and contribute to the story, but there are space telescopes too. Everybody's heard of
Hubble, it's still going. It has a mirror, two and
a half meters across. The Spitzer Space Telescope, which finished its campaign
a few years ago is, or was, a smaller telescope,
but very powerful, because it was working in the infrared. And now, we have the James
Webb Space Telescope, which has a mirror 6.5 meters across. So, is considerably more powerful. I should emphasize that
the power of a telescope is governed by the area
of the primary mirror, which is the light collection
that focuses the light from distant objects onto
the various instruments. So, generally speaking,
the power of the telescope goes as a square of the
diameter of the telescope. So, the 200 inch, if
you've ever visited it, and now if you are ever
contemplating a trip to California, it's well worth a visit, was the brainchild of this
guy George Ellery Hale. Sadly, he died before the
telescope was finished, but he single-handedly
raised private money for all of the world's largest telescopes. Three of them in succession, a 60-inch, a 100-inch on Mount Wilson, and the 200-inch on Mount Palomar. When I was eight years old, my sister and I had a encyclopedia and in the encyclopedia was
this cutout of an observatory. And it didn't just say
which observatory it is, but it's obviously, the
Mount Palomar Telescope. And so it was amazing to
look at this cutout picture and I kept turning the pages
back to it time and time again. So, Hale, I arguably,
Hale was the first person who really got inspired by this idea of looking back in time. Firstly, he hired Edwin Hubble, whose name graces the space telescope. He also hired this man, Harlow Shapley, who used the largest telescope at the time that Hale had raised the money for, to measure the distance to
this star cluster Messier 13, what we call a globular cluster
just outside the Milky Way. And he realized that this star cluster was something like
36,000 light years away. And therefore we had the capability to see that cluster of stars, you know, before civilization
really developed on Earth. And this inspired him to
create more powerful telescopes and to raise money from wealthy people like Andrew Carnegie and
the Rockefeller Foundation. In 1928, Hale raised $6 million for the 200-inch telescope on Palomar. It was the largest scientific donation, donation to any scientific endeavor, in history at that time. And this sentence was used in his proposal to the
Rockefeller Foundation. You know, I love it. "Like buried treasures,
the outpost of the universe have beckoned to the adventurous
from immemorial times." So, Edwin Hubble appears on the scene, he is an interesting man. He basically, came to Oxford University as a Rhode scholar and studied law, but then he went back and decided he wanted to be an astronomer. He left Oxford back to California with an affected English accent, which really offended
his American colleagues. But sadly, although he was
waiting for the 200 inch, he died from a heart
attack just a few years after the 200 inch was ready for action. And so, he handed the baton to
his disciple, Allan Sandage. And Allan Sandage had a competitor, this man here who's still alive, Jim Gunn. And the two of them, you know,
fought over telescope time on the 200 inch to look
further and further back. Now, you probably think astronomers are, you know, surely they're
just, you know, simple people. They, you know, they go to the mountain, they look through the eye piece, they're very pleasant,
easygoing people that, you know, spend their
nights alone and everything. You can't imagine that
they could be competitive and, you know, cutthroat and you know, trying to prevent each other from getting on the telescope. A few years ago I found
an article in The Times, which had a list of, you
know, the various professions and the stress levels of the professions. And at the top were things like surgeon, you know, stockbroker, politician, and then way down the list was astronomer. In fact it was under vicar, you know, and I thought this is just not right, because astronomers are just as cutthroat and competitive as politicians. So, these two guys fought it out trying to get observing time
on this mighty telescope, which for 40 years was the most powerful telescope in the world. And then along came a woman, Beatrice Tinsley, a New Zealander, who persuaded them that the project they were doing was futile. They were trying to measure the rate at which the
universe is slowing down. And what they were doing
was they were assuming that galaxies were standard objects and if you measured their red
shift and their brightness, then you would be able to
compare the motion of the galaxy due to the expansion of the universe with the distance and
hence the lookback time. And so, they basically,
were trying to measure how the rate of the
universe was slowing down. And Beatrice pointed out to them that galaxies changed
their brightness with time, and so, they evolve. And this was a huge paradigm
shift in the subject when I was a postdoctoral researcher at Durham University in the late 1970s. So, we now, have developed technologies to explore the earlier universe. So, when I first started as an astronomer, believe it or not, we were
using glass photographic plates. So, these are, you
remember the old pictures of the photographer with a tripod and he would have a put a
glass photographic plate in and he would slide the shutter out. And in the 1960s and seventies, that's how a faint object
astronomy was done. And then along came the
Charge Couple Device, the CCD, the digital detector that's
in many of your phones. And that instantly was
30 times more sensitive. So, it's like having a
telescope 30 times bigger than the one you've been using
with photographic plates. And now, these CCDs can be mosaiced, make, you know, megapixel
cameras, hundreds of megapixels. So, we could take a
panoramic picture of the sky, such as this beautiful photograph
of the Andromeda spiral. So, that's the first revolution that I was very fortunate
to witness during my career. The transfer from photography to digital, highly-efficient detectors. The second big thing
was bigger telescopes. I told you the size of
the telescope mirror is the most powerful indicator of the performance of the telescope. It's the light gathering power. So, the Palomar Telescope,
the so-called 200 inch, has a mirror that's five meters across. And these mirrors, such as
the twin Keck Telescopes have mirrors that are 10 meters across, or the Gemini Observatory
has single mirror that are eight meters across. Now, what's the limiting factor in making a mirror, a
bigger and bigger mirror? And that is about eight
meters it turns out is about the largest size for what we call a monolithic piece of glass that can be supported and transported. Imagine taking something
like that up a mountain road. So, the breakthrough largely
first at the Keck Observatory was to make a mirror
from hexagonal segments, 36 segments each about a meter across. If you look very closely,
especially on this slide, you may see the individual segments. If you've got sharp eyes. And of course, the technology,
then all of these segments have to be supported to make a parabolic or hyperbolic surface with high accuracy. And many telescope manufacturers thought this was never gonna be possible, but a man called Jerry Nelson pioneered this technique
on the Keck Telescopes. And then my final technological
advance is robotics. Now, you see those two
sparring astronomers, Sandage and Jim Gunn, were
measuring galaxies one by one. And you know, sometimes with photography they were taking two night exposures. They would start the
exposure on a Monday night and then at the end of the night they'd put the shutter back in and then they'd come back on Tuesday night they open the shutter and carry on. And so, you know, it was really hard work and in the number of galaxies that they could do was very limited, 'cause they were doing them one at a time. But in the field of view of the telescope, there are many galaxies. And so, if you couldn't
use optical fibers, like it's a sort of plumbing really, then the light from all of
these individual galaxies can be collected and
fed into an instrument that measures them all at the same time. And so, we championed this
originally in Australia. This is a sort of manual version where we're plugging the
fibers into a brass plate with the holes in this brass plate are drilled at the positions of all the galaxies in the field of view. So, I don't know if you can see, but I've got a pen and pencil here and every fiber has a number
and every hole has a number. And I'm writing down which
fiber number goes in which hole. And heaven forbid if you
lose that piece of paper, because then you won't know
what object is which, okay? And eventually, we decided
to automate this process and this instrument has the very inspirational name of Autofib. And rather as a publicity
stunt, we use this robot. It comes along and it picks up each fiber and moves it to a particular spot here. The light comes from down from above here and enters a right angle prism that reflects the light
down the fiber like so. And as a publicity stunt, we used this robot to
make a map of Australia, to which the frequent comment
was what about Tasmania? (audience chuckling) Finally, we managed to do
this 400-object robots, which was very, very successful. So, those three technologies
transformed our ability to survey the distant universe. Better detectors, bigger mirrors, and what we call
multi-object spectroscopy. Doing, gathering the
light from many objects simultaneously to make
statistical progress. So, how do we choose which
galaxies we want to observe? How do we get a head start on
which are the most distant? I've told you that a faint galaxy needn't necessarily be distant. It could be a remarkably
feeble object nearby or it could be a luminous
object at great distance. But there's one very nice trick and that is the universe is
full of hydrogen, hydrogen gas. There's hydrogen gas in between the stars. There's even hydrogen gas
in between the galaxies. It's very tenuous, but it's there. And hydrogen has a very important feature. It absorbs light in the ultraviolet. And so, if you take a
picture in red light, in green light, and a certain
kind of ultraviolet light, then the galaxy that's the
most distant disappears. And whereas all the other
galaxies are still there. So, this is a telltale indication that this particular
galaxy is far more distant, because it's behind a screen of hydrogen that's cut it off in the ultraviolet. Now, the Hubble Space Telescope
has many color filters. There are blue ones,
green ones, yellow ones, red ones, and infrared ones. And as the galaxy in this simulation, as the galaxy moves to higher red shift, and hence more distant objects, you can see it disappears
successively in each filter. So, all you have to do then is to take color pictures with Hubble and determine in which color
filter the galaxy disappears. And that gives you an
approximate red shift and hence an approximate
lookback time to that object. Now, just to, as an interlude, what's it like to go to a big telescope and observe how does it work? And the answer is we
write proposals and time, if the proposal is successful, time is scheduled in six-month blocks and every astronomer is allocated either one or two or three nights on a particular calendar date. And if you go to the telescope, basically, you know you are scheduled
on those particular dates. You have to get there unless
you're gonna observe remotely. And you know, it's very exciting. I'm still a romantic at heart. I stand on a mountain top
and I watch the sunset, you know, far from home. And I look at the night sky
and then I go into the dome and I think, what discoveries
might I make tonight? And let me tell you, making a discovery in real
time is inspirational, particularly for young students. So, here's a student,
former student of mine, operating the Keck Telescope in Hawaii. And here's another one. And if they make a discovery,
it's inspirational, you know, it's telephone
calls home, champagne at dawn, maybe if it's important,
you know, some surprise. A new result that changes the subject. Now, that happens very rarely. Unfortunately, the
downside is cloudy weather. You go all the way to Hawaii or Chile, and remember you've been
allocated only those nights. There's no rain check if it's cloudy, you know, there's somebody
breathing down your neck coming on tomorrow who's
got another project. And the most annoying thing
is it's cloudy for your run. And then miraculously, when
the next guy comes, it's clear. You know, you have to say, "Oh, very nice, you're lucky." You know, and then fly all the way home. So, this is a cloudy
night photo, all right? This guy here, these
are all former students, and they've all done very well. This guy here has finished his thesis. He's cheerful, but he, you know, he feels sorry for the cloudy weather. This guy here is Italian, I don't know, they're always happy. This guy here with his head on a side, his thesis is rapidly
going down the drain, because it's, you know, the
fourth cloudy night in a row. And so, he's wondering
what he's going to do for the rest of his life. This is where the professor has to, you know, my role is then the cheerleader. I have to buy the pizza
and the bottles of wine. And that's why I think this
is slightly blurred, probably. (audience laughing) Okay, so how far, I'm heading
in the right direction. I'm nearly at James Webb. So, how far back did we look with Hubble? Well, we used two techniques. This one, is to point Hubble in a non-interesting area
of sky for two weeks. And I remember somebody,
one of my colleagues, a professor who's very critical actually. And he said, "You know, Richard, that is the most stupid thing. Just, you know, it needs
no intellect at all. All you'll do is steer this telescope, open the shutter for two weeks. You know, it's not imaginative." But that's what we did. And there are 3,000
galaxies in this field. It's a size across here is about a 10th of the diameter of the full moon. And it's called the Ultra Deep Field. It's the deepest picture
we ever took with Hubble. And it was taken in 2012. Now, there was, you know,
okay, there was the Deep Field, then there was the Very
Deep Field, you know, and this is the Ultra Deep Field. And so, I'm privileged
that I had the final word in the Deep Fields with Hubble. Now, these objects marked with
colored squares and numbers are the most distant
objects in this image. And we located them with those color, remember those filters that slid back and the object disappeared? That's how we knew that
they were the most distant. And we thought this object was by far and away the most distant. We thought it had a red shift of 11.9, which would mean it was being seen when the universe was about
4% of its present age. But we, you know, we
weren't completely certain. And this was a collaboration
with colleagues at the Royal Observatory in Edinburgh. If any of you have been to Blackford Hill is a beautiful spot. And that was what we did. That's the first way of
looking at great distances. The second method is this
gravitational lensing. So, let's go into gravitational lensing in a little bit more detail. Has anybody ever heard
of gravitational lensing? Mm, very good. Excellent, okay. So, Einstein basically, postulated that light could be
deflected by massive objects. Space can be shaped when
you have a massive object. It distorts space around it. That's the origin of gravity. Newton was very worried. How does the Earth know the Sun is there? How does it know to go in a circle? The answer is the Sun distorts space and the Earth is going round
in curved space around the Sun. And there was a test of this, a light ray, you can see the deflection here of space. A light ray would be deflected by the Sun. Now, you can't measure a star normally, 'cause the Sun is too bright. But at the time of an eclipse, you could measure the
positions of the stars and you could see if they
were in the same place or not as when the Sun isn't in the way, and they should be deflected
according to Einstein. And this inspired this guy, Sir Arthur Eddington at
Cambridge, brilliant theorist, but he decided wisely
to become an observer for this particular experiment. He went to Principe, an island
off the west coast of Africa, took these photographs and proved that the stars were not in the same place as when the Sun isn't there. And you would've thought
he would be famous, but it really catapulted
Einstein into fame. My wife gave me a Einstein
calendar a few years ago, you know, every month had a picture of Einstein doing something different. There was Einstein on a bicycle, Einstein against the blackboard, you know, Einstein pulling a face. And then I realized by
the time we got to April, he only had one suit. It was always the same suit. Eddington was contacted
by The Daily Telegraph when this fantastic verification of the bending of light came out. And a journalist asked him said, "Professor Eddington, it's suggested there are only three people in the world who understand Einstein's theory." To which apparently Eddington said, "Who's that third person?" So, he was a bit of a puckish guy. Okay, so back to Joe Biden again. Here's the cluster of galaxies. Now, we see the deflection can be used as a powerful magnifying glass to get a sort of free
additional boosting power for the Hubble Space Telescope or any ground-based telescope. And here's a simulation
of a transparent lens moving across a field of the sky. Is a simulation obviously, but you can see that the
magnifications can be enormous, if the alignment between
the background object and the lens and the
observer is very accurate. Even far away from the center of the lens, you can see the images are
stretched and hence magnified. So, this technique has been
used by Hubble as well. Here's an example. Here's a cluster of galaxies. You see, we can get multiple images. You can see A, B, and C are
three images of the same object. And you can see the images of A, here A and B, are stretched. And so, the light is magnified
by this foreground cluster. So, those two techniques used by Hubble, you know, the mundane project to point in a boring area of the sky and expose for two weeks and to look through a
series of lensing clusters. And this is where we got to with Hubble. It's the census of how many galaxies there are per unit volume
as we go back in time. So, if you like, just
focus on the top axis. This is the age of the
universe in billions of years. So, here's a billion years,
here's half a billion years, and remember we're way over
here, 13.8 billion years. It's a logarithmic scale. So, from minus one to minus
four is a factor of 1,000. So, clearly we're running outta galaxies. There are far fewer galaxies
out here than there are here. So, we're seeing the birth of galaxies and the continuous assembly. More and more galaxies
forming all the time. And if we extrapolate this to zero, you would think that where that's, you know, that's where it all started. Unfortunately, you know, with Hubble there were two teams
and they didn't agree. This team felt that the numbers
were falling very sharply. This team felt that they were
declining more gradually. And you can see it makes a big difference as to when Cosmic Dawn would've occurred. Already this is outta date in six months with the James Webb Space Telescope. There's one other
technique that you can use to try to pinpoint when all this happened, when all this starlight first occurred, and that is to go to
a very distant object. So again, this is age of the universe. Find some of the most
distant objects out here, like this one, and try to
estimate how old they are. And the analogy here is, you
know, you walk down the street, you see a four-year-old boy, you weren't there when he was born, but if you can figure out how old he is, then of course, you can say
exactly when he was born. Likewise, if we can go, if
we can find a technique, for determining how long this
galaxy's been forming stars, how old are the stars, then even though we can't use Hubble to look further out here, it just doesn't have the capability. Then we can pinpoint when
Cosmic Dawn occurred. So, here at UCL, that's what we did just before James Webb was launched, we went this time to Chile,
to the Atacama Desert. No trees, very, very dry. In some places it's never
rained in recorded history. Can you imagine? Here's the galaxy that's
very distant object. And here we are using
the very large telescope to measure the age of this galaxy. Europeans love their comfort. This is the only observatory
with a swimming pool. No expense spared of course. And so, we applied this
technique to six galaxies and we estimated their ages and we predicted when
Cosmic Dawn occurred, somewhere between 250
and 400 million years after the Big Bang. And crucially, we calculated that the soon to be launched
James Webb Space Telescope had the capability to look
that bit further back in time and detect these objects
in their earlier state. So, James Webb, I was very
lucky just before the pandemic, I was at a conference in California and I was able to visit the
James Webb Space Telescope in its clean room in El
Segundo, Los Angeles. Here's a human. And as you can see, it's a
segmented mirror telescope. It's got 16 segments and the
aperture from here to here is six and a half meters. You can see it, the mirrors can be folded so that it can fit in the
nose cone of a rocket. The mirror is too big to be
launched in its open format, it has to be folded. So, that's one risk. You know, when it's in space,
it has to open up again. These mirrors are gold coated. They're actually, they're
made of beryllium. Beryllium is the lightest metal. They are gold coated, because gold is almost perfect
reflector in the infrared. In the optical it's too expensive. So we use aluminum, but
in the infrared aluminum it's reflectivity falls off. And so, to ensure the
best possible performance, no expense spared, the
mirrors are gold coated. Now, my history with this
project goes back to 1996 when NASA set up a committee
called, as you can see, HST, Hubble Space Telescope and Beyond. And I was the only
European on this committee. I was at Cambridge University at the time. And we proposed in this report in 1996, the next generation space telescope. And so, that's 25 years from that report to the launch on Christmas Day 2021. And that's, you know,
that's what it's like in space astronomy I'm afraid. It's a very expensive mission $10 billion. We can discuss that if you're interested. So, here's a very painful moment where the $10 billion
facility is hanging by a hook. You know, I hope they took some tablets and it's being transported
to the nose cone of this Ariane rocket in
Guiana in South America. One of my former students,
Anna, former postdoc of mine, flew to Guiana and watched the launch, but you know, I decided to
watch it on TV Christmas Day. And here's the launch on Christmas Day. So, you can see in this schematic here, it's in the nose cone of this
rocket, the Ariane rocket. Here's the launch, here's
the last view of James Webb over the Horn of Africa on its way to 1.5 million kilometers. Now, Hubble orbits the Earth and of course, you remember
that it could be correct, it could be maintained and
upgraded using the space shuttle. No such luck with James Webb, because it's an infrared telescope. It has to be cool, it has to be out in deep
space, beyond the Moon. It's at a very special place
called the Lagrange Point. This is the Earth, this is the Sun. The significance of this point here is that the gravitational pull that James Webb gets from
the Earth plus the Sun is the same gravitational pull that the Earth gets from the Sun alone. And what that means is that
the Earth and the James Webb orbit the Sun at the same angular speed. So, they're always in sync. And that's, of course, very
important for communications. It would be really hopeless, if James Webb was the
other side of the Sun. So, what have we found? So, in the space of, must
be now six months or more, seven months probably, there are 75 papers on the
internet about distant galaxies with the James Webb Space Telescope. I've selected one figure here
from the group at Edinburgh. This is the same figure
that I showed you before, the number of galaxies per unit volume. And you remember there was controversy, whether the numbers were falling steeply or going continuously. This is how far we could look with Hubble. And you can see we can now
extend this diagram out to a red shift of 16. There's some controversy
about this last point. And the implication is that Cosmic Dawn, the so-called holy grail, which is this little symbol
here, is within sight. Now, let me just pause at this point, go back to this point. Remember these red shifts are determined with that color technique where the filter, you remember that slide where the images drop out and so forth. It is an approximate method and it has been known to be wrong. And so, getting the spectrum of the galaxy in order to measure the
red shift accurately is the next step. And the first results are very promising. And I've decided to show the object that we found with Hubble that we thought was at
11.9, but we weren't sure. And Emma Curtis Lake, who's an astronomer at the
University of Hartfordshire, managed to get this spectrum. And here's that hydrogen absorption, there's no question it's
at a red shift of 11.6. So, we're very pleased about that. And here's another spectrum. So, where we can see the
fingerprints of nitrogen, helium, carbon, magnesium, oxygen, neon, and a galaxy at a red
shift of of 10.6 or so. So, this is the beginning of chemistry, which we couldn't do with Hubble at all. So, you know, the logical step now, to go back to this decline, is we would expect the
chemical composition of these objects to be going down, because the stars have had less time to synthesize the heavy
elements that we see today. And so, you know, the logical thing would be to find an object
that's chemically pristine. And that would be the
first telltale indication that we finally reached
the beginning of the story. So, I'm more or less done. You know, this key signature is gonna be the telltale signature that we
don't see the heavy elements that we see around us today
in these early galaxies. That would be an indication that we finally reached the beginning. We're witnessing an early
object emerging from darkness. It's not gonna be easy. These spectra are very challenging to get. The period in time where a galaxy is unpolluted is very, very short. So, these objects may be very rare. We may have to do a statistical experiment to get the final answer, but we have 15 years we hope of successful observations ahead of us. And when I look back over my career and all the facilities I've used, all the telescopes I've
used have done far more than they originally predicted they would. Astronomers, unlike politicians, deliver far more than they predicted. So, on that cheerful
note, thank you very much. (audience applauding)
