(strange curious music) (audience applauding) - Thank you. Thanks. Thank you, it's an honour and a privilege to talk in this room, so thank you for coming and
helping make it possible. And thank you for joining me on, it's a very exciting day for me at least, which is the day that my new book, "Our Accidental Universe," has finally hit the press. And so that's our topic this evening. It's a set of stories of how astronomers
actually make discoveries and how we find out about the cosmos. And this is really important to me because I think, especially when speaking in venues like this on stages like this, it's quite easy to give
the wrong impression. It's quite easy, I think,
to give the impression that we know what we're doing. And this is sort of played into by the way that we teach
science often, you know? Science is, to some people, a method for testing hypotheses, right? What we do is we all sit
round, we think hard, we come up with an idea, we
work out a way to test it. We run to our laboratories
or our telescopes, we test it, we say yes, we were right, and then we spend the rest of our careers telling our colleagues that we were right and maybe writing books that say we were right
and things like that. And actually that's
not the fun bit at all. It almost never works like that. Actually, science progresses
in a chaotic fashion. Astronomy in particular progresses based on a series of accidents, things we stumble across in the cosmos, things sometimes the visit
our solar system unexpectedly or which turn up in telescopic images that we weren't expecting. And those, those moments
where you don't know what you're seeing, those moments where you don't
understand what's going on, those moments where you stumble over and are surprised by a new
idea, those are the fun bits. And I think that by thinking
about those surprises, those happy accidents
in studying the cosmos, it really helps us think about
our place in the universe. So for example, we should think a bit about how to think about beings
that exist in a universe, not just on a planet. This is possibly the worst picture anyone's shown at the Royal Institution, which is rather nice. It's a shot of a night
sky just after sunset. There's a horizon without
much definition to it. A few hills in the distance
and the sun has just set. And I dunno if you can see on the screen, but there's an evening star in the sky. If you were outside
tonight and it was clear, this is perhaps the
view you might have had with Jupiter low in the west at this time of this year. In this case, if we zoom in, turns out that star is double. There are two stars there. And that's because this is a shot not of an earthly landscape, but of a landscape on Mars taken by a Mars rover that landed there. And that evening star in
the sky isn't Jupiter, it's the Earth with the moon next to it. And so we have this
really wonderful, I think, juxtaposition of something very banal. This is a terrible shot of an evening sky and something really profound, which is seeing our planet reduced to Carl Sagan's
famous pale blue dot. And I think there's lots
more to say about this image, but one of the things I want to draw out this evening is no one built a Mars rover, spent billions of dollars
sending it to Mars to land to look back at Earth. It's there because we want to study Mars, for all sorts of good reasons. And indeed we could be surprised by Mars, which turns out to have a richer history than many of us suspected 10 years ago. But we also get these lovely side effects that teach us about the
universe and our place in it. And actually this theme
of accidental discoveries is particularly prevalent in spacecraft as they've gone and
explored the solar system. So I thought I'd start with my editor's favourite story, the one we kept coming
back to in the book. And it's a story about this
place in the solar system. So this, of course, is
Saturn, the show off planet, the planet with the rings. And it's been an object of fascination and study for hundreds of
years, longer than that really. But since Galileo
discovered the ring system using the first astronomical telescope. And Saturn was visited by the Pioneer probes in the '70s and then the Voyager
probes which flew past, but really, a planet of this complexity, a place that has some of the
solar system's fastest winds, a place that has gas dynamics, in an atmosphere that's so complicated that we still don't quite know what the length of a day is on Saturn. A place that has these magnificent rings made up of millions of icy particles arranged into these
incredibly thin structures. The width of the rings is shorter than, is smaller than some of the
buildings around us here in the centre of London. It's no more than a couple of stories and yet they're there and
apparently long lived. And a place that has a retinue
of moons including one Titan, which is the only moon in the solar system that has an atmosphere, a
thick atmosphere of nitrogen, methane and much other
complexities as well. We needed to send a probe
there to tour the system, to spend time there, not
just fly past but to visit. And that was the Cassini probe, which was launched from the space shuttle and got there in the 2000s. And Cassini was built to study the planet, to study the rings, study Titan, but on its way in, it went
past a moon called Enceladus. Now Enceladus had been discovered more than a hundred years earlier. It's one of the larger moons,
but it's fairly nondescript. This is the best image that existed before Cassini got there. This is a shot from the Voyager spacecraft and you can see it's an icy body the size, it's about the size of the British Isles. So it's a small bit of icy rubble, a leftover, presumably from the early days of the solar system from the time four and
a half billion years ago where the planets were
forming captured by Saturn and in orbit around it ever since. And we can make it look good, you know, here's another early image of Enceladus and all right, if you
put it with Titan there and the rings in the
background, it looks great, but it's essentially just an ice cube in orbit around Saturn. And it was coincidence that
on one of the early loops that Cassini took around
the Saturn system, it happened to be going past Enceladus. Most of the team were focused
on studying the planet itself, on studying the upcoming encounter as it swooped around the
planet and around the rings. And so on that first fly by of Enceladus, no cameras were turned on and most of the instruments
were not taking data. The teams were busy getting
ready for what comes, what was to come a few days later. The one exception was a team behind an instrument
which lived on a long boom that stretched out away
from the Cassini spacecraft, an instrument built and run by a team at Imperial College London by Michele Dougherty and co. And their instrument studied the magnetic field around Saturn. They were interested in the
planet's magnetic field. We know that Saturn has a
aurora, it has northern lights and southern lights just
like the Earth does. And we know that that
magnetic field interacts with Titan's atmosphere. And so Michele and co thought they'd use the Enceladus encounter as a dry run, that they'd check that their
instrument recorded no change as it flew past a small inert ice cube, should have no effect at
all on the magnetic field. And when they came to analyse the data, they were surprised to see
that there was a change, that something near Enceladus was affecting the
magnetic field of Saturn. In other words, there
was some activity there that something was
happening around this moon. They went and talked to their colleagues who were running the other
instruments on the mission and it was agreed that they
would take a closer look at Enceladus and they flew
back over the moon's south pole passing just a few
hundred kilometres I think above the south pole with
cameras on this time. And what they discovered
was completely unexpected. What they discovered was
that Enceladus has fountains, that from its south pole,
water is shooting up into space and they'd just given their spacecraft the first interplanetary bath
recorded in human history. They never went back this closely again because it's presumably quite
dangerous for a spacecraft with sensitive electronics
to fly through a car wash, even one provided naturally
in the Saturnian system. But this is a remarkable discovery. We have water flowing from a
moon that should be frozen. That means that underneath the icy surface there's presumably an ocean. Later experiments as Cassini
went back to Enceladus, which became a focus of the mission. Later experiments showed
that the water was salty, which tells you that
there's not just an ocean but there's an ocean floor down there, a place where water comes
into contact with rock. A place that begins to feel a
bit like the places on Earth where we think that
life might have started, places in the deep sea where hydrostatic vents heat water and provide a strange but rich habitat for all sorts of life. And so from an inert ice cube, Enceladus has become a
place in the solar system where we think we have a good, well actually, that's not fair. It's become the place in the solar system where we think we have the best chance of finding other life. Of course we have to answer questions. We have to answer questions, for example, about whether the ocean is long lived. Have we been lucky? And actually we've managed to solve that because it turns out, and this is my favourite
shot of Enceladus. Enceladus in the centre of this image. What you're seeing there is the water that's spraying from the moon is feeding into a ring around Saturn. It's called the E ring. It had been discovered
long before any probes visited the Saturnian system. It's the outermost, she's
not quite the outermost, it's the most tenuous of Saturn's rings. And it's so substantial that we know that the
ocean must have been there and these fountains must have been active for certainly millions of years. And so Enceladus is suddenly this place that could be a habitat, it became a huge focus
completely unexpectedly. Cassini hadn't planned to spend any time doing
more than taking a couple of pictures of Enceladus. And it's become the major discovery from what was a 17-year mission. And it adds to a picture
of the solar system where ice worlds, worlds with water locked
underneath thick, perhaps icy caps are increasingly common. We see them in Jupiter's
moons, we see Europa, the large picture here, and
Ganymede in the top right, two large moons of Jupiter have patterns on their surface that seem to suggest that
underneath their icy surfaces there are also oceans. Even Pluto pictured in
the bottom right there is seen by the New Horizon spacecraft, which had this heart-shaped feature now named Sputnik Planitia on it, the smooth area you can
see on this picture. A good explanation for why that's smooth is that there's an underwater
ocean with currents that are able to replenish the surface. And so viewed like this, if you ask where the most common habitats for life in the solar system are, the answer isn't in a nice habitable zone, a region around a star where you can exist and wander around on the surface of a planet, it's actually safely locked away under the icy cap of an
outer solar system moon. And if that's true, and let's say these places are inhabited, let's say there is bacteria
or squid or dolphins or who knows, whatever you want to imagine swimming around in the oceans of Europa or underneath Enceladus's icy cap, they, they've reached intelligence, would consider our existence
to be horribly precarious. I mean, how can you live
on the outside of a planet? You know, you're exposed to
solar radiation and cosmic rays and all sorts of things. It would be ridiculous. You can imagine alien
astronomers in these moons putting forward really,
really convincing arguments that the only places you could live are safely protected from
the rest of the solar system. We will look strange to them. Of course, their astronomy
would be a bit different. They haven't been able to see the sky. Maybe they've discovered radio astronomy. One can speculate about what scientists in such
an ocean world would find, but maybe we'll save that for conversation or questions later. The discovery of habitats on the icy moons at the outer planets of Jupiter and Saturn have broader implications still. When we look up at the
night sky, we now know, and this is a completely
gratuitous picture of the night sky by the
way, take a by Will Gater. When you look up at a night sky like this, up at the stars that we see in the sky, you should realise that we now
know that planets are common, very common in the galaxy. One of the great discoveries of the last 10 years has been the idea that the galaxy likes creating planets. That the physics and chemistry that acted in our solar system, which we don't understand perfectly, but whatever processes acted to produce our solar system also acted throughout the galaxy. And so if you go outside tonight and look up, that most of
the stars that you can see, have planets going around them, we think. And therefore we can ask the question whether some of those planets
are suitable homes for life. And there's been an enormous
focus, a targeted effort with dedicated spacecraft and much angst and
argument about statistics to try and determine what percentage of those worlds are Earth-like in the sense that they might support our kind of life and the kind of habitat that we've become used to thinking about here on Earth. But with the icy worlds, we now know that this is not quite the right question. We have to include not
just Earth-like planets in Earth-like orbits. But we might want to
include when we see a star that has a Jupiter sized
planet going around it, we could assume perhaps that
such planet would have moons. We don't know yet. We haven't discovered a
moon around another planet for good reason. It's difficult. But we could assume moons are common in our solar system, so maybe they're common elsewhere and we could assume that
we have to add those to the cosmic calculus as well. And when you do that, you
quickly get to an assumption that there are hundreds of
billions of potential homes for life in the Milky Way galaxy alone. And this creates, I don't
know, how are you feeling? Existential dread, something like that? I don't know, a feeling of of aloneness. It adds to what tends to be known as the Fermi paradox, which is this question of if
life is common in the galaxy, where are all the aliens? And the book is not, I promise,
there's no final chapter that says, and they're here. I thought about it. But yeah, one wants to stay
close to actual science. You know, we don't see UFOs, we don't see signals
bouncing around the cosmos. And so the fundamental mystery
I think in astrophysics at the minute is that we
know that there are places where life could exist. Where we have the raw
ingredients for the kind of life that we see around us
abundantly here on Earth, but we don't see any
evidence of life itself. So there are many possible
answers to the Fermi paradox, which range from, I don't
know, the depressing, you could pick an answer like the fact that you might believe that whenever a society gains technology, I'd say about the level
that we've managed it, it inevitably destroys itself. Might seem plausible on a bad day maybe, but it's not very cheerful, is it? You could reach for, well let's have on the other side you can have a very optimistic solution. My favourite of the optimistic solutions is called the National Park Hypothesis, which is that there's a
sign a few light years away that says, "Leave them alone
until they grow up a bit." That we're a reserve waiting for cosmic maturity. At which point, you know, the
wise species of the cosmos will come and give us their secrets. And if science fiction's
anything to go by, strange drinks that are
mostly blue for some reason. Quite looking forward to that bit. We can have scientific answers. I like the blame the biologists solution. You know, we don't know. I've said there are habitats for life, but we don't know. If I give you a planet or a moon and say, what are the odds of life getting started
given those conditions? We don't know how to answer that question. And so maybe life itself is rare in the cosmos and we've already won the cosmic lottery by existing at all. That we do face an empty,
mostly lifeless cosmos. But our place in it is special. I think we'll put that
in the complicated box. I'm not quite sure how
to feel about that one. Or maybe life is common. An argument made by Simon Conway Morris, the great palaeontologist who thinks that life will
be very common in the cosmos but intelligence will be rare. So maybe life gets started quickly. You can argue that it got started quickly
on Earth, for example. Life appeared very quickly after the Earth reached
suitable conditions. But intelligence, which,
as ever I'll define as having professional astronomers and gins and tonic was reached somewhere in the 18th century by that metric. And so we are new in the cosmos and perhaps this idea
that life will be common but we won't find anyone
to talk to is the solution. Now, I don't know, I'm not going to answer
this paradox this evening. We could keep going and pick many, many solutions ranging from deciding that it's crucial to have a Jupiter in your system to maybe deciding that
the moon is special. But we have looked, of course, if I'm talking about cosmic surprises, the ultimate surprise I think would be a signal from an
apparently intelligent source. And there are plenty of times
in the history of astronomy where just for a moment, we've thought about
whether we might have found such a signal. Usually traditionally, at least, this is the domain of
the radio astronomer. And I don't have time
to go into the history of radio astronomy today, but one of the great joys of the book has been reading up on the history of the frankly slightly
eccentric bunch of engineers who invented a whole new science, a way of listening to the cosmos of using technology
developed for communication here on Earth and then for radar during World War II to detect what was
originally called star noise. Radio signals coming from the cosmos and the way that they were pooed pooed by pretty much every
professional astronomer going, because they didn't use mirrors and they didn't map stars, so
what could they possibly know? That's a whole other story. But originally it was
thought for a long while that aliens would communicate with radio. It's a cheap way of sending
long distance messages across the cosmos. And so when Jocelyn Bell Burnell, working on an experiment
in a field in Cambridge covering 57 lawn tennis
courts with antennae in order to detect
distant sources of light, distant sources of radio waves and try and determine in fact whether they were distant sources coming from distant galaxies
or whether they were nearby. Found what she described as a scruff, on a piece of scruff labelled
just over here as CP 1919. That little squiggle in the signal coming from her radio telescope. One of the first thoughts of
the team who'd seen the signal that was pulsing very rapidly,
several times a second, one of the first thoughts was that this might be an alien signal. And the signal was nicknamed
in a well-known story. It was nicknamed LGM-1
for little green men 1. Jocelyn's written about
this in many places, but I really liked the story that they were very relieved
when they found LGM-2, little green men 2, which
was a similar signal elsewhere in the sky because it was felt implausible that they'd find two sets of aliens sending exactly the same signal or same sort of signal. And so they thought this
has to be something natural. And it turned out to be these are pulsars, these are the dead remnants of massive stars spinning rapidly and sending radio waves
out into the cosmos. It's an early reminder
that radio could be used for this sort of SETI, this
search for life in the cosmos. These days we do targeted searches. This is the big Dish
at Parkes in Australia. I described this earlier
today as on the radio as Australia's Jodrell Bank and managed to offend both Australian and British radio astronomers. So it's its own thing,
it's known as The Dish. This is the instrument
that, in its spare time, carried some of the video signal from the Apollo moon landings to Earth enabling us to watch that one small step onto
the Sea of Tranquillity. And one of the things
that Parkes specialises in is in looking for things
that change in the radio sky, finding rapidly changing
sources like pulsars. It was instrumental in the discovery of a surprising new class
of object a few years ago named with, I guess
some economy of thought, these things are known
as fast radio bursts because they are fast
bursts of radio waves that we see coming from all over the sky. They're interesting, some of them repeat, a couple of them have been identified as definitely coming from distant galaxies and there's one that seems to come from within the Milky Way. Sometimes some of them don't repeat and some of them jump about
from different frequencies and we don't know what these things are. We're currently at the
sort of hand wavy stage where they may be something
to do with magnetic fields, maybe something to do with dead stars, maybe something to do with exotic form of the same type of object that powers a pulsar. But the search for fast radio bursts also contains within it a lovely story about the need to be careful when you are surprised by the cosmos. Along with the fast radio bursts, there were a set of different signals which the team at Parkes called peratons that we're seeing coming
again from the whole sky. So the fact they're coming
from all over the sky tells you that they're not
coming from the solar system because the solar system, all
the planets orbit in a disc. So we then expect if you saw them coming
from around the zodiac, then you've got a solar system source. We also know because they're
coming from all around the sky that they're not coming
from the Milky Way. Because the Milky Way, if you go out and see it on a dark sky or if we look at Will's wonderful photo, you've got the stripe of the
Milky Way there, it's a disc. So we'd expect things, if these
things come from our galaxy, they should follow the
Milky Way, but they don't. They come from the whole sky and they were all at
exactly the same frequency. So there's obviously something special about whatever's producing these things that means that they were
all at the same frequency, like the same channel on your radio picking up on these new cosmic sources. The only problem with these things, with these peratons came when somebody noticed there was a very distinctive
feature about them. And that was that they all
happened around lunchtime. And if you think about it, distant cosmic sources shouldn't know and
certainly shouldn't care when it's lunchtime in Australia. That would be weird or
worrying or possibly both. The mystery resolved itself
when a retired engineer saw one of the papers
that had been published on these things and knew exactly what it was
from the frequency response. It turns out the microwave in the visitor
centre was malfunctioning. In particular, if you obeyed
manufacture instructions, all was well, but if you were impatient and opened the door before it had pinged, it didn't shut off straight away. It inn fact generated
a source of microwaves that could be picked up
by the radio telescope. So we can create cosmic
signals using a microwave. The fun thing is that there's a story which I desperately tried
to pin down for the book and couldn't get anyone
to tell me on the record. So you may not, you can
choose not to believe this, but I know of at least two
people whose summer projects at radio observatories around the world involved trying to break
microwaves in the correct fashion so as to generate peratons. And I love this idea. Imagine turning up, you know, you're 20 or something,
you're a university student, you've got summer doing research at insert name of radio facility here. You're gonna discover
things about the cosmos and you're given a microwave and a hammer. Like, I think, yeah. Now we're talking about how
science is really done, I think, I'm sure those people learn lots. But this idea of needing to be
careful is of course crucial. The other image on this
slide is an artist impression of a planet around Proxima Centauri, the nearest star to the sun. And one of the great joys of doing SETI, of looking for aliens at the minute is that we know now where
some of our nearby planets are and it seems that our nearest star has planets going around it. And so we can concentrate our search on places where we know
there might be places where there might be life. Indeed, Parkes in 2019 picked up what appeared to be a signal that was consistent with what you'd expect from a transmission coming from a planet around Proxima, it moved in the way that we'd expect a planet
around this star to move. This was part of a search for alien signals called
Breakthrough Listen. And the signal was given the name BLC, we've moved on from LGM. BLC, Breakthrough Listen candidate one and the team said about trying
to find out what it was, it seemed real, it seemed to come only when the telescope was pointing at Proxima and not when they pointed elsewhere. By the time they found
it in the archive data, they went back, it wasn't there anymore. So it may have been a one-off and at this point it
leaked to the "Guardian" the sample that the "Guardian"
got hold of the story and wrote it up. And they were very cool aliens,
you know, not aliens found, but astronomers have signal
which maybe, possibly might, could be once we've ruled
everything else out. There's an excellent
piece of science writing that the team I think were quite annoyed that possibly maybe had
escaped into the world. The thing is that once
they'd found the signal, they're able to reverse engineer it. They went looking for things
in the data from Parkes that looked the same as the signal and they found many, many, many of them from all over the sky. It may not have been a microwave, it was probably a
malfunctioning satellite, but it's not aliens. And actually our search,
despite these habitats, as you'll know from the
paradox that I brought up, hasn't found us any alien radio signals. But instead we've started to think about other ways
we might detect life, other ways we might be
surprised by life in the cosmos. I got involved in this myself by accident. One of the things I do
with my team in Oxford and with volunteers online via the Zooniverse
citizen science platform is look for planets. This is part of the evidence that backs up the thing
I told you 15 minutes ago that most stars have
planets going around them. We can't see the planets directly but we can detect their effect on a star. So this is the sun, which
you'll remember from last year. And this is a video from 2012 where Venus passed in front of the sun, something that's happens
as seen from Earth only twice a century or so. And what you can see on
the left is the nice image and on the right is the even better graph showing the transit and the
graph just shows the brightness of the sun over time. We just took a light metre out into the university parks in Oxford. And what you could see, and this is one of the things
I really love about this, is this measurement will go on to have deeply profound consequences. But it's wonderfully
simple in astronomy, okay? The basis is when a planet
is in front of the sun, you see less of the sun. So it gets a bit fainter, right? That's as sophisticated
as if I hold my finger in front of a light bulb, I see slightly less of
the light bulb, right? But you can tell that the finger is there, you can tell that the
planet is there from the dip and hopefully you can tell
how big the planet is, how much of the star it's blocking and maybe if you're clever, you can start to work things
out about its atmosphere. So this is the game and what we do is we take data from, we used to take data from a
NASA satellite called Kepler. We now use a NASA satellite called TESS, put the data online. You can go to planethunters.org
and sort through that data and look for these dips that tell us that there are planets there. Every month we get to email people and say, we think you found planets. It's great fun. I highly recommend it. Does mean looking at
graphs in your spare time. But I think you're okay with that. Let's look at some
graphs in our spare time. I particularly want to show you this one. This is the data that we had for what turned out to be a
very, very interesting star. So this is a star that has
gone through many names, but when we started looking at it was known as KIC 8462852, which you'll know intimately I'm sure. And this graph just shows
the brightness over time as seen by the Kepler satellite. You can see that just after
we started monitoring it, there was this dip in brightness. So that could be a big planet getting in the way of the star. And in fact it repeats. So now we know that there, we think there could be a big planet and it goes round every couple of months, but actually there's no third
dip, there's no third transit and planets don't take breaks, right? You can't have a planet
that goes round and round and then stops for a bit. So whatever's causing these
dips isn't a normal planet. Didn't think too much about this until about a year later where our volunteers noticed
that there was a very big dip. And that's only in the Royal Institution you get gasps of wonder from a graph. This is brilliant, you
are clearly my people. This is great, but it is dramatic. You were right to gasp. It's a 20% dip in brightness that lasted maybe a week or so and then the star came
back to full brightness and carried on as if nothing had happened. Stars don't do this. Quantitatively, none of
the other 190,000 stars studied by Kepler in its main sample ever did this in the three-year omission. At this point it was
noticed by our volunteers who started wondering about it and then they really started
wondering about it a year later when it did this, I don't even have a
technical term for this other than went on the blink, I suppose. The volunteers got very
interested in this. They called it the WTF star and started coming up with ideas as to what might have happened. They suggested that maybe
there was a dust disc around the star that was
blocking out some of the light. We looked in the infrared,
there's no glowing dust. So we ruled that out. We started getting paranoid. We spent ages doing things like working out which pixel on the camera the star's light was landing on in case there was a duff pixel somewhere. We checked neighbouring stars, we checked the star with other telescopes. It's a perfectly normal middle aged star. It shouldn't be doing this. It was really confusing. And eventually we just wrote a paper which we submitted to the
journal with our volunteers as well led by Tabby Boyajian
who's now at Louisiana State. And we said, we don't know what this is. We found a weird star. It was great, it was really good fun. This is the kind of astronomy
I get excited about. And the journal editor wrote back and we got quite a good report and he said, look, the paper's okay, but there's two problems. Problem number one is that
you've called this the WTF star and our rule is that all acronyms have to be spelt out in full. So WTF stands for where's the flux? (audience laughing) Not my joke but it's excellent. That actually came from
one of the volunteers. So that's good. If you don't know why the older people in the audience are laughing, that's fine. Second thing is they said you
can't and I disagree here. They said, you can't just say it's weird, you have to have a hypothesis, right? Because that's how we pretend
science is done right? We have a hypothesis and we test it. So we scratched around and said okay, the best idea we've got is that there was a comet
in orbit around this star. Comets are icy bodies. We see them in the solar system. They swing into the inner solar system. And sometimes when that happens it's happened to some very famous comets over the years, they break up into bits. The bits by the way are called cometlets, which is one of my favourite facts. And so we said, okay, so
what's happened here is a comet has swung in towards
the star, it's broken up and we have a string of comet bits and every time a comet bit goes in front of the star, we get a dip. Bigger ones cause bigger dips and so on. And we created an unconvincing
artist's impression of exactly such a system. There you go. Apologies to the artist. And we said, okay, this is our explanation and immediately you'll be ahead of me perhaps that there are a
couple of problems with this. One is that I can explain
absolutely anything with this idea 'cause I can arrange my bits
of comet however I like. So does that count as a
proper scientific hypothesis? Not sure. The other thing that
happened was that people who know about comets
got quite angry with us because we know quite a lot about comets. We know for example, that they're typically
a few kilometres across. Here's a scale model of
comet Churyumov-Gerasimenko, the target for ESA's Rosetta probe menacing the city of London. It's about, you know, it's a few 10, a few kilometres across. We would need the largest comet ever seen by a factor of about 10,000
to have just broken up just before we happened to
look at this particular star and that only to have
happened around this star, and not any of the others
that we were looking at. So we were asked sensible questions like how are you forming this
big comet then and so on. So we abandoned the comet idea and other people started
putting forward ideas. The most prominent of them was a group led by Jason
Wright at Penn State who put forward an idea in the main astronomical journal, the astrophysical journal. He said, look, maybe this
is an alien mega structure around the star. That what we have is not a comet, but what's causing these dips is the construction of a
set of alien solar panels. 'Cause surely an advanced civilization would get its energy from orbiting solar panels
in orbit around the star. Obviously they've
constructed large panels, they get in the way of the
star and they block the light. And that's what we're seeing. I think to be fair, they said we should
consider this hypothesis. The media considered this
hypothesis in great detail. I found out about it
when I picked up my phone on a Monday morning and
this voice said, "Hello, this is somebody from the 'Daily Mail.' I hear you've discovered aliens." (audience laughing) I hadn't had coffee. I genuinely said, "I don't
know, I'll check my email and see if we have." I'm gonna show you. I've got a collection of front pages, but I really like the "Independent" because they're the only people who used the word may have
discovered, which was nice. Is this a good idea? Had we discovered aliens? Well it's got the same, you
can criticise it the same way you can criticise our comet hypothesis. You can arrange your alien
solar panels however you like. You can explain any pattern this way. Nonetheless we'd like to rule it out. So we devised a programme of space. We kept an eye on the star using a network of telescopes like this one on Maui. This is the LCEOGT network. LGOCT, one of the two,
network of robotic telescopes. And every time it was
clear they kept an eye on what's now known as Boyajian's star. Sadly the WTF star didn't catch on and we waited for it to dip again. When it did, we used an
advanced communication network to alert astronomers around the world. And people, amateur astronomers, professional astronomers rushed
to observe the star for us. And this time we got
a crucial observation. What we saw was that if you looked at the star with cameras that were sensitive to different colours, so if you looked for
example in the red here with a camera that was
sensitive to red light and one that was sensitive to blue light shown in blue, you can see you get a dip
in brightness both times. But they're different depths. So the amount of dimming
depends on colour. And what that tells you is that this isn't a solid
object blocking the light. 'Cause a solid object would block all colours of light equally. So no alien solar panels, I'm afraid. We did run the numbers
for alien solar panels with Christmas lights on the back. And that doesn't get you out of this. It's probably a cloud of dust
in orbit around the star. And I don't have time to tell
you the rest of the story, but I think today in particular,
it's worth talking about where that dust might have come from. Because in the news today,
in "Nature" this morning, there is a story that says
at least one in a dozen stars shows evidence of planetary ingestion. So this is a story about
planets eating stars. This is hot off the press, it's a really clever study actually. I'm gonna do what they
did. It's a bit dry. So there's the paper and there's
some quite technical text and some graphs, but they provided an unconvincing artist's
impression as well. So let's do that. There we go. Clearly that's what a star
eating a planet would look like. Let's go with that. But the study's really clever. What they did was they took binary stars, pairs of sun-like stars that
are in orbit around each other. And we think that these stars
will have formed together in the same place made
from the same material. And so they should have
the same composition. Most stars are mostly hydrogen, but they have trace elements from carbon and oxygen,
nitrogen and all the rest. So the two stars should
have the same composition. And what they did was they
studied about 50 of these pairs and they found that in seven or eight of them, I mean it's seven or eight, I just can't remember which it is. But you get the idea, there's a significant
difference between the two. One of the stars has more stuff, more stuff that isn't hydrogen. And the hypothesis is that that
difference can be explained by that star having
consumed a planet or so and done so while it was
in its sedate middle age. So this is interesting,
it's a nice quirk of nature, maybe, small one. But what it made me think about was the stability of our solar system. If these systems are eating planets, are we safe? Like, are we okay? Now I should say that
this is breaking news. And so half an hour ago I
saw a response to this survey by a astronomer called Sean Raymond who knows about these things, who pointed out that we
probably shouldn't worry from a solar point view because these are double stars. There are two stars in
orbit around each other, and they're quite a long way
apart each of these systems. And that means that the stars are affected by galactic tides. They feel the gravity of
the rest of the galaxy. And so every so often these stars, the orbits aren't quite stable. They will move relative to each other 'cause they go through
a spiral arm or so on. If you move a star around, you probably disrupt a planetary system. So maybe we don't have to worry. But it turns out that when you
think about our solar system, we should be, I think, slightly surprised that it seems to have been stable for the last 4 billion years or so. There were some studies about 10 years ago that ran computer simulations
of the major planets and the sun in our solar system. And we understood if you
just had the sun and a planet and the planet's in orbit
around the sun, things are fine. The planet just goes
round and round and round until the sun dies in
about 5 billion years time, which is a long term problem that we won't consider this evening. Once you add in a couple of planets, their gravity starts to mutually interact. The Earth is pulled not just by the sun, but by Jupiter, to a
lesser extent by Saturn and indeed even by Venus and Mars, even though they're small, they're relatively close. And calculating what happens in the long term becomes difficult. This is a chaotic system. The experiments that were
done about 10 years ago showed that this system
often went haywire, that Mercury flew off its
orbit, disrupted Venus and Mars, disappeared into the sun reasonably often. And it was actually quite disturbing because if you can't predict
that we were going to be stable for the next billion years, you have to ask whether it's weird that we've been stable for the last four. So either we're lucky or there's something
about our solar system that means we're prepped
for long-term survival. And actually recent work has shown that actually the precise configuration of the planets in our solar system, the presence in particular of a large Jupiter like planet
in a Jupiter like orbit, means that we are sitting pretty, that there's only one in two
and a half thousand chance that Mercury will do something odd in the next billion years. So having made you worried about the instability of the solar system, I now want you to relax. It's all fine. We're not going anywhere. But there's another type
of accident here as well. I think the fact that we find ourselves
in this solar system, we don't know which bits of what we see are genuinely just a roll of a dice. For example, I bet that there's nothing
special about the fact that we have eight
major planets and Pluto. Pluto, not a major planet. We can argue about that later if you like, especially people watching online. But my guess is that the
solar system would be fine, that we'd be just as habitable as a planet with seven or nine or 10
or 14 or six major planets. But maybe it's important
that Jupiter's where it is. For starters, it catches lots of asteroids that come in towards the
centre of the solar system. It's certainly important
that we are where we are on our habitable zone. If we were closer in,
things would be different. One of the stories that I tell in the book is a story about conditions on Venus. Venus should be Earth's twin. It was about the same size as the Earth, formed in the same part of the
disc as the Earth presumably. And yet it couldn't be more different. It's a place with a thick atmosphere of sulfuric clouds with an atmospheric pressure
that would crush you, an atmosphere that would dissolve you. It's so acidic. It's about the same
acidity as sulfuric acid on a school lamp bench. And it has some of the, it's the hottest place
in the solar system. So you'd also melt on the surface. It has active volcanoes,
no plate tectonics. It's a very strange place. And yet recent results have shown that high, from this telescope, the James Clerk Maxwell
Telescope in Hawaii, that high in Venus's atmosphere, there's a layer where conditions
are a bit more temperate, where it's still acidic. Don't go there on holiday, but it's sort of balmy
Earth-like temperatures of about 20 degrees centigrade,
Earth-like pressures. And in that layer, a remarkable woman called
Jane Greaves from Cardiff and her team have shown that there's a chemical called phosphine present in the atmosphere. And that phosphine is interesting because on Earth only
life produces phosphine counting us and our factories as life. But it's not produced naturally. In fact, a major source of it
on Earth is in penguin poo. And it's been used to
detect penguins from space. You can count how many penguins there are by detecting the phosphine
on the ice in their poo. Didn't expect that from an
astronomy talk, did you? So phosphine is what we
call a bio signature, a chemical whose presence appears to portray the presence of life. Now we found it in the
atmosphere of Venus. Does that mean there are penguins in the atmosphere of Venus? Any question, any title, any statement that has a question mark at
the end means the answer is no. So I don't think there are penguins, but could there be phosphine
producing bacteria? Potentially. We don't understand the chemistry of Venus's atmosphere enough to answer this question definitively. But if there is life high in the clouds of Venus, then one way to think about it is it's the last vestiges of what would've been a
very hospitable planet. Early in the days of the solar system, Venus would've been a second Earth. It would've been temperate before there was a
runaway greenhouse effect. You can imagine life
developing on the surface to the same extent that life
developed here on Earth. You imagine a rich biota of
fill in whatever you want to imagine on Venus. Let's have Venusian elephants
and palm trees today, why not? But you know, pick your own species and then the planet warms up. It just through no fault of its own because it's close to the sun has this runaway green away effect. And the bacteria that may be
producing that might exist, that may be producing phosphine
high in the atmosphere would be the last remnants of life clinging on in the last habitable place on the planet. And when you think about that and then you come back
and look at the Earth, you realise the accidents that
have led to us being here. And I write in the book about the fact that once you start realising that we're not doing hypothesis testing and exploring the cosmos, you
end up thinking about the fact that there's a historical story to tell about how we ended up
here on Earth as beings that are capable of
contemplating the cosmos. And you can work backwards from the fact that it was probably good for us that an asteroid happened to
collide off with the Earth off the coast of Mexico and do for the dinosaurs so that scurrying mammals could flourish and end up producing us. It was good for us that the moon exists, something the size of Mars hit of the Earth four and a
half to 5 billion years ago creating the moon, which
stabilises our axis. May have played a crucial role in providing tidal spaces on Earth so that land-based life could develop. It's lucky for us perhaps
that Jupiter exists, as I've already mentioned,
and we may even go back to the fact that the only
reason the sun exists is because a small galaxy collided with the Milky Way
about 6 billion years ago, triggering a burst of star
formation that led to a supernova which sent shock waves rippling through this part of the galaxy, which triggered a burst of star formation that may have included the sun. So we may owe the fact
of the Earth's existence to a particular collision
with a neighbouring galaxy. We have a historical story
to tell about why we're here, as well as explaining the physics and chemistry that led to the processes that powered that supernova,
that produced that star, that formed that planet, that caused the formation of the moon that meant that the asteroid hit us. There's also this sort of historical story and I think we can bring both of those things together when we look out at the universe. So I want to finish with one final story of an accidental discovery. This is my favourite, started
with my editor's favourite, and we'll finish with my favourite. And it's to do with this thing, which is my favourite telescope. This is of course the
Hubble Space Telescope. The first great observatory. Planned since the late '50s, launched into space in 1990. The whole point of Hubble was to get above the Earth's atmosphere, to get away from the pesky interference that we astronomers have
put up with for too long of the atmosphere that yes, we enjoy breathing like the rest of you, but it is a nuisance when you go out and look at stars twinkling. They're not supposed to do that. And it's intensely frustrating if you're trying to take
sharp images of the night sky to look up at the stars
and see them moving around. So the point of Hubble
was to get above all that, to get crystal clear images of the sky. Hubble's not a particularly big telescope. It wouldn't have been the
biggest telescope on Earth in the 1950s, but because it's in space, it was designed to have
the sharpest resolution that had been achieved. And so it was a disaster just after launch when it turned out that Hubble's images looked pretty much like those you'd get from similar telescopes here on Earth. This is the first image
that was sent back. This is Hubble on the right and a ground-based telescope, I think in California on the right. These are two telescopes of the same size, and you might be able to see that maybe Hubble is slightly sharper, but it's not expensive billion dollar space telescope obvious. This was a disaster and it got worse as it became clear that this sort of problem,
this blurred vision, was affecting all of Hubble's instruments, which meant that it was a problem, not with a particular camera, but with the Hubble's main mirror. It had in fact, due to a washer no more than a millimetre thick that was in the wrong place on
a piece of testing equipment, it turned out. The mirror had been precisely fashioned to the wrong shape in an act of precision engineering that was utterly misguided. The team had kept grinding the mirror until it was just ever so
slightly the wrong shape and produced this blurred vision. A fix was needed. NASA couldn't afford to wait. And I should say, I always say NASA here, but Hubble is a Canadian,
European, and American mission. So we should take some of
the blame and credit as well. We actually caused our own problems with the solar panels, but
that's a whole other story. NASA couldn't afford to
wait to build new cameras with adjustments built in. And so they built this
remarkable thing called CoSPA, which looks, it's on the right here, which looks, sorry on the left here, which looks like a sort
of set of dentist tools. Had all of these little
mirrors that stuck up. It was installed by astronauts from the space shuttle into Hubble. All these mirrors popped up
and they corrected its vision. So it's like fitting glasses to three cameras simultaneously. This was a remarkable mission.
It was intensely complex. It involved fixing bits of Hubble that were not supposed to be fixed by astronauts wearing gloves that made it hard to manipulate things. It was a remarkable piece of engineering and human ingenuity. And it worked brilliantly. So this is now Hubble
before and after the repair. This is a famous nearby galaxy. You can see the sharpness
of the new images that were achieved with CoSPA that we were able to see. And so the first few years after the fix from '93, I think to '95, astronomers from all over the
world clamoured to use Hubble, its team worked hard to get
back on track to do the science that it was supposed to be doing
and to keep everyone happy. Now, one of the things that people wanted to do with Hubble was to stare into deep space. In particular, astronomers
had identified a place that they wanted to stare. This is the northern night
sky as seen from the UK. Many of you might recognise the plough. And there's a small patch of sky. It's about a 2/24000000th of the sky, which is about a pin head at
arm's length that lies here, that has absolutely nothing
of interest within it. No stars, nothing. And the idea proposed was to point Hubble at that patch of sky and then wait and try and see the most
distant galaxies ever seen. And this was considered a ridiculous idea for two reasons. One, we've just repaired your billion dollar space telescope. Why do you want to point it at nothing? Are you trying to create a metaphor? You know, this doesn't, it's not good PR. But secondly, eminent astronomers argued that if you assumed that
the distant universe was like the universe
that we see around us, then Hubble would discover no new galaxies and therefore this was
a pointless observation. So we did it anyway, but
only because of one man. There was a guy called Robert Williams who directed the Space
Telescope Science Institute that ran, still runs Hubble. He was the director. He gets a little bit of telescope
time in his personal gift. He can do whatever he wants with Hubble that's safe for the telescope. You're not allowed to point
it at the sun, for example. He also had a problem, which is that his team
were incredibly tired after rushing to get
Hubble back up and running. And so over Christmas in 1995, he decided to do the
simplest possible thing to point Hubble at the same
patch of sky for a hundred hours to allow his team to
take it easy for a bit and see what they could see. And the result of that was that this tiny patch of sky
was transformed into a field of about 10,000 distant galaxies. This is the Hubble Deep Field. There are four stars in this image. Everything else you can see is a galaxy. And these galaxies are so distant that their light has been
travelling towards us for more than 10 billion years. And so we're looking at
the early universe here. This became something Hubble did. Here's an extreme deep field,
which is a very similar thing. Again, you're looking at galaxies as they were in the first
couple of billion years of cosmic history. And the mistake that we'd made was assuming that that early universe would be like the one
we see around us today. It turns out it's much more interesting. It's an early universe
filled with fireworks, with dramatic star formation, with collisions between galaxies with black holes eating material at a rate that hasn't
been surpassed since. The early universe is full of fireworks. And it surprised us to see them, but they were revealed by
taking a punt on an observation that most people didn't think would work. It's about as far from the school textbook method of science as I can imagine, there's
no hypothesis here. It was, let's look and see what we've got. It's a pattern that's been repeated. The new toy, the JWST, the
just wonderful space telescope that launched a couple of years ago with its golden mirror
tuned in the infrared that one of the first things it did was to look at the distant universe and this is a nice galaxy cluster, but the interest here is
in a set of faint red dots, galaxies captured as they were just a few hundred million years after the Big Bang. And once again, I and my colleagues have been surprised by the fact that the early universe is not
like the one around us today, that it's full of fireworks, of more star formation of galaxies forming earlier than we anticipated. Wherever we've gone in the cosmos, whenever we're trying to discover and understand life in the solar system from the clouds of Venus to
the fountains of Enceladus, whether we've tried to
explore the Milky Way galaxy to find weird stars like Boyajian's star, she's still the WTF star to me. Or when we've looked out
to the distant universe, whether we've used radio astronomy or optical telescopes, particles or gravitational waves, ripples in space to look at the cosmos, we've always been in
our best as astronomers when we've been surprised and discovered that we live in this accidental universe. Thank you very much. (audience applauding)
