Invisible Universe

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Hello, I'm Robin Inks.

And I'm Brian Cox.

And in a moment, you're going to be hearing me saying, hello, I'm Robin Inks.

And I'm Brian Cox.

Because this is the longer version of the Infinite Monkey Cage.

This is the podcast version, which is normally somewhere between 12 and 17 minutes longer than that that is broadcast on Radio 4.

It's got all the bits that we couldn't fit in with Brian over explaining ideas of physics.

I do object to the use of the word longer, though, because that's obviously a frame-specific statement.

Yeah, we haven't got time to deal with that because, even in the longer version, we can't have a longer intro.

Can we just let them listen?

I've got an idea.

Can we just not have a podcast version of this intro to the podcast, which can be longer than the intro to the podcast?

Yeah, and then we can have a podcast version of the podcast intro to the podcast.

We can't get started by now, but if you're still hearing this, I don't know what's going on.

And then we can have a podcast, podcast, podcast version.

Hello, I'm Brian Cox.

And I'm Robert Entz, and today we are coming from the Museum of Science and Industry in Manchester.

Originally a railway station, it opened on the 15th of September 1830, making it the oldest

intercity passenger railway service in the world.

And there are still some people waiting on platform 7 for the 1845 to Liverpool.

That's because the station closed to passenger services on the 4th of May 1844.

It was a year, not timed, you see.

Very clever.

And this being the oldest railway station in the world, we thought we'd also do the oldest joke about the oldest railway station in the world.

So there we are.

It's all themed.

Anyway, today's show is about something that we can't see and we have no idea what it is.

Basically, it's what I like to call ghost physics.

There's no such thing as ghosts.

Yeah, but there might be ghosts if they are made of dark energy.

They're not.

Did you hear them?

They were there.

A whole load of them.

Are you saying if you don't know what dark energy is

and you don't know what ghosts are,

then, therefore, dark energy is made of ghosts?

No,

Brian, that is not scientific.

What I'm saying is dark energy might be made of ghosts.

It's possible.

Today's show is all about the invisible universe, dark energy and dark matter.

Together they make up over 95% of the universe, yet we're oblivious to their existence in everyday life.

We're made of star stuff, said Carl Sagan, but the star stuff is less than 5% of the energy density of the universe.

The evolution and fate of our universe today is determined by something different to the stuff that makes the stars, planets, and human beings.

We are all made of star stuff, and in our explanation of the cosmology.

Hey, cool, sure.

I do the Sagans on this show, right?

13 series of the universe is expanding, and within it contains many, many mysteries.

We stand on the shores of cosmic time and cosmic oceans.

Comedic jousting.

It's brilliant, isn't it?

I think we should have a blessed off.

Yes!

Oh, not so fast, underdog.

Oh, you could save pounds!

Poor shaw, I shall crush you!

You'll die today!

Faker off!

Well, yes, this is all very, very, very fascinating indeed.

And of course, yes, the Blenovich limitation effect.

I wondered if we're going to discuss that.

That almost caused me to regenerate from John Pertree into me, but of course,

what happened was I wandered into a cave and there there was some very large spiders there, voiced by Kismet Elgado, and I was overcome by radiation, and then I turned

yes into me, and then yes, I fell off the Lovell telescope and became Peter Davison.

What a very cool way to regenerate, yeah.

I did Colin, not Tom.

Are there any more you can do?

Uh no well, not uh not well I was gonna say not many that are relevant, but I think we started there, didn't we?

So uh

it is nearly John Peel Day when we're actually recording this, but uh there's no there's no point in talking about that now.

Because of course, one of my favourite things is actually the music of the spheres.

And I was going to listen to that on a Friday.

Yes, those wonderful pauses that John Peel would put in just before the record started and sounding very quizzical along the way.

This is wardrobe pump.

Good night and good riddance.

I should say, actually, I'm very relieved that we've avoided the cocks off.

One of the most wonderful things

about being in a helicopter is the way that it just moves my hair magically and

hypnotically.

And often I think, oh, people are listening to the physics and the ideas of the muons and the gluons, but they're not.

They're looking at my beautiful, beautiful face.

But the thing to remember is which part of the words you exaggerate.

and there are all these different versions of Brian surrounding the real Brian and the causality of that is to create a negative reality inversion which if extrapolated to its infinite point I've run out of words now

come to shot of Saturn

they say say to me, like, that's a lovely galaxy.

You'll be fine.

Well, that's what I found that eventually I remember touring and you ended up being Orville, basically.

That was the.

I wish I could fly, but I can't.

It's against the laws of physics.

Have we actually said what the show's about yet?

Yes.

Oh, okay, good.

Let's move on.

So today, how much do we really understand about what the universe is made of?

We have two experts and an impressionist.

See if you can spot which one is which.

And they are.

I'm Tim O'Brien, I'm a professor of astrophysics at the University of Manchester at Jodrill Bank Observatory.

And I've been asked to say what my favorite greatest mystery of the universe is.

I think it's where are all the aliens?

Why aren't they here?

Okay, hi, I'm Sarah Bridal.

I'm also a professor of astrophysics at Jodrell Bank and at the University of Manchester.

And for me, the biggest mystery in the universe is why is the universe expanding faster and faster and faster?

John Coleshaw, impersonator, comedian, amateur astronomer, and the biggest mystery in the universe for me is: when is the point when everything mysterious now will cease to be mysterious?

And at that point, what will the mysteries be then?

Just as Henry VIII would have had no recollection or understanding of Wi-Fi, there are things that we don't know, and I just am very curious about anyway.

This is our panel.

There's a lovely bit, John, when you're actually just leaning in saying that, where some people are looking going, is that his voice?

No, no, was it not at all?

No, I didn't mean like, is that his voice?

I went, is that it?

I meant it was more enigmatic rather than insult.

Well, this is turned several early on this panel.

Several of us have a gormless Lancashire tone on this panel, actually.

Tim, we'll start off with you, which is when did we start to realise that we actually didn't know what most of the universe was made of?

Because there must have been until relatively recently, certainly within the last century, where we kind of went, well, that's the universe, and we've got some idea of what it is made of.

Yeah, I mean, I think it does date back to the early part of the 20th century, so it's back to the 1930s.

And there's an astronomer called Fritz Zvicky,

who's an interesting character.

But what he noticed was that he was looking at galaxies and he was measuring how fast they move.

So they're sort of orbiting one another in groups.

And he was measuring the speed at which they're moving.

And he was adding up how much mass there was in the galaxies.

So he looked at how bright they were and understanding stars to some extent, which we did, you could estimate how massive the stars were, and you could add it all up.

And there wasn't enough mass in this group of galaxies, in this cluster of galaxies, to make them orbit as fast as they were orbiting.

And so, he realized there was something there in those clusters that had gravity but couldn't be seen.

So, there was no light of any type coming from it.

So, you know, it was it was a sort of that was the realization, and that's the first evidence there was of something called dark matter.

And when did that term enter astronomy?

I think he might have actually maybe don't.

I don't know whether Fritz Vicki come up with the idea of the name dark matter.

It sort of developed.

I mean, he was the first to sort of study.

I mean, the other famous example is Vera Rubin.

So, Vera Rubin was she was

another American astronomer, and she looked at individual galaxies.

So, she looked at an individual galaxy and measured how fast they were spinning.

And again, it's just like you know, planets orbiting the Sun, the speed at which they move depends on how massive the Sun is, because that determines the gravitational force between them, and that's what

causes the motion, the orbital motion.

But they looked at these spinning, she looked at the spinning galaxies and saw that they were actually spinning faster than the mass that was inside the galaxy that she could add up from all the light that

she could see.

And that was another key piece of evidence for it.

In one minute or less, how you measure the rotation rate of a galaxy, because obviously you can't wait for it to go around.

The Milky Way is about a quarter for how long?

200, just over 200 million years for the Milky Way to go all the way around.

Yeah, so you can't watch a galaxy spin, sadly.

It's one of the frustrating things about astronomy, of which there are many, but

time scales are quite long

generally.

So, no, what you do is

you can sort of see the light, the visible light from the stars.

So, they're hot things, the surfaces are like 6,000 degrees, they glow in the visible part of the spectrum.

But you can also see other parts of the spectrum.

So, by the time Vera Rubin was doing this work, we'd already found radio waves coming from outer space, and she was able to look at the radio emission from hydrogen gas clouds in the very outer parts of the galaxy, so well beyond all the other visible light, the stars, and see that they were moving at the same speed as the stuff sort of inside them.

And what that told you was there was more and more.

The farther out you went, the more mass there was.

But you couldn't see it directly, you could only infer its presence by the speed at which these gas clouds were rotating, which you could see with these

radio telescopes.

Fritz Ricky, Wicky, was he the one who was a very rude man who used to call people spherical bastards?

That's yes.

That's why

I was moderating my language and saying he was an interesting character.

Yeah, he was.

No, I couldn't remember if he was the one who did it, because that's what I was really enjoying the scientific explanation, but I mainly had swearing in my head then.

So

spherical bastard meant you were bastard from whatever angle you were looking at.

Exactly.

There is a

Rutherford said once of an official in government, he said he was like a Euclidean point because he had position position but no magnitude.

Great.

So, what was the initial reaction though to when that comes up, the idea of dark matter, the idea of suddenly this invisible universe?

What was the initial reaction?

So, I mean, I'm sure there must have been an enormous amount of debate about that when something like that is published.

Yeah, scepticism.

I suppose everyone's trying to come up with what's wrong with those observations that were taken, and then eventually kind of come up with different theories.

Maybe there's something wrong with the law of gravity, maybe maybe there's some other explanation for why there's these strange motions.

And, John, as someone who, you know, you're very keen amateur astronomy, you do a lot of photography as well of images of the galaxy.

When you first found out about this idea, that you are looking, you believe you're looking at the whole universe, you know, seeing all of these one things, and then suddenly you find out, well, actually, you're missing out on 96% of it, and we don't even yet have a proper explanation of what we're actually missing out on.

We have some beautiful conjecture, we have theories that are growing.

How do you feel about that?

I think that's absolutely wonderful, this whole other layer of mystery and fascination.

I do love astronomy to be a real thing of wonder, and for there to be so much that we don't understand.

And it just makes you hungrier to explore.

I once heard an idea that could these objects be moving faster because there's nothing to stop them.

That's one theory I heard one time.

Well, if you throw something and then nothing to stop it, then it's going to keep moving, but it's not going to get faster and faster.

So you've got to explain why something's going to get faster and faster.

And that's where this mystery of, you know, we could call it pink elephants, it's just we have no idea what it is.

Look at dark matter is, so you say it goes back to the 1930s and these observations,

but was controversial initially because you've got to think about the nature of it, what it might be.

So

do we have any theories?

What do we think it might be?

Yeah, I mean, usually, to be honest, when I admit the embarrassing fact that we only understand 5% of the universe, you know, and twenty-seven percent or whatever it is is dark matter, and the rest of it's this this dark energy.

I usually say it's uh Brian Cox's fault, actually.

Because

because actually we think we think probably this dark matter's uh is a particle, probably.

So, I think it's in the realm of particle physics.

Uh that's our best guess, I would say, about um what dark matter is.

So, so you know, there's a particle that we can't that f doesn't interact with with matter and the electromagnetic field in in the same way that normal matter does, so it doesn't produce the photons that we can detect with our telescopes.

That's why we can't see it.

So, in a sense, you know,

it's down to the particle physicist, I think, to find the candidate dark matter particles, which we really do think must be there.

There's plenty of other pieces of evidence that show that

dark matter's there, even though we haven't found it directly yet.

Sarah, you mentioned that today

we have

many more very high-precision measurements of the amount of dark matter in the universe relative to the amount of matter and dark energy.

So, could you just sketch out those today's best measurements of the amount of dark matter?

Yeah, so the best way to learn about the dark matter is through a technique that I work on, so that's why it's best.

It's called gravitational lensing.

And basically,

if you've got a clump of matter, a clump of mass of any sort, whether it's ordinary matter or dark matter, then it distorts space-time.

So, in fact, the light light travels in straight paths in a curved space-time, as you know.

So, therefore, if the light is traveling along towards us, then the light path bends around a big clump of dark matter and then comes towards us.

So, in fact, if it's a bit like if you're looking in your bathroom window,

in fact, the equations are exactly you can map the equations exactly to light traveling through glass of varying thicknesses.

And so, if you look through your bathroom window at street lamps, then you'll see the street lamps look distorted.

Okay, so in fact, if we look at the universe and we look at galaxies which are far away in the universe

through curved space-time, which is distorted by the dark matter, then these galaxies will look distorted.

And if we look at the shapes of these galaxies, we can make a map of the dark matter, and that's the best way to see the dark matter.

I know, John, you used to went on the sky at night a lot, and knew Sir Patrick really well.

And I remember going on the sky at night once, the 700th anniversary

and talking to him about relativity.

And he almost spoke about it, obviously New, but he almost spoke about it like it was very modern physics, even though it's 100th anniversary this year, actually.

Did Do you know what he made of these observations?

We were inventing all this stuff.

We've invented 95% of the energy density in the universe is something else because we can't explain the observations of galaxies and lensing, et cetera.

I think he always spoke about it with a great fascination and for him it was a sign about how astronomy was continuously developing and was always fresh, always brand new, and denoted a time that we're probably never going to know everything.

And I hope it is always like that because it keeps it fascinating.

But he really did sort of, yes, he would talk about the Crab Nebula and the planets and the orbits that they follow.

And then this subject of dark matter, and that eye that closed will close a little more sharply, and he would speak with greater fascination.

What on earth is going on here?

I know there are sultanas held up by the jelly, but visible matters in the universe is quite quite different.

Yes.

Quite, quite different.

He really did.

He did sort of perk up at this

and he'd say, Chris Lintott, what do you think?

You shouldn't avoid the data.

There's a danger, isn't there, admitting that you don't know what 95% of the universe is because it gives it gives the impression that you don't know what you're doing.

You know

what are these people playing at?

But actually, it doesn't.

So, we are, we do make progress every day, and what we've discovered so far does not get chucked away just because we discover that actually there's a large fraction of

the mass energy density of the universe that we don't know what it is yet.

So, you've got to be careful about that.

It doesn't destroy all our other knowledge about you know all the matter that we do understand.

This stuff um was made inside stars and so on that we discovered in the nineteen fifties and uh uh and and so that's that that's just be careful about that.

Don't think we're totally useless.

Sorry,

yeah, well, yes, it so so it could be there's lots of possible theories in particle physics for dark matter candidates, but there's no good theory for what the dark energy could be.

And I think you've got to say, if there's two things in the universe that we we don't know what they are, you've got to ask, is this like epicycles when people were trying to understand the motions of the planets and they thought the planets are moving around the earth and they couldn't quite understand these orbits and then they had to come up with more and more explanations for details on how they could explain this.

And then eventually someone says, ah, maybe it all goes around the sun, and suddenly you've got a new explanation for the whole thing.

I think it's a bit fishy that we've got, you know, dark matter was kind of bad enough, but to have another ingredient when we have really no good theories, you've got to ask, is it like epicycles?

Well, perhaps

we should talk about dark energy because we've mentioned it in passing.

So we've we've talked about dark matter.

Sorry, quick

thing.

Dark energy,

just before we get,

it does seem to be the good thing about this terminology is it really does immediately excite people.

The moment they see, we were talking ages ago, do you remember about eight years ago?

We did an event where a 10-year-old boy put his hand up and you thought he was going to ask you what your favorite colour of planet was.

And he went, Dark energy, Professor Cox, will we ever have an understanding, or is it really just an area of knowledge made up by scientists for something we'll never understand?

And he went, We'll move on.

Next question.

But he was, he was 10-11 years old, and he'd read something just that was enough to go, I may not understand this all, but I'm hooked now.

And I don't know what he's doing, 18, 19 years old, but he really had an excitement in his eyes at the very terminology, the first inkling of that.

And I think, you know, we should remember the terminology is just because there was already this huge chunk of the universe that dominates normal matter called dark matter.

And then we discovered this other even bigger chunk of the universe we didn't understand, so we just called it dark energy.

The name just comes because we dark means unknown, you know.

So, Sarah, could you outline the measurements that led us to suspect this stuff is there, dark energy?

Yeah, so in 1998, they were trying to find out how fast the universe was expanding and how much it was slowing down.

So, they thought the universe was slowing down because you'd expect gravity to pull the universe back in again.

So, the universe expanding, and then gravity is pulling everything together.

They were trying to measure how fast it was slowing down.

What's the deceleration rate of the universe?

And then, when they looked at the data, they looked at supernovae.

So, they looked at these exploding, um, these exploding stars where you've got a red giant is depositing mass onto a white dwarf and it explodes.

And they looked at how bright those were, they looked at how bright they looked at different distances from us, and they found that these supernovae were fainter than they expected.

And then, the way the way that that could be interpreted, the only way they could interpret that was to say that the universe is actually accelerating in its expansion, and that was awarded the Nobel Prize in 2011.

But how does that lead to the statement that what about 70% of the energy in the universe is taken up through that expansion?

So, to cause this amount of acceleration, then you can say how much of this dark energy do you need to match this acceleration rate, and that's where the 70% comes from.

So, it's literally, we picture the universe as a

space and time stretching after the Big Bang, and that rate of stretch is now increasing, is the measurement.

So, yeah, and you fit a cosmological model to the data, you make your measurements of the brightness of the supernovae, you plot them against their red shifts, which relates to the distance, and you know, you can calculate how bright they should appear.

And they were basically, as Sarah said, fainter than they should be.

The amount by which they're fainter tells you how much of this dark energy there must be.

And historically, because this is the hundredth anniversary of general relativity this year, so there's the famous story about Einstein's cosmological constant that he stuck into general relativity, then said it was a or possibly said it was his greatest blunder.

Historians are always arguing about stuff, aren't they?

They argue about that.

Did he say it?

But he said it was his greatest blunder, took it out again, and now it's back in again after this measurement, which you say is remarkably recent, late 1990s.

So, could you talk a little bit about that and

how that was in the theory and what the cosmological constant is?

Well, so nobody has a clue what this is, and you could, I mean, when you when you uh

it is it is frightening, um it's almost almost like a biology panelist.

Oh, no, no,

yes, so Einstein, when he looked at his equations, he saw that the universe

should be contracting and he wanted it to be static.

And so he looked back at his equations and found this missing constant of integration in his equations.

And in physics, when you have a constant of integration, there usually turns out to be some really interesting physical interpretation of that constant of integration.

So that's what we're really looking for when we say that maybe there's some new stuff in the universe.

We're trying to explain a physical understanding of what that constant of integration is, and we're saying it might not just be a constant integration, it might actually be much more interesting than that.

But, in fact, you know, you need more than one piece of evidence to really make some sort of massive conclusion like that.

And so, supernova is just one piece of evidence.

And you mentioned the cosmic microwave background radiation, and for me, that's actually even more compelling but much more difficult to explain.

So, I think that's why people always talk about supernova pictures.

How much does this

the radio telescope?

Obviously, you know, you work at George Bray, how much did that change when we went from you know the these grand, these beautiful, you know, I was down in Hurstmontso recently, there was incredible observatories there and a beautiful history of telescopes, and then we have the radio telescope.

What changes when we go from the traditional lensing to the radio telescope?

Everything, yeah.

I mean, you know, everything literally.

I mean, you know, you go out in a nice, clear, dark sky, uh, and you and you look up, you see, you see the Milky Way arching overhead.

If you look if it's dark enough away from light pollution, But what you're seeing are the stars in the Milky Way.

If you could look up with radio eyes, if you had sort of radio dishes for eyes, what you would see is you would still see the Milky Way arching overhead, but you wouldn't be seeing the stars, you'd be seeing the stuff between the stars.

So you're seeing radio waves coming from electrons that are spiraling around the magnetic field of the galaxy.

So it's a different component of the universe that you just don't see with your eyes.

And then sort of scattered around the sky, there are what look like stars, and they were originally called radio stars.

So bright points of radio light scattered around the sky.

They turned out we didn't know what they were.

We first we thought they were just some particularly special type of star, and it took a while, took until the into the 1960s before we realized what they were.

They're actually things called quasars, so they're distant galaxies, they're powered by supermassive black holes.

So, as stuff falls in towards a supermassive black hole weighing billions of times the mass of the Sun, you get energy from that gravitational field, and that's what generates the power that lets you see these things right the way across the universe.

We did not know those things existed before we looked at the sky with radio eyes, so it did revolutionize our view of the universe.

What a fantastic invention, which I hope happens around about 2070.

Spectacles, where you can have those radio eyes, maybe those Google specs at the start, and I hope it leads to that.

The problem is, yeah, it's 21-centimeter wavelength.

You'd have to have big eyes.

It's true.

I loved it.

John, Tim was saying there, I loved there was an aside there about the, so it's really about the hidden universe, you see things you didn't know with radio waves.

But you just said, uh, so it's a supermassive black hole, millions of times the mass of the sun, all this stuff falls in, it's bright, and it as an aside, that's the great thing about astronomy, isn't it?

That it every sentence is stunning.

Exactly, there's uh you almost get sort of like overloaded on it.

I've um I'm always fascinated with the heat death of the universe.

That was one of my favorite uh uh parts of uh of Wonders of the Universe, when that description of when star formation fades and dies and ceases to be, black holes just evaporate until we reach a point where eventually that is it.

There is nothing left, everything is just still.

I wonder what happens to dark matter then.

Will it be just there, dominating, ready to strike again, building up sort of latent energy until maybe another big bang happens?

I wonder.

Well, you know, there could be another big bang.

I mean, that's the, you know, that's one of the current, I mean, one of the big things, one of the big problems with the universe, I worry about the universe sometimes at night.

You know, late at night you wake up three o'clock in the morning.

Um but yeah, I mean you know we don't know how big the universe is, uh we don't know whether it's infinite.

Um uh and it often strikes me that that the I mean I think the universe being infinite or not infinite, those two options are equally unpalatable.

Because I I find it hard to imagine something going on forever and then it's hard to imagine something that doesn't go on forever.

How how does that work?

It sort of has to wrap back on itself.

But one one possibility is that there's

another Big Bang might happen, and so you can get, you know, we just sit inside

this particular universe that was created with our particular Big Bang, and then you know, some property of space results in some fluctuation results in another big bang.

I mean, another possibility is that we're saying that this universe has got lots of dark energy in the universe.

Well, one possibility is that this dark energy is eventually going to dominate everything and it's going to dominate all the other over the forces that hold together atoms and nuclei.

So, in fact, the universe could then have this thing called a big rip, where the universe is then, all the atoms and nuclei are torn apart by the effect of dark energy.

And we don't know if that's going to happen or not.

If the universe is accelerating its expansion, I should just ask you first.

John's good comment on this.

Presumably, the answer to the question about the heat death is that makes it the most likely explanation, doesn't it?

For the future of the universe, that it will continue to expand.

You said you may even get this big rip where matter itself is ripping.

I mean, one of the things that we're trying to do in lots of different ways, actually, and Sarah's experiment, the Dark energy survey is is is doing it one way by looking at the distortions in these shapes of galaxies but there's lots of people doing it trying to do it different ways which is science you know you do independent measurements and and and see if they agree but is to is to sort of map uh the expansion rate of the universe back through time so so you look farther and farther and farther away you see farther and farther and farther back in time and so you can look at the history of the expansion of the universe in detail and that tells you how how dark energy has evolved how dark energy behaves uh and it looks like it's something

like a property of space.

So it's almost as if, you know, as space expands,

there's more dark energy because space is bigger, if you like.

And so the influence of dark energy is increased.

So in the early part of the

universe's expansion since the Big Bang,

it did slow down.

So the gravity acting on the matter in the universe did try to pull the universe back together.

So its expansion was gradually slowing.

But then what we think we've hoping to see directly by making these measurements, and what the theory suggests, is that you that then turns over or turns round so that then the expansion of the universe accelerates.

So it's sort of slowing down and then it starts to accelerate.

And that's because, in a sense, that if the universe has got big enough, that the dark energy dominates over the gravity term, so the anti-gravity dominates over the gravity basically.

And we're now in this phase where dark energy is starting to dominate the expansion.

And then, yeah, you would end up with a it unless unless there's something about dark energy we don't understand that changes things later, it would just keep

something in it.

Sorry, John, you had a point.

No, I was just thinking, last time I was on the program, and Jeff Forshaw was on, and he said the most

fascinating phrase, which was infinite in all directions.

Meaning that not only is interstellar space and the universe infinite in that direction, but if we start measuring on the particle scale as well, that can continue to shrink shrink and shrink and shrink until that's infinite too.

So, what are the smallest particles that we're aware of at the moment?

Maybe dark energy is made up of particles too small for us to see, and so we can't see their influence because maybe they are smaller than photons.

So, I love daydreaming and guessing like this.

But, one question I do get often asked is: could it be some particles which make up the dark energy?

But the crucial thing is that they've got to do something different to ordinary particles to cause acceleration.

I think that's really the crucial thing.

That

this dark energy, if you had a box of this dark energy and you expand the box,

then in fact, you end up with more dark energy in that box than you started with, and that's just completely different, obviously, to ordinary matter.

Whereas, if you've got a box of dark matter, you expand the box of dark matter, you've still got the same amount of dark matter in that box.

Yeah, so a lot different.

In terms of dark energy, that as you say, yeah, this is still this, this is the answer that's being searched for.

But what are the other possibilities?

It's a reasonably short history of human beings having

journeying in this direction.

So, what are the other possibilities, or what are the ones that were briefly mooted and have disappeared?

Well, the thing that I'm most excited about is that we've never really tested general relativity in this regime.

So, it's possible that general relativity itself is wrong.

I mean, there's a history of you know, when we see strange things about gravity, for example, the orbit of Mercury around the Sun, we knew that that didn't fit with Newtonian gravity,

and so then it then that was one of the things that general relativity solved.

But before that, people have said maybe there's another planet.

So they'd already discovered, just gets right, they discovered Neptune because they could see the orbit of Uranus was not as expected.

And so they actually thought, well, maybe there's another planet causing that.

And they looked and then they found it.

So then when they saw that Mercury was orbiting the Sun in a surprising way, they then looked for another planet.

They didn't find it.

They actually found general relativity.

And so they changed the law of gravity and that fitted this new observation.

So maybe that's the same thing going on here with dark energy.

They're still saying that on Twitter actually, they're still saying there's another planet.

People keep asking me about something called Nibru or Nobru or whatever it is.

You get asked those questions.

What's that?

Nibru?

I don't know.

They just tweet me and say, what about this other planet is going to destroy us tomorrow?

And they say, really?

We need to know which fictional planet this isn't and which on it is.

I thought it was a possible restaurant.

Your daytime is wigs and teeth and all of that kind of thing.

And there's so many people who are going, you know, oh, I really want to be in show business.

You're in show business.

Do you spend almost every day going, oh, I wish I was working in, you know, the world of radio telescopes?

Is there something do you look now and you hear these kind of conversations?

You think, oh, that's what I want to be doing?

Exactly.

It's a whole new ambition.

I mean, I've always been an enthusiast about astronomy and science and so on.

And to be sort of slightly more involved with it these days on panels such as this is absolutely wonderful.

I suppose

I like to ask the kind of questions that the viewers of any programme might have, and I like like to chip in from that direction.

You are a very keen amateur astronomer, aren't you?

Oh, yes.

Particularly your photographs I've seen, which are quite spectacular.

Yes, I love to chase eclipses and so on, and take shots of the phases of the moon just with a little smartphone.

If you find the right eyepiece for your telescope, find one that sort of syncs with the lens in your smartphone, and just with a bit of practice, and the image goes click like that, and you can just press it like that and just grab them.

And there's something wonderful about that anybody can do it as astronomy is so

the most profound thing but yet the most accessible and it's very good for the soul astronomy it really is I love what you said there you said you can take these pictures with a smartphone attached to a telescope

it's quite a big telescope you've got

I wonder you know for both of you you know working in an area where in one way the progress you said is being made

though we live in a world where people want you know immediate they need it that patience but at the same time, how do you maintain that excitement?

I mean, I can understand how you do, but what is it that you just think this I'm hooked?

Yeah, I mean, I certainly go out and I look up and I spend a lot of time looking up at this.

If it's a clear, you know, who can't resist looking up, well, who can't resist looking up on a clear night and seeing those stars, you know, that you know you're looking at you're looking back in time as you look out into space.

I mean, it does, you know, on a day-to-day level, I mean,

Sarah was right.

You know, we sit there and we sit in front of a computer and we analyse data like

a lot of scientists, but you're very clear that it connects to this incredible thing.

I feel very lucky myself to be able to have a job where that's what I do.

It takes a huge amount of time to plan these telescopes.

I mean, after the discovery of the accelerating universe, there was a whole series of investigations to see what's the best way to find out what's causing the acceleration.

And that led to a whole load of projects like the Dark Energy Survey

that were put together and are now operating.

So now is the time.

We're two and a half years in to the five-year observations from the Dark Energy Survey and there's more telescopes to come after that.

And so now we're just analysing this data for the first time and it's taken this ten year period really to plan these telescopes, build the telescopes, do the observations and now we're at the time when we're going to start finding out the answers from these telescopes.

You get the sense in which we're at a a position now in in cosmology.

The the the sort of position we were in a hundred years ago on on the just before if you go back to sort of eighteen ninety, I suppose, you don't have quantum theory, you don't have special relativity, you don't have general relativity, you have none of the real planks of modern physics.

Is there a sense in which you think these observations are pushing us towards a place where we might be on for a real paradigm shift, if you want to use those words?

That was such a Manchester way of putting it.

On for a real paradigm shift.

Are you on for a paradigm shift?

He's up for it.

I mean, yeah, I know the historians of science hate that language, so I was trying to find some other language.

In the end, I gave up and said, sob, the historians, I'll just say it.

We'll get them there.

I mean, you know, I don't hold with that sort of talk.

I mean, you're right, there was that shift, you know, obviously, in the early part of the 20th century, well, that, you know, late 1900s, early 20th century.

And I don't...

you know, I don't like thinking about things that way.

I think we should, you know, I think we have a good system for progressing.

with, you know, we do these observations, we compare them to the data, and we work that way.

And I don't think you can predict in advance that you're going to have a paradigm shift,

actually.

I disagree with that.

I want a paradigm shift.

But I think the reason why we're wondering if there is one is because there is no good theory of what the dark energy is.

And in fact, the simplest theory, the best theory, predicts an amount of dark energy which is massively much bigger than what we see in the universe.

So,

if you put a one followed by 120 zeros, that's how much bigger it is than what that's how much we expect it to be compared to what we see in the universe.

So, there's a real problem there, and so some solution would be great, which was, you know, we need some other solution which no one's thought of yet.

That is, I think, actually, what should really be above every single laboratory is just a little slogan: some solution would be great.

If you could come up with anything.

Well, this brings to mind one of my favourite Arthur C.

Clarke phrases, which is the universe is not only stranger than we imagine, it's stranger than we can imagine.

Lovely back because that is a great Arthur C.

Clarke impersonation, but that's one of those more niche ones that didn't necessarily make it to the mainstream Dead Ringers TV show.

I thought I could do Arthur C.

Clarke as a.

No, no, no, no, no.

So this is, we asked the audience a question as well, and we asked them today, what do you hope might be hiding out there in the universe?

I haven't seen any of these answers yet, so a full-price DFS sofa.

I've got an army of zombie strawberries, which is one for the monkey cage aficionados.

There, there's actually a picture of a strawberry that says both alive and dead, and it's a zombie.

John's got some.

This is rather lovely.

A giant wheel of cheese that is, in fact, the real centre of the universe.

I hope it's mature.

By Dave B, aged 29 and three-quarters.

It's a smaller vision, this one.

All Beverly wants is a huge laundry bag with all my missing odd socks.

You know, that's more likely than the giant cheese wheel.

A planet identical to Earth in every way, bar the minor detail that Brian and Robin have each other's hair.

Oh, the delight.

I had so much hair when we started this series, and then he's created some kind of physics machine that sucks my life force out so he can stay on tele.

Do you remember Dar O'Brien did the first star gazing?

Great big Afro.

Anyway,

thank you very much to our guests, John Coolshaw, Sarah Bridle, and Tim O'Brien.

Next week, we'll be back in London, but before that, we're off for a day trip, in fact, to Dodgerall Bank to record a programme that was broadcast in the past due to the curvature of space-time.

It is true, I can tell you, we have a Monkey Cage general relativity special, which is going to be on before Christmas.

This is going to be on after Christmas, and that's caused us a problem because we want to advertise the general relativity special on these programmes.

However, it's going to be on before these programmes are broadcast.

We've found a way out of that in general relativity.

And with iPlayer.

So, anyway, I'm very much excited to be going to Jodril Bank because it means that the technology will be strong enough for me to be able to understand what is in wait for me as a Pisces.

Radio astrology is very strong, very strong.

Thank you very much for listening.

Goodbye.

monkey cage,

in the infinite monkey cage,

in the infinite monkey cage.

Podcast podcast version of the podcast podcast.

Brian doesn't even know that you have actually now listened to the whole of the show.

And this is all he's been doing

for the last 47 minutes.

And it's not going to end for a while either.

It's a nested infinity of podcasts.

So then you could probably sum it up like a cheese.

This is my life.

You just end up with a podcast.

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