Episode 2

This BBC podcast is supported by ads outside the UK.

It's Bretzky, baby, and I don't know why they let me on the radio, but I do know you're in California, which means you can play on SpinQuest.com with over a thousand slots and table games absolutely free and with the ability to win real cash prizes with instant redemptions.

Your first $30 coin package is only $10 today.

Hurry up, SpinQuest.com.

SpinQuest is a free-to-play social casino.

Voidwear prohibited.

Visit spinquest.com for more details.

A happy place comes in many colors.

Whatever your color, bring happiness home with CertaPro Painters.

Get started today at Certapro.com.

Each Certipro Painters business is independently owned and operated.

Contractor license and registration information is available at Certapro.com.

Hey there, it's Ryan Seacrest for Safeway.

Cough and cold season is coming, so make sure you're prepared and stock up on your family's favorite personal wellness products.

Now through October 7th, shop in-store and online for savings on products like Mucinex, Kickstart Combo, Zeertech, Allergy Relief Tablets, or Liquid Gels, Halls Cough Drops, and Mucinex Fast Day and Night.

So, you and your family are armed and ready for the season ahead.

All friends, October 7th, restrictions apply.

Offers may vary.

Visit safeway.com for more details.

This is a download from the BBC.

To find out more, visit bbc.co.uk slash radio4.

Hello, I'm Robin Ince.

And I'm Brian Cox.

Now usually we present the Radio 4 show The Infinite Monkey Cage, but last week, Brian very kindly took me out of the studio to celebrate the 100th anniversary of Einstein's theory of general relativity.

Now to be honest, as anyone who listens to Monkey Cage regularly knows, I didn't have a great deal of hope of teaching you very much.

But I and others tried.

What do you learn, Robin?

Well, it all starts with thinking about falling down on a lift.

General relativity follows on from special relativity, that's C equals M C squared.

This means space and time is really space-time.

You can't have space without time or time without space.

They're inextricably linked and gravity is the curvature of space-time.

Gravity is not a force.

And that g mu nu equals t mu nu, that is a tip-top equation.

If anyone from another universe wants you to sum up your universe in just a few letters with one equation, well, that's the one to go with.

All in all, my head feels like it is spinning.

I think I have vertigo and I don't know whether I should have vertigo anymore now that I've found out about the geometry of space-time, but that's the way it went for me.

That is not bad, actually, Robby.

I'm quite surprised.

We're beginning to get somewhere.

G mu nu equals t mu nu.

Now that I know it, I'm not going to skimp on any opportunity for saying it over and over again.

No.

Well you missed a few things out.

There's an 8 pi g over c to the 4 in front of the t mu mu and you could put the cosmological constant in if you wanted.

So what's the longest version you think I can get away with?

Or the longest version for beer old days.

No, but I can get away with.

Not a physicist, me.

Just say that g mu mu equals 8 pi t mu mu.

About 25-ish.

So a factor of 25.

You can set g and c to 1.

Oh, I'll stick to that.

That's fine.

So last week we talked about the equation itself.

Now,

what about the the practical uses of that equation?

How, over the last hundred years, it has been used.

Well, we're going to look at what understanding the geometry of space-time means for our understanding of the universe, its origin and evolution, and the contents of the universe, from pulsars and quasars to black holes.

Also, this gave us an excuse to climb up a radio telescope, in this case the Lovell Telescope.

And if you've never had a chance to stand in the dish of the Lovell telescope, find a chance somehow get in there I highly recommend it it's it's the best holiday I've had in the last 10 years but before that we asked cosmologist and science advisor on the film Thor Bryan we always have to remember that indeed we do Sean Carroll what general relativity means to his work if you're going to be a cosmologist like me looking at the expansion and evolution of the universe general relativity is the first tool in your toolbox if you're studying astrophysics and the evolution of neutron stars and black holes, then you absolutely need general relativity.

If you want to know about dark matter, even if here in the solar system, if you want to know how to tune your GPS system to figure out where you are in your car when you're turning left and right, general relativity is a tool that everyone must use.

Improviser and former physics student Richard Ranch sees general relativity in art as well as science.

Oddly, it was Freddie Mercury, I think, who summed up the whole problem.

Is this the real life?

With his line, is this the real life?

Is this just fantasy?

Caught in a landslide.

And in a sense, that's what physicists are trying to find out.

What's real, and it turns out that real is pretty weird.

It's not just Brian May who has a grand understanding of the nature of physics and our universe in Queen.

Look up to the skies and see.

Thanks, Freddie.

Back in October, we went to one of the UK's great scientific instruments, the Lovell Telescope.

100 years after Einstein's theory, the Lovell Telescope is still testing general relativity to its limits.

You see, a theory like general relativity is no good at all, no matter how beautiful, unless its predictions agree with observation.

And to observe the universe, you need vast instruments like like the Lovell Telescope.

So, we did really need to go there, didn't we?

We should make this clear.

It's not just an excuse to go up a telescope.

I mean, we couldn't have made this program without going up the telescope and having that brilliant day.

Well, it's not far from my little house in Oldham.

Well, that was my first visit there, and it is a remarkable and beautiful steel structure, right in the midst of the countryside.

Not Brian's first visit there, as I often tell people, of course, he's used his connections many years ago to abuse the dish of the telescope by recording a D-ream video there.

See, that's beautiful because that is like Tom Baker in Legopolis, who of course he falls off the Lovell telescope, I believe, at the end.

In the same way, what happened was the meeting of your keyboard world with it's like, Brian, do you want to come down for the telescope?

No, you keep being in a band.

I'm gonna stay here and observe the universe.

It's a beautiful story, you regenerated.

Handing the baton of knowledge to me, which I grasped with both hands and stayed staring at the stars rather than topping at the pops.

Tim O'Brien, professor of astrophysics and associate director of Jodril Bank, has the keys to the telescope.

So he unlocked the gate and took us into the meadow that holds one of the world's greatest instruments for interrogating the universe.

What I find, you've spoiled this actually

in some ways because I think this is an incredible human-made structure and yet now I've immediately had a flashback to you doing a pop video with De-Reem where you misused your connections to sit in the middle of that, didn't you?

Put that in the middle of your mind.

Look at this.

This is a thing.

This is magnificent, but it's been besmirched by

physics pop fools using their power to sit in the middle of it.

I look at it.

I don't know what Tim thinks about this.

I look at it another way, I would say that this is one of the iconic architectural structures in Britain, as well as an iconic scientific structure.

Oh, I would say all those things.

It should take its place as a valid, a valued cultural icon, and we should not pigeonhole it as merely a scientific instrument.

We should say that it's part of our cultural heritage.

Even if it was just a structure, you'd go, that's pretty good.

Oh, and it works as well.

This is really now getting incredible images which are putting together our understanding of the the universe.

One of the things I find remarkable about these precision scientific instruments that are also vast because

how precisely can you position this structure that what's the mass of the Lovell telescope?

3,200 tons.

3,200 tons of steel.

How precisely can you position it?

So we measure its position to a thousandth of a degree.

It's positioned.

But the problem with that, of course, is that it's a real thing.

The steel bends and flexes and so you do get things we have to model model out on that.

And in fact, in fact, the whole ball of the telescope sags under its own weight.

So, as you tip it to a different angle, it sags and moves away from its real shape.

So, all these very pragmatic, very real things that you need big spanners to deal with, all those sorts of things come into play in order to test Einstein's general theory of relativity.

And you can keep it pointed at an object that's, what, three-quarters of the way or further out to the edge of the observable universe?

12, 13 billion years, the radio waves have been travelling from some of the things we look at, yeah.

So, right to the edge of the observable universe, and you could do that with 3,200 tons of Scunthorpe steel.

So, how high are we going to climb and also be taken up?

Yeah, so this is so that the big ball is 76 meters in diameter, 250 foot in old units.

So, the top edge is somewhere like 90 meters off the ground.

It's actually within about a metre of the same height as the very top of the spike on the top of the Big Ben clock tower, if you can imagine that sitting next to the houses of parliament, the Loral Telescope's as high as the top of the Big Ben clock tower.

This is a pearl.

I've never known if I have vertigo.

This is a test, isn't it?

This is brilliant.

Going through this door is the test as to whether you've got vertical, because that's the point at which you realise you're now a long way above the ground.

Right, okay, so you see down.

So now we're going to find out if this is also going to be a special with Claudia Hammond about how I um cured my vertigo.

Here we go, we've got intellect.

Oh.

Oh, there we are.

Oh, this is the

bat.

That is.

So what is, I mean this, the original dish,

what is it made of?

What is it?

The key thing about it is it's the right shape.

We have birds living in here as well.

So it's the right shape.

So it's a paraboloid in the shape of parabola.

It collects, reflects all the radio waves and brings them to a single focus, which is where you put your radio receiver.

so the shape's the key thing

it's not a cliched use of the word dizzying this is the thing that gathers information about the distant reaches of the universe and it's all focused in here onto the radio receiver up there on the tower and it allows us to to tell the story of the origin and evolution of the universe.

I think it's a wonderful thing.

And test this theory, this hundred-year-old theory.

I just, wouldn't you have loved to show Einstein around the Lovell telescope?

Absolutely.

Well,

he only just just missed it, in fact.

It would have been under construction.

When did he die?

He died in 1955.

Yeah, it would have been, actually, it would have been rising up already from the Cheshire Fields, yeah, poking up above the hedgerows.

So, yeah, started in 1952 and finished in 1957.

Yeah, so it just overlaps with the end of Einstein's life, and then 50 years later, keeps proving him not wrong.

That's right, yeah, yeah.

You don't really know whether he's right.

How's your vertigo, Robin?

There's nowhere I can go down.

I just remembered I was always able, as a kid, I was able to climb, but I wasn't able to abseil.

So this is where I'm living now.

So if you could just drop tinned meat on me every now and again.

It's pretty peaceful up here, actually.

It is.

It was, till I got here.

While we were up there, I think we were so awed just by the surroundings that perhaps we didn't talk as much as we should have done about general relativity.

But

pulsars are a vital part of understanding general relativity, aren't they?

They're essentially clocks.

General relativity is a theory of space and time.

And pulsars are collapsed stars, perhaps the size of a city, 10 kilometers across, but with a mass one and a half times that of our Sun.

And they spin many, many times a second on their axis.

So they keep perfect time, which means it's like throwing a watch into some strong gravitational field and watching how the watch ticks.

So when they first started monitoring pulsars, I mean what were they observing?

Telescopes like the Lovell Telescope can observe the regular radio pulses that are emitted from pulsars, which tick.

The most accurate watches are some of the most accurate watches in the universe that allows you to probe the structure and curvature of space and time.

Open your eyes,

look up to the skies and see.

So we're currently in Jodrell Bank.

We're actually in the control room of Jodrell Bank.

Lovell Telescope is behind us.

So, but why are we here?

This is the first thing that we're doing.

We're joined by Tim O'Brien and Sarah Bridel.

And for a lot of people, they might think, oh, general relativity, that's pretty much dealt with by equations, isn't it?

You don't need to create a really big telescope.

Now, possibly, I think still currently the third biggest in the world, but soon maybe the fourth biggest in the world.

It's a magnificent human-made structure, and many people will probably think that general relativity, well, that's just maths, isn't it?

Einstein, it just scribbles down equations.

Why do you need a great big third or fourth biggest telescope?

I think Robin's thinking of the sort of a pseudo-Feynman story.

You're imagining Einstein walking into this control room, aren't you?

And looking up at that thing and saying, Don't you trust me?

Yeah,

I've done the equations, why have you built the thing?

Yeah, I mean, we

obviously use this telescope for lots of different things.

So, it's a real multi-purpose instrument.

So, it looks at radio waves coming from space.

That'll tell us lots of stuff about stars forming, stars dying, distant galaxies.

But there's a few key areas in which general relativity is applied.

One is pulsars, another is gravitational lenses, so

how space-time is distorted by mass, and we can see the effect of that

in these observations.

In fact, the very first gravitational lens ever discovered was discovered from observations with this telescope back in the 1970s.

Well, I need to check.

So, what is gravitational lensing?

I mean, I've seen posters all around this building on gravitational lensing.

Sarah, gravitational lensing.

Yeah, so basically, in gravitational lensing, the space-time gets distorted by the presence of heavy stuff, lots of dark matter, for example.

So, space-time gets curved, and then light travels towards us, and the light rays get bent by this curved space-time.

So, it's a bit like if you, if you look, say, through your bathroom window and the objects behind that bathroom window, you see, you see, are distorted.

So, in fact, all galaxies in the universe have been distorted very, very slightly by the curved space-time by this gravitational lensing effect.

So, by looking at the shapes of distant galaxies, we can reconstruct the distribution of mass in the universe, make a map of the dark matter in the universe using gravitational lensing.

So, without general relativity, would we be looking up at the sky and going, I th that galaxy should not be there, and that gut there would be a confusion if I clumsily say the geography of the sky

would be somehow confused because without general relativity, we wouldn't why is that there?

Yeah, so it's basically you can do some calculations without general relativity, which are wrong by a factor of two.

So you'd actually get the wrong impression about what was out there in the universe if you didn't use general relativity.

In terms of during Einstein's lifetime, what were the most important observations that were made?

We had Arthur Eddington in 1919, that was the big moment in terms of front page splashes, etc.

What else after that?

Well, just a few years after Einstein published these equations in 1915, we discovered that the universe was expanding.

So Hubble and collaborators found that the distant galaxies are all moving away from us.

And that you know, that was then you know became a solution of Einstein's equations, an expanding universe.

The 1930s, we discovered dark matter, the first evidence for dark matter, which again has to be folded in as a component of sort of mass-energy

in his equations.

And then, in the

actually, in the 1940s, there was the first suggestions that there might be a Big Bang, a remnant radiation from the Big Bang,

was predicted.

but it wasn't until the 1960s that that actually was detected.

So there were a series of things that actually all fitted into that framework.

You know, it was a remarkable sort of result, I think.

General relativity is a hundred-year-old theory.

It's still at the frontier of modern physics today.

Will it remain so, you think, for the foreseeable future?

It's certainly the frontier today.

In fact, you know, as we stand here at Jodrell Bank, basically 24 hours a day, that telescope is doing observations that rely on Einstein's theory, general theory of relativity, published 100 years ago.

And that's that's still the framework in which we interpret these observations.

And it still works for us, and we'll use it as long as it continues to work for us.

Yeah, absolutely.

I mean, general relativity underpins all of our forecasts and expectations about what we see when we look at cosmological observations of the universe.

And so when we make those observations, we're actually testing general relativity by seeing if it fits the observations or not.

And there's certainly a lot of people in cosmology today who are wondering whether we'll still get observations which fit this theory.

It's interesting you used the Tim used the word framework.

So

it's not just a theory that makes predictions that we test.

It's the theory that we use to interpret pretty much every observation that we make in modern astronomy.

If we were looking up in the sky, if we had our radio eyes looking up in the sky now, looking straight through these clouds, which is handy from England, out into the universe, we see these points of light, scattered radio waves, scattered around the sky.

They are generated by supermassive black holes in the distant universe.

That's where that energy is coming from.

That we see.

That was the very first solution of Einstein's field equations by Carl Schwarzschild, just a year after Einstein published those equations.

And there we are, they're still there in the sky above us, and we're observing them with this telescope now.

So it's really basic, isn't it?

You wouldn't understand the radio sky without that theory.

You'd look at it and say, I don't know what's happening in the minute sky.

And we found those things

first in the 1940s, and it wasn't wasn't until the end of the 1960s that it was realized that the black holes were the energy source but the black holes themselves had been predicted by Einstein's equations decades before do you think Einstein would have been surprised to see that his theory lasted a hundred years and survived such precision tests or do you think he would have

the stories are that he thought that it was so beautiful that it couldn't possibly fail any experimental tests maybe that's overselling it a bit.

But do you think you'd have been surprised and delighted?

Yes, I think it's amazing that Einstein's general relativity still fits all the data today.

And one of the really interesting things that's happened over the years is that it seems like we only understand only five percent of what the universe is made of.

There seems to be weird dark matter, weird stuff we call dark energy, which seems to make up the majority of the contents of the universe.

So then we're looking at these observations and we're trying to understand, well, how can we tally all of that together?

And since we don't really know what any of this, most of the universe is, then you have to ask the question, well, maybe there's something wrong with the fundamental theory that we've got to describe the universe.

You know, in a sense, we would love to prove Einstein wrong because that would be a great step forward in our understanding of physics.

But in fact, we're just continually proving him ever more right, I think, at the moment.

I've got loads of emails in my inbox of people who've proved Einstein wrong.

Surely one of them will be right.

So for the purposes of this programme, and in fact for the purposes of physics at large, we can take it that Einstein remains right.

Well, we can certainly for the purposes of my inbox.

But actually, we've talked to the observational astronomers there.

It's worth talking to a theorist,

a modeller of universes, to see where the boundaries of general relativity might lie.

So we went back to Durham to talk to Professor Carlos Frank.

Why do we go back to Durham?

Why don't we just do it the first time we went to Durham?

This has been very poorly thought out.

Yeah, I mean, today actually it's paradoxical that the universe, we know a lot more about the universe than we know about Robin Inz or about a human being.

Even though the universe is very big and seemingly very complex, it is the application of Einstein's theory that simplifies it and makes it, in fact, a very, very simple object to study, far simpler than a human being, let alone a human mind.

And so it is thanks to Einstein that we conceive, at least us cosmologists, of the universe as a simple system.

And we're actually lucky that we are physicists and not biologists because we deal with a system that is easy to understand and we can calculate things and we can make predictions, which is what physics is all about.

Whereas our poor biological colleagues have a really hard time, they're studying something far more complex and they haven't had that Einstein to simplify the system.

So, all we know about cosmology today is possible thanks to the genius of this one man.

I just wait to ask what the cutting edge of research into general relativity itself is today.

Right.

So general relativity is part and parcel of our...

It's a tool of the trade for us today.

However,

one of the things that has people very puzzled is one of the most dramatic discoveries in science of the last 15 years, and that is that our universe is going to be Zerk.

So our universe is not behaving as Einstein thought it would,

and as you might expect any reasonable universe to behave.

a universe has gone into a phase in which it's expanding at an ever-accelerating rate.

So the expansion is getting worse and worse and worse and worse.

Now that is exactly not what you would expect because if all the universe

was matter, mass, mass produces gravity.

As the Americans like to say, gravity sucks, meaning that gravity pulls.

So gravity would start to slow down the expansion of the universe because it's attracting matter onto itself.

And yet, astronomers discovered about 15 years ago that the opposite is happening.

Our universe is accelerating in its expansion.

The expansion is getting faster and faster and faster.

Why is it doing this?

What's got into our universe?

And we really don't know.

And one sign of when scientists don't know what they're talking about is they come up with a very elegant label for what they're doing.

So we call this dark energy.

Isn't that beautiful?

Suggestive?

Dark energy, but to me it suggests we have no clue of what we're doing.

And that's exactly what is happening.

Now, there are two explanations.

I don't know which one is more distasteful than the other for the dark energy.

One of them is that Mr.

Einstein was almost right, but not quite right.

And that the Einstein equations need to be modified.

And we say that we shiver, we shake before we say something like that, because Einstein's equations are so beautiful, so well tested, that if you want to tamper with them, you better do it in a very careful way.

And

that's what many people are doing now, and

under the label of modified gravity, trying to modify Einstein's equation, subtly, subtly, you cannot do it in a very impertinent way because it will come to haunt you because as I said, relativity is tested.

But one way to understand dark energy is that there's more to gravity than Einstein.

So that's one.

The other explanation for this accelerated expansion of the universe is even more distasteful.

And it has to do with the multiverse.

So this explanation is that in fact

there's not just one universe, but there's a multitude of universes.

Now, in this view of the multiverse, there are many, many instances of the universe.

Some have general relativity, others don't.

Some have dark energies and others don't.

But in this vision, you could imagine that relativity wouldn't really necessarily apply in all these parts of the multiverse.

And I feel very sorry for, well, there wouldn't be any beings, but if there were beings in the universe without general relativity, they would really be missing out on something great.

So for all of the talk over the last two shows, we still have one big stumbling block, don't we?

Which is the idea of bringing together Einstein and quantum mechanics.

Yeah, ultimately, that the problem might be a theoretical one.

in that we have two superb theoretical structures that describe the universe on the very large scales, that's general relativity, and the universe on the very smallest scales, and in fact the rest of the universe, which is quantum theory.

Here's Sean Carroll, science advisor on Thor.

I think there's no question we need a better theory of gravity.

As wonderful as general relativity is, it's my favorite single theory,

it doesn't play well with quantum mechanics.

And quantum mechanics is sort of more important than general relativity in some sense.

General relativity, even though it changed our notions of what space and time were, it still spoke the language of classical Newtonian mechanics.

There's stuff, which is the curvature of space-time.

It evolves, you can observe it perfectly, it's deterministic, and so forth.

And we know that the world is fundamentally quantum mechanical.

And that plays along with the fact that general relativity makes predictions we don't think can be right.

General relativity predicts that the curvature of space-time becomes infinitely big at certain places like the Big Bang.

So we need a better theory.

If we're going to actually understand what happened at the Big Bang, we needed a theory

that at the very least includes quantum gravity and might end up looking completely different.

Whether it will be as beautiful as general relativity is not my job to say.

I have a feeling that the correct theory of the world will be beautiful, but our job as physicists is just to find the theory and then we'll decide afterwards whether it's beautiful or not.

Will the idea of space-time and

the geometry, this stuff, the fabric of the universe, will that survive, do you think, in any form?

Or is it some kind of emergent property and there'll be a deeper explanation for it?

My own guess is that space-time is definitely emergent.

In fact, I think that space has almost no hope of surviving to be a fundamental part of our universe.

And this is one of the things I'm doing research on myself right now.

How does space, the very idea of space, emerge from a more fundamental quantum description?

Time has a chance of surviving.

That's kind of an open question.

There's sort of different versions of quantum mechanics.

In some of them, time plays a fundamental role.

In others, time itself is emergent.

So we have to, you know, take Einstein's example seriously, not in promoting space-time, but in being open and willing to go where the theory wants us to follow it, rather than deciding ahead of time what the answer is going to be.

Well, that's worrying, isn't it?

No space and no time.

Where am I going to live?

Typical comedian, self-centered.

The universe doesn't care about you, you know.

It's not about giving you a home.

That's not what the universe is there for.

A home for comedy.

That's probably a BBC channel.

Yeah.

So where does this take us then?

Well, we have a theory a hundred years after it was first published that has passed every experimental test that's been thrown at it and yet that we think cannot be the whole story.

So it's an intriguing position to be, for physics to be in at the turn of the 21st century.

That's what I love about science.

It always ends with to be continued.

It does.

And Carlos Frank has got an extremely worrying theory about how it might continue.

And there must be something bigger than relative to what shape it will take, whether it would be a marriage with quantum physics, whether it would be a stroke of genius by a new Einstein.

We can only speculate because we haven't got the answer.

So

I'm hoping there will be, you know, Robin Einstein or somebody who will come along.

No one will be more surprised than me if Robin Einstein comes along solves the problem.

I would prefer to play an Einstein than if you were surprised.

Well, in this universe, but in another universe, I'm really clever, apparently.

That's why I always read about the multiverse, the hope of someone better than me.

You'll have a thing now on the train back from Durham.

You'll almost be London ring you up and I've got it!

Well, fancy that.

In the infinite monkey cage.

In the infinite monkey cage.

In the infinite monkey cage.

Till now, nice again.

The Mercedes-Benz Dream Days are back with offers on vehicles like the 2025 E-Class, CLE Coupe, C-Class, and EQE sedan.

Hurry in now through July 31st.

Visit your local authorized dealer or learn more at mbusa.com/slash dream.