Episode 1

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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.

And we spend most of our time on Radio 4 presenting the science panel show The Infinite Monkey Cage, but today we're doing something different.

We're presenting a documentary about one of the most wonderful ideas to come out of a human mind.

So, like all documentaries, we are going to take you on a journey.

Though in this case, it's quite a short journey falling down a lift shaft.

Or, more correctly, according to Einstein's theory of general relativity, a journey floating in an inertial frame of reference, waiting for the bottom of the lift shaft to hit us.

Are you being served is and was always meant to be I think a tutorial on general relativity.

Good.

So 10 years ago we celebrated the centenary of special relativity which is E equals mc squared the most famous equation to exist in the history of human civilization.

Which gives me some hope, actually, for popular culture, because the fact that there is a most famous equation means that we're not floating in an all-enveloping darkness of trivia.

See, that's the problem, though.

It's very easy.

When you get one of those shows, the countdown of the top ten equations, we always know E equals M C squared is going to be number one, but no one knows the position of any of the other equations.

F equals M A.

Oh, that probably would be number two, wouldn't it?

Anyway, so E equals M C squared.

Brian, what does that mean?

Well, it really means means that energy and mass are interchangeable, but it comes from special relativity, which is a theory of space and time.

Space and time are no longer to be considered separate entities, they're merged together into a structure called space-time.

So 10 years after E equals MC squared, now we celebrate general relativity.

General relativity.

I think the majority of people wouldn't necessarily know the equation for general relativity, so that is.

Well, the equation is g mu nu equals t mu nu with a few pi's and Newton's gravitational content scattered all over the place but essentially what it means is that space-time can curve and in the immortal words of the great physicist John Wheeler matter and energy tells space-time how to curve and space-time tells matter how to move so g mu nu equals t mu nu but why why was that pi g over c to the four t mu mu mu mu mu nu mu this is uh it's lovely isn't isn't it?

When it has one moment, it's Einstein, the next moment it's Edward Lear.

But what is it?

What is it about this particular idea that makes it so admired by physicists, cosmologists, and indeed failed physics students?

Because it's ripe primarily.

Yeah, no, but there's lots of other physics that's ripe.

You don't get people going on about it as much as.

I mean,

just the first time the universe appears in an equation.

It's the first time that mankind attempts to write down some maths that describes the entire universe and everything in it.

The general theory of relativity is the most beautiful physical theory ever invented.

I think that that's a very, very defensible statement.

And there's some pretty beautiful physical theories out there.

But the way that it's self-contained and elegant and very, very compact and precise and how difficult it is to mess with it.

You know, like every time we try to fix it or make it better, we end up making it worse.

What he did with general relativity is of such a different scale, it's almost impossible to describe.

He gave us a fundamentally new language and a totally, totally different way of thinking about the world.

I can't really parallel it with anything else in the history of knowledge that I know of.

The reason John Little is beautiful because it was one of the great genuine Eureka moments where somebody, through sheer brain power, realized that we were looking at the universe the wrong way and that actually the relationship between what's in there and what's space around them and all that is completely different to what we thought.

That's all you please don't do the journey.

The journey through the equations is really long, but the results, oh, the results are beautiful.

So we've been warned by Dara not to go on the mathematical journey.

So would you say that perhaps two half hours on Radio 4 won't manage to be quite enough to cover what is normally done in three years of undergraduate physics?

No, because

the story of what the mathematics tells you is explicable and understandable, as we hope to show.

Let us see if we can achieve that.

We will return to the cosmologists.

But first, we set a just-a-minute task for three physics students who were wooed wooed away from physics by show business.

Quite the opposite, of course, of your own journey, Brian.

My name's Ben Miller.

I am a comic actor and I started life as a physicist.

I did a degree in physics and I did about half a PhD in physics as well.

My name is Dara O'Brien.

I have a BSc in Mathematical Physics and Mathematics from University College Dublin, awarded sometime in the mid-90s by via a very circuitous route around the department.

My name is Richard Vranch and although I now work as a comedian improvising at the comedy store I did study at physics and I did a PhD and I was briefly a fellow of St.

John's Oxford and I'm a sort of a lapsed physicist I suppose.

So Richard Vranch you have one minute on general relativity starting now.

General relativity is a lot more complicated than it looks, but that's true of a lot of physics.

Even Einstein's most famous equation, E equals M C squared, contains a lot of hidden treachery.

So even in that, it's not quite as complicated.

It's much more complicated than

damn.

There we go, a challenge, hesitation, or repetition of damn.

Dara, you have 33 seconds on general relativity, starting now.

The best way to explain general relativity is that it gives a view of the universe around us us that shows that matter

mass of an object shapes the space that surrounds it that the very nature of the surrounding oh i know i said surround twice but how can you not say space twice there's no like euphemism for space Space is space.

This is impossible.

Dara, you correctly challenged yourself there with repetition.

but as challenging yourself, we're actually going to pass it over to Ben Miller.

Ben Miller, you have seven seconds on general relativity starting now.

General relativity is a theory proposed by the physicist Albert Einstein.

He finished in 1915.

It essentially describes gravity as an acceleration within a higher dimensional space rather than a force which occurs between objects that have mass.

Its implications are enormous because it teaches us not only that distant galaxies will have their light red-shifted because they are moving away from us, but also if that light passes through a gravitational field.

If you like, the light has to struggle up through the four-dimensional well of space-time to reach our eyes and becomes stretched and crimson as a result.

See, I avoided red.

Well done Ben.

But Richard Vranch has challenged the very nature of the time measurement we are using for this particular take on just a minute.

So Richard Vranch, you have however long I suppose it's going to take to explain how the nature of time that we're using is in some ways forfeiting the entire conceit.

If you did have a minute to describe general relativity and you were travelling quite quickly, the good news is you'd have just over over a minute because people looking at you would see your minute clock ticking down slightly more slowly than you saw it so you'd have longer to say this than you thought you had though it wouldn't make it any easier.

Oh we have a challenge there from Professor Brian Cox.

Yeah he's not at liberty to change the rate of passage of time in his own frame of reference.

I think that is a correct challenge, though to be honest, I don't really have any idea, but you have done a lot of study on this thing, so I'm going to give it to you.

So Brian Cox, you win that round.

There is no choice, choice.

You get very cross if you don't win things.

Now it's time to regain control of this program.

Rest the tiller back from the showbiz hordes.

We are talking about the most celebrated theory in all of physics.

So what motivated Einstein to come up with this radical new theory of gravity which is after all a totally different way of thinking about our universe?

Sean Carroll is a leading cosmologist at Caltech.

Yeah, he was also scientific advisor on the Hollywood film Thor, so a little bit showbizzy.

It's always very interesting interesting to see how genius physicists do their work because they're all different.

You know, the styles are always different.

One thing that actually strikes me about the personalities of many successful genius physicists over the course of history is how stubborn they are.

He just got this thing in his mind that he was going to fit gravity into special relativity.

And the thing that was weird about it was that there is very little experimental demand for such a theory.

You know, we had Isaac Newton's theory of gravity.

It did perfectly well as far as anyone knew.

There was like a couple of things here and there, like the orbit of Mercury maybe didn't quite fit.

But mostly, Einstein was driven by the demand that all of our different pieces fit together when it comes to our theories of physics.

He was a pioneer of special relativity, and he knew that Newton's theory of gravity, as good as it was, didn't fit.

with special relativity.

We didn't need to make them fit in terms of fitting the data at the time, but this just bugged him, this inconsistency.

And so he just, you know, without much experimental input at all, he made conceptual leap after conceptual leap.

And to his enormous credit, he didn't get stuck in a rut, you know, like he was willing to change his mind and do different things.

And, you know, later in life, famously, people make fun of Einstein for getting stuck in a rut.

But, you know, if you have Einstein's track record, I think that you get some

credit later on in life, no matter what you do, because you were so right so many times.

I'm going to give you the slack.

So this is where I have the first kind of impasse.

So Newton is his idea of gravity, one of the, again, one of the most famous ideas in the whole history of science.

It's wrong.

There's something that doesn't work out when Einstein looks at it.

That's right.

We now have a more accurate theory.

So Newton's theory was that there is a force between massive objects like the Earth and the Sun which pulls them together.

Einstein's radical suggestion which leads to a more accurate theory is no.

There is no magical force between objects that pulls them together.

What we're feeling when we experience the force of gravity is the geometry of the universe itself.

So why is my apple falling?

Well Einstein would say the apple isn't falling.

The apple is minding its own business with no forces acting on it, traveling a perfectly straight line through space-time and the Earth gets in the way.

So the picture really is that the ground is accelerating up to meet the apple.

And this is where the happiest thought comes in, which is, it's not often a happiest thought is plummeting to the ground in a lift though.

Here's former physics student Ben Miller explaining that happy thought of Einstein's.

What if I was in a lift?

in space stick with it because it's brilliant so okay now imagine i'm in a lift and i'm so far away from any gravity that there's no gravitational effect on me at all.

He said, If I was in this lift

and the lift were accelerated,

let's say up, you know, he said, I would feel like the bottom of the lift was pushing on my feet, so I would feel like I had weight.

And

this you have to be Albert Einstein to think of this.

He said, Okay, so if I'm in a lift in space and the lift accelerates, I feel like I've got weight.

What if weight

is an effect of acceleration?

Can we just ask you, Mr.

Inman, when you say I'm free, you mean that very much from the perspective of the forces of the universe?

He means I'm free falling.

That's what he means.

I'm in free fall.

Which means we're no forces acting.

That's what he meant.

Mr.

Humphreys, are you free-falling?

I'm free-falling.

So this is just about gravity, then.

So that's what we're talking about.

Then it illuminates us in terms of what gravity means to the universe.

Well, it's much more than that, which is why general relativity is one of the pillars of 21st century physics, and of mine 20th century.

It's about space and time, and it is also a theory that applies not just to a solar system or the Earth going around the Sun.

It applies to the whole universe.

Well, that means we need obviously to journey further, not only down the lift shaft, but also to Durham.

Which, yeah, you see, it's a segue, isn't it?

And we went to see Carlos Frank, who wonderfully in the reception area outside his office actually has a bust of Albert Einstein, which watches you as you walk around.

So when he's thinking of ideas, he makes sure that Einstein's looking at him all the time.

So here's Professor Carlos Frank.

Everything we know about the universe ultimately boils down to the ability to solve Einstein's equation.

The Big Bang, the expansion of the universe, the origin of the chemical elements, the existence of dark matter, the formation of galaxies, all can be traced back to this man

thinking deeply around 1916.

So special relativity, she said, 1905 equals mc squared, which is the thing that is probably most famous for in the public mind, the most famous equation in physics.

But then so space-time enters that equation, or that theory, or something you can kind of take it or leave it.

It's quite nice in special relativity, isn't it?

Space-time.

Yeah, do you think he had any inkling that that concept could be turned into a theory of gravity and a theory of cosmology, the theory of the universe, back in 1905?

Well, I think that

I'm now second-guessing one of the greatest minds that humanity has produced, but I can see a link between Einstein's thinking in 1905 and then his thinking 10 years later when, or a bit more than that, when he developed general relativity.

Because when he was thinking about special relativity he had objects that were only in constant motion moving always with the same speed and then the minute he said what happens if the speed changes then that change of speed is called an acceleration accelerations are produced by forces and at then at that point he had to think about forces gravitational forces for example and he had a certain reluctance to think in terms of forces so when he started thinking about objects changing speed he thought well how do do you accelerate them?

And here was the genius.

He then said, you don't need a force, you just need to change the geometry of space-time, and that will cause acceleration.

So that was, I think, if you have to put your finger on where

the genius is in Einstein, is in realizing that you can do away with forces and explain everything in terms of geometry.

of space-time.

Now the first time you hear this, you'll be traumatized like I did the first time.

I go, what on earth?

Geometry of space-time?

What do you mean space?

What geometry?

Well, it takes a little while to get used to the idea.

So, we physicists like to have analogies.

So, you imagine, for example, a cannonball on a rubber sheet.

So, the rubber sheet is space.

And first, it's flat, then you put a cannonball and it bends.

So, that gives you a kind of feeling for the distortions that gravitational heavy objects can produce on, in this case, the fabric of space.

And then it takes a further leap of imagination and probably a few years of thinking about this to add time into the equation and to recognize, well, time is the same as space.

And gravity distorts not just space like a rubber sheet, but the whole of space-time.

There is something when we were sitting opposite Carlos there, the excitement, the gleam in his eyes, the talk of the fact that, you know, he is just, there he is, having his Cocoa Pops in the morning and thinking, I'm just thinking about general relativity.

And the beauty, that's what he kept stressing when we were sitting in his office: the beauty of the theory.

Yeah, I think it's something that everybody who studies general relativity in any depth experiences.

Because although mathematically, so technically, it's a complicated theory, in terms of the basic ideas, it's elegant and simple.

See, we already had the idea of space-time that dates back to special relativity, 1905-1906.

And we had Newton's laws, which tell us there's a force between objects, that's what gravity is, a force between massive objects.

What Einstein does is simplify that and say, no, there isn't a force, a fundamental force between massive objects.

There's just space-time.

And there's the way that massive objects curve and warp and bend space-time.

See, that's what I find exciting as well, which is he's made things less complex, which means that I will have to spend even more years studying it to find out that things are much simpler than we first thought which is why I went to Imperial College to see professor of theoretical physics Faye Dauker where she's doing her introductory lecture on general relativity.

Unfortunately it's an introductory lecture for fourth-year physics students so let's see how long it takes for me to get a little bit lost.

I'm currently sitting in the front of a lecture hall to listen to Faye Dauke's introductory physics lecture and this is the first time I've been in a university lecture hall, I think, since a lecture on Andrew Marvel, the poet, in probably 1989.

And on the blackboard, Faye has just put that gravity should be innate, inherent, and essential to matter.

She hasn't finished writing the quote yet.

I'm now going to see how far I can get before I become bamboozled and confused.

Welcome to this course on general relativity.

GR is one of the great treasures of scientific knowledge.

GR

introduces to science a new physical, dynamical substance, which is a four-dimensional,

dynamical, curved fabric, which bends and warps and ripples and carries energy.

And the reason that general relativity is so fundamental and the reason that it constituted such a great revolution in physics is that this fabric, this four-dimensional fabric, is space-time itself.

So, nothing so you're all right at this point, Robin?

I think for the first 20 minutes, I'm fine.

Even the fourth-dimensional stuff, I think we've had enough car journeys with you explaining that to me, that some of it, some of it has been absorbed.

But, well, we're just coming up to the point now.

A Lorentz transform set of coordinates.

And if we take the Lorentz transformation to be going in the positive x direction,

then the Lorentz.

So, it's there now, and I think if there is a graph which can be made out of my attempts to understand contemporary physics, then there is always a downturn when we get to Lorentz.

It is the Lorentz rule of my incomprehension.

Well the Lorentz transformations are not too difficult actually.

You do those in the first year.

But but general relativity is a difficult theory.

I was taught it actually by Faye's dad in in my final year at the University of Manchester.

And I sort of understood it a bit then.

But you have to hear it more than once and you have to think about it many more times than once.

And actually, it was only relatively recently, talking to Faye, in fact, and having it explained for the fifteenth time that I began to really get a a clear picture of what general relativity is all about.

Is this the beginning of a new career for you?

Are you going to leave comedy behind and move into the the real world?

Some people say I left it behind a long time ago and became a performance artist, obviously.

The uh but it was I just found it very i exciting to pick up on other people's excitement.

Again, this is this idea anytime where physics is described as some kind of cold pursuit.

And then talking with Fame, with other people as well, about the fact that this was front page news as well, not 100 years ago, 96 years ago, 1919.

Einstein's theory, there are observations made that go, yep, this is a good theory.

Arthur Eddington.

But how do you make those observations?

Well, Eddington observed the bending of starlight around the Sun.

And to be able to see stars close to the Sun, you need to obscure the Sun.

So he ran an expedition to observe a total solar eclipse.

And the reason for that is that the sun's light is blocked out by the moon, so you can see the stars behind it.

And he measured the bending of starlight.

And that's why I think this was front-page news, because it's a very simple concept and an evocative concept.

The words are that you're seeing starlight bent by the sun.

And the reason that the starlight curves around the sun is because space and time themselves are curved by the mass of the Sun.

And that's an easy thing to write headlines about, even if the mathematics is extremely complicated.

I love that image there as well of just the fact of front page news, a man picking up his Times newspaper as he's dunking his toasty soldier into a runny egg and going, I told you, Molly, I told you it is curved.

I was right all along.

Anyway, we asked cosmologists John Eleven and Brian Green, why was this headline news?

Well, I think there's probably two reasons.

One reason is scientifically it was, it was just opened up an entire world, completely changed the way we viewed everything.

There were consequences of general relativity that even Einstein didn't foresee.

And so it is incredibly exciting to follow a theory to conclusions you didn't foresee, and that's quite thrilling.

But I think there's also was kind of a political reason that the world was in trouble and there was a lot of strife and a lot of nationalism and coming out of World War.

And I think Einstein represented something, something else to people that transcended that kind of nationalism.

That was a gift from humanity.

It was a humanity's accomplishment in some sense.

Yeah, the other part of it, too, is that Einstein was described as having toppled Isaac Newton, right?

So you had this giant of science who had given the world an understanding they thought of the theory of gravity.

And here comes Einstein to give a radically distinct picture that went head to head with Newton's approach in these eclipse observations of 1919.

And when the eclipse observations showed that Einstein was right and Newton was wrong, that's when the New York Times, that's when the Herald Tribune, that's when the London Times, that's when the papers around the world blared out these headlines that Einstein had toppled Newton, and that's when the world took notice.

The wonderful thing about general relativity is we've heard throughout this program about this complex theory you only begin to learn about in the fourth year of a physics degree describes the whole universe and it's an an act of genius.

Undoubtedly, all those things are true.

But at its heart, there are very simple concepts.

And essentially, what general relativity says is that we can dispense with this force of gravity and we can replace it with just the way that objects move around in curved space.

And it's something that's easier in that sense than the Newtonian theory.

Well, I asked Faye if there was a way of kind of comprehending it without having to wait for an eclipse.

You can have the experience which tells you that there's no force of gravity pulling you down.

So the idea that there is a force of gravity pulling you down is at odds with your experience, your actual experience, which is that your chair pushes up on you.

It's pushing up on you right now.

You can feel it.

You do not feel any force

acting on you, pulling you down.

What you feel is your chair push, the pressure of your chair upwards on your bottom right now, as you're sitting there in your chair.

And that's totally in accord with general relativity, but at odds with the Newtonian theory.

The Newtonian theory says that there's a force pushing up on you from your chair, but also a force pulling you down, the force of gravity pulling you down towards the center of the earth.

Geological.

Sorry, stop for a moment.

I want everyone just to think.

Because the people are sitting there now.

Yes.

Yes.

And they need to feel that.

They do need to feel it.

This is for me a perfect example, probably the best example, of the power of physics and the power of thought.

I mean, we have a theory that came essentially from Einstein's head, a remarkable theory, which makes extraordinary predictions about the universe.

It predicts the existence of black holes.

It predicted the Big Bang.

It describes the orbits of planets around stars.

It describes the orbits of neutron stars, of pulsars around other pulsars, of pulsars around black holes, the behaviour of the most exotic objects we've yet discovered in the universe.

And indeed, the behaviour of the universe itself is predicted with accuracy, as far as we can tell, by this single simple theory.

So hopefully, even if you haven't fully grasped what g mu nu equals t mu nu necessarily entails, you have got perhaps a little bit of a change of the sense sense of the feeling of gravity around you.

And next week, we look to the future of general relativity.

I think they're going to keep it going for a while, aren't they?

As a system of running a universe, it works.

What is the future of general relativity?

They got rid of it.

It just

got new universal rules.

And do remember, there's no unique definition of past, present, and future in relatives.

Right, I think we'll just sit here and just feel our chairs.

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