Brian and Robin's Infinite Inbox

This BBC podcast is supported by ads outside the UK.

What's going on, California?

It's Bluff here.

You know what's better than a relaxing day at the beach?

A relaxing day at the beach with SpinQuest.com, America's number one social casino, with over a thousand slots and table games available to the comfort of your own phone, with instant cash prize redemptions, and new users get a $30 coin package for only 10 bucks.

That's SPINQUEST.com.

I'll see you there.

SpinQuest is a free-to-play social social casino.

Voidwear Prohibited.

Visit SpendQuest.com for more details.

Suffs, the new musical has made Tony award-winning history on Broadway.

We demand to be home.

Winner, best score.

We demand to be seen.

Winner, best book.

We demand to be quality.

It's a theatrical masterpiece that's thrilling, inspiring, dazzlingly entertaining, and unquestionably the most emotionally stirring musical this season.

Suffs, playing the Orpheum Theater, October 22nd through November 9th.

Tickets at BroadwaySF.com.

Hey there, it's Ryan Seacress for Safeway.

Feel good and look good this summer with savings on your personal care favorites and earn four times points.

Now through September 9th, shop in-store or online for items like Dollar Shave Club Razors, Hydro Silk Razors, and Edge Shave Gel.

Plus, some favorite brands like Tampax Pearl, Depend, and Poise to earn four times points to use for later discounts on groceries or gas.

Hurry in before these deals are gone.

Offer on September 9th.

Restrictions apply.

Offers may vary.

Visit Safeway.com for more details.

Hello and welcome to Brian and Robin's Infinite Inbox.

I'm Robin Ince.

I'm one of the presenters of the Infinite Monkey Cage on Radio 4.

Across from me is Professor Brian Cox.

I'm the other presenter of the Infinite Monkey Cage on Radio 4.

And I have lots of questions for him which were sent by listeners.

I presume they're listeners or they're just people are shot in the dark imagining what's on the show that have somehow emailed us.

They're not just for me though, they're for you as well.

I think you should feel qualified to answer some of them.

How many?

We've done 100 monkey cages now.

100 monkey cages.

Some of it should have seeped in.

But I don't want the illusion.

You're an English graduate.

What is it?

Seps or seeped?

Seeped.

Seeped in.

Yeah.

Sept.

Sept in is if something seeps in and then actually creates an infection.

That's when it sets in.

Yeah, just so you know.

So anyway, we've received lots of questions based on the last series and also some general questions.

And so, Brian's mainly going to do the talking, and I'll do different voices for each one of the letters in the style of all of the We've Received a Letter programme, such as points of view, etc.

And if you could sing a little bit, because we are in the BBC Radio 3 studio for the benefits of the listeners, the grand piano.

So, this is the first letter that we've received.

This is from James Davis.

He's from Garstang in Lancashire.

I'm not going to attempt to do an accent for that because you get a lot of complaints for that kind of thing.

I'll do a Radio 3 accent then.

Well, this is from James Davis in Garston, Lancashire.

His question, Brian, is this.

And if you get this right, it means the rest of the show we don't have to do and it just goes straight into playing Rites of Spring.

Could you summarise all the laws of physics on a stamp such that it could be read with moderate reading glasses?

So.

I think you could.

I mean, this is, in some sense, a notational question because, of course, mathematical notation is extremely compact and hides a lot of complexity.

But if I was to do that, I would write down the standard model Lagrangian,

which is usually presented as four lines of mathematical symbols and not too many symbols.

The top two lines describe how the forces interact with the particles of matter that we know of.

So 12 particles of matter interacting through three forces of nature, the strong nuclear force, the weak nuclear force, and electromagnetism.

And the bottom two lines, as usually presented, describe the Higgs mechanism, which gives mass to the other particles.

So that's all the quantum mechanics that we know,

summarized in this thing called the standard model-Lagrangian, about four lines.

And then general relativity, which is a very simple one-line equation, which is Einstein's theory of gravity, but also

includes in that notation special relativity as well.

So that's essentially it, as far as fundamental physics is concerned.

Standard model Lagrangian, Einstein's theory of general relativity.

And that would fit on a stamp.

And you could just about read it in compact notation, certainly with a magnifying glass.

So, we'll probably be looking not at a bog standard stamp, but maybe a commemorative stamp for, say, you know, a British person who's won the Nobel Prize or something involving a Doctor Who commemorative first day cover.

Yeah, but

the sense of the question is, yes, you could, with a very fine pen,

a human being, could write down the standard model Lagrangian and Einstein's theory of general relativity on the back of a standard-sized stamp.

The danger, of course, would be as you go to lick the stamp, not realising that you are licking off all the laws of the universe, then briefly giving you a god complex.

Well, it is true that if you only licked off the Higgs sector from the standard model Lagrangian, then you'd immediately fall to bits because you'd become massless.

So, you wouldn't want to do that.

See, that is a beautiful image, but there are people at home.

But obviously, they're also having to use historical stamps because I think they've all got glue on the back now.

But anyway,

you wouldn't

right.

Gluons pun.

He's done a gluon's pun.

Right, we'll have to go straight to the next letter.

But if you would like to play a god at home, then you know all the rules.

We've just given them to you.

So here's another one.

This is from Tim Bowers.

And he says, hi, Brian and Robin.

Brian, you're my idol.

And that's enough of that.

Boring question.

You're Brian.

You're just rude.

Why not just say hi, Brian?

You're my idol.

Hi, Brian and Robin.

Just so you know, Robin, just to remind you, you're far less a human being.

Anyway, so Tim continues.

Brian, you're my idol.

Self-loathing comedian.

And I hope.

No, I don't have to do it myself.

There's lots of others who are getting involved now.

I hope you one day to also, I hope one day to also play a keyboard and stand inside a giant satellite dish.

Anyway, when talking about relativity, you mentioned that gravity or the effects thereof are caused by the curvature of space-time.

Does this in fact mean that gravity, as a force that pulls things together, simply doesn't exist?

There is no force.

The first bit is absolutely correct.

Well, you're his idol.

No, the second bit.

Right.

So there is no force in the conventional sense in Einstein's theory of general relativity.

As the writer says, what's his name?

It's Tim, Tim says.

Tim, as Tim says.

The space and time are curved, and the rule is that everything moves in a straight line through that curved space-time.

And the analogy that I always think of is to imagine standing on the equator of the earth with a friend and agreeing to walk due north.

So you set off.

So you walk parallel to each other.

You don't deviate from your straight line.

But you find as you approach the North Pole that you get closer and closer to your friend because you would bump into them at the pole because the parallel lines on the surface of the Earth are lines of longitude and they meet at the pole.

So if you didn't know you were on a curved surface, you would conclude that there is a force pulling you together, a force of attraction.

But in fact, it isn't.

It's an artifact of the geometry of the surface on which you're moving in a straight line.

And that is exactly what happens in Einstein's theory of general relativity.

Do you find it problematic that as human beings have a greater understanding of the curvature of space-time, we are currently having a boom in flat earth societies?

I'd not noticed.

Of course I'd noticed.

I'm still not sure if it's real or if it's all a kind of Dardarist prank.

That's what I'm trying to work out.

It can't be real.

What is interesting?

about the flat earthers, and I think they are real actually.

And

there's one thing they've got right which is they explain in inverted commas the the feeling of the force of gravity by saying that the ground is accelerating and they are correct in that that is absolutely the foundation of Einstein's theory of general relativity.

What they're missing is that the ground is accelerating in a particular way which is

essentially caused by the curvature of space and time and we are standing on a sphere.

So they miss that bit.

You don't have to.

It's actually quite a deep and interesting thing to think about.

The ground can be accelerating upwards at 9.8 meters per second squared and yet the Earth is not expanding.

And that's the wonder of the curvature of space and time.

But that's the bit where they get confused.

So the Earth is spherical.

So the so you say...

This is an interesting thing where I've noticed that there have been various articles written saying this starts from a very positive positive position.

It starts from the position of human beings not wishing to take on received wisdom as they see it from a position of authority.

But it seems that maybe flat earth is not the right place to

actually work out where you should be questioning and what should be the things to question and why the idea of a flat earth, even if you just go back to the Greek philosophers who look at the sails disappearing on the horizon.

One of the key things about science is that it's an integrated picture of nature.

So

the big theories that we have today, the standard model of particle physics, general relativity, or indeed Newton's laws,

in a more approximate sense, describe the action of gravity.

Those theories describe a vast range of phenomena.

They describe a lot of things.

So if, for example, you say, I don't like the idea of a force of gravity, which is what the standard kind of flat Earth conspiracist would say, then you have to explain, for example, what a pulsar is.

So in the Crab Nebula, there's a radio source, and we measure the pulses from the radio source with radio telescopes like Jodrel Bank.

So you have to explain what it is.

Now, we know what it is.

It's a neutron star, which is a spherical,

super-compressed remnant of a dead star, which is spinning very fast because of the conservation of angular momentum and because of the way the magnetic fields interact with these pulses of radio waves.

So there's all sorts of physics in there, 20th, actually 19th, 20th and 21st century physics, that describes a thing that we see.

So if you pull away at one thread and you say, well, I don't believe that there is such a thing as the force of gravity.

I think the earth is flat and the whole thing is accelerating upwards.

You can say with precision actually, well, that's locally, if I'm in this room now, not looking outside the room, it is true that I can't tell the difference between the floor accelerating me upwards and a force of gravity pulling me downwards in Newton's language.

But if you remove that idea of a force of gravity or general relativity, you have to explain the observation of, let's say, a pulsar, or you have to explain the motion of the planets against the fixed stars, or you have to explain the observation of the rotation of galaxies.

You have to explain things like the cosmic microwave background radiation.

Where did it come from?

Again, our understanding of that observation that the universe glows at a temperature of 2.7 degrees with absolute zero, the explanation comes from Einstein's theory of general relativity, that there was a time when the universe was hot and dense and it's been expanding and cooling ever since.

So you've got to explain that.

So that's the problem with all conspiracy theories, or most of them, tend to be able to explain something if they focus only on that and not the consequences of the explanation for the bigger picture.

And the picture we have of nature is tremendously successful, wide-ranging and self-consistent.

We don't need to buy a telescope, then why would we be I I mean, maybe I haven't understood the flat earth thing, but why would we be the only planet that we're observing, standing on it, that happens to be flat?

And we just happen to be surrounded by, or is that, are we then meant to believe that somehow the whole sky has been projected, it's a kind of even hydrogram, perhaps?

And why?

Why?

The point is, there's no point debating particular conspiracies, but I think the interesting thing is that the wider point that science

is an integrated and self-consistent picture of a lot of different things.

So, you can't prod away a little bit.

It's like you can't say the Earth's 6,000 years old.

If you say the Earth's 6,000 years old, you've got to explain a lot of things away.

You've got to understand what's wrong with radioactive dating of rocks.

You've got to understand what's wrong with carbon dating.

That says you've got to understand what's wrong with nuclear physics.

And nuclear physics also explains the way the sun shines, it explains the way nuclear reactors work.

So, you've got to be very careful that if you prod away at one thing because you don't like it, then the consequences for explanations of other things are often devastating to your arguments.

Anyway, so points of view never gave anyone this amount of homework.

So you've got about seven different things to do.

We move on to the I'm taking a mouthful of pasty.

Carry on.

Yeah, this is very exciting, by the way, for the listeners who

just before the show, Brian bit into a pasty and discovered that the entropy had not been great enough within the pasty for him to be able to swallow it without going hot, hot, hot.

So there's a lovely thing which is you've just heard

pasty.

Well, the high temperature.

That's what I mean.

Yeah, but it had a lot of temperature.

The heat death of the pasty had not got to the point where

a lot of phase space for motion of the molecules in the carrots.

But there's a real joy in seeing someone who can so elegantly describe the universe also just going, hot, hot, hot, not understand food hot.

Hot come from oven, but still hot.

Do you know what?

I don't think we're going to have time on this show unless there's a brilliant edit, which there may well have been already to fit in any more questions apart from those about the general relativity specials.

We're going to even get to the series, I'm going to have another bite of past.

You have another bite of pie.

I'll try and drag this letter out for long enough for you to...

Oh, ho, ho, ho, oh, pie stole, hot.

So we'll move on.

If you would like to know more about general relativity, the two specials I think are still available on the BBC website, and it was just called A Monkey's Guide to General Relativity.

Or you can do a degree in theoretical physics.

Yeah, if you haven't got time to do a degree in theory,

it's your third year before you even get on to.

So yeah,

if you have the patience, the integrity then go for it i would i would uh i'm sure it's very rewarding uh so this is well this is actually probably a very good thing so because this letter is from an 11-year-old uh who obviously we would like to and he feels reasonably inspired already hello brian hello brian not even mentioned not even uh ridiculous this is getting i'm not enjoying this show at all hello brian and and robin and robin eve hello brian i hope you say hello brian and robin that's what it says there's nothing wrong with that it's alphabetical hello brian and Robin.

No, I've added the Anne Robin.

I thought that might have been nice.

I'm going to blame Eve Mogridge, because even though it's from her account, it's actually her son who sent this.

Anyway, so hello, Brian.

I hope you are well.

That's the first question.

Are you?

I'm very well, thank you.

Good.

My name is Theo King.

I'm writing through my mum's account because I'm an 11-year-old boy.

Last Bonifaci night, I was talking to a friend of my mum's about my understanding of science stuff.

I've known him since I was two.

He was impressed by my knowledge of the subject.

He studied to degree.

He has studied two-degree-level physics and chemistry.

He has now challenged me to understand strong nuclear force by Glastonbury 2016 for £50.

So this is a money.

I don't even know if we're allowed to on the BBC because this has now become a money-based challenge.

I have gone to both my science teachers, family, friends, Siri and Google search.

I often listen to the infinite monkey cage and learn a lot from your explanations.

I thought you might be able to help.

Strawberries die when they're digested and there's now such a thing as an infinite monkey cage because a cage has edges.

So

can we therefore strong nuclear force?

There's 50 pounds resting on this.

It depends what you mean by understand, I suppose, the theory of the strong nuclear force.

Yeah, I suppose

beyond mere words, but to have some sense that as you hear those words and as you think about them in your mind, you also have some sense of the reality they create.

If you think about electromagnetism first, then the way a particle

physicist would describe it, let's say that the force between two electrons, they have negative charge.

That means, in particle physics language, that they can exchange photons, which are particles of light,

between them.

And those are the force carriers of the electromagnetic force.

And that's our quantum picture.

of electricity and magnetism.

It's called quantum electrodynamics.

So you picture two electrons exchanging photons between them because they're electrically charged.

And that causes them, in this case, because they've got the same charges to be be repelled away from each other.

The strong nuclear force is the same conceptually.

It operates between things that have a different kind of charge which we call colour charge.

So quarks for example carry both electric charge and colour charge and the force is carried by particles called gluons.

There happen to be eight of them rather than one of them for a photon.

And that's because of three different colour charges.

And the gluons,

the difference in behavior, most of the difference in behavior between the two forces, is called because gluons can interact with each other.

So they carry also the charge.

So it's like having an electrically charged particle of light.

And imagine what that would be like.

It'd be strange.

Because as the great Richard Feynman always said, one of the wonderful things about light is that I can see you across the room, even though there's all sorts of other light whizzing in every direction.

And they don't bump into each other.

The photons don't bump into each other, which is why we can see long distances.

But what we can see to the edge of the universe, in fact, because light travels in straight lines through curved space, it should be said, it's a caveat.

But photons don't bump into each other.

Gluons do bump into each other.

So I suppose the answer would be it's conceptually the same as electromagnetism.

It's carried by a force carrier called a gluon.

But it's different because there are three different charges rather than one.

And that means there are eight different gluons, which is consequent of that.

And the gluons can talk to each other as well as to the things that carry the charge because they also carry charge.

Well, I hope that's won you £50,

Theo.

Or Eve Mogridge, pretending to be Theo, and pretending to be 11 years, to win 50 pounds.

I should say, it's one of the great triumphs of modern physics, the quantum chromodynamics.

It's a very,

it's a difficult theory to calculate in.

And it has these strange properties.

I said, asymptotic freedom, where the...

So...

Another strange property is if you, which you see in particle physics all the time, is it...

So I said that the force kind of when things what happens when things separate away from each other?

If you knock a quark out of a proton, what happens?

And it's like having an elastic band between the quarks that stretches and stretches and stretches and then snaps and makes more quarks.

And so you get this shower of new particles created when you try to separate quarks from each other, which is very unusual.

The force gets stronger and stronger and stronger the further away the quarks are from each other.

So it's the net effect is kind of the opposite.

It's like an elastic band rather than being a charge in in the usual way you expect as you move things apart the force gets weaker.

But it goes straight, it's straight qua yeah, the quantum crynamics is a difficult theory.

So how long, Theo, he's eleven years old, so he's got time on his hands.

What how I mean at that point, that what you've just been talking about now and your level of understanding,

how long did that take you?

At what point do you think in terms of going through education,

you thought right now, this is a new area of

the beginning hints of understanding?

Well, I mean, you learn that

in just superficially, very superficially, the introduction to it is a postgraduate degree course.

It was when I did it.

And then you have to be an expert to really do calculations in it.

And I couldn't do it because that was not my

thing.

So to do...

calculations in quantum chromodynamics is a really specialist area that specialist physicists do theo's watching that 50 pounds drift further and further away.

It's an expert field because it's difficult.

Well, now we move on to, quickly move on to the actual series itself.

Our first episode was about artificial intelligence.

And the question there was, can you tell me if there is a difference between artificial intelligence and computing power?

This is from Alan Dedden.

Well, it seems to me you could have a computer of arbitrary power, but if you've got no software running on it, then it's not going to be doing anything.

Well, let's find out because we went to Anul Seth, who was one of our guests, and we asked asked him.

And he says, having more computing power can certainly help build more powerful AI systems, but this is only part of the story.

The real challenge for AI is to figure out the principles, the algorithms that enable artificial systems to do smart things.

It's not what you've got, it's what you do with it.

And then Alan Winfield, who was also on the programme when we talked about some very interesting small robots he'd made, although I'm basically saying exactly the same thing as Anil, I would answer it in a different way.

To build a cathedral, you need a lot of marble, but having a huge pile of finest Italian marble isn't enough to build a cathedral.

You also need the design, the architect's drawings.

Computing power is like marble, and AI is like a cathedral.

Computing power is the raw material needed to build AI.

Yes, you need lots of it, but without the architect's drawings, you'll never build a cathedral.

So, there's more homework for you.

But it's a metaphor, isn't it?

It doesn't mean that you're not.

He is a metaphor, but you can also use it.

He doesn't really mean build a cathedral.

That doesn't mean we can't take the information he's given us and gone, do you know know what?

I don't think I'm going to get very far with AI, but there's lots of cathedrals, so I reckon I've got a higher chance.

Look, the choice of what you want to do with your own marble is up to you.

You can either build a marble giant that you hope is artificially intelligent or a cathedral.

All I'm saying is, I think you'll finish a cathedral first.

But I don't think there are any cathedrals built out of marble.

I mean, what's York Minster built out of?

It's not marble, is it?

It's stone.

Well, that's.

Well, marble is a form of stone, but you're probably right.

So, the.

What we're saying is that Alan's answer was very good and a metaphor.

What is York Minster made of?

I didn't find any matching places.

Do you know what I think is delightful?

Is here we are dealing with artificial intelligence, and you ask your artificially intelligent phone a simple question like, What is York Minster made out of?

And he goes, Do you want to see Forest Gump?

So, let's move on to the next question.

This is from our show that we did about the nature of race and understanding of of it.

So this is from David Davison.

He says, listening to the show about genetics and how everyone in the world can be traced back to a common ancestor about 6,000 years ago, just worried that sounds like creationist religion.

No, it isn't.

It's statistics.

It was actually, I must say, that I had to think where it's

initially.

The guts reaction to that is 6,000 years for us to have a shared common human ancestor.

What would be, is that the so that's not a mitochondrial Eve?

The first time you hear it, it's surprising.

And I was surprised.

I said, really?

But then you think about it, and it was explained then.

What you're saying is that I have two parents and four grandparents and eight great-grandparents, and you go back and back and back.

And so obviously you're doubling every time.

At some point, you get to a point where your ancestor number exceeds the population of the Earth, very quickly, in fact.

And so you just ask the question: well, at what point does that happen?

And then, of course, it is true that there's inbreeding and all those things, and so that's not the way it works.

But broadly speaking, you can make a statistical statement that

you can't have an independent family tree from anyone else on the planet if you go back so far that the number of ancestors would be 10 billion, which is not that very far, actually.

In fact, it's 2 to the n, where 2 to the n equals 10 billion.

What is that number?

Sirik, no.

But that is one part of the joy, isn't it, of when you are wandering around.

N log.

If you see someone who has facial characteristics very similar to your own facial characteristics, then that's an early sign to suggest that you won't have to go that far back in that person's family tree to find that you have common ancestors.

Because they interlock, yeah, and overlap not too far back.

And that's where this number of a few thousand years comes from.

Because any further back than that, and all everyone's family tree overlaps with everybody else's, which is that's the statement, essentially.

It's just a purely statistical statement.

That's why you get that thing when people go, if anyone marries the royal family who appears to be a commoner, and they go,

they're actually related to Henry VIII.

Yeah, yeah, yeah.

The point is that we're all related to anyone who had any offspring a thousand years ago,

basically.

And that was the surprising thing.

When you first say that, it took me by surprise.

But then you think about it and you go, yeah, of course, it must be the case.

Because there weren't that many people in Britain a thousand years ago.

Even if we just confine the thing to Britain,

we're related.

We're all related.

This is from our episode, What is Reality?

Question from Mark.

And he says,

If I am in a football stadium and listening to the clapping and wish to join in, how come I am in time with the other clappers and not half a second late?

Is this my perception of reality or am I out of sync with the crowd?

How did they manage to get in sync?

No.

One of the most interesting things in the reality programme, I thought, was that the speed of your conscious experience, of your perception of the world, is surprisingly slow.

So

I didn't know that you recreate reality, but with something like a half a second delay.

So, you have kind of, it takes a long time to sync up that what you see with your eyes, what you hear with your ears, what you feel with your fingers.

It takes a long time to synchronize all that, even with the processing power in the brain.

And I did ask that very question to David Eagleman, and here's what he said: So, it turns out your unconscious brain, which is most of what's happening, can do extremely sophisticated things.

So, for example,

you know, people hit fastballs in baseball all the time.

Those are traveling at least 92 miles an hour.

The ball travels from the pitcher's mound to home plate in four-tenths of a second, which is faster than your conscious mind can keep up with.

And as we automatize things, that's what our life becomes.

When you ride a bicycle, or walk, or eat, or do a hundred other things, you don't even have access anymore to how you're doing it, but nonetheless, your brain can take care of it.

So, that means that you can, if you say a baseball is coming towards the bat, then that timing of the hit, which we can time very accurately if you're a good baseball player,

that's unconscious.

It takes precedence.

So, somehow your brain prioritizes that information and says, do this first, and I'll build the model of reality and experience it afterwards.

Exactly.

There are shortcuts where you can have visual information coming in, making decisions, hitting the motor cortex, signals go down your spinal cord to your muscles.

You're making feedback corrections on the swing.

All of that happens, and this just underscores the point that putting together the story of your conscious experience is a separate process that's very slow.

There we go.

And that excerpt of David Eggman was taken from the extended version of the Infinite Monkey Cage: What is Reality?

That's the only thing that's extended because we just take the radio from which it emanates and accelerate it at high speed past a stationary observer.

Well, that can be done as well.

No, we have actually,

there is more content, there are more words within it.

But if you would like to do that with your radio as well and extend it in your own particular manner, that's another little bit of homework once you've got your helio, seismograph, whatever into your cathedral.

If you put your radio on a pendulum

and swung it backwards and forwards, it would be moving relative to you, the stationary observer.

So therefore, time would be passing more slowly for the radio.

So that would extend it as well.

So you can extend it even if you haven't got.

That's the answer when people say, well, it's all right very well in these podcasts, but I have no computer, a way of downloading them.

And you say, well, you can extend it another way by just moving your radio around.

And the closer to the speed of light you move it, the longer the broadcast will be.

Can I just make it clear, by the way, that anyone who would now like to send in the bills for their broken radio after they have accidentally swung it, not having worked out that the radio, much like a cat, may well occasionally hit the walls when swung, all of those bills could go directly to Professor Brian Cox, not to the Infinite Monkey Cage or me.

It was Brian's idea for you to put your radio on a pendulum, and I have no idea why you did it.

Meaning she's a particle physicist does not mean he knows much about pendulum radio work.

Can I also say that if you do that experiment with your cat to check what Robin said, then don't send the pieces of cat in to the BBC.

What we would say is, if you do do that, get someone else to do it with the cat and then never open the door of the room where the man has swung the cat.

Yeah.

We refer you to some earlier thought experiments from the 1930s.

It's actually a unification of relativity and quantum theory, that.

So you're accelerating or moving a cat cat around very quickly relative to the stationary observer to test relativistic effects, but also the possibility you bump it into the wall and kill it will not be realized unless you open the door.

So this is probably other than Hawking radiation, I'm not aware of any other unification of special relativity and well, of relativity in quantum mechanics.

And like all Radio 4 Extra shows, we will be publishing this as a paper sometime in the next couple of years.

So we now have, we move on to the more general.

Well, in fact, I would like to go back, if I'm allowed to, by a producer who silently sits there, well, she she silently sits there in the edit but she's been babbling all the way through this quite cross with us i would like to just very quickly um go back to general relativity and just ask hannah's question hannah greenwood uh sent in three questions and they see if we can do this as quickly as possible

in just a minute yes just a minute without hesitation deviation or repetition the idea of you doing it without deviation even though in many ways it remains within the subject of particle physics or cosmology when you deviate nevertheless i'm going to remove deviation because i've talked to you which are geodesic

well there we go there's deviation so hi there monkeys, I enjoyed the Infinite Monkeys Guide to General Relativity.

However, I have three questions.

If gravity doesn't exist, one, how can the Earth be rushing towards people on all sides of the planet at the same time?

Surely it can only rush in one direction.

It's a very good question.

The answer in

one sentence is because space-time is curved.

Brilliant.

Two, why is the fact of gravity still being taught in schools so that people like me are convinced it does exist?

Now, that is an issue that I had as well, the fact that we're continually taught the idea it's it's a false.

If you want to be a purist, then what you should say is that we have models for the way the universe behaves.

And a model is Newton's law of universal gravitation, which is a good enough model to send spacecraft to the outer edge of the solar system, land people on the moon, etc.

It works.

We add another model, which is Einstein's model, which is more accurate.

It produces more accurate descriptions or more accurate predictions, which can be tested against the way nature behaves.

For example, in the orbit of Mercury, producing the orbit of Mercury.

It's also the framework for cosmology.

So it's a more accurate model.

Whether there is a yet more accurate model in which, for example, there are force-carrying particles of gravity, which are called gravitons, that would be a quantum theory of gravity.

Whether that exists or not, most people

believe that it does, but we don't have it yet.

So I would, the pure answer is that these are models.

And you apply, you choose the model that best allows you to make some calculation that you want to know the answer to or make some prediction.

So if you want to fly to Jupiter, you wouldn't use general relativity.

You don't need to.

You'd use Newton's laws.

It's easier.

And question three from Hannah is: if the Earth is spinning through space really fast and there is no gravity to hold us on, why aren't we all falling off it?

Well,

it's probably question one again, isn't it?

As I say, I mean, I think it's interesting, isn't it, that you can you're asking the question which one's the real description?

Is there a force or is there essentially a fictitious force which is due to the geometry of space-time?

And it's true that the most accurate theory tells you there's a geometry of space-time.

It works.

So Einstein's theory doesn't fall to bits when you say, well,

why am I fixed to the surface of the Earth spinning as it orbits the Sun?

The theory perfectly well describes why you stay fixed to the surface of the Earth as it orbits the Sun.

So it works.

It's just a rather more counterintuitive description, which is based on the curvature of space and time.

But you can still do it though.

You can still take Einstein's theory and work it all out and you will find that you don't go flying off the Earth.

If you did according to Einstein's theory then it would be wrong because we don't go flying off the Earth.

So you can rest assured that the predictions of Einstein's theory match all observations that we've made of simple things like everyone standing on the surface of the Earth or flying to the moon or whatever it is.

But they also match all the rather more exotic observations we've made of the universe, like pulsars orbiting around each other,

black holes, all those things that we can see or infer the existence of in the universe.

General relativity explains those as well.

So if it didn't, it would fail.

There is a delightful image of that moment where the scientist, as he disproved Einstein, he looked out his window to see his family flying off the earth and everything else with it.

Here's a question returning to something we've talked about before.

This is from Ken Ryan, who is somewhere in Canada.

I have a problem with the title of your show that I'm sure has been previously addressed.

I believe a cage would be defined as an area bounded by bars.

This side of the bar is not in the cage.

That side of the bar is in the cage.

The bars define the boundary of the cage.

If the cage is infinite, then there is no boundary.

That is the essence of infinity.

No ending.

Therefore, without boundaries, there cannot be bars.

So there cannot be an infinite cage, only infinite space and a whole lot of monkeys.

Now, I should, of course, refer to the fact that we have realised that it's not an infinite cage.

It's actually an infinite monkey.

and then the cage around it.

But that probably doesn't help things, does it, Ken?

Well, this being the BBC, this being the BBC, we've managed to make a phone call and we've managed to draft in Hannah Fry, mathematician, in order to answer a very specific question.

So, Hannah, this is from Ken, and this is actually not relating to the show we did with you on statistics of love

and sex.

We had to just put ansex like that, but it was on radio four, and we were, of course, slightly embarrassed by that.

David Spiegelhalter really wasn't embarrassed enough, as you can hear.

No, I mean, they're all from the home counties and things, and within the confines of their own house, I'm sure they're not going to be able to do that.

They can do whatever Robert Winston tells them to do on the programme.

We received a question from Ken Ryan.

Now, we've had this come up many times about the title of the show, The Infinite Monkey Cage.

How do you feel about Ken's

positive?

May I just say that you could phrase this question.

We also noticed there was a grammatical ambiguity.

So, infinite monkey cage can either mean there's an infinite monkey in a cage or an infinite cage in which there

is a monkey.

So you could have raised a question, can you fit an infinite monkey into an infinite cage?

Well so you can certainly contain infinite things within a finite space.

So a really good example of this is fractals.

So there's something called the cock curve which you can make by,

you can imagine making it with a piece of string which you halfway along the string you pull upward so that it creates almost like a triangle and you continue doing that on every straight section of string you continue creating another triangle another triangle another triangle now if you drew that on a piece of paper what you would have would be a line that was infinitely long with infinite bends and bumps on it but that's contained within a single piece of paper so it's certainly possible that you could have something that's infinite that can have boundaries so i think that's that's kind of fine the infinite number of monkeys though well it depends what type of infinite you mean there are lots of different types of infinity do you mean count of do you want to be able to count the number of monkeys that you have you want to be able to count okay so LF0 is is a countable infinity right so it's the number of hours in forever if you like or or also the number of seconds in forever it's something that the number of integers or the number of integers exactly so the number of integers is an infinite number but it's one that you can write a list you can start at the beginning and you can you can know that you're not missing any of those out you can also do the same with with fractions you can you can write out all the fractions in particular ways.

But if you want to include all of the irrational numbers, you can't count the number of irrational numbers.

You can't be sure that you've got all of them.

So these are the numbers, the infinite decimal, pi.

Exactly.

Is an example.

Exactly.

Yeah,

the argument's called Cantor's diagonal slash, isn't it?

Is indeed.

Oh my gosh.

I'm about to be tested on Cantor's Diagonal Slash.

Yes, you're right.

So the idea is you can write down all the integers.

Imagine writing the list of integers, all of them, down.

And then next to each integer, writing down one of the irrational numbers.

You can always show, by essentially by going down the diagonal of all your irrational numbers and adding a one on the diagonal to each one, then you create a number that's not in the list, because it differs by at least by one in at least one place in every number.

So you can make one more.

So there's at least one more of those than

there are the infinite numbers of

integers.

So would it be easier if we go back to Hilbert's hotel, which we referred to in an earlier series, rather than have one cage,

if we put the monkeys in Hilbert's monkey cage hotel

where each monkey has a separate cage, will that make it easier rather than just having one cage?

I'm just trying to think of the best way of housing the monkeys.

So, if you go for Hilbert's monkey cage, yeah, I think so.

I think, yeah, having an infinite number of rooms.

Well, the problem, of course, is you have to have an integer number of monkeys, right?

So, it's clear that

they're countable.

They have to be, right?

Yeah, they have to be.

We can't have a non-integer number of monkeys.

So that's why I'm saying that rather than just have this big cage, we go for Hilbert's Monkey Cage Hotel.

And then each time the new monkey arrives, we just move more along the corner.

If you have an infinite...

This is the Hilbert's cage argument, isn't it?

The question is: if you've got an infinite number of monkeys in a cage of infinite volume, is there room for another monkey?

Absolutely.

That's the answer then.

Thanks very much.

I hope that's helped you, Ken.

Thank you, Hannah.

You may go back to making your other BBC programs now.

Thank you.

Now, of course, the strawberry question comes up again, Brian.

As for those of you who've never listened to before, some years ago, we ended up in a peculiar debate about when is a strawberry really dead?

And Obi has sent in this: Can't we consider the strawberry both dead and alive until we attempt reviving it?

Brian?

Well, that's Schrodinger's cat.

That's true.

So It is true that if you

believe you can write down a wave function for a strawberry, and there's not some kind of process,

some kind of

we call it decoherence, but there's some kind of way that you could isolate it from the rest of the the universe, then you have to write the thing as a linear superposition of alive and dead, as we keep saying all the way along again.

You can just ask a botanist.

And so you see about

In fact, I think the final episode of the previous series was a botany special.

So

if you go back to that, again, that's still available on the BBC website, you will hear someone give a very lengthy, specific, and botanical answer.

Because I think sometimes, I know you think physicists should answer everything, but just occasionally, when it comes to berry-based questions, botanists have an angle.

This is from Michael Hancock.

How does it make any scientists on the panel feel to know that in a few hundred years, your average schoolchild might know more and understand the universe deeper than you can?

They'd be delighted.

That's what I think, because Michael says sobering thought, but I think it's sobering in a very delightful, sobering way.

No,

the best expression of this

way of thinking that all scientists subscribe to was given, not surprisingly, I think, by Richard Feynman, who called science a satisfactory philosophy of ignorance.

By which he means that you are to be delighted when you don't know the answer to something, and you will search for it.

And if you don't find the answer, you will be curious and happy that you haven't found an answer.

It's a misnomer that scientists like to know everything.

It's completely wrong.

A research scientist will go and seek out the things that are not known and spend all their time trying to know them.

And if they find out, they will go and find something else that's not known and have a go at that.

So

we would be out of a job if the known were saturated.

If we knew everything, there would be no job for scientists to do.

So,

now finally, at the end of our What Is Reality show, Brian listed a number of things which he decided were not real.

No, no, no, I listed a number of things that don't exist.

You okay, don't exist, not real.

Okay, so don't physically exist.

They may well exist as ideas in people's minds, but you believe that they don't have a physical existence.

No, no, no, in reality, they don't have a physical existence.

Okay, well, that's what I'm saying.

They may exist in people's minds, but they may not exist in a physical reality.

They don't exist.

Well, let's find out, because not all the listeners agreed, Brian.

Dear Robin and Brian, correct order, well done.

I enjoy your shows immensely and listen to all of them via the Miracle Podcast.

I must, however, take issue with the list of things that Brian stated are not real at the end of last week's What is Reality?

Can I just say that podcasting isn't a miracle?

Well, it's based essentially on quantum mechanics.

Right, you can say that, but this is that don't try and shy away from a very important question about Bigfoot.

Clearly, Bigfoot does exist.

Well, that's what I take issue with myself then, because it's clearly not against the laws of nature that Bigfoot can exist.

If you define Bigfoot as a species of

a species of ape, let's say, or some species of

hominid, a hominin, whatever these people,

one of those.

If you describe it as a species

which has not yet been discovered, then of course that could exist.

So I disagree with myself if I said Bigfoot doesn't exist.

Excellent.

That's very good.

It might exist.

I doubt it, but it's not impossible.

If a biologist were here, I suspect what they would say is that the same as a Loch Ness Monster.

If you're going to have some species

that exists on Earth, you need enough of them to have a viable breeding colony.

You can't have one.

Obviously, you can't have one.

because it will die and then there won't be any.

So you've got to have enough to breed and to have a gene pool that can maintain itself and that there's a species there that's viable.

So you need a lot of them.

So you can't just have big foot.

You need big feet.

And that's probably what I meant when I said big foot, singular, big foot, singular, lot less monster, impossible, cannot exist.

With, I suppose, the caveat for the pedantic listener that it could be the last.

So you can have, you can't, I suppose there will be a time when if a species becomes extinct, there is one left.

Like the dodo on Pirates and an adventure with scientists, scientists, which is a great film, I think.

So, so you can have one, but that would be the last one.

So, you can't have one that just persists.

You've got to have a breeding colony of them.

And that's why I think it's unlikely that there are very big animals out there that have not been discovered, because you can't just have one or two of them.

Especially land mammals, big land mammals.

I should say, of course, that the reason that Alan sent this in is possibly because he works for Bigfoot Programme and Project Support Limited.

So, there, there's certainly one form of Bigfoot that does exist.

Now, here's another thing on the list.

This is from Chris.

He says, Brian's ideological response that there are no ghosts is very simply unscientific.

Rubbish.

A logical rather than ideological view might be.

One, current science has defined no actual mechanism for ghosts to exist.

Two, yet many people report ghost experiences.

Three, I can't dismiss them all as hallucinating subhuman nuck.

No, I probably can't say that, but can I?

I can't all dismiss them as hallucinating subhuman fools.

Well, nobody said that.

Richard Feynman, again, again, we mentioned Richard Feynman many times on on the series.

Richard Feynman.

On this episode yeah um what he would say is that he say he actually used this argument uh to describe the the sightings of aliens and why it's unlikely that that UFOs and and alien sightings are actually um due to the efforts of an extraterrestrial civilization.

And people said it's very unscientific, you can't say that, you can't rule it out as a scientist.

And ultimately he said, no, I can't rule it out.

So but I'm dealing with things that are more likely or less likely.

So it is more likely that what we see when we are studying the phenomena of people seeing ghosts and apparitions and spirits, what we are seeing are malfunctions in human perception, which doesn't mean the people who see them are abnormal in any way.

We make many, many observations all the time.

We all misinterpret them from time to time.

It is more likely that's the case than having to completely tear up the laws of physics as we know them and rewrite them in order to permit the existence of life after death.

That's the key point.

Now, that's going to get loads of letters, isn't it?

Because that steps on many philosophical and intellectual toes.

Though, well, Chris End's letter trumps you with a bit of Wittgenstein, whereof one cannot speak, thereof one must be silent.

Wittgenstein.

Wittgenstein, yeah.

Trumping it stands.

So, quoting a philosopher

is winning an argument.

Well, no, he's got a lot of other points, which is quite a long letter.

I can win lots of arguments by just quoting philosophers, isn't it?

Okay, go.

As Plato once said, come on.

You're round.

Exactly, exactly.

You are quoting Monty Python's apparent quoting of Philosopher's.

No, she's very quick.

The Platonic Solids.

Right.

Anyway, there.

So that's Bigfoot's general relativity and the nature of infinity dealt with in half an hour or longer.

If you've listened to the extended podcast, thank you very much for listening to Brian and Robbins' Infinite Inbox.

You can listen to all of the episodes that we've talked about and others on the BBC website

for, well, for a very long time.

Not necessarily infinity, but probably some definition of infinity, or at least to the heat death of the universe or the heat death of the BBC, whichever comes first, or indeed the heat death of Brian as he yet again attempts a pie in an unruly and foolish manner.

Remember, just because you understand physics and cosmology generally doesn't necessarily mean you understand the nature of pies.

Is that a thought for the day?

Yeah.

Your version of thought for the day.

My version of me just throw it away

in the infinite monkey cage.

In the infinite monkey cage.

In the infinite monkey cage.

Till now, nice again.

Sucks.

The new musical has made Tony award-winning history on Broadway.

We demand to be home!

Winner, best score!

We demand to be seen!

Winner, best book!

We demand to be quality!

It's a theatrical masterpiece that's thrilling, inspiring, dazzlingly entertaining, and unquestionably the most emotionally stirring musical this season.

Suffs!

Playing the Orpheum Theater October 22nd through November 9th.

Tickets at BroadwaySF.com.