In Our Time - The Vacuum of Space

Episode Date: April 30, 2009

Melvyn Bragg and guests Frank Close, Jocelyn Bell Burnell and Ruth Gregory discuss the Vacuum of Space. The idea that there is a nothingness at the heart of nature has exercised philosophers and scientists for millennia, from Thales's belief that all matter was water to Newton's concept of the Ether and Einstein's idea of Space-Time. Recently, physicists have realised that the vacuum is not as empty as we thought and that the various vacuums of nature vibrate with forces and energies, waves and particles and the mysterious phenomena of the Higgs field and dark energy.

This BBC podcast is supported by ads outside the UK. Every Sunday, we talk about the week's tech news on this week in tech. Hi, this is Leo Leport. inviting you to join me this week with Lisa Schmeiser, Dan Patterson, and Yanko Rekkers. We're going to talk about the new 49 megabyte web page. It's the standard, you know. We'll also talk about Elon Musk. You've got some spleenin to do and the Yassify filter, new from Nvidia.

That's this week on this week in tech. You'll find it at Twitter. or wherever you get your podcasts. Thanks for downloading the In Our Time podcast. For more details about In Our Time and for our terms of use, please go to BBC.co.com.uk forward slash radio four. I hope you enjoy the program. Hello, when contemplating the vacuum of space in the 17th century,

the physicist Blaise Pascal claimed, The eternal silence of these infinite spaces fills me with dread. But we're here around today, Pascal's anguish might have been assuaged for the vacuum of space, while certainly silent and possibly infinite, is by no means empty. It's a seething mass of particles, of interactions, forces and energy. To study it, undermines the distinction between something and nothing. But by examining the nature of the vacuum, we get closer to understanding the fabric of reality and the expansion of the universe.

With me to discuss the vacuum of space at Jocelyn Bell-Burnell, visiting professor in astrophysics at Oxford University, Ruth Gregory, Professor of Theoretical Physics at Durham University, and Frank Close, Professor of Physics at Exeter College University of Oxford. Frank Close, the idea of nothing was something which preoccupied the Greeks. Yes, Aristotle, I think, decided that there was no such thing as nothing. And the idea that nature abhors a vacuum, which is a phrase that everybody's heard, but probably what does it actually mean,

held sway for 2,000 years. and in the Middle Ages there was a lot of religious conflict as well the idea that God would make nothing was regarded as heresy if you said that you believed in a vacuum you had problems unless you were very clever and said well if God wishes to make a vacuum

God can make a vacuum the idea that nature abhors a vacuum though is because so many things that you do give the impression that it doesn't for example if you try to suck the air out of a straw the air rushes in at the other end stick the straw into a glass of water, the water starts sucking up.

So everything seems to be stopping you making the vacuum. Of course, what we now know to give the punchline away is that on every square metre, there's 10 tonnes's weight of atmosphere pressing down on you and me, as we're speaking. Aristotle set the pattern for that as for so many things, extraordinary, for about 2,000 years. And it was in the 1600s with Galileo and his pupil Torricelli, They began experiments which tried to prove the opposite.

Can you tell me what they did and tell listeners how they went about it? Well, Galileo and many people were aware that you couldn't lift water up more than about 10 metres. So it was as if nature abhorter vacuum up to a point. And Tori Shelley, who was Galileo's student, then did the famous experiment with mercury, choosing mercury, I guess, because it was the densest liquid there was. and he discovered that a column of mercury could only stand about 76 centimetres tall and we now know as you vary atmospheric pressure on bad days and good days it'll rise or fall a bit relative to that

by going up mountains the next thing he discovered was that the height of the mercury got less and less the higher at the mountain you went and the reason of course is the higher you are up the nearer to the top of the atmosphere you are so like a swimmer that's coming up from under the sea to the surface of the sea As you go up to the surface of the atmosphere, there's less atmosphere above you pressing down, and hence the mercury column falls down as well. So this gave the idea that what is it above the mercury column if you've got it inside a closed tube? There appears to be nothing.

And the nature of this nothing was what then began to intrigue them. And Pascal, who you mentioned did a beautiful demonstration, a very dramatic one in France, with water. and wine in a column which is 10 metres high. He had a column of water, 10 metres high, a column of wine. And he was interested in... And an audience of 700 people? Only 700? Well... As in my note, it's 700.

Wow. That is great. I mean, that's what brings science home to people. It really turns them on. He wasn't actually just doing it for a demonstration. There was a real purpose to this, because the question was, above the mercury in Torricelli's tube or in your barometer, is there nothing? or is it mercury vapour that's stopping the mercury column getting to the top? And Pascal realised he could test this because wine is less dense than water. So if there was nothing in there, the wine column would be higher than the water column. But you know that wine smells a lot and water doesn't, unless it's chlorinated. So if the wine vapour was stopping the wine getting up, the wine would actually be lower than the water.

He did the experiment in Ruan. 700 people watched it and all verified indeed. what happened, which was basically there is nothing in the gap above. The wine column was the one that was higher. And this idea of, was it taken on, when Newton fell in with the idea that there was an individual medium called the ether, which went through the universe, what was he supporting? What was that idea briefly?

Well, the idea of the ether is something that's developed over a long time and means different things for different generations. Newton had the idea that, if you like, there's an invisible graph paper up, down and sideways that we are moving through, that even though space appears to be empty out in space, you can imagine above the atmosphere nothing at all, and yet somehow nature knows up, down and sideways.

And you can imagine this yourself. You sit on a roundabout in a kid's park. You can close your eyes, close your ears, so you could have all sensory feeling, but as the roundabout goes around, you can sort of feel space moving through you. We all know it, but what does it actually mean? So Newton had the idea there is some pre-existing space and we move through it.

Jocelyn Belbinel, could you take that idea, excuse me, could you take that idea of ether on through the 17th to 18th, 90th century? So I understand it. It became a prevailing idea and was extremely useful in answering several questions at the time. Yeah, the ether had its heyday in the 1800s, largely. and it was killed off in about 1880, 1890, really. Although I think a lot of the physics community didn't recognize it was killed off. We have an ability to ignore awkward results if they don't fit with what we want to hear.

And I think what was concerning people was we know that bodies can exert gravity on each other. The sun exerts gravity on the earth and so on. And we also know that things like light, propagate through space. Now, surely these things need some kind of medium, some kind of vehicle to carry. For instance, light they were beginning to recognize was a wave. So what is it that's waving up and down?

There has to be something that's waving. And the concept of ether got turned into this something. It had an interesting conclusion. Let me before we get to the conclusion, Jocelyn. and I want you to talk about the conclusion in a moment. Can you just give some people, myself included, enlightenment about this ether? So let's take Newton as a figure. What did he think the ether was and what was it doing?

It was conducting everything through the universe. What was it? Where was it? How did he got there? Can you give us some more about this ether? It was everywhere. It had mechanical properties, it seems, so that there was something physical there

and there were people who tried to measure the mass of the ether and things like that and there were wonderful pictures like ether being a whole sort of jammed together set of ball bearings and the mass of bodies were in the little gaps between the ball bearings. They actually had a lot of different pictures of it. But it was the carrying mechanism to do it? Yes, the mechanism that allowed things to get from there to hear.

All the forces that we're going to talk about and all the forces that we know about. All that they knew about. All they knew about. All they knew about were carried on this invisible ether. Did they ascribe it any weight? Did they ascribe it any force of its own? Or was it merely a conductor?

It was primarily a conductor, but there were physicists asking about its properties itself. And some of them kept on asking, long after they should have laid it to rest. but that's humanity for you. Now it was laid to rest, and it was right to rest as a sort of law of unexpected consequences when they were doing something else, as I understand it,

but could you tell us how this idea, which had prevailed for two or three hundred years? Yes, yeah. And being very strong, and when people, great physicists had used it, when it was curtains. Yes. If there is an ether out there, then as the earth goes round the sun, for instance,

it's likely moving through the ether. so it's like having a wind blowing past the earth and if you think of how light waves might travel through this moving medium this wind you could see that the light waves that are trying to travel upstream would have a tougher time than the light waves that were trying to travel downstream and they two gentlemen to Americans called Michelson and Morley

invented an experiment to try and test this they sent out two light beams with a mirror at the end so the beams got reflected back they sent out the two beams at right angles and they looked to see... Why is that? Partly because it gives you a control

one light beam it's always risky to do results with just one thing you need something to serve as the base and they look to see if there's any evidence of the two light beams travelling at different speeds This was quite a compact experiment. It was done within a laboratory. It wasn't done on interstellar scales.

And they didn't get any effect. They had a very clever contraption. They had their apparatus on a little platform, a little floating platform, floated on a large pool of mercury. And they could turn the whole thing round so that their beams were then going in different directions with respect to the way the earth was moving.

through the ether, and they still didn't see any effect. Now, this was such a contradictory result to what most other physicists believe that a lot of them, I think, had trouble taking it on board, and there were people pursuing escape routes. Maybe the earth is cocooned. Maybe the earth doesn't feel the full blast of this wind as it moves through space. And so there was that kind of argument, but ultimately it was all dismissed. Michelson and Morley demonstrated that light goes at the same speed in every direction, regardless of the ether and regardless of our movement through it. So the idea of ether was gone?

That's the neatest way of answering that experiment, yes. Ruth Gregory, can you explain how Einstein's special theory of relativity finally replaced ether? Yes, well, I mean, I think the problem with the ether was not so much that nature abhorred a vacuum, but I think that humans did or scientists did and they were incapable of really thinking that there was absolutely nothing

not even some medium to propagate these waves of light or to allow gravity to the gravity of the sun to keep the earth in orbit around it and when these experiments of Mickelson and Morley actually demonstrated that light, the speed of light

seemed to be the same for everyone at the time I think people were probably trying to find ways of explaining that, perhaps, you know, with equations. Why is the speed of light so central to the demolition of the ether? Why is that? Well, I think this was really this sort of radical, I think, conceptual step that Einstein took. So he felt that this constancy of the speed of light, the fact that we all agreed on the speed of light, he felt there was something fundamentally important in that, and that was actually telling us something about nature,

the fact that everybody agreed on the speed of light. How did that cancel out the ether then? Well, so what he then did was he tried to sort of take these steps to their logical conclusion. So he asked himself a question. He said, what if I'm going at the speed of light and I look in a mirror, what do I see? Well, of course, if you're going at the speed of light, the light can never get to the mirror to be reflected back at you. Why is that? Can't it go at the speed of light to the mirror?

Well, because you're travelling at the speed of light already. So if there's a light wave that leaves your face, it doesn't actually leave your face. It's keeping pace with it. This was his thought experiment. So time stopped. So time had stopped. We know that now, or this, you come out with that immediately,

which is incredible, but at the time, nobody would have thought of that. At all. At all. So just a second ago. this is key. He's supposed to have come from a vanity moment. He's looking in the mirror and say, what would I look like if I was going at the speed, if I were going, at the speed of light?

And can you say that again? Because I think it's fascinating. Yeah, so he realised if he was going at the speed of light, he would not see his face in the mirror because the light would never leave his face to even get to the mirror in the first place.

And so he realised, therefore, if he can't see himself, the only way that that makes sense with our normal experience of looking in the mirror and actually seeing a reflection is if somehow his perception is switched off at the same point. So that means, in other words, time has stopped. Now, in reality, it's what he used was this idea of inertial frames, the idea that if we are moving in a train, as long as, well, actually,

having the train journey I had yesterday, maybe that's not quite true. Let's take a plane, but a nice smooth day. We're not aware that we're moving at hundreds of miles an hour. We feel as if we're sitting at rest. And so, in other words, people moving are equivalent to people who are at rest. We think we're in the same state. And we both agree on the speed of light. And the amazing thing is that taking those two things as fundamental and true

leads you to Einstein's theory of special relativity, which tells you that time and space are no longer separate entities. They're part of a single unit and that we don't need an ether to actually have waves propagating because the waves themselves just move in this space time. So they need nothing to conduct this room? They don't sort of have, in the sense, in the mechanical sense that the people in the 19th century and 18th century thought of. the ether. So in the sense that they were thinking of something like the surface of the sea, we're very used to seeing waves. We have a very good intuition about waves, but the surface of the sea

is very much a mechanical medium and it behaves in certain waves. Very close. Your train experience actually reminded me of one I had this morning, which is a perfect example of this. We were sitting in Reading Station apparently forever and was a train on the other platform sitting adjacent to us. and I was looking at that train, and I suddenly thought we were off, and then discovered it was the other train that was going off, and we were still sitting still. So this concept of the relative motion of the two trains,

we've all experienced it. It was, I knew that I was at rest because Reading Station was still at rest next to me. And in the universe of the ether, the Reading Station was the rest frame of the ether, and there was an absolute meaning to me sitting there and the other train going off towards Swindon. Einstein did away with Reading Station.

what a wonderful concept. It's unfair, come on. It has its use. So it's a complete choice as whether that train is going off or I'm going off. It's the relative motion that all matters. Just let's look at the contemporary picture now.

Let's imagine, try to imagine, a square meter of empty space at the... Sorry about that. I'm sorry about that. Do you mean a cubic meter, actually? Thank you. I just make a little... I'll just make a little... I can see.

From now on you're on your own, okay, but under some steers I've got here. Let's imagine the cubic meter of empty space. Can you tell us what might be in that at the macro level? We think it's empty. We look at empty space. We see black emptiness. Now, what is really in that cubic meter? Well, very little, and if it shows black, it shows there's very little in it.

We see things around us because light from the sun and light from lights bounce off those things and into our eyes. But if space looks black, it means there's nothing there for light to bounce off. There may be some light going through your cubic meter because there will be some stars and galaxies around studded in the black. So they'll have to go through that to get to the stars, don't they?

To get from the stars. Yeah. So, yeah, if you look directly at a star through your cubic meter, you'll see a pinpoint of light, but the rest of it will be black. But what's in there? We think there's nothing there. What is in there?

There's actually nothing, no place where there's absolutely nothing. There's always a little bit of something. So can you give us a hint of what might be there in that cubic? I stress cubic a metre. Thank you, yes. It does help. Besides light that might be travelling through from here to there or hither to thither, there could be radio waves and x-rays and gamma rays, things like that. in addition to light and radio waves and so on

which are what we call electromagnetic waves there'll likely also be gravity waves which you can think of as ripples in space time so that's going chuntering through as well but there's also a lot of particles milling around in space neutrinos and cosmic rays and things like that so actually there's quite a lot going through and there may even be a few resident particles

and how many just depends where in space you are. Frank Close, we've looked at the macro level out in space. What about the same thing, cubic metre, in the micro quantum level? What's happening there? Well, for about 100 years, we've known that when you look at matter at very fine resolution, smaller than the distance scales, even of atoms, that it takes on a very different character than what we're used to.

Before we get it now, can I just ask you to do one thing? We're going to talk about atoms and what's inside. Can you just give us some idea how big is an atoms and what we're talking about? I'm sorry about that. I'm on my own here, right, okay. Yes, how big is an atom? You could probably put a few million

across the wits of a hair to give you an idea. So it's small, but not so small you can't imagine it. Although you put a few, I'm not being sort of, oh gosh, but just. to get it straight, across the width of a hair you can put a few million atoms. So that's our starting point. Right. Right. Back to the original question.

One further step before we get to that. The atom, if I expanded the atom to the size of the longest hole on the St Andrews golf course, then the nucleus in the centre of the atom is the size of the little hole you're trying to get the ball into. So you get a sense of matter being incredibly empty

except, as Diosyn said, the atoms are full of electric and magnetic fields that are holding them together. When you start looking at those atoms very carefully with special microscopes like particle accelerators, you see that they are not static things, but they are fluctuating all the time in what's called a quantum uncertainty. And that the fields that are holding the atoms together themselves can be producing little particles of matter and antimatter, bubbling away all the time. Now this sounds like you know you've come in contact with somebody who's totally crazy,

Bertin to the studio who's telling you things that you have to take on trust. We can do experiments which show that nature is indeed like that. That the more resolution that we have available, the more of this bubbling away we see there. Inside the atom, because the item was considered to be an empty space, wasn't it, until you got closer and closer. You discovered the nucleus, which you talked to. If the item is St. Andrew's golf course,

the nucleus is the size of a single hole on the golf course. And inside that we've got neutrons of proteins, whizzing around electrons. So, but what about the spaces between? That is the thing. It is for, the space between the nucleus and the particles and the outer reach of the atom is full of electrical forces. Can you take us a bit further in that, Ruth Gregory?

We're inside the atom. It's tiny, but it's massive. So we're talking about relatively massive compared with the nucleus, and then inside the nucleus of this other thing. And so there's stuff going up. What about the gaps in between? Is that not nothing? Well, no.

Again, we seem to, nothing seems to be a very elusive concept. The more, I sometimes like to think of the vacuum, if on a large scale it looks like there's nothing. But in fact, I try and think of it like a can of worms almost, something seething, something that's sort of, if you look in detail, there's actually an awful lot going on. But in reality, we don't, we don't,

don't, we're not allowed to see that except in some very special cases because this is a... I don't get not allowed. It's what Frank used the word, this quantum vacuum. So in quantum, in quantum mechanics, quantum field theory we have this idea, it's something called uncertainty,

which means that there are certain things that we're not allowed to know too precisely. It's simply a law of nature. I'm really, sorry about this. I'm not tripping out. I'm just totally intrigued. Not allowed. Not allowed. I'm intrigued by the word of. Who doesn't allow you? Does the subject not allow you? The instruments not allow you? What doesn't allow you?

So the uncertainty principles usually presented as this idea that you cannot know exactly where you are and exactly how fast you are going at any one time. And the key lies in saying what do you mean by knowing something. So knowing where you are, if I want to know where this table is, I actually say, well, I see it. because I see light bouncing off the table. Now, that's something fairly definite because this is something at a human scale. But as you go down to the scale of the atom, this one millionth the size of a hair, and you want to now be certain where that is sitting,

you have to start using light or this electromagnetic radiation, which has a very short wavelength. So if you imagine trying to sort of say something is there and you're throwing a wave at it. If you throw a very long wave, like one of the waves on the sea, you're never going to be certain about where it is within the size of that wave. So the smaller the scale you want to be sure about, the shorter the light ray, the light wavelength that you have to use.

And of course, one of the things that is fundamental to quantum mechanics is that light comes in little packets, little quantum. and the energy of those little packets, it gets bigger, the shorter the wavelength. So, yes, you can see where something is to greater and greater precision, but the act of kicking the light ray off it means you're less and less sure about where it could move, it's speed. So there is a fundamental limit to how well you can pin something down.

It gets to be something. It's called phone, is it? Oh, well, I see. You're real. And we're getting to where we come, anyway, Frank, we're getting to, and maybe we'll get there before the end of the programme, get into where you can't measure, and then we're thinking about, well, Frank, close.

You mentioned energy, and I think that's a very nice example of the weirdness of the quantum. We know that in everyday affairs, energy is overall conserved. It changes from one form to another, but the book's always balance. Can you give an illustration of that? If I dropped something off the table in this room,

it would fall to the ground, and it would get faster and faster the further it fell. It would be turning its what we call potential energy. Sitting on the top of the table it has the potential to turn into emotional energy, kinetic energy. So that's changing potential

into motion. The steam engine is turning heat into power and so on. So the whole of industrial society in the 19th century was built on the conservation of energy and its consequences. In the quantum world we discover that if you do measurements on very

very short time scales, that the energy isn't conserved on that. It can fluctuate. Like in the old days when we had sensible banks, it's the old analogy of you borrow your money on Friday, and as long as you get it back by Monday, nobody notices. And it's a bit like that in the quantum world, that energy is not conserved on very, very short distances.

So if you start looking at your one cubic meter black box in the middle of space, you will discover that energy is bubbling up and down in there in a paradoxically unmeasurable way. even though you are aware of it by subtle experiments. Joseph Belbinard, can you take us further in that? Still inside the atom, continue to take us there where we're talking also about virtual particles and I'm trying to get at where people can reasonably expect to say

there might be nothing there, there might be a complete emptiness, because now I've got these sizes that Frank graphically tell us about St Andrew's golf course is the atom, a hole on the golf course is the nucleus, inside the nucleus is I think, and whizzing around our electrons, it still seems to me the possibility of a lot of emptiness.

Now, I mean, I'm so far off the pace, but that's what it seems to me as an observer. Can you just take us further into that? Why is there not a lot of emptiness and nothingness and an illustration of more universal nothingness there? If you have a picture of the atom where there is this very heavy but small central nucleus and electrons whizzing round outside, and if you think of those electrons as being identifiable, particles like other golf balls on the golf course, if you like,

all trying to get into this central hole, then, okay, there is space between the particles. But what we're doing here today is moving the argument on a stage and saying we're not just talking about physical things like golf balls. We're actually talking about the forces between the golf balls. We're talking about radiation that might travel between them. And these forces and this radiation and this connectivity is the seething stuff that's going to prevent you from ever having a perfect vacuum.

Connectivity, a beautiful world, space is filled with connectivity. It's the forces that grip things together. Can I step where I fear to trade, which is into virtual particles. Now, where does that take us, Chasler? Going back to what Frank was saying about borrowing money from the bank on a Friday and paying it back on a Monday. And accruing no interest, so there's been no, as it were. The bank manager doesn't notice. Because you're not in, right, okay.

He's not in that. Let's not talk about the banks. Sore point? No, I don't want to talk about it. Right, let's go on. No, with everybody. One of the versions of the uncertainty principle that Ruth was talking about, she was talking about measuring position and speed accurately simultaneously.

Another version of that uncertainty principle is talking about measuring energy and time. And the analogy I use is you can borrow money, you can borrow energy from the bank briefly, but as long as you pay it back quickly, that's okay. Now, if you borrow energy, you can use that energy to create particles, ideally pairs of particles, probably matter and antimatter pairs. And you can play with those as long as you turn them back into energy and pay them back to the bank within this time limit. Can you develop that, Ruthel,

would you care to develop that virtual particle argument? Well, so the idea then is that at all... We're still inside the atom? We're still inside... Well, we don't have to be. We could be in any...

Yes, we could... So we can... As both Jocelyn and Frank have been saying, if we're careful or what the quantum vacuum does, is it does this all the time. It borrows this energy, creates pairs of particles, and these pairs exist for a very, very short time. Then they come back, re-anihilate, and the energy is paid back, and nobody is ever any the wiser. So you might say,

well, why? How do you know this? Well, there are two, there are two physics, sort of circumstances where we can actually spot this going on. One is, unfortunately it's not yet been seen, but the other has. So one thing that listeners have probably heard about is hawking radiation, which is this idea that we have these massive objects, which are black holes in space, but they're not really black, and they actually radiate. And this is, one way of visualising this,

is due to this quantum vacuum, this picture of the vacuum as being this seething mass of virtual particles. because outside a black hole, again, the vacuum tries to borrow the energy to produce this pair of particles, but because it's near the black hole, it's possible for one to fall in and one to zip out to infinity where it can be seen.

So there's another effect where we can measure or see the effect of this vacuum, and that is where something which is called a Casimir effect. So if you're on a ship... That's an experiment. It's an experiment. It's an experiment. Well, Casimir predicted it.

About 50 years ago now, it was a roughly, maybe even 60. So if you're in a boat, I mean, and I suppose depends how many people are with boats, but if you have two boats going along very close together, they tend to be pulled together. I think there's a sequence probably in a James Bond

or probably all sorts of action movies where, you know, there's something zipping between two large boats. And it's basically this idea that outside the sea can have lots and lots of waves of all different lengths, but in between the boat, you can only have waves that can actually fit between the boat. And this means that there's a difference between the in-between space and the outside space, which causes a sort of pressure inwards. And this is the same with the quantum vacuum. If you have two very parallel conducting plates, it has this.

similar effect. It won't let you just pair create anything you you want. Frank can take it? Frank you want to get out and please do but can you just keep us in the loop about the possibilities of a vacuum as well as everything else? Yes I mean an example we're talking about

the atom and the force that holds those electrons in the outside of the atom the electric field inside the atom that Newton described what was called the inverse square law that the further apart to electric charges are the force dies away like the square

of the distance and that is what's called classical physics. It works for gravity, it works for electrical forces. It turns out that if you measure the force inside the atom of hydrogen the symbol as one of all, you find that it at first sight looks like the inverse square law. But if you do very

precise experiments, you discover that it's not quite inverse square. There are deviations from it and the closer you look the more the deviations show up. And these deviations fit exactly with the quantum theory which says that the electron here and the nucleus over there

while the connectivity if you like to use Jocelyn's word the force of attraction between them was transmitted across along the way it bubbled into particles and bubbled back again and that subtly changed the nature of the force between them these things have been measured to

one part in a billion it's quite remarkable and it all works What sort of evidence do we have for this Jocelyn? The Hadron Collider is under repair at the moment and looking for the Higgs boson which is central.

Let's jump a bit and talk about the Higgs boson and dark energy. I've got stuff here and Frank if you want to bring in fluctuations and so on, bring in it in a let's move to what's now. What do you think is there now because there is a case in what I've read of the note in one of your

notes, one of the three of you're saying or modern physicists say that there is a possibility that there is a vacuum somewhere. So what are we doing with Higgs boson why? Is that important? Has it replaced the ether? It's not been identified yet. Where are we? Where are we? We are waiting in a state of excitement for a number of issues to resolve themselves.

One of them being the Higgs boson. And this is a particle that was predicted by Peter Higgs of Edinburgh University. Very interesting prediction. The best one, I think I have of explaining a Higgs boson is imagine a crowded room, maybe a party. And you appear at the door and say, can anybody lend me 20 quid? You don't get much of a response.

If you appear at the room of the door, the door of the room, sorry, and say, I've found 20 quid, does it belong to anybody? You're besieged. The Higgs boson, is the particle that gives mass to things and it's like you having the 20-pound note on offer. You can't move. You've suddenly got great mass because you're offering 20 quid. The Higgs boson determines whether it's like a person offering 20 quid

or a person trying to borrow 20 quid. It's how much stuff accretes around you and means that you're nimble or you're ponderous. But as far as I can make out, Frank Close, or just as over, this is still theoretical. We've got this 24 kilometres under a Swiss mountain, and rightfully, my view, billions of pounds being spent on it, and they still haven't found a trace of it, literally.

So, I mean, I'm not against anything. But we're still talking theoretically, as we were about the ether, for instance, earlier, as we were earlier about, as Aristotle, but we are still in the, and we've got a professor of theoretical physics with a finger up on one left. So, Jason, if you want to come in, Frank, can we just talk about this

and how the Higgs-Boson fits in with the idea that there might be a vacuum? Well, to turn the thing full circle, the idea now is that space is actually full of something called the Higgs field. In a sense, the ether is there. It has very special properties. And just as we talked about the idea of the electrical field that was known in the night, 19th century and that you can make it wobble and give electromagnetic waves which in quantum manifest themselves as bundles of light called photons. So the quantum says that the Higgs field can wobble and manifest itself as particles called Higgs bosons. And there is not yet any direct

evidence for the Higgs boson. That is indeed true. But there is indirect evidence for it. In that, just like earlier on we were saying how the force inside the hydrogen atom can be subtly modified by these little quantum effects as the force tries to transmit across the atom. Likewise, very precise measurements at CERN in the 1990s showed that the numbers didn't quite balance, but they didn't quite balance in a way that suggested the Higgs particle on route was affecting things even though you weren't yet able to make it. So how does this fit in, Ruth Gregory, with the idea of the idea, I mean the exploration of the vacuum over the last three centuries, looking if there's nothing, there's yielded a great number of positive results for science and taking it forward.

But how does the Higgs boson, where are we now, if we were saying, is there a vacuum in space, if we were saying, or anywhere, is there emptiness anyway, if we were saying that where are we now? In our understanding of the vacuum, well, actually, this was why I was wanting to come in earlier, you were saying this was all theoretical and despite being, as you pointed out, a theoretical physicist,

I wanted to say, but wait, no, we have actually some practical experimental, or should I say observational results that tell us something extremely interesting about the vacuum. So we can, in cosmology, we have various ways of actually trying to put together our detective story

of what's happened to our universe and about just over 10 years ago there was a set of various projects that were looking at distant supernovae. So a supernova is a star that basically explodes when it comes to the end of its life. It's a catastrophic event. It's very bright.

You can see it from a very long way away. And so these various different projects were looking for these supernova that were happening a very, very long way away. And what they could do is they, when you are going, when you are a long way away in the universe, what happens is as light comes from that star supernova galaxy, whatever, to you, it has to come through a universe which is expanding. And this stretches out the light as it comes to you, which means that the light goes through the spectrum from the violet to the red. So this causes what we call a red shift in the light. And so what these what these astronomers measured was the red shift. of these distant supernovae, and they found that the universe,

although it was expanding, it was not, as we had expected, slowing down. It was not decelerating like it was coming up to a red light, but in fact it was accelerating like it was going to an ambolite. Jocelyn, there seems agreement that the universe is expanding,

and there's a great deal of talking now about dark energy, and most of the universe is full of dark energy, and the stars are the tiniest, almost tiny as possible part of what's going on there. How does the expanding universe, what's expanding into, something or nothing? The thing that's expanding is space itself. So if you think of space as a stretchy rubber membrane, the rubber membrane is getting stretched out more

and carrying the galaxies further apart. And as Ruth said, you would expect gravity between the galaxies to slow that stretching. In fact, the stretching's getting faster and faster. and faster. So we might live in a big rip. You never know. We will know one day, but not yet. The source of this acceleration,

it's like an anti-gravity. It's something pushing the galaxies apart. So it's counterintuitive in that sense, isn't it? Absolutely. And it's very uncomfortable. When we are uncomfortable with things, we try to make ourselves more comfortable, we give them a name, and it feels better.

So we've called whatever is causing this acceleration, dark energy. And for a few mad moments, we wondered if it was these virtual particles. The particles, the pair of particles that got created temporarily, could they somehow be helping

push the galaxies apart? Unfortunately, that's not the solution because that vacuum energy, there's far, far too much of it. We'd have had much more acceleration if that was the cause. So it's something else. At the moment we know,

remarkably little about it. We don't know for sure whether it was always there and in the past, masked by other effects, and we don't know yet if it's everywhere, but it's certainly around here at the moment. Well, thank you all very much indeed. That was a real one

around the block, and thank you very much for coming and giving us such insight. Hi, that was terrific. Thank you, Ruth Gregory, Franklis, Jocelyn Bell-Bernel. Tonight at 9 o'clock there's a programme on the new Galileo's, the new giant telescope builders, before we come on at 9.30,

and next week we're talking about the Magna Carta. Thanks for listening. We hope you've enjoyed this Radio 4 podcast. You can find hundreds of other programmes about history, science and philosophy at BBC.com.com.uk forward slash radio 4.