Reality Goes Deeper Than We Thought

Added: 2026-05-09

[00:00:00]Ever since the ancient Greeks, there has been this desire to find the basic elements. By the 1950s, things got extremely complicated. Suddenly, a whole zoo of particles appears. Quarks, lepttons, and the nutrino, the muon, pentaquarks, gluons. It then took just the next 50 years to get through through that culminating in the discovery of the Higs boson. Having lived through discovery, it's a bit like trying to get to the end of the rainbow. We're obviously way way along, but how much there is still to go? Who knows?

[00:00:39]Frank, thank you so much for joining scientists today. I wanted to start with a quote from Isaac Robby from the early 20th century. And upon hearing the news that the muon had been observed, this heavier cousin of the electron, he said, "Who ordered that?" kind of with surprise at the fact that this other particle than the ones we knew familiarly at the time existed. And almost a century later, we've really filled out that kind of zoo of particles and we've found many more. We're still observing more and we're still finding more. But are we any closer to understanding just why they all exist or or kind of finishing that picture?

[00:01:13]>> Well, I think Rabbi asked that question 80 plus years ago and it hasn't been answered yet. Uh we certainly know much more now than we did then, but uh it's a bit like trying to get to the end of the rainbow. We are obviously way way along, but how much there is still to go, who knows?

[00:01:33]>> And you've worked on particle physics for a fair amount of time, and you've had a real front row seat to watching discoveries, new particles being observed. When you look back at it, does it seem like a kind of steady drum beat of progress or are there particular moments that stand out to you? Well, I guess I feel very lucky to have lived my professional life from around 1970 onwards which in particle physics was the time when things began to fall into place. When I was at school, the beginnings of particle physics after the war with the discoveries in cosmic rays and then the building of accelerators which started producing lots and lots of particles, a veritable zoo of particles and it must have been a complete and utter mess. what was going on. Um it was the late60s when things began to fall into place though I don't think it was appreciated straight away. A lot of these things it's all obvious after the event you know but in the late60s there are experiments at Stanford in California which in effect were the first clean way of looking inside a proton. the proton, the basic seed of hydrogen and and the nuclei of all atoms and discovered this new layer of the cosmic which we call quarks.

[00:02:52]And that experimental discovery was the first thing that began to show that the real theories applied at the level of quarks and that protons and all these mysterious particles that were appearing were actually combinations of quarks in in different ways. So that was an experimental side. On the theoretical side, the focusing on the quark layer of reality uh surprisingly with hindsight I suppose showed that apart from gravity all of the forces the electromagnetic force which everybody knows of and like charges attract, light charges repel and so forth which radiates light. There had been a theory of that since the 1940s.

[00:03:38]Quantum electronamics meaning combine quantum field theory and relativity and the electromagnetic force and you have a complete theory of all uh electromagnetic phenomena which worked to better than one part in a billion. So that was clearly correct. The surprise, at least to me, was that the theories that emerged of the strong force between quarks and the weak force of radioactivity followed the very same mathematical rules as quantum electronamics.

[00:04:13]>> It was just that whereas in QED as it's called the electric charge is a certain number of of kulums. So there's a number in there. Mathematically if you replace the number by a matrix that's a little array of numbers 2 by two in the case of the weak force 3x3 in the case of the force acting on quarks the mathematics was exactly the same and that discovery in the 1970s really paved the way I think that I was then getting into my post-doal career and there was a clear way forward >> and It then took just the next 50 years to get through through that um culminating as we'll probably talk about later in the discovery of the Higs Bzon which in a sense is the capstone of the whole thing that emerged from that. It took a long time but I was lucky to live through that and having now retired in the sense that they no longer pay me for being interested in this stuff but you remain interested for the whole of your life that it was very fortunate to have actually experienced that from the inside.

[00:05:23]Um, one thing that occurs to me, I'm not sure whether this is a good thing to say to people out there, but as it is, you know, at school we all learn stuff, you know, right back to Pythagoras and Archimedes and the whole lot and Isaac Newton and Galile, it's all in the textbooks. It's sort of correct.

[00:05:41]>> And when I finished as an undergraduate at St. Andrews. I remember my professor there saying to me just as I was about to leave and come down to Oxford to do my my PhD, he said, "From today on," he said, "Everything in science is going to be different for you. You'll never quite believe it the same." And I now know what he he meant. It's that having lived through discovery and seen a lot of long wrong paths along the way, um you never feel quite as confident in the reality of what you have seen your colleagues and people that you know and everything like like that do to accept that that's the same as what Isaac Newton and Albert Einstein and all those people back then were doing. Whereas of course now there's a new generation who are probably quite shocked think all the stuff that went on through my era is solid in the textbooks. I don't want to disavow you of that but uh it's an interesting thing I hadn't anticipated.

[00:06:39]>> Absolutely. I mean one thing that is undeniable in some ways is that we have observed lots of new particles. We have fleshed out that that zoo of particles and and there's hard data to back that up from the colliders. when we're describing these particles, often there are terms attached like exotic or or or kind of rare. Could you kind of explain why there are so many different particles possible and and what it means to have an exotic particle?

[00:07:06]>> I suppose first of all the word exotic um I mean to the average listener of this probably all particles are exotic.

[00:07:14]going back, you know, to the start of the last century, this discussion might have been much easier because, well, maybe not that ever since the ancient Greeks, there has been this desire to find the basic elements. This belief that all of the wonder that we see around us uh is composed of a few elements. Mhm. And indeed the original idea of air, earth, fire and water, we we call them the elements today, although we now know that air, earth, water and fire are made of of stuff. Um, by the end of the 19th century, the idea of the elements was the atomic elements, the order of 90 or so of them. Um, and if we were having this discussion, then we'd have said, oh, the basic elements are the the atoms of the different atomic elements.

[00:08:04]By 1910 to 20 all of those atoms were now understood to be made of a deeper layer of reality. Originally you know atoms were thought to be the smallest thing possible like miniature bills in some sense. All the atoms of gold being identical. The only difference between an atom of gold and atom of hydrogen is that gold is much heavier than atoms. So a different than hydrogen. So it has a different atomic weight. But um why nobody knew that was just an empirical rule. Then along comes Ernest Rutherford who discovers that well before him Thompson in Cambridge in 1897 discovers the electron negatively charged constituent of all atoms. So this is the first direct evidence I suppose that there is structure within the atom. The electron carries negative electric charge and so there must be something positive to balance it. In fact, there's little just to digress slightly. While I was writing a book about electric charge, I'm still amazed that matter is overall neutral. The negative charge of the electron perfectly balances the positive charge of the protons. And to show how critical that is that every breath that we're taking, you're breathing in a million million million million atoms of oxygen and nitrogen. And in each of those there's a few electrons. So you're breathing in if that was the whole story you'd be breathing in I think it's of the order of 15,000 kulum of charge with every breath.

[00:09:37]Now what is 15,000 kum of charge correspond to that would be enough to ignite about a thousand lightning bolts.

[00:09:45]>> And the reason why we don't fry with every breath is because of this perfect balance between the negative and the positive charge within the atom. And I think it's fair to say that we still do not understand but isn't clearly an empirical truth. So relevant has found that the positive charge lives on the massive nucleus in the middle. And then by 1932 they found two types of thing that make the nucleus. A positively charged proton and its near twin the neutron which is almost the same as a proton except it's got no charge hence neutral. So protons and neutrons combine to make atomic nuclei. Electrons surrounding them. That's the picture of the atom. And so through 1930s you might say so what are the basic particles? Oh electron, proton, neutron. That's it.

[00:10:35]>> Except the experiment has a habit of getting in the way of beautiful theories. And what happened was that very precise studies of a form of radioactivity called beta decay showed that that couldn't be the whole story. That when in beta decay, one atom of one element turns into an atom of another element by emitting an electron. For example, >> if that was the whole story, the difference in the E the MC squed of this one at the start and this one at the end would always be the same. And so the electron would always come out with the same amount of energy. But the careful measurement showed that sometimes it came out faster and sometimes it came out slower. So there was a spread of the energy. So what do you do with that?

[00:11:20]Well, Neil's bore who was probably one of the greatest theorists of the 20th century was prepared to give up the idea of energy conservation >> at the nuclear level. And I just say that as an example of you, you know, it's in the textbooks, but that doesn't mean to say it's the final word.

[00:11:35]We now know that that wasn't the explanation that Pi proposed that rather than just an electron coming out, there was another little particle called the nutrino.

[00:11:45]>> So that the energy was being shared between these two. Sometimes the nutrino had a little and the electron had a lot.

[00:11:51]Sometimes the electron had a little and the nutrino had a lot.

[00:11:54]>> And the nutrino has no electric charge.

[00:11:59]>> It has we now know a tiny bit of mass, but you know, it might have had no mass at all. So it was almost like a ghostly particle that played no role other than balancing the energy books. Now at the time that idea of pi I mean today we might say okay obvious tick the box but back in the 1930s the idea of increasing the three known particles by another one >> was very radical.

[00:12:25]>> Though we now know that that was correct. So there we would have been at the end of the the third is electron and neutrino, proton and neutron.

[00:12:35]>> So two and two you've got a hint there of something going on but exactly what you do with it. There we are.

[00:12:43]>> Then come along well two things I guess.

[00:12:47]The first thing is the role of theory in a man called Paul Durak and I find this very eerie. Paul Drack was a mathematician at Cambridge University in the late 1920s and he tried to describe the electron the simplest particle of all uh using the two great theories of 20th century the quantum theory and Einstein's theory of special relativity and he applies the equations of these things to the electron and he discovers that the mathematics can't sort of balance the books in a certain sense If there's only an electron >> and that to make the whole thing work there also has to be in in nature a positively charged analog which we call the positron >> and that particle exists and it is the first example of antimatter as we call it but what I find eerie is that here is dra in 1928 I think it is writing down these equations and the equation implies that there is this posetron on this antimatter thing and then it's another three or four years before experiment in in cosmic rays discovers the cosmic radiation hitting the upper atmosphere spewing particles including antimatter particles like the positron. So the mathematics knew this before we did which is a very well it's a testament to the power of mathematics but at the same time I find it quite remarkable but that is the way way things go but the existence of antimatter has now appeared in principle there are anti- particles to all the particles we know and in with no reason to believe other than that and indeed every antiparticle that we've been able to discover is matched by a particle So there's nothing mysterious there.

[00:14:40]There is something mysterious as to why you and I having a conversation when we're made of matter because everybody knows from Star Trek that when matter and antimatter meet, they annihilate.

[00:14:48]>> And presumably the big bang produced matter and antimatter in perfect balance out of the energy. So where did all the antimatter go? Put that down on the list of questions to be discussed, you know.

[00:14:58]Um but the uh development of I suppose photographic plates the development of technology then enables experiments to do things they hadn't done before. So putting photographic plates in balloons, flying them up the atmosphere, go to the top of mountains and when cosmic radiation little particles come through the photographic plates, they leave a trail and from this you started discovering the existence of things which we had not previously seen on Earth.

[00:15:30]>> So everything we knew up to 1940ish uh could be explained as necessary to our existence. electrons, protons, neutrons, and ne nutrients to balance the books, antimatter as well. But then along comes the discovery in cosmic rays of what was called the muon, >> which appeared to be and pretty much still appears to be identical in all respects to an electron except that it's about 200 times heavier.

[00:16:01]>> And there was no rhyme or reason for that other than it clearly exists. And that was the thing that Rabby said, who ordered that?

[00:16:09]>> After the war, the discovery of other particles in the cosmic radiation, some of them with strange properties which became known as strange particles, >> uh soon leads to the ambition of replicating the cosmic rays on earth by building um dedicated accelerators of particles. Mhm. So the part of accelerators are producing beams of high energy particles which are the analoges of the cosmic rays. But whereas in cosmic radiation you're just waiting for one to come along if you're lucky. Um and then you have to make use of what you got by making beams of particles and firing them at targets of material. um you can increase the rate of getting interesting things to look at and you can control what you're doing to look for particular things and and so on. And so that was how through the 50s suddenly a whole zoo of particles appears that had no obvious rhyme or reason at all other than that they clearly exist and have to be explained.

[00:17:11]>> Um so by the 1950s things got extremely complicated.

[00:17:16]that is like the world when I got interested in particle physics. Um I was at high school in the 60s and the theorists were beginning to start noticing among this zoo of particles sort of commonalities that they could put them into families. Mhm.

[00:17:33]>> And Abdul Salam who later won the Nobel Prize and was professor at Imperial College. He was on the radio a lot and those were the days when they had serious science programs on the radio on one evening a week and Salam was on the radio and he was talking about some mathematical scheme to bring all these particles together and I remember I didn't understand a word of what was going on but it was clearly very exciting that was on the the the edge of something wonderful and I knew I wanted to be a part of it and so that's really I where I became excited at the idea of particle physics.

[00:18:15]Then in the final year at the sixth form, it was our chemistry teacher who told us the world was made of atoms.

[00:18:22]That's quite astonishing thing to say.

[00:18:24]It wasn't in our physics class. It was the chemistry teacher who told us the world was made of atoms and the atoms are a nucleus with electrons whirling around and the only difference between one and the other is the number number of electrons. And I thought, wow, great.

[00:18:35]because chemistry was extremely difficult for me. There was so many facts and I thought well maybe here knowing these little basic rules we can work out everything. So that's how I became interested in physics and reductionism. I still haven't worked out chemistry from it. Um and so that was the nature of the world in the 50s and 60s and then I started as a graduate student and professional into the 70s when at last this complexity was beginning to be partly explained in the form of there being another layer deep down and today the quarks which are the constituents of many of these particles the one all the ones that feel what's called the strong interaction >> and then lepttons the generic name for the electron, the nutrino, the muon and another nutrino and so forth. So there are these two distinct family of basic particles electron and its friends there's six of them all together electron muon tow and three nutrinos and then the quarks six of them up and down charm and strange top and bottom six and six must be something going on there but what it is I don't know but that's where we are today >> now whether that is the end of the cosmic onion or whether if somebody in 100 years would be doing an interview like this they'd say oh 100 years ago they thought is but now we know that that I don't know >> some of the particles are very strange to use the normal definition of the word strange like pentaquark tetraquarks and uh proposed things like glue balls which I know you've also written about could you just explain what some of these really exotic particles are and what they're telling us about the nature of the universe >> yes I I guess the word exotic means things that are not in your present lexicon so um in 1930 30 even a sort of like short-lived resonance of the proton would be regarded as exotic whereas today we wouldn't regard that. Now that we know that the proton is made of three quarks any particle that's made of three quarks dancing around in whatever which way would not be regarded as exotic but if you found a particle made of something other than three quarks or a quark and anti-quark which is the other way that we we we know that would be called exotic. So you mentioned words like penta quarks. Well I guess you can tell from that pent is five. So um if you've got something made of well three four quarks and one anti-quark because it's the quark and the antiquark if you like cancel out. You got to be left with three overall but four and and one. That is a combination which we now know in theory can exist.

[00:21:18]But it was it's outside the original simple set of things that were discovered 50 years ago that set this whole thing in train. I should probably make this a little bit clearer.

[00:21:30]The proton and the neutron back in 1960s were established to be made of three quarks. Two ups and a down make a proton. Two downs and an up make a neutron.

[00:21:46]The theory of how quarks interact with each other is called quantum chromodnamics QCD. Very similar name to quantum electronamics QED. And the reason for the similarity in the name is because they're almost the same theory.

[00:22:01]>> Um whereas electric charge is described by a number. Whether it's positive or negative, it's a number. Quarks carry a funny thing called a color charge. It's not real color, but there's just three different varieties. And so replace that one number by a 3x3 array of numbers.

[00:22:20]The state the equations of QED become the equations of QCD. And that is remarkable. It shows that the the fundamental force that is binding those quarks together is following very similar mathematical rules to the way that electrons and things work. So there is a clue actually that electrons and quarks somehow are related but don't know what to do with that. So anyway we've got the theory QCD that describes how quarks work and then you can start working out consequences of that theory.

[00:22:52]One understands why three quarks like to clump together and this actually is a beautiful example of the similarity. The rules of electrostatics are like charges repel and unlike charges attract.

[00:23:07]take those rules over to we'll call it chromostatics. The rules of color charges. So just give them the name red, blue, and green. The three positive color charges.

[00:23:20]One quark here. Let's suppose it's red colored. If I bring another red colored quark up, like colors repel.

[00:23:26]Bring up a blue colored quark. Unlike colors can attract. Boom. Red and blue.

[00:23:32]Bring up a third quark. If it's red, it's repelled by the red one. attracted by the blue one. So, it's sort of neutralish. If it's green, it's attracted by both. So, you've got three.

[00:23:42]Now, bring a fourth quark up. There's only three color charges available. I don't know why. That's how nature did it.

[00:23:51]>> It must therefore have the same color as one of these quarks already there and be repelled by it. It'll be attracted or it can be attracted to the other two. And it turns out that the amount of repulsion by this pair perfectly counterbalances that. So this is sort of left over looking for two more to join with. So that's why they join up in threes.

[00:24:10]>> So it's the three color charges following the same rules that you're used to with electric charges that end up with three quarks clumping together.

[00:24:22]Now you can then start looking a little a little more deeply into this and you discover that just like electric charges radiate photons.

[00:24:32]So color charges will radiate colored photons. The jargon we call them gluons.

[00:24:40]And these are things if you like that glue the quarks together. They are deep down the fundamental carriers of what we call the strong force that eventually build up different clusters of these things to build up atomic nuclei.

[00:24:54]So we know the rules of how it all works and then there's two things you can do.

[00:24:59]One is to try and solve those equations in detail which is very difficult and that's given rise to a whole new area now what's called latis QCD. it's a huge technology or you can start looking for other consequences of those basic things and that was the path that I was very much interested in for many years. So we've got starting off with three quarks clumped together you radiate a gluon and it could turn into a quark and an anti-quark.

[00:25:28]So you could imagine having four quarks and one anti-quark. That would be a pentaquark.

[00:25:34]>> Mhm.

[00:25:35]and experimentally pentaquarks have been found which to me is not a surprise because they are if you like the simplest consequence of this underlying fundamental theory. So in that sense they are a very reassuring confirmation that my confidence that the basic rules of quantum chromodnamics are indeed analogous to those of quantum electronamics that that is indeed true which is very profound because it's given you a very clear clue of where you might now want to push the boundaries that this similarity can't be an accident that must be part of nature's big game. Can you bring these two equations together to build a unified theory of these different forces? The other thing though that excited me was the gluons because you've got three different colored quarks and when they rad if a red quark radiates a gluon that red quark might turn into a blue quark and the gluon carry off the color itself. So there's a difference between gluons and photons.

[00:26:39]Photons have no electric charge. They they couple to electric charge but they don't have any.

[00:26:46]>> So photons are blind to one another. I mean we're able to see each other because the photons just travel between us without interruption.

[00:26:54]Gluons carry color charge themselves.

[00:26:58]So if a gluon was shooting off from me towards you, it would suddenly get attracted to another gluon.

[00:27:06]In fact, it would form what we call a ball of glue, the glue ball within about the size of an atomic nucleus.

[00:27:15]So that small mathematical difference has a huge phenomenological diff consequence. the fact that electromagnetic rays can travel throughout space without interruption whereas the the colored gluonic rays if you like are trapped within the size in the confines of a single particle within the atomic nucleus.

[00:27:38]>> So I was interested in are there glue balls and if so what is the evidence for them? what would we have to do to establish them and so on. And that question I was really pursuing about 30 years ago >> amidst that backdrop of exotic particles um and this kind of steady drum beat of of finding new ones and and building out the theory as you say of quantum uh chromamics and quantum electronamics. Um there was this huge moment in 2012 of confirmation of the Higs Bzon being discovered. you were writing about at the time you're speaking with Peter Higs after which the particle is named.

[00:28:18]Looking back at that moment kind of more than a decade afterwards. Um does that still seem as big of a moment as it seemed at the time?

[00:28:27]>> Oh, the short answer to that is very much yes. I'm reminded the quest for this thing which in a nutshell if we imagine everything that has been understood since the 1970s the the existence of these six types of electron-like particles and six types of quarks and photons and gluons and and so on and so forth. That whole lot together is called the standard model. It empirically describes pretty much everything that we we know. There's nothing that goes against it. It doesn't answer all the questions like why isn't there any antimatter around and so forth. It doesn't answer the question why do the particles have the particular masses that they have for example but that standard model is clearly how things are. Um and the the completion of this era of discovery that one has identified the fundamental particles and the interactions between them which all follow a a common mathematics QED, QCD and an analogist thing for the weak force all has one well more than one But it would all be great if these things had no mass at all.

[00:29:43]Empirically, things have masses. If they didn't, you know, we wouldn't be have here. There'd be no structure. In the absence of mass, there would be no structure at all.

[00:29:52]>> So, to me, the question is less one of mass but more of structure. Why are there structures in the universe? And the whole Higs business, if you like, was theoretically an answer for that.

[00:30:10]And it implied something very profound, if true, that if you could imagine removing all of the particles and all of the forces, literally everything out of the universe, um, what you were left with, the vacuum would be unstable if it was empty. M but if you added some stuff which we call the Higs field to it that would stabilize it. Now it sounds a bit counterintuitive the idea adding stuff to nothing stabilizes it but that's part of the magic. Okay. So there was this theoretical idea that we're immersed in this stuff and I sort of draw an analogy. No, we're immersed in this stuff just like a goldfish needs water to exist. We need this he stuff to exist theoretically. Now, how would the goldfish know that it was immersed in water? Well, maybe if you could excite waves in the water. And by analogy, if you can excite waves in this Hig stuff.

[00:31:08]And in quantum theory, waves like particles. So what the Higs Bzon the theoretically predicted Higs Bzon was is would be the proof that we are immersed in this stuff and that if we can focus just enough energy into a very small region of this stuff it can bubble up as one of these particles. So find this Higs Bzon and that would prove that we're immersed in in this this stuff and that would be the completion of explaining why all of this structure that we've been dealing with for 50 years is as it is. The idea of Higs emerged in 1964.

[00:31:53]It was pretty much ignored at the time and it was only a few years later the first steps in beginning to understand how the electromagnetic and the strong force and the weak force of radioactivity followed the same mathematics with one key problem that the weak force of radioactivity followed the same mathematics except that the analog of the photons and the gluons things called W and Z bzon have mass empirically >> and just putting masses into the equations ruins everything. It turned out that this I'll call it a trick if you like this mathematical trick of Higs and others could enable mass to appear spontaneously and leave all the beautiful mathematics pristine.

[00:32:42]And the experimental discovery of the W and the Z boson uh was the first confirmation that we were clearly on the right track. And it gave very careful precision measurements then of those particles enabled us to work out how far away the Higs boson must be. Whether that was going to be a particle or something complicated, we didn't know.

[00:33:04]We just knew how far we had to go. So the designing the machine, the Large Hadron Collider at CERN. Um the the requirements of that were pretty clear.

[00:33:17]uh the technology of it was superb and it was not at all clear that you could actually even achieve it. But, you know, that was a 20-year project that that led to that. And in the years leading up to it, you know, excitement was building and to help the public appreciate this, one of the ideas was to um use Peter Higs, who was British and um it was a would be a great triumph for for British science um for him to sort of talk about it. Now, Peter was a superb lecturer um in a sort of closed group and so forth, but he wasn't a natural performer on stage. Um so, one of the things that was done was that I went on stage with him oh half a dozen times over several years sort of having a conversation like like we're having here to help him bring out his story to the audience. And uh I realized that I'd been very privileged to have experienced over this six years with him the leadup to the actual discovery and then the the period afterwards which is what led to me writing about it. But your your question really was is it or was it really as big as it's been made out to be? And I would say yes because the very first time I had one of these interviews with Peter Higs was at a festival in Melrose in Scotland and James Noctti uh was there and I realized I'd been on stage many times and given talks but I'd never interviewed somebody before and so I said to Noctti before I went on I said how do you do it? He said oh interviewing people's easy I thought well it is for you you know but not not for me. And then I thought, if you were going onto the stage now with Peter Higs, what would you be asking him? Now, by chance that morning, there had been a a leader article in the Times newspaper going on about the Higs Bzon and people beginning to think he was going to get discovered and so on so forth. And so, Noxy thought for a moment and then he said to me, "Contextualize it."

[00:35:23]And I thought, "Yes, um, what what do you mean by that?" And then he said, "Well, is all of this hype and things about the or the excitement about the the Higs Bzon, is it all hype that's been generated by the Sinovic community and the media or would its discovery really be a singular moment in human culture?" And that was the thought.

[00:35:47]That's the answer. It would be a singular moment in human culture because for the last 50 years we have suspected that this if you like is the reason for all of everything that we've been discovering and working towards. But we don't know for sure. The the hard thing about being a theorist is you can have wonderful ideas but if nature doesn't follow them it's not of immediate use.

[00:36:14]And that's why when I introduced Peter the first time, I said it is easy to be Shakespeare or Beethoven than a theoretical physicist. You know, make one note different in Beethoven or one line different in Shakespeare. Well, maybe to be or not to be, but other than that, you get the idea. You still got a wonderful work of art.

[00:36:32]>> Change something in the equation and it doesn't work at all. Um, so that was what we were all getting excited about.

[00:36:40]And indeed when it was discovered um I wasn't at CERN. I was over in the UK watching the live feed um from CERN and it was a hugely emotional moment. I mean it takes me back to what I was saying earlier about Dearak writing equations on a piece of paper and the equations seem to know more than we do and then along comes antimatter and proves the equations were right. 1964 Peter Higgs scribbling equations on a piece of paper 50 60 years later the experiment proves that it is right um it is remarkable testimony that something about maths is is the clue and that is why I'm so confident that the fact that the equations of electromagnetism the weak force and the strong force are so similar that has to be if you like my faith is that mathematics tells us what to do And that is why I am excited that there must be something that brings these things together, if only we can find out quite what and how.

[00:37:45]>> Given that we've discovered the Higs and and we know the energy it exists at or or the mass it exists at, there are still many other questions we have about the Higs and and it's one of the large reasons that scientists are still at CERN right now working on the Large Hydron Collider. What are some of those things that we don't know about the Higs that are still kind of deep mysteries and and and what would that tell us about how the Santa model works?

[00:38:07]Well, we don't know what the Higs actually is. I mean, we we know how much energy is required to make it. In other words, we know what its mass is. 125 GV in the units of about 50 times heavier than a single proton.

[00:38:25]We know that it has no sense of direction in in the jargon. It's a scalar particle.

[00:38:30]We know that when it we know that it's unstable, so we know how long it lives for. unimaginably short time.

[00:38:38]>> Just how short are those times?

[00:38:40]>> 10 to the minus a lot. It's in the data table somewhere. But what we observe is not the Higs but the things it decays into.

[00:38:50]>> Uh that's the nature of particle physics when it's always if you like seeing the fossil relics of of something and having them to backineer to where they've come from. The great thing about quantum mechanics is you don't know on an event bye-byevent basis what's going to happen but you know that if you do 10 million know 50 million will be this 10 million be that and so on and so most particles of the Higs mass we would say it will go to this type of thing that often and this type of thing that often and so forth but the Higs is unique in that it likes to interact with things. The more mass you've got, the more friendly you are to the Higs.

[00:39:30]>> And so the Higs will decay into heavy particles relatively more often than it should do compared with normal experience. And that is indeed what has been found qualitatively.

[00:39:45]I mean quantitatively up to a certain error. And what one is hoping I mean the frustration is that how many years now is it since the discovery? nearly 15 years after the discovery that everything about the Higs is fitting precisely what that simplest equations of 1964 predicted. What we're hoping is that something will be different. Uh you you need a you need a paradox or a signpost to point you which way to go. In the absence of that, you're sort of looking everywhere. So one of the things is to improve the the quality of how we can look at the Higs and measure its properties more precisely in the hope that we will find something anomalous in there and that that anomaly will give us the clue where to go next. So that is one pursuit for making more and more better precision measurements of the Higs itself.

[00:40:40]um whether there are other things in addition to the Higs I mean Higs and people came up with this idea in 1964 they wrote the simplest thing down you could imagine and remarkably it's the simplest thing that we have confirmed is that the whole story or are there less simple things also that this Higs if you like is a portal to um but to me the big strategic question uh is that the Higs bows on itself if you like Well, that's interesting. But that's your starter for 10 really. That um the the thing that is remarkable is as I said, if we removed everything, we would be immersed in this field, the Higs field, whatever it is, just like the goldfish being immersed in the water.

[00:41:29]And to repeat that analogy, this very clever goldfish has discovered a molecule of H2O which proves to the goldfish that the idea of water is right. That molecule of H2O is the analog of the Higs Bzon which proves that this Higs field is right. But think about water for a moment.

[00:41:51]The goldfish likes water, but it doesn't like ice and it doesn't like steam. Are there different phases of the Higsfield?

[00:41:59]Does the Higsville itself have deeper structure? Is there another cosmic onion going on inside there and so on? We simply don't know. And the strategic question really is what is the nature of this stuff which has given the particles the masses they have the properties they have that make the structures that we experience.

[00:42:20]And to answer that, the simplest thing is to take the next step, which is not to produce a single Hig Bzon, but to produce two at the same time to see how they merge together, if you like, how two molecules of H2O fuse together to start building up water.

[00:42:40]And to do that, you know exactly how much energy you need and how much intensity of beams you need. And so that is what one of the future uh goals or the current goals of improving the large hunter and collider intensity and the detection ability at CERN is geared towards you know precisely what you need to achieve that it's not it's not relying on a big unknown so to speak.

[00:43:09]When the Higs was discovered in 2012, you actually wrote at the time that if we imagine the total energy scale u possible between a summer's day and the very smallest one, which is the plank energy, then at the LHC, we're still only really halfway between those two energy scales. And that in the foreseeable future, we're not going to get that much closer to the very smallest energy scale that you would need to start answering some of those questions. Is that still your opinion?

[00:43:35]Do you still think we need something else to get us there further and start answering some of those questions you were describing?

[00:43:42]>> Well, when I said halfway, I mean in orders of magnitude.

[00:43:45]>> Sure.

[00:43:45]>> Right. Um when you think of I mean the the summer's day feels warm but uh you know from striking a match working your way all the way through the structure of molecules to the structure of atoms to the energies in the stars which you're still hardly starting. You haven't even really got to the energies that particle physics is exploring. um we are now exploring energies which were present in the immediate aftermath of the big bang.

[00:44:20]In a sense, one of the big changes, I should have probably thought of this earlier on in the conversation, the big breakthrough to me psychologically in the 1970s, was that up to that time we had been trying to find what matter is made of. And suddenly now realize that actually what particle physics is doing is like experimental cosmology. that when you were smashing particles together, in particular when you smashed electrons and their antimatter positrons together head on at CERN in what was called LEP, the large electron positron collider, their annihilation produced in a small region of space for a very brief moment. The sort of energy conditions that the universe as a whole experienced in the immediate aftermath of the big bang. So what we were doing was simulating the immediate post big bang conditions and seeing or discerning what the laws of physics were like back then.

[00:45:17]And so that I think was when particle physics suddenly became something of relevance to the whole thing. And perhaps Steven Weineberg's book the first three minutes was the real starter to that. So the energy scales between that and the striking a match there's been so many different things going along all the way to get to that and then the Higs Bzon is still only of that same order of scale of energies there's so much happened in there the idea that then there's nothing all the way out to the plank scale where we could no longer ignore gravity that gravity becomes so strong that space and time itself what you actually mean by it becomes uh contentious and I have nothing to offer on that other than to say I I work down here. That's here's hard enough, you know. Um but the idea that there's nothing between here and there, it seems to me either tremendously optimistic or tremendously arrogant or but I mean maybe that is how it is. But uh uh I mean my my my half glass full fear is that the plank scale way out there, the thing that we're referring to is where everything naturally happens.

[00:46:35]>> There's just a handful of bits and pieces which have sort of dribbled off and that's what we are.

[00:46:41]>> And we've discovered all those bits and pieces and discovered some hints in there. But the final answers are indeed way out there. Um I hope not.

[00:46:53]>> So in that kind of desert or or whether it's full of new phenomena, new particles, there could be some some much more exotic physics and particles. One of those that was talked about a lot before the Higs and is still spoken about in some quarters is this idea of super symmetry and whether there might be another family of particles um hiding out there.

[00:47:13]Do you think that idea still has merit and is that something that we could find at higher entries?

[00:47:19]>> Well, it certainly has merit as a a theoretical idea. Whether experiment whether nature makes use of it, of course, is the question that experiment can hopefully tell us. I mean, as I've said on a couple of occasions earlier, mathematics does, for some profound reason, prove to be an excellent guide to the way that nature works. And it is indeed also that what we make progress with is when we find something paradoxical, then that identifies something that has to be answered. And so the mathematical structures that we have at the moment, all of which up to the discovery of the Higs have sort of fitted with that nonetheless contain some implicit not exactly paradoxes but issues. Let's let's say um that the Higs Bzon is fine. It fits in with everything we anticipated. But then when you start asking questions but you know we live in the world of the quantum quant I mean the Higs field is a field and quantum field theory applies to that we know how to do that and that then starts having implications like if the Higs Bzon is linked to the origins of mass where does the Higs Bzon's mass come from other than itself >> and that's fine you can deal with that mathematically but then it starts saying why is it so relatively speaking light?

[00:48:49]I mean what stabilizes it? How does it all work? So you can create mathematical conundrums and then the challenge is to find a solution to those conundrums. They may be purely mathematical and we might find that there is no answer to them and that this is the first clue that we're somehow on the wrong track >> or they may lead you to something that you can experimentally look for and if you find it that directs you. So one of the mathematical advances or applications that could answer this question of what stabilizes the whole Higs business is that there's a phenomenon called super symmetry. And the empirical evidence for that is that to every particle that we know at the moment there is a another particle whose intrinsic spin is we haven't talked about spin but there are particles that are called firmians that mathematically spin at half integers relative to plank's quantum and the things called bzons that have zero like the higs bzon or integer amounts of the things and they behave very differently. Bzons are like penguins.

[00:50:07]The more the marrier.

[00:50:08]>> So you can make laser beams of photons as intense as you like. Whereas firmians are like cuckoo that more than one in the nest is one too many.

[00:50:18]>> The ply exclusion principle says well you can't put firmians anywhere and that is what causes structure. Electrons are examples of firmians. They build up structure. So you've got firmians and Bzons and super symmetry says okay well why not to every bzzon have a corresponding firm and to every fian have a corresponding bzon mathematically a lot of interesting things happen experimentally the best you can say is we found half of them so far right there is no direct evidence I don't think I'm saying anything radically here I don't believe there is any direct experimental evidence that super symmetry is used in the particle families at least as far as we are able to say at the moment. It is possible that super symmetry is manifested at energies we have not yet accessed. I mean let let's face it all the beautiful mathematics that led us to the Higs was mathematics that worked in a world with no mass.

[00:51:22]The Higs mechanism is what I really should be called the mass mechanism because there several people came up with it not just Higs. Higs identified the Bzon that's correctly named. But the mass mechanism is a way of getting the mass into the equations while maintaining the beauty of the equations and the success of them, the self-consistency of them. So we can start saying there's a a lot of sort of bodies could be buried in this mass business. And so super symmetry is another example of beautiful mathematical equations which may all be hidden by the masses.

[00:51:56]And if the masses are very large in the super symmetry world, in other words, if there is indeed something out there in that desert and it's super symmetry, we have not yet been able to access it.

[00:52:07]What we have been doing at CERN is to use the other advantage of quantum theory which is that you don't necessarily have to get there all the way because quantum theory can once in a while give you a glimpse of something. You can sort of look around the corner quote unquote the uncertainty principle. And so by doing very precise measurements at CERN um and looking for things that don't quite fit with the mathematical predictions you might get the first glimpse around the corner and that is what has been going on for the last 10 years or so really zoning in more and more and more. So although to uh people at large it gives the impression that nothing has happened at CERN in 10 years actually far from it with regards to super symmetry. The ability to hone in and make the the area of where you can hide super symmetry getting smaller and smaller is as near as one can currently get to saying well either it doesn't exist or it's it's hidden somewhere like that. Which of those two we cannot yet know. this picture that you've painted of new mathematics or or mathematical advances kind of guiding the theory and then that steering uh humanity towards what we should look for and what we find um is a really interesting pattern over the history of particle physics and as you pointed out earlier it you had examples like DRA uh seeing the existence of antimatter within the quantum relativistic equation you then had kind of group theory and and representation theory and symmetry informing uh the standard model of particle physics and and the that structure that you painted out earlier. Do you think that there is a need for new mathematics kind of guiding the theory of particle physics and and and is that relationship does it still exist as it kind of played out in the 20th century?

[00:54:02]>> Well, of course there's plenty of new mathematics. I mean mathematics is a discipline which is creating you know all the time. The question is uh whether there are applications of mathematics that can help us understand phenomena in particle physics or in in other areas of science. Um that of course I I don't know. I mean but uh when and if it happens I can answer your question but uh no I suppose there I mean string theory is obviously an example that um back in the 1990s the discovery that certain symmetries and bringing together of uh disperate ideas in principle even including gravity um mathematically uh could be achieved. But if we lived in a universe not of four dimensions but of 26 or 10 or something you know higher dimensions and that created a lot of excitement because a lot of the well as I said earlier that if you can find a paradox in your mathematical structures that is a clue as to where to push. And so one of the paradoxes is if you take conventional quantum field theory as we have for the electromagnetic strong and weak forces um and Einstein's general theory of relativity which applies to gravity they're perfectly fine as long as you keep them apart but the higher energies you go to the nearer you get to this far remote plank scale the more you're encroaching upon the region where you can no longer ignore gravity and so I mean now we have certainly with the beginnings of gravitational astronomy and the ability to observe the collisions of black holes and so forth are beginning to directly measure phenomena at which one can no longer will no longer be able to completely ignore this problem of how to bring quantum theory and gravity together. And in string theory in higher dimensions was a possible route or is a possible route depending on how optimistic you are towards this. And there was great excitement that at last maybe we'd found the answers you know by chance or whatever it is and can can we sort of reverse engineer and get there. Well 30 years later the relevance of string theory to particle physics to my mind is still completely open question. It's a very interesting area of mathematics. It has dealt with lot it has developed a lot of things in disperate areas of science but for the original hope of it answering the questions of quantum gravity and particle physics needs today still open question >> unfolding alongside the the the building out of these huge colliders and these large experiments like at CERN has been studying neutrinos. Um, and you mentioned earlier that again they they kind of popped out of an equation that I think PI was looking at. We've now got fantastically sensitive detectors and and the the advent of kind of neutrino astronomy and nutrino physics is far beyond where it was in the 70s and ' 80s. Um, what are nutrinos telling us about the picture of particle physics and how do they fit into this whole picture?

[00:57:22]The nutrinos are the most enigmatic of all the particles because they are so shy. Um, they've got no electric charge.

[00:57:33]They've got almost no mass at all. I mean, you could put 100,000 nutrinos together and it still would only weigh as much as one electron. So, there's something about nut. If nutrinos were absolutely massless, in a sense, they might be easier to understand. And it's just the fact they've got the the dribblest bit of mass that there's something weird about them. And they're very hard to study because they only interact through either the gravitational force which is immeasurable in practice. Um or the the weak force and by its very name weak shows you it doesn't sort of reveal itself very easily. So we know less about nutrinos than we do about all the rest put together. There are also some mathematical hints that nutrinos might be the the portal to understanding the matter antimatter asymmetry of the universe. um we haven't really discussed it but just to assert that dear equation and everything basically that we've known says that particles and antiparticles of matter and antimatter apart from their electric charge swapping um they are otherwise perfectly symmetrically balanced and when they meet they would annihilate and so it's easy to see from that that oh okay big bang heat energy produces particles and antiparticles an equal amount and then of course they annihilate but there's enough left over to make us. So something must have happened to disturb that balance and one possibility is that there are big domains of antimatter out there and we happen to be living in a domain of matter down here. Um there's no evidence really support of that because where domat matter and antimatter meet interesting things should be going on that the astronomers will be picking up all the time or there is something fundamentally asymmetric between matter and antimatter.

[00:59:23]Well, mathematically um again 40 50 years ago the theories that were beginning to be developed to describe you know electron and neutrino up and down quark two and two then nature seems to have repeated it twice over up and down quarks charm and strange top and bottom >> and the mathematics that described this turned out to have a very interesting implication in quantum theory. that you applied the mathematics to the three generations, we call them, of quarks, and then you applied the mathematics to the three generations of anti-quarks.

[01:00:04]And it turns out that in the quantum description, a thing called the phase of the wave function didn't have to be necessarily the same for both of them. H and that would give some very interesting possibilities which would be that the way that quarks behave and the anti-quarks behave isn't quite the same. And the way to experimentally look for that would be biggest in what was called the bottom quarks the the the third the heaviest generation.

[01:00:35]And specialized facilities were built to produce particles making containing bottom quarks in large numbers and bottom antiquarks in large numbers. And they indeed proved that the little asymmetry is there. Which was the first direct proof that there is an asymmetry between matter and antimatter. But nothing at all like would be needed to explain the large scale >> asymmetry that that we experience.

[01:01:03]But the mathematical idea can equally well be applied to the three generations of the electron and nutrinos.

[01:01:10]>> In particular, the nutrino, the bottom thing, it's the friend of the electron, the one that's the friend of the muon, and the one that's the friend of the tower.

[01:01:20]And the mathematics implies that when a nuclear reaction for example produces in the sun produces an a nutrino of the electron type by the time it has got here to earth if it's got a little bit of mass quantum says oh it can actually change into one of the muon type or the tower type and experimentally we we know that's the case that's been known now for 30 years but it turns out that if you could measure the way that nutrinos change one into the other and compare very carefully with how their anti-utrino counterparts change one into the other are they the same and mathematically they don't have to be and it turns out mathematically that if there are differences there unlike the case of the quarks where it turns out to be a very subtle thing in the case of the nutrinos it could be quite a big thing and if so that would be the first step.

[01:02:22]There's a second thing that's also needed which is that in addition to the nutrinos that we know there has to be a very massive neutral analog of them which is yet to be discovered. Um but if that would be the case then there is the possibility that one may have the way towards the route towards the explanation of the matter antimatter asymmetry. So that is a reason why now very precise studies of nutrinos and anti-utrinos are being made again at facilities specifically designed to measure these things and so on. So, nutrino factories as they're called >> the the standard model and and the building out of that particle zoo that we referenced at the beginning has been extraordinarily successful and we've found most particles that have been predicted and and the sound model is one of the most rigorously tested theories of physics that we have.

[01:03:16]Is it frustrating how correct it's been and how right it's been and and how much we're kind of scrambling around now for new physics.

[01:03:26]If you look back on the past 50 years, um is there is there a sense among physicists somehow that we've been too good at predicting reality and we've been too correct?

[01:03:37]>> Surely not.

[01:03:39]Um, no, it's a very interesting question that as I said at the start, I'm very lucky that I've lived through the period when a revolution was happening and we're now in that sort of postrevolutionary period.

[01:03:57]Whenever you answer questions, you create new questions. I say it's a bit like trying to get to the end of the rainbow. you know that that you never get there, but along the way you pass things that you didn't even know were there to see. And that has certainly been the case in the the last 50 years that we've got to this situation now that we do recognize that we're immersed in this weird field which gives the particles their properties. But that shows that indeed everything we've been doing is indeed correct. In fact, you can say it back engineers and explains everything way back to the questions the ancient Greeks were answering. Of course, what we want to know is where where could we go on the other side? What does the the greater unknowns? There's always more unknown than you know. Um and the great challenge of culture is really to understand what it's all about. Why are we here? I find it I mean I'm not not a religious person in a conventional sense, but I think the idea of science fiction.

[01:05:11]Imagine you're a god and you're going to make a universe.

[01:05:15]Who would ever think that you're going to do it? We make things called electrons. We make things called quarks.

[01:05:21]We won't even make protons and neutrons.

[01:05:22]We make things called quarks first so that they can make the protons and neutrons. So the electrons and then we're going to have to make the protons and neutrons make clumps of different sizes so they can hold different amounts of electrons around them. And changing one electron from one side to the other or changing the charge in here is going to completely change the properties of different things. So there'll be a whole variety of chemical elements, but it'll only happen if you happen to live within a certain temperature range. You is that how you go about making universe? But it works and it makes DNA and all that stuff and so forth and it's hard to well I'm not quite sure but I'm I start feeling that I'm trying to eat porridge with my fingers that I'm I'm on the edge of enlightenment but I just can't quite see there thinking wow you cannot fail to be impressed that's why I became a scientist I I just wanted to understand >> well hopefully in the coming years we'll get slightly further further into that porridge and understand a little bit more. Frank Close, thank you so much for speaking with New Scientist today. It's been a pleasure.