Sean Carroll - The Particle at the End of the Universe: Q&A

[Music] [Applause] well Shawn clearly no questions left I expect there are lots of questions in fact and there are microphones I expect going round right now um whilst those microphones go put your hands up with your questions of course we'll get a microphone to you wait till the microphone gets to you and we'll come to you guys upstairs as well although we can't actually see you because of the intense electromagnetic field direction from up there and before I come to you guys though if you can pick a question from each side they we could start with there I would ask questions okay I think I get two right now I've read a description of the book you've written I believe you've written a book I've written a book I wrote a description about how the Large Hadron Collider was built it was a long project decades political shenanigans you write about skullduggery it's got a bit of naughty behavior from scientists tell us a bit about the naughty behavior and a skullduggery involved in building this monumental machine the Noddy yeah the naughty behavior I'm not sure if I have a good LHC based so I mean there's in the history of particle physics there are many fun stories about naughty behavior there's at least this is just the truth there's at least one Nobel Prize winner who went up to a competitor's experiment and urinated on it I'm not gonna you can google it okay well you know he knew that it was but it's a symbolic gesture he was not trying to in the in but but the Pope the problem is as far as my book and and the in these stories inside it are concerned is that the stories don't come out until much later so the LHC is all you know there was there was political intrigue because things were happening like Europe was reuniting ok one of the major monetary contributors to CERN is Germany and in the early 1990s they had other things to worry about than the search for the Higgs boson they were trying to absorb East Germany and so forth so there was a lot of you know patting of the back and and and so forth here in Britain David wall de Greve was the science minister and he very famously was talking to the particle physicists and he and after talking to the particle physicists for a certain amount of time he said guys I've no idea what you're talking about come back tomorrow and give me a one-page long description of the Higgs boson if you can do it I will give you a bottle of champagne and vote for the LHC if you can't sorry so David Smith was the winner of the of the bottle of champagne and he gave the analogy of two people moving through an empty room me he didn't use me I can use me and Margaret Thatcher and we imagined that if the room is empty we both move at the same speed but if the room is full of British people suddenly Margaret Thatcher is a celebrity and I'm not so Margaret Thatcher is slowed down moving through the room whereas I can walk at the same speed so the people in the party play the role of the Higgs field filling space that is a story that I tell in the book it's not nearly as good as the old school stories like like Carla rubia you know he had his experiment ready the previous Large Hadron not as large but large Collider at CERN he had its experiment it was almost ready it was this gold-plated wonderful experiment he had competitors who were sort of doing a smaller experiment it was it was cheaper it was not supposed to be as good but they were ready first so Sauron tried to turn on the machine and he flooded the tunnel so they couldn't turn on the machine until his experiment was ready in the he later won the Nobel Prize for discovering Big W boys let's go for a question form over here so how about you at the front there and then get ready with a question here as well okay okay first of all I love the book great stuff I wonder if you could just talk a little bit about the idea that Higgs is a scalar field and does the discovery of the Higgs make other hypothesized scalar fields like the inflaton field more likely someone has been cheating you know learning about particle physics before coming to the talk so there it turns out that of course there are many different fields that we saw on the plot you know here are just some fields that we are imagining one way of talking about the fields is how many different components they have because you know sometimes I mentioned the electromagnetic field other times I mentioned just the electric field or the magnetic field the electric field is something that is not just a value at every point in space it's a little arrow at every point in space it has a magnitude and a direction likewise the magnetic field has a magnitude in a different direction in principle but back in the 19th century people figured out Faraday played a big role in this how to marry together the electric field the magnetic field to make one thing called the electromagnetic field so there are different categories of fields as the fermions the bosons etc there was remember the flow chart that you memorized earlier the Higgs boson is all by itself up there why is that well one reason is because it is all by itself there's only one field it's one number it is not a little arrow it does not have multiple components there's no anti particle for the Higgs field it's just the Higgs field there's the Higgs boson field so the label we attached to that is it is a scalar field is just a single number at every point in space all the other fields here have more than one thing going on none of them are scalar fields and so before we discovered it there was this thought among physicists you know this this idea of the Higgs boson a scalar field plays this hugely important role in our theory of the standard model but we've never found a scalar field we found all these you know fermions and and spin 1 bosons and spin 2 bosons and so forth but now we have found the Higgs boson so now all those snipers who didn't you know who said well you haven't found a scalar field well now we can say look you know nine billion dollars later we found it that means that we're now even more licensed than we were before to invent new scalar fields and we do that especially cosmologists like myself love to invent new hypothetical scalar fields to get the universe going at early times to be the dark matter to give rise from new long-range forces and so forth so you know but to be honest and to answer your question we weren't really shy about doing that before so it makes it a little bit more legitimate this scalar field ology because now we've actually found one but you know we're pretty shameless when it comes to that so I'm thanks for your talk it was wonderful and I realized that what I had learnt about physics at school was from 1935 so good really good to be updated and I was wondering why when the protons collide and in the LHC why would you expect to see a Higgs boson if it's outside of the hey John that's a very very very good question I don't think I actually have a little diagram here but let me wave my hands that's a traditional response so the proton is made of up quarks and down quarks held together by gluons so you see on the Left we've indicated here there are gluons that I didn't draw but they're holding these things together so when you smash two protons together what's really going on is that inside the protons there are quarks and gluons and it's not the proton that hits the proton it's one of those quarks or gluons it's one of the other courts or gluons sometimes the analogy is made that it's like smashing two wristwatches together and seeing what comes out and trying to figure out how wristwatches work by doing that that is a bad analogy because there are no Higgs bosons inside the proton which is exactly your question so it's more like smashing two time X's together and hoping a Rolex is spontaneously assembled by doing that because what you're doing really is setting up vibrations in the fields so two gluons or two quarks come together they're both vibrations and fields and because you put so much energy into these protons they're vibrating to beat the band okay so they're vibrating with a huge amplitude they come together and it's like if you you play the piano in one room a piano in the room next to you will start humming in sympathy and residence so these vibrating fields start all the other fields around them vibrating along with them and then quantum mechanics gives you a probability that all those vibrations will show up in your detector as certain specific kinds of fields the more energy you have in those vibrations the heavier the new particles you can produce really are so e equals mc-squared right so this is actually the fact that particles can turn into other particles is something that only makes sense because the world is really made of fields if it were back when it were just particles before quantum field theory was invented we didn't know how to describe the changes the transformations of one kind of particle into another now we know that at every point in space all of these fields are vibrating and they're all gently talking to each other and only when they're vibrating like crazy in the LHC can you create something new and heavy like the Higgs boson we're gonna insist that the snappily dressed young man ask the question when you were talking about Dark Matter you said that well you said that well this way more matter in the universe understand you didn't account for what you mean by that yeah I mean what do you mean what do I mean that's what I mean model theory say that they can only be a finished mass of mass from universe no that's right that's it there's a very very good question so here's this the simple-minded thing that we do is we look to see how much matter there is in the universe you know we count the number of stars and galaxies and also there's invisible matter in between the galaxies but if you look using x-ray telescopes you can even see that invisible matter and then we weigh the galaxies and the groups of galaxies and we find that there's much more matter there than what we counted you might if you were a conservative you know nose to the grindstone kind of scientists say well maybe you just missed it maybe there's matter that you don't see but it's still there but it's still the standard model right I mean that's obviously your first idea however we have independent ways of saying exactly how much standard model there is in the universe and that's because the universe started 13.7 billion years ago with the Big Bang we didn't talk about that but you know everything was fit very tightly together in a hot dense smooth state and as the universe expanded and cooled it went through a set of phases where all the matter interacted with each other it went through a phase where the universe was a nuclear reactor it was turning protons and neutrons into helium and lithium and deuterium it went through another phase where it went from being opaque to being transparent and in every one of these phases it leaves behind fingerprints how much helium did you get from the early universe what kind of shadows do you see from that moment when the universe became transparent and all of these moments all of these clues that were left behind depend on the amount of ordinary matter in the universe the amount of quarks and leptons the standard model of particle physics and the state and whether we either look at the universe today or look at the products from its phase as a nuclear reactor or look at that moment when it became transparent we get the same answer every time there's this much ordinary matter and it's only one-fifth of what we need to explain the gravitational field and galaxies and clusters so the extra matter we need to explain gravity is not standard model matter or all those predictions from the early universe would have been false and how does it make scientists feel when they realize that what they thought was a complete theory is actually very incomplete they met scientists is everything makes them feel awesome right I mean if they've been right they've been like awesome we're right when they're wrong they're like awesome there's new things to discover right but it crept up on us the the idea that there is dark matter goes back to the 1930s Fritz's wiki was a Swiss American physicist who worked at Caltech he did he weighed the Coma Cluster of galaxies is a nearby cluster of galaxies and he showed that there was a lot more matter that we could account for by ordinary means in the 1930s we didn't know enough particle physics to say how much standard model want matter that really was in 1970s view Rubin an astronomer showed that galaxies you'd expect that galaxies you can see what they look like right you can see there's a lot of matter in the center and less on the outskirts so she measured it and she found that actually there's more and more matter as you go further and further away from the galaxies so that's dark matter also but this idea your question that we know how much ordinary matter there is as opposed to dark matter it was put forward in the 70s but no one believed it because it was astronomers not particle physicists in the 80s it got better and yeah by the time I was in grad school late 80s early 90s all right-thinking cosmologists accepted that this was true it was discovered or measured in their nineties and the Nobel Prize was given any a few years ago yeah that well so there's dark matter and then there's dark energy right so the pie chart is about 4% of the universe is ordinary matter so this wonderful thing I'm celebrating our discovery of you know this stuff 4% of the universe is this stuff 23% or so of the universe is dark matter and another 73% is this dark energy stuff which isn't even made of particles and by the mid-1990s we knew that it couldn't all be simple we knew that something complicated was going on but we didn't know what in 1998 two groups of astronomers showed that the universe is not only expanding but accelerating and the only way to explain that is dark energy and everything snapped into place okay dark energy there another question here from Kevin sure thank you very much fantastic talk you should write a book I could write a book I know and is it possible that the fundamental truths will remain unknowable because you point out there that it takes nine billion euro dollars whatever and three thousand scientists to know these things and so that seems a geometric increase in the number of people or resources that you require to know the truth that special relativity is had by one person less than the century before is it possible that the truth is beyond their resource in terms of intellectual power and collaboration and all financial resource it is possible it is possible that the Sun will use up its nuclear fuel and and life on Earth will cease because it becomes cold and dark but these are long term worries there's plenty in physics that we don't know the answer to so one an implicit message here which I didn't spell out very carefully but I could is that quantum field theory lets us define much better than ever before the regime of what we do understand the boundary past which you know alright I understand everything going on in here but there could be surprises beyond that boundary and that boundary is you know getting more expensive to to cross and the LHC is a reflection of that on the other hand just so but there's two things one is we know that there's stuff beyond that boundary dark matter and dark energy the Big Bang ensure that there is stuff there it may become harder to find but it's there and so we have to look we don't know and it could be a cornucopia we could double the number of particles and you know in the next five years and the other thing is just because we understand quarks and leptons and and the four forces of nature doesn't mean we understand economics it doesn't mean we understand neuroscience or how hurricanes work or for that matter how this table works really it's it's the difference between knowing how the night moves on a chessboard and being a grandmaster chess player right we now know the rules of chess as in terms of the fundamental workings of our little corner of reality we're not very good at playing the game of putting those underlying laws to work in explaining things like the origin of life or other interesting questions so of all the possible things that I could spend time worrying about running out of either interesting questions to ask or the resources to answer them is not in my top 100 person hi and I'm a bit of a physics ignoramus so mine's quite a basic question but and I get the impression that the LHC was something incredible and new and I was just wondering when they built it and they started to experiment was there any chance that something absolutely disastrous and awful and unpredictable could happen like the world would explode or Switzerland would explode I just wondered how risky and mysterious it was you know it is it is actually a good question people for example there are respectable scientific theories that if they had been right along with Higgs bosons the LHC would have been making small black holes and you might worry that one of those black holes would get captured by the earth go down into the middle eat up all of the earth and the earth would collapse into the black hole okay so number one the same theories that predict those black holes also predict that they would evaporate in a tiny fraction of a second so it's hard to take the prediction half way number two if they didn't have a parade and they did fall into the center of the earth you could calculate how long it would take for the earth to be eaten up it's hundreds of trillions of years much longer than the current age of the universe number three and most importantly all the other things are just window dressing there's even though the LHC does things that we human beings have never done before it doesn't do anything the universe doesn't do all the time we the earth is bombarded by high-energy cosmic rays which collide with particles in our atmosphere with much higher energies than we create at the LHC so it's not an airtight argument but he would certainly expect that if anything terrible had gone wrong making black holes or new phases of matter that would change things in any dramatic way it would have happened a long time ago because the universe has been doing this experiment for a long time having said that physicists took all of the possibilities very very carefully they wrote many white papers going through the argument the best they could and they decided there was no substantial risk and just to put an exclamation point on it if you go home tonight and you make pasta with tomato sauce and you open the jar of the tomato sauce is it possible that inside that jar there's been a pathogenic mutation which will release a virus and kill all life on earth it's possible but you're gonna open the jar anyway even though you get just this tiny little benefit we are always balancing terrible sounding but radically unlikely consequences off of our everyday means so as far as the LHC is concerned the payoff was much larger than a nice bowl of spaghetti so it wasn't a hard problem someone in America tried to sue there was easy organisers to stop them from starting the healthy in the first place yes there was a gentleman named Walter Wagner who's a high school science teacher who made his living he used to be a high school science teacher now he makes his living suing people and he sued the LHC in the district court in Hawaii saying that they had not prepared a respectable responsible environmental impact statement of destroying the world would be the environmental impact that he was worried about and it was thrown out our question up here yes thank you very much really learnt something here which is some great brilliant lecture and you've explained obviously that our universe is composed of them I would say various but I guess it's got to be different fields what I'm interested is looking at the ideas of parallel universe in the multiverse would you expect therefore that there might be slight variations in those fields as well as the possibility of different fields and has there been any evidence produced of any slight variations in the fields or indeed different fields yeah that's a very good question so there are two things two things you need to tell me to construct the laws of physics one is what are the field and the other is what are the numbers that characterize those fields and how they interact with each other what is for example the strength of gravity what is the mass of the electron which is just a way of saying what is the way the electron interacts with the Higgs boson so the number of fields is a discrete number it's not something that can change just can smoothly if it's a you know it's an integer okay you can't go from 11 fields to 11.9 fields or something like that but the parameters the mass of the electron for example that you could imagine changing gradually over space or over time it is possible that it does it is possible there is a multiverse of the kind where far outside the part of the universe we can see that the constants of nature the parameters of physics take on very very different values within our observable piece of the universe we have looked we've looked a lot so for example your question about the density of ordinary matter I said well you can test that using the fact that the early universe was a nuclear reactor another thing you can test is was the mass of the proton and the neutron the same 1 minute after the Big Bang as it is now because if it were different the nuclear reactions would have been different everything we've done is compatible with the idea that the constants of nature are constant they have not changed but maybe we just haven't looked carefully enough that's definitely an ongoing project you know those are and find something much more interesting and cheaper imagine maybe that's the scientific advice is holding a film it's just fun the next generation possible Collider really great lecture thank you I was wondering what's the difference between the vibrations of fields and say the vibrations of super strings ah that's a good is a good question so my computer ran out of electricity so I hope you don't want any more pictures there is this idea out there called string theory and your question is actually quite subtle so I kind of wish you hadn't asked it but when we think about particles and feels relationship between particles and fields we say well what really exists are fields and if you look closely at them they resolve into particles and when physicists invented string theory what they said was just sort of quasi out of the blue they said well what if we replaced the particles with little vibrating strings they were hoping to understand some features of the strong interactions of nuclear physics but what instead they predicted was gravity and so string theory today is still the leading candidate we have for a quantum theory of gravity well we don't quite have is what you would call string field theory the string theory analog of quantum field theory for particles so if in particle physics we say what really exists our fields and they vibrate you look at them and you see particles there should be something called string fields and when they vibrate you should look at them and you should see strings we're not really quite sure what a string field would be it's part of the fact that we don't really know what string theory is right it's a it's an idea we we make a lot of progress thinking about it but just like Isaac Newton didn't understand action at a distance we don't understand string theory really and it's all of its predictions so far outside the realm of experimental testability so we're not getting any help from the data either so I will just leave you with that's a really good question go to school answer it and you'll feel in your Nobel lecture you'll footnote this I was in the Royal Institution you heard this lecture I'd be happy to be thanked we've only got a few minutes left so what I might do is ask get a few questions then you can give rapid answers now you can keep your questions really really quick we can actually get maybe Shawn to answer all of them okay quickly the quick version of the question is given the expansion of the universe what does that mean for conservation of energy photon stretch gravity stretches out vacuum energy stays pretty constant right the answer is energy is not conserved Oh but you said I had to give a short answer to all the questions no no no no no carry on if you google energy is not conserved you'll find a blog post by me the reason you thought energy should be conserved is because you're used to being in a world where the ground beneath you is not changing in an expanding universe it is and energy is no longer concerned could you give us a sense of the amount of data and the amount of analysis that was needed for the physicists at CERN to convince themselves that those bumps on the graphs were ready the Higgs boson and not really big amount of data CERN is the biggest database in existence here on earth it's the fastest information transfer between centers it's just petabytes of data and you know we we've only just scratched the surface we're collecting not only the same amount of data every year but every year we go we're collecting as much data as we have every year before combined and they have to invent a completely new way of a adoring allsorts analyzing data which we're gonna use one day is a success successor to the web I mean they're that geniuses up there yeah so they say that the gravity of Matsu is the graviton so why is it so hard for you guys to detect it aside they haven't proved it yet there is a particle called the graviton according to theory we've not detected yet just because gravity is a very weak force and therefore gravitons individually don't interact in a noticeable way they interact but we don't notice okay we're coming up to the end so I'm gonna ask one more question about the Higgs boson now there is Shawn and we all talk about the Higgs boson giving things mass then you've made sure that that's not how you describe it in your book but let's the communities talk about how how much of something's masked Higgs boson actually gives what it's not this is a mistake that people make people think particles mass Higgs boson it turns out that's not quite the picture is it it's really not the picture what I'm being careful hopefully I was careful throughout the talk the Higgs field filling empty space gives mass to elementary particles that is to say W bosons electrons the up quark the down quark it doesn't give mass to protons and neutrons because they're not elementary particles they're combinations of quarks and gluons and so forth it turns out that the mass of a proton is much more than the mass of the quarks inside the proton it's the energy holding them together that really gives the proton and neutron their mass and most of your mass comes from protons and neutrons not from electrons and quarks so if around you someone turned off the Higgs field you that's not a good diet plan okay you're not going to lose a lot of weight by someone turning off the Higgs field instead all of your atoms would disintegrate and you would cease to exist so most of your mass comes from the strong interactions not from the Higgs field but the Higgs field does make you possible just one final thing you know what's the point of a star can we find a use for it and most importantly can a superhero use it in some way yeah do something Avengers movies no now in fact in one of the chapters of my book I try to be as honest as I can you know throughout the history of physics fundamental physics just eye in the sky eye in the sky trying to understand the fundamental laws of nature has always paid off technologically whether it's magnetism or quantum mechanics or superconductivity or whatever but there we were always discovering phenomena that were always right in front of us we just didn't know it the Higgs boson is not right in front of us it's you need that Large Hadron Collider to make it and you're not going to carry around a portable version of the Large Hadron Collider the there are spin-offs from this kind of research computing power the world wide web was invented at CERN as a spinoff superconductivity technology and so forth so the for every dollar that you put into building the LHC the world economy gets many dollars back but that's not why we do it we don't do it for better technology we don't do it for spin-offs we don't do it for economic gain we do it because we want to know the answer we want to know how nature works you have to spend billions of dollars to do it and we've been lucky enough to live in an era where the answers have been coming quite frequently Shawn thank you very much I don't need to encourage you to put hands together but also just don't remember remember sure we'll be signing his book just outside so Shawn thank you very much [Applause]

Channel: The Royal Institution

Views: 66,718

Rating: 4.9199109 out of 5

Keywords: Particle Physics, Science, LHC, Large Hadron Collider, Energy, Mass, Higgs Boson, Royal Institution, Sean Carroll, Space, Cosmology, Dark Matter, Dark Energy, Universe

Id: aom5SiHakGM

Length: 30min 47sec (1847 seconds)

Published: Fri Jan 18 2013