Q&A: The Concept of Mass - with Jim Baggott

[Music] hi thank you very much for the talk and you were talking about those elementary particles not having any mass than being massless yet on the chart of them there was reference to the mass being 1/3 and 2/3 and 0 and such right ok that's there shouldn't be any contradictions but let's go back to the picture well let's stick with this one so indeed you're right this little chart shows a couple of things properties of these elementary particles one is is is the mass notice that they're given in things obscure units called mega electron volts divided by C squared but that's nothing other than Einsteins m equals E over C squared again so that's an energy divided by C squared so what you've got is the energies if effectively of the up and down quarks but you've also got things called charges now I didn't go into this because I didn't want to get bogged down in too much detail but we're used to thinking of a proton with a single positive charge an electron with a single negative charge well protons composed of quarks the quarks themselves have fractional electric charges two ups and a down is two times two thirds of a charge minus one-third of a charge giving a single positive charge and finally they have something called spin all matter particles have a spin of 1/2 they call fermions again it doesn't really matter what that means but it means when they spin round they have to spin round twice to get back where they started really easy to understand okay over there you see there are numbers the gluons and the photons have 0 0 1 0 means they have no mass so these are massless particles they have 0 charge and they have one unit of spin they only have to spin around once to get back to where they started ok and the Higgs boson has a big big mass it has no charge and it has no spin it is a so-called scalar particle does that answer the question the masses of the quarks of the up and down quarks in particular are very very hard to pin down by the way there's a lot of jiggery-pokery and are required effectively what you're doing is if you think back to the picture I showed you of accelerating that particle up to the speed of light when you've got two protons smashing into each other in the Large Hadron Collider they smash into each other not as as cannonballs but is almost like flat dinner plates so think what that happens that means that the quarks embedded in those protons are like little current stuck to those dinner plates and and so as a result of investigating the fallout from those kinds of collisions the theorists can get hold of a sense of what the masses of the up and down quarks actually are but those are fairly good numbers there's some margin of error and they fall a lot short of what we ultimately need to explain the mass of the proton or the neutron thank you young man in the middle of the microphone I just wanted to ask does that dark energy of anything to do of this okay so I had a choice this evening I can talk about matter and mass on a effectively a microscopic scale going smaller and smaller into you know atoms and nuclei or I could talk about matter and mass on a cosmological scale the universe as a whole your question relating to dark energy relates to what goes on in the universe as a whole it was discovered in 1998 as a result of making observations of of supernova explosions that we know that the universe is expanding right but it was understood that that expansion began in the Big Bang and would be you know slowly slowly declining the expansion rate would be slowly declining but it was discovered in 1998 as a result of making these observations that's actually the expansion of the universe is accelerating it's expanding faster than we anticipated and that can only really be for one reason and that is because space-time isn't empty it's got some stuff in it that we don't understand and when physicists don't understand something they tend to call it dark I think it's probably there were grew up with Star Wars or something it's the dark force so they call it dark energy so the universe is filled with with dark energy or if you familiar with the term it has a positive cosmological constant which was Einstein's famous fudge factor from 1917 so dark energy is one thing that accounts for something like 70% of the total mass energy of the universe yeah we don't know what it is the other question that you might have is of course concerning dark matter now dark matter again is somewhat hypothetical it comes from looking at the large scale motions of galaxies and the current understanding but it's always a disputed current underst is that in the early stages shortly after the Big Bang expansion of the universe we had matter we don't know what it is that's why it's called it doesn't interact with anything which is another reason why it's called dark but we know it has gravitational effects and if it hadn't been for the dark matter forming what's known as halos clustering together concentrating the matter we do know and care about baryonic matter protons and neutrons and then atoms at the center of these halos they would never have been stars and galaxies at all so thankfully if dark matter really exists we owe it a lot because we wouldn't be here if it didn't exist but we don't know what it is it's not there in the standard model of particle physics there's no particle we can point to and say look there's dark matter we don't know so I haven't answered your question but it has nothing at the moment to do with the version of events that I've given you which is about drilling into the nature of substance inertial masses mass no no I'm not being no I'm not being I'm not being facetious that there is there was as you can see a Newton never gave a satisfactory definition of mass and in actual fact even if we use Newton's second law forces mass times acceleration and use that to try to define mass that's still circular because we needed to define force in the first place mass is best understood as the inertia of an object and again I haven't made a big deal of it of course the big difference between weight and mass is that weight is what we get as a result of making measurements in Earth's gravity but mass is something that's intrinsic and independent largely of gravity so when you see old footage of the moon landings and the astronauts bouncing around bunny-hopping as it were on the moon and then suddenly falling into a kilometer spin because they realize in fact they can't move or turn quickly because they still have inertia even though they weigh a lot less on the moon because the moon's gravity is much weaker so that's understood inertia is a property linked directly to mass itself but we still don't know what that is and increasingly if you accept Einstein's conclusions mass equals the over C squared then principally we're talking about the mass the inertia of energy not so much even the inertia of mass so the answer to your question is there's an argument that says we don't know what inertia is either really we can't define mass so kind of by definition we can't define inertia really very well any as well I like not being able to explain stuff thanks the question any more questions has gone at this side of the room very inquisitive this side you obviously just know it all already so can we quoted a character in a book who explained that the act of observation generates its own reality if you like crystallizes the nature of something yeah we discovered the Higgs boson by firing particles at other particles smashing them together and whoop d-duck we've discovered the Higgs boson which we were looking for does that actually happen in nature and if it doesn't surely that means there's no active observation it doesn't exist exposed on well the intriguing thing is is that the discovery of the Higgs boson funnily enough was not about the Higgs boson I know that sounds like an anachronism but it was about the Higgs field the Higgs boson was the final telltale piece of evidence that the Higgs field really exists it really does exist now that Higgs field if he honestly if it wasn't present throughout the universe we really wouldn't be here so to a certain extent given that we've shown that the Higgs boson really exists the Higgs field really exists at least again as far as our present understanding is concerned then then we understand you know the large scale properties of the visible universe in terms of the presence of that field in answer to your question yeah so the purpose of the of particle colliders like the Large Hadron Collider is to create energies collision energies high enough to tease these particles to come out of hiding you're right the you know in a in a vacuum of empty space you don't have necessarily Higgs bosons constantly coming into and out of existence there's a caveat I want to give to that but but nevertheless certainly very very shortly that the energies of the collisions in the Large Hadron Collider actually if you can also think about them this way they wind the clock back to some of the very very earliest stages a trillionth of a second after the Big Bang which i think is pretty amazing by the way a trillionth of a second after the Big Bang and what the higgs field would have done is it would have triggered a divergence between something called the electroweak field into two distinct forces electromagnetism and something called the weak interaction and again if then hadn't happened a trillionth of a second after the Big Bang we again wouldn't be here debating the finer points of it so this is not about having some kind of esoteric game with nature where we we produce these but they don't really exist anywhere these things are betraying the secrets of nature that they're telling us that this thing called the Higgs field really does exist and we can explain quite a lot of what we see today in terms of the existence of that field thank you the back in the green t-shirt yeah yeah I just just gonna ask it one earlier in the talk he's you you talked about the wave the slit wave slit experiment yeah and you said just think about the fact that it's an electron going through the slit yep can you kind of enlarge on that because I get that it's got mass as its to do with the fact that well well you know the the the the realization is this very much a contemporary debate I happen to be in Oxford on Saturday giving a talk about the nature of quantum reality this is what I do in my spare time and I want to be absolutely clear I'm not trying not to answer your question but but this is very much a contemporary debate that still rages ninety years after quantum mechanics was first discovered just exactly what is going on is this wave function or this field real does it actually have a real physical interpretation if you accept that it does then you're torturing yourself with okay what's going on with the mass and how does the mass get plucked out of the field when there's an interaction and what triggers that interaction and and how come it's random well you know what is the nature of quantum probability lots of really difficult I would say even philosophical questions the other route you can take is the route in fact that Niels Bohr took in his famous debate with Einstein that's to say in fact his quote I can I can give it to you off the top of my head he argued that there is no quantum world there is only an abstract quantum physical description it is a mistake to think that physics tells us how nature is physics concerns what we can say about nature well that's our very what I call an anti realist interpretation but it's basically saying the entire structure of quantum mechanics is just a very very convenient though very complicated way of coding information allowing us to predict the future on the basis of the past the minute you strike starts who want to manifest some sense of physical significance in some of the concepts and the equations of quantum mechanics is the minute you thought then start to get troubled by questions like what happened to its mass is it what happens in the collapse of the wavefunction Einstein his God does not play dice argument was really all about appreciating how can something that's distributed you know I'm making these kinds of hand waving gestures but experiments have been we're distributed means on a different island off the coast of Spain 140 kilometers away so we were we're not talking this kind of distance we're talking about big distances where quantum effects entangled quantum effects are still able to be seen and tested experimentally so we know this is correct the minute you start to get your head into some of these is the minute you start to get a headache trying to understand what it's trying to tell you okay if the mass of the gluon is given as zero then does that mean that's it's suddenly stops interacting with the Higgs field as soon as it's not holding quarks together interesting question I don't know is the short answer because because gluons have a and quarks for that matter have a very singular set of properties no one has ever seen a single quark no one has ever seen a single gluon for the simple reason is that the force that's going on inside the proton holding these quarks together is not like a force you're familiar with we tend to think of let's say the electromagnetic force or the force of gravity as declining with distance okay it's biggest closer to the source of the electrical charge or the source of the electromagnetic field and it tails off with distance the strong force carried by gluons doesn't work that way in fact the strong force is at its weakest when the two quarks are close together it starts to kick in as you try to tear these quarks apart think of the quarks as being tethered by two really really tough Springs as quarks go back and forth between the as the gluons go back and forth between the quarks the minute you try and pull these quarks apart now what happens is that as you start to rip if you can try to rip a quark out of a proton for example the energy is to do that start to get so high that they actually kunja particles out of the vacuum out of nothing I can explain that mechanism but that will require several pints of beer and and you seem too young to be buying new points of view and that's the problem so you know you never see a quark without a chaperone the minute you start to pull a quark out you can do these kinds of experiments at the Large Hadron Collider you never see a single quark no one's ever seen a fractional electric charge and which is why there was a lot of speculation in the 1960s at late 1960s early 1970s I still whether these really existed Stephen Weinberg who kindly wrote a foreword for my book about the Higgs explained in fact that the reason he he never talked about protons and neutrons in in a seminal paper he wrote in 1967 which eventually won him the Nobel Prize was because he didn't believe in quarks so it's a real hard thing for further physicists to get to grips with but there's now more than more and more enough evidence to explain some of the things that we do see at the Large Hadron Collider as though quarks and gluons really do exist so there's good evidence to believe in them but we've never seen them singly and that's really what's going on inside a proton the energy involved in in binding up these quarks is so high so high that's why it accounts for a 98 99% of the mass of the particle at the end of the day fantastic we've got some a few more questions I am keenly aware that we've only heard from men this evening so if there are only women that have any questions I've noticed a few young young women here wife is going for diversity and inclusiveness here I'm very keen to hear from anyone who isn't a white man like me or him or everyone else and spoken thank you okay I'm kind of curious about how vacuums fit into this then so you can obviously have energy and electromagnetic waves flying through a vacuum but there's no mass so just wonder does that mean this is no Higgs field that there is mass there is mass I think we've actually come to an understanding in contemporary theoretical physics and in for that matter in experimental physics that there we have a real hard time with the concept of the word vacuum there's actually really nothing about space-time that can ever be empty there's always something in it at the very least there's a Higgs field in it at the very least that there's something called Heisenberg's uncertainty principle which is a cornerstone of quantum mechanics and Heisenberg's and center principle will it's got a very very long story very very short allows particles virtual particles to fluctuate in and out of existence they appear and then they disappear and they're allowed to do that so long as the energy they take from empty space is given back within the time prescribed by Heisenberg's uncertainty principle so even in empty space there is still this notion that we have virtual particles fields coming in and out of existence so there's no such thing as a vacuum in fact in many ways Aristotle was right all along nature abhors a vacuum so think of empty space there's this dark energy the question at the back the cosmological constant energy is somehow manifested in in space itself is pushing space-time causing space-time to expand if you can get your head around that then you've got the Higgs field and you've got virtual particles you begin to realize there's an awful lot going on in a vacuum so we've just got time for a couple more questions I regret we don't have a microphone up in the gallery but if anyone up in the gallery wants to ask a question please do shout it out and I'll try and repeat it with the rest of the audience somebody right over there I can see you sir I can hear you yeah I I think I think the Greeks had it right absolutely right what what you have to do is to accept that also into the accounting you need to include energy now it's the energy of something and in this particular case it would be the energy of quantum fields so to a certain extent the Greeks were absolutely right and they were right to say that I simply cannot divide something into absolutely nothing the best I can do is to divide something into the energy of its quantum fields now Epicurus would never have understood that but nevertheless that's one way of interpreting what he had to say in the beginning gentlemen the front here has been waiting very patiently I think probably be our last question I think I'm just wondering if you were to melt your ice cube yep so you're adding energy in what happens to the model I'm do you get more glue on today or is it you talking about them ripping apart they increasing an energy well so there's a couple of ways of thinking about the answer to that question firstly when when you you add you add energy to to induce something called a phase transition in this particular case we miss solid and a liquid you have to put energy in to overcome that the forces that you you couldn't really see it but if you go back to my hang on yeah no so so what what you doing I mean arguably yes you are increasing the weight but it's a very very small in a very small way so you see these little dashed lines that they represent something called hydrogen bonds holding hydrogen atoms and oxygen atoms you know in a correlation that's what locks them in the lattice so it's it's called something called lattice enthalpy in effect what you do is you you break those little dashed lines and and the the water molecules dissolve yes you're putting energy in but you're putting energy in to overcome something so you're trading off so that energy is not coming out as such latent heat is the phrase that I was actually looking for maybe have just time for one more then no you had a question do you want to normally a bit of a cheeky one those questions I wish phone's slipping a couple of extra they won't so your estimation from nothing comes out of nothing did obviously there wasn't the creation a Big Bang well before that well that that depends on on who you prepare to believe in what you read so so let's let's let's face it I wrote I wrote a book those published a couple years ago called origins which effectively attempted to trace the scientific story of creation right from the Big Bang to the origin of human consciousness this is what I do in my spare time and I said basically there are three there are three gaps in our current scientific understanding of course the first is the Big Bang itself extrapolate our current scientific physical theories right to the very beginning of everything and those theories kind of by definition break down so we can't explain the very beginning the second explanatory gap is the origin of life on planet Earth and the third is arguably what consciousness is that let alone the origin of consciousness although there's some good ideas about where that Springs from however one of the problems with the current Big Bang model is that it invokes or or implies something called a singularity it's where everything is compressed to infinite density infinite energy and zero well in fact space-time is born in that explosion of stuff erupts and and we get we get the universe as we know it today however if you so so that's a consequence of something called Einstein's general theory of relativity space time is now so curved if you like that it's become infinitely curved and that's what a singularity is but Einstein's general theory of relative is it a theory of classical physics it's not a quantum theory and the minute you start to try and tie up the idea of quantum theory with gravity is the minute you run into the idea that actually maybe there's no singularity singularity infinity doesn't exist in nature so there's no singularity at all what you get with is a residual compressed bit of space-time that some theorists are now calling the Big Bounce so if the universe existed before and collapsed it would have collapsed to a very very high density but not zero or infinite density and then the universe bounced from that position again now it's all very speculative somewhat even metaphysical but that's where a quantum theory of gravity will eventually take you so who knows I don't on that note just wrap up tonight's evening before we thank our speaker again it forced me to remind you there are copies of Jim's latest book mass will be available outside I'm sure if you'd ask him nicely he'll also write his name on it for you in the traditional way and yes and so that just remains to me to thank you all for coming and thanks very much to Jim for a fascinating talk thank you [Applause] you

Channel: The Royal Institution

Views: 53,210

Rating: 4.8720002 out of 5

Keywords: Ri, Royal Institution, lecture, matter, mass, particles, Jim Baggott

Id: wKavBNKP1wA

Length: 26min 48sec (1608 seconds)

Published: Wed Sep 27 2017