The Concept of Mass - with Jim Baggott

[Music] now this is called mass but I'm not taking confession well if you really insist and make me beg me maybe later on we can do something along those lines over a pint of beer in the pub afterwards I know it doesn't always seem like it but trust me an author really does need a reason to sit down and write a book so my reason for wanting to write this particular book was to try to convey something some sense of what has been an understanding in contemporary physics for already quite a number of years but which I felt actually wasn't really that wonderfully well understood or commonly understood and that is the way that modern physics conceives the nature of matter and in particular the property of mass so what I want to try and do is to give you a sense of the journey that I went on myself researching and then writing this book to give you some sense perhaps also of the maybe sense of astonishment or wonder where contemporary science feels that we've landed up and I'm gonna give by setting myself a hopefully not too difficult mission so this is my mission Jim should I choose to accept it here's a cube of ice and I'm gonna ask myself to really hopefully quite simple questions about this stuff I want to know what is it made of and I want to try to answer the question where would I look to find its mass so we know ice don't we it's what you put in your gin and tonic or increasingly the cosmopolitan is among you in your glass of Sauvignon Blanc as the Italians do we know it's made of water and we're going to start the story with the ancient Greeks because much of our common understanding of the nature of material substance actually comes from a handful of Greek philosophers dating back about 450 years before Year Zero before the Common Era names like Leucippus if he really existed Democritus then later a hundred years later or so Epicurus and much of Epicurus work was actually translated into a grand poem by the Roman poet and philosopher Lucretius and a great place to start because Epicurus once said nothing comes into being out of what is non-existent that's philosophers for you I can guarantee you the cryptic crossword puzzles were ace in ancient Greek times we're talking of course about the famous Greek elements earth air fire and water that's good because we know ice is made of water and we're interested in exploring a little bit more about what iswhat what that water is made of and we get the sense that nothing comes out of stuff that doesn't exist a great start what Epicurious is really saying is it's our common observation that nothing magically appears out of nothing stuff just doesn't appear and there's a corollary to that if it's a common experience that stuff doesn't magically appear it is also our common experience that stuff doesn't magically disappear push that to its logical conclusion and you end up in a situation where you have to accept that nature resolves everything into its constituent atoms and nothing no substance can be resolved completely into nothing it's a simple logical consequence if nothing can come from nothing and nothing can be resolved into nothing then by definition when I have something it must resolve into some indestructible individual indiv indivisible bits stuff what the Greeks called atoms even better we know that the ancient Greeks speculated that if you accept that substance like water consists of atoms then by definition atoms must be moving in something which the Greeks called the void empty space is how we think of it today and there had to be a reason for that motion and so the Greeks had no real difficulty in ascribing properties to these atoms as you can see from the little diagram they gave them different shapes some were spiky with hooks that would cling to each other giving them certain characteristic properties that we can actually see manifested in our experience of different substances but if they were perpetually in motion then the argument went they must have something called wait they you know fall through the void much like heavy rain drops will fall from the heavens on an otherwise warm June Sunday afternoon ok even further sea water being fluid ok must consist of round atoms so here we're getting quite a few answers to our opening questions what is it made of well ice is made of water water is made of hard round atoms that are indestructible and indivisible and those atoms in their turn must have the property of weight okay good start everyone happy everyone happy thank you alright then we have to wait Oh quite a long time I don't want to give you the impression that there was nothing going on in the thirteen or fourteen hundred years between the ancient Greek philosophers and the times perhaps a little bit before Isaac Newton the times of Galileo bacon Robert Boyle and others contemporary with Newton but I just thought I'd pull this quote from an online encyclopedia of philosophy called the Stanford online encyclopedia of philosophy and at this when I read it at really struck a chord here is a recipe for producing medieval philosophy and the stuff that was going on in the thirteen hundred years between the Greeks and Newton combine classical pagan philosophy mainly Greek but also in its Roman versions with the new Christian religion seasoned with a variety of flavoring from the Jewish and Islamic intellectual Heritage's stir and simmer for 1300 years or more until done so there was a lot going on but most of the intellectuals most of of the minds of thinkers in this period were devoted to trying to reconcile the pagan philosophical texts of the Greeks with the demands effectively of the Catholic Church and other orthodoxes and eventually things started to free up the first universities of course were created out of out of monasteries to all intents and purposes so that kind of sense of monastic scholarship translated itself into academic scholarship and it's slowly over a long period of time began possible to start speculating along lines that were not so long not not any longer theological you could start to speculate about the nature of the natural world that didn't necessarily have always to reference back to some kind of religious orthodoxy so to be fair though Newton we tend to regard Newton as one of the the first among a generation of scientists but in truth Newton was a mechanical philosopher his famous book published in 1687 was it's English tragic English title is the mathematical principles of natural philosophy so these folks understood that they were doing natural philosophy but of a particular mechanical kind it was the mechanical investigation of nature Nutan of course had a lot to say about things like motion and gravitation which we'll talk about in a little while but these philosophers these mechanical philosophers also held an understanding that substance was ultimately composed of indivisible hard atoms but their concept of mechanical atoms was not really that much more sophisticated than the conceptions that the ancient Greeks had put forward hundreds of thousands of years before all right Newton Oh went further Newton speculated that not only were these little hard billiard balls of substance moving in the void that they might also actually have forces acting between them that was something the Greeks never latched onto as far as they were concerned all of the motion was due to the weight of the atoms the idea that there might exist different kinds of forces between atoms was new but very speculative Newton had no experimental grounds for making that kind of statement the other thing that we would look to Newton for is really a good understanding of things that are manifest in our visual world of experience to do with the motion of objects things with mass things with acceleration as a result of the acting of a force of some kind and so here at least if we can't get further insight into the nature of atoms themselves we can at least get some insights into the nature of this thing that we're calling mass or weight which are not differentiating between in these in this talk and indeed there is a definition of mass in Newtons mathematical principles of natural philosophy and it reads something like this the quantity of matter or mass is a measure of the same arising from its density and bulk which we can interpret as volume conjointly see anything wrong with that it was Ernst Mac coming a couple of hundred years later who actually pointed out the formulation of Newton is unfortunate as we can only define density as the mass of a unit of volume the circle is manifest and that by the way in the corner there is a vicious circle so Newton who would expect to be the champion of clarity his second law of motion is force equals mass times acceleration these are concepts that are embedded deep in our common understanding of what's known now as classical physics and and I would say that's a physics that is just consistent with our everyday observations a watch a game of tennis watch Andy Murray lose in the semi-final of the French Open to Stan Wawrinka and you get a sense for the way that their motion of the tennis ball is affected by a force watch a game of snooker on the TV get in your car and accelerate at high speed along the m4 well until you get to the first set of traffic cones and you get a sense for what Newton's classical physics is trying to tell you but start to pick at it and you'll find that some of the fundamental concepts that we are so very familiar with and start to unravel a little bit because in truth something as important and fundamental as mass was never really defined properly in the first place mark had a go at defining mass but only relative to other masses there was no real attempt to come up with a a firm understanding at a derivation almost as to what mass is all right so we've got some problems we have not any further along with our understanding of the nature of atoms and we've got this bit of a wobble when it comes to understanding what mass is but let's keep going those two questions where I started at the beginning seemed so fairly straightforward we've should surely be able to get some light at the end of the tunnel if we keep our heads down and keep going okay move on well when you don't get clarity from the chemists from the physicists you can always rely on chemists and some hundred years after Newton again John Dalton wasn't the only one here I'm picking out and singling out these heroes just really to encapsulate what was essentially a movement the responsibility of many individuals involved in its development but John Dalton famously said that he'd come to some enlightened understanding of the nature of chemical substances by looking at their weights and understanding in fact that he could understand chemical substances in terms of the nature of the atoms that they contained so this is the beginnings of a burgeoning understanding of chemistry and in fact if I'm honest really the foundations along with the development of the science of thermodynamics the development of the beginnings the seeds of the Industrial Revolution Dalton was was pretty commercially when it came to an understanding of the composition of water as far as he was concerned it was one out of them hydrogen and one atom of oxygen Antoine Lavoisier wasn't sure but Antoine Lavoisier didn't survive the French Revolution I'm afraid he was guillotine for his efforts not for his scientific efforts I have to say but for his efforts as a tax collector and it took a little while after some confusion maybe the clarifying voice was an Italian chemist called Stanislaw karat sorrow who in this quote makes it quite clear what he thinks the nature of chemical substance is all about the difference the different quantities of the same element contained in different newt molecules are all whole multiples that was the singular thing that the chemists were observing all whole multiples of one and the same which always being entire has the right to be called an atom I love that quote and of course coming out of the work that was being done on understanding the nature of the relationships between the constituents the atomic constituents of different molecular substances we've came to the firm understanding that water is a molecule of h2o okay I won't tell you the amount of confusion created around even that simple understanding because of course if you take hydrogen as a gas your instinct is to think that it's a monatomic gas it's one atom of hydrogen if you take oxygen as a gas your initial instinct is to think of oxygen as a monatomic gas Oh but when H and O were combined to produce water things didn't work out and it was only the realization that Mollick hydrogen is actually a molecular gas its h2 and oxygen is a molecular gas o2 combine those and you can then begin to work out how water can be h2o all right so we've come quite some way this looks I actually think we're up for a mission update okay so we started off this evening with two very simple questions around this cube of ice and as a result of endeavors beginning with the ancient Greeks two and a half thousand years ago we've understood that ice being water is made of round atoms with weight we've got a lot more sophisticated thanks to the efforts of the mechanical philosophers in the 17th 18th centuries and in the chemists in the 18th 19th centuries and we now understand that we can drill in to ice as a substance and what we'll find is a lattice of molecules of h2o here the red ball represents an atom of oxygen and the two little white balls represent atoms of hydrogen so ice is a regular lattice of water molecules which we write as h2o where would we then look to find its mass well we can find its mass or its weight I'm not differentiating in the mass or weight of its hydrogen and oxygen atoms but we have to remember the caveat whatever that is because we haven't got a good definition of mass yet okay everybody happy we all knew this right but I'm sorry I feel I might have wasted 20 minutes of your lives going through stuff you already know but I think it's important you understand the nature of the journey that we're on okay so that's good let's move forward a little further ah now see pesky physicists are now back in the picture you can't trust them just at the time at the beginning of the 20th century when we were starting to get hold of evidence that atoms really existed they weren't just figments of a fertile imagination just at the time when we were getting evidence that atoms really existed physicists were working out how to split them apart I don't know honestly not to be trusted and again this is a model that should be very familiar the kind of planetary model of the atom Rutherford famously did some experiments bombarding thin gold foil with something called alpha particles effectively the nuclei of helium atoms and was astonished expecting that this is like shooting 15-inch shells at a piece of tissue paper how astonishing was it then to find some shells bouncing back at him and what that meant simply was that all of the mass of a Gold atom or any atom is actually concentrated firmly concentrated in a small central nucleus and in fact we now understand that oxygen atoms consist of nuclei surrounded by orbiting electrons and those nuclei contain a total of 16 particles 8 protons positively charged eight neutrons neutral hydrogen is the periodic tables lightest element it consists of just a single proton in its nucleus well fantastic so time for another mission update okay so we've gone a bit further okay the physicists have meddled but we've gone a bit further we now understand that in fact our molecule of water can be imagined as hard sent or nuclei oxygen to hydrogen atoms in a structure around which are wrapped orbiting electrons and it's the nature of the way that the electrons wrap around these three atoms that create the molecular properties of something like water fantastic even better news is 99% of the mass of an atom is to be found in its nucleus yay oh we still don't know what mass is but we know where to look for it that's good news okay we can worry about what it is later okay so our attention now turns to the nature of the protons and neutrons in the nuclei of atoms themselves that's where we look to find we now know what water consists are we now its atomic structure we know its nuclear structure we're going an awful long way to answering the first question what is water made of what is the IceCube made of and we are think at least we're getting some clarity and where we think we need to look to find its mass okay keep going oh now I can't tell you what kind of mess this makes again just when you thought things were starting to become clearer we hit this period of scientific scientific endeavor where we get nothing other than madness and confusion so we can credit Prince Louis 5th Duke de Blois with the insight that the discovery made by Einstein in 1905 what did Einstein discover in 1905 he discovered that light waves can be particles what we now know as photons Louis dubrow speculated that a result of some further observations in experimental science over the subsequent nearly 20 years then maybe it's also a possibility that electrons can be waves now we'd always cherish the notion right from the beginnings of the speculations of the ancient Greeks that we would be able to take material substance except that it ultimately we must hit a final kind of indivisible stuff out of which everything is made and now we've got this French French Prince telling us well actually you know what you thought were little hard billiard balls of material substance that happened to be negatively charged electrons can also be waves why is that a problem well let's have a quick look I'm just want to spend a few minutes talking about what I call the essential mystery of quantum mechanics there's a famous experiment it may already be familiar to you it's called the two-slit experiment and it's easy to understand what we see in the context of a wave theory of light we take a light source we take two narrow slits or holes and we shine the light through these now there's only one caveat the distance the spacing between the slits has to be of a certain magnitude and the slits themselves have to be of the order of the wavelength of light and the chances are you're going to see what you need to see only if that light itself is monochromatic in other words it has a single wavelength it's not contaminated with different colors do that and what you see projected on a far screen is what's known as the two slit interference pattern it's very easy to understand as the light waves squeeze through the slits they diffract they spread out beyond and in the space beyond where a wave crest runs into a wave crest coming from the other slit you get what's known as constructive interference the waves add up to give a stronger wave where a trough meets a trough you're going to deeper trough constructive interference but where a wave crest meets a wave trough you get a cancellation destructive interference and the result is a pattern of alternating light and Frenchy's these were first discovered by Thomas Young in about 1804 easy to understand with a wave theory of light but debris is now telling us electrons can be waves so how about if we do that experiment with electrons and how about we do that experiment in such an arrangement so that only one electron goes through these two slits at a time think about that for a second an electron is an individual indivisible bit of it's a fundamental particle the elementary particle does a negative electrical charge but it also has a mess whatever that is we anticipate that the electron surely must go through one or other of these two slits and the one thing that you don't expect to get is an interference pattern coming out of that how can it possibly but debris was saying electrons can also be waves and a wave passes through both slits simultaneously to interfere on the far side so let's do the experiment here's what we see when a few electrons have passed through these two slits this is fine what we see is for each electron we see a definitive spot it says an electron hit here struck here and that seems very entirely entirely consistent with the idea that a single electron maintains its integrity goes through one of the other slits to be detected on the screen on the far side then let's let in a few more electrons and a few more electrons and a few more now although the resolution is a little bit fuzzy and this is not HDMI quality we get the sense that even though these electrons are passing through this apparatus one at a time what we're seeing is an interference pattern of light and dark fringes what I love about this experiment is if indeed the electron is passing through both slits simultaneously as a wave what happens to its mass while it does that now I don't know how many of you familiar with the work of Tom Stoppard he wrote a play called Hapgood was put on stage in I think the late 1980s 1988 or there abouts he had a character Koerner it was a play about double agent in mi6 I think but the double agent was a metaphor for wave particle duality stop art is a clever guy and Koerner said every time we don't look we get wave pattern because of course faced with that kind of puzzling experiment you might be tempted to say okay well I'm bloody well going to trace the path of an electron through this thing I'll show you but the minute you do that every time we look to see how we get the wave pattern we get the particle pattern the act of observing determines the reality and that's the essential mystery okay Einstein and Bohr had a famous debate the problem with this kind of thing is that when we see a single spot on the far screen there's a phrase it says it says that if the electron is described as a wave it's kind of distributed it could be anywhere across that screen it ends up being in only one place it's detected there but that place cannot be predicted it's left to chance it seems that's the nature of quantum probability and Einstein didn't like that he said God does not play dice Bohr on the other side of course answered it is not for us to tell God how he should run the world all right so this is the mystery of quantum mechanics we were doing so well we'd started with our cube of ice got molecules of water in a regular lattice we found the mass of molecules of water in the nuclei of its the protons and neutrons in its nuclei and and now we run into this sea of confusion called quantum mechanics I'm going to press on because okay the thing about quantum mechanics is that it works really well it is by far and away one of the best theories of physics that have ever been designed even though it's bizarre and nobody understands it do you think I'm joking I'm not there's an extension of quantum mechanics perhaps less familiar than some of these things called quantum field theory and one of the first successful developments of quantum field theory was this guy here the charismatic American physicist Richard Feynman but there were others involved julian schwinger Sinha taro tominaga and an English physicist called Freeman Dyson were responsible for putting it together it's called quantum electrodynamics and the subtlety and sophistication of quantum electrodynamics is a thing to behold I think Feynman once said that the prediction is the things you can calculate with quantum electrodynamics is like knowing the distance from San Francisco to New York to within the width of a human hair it is so precise that you can't but accept that this version of quantum field theory is is it's got some essential truth in it despite the fact that we don't understand it and that was fine QED worked really well but then when physicists theorists started to assemble 28 20 years after this something called the second world war intervened 20 years after afterwards when theorists started to try to create a quantum field theory to describe protons and neutrons they hit a snag in the meantime quantum waves by the way so we've not lost the idea of wave particle duality in this we still have to deal with this confusion it's just that those wave ideas have been translated into a field it's still an extended distributed structure we've still got the problem of the collapse of the wavefunction we still understand that in Truong field somehow interacts with the screen and ends up producing a single dot over here in a way that cannot be predicted there was a problem and that is that early quantum field theories they dealt with only massless particles now the photon is a good example of a massless particle and so having got the clarity even though I use clarity probably in the inverted commas having got the clarity of quantum mechanics and quantum field theory we're now at a situation where things have gone horribly wrong again and we've lost sight of mass we cannot get to the mass of protons or neutrons even though we know that these things do have a mass so what do we do well actually the first thing to do so actually understand what a massless particle actually looks like and for that I'm afraid I'm going to have to ask you to indulge me a little bit of Einstein's special theory of relativity I promise not it won't hurt too much so here's a particle very simply conceived it's a billiard ball type thing it has a diameter I called it d0 you're with me okay I'm going to push that particle to travel it's travelling with a velocity V and I'm going to push that particle so that it moves at ever increasing speeds up to the speed of light which is given the special symbol C all right now to understand what goes on I need to recognize one of the effects of Einstein's special theory of relativity is that distances contract and time dilates don't ask me to go into that right now but anyone who wants to buy a beer afterwards for me I will happily regale them with the reason why that happens so what we do is we push our particle let's push it to something like 87 percent of the speed of light this factor here given the Greek symbol gamma is called the Lorentz factor you don't have to worry where it comes from or what it represents you just need to know that it started off with a value of 1 and now it has a value of 2 and what it means according to that little equation up there it means that the diameter of this particle in the direction of travel has compressed to half its original diameter that's special theory of relativity for you push it a little bit further now 98% of the speed of light by the way we're getting now to the kinds of speeds at which protons are hurled around the Large Hadron Collider at CERN they get up to about 99 percent of the speed of light we see now that this Lorentz factor gamma is moved to a value of about five that means the diameter of this particle is 1/5 of its original diameter in the direction in which it's moving I think you can figure out what's going to happen if we push this all the way to the speed of light we're going to end up with the thing going off the top there and we end up with effectively a dimensionless a two-dimensional particle if that makes sense now in truth we can't accelerate we can't move particles with mass at the speed of light only mass less particles can travel at this speed it's a characteristic and by the way massless particles only ever traveled at the speed of light okay so what that means is a massless particle traveling at the speed of light is flat or two-dimensional it's kind of lost the third dimension it cannot possibly exist in a third dimension and in fact for those of you who know about light polarization you'll know that light actually has only two states of polarization which we can think of perhaps as vertical and horizontal there's no light polarization in this direction if this is light traveling towards you here it's either I always say horizontal when I do that and then vertical vertical or horizontal there's no polarization in this direction for the very simple reason is that has no third dimension to travel in what a pot to be polarized in okay so that's a bit of a problem so in effect to fix this problem in quantum field theory in the early 1950s what you need is a trick we need massless particles going in we need something magical to happen and we need to get particles with mass coming out you know what this is it's called the Higgs field and the fundamental particle of the Higgs field is this thing called the Higgs boson now here's a dirty little secret about theoretical physics if you're a theoretical physicist sitting down pondering great thoughts about the nature of material substance and elementary particles you are your mission is to get the maths to work out correctly that's your first priority get the maths to work in a way that's consistent with theoretical structures that have gone before and and hopefully in such a way that might give you some insights as to a experimental test you can do or give you something to look for in a in a laboratory like CERN but these theorists are not overly concerned as to what it means and it's then left when these things do turn out to have a bit of life to them it means that we're left scrambling to try to understand what on earth this means as far as they're concerned they've got a mathematical trick they invoke something called a Higgs field and suddenly mass is switched on as a result what is supposed to happen well believe it or not politicians get puzzled by this - and if you can cast your mind back those of you are old enough to another conservative government that actually in the end became a minority Conservative government under John Major in the 1980s John Major had a science Minister called William Waldegrave and William Waldegrave was facing a challenge of understanding as to whether it was worthwhile for the UK to continue funding the European Center for Nuclear Research CERN I think we spent in those days about 50 million pounds on CERN and of course the message he was getting from high-energy physicists we need to find the Higgs boson and William Waldegrave said so tell me what the hell this is on one sheet of a4 paper and I will give the best entry a bottle of vintage champagne as a reward and he got many entries and in fact he got many good entries but perhaps the best one actually comes from a guy called Professor David Miller close by here at the University of College London who said well maybe think of it like this imagine a singularly important personality in Conservative Party politics Thatcher had gone but let me tell you now she was still a force to be reckoned with and imagine that we have a room here full of conservative party workers this is the Higgs field now facture being two dimensional and massless comes in to this room of Higgs field and immediately the field starts to cluster around her because we all want to hear what she has to say we're waiting for her to pronounce on you know polit political decisions the big political decisions of the day and as a consequence of this grouping of this clustering of the field around a massless particle its motion is impeded it can't get through the room in quite the speed of light that it was travelling before and as a consequence it has acquired mass now it's an imperfect analogy but William Waldegrave kind of liked it okay so that's how the Higgs field gives elementary particles mass what about the Higgs boson itself well well the Higgs boson is like a softly spoken rumor of course this is clearly something that's contentious we don't want everyone to be hearing this so as the rumor goes around the room the party workers cluster to hear what it says and that motion that clustering of the field itself is the Higgs boson all absolutely clear now good alright so actually a you know the story there was a search for the Higgs boson it was discovered or found in 2012 I rather incredibly had a book about this discovery in stores only six weeks after the discoveries announced I had an agreement with my publisher I will write a book that is 95% finished which you then print and then we wait and I actually listened to the live webcast from CERN on the morning of the 4th of July 2012 and and finished the the chapter and the book was then as I say in the store six weeks later I thought was quite good but so completing finding the Higgs boson completes the standard model now this is effectively the particle physicists equivalent of the chemists periodic table these are the ingredients that we need finally to get to our current contemporary understanding of the nature of matter we don't need all this though that's the good news we can shrink this down to just a few bits what we need is two things called up and down quarks these combine in triplets in threes to form protons and neutrons so protons and neutrons are not in themselves elementary particles any longer we need these things called gluons these gluons literally glue physicists have limited creativity really at the end of the day when they come up with these names they're normally pretty obvious what they're kind of getting at so gluons glue the quarks together inside protons and neutrons we need electrons obviously electrons are still the thing that it counts for most chemistry and most molecular biology at the end of the day so we need them and they form patterns around the outside of the atomic nuclei the force that holds the electrons and the nuclei together is the electromagnetic force and that is force that's a force that's carried by photons familiar particles of light we also need this thing called the Higgs boson because the Higgs boson is about the Higgs field and the Higgs field Higgs field is necessary in the standard model of particle physics to give particles mess right mission update are we ready so we learned that cube of ice consists of a lattice of water molecules h2o we learned that an oxygen atom has a central nucleus with 8 protons 8 neutrons hydrogen atoms have a central nucleus each of 1 proton we drilled into the proton itself I'm glad you didn't all run screaming from the room now we have a real problem because you kind of would expect that if we can trace the history the map the mass of substance like a cube of ice to its molecules to its atoms to its atomic nuclei to its protons and neutrons and we learn that protons and neutrons are themselves composed of quarks you might expect now ok those quark masses are coming from interactions with the Higgs field let's not get too detained by that they have a mass we know what that is but when we do the sums we find that a mass of a proton only 1% of the mass of a proton is accounted for by adding up the masses of its two up quarks and one down quark something seems to have gone horribly wrong fortunately there was this guy called Einstein and he wrote a paper in 1905 you know what's einstein's most famous equation everybody knows that equation right maybe you'd be a little bit disappointed to learn that in his singular paper in 1905 about this aspect of special relativity that equation doesn't appear at all what Einstein discovered his big insight is actually not a equals MC squared it's this M equals E over C squared mass is the measure of the energy content of a body now I got to tell you I mean who remembers the Quatermass experiment on BBC television all those years ago I see a smile in the audience yes a kindred spirit who remembers video footage of atomic explosions in the 1960s 1970s frighten you to death as these bombs got ever bigger you take the fishing of a uranium nucleus uranium-235 nucleus and a fifth of the mass of one proton is converted into the energy of an atomic explosion you kind of have that almost cultural understanding that e equals mc-squared represents the vast reservoir of energy that is somehow locked up in mass and when you convert mass into energy as was done towards the end of the Quatermass experiment you get this enormous release but that wasn't Einstein x' inside despite the fact that the e equals mc-squared became the most known well known equation in the whole history of physics so here's what's really going on it's math Jim but not as we know it the mass about 1% of the mass of a proton let's say comes from interactions between otherwise massless quarks and the Higgs field which is all around us by the way if it didn't exist if it were somehow magically switched off we'd all explode well and not in an aspect spectacular explosion but we'd all would there be out all our particles will become massless there'd be no mechanism to give them mass so you hope that Higgs field stays switched on okay so it comes from the energy of these particles interaction of the Higgs field but it's only 1% of the total sum where's the rest of it the bulk of the proton mass comes from the energy of the blue ones that are dancing back and forth between the quarks holding them together the gluons are massless particles but they possess very very very high energy and once they're locked up in the confines of a proton or a neutron that energy translates into what we understand and perceive as mass front we'll check who is one of the architects of the standard model worked on something called quantum chromodynamics which is the theory that describes quarks and gluons put it this way if the body is a human body whose mass overwhelming it arises from the protons and neutrons it contains the answer is no clear and decisive the mass of that body with 95% accuracy is its energy content I would quite like to do something about the energy content of a certain part of my body but so far I haven't come up with a diet that will actually disconnect the Higgs field just in this specific region but who knows I'm hopeful well this is this mass without mass in scrambling to try and find a way to articulate this in the book I said look mass is not a property ever since the ancient Greeks we've always understood that atoms would have weight weight or mass being an intrinsic or primary property of these indivisible indestructible bits of substance but now we learn that mass is actually not a property it's not something that matter has it is rather a behavior it's something that quantum fields do now this isn't the end the standard model of particle physics has lots of explanatory holes the one thing that it doesn't do is it doesn't explain for example gravity and at the moment there's a lot of endeavor there's a lot of work going on both in the string theory community and in another area called loop quantum gravity to try to devise a quantum theory of gravity there may yet be more to learn however I'm pretty confident that our understanding of matter and the nature of mass is not going to change as a result of these endeavors so get used to it when you climb on the scales in the morning you're weighing the energy content of the gluons locked up inside the protons and neutrons of your body I don't know whether that will make a difference to what the scales were sir but sometimes a bit of enlightenment is a good thing now I want to thank you I've gone on a little bit longer than I'd intended I want to thank Carlo Rovelli is an Italian theorist who very kindly agreed to read the manuscript over my shoulder and make sure I didn't commit any howlers laughs ah Jenny Phil who's in the audience our folks at Oxford University Press who helped turn my ramblings into a hopefully readable book my mother well we should all thank our mother right but my mother who's 80 this year I've got to tell you she has an endless curiosity in her seventies she decided that she would study for a degree in history at the University of Warwick which he did part-time blessin and she agreed to read the manuscript coming back saying Jim why do you have to use all these big words can't you make it just a little bit simpler which I did try to do Martin Davis who introduced me thank you very much for asking me to come along this evening and of course you for being so very patient thank you very much you

Channel: The Royal Institution

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

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Length: 49min 35sec (2975 seconds)

Published: Wed Sep 27 2017