Quantum Fields: The Real Building Blocks of the Universe - with David Tong
What this covers
According to our best theories of physics, the fundamental building blocks of matter are not particles, but continuous fluid-like substances known as 'quantum fields'. David Tong explains what we know about these fields, and how they fit into our understanding of the Universe.
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David Tong is a professor of theoretical physics at Cambridge University, specialising in quantum field theory.
The Ri is on Twitter: http://twitter.com/ri_science and Facebook: http://www.facebook.com/royalinstitution and Tumblr: http://ri-science.tumblr.com/ Our editorial policy: http://www.rigb.org/home/editorial-policy Subscribe for the latest science videos: http://bit.ly/RiNewsletter #QuantumFields #DavidTong #TheoreticalPhysics #BuildingBlocksOfUniverse, #QuantumMechanics #quantumphysicsexplained #quantumphysics #sciencelecture --- Chapters: 0:00 Introduction 3:09 The periodic table 6:00 Inside the atom 11:27 The electric and magnetic fields 33:32 The new periodic table 35:06 Four forces 37:42 The standard model 39:08 The Higgs field 42:25 The theory of everything (so far) Electromagnetism 44:01 There's stuff we're missing 45:49 The Fireball of the Big Bang 47:17 What quantum field are we seeing here? 49:21 Back on Earth 50:30 Ideas of unification
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The fundamental building blocks of nature are not particles but quantum fields—fluid-like substances spread throughout the universe whose ripples and interactions, governed by the Standard Model equation, comprise everything in existence, though deep mysteries remain about unification, dark matter, inflation, and the nature of reality beyond current theoretical understanding.
- Particles are not fundamental; they are quantized ripples (excitations) of underlying quantum fields
- The Standard Model equation unifies 16 fields (12 matter, 4 force fields) and perfectly predicts all terrestrial experiments, but leaves unexplained phenomena like dark matter, dark energy, and cosmic inflation
- Despite elegant theoretical frameworks (grand unification, supersymmetry, string theory) suggesting deeper structure, the LHC has found no experimental evidence for physics beyond the Standard Model, forcing reassessment of theoretical assumptions
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Faraday's famous electromagnetic induction demonstration—moving a magnetic field through one coil to induce a current in a nearby coil, making a needle flicker without physical contact—provided the first empirical evidence that fields are real physical entities through which one can affect distant objects without touching them.
“He simply moved this small coil A through this big coil B like this. And something miraculous happened. When you do that, there's a moving magnetic field. Faraday's great discovery was induction. It gives rise to a current in B which then over on this end of the table makes a a needle flicker like this... you were doing something and affecting the needle on the other end of the table, yet you never touched the needle... This was the first time it was demonstrated that the field is real. You can communicate using the field. you can affect things far away using the field without ever ever touching it.”
When quantum mechanics is applied to the Schrödinger equation, the discreteness of particles is not built into the heart of nature but emerges as a property that arises when solving the equation for continuous, wave-like quantum fields.
“There's nothing discreet about the Schroinger equation. The Schroinger equation is is something you know to do with a smooth uh fieldlike like wave function. The discreetness is something which emerges when you solve the Schroinger equation. So it's not built into the heart of nature.”
Neutrinos are everywhere—since the speaker began talking, approximately 10^14 neutrinos have streamed through each person's body, roughly equal numbers from above (outer space) and below (through the earth), and they rarely interact with matter.
“These nutrinos are everywhere. You've never noticed them, but since I began this talk, something like 10^ the 14 of them have streamed through the body of each and every one of you. Uh, as many coming from above from outer space as actually coming from below because they stream all the way through the earth and then then keep going. They're they're not very sociable. They they they don't interact.”
The Standard Model of particle physics—represented by a single mathematical equation that unifies quantum field theory, relativity, and all known forces and particles—is the greatest theory humanity has ever developed, despite being given a misleadingly mundane name, and it correctly predicts the results of every single experiment ever conducted in science.
“We have uh a theory which uh underlies all this. Uh it is to put it simply um the pinnacle of science. It's the greatest theory we've ever come up with. Uh we've given it the most astonishingly rubbish name you've ever heard of. Uh we call it the standard model... it should really be replaced with the greatest theory in the history of human civilization... This equation correctly predicts the result of every single experiment we've ever done in science. Everything is contained in in this equation.”
Despite the elegant picture of atoms constructed from electrons, up quarks, and down quarks—three fundamental particles that comprise all ordinary matter—this picture is misleading because the best theories of physics do not actually rely on particles as fundamental; instead, the fundamental building blocks are quantum fields, which are fluid-like substances spread throughout the universe.
“It's a very nice picture. It's a very comforting picture. It's the picture we teach kids at school. It's the uh picture we even teach our students in undergraduate university. And there's a problem with it. Uh the problem is it's a lie. It's it's a white lie. It's a white lie that we tell our children because, you know, we don't want to um expose them to the the difficult and horrible truth too early on... The best theories that we have of physics do not have underlying them the quark particle and the two quark particle and the the sorry the electron particle and the two quark particles. In fact, the very best theories we have of physics don't rely on particles at all. The best theories we have tell us that the fundamental building blocks of nature are not particles but something much more nebulous and abstract. The fundamental building blocks of nature are fluid like substances which are spread throughout the entire universe and ripple in strange and interesting ways.”
Quantum vacuum fluctuations—microscopic ripples in quantum fields 10^-30 seconds after the Big Bang—were stretched across the entire 20-billion-light-year sky by cosmic inflation, and these stretched fluctuations are the ripples we now observe in the cosmic microwave background radiation.
“when the universe was very very young, soon after the big bang, there were no particles, but there were quantum fields because the quantum fields were everywhere. And there were these quantum vacuum fluctuations. And what happened was the universe expanded very very quickly and it caught these quantum fluctuations in the act. So the quantum fluctuations were stretched across the entire sky where they became frozen and it's these vacuum fluctuations here which are the ripples that you see in the fireball.”
In an 1846 lecture Faraday idle speculation, Faraday suggested that light itself is comprised of ripples in electric and magnetic fields, an astonishing prediction that took 50 years (with work by Maxwell and Hertz) to be experimentally confirmed.
“he gave this lecture in 1846. um gave many lectures uh in 1846 but there was one in particular where he he finished 20 minutes early. He he ran out of things to say. So he engaged in some idle speculation for for 20 minutes and uh Faraday suggested that uh these invisible electric and magnetic fields that he had postulated were quite literally the only thing we've ever seen. He suggested that it's ripples of the electric and magnetic field which is what we call light. So it took of course 50 years for people like Maxwell and Herz to confirm that that this is indeed what light is made of.”
When one removes all particles and atoms from a box, what remains is not empty nothingness but a quantum vacuum filled with quantum fields that constantly bubble and fluctuate according to Heisenberg's uncertainty principle, even in the complete absence of particles.
“take a box and take every single thing that exists out of that box. Take all the particles out the box, all the atoms out the box. What you're left with is a pure vacuum... even when the particles are taken out, the field still exists. The field is there. But what's more, the field is governed by the rules of quantum mechanics. And there's a principle in quantum mechanics which is called the Heisenberg uncertainty principle which says you're not allowed to sit still and the field has to obey this. So even when there's nothing else there, the field is constantly bubbling and fluctuating in what's quite honestly a very complicated way. Okay, these are things that we call quantum vacuum fluctuations.”
The fact that everything in the universe—all matter, all diversity in nature—is constructed from just three particles (electron and two quarks) rearranged over and over again is astonishing and illustrates a fundamental lesson about how the world is put together.
“That's kind of astonishing. You know, it's uh we sort of take it for granted. We learn this in school. We don't really think about it deeply. Everything we see in the world, all the diversity in the natural world, you, me, everything around us, we just the same uh three particles with slightly different rear arrangements repeated over and over and over again.”
Quantum vacuum fluctuations are not merely theoretical; they are measurable physical phenomena that can be detected through effects like the Casimir force—a force between two metal plates pushed together because there is more quantum vacuum fluctuation outside the plates than between them.
“these quantum fluctuations that are there in the pure vacuum are things that we can measure. Uh there's something called the Casemir force. The Casemir force is a force between two metal plates uh that get pushed together basically because there's more of this stuff on the outside than on the inside. And uh you know these are real. These are things that we can measure and they behave just as we would uh predict they would from from our theories.”
The first term in the Standard Model equation was written by Albert Einstein and describes gravity; solving just this tiny part of the equation allows predictions of apple-falling, planetary orbits, black hole collisions, and universal expansion.
“the first term here uh was um written down by Albert Einstein and describes gravity. What that means is that if you can solve this tiny little part of the equation, just this excuse me, uh just this r, uh you can for example predict how fast an apple falls from a tree or the fact that the orbits of the planet around the sun form ellipses. Or you can predict what happens when two enormous black holes collide into each other and form a new black hole sending out gravitational waves across the universe. or in fact you can predict how the entire universe itself expands.”
Quantum field theory mathematics is substantially more difficult than the mathematics in any other area of physics or science, with the fundamental problem of understanding patterns in quantum vacuum fluctuations being one of six Millennium Prize Problems in mathematics—worth one million dollars for a solution.
“The mathematics that we use to describe quantum fields to describe everything that we're made of in terms of quantum fields is substantially more difficult than the maths that arises in any other area of physics or or science... There's a list of uh six open problems in mathematics. They're considered to be the six hardest problems in mathematics... You win a million bucks if you can uh solve any one of uh these problems... this is one of those six problems. You win a million dollars if if you can understand this.”
Nature has inexplicably chosen to replicate the fundamental particles (electron, up quark, down quark, neutrino) not once but twice, creating heavier copies (muon, tau; charm quark, strange quark; top quark, bottom quark; electron neutrino, muon neutrino, tau neutrino) whose purpose and existence remain completely mysterious and unexplained by current theory.
“for a reason that we do not understand at all, nature has chosen to take these four particles and reproduce them twice over... the muon which has a mass of something like 200 times the electron and the tail particle which is 3,000 times heavier than the electron. Okay. Why are they there? We have no idea at all. It's one of the mysteries of the universe.”
Calculations made to understand what quantum field would produce the observed cosmic microwave background match perfectly with the actual observations, representing another triumph of quantum field theory.
“And yet you do the calculations for this and it matches perfectly what you see here. So this is another of the great triumphs of of quantum field theory.”
The electron magnetic moment—a measurable property describing how quickly an electron's spin axis rotates when placed in a magnetic field—has been measured experimentally and calculated theoretically with an agreement of approximately 12-13 significant figures, representing the most precise agreement between theory and experiment anywhere in science.
“the first number is uh the result of many many decades of painstaking experiments measuring very very precisely the uh uh this feature of the electron... the second number is the result of many many decades of very tortuous calculations... you can see it's it's simply spectacular and that there's nothing like this anywhere else in science with an agreement between uh the theoretical calculation and the experimental measurements. It's sort of I think it's it's 12 or 13 uh significant figures.”
The Higgs field and Higgs particle are important for two reasons: (1) the Higgs field is responsible for the mass property of particles—mass is not an intrinsic property but emerges from how particle fields interact with the Higgs field; and (2) the Higgs discovery completed the Standard Model, providing the final experimental confirmation that the theoretical framework is correct.
“the first is that this is what's responsible for what we call mass in the universe... the property that we call... mass is the statement about how it interacts with the Higs field... The other reason that it was a big deal is this was the final piece of our jigsaw. We we had this theory that we called the standard model. We've had it since the 1970s. This was the final thing that we needed to discover to be sure that this theory is is correct.”
Physicists understand quantum fields very well when vacuum fluctuations are calm and tame, but understanding becomes much more difficult when fluctuations become wild and strong.
“So there there are times uh where we understand extremely well what's going on with quantum fields and that happens basically when these fluctuations are very calm and tame when they're not wild and strong. These ones are big but when they're they're much more calmer when the vacuum is much more like a mill pond than it is like a a raging storm. In those cases we really think we understand what what we're doing.”
After two years of operation (at double the energy of its initial run that discovered the Higgs), the LHC has found absolutely no evidence of new physics beyond the Standard Model—none of the theoretically predicted particles or phenomena from supersymmetry, grand unification, or other beyond-Standard-Model theories have been observed.
“The LHC has been running, it's been running for 2 years. It's been running like an absolute dream. It's just it's a perfect machine. Uh 2 years uh this is what it's seen. Absolutely nothing. Okay, all of these fantastic, beautiful ideas that we've had, none of them are showing up at all.”
The three fundamental forces (electromagnetism, strong nuclear force, weak nuclear force) have nearly identical mathematical forms with only minor differences in notation, suggesting they might not be three separate forces but rather one unified force viewed from different perspectives—a concept called grand unification.
“This is the equation uh that describes the force of electricity and magnetism and it's almost the same as the equations which describe the forces for the strong force and the weak nuclear force... you can see I've just changed letters... The three forces really look similar. So, you might wonder, well, maybe there's not three forces in the universe. Maybe those three forces are actually just one force.”
The universe is 13.8 billion years old; for the first 380,000 years it was a fireball filled with light and particles; observations of the cosmic microwave background radiation (the cooled light from that ancient fireball) allow us to photograph and study the early universe.
“The universe is 13.8 8 billion years old. And uh we understand fairly well, well, we don't understand at all how it started. We don't understand what kicked it all off at time t equals 0, but we understand fairly well what happened after it started. And we know in particular that for the first um uh the first 380,000 years of the universe, it was filled with a fireball.”
The Standard Model successfully explains every experiment conducted on Earth, but when examining the cosmos, there are phenomena that the Standard Model cannot explain: dark matter (invisible particles more numerous than visible matter), dark energy (a mysterious force causing the universe's accelerating expansion), and inflation (the rapid expansion of the early universe in the first fractions of a second after the Big Bang).
“although this explains every single experiment we've ever done here on Earth, if we look out into the sky, there's extra stuff which is still a mystery... there are invisible particles out there... we call them dark matter... there's something called dark energy which is spread throughout all of space... causing everything in the universe to repel everything else... the first few fractions of a second after the big bang the universe underwent a very rapid phase of expansion that we call inflation. We know it happened but it's not explained by that equation”
Mathematical patterns in the Standard Model equation suggest connections to condensed matter physics and quantum information science, fields that are generating new ideas that could inform fundamental particle physics research in ways not previously considered within the particle physics community.
“there are hints in this about you know mathematical patterns that we haven't explored. that there's hints in this about connections to other areas of science. Things like condensed matter physics, which is the science of how materials work, or quantum information science, which is uh the attempt to build a quantum computer. All of these fantastic subjects have have new ideas which sort of feed in to the kind of questions that that we're asking here.”
The speaker feels energized rather than discouraged by the LHC's null results because experimental failure prompts theoretical progress; when theoretical predictions fail, it signals the need for fundamental reassessment of theoretical assumptions rather than mere refinement of existing frameworks.
“I I feel quite energized actually by the lack of results for the LHC. You know, I I sort of it feels good to me that everyone was was wrong. You know, it's when we're wrong that we start to make make progress. Uh so I I sort of feel quite happy by this about this.”
All electrons in the body are not fundamental but are waves of the same underlying electron field, meaning all electrons are connected to each other as ripples of the same field, just as all ocean waves belong to the same underlying ocean.
“All the electrons that are in your body are not fundamental. All the electrons that exist in your body are waves of the same underlying field. Okay? We're all connected to each other. It's like, you know, the waves uh on the ocean all belong to the the same underlying ocean. Uh the electrons in your body are the ripples of the same field as the electrons in my body.”
Despite possessing the correct equations, physicists have been unable to calculate the mass of the proton from first principles with accuracy better than 3% after approximately 40 years of effort using the world's most powerful computers and large teams of researchers, illustrating that possessing the correct theory does not guarantee the ability to solve it.
“It should be possible for us to sit down and calculate from first principles the mass of the proton... we've been trying to do this for about 40 years now. Uh we can get it to within an accuracy of something like 3%... the reason is is very simple. you know, we've got the right equation... it's simply that we're not smart enough to solve it. Okay, 40 years, the world's most powerful computers, lots and lots of smart people”
The particle physics community is 'shell shocked' by the LHC's failure to discover new physics, with no consensus on how to proceed, though there are three primary responses: (1) patience—new physics will be discovered next year or the year after; (2) build a bigger machine; or (3) return to first principles and challenge theoretical assumptions made over the past 30 years.
“my impression is that most of my community is a little bit shell shocked by by what happened. Um there's certainly no consensus in the community to move forward, but I think there's three responses that that sort of various people have had”
Response 2 to null LHC results: Build a bigger machine—construct a particle collider 10 times larger than the current LHC at a cost of $10 billion, requiring government funding that is realistically only available from China, and taking approximately 20 years to build, though this response assumes the problem is insufficient energy rather than incorrect theory.
“well, all our theories are so beautiful, they absolutely have to be correct, and what we really need is a bigger machine... 10 times bigger... they they might be right... a new machine costs $10 billion. And there's not too many governments in the world that have $10 billion to spare... The one is China... the Chinese government would would see it as extremely attractive if the whole community of uh particle physicists... move to a town that's slightly north of Beijing... there's a real chance that they may decide to build this machine. If they do, it's about 20 years uh for it to be built.”
J.J. Thompson discovered the electron in 1897 at Cambridge, a particle smaller than an atom, which he announced in this very lecture series to a stunned audience, with at least half of them disbelieving him and one distinguished scientist calling it a hoax.
“the first person to realize there's that there's something deeper uh than this um was a Cambridge physicist called JJ Thompson. So at the end of the 1800s, JJ Thompson discovered a particle that was smaller than an atom uh that we now call the electron. And in 1897, he announced this uh in this room. In fact, in in this very lecture series, um to a stunned audience, an audience that was so stunned, at least half of them didn't believe what he was saying. There was one very distinguished scientist who afterwards told JJ Thompson he thought the whole thing was a hoax”
The periodic table of elements, while a great achievement of 19th-century science, is not a fundamental classification of nature—it is merely a taxonomic ordering of 120 different elements whose deeper structure was not understood by Victorian chemists.
“This is the periodic table of elements. Okay, it's one of the most iconic images in in in all of science. What we have here are 120ish different elements... any material you get you can distill it down into its component parts and you'll find that all of those component parts are made of one of these 120 uh elements.”
Michael Faraday initiated the Friday evening discourse lecture series in 1825 at the Royal Institution and gave over a hundred lectures, the vast majority on his own discoveries in electricity and magnetism, during which he developed the intuitive concept of electric and magnetic fields existing throughout space.
“It's an idea um which dates back uh almost 200 years. And like so many other things in science, it's an idea which originated in this very room because um as I'm sure many of you are aware, this is the home of Michael Faraday. And Michael Faraday uh initiated this lecture series in 1825. uh he gave over a hundred of these Friday evening discourses and the vast majority of these were on his own discoveries on the experiments he did on electricity and magnetism.”
The question of what we are made of has been asked for at least 2,500 years, going back to the ancient Greeks, and has been discussed many times in this room over the past 200 years.
“Tonight, I'd like to tell you about one of the big questions in science. It's a question that goes back at least 2 and a half thousand years to the ancient Greeks. And it's a question that has been discussed in this room many, many times over the past 200 years.”
The identity of the field responsible for the cosmic microwave background fluctuations is unknown—the only Standard Model field it could plausibly be is the Higgs field, but most physicists believe it is a new, undiscovered field, making the identification of this field a major goal of future cosmological observations.
“The most important one is which field are we seeing here? uh which field is this that's imprinted on on the the background radiation? And the answer is we don't know. Uh the only one of the standard model fields it has a hope of being is the Higs, but most of us think it's not the Higs, but probably something new.”
One fundamental implication of quantum mechanics is that energy is not continuous but always parceled into discrete lumps called quanta—which is the meaning of the word 'quantum'—a principle that created a fundamental tension when trying to reconcile quantum mechanics with Faraday's conception of smooth, continuous oscillating fields.
“one of the punchlines of quantum mechanics. Um one of the punchlines is that uh energy isn't continuous. Energy in the world is always parcled up into some little discrete lump. Okay, that's actually what the word quantum means. Quantum means discreet or or lumpy.”
Ernest Rutherford discovered that atoms consist of a tiny nucleus (metaphorically like a fly in the center of a cathedral) orbited by electrons in blurry orbits, fundamentally changing the understanding of atomic structure within 15 years of Thompson's electron discovery.
“within 15 years of JJ Thompson's discovery, his successor in Cambridge, a man called Ernest Rutherford had figured out exactly what these atoms are made of. And this is the picture that uh that Rutherford came up with. So we now know that each of these elements consists of a nucleus uh which uh is tiny. The uh metaphor that Rutherford himself used was it's like a fly in the center of the cathedral and then orbiting this nucleus in I should add fairly blurry orbits are the electrons”
In the 1970s, physicists discovered that protons and neutrons are themselves composite particles, each containing three smaller particles called quarks—specifically two up quarks and one down quark in a proton, and two down quarks and one up quark in a neutron.
“in the 1970s uh we learned that the protons and neutrons aren't fundamental either. So in the 1970s we learned that inside each proton and neutron are three smaller particles uh that we call quarks... The up quark and the down quark. Okay? For no good reason. It's not like the up quark is higher than the down quark... The up quark and the down quark. So, the proton consists of two up quarks and a down quark. And the neutron consists of two down quarks and an up quark.”
In the 1920s, Heisenberg and Schrödinger developed quantum mechanics, which revealed that the microscopic world operates according to principles fundamentally different from and much more mysterious than the classical Newtonian mechanics that dominated understanding of macroscopic phenomena.
“in the 1920s uh we realized that the world is very very different from uh the common sense ideas that Newton and Galileo had handed down to us centuries before. So in the 1920s people like Heisenberg and Schrodinger realized that uh on the smallest scales on the microscopic scales the world is much more mysterious and counterintuitive than uh we ever really uh imagined it could be. Uh this of course is is the theory that we now know as quantum mechanics.”
A field, in physics, is something that is spread everywhere throughout the universe, takes a particular value at every point in space, and whose value can change in time—conceptually analogous to a fluid that ripples and sways throughout the universe.
“the physicist definition of a field is the following. It's something that as I said is spread everywhere throughout the universe. It's something that takes a particular value at every point in space. And what's more that value can change in time. Okay. So good picture to have in your mind is a field sorry a fluid which uh ripples and sways throughout the universe.”
There exist 12 fundamental particle fields in the universe: three matter fields (electron, up quark, down quark) that compose ordinary matter, plus a fourth particle field (neutrino), and these particle fields interact through four force fields (electromagnetic, strong nuclear, weak nuclear, and gravitational), for a total of 16 quantum fields.
“There are 12 fields that give matter... I'll call them matter fields and four other fields that are the forces. And the world we live in is uh these combination of the 16 fields all interacting together”
The Standard Model equation is often written on t-shirts and is compact enough that it fits in a small space, despite containing all known physics.
“you can put it on a t-shirt if you want to. In fact, if you go to CERN, you can buy a t-shirt with with with this equation on it.”