The STANDARD MODEL: A Theory of (almost) EVERYTHING Explained

this video is sponsored by the great courses plus you've probably heard that the holy grail of physics research is a theory of everything this is a theory of mythical proportions that would explain all particles of phenomena in the universe an equation that would unite quantum mechanics with general relativity and reveal how all particles and forces manifest at the tiniest scales and thus be able to explain all things stephen hawking famously said that if we discover this theory then we would know the mind of god this has led to at least one physicist calling it the god equation what gets lost in this narrative is that we already have a pretty good model that gets us a significant part of the way to an all-encompassing theory of everything in fact it is the most accurate three we've ever had and that is the standard model of particle physics it describes all fundamental particles that we are aware of and three of the four known fundamental forces electromagnetism strong and weak interactions it just doesn't include gravity now don't let this simple chart fool you this chart is just the most intuitive and visually appealing way to show something that is quite complex there's actually complicated mathematical formulations behind the model that can take years of graduate level study to fully understand it was developed by hundreds of scientists over several decades but all that math can be roughly represented by this equation this is the standard model lagrangian it represents the apex of human knowledge and understanding of how the universe works today i'm going to explain the almost theory of everything in the most intuitive way that i can think of so if you want to know how the universe works as best we understand it you won't want to miss what's coming up right now before we get into the math let's get a little more familiar with this chart on the left we have the fermions and on the right we have the bosons the fermions make up all the matter that we are aware of and the bosons are particles responsible for the three fundamental forces and the higgs field these are fundamental particles meaning we don't know anything smaller that they could be made of ordinary matter that we experience around us is really just made of four of these particles the up and down quarks which make up the protons and neutrons in the nuclei of atoms and electrons which form a cloud around the nucleus and a near massless particle called the electron neutrino which is created during the fusion process and stars like the sun the other particles are rare and don't typically exist in ordinary matter they're created inside particle accelerators like the large hadron collider in geneva or from cosmic rays hitting the atoms in the earth's atmosphere they're very unstable and decay in a fraction of a second it's a bit like on the periodic table where some of the heavy elements bigger than uranium are also very rare because they tend to decay fairly quickly the fermions can be further divided into leptons and quarks the difference between quarks and leptons is that the quarks interact with the strong nuclear force which binds the nuclei of atoms together whereas leptons do not the bosons on the right hand side are the force carriers the gluons carry the strong force which binds the nuclei of atoms the w plus w minus and z bosons carry the weak force which is responsible for some kinds of radiation and the photons carry the electromagnetic force responsible for all electricity magnetism and chemistry lastly we have the higgs boson which is important for giving mass to all fundamental particles it's called a scalar boson because the higgs field has a value at each point in space but no direction unlike the electromagnetic field which has both a value and a direction the standard model is actually represented by a complex set of equations but we can simplify all this and write it in one equation known as the standard model lagrangian don't get intimidated by how complicated it looks because i'm going to explain this intuitively a lagrangian is just like the sum of all energies remember that einstein's equation equals mc squared says that mass and energy are equivalent the entire universe can be represented by the mathematics that accounts for energy that's what the lagrangian is it's important to understand that the standard model is a quantum field theory this means that when i say fundamental particles what i mean more precisely is that these are really an excitation in a quantum field it's not like a tiny marble but like a tiny wave so for example an electron is an excitation in the electron field a photon is an excitation in the photon field and so on for all the particles that you see in the standard model the first term is composed of two matrices f submu nu and f superscript nunu normally f represents only the electromagnetic field strength tensor but in the context of this simplified equation this term represents all the ways that all the force carrying particles the bosons interact with each other only the higgs is not included in this term mu and nu are just indices that represent the four components of space time the three spatial dimensions and one time dimension if this term was more fully expanded to show the interactions of the individual bosons this is what it would look like the first term with b sub mu roughly represents the field of the electromagnetic force the w submu nu a matrices represents the field of the weak force and the last term g mu nu a represents the fields of the strong force the a and the w matrices represents an index that takes into account roughly speaking the three different weak force bosons w plus w minus and z the a in the g matrices represents an index that takes into account the eight different color gluons there is no a present in the b matrices because there's only one photon field photons don't interact with each other unlike w z and gluons which do interact with each other so the matrix is less complicated for electromagnetism we can see this more simply in feynman diagrams because these diagrams represent the mathematics of these interactions in a much more intuitive way so gluons for example are color charged and can have a three gluon vertex or a four gluon vertex a z boson or a photon can result in a w plus and w minus boson or a w plus and w minus boson can annihilate to create a photon and z boson the next term in the simple lagrangian refers to the fermion fields and their interactions with the gage fields simply put it describes how matter interacts with forces this term when more fully written out would look something like this so what's going on here first you'll notice there's a factor i in these terms this is the imaginary number defined as the square root of minus 1. imaginary because you have to imagine that it exists you might ask why do we have imaginary numbers in physics in the first place the short answer is that it's a mathematical tool that allows the use of more numbers so we're not constrained to only use the simple real numbers this is allowed in physics as long as your final result representing physical values does not contain imaginary numbers because that would indicate that something is wrong because it is not physical so using imaginary numbers is fine as long as they don't end up in the results the term q and q bar just refers to the quarks and antiquarks furthermore we have this gamma mu d mu which couples the quarks to the force fields in other words it represents how the quarks interact with the electromagnetic weak and strong force and this is summed up over all the six different quarks of the standard model the next two terms contain and represent the leptons specifically left-handed and right-handed leptons particles have a property where they are either right-handed or left-handed right-handed means that the spin of the particle is in the same direction as the motion of the particle left-handed means that the spin is in the opposite direction of motion it's important for leptons because it turns out that only left-handed neutrinos exist but electrons and its heavier cousins the muon and tau particle can be both left or right-handed so the two scio and psi r terms represent the interactions of the left and right leptons which is not quite the same just like with the quarks we sum over the different particles and we also have the part gamma mu d mu here that represents the interactions of the leptons with the three forces these three terms form the fermion lagrangian which gives us the finemen diagrams for how the matter and the universe interacts with the forces in the universe the gluon is very simple as it only interacts with quarks and the neutrino only interacts with the weak force and all other particles except neutrinos interact with the electromagnetic force the next two terms are related to the higgs mechanism the first term describes how the force-carrying particles interact with the higgs field this term represents the part that gives mass to the weak force particles the w plus w minus and z bosons the second part gives us the interactions of higgs with itself the first part contains d mu which represents the gauge bosons psi and psi dagger represent the higgs field thus this term couples the higgs to the gauge bosons in practical terms however this only applies to the weak force bosons as they are the only bosons that have mass photons don't obtain mass by the higgs mechanism and thus are massless gluons the strong force carriers are massless because they do not couple to the higgs field so in short this represents the higgs mechanism giving mass to the weak force bosons w plus w minus and z bosons this leads us to the following finding diagrams with the higgs boson interacting with the weak force bosons the first feynman diagram for example shows two w bosons turning into higgs boson the second diagram shows two z bosons turning into a higgs particle the second part of the equation represents the higgs potential higgs is the only field in the standard model that has a potential the haze field lies at the value of the minimum which is non-zero and this in turn gives mass to particles that interact with it this potential not only gives mass to matter particles but also to itself the higgs boson itself has mass in terms of finding diagrams this term gives us the different self-interactions of the higgs boson a bit like what we saw with the gluons of the strong force the potential in the term is what is responsible for mass but the next term in the lagrangian describes mathematically how matter particles interact with the higgs field to obtain mass this term actually hides three terms thus actually we would write the following the subscripts r and l again refer to the left and right handed particles the gamma represents the yukawa couplings of each particle to the higgs field yukawa coupling just describes how strong the coupling of individual matter particles is to the higgs field the stronger the coupling the higher the mass that the particle acquires phi represents the higgs field now to be more specific the first term is the leptons and how they couple to the higgs the second term is the down type quarks such as down strange and bottom cork and their coupling to the higgs field the last term is the up type quarks thus the up charm and top fork and their couplings to the higgs field these terms are physically important because they connect the fermions with the higgs and result in masses that the fermions have in terms of feynman diagrams here's what some of these would look like for example the higgs can decay into a tau and anti-tau pair finally the last term is this hc term and that just means permission conjugate while the prior term describes the interaction between a higgs particle and matter particles the hermitian conjugate describes the same interactions but with antimatter particles we have to take antimatter particles into account in this lagrangian because they also exist technically there would be other hc terms and this will range in as well that would describe how antimatter particles interact with forces thus if we combine everything we just discussed a more expanded lagrangian would look like this but you have to keep in mind that even this is a shortened version of what all the equations expanded out fully would look like but for now the shortest version looks like this and what the various terms represent if simplified to its essence this is really describing what almost all the universe is made of as we understand it today the first term is how the quantum forces of the universe interact with each other the second term is how matter interacts with all the forces the third term is how forced particles gain mass the fourth term is how the higgs interacts with itself the fifth and sixth terms describe how the matter and antimatter particles gain mass you should know that although this is the best and closest thing we have to a theory of everything it has some problems one of the biggest gaps of course is that gravity is not accounted for and the other big problem is that dark matter and dark energy which scientists believe make up about 95 of the universe is not in this model so there's plenty of work to be done check out this video by the online blackboard where they go deeper into the standard model and some of its problems but still i think and i hope you'll agree that it's astonishing that in less than a hundred years we humble humans have been able to figure out so much of the universe that our ancestors believed was utterly unfathomable and that we would never figure out never bet against human advance if you'd like to learn more about the many aspects of a potential theory of everything there's a superb course available at the great courses plus today's sponsor called the theory of everything the quest to explain all reality it consists of 24 college level lectures by one of my favorite science educators don lincoln of fermilab his lectures walk you through just about everything we know so far about all the particles and forces of the universe and where we need to go to fill gaps in our knowledge at great courses plus you can enjoy in-depth lectures by not only dr lincoln but also some of the best educators in the world you'd be hard-pressed to find a better online learning service i myself have been a subscriber for a long time even prior to their sponsorship it's really easy to sign up right now because they're offering a free two-week trial and you can cancel at any time so there's really nothing to lose if you want to support this channel and greatly expand your knowledge at the same time be sure to click the link in the description and if you have a question leave it in the comments because i try to answer all of them i will see you in the next video my friend [Music] [Applause] you

Channel: Arvin Ash

Views: 163,828

Keywords: standard model explained, standard model lagrangian, standard model of particle physics, the theory of everything, theory of everything explained, standard model lagrangian equation, standard model lagrangian explained, gauge function for lagrangian, fermions and bosons, fermion lagrangian, left and right handed particles, higgs lagrangian, yukawa lagrangian, yukawa lagrangian standard model, standard model problems, theory of almost everything, particle physics

Id: asEtNJ9sRcQ

Length: 16min 4sec (964 seconds)

Published: Sat May 01 2021