Why Don't Protons Fly Apart in the Nucleus of Atoms? RESIDUAL Strong Force Explained

this video is sponsored by brilliant please sign up for free and support this channel at the link in the description there are thought to be just four fundamental forces or interactions in nature gravity which keeps you on the surface of earth the weak force which is responsible for some kinds of radiation electromagnetism which is responsible for all chemistry and the strong force which keeps protons and neutrons tightly bound together in the nucleus of atoms you're probably most familiar with gravity which at the skill of the earth the solar system and beyond dominates the universe but at the quantum scale the other three forces dominate for example electromagnetism is a whopping 10 to the 37 times stronger than gravity it's responsible for keeping the negatively charged electrons near the positively charged protons in atoms so now you have to ask since electromagnetism is so strong then multiple protons in the nucleus of any atom like helium and beyond should repel each other very strongly according to coulomb's law the two protons in a helium atom experience a repulsive force equal to about 90 newtons or 20 pounds for something as small as a helium atom this is a huge force they should repel each other and fly apart instantly the reason that these protons don't fly apart is because they are kept glued together by a force that is even stronger than electromagnetism about a hundred times stronger called the strong nuclear force it is the strongest force in the universe at the scale of the nucleus this force is not simply the opposite of electromagnetism but works through an entirely different mechanism which unlike chemistry is typically not taught at the pre-college level so most people are not familiar with it i want to give you a glimpse of the fascinating world of quantum chromodynamics and show you exactly what goes on inside and in between protons and neutrons in the nucleus of atoms that keeps them so strongly glued together against the enormous repulsive force of electromagnetism that's coming up right now [Music] even though we don't directly experience the strong force you can get a glimpse of its power by watching any footage of a nuclear bomb explosion because the enormous energy that you see comes from the binding energy that keeps protons and neutrons within the nucleus of atoms this binding energy is due to the strong force and in fact this binding energy is responsible for about 99 percent of the mass of ordinary objects that you see all around you contrary to what some people believe only about one percent of the mass of objects comes from the higgs field almost all of it comes from the strong force so how does this force work we have to start with what protons and neutrons are made of they're made of more fundamental matter particles called quarks and force particles called gluons a proton and neutron each contain three quarks a proton is made of two up quarks and one down quark while a neutron is made of two down quarks and one up quark gluons within these nucleons are virtual particles so the number fluctuates we can't say exactly how many are inside but there are eight total different types of gluons which keeps quarks together both of these quarks and gluons carry what is called a color charge it's analogous to an electric charge but works via a completely different mechanism and although it's called a color charge it has nothing to do with optical colors that you can see with your eyes it's just a metaphor to describe a different kind of charge that these fundamental particles associated with the strong force have it is just a property that some particles have and quantum chromodynamics provides a very good description of how the color charge works an important thing to remember is that the color charge carried by gluons is not the same as electrical charge and here's how the color charge works there are three kinds of color charges red green and blue and the way to think of this is that red green and blue combine to make a neutral white analogous to the way it works for optical colors so like electrical charges are conserved or balanced positive with negative to make neutral color charges also have to be balanced by either a combination to make a neutral white or by color anti-color charges that's right there are anti-colors too like red and anti-red green and anti-green and blue and anti-blue which also combine to become neutral so any combination of color charges has to be either red green and blue together or a color and anti-color together such that we get a neutral color charge a combination of three quarks in which two of them carry the same color cannot exist both quarks and gluons carry these color charges and that's why gluons interact with quarks and bind them together the only fundamental particles that are affected by the strong force are quarks and the particle that mediates the strong force is the gluon now gluons bind quarks together by constantly exchanging color charge between them gluons mediate the strong force analogous to the way photons mediate electromagnetic force between particles with electrical charges very simply stated it is this constant exchange of gluons carrying the color charge that causes the quarks to stay bound to each other this exchange occurs continuously the animation you're seeing here is slowed down to show what we believe is really happening but you should know that this is happening so fast and continuously that there's no distinct gluons that could be detected the constant exchange of gluons creates a kind of continuous bridge between course called a flux tube now there's an important distinction between the way the strong force works with color charges versus the way electromagnetism works with electrical charges electromagnetism like gravity gets weaker as objects get further apart the force between two quarks however actually gets stronger as they get further apart it works like a rubber band or a spring if you try to pull two corks apart the force between them gets stronger and stronger the further apart they are this tends to pull a cork back into the protons or neutrons as they get further apart however if the quarks get too far apart then the rubber band breaks an interesting thing that happens at this point the cork is not released but the energy required to break the rubber band creates a new fork and an anti-cork pair this quark anti-quark pair is called a meson now what i just described is called confinement in quantum chromodynamics because you cannot have three quarks they're always confined together with at least one other quark going back to the newly created meson from the breaking of the rubber band this is the key to understanding how protons are kept together with other protons and neutrons in the nucleus by the way what i'm calling the rubber band is really a quark gluon flux tube which connects quarks together it turns out that these mesons act as the force carrying particle for the residual strong force that keeps them bound now i'll explain how this works but first let me explain why mesons are formed in the first place what causes a cork gluon flux tube to break and create a meson what i didn't tell you earlier is that although the color charges with the collection of the three quarks within protons and neutrons combine to form a neutral color such that the net color charge cancels out quantum fluctuations ensure that this cancellation does not happen perfectly this is especially true when nucleons are very close together some color charge remains this imperfect balance of color charge causes a residual strong force between nucleons this residual force is called the strong nuclear force rather than the strong force it's mediated not by gluons but by the exchange of mesons between two nucleons and by the way nucleons in this context are either protons or neutrons now let's look at the details of how exactly this interaction happens using feynman diagrams quantum theories can be complicated but american physicist richard feynman came up with an ingenious way to represent these interactions in what's now called findment diagrams and even though these diagrams represent complicated mathematical equations they can be visualized intuitively and drawn for any process using some simple rules one of the simplest diagrams shows how a pair of quarks simply change color through the exchange of gluons as i said earlier this color charge exchange is the glue that binds the corks together and keeps them confined to the inside of nucleons a blue and red cork for example can change colors by the exchange of a glue on so on this diagram we have a red quark coming from the top left it emits the gluon with a combination of red and anti-blue color charge by the way gluons always have a combination of color anti-color charges the outgoing anti-blue of the gluon immediately turns the cork into a blue cork the blue cork at the bottom absorbs this gluon its blue color gets neutralized by the anti-blue contained in the gluon and this quark turns red by absorbing the red that was also part of the gluon note that color charge is conserved in this interaction let's now consider a more complicated finding diagram which represents the residual strong force interaction that binds protons and neutrons together in the nucleus this is a critical interaction because without it there would be no atoms heavier than hydrogen because two protons could not bind together in the nucleus and life as we know it would not exist essentially this diagram shows how a proton and neutron interact with each other via the exchange of mesons and again mesons are a combination of a quark and antiquark pair we have a single proton up top and a single neutron at the bottom time flows from left to right keep in mind that color must always be conserved that is the three quarks inside a proton or neutron must be a combination of red blue and green which combine to make a neutral color charge let me clarify again that this is the same way that optical colors combine to make white but color charge like i said earlier is just a metaphor and has nothing to do with colors that you can see with your eyes inside the proton the blue up quark interacts with the red down quark via a gluon this turns the up cork red and the down quark blue as this down quark tries to leave the proton the rubber band like stretching of the flux tube results in energy that creates a quark anti-cork meson these newly created mesons consisting of a blue down quark and anti-blue anti-down quark form a color and charge neutral pi mesa note that the quarks of the proton change colors but remain within the proton the pine meson now interacts with the neutron at the bottom the anti-down quark of the meson annihilates the down quark of the neutron the down quark of the same meson joins a neutron by taking the place of the annihilated down quark note that the exchanges of colors are taking place with the overall result that both the neutron at the bottom and the proton up top remain color neutral that is their three quarks maintain a combination of red green and blue colors these virtual meson interactions are what keep protons and neutrons bound together in atoms it is a kind of residual force of the strong force and it's called the strong nuclear force but note that this is distinct from the strong force which works within the nucleons keeping the quarks tightly bound together and that is mediated by gluons but the strong nuclear force which keep protons tied to other protons or neutrons is mediated not by gluons but by mesons remember that this force is caused by the not quite perfect neutrality of the color charges within nucleons that's why it's referred to as a residual force and although this force is much weaker than the strong force keeping quarks tied together in nucleons and mesons it is still much stronger than the electromagnetic repulsive force between two positively charged protons so protons are still glued together even though they feel a strong electromagnetic repulsion due to both of them having a positive electrical charge but this strong nuclear force diminishes rapidly with distance it's effective only at very short distances on the order of one femtometer which is about the diameter of a proton when distances between nucleons are much larger this residual strong force has almost no effect and it's this aspect of the strong nuclear force that limits the size of atoms because nuclei beyond a certain size are not stable you can think of this like velcro if you bring it close together it grips tightly but move them apart and it has no effect now i explained this in the simplest way i could think of obviously there are more complicated details involved in quantum chromodynamics but i hope this gives you some idea of how this very important phenomena of nature works without which there would be no objects we could see nor life as we know it and if you enjoy science like this but sometimes feel lost because perhaps you never learned the fundamentals then let me suggest a couple of courses that i think you'll find very useful and enjoyable they're available on brilliant.org today's sponsor one of them is a brand new course called quantum mechanics with sabina it was developed as a collaboration with my friend and fellow youtuber sabina hassenfelder what i found really great about this course is that it walks you through the fundamentals of quantum mechanics including superpositions and entanglement through a series of short interactive quizzes this is so fun that you might not even realize you're learning some pretty high level stuff but if that seems a bit advanced and you want to brush up on more fundamental concepts first then brilliant scientific thinking course would be a great place to start this course teaches you essential scientific principles not through number crunching but physical insights it's a great way to learn physics without being overwhelmed with the math brilliant has a special offer for arvind ash viewers right now get started for free by clicking the link in the description the first 200 people will even get 20 off their subscription this is a great opportunity to give brilliant a try so be sure to click the link in the description below and you'll be supporting this channel when you do that so many thanks for that and if you enjoyed this video then please smash the like button and feel free to share this video i'll see you in the next video my friend [Music] [Applause] [Music] [Applause] [Music] [Applause] you

Channel: Arvin Ash

Views: 303,426

Keywords: strong nuclear force, particle physics, strong force, nuclear force, the strong force, four fundamental forces, nuclear physics, quantum physics, quantum mechanics, what holds the nucleus together, fundamental forces, how virtual mesons are formed, what keeps protons bound in the nucleus, QCD, quantum confinement, color confinement, strong nuclear force explained, strong nuclear force explanation, strong force explained, quantum chromodynamics explained, Residual strong force

Id: WF2c_jzefKc

Length: 16min 7sec (967 seconds)

Published: Fri Jul 29 2022