Weak Interaction: The Four Fundamental Forces of Physics #2


Today we continue our series on the four fundamental forces of physics, a mere four forces that make the whole universe work. And in this installment, we’re talking about a force that acts over very very teeny teeny tiny distances: the weak force. [Intro] Without it, the sun would not shine, we would not have elements like radium or plutonium, and we wouldn’t have carbon-14 dating. All of these things require one particle to turn into another particle through particle decay. Remember strong force? It acts on a proton or a neutron to hold its component quarks together, and one way that we describe quarks is by their color. It’s just a characteristic of a quark sort of like a charge is a characteristic of an electron. Weak force acts on quarks just like strong force does, but instead of changing its color, it changes its flavor. There are six flavors of quarks: lemon, lime, root beer, hazelnut… sorry. Seriously, you’ve heard of these — up, down, strange, charm, top and bottom. Up quarks have a slight positive charge while down quarks have a slight negative charge, and they both have the smallest masses of all the quarks. The other quarks have charges too, but they’re all much heavier and much rarer because they quickly decay into up and down quarks. Up and down quarks are what most stuff is made of. Neutrons are made up of one up quark and two down quarks, while protons are two ups and one down. Now, the weak force changes quark flavor, so when a quark inside of a particle changes, that changes the whole identity of the particle. This is crazy stuff to me, to think that you can actually, like, just, through this force change a proton into a neutron. It’s nuts. In addition to quarks, and thus neutrons and protons, weak force can also interact in a similar way with leptons, the most famous of which is the electron but also including neutrinos. And as with all fundamental forces, the weak force involves an exchange of particles called force carriers, which are these weird, barely-existing particles that convey forces between other particles. Weak force has two force carriers, the W bosons, which can be either positively or negatively charged, or the Z bosons, which have no charge. Now let’s watch some weak interaction at work. How about we make a neutron change or decay into a proton. To do this, we’re gonna need a neutrino passing by. So remember, neutrons are one up quark and two down quarks, and protons are two up quarks and one down quark. The weak force is called weak because it only operates within a teeny tiny tiny tiny range; about 0.1% of the diameter of a proton. So, say our neutron comes close enough to a neutrino. A positively-charged W boson would travel from the neutrino to that neutron. That’s the weak force, right there. The neutrino, having lost a positive boson, becomes negatively charged, turning it into an electron, and over on the neutron, meanwhile, the positive W boson encounters a down quark and changes its charge from slightly negative to slightly positive. And since neutrons and protons have a difference of just one quark flavor, this changes the neutron into a proton. With the composition of the nucleus that contained this neutron having changed, the atom itself has changed too, into an entirely new element. If this was a carbon-14 atom, with six protons and eight neutrons, through the weak force it just decayed into a nitrogen-14 atom, with seven protons and seven neutrons. And that actually happens. It happens all the time, and it’s how carbon-14 dating works. So, there it is. The weak force is actually able to change the identity of particles when they come very very very very very close to each other. Thank you for watching this episode of SciShow. If you would like to know more about the four fundamental forces of physics, you should go to youtube.com/scishow and subscribe. If you have any questions or ideas or comments, you can leave those for us on Facebook or Twitter or of course in the YouTube comments below. Goodbye.

100 thoughts on “Weak Interaction: The Four Fundamental Forces of Physics #2

  1. Great explanation. However, where do these neutrinos come from?
    I only know about the electrons and positrons surrounding the nuclei of matter and antimatter. And that they move closer to the nuclei when loosing energy emitting photons.

  2. Wait, I have a question here. You're telling me that radioactivity and nuclear decay happens because neutrinos brush past atomic nuclei?

  3. Wait, so you have a neutrino VERY close to a neutron, which then becomes a proton and an electron after the exchange of W+. But proton being positively charged and have significant mass, and our electron being negatively charged, at that close distance wouldn't the electron be pulled in towards the proton? Note I am completely ignoring the remaining protons in the the nucleus for the sake of the example.

  4. Extra: to make plutonium is as easy as hiting natural ocurring uranium (U-238) with a neutron, creates U-239 wich, as shown in this video, transforms 2 protons to 2 neutrons making plutonium-239, the one used in nuclear bombs. To get neutrons is as easy as, when an alpha particle hit beryllium or alluminium gives a neutron, so you encapsulate the uranium in a neutron reflector box (like tungsten carbide), put beryllium in wait and get it out, and chemically separate the plutonium, start the proces again. Warning, do not exposure too long or Pu-240 will be produced, wich is bad because it can fissile automaticly, starting a chain reaction.

  5. Wrong info given here. Neutron mass = electron mass + proton mass
    Clearly Neutron decays into electron proton pair

  6. If a neutrino gives up a W+ boson to become an electron, where does it get the extra mass from (electrons have much greater mass-energy than neutrinos as far as I know)?

  7. Where did the charge comes from?
    Kindly make a video about this. Because its confusing that no one could answer correctly.

  8. You said the SNF helps keep quarks of protons and neutrons together, could've sworn it only holds the protons to other protons >.>

  9. What If there are 2 up quarks and 1 down quark and the W boson interacts with the 1 down quark via the weak force? Would that mean all the quarks would face up? If so, what does this mean for the neutron/proton?

  10. Wait – if the up quark has a poitive electrical charge, and the down quark has a negative electrical charge, and neutrons consist of one up and two down – then shouldn't the neutron be negativly charged!?

  11. Hank seems to have misinterpreted a Feynman Diagram of beta- decay, where the anti-neutrino's arrow is drawn in the opposite direction (as is convention for antiparticles). The weak decay happens spontaneously (without a coincidental neutrino) and a W- boson is emitted, which quickly decays into an electron and an electron anti-neutrino.

  12. I understand that it is the Pauli exclusion principle "force" that supports a white dwarf star. That is, the electrons don't want to occupy the same quantum state and so resist the collapse of the white dwarf. So this appears to be a force that opposes gravity and prevents a white dwarf from collapsing. But which of the four forces is this?

  13. what if a negatively charged boson approached a neutron (or a proton)?… or, does that not happen in nature (as far as we can detect as of yet?).

  14. Hi Hank, thank you for making this wonderful video. If and when we can make particle detectors that are "quantum-ly fast" or sensitive enough to inspect the transformations of protons into neutrons and large mass quarks' transformation into down quarks, do you think we might observe other "ghost" particles, force carriers, or perhaps other unidentified subatomic elements we haven't observed yet? I ask this since quantum computing may be able to help us observe the sub-atomic world better in the near future and was wondering if you in academia-world heard of anything in the works. Thank you for your time! You have a new subscriber!

  15. I don't get how this is a force. Ok, it changes the identity of the particles involved in the process. Soo, shouldn't it be considered a reaction instead of a force? I mean if it is a force it should accelerate a particle, or (together with other forces) put it at a rest state, right? Before this video I used to think this was the force which prevents the electrons to collapse into the atom core by electromagnetic attraction

  16. Hey yall Ive noticed that the 4 fundamental forces parallel the "4 Loves" that CS Lewis identified.  I hope y'all check that out (the book and the connection [and what it might mean])

  17. the four fundamental forces have all ready been described in hinduism
    please read this kindle ebook
    https://www.amazon.in/dp/B07CWB47H1/

  18. of course all this is only a observation of what happens when you add energy to a group of partials in an atomic accelerator and collided them , so its only the extemporaneous forces of the collusion they managed to capture and name according to the movement of a track left in a medium which is presumed to be but may not actually represent the fundamental forces which are repulsion and attraction a derivation of temperature and function of the excited state of a string which in compensating to the excitation internal bifurcates giving rise to wave functions which allowed through the action of that function balance in the creation of compensatory photon mass at varying levels of excitement,,,,,,flavors ???some one be on the hooker to long

  19. The weak force is not weak due to interaction distance, but due to the mass of the force carriers. For an introductory explanation by a man sporting a bad mustach, see https://www.youtube.com/watch?v=yOiABZM7wTU (Just after 8 min)

  20. So, does the weak interaction interact ONLY between a neutron & a neutrino?
    Or between ANY two particles consisting of quarks?

  21. Elementary Particles like quarks, leptons, antiquarks, and antileptons are they inside Proton OR Nucleus? Anyone?

  22. How long does the process of a carbon atom decaying take? Does it have to sit around for a while or does it change as soon as it interacts with a neutrino?

  23. Brother,,,I just wanted to compare all fundamental four forces,, i am 12th grade student,,,my question is straight…Mathematical representation of weak and strong nuclear force

  24. It all sounds like crap to me.
    I'm not convinced that there are any such beasts as protons and neutrons –
    they are just mixtures of quarks – whatever they are.
    So the nucleus of an atom is a mixture of quarks & by the principles of quantum physics they
    can be in more than one location at the same time.
    Therefore – you can't say that – " there's a proton and there's a neutron."

  25. a force for really small things (Weak)
    a force for a small things (Strong)
    a force for big things (EletroMag)
    a force for really big things (Gravity)

  26. I don't get one thing… It wasn't mentioned in the video but it still has to do with this topic. More specifically, I don't understand why there is a electron anti-neutrino in beta decay. In the equation it makes sense because we need an anti-lepton to make the equation correct but I don't get where its coming from. Is it another part of the electron neutrino which gets 'emitted'? Or anything else?

  27. That was "the best" explanation of the "weak force" I have ever heard. But it leaves a question.
    Is it appropriate to call it a force? For example, does it, applied over time, create a change in momentum? Or should it be called an interaction, but not a "force"?

  28. It's very easy to understand why electromagnetic force and gravity are inversely proportional to the distance squared. There is also the London dispersion force, which is inversely proportional to the sixth power of the distance due to being based on fluctuations in charge distribution. I always wondered why the weak interaction has such a short range. Is it due to the short life of the W and Z bosons?

  29. Standard model is wrong because there is no association between quarks and leptons. During beta emission, a neutron within an unstable nucleus will emit out "some"' energetic electrons before it itself turning into a proton. Therefore without any doubt that a neutron has an element of electrons within itself. This clearly shows that standard model is wrong. We  know electrons have very huge kinetic energy that they derived from the dynamic of the universe (e.g. imminent implosion or Big Bang). Do we wonder nucleons also have huge kinetic energy that they derived from the dynamic of the universe too? Yes indeed it is true that nucleons also possess huge kinetic energy where they balance themselves out while they are arranging within a unique nucleus structure that help squeeze them against their repulsive forces. During proton emission or neutron emission, the emitted nucleon also possesses huge kinetic energy in some range of MeV. This clearly shows that it is the strong kinetic energy of those nucleons that manage to squeeze those nucleons together within the nucleus. Why the existence of radioisotopes? The continuous expansion of the universe will cause nucleons to transform more and more of their kinetic energy to the universal gravitational potential energy in parallel to the expansion of the universe in which this will eventually causes continuous weakening to angular momentum of the nucleons where they started to fail  in overcoming their repulsive forces among themselves that they eventually transform to become radioisotopes. If you are interested in real discoveries, I would recommend you to read my book, The Unification Theory – Volume One and you will be amazed with lots of new, interesting discoveries. In God I trust.

  30. Since strong nuclear force is short range then why tritium with truly small nucleus of several femtometres is radioactive in nature? It is not true the existence of strong nuclear force would keep the nucleus of a stable element cohesive together. Electrons possess huge kinetic energy that they derived from dynamic of the universe, especially the imminent implison. Likewise, nucleons also possess huge kinetic energy that they kept in the form of angular momentum that manage to squeeze those nucleons together within a stable nucleus. By right tritium should be stable element but due to its unique mosaic of elastic magnetic field and electric field that it fails to top up sufficient stationary photons onto its nucleons during the imminent implosion to resist strong repulsive forces of its single proton and two neutrons. Again this very example shows that neutrons are not completely neutral at all. Otherwise tritium should be stable element of hydrogen.If you are interested in real discoveries, I would recommend you to read my book, The Unification Theory – Volume One and you will be amazed with lots of new, interesting discoveries. In God I trust.

  31. I have a whole other design for how the atom works. I would love to know how much of the atom they can actually see or detect. I think its obvious that this Idea of Bosons attracting is false. They would have no sense where something else was to attract to it. There is a illusion we have and it causes us to assume an attraction where nothing is actually aware of anything else and there is no force between them. So particles could not provide attraction.

  32. Force (physics) does not exist physically in the same way that an object with mass, thus making it “not” the initial cause of pushing, pulling, shaping objects, motion, work or being a Vector Quantity (Magnitude + Direction).

    In physics, the word, “Force” as we know it, turns out to be nothing more than an expression to express an idea, like one would use the word “Love” to express one's feelings. But, physics and in mathematics, still use “Force” as thou it were something physical that could enable the initial cause of motion making it counterintuitive.

    Example: Without applying the Energy from within you, choose an object of your choices to push and pull by simply applying “only” the Force or Net Force.

    Meaning that Energy (applied energy) is the origin of motion and not “Force”. Once Energy (E) is applied, it creates what is known as Momentum (p). When this Momentum (object in motion) comes in contact with another object(s), it makes a surface contact that will enable you to push and pull. Example: Ep=ma, Ep=mv and so on. Note: Ep is not to be confused as Kinetic Energy in any way.

    Momentum represents things like work, wave, gravity, light, lightning, tsunami, earthquake, current, electricity, motion, magnetism, etc.

    Without Energy, there is no Momentum. Without Momentum, there is no surface contact on an object(s) to push, pull, work, shaping objects, motion, etc. Momentum does not and cannot exist without the applied Energy that creates it. Energy and Momentum or “Ep” is the one and only common denominator that links all fundamental forces of nature. Without Ep, all fundamental forces of nature would be inert and non-existence.

    Energy is energy, but it’s when Energy (E) is being applied that creates the Momentum (p) making it the initial cause of motion. Example: Ep.

    By applying the right amount of Energy, nothing is immovable or unstoppable. ~ Guadalupe Guerra

  33. I wonder if the weak force is actually related to some type of electromagnetism decay and gravity is related to the strong force . A miniaturized version of each other seamlessly unaware of the other but entangled with each other none the less.

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