The Weak Nuclear Force: Quantum Chameleon


Of the four known forces, one of them stands
out as having some unique properties. I’ve spoken in another video about the manner
in which the weak force only interacts with particles of a certain spin configuration
and antiparticles with the opposite spin configuration. But in this video, I want to talk about the
manner in which particles decay via the weak force. Now there is an extensive history of how this
has been observed that long predates our current understanding of the universe, but I will
explain the phenomenon strictly in terms of the Standard Model. So I made another video that introduces the
Standard Model, but let me remind you that there are three forces that are understood
in the quantum world. They are the strong nuclear force, the weak nuclear force and
electromagnetism. Each force is transmitted by one or more particles
called bosons. For the strong nuclear force, this particle is the gluon. For the weak nuclear
force, they are the W & Z bosons; and for electromagnetism, it is the photon. So let’s see what happens when a particle
emits another particle governed by the rules of each of these forces. So what would happen if a particle, say a
top quark, emitted a photon? Well, as we can see in this diagram, you start with a top
quark, it emits a photon and continues along as a top quark. The particle doesn’t change
its identity during the emission. Now if you are a physics minded individual,
you will probably be wondering about energy and momentum conservation in that interaction.
This requires that the top quark before the emission to have a mass that differs a little
from the number you can find in text books. This is one of those things that is allowed
under the laws of quantum mechanics and you’ll have to trust me on this. If you want to explore
this on your own, google the term “virtual particles.” Now getting back to the decay, I want to redirect
your attention to the fact that before and after the electromagnetic interaction, the
particle is the same. Now let’s look at what happens during a
strong force interaction. The same top quark might emit a gluon and would continue on as
a top quark. Because the gluon carries color, which is what physicists call the strong force
charge, the top quark will change its color, say from red to blue. And if you want to learn
more about those details, my videos on quantum color and the strong nuclear force will be
helpful. However, the key point here is that the particle
before and after the gluon emission is the same particle. But let’s see what happens when a particle
emission occurs that is governed by the weak force. There are two particles that transmit
the weak force: the W and the Z bosons. So let’s see what happens for the Z boson. When a top quark emits a Z boson, it stays
a top quark. Basically, it’s a lot like the electromagnetic emission of a photon.
Nothing weird there. But when the top quark emits a W particle,
something very different happens. Before the emission, we have a top quark and after the
emission, we see a bottom quark and a W boson. The weak force has changed the identity- what
physicists call the flavor- of the particle. This behavior is unique to the weak force.
And we call this phenomenon “flavor changing.” While this property is unique to the weak
force, it is not unique to the top quark. A bottom quark can emit a W boson and make
a charm quark; and a charm quark can emit a W boson and make a strange quark or a down
quark. On the lepton side, a tau lepton can emit
a W boson and make a tau neutrino. And a muon decays by emitting a W boson and making a
muon neutrino. There are many ways in which quarks and leptons
can change their flavor. And it only happens when the weak force is involved and only when
a W boson is emitted. So that last statement is interesting. Why
is it the only flavor changing weak interaction is the one with the W boson? Why is there
not one with the Z boson? Well let’s explore what that would look like. So the Z boson has zero electrical charge,
so that means when it’s emitted that the emitting particle can’t change its charge. The top, charm and up quarks all have the
same electric charge, specifically +2/3 that of a proton, while the bottom, strange, and
down quarks all have the same charge as well, this time with a charge of -1/3 that of a
proton. The three leptons, the tauon, the muon and the electron all have a charge of
-1. I already said that the interaction in which
the top quark emits a Z boson and stays a top quark is OK. And this is true for all
of the other particles as well. But what about a case like having a top quark emit a Z boson
and become a charm quark? That seems like it would be possible. But is it? Scientists have a name for this- they call
it a flavor changing neutral current, or FCNC for short. Flavor changing comes from the
fact that the particle identity is changed and neutral because the particle charge is
unchanged. So have FCNCs been observed? No. And that
was pretty mystifying until 1970 when Sheldon Glashow, John Illiopolous and Luciano Maini
were able to show that flavor changing neutral currents were forbidden if quarks came in
matched pairs, one with a charge of +2/3 and the other with a charge of -1/3. That’s
why scientists were pretty sure that the charm quark existed before it was discovered in
1974 and that the top quark existed before its discovery in 1995. Since flavor changing neutral currents are
essentially impossible in the Standard Model, there is a cottage industry looking for them.
If they are observed, that is a surefire signature that something new has been discovered. Unfortunately,
so far, no luck. But the flavor changing properties of the
weak nuclear force are very interesting and are probably telling us something profound
about the universe. The question, of course, is just what is that message? I don’t know
and, well, neither does anyone else at this point. It’s just one more mystery that needs
some bright young mind to solve. So what about it? Are you up for a challenge?

86 thoughts on “The Weak Nuclear Force: Quantum Chameleon

  1. I still think space is moving and relativity influences that, resulting in empty space (slow moving) and (apparent) solid particles (fast moving).
    The movement is some sort of spin, resulting in patterns/structure forming with properties we observe. gravity magnetism.

  2. AT 6:09, these pictures seem to have a lot of information within them, do they repeat exactly in detail and when a v.p. changes might it also retain its information before said change along with its new description?

  3. Are people trained to become almost audibly imperceptible when they are in a position to educate? Sure, the first half of the spoken sentence is accentuated, but the second half tapers into a mumble that makes learning and staying focused hard.

  4. Because so little is being told about Z-Bosons, I tried to do a bit of online research to find out if there are any important reactions with them. The only one I think I can think of is in supernovae where neutrinos help to jumpstart the explosion. Can anybody confirm this (that these are indeed Z-Boson interactions) or tell of other important Z-Boson reactions?

  5. It might be helpful to explain charge conservation by stating that the W boson has a charge. Most people might already know this or infer it from the video, but I had to quickly google it. Hopefully I didn't miss you explaining it in the video. Thanks for making this content!

  6. Wait; the exception made for W bosons exists for what reason? — and I am attempting to appreciate the charge. Almost certainly unwisely, I make habit of incorporating the pauli exclusion principle and how it relates to spin, into anything new learnt of physics, this despite an admittedly tenuous grasp.

  7. [01:01] plus, technically, also the pion for the "residual strong force" e.g. proton collisions;
    [02:59] emission of a Z⁰-particle is curious as the Z⁰ is the third-option in electron-positron collision {γ-ray pair, ν anti-pair, Z⁰ single (assuming reversibility of Z⁰ decay→e⁻+e⁺)};
    [03:09] emission of W⁺/W⁻ looks curious too—Do t-particles cycle t→b→c→{s/d}→…

  8. It feels good when you finally get to learn something new about quantum physics.
    The weak force is so wonderfully weird.

  9. At the end, you state that quarks come in matched pairs and that FCNC is forbidden (5:40). How come a bottom quark can change to a charm quark then (3:40)? Is it allowed for a quark to change into another quark that it is not in matched pair with? How come FCNC isn't possible then?

  10. neutral particles are just balanced electrical charged particles with no dominant charge to measure the other particles that are positive or negative are unbalanced charged , with a dominant charge you measure and a minor opposite charge you can not measure in the particle with your instruments , .666 is the positive quantum mass 1.0 is the negative quantum mass so a neutral particle is a combination of this 3 positive and 2 negative equal a balanced charge in its construction of quantum mass particles of a neutral charges

  11. thats why these quantum particles have particle to emit these smaller sub quantum particles can be magnetically bound to orbit these quantum constructions like an atom

  12. two questions only:
    how did you invent all this nonsense ?
    Who (fool) pay to you for these unreal fabrications/fantasies ?
    :)))

  13. Talking about fundamental force, what would be required to prove or disprove the existence of Graviton particles?

  14. I truly believe that the weak nuclear force should be called the strong. it was mankind's first real intuition of antimatter.

  15. Given that Z0 and W+/W- appear to have somewhat different properties, should there be two weak forces, not one?

  16. I don't have physics classes anymore, and even then these topics weren't covered, but dr Don, you have a special spot in my heart!

  17. question: can the double slit experiment be performed in a cloud chamber with the particles that form the trails? if the cloud chamber is off is there interference?

  18. Googled virtual particles. Now I have stripping leptons on my desktop and I'm pretty sure it's a virus. Thanks anyways.

  19. Dear Sir:
    I believe you made a video mentioning the odd fact that there in no antimatter around.
    Here is a factoid I have not heard mentioned:
    Why are there the same number of electrons and protons?

    Brainstorming, based on no actual knowledge…

    Are there the same number of these 2 charged particles?
    Is there any evidence that matter we see doesn't have a net charge?
    Would galaxies look different if they had a non-zero charge?

    If all particles originated early in time, from a much more energetic environment, and we expect the same number of electrons and anti-electrons, them perhaps there WERE equal numbers. Perhaps they later found one-another and annihilated one-another.
    Perhaps the electrons we see came from some other process, which resulted in an equal number of positive and negative particles, although not of identical types.

    Or perhaps antimatter was important in the formation of protons, (and internal charged quarks). So they were consumed while producing an equal number of protons and electrons.

    I hope there is at least an interesting question in my blathering.
    Why is there a proton for every electron?

  20. Why is a color change considered the "same" particle with a different color, but a flavor change considered an entirely different particle, instead of "the same particle with a different flavor"? Are flavor and color fundamentally different or is that just convention?

  21. So where does the energy needed to make a photon come from if the particle does not change? :/

  22. One of my persistent problems along these lines is this:
    In the first example with the top-quark decay, if the top quark has any finite mass it will be traveling at less than the speed of light; therefore is has a rest frame. So I place myself in that frame. Now I see the top quark spontaneously emit a photon and then travel away. But the top quark hasn't changed, it still has the same characteristics. So apparently energy has been created from nothing. Dr. Lincon says to ignore this? I find it hard to do that. Does the top quark has excited and unexcited states?
    Does the top quark just go on through life, admittedly a short one, emitting a continuous series of photon's and changing direction and speed?

  23. I was already planning on going into particle physics but now I have a goal

    Study the weak nuclear force and name an interaction flavour blasting

  24. Thanks Dr. Don for your teaching style (Humility) which allows mere mortals to glimpse His mind. When any subject is studied at the limits of our knowledge, our choice is always humility or frustration, working out the puzzle of apparent contradictions. Thanks for your all your Videos.

  25. Guessing isn't the way to do science, so I'm not going to say it's 3 combinations of 3 states conforming to the wave-particle shape of quanta, (every identity looks like either a neutron or Hydrogen atom bound in some combination of structures), pivoted on harmonics, am I? Not when there are millions of physics students who have the qualifications to elaborate the detail.

  26. Even though I'm a mathematician, I love the qualitative explanations. I've seen some good videos on how magnetism is a relativistic force and essentially the same thing as the electric force. Is it possible to explain the unification with the weak force in such a qualitative way? I would love to "understand" how that works.

  27. I can SORT OF follow all the quantum physics stuff, but, there comes a point where it just sounds like people chanting "HASTUR HASTUR HASTUR"
    Like… I'm SURE there's a reason, I just feel like bits are missing, and those bits are incredibly complicated quantum mechanics. (And before you ask, I had to take quantum mechanics in my course work for electrical engineering. Still baffling.)

  28. what causes weak interaction to change quark flavor in radioactive nuclei, and why it is not happening in non radioactive nuclei.

  29. Is there a place we can go to find a list of these lectures in chronological order so that we can follow these in a chronological order?  Thanks.

  30. but… don't the quarks have different masses? what about energy conservation? and how can a top quark be discovered individually, while it has a color charge?

  31. These Fermilab videos are great, and very much appreciated. But hearing "zee" for z (zed) takes some getting used to. So it goes.

  32. The beginning of the answers to all of this begins in chapter 24: https://instantiationoflife.wordpress.com/
    But leave your 'dismissisism' at the door, because relative time was very dismissable in 1905 as well.

  33. are there any other physics newbies that love watching these videos? I'm not even in undergrad yet (I start in the fall) but I love trying to learn more about the universe

  34. Why can't a bright "old" mind be challenged to solve the flavor-change problem? Actually, I'm one of those old ones, but I don't have the math background plus I'm too busy dealing with more mundane stuff. Maybe I'll have my descendant, AI, work on it.

  35. Flavor changing property of weak interactions is indeed interesting and probably have to do something with the fundamental property of the quantum field that produce virtual particles.

  36. Flavor changing, top, bottom, charm, strange color … what the hells wrong with you people? What's next, smell? I can see it now. The colon particle emits the smell virtual particle and becomes the offended boson …

  37. Standard model is wrong as there is no association between quarks and leptons. During beta emission, a neutron within an unstable nucleus emitted out "some" energetic electrons before it itself transforming to a proton. This implies that a neutron has an element of electrons within itself. This clearly shows that somehow there is an association between nucleons and electrons. Electrons possess huge kinetic energy that they derived from the dynamic of the universe. We reckon that nucleons also possess huge kinetic energy that they derived from the dynamic of the universe. It is the huge kinetic energy of those nucleons that manage to squeeze them together within the nucleus in overcoming their repulsive forces among themselves. We don't need strong nuclear force to help explain how nucleons able to overcome their repulsive forces within a nucleus. Then, why the existence of radioisotopes?The continuous expansion of the universe will cause more and more of angular momentum of nucleons transforming to universal gravitational potential energy in parallel to the expansion of the universe. The weakening of angular momentum of nucleons until a certain point that nucleons are unable to resist the repulsive forces among nucleons themselves that restructuring on the unstable nucleus will inevitable take place.  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.

  38. One of your contemporary physicists on YT, David Butler, referred to electrons as a standing wave, rather than orbiting the nucleus. How would an electron shell hold position as a standing wave in a spherical form? Would all free electrons exhibit this behavior if stripped from their nuclei in a larger volume of matter?

  39. I imagine the scientist creating those names: "You know what? Since I'm the first, I will name this property the 'flavor of the quarq' and everybody after me will have to repeat this in public, this will be great!".

  40. 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, hurricane, 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

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