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Flip Tanedo | USLHC | USA

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Name these brands/plants? Name these particles!

I don’t know the original source, but there’s an image that has gone semi-viral over the past year which challenges the reader to identify several brand names based on their logos versus plant names based on their leaves. (Here’s a version at Adbusters.) The point is to contrast consumerism to the outdoors-y/science-y education that kids would get if they just played outside.

This isn’t the place to discuss consumerism, but I don’t agree with idea that the ability to identify plant names carries any actual educational value. Here’s my revision to the image:

Adapted from the original “Name these brands/plants” image (original source unknown).

On the right we’ve encoded all of the particles in the Standard Model in a notation based on representation theory. In fact, this is almost all of the information you need to know to write down all of the Feynman rules in the Standard Model (more on this below).

Tables that the one above are a compact way to describe the particle content of a model because the information in the table specifies all of the properties of each particle. And that’s the point: whether we name a particle the “truth quark” or the “top quark” doesn’t matter—what matters is the physics behind these names, and that’s captured succinctly in the table. Science isn’t about classification, it’s about understanding. I leave you with this quote from Feynman (which you can watch in his own words here):

You can know the name of a bird in all the languages of the world, but when you’re finished, you’ll know absolutely nothing whatever about the bird… So let’s look at the bird and see what it’s doing — that’s what counts. I learned very early the difference between knowing the name of something and knowing something.

 

Addendum: naming those particles

For those who want to know, the particles in the table are, from top down:

  1. The left-handed quark doublet, containing the left-handed up quark and left-handed down quark
  2. The anti-right-handed-up quark
  3. The anti-right-handed-down quark
  4. The left-handed lepton doublet, containing the left-handed electron and left-handed neutrino
  5. The anti-right-handed electron (a.k.a the right-handed positron)
  6. The anti-right-handed neutrino
  7. The Standard Model Higgs

SU(3), SU(2), and U(1) refer to the strong force, weak force, and hypercharge. Upon electroweak symmetry breaking, the weak force and hypercharge combine into electromagnetism and the heavy W and Z bosons. Here’s how to read the funny notation:

  1. Under SU(3): particles with a box come in three colors (red, green, blue). Particles with a barred box come in three anti-colors (anti-red, anti-green, anti-blue). Particles with a ‘1’ are not colored.
  2. Under SU(2): particles with a box have two components, an upper and a lower component. That is to say, a box means that there are actually two particles being represented. More on this below. Particles with a ‘1’ do not carry weak charge and do not talk to the W boson.
  3. Under U(1): this is the “hypercharge” of the particle.
  4. The electric charge of a particle is given by adding to the hypercharge +1/2 if it’s the upper component of an SU(2) box, -1/2 if it’s the lower component of an SU(2) box, or 0 if it is not an SU(2) box (just ‘1’).

As a consistency check, you can convince yourself that both the left- and right-handed neutrinos carry zero electric charge. Note, also, the fact that we’ve written out left-handed and right-handed particles differently. This is a reflection of the fact that the Standard Model is a chiral theory.

Finally, I said above that the table of particles almost specifies the structure of the Standard Model completely, the additional pieces of information required are:

  1. Which of the above particles are fermions and which are scalars (the gauge bosons are implied)
  2. Write down the most general ‘renormalizable’ theory (we write only the simplest interaction vertices)
  3. Specify the pattern of electroweak symmetry breaking (the Higgs)
  4. Specify the flavor symmetries (three of each type of matter  particle)

From this one can write the complete mathematical expressions for the Standard Model. One then just has to fill in the observed numerical values to be able to calculate concrete predictions for actual processes.

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12 Responses to “Name these brands/plants? Name these particles!”

  1. Filip says:

    Great post, I always admired Feynman and the story about the bird was really revealing when I heard it for the first time.
    An excellent example with ‘name that particle’.

  2. A corporate logo only carries a very small amount of information, and so even crude representations convey the correct message. However, the plant images as presented are so crudely done, so generalized that they do not carry enough information for even an expert in plant ID to do anything more than guess at the genus (e.g. maybe a maple). So an accurately illustrated leaf carries way more infomation if you have the experience to perceive it, and that means we have way more knowledge conveyed than just a name. To a botanist, top quark is nothing but a name, so all this example tells you is what subject Feynman studied.

    • Flip Tanedo says:

      Hi Phytophyactor—thanks for the comment, and love the username. I disagree slightly on your final point. While I agree that the particle notation may not carry much significance to those who aren’t in the field, I wanted to convey that the information in the notation carried the science and that this is different from a name.

      This is the same point that I think you are getting to: to a trained eye, the leaf of a particular plant can tell you a lot about the plant. I’m not in the field, but I know that the aloe vera plants on my window sill store water in their leaves and are able to live in arid environments. But the name of the plant, “aloe vera” doesn’t mean anything in itself. I could go around saying “this plant is aloe vera!” and not appreciate how this plant evolved to survive in a particular environment, for example.

      At any rate, I think we agree that the science of botany (and particle physics) goes much deeper than being able to recite scientific names, and this was my main point.

      A corporate logo is meant to be easily identifiable with a brand name. A scientific idea, on the other hand, is much richer than its label

      Thanks for the comment!
      Flip

  3. J Perry says:

    I don’t think you should be too hasty about declaring science to be ‘about’ one thing or another. Classification is a necessary part of any scientific endeavour, if you’re going to have even a glimmer of understanding of a diverse world. And it’s not about the names! It’s about being able to make generalisations at the correct level – if everything is just a tree to you, you’re not going to be able to talk about the special properties of the oak. Even the names are necessary, if you want to actually talk about what you know. I always found that particular Feynman story rather strange – it seems to be aimed at people who are just interested in knowing the name of something and are willing to stop there, but I’m not sure I’ve ever met such a person. Even the very act of identifying something requires you to have some knowledge of its properties.

    • Flip Tanedo says:

      Hi JP, thanks for the response.

      You’re absolutely right that names have their own importance—as you explain, having a word for an idea separates signal from background. As you say, otherwise ‘everything is just a tree.’ ((This is why people like to believe that Eskimos have hundreds of words for snow, it ‘makes sense’ that a people who live in such a climate should distinguish between subtle difference in snow and that this should trickle into their language.)) In other words, I agree that [especially in science] the ideas which are given names are important ideas, and further that the scientists who end up learning these names almost always do so because they’re using those ideas.

      But this isn’t always the case. I recently learned about a gene that has a delightfully silly name, the Sonic hedgehog gene. I have no idea what it does nor do I appreciate it’s significance and why it deserves a name, but I can happily answer a pub quiz question about a gene named after a famous video game echinoderm. It would be silly of me to say that “ah, I understand the Sonic hedgehog gene.”

      Another silly example, suppose I can recite the date in which the Mona Lisa were painted. While this is perhaps useful knowledge for Jeopardy, it says very little on its own without some contextual background of what was going on in this time period.

      I think this sort of thing is what Feynman’s anecdote is addressing: he wants to impress upon people that there’s more to appreciating an idea than being able to recite the superficial factoids around it. I don’t think he was talking to scientists when he said this—but rather the general public, who does not necessarily spend their time thinking about their work in the same way that scientists think about theirs. People can grow up watching Jeopardy (or your favorite trivia game in the UK) and think they’re ‘learning’ by memorizing trivia answers, but this sort of knowledge is empty without the context which you write about. And I think Feynman’s purpose was to grab these people by the shoulders a bit and say, “hey, there’s a lot more out there to appreciate than just the superficial information.”

  4. terryp says:

    Where does the identity/box/box-bar notation come from? It’s not something I’ve seen before (e.g. Griffiths, Peskin & Schroeder, Aitchison & Hey).

    • Flip Tanedo says:

      Hi Terry, the boxes are called Young tableaux and can be handy when reducing representations of a group; for example, when determining the possible representations of a composite state built out of particles of a given representation.

      A nice place to learn about these in a physics context is the older book by Cheng and Li, “Gauge theory of elementary particle physics,” chapter 4.3. I believe Terning’s “Modern SUSY” also does a bit with Young tableaux.

      You might also get some mileage by looking at textbooks on representations of Lie groups. The book by Georgi comes to mind, as well as the book by Cahn. I suspect more advanced quantum mechanics textbooks may also have good treatments. -F

  5. Tim MacEachern says:

    Um, since when are there right-handed neutrinos?

    • Flip Tanedo says:

      Hi Tim, right-handed neutrinos are not part of the Standard Model per se, but the experimental observation of neutrino mass directly implies their existence. For a quick way to see this (depending on your background): a non-zero neutrino mass means that an observer can, in principle, zoom past a neutrino so that it appears to rotate in the opposite way, turning a left-handed neutrino into a right-handed neutrino. -F

  6. Ed says:

    in theory, the graviton has spin?

  7. website says:

    What were the answers to the leaves?

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