What “The God Particle” Hath Wrought

You’ve doubtless heard the joke: We can’t call the Higgs boson the “God Particle” any more, because now we have tangible evidence that it exists.

But the label “God Particle,” attached to the poor unsuspecting Higgs boson by Leon Lederman and Dick Teresi, continues to wreak havoc on physicists’ attempts to clearly explain what is going on. Last week’s announcements from CERN that the new particle discovered last July is looking more and more like the Higgs predicted by the Standard Model generated stories like this one, from CBS news:

The Higgs boson is often called “the God particle” because it’s said to be what caused the “Big Bang” that created our universe many years ago. The nickname caught on so quickly (even though scientists and clergy alike do not care for it) partly because it’s a great explanation of what it’s supposed to do — the Higgs boson is what joins everything and gives it matter.

That might be the worst paragraph I’ve ever read about the Higgs boson, and I’ve read quite a few. (H/t Faye Flam.) Originally I thought the journalist was just making things up, but it turns out that it’s Michio Kaku’s fault. (H/t Matt Strassler on Facebook.) There is a video linked to the article, in which Kaku says that the Higgs helped cause the Big Bang, and that’s why it’s called the God Particle. Another example where it would have been tempting to rag on sloppy popular journalism, where actually it’s a supposed scientist who is largely to blame. (Although the above paragraph is also wrong about things it should be easy to get right.)

For the record, the Higgs had nothing whatsoever to do with causing the Big Bang. (Kaku tries to link it to inflation, but they’re not related.) It also doesn’t “join everything,” whatever that means. It does give mass to elementary particles like electrons and quarks, which isn’t the same as giving “matter” (since that kind of doesn’t make any sense), and besides which it doesn’t give mass to protons and neutrons and therefore most of the mass in ordinary objects.

The “God Particle” label, despite being very catchy and therefore leading to more publicity than most elementary particles manage to muster, has done more harm than good for the public understanding of science. Non-experts, hearing that physicists have named something after God, might actually think they were being serious. Imagine that.

[Update: Matt Strassler adds his take.]

It’s not going away any time soon. Leon Lederman and Chris Hill have a sequel to the original book coming out, Beyond the God Particle, due later this year. I’m sure the book will be great at explaining the physics, and I’m equally sure the title will generate a lot more confusion. Get your disclaimers ready!

  1. Would you explain what it means to say that the Higgs gives mass to elementary particles like electrons and quarks but not to protons and neutrons. What mass do protons and neutrons have that aren’t due to the mass of quarks?

    Thanks.

  2. You guys know that I did write a book about this, right? :)

    The proton gets mass from the strong nuclear force — the gluons holding the quarks together, not from the quarks themselves. Adding up the mass of the quarks inside a proton would get you only about one percent of the proton mass.

    Admittedly, it’s a very tricky thing. One quark by itself would have so many gluons around it that it would have infinite mass. That’s one way of saying that quarks are “confined,” we don’t see them by themselves. Bringing three quarks together in the right way lowers the total mass from infinity to the actual mass we see; but that mass is still much larger than the masses of the individual quarks in an imaginary world where there weren’t any gluons at all.

  3. I can understand Leon Lederman passing the blame once to his publishers for the title. But twice?. He’s just as guilty for “god particle” mess as any publisher is.

    rey

  4. Sean! you are missing a golden teaching moment here…

    The reason a proton has mass is utterly fantastic: the quarks that make it up, bound together by the gluonic forces that won’t let them out, nevertheless have such a high velocity that they acquire mass via relativity. We all know E = mc^2, but that’s not quite right: it’s E = gamma mc^2 where gamma is a measure of how relativistic a particle is because it’s moving so close to the speed of light.

    That’s right: every proton (and neutron) in the atoms of your body has the mass that it does because the quarks inside it are whirling around at relativistic speeds. It’s really mind blowing…

  5. So, Higgs gives elementary particles mass and thereby inertia. The Higgs does not give gluons its mass.

    So, where do the gluons get their mass from, and do they have inertia? I’m confused.

  6. John, I don’t think that’s really true and/or helpful. It is true that the quarks move rapidly, at least to the extent that “the velocity of a quark inside a proton” can be defined. But it’s not where most of the proton mass ultimately comes from. (If it were, neutrons would naively be much heavier than protons, since the down quark is heavier than the up.)

    The truth, alas, is messy (as you know, probably better than I do). There’s a lot going on inside the proton — many more virtual quarks and gluons than the three valence quarks. I think it’s best to be accurate if not completely precise, and attribute the proton mass at the end of the day to the residual energy of the strong force (which technically includes both the gluons and the virtual quarks).

  7. “If it were, neutrons would naively be much heavier than protons, since the down quark is heavier than the up.”

    Would it be almost correct, though, to say that the mass is due to the kinetic energy of the quarks, and the quarks get their kinetic energy from being pulled in so tight by the strong force, just like meteors get their kinetic energy from being pulled in by gravity? The down quark is heavier than the up, but it wouldn’t move as fast when acted on by the strong force because the strong force is not proportional to mass.

  8. Bo,

    Gluons are massless, like the photon. Furthermore, “inertia” is only a descriptive idea, not a proper physical quantity, so you are better off without ever referring to it. :-) Rather, talk just about mass (i.e. the “rest-mass”) and energy, without introducing “inertia”. Gluons have energy (kinetic and potential) and have zero mass. Quarks also have energy (kinetic and potential) and acquire some small nonzero mass, due to the interaction with the Higgs.

    When you make up a proton or a neutron, its total mass is determined by its total energy and the equation E=mc^2. And the total energy of a proton is a sum of the rest-energies of three quarks (i.e. the Higgs-generated masses), kinetic energies of quarks and all gluons inside, and potential energies of quark-gluon and gluon-gluon interactions. When you sum up all those energies, you get a result that is very different from the sum of just the three quark masses, since the potential energy of the strong interaction is… well… strong. :-)

    The problem here is that the total energy is actually negative, since the proton is a bound state. And then something called “renormalization” steps in, all hell breaks loose, and after the dust settles, you should end up with a total energy that is positive, and in addition much bigger than the initial masses of the three quarks. That should provide for the total mass of the proton.

    I am saying “should” here, because nobody has actually managed to perform that calculation, not even numerically (despite some valiant attempts). We don’t know how to calculate QCD-anything in the infrared regime. People have managed to calculate the “mass renormalization” (as it is called) in some much simpler toy-example models, and this suggests that something similar is probably happening also in full QCD. But there is no proof yet. One of the Millenium prizes is still waiting for someone to at least prove that a solution exists. 😉

    HTH, :-)
    Marko

  9. Wasn’t it supposed to be called the “goddamn” particle because it was so damn hard to find? That made a lot more sense than the alternative…

  10. No, I’m not dismissing that work — I noted that there are some valiant attempts. But the issue is that in all calculations of proton mass that I have seen so far (though I probably haven’t seen them all), the only thing that is being calculated is the ratio of the proton mass and some other hadron mass, the latter being taken as experimental input. While a 2% accuracy is a great achievement, it still falls short of an “ab initio” prediction of the proton mass — calculated from nothing else but Standard Model coupling constants and the Higgs mass.

    As soon as your input contains some experimentally determined hadron mass, you are taking a shortcut and effectively cheating the ab initio calculation. Even those shortcut calculations are formidable (and deserve every respect!), so I doubt that a true ab initio calculation will be possible in the forseeable future. But people should keep trying. :-)

    Best, :-)
    Marko

  11. Sean – I am a little puzzled at your criticism of John Conway’s comment. The mass of the proton is a complicated combination of things, but certainly a major component is indeed the kinetic energies of the relativistic quarks, gluons and anti-quarks inside. Of course there is also binding energy and that is equally important. But when you say “it’s not where most of the proton mass ultimately comes from”, I don’t follow your logic. I would say it’s certainly a substantial contribution.

    I am also puzzled by your remark that the neutron would end up much heavier than the proton if John were right. I don’t see why. The difference between the proton and neutron involves the exchange of a single up quark for a single down quark, a tiny fraction of all the particles inside. For two relativistic particles with large energy E and different small masses m_1 and m_2, the difference in their energies is (m_1-m_2)^2/2E, a small number, not a large one. Meanwhile, to show that the difference between the neutron and proton mass is pretty much the difference between the down and up quark masses (with a bit given back because of the proton’s charge) doesn’t require any assumptions about the internal dynamics of the proton or neutron; it mostly follows from symmetry-breaking considerations. So you can’t determine anything about the internal dynamics of protons and neutrons from the neutron-proton mass difference.

    Anyway, while John’s remark could be refined somewhat, I don’t think it’s as fundamentally misleading or wrong as you suggested.

  12. Marko – your statement “The problem here is that the total energy is actually negative, since the proton is a bound state” regarding the proton mass isn’t right. The energy between quarks does not go to zero at infinite distance (since quarks are confined) and so the binding energy is not negative. Consider as a toy model (not the real thing by any means) two particles bound by a potential V(r) = -e^2/r + C r. The bound states do not all have negative binding energy, and indeed if C is large compared to e^2 they may all have positive binding energy.

  13. Matt,

    Yes, you’re right, my fingers were faster than my brain, sorry… :-) What I wanted to say was that quarks do not have enough kinetic energy to get out of the potential well. And since the well is infinitely tall (as your toy example illustrates), they are always confined to a bound state.

    But the main point of my post was that the calculation of the proton mass straight from the SM parameters is still not there, and that this is a hard problem.

    Best, :-)
    Marko

  14. Has the quark-mass-through-Higgs idea been firmly established (as firmly as things can be in QFT)? I understand that mass mechanism was initially proposed to explain the electroweak interaction alone.

  15. I hereby propose that the Higgs Boson henceforth be known as the “Grand OlD Particle”, the G.O.D. Particle.

  16. Matt Strassler said: “The mass of the proton is a complicated combination of things, but certainly a major component is indeed the kinetic energies of the relativistic quarks, gluons and anti-quarks inside.”

    Eh? Haven’t we been trying to kill the concept of “relativistic mass” for decades now? The mass of a system of particles is not usually the sum of the masses of the particles, but that is *not* because “kinetic energy contributes to the mass”!

  17. I tried to figure out what he might be thinking to justify to himself what he said. My guess is that a few times he said the Higgs “belongs to a family of particles” and at the end he mentioned the inflaton. So maybe he was thinking, “scalar field” and then justified equating the Higgs and the inflaton since they are both scalar fields. My guess is that is how he would reply if pressed.

  18. FYI, I posted a comment on the CBS article linking to this and Matt’s blog post.

    – Kyle Carnmer :-)

  19. My understanding from past conversations with lattice gauge QCD theory types was that the majority of the nucleon mass can be ascribed to the quark kinetic energies. I’ll have to ask one again sometime soon…fun discussion! :)

  20. The concept of relativistic mass is indeed a very bad idea, but that is not what Matt was talking about. The kinetic energy of constituent particles is not the same thing as relativistic mass.

    HTH, :-)
    Marko

  21. Wasn’t the higgs field responsible for causing infation? I mean, didn’t the higgs (in guise as the infalton field) cause inflation to occur?

  22. Why does Kaku always present that science that actually isn’t? If it’s not misleading about what is known now, it’s complete speculation about what might be possible in the future. Unfortunately because he has an engaging and enthusiastic manner, and his pronouncements are always exciting sounding, he gets lots of exposure.

    I’m sure he is a brilliant physicist, but he’s not a helpful science communicator.

  23. Someone on a non-science forum I frequent posted the other day about the Higgs that it was called the God particle for two reasons: It caused the big bang (maybe they got that from the CBS article) and it is not a particle but a “kind of energy/form”. As a theist they were very excited by the news that the particle found was confirmed as the Higgs. I presented the facts about particles, fields, and the Higgs, with reference to your talk at the Ri, Sean. It’s online now so I embedded it. I hope she watched it, and maybe some other people did too.

  24. I have a comment and a technical question. I think Kaku’s hype (white lie!) is not bad. It generates excitement. Remember the answer to congressman’s question “Will the machine help us in understanding God?The answer “no” killed the supercollider. Yes would not have been bad in the sense that we will understand God’s creation better.
    Anyway, the question is: In the Lagrangian derivation of spontaneous breaking of symmetry, you change the sign of (mass)2.This seems to me an uncomfortable mathematical jugglery! Admittedly after getting a new lower vacuum, all the (mass)2
    are positive. Is there any physical understanding of what you are doing. Is there a better derivation which does not do this trick? Thanks. Only recently I became aware of your blog. I plan to read it regularly.

  25. Hadron masses are currently required as input into lattice QCD calculations because the SM of particle physics does not predict the quark masses – they are parameters. Further, the overall scale of the strong interactions must be determined. Once these few parameters are fixed, then everything else is a prediction with fully quantifiable uncertainties. Currently, there is no algorithm to perform Lattice calculations of chiral gauge theories and so calculations directly from the SM are presently not possible. The current calculations of the hadron masses are impressive, but more computational resources are required to reduce further the uncertainties in these quantities, and to calculate more complex strongly interaction systems such as nuclei. The mass difference between the proton and the neutron has been calculated with Lattice QCD, including the contribution from the up-down quark mass difference and from electromagnetism.

  26. I used to be annoyed at the “God Particle” name. Then someone pointed out to me that it is the reason Catholics have mass, after all.

  27. I propose a physics face off. Live on Science channel. Uniform is various joint braces and plaid suits.

  28. face off between Kaku and Carroll that is. Moderated by Neil Tyson.

    I think Kaku assumes that certain things are true which have not been proven yet; which is why his answers would irritate someone as grounded in “what is known” such as yourself Sean Carroll. We’re talking about a guy who won his $1 million for cosmic string field theory (or something) and has high hopes for SUSY despite recent results.

  29. How does the “Higgs” give (rest) mass to particles ? In a nutshell, we knew how to “give rest mass to particles” simply by including a term in the Lagrangian which contains (mass) times (field)^2. Here, the field is the quantum field of which the particle are the excitations. The problem is that the electroweak interaction has a symmetry which makes us put the fermion fields in two pieces in the lagrangian, the left-handed one and the right-handed one, and both undergo different symmetries. And this messes up our mass term (mass) times (field)^2, because in “field” we need both components (the left-handed and right-handed parts). In other words, if we bluntly put, as we used to do since 100 years or so, a term (mass) times (field)^2 in the lagrangian, the two different symmetries of the left-handed and right-handed parts don’t work out anymore. So we cannot put this mass term anymore in the lagrangian, which would mean that the fermions cannot have rest mass anymore. Shit.
    Now, for actually unrelated reasons, one needed a scalar field called the Higgs field. FIELD, and contrary to most particle fields which are “zero” at rest, this field was postulated to have a finite constant value at rest. You could also excite it, and then it would give particles (Higgs particles), but one didn’t need those particles. What one needed was a field with a finite nonzero value at rest.
    Now, in as much as (mass) x (field)^2 gives you mass, (field1) x (field2)^2 gives you an INTERACTION between particles of type 1 and particles of type 2.
    And now people invented the following trick:
    consider an interaction between the Higgs field, and a fermion field. Then we have (Higgs field) times (field)^2, and at rest, the Higgs field has a finite value. So this LOOKS EXACTLY LIKE A MASS contribution !
    For other fields, interactions don’t produce mass because their rest field value is 0. But the Higgs field is postulated to have a finite value.

    And for reasons that are too complicated to explain here, because the Higgs also transforms under the the left-handed and right-handed weak interaction symmetries, this term (Higgs field) times (field)^2 DOES work out well with these symmetries.

    So in short: the term (Higgs field) times (field)^2:
    – looks like a mass term because of the non-zero value of the Higgs field
    – doesn’t have the problem with left-handed and right-handed symmetries as has a normal mass term. This kind of term is called “Yukawa coupling”.

    So this was proposed as a solution for the problem of not being able to write a normal mass term in the Lagrangian. It’s ugly and contrived, but it works on paper.

    It ALSO implies a genuine interaction between a Higgs PARTICLE and a fermion, but that’s on top of it.

    The rather mind-blowing fact is that this ugly trick on paper seems to correspond perfectly with what is observed at colliders for more than 40 years!

    So you can tell a lot of mystical mumbo-jumbo of “giving mass” and so on, but at the heart of it was a mathematical proposition of a solution because the standard way of introducing mass, namely writing a term (mass) x (field)^2, was forbidden because of a chiral symmetry problem, and the trick was by replacing the constant “mass” by a field which had a non-zero value (for other reasons).

    And again, it is the FIELD which gives (rest) mass to fermions, even without Higgs particles. The Higgs particles are nothing else but excitations of this field (just as electrons are excitations of the electron field, and photons are excitations of the electromagnetic field). But in quantum field theory, every field needs to have its associated particles. So if the Higgs field exists, one needed to find the particles that correspond to it. That seems to be done now.

  30. Hi Sean, my own feeble response is to use ‘god particle’ with a small g.I found non-physics colleagues kept referring to my talks on the subject as ‘it’s about the god particle’ , so I eventually gave in (just as we all did with the moniker ‘big bang’). But it’s just laziness, I agree.
    Re news clip, I suspect the journalist simply confused two separate ideas – a) the mass-giving property of the Higgs field and b) the discovery of one particular scalar field, which is only relevant to cosmology in that it gives us confidence that scalar field can exist, as you know! What a glorious conflation – but actually I’ve seen it before!
    Regards, Cormac

  31. Matt, John, and the other experts here — I still don’t understand how this could be true, although if people who are more expert than me keep saying so I might end up learning something. Is there some calculation (lattice or otherwise) of the mass of the proton that divides the total into contributions from valence quarks/sea quarks/gluons, and shows that the first contribution is dominant? If that’s true, I would be willing to accept the “quark kinetic energy” explanation. If it’s not, then I don’t think it’s a fair translation.

  32. regarding the cause for the mass of the proton, I would claim that John Conway’s and Sean’s explanations are equivalent on the basis of the work-energy theorem: The change in kinetic energy is equal to the work done by the net force acting on it. Since the gluons carry the strong force between the quarks they will give them the kinetic energy they have.
    The virtual quarks are just part of the interaction between the valence quarks.

    I believe this theorem should hold whether you work in classical mechanics or quantum field theory. It becomes more complicated on paper for the latter, but the principle is the same: stuff doesn’t move if not pushed.

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  35. By coincidence, I happened to glance at arXiv:1111.1600 shortly after reading the comments above. That lattice calculation finds (Eq. 48) that only 3–8% of the nucleon mass is attributable to the light and strange quarks, with the (quenched) strange-quark contribution consistent with zero (Eq. 45). If I understand the paper correctly, this result comes after an extrapolation to the physical average up–down quark mass, but without a continuum extrapolation.

  36. Would one of you kind posters enlighten me on a macroscopic quandary? If KE = 1/2mv2, assuming no relativistic effects, velocity with respect to what? The nearest planet? The center of gravity of the universe? That would be neat if the universe had a center.

  37. @David Gentile:

    With respect to your chosen frame of reference. Energy is one of those things, like time and distance, whose measured value varies between different frames of reference.

  38. You mention that Higgs field,

    “it doesn’t give mass to protons and neutrons and therefore most of the mass in ordinary object”

    but

    “It does give mass to elementary particles like electrons and quarks”

    Can massless quarks give proton mass? Can proton exist when quark is massless? Will massless gluon and massless quark create proton/matter?

    terry