How is a massive particle (W boson) emitted by the decay of a smaller one (quark)?

In The Particle at the End of the Universe about the hunt for the Higgs boson, it says W bosons are roughly as massive as a zirconium atom. It also says a down quark can emit a W[sup]-[/sup] boson and turn into an up quark. Quarks make up protons and neutrons so they must be smaller than the boson, so where does this mass come from. Is it converted from energy and if so, is it the energy of the quark, or is it from the Higgs field (and this is what they mean when they say the Higgs field gives mass to the W boson)?

I feel like I’m missing a fundamental concept that will make the rest of the book impossible to follow if I don’t get it.

And if you really want to help my understanding, I’m having trouble reconciling the idea that W and Z bosons have mass but don’t take up space.

The W- emitted can be a virtual particle, which basically means that the particle can “borrow” the energy required to make the particle so long as it returns it quickly, either by reabsorbing the particle or having it decay quickly into an electron and anti-neutrino (which combined are less massive than the d quark, so no problem there).

Alternatively you could describe the process as the d quark disturbing the W field in a way that does not create a particle (because it doesn’t have enough energy to), but that allows the energy to “leak” into the electron and neutrino fields.

OK, I’ll have to ponder on that a bit.

Where does the “borrowed” energy come from?

Probably from the quantum vacuum which is often described as a seething field of virtual particles and antiparticle constantly popping into existence, annihilating one another and then returning back to the void.

This vacuum energy is in fact real and is the basis for Hawking radiation and the Casimir effect.

Here’s a thread from a year or so ago on virtual particles.

If it’s any help, OP, my brain is slightly less pea-sized now on that one, thanks to the Dope.

Without the so-called Weak Interaction transmuting protons into neutrons and vice-versa, there would be nothing in the universe more complicated than a hydrogen atom; yet the tentative explanations in this thread so far show that it still remains a bit of a mystery, at least to this non-scientist! I think we need to go back to TroutMan’s original question for some more clarity. “How is a massive particle (W boson) emitted by the decay of a smaller one?” What puzzles me is how physicists have calculated a precise measurement for the W boson that is SO MUCH GREATER than that of the masses of both the initial and final states of the ‘decay’ process. We’re talking about a monster particle nearly 100 times more massive than the proton or neutron, which are roughly the same mass as one another; and the masses of emitted electrons, neutrinos etc are negligible. The Electromagnetic and Strong forces are carried by photons and gluons which are entirely massless, so what’s so weird about the Weak Interaction?

It is not correct to say that the weak force remains a mystery. It is instead correct to say that it’s really tough to explain it in English. The actual mathematical theory which describes the weak (and electromagnetic) force is exquisitely precise, accurate, and well-understood by those working with it.

And if you prefer, instead of saying that virtual particles borrow energy to make up their mass, you can say that they’re allowed to temporarily have the “wrong” mass. So a real W would have a huge mass, but the virtual W involved in beta decay has only a very tiny mass, which is allowed so long as it doesn’t last long.

As someone with a scientific background, this is almost exactly how I would explain the forces. I always assumed that everyone else understood this “weak force” thing better than I did, but I was a bit afraid to admit it.

Here’s an explanation of virtual particles which is just complex enough to give a reasonable idea of what’s going on. It isn’t mathematical, so it won’t give you anything like a full picture, but the very simple concept here can at least be glimpsed in English.

When physicists say the only way to understand quantum mechanics is to study the math behind it, they’re not just blowing you off. A fairly good understanding of the current well-known quantum theories is, in some sense, simpler to obtain than a really thorough understanding of the current tax code: There are fewer rules to learn for the physics, and more of it is derived logically from first principles. However, it’s a world which is mostly decoupled from the bulk matter universe you observe directly, and so your common-sense intuition will be of very little use. You need to learn math to understand it primarily because math is the only language we have without that common sense baked into it.

My point is, if you think the theory is wrong but you can’t write down the equations and point out why they fail in quantitative terms, you aren’t even talking about the actual theory.

Personally, I think that the first step to explaining the Four Forces in human language is to replace the word “force” with “interaction”. In all interactions, you have some set of particles going into the interaction, and some set of particles coming out of it. In most of the interactions we’re familiar with, these two sets of particles are identical, so the interesting questions are all things like how each individual particle’s momentum is changed: Hence, forces. But while the weak force does have some interactions like this, they’re mostly things that can also be done via the electromagnetic force, and under most circumstances, the electromagnetic force dominates. And for those few that can’t be done electromagnetically, the interesting part is usually restricted to neutrinos, which are so hard to detect that we usually ignore them. So most of the interesting weak interactions are the ones where the set of particles coming out isn’t the same as the set going in, like beta decay. And we can’t really ask “how does this particle’s momentum change”, when that particle isn’t even present on one side of the interaction, so describing the interaction as a “force” doesn’t really make sense.

Who here thinks a unified field theory will make both quantum mechanics and relativity so simple that even an average person with a high school education or less could easily grasp it? Or will it be the opposite, and the math and science will be so rigorous and non-intuitive that only a few humans could ever truly understand?

Excellent. Thanks.

I’m sitting on my hands here.

As someone pretty ignorant of QM, my wild-ass guess is that perhaps QM is an emergent property of a lower substrate, just as is everything we’ve discovered in physics so far, except possibly gravity (and even that might be thought of that way.) Not that I’m trying to push hidden variables into the equation. My understanding is that hidden variables are dead, and their last possible loophole just closed.

I’m curious how QM-savvy folks think on this. Is there any way to know when one is really down to brass tacks? Or could there be more turtles?

[Note: There’s always the theoretical possibility that any system is a model based on a sufficiently powerful alternate system. But if there are no physical consequences, that doesn’t matter to me, even if it is “real”. For example, we could be living in a computer model of a universe. If so, that model could be running on a Turing machine, or any equivalent machine. As an empiricist, it’s unimportant to me which type of computer, or anything other than the fact that a Turing machine is sufficient. So, this isn’t that kind of philosophy question.]

…except that even the formulas given for gravity and electromagnetism are classical oversimplifications. The bit about gravity doesn’t mention anything at all about general relativity, and Maxwell’s equations are a long way from the QED lagrangian. Gravity and electromagnetism are familiar interactions that have convenient large-scale, qualitative, classical descriptions. The weak and strong interactions, not so much. There’s no classical analogue to what’s going on. It’s just math and physics all the way down.