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by ClayFerguson
3412 days ago
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You can google the phrase "Standard Model" or look it up in any physics book you want, and there will always be a table labeled "Standard Model" that shows all the particles, which relate to the 4 fundamental forces (carriers), charges, spins, masses, etc. I'm sure you're familiar with this chart. The graviton is on that chart and is specifically describing gravity based on each mass value of each particle (hardly "silence" there). I mean literally every particle type has a mass value (even when zero) right? Is that silence? The general laymans meaning of "Standard Model" means everything in physics that is referenced on that chart (including gravity), and that's how I meant it. However, what YOU apparently mean by "silent on gravity" is referencing the fact that the Standard Model is incomplete for gravity, because General Relativity is not yet accounted for. I should've realized you might be referring to the lack of any unified field theory, but I didn't. If you had said "doesn't fully explain" rather than "is silent on", it would've sounded perfectly fine to me. |
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You can certainly describe gravitation using a massless spin-2 graviton, and perturbative quantum gravity -- another specific quantum field theory -- does exactly that, and is a perfectly fine effective field theory that entirely matches General Relativity absent superposed sources and outside of strong gravity (which is defined by the EFT's renormalization group flow).
You can add this graviton to a particle zoo. But then it's not the particle zoo of the Standard Model, any more than writing down an "action of everything"[1] gives the action of the Standard Model.
> The general laymans meaning of "Standard Model" means everything in physics that is referenced on that chart (including gravity), and that's how I meant it.
is only correct if you underline the "how I [mean] it" part and make that central to evaluating the sentence's truth. It's hard to disprove solipsistic physics, though, and rarely interesting.
Additionally,
> which relate to the 4 fundamental forces (carriers) ... I'm sure you're familiar with this chart.
Sure, but there are several such charts, and they're not all the same. Here's one from Fermilab and SLAC, institutions that are pretty familiar with the Standard Model: http://www.symmetrymagazine.org/standard-model/ (There's no graviton in it).
Fundamental forces come from fundamental interactions, but there is no force police force enforcing a law that there are four of them or that the carriers are gauge bosons in a particle zoo. The Higgs interaction can be treated as a force[2] and its mediator is a scalar boson rather than a gauge boson, so does the Standard Model have four fundamental forces? One can take differing views of the electroweak interaction above 80-90 GeV: does the Standard Model have only two fundamental forces?
One can certainly treat Einstein gravity as at least a d'Alembert force arising from the affine connection; but alternatively one could take the position that d'Alembert forces generically depend on a choice of frame of reference and on that basis they cannot be fundamental. Is gravity a force? You get a different answer from Newton (yes) than you do from either Einstein (yes, but it's fictitious) or Misner, Thorne & Wheeler (mu, there is only spacetime geometry).
So an argument that as there are four fundamental forces there must be four force carriers is on shaky ground to start with. Even if we were to accept that, it does not follow that all the forces in question relate to the local symmetries of the Standard Model.
[1] For example, Carroll's "core theory" here: http://www.preposterousuniverse.com/blog/wp-content/uploads/...
[2] as discussed at last year's Moriond EW, for example, the Higgs force can be measured using atomic spectroscopy: https://indico.in2p3.fr/event/12279/session/7/contribution/1...