system
Given the following post, respond as if you're commenting on Reddit:
human
Isn't it not technically correct to say there are four fundamental forces anymore?

It seems like there's 6 to me. As far as I know, each boson (group) mediates one force:

* Photon - Electromagnetism
* W and Z Bosons - Weak Force
* Gluon - Strong Force
* Graviton (theoretical, of course) - Gravity

However, it seems that there are two other groups, the Higgs Boson (the mass interaction? Not sure what to call it), and the X and Y bosons (proton decay, iirc). So are these forces just like the others? If not, why, and if so, why do we still seem to stick to those four as *the* fundamental forces?
gpt
The Higgs is not the mediator of a "fundamental" interaction. The "four forces" are gauge interactions, and are mediated by *vector* bosons (the Higgs is a scalar). Gauge theory isn't exactly a trivial subject so it's almost universally omitted in divulgation, but that's basically what is meant by fundamental interaction. The Higgs' coupling to fermions instead is a simple, non gauged, Yukawa coupling.

About the X and Y boson, these are hypothetical gauge bosons of most GUT (grand unification theory) proposal. A GUT is a single gauge interaction unifying the electroweak and strong interactions into a single gauge group, not an additional gauge interaction.

Finally, it's important to say that the subdivision of the gauge interactions, along with the subsequent "counting", it's somewhat arbitrary and at the very least a bit technical. The scheme is as such:

- gravity is a gauge interaction but it's quite different from the others, so set it aside
- the Standard Model is a gauge theory over the group U(1)×SU(2)×SU(3). This group is semisimple, not simple ("simple" is a tecnical term) and decomposes into three factors, which are
- U(1), which is weak hypercharge, mediated by a boson usually called B
- SU(2), weak isospin, mediated by three bosons W^1 , W^2 , W^3
- SU(3), the color or strong interaction, mediated by eight gluons.

This makes four gauge interactions if the criterion is that the generators between two different interactions commute.

Now, as a consequence of the Higgs mechanism, there is a certain mixing that happens in the U(1)×SU(2) sector (electroweak). Basically the B and W^3 bosons are mixed into the photon and the Z^0 , while W^1 and W^2 are recombined into the W^+ and W^- . Note that the total number of gauge bosons hasn't changed! So instead of weak isospin and hypercharge at low energy one usually talks about

- the EM gauge interaction, mediated by the photon and with gauge group U(1) (but it's a different copy of U(1) than weak hypercharge)
- the "weak force", which by itself isn't a full gauge interaction and is really a weird hybrid thing reflecting its "mixed" origin, mediated by the Ws and the Z.

That's the list that is usually given and it still gives four.