I recall being taught how everything with mass is made of matter. Ok, I accepted this carte blanche for a life time. But, wait a minute… What about massless particles? Are they considered matter, too? Or, are they categorized as something? And, what about antimatter, or is that its own category?
I did Google around, but I find definitions of matter that link the definition to mass. And, I found a question if matter has mass, does all matter have a gravitational pull (for which one answer is that the gravitational force between neutrinos may exists; however, it may be too weak to measure.)
Off the top of my head: there are particles that compose matter, and there are particles that carry forces. All matter particles (mesons and baryons which are made of quarks, and leptons (electrons, neutrinos and their equivalents in other “generations” (muons, tau particles, muon neutrinos and tau neutrinos)) have some mass (though the neutrino masses are very small), while only some force-carrying particles have mass.
Andy L, the categories you’re referring to are the fermions and the bosons. But your description of them is a bit over-simplified: Not all bosons carry force, for starters (the mesons are sort of the carriers of the nuclear force, but not really, and the Higgs doesn’t carry any force). Fermions have the whole “no two particles in the same state” thing going on, which we think of as a matter-ish property, but mass is really the essence of matter-ness. And even when we thought that neutrinos had zero mass, they were still unambiguously fermions.
When it comes down to it, I’d be quite comfortable with saying that the W, Z, Higgs, and mesons are matter, and neutrinos are matter but only barely, while photons, gluons, and gravitons are not matter.
Really, “matter” and “antimatter” aren’t even particularly well-defined categories. It’s easy to say that the negative electron and positive proton are matter and their opposites are antimatter, but of the charged pions, which one is the “matter” one and which one is the “antimatter”? And then you’ve got particles like the neutral pion and the Z which are their own antiparticle (and neutrinos might even be in that category, too). It gets even more fun when you get to the neutral kaons: You can speak of the k[sup]0[/sup] and the k[sup]0[/sup], which are antiparticles of each other, or equivalently you can speak of the k[sub]s[/sub] and the k[sub]l[/sub], each of which is its own antiparticle.
Thanks Chronos. I was deliberately avoiding the terms fermion and boson; I appreciate your clarifications (and yeah, it does make sense to say "matter " is stuff that has mass).
“Matter” doesn’t have a fixed, formal definition. It’s very context dependent, and even then it can still be ambiguous.
In everyday speech, there aren’t things like bosons and special relatively and whatnot to think about, so “matter” does essentially mean stuff with mass, which in turn means “everything except light and energy” (using lay terms here, since that’s the context here).
If you take the leap and try to define it in terms of fundamental physics, you run into complications like “a collection of photons can have mass, even though each photon has no mass of its own” and “a Z boson is a massive particle, but it’s fundamentally not very different from a photon” and “none of the stuff that one thinks of as matter in an everyday sense has neutrinos/pions/muon/etc. in it”.
To me, “matter” in a fundamental particle physics context is not synonymous with “has mass” or really any other common taxonomy.
(1) In certain contexts, “matter” is used simply as the antonym of “antimatter” (e.g., electron versus positron). In limited contexts, “matter” and “antimatter” are reserved for baryonic states or even atomic states (e.g., hydrogen versus antihydrogen), with “particle” and “antiparticle” being used for more fundamental objects (e.g., electron versus positron). Whichever the context, these uses do find a home in formal discussion.
(2) In the informal context of “What is matter made of?” or “What particles count as matter?” – where “matter” means “stuff” and not “opposite of antimatter” – you won’t find a universal definition. My own definition would include only fundamental fermions and bound states of fundamental fermions. So for me:
Is it matter?
fundamental fermions (electrons, neutrinos, quarks, …) – yes
quark bound states (protons, pions, …) – yes
bounds states of any of the above (atoms, positronium, …) – yes
Pasta, what about a bound state of a fundamental boson and a fundamental fermion (say, an electron orbiting a W+)? Would that count as “matter”, in your definition?
My point with such an answer, of course, is to convey that I don’t think it’s helpful or meaningful to force the taxonomy that far. It starts to feel akin to “What does purple smell like?” A bound state like that is so far removed from anything that anyone would every think of as, well, “matter” that it’s (to my mind) outside the bounds of relevance.
(If I were forced to answer “What does purple smell like?” in this case, though, I might lean toward calling your suggested bound state “matter”. I just wouldn’t be happy about it.)
I remember someone asking me if magnetic monopoles were found, which one would be the antiparticle; I had to explain that that question didn’t really make sense.
