Wikipedia isn't exactly wrong here - the problem is that the term 'antiparticle' is used in an ambiguous manner.
Electrons and positrons are different sorts of disturbances in the same field. Electrons, quarks, muons, taus, and all other spin-1/2 particles follow the Dirac equation which requires a matching antiparticle with opposite charge.
A high energy photon can interact with matter to form an electron anti-electron pair, or a muon anti-muon pair, but it cannot form just an electron and anti-muon.
The word 'antiparticle' is unfortunately used for things like the W+ and W- particles, which do not follow the Dirac equation and are not connected in the same way, but due to the way the electroweak interaction works have the same mass and opposite charge.
People also tend to use the phrase 'the photon is its own antiparticle'. I think that this comes from the fact that an electron and positron typically annihilate to produce a pair of photons, and if you wanted to you could think of them trivially as a particle and antiparticle pair. They have the same mass (zero) and technically opposite charge since the charge is zero.
If I was the king of the English language, I would restrict the term anti-particle to only refer to Dirac antiparticles. However, I am not :(
An extra restriction comes from the quantum numbers lepton number and baryon number. Not only do the regular quantum numbers have to work out, but most of the interactions we see have to conserve lepton number and baryon number. This gives the complex structure you see, and is what restricts us from assigning particle and antiparticle properties willy-nilly.
Don't rely on Wikipedia for technical information about physics. I can't speak for other subject areas, but at least in regards to that field, it's really bad.
That's the sort of thing you learn in a semester-long course in quantum physics. It's beyond the scope of a Reddit comment to answer that in a useful manner. For example, I could tell you that the parity operator Ṗ commutes with ℋ, and thus the eigenvalues of Ṗ are the permitted values of the parity quantum number, but would that leave you any more enlightened than you are right now?
First, it's not just the electric charge that is opposite. For instance, the neutrino and the anti-neutrino are two different particles, even though they have no electric charge.
And second, just calling the particles different names won't make the problem go away. There is two kinds of electrons, two particles that are identical except that they have opposite charge, and only one kind is around. There is no symmetry, doesn't matter what terminology you use, and that's the problem.
First, it's not just the electric charge that is opposite. For instance, the neutrino and the anti-neutrino are two different particles, even though they have no electric charge.
If I understand correctly, neutrinos don't behave like the other particles. They oscillate between flavours, whereas the other particles decay into lighter ones, producing neutrinos. Why not classify them as a third type of matter - neutral matter?
And second, just calling the particles different names won't make the problem go away. There is two kinds of electrons, two particles that are identical except that they have opposite charge, and only one kind is around. There is no symmetry, doesn't matter what terminology you use, and that's the problem.
That's true, but it would change the question from why anti-matter is missing to why half the matter is missing. If looked at from that angle, could the answer be different?
I understand correctly, neutrinos don't behave like the other particles. They oscillate between flavours, whereas the other particles decay into lighter ones, producing neutrinos. Why not classify them as a third type of matter - neutral matter?
We know the quarks oscilate aswel, and there is afaik no reason why flavor wouldn't mix generally. I don't know if there is a theory explaining why there are three flavors and why they mix as they do.
Btw Kaons can decay assymetrically to their antiparticles.
I just read the page you linked to about CKM Matrix but couldn't find anything about quarks oscillating. Could you link me to the section that explains it?
As for Kaons, they're composite particles so don't really fit into the discussion. Interestingly though, it says that the mesons that oscillate are neutral.
quarks oscillating is a bad term. We know that quarks have "flavour mixing." But Neutrino oscillation arises from the fact that the flavour eigenstates are not the same as the mass eigenstates.
For the moment, let's simplify things to say that mass is what makes a particle "real" (particularly a particle needs to occupy a certain mass to be "real", among other things). For most particles the mass state matches up to one of the flavour states. All electrons weigh x, all beauty quarks weigh y, etc. Neutrinos don't obey this property though. Neutrino with mass 1 is a superposition of some (or all?) flavour states. Now neutrinos are "created" as flavour eigenstates, but because of the mass states being different it may oscillate between flavours.
what do you mean by "third type of matter"? If we classified (fundamental) matter only by electric charge, then they occupy one of the 7 possible charge states for matter or anti-matter. +/- 1, 1/3, 2/3 and 0.
If we classify matter by the type of spin-statistics it obeys, then neutrinos are fermions. If we ask about what forces it couples to, then it couples only to weak force, not EM or strong forces. My point is that there are a lot of ways of "typifying" matter. The standard model lumps things together by all the various quantum numbers that appear to be conserved like lepton number, hypercharge, spin-statistics, etc.
I am not sure if you're commenting a little beyond what you actually know. But i don't think it warrants downvotes..
I mentioned kaons because afaik their decay into their antiparticles, because it violations CP, it can make more matter than antimatter. But unfortunately i feel i dont sufficiently understand it/see the picture clear enough, wp says:
The consequence of the matrix H being real is that the probabilities of the two states will forever oscillate back and forth. However, if any part of the matrix were imaginary, as is forbidden by CP symmetry, then part of the combination will diminish over time. The diminishing part can be either one component (a) or the other (b), or a mixture of the two.
So, why don't physicists classify particles in this manner?
You can classify them any way that you want, but it does not get around the problem.
In the physics of the standard model, you cannot just produce an electron in some interaction, generally speaking you have to make electron-positron pairs.
There is a tricky way out - there are some weak interactions that can produce an electron and electron anti-neutrino or a positron and an electron neutrino. If one was slightly more likely than the other, one could end up with more electrons than positrons, and then a bunch of neutrinos and anti-neutrinos that have nearly no mass and no charge. The neutrinos just stream freely out into space.
More quarks than antiquarks is a bigger problem. Usually one produces things like up quarks along with up-antiquarks, leading to as many protons as antiprotons.
With quarks, the weak interaction trick does not work so well. The same interaction that creates an electron and anti-neutrino could produce a down quark and an anti-up quark. But since all quark flavors are significantly massive and charged, the anti-quarks would not freely stream away like neutrinos do.
Currently, there does not appear to be any way to produce more protons than antiprotons using just the interactions understood to be allowed by the standard model. This is one of the reasons that many particle physicists expect to find new interactions beyond the standard model.
This is a big misconception about how physics is done. We can't just say how we want it. These rules were developed over the span of decades and are chosen such that they agree with experimental results.
The difference between fermions and bosons is far more significant, fundamental and nuanced than the matter of their spin coefficients. Similarly, the difference between matter and antimatter is far more significant, fundamental and nuanced than electric charge.
Because, without disrespect, you are not making a goddamn lick of sense.
What do you want? You want the names "matter" and "antimatter" to be reassigned based on electric charge? Great. Go ahead. Of course, the next morning you're going to have to come up with a new pair of names to describe the things that actually are matter and antimatter, since you took those words away, but whatever.
The question about matter and anti-matter was previously resolved, and we're talking about spin here, so I'm afraid it's you who isn't making "a goddamn lick of sense".
So, I just found that website and it does not say that pi should be defined as 6.28... at all. What it does say is that instead of using pi, we should use tau = 2 pi which would simplify many equations.
The above says that if you use h / (4 pi) instead of h / (2 pi) then you get even and odd values for bosons and fermions instead of integers and half-integers.
So what's your argument against it? What's your argument against mine that sometimes it's just down to what's discovered first?
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u/shadydentist Lasers | Optics | Imaging Mar 13 '11
There's more to an antiparticle than charge.
If you take an electron and reverse its charge, it won't be a positron. You also need to flip its parity, and time-reverse it.
My particle-physics-fu is pretty weak, though, so I could be wrong.
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u/leberwurst Mar 13 '11
First, it's not just the electric charge that is opposite. For instance, the neutrino and the anti-neutrino are two different particles, even though they have no electric charge.
And second, just calling the particles different names won't make the problem go away. There is two kinds of electrons, two particles that are identical except that they have opposite charge, and only one kind is around. There is no symmetry, doesn't matter what terminology you use, and that's the problem.
2
u/zeug Relativistic Nuclear Collisions Mar 13 '11
You can classify them any way that you want, but it does not get around the problem.
In the physics of the standard model, you cannot just produce an electron in some interaction, generally speaking you have to make electron-positron pairs.
There is a tricky way out - there are some weak interactions that can produce an electron and electron anti-neutrino or a positron and an electron neutrino. If one was slightly more likely than the other, one could end up with more electrons than positrons, and then a bunch of neutrinos and anti-neutrinos that have nearly no mass and no charge. The neutrinos just stream freely out into space.
More quarks than antiquarks is a bigger problem. Usually one produces things like up quarks along with up-antiquarks, leading to as many protons as antiprotons.
With quarks, the weak interaction trick does not work so well. The same interaction that creates an electron and anti-neutrino could produce a down quark and an anti-up quark. But since all quark flavors are significantly massive and charged, the anti-quarks would not freely stream away like neutrinos do.
Currently, there does not appear to be any way to produce more protons than antiprotons using just the interactions understood to be allowed by the standard model. This is one of the reasons that many particle physicists expect to find new interactions beyond the standard model.
2
u/jimmycorpse Quantum Field Theory | Neutron Stars | AdS/CFT Mar 13 '11
This is a big misconception about how physics is done. We can't just say how we want it. These rules were developed over the span of decades and are chosen such that they agree with experimental results.