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<blockquote data-quote="freyar" data-source="post: 5186326" data-attributes="member: 40227">If I hadn't been grossly oversimplifying in my previous post, that's basically exactly what I would have been saying.&nbsp; But that's not quite right.&nbsp; I'm going to delve into technical stuff for Umbran and the other physicists, but I'll set aside parenthetical explanations of what I'm talking about.Neutrinos can't be their own antiparticles.&nbsp; First of all, there's lepton number (which essentially counts the number of electron-like particles).&nbsp; Neutrinos, which are always left-handed helicity (if they move along your left hand thumb, they &quot;rotate&quot; in the direction of your left-hand fingers), have L=+1, but right-handed anti-neutrinos have L=-1.&nbsp; This is in the Standard Model (of particle physics, and, yes, it's supposed to be capitalized <img src="https://cdn.jsdelivr.net/joypixels/assets/8.0/png/unicode/64/1f61b.png" class="smilie smilie--emoji" loading="lazy" width="64" height="64" alt=":p" title="Stick out tongue&nbsp; &nbsp; :p"&nbsp; data-smilie="7"data-shortname=":p" />), and it's also experimental observation.&nbsp; But lepton number isn't precisely conserved, so you might want other reasons neutrinos and anti-neutrinos are different.&nbsp; The answer is that neutrinos are charged under the weak force, and the anti-neutrinos fall in the conjugate (&quot;opposite&quot;) representation (&quot;charge&quot;) (like the antiparticles of electrically charged particles have the opposite electric charge).&nbsp; The confusion has to do with my statement about &quot;real&quot; vs &quot;complex&quot; numbers for fermions (particles like electrons, protons, etc).&nbsp; There are two distinct ways to cut a normal &quot;complex&quot; fermion into half (make it &quot;real&quot;).&nbsp; One way is to make the particle the same as the antiparticle.&nbsp; The other way, which applies to neutrinos is to split the regular fermion into so-called chiral fermions.&nbsp; Each chiral fermion only transforms under (pays attention to) half the Lorentz group (changes of velocity as well as rotations); neutrinos only transform under the &quot;left&quot; half.&nbsp; But for massless particles this ends up meaning that they are always left-handed helicity (spin as we've talked about before).&nbsp; As Umbran says, we know that neutrinos have some tiny mass, but the question is whether they get this mass in a way that requires right-handed neutrinos to exist or not.&nbsp; We don't know that yet.</blockquote>

[QUOTE="freyar, post: 5186326, member: 40227"] If I hadn't been grossly oversimplifying in my previous post, that's basically exactly what I would have been saying. But that's not quite right. I'm going to delve into technical stuff for Umbran and the other physicists, but I'll set aside parenthetical explanations of what I'm talking about. Neutrinos can't be their own antiparticles. First of all, there's lepton number (which essentially counts the number of electron-like particles). Neutrinos, which are always left-handed helicity (if they move along your left hand thumb, they "rotate" in the direction of your left-hand fingers), have L=+1, but right-handed anti-neutrinos have L=-1. This is in the Standard Model (of particle physics, and, yes, it's supposed to be capitalized :p), and it's also experimental observation. But lepton number isn't precisely conserved, so you might want other reasons neutrinos and anti-neutrinos are different. The answer is that neutrinos are charged under the weak force, and the anti-neutrinos fall in the conjugate ("opposite") representation ("charge") (like the antiparticles of electrically charged particles have the opposite electric charge). The confusion has to do with my statement about "real" vs "complex" numbers for fermions (particles like electrons, protons, etc). There are two distinct ways to cut a normal "complex" fermion into half (make it "real"). One way is to make the particle the same as the antiparticle. The other way, which applies to neutrinos is to split the regular fermion into so-called chiral fermions. Each chiral fermion only transforms under (pays attention to) half the Lorentz group (changes of velocity as well as rotations); neutrinos only transform under the "left" half. But for massless particles this ends up meaning that they are always left-handed helicity (spin as we've talked about before). As Umbran says, we know that neutrinos have some tiny mass, but the question is whether they get this mass in a way that requires right-handed neutrinos to exist or not. We don't know that yet. [/QUOTE]

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