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<blockquote data-quote="freyar" data-source="post: 5884412" data-attributes="member: 40227">This is sadly, a pretty crappy article in some respects.&nbsp; In particular, this quote:is 100% incorrect on the difference between fermions and bosons.&nbsp; A bit above this, they give a partially correct explanation in saying that fermions follow the Pauli exclusion principle and bosons don't.&nbsp; I believe the BBC article on this was a bit better, but I don't have time to search for it right now.Here is the correct story:Fermions have what we call 1/2-integer spin (like 1/2, 3/2, etc), so they are always rotating in some sense.&nbsp; For technical reasons, this means that two identical fermions can never have the same state --- meaning two electrons can't be in the same place, for example.&nbsp; Bosons have integer spin (0,1,2, etc).&nbsp; Two identical bosons are allowed to have the same state --- this phenomenon is what allows us to make lasers, since photons (spin 1) are bosons.That's the difference between bosons and fermions.&nbsp; Note that I said nothing about antiparticles.Now, here's the thing about antiparticles.&nbsp; It really comes down to the difference between real and complex numbers.&nbsp; A particle and its antiparticle are the same if the particle is associated with a real number.&nbsp; A photon can be described by real numbers, so its antiparticle is still a photon.&nbsp; An electron, which is a Dirac fermion like Umbran says, must be described by complex numbers, so its antiparticle, the positron, is different.&nbsp; A W-boson is like a photon in lots of ways, but it is a complex number particle, so it has a different type of antiparticle (the W and its antiparticle are called W+ and W-).&nbsp; Majorana fermions are like electrons except they can be described by real numbers, so they are their own antiparticles.None of this really talks about annihilation of particles.&nbsp; In principle, a particle and its antiparticle can always annihilate into something else.&nbsp; W+ and W- bosons can annihilate, for example.&nbsp; Photons would be able to annihilate if there were something lighter for them to annihilate into, but they're massless, so there's nothing lighter!&nbsp; That's why photons can't annihilate, not particle-antiparticle business.And this is a really important point that the article just glossed over.</blockquote>

[QUOTE="freyar, post: 5884412, member: 40227"] This is sadly, a pretty crappy article in some respects. In particular, this quote: is 100% incorrect on the difference between fermions and bosons. A bit above this, they give a partially correct explanation in saying that fermions follow the Pauli exclusion principle and bosons don't. I believe the BBC article on this was a bit better, but I don't have time to search for it right now. Here is the correct story: Fermions have what we call 1/2-integer spin (like 1/2, 3/2, etc), so they are always rotating in some sense. For technical reasons, this means that two identical fermions can never have the same state --- meaning two electrons can't be in the same place, for example. Bosons have integer spin (0,1,2, etc). Two identical bosons are allowed to have the same state --- this phenomenon is what allows us to make lasers, since photons (spin 1) are bosons. That's the difference between bosons and fermions. Note that I said nothing about antiparticles. Now, here's the thing about antiparticles. It really comes down to the difference between real and complex numbers. A particle and its antiparticle are the same if the particle is associated with a real number. A photon can be described by real numbers, so its antiparticle is still a photon. An electron, which is a Dirac fermion like Umbran says, must be described by complex numbers, so its antiparticle, the positron, is different. A W-boson is like a photon in lots of ways, but it is a complex number particle, so it has a different type of antiparticle (the W and its antiparticle are called W+ and W-). Majorana fermions are like electrons except they can be described by real numbers, so they are their own antiparticles. None of this really talks about annihilation of particles. In principle, a particle and its antiparticle can [b]always[/b] annihilate into something else. W+ and W- bosons can annihilate, for example. Photons would be able to annihilate if there were something lighter for them to annihilate into, but they're massless, so there's nothing lighter! That's why photons can't annihilate, not particle-antiparticle business. And this is a really important point that the article just glossed over. [/QUOTE]

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