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Some other notes from what I understand of current mainstream physics: - elementary particles have no defined size in QM (electrons, quarks, neutrinos, photons

Some other notes from what I understand of current mainstream physics: - elementary particles have no defined size in QM (electrons, quarks, neutrinos, photons etc); there is no known lower-bound on how small they could be, and there are serious mathematical issues both with assuming a non-0 radius, but other problems with assuming a radius of 0 - composite particles like a proton or a hydrogen atom have a size because of the relative strengths of the forces holding together their components; for example, the three quarks making up a proton must exist at a certain distance from one another because of the properties of the strong force; the electron of a hydrogen atom must "orbit" the proton at a certain distance because of the properties of the electrical force - QM spin is not a rotation speed of any kind; QM particles are not little balls rotating around their center; quantum spin has no known relation to the speed of light - replacing one constant of nature (the size of a proton, or at least of an elementary particle) by another constant of nature (the speed of light) is not really simplifying the theory; one could just as easily go the other way, and say that the speed of light is derived from the size of elementary particles in some other way

jiggawatts 3y ago
> elementary particles have no defined size in QM That's only kinda-sorta true, and only in a very restricted sense. All particles have a wavelength, but that can change depending on their velocity. In QM models, it is a simplification to treat particle as point-like to make the mathematics tractable. It isn't necessarily an accurate picture of the underlying reality. > QM spin is not a rotation speed of any kind; QM particles are not little balls rotating around their center; quantum spin has no known relation to the speed of light That's not exactly the case. From my best understanding, Spin is just the Dirac Belt Trick, an indication that particles are part of the spacetime fabric and attached to it. When they rotate, the fabric rotates with them locally. This requires two full rotations (720 degrees) to go back to the original state, which is why you have "spin 1/2" and the complicated maths. Two good visualisations are here: https://youtu.be/LLw3BaliDUQ https://youtu.be/LLw3BaliDUQ and: https://youtu.be/jdVoFr5d4Rw https://youtu.be/jdVoFr5d4Rw
- simiones 3y ago
  > In QM models, it is a simplification to treat particle as point-like to make the mathematics tractable. It isn't necessarily an accurate picture of the underlying reality. As far as I understand, it is more than that: it is an explicit assumption of the theory that elementary particles do not have an internal structure, and so their radius must be 0. This is not to be confused with the wave-like representation, which of course does have a size in space. On the spin question, I will not claim I understand enough to actually go into more detail than the (probably simplistic) observation I've read that quantum spin can't be understood in terms of classical rotation/movement.

jiggawatts 3y ago

> elementary particles have no defined size in QM That's only kinda-sorta true, and only in a very restricted sense. All particles have a wavelength, but that can change depending on their velocity. In QM models, it is a simplification to treat particle as point-like to make the mathematics tractable. It isn't necessarily an accurate picture of the underlying reality. > QM spin is not a rotation speed of any kind; QM particles are not little balls rotating around their center; quantum spin has no known relation to the speed of light That's not exactly the case. From my best understanding, Spin is just the Dirac Belt Trick, an indication that particles are part of the spacetime fabric and attached to it. When they rotate, the fabric rotates with them locally. This requires two full rotations (720 degrees) to go back to the original state, which is why you have "spin 1/2" and the complicated maths. Two good visualisations are here: https://youtu.be/LLw3BaliDUQ https://youtu.be/LLw3BaliDUQ and: https://youtu.be/jdVoFr5d4Rw https://youtu.be/jdVoFr5d4Rw

simiones 3y ago
> In QM models, it is a simplification to treat particle as point-like to make the mathematics tractable. It isn't necessarily an accurate picture of the underlying reality. As far as I understand, it is more than that: it is an explicit assumption of the theory that elementary particles do not have an internal structure, and so their radius must be 0. This is not to be confused with the wave-like representation, which of course does have a size in space. On the spin question, I will not claim I understand enough to actually go into more detail than the (probably simplistic) observation I've read that quantum spin can't be understood in terms of classical rotation/movement.