Originally posted by twhiteheadI think the attribute we call spin is more like the north and south of a magnetic field than an actual physical spin. I don't think it involves an actual magnetic field but Kaz can probably shed more light on that subject. No pun intended
KazetNagorra has said he could answer a few questions in quantum mechanics. so here goes:
1. Can you describe electron spin. Does it have a specific direction in space? Can any electron point in any given direction?
2. Is it related to the polarity of photons? Does polarity have a specific direction for any given photon?
Originally posted by DeepThoughtI don't really have a simple analogy for spin. Mostly it's just an intrinsic property of matter that manifests itself in certain measurable ways.
This is a bit of a painful question, because the answer is so abstract. In classical physics the spin of a planet, say, is really just orbital angular momentum of the material in the planet about its axis of rotation. In quantum mechanics even elementary particles, such as electrons, which should be point-like and therefore not be able to spin possess ...[text shortened]... lves complex vector spaces and some group theory concepts. Kazet may have a simpler picture.
Originally posted by KazetNagorraI don't necessarily need a specific analogy, I just want to know some of its properties.
I don't really have a simple analogy for spin. Mostly it's just an intrinsic property of matter that manifests itself in certain measurable ways.
Originally posted by twhiteheadDoes it point in a specific direction?
I don't necessarily need a specific analogy, I just want to know some of its properties.
Does it point in a specific direction?
Does it change over time?
Is it related to the fact that only two electrons can share a given part of the electron shells?
Is magnetism related? Why is iron magnetic and almost nothing else?
Originally posted by KazetNagorraSo an electrons spin may change over time? I believe people have come up with storage based on spin. Is this storage using single electrons or large groups? Does it manipulate the spin, or separate out those with a given spin? I know these might be outside your field being engineering rather than pure quantum mechanics.
Spin is described by a matrix, which can depend on time.
Originally posted by KazetNagorraYes, the Pauli exclusion principle for fermions is a very important feature of the world.
If you have a wavefunction describing two (or more, but for the sake of argument consider two) indistinguishable particles, the probability distribution must be unaffected if you interchange the two particles...
Originally posted by Paul Dirac IIThis is another question with a painfully abstract answer. Essentially it's because of the mathematical structure of the theory. Swapping an electron for a positron changes the order of some terms in the corresponding matrix element, and this changes the sign of the effective potential, depending on the structure of the bosonic propagator. Sorry really can't do better there, this is Quantum Field Theory, and some of the results are just plain mathematical.
Yes, the Pauli exclusion principle for fermions is a very important feature of the world.
But my question above does not have anything to do with that (at least not in any obvious way).
A pair of electrons repel one another through a field of spin-1 virtual photons. But they also attract one another (to a far, far lesser degree, granted) through ...[text shortened]... e fields. I have never come across the mathematics that make it clear why it has to be that way.
Originally posted by twhiteheadElectron spin has a given orientation in space - only once you force it to assume a given orientation by measuring it, according to quantum mechanics. Until then, the wave function just makes it assume a superposition of all possible orientations...
KazetNagorra has said he could answer a few questions in quantum mechanics. so here goes:
1. Can you describe electron spin. Does it have a specific direction in space? Can any electron point in any given direction?
2. Is it related to the polarity of photons? Does polarity have a specific direction for any given photon?
Originally posted by ptoblerThat depends on how "tiny" the fraction is.
Electron spin has a given orientation in space - only once you force it to assume a given orientation by measuring it, according to quantum mechanics. Until then, the wave function just makes it assume a superposition of all possible orientations...
Similarly for the polarisation of photons... a photon only has a given polarisation once you force it to as ...[text shortened]... ny fraction of a second later they might have a totally different orientation or polarisation...