# Spin

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But do we know why it is doing this very thing that we observe and then model and then predict.

I don't think "why" is a well-posed question for physics to answer. The best we can really do is explain what is happening within the framework of our models.

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They don't. They aren't the same thing. It's not the deBroglie wave function. There's a wave function, and there's a deBroglie wavelength. (A particle with an exactly known momentum will have a spatial wave function with infinite wavelength)

But if I graph the probability of say, finding a ground state electron in the ground state, the graph goes on infinitely, even though in order for it to have probabilities going in places other than the Bohr radius, a graph of the probability of finding it at any distance away from the nucleus would go on infinitely never reaching 0, but the exact momentum is undetermined though, isn't it?

Also, someone mentioned that the uncertainty principal doesn't apply in an atom, or bound electrons. But, in order to have the current model of an atom that we have, it has to follow the uncertainty principal.

Since an electron has a small mass, it occupies a larger region of space in an atom. Since a proton has a very large mass, it occupies a very small region in an atom, and the result would be the massive nucleus surrounded by very large electrons.

Edited by steevey

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But if I graph the probability of say, finding a ground state electron in the ground state, the graph goes on infinitely, even though in order for it to have probabilities going in places other than the Bohr radius, a graph of the probability of finding it at any distance away from the nucleus would go on infinitely never reaching 0, but the exact momentum is undetermined though, isn't it?

That doesn't make sense. Probability of finding an electron in an energy state is not a spatial function. It's found by using the hamiltonian operator on a wave function. How can it have a wavelength or go on infinitely?

Also, someone mentioned that the uncertainty principal doesn't apply in an atom, or bound electrons. But, in order to have the current model of an atom that we have, it has to follow the uncertainty principal.

Doesn't apply? Who said this and where?

Since an electron has a small mass, it occupies a larger region of space in an atom. Since a proton has a very large mass, it occupies a very small region in an atom, and the result would be the massive nucleus surrounded by very large electrons.

Protons do occupy a small region as compared to electrons.

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I don't think "why" is a well-posed question for physics to answer. The best we can really do is explain what is happening within the framework of our models.

If not why perhaps How ?

Could you possibly ease me into AntiSymmetrical going a little easy on the maths. Perhaps the maths but with a translation of the maths into words or concepts.

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Basically, antisymmetric means you use the "Koszul sign rule" when you pass objects past each other.

So, antisymmetric simply means $ab = -ba$.

Symmetric would mean $ab = ba$.

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Basically, antisymmetric means you use the "Koszul sign rule" when you pass objects past each other.

So, antisymmetric simply means $ab = -ba$.

Symmetric would mean $ab = ba$.

So does that mean , that when the two electrons trying to occupy the same proximity with both " ab" ( namely the same quantum number say both up spin ) that following this antisymmetry idea for two objects past each other, that one of the electrons will go to a " -ba " mode ( namely a different quantum number say down spin ) ie one up spin one down spin.

Or have I got the wrong end of the stick ?

Edited by Mike Smith Cosmos

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That doesn't make sense. Probability of finding an electron in an energy state is not a spatial function. It's found by using the hamiltonian operator on a wave function. How can it have a wavelength or go on infinitely?

Because its improbability. You can find an electron really far away from the atom its bond to, but its just really unlikely. Think of it this way: Gravity goes on indefinitely through space, but its force gets very very weak over large distances. Its the same sort of principal with the electron acting as a wave. Its wave extends indefinitely through space, which other physicists have told me causes a lot of confusion, but its just very improbable to find the electron large distances away from its most probable place.

Doesn't apply? Who said this and where?

I think it might have been more about a wavelength

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Because its improbability. You can find an electron really far away from the atom its bond to, but its just really unlikely. Think of it this way: Gravity goes on indefinitely through space, but its force gets very very weak over large distances. Its the same sort of principal with the electron acting as a wave. Its wave extends indefinitely through space, which other physicists have told me causes a lot of confusion, but its just very improbable to find the electron large distances away from its most probable place.

But what you mentioned was the probability of finding an electron in the ground state, which is a question of energy, not position.

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But what you mentioned was the probability of finding an electron in the ground state, which is a question of energy, not position.

But if its energy changes, so will its position anyway. Also, why would that only apply for a single electron at the ground state? Atoms in other orbitals are subject to the same type of randomness aren't they?

Edited by steevey

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But if its energy changes, so will its position anyway.

And the uncertainty principle applies to energy as well as position, so you can't just tie them together.

Also, why would that only apply for a single electron at the ground state? Atoms in other orbitals are subject to the same type of randomness aren't they?

I never said they weren't.

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I never said they weren't.

Then why did you point out that I was describing an atom in the ground state if its true for every other state the electron has?

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Then why did you point out that I was describing an atom in the ground state if its true for every other state the electron has?

I didn't. I was pointing out that you were talking about the probability of finding an electron in a certain energy state, not a certain position. They are completely different things. There is an uncertainty relation for energy as well as position and momentum.

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I didn't. I was pointing out that you were talking about the probability of finding an electron in a certain energy state, not a certain position. They are completely different things. There is an uncertainty relation for energy as well as position and momentum.

But I was talking about an electron at the ground state having a probability of its position extending indefinitely through space, however its position appearing large distances away from its most probable location is highly improbable.

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But I was talking about an electron at the ground state having a probability of its position extending indefinitely through space, however its position appearing large distances away from its most probable location is highly improbable.

You said:

But if I graph the probability of say, finding a ground state electron in the ground state

Which I interpreted as a question of probability of finding it in a certain energy state, not a certain position.

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You said:

Which I interpreted as a question of probability of finding it in a certain energy state, not a certain position.

I guess that makes sense. But, what I'm saying is, if I have an electron in the ground state or I suppose any state, then it could appear pretty much anywhere in the universe, but the chances of its position being anything like that away from its most probable location is highly unlikely, right? Even for a bound electron to appear any observable distance away from its most probable place is 1 in a very large number.

Edited by steevey

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But if its energy changes, so will its position anyway. Also, why would that only apply for a single electron at the ground state? Atoms in other orbitals are subject to the same type of randomness aren't they?

Position is not completely determined by energy — there are overlaps in orbitals.

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It represents spin as the energy flow of a wave packet of limited size around z-axis. However the spin does not depend on the packet size. Factually it is shown that a vector field has spin 1 and spinor field does 1/2. We knew this without wave packets.

Hello BoB ,

I am heading down to our house in the Appenines in Italy mid April. I would enjoy having a discussion with you over the Forum - Physics -Quantum-Spin about some of the aspects of electron Spin and the Pauli exclusion principle, before I go, as I will not find it easy to get to the internet , up in the hills and forest ( After 14th April untill September ).

I seem to have got as far as the antisymmetry aspect of 2 electrons attempting to be in the same energy level , where this is only possible by one of two states described as up spin and down spin. What I am having some difficulty is how this exclusion works in practical reality as opposed to a mathematical formulae. Any descriptive information as to what is going on, would be appreciated. As most of chemistry, the atomic structure, the universe as a whole seems to be based on this exclusion issue putting some (expansion pressure - loosely put ) upwards and outwards, to hold the atoms away from the lowest energy level. I would really like to know the nature of the exclusion principle, not just the maths that models it.

Edited by Mike Smith Cosmos

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Hello BoB ,

I seem to have got as far as the antisymmetry aspect of 2 electrons attempting to be in the same energy level , where this is only possible by one of two states described as up spin and down spin. What I am having some difficulty is how this exclusion works in practical reality as opposed to a mathematical formulae.

If the spins didn't weren't opposite, then the electrons would cancel out each others existence. I think existing is useful for accomplishing pretty much anything. And I think because two electron can't occupy the same exact place at the same time, that if you can play around with spins and charges the right way that you can force electrons out of an atom to build up a charge. I think there's some type of medical equipment that relies on spin to do that, it might be a defibrillator. Now that I think about it, it might rely on the spin of protons of hydrogen nuclei.

Edited by steevey

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It's called angular momentum because it's angular momentum. Whether this "logically relates" to ability of something spinning depends on your "logic." This is quantum mechanics. If "logic" means using classical physics as a premise, then the answer is no. The electron spin is inherent and quantized. Its magnitude never changes — all you can do is change the orientation.

There are spin behaviors between electrons. Did you read up on the Ising model link ajb provided?

Where or what is the Ising model link. I seem to have missed that one. Could you repeat the Link . Thanks.

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you know when an atom (which spins in a direction around its origin), is spinning around an outer point,

it just looks like how a planet is moving through space in a group ...

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you know when an atom (which spins in a direction around its origin), is spinning around an outer point,

it just looks like how a planet is moving through space in a group ...

Well, swan's going to probably punch you because he firmly believes that spin isn't physical in any sense.

Though I do have to point out that a magnetic field is a moving electrical field, so when an electron has a magnetic field oriented which ever way, what's moving the electrical field if not the particle itself in some way?

Edited by steevey

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If the spins didn't weren't opposite, then the electrons would cancel out each others existence. I think existing is useful for accomplishing pretty much anything. And I think because two electron can't occupy the same exact place at the same time, that if you can play around with spins and charges the right way that you can force electrons out of an atom to build up a charge. I think there's some type of medical equipment that relies on spin to do that, it might be a defibrillator. Now that I think about it, it might rely on the spin of protons of hydrogen nuclei.

Yes, well I'm not sure about all that you say, but you did mention previously about the tremendous forces present in collapsed stars which are held up by the very exclusion principle electrons not accepting to be identical in the same energy band. If this force is so great to operate under those vast conditions the exclusion principle must itself be quite something just between two electrons , being asked to occupy the same energy level with identicle quantum numbers ( which of course they refuse to do. )

So I am still trying to find out off someone What quite is it? ( other than the maths ) that is preventing the two identical electrons ( same quantum numbers ) from occupying the same energy level. I know the Pauli exclusion principle says so ( but a principle itself has no Force , it must work through something ! )

Is it the repulsive charge E1E2/r squared where r is so infinitessimally small that the electrostatic repulsion becomes infinite .

[ This is not put forward as fact , just a question ]

Edited by Mike Smith Cosmos

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Well, swan's going to probably punch you because he firmly believes that spin isn't physical in any sense.

Though I do have to point out that a magnetic field is a moving electrical field, so when an electron has a magnetic field oriented which ever way, what's moving the electrical field if not the particle itself in some way?

Electrons can have angular momentum from orbiting the nucleus, which creates a magnetic field. That is indeed a physical phenomenon. The only non-physical spin is the electron's intrinsic spin angular momentum.

Atoms are also allowed to spin and vibrate.

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Well, swan's going to probably punch you because he firmly believes that spin isn't physical in any sense.

Though I do have to point out that a magnetic field is a moving electrical field, so when an electron has a magnetic field oriented which ever way, what's moving the electrical field if not the particle itself in some way?

It's not my belief.

Take the electron charge and the experimentally determined size limit of the electron. Calculate how fast it would need to spin in order to generate the magnetic moment. Compare with c.

Where or what is the Ising model link. I seem to have missed that one. Could you repeat the Link . Thanks.

It was in a different thread

http://www.scienceforums.net/topic/54984-if-magnetism-is-the-result-of-angular-momentum/page__view__findpost__p__590682

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