Spin

[Klaynos]

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Moderator Note

Please keep speculative answers and your own pet theories to their own threads in speculations.

So, Lemur feel free to answer Mike Smith Cosmos but in a separate thread.

[Mike Smith Cosmos]

!

Moderator Note

Please keep speculative answers and your own pet theories to their own threads in speculations.

 

So, Lemur feel free to answer Mike Smith Cosmos but in a separate thread.

 

Sorry. I have removed the questions that could lead to speculation. I have been trying to stimulate a meaningful discussion on Spin and thus angular momentum.

[Klaynos]

Sorry. I have removed the questions that could lead to speculation. I have been trying to stimulate a meaningful discussion on Spin and thus angular momentum.

 

We try and keep the science forums to mainstream science, feel free to start a thread in speculations asking for peoples own ideas though.

[steevey]

Mass is not conserved, so why would matter be conserved?

 

 

 

See, you just did it again. Claimed to be right, but you have given no supporting evidence. No physics argument, no link. Consider the possibility that your understanding of what you heard is wrong or your memory is wrong. Come up with e-v-i-d-e-n-c-e as a rebuttal, not just contrariness.

 

 

 

I will reiterate: what you want to call "real" is a matter of debate. In another thread.

 

The evidence was that wiki-article of mass-energy equivalence which I'll post again here. I'm not insisting I'm right, I'm insisting that the information given to me from wikipedia is right which had already been posted

http://en.wikipedia....rgy_equivalence is right.

I already did consider the possibility that I was wrong which is why I was agreeing with this that neither matter nor energy can be created or destroyed, but the units can be changed, which means I was previously wrong before that in saying that matter can transform into energy, since that would require an amount of energy to be created. So, a good explanation would be that only the location of energy changes, which as far as I know can only assume that it can be more concentrated or less concentrated in certain regions, i.e. a single atom can have more energy or less energy.

Edited March 1, 2011 by steevey

[Mike Smith Cosmos]

We try and keep the science forums to mainstream science, feel free to start a thread in speculations asking for peoples own ideas though.

 

I am not totally certain where " a thread in speculations " is ? Do you mean I should start a new thread in forum with the name "speculation" in the title ? do you mean the thread "Ideas"? Perhaps you could clarify. Also what happens in the subject areas of quantum theory where nobody really knows whats going on properly and there are a lot of different ideas currently being proposed even in string theory and multiverses where little is proven if anything ?

Edited March 1, 2011 by Mike Smith Cosmos

[ajb]

Also what happens in the subject areas of quantum theory where nobody really knows whats going on properly and there are a lot of different ideas currently being proposed even in string theory and multiverses where little is proven if anything ?

 

I would say that if there has been at least one publication on the subject in a peer review journal then it can be discussed in "physics". If it is your own pet idea, and especially if it is not compatible with established physics the it is better off in "speculations".

 

One key thing here is that, for example string theory has a mathematical framework and as such we can perform calculations. Most of the "theories" in the speculations section are not like that at all.

[Mike Smith Cosmos]

I would say that if there has been at least one publication on the subject in a peer review journal then it can be discussed in "physics". If it is your own pet idea, and especially if it is not compatible with established physics the it is better off in "speculations".

 

One key thing here is that, for example string theory has a mathematical framework and as such we can perform calculations. Most of the "theories" in the speculations section are not like that at all.

 

Where is this speculations section ?

[ajb]

http://www.scienceforums.net/forum/29-speculations/

[Mike Smith Cosmos]

http://www.sciencefo...9-speculations/

 

Ive looked at the speculations section .

 

I will probably try a few speculative ideas there sometime, However I would like to keep this very interesting subject of Spin going on a serious note If thats O.K.

[swansont]

The evidence was that wiki-article of mass-energy equivalence which I'll post again here. I'm not insisting I'm right, I'm insisting that the information given to me from wikipedia is right which had already been posted

http://en.wikipedia....rgy_equivalence is right.

I already did consider the possibility that I was wrong which is why I was agreeing with this that neither matter nor energy can be created or destroyed, but the units can be changed, which means I was previously wrong before that in saying that matter can transform into energy, since that would require an amount of energy to be created. So, a good explanation would be that only the location of energy changes, which as far as I know can only assume that it can be more concentrated or less concentrated in certain regions, i.e. a single atom can have more energy or less energy.

 

You should read the included link, which explains how mass and matter are not actually conserved, in general.

 

the principle of matter conservation (in the sense of conservation of particles which are agreed to be "matter") may be considered as an approximate physical law, that is true only in the classical sense, without consideration of special relativity and quantum mechanics

…

Mass is also not generally conserved in "open" systems (even if only open to heat and work), when various forms of energy are allowed into, or out of, the system (see for example, binding energy).

 

http://en.wikipedia.org/wiki/Conservation_of_mass

[steevey]

Does the property of spin act as if the electron were a single point in space? I can see how a wave will change its frequency and its oscillation and how a wave on an oscillometer coincides with the way the electron acts, but I still don't see how a wave like an electron has a specific angular momentum or spin unless the angular momentum is a property of an electron being like a particle and not only as a wave.

Edited March 2, 2011 by steevey

[Mike Smith Cosmos]

Does the property of spin act as if the electron were a single point in space? I can see how a wave will change its frequency and its oscillation and how a wave on an oscillometer coincides with the way the electron acts, but I still don't see how a wave like an electron has a specific angular momentum or spin unless the angular momentum is a property of an electron being like a particle and not only as a wave.

 

Steevey, I have been asked by the moderator and resident expert to keep these main Physics forums to strictly answers supported by published scientists rather than our own ideas. As such I need to do some more research, to dig up some published works on spin. However I feel we could throw this question of spin open to the greater scientific community in case there are some eminent scientists, who visit this forum, who are publishing scientists in this field . So :-

 

 

Is there is anyone out there who can explain HOW/WHY the, Pauli exclusion principle, which we believe is responsible for the quantum property of only allowing one up spin and one down spin in a single electron pair. ( eg first orbit ) ?

Edited March 2, 2011 by Mike Smith Cosmos

[swansont]

Spin 1/2 particles (Fermions) have antisymmetric wave functions. Integral spin particles (Bosons) have symmetric wave functions. That has ramifications for what happens when you have two identical particles trying to occupy the same state, but the details of this requires that you understand something about quantum mechanics

 

http://en.wikipedia.org/wiki/Pauli_Exclusion_Principle#Connection_to_quantum_state_symmetry

 

The short answer is that switching two particles should give you the same answer regarding the wave function — they particles are identical — but for antisymmetric particles, that can't happen if they are in the same state: you get the opposite sign. It only works if the occupation that system state is zero.

[Klaynos]

I feel it is probably worthy of note at this point that an electron is neither a wave nor a particle. It has properties that are wavelike and properties that are particle like, it is something else.

 

I'll try and find a good reference on the Pauli exclusion principle, I can't remember the integral I am trying to at the moment which I seem to recall will aid understanding here. Might have to wait until I get home.

[steevey]

Spin 1/2 particles (Fermions) have antisymmetric wave functions. Integral spin particles (Bosons) have symmetric wave functions. That has ramifications for what happens when you have two identical particles trying to occupy the same state, but the details of this requires that you understand something about quantum mechanics

 

http://en.wikipedia...._state_symmetry

 

The short answer is that switching two particles should give you the same answer regarding the wave function — they particles are identical — but for antisymmetric particles, that can't happen if they are in the same state: you get the opposite sign. It only works if the occupation that system state is zero.

 

Can spin occur without the Pauli exclusion principal, like with a free electron or a photon? Because it seems like spins are only being used when you need to use combined wave functions to describe two particles in the same states, or that they need to have a different property of angular momentum to "avoid" each other and not be in the same place at the same time, and thats it.

 

I feel it is probably worthy of note at this point that an electron is neither a wave nor a particle. It has properties that are wavelike and properties that are particle like, it is something else.

 

Well I think an electron is a wave and a particle in the sense that photons are a wave and a particle by seeming to exist in specific regions at a time but also spanning over undefined areas and having things like a wave oscillation. Whether any piece of matter in the universe is actually a wave and a particle, I guess scientists can't say for sure, but if I put an electron through a slit, it acts just like a wave of probability, and the mathematics which describes it accurately also states an electron is a wave, so why wouldn't it be a wave at least some of the time?

I think whats going on is that an electron doesn't physically move distance in a pattern determined by spin an angular momentum, but that spin an angular momentum effect the pattern of where the electron shows up, almost classically in fact. I'm going to work on an art thing to show you what I mean.

Edited March 2, 2011 by steevey

[swansont]

Can spin occur without the Pauli exclusion principal, like with a free electron or a photon? Because it seems like spins are only being used when you need to use combined wave functions to describe two particles in the same states, or that they need to have a different property of angular momentum to "avoid" each other and not be in the same place at the same time, and thats it.

 

Only half-integral spin particles are subject to the Pauli exclusion principle.

 

Well I think an electron is a wave and a particle in the sense that photons are a wave and a particle by seeming to exist in specific regions at a time but also spanning over undefined areas and having things like a wave oscillation. Whether any piece of matter in the universe is actually a wave and a particle, I guess scientists can't say for sure, but if I put an electron through a slit, it acts just like a wave of probability, and the mathematics which describes it accurately also states an electron is a wave, so why wouldn't it be a wave at least some of the time?[/font]

 

I think whats going on is that an electron doesn't physically move distance in a pattern determined by spin an angular momentum, but that spin an angular momentum effect the pattern of where the electron shows up, almost classically in fact. I'm going to work on an art thing to show you what I mean.

 

I'd rephrase Klaynos's statement slightly. A QM "particle" behaves like a wave, but also has characteristics that we do not associate with waves, like localization, which are more commonly associated with particles. It's not really quite the either/or situation that is described in beginning physics; that's used as a simplification. The actual behavior is more complex, and in trying to extrapolate from that simplified model you are going to miss things.

[Mike Smith Cosmos]

Spin 1/2 particles (Fermions) have antisymmetric wave functions. Integral spin particles (Bosons) have symmetric wave functions. That has ramifications for what happens when you have two identical particles trying to occupy the same state, but the details of this requires that you understand something about quantum mechanics

 

http://en.wikipedia...._state_symmetry

 

The short answer is that switching two particles should give you the same answer regarding the wave function — they particles are identical — but for antisymmetric particles, that can't happen if they are in the same state: you get the opposite sign. It only works if the occupation that system state is zero.

 

I understand , I believe, that the de broglie wave function is a probability wave associated with everything but mainly significant at atomic levels. You are saying I believe ( do put me right ) that the electron being a fermion has an (asymmetric or antisymetric ?) wave function , not the textbook small sinusoidal rising to large sinsoidal falling to small sinusoidal again symemetrically about the peak.

 

I have asked this before. How do these probability waves compare with ordinary constant amplitude sinusoidal Electro magnetic waves, or are they somehow part of the same thing ?

Edited March 2, 2011 by Mike Smith Cosmos

[steevey]

Only half-integral spin particles are subject to the Pauli exclusion principle.

 

 

 

I'd rephrase Klaynos's statement slightly. A QM "particle" behaves like a wave, but also has characteristics that we do not associate with waves, like localization, which are more commonly associated with particles. It's not really quite the either/or situation that is described in beginning physics; that's used as a simplification. The actual behavior is more complex, and in trying to extrapolate from that simplified model you are going to miss things.

 

Think about the fact that atoms bond at specific angles. This is due to how the electron cloud is shaped, but its shaped in specific ways in specific shapes at specific places around the nucleus according to properties such as angular momentum.

 

Imagine this as a clip of relatively where the electron is appearing and disappearing to

 

 

And if you looked at all the places the electron has been through the course of its movement, it would have some type of angular momentum-like appearance like this

only in a real atom, it would be doing this is a spherical or helical manner

 

The reason electrons appear to have spin or angular momentum is because there is an almost physical angular pattern or a pattern at which electrons appear and disappear to.

 

For instance, an electron at the ground state would appear to have a spin 1/2 and combined with the other properties, the electron appears and disappears in a way that makes a symmetric cloud in all directions, known as a sphere. So the things that appear to be physical spinning or angular momentum is because of how the electron appears and re-appears in certain regions.

 

Spin is also said to generate a magnetic field, and a magnetic field is a moving electrical field, which means electrons actually are rotating some way as to cause this electrical field motion, or its something to do with how an electron moves like a I stated, which came from this http://www.angelo.ed...tum_Numbers.htm

According to that, electrons are somehow actually spinning, which is causes their magnetic field.

Edited March 3, 2011 by steevey

[swansont]

Spin and orbital angular momentum are separate things.

 

http://www.angelo.ed...tum_Numbers.htm

According to that, electrons are somehow actually spinning, which is causes their magnetic field.

 

It's wrong.

 

I understand , I believe, that the de broglie wave function is a probability wave associated with everything but mainly significant at atomic levels. You are saying I believe ( do put me right ) that the electron being a fermion has an (asymmetric or antisymetric ?) wave function , not the textbook small sinusoidal rising to large sinsoidal falling to small sinusoidal again symemetrically about the peak.

 

I have asked this before. How do these probability waves compare with ordinary constant amplitude sinusoidal Electro magnetic waves, or are they somehow part of the same thing ?

 

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)

[Mike Smith Cosmos]

Spin and orbital angular momentum are separate things.

 

 

 

It's wrong.

 

 

 

 

 

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)

 

Thanks I am just trying to get my head around the Pauli Exclusion principle Wikipedia Link you gave me yesterday. Can't quite get my head round the " antisymmetric rank two tensor " and the state they get themselves in. I might need a little while and a few paracetamols. Any translation would be gratefully received.

[ajb]

Can't quite get my head round the " antisymmetric rank two tensor " and the state they get themselves in. I might need a little while and a few paracetamols. Any translation would be gratefully received.

 

You pick up a minus sign when you interchange the order in some ordered collection of objects, say the indices of a tensor:

 

[math]T^{AB} = - T^{BA}[/math]

 

Consider a system with two electron states, then we have

 

[math]\psi(e_{1}, e_{2}) = - \psi(e_{2}, e_{1})[/math].

 

(as quantum particles all electrons are indistinguishable. The e's really refer to the possible states rather than the electrons themselves.)

 

Now suppose we try to put these two electrons in the same state:

 

[math]\psi(e_{1}, e_{1}) = - \psi(e_{1}, e_{1}) = 0[/math].

 

Then we see that the result vanishes and thus we cannot put two electrons in the same state.

 

The Pauli exclusion principle is really identical to the antisymmetry of the wave-functions.

 

Bosonic particle have symmetric wave-functions, so you can put as many as you like in the same state.

[swansont]

Thanks I am just trying to get my head around the Pauli Exclusion principle Wikipedia Link you gave me yesterday. Can't quite get my head round the " antisymmetric rank two tensor " and the state they get themselves in. I might need a little while and a few paracetamols. Any translation would be gratefully received.

 

The very basic answer is that there is a way (via interference effects) you could tell the electrons apart, and they're supposed to be identical. That's contradictory. Thus, the particles cannot be in a condition where you could do this. The rank two tensor is part of the math which describes the states.

[Mike Smith Cosmos]

You pick up a minus sign when you interchange the order in some ordered collection of objects, say the indices of a tensor:

 

[math]T^{AB} = - T^{BA}[/math]

 

Consider a system with two electron states, then we have

 

[math]\psi(e_{1}, e_{2}) = - \psi(e_{2}, e_{1})[/math].

 

(as quantum particles all electrons are indistinguishable. The e's really refer to the possible states rather than the electrons themselves.)

 

Now suppose we try to put these two electrons in the same state:

 

[math]\psi(e_{1}, e_{1}) = - \psi(e_{1}, e_{1}) = 0[/math].

 

Then we see that the result vanishes and thus we cannot put two electrons in the same state.

 

The Pauli exclusion principle is really identical to the antisymmetry of the wave-functions.

 

Bosonic particle have symmetric wave-functions, so you can put as many as you like in the same state.

 

 

Are you saying that because the maths comes out with a zero that means it cant happen because this is a probability zero.

the wave function presumably is the schrodingers equation with psi the wave function . I get a little worried when maths predicts something, yet one is very unsure ( or at least I am that I am totally at sea as what ( dare I say it physically ) is actually causing the electrons to put up the most giant resistive pressure to refuse to be put in the same quantum state. ( ie in collapsing stars. ) I worry that maths is describing whats happening rather than telling us what actually is happening. Are you saying that there are NOT two electrons there, these are just possible states and thus you can not put then in the exactly the same state twice at the same ( EEk Time ).

 

The very basic answer is that there is a way (via interference effects) you could tell the electrons apart, and they're supposed to be identical. That's contradictory. Thus, the particles cannot be in a condition where you could do this. The rank two tensor is part of the math which describes the states.

 

I think I need to go and lay down or go for a cycle ride and look at birds. My head hurts ! Thanks . Speak to you later.

Edited March 3, 2011 by Mike Smith Cosmos

[ajb]

I get a little worried when maths predicts something, yet one is very unsure ( or at least I am that I am totally at sea as what ( dare I say it physically ) is actually causing the electrons to put up the most giant resistive pressure to refuse to be put in the same quantum state. ( ie in collapsing stars. ) I worry that maths is describing whats happening rather than telling us what actually is happening.

 

It is an observed fact that you cannot put two electrons in exactly the same sate. For example, we see this in the spectra of the hydrogen atom.

 

In modelling this natural phenomena we employ antisymmetric wave-functions.

 

I am not sure one can say a lot more than this. We use the mathematics to model the system and make predictions that we can test. Is the mathematics "real" or not is in my mind quite philosophical.

[Mike Smith Cosmos]

It is an observed fact that you cannot put two electrons in exactly the same sate. For example, we see this in the spectra of the hydrogen atom.

 

In modelling this natural phenomena we employ antisymmetric wave-functions.

 

I am not sure one can say a lot more than this. We use the mathematics to model the system and make predictions that we can test. Is the mathematics "real" or not is in my mind quite philosophical.

 

 

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

 

Am I up against the Feynman statement of yes it (QM ) stacks up to 10 to the umpteenth decimal place but we don't understand it. I have been reading about Pauli thinking about this a lot and Goodsmit and Uhlenbeck thinking a lot about it but then it goes a bit mathematical.