What exactly is "spin"?

[Jakob]

This attribute of elementary particle/waves enables properties to communicate/travel (virtually) instantly.
What causes it?

[Anthem]

It's a way to describe the angular momentum of a particle. What causes it? No idea. Maybe some particle physicist can give an explanation.

The other part of your question is about entanglement. It's not really instant communication.

Interesting note about spin:

One consequence of the half-integer spins of neutrons and protons is that nuclei with an odd number of nucleons must have half-integer angular momentum, while nuclei having an even number of nucleons must have integer angular momentum (in units). Another consequence is quite bizarre: objects with half-integer spin must be rotated by 720° (not 360°) before they return to their initial state! This peculiar behavior has been demonstrated using very slow (ultracold) spin-oriented neutrons from a reactor, which are split into two beams. In one beam the neutrons are rotated about an axis along their direction of motion through some angle, and then the beams are recombined. It is found that when the rotation angle is 360°, the combined beams are out of phase and cancel, (meaning that they are shifted away from the detector) while after 720° of rotation the beams are in phase and reinforced (meaning that they show a large signal at the detector). A rotation of 720° is needed to put the neutrons back in their original state.

[north]

the circular rotation speed of the electron around the proton of an atom

sometimes though the electron dives down towards the proton , rare , but it happens

[Anthem]

It's the spin about its own axis, north.

In atomic physics, the spin quantum number is a quantum number that parameterizes the intrinsic angular momentum (or spin angular momentum, or simply spin) of a given particle. The spin quantum number is the fourth of a set of quantum numbers (the principal quantum number, the azimuthal quantum number, the magnetic quantum number, and the spin quantum number) which describe the unique quantum state of an electron and is designated by the letter s.

And where are you getting your information about electrons 'diving down' to the nucleus?

[north]

It's the spin about its own axis, north.

not sure what you mean by " own axis "

In atomic physics, the spin quantum number is a quantum number that parameterizes the intrinsic angular momentum (or spin angular momentum, or simply spin) of a given particle. The spin quantum number is the fourth of a set of quantum numbers (the principal quantum number, the azimuthal quantum number, the magnetic quantum number, and the spin quantum number) which describe the unique quantum state of an electron and is designated by the letter s.

And where are you getting your information about electrons 'diving down' to the nucleus?

a few years ago I got into non-destructive testing , there is maths invovled , and one of the instructure's was from Dafasco steel plant in Hamilton , Ontario

they had a a small , particle collider ( wow , who knew , and I only lived an hours drive from there !!!)

he told me of the electron diving down towards the proton

[Anthem]

not sure what you mean by " own axis "

Its own axis. Like this:

a few years ago I got into non-destructive testing , there is maths invovled , and one of the instructure's was from Dafasco steel plant in Hamilton , Ontario

they had a a small , particle collider ( wow , who knew , and I only lived an hours drive from there !!!)

he told me of the electron diving down towards the proton

I think you might be confusing what a particle accelerator can do with what an atom can't do. Electrons don't really orbit the nucleus the way a planet orbits a star, and electrons don't lose energy and spiral into the nucleus, if that's what you mean.

[Jakob]

It's a way to describe the angular momentum of a particle. What causes it? No idea. Maybe some particle physicist can give an explanation.

Is spin also applicable to the angular momentum of the earth orbiting the sun?

The other part of your question is about entanglement. It's not really instant communication.

Ok, but it seems instant compared to the speed of light.

" Another consequence is quite bizarre: objects with half-integer spin must be rotated by 720° (not 360°) before they return to their initial state!

"It is found that when the rotation angle is 360°, the combined beams are out of phase and cancel, (meaning that they are shifted away from the detector) while after 720° of rotation the beams are in phase and reinforced (meaning that they show a large signal at the detector). A rotation of 720° is needed to put the neutrons back in their original state.'

Cool!

[Anthem]

Is spin also applicable to the angular momentum of the earth orbiting the sun?

I believe it's at least analogous, if not the same thing (some particle physicist can set me right if I'm wrong on that).

The spin of 1/2 associated with an electron is kind of simplified. An electron's angular momentum is h bar over 2, with h bar being the reduced Planck's constant. This would lead to a value of about 5.27285×10^−35 J s.

Compare that to 7.089 x 10^33 J s I got for the earth. 68 orders of magnitude difference. Now, that's the earth rotating about itself, like in the gif I posted earlier. As for the earth rotating about the sun, well, WolframAlpha tells me that it's 2.662x10^40 J s (joule seconds) (with respect to Sun). 75 orders of magnitude there.

It's kind of interesting that you asked if it was applicable to the angular momentum of the earth orbiting the sun, because that same search on WolframAlpha returned this result:

2.524x10^74 (h bar) (reduced Planck constants)

Again, compare that to the angular momentum of an electron, 0.5 (h bar), and you get the same 75 orders of magnitude.

Ok, but it seems instant compared to the speed of light.

Well, that wikipedia article I linked to says it better than I'll be able to:

Observations pertaining to entangled states appear to conflict with the property of relativity that information cannot be transferred faster than the speed of light. Although two entangled systems appear to interact across large spatial separations, the current state of belief is that no useful information can be transmitted in this way, meaning that causality cannot be violated through entanglement. This is the statement of the no-communication theorem.

Even if information cannot be transmitted through entanglement alone, it is believed[who?] that it is possible to transmit information using a set of entangled states used in conjunction with a classical information channel. This process is known as quantum teleportation. Despite its name, quantum teleportation may still not permit information to be transmitted faster than light, because a classical information channel is required to complete the process.

In addition experiments are underway to see if entanglement is the result of retrocausality.[4][5]

Cool!

I know, right?

[Jayson]

This attribute of elementary particle/waves enables properties to communicate/travel (virtually) instantly.
What causes it?

Split a photon.
You'll get what you need.
Two types of eddies; one side will be an electron spin; the other a positron spin.

Where's Farsite?

[Anthem]

Why do you think fluid flow is a good comparison?

[Jayson]

Why do you think fluid flow is a good comparison?

If you were asking me this, my answer is:

Well...honestly, I would have rather preferred a picture of water than air, but same difference overall for your question I suppose.
In answer, because a photon is a wave in the same way that a wave is a wave in the water.

Instead of thinking of it from the top of the water, like we think of more often when we diagram it as a wave, think of it inside of the water where it isn't a thing separate from the water, but instead is a displacement in the water.

Same goes for a gust of air.

They aren't separate things, but displacements moving along within.

A photon is being shown the same way.
It is being shown as not a separate thing from space, but a displacement of it rippling through it in a wave that is more or less eye shaped length wise.
Just like the wave in the water; the wave is just a force of displacement in the water...not the water itself.
I know is sounds like I just countered myself, "It's the same as the water, but not the water"...what I mean is that in being the force of dispacement inside of space/water/air, then you have it trapped (for lack of a better term) from being separate from space/water/air, but it isn't the space/water/air itself, but the force of a single "particle" of displacement (the photon) in space.

When it is split, we know what we get.
We get the electron and the positron.

And we know that the spin of an electron is opposite spin of the positron spin.

This kind of starts to fall into place on it's own with that last bit...you started with one thing A moving along and then it is "hit" by something B and as a result you have A1 and A2 off-shoots and when you have A1 and A2, you find that A1 rotates one direction and A2 rotates the opposite direction.
Then you are told that neither A1 or A2 can be tangibly seen, and that as a result of this A1 and A2 not directly being "held" or seen that an entire set of physics exists to explain that a string in another dimension is bouncing and the tip of that string in this dimension is what gives us A1 all over the place randomly seeming instead of in one direct spot, but still with it's rotation intact.

Or...A is a wave displacement that split when hitting B length-wise, and that A1 and A2 are spinning in opposing directions because they are on opposite sides of B width-wise and the remainders of A when it hits B.

And the way I showed that is pretty simplistic form of it...water, or air, are actually more alive and less predictable as that nice and tidy diagram, and particles are absolutely no different.













Very fluid.

[Anthem]

You can't show pictures of a bubble chamber which induces the helical motion from a magnetic field to prove your point. It might look curvy and liquidesque and turbulent, but that's from the parameters of the experiment.

Pair production is a whole lot different than turbulence, which is a whole lot more complicated than clockwise flow and counterclockwise flow.

[Jayson]

Like I said before...I lack the ability to explain this really accurately...
Farsite is far better, as it's his product I'm really relaying (and probably not terribly well), but he does a very nice job explaining this.

If you drop him a PM, he might be able to explain this better.


But I wasn't saying it is directly like water or air fluid motion, but instead that this is the closest mental model to use.
Obviously it's not directly the same, because the spins are in the opposite directions that you would get if it were directly the same.

[Xunzian]

Isn't is just a term they've applied to a particular quantum state? I'm no physicist, but isn't it kind of like asking what exactly are "latitude and longitude"? They certainly can be used to correspond to real places but latitude and longitude are just mathematical operations used to identify those places. What they are terms in a mathematical model. A big, nasty mathematical model. Describing them beyond the language of math is pretty difficult because, well, that is where they exist. And translating math into English or any other spoken human language can be pretty difficult.

[Anthem]

It's an actual thing, not just a number. It's not exactly like a spinning top or planet, but, well...here:

It turns out that the spin vector is not very useful in actual quantum mechanical calculations, because it cannot be measured directly — sx, sy and sz cannot possess simultaneous definite values, because of a quantum uncertainty relation between them. However, for statistically large collections of particles that have been placed in the same pure quantum state, such as through the use of a Stern-Gerlach apparatus, the spin vector does have a well-defined experimental meaning: It specifies the direction in ordinary space in which a subsequent detector must be oriented in order to achieve the maximum possible probability (100%) of detecting every particle in the collection. For spin-1/2 particles, this maximum probability drops off smoothly as the angle between the spin vector and the detector increases, until at an angle of 180 degrees — that is, for detectors oriented in the opposite direction to the spin vector—the expectation of detecting particles from the collection reaches a minimum of 0%.

As a qualitative concept, the spin vector is often handy because it is easy to picture classically. For instance, quantum mechanical spin can exhibit phenomena analogous to classical gyroscopic effects. For example, one can exert a kind of "torque" on an electron by putting it in a magnetic field (the field acts upon the electron's intrinsic magnetic dipole moment — see the following section). The result is that the spin vector undergoes precession, just like a classical gyroscope.

Mathematically, quantum mechanical spin is not described by vectors as in classical angular momentum, but by objects known as spinors. There are subtle differences between the behavior of spinors and vectors under coordinate rotations. For example, rotating a spin-1/2 particle by 360 degrees does not bring it back to the same quantum state, but to the state with the opposite quantum phase; this is detectable, in principle, with interference experiments. To return the particle to its exact original state, one needs a 720 degree rotation. A spin-zero particle can only have a single quantum state, even after torque is applied. Rotating a spin-2 particle 180 degrees can bring it back to the same quantum state and a spin-4 particle should be rotated 90 degrees to bring it back to the same quantum state. The spin 2 particle can be analogous to a straight stick that looks the same even after it is rotated 180 degrees and a spin 0 particle can be imagined as sphere which looks the same after whatever angle it is turned through.

[Jakob]

Isn't is just a term they've applied to a particular quantum state? I'm no physicist, but isn't it kind of like asking what exactly are "latitude and longitude"? They certainly can be used to correspond to real places but latitude and longitude are just mathematical operations used to identify those places. What they are terms in a mathematical model. A big, nasty mathematical model. Describing them beyond the language of math is pretty difficult because, well, that is where they exist. And translating math into English or any other spoken human language can be pretty difficult.

Math without physics strikes me as nonsense. This is a huge topic in itself, much larger than what spin is, and I take a very blunt position, possibly out of ignorance. But I think that mathematics, since it is derived of physics, should always allow itself ot be verified by physics, and therefore can never amount to ''something'' wholly separate from physical reality. And what I've often read (and noticed) is physical theories can, when they're sound, usually be explained in layman terms. String theory, to illustrate my perspective, does not qualify as a physical theory, because it cannot be verified, and needs all these bizarre hypotheses about physical reality such as coiled up dimensions. That seems like a mathematical 'thing'.

Spin on the other hand was explained to me in quite simple terms here by Anthem, and as a result I 'sense' it. I realize it's not exactly the same as a planets orbital momentum, expecially because it has to do with fixed states, steps, whereas in the case of macro objects there is a continuum. But with this analogy I can kind of graps the concept. I could also imagine what entanglement would mean if it was applied to orbits of planets around stars or moons around planets - but that is of course strictly hypothetical since no planet or star is of an exactly equal mass. Still, the average persons imagination works quite well in accordance with physics, less so with mathematics... but I'm not sure this means mathematics is 'deeper'. just more abstract and hence infinitely complicated.

Observations pertaining to entangled states appear to conflict with the property of relativity that information cannot be transferred faster than the speed of light. Although two entangled systems appear to interact across large spatial separations, the current state of belief is that no useful information can be transmitted in this way, meaning that causality cannot be violated through entanglement. This is the statement of the no-communication theorem.

Even if information cannot be transmitted through entanglement alone, it is believed[who?] that it is possible to transmit information using a set of entangled states used in conjunction with a classical information channel. This process is known as quantum teleportation. Despite its name, quantum teleportation may still not permit information to be transmitted faster than light, because a classical information channel is required to complete the process.

In addition experiments are underway to see if entanglement is the result of retrocausality.

Thanks for clarifying. That's a bit of a disillusionment of course - quantummechanics always suggests these gigantic possibilities for manipulation of matter, and then it turns out Newton still has the final verdict.

[Mr_Anderson]

dp.

[Mr_Anderson]

Isn't is just a term they've applied to a particular quantum state? I'm no physicist, but isn't it kind of like asking what exactly are "latitude and longitude"? They certainly can be used to correspond to real places but latitude and longitude are just mathematical operations used to identify those places. What they are terms in a mathematical model. A big, nasty mathematical model. Describing them beyond the language of math is pretty difficult because, well, that is where they exist. And translating math into English or any other spoken human language can be pretty difficult.

They apply to a physical state and are corelated in polarity up or down at angle x, hence polarisation of light. Charge etc.

You can filter out some wavelengths by using polarised windows etc. So it is definitively and intimately related, it might not be an exact pictorial representation it's not possible to tell with light or electrons exactly, but fremions do have half integer spin and they do have angular momentum and we do use the spin to indicate a change from positive to negative charge or polarisation of light etc and the forces which have poles.

wave function goes between 0 and 1/2 in x.

Goes between -1,-1/2,0,1/2 and 1 in an electron, hence spin. And hence the circle is a representation of a wave ie cos sin etc as a cyclic rotation or of 360 as say frequency goes from + to - or we traverse the circle as the charge goes from + to - etc.

All known fermions are particles with half-integer spin: as an observer circles a fermion (or as the fermion rotates 360° about its axis) the wavefunction of the fermion changes sign. In the framework of nonrelativistic quantum mechanics, this is a purely empirical observation. However, in relativistic quantum field theory, the spin-statistics theorem shows that half-integer spin particles cannot be bosons and integer spin particles cannot be fermions.[2]

In large systems, the difference between bosonic and fermionic statistics is only apparent at large densities when their wave functions overlap. At low densities, both types of statistics are well approximated by Maxwell-Boltzmann statistics, which is described by classical mechanics.

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


y = Sin(x)

[Farsight]

Hi guys.

See http://en.wikipedia.org/wiki/Spin_(physics) which describes spin as "a fundamental characteristic property of elementary particles" and doesn't really get to the bottom of it. To understand what exactly it is, you need to pull back to the photon and the electromagnetic field, and check out pair production and annihilation to understand the electron. There are bona-fide peer-reviews papers on this, like http://arxiv.org/abs/0803.2596 and http://arxiv.org/abs/physics/0512265, but they haven't hit the popular media yet. What they're saying is that spin is a real rotation. It has to be, the electron really does have angular momentum.

In a nutshell you take a tip from LIGO, which is searching for gravity waves. These are expected to change the length of the arms of the interferometer. Then you say to yourself that a gravity wave is a wave of "spacewarp", and treat the photon as something similar. It's an electromagnetic wave in space, but what exactly is "waving"? There's only space there, so you have to look past the electromagnetic field and say "space". That means the photon is a wave of spacewarp too. It normally travels laterally at c, but pair production converts a +1022keV photon into an electron and a positron. These aren't travelling laterally at c, but they have opposite spin, so it is rather like the two opposite eddies that TheStumps mentioned. The spacewarp isn't travelling laterally at c any more, because it travels through itself. It's travelling through warped space, so it doesn't travel in a straight line. Instead it goes round and round.

However when you look into the mathematical details of this, (see http://www.cybsoc.org/cybcon2008prog.htm#jw) you find that rotation has to be in two dimensions. The best way to think of it is like the rotation of a steering wheel coupled to the rotation of a smoke ring. With this double rotation, you can no longer define which direction the spin is going. To understand this, think of ordinary spin as flying around the equator. It's a nice tidy circle with a nice tidy orientation, and you can adjust your flight path to fly from pole to pole. That's another nice tidy circle with a nice tidy orientation. But if you're continually adjusting your flight path so that you fly around the earth in a figure-of-eight motion, what direction are you flying in? You can't really say, because it keeps changing, and for the same reason you can't really assign a direction to electron spin. However if you flew backwards in the figure-of-eight loop, there is a clear difference. This is why we can distinguish electron spin and positron spin. Here's a depiction to give you an idea. The dark black line is the figure-of-eight loop, rearranged a little to map out a toroid rather than a sphere:



As for what's spinning, the electron is made via pair production. You start with light. You can then destroy the electron via annihilation, and the result is light. Basically what's spinning, is light. It's all spelled out in layman's terms in http://www.amazon.co.uk/RELATIVITY-Theo ... 0956097804. Even a child can understand it.

[Mr_Anderson]

Interesting Farsight. Not seen it described that way before, I'm not sure how empirically valid it is but then spin is an issue that doesn't lend well to classical representation, nor is it tidilly represented by maths as such. I'm the last person to think that anyone has really nailed the actuality beyond the equations and there are a million and one formulations. What we end up with is the fact that waves are wave like and adequately described by formulations of angular momentum, and they may change sign or polarity and they may not according to which fermion they are, beyond that it's very much a matter of interpretaion and ideally philosophical.

No a child can't understand it, even an adult can't that's why it's called science, most people wouldn't know there arse from their elbow, even some people in science. And even I to some extent.

That said I'm confused about pair production here? Not sure what you are saying?

[Jakob]

As for what's spinning, the electron is made via pair production. You start with light. You can then destroy the electron via annihilation, and the result is light. Basically what's spinning, is light.

Greetings Lord Farsight. Thanks for this long awaited response.
Is it correct to say that light is made into an electron through the mechanism of spin? That's what I get out of this at first glance. That light is trapped into a self referring path, by splitting in two and revolving around itself, so to speak. Confining it to a more or less set location, making it into something resembling a particle, by inter-inter-interference.

[Mr_Anderson]

As for what's spinning, the electron is made via pair production. You start with light. You can then destroy the electron via annihilation, and the result is light. Basically what's spinning, is light.

Greetings Lord Farsight. Thanks for this long awaited response.
Is it correct to say that light is made into an electron through the mechanism of spin? That's what I get out of this at first glance. That light is trapped into a self referring path, by splitting in two and revolving around itself, so to speak. Confining it to a more or less set location, making it into something resembling a particle, by inter-inter-interference.

Not sure I agree with that formalisation but it's a semantic issue anyway light is made out of energy, electrons are energy, thus all particles ultimately decay to photons or energy, even electrons which are themselves "fundamental" fermions. The mathematics of spin are fairly obviously correct within the axioms of maths and science. The interpretational issues are obviously a matter of taste though hence Bohmian, RSM, statistical ensemble, Shut Up, No Really Just STFU (SUNRJSTFU), and Copenhagen and Many worlds etc. Also hence various background dependant hypothesis such as the standard models Higgs, Loop Quantum Gravity, String Hypothesis and the above model by Farsight also I presume hypothetical, or probably based on a reworking of many others hypothesis? Don't know...

Background independant models like String Theory which is of course made up by maths people for maths people to ponder, and determine a use outside of physics for, or to pass on to M-Theorists also a misnomer who then build an extra level on top of it commonly known as a crock or "Science" with a capital S for Special.

[Jakob]

References! Names! You can drop many, I have to admit it. I could also drop them. But it's not fame I'm after, not association with famous people, but to lay bare the simplicity of the mechanism so I can understand it.

I am also in the dark about pair production. This seems to be the mechanism which underlies spin, the method by which light is transformed from a singularity into a duality, and so takes on substance. It could be a metaphor for the entire human condition. The pure body of light, Adam splitting in two becoming a pair and subsequently being bound to matter, revolving around itself, and revolving together around a core. Human interpretation, that's all it is on whatever level. But how does it happen?

It seems that physics is the art of predicting which state will transform into which. The laws of the universe are understood as A + B => C. But the => itself is never touched upon. Physicists have enough respect for it, reverence even, to understand that this is exactly what needs to be danced around.

[north]

References! Names! You can drop many, I have to admit it. I could also drop them. But it's not fame I'm after, not association with famous people, but to lay bare the simplicity of the mechanism so I can understand it.

spin is the resultant of confined energy and/or movement , within a confined space

I am also in the dark about pair production. This seems to be the mechanism which underlies spin, the method by which light is transformed from a singularity into a duality, and so takes on substance. It could be a metaphor for the entire human condition. The pure body of light, Adam splitting in two becoming a pair and subsequently being bound to matter, revolving around itself, and revolving together around a core. Human interpretation, that's all it is on whatever level. But how does it happen?

yet the proton spins in the hyrogen atom

where there is no electron

[Jakob]

References! Names! You can drop many, I have to admit it. I could also drop them. But it's not fame I'm after, not association with famous people, but to lay bare the simplicity of the mechanism so I can understand it.

spin is the resultant of confined energy and/or movement , within a confined space

not also it's cause, or at least it's enabler?

I am also in the dark about pair production. This seems to be the mechanism which underlies spin, the method by which light is transformed from a singularity into a duality, and so takes on substance. It could be a metaphor for the entire human condition. The pure body of light, Adam splitting in two becoming a pair and subsequently being bound to matter, revolving around itself, and revolving together around a core. Human interpretation, that's all it is on whatever level. But how does it happen?

yet the proton spins in the hyrogen atom

where there is no electron

Ah, really? I didn't realize protons spin. As a unity, or is it also split up?