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Offline BenVitale

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« on: 01/12/2007 07:19:13 »
why does an electron have intrinsic spin?

There's something I fail to understand.



 

Offline BenVitale

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« Reply #1 on: 01/12/2007 07:39:41 »
Pauli and Dirac matrices show the existence of spin, but this doesn't really explain the physical origins of the spin. One may says that spin is an intrinsic property of the matter.

Can anyone explain the nature of spin?
 

Offline syhprum

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« Reply #2 on: 01/12/2007 10:52:00 »
Can we really think of an Electron having spin in the simplest meaning of the word ?.
One theory says that an Electron is a point object hence any spin would produce an infinite speed on its equator if indeed it could be said to have one!.
other theories credit the electron with a radius (defined to 3 decimal spaces !) hence if it is spinning there must be equatorial speed, how much ? more or less than c ?.
If an electron is not a singularity what is its density ? and why does it not evaporate like a black hole ?.
It is well established that an Electron "orbiting" a Proton produces a strong magnetic field (45 T ?), does a spinning electron do the same ?.
 

Offline socratus

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« Reply #3 on: 01/12/2007 19:15:31 »
why does an electron have intrinsic spin?

There's something I fail to understand.
=========================================================================
In 1687, the book "Mathematical beginnings of natural philosophy"
by Isaac Newton was printed out. In the foreword to this book, Newton has written:
"All the difficulty of physics, as it will be seen, is in recognizing
forces of the nature by the phenomena of motion,
and then to explain other phenomena according to
"The First Newton's law" breaks on the spot
this well formulated logical thought.
It states:
"Any body, until it remains insulated,
saves its state of rest or rectilinear motion".
This law of motion is considered fundamental in classic physics.
However, it permanently causes critics of initial positions of mechanics.
Because in earthly conditions it is defaulted.
This law does not take into consideration influence of external forces
; it also says nothing about internal forces. The reason on which the body
is moving or rests is not clear. This law is abstract.
Newton perceived illusiveness of this law. His scientific slogan was:
"I do not invent hypotheses".
He said: "I shall not mix conjectures with reliability".
He aimed to build a building of science without hypotheses.
Therefore, he wanted to correct somehow, to change his formulation.
But all attempts were unsuccessful.
However, this law is useful and necessary to explain then accelerated motion.
For this reason, this postulate of Newton
was forced and wrongfully erected to a rank of the law.
And from a school bench the person learns this postulate
as the law (unproved supposition). Here we have the paradoxical situation.
The Bible begins with the unfounded statement
"In the Beginning there was a Word ",
and classic physics begins with the unfounded statement
" In the Beginning there was the First Newton's law ".
The science states that the origin of the World according
to the religious version is not reliable, and builds the scientific
foundations based on abstraction. As a result, both formulations
(religious and scientific) are unsatisfactory from the point of view of logic.
====================================
Newton,s dream was realized by Planck.
let us analyze the discovery of quantum of light by Planck.
M. Planck in 1900 offered to examine the radiation emanating from
absolutely black body (Vacuum radiation of Kirchhoff /Max Laue / ),
as separate portions (quantum).
If the quantum of light will penetrate inside this absolute black body
and will not reflect back, the radiation and heat will die.
That it will not happen, the ideal black body should reflect
(radiate) this quantum of light back. Then and only then,
this initial (natural) radiation of quantum of light is characterized
by the constant of Planck -h .
The quantity of this particle, s impulse is h=1.
Under influence of this impulse the particle moves with speed c=1.
The particle has the form of a circle.
This quantity is described with a formula (h=Et) and has a title of
“the least quantum of action”,“ internal impulse of particle”, “spin”.
================================
Einstein realized Newton,s dream in another way
For the basic point of his argumentations, Einstein
took the constant of Boltzmann R/N = k
and coefficient ( from the formula of radiation of Wien.
The multiplication of these two quantities gives the formula
of “ internal impulse of particle”, “spin” h = kb.
================================
Quantum of light is a privileged particle.
Only the speed of a light quantum in Vacuum has
a maximal, constant, absolute quantity of c=1.
No other particle can travel with the speed c = 1.
If quantum of light flies always rectilinearly c=1, it is a mad one.
Is he really mad?
========================================
No.
Another impulse (spin) in 1925 was found by
Goudsmit-Uhlenbeck .
They came to a conclusion, that the particle should have other impulse.
Quantity of this impulse is described with a formula : h = h/ 2pi,
forcing a particle to rotate around his diameter.
This means that it particle does not move rectilinearly,
but rotates around the diameter (has the form of a sphere).
The rotation of these particle creates electrical waves.






 

Offline lightarrow

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« Reply #4 on: 01/12/2007 20:53:55 »
Another impulse (spin) in 1925 was found by
Goudsmit-Uhlenbeck .
They came to a conclusion, that the particle should have other impulse.
Quantity of this impulse is described with a formula : h = h/ 2pi,
forcing a particle to rotate around his diameter.
This means that it particle does not move rectilinearly,
but rotates around the diameter (has the form of a sphere).
The rotation of these particle creates electrical waves.
So, how it's made the electron? How big is it? What should be rotating inside of it? Mass, charge, energy? In which way?
 

Offline syhprum

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« Reply #5 on: 01/12/2007 21:52:07 »
It is a good time to ask these questions, this article published in NATURE predicts that Hadrons, leptons ect are built from even more basic particles



http://www.nature.com/news/2007/071130/full/news.2007.292.html
 

lyner

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Electron
« Reply #6 on: 06/12/2007 16:05:55 »
Quote
Quantum of light is a privileged particle.
What do you mean by 'particle'?
 

Offline turnipsock

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Electron
« Reply #7 on: 08/12/2007 16:10:59 »
Do all electrons rotate at the same rate?
 

Offline JP

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« Reply #8 on: 08/12/2007 20:38:22 »
Do all electrons rotate at the same rate?


Yes.  They have two basic states ("up" and "down"), which you could equate to "clockwise" and "counterclockwise" if you want to use the rotation metaphor.  But the rates of rotation are the same.  However, as Syphrum mentioned, thinking of spin as a rotation is a great model, but it may or may not be physically accurate.  (Traditional quantum mechanics treats the electron as a point, and so it isn't physically rotating.)
 

Offline syhprum

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« Reply #9 on: 08/12/2007 21:18:25 »
If an electron Can be said to be spinning it would produce a magnetic field, how strong is this field and do electons with opposite spin attract each other
 

Offline syhprum

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« Reply #10 on: 08/12/2007 21:23:34 »
If Electron can be said to be spinning they would produce a magnetic field, how strong is this field and do Electons with opposite spin attract each other ?.
Are the spin axis always at 180° and do they precis ?.
 

Offline turnipsock

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« Reply #11 on: 08/12/2007 22:56:23 »
If Electron can be said to be spinning they would produce a magnetic field, how strong is this field and do Electons with opposite spin attract each other ?.
Are the spin axis always at 180° and do they precis ?.

Precession was part of the reason I posed the question. If electrons have mass and a finite size, they must precess if they are rotating. Mustn't they?
 

lyner

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Electron
« Reply #12 on: 09/12/2007 00:48:21 »
If you put a strong magnetic field around an atom, the spins of half of the electrons  will cause them to precess differently from the other half. This produces a separation in energy levels and 'line splitting' in the spectrum; two lines where there was one withot a field - the frequency being proportional to the field strength. The Zeeman effect, if I remember right. This line splitting was what revealed and was explained by the spin of electrons.
 

lyner

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Electron
« Reply #13 on: 14/12/2007 19:39:57 »
There are a lot of confuse ideas here.
Let me add my bit of confusion.
The spin quantum number given to an electron, when it is in a bound state cannot really be described as a 'spinning object'. What is meant is that 'something in the atom system' exhibits a property which can be treated as if it were spinning. In the bound state, the electron is very much a wave function and doesn't 'actually exist' anywhere in particular. It doesn't have a 'size'; its presence is spread all around the atom in some fuzzy probability density function (i.e it is more likely to behave as if it is some places than in others). Another property it has is that it exhibits angular momentum. This doesn't have to mean it is spinning at a certain rate - as its 'size' is undefined then its rotation speed is also undefined. The good thing about angular momentum is that it can be treated on its own - you don't need to know speed and rotation. When you put an atom in a magnetic field, the 'line splitting that you get can be explained in terms of something with spin.
It's along the same lines as momentum - you don't care whether it's a photon or a lump of something hitting you - they can both transfer momentum to you, although the momentum is calculated in different ways.
As soon as you get into quantum world you need to put on your Eastern Mystic hat and be prepared to think way outside of your normal box. Newton is just not enough for the purpose of understanding or explaining it. Some conventional models take you some way there but you can't extrapolate on what your granny told you.
 

lyner

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Electron
« Reply #14 on: 14/12/2007 19:40:32 »
No offense to the brilliant grannies who are around! XXXX luv U gran.
 

Offline chrisdsn

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Electron
« Reply #15 on: 22/12/2007 04:46:28 »
Put simply: 'cause it does. That an electron has a spin quantum number
("has intrinsic spin") is not a prediction of any accepted scientific
theory. It's a fact that put in "by hand" to the Standard model. The
predictions of the Standard model have undergone rigorous checking, so
it is certainly true that thinking of an electron as having intrinsic
spin (and being a fermion, like the quarks and leptons) is a superb
description of nature. An understanding of why this should be so from
some simpler theory is currently lacking, however.

Although this was mentioned in some previous posts, I would like to
re-iterate that you should think of "having an spin quantum number"
as being the same as a particle that is spinning. Something can spin
about any axis, the the axis for a measurement of a quantum system is
defined by the measuring apparatus, and with respect to that apparatus,
the spin will be either up or down. Quantum mechanics is weird. 



   
 
 

Offline lightarrow

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« Reply #16 on: 22/12/2007 10:37:15 »
Put simply: 'cause it does. That an electron has a spin quantum number
("has intrinsic spin") is not a prediction of any accepted scientific
theory. 
Are you sure? Maybe I'm wrong but I think it should come from QED and relativistic rotation symmetry; IIRC, it should also be one of the greatest success of QED.
 

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Electron
« Reply #16 on: 22/12/2007 10:37:15 »

 

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