Notices
Results 1 to 18 of 18
Like Tree1Likes
  • 1 Post By jmd_dk

Thread: electron spin

  1. #1 electron spin 
    Forum Sophomore
    Join Date
    Feb 2008
    Posts
    111
    The electron spin(or for that matter spin of any elementary particle) is taken as its fundamental property. According to classical mechanics there should be a torque to cause spin. what is the source of this torque?


    Reply With Quote  
     

  2.  
     

  3. #2  
    Forum Freshman jmd_dk's Avatar
    Join Date
    Nov 2008
    Posts
    32
    The analog between classical spin (physical rotation) and the quantum mechanical spin of elementary particles is subtle. But I think I can answer your question purely classical:

    Torque is the cause of angular acceleration (change in the velocity of the spin). The spin of an elementary particle is always the same (at least it's quantized, meaning no continues angular acceleration being applied to it). No angular acceleration requires no torque .

    I hope it's a satisfying answer. Why/how these particles have spin at all (when the source isn't torque), is an other, tougher question


    Robinol likes this.
    ω
    Reply With Quote  
     

  4. #3  
    Forum Radioactive Isotope MagiMaster's Avatar
    Join Date
    Jul 2006
    Posts
    3,440
    I think the basic answer is that just because we call it spin doesn't mean it's actually spinning.
    Reply With Quote  
     

  5. #4  
    Forum Freshman
    Join Date
    Oct 2010
    Posts
    62
    Quote Originally Posted by parag1973 View Post
    The electron spin(or for that matter spin of any elementary particle) is taken as its fundamental property. According to classical mechanics there should be a torque to cause spin. what is the source of this torque?
    The electron has an inherent frequency/wavelength. When electrons are emitted in the form of beta rays, the wavelength lies in the UV region. Utilize this frequency and the size of an electron and you can picture an electromagnetic resonant field wave moving at or near the speed of light. You may be able to find your own picture of electron spin. Simply saying that it is an energy phenomenon doesn't give much perspective.
    Reply With Quote  
     

  6. #5  
    Forum Bachelors Degree Waveman28's Avatar
    Join Date
    Mar 2009
    Location
    Australia
    Posts
    417
    Quote Originally Posted by MagiMaster View Post
    I think the basic answer is that just because we call it spin doesn't mean it's actually spinning.
    ^ This. In the context of 'particles', Spin is essentially a fancy word for Phase.
    "Doubt is the origin of Wisdom" - Rene Descartes
    Reply With Quote  
     

  7. #6  
    Moderator Moderator Janus's Avatar
    Join Date
    Jun 2007
    Posts
    2,164
    Quote Originally Posted by Waveman28 View Post
    Quote Originally Posted by MagiMaster View Post
    I think the basic answer is that just because we call it spin doesn't mean it's actually spinning.
    ^ This. In the context of 'particles', Spin is essentially a fancy word for Phase.
    No, it isn't, not by the accepted scientific definition of spin. Please restrict your posts to the discussion of established physics.
    "Men are apt to mistake the strength of their feelings for the strength of their argument.
    The heated mind resents the chill touch & relentless scrutiny of logic"-W.E. Gladstone


    Edit/Delete Message
    Reply With Quote  
     

  8. #7  
    Forum Bachelors Degree martillo's Avatar
    Join Date
    Apr 2005
    Location
    Uruguay
    Posts
    454
    Actually the called "spin" of the basic particles relates to the magnetic moment of them which can be measured experimentally in their interactions with magnetic fields.
    The problem is that current theories (as classical physics does) assume the elementary particles being "point-like" (with no dimensions) and so there's the problem on how a magnetic moment can be generated by a point since in theory a magnetic field can only be generated by an element of electrical current which implies in some dimension since current=charge x displacement.
    Reply With Quote  
     

  9. #8  
    Forum Freshman
    Join Date
    Oct 2010
    Posts
    62
    Quote Originally Posted by martillo View Post
    Actually the called "spin" of the basic particles relates to the magnetic moment of them which can be measured experimentally in their interactions with magnetic fields.
    The problem is that current theories (as classical physics does) assume the elementary particles being "point-like" (with no dimensions) and so there's the problem on how a magnetic moment can be generated by a point since in theory a magnetic field can only be generated by an element of electrical current which implies in some dimension since current=charge x displacement.
    In classical physics, the definition of current is the number of electrons passing a certain point per unit time. However, that does not rule out a definition of electric current that also include spatial terms. In fact, that is exactly what my studies have involved - - - and using classical theory. There are many electrons involved in most any electrical current, so including spatial terms for each one would be quite a task. However, get down to one or two electrons and you have a much easier solution.
    Reply With Quote  
     

  10. #9  
    Forum Sophomore
    Join Date
    Feb 2008
    Posts
    111
    what is the most exclusive application of electron spin? how can electron spin then be interpreted.
    Reply With Quote  
     

  11. #10  
    Suspended
    Join Date
    Oct 2006
    Posts
    769
    I don't know of the most exclusive application, and it's usually described as "intrinsic", but the Einstein-de Haas effect "demonstrates that spin angular momentum is indeed of the same nature as the angular momentum of rotating bodies as conceived in classical mechanics." The electron has a magnetic dipole moment too, which again suggests rotation. Pay special attention to "The factor of two difference implies that the electron appears to be twice as effective in producing a magnetic moment as the corresponding classical charged body" which relates to spin ˝. A moebius strip has something like a spin ˝ characteristic, and there is another type of electromagnetic current: displacement current. It "is not an electric current of moving charges, but a time-varying electric field", just like you get in an electromagnetic wave. So you should interpret electron spin in terms of an optical vortex. Without worrying about dimensionality, work this out: 4π / c. There's a small binding energy adjustment, but even without it you should recognise the number. Don't forget that spherical harmonics apply in the hydrogen atom. We can diffract an electron. It has a wave nature. It is not a point particle.
    Reply With Quote  
     

  12. #11  
    Suspended
    Join Date
    Aug 2009
    Location
    Israel
    Posts
    272
    because the electron move back and forth in time its spin is ordenery but again because it superposition in time , now have many option . thanks
    Reply With Quote  
     

  13. #12  
    Suspended
    Join Date
    Aug 2007
    Location
    grail search
    Posts
    811
    Quote Originally Posted by parag1973 View Post
    The electron spin(or for that matter spin of any elementary particle) is taken as its fundamental property. According to classical mechanics there should be a torque to cause spin. what is the source of this torque?

    Is not the spin of an electron more fundamental to torque? Is this what you are trying to ask?
    Reply With Quote  
     

  14. #13  
    Forum Junior
    Join Date
    Mar 2008
    Posts
    267
    torque is only needed to change spin
    Reply With Quote  
     

  15. #14  
    Suspended
    Join Date
    Oct 2006
    Posts
    769
    Here's another number to work out: c˝ / 3π

    A guy called Andrew Worsley told me about it, he's using spherical harmonics not for a hydrogen atom, but for the particles themselves. I think it needs a bit more work, but I really think he's on to something.

    Reply With Quote  
     

  16. #15  
    Suspended
    Join Date
    Feb 2012
    Posts
    475
    Quote Originally Posted by martillo View Post
    Actually the called "spin" of the basic particles relates to the magnetic moment of them which can be measured experimentally in their interactions with magnetic fields.
    The problem is that current theories (as classical physics does) assume the elementary particles being "point-like" (with no dimensions) and so there's the problem on how a magnetic moment can be generated by a point since in theory a magnetic field can only be generated by an element of electrical current which implies in some dimension since current=charge x displacement.

    I simply couldn't not reply to this post. Martillo raises a very interesting and pretty important question, for two reasons. The first being is that my theory http://www.thescienceforum.com/new-h...ic-moment.html states that there can be what is called a ''semi-metric'' and in mathematics that has an appearance of ... these allow what are called spin-microframes, two degrees of freedom inside of the particle (within the boundaries of it's compton wavelength) which means a particle is not zero dimensional at all. It can be one 1-dimension or 2-dimensions but not three or zero. It does not make sense to speak of time, as that is not an observable quantity.


    this has been taken from work written by me


    '' The classical electron, is believed to be a sphere with a radius of (e˛/Mc˛). This is not a measured value. It's a careful analysis of the dimensions of the equation of the radius which says it depends on the electron charge (squared) e˛ the mass M and the speed of light (squared) c˛. The quantity in the denominator Mc˛ actually makes up the rest energy of a particle E_0. The rest energy will be explained in greater detail in the Chapter discussing relativity.

    The Classical Electron Radius is in fact 1/137 times larger than the Compton Wavelength. The Compton Wavelength is (h/Mc) where h is Plancks Constant and it has a value of 6.62606957(29)×10^(−34) j.s. The Compton Wavelength itself has a value for the electron as 2.4263102175±33×10^(−12) m (the value varies with different particles) and is a measure itself of the wavelength of a particle being equal to a photon (a particle of light energy) whose energy is the same as the rest-mass energy of the particle. Complicated? Yes it can be.

    Basically, all particles have a wavelength. Photon's can never be at rest (again reasons why will be given in the relativity chapter), but the energy of a photon can be low enough to have it's wavelength match any particle who is at rest. It's often seen in the eye's of many scientists as the ''size'' of a particle. Actually, a more accurate representation of the size of an object would be the Reduced Compton Wavelength (reasons given in the chapter references under [1] ). This is just when you divide the Compton Wavelength by 2π and it gives a smaller representation for the mass of a system.

    Now, going back to the electron, the electron as a sphere was accepted by most physicists until the age of the revolutionary quantum field theory. A physicist by the name of Wolfgang Pauli actually predicted a very strange property of all subatomic matter. Using careful experiments, he was able to deduct that particles behaved as though they possessed a spin, just like a spinning top or even better to imagine, the spinning surface of a planet like the Earth.

    Wolfgang didn't actually name it spin however, that was later coined by Ralph Kronig, George Uhlenbeck, and Samuel Goudsmit in 1925 and then a mathematical theory was developed by Pauli in 1927. The classical idea of spin came from Noether's (a mathematician) ''generator of rotations'' where it describes a real physical rotation of quantum objects.

    This idea soon ran into problems however, because modern quantum field theory did not really believe an electron was classical at all, possessing a radius. In fact, as far as physicists can tell, any attempt at measuring a radius for an electron failed and all experimental data seemed to suggest that the electron was really a pointlike system - that is , a particle which does not have any dimensions which we can obtain from the classical radius. It was just a point and thus some problems began to arise from the mathematical theory.

    A classical radial system can indeed rotate like a planet. In fact, an electron under this theory could make a 360 degree turn in space and as would be expected would return to it's original orientation. However, for a pointlike system to achieve a rotation and return to it's original orientation it would need to make twice as much as this angle (720 degrees). See, pointlike systems when in accord to rotations don't act like classical radial systems.

    So it seemed there was a problem. Either particles do not physically rotate yet still possess an angular momentum with a classical radius, or that quantum particles don't physically rotate but still have a quantum spin and intrinsic property no less. It was decided that spin could not be a real physical spin [2]. Instead, the classical electron would fall into the archives of physical curiosity and the idea that spin was some inherent, instrinsic and fundamental property would live on. I believe this might have been a mistake. The fact that we haven't been able to observe the radius as of yet should not indicate an electron has no size. In fact, scientists have just recently attempted to measure the shape of an electron by measuring it's wobble in a magnetic field.''
    Reply With Quote  
     

  17. #16  
    Suspended
    Join Date
    Feb 2012
    Posts
    475
    Quote Originally Posted by Farsight View Post
    I don't know of the most exclusive application, and it's usually described as "intrinsic", but the Einstein-de Haas effect "demonstrates that spin angular momentum is indeed of the same nature as the angular momentum of rotating bodies as conceived in classical mechanics." The electron has a magnetic dipole moment too, which again suggests rotation. Pay special attention to "The factor of two difference implies that the electron appears to be twice as effective in producing a magnetic moment as the corresponding classical charged body" which relates to spin ˝. A moebius strip has something like a spin ˝ characteristic, and there is another type of electromagnetic current: displacement current. It "is not an electric current of moving charges, but a time-varying electric field", just like you get in an electromagnetic wave. So you should interpret electron spin in terms of an optical vortex. Without worrying about dimensionality, work this out: 4π / c. There's a small binding energy adjustment, but even without it you should recognise the number. Don't forget that spherical harmonics apply in the hydrogen atom. We can diffract an electron. It has a wave nature. It is not a point particle.
    This magnetic dipole moment suggestion was a good one at that.

    I think in the end of the day, we opted for dimensionless objects because they are easier to work with. I am sure objects of sufficiently small sizes could seem like to us to appear as though they act like they have no dimensions, when really they are just to small to observe as of yet. Indirect evidence like what you suggest here should not be ignored.
    Reply With Quote  
     

  18. #17  
    Forum Freshman Robinol's Avatar
    Join Date
    Feb 2012
    Location
    India
    Posts
    39
    Could you tell me what initiates there spin?
    Reply With Quote  
     

  19. #18  
    Brassica oleracea Strange's Avatar
    Join Date
    Oct 2011
    Location
    喫茶店
    Posts
    16,686
    Quote Originally Posted by Robinol View Post
    Could you tell me what initiates there spin?
    Nothing initiates it; it is just a property they have. They are created with it - note that spin is conserved (like charge) so the total spin before and after any interaction is the same.
    Without wishing to overstate my case, everything in the observable universe definitely has its origins in Northamptonshire -- Alan Moore
    Reply With Quote  
     

Similar Threads

  1. Spin-spin coupling or spin-spin splitting in NMR
    By shanshan in forum Mechanical, Structural and Chemical Engineering
    Replies: 0
    Last Post: February 24th, 2010, 02:18 PM
  2. Spin columns
    By forest_guy in forum Biology
    Replies: 3
    Last Post: November 8th, 2008, 11:55 AM
  3. the big spin
    By dejawolf in forum Astronomy & Cosmology
    Replies: 13
    Last Post: July 24th, 2008, 04:35 AM
  4. a new spin on einstein
    By streamSystems in forum Personal Theories & Alternative Ideas
    Replies: 23
    Last Post: June 20th, 2007, 06:52 PM
  5. Electron spin
    By leohopkins in forum Physics
    Replies: 2
    Last Post: January 17th, 2007, 04:04 PM
Bookmarks
Bookmarks
Posting Permissions
  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •