History of Spin

After too many attempts, I just understood the correct way to go through Quantum Mechanics. 

    

      "Don't waste time on the postulates of Quantum Mechanics". 

because for me it is just a great mathematical technique to understand the results of Nature. Understanding the reason for the technique should be handled separately only after you have some practice on it. 

       Currently, it is the spin that I concern the most. We know that the development of quantum mechanics begins from the field of spectroscopy.

       When any element is heated it produces energy in the form of light. This so called emission spectrum has distinct properties varies for different elements. By passing the light through a spectroscope [Instrument prepared to separate components of light since wavelengths of different light are different e.g.prism] its spectrum is analyzed. 

      The above is for just simple idea, but spectroscopy is really a big deal in Physics. 

      The developments in spectroscopy lead to more knowledge about the fundamental elements in Nature. The astounding result of these spectrum analysis is that they are not continuous but discrete in Nature. 

     Lets get through this..

I am heating an element and it produces light but in discrete units. But I know all these phenomena are due to proton and neutron because change in nucleus will result transmutation in element. So, it is entirely due to the electrons in the atom. From heating, we are just giving energy to this system. 

    Thus some kind of transition between electrons produce the energy and the essential point is that the transitions are discrete. Not everything is allowed in Nature. Nature is quantized.  

    This is the question that led to quantum world and  models were created to explain this. 

     But the concept of spin has to do more with the analysis of the spectrum in the presence of Electric and Magnetic fields. It has its own name respectively, Stark effect and Zeeman effect. Especially Zeeman effect arises due to magnetic properties of atom. 

     It is observed that before the field is applied there is only one line but when it is applied it splits into more than one line. This shows that magnetic field has somewhat to do with the energy levels of the electron. 

      From Electrodynamics we know that moving charges produces magnetic field and so it implies that there are some intrinsic rotational motions in the atom to produce the magnetic effects. Note that it is not the motion we are accustomed with day to day life. Only the mathematical formulation is similar to the one in classical.   

      

    Hence the concept of angular momentum aroused automatically in the quantum view. Careful analysis of the spectrum showed there is always an addition of angular momentum in terms of discrete units. And this extra term is known to be the result of spin of electrons. It is just a name given to the property of these fundamental particles. It is not the real spin. 

    

    Why it is not the real spin? 

How angular momentum plays the major role?

All these could be understood from the concept of magnetic dipole moment.