Asked by: Joshua Johnson

What is the physical origin of this constant? Well, it is related to the so called Fine Structure - closely spaced groups of optical spectrum lines of elements like: hydrogen and helium. These optical spectrum lines are in a way the fingerprint of the element's energy levels. Since the energy levels of any given element are quantized (i.e. only discrete energy levels are available) the optical spectrum appears as a series of lines instead of a continuous spectrum. With each such optical spectrum line one can associate three numbers:

(an additional quantum number also can be considered that will give rise to

Each group of spectral optical lines mentioned above has a same n - number, but different values of l and j numbers. According to P.A.M. Dirac's relativistic quantum mechanics, energy levels of a one-electron atom (hydrogen is a good example) which have the same n and j numbers will coincide exactly - but their value will be different from that predicted by the Bohr's theory by an amount that is proportional to the

There have been deviations from Dirac's theory discovered in 1947. Namely, the level having l=0 does not coincide with that having l=1. This discrepancy was later named the Lamb shift (after its discoverer Willis Lamb, Jr.) and is due to the interaction of an electron with the zero-point fluctuations of the electromagnetic field.

As mentioned above in a multi electron atom systems the spin-orbit interaction becomes important too and the number of optical spectrum lines in the groups becomes even more numerous.

Answered by: Anton Skorucak, M.S. Physics, PhysLink.com Creator

'A theory with mathematical beauty is more likely to be correct than an ugly one that fits some experimental data. God is a mathematician of a very high order, and He used very advanced mathematics in constructing the universe.'**Paul Dirac**

(*1902-1984*)

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