In one of my papers, I debunked the myth that the Lamb shift would require a new theory: classical quantum mechanics (think of Richard Feynman’s treatment of the interaction between the magnetic moments of the electron and the proton in a hydrogen atom, for example) will do.

I will, therefore, not waste too much time and space on this, and refer you to the paper I did on this. I will just copy the introduction to it to wet your appetite. đ

According to the Wikipedia article on the Lamb shift[1] (which is only useful because it *parrots *the rather fantastical mainstream explanation of this tiny split in spectral lines), we should think of the Lamb shift as a small difference (in energy) between the ^{2}*S*_{1/2}Â andÂ ^{2}*P*_{1/2} orbitals in a hydrogen atom which can only be explained in terms of quantum field theory and which, therefore, basically confirms this theory.

How small? It is usually expressed as a fraction of Î±^{5}Â·m_{e}*c*^{2} = Î±^{5}Â·E_{e} but in *absolute *terms, itâs equal to about 4.372 *millionths *of an eV. Hence, the order of magnitude (in eV energy units) is 10^{-6}. So that is *very *small, indeed. The Planck-Einstein relation tells us that corresponds to a frequency of a bit more than 1000 *mega*herz. That is *much *below the frequency of visible light (430 to 770 *tera*herz) but still corresponds to an easily detectable *radiowave *frequency.

Can we compare it with anything? We can. The order of magnitude is about the same as the energy difference between the spectral lines that are separated by the *spin *of an electron (the splitting that is referred to as the Zeeman effect) or the *fine structure* of the hydrogen spectrum. To be precise, it is one order of magnitude smaller: the Lamb shift is measured in terms of 10^{-6} eV, while the Zeeman effect or the energy difference between the *fine *lines of the spectrum is about 10 times larger.[2] The order of magnitude of the Lamb shift is, in fact, the same as that of the *hyperfine *structure, which is associated with the 1420 MHz radio *hiss *coming from outer space. This radiation comes from *spin flips *of the proton and the electron inside of the hydrogen atom.[3]

We are all very familiar with proton spin flips nowadays because of their use in magnetic resonance imagining. Indeed, I must assume that â if you have ever had one â you also *googled *and watched one or more YouTube videos explaining the physics underpinning this amazing technology. If not, I warmly recommend you do so because they are often better than Wikipedia explanations.[4]

The point is this: for the *novice* in physics, these mainstream explanations in terms of quantum field theory comes across as somewhat *bizarre*. We explain the Zeeman effect and the fine and hyperfine structure of the hydrogen spectrum in terms of the *orbital *and *spin *angular moment of the electron and â in case of the hyperfine structure â of the proton (or, more generally speaking, the *nucleus *of the atom that we are looking at). For the Lamb shift, however, we are fed a *very* different story line. It goes like this:

Diracâs equation â for a bound electron[5] – does *not *predict this tiny energy difference. Diracâs equation must, therefore, be totally wrong. We can *only *explain this in terms of âinteraction between vacuum energy fluctuations.â

Let me quote Wikipedia in full here:

âThis particular difference is aÂ one-loop effectÂ ofÂ quantum electrodynamics, and can be interpreted as the influence of virtualÂ photonsÂ that have been emitted and re-absorbed by the atom. In quantum electrodynamics the electromagnetic field is quantized and, like theÂ harmonic oscillatorÂ inÂ quantum mechanics, its lowest state is not zero. Thus, there exist smallÂ zero-pointÂ oscillations that cause theÂ electronÂ to execute rapid oscillatory motions.â[6]

I will let you digest this for a second. [âŠ]

It sounds fantastic, doesnât it? Willis Eugene Lamb Jr. got a Nobel Prize in Physics for his discovery in 1955. He had to share it with Polykarp Kusch. To be precise, Lamb got his half of the prize âfor his discoveries concerning the fine structure of the hydrogen spectrumâ (the Lamb shift), while Polykarp Kusch got it âfor his precision determination of the magnetic moment of the electronâ (the so-called anomaly in the magnetic moment).[7]

You should note that Lamb did *not *get it for the above-mentioned *explanation* which, judging from some of the later publications of Lamb, he found rather fantastical as well.[8] Likewise, Kusch had *measured *the anomaly but left the explaining of it to (other) physicistsÂŸsome more famous names you probably are more acquainted with, such as Julian Schwinger and Richard Feynman. The latter, together with Sin-Itiro Tomonaga[9], effectively got the Nobel Prize – almost 20 years after Lambâs discovery[10] and Betheâs first work on it[11] – for *explaining *these seemingly strange measurements using even stranger theories (renormalization and quantum field theories).

[As mentioned above, this is just the introduction. The paper itself shows why and how we can interpret the nature of the Lamb shift as beingÂ *exactly *the same as that of the hyperfine structure.]

[1] See: https://en.wikipedia.org/wiki/Lamb_shift, accessed on 29 March 2020.

[2] The *Hyperphysics *site (http://hyperphysics.phy-astr.gsu.edu/) gives an energy difference of 4.5ÂŽ10^{-5} eV between the two (fine) lines for the 2*P* level. The same site also calculates an energy difference between lines split by the Zeeman effect equal to 5.79ÂŽ10^{-5} eV. These calculations are quite tricky because they depend on the *strength of the magnetic field *that is being applied to create these splits. The 5.79ÂŽ10^{-5} eV energy difference, for example, is calculated for a magnetic field of 1 T (*tesla*). We mentioned the Î±^{5}m_{e}*c*^{2} unit: itâs equal to about 1ÂŽ10^{-5} eV so its order of magnitude effectively seems to *connect *all of the mentioned finer divisions of the hydrogen spectrum.

[3] The reader should not confuse this with the cosmic microwave background radiation, which is understood to be a remnant from the Big Bang. The 21 cm line was discovered in the 1930s, and was confirmed to be a hydrogen spectrum line in 1951. In contrast, cosmic background radiation was accurately measured in the 1950s and 1960s only and â as mentioned â it is associated with a *temperature* (about 2.725Â degrees Kelvin, to be precise). It is, therefore, *not *related to any specific spectral line. For all practical purposes, one might say the cosmic background radiation reflects the *temperature *of the Universe, which is close to but *above* zero.

[4] From the two or three we watched, we would single out the one from Doctor Klioze: https://www.youtube.com/watch?v=djAxjtN_7VE. It is almost half an hour long, but well worth spending the time!

[5] Dirac first developed a wave equation for a free particle (*Principles of Quantum Mechanics*, section 30), which is a particle free of any forces. Section 39 of the *Principles *then further use this theory to deal with what Dirac refers to as the electronâs âmotion in a central field of forceâ, based on which he then develops a wave equation that gives us the energy levels of the hydrogen atom (section 40). This is, basically, a modified version of SchrĂ¶dingerâs wave equation for the hydrogen atom. We note that Dirac consistently describes his equations as the âequations of motionâ of the electric charge. We also think all of physics can and should be expressed in terms of the equations of the motion of charges. We, therefore, like the conclusion of his *Principles* very much: â*It is to be hoped that with increasing knowledge a way will eventually be found for adapting the high-energy theories into a scheme based on equations of motion, and so unifying them with those of low-energy physics.*â We could not agree more.

[6] We quote from Wikipedia (https://en.wikipedia.org/wiki/Lamb_shift, accessed on 29 March 2020) to make sure we are *parroting *the right phrases here.

[7] See: https://www.nobelprize.org/prizes/physics/1955/summary/, accessed on 29 March 2020. We write the âso-calledâ anomaly because we do not think of the anomaly as an anomaly. We think it is a perfectly normal deviation from some theoretical value. Indeed, one would always expect the measurement to be slightly different from its theoretical value. Why? Because a theoretical value is always based on mathematical idealizations that do not *really* exist. In this particular case, we should just acknowledge that zero-dimensional charges do not *really *exist: they must have *some *(spatial) dimension. Once one accepts that hypothesis, there is no longer any mystery in quantum mechanics. Moreover, because the deviation is *systematic*, one should learn from it so as to detail the modelâwhich is exactly what we have been trying to do.

[8] See: W.E. Lamb, *Anti-photon*, Applied Physics B volume 60, pp. 77â84 (1995). We offer some comments on this remarkable paper â which Lamb wrote when he was over 80 years old â at the end of our paper.

[9] Unlike what you might think, Tomonaga was *not *working with Schwinger, Feynman or any of the other American scientists. He apparently discovered the renormalization method independently of Julian Schwinger and calculated physical quantities such as the Lamb shift at the same time. See: https://en.wikipedia.org/wiki/Shin%27ichir%C5%8D_Tomonaga

[10] The Lamb shift was measured in the Columbia Radiation Laboratory in 1947. From W.E. Lambâs Nobel Prize Lecture, I gather the heavy lifting was actually done by one of his graduate students, Robert Curtis Retherford, whom, sadly, is only mentioned once in Lambâs Nobel Prize lecture, and who did *not *share in the Nobel Prize.

[11] For a good overview of the rather âdirty workâ that Bethe seems to have done, see: Oliver Consa, *Something is rotten in the state of QED* (https://www.researchgate.net/publication/338980602_Something_is_rotten_in_the_state_of_QED). As for the theorists getting the prize only 20 years after the experimental discovery, it should be noted this is not unusual: the Nobel Prize Committee has tended to favor new experimental results above new theories. An exception was probably made in regard to the Higgs hypothesis â as theorists received their prize (for theoretical work that was actually done in the 1960s) almost immediately after the CERN âdiscoveryâ of the Higgs fieldâor Higgs particle or whatever it was they claim to have measured.