Field of Science

The jewel of physics faces the 4% challenge

The size of the proton has shrunk by 4%, or so they tell us. The research which was published in Nature and has created waves apparently interrogated the proton with a much more reliable subatomic entity, the muon, which led to a more accurate result. The result of course testifies to the incredible power of modern science to divine such unbelievably small numbers.

But according to a NYT article, this might mean that the "jewel of physics", quantum electrodynamics, may be in trouble. QED which was developed by Richard Feynman and others is the most accurate theory known to science, and has calculated the magnetic moment of the proton to an accuracy of ten significant figures with respect to experiment. As Feynman himself said, this is like calculating the distance between New York and New Orleans to within the width of a hair.

The present measurement could shake up this success a bit according to the article:
When that new radius, which is 10 times more precise than previous values, was used to calculate the Rydberg constant, a venerable parameter in atomic theory, the answer was 4 percent away from the traditionally assumed value. This means there are now two contradicting values of the Rydberg constant, Dr. Pohl explained, which means there is either something wrong with the theory, quantum electrodynamics, or the experiment.

“They are completely stunned by this,” said Dr. Pohl of his colleagues. “They are working like mad. If there is a problem with quantum electrodynamics this will be an important step forward.”

The late Caltech physicist Richard Feynman called quantum electrodynamics “the jewel of physics,” and it has served as a template for other theories.

One possibility is that there is something physics doesn’t know yet about muons that throws off the calculations.

Or perhaps something we just don’t know about physics. In which case, Jeff Flowers of the National Physical Laboratory in Teddington in Britain pointed out in a commentary in Nature, a new phenomenon has been discovered not by the newest $10 billion collider but by a much older trick in the book, spectroscopy.

“So, if this experimental result holds up, it is an open door for a theorist to come up with the next theoretical leap and claim their Nobel Prize,” Dr. Flowers wrote.
In other news, a physicist has postulated that gravity is not really a fundamental force but could be a manifestation of the second law of thermodynamics.

Who said challenges do not abound in modern physics!


  1. I realize that one can't simultaneously measure position and velocity to desired degrees of accuracy. But, quantum mechanics is silent about size apparently. The proton is pretty small. Isn't there some sort of uncertainty principle about size measurement?


  2. I think QM regards all particles as point particles. Otherwise you run into paradoxes such as a point on the circumference of a finite-sized electron moving at several times the speed of light.

  3. QCD has ways of dealing with point particles like electrons, but regardless the proton is not a point particle. It is made of three valence quarks (and a jumble of virtual quarks and gluons also) and so has a definite non-zero size.


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