Comment: Feedback Physics World  May 2021

Fritz Zwicky and the earliest prediction of dark matter

In response to the feature article “The 10 greatest predictions in physics” by the science writer David Appell (January 2021), which included Vera Rubin and Kent Ford Jr’s prediction that dark matter can account for the unusual motion of outer stars in the Andromeda galaxy.

 

Look again The observation that the outer stars in a spiral galaxy – like NGC 1232 here – orbit at the same speed as those further in led Vera Rubin and Kent Ford Jr to make predictions about the existence of dark matter. But should Fritz Zwicky instead be given the credit? (Courtesy: ESO)

The historical record of physics and science is not served by the suppression of inconvenient truths or inaccurate assertions that advance a particular angled narrative or social engineering to elevate one scientist to grandiloquent heights while disregarding the original pioneering work of another.

Appell’s article reveals a deficit in comprehension of my father Fritz Zwicky’s pioneering work regarding what he called dunkle (kalte) Materie, or “dark (cold) matter”, and inference of the gravitational phenomenon by measuring the rotating mass of the Coma cluster. There is ostensible mention of my father in this article, which is disgraceful, when in fact he is the father of dark matter.

As he wrote: “I consequently engaged in the application of certain simple general principles of morphological research, and in particular the method of Directed Intuition that would allow me to predict and visualize the existence of as yet unknown cosmic objects and phenomena.”

Fritz Zwicky’s eidolon was realized from the results of his observations published in his 1933 paper “Die Rotverschiebung von extragalaktischen Nebeln” (“The redshift of extragalactic nebulae” Helv. Phys. Acta 6 110).

Zwicky discovered dark matter and coined the term “cold dark matter” in that paper. The mass-radial acceleration discrepancy – obtained by measuring the speeds of galaxies in the Coma cluster – originated with Zwicky, not Rubin, using the more challenging methodology of the virial theorem, by relating the total average kinetic energy and the total average potential energy of the galaxies of the Coma cluster. Zwicky then used the position and velocity measurements to determine the mass of the galaxy cluster.

A vigilant editor should always be on guard for any such miscarriage of construct before publication in a prominent physics publication that has a responsibility to the readership and not rely on claims by freelance journalists.

Barbarina Zwicky

Palm Springs, California, US

Zwicky is an American astronomer of Swiss origin. He is, by the essential spirit of America, both American and Swiss. Astronomer is a slight misnomer; any title falls short of the career magnitude Zwicky embodies. As the Harvard University astronomer Cecilia Payne Gaposchkin once wrote, “he gave the impression of thinking for himself on every subject, of making his own decision on every point; his ideas were so fertile and his projects so vast that he could have employed all the facilities of a great observatory”.

In Zwicky’s 1933 article, he puts forth his observations, calculations and assessment of the Coma cluster of galaxies. His conclusions, translated here from the original German, are that: “dark matter is present in a much greater density than luminous matter”; “the necessity for an enormously large density of dark matter remains standing”; “if the observed velocities are nevertheless true, then the Coma system must also fly apart with time”; and “one must still have a much greater density of dark matter”.

Zwicky closes by noting that “proceeding out of these considerations, the large scattering of velocities in the Coma system (and in other dense nebulae) presents a problem not yet clarified”. If dark matter is truly a great prediction, then Zwicky is the great predictor. Appell’s article is, however, entirely premature, and the physics world should admonish him for asserting a claim of prediction. In over 50 years of intense searching for a dark-matter particle, nothing has provided evidence that it exists. On the contrary, the extensive experimental results indicate that such a theoretical particle does not exist.

The discovery of the “gravitational anomaly from expected” that he termed dark matter is Zwicky’s, which was reclaimed by the accidental yet meticulous work of the observing partners Rubin and Ford extending to individual galaxies. Only a conceptual connection is left to be made advancing from the devoted work of many, and that connection is for every human being to make for themselves. Following in Arthur Eddington’s footsteps, a person’s focus should be trained on the cosmological constant’s significance and characteristics in the general theory of relativity.

To mistakenly claim a prediction as true and great before its full maturity, as this 10th prediction does, exposes the prediction to the vulnerability of being wrong and to ironically witness the 10th “greatest prediction” appear first on a top 10 list of “greatest blunders.” I do not wish that for Rubin or Ford.

Johannes Meyling

Whidbey Island, Washington, US

The prediction of dark matter is important because it spurred much theoretical and, now, experimental work to understand and verify it

David Appell replies:

Who, or what, says that my choices for the top 10 predictions in physics have to have been experimentally verified?

The prediction of dark matter is important because it spurred much theoretical and, now, experimental work to understand and verify it. Einstein’s prediction of gravitational waves took about 100 years to be fulfilled (though, like Rubin’s prediction, there were strong hints earlier). Does that mean it wasn’t a great prediction until the LIGO detector found gravitational waves in 2015? I don’t think so. Similarly, the Higgs boson was found 50 years after its prediction – and also inspired important theoretical and experimental work. The same is undoubtedly true for dark matter – just look at all the current efforts going into its detection.

Cosmologists certainly think there is ample evidence for dark matter in the fluctuations of the cosmic microwave background, and can put a precise number on it. Yes, there are competing theories, but the ΛCDM model is the leading picture of the Big Bang cosmological model.