Mysterious Particles

Some physicists sometimes act as if the hypotheses they propose to explain the mysteries of the universe are always true. But a hypothesis is nothing more than a proposal to explain a natural phenomenon, and it cannot be considered a confirmed theory until it has provided one or more surprisingly accurate predictions. This last detail, which is essential, is usually omitted.

In 2020, I read two popular books on cosmology and particle physics (the two branches of physics are closely related):

• The Big Bang, by Joseph Silk (2000). This book was recommended to me as a good popularization of the Big Bang theory. The problem is that it discusses several strange theories, and several particles whose existence has been proposed, as if they had been confirmed. Thus, reading the book could confuse uninformed people, contrary to the primary objective of popularization: to make those people know more about cosmology and the history of the universe. Among the hypotheses accepted as valid are string theory, currently in question, and cosmic inflation, which so far has not been confirmed.
• The Dark Universe, by Catherine Heymans (2017). A good summary of the current status of the standard cosmological model, focusing primarily on the supposed existence of dark matter and dark energy, where the word dark should be understood to mean that we have no idea what it is. In this book, the author makes a typical mistake: sometimes (not always) she confuses model predictions with model adjustments. Predictions are made when the model is used to predict something we didn't know. As I said in the first paragraph of this article, confirmed predictions validate the model. On the other hand, when a model is developed, known data are used to adjust its parameters, but that doesn't validate the model. Heymans correctly describes the use of baryon acoustic oscillations to adjust the parameters of the ΛCDM model, but she is wrong in considering that the model has been validated by studying the RCFM thermal power spectrum, which was not a prediction, but an adjustment.

There are many particles whose existence has been proposed to solve the mysteries of the many things we don't know about cosmological theories. Some are very imaginative. The trouble is that their existence is almost never confirmed, although authors of popular books often speak as if they are real, and not mere hypotheses. Here are a few examples:

• Magnetic monopoles, about which Silk's book says this: searches have found that monopoles are few and far between in our galaxy. The truth is that not a single monopole has ever been detected. Silk's statement gives the impression that they really exist, as if the existence of theoretical particles were proven by the fact that there is a theory that predicts them.
• The photino: This particle, predicted by supersymmetry theories, has never been found. However, Silk says this: We know precisely how frequently [the photino] annihilation process occurs, because once, long ago in the very early universe, it occurred very frequently. How do we know, if it's quite possible that the photino does not exist?
• Silk also mentions the chargino. About this hypothetical particle, he says this: Experiments have shown that the actual chargino abundance in terrestrial rocks and seawater is far less than the predicted upper limit. This way of expressing it gives the false impression that the existence of the chargino has been proved. To prevent misunderstanding, the paragraph should be rephrased thus: As the chargino has not been detected in rocks or seawater, its abundance, if it actually existed, would be much lower than theoretical predictions.

Curiously, in Chapter 17 Silk jokes about this supposed abundance of undetectable theoretical particles, when he says this: ...the exotic weakly interacting particle candidates, of which there must exist a number about equal to the square root of the number of particle physicists. In other words, Silk is aware of the current precarious state of the predictions about the existence of exotic particles that would explain dark matter, but sometimes he is carried away by the optimism of other physicists.

As an example of the precariousness of these theories, which often fail when subjected to experimentation, let's look at this news article published in PhysicsWorld on March 27, 2025:

Atomic anomaly explained without recourse to a hypothetical ‘dark force’

To summarize the news: in 2020, a team from MIT detected a deviation in the theoretical predictions of the energy levels of the ytterbium atom, a rare earth, which they immediately attributed to the existence of a previously unknown dark force, which would naturally imply the existence of new particles. As usual, when a prediction fails, physicists immediately propose the existence of dark matter or dark energy and the corresponding mysterious particles.

Fortunately, this time things didn't go very far. In 2025, a team of German physicists confirmed the anomaly, but managed to explain it without resorting to dark forces or hypothetical particles, by studying the interaction between the neutrons in the nucleus and the electrons in the ytterbium shell.

But I have no hope that this success of current theories over speculation will curb the imagination of those physicists who, rather than science, seem to be doing science fiction.

The same post in Spanish

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Manuel Alfonseca

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