Particle physics – a brief history of time-wasting? | letters

Sabine Hossenfelder (No one in physics dares say so, but the race to invent new particles is pointless, 26 September) has missed the point of a big part of particle physics, and indeed fundamental research as a whole. While we’d all like to revolutionize our respective fields by discovering a new particle or otherwise, in reality, winning out the impossible – the particles that don’t exist – is an equally important, if painstaking, function of science. Nature has an infinite capacity to surprise, and our scientific forebears learned long ago to take nothing for granted. Every impossibility proved gets us closer to a deeper understanding of the real universe; it’s just as important to know that faster-than-light travel is impossible as it is to understand that light is made up of photons, for instance.

It would of course be tremendously tedious to rule out every last outlandish possibility (Hossenfelder’s octopuses on Mars, for example), and so we need a set of principles to guide us on where to look. There is general disagreement about what works best, but many of the hypothetical particles mentioned in the article have been designed with useful functions in mind – breaking cherished principles of the standard model for instance, or adding new features to it. What we’re testing are the principles themselves, not the particles; while some of them might really exist, others are simply straw men to help us formulate useful tests.
Dr Phil Bull
Reader in cosmology, Jodrell Bank Center for Astrophysics

Sabine Hossenfelder argues that particle physicists are far too eager to speculate about new particles, suggesting that this is done for reasons of career advancement, rather than a sincere desire to advance our understanding of the universe. In fact, we develop and propose new theories and new particles because there are real puzzles and open questions that our best current theory, the standard model, cannot address. This is how science is supposed to work.

The neutron was proposed in 1920 and discovered a dozen years later. Similarly, positrons, pions, neutrinos, quarks and so on were each hypothesized by physicists well before they were observed in any experiment. Most recently, the Higgs boson was discovered in 2012, having been proposed a half-century earlier. I wonder how many of these discoveries would never have been made if physicists had taken Hossenfelder’s advice about their approach to science.

Hossenfelder’s claim that the standard model “works just fine the way it is” is simply not true. The standard model predicts that neutrinos should be massless (they aren’t), that the neutron’s electric dipole moment should be large (it’s undetectably small), and that there should be equal abundances of matter and antimatter in our universe (there are not) . Furthermore, most of the matter in our universe consists of dark matter, which is not described by the standard model. These are not the characteristics of a theory that “works just fine the way it is”.

Of course, most of the particles that my colleagues and I speculate about will not turn out to be real, and that’s fine. No one would expect every suspect in a criminal case to eventually be found guilty either. The point of these investigations isn’t to be right all of the time. Instead, it’s to rationally consider the possibilities, investigate their consequences, decide which experiments to construct and carry out, and ultimately to learn as much as we can about our universe.
Dan Hopper
Professor of astronomy and astrophysics, University of Chicago

Particle physics is a great deal more than just inventing and searching for new particles, or “bump hunting” as we call it. The Large Hadron Collider (LHC) was built with two main goals: to find the Higgs boson, predicted by the standard model of particle physics, and to search for new phenomena needed to explain some of the fascinating details of our universe for which we have at present no explanation, such as dark matter.

There is no nice model to guide us where to look for empirical evidence, just lots of theories, some predicting new particles. We are feeling around in the dark, looking for evidence to send us in a new direction. Part of this is bump hunting and, as Sabine Hossenfelder rightly pointed out, this method has not yielded new discoveries and is less likely to do so now as many of the possibilities have been ruled out. But the unknowns are still there and the universe has once again proved to be subtle and mysterious. What we at the Cern LHC are doing now is making more and more precise measurements with the data we have, looking for small deviations from the standard model to guide us to where we should look for new phenomena.

There are many analogies in the history of science for this process – Albert Einstein tweaking Isaac Newton some 250 years after the Principia, and more recently the Cern LEP machine, a precursor of the LHC, finding anomalies that guided us where to look for the Higgs boson. Just because there is no low-hanging fruit, it does not mean there is no fruit to be found.
Roger Rusack
Professor of Physics, University of Minnesota

As a professional astronomer, I fully share Sabine Hossenfelder’s point of view on physics. Unfortunately the situation is no different in today’s astrophysics, which is full of pointless articles on the properties of dark matter and dark energy, on which countless brilliant careers have been built.

As in the case of physicists, privately many astrophysicists would question the existence of these entities, even though no one is openly stating it (let alone writing it in a paper). The situation is ridiculous to say the least.

Any voice contrary to mainstream astrophysics is in effect shut down by the referee system, which ensures that only orthodox results appear in technical journals. The James Webb space telescope will most likely provide enough evidence to change the status quo, with important consequences for fundamental physics.
Dr Riccardo Scarpa
Brena Baja, La Palma, Spain

Sabine Hossenfelder provides a valuable insight into how the mechanical application of mathematics may be falsifiable, satisfy peer review and meet funding requirements. But her central point of her, that there is little point in theories that are falsifiable but untestable, has wider lessons.

Thinktanks and institutes have generated much social and economic theory and, as with particle physics, there is no shortage of well-researched, peer-reviewed and well-funded ideas to inform policy in government, business and our private lives. Like dark matter and dark energy, inequality, poverty and lack of opportunity may be measured, analyzed and theorized from every angle. But does this intellectual output improve matters in proportion to the effort extended? Many think not.

More insight and less rot ideology is the call. Economists and social theorists, please take note.
Them O’Leary
St Albans, Hertfordshire

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