Particle physics impasse

Physics is the study of the physical universe. As a science, it involves a process consisting of two components. The theoretical component strives to construct theoretical models for the physical phenomena that we observe. The experimental component tests these theoretical models and explores the physical world for more information about phenomena.

Progress in physics is enhanced when many physicists using different approaches tackle the same problem. The diversity in the nature of problems need to be confronted by a diversity of perspectives. This diversity is reflected in the literature. The same physical phenomenon is often studied by different approaches, using different mathematical formulations. Some of them may turn out to produce the same results, but some may differ in their predictions. The experimental work can then be used to make a selection among them.

That is all fine and dandy for physics in general, but the situation is a bit more complicated for particle physics. Perhaps, one can see the reason for all these complications as the fact that particle physics is running out of observable energy space.

What do I mean by that? Progress in particle physics is (to some extent at least) indicated by understanding the fundamental mechanisms of nature at progressively higher energy scales. Today, we understand these fundamental mechanisms to a fairly good degree up to the electroweak scale (at about 200 GeV). It is described by the Standard Model, which was established during the 1970’s. So, for the past 4 decades, particle physicists tried to extend the understand beyond that scale. Various theoretical ideas were proposed, prominent among these were the idea of supersymmetry. Then a big experiment, the Large Hadron Collider (LHC) was constructed to test these ideas above the electroweak scale. It discovered the Higgs boson, which was the last extent particle predicted by the standard model. But no supersymmetry. In fact, none of the other ideas panned out at all. So there is a serious back-to-the-drawing-board situation going on in particle physics.

The problem is, the LHC did not discover anything else that could give a hint at what is going on up there, or did it? There will be another run to accumulate more data. The data still needs to be analyzed. Perhaps something can still emerge. Who knows? However, even if some new particle is lurking within the data, it becomes difficult to see. Such particles tend to be more unstable at those higher energies, leading to very broad peaks. To make things worse, there is so much more background noise. This makes it difficult, even unlikely, that such particles can be identified at these higher energies. At some point, no experiment would be able to observe such particles anymore.

The interesting things about the situation is the backlash that one reads about in the media. The particle physicists are arguing among themselves about the reason for the current situation and what the way forward should be. There are those that say that the proposed models were all a bunch of harebrained ideas that were then hyped and that we should not build any new colliders until we have done some proper theoretical work first.

See, the problem with building new colliders is the cost involved. It is not like other fields of physics where the local funding organization can support several experimental groups. These colliders require several countries to pitch in to cover the cost. (OK, particle physics is not the only field with such big ticket experiments.)

The combined effect of the unlikeness to observe new particles at higher energies and the cost involved to build new colliders at higher energies, creates an impasse in particle physics. Although they may come up with marvelous new theories for the mechanisms above the electroweak scale, it may be impossible to see whether these theories are correct. Perhaps the last energy scale below which we will be able to understand the fundamental mechanisms in a scientific manner, will turn out to be the electroweak scale.

Glad I did not stay in particle physics.