Which predictions can be made with theoretical models?
What we know for certain about elementary particles and their interactions is reflected in the Standard Model of elementary particle physics. From a mathematical point of view, the Standard Model is based on a surprisingly compact equation. It has been confirmed with a high degree of precision in a large number of experimental tests and is deemed to be one of the most thoroughly tested theories of modern physics.
The last missing particle was detected in July 2012 at the LHC - the Higgs boson, postulated in order for the Standard Model to be mathematically consistent. This success would not have been possible without precise theoretical predictions. It also shows how important the interplay between theoretical and experimental physics is.
From a conceptual point of view, however, the Standard Model contains a few weak points. Physicists have constructed numerous new models in their attempts to overcome them. These extended models typically contain a great many unknown parameters. But precise predictions are also important here: In order to be able to distinguish these models from each other as well as from the Standard Model – or to be able to exclude them completely.
Researching is like detective work
The work of phenomenologists consists in computing the specific predictions of a model in order to then compare them with experimental measurements. The physicists work mainly with data from accelerator experiments like those conducted with the Large Hadron Collider particle accelerator at CERN, for example.
The way they work is like playing detective: What is the best way of measuring an unknown particle? How can different models be distinguished experimentally from each other? Or: Which measured quantities have the greatest sensitivity for an unknown model parameter?
The list of questions can be expanded in many directions – and every new answer raises new, more profound questions.