In the process of trying to outline the most salient aspects of the particle model, a degree of ambiguity over the semantics used to describe certain concepts may have crept in. We might characterise this ambiguity in the following questions:
Is there a point when the semantics of particles and fields converge?
How does the semantics of an interaction differ from a force ?
In this context, the word ‘semantics’ itself is used to highlight a range of different meanings, i.e. from common usage to the implication of quantum physics. We have already discussed the ambiguity of the first question above in terms of the wave-particle duality, although we might also cite the more tangible issue of the ‘substance’ of an elementary particle. While quantum physics, like so many other specialist subjects, has assigned an alternative meaning to certain words, it is not always obvious whether the re-definition has any tangible reality beyond its mathematical description. Therefore, the goal of the following discussions is simply to highlight a number of conceptual issues for further consideration, prior to the main discussion of quantum field theory;
In the semantics of particle physics, a fundamental interaction is analogous to what classical physics might describe in terms of the fundamental forces. As such, the description of the four fundamental interactions aligns to what were previously described as the four fundamental forces, i.e. electromagnetism, strong nuclear, weak nuclear and gravitation. However, within the context of particle physics, the semantics of an interaction is used because the interactions are often described in terms of a methodology known as perturbation theory, which involves the exchange of gauge bosons between particles. While the role of gravity is not really integrated into quantum theory, it might be worth highlighting that the theory of general relativity has also questioned the idea of a ‘force’ in preference to its description of curved spacetime. The following quote by John Wheeler possibly captures how the idea of gravitational force is replaced by geodesic curvature of spacetime:
“Matter tells spacetime how to curve,
and spacetime tells matter how to move”
However, on a more reflective note, we might wish to challenge some of the semantics in the quote above. For example, do we ultimately have to replace the physicality of matter with some form of localised energy density? How does this energy density actually ‘curve’ spacetime and what physical mechanism can ‘move’ energy in spacetime?