Ayer leí por encima el "paper" The concept of particle in Quantum Field Theory en http://arxiv.org/ftp/arxiv/papers/0907/0907.0178.pdf. No es un "paper" fácil, pero describe el estado de la situación de las partículas en las teorías cuánticas de campo. Quiero compartir las conclusiones:
After this complicated trip in the endless field of theoretical physics, we still are in a state of uncertainty. The naïve concept of particle, adopted by most practitioners of QFT, evidences intrinsic contradictions and therefore should be abandoned. This in turn implies a deep reformulation of the whole apparatus of QFT. In this regard, however, all proposals so far made are plagued by serious shortcomings which, so far, prevents from the introduction of a new, and more firmly grounded, concept of particle. It seems, after all, that we do not need a rigorous definition of the latter. QFT can work and produce acceptable previsions even in absence of it. Nevertheless, from a practical point of view, we need to summarize a number of experimental facts and theoretical features by introducing the concept of particle which, undoubtedly, allows more economical descriptions and more easily understandable pictures of dynamical phenomenology. Within this context, we can be satisfied with a definition of particle as a construct having a citizenship within an effective field theory, more or less like quasi-particles. As such, this construct must necessarily be endowed with dynamical features, which were absent in the old models of pointlike articles. Of course, the technical ingredients needed to introduce the new "effective" definition of particle are still incomplete and lot of work is necessary before obtaining significant advances along this direction. While this situation is satisfactory for most physicists, we acknowledge that it could be embarrassing for those searching for the "fundamental particles". However, nobody prevents from thinking that, at very high energy, the "effective" description of particles will reduce to the one of (almost) pointlike particles. And most actual efforts of theoretical as well as experimental physicists try just to prove the validity of this hypothesis. The ones which will remain unsatisfied for this state of affairs are the philosophers (or at least some of them). Namely the solution we have sketched above entails the disappearance of the haecceitas of particles, which are reduced to mere auxiliary constructs, useful for practical purposes, but in turn making reference to deeper constructs. For these philosophers the problem now becomes: what are these constructs? Do they coincide with fields? In this regard there are already some indications about a possible negative answer to this question (Teller, 1990; 1995). Perhaps, as suggested by Cao (see, Cao, 1997; 1999), the best ontological basis for QFT is given by its structure itself (inextricably connected with the processes it describes) rather than by specific entities (particles or fields).
Prácticamente ningún físico se preocupa por estos temas, pero vean que no está del todo claro la situación de las partículas. ¿son reales, representan algo de la realidad? ¿o lo real son los campos, y las partículas son como un "emergente", apenas nuestra forma de ver una consecuencia de la existencia o funcionamiento de algo real que representamos como campos?
Las citas que menciona son:
Teller, P. (1990). Philosophical Topics, 18, 175.
Teller, P. (1995). An interpretive introduction to Quantum Field Theory. Princeton University Press: Princeton, NJ.
Cao, T.Y. (1997). Introduction: Conceptual issues in QFT. In Cao, T.Y. (Ed.). Conceptual Developments of 20th Century Field Theories (pp. 1-27). Cambridge University Press: Cambridge, UK.
Cao, T.Y. (1999). Conceptual Foundations of Quantum Field Theories. Cambridge University Press: Cambridge, UK.
Tengo pendiente de ler los dos libros de Cao (el de 1997 es una compilación de varios autores, muy interesante; el de 1999 es un gran trabajo de Cao sobre el desarrollo histórico de los conceptos que llevaro a las QFT).
Angel "Java" Lopez