Philosophy

A. Casella and G. Giuliani

This is an abridged translation of the paper by Casella and Giuliani published in the volume "Ancora sul realismo..." in the series Percorsi della Fisica. Some points of the original paper have been modified.

1. The presuppositions of science

The historical evolution of science shows that science has grown on the foundations of a realistic stand that allows statements about the existence of something and statements about properties of the world:

A1 A world exists, independent from the observer, whom the observer belongs to

In the historical development of science, we can find positions that have denied or considered worthless the realistic stand. Nevertheless, the realistic stand has constituted the underlying layer of the scientific enterprise. Two other presuppositions have grown on this basic layer:

A2 Every event has a cause (causality principle)

A3 World's behavior is constant in time (phenomena are reproducible)

We can assert that A1 is a ruling principle for common sense and science, particularly in its experimental component; a stand oriented by A2 has strengthened the predictive and explicative capacities of science; A3 has been, up to now, reasonably corroborated.

These three presuppositions also support common sense when rationally oriented.

2. The fundamental problem of realism

The fundamental problem of realism may be stated as follows: what are the relationships among the world, phenomena, experiments, theories, and images of the world?

For the sake of clarity, let us define the terms used.

• WORLD: The world independent from the observer of presupposition A1.
• PHENOMENA: Manifestations of the WORLD detected by our senses and/or measuring instruments.
• THEORIES: Descriptions (mathematical) of PHENOMENA or parts of the WORLD.
• EXPERIMENTS: Practical activities aimed at testing the soundness of hypotheses or theories.
• ACQUIRED KNOWLEDGE: The set of theoretical and experimental knowledge considered reasonably consolidated.
• IMAGE OF THE WORLD: Description of the WORLD ontologically founded.
• SCIENCE: The set of philosophical, theoretical, and experimental activities aimed at describing PHENOMENA or parts of the WORLD and at the building of an IMAGE OF THE WORLD.

We shall discuss the fundamental problem of realism in the case of Physics: the considerations developed below can be extended to other experimental disciplines with suitable modifications.

3.1 Theoretical entities and physical quantities

Physical descriptions assume the form of mathematical theories that use two types of concepts: theoretical entities and physical quantities. The main theoretical entities of twentieth-century physics are particles, waves, and fields.

Other theoretical entities are, for instance, those of atom, proton, electron, etc. Physical quantities describe properties of theoretical entities or interactions or relations between theoretical entities: their fundamental feature is that they can be measured. For instance, the concepts of mass, charge, spin, and magnetic moment are physical quantities that describe the properties of the electron or other particles; the concept of force allows the description of the interaction between, say, two electrons; the concept of velocity describes a relation between two theoretical entities, for instance, two reference frames.

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Angelo Loinger (Verona, 1923 - Pavia 2020) has been Full Professor of Theoretical Physics at the Universities of Messina, Pavia and Milano. He has published many papers on: foundations of Quantum Mechanics (particularly on the theory of measurement), classical and quantum ergodic theories, statistical mechanics of systems with infinite degrees of freedom, gauge fields, some basic issues of general relativity - et cetera.

He has been member of the Istituto Lombardo di Scienze e Lettere. In 1970, he was awarded the 'Prenio triennale per la Fisica F. Somaini'.