Faced with the complexity of the universe and the diversity of possible mathematical models, science provides itself with various world representations, which act as a guide for research. This diversity can raise some contradictions which the scientist will try to overcome or interpret. In this case he will question the epistemological worth of the system of concepts he is using. The physicist's knowledge, being specific, cannot deal in the long run without certain philosophical issues.

With the arrival of relativity, and then of quantum theory, these questions became particularly interesting and difficult. If as Einstein thinks, one must question the existence of something that has an abstract representation, then any overall world view will imply certain metaphysical questions, which will more particularly concern the nature of energy and basic elements.

Moreover, they will be important enough to necessitate a regeneration in philosophy. Which philosophical principles can be reconciled with science as it now stands? How can one widen the basic concepts of physics in order to include theories the differences of which seem irreducible? Which formalism should a world view take so that it may be used by physics? These are a few of the themes that the author deals with in this book, sometimes tracing a path through philosophy, sometimes one through science.

A general theory of the universe must touch on the notion of instantaneous effect at a distance, more or less present in quantum theory. On the one hand we must understand how it is intellectually possible to include this idea, and on the other, discover what this approach teaches us about the consistency of the universe, about the harmony of its laws. Within the concepts of mass, space, inertia, impulse and even time, there is always an important question: " what is energy?".