and quantum theory, making them relativistic quantum theories. Maxwell’s electro-magnetism, also known as electrodynamics, respects relativistic invariance but is not formulated in a quantum framework. It is only between 1920 and 1950, through the works of Dirac, and later, Feynman, Schwinger, and Tomonaga, that quantum electrodynamics emerged.

Intense work was then undertaken to establish a unified framework for the weak, electromagnetic, and strong interactions. This work culminated in the 1970s, nota-bly through contributions from Glashow, Salam, and Weinberg, in the develop-ment of the so-called “standard model”, which unifies the first two interactions. Theories of “grand unification”, also developed in the 1970s, have sought and con-tinue to seek to unify the three interactions into a coherent whole. This remains, in part, still prospective, as competing models have not been adjudicated, primar-ily due to the very high energies required to test them experimentally.

As for gravity, although Einstein provided it with a relativistic formulation, it still needs to be reconciled with the principles of quantum theory. This quantum gravity represents the Holy Grail for many theoretical high-energy physicists. One can wager that this theory, if it ever materializes10, will also lead to a conceptual revolution in our understanding of the world. Indeed, since Einstein established a profound correspondence between gravitation and space-time, the quantization of one should ipso facto entail the quantization of the other, at the characteristic scale of quantum gravity, the Planck length, LP = 10−34 cm. This would imply a radical upheaval in our conception of space-time, which, perceived as continuous on our scale, would be revealed as discrete on the Plank scale. Approaches such as string theory, loop quantum gravity, or emergent gravity11 have been proposed, but none have yet received experimental confirmation, as the relevant length or energy scales are entirely inaccessible with current technical means.

Quantum Mechanics: What Revolution?

Having sketched an overview of the major revolutions in physics, it is time to focus on the particularly singular situation of quantum mechanics. Singular, firstly, because, as we have already mentioned, it is the theory that allows pre-dictions of unparalleled precision in all sciences. Singular, secondly, because it profoundly disrupts the foundations of classical physics and, consequently, our worldviews derived from it. Singular, finally, because of the ambiguities it leaves over the nature of the relationship between the elements of its mathematical formalism and the physical reality they are supposed to describe, making it very difficult to clearly answer the question of the nature of the revolution that followed the advent of the theory.

Indeed, although the theory of relativity has radically transformed our concep-tions of space and time, which, previously absolute, become relative, it never-theless retains a fundamental characteristic: objectivity. Within the framework of relativity, the elements of physical reality, such as intervals of space, time, and speeds, indeed depend on the relative motion of the observer with respect to the events considered. However, they remain objective quantities, if only because their variations from one observer to another follow universal laws (the famous Lorentz transformations), which are entirely independent of the observer’s subjective inter-pretation. This objectivity persists equally within the framework of general rela-tivity. Finally, the elements of the formalism of these theories are in direct corre-spondence with the elements of physical reality. In quantum mechanics, however, this objectivity disappears, giving way to a radically different relationship between physical phenomena, their measurements, their observers, and the formalism that describes them. Thus, without prejudging the future, quantum mechan-ics could constitute a pinnacle in the evolution of our knowledge of the world.