“In the clear blue sky of physics, two little clouds of incomprehension remained on the horizon that obscured beauty and clarity. (“Knowledge in physics is like the great blue sky, which remains on the horizon only two little clouds of incomprehension.”) These famous words were uttered, In 1900, by the great British physicist Lord Kelvin – the creator of the “absolute zero”, from which the temperatures bearing his name are calculated – in front of his peers at the Royal Institution of London.

These two “little clouds” were, one, an inconclusive result of the Michelson and Morley experiment, which failed to show a discrepancy in the speed of light propagation in space, and the other, a problem posed by the so-called “black”. body’ emitted from an object heated to a high temperature. Lord Kelvin believed that there was an anomaly in the details, as there was nothing new to discover in physics, after Newton’s universal gravity and Maxwell’s electromagnetism, only the measurements to be revised.

From clouds to devastating storms

However … behind the first of these two clouds was no less than the theory of relativity, behind the second quantum mechanics! Consider the two main theories on which twentieth century physics was built.^e century which radically changed our view of concepts as fundamental as time, space, matter or energy. This often-reported anecdote can be the starting point for the new article of the philosopher and astrophysicist Aurélien Barrau, devoted precisely to these small anomalies, which sometimes make us jump from one model to another.

More than a century after Lord Kelvin, the situation in this regard has not fundamentally changed. Organized around “standard models” (particles for the infinitesimal, cosmology for the infinitesimally large, etc.), contemporary physics also faces its share of deviations. It also has two – or three or four… – “little clouds”, at least some of which (but which ones?) will sooner or later end up exploding in destructive storms, which puts forward our most solid theories. And Aurélien Barrau explains to us that it will always be so… and for this reason, he warns us from the start, “Literally, all theories are wrong”!