Et si le temps n'existait pas? Un peu de science subversive by Carlo Rovelli.

Due to a prolonged flue I had the nice "opportunity" to stay two weeks at home in the first half of January, thus I made some readings that deviates from the usual home and work back and forth routine.

Rovelli, twenty years ago, was one of the founders of a particular approach to unify Einstein general relativity and quantum mechanics. For me the booklet is quite intriguing for the rediscovery of the different conceptions of time and space, and in particular to realize we are often driven by a priori conceptual models of which we ignore the force or, worst, we are not even conscious.

Roughly speaking, in Newton age there was a debate on the nature of space and time. Newton made his proposal, of whose limits was himself well aware, and given the incredibly strong explicative and predictive power of his machinery, his ideas dominated human minds for more than three centuries. Newton equations and Newton gravitation law required a fixed spatial background, a kind of box containing all the objects, with an existence in itself, over or better inside which all the events unroll.

Pascal and Leibnitz, each one with some differences, thought that the space do not exists in itself, but it is just the set of relations between the objects. For them, the absolute space cannot exist: of a single object we cannot say if it is moving or at rest, it is meaningless the question itslef given the absence of any reference.

About the time, from an operational point of view, what an experimenter do is to take a physical phenomenon as a reference and compare the phenomenon under study to it. She will use for instance the small pendulum oscillations (as Galileo) or refer to more modern things as the emission or absorption of photons between two specific energetic level of a given atom ("atomic" watches) ... but the essence will be always the same. She also need to set up a well defined system to make the comparison, given that to define simultaneity of events not spatially co-localized will require some sync work, that is (not immediate but) feasible.

Thus, as Newton observed, there's no way to evaluate the absolute time, nevertheless its introduction will far simplify the equations and forced him to use it. What is the simplification? Suppose, for instance, to have five physical measurable things A, B, C, D, E ... (energy, position, velocity, ...). If you can assign to each of them a running label t (as time) you end up with just five temporal functions A(t), B(t), C(t), D(t), E(t). That's all. Otherwise you are forced to make all the comparison of each one to the other, that is A as a function of B, C, D. E, B as a function of C, D, E, ... and so on ... that is twenty-four functions!

Newton ideas had a well-deserved place in our scientific development, he was one the "Great", and his game worked very very well, partly even after Einstein, at least up to now :-).