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Pré-Publication, Document De Travail Année : 2022

Review of the status of the "speed of light” and examination of some cosmological problems

Résumé

In spite of our habits, it is not immediate for us to give a meaning to the speed c of light, expressed by a number in meters per second. This supposes, on the one hand, that meter and second (space and time), are defined in a preliminary and independent way (but how to do it without supporting them on the phenomena?); and, on the other hand, that we consider light alone, without comparing it to any other phenomenon (with Poincaré, let us recognize however that only relations between quantities associated to the phenomena are accessible to us, according to a relational approach).The history of science supports these reservations: the speed of light is never estimated by the ratio of an interval of space to an interval of time, but always by the dimensionless ratio of two movements put in correspondence; we write it v/c, where v refers to another phenomenon than light. We can speak of a speed ratio, but this already supposes that time and space are defined, and, in all rigor, this is not appropriate. Symmetrically, the evaluation of a velocity v alone, for a phenomenon other than light, is not possible without involving light: one falls into a circle of endless regressions, where one only compares ratios of type v/c between them. This circle is stopped by deciding by decree (cf. the definition of the meter, 1983) the value of c = c0, which amounts to fixing the ratio between two "speeds", that of "one meter per second" and c. It is then to choose a standard, useful to compare between them all the phenomena of propagation (and to define in the process a space-time frame). In our terrestrial situation, this allows us to focus on the comparative quantification of the different velocities v (this is what interests us), referring to a fixed c0. However, it should be remembered that, in this understanding, all the motions that we measure on earth or in cosmology only refer at the beginning to ratios of the type v/c whose denominator is not more known than the numerator. Depending on the situation, we could fix one or the other, or consider that one or the other varies with respect to "values" that it has in other conditions. It seems to us in this context that we have the "right" to compare the "speed" of light to itself elsewhere or at another time, as for example that of its "local" apprehension c0 in the solar system compared to that in its cosmological paths, covering intergalactic distances. It happens that a certain number of important problems of cosmology show up by anomalous velocities v (higher than those expected) measured from the earth (dark matter, dark energy...), while each time, it is still only a ratio of the type v/c that is evaluated. One way to solve these difficulties is to assign to the speed of light in the denominator of the v/c ratio a value lower than the c0 value (the assignment of a macroscopic speed lower than the local one in the traversing of a refractive medium is a comparable approach). This is balanced by decreasing v from its initial value in our local units, and thus understanding the problematic excess that was observed. This approach seems to us to be promising and worth testing for various questions (including those concerning the shape of the rotation curves of stars in galaxies, cosmic inflation, Hubble tension, etc.). It does not prevent us from relying on the Lorentz transformation which expresses the relativity of the time and space scales associated with the motion chosen locally as a reference, and provides a fundamental structural framework for physical quantities (cf. Magueijo's analyses on the variable speed of light; our approach is not identified with his). It leads to a lengthening of the history of the universe, without compromising the scales of distances nor the sequence of stages defined by physicists. It also opens the debate on the coupled variation of the constants of physics (G, c...) already evoked in the literature.
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hal-03737259 , version 1 (24-07-2022)

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  • HAL Id : hal-03737259 , version 1

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Bernard Guy. Review of the status of the "speed of light” and examination of some cosmological problems. 2022. ⟨hal-03737259⟩
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