On the Incompleteness of Birkhoff’s Theorem: A New Approach to the Central Symmetric Gravitational Field in Vacuum Space

Birkhoff’s theorem (1923) states that in the framework of General Relativity the only solution to the central symmetric gravitational field in vacuum is the Schwarzschild metric. This result has crucial consequences in the resolution of the dark matter problem. This problem can only be solved through the discovery of a new type of matter particles, or by the introduction of a new theory of gravitation which supplants General Relativity. After reviewing Birkhoff’s theorem, it was discovered that by starting the calculation of the metric from an indeterminate metric whose coefficients are locally defined, we obtain a solution containing two arbitrary functions. In general, these functions do not induce any difference between this solution and the Schwarzschild metric. However, it can be seen that if we choose a triangular signal for these functions, the situation changes dramatically: (1) the metric is broken down into four distinct metrics that replace each other cyclically over time, (2) for two of these four metrics, the coordinate differentials dr and dt switch their spatial/temporal role cyclically, (3) the four metrics are not separable: they form a single logical set that we call a 4-metric and (4) this 4-metric cannot be transformed into the Schwarzschild metric by any coordinate change. According to these findings, there is a second solution in the spherical space, in addition to the Schwarzschild metric, and thus, Birkhoff’s theorem is incomplete. In the 4-metric, the orbital velocity of a massive particle does not depend on the radial distance. This 4-metric is thus in agreement with the baryonic Tully–Fisher relation (BTFR), (consequently BTFR is in agreement with a solution of General Relativity without presence of dark matter and without hypothesis on the distribution of stars in galaxies). By combining the 4-metric with the Schwarzschild metric, another 4-metric in agreement with the observed galaxy rotation curve can been obtained. The calculation of the light deflection in this space is also exposed in this paper. According to these findings: (1) it is not necessary to introduce the notion of dark matter or the notion of distribution of stars in galaxies in order to find the observed galaxy rotation curve in the framework of General Relativity, (2) the modification of the metric with respect to the Schwarzschild metric appears to be due to the existence of a lower bound of the space-time curvature in galaxies (without external field effect), this phenomenon leading to a temporal oscillation of the space-time curvature, (3) an analysis of the external field effect for the Milky Way-Andromeda couple allows to model the rotation curve of the two galaxies beyond the plateau zone. The validation of these findings would be the first step toward challenging the standard model of cosmology ([Formula: see text]CDM), as the [Formula: see text]CDM model cannot be in agreement with the observed galaxy rotation curve without presence of dark matter. The second step would be the demonstration that there is no dark matter in intergalactic spaces (not included in this paper).