Absence of a fundamental acceleration scale in galaxies

Dark matter is currently one of the main mysteries of the Universe. There is much strong indirect evidence that supports its existence, but there is yet no sign of a direct detection(1-3). Moreover, at the scale of galaxies, there is tension between the theoretically expected dark matter distribution and its indirectly observed distribution(4-7). Therefore, phenomena associated with dark matter have a chance of serving as a window towards new physics. The radial acceleration relation(8,9) confirms that a non-trivial acceleration scale a(0) can be found from the internal dynamics of several galaxies. The existence of such a scale is not obvious as far as the standard cosmological model is concerned(10,11), and it has been interpreted as a possible sign of modified gravity(12,13). Here, we consider 193 high-quality disk galaxies and, using Bayesian inference, show that the probability of existence of a fundamental acceleration is essentially O: the null hypothesis is rejected at more than 10 sigma. We conclude that a(0) is of emergent nature. In particular, the modified Newtonian dynamics theory(14-17)-a well-known alternative to dark matter based on the existence of a fundamental acceleration scale-or any other theory that behaves like it at galactic scales, is ruled out as a fundamental theory for galaxies at more than 10 sigma.