A team of scientists from the LIGO and Virgo collaboration found no signs of a "leak" of gravitational waves due to hypothetical extra dimensions. This allows us to reject a number of theories that include gravity in the Standard Model (describing the properties of all known particles and three of the four fundamental interactions), that is, they are candidates for the role of the Theory of Everything. The results of their work, published in the Arxiv preprint repository, support Einstein's theory of general relativity.
On August 17, 2017, the detectors of the gravitational observatories LIGO (Laser Interferometer Gravitational-Wave Observatory) and Virgo first recorded the signal GW170817 from the merger of two neutron stars. The disaster generated gravitational waves and a kilon wave, accompanied by a short burst of gamma radiation, a bright flash in the optical and infrared ranges, and a long afterglow in X-rays and radio beams. The observations made it possible to establish strict limits on the difference between the speed of light and the speed of gravitational waves, on violations of Lorentz invariance and the Shapiro effect - the time delay of electromagnetic signals in a gravitational field.
In general relativity, the speed of gravitational waves is equal to the speed of light, however, more exotic models, claiming to be the Theory of Everything, assume that, depending on the distance of the source, specific effects can affect the propagation of gravitational waves. For example, waves can be subject to dispersion due to Lorentz invariance violation or attenuated due to extra dimensions. Gravitational leakage occurs due to the leakage of gravitons into a more multidimensional space, which is proposed in the framework of various theories of quantum gravity.
Since the gravitational "leak" depends on the number of extra dimensions, the approximate number of these dimensions can be determined from the change in the amplitude of gravitational waves. If the latter exist, the distance from the source, determined from gravitational waves, must exceed the distance determined from electromagnetic radiation. According to many exotic models, light and matter can only move in four dimensions. The researchers concluded that the data currently available are consistent with the model of a four-dimensional universe.
Scientists emphasize that some models, assuming the presence of extra dimensions and "gravitational leakage that suddenly manifests itself at great distances", have not yet been completely rejected. However, future observations with gravitational detectors will make it possible to test them too.