“Although the cosmological constant cold dark matter model is very successful in explaining almost all observations, it has some theoretical issues within its backbone structure. These include the mysterious physical origin of the two largest contributions to the energy content of the late-time Universe: cold dark matter and the cosmological constant, together with the unsatisfactory predictability and test-ability of the inflation theory. Therefore, it is important to explore alternative explanations for the late-time acceleration of the Universe. There have been several proposals . . . hints remain from the Dark Energy Survey and several previous galaxy surveys that the Universe today is a few percent less clumpy than predicted. . . . On the other hand, massive binary black holes as standard sirens have the disadvantage that the redshift needs to be measured independently of the gravitational wave observations. If we identify the host galaxy then it should be possible to determine with joint events whether long-wavelength gravitational wave and short-wavelength electromagnetic radiation have the same number of spacetime dimensions. . . . Also, there have been studies considering the propagation from the inspiraling of compact binary systems within the context of teleparallel gravity theories . . . meanwhile it is important to mention that these studies are in the context of a scenario where the general relativity cosmological model is considered as an effective fluid in the standard perturbations equations.” – Sebastian Bahamonde, et al., “Teleparallel Gravity: From Theory to Cosmology”