Cosmological physics hypotheses are testable to some extent. This is because several predictions made by these hypotheses can be tested through observations and experiments. For example, the theory of the Big Bang predicts the existence of a cosmic microwave background radiation, which was later observed in the 1960s. This radiation provides strong evidence for the Big Bang theory.
Additionally, the theory of dark matter predicts the existence of an unseen mass that makes up a significant portion of the universe. This hypothesis has been supported by various observations, including the rotational speeds of galaxies, galaxy clusters, and gravitational lensing. However, the search for dark matter particles in experiments has not yet yielded conclusive evidence.
Similarly, the theory of cosmic inflation predicts the existence of slight variations in the cosmic microwave background radiation. These predictions have been confirmed by various observations, such as those with the Wilkinson Microwave Anisotropy Probe and the Planck Space Telescope.
While some aspects of cosmological physics hypotheses are not directly testable, predictions made by these theories can be tested through observations and experiments, providing empirical evidence to support or refute them.