Gravitational waves, ripples in spacetime caused by the acceleration of massive objects, could provide valuable insights into the expansion rate of the universe. This is because the expansion of the universe affects how gravitational waves propagate through space. By measuring the properties of gravitational waves, astronomers can infer information about the rate at which the universe is expanding.

One specific method involves using gravitational waves to measure the Hubble constant, a key parameter that describes the rate of expansion of the universe. The Hubble constant can be determined by observing gravitational waves from merging binary neutron stars, which emit strong and well-understood gravitational wave signals. By measuring the time delay between the arrival of gravitational waves and electromagnetic counterparts (such as gamma-ray bursts) from the same event, astronomers can calculate the Hubble constant. This method has the potential to provide precise measurements of the Hubble constant, helping to constrain cosmological models and better understand the expansion history of the universe.

Gravitational waves can also be used to probe the properties of dark energy, a mysterious component that is believed to make up around 68% of the universe's total energy budget and is responsible for its accelerated expansion. By studying the effects of dark energy on the propagation of gravitational waves, astronomers can gain insights into its nature and evolution, shedding light on one of the most enigmatic aspects of the universe.