sort of standard sirens to measure the expansion rate of the universe. Abbot et al. 2017 measured the Hubble constant value to be approximately 70 kilometres per second per megaparsec. The amplitudes of the strain 'h' is dependent on the masses of the objects causing waves, distances from observation point and gravitational waves detection frequencies. The associated distance measures are dependent on the cosmological parameters like the Hubble Constant for nearby objects and will be dependent on other cosmological parameters like the dark energy density, matter density, etc. for distant sources. Explanatory models Dark energy The most important property of dark energy is that it has negative pressure (repulsive action) which is distributed relatively homogeneously in space. where is the speed of light and is the energy density. Different theories of dark energy suggest different values of , with for cosmic acceleration (this leads to a positive value of in the acceleration equation above). The simplest explanation for dark energy is that it is a cosmological constant or vacuum energy; in this case . This leads to the Lambda-CDM model, which has generally been known as the Standard Model of Cosmology from 2003 through the present, since it is the simplest model in good agreement with a variety of recent observations. Riess et al. found that their results from supernova observations favoured expanding models with positive cosmological constant () and a current accelerated expansion (). Phantom energy Current observations allow the possibility of a cosmological model containing a dark energy component with equation of state . This phantom energy density would become infinite in finite time, causing such a huge gravitational repulsion that the universe would lose all structure and end in a Big Rip. For example, for and =70 km·s−1·Mpc−1, the time remaining before the universe ends in this Big Rip is 22 billion years. Alternative theories There are many alternative explanations for the accelerating universe. Some examples are quintessence, a proposed form of dark energy with a non-constant state equation, whose density decreases with time. A negative mass cosmology does not assume that the mass density of the universe is positive (as is done in supernova observations), and instead finds a negative cosmological constant. Occam's razor also suggests that this is the 'more parsimonious hypothesis'. Dark fluid is an alternative explanation for accelerating expansion which attempts to unite dark matter and dark energy into a single framework. Alternatively,