Three ways to measure distance in the universe

Nature : Since the Big Bang , the universe’s initial expansion has been gradually slowed by the gravitational pull from the mass it contains. Most of this mass is in the form of invisible and mysterious dark matter . Today, however, the universe seems to be re-accelerating under the influence of even weirder stuff dubbed dark energy .Almost nothing is understood about either dark matter or dark energy—but both are many times more common than visible matter.Tracking the expansion of the universe, from which the relative amounts of dark matter and dark energy can be inferred, requires measuring the distances to galaxies. Distances have always been the bane of astronomy: there are no simple red and green glasses to extrude our two-dimensional picture of the sky into an expanding movie.Three rival techniques are currently trying to establish themselves as the best probe of cosmological expansion: observations of exploding stars called type Ia supernovae , the focal lengths of gravitational lenses , and baryon acoustic oscillations .Astronomer Richard Massey from Edinburgh’s Institute for Astronomy assesses the advantages and disadvantages of the three techniques. Related Link Cosmology: Dark is the new black