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
