Astronomers theorize that the faster expansion rate is due to a mysterious, dark force that is pulling galaxies apart.
This diagram reveals changes in the rate of expansion since the universe's birth 15 billion years ago..
Note that this value changes over time: The critical density changes with cosmological time but the energy density due to the cosmological constant remains unchanged throughout the history of the universe, because the amount of dark energy increases as the universe grows but the amount of matter does not..
The linear growth factor g u226.
Astronomers theorize that the faster expansion rate is due to a mysterious, dark force that is pulling galaxies apart.
This diagram reveals changes in the rate of expansion since the universe's birth 15 billion years ago.
The more shallow the curve, the faster the rate of expansion..
Similar results hold for a cosmological constant dominated universe
Thus for general dark energy models the state of structure formation at various redshifts could probe the equation of state, and even its time variation (we fix the sound speed to its canonical value, cs = 1)
While doing so, we explain how measurements of growth can be used to understand theory
We then review how some of the most mature cosmological probes - galaxy clustering, gravitational lensing, the abundance of clusters of galaxies, cosmic velocities, and cosmic microwave background - can be used to probe the growth of structure
Cosmic structure formation and evolution provides an additional path to exploring the cosmological model besides mapping the expansion history
Many of the observational probes employing structure rely on the growth dynamics of density fluctuations, in either the linear or non-linear regime
