Combining Constraints

Constraints from Supernovae:

Remember, they tell us that the universe is accelerating in its expansion. So what does that mean for the universe's cosmological parameters?

Think about plotting a "plane" of all possible OmegaM, OmegaL values. On this plane we can also plot regions that show
  • shape of space
  • accelerating / decelerating universe
  • final outcome (expands forever or recollapses)

So what values for lambda do we get from the supernovae? Acceleration means OmegaL is "beating" OmegaM.

Things to notice.

  • An accelerating Universe is older. (ie the expansion rate was slower in the past, so the universe took longer to grow to its present size.
  • Even universes which expand forever can be spatially flat or closed, and universes which collapse may yet be spatially open.
  • As time goes by, Lambda wins. Flambda ~ R, Fgravity ~ R-2. If the cosmological constant exists, it was end up dominating the expansion.
Wild times indeed...

A "union" plot-- multiple datasets, multiple methods

CMB = microwave background, sensitive to shape of space

SNe  = supernovae, sensitive to R(t), the rate of expansion of the universe

BAO = tracing large scale structure of galaxies, sensitive to matter density parameter.

Working together, they suggest we live in a universe with:

  • OmegaM ~ 0.25
  • OmegaL ~ 0.75
  • Other observations give H0 ~ 69-72 km/s/Mpc
  • Results in t0 ~ 13.8 Gyr