Combining Constraints


Constraints from Supernovae:

Remember, they tell us that the universe is accelerating in its expansion -- Lambda must be winning today.
 
Note that just as we wrote Omega to mean the density of matter relative to the critical density, we can write another Omega to mean the energy density of "lambda" relative to the critical density.

So we now have OmegaM and OmegaL, and if the universe is critical (flat), then OmegaM + OmegaL = 1.

So what values for lambda do we get from the supernovae?

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 = the amount of galaxy clustering, sensitive to matter density parameter


Working together, they suggest we live in a universe with:
  • OmegaM ~ 0.25
  • OmegaL ~ 0.75
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