The Cosmological Constant
Remember, Einstein didn't like a expanding/contracting
he put it a term (called the cosmological
to counteract this and produce a static universe. When Hubble
the expansion of the Universe, Einstein called the cosmological
his "biggest mistake."
If you go back to the Einstein field equations and work
out the most general form of the dynamical equation, you get
With this term, the Friedmann equation looks like
What is this Lambda term? It corresponds to an additional form of energy in the Universe,
which provides an
outwardly directed force on the Universe, like a pressure
could in principle balance the force of gravity).
But what is it????
The cosmological constant
Sounds like a great problem for the physicists! Models
explain the cosmo constant abound, including some very creative ones.
predictions for the magnitude of the cosmological constant are
orders of magnitude off from the current (tentative!) observed
- ... seems to be a manifestation of the energy
density of empty space...
- ... may(?) come from the energy associated with
- ... affects the
of the Universe...
- ... seems like it
(based on observations of the universe)!
|Note that just as we wrote Omega to
mean the density
of matter relative to the critical density, we can write another Omega
the energy density of "lambda" relative to the critical density.
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
Things to notice.
Wild times indeed...
- An accelerating
Universe is older.
(ie the expansion rate was slower in the past, so the universe took
to grow to its present size.
- Even universes
can be spatially flat or closed, and universes which collapse may yet
- As time goes by,
Flambda ~ R, Fgravity ~ R-2. If the
constant exists, it was end up dominating the expansion.
Latest "union" plot-- multiple datasets,
CMB = microwave background, sensitive to shape of space
SNe = supernovae, sensitive to curvature in R(t)
BAO = galaxy clustering, sensitive to matter density parameter