So, constraints from Big Bang nucleosynthesis from type 1A super novae
surveys from the cosmic background and from many other sources have been put
together into this best fit that tells us the parameters of our universe, which I
used as input for my description of the history.
So, let's see how these parameters are put together.
what we see here is a plot of matter density today versus cosmological dark
energy density today. the line here is the line diagonal where
the sum of the two densities is one. Remember, that's total energy density one
that corresponds to flat universes. Above it, we have positively curved universes,
below it negatively curved universes. And these concentric curves are, are curves
of within which, outside of which you can exclude being with increasing certainty
based on various measurements. So, for example, the Super Nova survey,
remember, was measuring the deceleration parameter, if you remember, that
corresponded to rho plus 3p/c^2 which ended up being half of the density of
dust plus the density of radiation, which is irrelevant, minus the density of dark
energy. And so, that's the slope of this graph.
We get a very good measurement of this quantity in this direction, but we get a
less of a sensitivity to the sum of this plus that.
Because if you increase the matter density and also increase the dark energy
density, the deceleration parameter doesn't change much.
So, the supernovae give us a good constraint in this direction but now much
in this direction. On the other hand, the cosmic microwave
background data is pretty much sensitive to the total density. Remember, we
measure the flatness of the universe, it lays us pretty much on this line.
Happily, these two are crossed and so between them they produce a very good
prediction. this is additional data sensitive mostly
to the density of dust because this has to do with looking at the galactic
distribution and corelations in distances and that's similar to the way we studied
the acoustic sound waves in the primordial plasma. And again, this is
supposed to track the wavelengths and fluctuations in the dark matter density.
And so this gives us a third and consistent constraint.
There are many other observations that go into the pot when making our best
estimate, but you see that we have both consistent and rather precise
determination of the parameters of our universe, and you see that we predicted
arc energy of about 0.75 of the critical density and a matter density of about
0.25 of the critical density, of which, remember, we have restrictions, let's
say, at most 5% is visible matter, so the rest are baryonic matter.
That's from among other things, baryogenesis and also the details of the
cosmic microwave background. So, we predict that the rest is dark and
we do know exactly what our universe is made of.
That's quite exciting.