Let us now take a more detailed look at
the 1 of the, more or less, state of the
art simulations using billions of
particles done by Max Plank Institute for
Astrophysics in Germany. This were done by
the Volker Springel and his collaborators.
The first movie will show gradual
expansion of the universe as cosmic web
forms. Then we will take a closer look at
what structure looks like at the end. The
simulation uses over ten billion
particles, over a gigaparsec region of the
universe. Now zooming in Mimics expansion
of the universe, and as you can see that
there is a gradual condensation of
material into these filaments. Again, this
is dark matter. If you could see dark
matter in color, this is what it would
look like. Now we are much too large scale
to see detailed merging but we're zooming
in closer and closer. Right now this is
super cluster of galaxies scale and as we
get closer in, you're going to see details
that are more like current clusters of
galaxies. For example, here this is about
the size of the local super cluster. And
zooming in further, we can see the
gigantic dark halo forms which is really
dark matter that belongs to a cluster of
galaxies or giant galaxy with a lot of
little dark matter halos that yet have to
merge together. And now pulling out, just
to see where this one little detail fits
within the whole large simulation. Now,
this is zooming in onto a particular small
region of the final simulation, flying
through it in 3D space, if you will. And
to just to give you the sense of the
richness of the structures that have been
forming. This is frozen moment in time,
it's the purpose is just to show you how
complex 3 dimensional structure of this
grid of dark matter really looks like.
Remember, variants falling to the
potential wells defined by the dark
matter. So, if you could see stars as
well, they would look somewhat like this
but more condensed. Here we are rotating
around a rich cluster of galaxies that is
formed somewhere in one of the ANSIs
peaks. This is not unlike c ore, or say,
Virgo cluster of galaxies or comma cluster
of galaxies, except, of course, the ANSIs
are the dark matter particles. The
different colors in this simulation
indicate different densities. They're not
representative of physical property or
dark matter in any way. They're just There
to make it easier to see the density
contrast. And now, let us zoom out again
from this cluster, and fly around it some
more. As you can see, these modern
simulations generate vast amounts of data
as numerical output, and analyzing them is
a very non-trivial problem. Then comparing
them with observations of real universe is
an even, trickier yet. Let's revisit some
snapshots from the simulation, just to
note some of the details. Here is a slice
at the very large redshift. The contrast
is not high yet. Dark matter potential
wells are still collapsing, forming the
first cores of galaxies, and clusters of
galaxies. This corresponds to redshift
18.3. Roughly the time when we think the
first stars may be forming. By about
redshift 5.7, at which point, the universe
is roughly a billion years old. You can
see a much more defined mesh of filaments.
Of dark matter with dense cores. Which are
the halos of first galaxies. Into which
baryons fall, and start making stars. By
about redshift 1.4, structure is really
well defined. This will be roughly the
time when solar system has formed in 1 of
these blobs that represent galaxies. And
finally, this is how the universe would
look today if you could see the dark
matter. And zooming in, this would be
roughly like the core of the variable
cluster today. Now one of the problem with
cold dark matter scenarios is, is that it
predicts a large number of this tiny
little dark narrow hallows and yet there
is no real good observational evidence for
them. Many different models have been
proposed how to get rid of excess of small
dark matter hallows. It's probably not a
very difficult problem, but we still don't
know for sure how it works. So one can try
different simulations using different
cosmologies which will then have different
expansion rates, and so the large scale
structure will be condensing in different
ways as the function of redshift. Those
can be then compared to observations from
redshift surveys [at the variety of
different redshifts. And not surprisingly,
cold dark matter model seems to work the
best or I should say cold dark matter
model involving cosmological constant, the
Lambda CVM model. You notice that the key
process here is constant merges of smaller
pieces into larger ones. Those are
symptoms presented through so-called
merger tree. Where it begins at the top
each little branch responds to dark halo
when 2 merge they become a larger branch
and so on. Until the end of simulation you
have one giant halo. You can track back
which part of it came from where.This can
be seen in simulation of the formation the
local group and milky way at least the
dark halo part there off. But Diemand et
al shown in the following The simulation
starts at the redshift of 12, a very low
contrast. And then universe expands, dark
matter condenses into lots and lots of
little dark halos which keep merging to
make the larger one, the progeniture of
the, the milky way galaxy. There is a lot
of chaotic merging that goes on. But on
the other hand it can be tracked very well
through numerical computation here because
it's just a simple Newtonian gravitational
physics, nothing else. And this is what it
will look like at the end.