Let us now complete this brief survey of 
history of cosmology with some more 
modern developments. 
Remember that, by 1970's, it became clear 
that galaxy formation evolution must play 
an important role. 
It must be understood before we can 
actually map out the universe, 
and both theoretical an observational 
advances were made. 
Three theorists deserve special mention. 
Jim Peebles in the United States, 
Yakov Zel'dovich in former Soviet Union, 
and Martin Reese in United Kingdom. 
At the same time, we saw development of 
numerical cosmology. 
it is impossible to analytically follow, 
how would systems of billions, larger 
numbers of particles evolve. 
But we can simulate them in computer. 
The improvements in computer technology 
enabled very sophisticated and ever 
better simulations to be done and here is 
just a set of snapshots from one by a 
tourist named Andre [INAUDIBLE]. 
Today this is a very well developed art, 
and this is just a small snapshot of one 
of the more modern simulations by so 
called Virgo Consortium. 
And it covers essentially the entire 
observable universe. 
We can also zoom in, in great detail and 
see how structures form on galactic 
scales. 
So then that has to be compared with 
observations. 
Observational cosmology really started 
blossoming from 1970's onward. 
And thanks largely to the development of 
many new technologies. 
And from. 
Both from the ground and space. 
This is a picture from Hubble Space 
Telescope from one of the Deep Fields 
that Hubble has studied, 
with many, many distant galaxies, 
but it's important to point out the 
important role that technology plays in 
our development of scientific knowledge. 
Ever better instruments is, including CCD 
arrays and computers, enable us to get 
much higher quality of data and much more 
data than we ever had before. 
And in both large telescopes on the 
ground like a twin keck telescope shown 
here and in space, like the hubble shown 
here also, play an important role in 
these studies. 
Another important theoretical development 
happened in 1980. 
Alan Guth came up with so called 
inflationary theory, 
and this was a very surprising thing, 
and it really addressed the number of 
important, questions in cosmology. 
It became a standard paradigm in which 
early universe his view. 
We'll talk about this is much more detail 
later. 
Other theories since kept developing 
better or more ornate versions of 
inflationary theory. 
One of which is the multiverse or 
megaverse, 
in which ours is just one of the many 
inflating bubbles in some much larger 
space. 
But so far that's entirely a hypothetical 
issue. 
1990s, mid-1990s really saw return to the 
classical cosmology or cosmological 
tests. 
Now we talk about precision cosmology. 
Two important paths will happen there. 
The first one was studies of a cosmic 
microwave background with exquisite 
precision, both from round, from balloon, 
burning instruments, and from space. 
And cosmic microwave background is not 
perfectly uniform. 
There are minor fluctuations, like parts 
in a million, that correspond to density 
fluctuations in the universe. 
Measuring their size, can constrain 
cosmological parameters. 
So this is now done with great precision, 
but second thing that happened was use of 
cos-, supernova explosions as standard 
candles, with more modern instruments, to 
push Hubble diagrams much deeper than was 
done before, and, turn out that, that can 
also constrain cosmological parameters in 
important ways, and it became one of the 
key ingredients in the discovery of dark 
energy. 
So this is just between illustrate the 
great precision by which we know 
cosmological parameters. 
You can look through them, and there are 
many different ones. 
But they're roughly known with pres-, 
with percent level precision. 
This is something that earlier 
cosmologists could only dream about. 
So cosmology is now a precision science. 
And we know properties of the universe 
with an amazing accuracy. 
Just to jump ahead, here is the 
punchline. 
Today, we know that the universe consists 
of about 73% of so called dark energy. 
Another 23 percent and so of dark matter 
which is not made of regular matter atoms 
and normal matter would be mobile 
constitutes only four percent. 
This is now the terming through many, 
many different observation using 
different methods and it is supported 
constantly and refined with new 
measurements. 
And so generally well accepted picture, 
and we'll talk how that's done in more 
detail later. 
So here is essentially cosmic timeline 
from the modern viewpoint. 
universe starts with Big Bang. 
There is a brief period of inflation, 
when universe is less than ten to the 
minus 32 seconds old. 
Then sometime later, physics that we know 
starts to come into play, such as 
formation of first chemical elements, and 
then slowly formation of large, of 
flunctuations, and the formation of 
galaxies and there evolution. 
Obviously the deeper in the past we push 
in this logorithmic scale, the less we 
understand, but it's actually impressive 
that, we can really address what happened 
in the universe when it was say 
nanoseconds old with reasonbly good 
accuracy. 
Here is a slightly different view that 
would be appealing more to physicists 
that expresses history not as a function 
of time but as a typical energies of 
particles at that time. 
Recall that the smaller and the denser 
Universe was the hotter it was and 
kinetic energies were higher. 
Well today they're roughly. 
Micro background photons, which is 
energies of one four thousandth of an 
electron volt, but early times, the 
energies are correspondigly larger, and 
inflation happened when, particles had 
energies of ten to the sixteenth giga 
electron volt. 
Just for comparison, the large hadron 
collider, produces particles of 100 giga 
electron volts, rest mass energy. 
Here we see, simulation of, what the 
early univers might have looked like, 
that was produced by the doubly map space 
mission team, and it shows fluctuations 
in the micro background that was studied 
with great precision. 
So at the beginning of one of them, you 
can sees schematically dark matter 
collapsing, making clumps, then stars 
igniting, first chemical elements are 
made, galaxies are slowly assembled. 
Another interesting way to visualize the 
history of the Universe is to say, if all 
of the age of the universe. 
13.17, 13.7 billion years today was 
squeezed in one day. 
What happened when? 
Well Big Bangs happens at the beginning. 
Pretty much everything that predates 
formation of our solar system is done in 
first few hours. 
On that time scale humans appeared four 
seconds before midnight. 
Four seconds out of an entire 24 hour 
day. 
And that gives you a little bit of a 
scale as to how significant our history 
is on cosmic scales. 
Martin Reese suggested that cosmology 
today is now developing in two 
directions. 
One of which he compared to chess, 
which is theoretical elegant cosmology, 
which is very precise and clean. 
And the other one, which is observations 
of galaxy formation, which is messy, 
and he compares it to mud wrestling. 
Both of them are important and 
interesting.