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Let us now complete this brief survey of 
history of cosmology with some more 

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modern developments. 
Remember that, by 1970's, it became clear 

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that galaxy formation evolution must play 
an important role. 

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It must be understood before we can 
actually map out the universe, 

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and both theoretical an observational 
advances were made. 

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Three theorists deserve special mention. 
Jim Peebles in the United States, 

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Yakov Zel'dovich in former Soviet Union, 
and Martin Reese in United Kingdom. 

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At the same time, we saw development of 
numerical cosmology. 

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it is impossible to analytically follow, 
how would systems of billions, larger 

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numbers of particles evolve. 
But we can simulate them in computer. 

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The improvements in computer technology 
enabled very sophisticated and ever 

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better simulations to be done and here is 
just a set of snapshots from one by a 

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tourist named Andre [INAUDIBLE]. 
Today this is a very well developed art, 

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and this is just a small snapshot of one 
of the more modern simulations by so 

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called Virgo Consortium. 
And it covers essentially the entire 

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observable universe. 
We can also zoom in, in great detail and 

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see how structures form on galactic 
scales. 

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So then that has to be compared with 
observations. 

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Observational cosmology really started 
blossoming from 1970's onward. 

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And thanks largely to the development of 
many new technologies. 

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And from. 
Both from the ground and space. 

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This is a picture from Hubble Space 
Telescope from one of the Deep Fields 

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that Hubble has studied, 
with many, many distant galaxies, 

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but it's important to point out the 
important role that technology plays in 

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our development of scientific knowledge. 
Ever better instruments is, including CCD 

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arrays and computers, enable us to get 
much higher quality of data and much more 

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data than we ever had before. 
And in both large telescopes on the 

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ground like a twin keck telescope shown 
here and in space, like the hubble shown 

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here also, play an important role in 
these studies. 

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Another important theoretical development 
happened in 1980. 

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Alan Guth came up with so called 
inflationary theory, 

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and this was a very surprising thing, 
and it really addressed the number of 

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important, questions in cosmology. 
It became a standard paradigm in which 

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early universe his view. 
We'll talk about this is much more detail 

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later. 
Other theories since kept developing 

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better or more ornate versions of 
inflationary theory. 

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One of which is the multiverse or 
megaverse, 

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in which ours is just one of the many 
inflating bubbles in some much larger 

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space. 
But so far that's entirely a hypothetical 

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issue. 
1990s, mid-1990s really saw return to the 

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classical cosmology or cosmological 
tests. 

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Now we talk about precision cosmology. 
Two important paths will happen there. 

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The first one was studies of a cosmic 
microwave background with exquisite 

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precision, both from round, from balloon, 
burning instruments, and from space. 

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And cosmic microwave background is not 
perfectly uniform. 

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There are minor fluctuations, like parts 
in a million, that correspond to density 

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fluctuations in the universe. 
Measuring their size, can constrain 

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cosmological parameters. 
So this is now done with great precision, 

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but second thing that happened was use of 
cos-, supernova explosions as standard 

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candles, with more modern instruments, to 
push Hubble diagrams much deeper than was 

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done before, and, turn out that, that can 
also constrain cosmological parameters in 

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important ways, and it became one of the 
key ingredients in the discovery of dark 

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energy. 
So this is just between illustrate the 

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great precision by which we know 
cosmological parameters. 

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You can look through them, and there are 
many different ones. 

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But they're roughly known with pres-, 
with percent level precision. 

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This is something that earlier 
cosmologists could only dream about. 

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So cosmology is now a precision science. 
And we know properties of the universe 

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with an amazing accuracy. 
Just to jump ahead, here is the 

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punchline. 
Today, we know that the universe consists 

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of about 73% of so called dark energy. 
Another 23 percent and so of dark matter 

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which is not made of regular matter atoms 
and normal matter would be mobile 

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constitutes only four percent. 
This is now the terming through many, 

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many different observation using 
different methods and it is supported 

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constantly and refined with new 
measurements. 

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And so generally well accepted picture, 
and we'll talk how that's done in more 

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detail later. 
So here is essentially cosmic timeline 

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from the modern viewpoint. 
universe starts with Big Bang. 

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There is a brief period of inflation, 
when universe is less than ten to the 

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minus 32 seconds old. 
Then sometime later, physics that we know 

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starts to come into play, such as 
formation of first chemical elements, and 

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then slowly formation of large, of 
flunctuations, and the formation of 

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galaxies and there evolution. 
Obviously the deeper in the past we push 

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in this logorithmic scale, the less we 
understand, but it's actually impressive 

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that, we can really address what happened 
in the universe when it was say 

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nanoseconds old with reasonbly good 
accuracy. 

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Here is a slightly different view that 
would be appealing more to physicists 

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that expresses history not as a function 
of time but as a typical energies of 

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particles at that time. 
Recall that the smaller and the denser 

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Universe was the hotter it was and 
kinetic energies were higher. 

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Well today they're roughly. 
Micro background photons, which is 

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energies of one four thousandth of an 
electron volt, but early times, the 

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energies are correspondigly larger, and 
inflation happened when, particles had 

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energies of ten to the sixteenth giga 
electron volt. 

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Just for comparison, the large hadron 
collider, produces particles of 100 giga 

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electron volts, rest mass energy. 
Here we see, simulation of, what the 

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early univers might have looked like, 
that was produced by the doubly map space 

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mission team, and it shows fluctuations 
in the micro background that was studied 

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with great precision. 
So at the beginning of one of them, you 

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can sees schematically dark matter 
collapsing, making clumps, then stars 

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igniting, first chemical elements are 
made, galaxies are slowly assembled. 

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Another interesting way to visualize the 
history of the Universe is to say, if all 

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of the age of the universe. 
13.17, 13.7 billion years today was 

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squeezed in one day. 
What happened when? 

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Well Big Bangs happens at the beginning. 
Pretty much everything that predates 

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formation of our solar system is done in 
first few hours. 

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On that time scale humans appeared four 
seconds before midnight. 

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Four seconds out of an entire 24 hour 
day. 

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And that gives you a little bit of a 
scale as to how significant our history 

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is on cosmic scales. 
Martin Reese suggested that cosmology 

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today is now developing in two 
directions. 

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One of which he compared to chess, 
which is theoretical elegant cosmology, 

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which is very precise and clean. 
And the other one, which is observations 

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of galaxy formation, which is messy, 
and he compares it to mud wrestling. 

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Both of them are important and 
interesting.