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.