0:01
Welcome back everybody.
Okay, so we're almost done now.
So let's do a brief recap of the entire history, of the universe.
Okay.
So I'm going to be reading this off here because there's so much that [LAUGH].
There's so much that happened!
0:14
okay.
So, we start off with, we don't know what.
Somehow, the whole period of expansion you know, begins.
Was it a quantum fluctuation from some space time,
other space time into this one, we don't know.
Somehow it gets started, right?
And so then in just the first few minutes
of its existence the universe goes through these remarkable changes.
For example, first we get all the quarks and electrons
and photons that are in this primordial soup, Eventually the universe
cools and expands to the point where the quarks actually start
becoming bound into hadrons and they will never be unbound again.
0:51
Then we reach a period around a minute or so where as the universe expands and
cools, the protons, which are collections of of quarks, can start
colliding with each other to form heavier nuclei, things like helium, et cetera.
For reasons we don't understand, the antimatter goes away, we
don't know where it went but it's not there anymore.
Then eventually, about three minutes, the universe gets to the point where
it's so it's expanded it and cooled enough that those nuclear reactions stop.
The era of big bang nucleosynthesis is over.
The universe continues to expand, and then around
300,000 years after its creation, what we get
is the recombination, or the first combination, of
the protons and the electrons into neutral hydrogen.
The photons now have no one to play with.
They are released.
They travel the universe forever and become
the cosmic microwave background that we see today.
They are fossils of the big bang.
1:48
Then so that's the beginning of what we call the
dark ages, because the universe now becomes almost entirely neutral hydrogen.
If we wait another 100 million years or
so, we start getting the first stars forming,
we start getting the first structures, we get
the first stars and the first black holes forming.
These first stars are enormous.
They produce a lot of ultraviolet photons and they begin ionizing the universe.
The stars and these black holes, which are sort of pronto-quasars.
So the universe goes back into an ionized hydrogen state.
And so light the light from the stars now can travel across enormous distances.
Proto-galaxies form around the proto-quasars, or they form together.
The population, three, population three stars, what we call population three
stars, the first stars explode, starts seeding the universe with heavy elements.
3:01
And you know, a whole range of, now working start getting, lower mass stars.
Things like one solar mass or even lower because you can't form
those without having some of the metals in their atmospheres and their composition.
And one particular star, in one particular corner
of the universe we end up with life beginning.
Life goes on to become more complex.
Takes a long time for it to become complex.
But once that complexity starts it explodes.
And eventually you get a species that develops
some degree of intelligence, some degree of technological intelligence.
Starts using that to look back at the world.
And ask questions about it.
And there you go.
The story of the universe starts getting told by the universe itself.
So the question is are there any other species out there that this is happening?
Are there any other planets out there where this is happening?
Are we completely rare?
Are we a, you know, one in a trillion
trillion chance to get all the accidents to happen
that you lead to a species that can ask
questions of the universe or ask questions of itself?
Or is self-consciousness just you know, as dull as dirt.
Every planet worth its you know, worth its name has a you know,
life and self-consciousness or evolving onto it
so, you know, that's the big question.
That is the, the ultimate question for us looking at the universe.
So, okay, so that's the story.
Now we're ready to ask address the final question for this section.
[BLANK_AUDIO].
Adam FrankProfessor
