Let's think a little bit
about what the Big Bang
theory suggests.
And then based on
the theory, what
we should be observing today.
So the Big Bang starts with
all of the mass in space
in the universe, an
infinitely, an infinitely dense
singularity.
And a singularity
is just something
that the math doesn't
even apply to it.
We don't even know how
to understand that.
But immediately
after the Big Bang,
so this occurred 13.7 billion
years ago, 13.7 billion years
ago, immediately after it, this
little tiny infinitely small
singularity begins to expand.
And so the first 100,000
years, it's still pretty dense.
So let me just to
show this right now.
So then it starts to expand.
So maybe it gets to this
level right over here.
And I do not know if the entire
universe is infinite or finite,
whether it's a four-dimensional
sphere, whether it goes
infinitely in every directions,
or whether it's just
slightly curved here and there
and maybe flat everywhere else.
I won't go into all of that.
But then it starts to
expand a little bit
from the singularity.
But it's still extremely dense.
It's still extremely dense.
So dense that atoms
can't even form.
So you just have the basic
fundamental building blocks
of atoms.
They're just all flying around.
Electrons and protons, they're
just flying around in just
this ultra-hot, ultra-hot,
white hot I could say,
or maybe even white hot plasma.
So I'll call it
white hot plasma.
And then if we fast
forward a little bit more.
And now this is a point that
we think we understand well.
But this number-- I actually
looked at some old physics
books.
And this number has changed in
really the last 15, 20 years.
So maybe it'll change more.
But after 380,000 years from
the beginning of the Big Bang,
300,000 years after
the Big Bang--
I'll call it the BB-- 380,000
years after the Big Bang,
and obviously this is give
or take a couple of years,
the universe expands enough, the
universe is now large enough--
and obviously, I'm
not drawing things
to scale-- the universe is now
large enough and sparse enough
that it can cool
down a little bit.
You don't have as
much bumping around.
It's still a hot place.
But now, it cools down
enough that electrons
can be captured by a proton.
And you could actually
have-- the first hydrogen
atoms can begin to form.
The first hydrogen
atoms begin to form.
They actually condense.
And we estimate this temperature
to be around 3,000 Kelvin.
So we've cooled to 3,000 Kelvin.
But this is still a
temperature that you would not
want to hang out in.
It's still extremely,
extremely hot.
Now why is this moment
important, the first atoms
forming?
So let's think about
what's happening here.
You have all of this
bumping and interactions.
And if because of a bump,
or some energy release,
or because of the
heat temperature,
if a photon is released
it'll be immediately absorbed
by something else.
If some energy gets
released, it'll
immediately be absorbed
by something else
because the universe
is so dense,
especially with
charged particles,
Here, all of a sudden,
it's not that dense.
So over here, things
that were being emitted
could not travel long distances.
They would immediately
bump into something else.
Well, you go over
here and the universe
is starting to look like
the universe we recognize.
All of a sudden, if one
of these really hot--
and it's still nowhere near
as hot as this universe
over here-- but if one of
these hot atoms emits a photon,
and they would because
they are at 3,000 Kelvin,
if they emit a photon,
all of a sudden
there's actually space
for that photon to travel.
So for the first time in
the history of the universe,
380,000 years after the Big
Bang, you now have photons.
You now have
electromagnetic radiation.
You now have
information that can
travel over long,
long distances.
So given that this
happened, it's
still roughly 13.7
billion years ago.
380,000 years is not a lot
when you're talking about 13.7.
It still wouldn't even
really change the dial
because we're talking in
the hundreds of thousands.
0.7 is 700 million years.
So this is actually
a very small number.
So it's still
approximately 13.7 billion.
It's really 13.7
minus 380,000 years.
But given that this was the
first time that information
could travel, that photons
could travel through space
without most of them having to
bump into something, especially
something that's
probably charged--
the other interesting thing is
that these atoms that formed
are now neutral-- what could
we expect to see today?
Well, let's think about it.
These left.
These photons were emitted
13.7 billion years ago.
And they were emitted from
every point in the universe.
So this is every
point in the universe.
The universe was a
pretty uniform place
at that time, very
minor irregularities.
But you could see because it
was this white-hot thing that
had just began to condense.
It hadn't formed a
lot of the structures
that we now associate
with the universe.
It was just kind of a
fairly uniform spread of,
at that time, reasonably
hot hydrogen atoms.
So this is every
point in the universe.
So let's think about
what's going on here.
Let me draw another diagram.
So we're talking
about this point
in the universe right over here.
The universe is, at even 380,000
years after the Big Bang,
still much, much,
much, much smaller
than the universe today.
But let's say that this is the
point in the universe where
we happen to be now.
At this point in time,
there was no Earth,
there was no solar system,
there was no Milky Way.
It was just a bunch
of hot hydrogen atoms.
Now if we were at this
point in the universe,
there must been
points in the universe
at that exact same time that
were emitting this radiation.
And actually, every
point in the universe
was emitting this radiation.
The point of the
universe where we are now
is emitting this radiation.
So the points that
were closer to us,
it was emitting that radiation.
But it got to us much sooner.
It got to us billions
of years ago.
But there are some points
that were far enough
that that radiation must
be getting to us right now.
Or another way to
think about it is
that radiation has taken 13.7
billion years to reach us.
So let me draw.
So if I were to draw the
visible universe today--
and you know from the
video about the size.
So it's not going
to be to scale.
It would have to
be far, far larger
than the circle I drew here.
But let's say that this
is the visible universe.
Let's say this is the
visible universe today.
We should be receiving-- and
we're in the center of it
because we can always look
roughly the same distance
in every direction.
We're not the center
of the universe.
I want to be clear.
We're the center of the
observable universe because we
can only observe the same
distance in all directions.
Now, we're receiving some light
from 100,000 light years away.
And then we're looking
100,000 years in the past.
We should be receiving
some light that was first
emitted a million
light years before.
And that's like looking a
million years in the past.
Because the light we see was
emitted a million years ago.
I think that's a bit redundant.
We could see light
that's just getting
to us after traveling
for a billion years.
And so we're actually
looking at those objects
a billion years
ago because that's
when they emitted the light.
So the same way, we
could look at objects
that emitted their light
13.7 billion years ago,
right at the beginning.
Right at this stage
over here, right
after 380,000 years
after the Big Bang.
And so since that light
is only just reaching us,
we will see it as it was
13.7 billion years ago.
So we should see this
type of radiation.
Now the other thing to remember,
the universe was expanding.
When this was emitted, the
universe was expanding.
The universe was expanding
at a very-- well,
it's all relative what's a
fast rate and all of that.
But it was expanding.
And we learned on the
video in red shift
that when the source of the
light is moving away from you,
or the source of the
electromagnetic radiation
is moving away from you,
the radiation itself get red
shifted.
So even though this is at a
relatively high frequency--
you can almost imagine it
was kind of red-hot gas.
It was at 3,000 Kelvin--
because it was moving away
from us, these things--
and we learned in the video
on the actual size of
the observable universe,
even though these
electromagnetic waves are
taking 13.7 billion
years to reach us,
in that time, this point in
space, the point in space that
emitted those
electromagnetic waves are
about 46 billion
light years away.
So that's our best estimate.
So this is still
stretching away.
So theory, if you
believe all of this,
that this was about 3,000
Kelvin and it gets red shifted,
theory would have
it that we should
see not something analogous
to electromagnetic waves being
released from a 3,000
degree temperature atom.
We should see
something red shifted
into the radio spectrum.
So we should be
observing radio waves.
And the reason why we're
observing radio waves and not
something of a higher frequency
is because it got red shifted.
It got red shifted down
into a lower frequency.
And remember, we
should be seeing it
from every point in the universe
where the photons have been
traveling for 13.7
billion years.
We should see it all around us.
This is almost a
necessity for us
to really believe in the
current Big Bang theory.
And it turns out that
we did observe this.
And this is very unintuitive.
Because you look at any
other point in the universe,
it's nonuniform.
Every other point
in the universe,
you have stars and galaxies.
These aren't atoms anymore.
These are stars, and
galaxies, and whatnot.
And so there's some
points in the universe
where you see a
lot of radiation.
And there's other points in the
universe where you see nothing.
It's just black.
But if this is correct,
if this really did happen,
we should be able to
observe uniform radio
waves from every
direction around us.
And you go 300-- or
more than 360 degrees.
We're going in three dimensions.
Any direction you point an
antenna, a radio antenna,
you should be receiving
these radio waves that
were at much higher frequency
when they were emitted.
They had been red shifted then.
But they were emitted
13.7 billion years ago.
And, it turns out
in the late 1960s,
they did find these radio
waves from every direction.
And these are
called the cosmic--
let me write this down.
This is the cosmic microwave
background radiation.
And it's this in combination--
so it's this data
that we're getting,
this observation,
in combination with the
fact that the further
we look out to galaxies
and clusters of galaxies,
they all seem to be
moving away from us.
They're all red shifted.
And they get red
shifted more and more
the further we look out.
So this and everything being
redshifted away from us
are the best two points of
evidence for the actual Big
Bang.
So hopefully, you found
that reasonably interesting.
This page was last edited on 29 July 2020, at 12:35