I want to move into the next Chapter, Chapter
18, that talks about cosmology.
Cosmology is the theory of the origin and
the evolution of the universe. Throughout
human history, many cultures from the ancient
times established their own cosmologies.
Stories as to how the world came about. It's
in human nature to see the causal chain of
events in development of anything, simply
because that's what we observe over our lifetime.
Kids are being born. They grow up, grow old,
and so on. Part of every culture had its own
cosmology.
What we will be talking about here is a scientific
view of cosmology. We will be using science,
in particular physical laws to gain an insight
as to how the universe was formed and how
it evolved.
There's a simple observation that hints to
the fact that the universe did not exist forever.
That it was born some finite amount of time
ago.
It's formulated in the famous Olbers Paradox.
There were people before him who pondered
the same things. Kepler was one of them, but
it was well formulated by Olbers. As a result
it's known as the Olbers Paradox.
The Paradox is in the following. If the universe
existed forever, for all times, and it is
infinite, and it is uniformly filled with
stars, then the night sky should not be dark.
The sky at night when the sun is on the other
side from us should be just as bright as the
sky during the day. The reasoning is as follows.
If these premises are correct, then regardless
of which direction you choose to look at,
you will always see a star.
These stars, some of them could be quite distant,
but if they lived forever, if they were there
for an infinite amount of time, the light
that they produce would have enough time to
reach us here on earth.
Regardless in which direction we would look
our eyesight should be on a star. We should
observe its light because it had enough time,
if the universe is infinitely old, it had
enough time that light to reach us here on
earth.
You can perhaps understand this a little bit
better through an analogy that is often used.
Imagine that you are in the middle, deep inside
the forest.
Anywhere you look, in any direction, you see
a tree. You look this way, you see a tree,
you look this way, you see the tree. In any
direction where you look you see a tree.
The line of sight always intercepts a tree,
just like here the line of sight always ends
up as a star. If this is the case, then the
night sky should not be dark as our observation
tells us.
The plausible resolution to this paradox,
seemingly paradox is that the universe is
not infinitely old. The light from very distant
stars did not have enough time to reach us
yet.
These stars do not hang around since infinite
past. The entire universe started at certain
time before, and the light from distant stars
did not have time to reach us.
For instance, this star here was very far
away, and the interval of time needed for
its light to reach us here is longer than
since the universe was formed then we would
not see this particular star.
This is a plausible resolution, and it was
provided by Edgar Allen Poe. You are familiar
with Poe? You know his poem Raven?
Even a simple observation like this and a
little bit of thinking, tells us that the
universe had to be formed some finite time
ago. It could not exist forever.
