Chapter 18: Cosmology
WHAT DO YOU THINK?
What does the Universe include?
 Did the Universe have a beginning?
 Is the Universe expanding, fixed in size,
or contracting?
 Will the Universe last forever?
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You will discover…
Cosmology, which seeks to explain how
the Universe began, how it evolves, and
its fate.
 The best theory we have for the evolution
of the Universe – the Big Bang.
 How astronomers explain the overall
structure of the Universe.
 Our understanding of the fate of the
Universe.
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In the Beginning – the Big Bang
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The Universe began 13.7 billion years ago with
an event called the “Big Bang.”
All of space-time, matter, and energy were
created at the Big Bang.
The left-over energy from the Big Bang can be
detected today as the Cosmic Microwave
Background Radiation.
The temperature of this radiation is only a few
degrees above absolute zero.
The Beginning – The Big Bang
In Search of The Earliest Photons
Wilkinson Microwave Anisotropy Probe
(WMAP) satellite, launched in 2001
WMAP’s Baby Picture of the Universe –
Cosmic Microwave Background Radiation
The Universe is Expanding
The Redshift of Superclusters shows us
that the Universe is expanding. This
Redshift is called the “Cosmological
Redshift,” because it is caused by the
expansion of space.
 The farther away a galaxy is from us, the
faster it moves away from us.
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The Expansion of the Universe –
Cosmological Redshift
Space itself is expanding.
Expanding Cake Analogy
Just as all the chocolate chips move apart as the cake
rises, all the superclusters of galaxies move away from
each other as the space of the Universe expands.
The Observable Universe
The cosmic light horizon today is about 13.7 billion
light-years away in all directions.
HST – Galaxies >13 Billion LY Away
This HST Ultra
Deep Field
Telescope
image shows
some of the
most distant
galaxies we
have seen.
Early Universe Temperature Variations
Tiny temperature fluctuations in the Cosmic Microwave Background
Radiation are related to the large-scale structure of the Universe
today, indicating where Superclusters and voids grew.
The First Stars – much larger than the Sun –
with much shorter lives
The burst of star formation that occurred within a
few hundred million years after the Big Bang.
Proto-Galaxy Formation
Hubble and Keck telescope images of two groups of stars that are
believed to be proto-galaxies, from which bigger galaxies grew
Creation of Spiral and Elliptical Galaxies
If the rate of star
formation was
low, then a
spiral galaxy
formed.
If the rate of star
formation was
high, then an
elliptical galaxy
formed.
A galaxy begins as a huge cloud of primordial
gas that collapses gravitationally.
The Fate of the Universe
The fate of the Universe depends on the
shape of space-time.
 The shape of space-time is determined by
how much total matter and energy there is
in the Universe.
 Space-time could have one of three
shapes:

 Sphere
= positive curvature = closed.
 Our floor = no curvature = flat.
 Saddle = negative curvature = open.
Possible Shapes of Space-time,
and the Fate of the Universe
•
Closed –
Universe
would
collapse.
•
Flat –
Universe
could slowly
expand
forever.
•
Open –
Universe
would
expand
forever.
Cosmic Microwave Background indicates that Spacetime is Flat – Universe could slowly expand forever
BUT – dimmer distant Supernovae mean the
expansion of the Universe is speeding up.
100 billion years
from now the
Universe will
appear frozen in
time as we look out
into space. Only
the light from the
Local Group of
galaxies will
remain visible, if
anyone is still
around to see it.
Expansion of the Universe is speeding up
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Very distant Type 1a Supernovae are not as
bright as they should be.
This means the expansion of the Universe is
speeding up instead of slowing down or staying
the same.
There is something really weird called Dark
Energy (not the same as Dark Matter) that is
causing this acceleration.
Dark Energy acts like anti-gravity, pushing the
Universe apart.
We do not know what this Dark Energy is, but it
makes up 73% of the total energy/matter of the
Universe.
Composition of the Universe
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Suppose all the matter and energy in the Universe is
$100 in your wallet or purse.
$73 would be Dark Energy – the mysterious energy
that’s pushing the Universe apart faster and faster.
$23 would be Dark Matter – matter that doesn’t give off
any kind of radiation, so we can’t see it – but it does
have gravity.
So out of your Universe of $100, $96 represents Dark
Energy and Dark Matter that have yet to be identified.
Only $4 would be visible matter – the regular stuff we
can see, like stars, gas clouds, and dust – the same stuff
we’re made of.
Of the visible matter ($4), only one-tenth of it shines as
stars. That’s 40 cents out of your total $100. The rest of
the visible matter is gas clouds and dust.
Composition of the Universe
Dark Energy (73%)
Dark Matter (23%)
Visible Matter except
Stars (3.6%)
Stars (0.4%)
WHAT DID YOU THINK?
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What does the Universe include?
It is all the matter, energy, and space-time that
will ever be detectable from the Earth or that will
ever affect us.
Did the Universe have a beginning?
Yes, it occurred about 13.7 billion years ago in
an event called the Big Bang.
Is the Universe expanding, fixed in size, or
contracting?
The Universe is expanding, faster and faster.
Will the Universe last forever?
Current observations support the belief that it will
last (expand) forever.