Download The Origin, Evolution, and Fate of the Universe

The Origin, Evolution,
and Fate of the Universe
Announcements
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Homework # 8 is available as of this morning in
OWL. Due date for is Friday Dec 9th
Exam # 3 will take place on Tuesday, December
6th;
Quiz # 7 will take place Thursday, December 8th.
Reading Assignments
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Units 75, 76, 79, 80, 81, 82
Summary of what we know…
q  The Universe is 13.7 billion
years old, and 4200 Mpc in
radius
q  It is mostly (96%) filled
with dark (non-baryonic)
matter and energy
q  It is expanding, following
the Hubble Law: v = Ho D
(Ho = 73 km/s/Mpc)
q As we look into its farthest
reaches, we are looking
back in time (the Universe is
a `time machine !)
A Consequence of the Hubble Law
More distant galaxies have higher
`recession velocities (they `run away
from us faster): v = Ho D
n  Their light shifts to redder wavelengths
(Doppler shift)
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Distant galaxies are REDDER (emit light
at longer wavelengths) than nearby
galaxies
The Universe as a time machine
The speed of light is finite: 300,000 km/s
n  It takes time for light to move through space
n  E.g. it takes 8 min to come from Sun, and
~230,000 years to come from Andromeda
n  When light reaches us, it shows us how those
sources were at the time it left them
n  Hence: the further we see in space, the further
back we see in time
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Distant galaxies are YOUNGER!
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No Dark Energy, no Supernova evolution
Does the universe have an
edge?
Universe has
no edge and no center!
A model universe:
two dimensional
Space is expanding with
time!
v No edge to space, and
no center.
v The distances between
galaxies increase.
v The velocity with
which galaxies escape
from each other
increases.
Olbers Paradox
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If you walk through a forest, you only see trees
to the farthest distance
If the Universe is infinite, every direction you
look, you should meet a star or a galaxy.
Thus, the night sky should glow like a star, and
should be as hot as the surface of a star!
Why is this not happening?
Olbers Paradox - 2
Because, even if the Universe is infinite in
space,
n  It is not infinite in time: the Universe had
a beginning time!
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It started about 13.7 billion years ago!
When you `peek’ at the Universe, you are
looking `through’ the surface of the balloon,
back in time.
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Because the Universe is expanding today,
it had to start from a more compressed
(smaller) region. If you could revert time,
the galaxies would come all together!
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There was a point in time and space when
everything was compressed to a `point ,
with enormous temperatures (T > 1015 K)!
The Big Bang: The Origin of the
Universe
It started as a `hot expansion’ that created space and time
The Big Bang was not really an explosion.
It is that the universe was born expanding.
This expansion happens everywhere in the
same way
Every observer sees the same thing
There is no center
The big bang takes place
everywhere!
The big bang is still going on!
Space and time were created
with the big bang and are still
changing!
The Universe and
Its Evolution:
Step by Step
At the Very Beginning…
u  In the `primordial soup temperatures are enormous;
u  All four forces are `unified into one;
u  Matter/antimatter and energy are in constant
interaction (think of the interior of a star, but many
billions times hotter), i.e., matter and antimatter change
into energy and viceversa, continuously;
u  Particles are very elementary: quarks and electrons
(and their antimatter counterparts) are just all there is
As the Universe expands, it cools down
The Particle Era
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10-10 s < t < .001 s
The four fundamental forces (gravity, strong, weak, and
electromagnetic) are separated!
Particles (both matter and antimatter) are created and
destroyed with equal efficiency.
At the end of this time, when the Universe cooled to 1012
K, it is no longer hot enough to spontaneously produce
protons and antiprotons.
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Because of a slight imbalance (Symmetry Breaking), for every
one billion antiprotons, there
were 1 billion +1 protons.
- All antiprotons annihilated with protons to produce photons (1
billion photons for each proton in our Universe).
The Era of Nucleosynthesis
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0.001 s < t < 3 minutes
During this time, hydrogen (the protons left over
from the Particle Era) is fused into helium and a
small amount of deuterium and lithium (behaves
like the interior of a star).
It is a robust prediction of the Era of
Nucleosynthesis that 75% of the Universe be left
over as hydrogen and the other 25% be helium
(plus trace amounts of deuterium and lithium)
At the end of this time, the Universe was too
cool for any more fusion.
The Era of Nuclei
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3 minutes < t < 300,000 years
This is the simplest the Universe has ever
been and will ever be.
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All that exists during this time is ionized hydrogen
and helium as well as lots of photons.
The Universe during this time (and all earlier
times) is opaque (think of the surface of a
star, matter and light interact constantly).
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At the end of this time, however, the Universe is
too cold to be opaque:
Light separates from matter (Cosmic Microwave
Background)
The Era of Atoms and Galaxies
300,000 years < t < 13.7 billion years
n  Universe is no longer hot enough to keep
matter ionized.
n  Structure formed and here we are.
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Observational Evidence for this
`Funny’ Story
Besides the observational evidence for the
expanding and evolving universe, we have the
confirmation of the two key big-bang
predictions:
1.  The abundances of light elements in the
Universe. We really do measure that about
25% of the Universe is helium, about 75% is
hydrogen, and we even get the deuterium and
lithium right!
2.  The Cosmic Microwave Background radiation
(blackbody radiation from the era of nuclei)
The Cosmic Microwave Background Radiation
(the fossil radiation from the Big Bang)
Arno Penzias and Robert Wilson
(1966)
The isotropic and homogeneous
radiation that was set free at the
beginning of the Era of Atoms, when
the Universe becomes transparent.
Evidence for the Big Bang
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Expansion of the Universe
Origin of the cosmic background radiation
Nucleosynthesis of the light elements
Galaxy and Structure
Formation
… or how we go from the Era of Atoms to the Era of
Humans
Vocabulary
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in astronomy, the term structure refers to
anything that s gravitationally held
together.
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Planets, Stars, Galaxies, clusters of galaxies,
etc. are all `structures’
Survey Question
Which of the following objects would not be
considered structure by astronomers?
a) constellation
b) planet
c) star
d) galaxy
e) cluster of galaxies
Hierarchy of Structures
Galaxy
Hierarchy of Structures
Galaxy Cluster
Hierarchy of Structures
The Local
Supercluster
of Galaxies
How did the Universe evolve
from a sea of atoms to the
organized structures we observe
today?
Was the Big Bang Homogeneous?
The light from the CMB has
the same temperature
everywhere and in every
direction.
However, it also shows tiny
fluctuations: these grew to
form galaxies and clusters
today.
We see the `seeds of
today s galaxies and
clusters!
The Universe as viewed in the Microwave by the WMAP satellite
This small anisotropy (~ 1/106) in the CMB, emitted 300,000 years after
the Big Bang, represents the small fluctuation in the matter distribution
which provides the seed for the structure formation in the universe.
Formation of the Large-Scale
Structure
Due to gravity,
acting on Dark
Matter, which then attracts regular matter
The Same Picture but made with
Galaxies (these are the Clusters)
How did we go from the clusters
of dark matter to the galaxies
of baryonic matter?
Collapse of baryonic gas clouds provided
the initial seeds for the galaxies.
Galaxies grew subsequently by
`merging’, i.e., by accreting other
galaxies
Galaxies interactions and mergers
have been a strong evolutionary
mechanism
(Movie)
Galaxies like to
cluster:
eg. M81 group
What will happen to the
Universe?
q  It depends entirely on how much total
gravitational `pull it has:
q  This depends on the total content of mass and
energy
q  A high content of matter and energy will cause the
Universe to `stop its expansion in the future (far
away), reverse the expansion into a contraction, and
produce the Big Crunch
q  A low (or `critical ) content of matter and energy
will cause the Universe to expand forever
q Current data suggest we are accelerating
q  The Universe will end up as a cold, dim expanse.
This ends our trip through the
Universe