Cosmology

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History of the Universe
TIME
Universe gets cooler and less dense as it
stretches Universe)
ROUGH SIZE OF UNIVERSE
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History of the Universe

• INFLATION age 10-35 s to 10-32 s
• space expands by huge amount (1050 times)
• needed to explain
• ?isotropic microwave background
• ?homogeneous universe

OBSERVABLE UNIVERSE THEN (BEFORE INFLATION)
OUR OBSERVABLE UNIVERSE
OBSERVABLE UNIVERSE AFTER INFLATION
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Thought Question

• Very early in the history of the universe, the
  part of the universe we can see today (the
  observable universe) was
  
• much larger than it is today.
• much smaller than it is today.
• about the same size it is today.

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Thought Question

• If the observable universe today is smaller than
  the size of the observable universe before
  inflation (expanded to the present day)
  
• all parts of the observable universe today should
  have about the same temperature.
  
• different parts of the observable universe today
  should have different temperatures.
  

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Cosmic Microwave Background Radiation
very small fluctuations in microwave background
point out where galaxies started forming
2 ? 10-4 K variations
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Matter and Antimatter

• Mass and energy can be converted, but only in
  certain ways
  
• Light can make a matter-antimatter pair of
  particles if there is enough energy
  
• Pairs of particles can annihilate and produce
  energy (light)

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Thought Question

• Electrons have less mass than protons, which have
  less mass than neutrons. Which of the following
  particles/antiparticles can still be made by
  thermal radiation photons via pair production at
  the lowest temperatures?
• protons and anti-protons
• electrons and anti-electrons
• neutrons and anti-neutrons

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Destruction of Antimatter
When temperature gets too low (stretching
Universe),
matter/antimatter ? light

• ANNIHILATION OF PROTONS/ANTI-PROTONS,
  NEUTRONS/ANTINEUTRONS
  
• age 10-3 s
• T 1012 K
• ELECTON/POSITRON ANNIHILATION
• age 15 s
• T 3 ?109 K

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Destruction of Antimatter
For some reason, there was more matter than
antimatter!
Why???
AFTER
BEFORE
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Summary of the History of the Universe
LIGHT, MATTER, AND ANTIMATTER
JUST MATTER AND LIGHT
NUCLEI, ELECTRONS, AND LIGHT
ATOMS AND LIGHT
GAS, STARS, GALAXIES, LIGHT
PROTONS
NEUTRONS
ELECTRONS
TIME PASSES AND TEMPERATURE DROPS
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Building the Universe
stars make heavy atoms (like iron, carbon, oxygen
)
universe becomes transparent
1 billion years old z ? 10 - 20 FIRST GALAXIES F
ORM
100 million years old FIRST STARS FORM
380,000 years old z ? 1100 T 3000 K ATOMS FOR
M
AS TIME PASSES, TEMPERATURE DECREASES
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Gravity pulls mass into denser regions universe
grows lumpier with time
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The Fate of the Universe?

• BIG CRUNCH (or gnaB giB)
• gravity strong enough to stop expansion and cause
  Universe to contract
  
• Universe ends in a hot, violent crunch

• BIG CHILL
• gravity unable to stop expansion
• Universe lasts forever, stars die out so cold,
  so dark.

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Fate(s) of the Universe

• How do we predict the future of the Universe?
• Determine ACCELERATION of the expansion
• Measure MASS
• ? Is there enough to stop expansion?
• ? DARK MATTER may be important
• Compare current expansion to past expansion
• ? Is Universe slowing down fast enough?
• ? DARK ENERGY may determine universes fate

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How Fast is the Universe Decelerating?
supernovas can be seen across the universe and
far back in time and sometimes we know their L
UMINOSITIES
SUPERNOVA
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How Fast is the Universe Decelerating?

• REDSHIFT tells us how much Universe has stretched
  since supernova went off
  
• DISTANCE (from its apparent brightness) tells us
  how far back in time the supernova happened
  
• a fainter supernova is
  farther away

SUPERNOVA
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a coasting universe expands steadily (NOT
decelerating)
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Slowing the Universe
acceleration of galaxy on sphere
US
If there is a high enough density of galaxies
(critical density), gravity can stop the
expansion
sphere surrounding us
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Thought Question
How could you draw this graph to describe the
motion of a ball moving away from you at constant
speed?
distance from you
time
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Thought Question
Which of these universes was expanding
(stretching) fastest in the past?
US
AVERAGE GALAXY SEPARATION (COMPARED TO TODAY)
1.
NOW
2.
3.
PAST
FUTURE
TIME
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Speed
Speed of ball is slope of line
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Coasting Universe (NO ACCELERATION)
OTHER GALAXIES WITH SUPERNOVAS
US
AVERAGE GALAXY SEPARATION (COMPARED TO TODAY)
age is exactly
1
more redshift
NOW
0
PAST
FUTURE
BEGINNING OF UNIVERSE
TIME
more distant galaxies
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Thought Question
What graph could describe the motion of a ball
that you throw straight up in the air?
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Acceleration
Acceleration involves changes in slope
ACCELERATION
CONSTANT SPEED
distance from you
distance from you
DECELERATION
time
time
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Fate(s) of the Universe
Current expansion rate H0 (galaxies near us) has
been measured
average galaxy separation (compared to today)
1
time
NOW
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Decelerating Universe
OTHER GALAXIES WITH SUPERNOVAS
US
universe CRUNCHES in future
universe stretched more quickly in past
AVERAGE GALAXY SEPARATION (COMPARED TO TODAY)
NOW
PAST
FUTURE
BEGINNING OF UNIVERSE
TIME
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Thought Question
What is happening to the red universe at this
point?
AVERAGE GALAXY SEPARATION (COMPARED TO TODAY)
NOW
PAST
FUTURE
TIME

• The universe is stretching the fastest it ever
  will.
  
• The universe has temporarily stopped stretching.
• The universe is shrinking the fastest it ever
  will.

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Thought Question
Which universe is decelerating most quickly?
average galaxy separation (compared to today)
1.
3.
2.
NOW
time
BIG BANG
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Critical Universe
universe slows, but never stops expanding
OTHER GALAXIES WITH SUPERNOVAS
US
AVERAGE GALAXY SEPARATION (COMPARED TO TODAY)
universe decelerates slowly in past
NOW
PAST
FUTURE
BEGINNING OF UNIVERSE
TIME
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Thought Question

• Using your radar gun, you can measure the speeds
  of cars and their distances (by how long radar
  takes to travel to them and back). If all the
  cars are decelerating when they see you, what
  would the graph below look like?

speed
distance
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Universe is Accelerating!
OTHER GALAXIES WITH SUPERNOVAS
US
universe stretched MUCH slower in past
stretching getting faster!!
AVERAGE GALAXY SEPARATION (COMPARED TO TODAY)
NOW
PAST
FUTURE
WHAT IS DOING THIS!?!?!?
TIME
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The Cosmic Pie

• Normal matter about 4
• Dark matter about 25
• Dark energy about 71

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Some Questions

• What is dark matter made of?
• What is dark energy?
• What was the Universe like very shortly after the
  Big Bang?