cosmology and the evolution of the universe...1 – 2 billion years formation of galaxies: young...
TRANSCRIPT
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Cosmology and the Evolution of the Universe
Edwin Hubble, 1929: -almost all galaxies have a redshift
-moving away from us -exceptions in Local Group
-with distance measurements - found a relationship
greater distance ➔ greater redshift
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Implications of the Hubble Law:
- Universe is changing (getting bigger!) - it is not static, unchanging
- Universe had a beginning !! - could not have been expanding forever
HUBBLE LAW: v = Ho r
v = velocity (speed); r = distance
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Rate of expansion: Ho= Hubble constant (slope of line)
The Hubble Constant tells us: - Size of observable universe
largest redshift = largest distance
- Age of universe how long ago everything was
together
- Fate of universe what will happen in future
Most accurate measurements (2015):
Ho = 73.5 km/s per Mpc
Age = 13.799 ± 0.038 billion years The Big Bang Model
Universe began from a single point - that was extremely dense and hot
➔ Cosmic Singularity
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- "Explosion" of matter and energy (and space and time!)
-today, space is still expanding
- properties of universe change with time - had different conditions in the past - will have diff. conditions in future
- ultimate fate is unknown
The Early Universe: Initially was very HOT!
- Hot enough for Hydrogen fusion everywhere in space!
- explains why 25% of universe is Helium
Basic Principles of Big Bang Model
1. Universe cools as it expands:
Time
Temperature
0.01 s
100 billion Kelvin
180 s
1 billion Kelvin
380,000 yrs
3000 Kelvin
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2. Initially, the universe contained only photons (no matter) - High energy photons create matter
➔ E = m c2
electron
Gamma Rays
positron
3. Energy of radiation (photons) depends on temperature of universe
- As universe expands and cools - radiation loses energy - universe is a blackbody
PREDICTION: According to Big Bang Model:
What is temperature of universe TODAY? Prediction: 3 Kelvin (1964, Peebles and Dicke, Princeton Univ.)
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1964, A. Penzias and R. Wilson (Bell Labs) -built antenna for satellite
communications -detected "noise" in all directions -background noise corresponds to temperature of 3 Kelvin!
➔ Energy leftover from the
BIG BANG !!!
“Cosmic Microwave Background” (CMB)
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1989, satellite COBE - accurate measurements of Cosmic Microwave Background
- Temperature of Universe: T = 2.725 +/- 0.002 K
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Expansion of the Universe:
- the space between objects is expanding
- objects are not moving through space.
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Cosmological Principle: - there is no center, no edge - every location appears to be at
center
- same at every location (large scales) “Homogeneous”
- same appearance in every direction “Isotropic”
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Clusters, Superclusters, Voids - origins should be seen in the CMB - 1992, temp fluctuations of 0.0002 K - seeds of large scale structure 1992 2003 2015
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Surprising Discovery in 1998:
- rate of expansion is increasing!
- previously thought that gravity would slow expansion over time
- what can overcome affects of gravity? - repulsive, anti-gravity force
- “Dark Energy”
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Fate of the Universe: Three Possible Fates:
- based on overall density of universe - need to know total mass - need to know overall size (Ho)
Closed Universe: - expansion will eventually stop
- gravity will cause universe to collapse
- Universe will end in "Big Crunch" - maybe start again (?)
Overall geometric “shape” of universe is spherical
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Flat universe: - expands forever, always slowing down
- not enough gravity to start collapse
- Universe will end in “Cold Death” - all forms of energy becomes evenly distributed in space. - everywhere in universe is same temperature -close to absolute zero
Overall “shape” of universe is flat.
- Flat universe is predicted by current theories.
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Open Universe:
- expands forever, possibly going faster and faster
- dark energy overwhelms gravity
- Universe will end in “Big Rip” - dark energy overwhelms all other forces. - expansion will accelerate so much, all matter will get ripped apart Overall “shape” of universe is hyperbolic.
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TIME EVENT 0 – 10-43 seconds
The Planck Time: Nothing is known during this time. ?
10-35 – 10-32 seconds
Inflation: Universe goes through period of enormous expansion, grows by factor of 1043!!
Radiation Dominated
Universe (Primordial
Fireball)
10-8 – 10 seconds
Production of Matter: quarks and electrons created from extremely hot photons
10 – 300 seconds
Nucleosynthesis Era: 2H and 4He created by fusion reactions throughout the universe
380,000 yrs Era of Recombination: Electrons combine with nuclei to form atoms; (T = 3000 K), space is now transparent
Matter Dominated
Universe (Transparent)
1 – 2 billion years
Formation of Galaxies: Young galaxies seen as quasars
9 – 10 billion years
Formation of Solar System: Sun and planets form within the Galaxy (4.6 billion years ago)
Today (14 billion years)
Universe still expanding; Average temperature T = 2.725 K
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