Transcript powerpoint version - University at Albany

Age, Evolution, and Size of the Cosmos
02.18.2015
Szydagis and Lunin
The Age of the Universe
• The Universe is 13.8 billion years old.
• How do we know this?
• The most important ingredient is the Hubble's parameter
• Various independent methods
– Type Ia supernova explosions
– Cosmic Microwave Background (WMAP, Planck)
– Crude lower bound: age of oldest stars
• All estimates agree within the uncertainties!
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History of the Universe
• The Big Bang
• Very Hot Universe (< 10-10s)
– quantum gravity
– Grand Unification
– Inflation
– Baryon asymmetry
• Hot Universe (< 1000s)
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– Formation of baryons
– e+/e- annihilation
– Neutrino decoupling
– Primordial nucleosynthesis
• Recombination (380 000 years)
• Formation of stars (~ 1 bn years)
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The Big Bang
0 seconds
Time
Temperature Infinity
Infinity
Energy
• The existing physical theories break down.
• Formal application of GR: naked singularity
• New physics is needed to resolve the singularity
 String theory?
 Loop quantum gravity?
• What happened before the Big Bang?
 traditional answer: there was no time
 speculative ideas: Big Bounce
• Big Bang is one of the greatest challenges in physics
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10 s
32
10 Kelvin
28
10 eV
Quantum Gravity
• All forces are carried by particles (photons, gluons, W/Z)
• Gravity must be carried by gravitons. Quantum effects are small
at low energies, but they dominate when field is strong.
• QG is still being developed (string theory, loop gravity, etc)
• Main applications of QG: Early Universe, black holes.
• Dynamics at this stage determines all subsequent evolution.
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End of the GUT epoch and Inflation
10 s
27
10 Kelvin
23
10 eV
• The strong, weak, and electromagnetic interactions are unified
into one force (the Grand Unification Epoch).
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End of the GUT epoch and Inflation
10 s
27
10 Kelvin
23
10 eV
• The strong, weak, and electromagnetic interactions are unified
into one force (the Grand Unification Epoch).
• The unification requires a doubling of the number of particles
at high energies (supersymmetry).
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End of the GUT epoch and Inflation
10 s
27
10 Kelvin
23
10 eV
• The strong, weak, and electromagnetic interactions are unified
into one force (the Grand Unification Epoch).
• The unification requires a doubling of the number of particles
at high energies (supersymmetry)
• After individual forces emerged, the Universe went through a
very rapid expansion (inflation).
• The entire VISIBLE Universe emerged from a TINY PART of the
Cosmos, this explains homogeneity and flatness seen in CMB.
• Inflation predicts multiverses with different physical properties.
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-5
10 s
12
10 K
8
10 eV
Formation of baryons
• Baryons consist of 3 quarks, mesons: quark + antiquark
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-5
10 s
12
10 K
8
10 eV
Formation of baryons
• Baryons consist of 3 quarks, mesons: quark + antiquark
• We see matter, but very little antimatter. The symmetry
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between the two was broken during baryogenesis (10 s)
• Free quarks cannot exist (confinement)
• In the early Universe, quark and gluons formed a distinct state
of matter called quark-gluon plasma (observed at CERN and
RHIC)
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• After 10 second quarks became confined within baryons and
mesons.
10
1s
1010 K
106 eV
Photons and neutrinos
• Neutrinos decouple after 0.2 s (1 MeV)
– The ratio n/p is frozen, it sets stage for nucleosynthesis
– Neutrinos keep cooling off ONLY due to expansion
• Photons are produced in e+/e- annihilation at t < 1s
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1s
1010 K
106 eV
Photons and neutrinos
• Neutrinos decouple after 0.2 s (1 MeV)
• The ratio n/p is frozen, it sets stage for nucleosynthesis
• Neutrinos keep cooling off ONLY due to expansion
• Photons are produced in e+/e- annihilation at t < 1s
• Only one electron per 109 e+/e- survives
• Photons keep cooling off MOSTLY due to expansion, the
ratio of photon/neutrino temperatures is set (>1)
• Remaining electrons will form atoms during recombination.
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200 s
8
10 K
4
10 eV
Primodial Nuocleosythesis
• Stars don't explain He abundance (25% of baryonic matter)
– Nuclear reactions: He abundance is related to luminosity
– Observations: less than 0.5% of He is formed is stars
• Light elements are produced through a chain of nuclear
processes involving deuterium and tritium
• Complicated equations predict the CORRECT abundances of
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He (25%), D (0.01%), Li (10 ), etc.
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380000 years
4000 K
0.3 eV
Recombination
• Nuclei and electrons bind to form atoms.
• Transparent Universe (end of the “Dark Ages”)
• CMB consists of photons produced at recombination.
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380000 years
4000 K
0.3 eV
Recombination
• Nuclei and electrons bind to form atoms.
• Transparent Universe (end of the “Dark Ages”)
• CMB consists of photons produced at recombination.
• The most accurate info about the early Universe
• Continuous improvements (COBE, WMAP, Planck
satellites)
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1 billion years
18 K / -255 °C
-3
1.5 10 eV
Formation of stars
• Cloud of hydrogen collapses due to gravity.
• High pressure ignites nuclear reactions.
• Heavy elements are produced as star burns, they are
dispersed through supernova explosions.
• Galaxies and galaxy clusters are formed.
• Younger stars and planetary systems are formed
– Solar system: 9 bn years after the Big Bang
• Life of Earth ~ 3.5 bn years ago (10.3 b.y. after the BB)
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What drives the expansion of the Universe?
• Spacetime tells matter how to move, matter tells spacetime
how to curve (J. Wheeler)
• Three forms of “matter” (energy) and their domination
– Hot matter (radiation & neutrinos) (t < 47 000 years)
– Cold matter (baryionic and dark)
– Dark energy (t > 10 bn years)
• Present breakdown: dark energy (68%), dark matter (27%),
ordinary matter (5%), radiation (tiny fraction)
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Content of the Universe
• Dark energy/matter/radiation fractions change with time
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The size of the Universe
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• Distance to the Sun is 1.5 x 10 m
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• Distance to the nearest star ~1pc = 3 x 10 m = 3.3 ly
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• The size of a galaxy 10 pc
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• The size of a galaxy cluster 10 pc
• Universe is homogeneous & isotropic above 108 pc
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• The size of the visible Universe is 10 pc
• The size of the full Universe is UNKNOWN.
• The Universe may be finite or infinite.
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The visible Universe
• The radius visible U. is 14 x 109 pc or 46 x 109 light years
• The naive radius of the entire Universe is 13.8 x 109 ly.
• Expansion of the Universe:
– objects move away after emitting light
– law of expansion and age give the size
• Cosmic horizon is expanding: new objects enter at the edges.
• Inflation: the Universe is at least 1023 time larger that the
observable part.
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Homework
• Read the links next to powerpoint version of this talk on the
course website syllabus table for Friday
• Complete written homework #4, also for Friday.
• Additional reading material will be emailed to you.
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