Study of the universe itself
Size - finite or infinite?
Evolution and ultimate fate?
The Redshift and the Hubble Law
Galaxies are receding with redshifts proportional to distances (Hubble law)
Vr velocity of recession
H Hubble constant = 71 km/sec/Mpc
The Expanding Universe
Entire universe is expanding - no obvious center.
All clusters of galaxies receding from each other.
General Relativity: space-time is expanding - galaxy clusters are NOT expanding into empty space
Universe 13.7 x109 yrs old
Evidence for the Big Bang
Recession of galaxies is consistent with Big Bang, but doesn't prove it
Cosmic Microwave Background Radiation (CMBR) suggests universe once hot and dense
CMBR - faint emission at ~ 1 mm, almost uniform intensity across sky
Predicted: Early universe contained hot matter, radiation
Characteristics similar to observed CMBR
As universe expanded, radiation redshifted
Almost uniform distribution
Black body temp. ~ 2.73 K now
Observed universe ~75% H, ~23% He
Source of observed He - nuclear reactions when universe hot, dense
To explain CMBR and observed He abundance, universe must have had a hot, dense phase.
Big Bang - The "Standard Model"
Universe - space, time, energy, matter originated in
Universe started to expand, temp. dropped, photons transform to particles & anti-particles and reverse
As temp. dropped below 1013 K at 10-6 sec, protons and neutrons no longer formed, but particles and anti-particles annihilated each other.
Matter exists because there were not exactly equal numbers of particles and anti-particles.
Few seconds later, electrons & positrons no longer created, most annihilated each other, leaving some electrons
After 100 - 200 sec, fusion produced deuterium, helium, small amounts of lithium, beryllium
Explains amount of He, H
Universe expands, time passes
t = 380,000 years, T ~ 3000 K
Nuclei capture electrons - producing neutral atoms
Space transparent to radiation (Decoupling)
Radiation expands through out universe, redshifted
Stars form 2x108 years later
Galaxies formed by t ~ 109 years
Top-down: superclusters, then clusters, then galaxies
Bottom-up: small galaxies, then large galaxies, then clusters, then superclusters (Hubble Deep Field)
The Future of the Universe
If mean density > critical density, gravity halts expansion, collapse into Big Crunch (closed universe)
If mean density < critical density, universe expands forever (open universe)
If mean density = critical density, universe barely expands forever (flat universe)
Omega (&Omega): ratio of observed mean density to critical density
Density of luminous matter 4.4% critical density, &Omegalum =.044
But there is evidence for dark matter
The Nature of the Dark Matter
We don't know
Baryonic matter: MUST BE < 20% critical density
Elementary particles: e.g. neutrinos, predicted particles
No models match observed universe
With dark matter, omega = 0.27
Why is omega so close to 1? (Flatness problem)
Horizon problem - when CMBR released, parts of universe we see now could not interact
How can all of CMBR have same properties?
Inflationary hypothesis - early universe experienced dramatically rapid expansion
Solves horizon and flatness problems
Hyper expansion flattens curvature until indistinguishable from 1
What caused inflation?
Long-Term Future of the Universe
Recent observations: omega = 1.0
Flat universe - expands forever
1014 years - all stars dead - white dwarfs, neutron stars, black holes
1020 years - galactic black holes & dead stars
Eventually - dead stars disintegrate - electrons positrons, neutrinos, and photons
Recent results of supernova surveys suggest expansion accelerating
Expansion dominated by repulsive force overcoming gravity
73% of universe is 'dark energy'
If repulsive force is strong enough - Big Rip.........
TO BE CONTINUED...............