Early (Expanding) Universe Average temperature decreases with expansion.
Particles & Anti-Particles Very short wavelength photons collide and form electron-positron pairs. E=mc 2 electron=matter positron=antimatter Early universe full of particles & radiation b/c of high temperature.
Freeze-out As universe cools, particles and anti-particles annihilate, but fortunately for us there are slightly more particles:
Fundamental Forces Unification of forces at very high temperatures. Unifies! Maybe?? String Theory
Grand Unified Theories Analogy: Phases of water
Eras of the Universe Earliest eras defined by the types of forces present in the universe (very short period) Later eras defined by the types of particles present in the universe (most of the age of the universe)
Planck Era Time<10-43 sec Temp>10 32 K No theory of quantum gravity All forces may have been unified (we really have no clue)
GUT Era 10-43 <Time<10-38 sec 10 32 >Temp>10 29 K Gravity becomes distinct from other forces Era ends when strong & electroweak forces decouple; inflation?
Electroweak Era 10-48 <Time<10-20 sec 10 29 >Temp>10 15 K Gravity, strong, & electroweak forces are distinct. Era ends when electrostatic & weak forces decouple.
Particle Era 10-10 <Time<0.001 sec 10 15 >Temp>10 12 K Amount of matter & antimatter nearly equal About 1 extra proton for every 10 9 protonantiproton pairs. Inequality very important!
Era of Nucleosynthesis 0.001 s<time<5 min 10 12 >Temp>10 9 K Begins when matter annihilates remaining antimatter. Nuclei begin to fuse Helium nuclei formed at ~ 3 minutes
Era of Nuclei 5 min<time <380,000 yrs 10 9 >Temp>3000 K Universe becomes too cool for photons to break helium apart (free-streaming)
Era of Atoms 380,000 yrs <Time <10 9 yrs 3000>Temp>30 K Atoms formed. Cosmic background radiation released.
Poll Question: What is the current temperature of the universe? A. absolute zero B. a few degrees Kelvin C. a few hundred degrees Kelvin D. a few thousand degrees Kelvin
Cosmic Microwave Background Time ~ 380,000 yrs Temp ~ 3000 K Atoms form (recombination) Universe becomes transparent to photons Surface of Last Scattering
Cosmic Microwave Background
Journey to the Big Bang
Cosmic Microwave Background 1965: Penzias & Wilson detected background noise (also available on your analog TV as 1% of signal)
Light & Temperature Nearly all large or dense objects emit thermal radiation, including stars, planets, & you. An object s thermal radiation spectrum depends only on one property: Temperature
Cosmological Redshifts
Cosmic Microwave Background
Cosmic Microwave Background Expansion of the universe redshifts the thermal radiation to wavelengths that are ~ 1000 times longer (microwaves) Current observed spectrum corresponds to temperature of 2.73 Kelvin
CMB History
Cosmic Microwave Background The universe at different wavelengths (all-sky maps):
Poll Question: Can the CMB spectrum be due to the combined light of stars & galaxies? A. Yes, the redshifted light from the first stars and galaxies can explain the CMB B. Yes, but astrophysicists prefer the explanation that the CMB is due to the Big Bang C. No, stars and galaxies have different temperatures and would not produce the perfect thermal spectrum at the single observed temperature D. No, stars and galaxies produce mainly optical, not microwave, radiation
Evidence for Hot Big Bang Key Observational Successes for the Standard Model: 1. Expansion of the Universe 2. Formation of Galaxies and Large-Scale Structure 3. Origin of the Cosmic Microwave Background 4. Nucleosynthesis of the Light Elements
1. Hubble Expansion 1929: Hubble shows galaxies receding and determines v R = H 0 D where H 0 is the Hubble constant (km/s/mpc) Hubble flow causes all galaxies to recede from each other.
Cosmological Redshifts
Cosmological Redshifts z = λ observed λ emitted λ emitted Cosmological redshifts are not Doppler redshifts z is due only to the expansion of space-time As the universe expands, light waves get stretched out, making them longer and redder.
2D Analogy of Expanding Universe Living on the surface: no center, no edges
Tutorial: Galaxy Classes