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Beginning of Time. AST 112. Keep in mind:. E = mc 2 Matter can convert to energy and vice versa I will use “Kelvin” (K) for temperature For this lecture, you can substitute o C for K Every particle has a corresponding antiparticle Electron and positron Proton and antiproton
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Beginning of Time AST 112
Keep in mind: • E = mc2 • Matter can convert to energy and vice versa • I will use “Kelvin” (K) for temperature • For this lecture, you can substitute oC for K • Every particle has a corresponding antiparticle • Electron and positron • Proton and antiproton • If a particle meets its antiparticle, the two annihilate and release energy
(Almost) To The Beginning • We can observe back to the hydrogen fog and no farther • CMB is an opaque “wall” that keeps us from seeing back farther • How can we say anything meaningful about earlier times? • Observations that we can make now must be consistent with the earlier universe • Ask the particle physicists.
Based on our knowledge of particle physics,we can predict what the Universe was like allthe way back to 10-43 seconds.After that it’s anyone’s guess – but cosmologists are willing toguess! (“Something from nothing”)
The Big Bang • Running everything backward, everything started from an infinitely dense, infinitely hot point • General Relativity breaks down at this point. We don’t know what it was like.
The Planck Era • The first 10-43 seconds of the Universe • Huge energy fluctuations from point to point, rapidly changing gravitational field • Need quantum mechanics and General Relativity to describe this time • Quantum Mechanics and General Relativity have not been shown to be compatible
Particles and Forces How many forces can you name?
Particles and Forces • We know of four distinct forces in nature: • Electromagnetic • Gravity • Strong Force • Weak Force
The Planck Era • Strong force, EM, Weak force all unify • Maybe gravity? • Water: • Ice, Liquid, Vapor • All still H2O • The Planck Era may have been run by one “superforce”
The Grand Unified Theory (GUT) Era • The Planck Era ended when the temperature dropped below 1032 K • Gravity separated from the “superforce” • Two forces: • GUT force • Gravity
The GUT Era • The GUT Era ended when temperature fell to 1029 • An age of 10-29 seconds • The GUT force split into the strong and electroweak forces • Released an enormous amount of energy
Inflation • The CMB is extremely smooth. • How did we go from such a chaotic, fluctuating universe to something so uniform? • Temperature and density must have equalized. All of the Universe must have been in “causal contact”. But opposite sides of the Universe are too far to influence each other.
Inflation • Draw some dots on a balloon and blow it up • The dots smooth out • Regions the size of an atom became the size of a solar system
Structure Formation • The atom-sized energy fluctuations that existed before inflation were blown up by inflation • These are the seeds of galaxies and larger structures
Uniformity • Say we look at the CMB in one direction. The light that left it is just now reaching us. • Look in the opposite direction – same thing. • What about before the time of the CMB? • Closer together, but only had 380,000 years for light to travel (see graph)
Uniformity • How can regions that cannot influence each other have the same temperature and density? • They were close enough to influence each other up until inflation at 10-38 seconds • Temperature and density equalized before this
Uniformity • Great book quote: • “Like criminals getting their stories straight before being locked in separate jail cells, the two regions came to the same temperature and density before inflation spread them apart.”
Inflation • But how can we justify this? • Our theories say that the separation of the strong and electroweak forces from the GUT force released a tremendous amount of energy
Was it closed? • Evidence points to a flat (and possibly infinite) Universe • So did it go from nothing to infinite? • It may have gone from closed and finite to flat and infinite
Inflation: Summary • So the GUT Era ended with a large inflation of the Universe • Smoothed out the Universe • Blew up the density fluctuations – “large but gentle” • May have gone from closed universe to flat universe
Electroweak Era • Universe filled with radiation that produced matter-antimatter pairs • They instantly annihilated each other • 100 million times hotter than the core of the Sun
Electroweak Era • Ended at 10-10 seconds • W and Z boson particles predicted above 1015 K • Found them! • Created in CERN (large particle accelerator) • We have recreated the Electroweak Era on a small scale.
The Particle Era • Subatomic particles (quarks) everywhere! • Formed protons and neutrons • Eventually too cool for spontaneous creation and annihilation of particles (1 millisecond) • Protons and anti-protons could no longer spontaneously form • Why is it really obvious that protons out-numbered anti-protons? (1,000,000,001 to 1,000,000,000)
The Era of Nucleosynthesis • At an age of 1 millisecond, nuclei began to fuse but immediately broke apart • Cooled off – nuclei fused for 5 minutes • Cooled off more – fusion stopped • 75% H, 25% He • Trace amounts of deuterium and lithium
Nucleosynthesis: Observations • Era of Nucleosynthesis began with a cloud of protons and neutrons • At 1011 K protons could convert to neutrons and vice versa • Number of protons and neutrons roughly equal • Universe cooled; protons became favored • Neutrons more massive than protons • Neutron-to-Proton releases energy • Proton-to-Neutron requires energy
Nucleosynthesis: Observations • Nuclei created by fusion could survive after the Universe was 1 minute old • Calculations show Proton-to-Neutron ratio was 7:1 • Nearly all neutrons absorbed by protons to make helium • 75% H and 25% He-4
Nucleosynthesis: Observations • We can calculate the density of ordinary matter during nucleosynthesis to help understand dark matter • In nuclear reactions, deuterium is an intermediate between H and He • Deuterium still exists in the Universe • Fusion stopped before it was all used up • More deuterium, higher density of protons and neutrons
Nucleosynthesis: Observations • By the time there were stable H and He nuclei, the temperature had dropped • Heavier nuclei (except for trace amounts of lithium) did not form • Reactions that create heavy nuclei are much slower
The Era of Nuclei • Nucleosynthesis ended at around 5 minutes • Universe was a hot plasma of H and He • Ionized and opaque • Remained so for 380,000 years • Universe expanded and cooled, electrons combined with protons • Recombination • The Universe became transparent
The Era of Atoms • Universe was a neutral hydrogen gas with freely streaming photons • Quantum fluctuations, blown up by inflation, lead to density enhancements
The Era of Galaxies • Density enhancements (made of dark matter and atoms) slowly collapse into protogalactic clouds • Galaxies began to form at 1 billion years • This era continues to today