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Beginning of Time

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

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  1. Beginning of Time AST 112

  2. 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

  3. (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.

  4. 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”)

  5. 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.

  6. 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

  7. Particles and Forces How many forces can you name?

  8. Particles and Forces • We know of four distinct forces in nature: • Electromagnetic • Gravity • Strong Force • Weak Force

  9. 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”

  10. 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

  11. 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

  12. 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.

  13. 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

  14. 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

  15. 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)

  16. 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

  17. 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.”

  18. 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

  19. 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

  20. 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

  21. 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

  22. 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.

  23. 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)

  24. 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

  25. 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

  26. 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

  27. 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

  28. 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

  29. 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

  30. The Era of Atoms • Universe was a neutral hydrogen gas with freely streaming photons • Quantum fluctuations, blown up by inflation, lead to density enhancements

  31. 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

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