Astronomy 1021 Chapter Notes - Chapter 17: Electroweak Interaction, Planck Units, Nucleosynthesis
29 May 2018
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Astronomy 1021
Chapter 17
How did Early Universe Change with Time?
•The Planck Era- first era after Big Bang, time before universe was 10-43 second old, don’t have a
theory to describe conditions in this era, only single force operated
•The GUT Era- 10-38s after Big bang, gravity and GUT operated in universe, ended when GUT
force split, energy released at the end of the GUT era might have caused a dramatic expansion of
universe called inflation (grown to size of Solar System)
•The Electroweak Era- 10-10s after BB; gravity, strong force, and electroweak force operated
(Electromagnetic and weak forces still merged), universe continues to cool and expand (drops to
1015K when it was 10-10 s), spontaneous reactions
-Have direct evidence about conditions in universe at the end of electroweak era, not before- correct
prediction of weak bosons (particles W and Z)
•The Particle Era- 0.001s after BB, time b/w end of electroweak era and moment when
spontaneous particle production stopped and photons become dominant form of energy in the
universe
oPhotons convert to quarks, by the end of era all quarks combined in to protons and
neutrons
oParticle era ended when universe reach age of 1 millisecond and temp was 1012K
oProtons must have outnumbered antiprotons during this era, or there would be no matter
left (all the pairs would have annihilated each other)
•The Era of Nucleosynthesis- 5 min after BB, protons and neutrons left after annihilation of
antimatter fuse into heavier nuclei, but universe was so hot that gamma rays destroyed any nuclei
(so couldn’t form heavy elements)
-Era ended when universe was 5 min old, at this time no more fusion possible b/c density was too
low
-When fusion ceased, universe was 75% H and 25% He, along with some deuterium and lithium
•The Era of Nuclei- after fusion ended, universe had a hot plasma of hydrogen, helium nuclei and
free electrons; fully ionized nuclei were free of electrons
-Era ended when expanding universe was 380000 years old, temp was 3000K, H and He nuclei
captured electrons forming stable neutral atoms for the first time
-Photons began to travel freely (i.e. light) b/c expansion; Universe goes from being opaque to
transparent
•The Eras of Atoms and Galaxies- universe had neutral atoms and plasma (ions and electrons) and
photons; gravity drew atoms and plasma into higher-density regions, eventually forming galaxies
-First full-fledged galaxies formed when universe was 1 b years old (start of the era of galaxies which
continues to present day)
