Evidence for the Big Bang

• How long ago did the Big Bang occur?

  13.7 billion years ago
• What happened to matter after the Big Bang?

  It expanded and cooled to form the Universe
• What does the Big Bang Theory suggest about the Universe's expansion?

  The Universe continues to expand from a single point
• What is the first key piece of evidence for the Big Bang theory?

  Galactic redshift & Hubble’s law
• How does galactic redshift provide evidence for the Big Bang?

  It shows distant galaxies are moving away
• What does Hubble's law state about galaxies?

  The further away, the faster they move away
• What does extrapolating Hubble's law back to time t = 0 suggest?

  All galaxies were once at the same point
• What is Cosmic Microwave Background Radiation (CMBR)?

  Radiation detected in all parts of the Universe
• What temperature does the CMBR peak correspond to?

  2.7 K
• How is the CMBR distributed throughout the Universe?

  It is extremely uniform throughout the Universe
• What does the CMBR map represent?

  • Closest image to a map of the Universe
  • Shows fluctuations in temperature
  • Redder regions indicate higher density of galaxies
  • Bluer regions indicate lower density of galaxies

  
• Why does CMBR provide evidence for a hot beginning of the Universe?

  It shows uniform black body radiation exists
• What does the redshift of CMBR indicate?

  The Universe has expanded and cooled over time

  
• What does CMBR represent in relation to the Big Bang?

  Radiation left over from the Big Bang
• When was CMBR emitted?

  When protons and electrons combined into atoms
• What is the initial condition of the Universe at the time of the Big Bang?

  Extremely hot and dense
• What happens to free neutrons in the early Universe?

  They decay into protons

  
• What is the ratio of protons to neutrons after decay?

  7:1

  
• What occurs during the fusion process in the early Universe?

  Hydrogen nuclei fuse into helium nuclei

  
• What is the relative abundance of hydrogen to helium in the early Universe?

  3:1

  
• How does the relative abundance of hydrogen and helium support the Big Bang theory?

  It indicates fusion occurred in the early Universe
• What do observations of the Universe's oldest objects show?

  73% hydrogen, 25% helium, 2% others
• What are the three key pieces of evidence for the Big Bang theory?

  1. Galactic redshift & Hubble’s law
  2. Cosmic Microwave Background Radiation (CMBR)
  3. Relative abundance of hydrogen and helium
• What should you practice explaining for the exam?

  • Galactic redshift and Hubble's law
  • Existence of cosmic microwave background radiation
  • Relative abundance of hydrogen and helium