The Big Bang Evidence

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The Big Bang Evidence

• The Science of Creation

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Goals

• What is the evidence for the Big Bang?
• What predictions does the Big Bang theory make?
• What observations can we make?
• How good of a theory is the Big Bang?

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Cosmological Principle

• Isotropy The view from here is the same in all
  directions. (observation)
• Homogeneity We live in an average place the
  same as any other. (statistics)
• This is the cosmological principle.
• Implies
• Universe has no edge!
• Universe has no center!

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Olbers Paradox

• Why is it dark at night?
• In an infinite and unchanging universe
• Every line of sight should end at the surface of
  a star.
• Either
• Universe has edge.
• Universe has a beginning.

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Concept Test

• Olbers paradox asks why the night sky is dark,
  when every line of sight must eventually fall on
  a star. Which of the following reasons would best
  explain the darkness at night? It is because the
  universe is
• Infinite and mostly empty.
• Clumpy, so not every sightline intercepts a star.
• Expanding, so distant stars are red-shifted.
• Young, so there are only stars to a finite
  distance.
• None of the above.

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Scientific Evidence

• A scientific model must do two things
• Explain what is seen.
• Predict what will happen accurately.
• Or, predict what can be seen before one thinks to
  look.

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Cosmic Microwave Background

• The Big Bang
• Massive amount of energy.
• Very high temperature ? thermal radiation
• As Universe expands
• Temperature cools ? thermal radiation gets
  redder.
• or
• Cosmological redshift ? same thing.

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Origin of the CMB

• Once cool enough for atoms, radiation could move
  freely through space.

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The Temperature of Space

• After 500,000 yrs T3000K
• lpeak a 1/T
• lpeak near infrared.
• The Universe was red.
• After 16 billion yrs
• Universe 1000x bigger.
• lpeak 1000x longer.
• lpeak microwaves (radio).
• T 3K!

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Where do you look?

• Recall Lookback time.
• Universe is a time machine.
• Look beyond the youngest galaxies.
• Look everywhere.

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What We See
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Cosmic Microwaves

• Big Bang theory predicted cosmic microwave
  background.
• In 1965 discovery of radio waves (microwaves)
  from sky.
• Prediction confirmed.

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COBE

• Early 1990s
• NASA Cosmic Background Explorer
• Measure the intensity of radiation at many
  wavelengths.
• 3K thermal emission!

lpeak (3 x 10-3 m/K) / 3 K 0.001m 1mm
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COBE cont.

• Also measure the (temperature) intensity and
  wavelength in various directions.
• Look for fluctuations out of which galaxies came.

V 600 km/s
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COBE cont.

• Also measure the (temperature) intensity and
  wavelength in various directions.
• Look for fluctuations out of which galaxies came.

V 600 km/s
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Large Scale Structure
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Concept Test

• The cosmic background radiation is visible in
  every direction because
• We are at the center of the universe.
• It is just now passing by us at the speed of
  light.
• It pervades all space.
• It has reflected in every direction over the age
  of the universe.
• All of the above.

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Evidence of Eras

• Cant see what happened before origin of CMB.
• Can estimate given change of temperature and
  density with time.
• Look for Proof.
• CMB (Age of Nuclei)
• Ratio of H/He and Li (Age of Nucleosynthesis)
• Weak Bosons (Electroweak Era)

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A Good Theory?

• The Big Bang is a very successful theory.
• Makes predictions
• CMB.
• Hydrogen, Helium, Lithium abundances.
• Formation of structure.
• Expansion of Universe.
• Are other Creation theories
• Scientific?
• Successful?

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Homework 19

• For Monday, read NY Times article plus WMAP
  website http//map.gsfc.nasa.gov/m_mm.html
• Answer the following
• What is the inflation theory?
• What new observations support the theory?
• How does this theory change/help/augment the Big
  Bang theory?