The Evidence for the Big Bang

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The Evidence for the Big Bang
Student Resource Sheet 5 Science and Religion in
Schools Unit 4a
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Evidence for the Big Bang

• The Big Bang model is a concise explanation for 3
  independent observations
• The red shift of light from distant galaxies
• The presence of large amounts of helium in the
  universe
• The cosmic microwave background radiation
• Each can possibly be explained in other ways, but
  the Big Bang model draws all of them together
  into a convincing story

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The red shift
Fraunhoffer lines
Spectrum of light from the sun
Light from a cluster of galaxies 109 light years
away
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Hubbles original data

• Red shift due to expansion
• Further away, the longer the light has been
  traveling
• Universe has expanded more
• Red shift is bigger
• The velocity (speed) is basically how much the
  distance to the galaxy has changed in the age of
  the universe

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Much improved data

• Distance scale 250 x bigger
• Much more convincing!
• Implication - the universe had a start

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Expansion of the universe

• Expansion of the universe is NOT a rushing to
  fill empty space
• The WHOLE universe is expanding - there is no
  empty space

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Helium abundance

• Universe is 24 He (by mass)
• Stars fuse hydrogen into helium
• In 14 billion years, stars have not burned hot
  enough, or long enough to make this much helium
• The oldest stars (11 billion years) also have
  24 Heso this He cannot have been made in stars!
• Big Bang - in early history the whole universe
  was the same temp as the inside of a star!
• Fusion in the first three minutes of history made
  the helium
• This shows that the universe was hot in earliest
  times

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Cosmic Microwave Background

• Arno PenziasRobert W Wilson (Nobel Prize, 1978)
• Persistent microwave noise independent of time
  and direction
• Relic radiation from Big Bang
• Thermal radiation now redshifted so it is in the
  microwave part of the spectrum

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CMB (Cosmic Microwave Background) for fun and
profit

• Dates to 300 000 years into history
• Epoch of recombination (bad name!)
• Before then, all matter ionized
• At this time temp of universe down to the point
  at which atoms could form
• All free electrons captured
• Thermal radiation decouples from the matter
• Imprint of matter density on temperature
  variations
• The density fluctuations seed galaxy formation

• WMAP whole sky map
• 200 ?K