17.3 The Big Bang and Inflation 17.4 Observing the Big Bang for yourself

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17.3 The Big Bang and Inflation17.4 Observing
the Big Bang for yourself
Our Goals for Learning What aspects of the
universe were originally unexplained by the Big
Bang model? How does inflation explain these
features of the universe? How can we test the
idea of inflation? How is the darkness of the
night sky evidence for the Big Bang?
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What aspects of the universe were originally
unexplained by the Big Bang model?
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How can microwave temperature be nearly identical
on opposite sides of the sky?
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How can the microwave background temperature be
identical to 1 part in 10,000 on opposite sides
of the sky?

1. It cant something must be wrong with the
   observations
2. Very small motions, producing very small Doppler
   shifts
3. Opposite sides of the sky must have been in
   contact with each other

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Regions now on opposite side of the sky were
close together before rapid inflation of the
universe pushed them far apart
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Mysteries Unexplained by the original Big Bang
model

• Where does structure come from?

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Mysteries Unexplained by the original Big Bang
model

• Where does structure come from?
• 2) Why is the overall distribution of matter so
  uniform?

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Mysteries Unexplained by the original Big Bang
model

• Where does structure come from?
• 2) Why is the overall distribution of matter so
  uniform?
• 3) Why is the density of the universe so close to
  the critical density?

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Mysteries Unexplained by the original Big Bang
model

• Where does structure come from?
• 2) Why is the overall distribution of matter so
  uniform?
• 3) Why is the density of the universe so close to
  the critical density?
• An early episode of rapid inflation of the
  universe can solve all three mysteries!

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Inflation can make all the structure by
stretching tiny quantum ripples to enormous
size These ripples in density then become the
seeds for all structures
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Overall geometry of the universe is closely
related to total density of matter energy
Density Critical
Density gt Critical
Density lt Critical
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Inflation of universe flattens overall geometry
like the inflation of a balloon, causing overall
density of matter plus energy to be very close to
critical density
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How can we test the idea of inflation?
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Patterns of structure observed by WMAP tell us
genetic code of universe
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Observed patterns of structure in universe agree
(so far) with what inflation should produce
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Our Universes Properties, as Inferred from the
Cosmic Microwave Background

• Overall geometry is flat
• Total massenergy has critical density
• Ordinary matter 4.4 of total
• Total matter is 27 of total
• Dark matter is 23 of total
• Dark energy is 73 of total
• Age of 13.7 billion years

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Our Universes Properties, as Inferred from the
Cosmic Microwave Background

• Overall geometry is flat
• Total massenergy has critical density
• Ordinary matter 4.4 of total
• Total matter is 27 of total
• Dark matter is 23 of total
• Dark energy is 73 of total
• Age of 13.7 billion years

In excellent agreement with observations of
present-day universe and models involving
inflation and WIMPs as dark matter!
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But what caused inflation?

• Good question.
• Currently (always?), science runs out of answers
  to why? questions at this point.
• But cosmologists have lots of ideas!
• String Theory
• The Multiverse

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Why is the darkness of the night sky evidence for
the Big Bang?
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Olbers Paradox If universe were 1)
infinite 2) unchanging 3) everywhere
the same Then, stars would cover the night sky
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Olbers Paradox If universe were 1)
infinite 2) unchanging 3) everywhere
the same Then, stars would cover the night sky
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Night sky is dark because the universe changes
with time
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Night sky is dark because the universe changes
with time
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What have we learned?

• What aspects of the universe were originally
  unexplained by the Big Bang model?
• (1)     The origin of the density enhancements
  that turned into galaxies and larger structures.
• (2)     The overall smoothness of the universe on
  large scales.
• (3) The fact that the actual density of
  matter is close to the critical density.

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What have we learned?

• How does inflation explain these features of the
  universe?
• (1)     The episode of inflation stretched tiny,
  random quantum fluctuations to sizes large enough
  for them to become the density enhancements
  around which structure later formed.
• (2)     The universe is smooth on large scales
  because, prior to inflation, everything we can
  observe today was close enough together for
  temperatures and densities to equalize.
• (3) Inflation caused the universe to expand
  so much that the observable universe appears
  geometrically flat, implying that its overall
  density of mass plus energy equals the critical
  density.

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What have we learned?

• How can we test the idea of inflation?
• Models of inflation make specific predictions
  about the temperature patterns we should observe
  in the cosmic microwave background. The observed
  patterns seen in recent observations by microwave
  telescopes match those predicted by inflation.

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What have we learned?
Why is the darkness of the night sky evidence
for the Big Bang? Olbers paradox tells us that
if the universe were infinite, unchanging, and
filled with stars, the sky would be everywhere as
bright as the surface of the Sun, and it would
not be dark at night. The Big Bang theory solves
this paradox by telling us that the night sky is
dark because the universe has a finite age, which
means we can see only a finite number of stars in
the sky.