Transcript 17.3 The Big Bang and Inflation

17.3 The Big Bang and Inflation
17.4 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?
What aspects of the universe
were originally unexplained
by the Big Bang model?
How can microwave temperature be nearly identical on
opposite sides of the sky?
How can the microwave background
temperature be identical to 1 part in 10,000
on opposite sides of the sky?
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1. It can’t – 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
Regions now on opposite side of the sky were close together
before rapid inflation of the universe pushed them far apart
Mysteries Unexplained by the original
Big Bang model
1) Where does structure come from?
Mysteries Unexplained by the original
Big Bang model
1) Where does structure come from?
2) Why is the overall distribution of matter so
uniform?
Mysteries Unexplained by the original
Big Bang model
1) 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?
Mysteries Unexplained by the original
Big Bang model
1) 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!
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
Density =
Critical
Density >
Critical
Density <
Critical
Overall
geometry of the
universe is
closely related
to total density
of matter &
energy
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
How can we test the idea of
inflation?
Patterns of structure observed by WMAP tell us “genetic
code” of universe
Observed patterns of structure in universe agree (so far)
with what inflation should produce
Our Universe’s Properties, as Inferred
from the Cosmic Microwave Background
• Overall geometry is flat
– Total mass+energy 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
Our Universe’s Properties, as Inferred
from the Cosmic Microwave Background
• Overall geometry is flat
– Total mass+energy 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!
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
• …
Why is the darkness of the night
sky evidence for
the Big Bang?
Olbers’ Paradox
If universe were
1) infinite
2) unchanging
3) everywhere
the same
Then, stars would
cover the night sky
Olbers’ Paradox
If universe were
1) infinite
2) unchanging
3) everywhere
the same
Then, stars would
cover the night sky
Night sky is
dark because
the universe
changes with
time
Night sky is
dark because
the universe
changes with
time
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.
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.
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.
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.