Two possible explanations for Hubble

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Two possible explanations for Hubbles Law. If
we assume there is nothing special about the
Earth, we can figure out which one is correct.
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The universe has 3 space dimensions but no center
and no edges (though there are limits to how far
we can see). The universe expands in the time
dimension.
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If our universe had 2 space dimensions (not 3)
plus 1 time dimension, it could be like the
surface of a balloon that expands with time. The
balloon's surface has 2 dimensions in which you
can move, but no center or edge. What does the
center of the balloon represent?

1. The physical center of the universe
2. The beginning of time
3. The end of time

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How do distance measurements tell us the age of
the universe?
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Your friend leaves your house. She later calls
you on her cell phone, saying that shes been
driving at 120 km an hour directly away from you
the whole time and is now 120 km away. How long
has she been gone?

1. 1 minute
2. 60 minutes
3. 120 minutes

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You observe a galaxy moving away from you at 0.1
light-years per year, and it is now 1.25 billion
light-years away from you. How long has it taken
to get there?

1. 8 million years
2. 12.5 million years
3. 8 billion years
4. 12.5 billion years

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Hubbles constant tells us age of universe
because it relates velocities and distances of
all galaxies Age 1 / H0
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Expansion stretches photon wavelengths causing a
cosmological redshift directly related to
lookback time
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The distances between widely separated galaxies
will change while light travels between them.
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The distances between widely separated galaxies
will change while light travels between
them. Astronomers often think in terms of
lookback time rather than distance.
lookback time
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The most distant galaxies we've found so far have
a lookback time of about 13 billion years. That
is, the light we see from them today took 13
billion years to reach us.How far away are those
galaxies today?

1. Less than 13 billion light years away
2. 13 billion light years away
3. More than 13 billion light years away

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Cosmological Horizon Maximum lookback time of 14
billion years limits how far we can see
(everything we can see is our observable universe)
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What have we learned?

• How do distance measurements tell us the age of
  the universe?
• Combining distance measurements with velocity
  measurements tells us Hubbles constant, and the
  inverse of Hubbles constant tells us how long it
  would have taken the universe to reach its
  present size if the expansion rate had never
  changed. Based on Hubbles constant and estimates
  of how it has changed with time, we now estimate
  the age of the universe at about 14 billion
  years, which restricts our view of the universe
  to lookback times smaller than that age.