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Discussion
Does this mean that the Earths radius is getting
bigger? How about the radius of Earths orbit,
is it getting bigger as spacetime between it and
the Sun expands?
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Discussion
We can observe Cepheids in the Andromeda galaxy.
Why cant we just use the redshift of Andromeda
along with its distance to figure out what the
Hubble constant is?
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Motions of galaxies apart from the expansion of
the Universe are called peculiar velocities.
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Hubble Space Telescope
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Discussion
If we can observe Cepheids in the Virgo cluster
galaxies, why is it that we still dont know for
certain the value of Hubbles constant?
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Discussion
The further out we can measure accurate distances
to galaxies, the better our estimate of the
Hubble constant will be. Why?
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Tully-Fisher relation
The faster a spiral galaxy rotates, the more
luminous that galaxy is.
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Discussion
Why do you think there is a relation between the
rotation speed of a spiral galaxy and that
galaxys luminosity?
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Discussion
But is it the stars that determines the rotation
curves of spiral galaxies?
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Dark matter/luminous matter connection
Because galaxies are made mostly of dark matter,
the Tully-Fisher relation makes little sense.
There must be a connection between the amount
of dark matter in a galaxy and that galaxys
ability to form stars.
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Discussion
Can you think of any ways the amount of dark
matter in a spiral galaxy can affect the
luminosity of that galaxy?
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Discussion
To use supernovae as distance indicators we need
to know what the luminosity is to use the 1/r2
relation to find the distance. Which do you
think better for this, supernova type Ia or
supernova type II and why?
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Distance ladder
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Discussion
Is the Universe infinite? How could you tell?
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Discussion
If the Universe is not infinite, do you think it
has and edge? What do you think might happen
if we traveled to the edge of the Universe with a
flashlight and pointed it outward? Which of
the possibilities do you prefer?
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Discussion
If the Universe were infinite with a uniform
density of galaxies would the night sky be dark?
Explain.
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Discussion
If the distribution of stars, or galaxies, is
uniform over large scales the number within a
given volume increases as the square of the
radius. But what about the intensity of light
change with distance?
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Discussion
What about all that dust and gas in the Universe?
Cant it block out the light and make the sky
dark?
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Discussion
Can you think of any other ways we could still
have a Universe infinite in space without having
an infinitely bright night sky?
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Dark skies
The simple observation that the night sky is dark
leads to the profound conclusion that the
Universe can not be infinite in both space and
time.
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Solutions to Olbers Paradox
The Universe may still be infinite in dimension
if 1) The Universe is not infinitely old 2)
The Universe is expanding uniformly
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Observable Universe
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Discussion
How can galaxies be infinitely redshifted? I
thought nothing could go faster than the speed of
light?
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Look back time
The further away from Earth we look the further
back in time we see
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Discussion
If the Universe continues to expand at a constant
rate, what will happen to all the galaxies we
currently see in the sky?
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Discussion
If all the galaxies in the Universe are attracted
to all the other galaxies in the Universe, would
you expect the expansion of the Universe to be
constant over time?
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The non-constant Hubble constant
H0 refers to the present-day expansion rate.
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The fate of the Universe
Will the Universe expand forever or will the
expansion stop someday and start contracting?
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Depends on the rate of expansion and the density
Density greater than critical value gravity will
halt expansion Density less than critical value
gravity will not stop expansion
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Discussion
Which type of Universe would you rather live in,
one that will expand forever, or one that
re-collapses in on itself?
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Discussion
How could we determine the fate of the Universe?