# Mastering Astronomy Chapter: 17

Flashcard maker : Lily Taylor
Notice that an observer located at the Local Raisin sees raisins 1, 2 and 3 all move away from her during the animation. But what would an observer located at Raisin 2 see?
An observer located at Raisin 2 would find that __________.
Raisin 1 and Raisin 3 both move away from her
The table in the animation shows you the speeds of raisins 1, 2, and 3 as measured from the Local Raisin. Suppose instead you measured speeds as seen from Raisin 2. An observer at Raisin 2 would measure __________.
Local Raisin speed = 4.0 cm/hr; Raisin 1 speed = 2.0 cm/hr; Raisin 3 speed = 2.0 cm/hr
The following statements describe ways in which the analogy might apply to the real universe. Which statements are correct?
~An observer at any raisin sees more distant raisins moving away faster, just as an observer in any galaxy sees more distant galaxies moving away faster.
~The raisins stay roughly the same size as the cake expands, just as galaxies stay roughly the same size as the universe expands.

~The average distance increases with time both between raisins in the cake and between galaxies in the universe.

Deep surveys of the universe indicate that the largest structures in space are no larger than about 50 Mpc in size.
True
If the universe had an edge, that fact would violate the assumption of isotropy in the cosmological principle.
False
Hubble’s law implies that the universe will expand forever.
False
The cosmological redshift is a direct measure of cosmic expansion.
True
The cosmic microwave background is the highly redshifted radiation of the early Big Bang.
True
Olbers’s paradox is resolved by
the finite age of the universe.
The galactic distances used to measure the acceleration of the universe are determined by observations of
exploding white dwarfs.
The age of the universe is estimated to be
greater than the age of the Milky Way Galaxy.
Homogeneity and isotropy, taken as assumptions regarding the structure and evolution of the universe, are known as:
the Cosmological Principle.
The concept that the direction of observation does not matter overall is
isotropy.
The concept that on the grandest of scales, the universe is similar in appearance everywhere is
homogeneity
What does the Hubble law imply about the history of the universe?
The universe had a beginning and has expanded since, giving it a finite age.
In which of the following models will the universe stop expanding?
Closed Universe
The presently accepted value of the Hubble constant gives an age of
14 billion years.
What is the meaning of a “closed” universe?
The universe will someday stop expanding and begin collapsing inward.
If the density of the universe is greater than critical, then
the universe is closed, gravity wins, and will shrink to the Big Crunch.
The expansion rate of the Universe is
increasing
In the critical density universe now proposed, the ratio of dark energy to matter is about
3 to 1
What temperature has the Big Bang cooled to by now?
Just over 2.7K
The discovery of the cosmic microwave background was important because
it was was experimental verification of a prediction from the Big Bang theory.
Concerning dark energy, we do know
its density remains constant over time, so it is not important in the early Universe.
What key event happened during the decoupling epoch?
expansion cooled the universe enough that protons could capture electrons in orbit.
The cosmological redshift is a direct measure of the expansion of the universe, thus independent of direction.
True
The cosmological redshift is actually not a velocity at all, but a measure of the expansion of space-time.
True
The Big Bang was an expansion of matter into empty space.
False
The universe has been expanding at the same rate since its formation.
False
The cosmic microwave background is the total of all the radio emissions from all the galaxies and quasars in the universe.
False
Because almost all galaxies show redshifted spectra, we know that
the universe is expanding.
The darkness of the night sky in an infinite universe is addressed in
Olbers’s paradox.
The redshift of the galaxies is correctly interpreted as
space itself is expanding with time, so the photons are stretched while they travel through space.
The latest studies from ________ led to the discovery of “dark energy.”
Type I supernovae at very large red shifts
The Big Bang formed
hydrogen and helium, but nothing else.
Before the decoupling,
the Universe was opaque to radiation.
The 3 K background radiation represents
the time of decoupling.
In the Grand Unified Theory, the superforce was
a union of the gravitational, strong and weak nuclear, and electromagnetic forces.
The satellite that found the ripples in the cosmic background that led to galaxies is
COBE
In 1992, COBE observations revealed
there are small ripples in the microwave background, the seeds of galaxies.
The tiny ripples in the background radiation COBE found are due to
a gravitational redshift caused by growing dark clumps.
An infinite universe is a basic assumption of the cosmological principle.
False
The cosmological principle is the ultimate extension of the Copernican principle to the entire universe, in that there is no center at all.
True
Olbers’s paradox seeks the explanation for why the night sky is dark.
True
Olber’s Paradox is solved in part by the fact that the universe is not infinitely large nor infinitely old.
True
In the Big Bang model, two possible fates exist: expansion forever, or cosmic collapse.
True
Gravity alone is sufficient to halt the expansion of the universe.
False
The latest observations of distant Type I supernovae suggest the universe is slowing down more than we had expected.
False
Like dark matter, the newly-found dark energy will also retard the expansion of the universe.
False
The 3 K background radiation is just the redshifted gamma wavelength radiation of the decoupling.
True
Decoupling refers to the separation of matter and antimatter during inflation.
False
Primordial nucleosynthesis implies the Big Bang makes all elements up to iron.
False
Deuterium abundance suggests that normal matter makes up only 3-4% of the critical density.
True
The COBE data allow us to test the isotropy of the universe.
True
COBE found the cosmic microwave background to be absolutely uniform everywhere.
False

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