astro 123 final
The three foundations for big bang cosmology are...
(i) the cosmological redshift, (ii) big bang nucleosynthesis, and (iii) the cosmic microwave background. These were all predictions which have been confirmed in great detail.
Today, dark matter makes up about...
25% and ordinary (atomic) matter about 5% of the total energy density of the universe.
If you want to check on what conditions were like in the universe a few hundred thousand years after the Big Bang, what sort of instrument would it be best to use:
a satellite with infrared and microwave telescopes on board
how do we know that the entire universe has reached thermal equilibrium (i.e. a constant temperature)?
because the density and temperature of the CMB are remarkably uniform
In the current epoch, roughly what percent of the mass and energy contents of the universe is made up of ordinary (atomic) matter?
5 percent
Roughly what percent of the mass and energy contents of the universe is made up of dark matter plus dark energy?
95 percent
Why did Einstein introduce the cosmological constant into the equations of his General Theory of Relativity when describing the universe?
Einstein's equations required the universe to expand or contract; he could not imagine or accept it doing either one, so he put a factor in to stop it from moving
what observation provided evidence for the existence of dark energy in our present epoch?
Observations of Type Ia supernovae indicate that we have entered an accelerating phase of the universe in the last ~2 billion years
When do astronomers now think that the "dark energy" began to accelerate the expansion of the universe?
a few billion years ago
what does the observed CMB show?
a lot of structure of regions of small over-density or under-density
what is dark energy?
a mysterious force that appears to be causing the expansion of the universe to accelerate
cosmic inflation
a short period of tremendous expansion of space in the very early universe.
Factoring in everything we currently know about the history of the universe, our best estimate for the age of the universe is
about 13.8 billion years
In our modern view of the expansion of the universe, we understand that it is space that is stretching; individual galaxies don't speed away from each other as if they were rockets. In that case, why do galaxies show a redshift?
as space stretches, the waves of radiation in space also stretch and their wavelength increases
If the universe consisted only of matter and its density were equal to critical, the universe would
continue expanding, eventually slowing down to zero
what can explain the uniform temperature of the CMB, along with the apparent special value of the universe's energy density (i.e. equal to critical)?
cosmic inflation
what can the observed density can be compared to?
critical density
what makes up the remaining 70% (about) of the total energy density?
dark energy
Based on many surveys of the average density of matter and energy in the universe, astronomers now conclude that the average density of the universe is
exactly equal to the critical density
Based on many surveys of the average density of matter in the universe (regular matter and dark matter), astronomers now conclude that the average density of the universe is
exactly equal to the critical density
Measurements of the cosmic microwave background provide strong evidence that the overall geometry of space is
flat, or zero curvature
How does a period of extremely fast inflation very early in the history of the universe explain the observation that the geometry of the universe looks flat (not curved) to us?
inflation increased the size of the universe so much that the resulting universe looks flat from any point of view
what happens if you ignore any effects of dark energy?
it results in a universe that continues expanding, expands and stops, or contracts eventually to a "big crunch."
what is the history and future trajectory of the universe's expansion determined by?
its expansion rate (the Hubble parameter, H) and the amount of mass/energy in the universe. The latter is described by a density, i.e. mass or energy per unit volume.
In describing the universe using his equations of general relativity, Einstein assumed that it was isotropic (the same in all directions.) What recent observations have confirmed that the universe is isotropic on the large scale?
measurements of the cosmic microwave background radiation
n describing the universe using his equations of general relativity, Einstein assumed that it was isotropic (the same in all directions.) What recent observations have confirmed that the universe is isotropic on the large scale?
measurements of the cosmic microwave background radiation
is there any direct evidence for the inflation hypothesis at this time?
no
The cosmological principle says that the universe...
on average is isotropic and homogeneous, i.e. it looks similar in all directions. This hypothesis was spectacularly confirmed by the measurements of the cosmic microwave background (CMB).
what did regions of under-density become?
regions of voids
cosmological constant
represents an accelerating influence on the universe's expansion. can describe dark energy
what were the regions of over-density?
seeds for accumulating matter, which became regions with clusters of galaxies
are the regions of over/under density in the CMB big or small?
small: at the level of about 1 part per 100,000
what do einsteins equations say about curvature?
that an overall geometry of space in the universe can be described by a curvature that is positive (spherical), negative (saddle-shaped) or zero (flat). This curvature is exactly tied to the universe's mass/energy density.
When we determine the age of the universe using the Hubble Time (1/H0), what important simplifying assumption goes into our calculations?
that the expansion of the universe has been happening at the same rate-neither speeding up or slowing down
what do the CMB measurements show?
that the universe's geometry is flat, and thus that the overall density is exactly equal to the critical density.
The reciprocal of the Hubble constant (1/H0) is a rough measure of the:
the age of the universe
The redshift observed in the light emitted by distant galaxies is due to
the expansion of space
We now know that the cosmological redshift is due to...
the expansion of space itself. This was a prediction of General Relativity, although not recognized immediately as such by Einstein.
The model of the universe that involves an enormous increase of size during a very short time in the early universe is called:
the inflationary universe model
what has happened as the universe has expanded?
the mass/energy density has become more dilute.
Recent observations indicate that the universe is expanding faster today than it was a few billion years ago (that, in other words, the expansion of the universe is accelerating.) What kind of observations have led astronomers to this surprising conclusion?
the measurement of galaxy distances using Type Ia supernovae
