ASTR 123 Module 7 & 8
Roughly what percent of the mass and energy contents of the universe is made up of ordinary (atomic) matter?
5 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
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
The three observational pillars of cosmology are the expanding universe, the cosmic microwave background, and
big bang nucleosyntheses
If the universe consisted only of matter and its density were equal to critical, the universe would
continue expanding, eventually slowing down to zero
When the age of the universe was about 10 seconds, it had cooled sufficiently for neutrons and protons to bind together and form the key nuclear species which allows production of helium to proceed. This key nucleus is called
deuterium
Where in space did the expansion of the universe begin?
everywhere at once
Based on cosmic microwave background (CMB) data, 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
What do the surveys of the three-dimensional distribution of groups of galaxies reveal about how groups and clusters of galaxies are organized?
galaxy groups are organized into huge filaments with great voids between them
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
According to the Cosmological Principle, the universe
is isotropic and homogeneous over large distances
Which of the following does NOT happen when two galaxies collide?
many of the stars in one galaxy collide with the stars in the other
Protons and neutrons are composed of other more elementary particles known as
quarks
Galaxies that we see as they were 11 billion years ago or more, as compared to galaxies today, are generally
redder and smaller
Which of the following did NOT happen during the first few minutes after the Big Bang?
some very massive early stars formed
The "horizon problem" is illustrated by what observation of the cosmic microwave background (CMB)?
that the temperature of disconnected regions is almost exactly the same
How do astronomers currently think the amount of detectable (observable) matter in the universe compares to the amount of dark matter?
the amount of detectable matter is about 1/5th the amount of dark matter
The three observational pillars of cosmology are the expanding universe, big bang nucleosyntheses, and
the cosmic microwave background
The redshift observed in the light emitted by distant galaxies is due to
the expansion of space
With enormous effort, a team of astronomers manages to collect enough light from a galaxy far, far away to produce a spectrum. That spectrum has lines from the elements carbon, silicon, and sulfur. This tells the team that
the galaxy must have had an entire generation of stars that was born, lived, and died
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
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
In the observation of galaxies, astronomers refer to look-back time, which means
the time it took for the observed light from a galaxy to reach us
What happened when the age of the universe was 380,000 years which allows us to observe the cosmic microwave background?
the universe cooled sufficiently to allow neutral hydrogen to form
The reason nucleosynthesis stopped when the age of the universe was about 3 minutes was
the universe was cooling too fast to produce elements beyond helium
The observed cosmic microwave background (CMB) is extremely uniform. What is the significance of the small deviations from uniformity which show up as red or blue regions in the CMB images?
they seed the large scale structure we observe today
