Solutions Physics 120 Quiz (2/13/2017)
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1. a) Which two ideas form the theoretical basis for the Big Bang model and lead to
predictions of verifiable properties of the Universe?
b) Which experimental evidence (name one for each) has been found to support
these theories?
a.) The Cosmological Principle and the General Theory of Relativity.
b.) The Cosmological Principle states that the matter in the universe is homogeneous and
isotropic on average over large distance scales. The CMB, which is the remnant heat
from the Big Bang, has been found to have a very uniform temperature over the entire
sky.
General Relativity is supported by every observational test thus far. Examples are the
bending of starlight around massive objects (stars), calculation of the motions of
astrophysical objects and the recent observation of gravitational waves in the collapse
and merger of two black holes.
2.a) Differentiate between the ways in which Newton’s and Einstein’s theories
describe gravity.
Newton’s theory describes gravity as an action at a distance between two massive bodies,
whereas Einstein’s treats it as a distortion of space and time caused by the presence of
mass and/or energy.
b) What dilemma posed by Newton's theory of gravitation was resolved by
Einstein's hypothesis of gravitational waves?
Newton's theory of gravity predicted that gravitational effects should propagate
instantaneously, but it is believed that no information can travel faster than light. This
dilemma was resolved by Einstein's hypothesis of the existence of gravitational waves,
which travel at exactly the speed of light.
3. Consider these two statements in our readings. “The only edge to space-time
occurs at the Big Bang” and “The Big Bang did not occur as an explosion at a single
point in space.” What is meant by these statements or what do they imply about our
universe?
Our universe encompasses all of space-time as we know it. We do not know what came
before it or caused it. The Big Bang and its subsequent expansion created space and time
for our universe.
4. a) Explain what is meant by the statement “we are all made from stardust”?
Most of the elements heavier than lithium that make up our bodies were made during
stellar evolution.
b) How are elements heavier than iron produced?
They are produced in the outer envelopes of super-giant stars and in supernova
explosions.
5. a) Name the 4 fundamental forces and the force carrier(s) (also known as
exchange particles) for each.
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a) The four fundamental forces (and force carriers) are gravity (graviton), the strong
force (gluon), the weak nuclear force (W and Z vector bosons) and the electromagnetic
force (photon).
b) Some force carriers are massless and some have mass. In general, how is the
range of a force related to the mass of its force carrier?
b) The range of a force is weaker the more massive the force carrier. For example, the
weak force is very short-ranged as its force carriers are very massive.
6. Describe the main feature in each of these three images and ascribe an origin of
each feature.
a.)
b.)
c.)
a) The main feature is the Yin-Yang structure (red-blue pattern, called a dipole
asymmetry), which is a result of our motion through the Cosmic Microwave Background
(CMB). This is a Doppler effect on the CMB radiation due to our motion relative to it.
b) The main feature is the red streak-like pattern across the middle (similar to an
equatorial plane). It is the background light from our Milky Way Galaxy, which is not
subtracted when taking away the Doppler pattern in image a.
c) The speckle pattern is a result of very minute deviations (fluctuations) in the observed
temperature pattern of the CMB. This exhibits the fact that the CMB is extremely uniform
in temperature.
7. a) There is considerable evidence for the existence of dark matter in the universe,
although we know not what it really is. Please name three observations that indicate
the existence of dark matter (from among several) in the universe.
Various observations indicate that there is dark matter in the universe.
• Perhaps the most persuasive is the result of the CMB fluctuation studies that
indicates that dark matter makes up about 23% of the mass-energy of our universe (or in
general that the visible baryonic matter in the universe is too low).
• The observation of the collision of a pair of galaxy clusters (Bullet Cluster)
indicates that more matter must have been present than is visible for the observed
dynamics of the collision and its radiation to have occurred.
• Motion of galaxies in clusters indicate the presence of more matter than is visible.
• Likewise, the odd rotation of spiral galaxies and the stability of disk galaxies call
for more matter than observed.
• Gravitational lensing of light from stars and galaxies (distortion of star-light due
to unseen masses) indicate unseen matter between them and us.
• Large scale structure in the universe suggests that there must be more matter than
is visible.
b) What is the effect of dark energy on the evolution of the universe?
Dark energy appears to be the cause of an accelerated expansion of the universe.
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