Chapter 17 astronomy
Based on our current understanding of physics, we can understand the conditions that prevailed in the early universe as far back in time as about ___________.
one ten-billionth of a second after the Big Bang
What happens when a particle of matter meets its corresponding antiparticle of antimatter?
The combined mass of the two particles is completely transformed into energy (photons).
What is the significance of the Planck Time?
Before it, conditions were so extreme that our current understanding of physics is insufficient to predict what might have occurred.
The four fundamental forces that operate in the universe today are ___________.
strong force, weak force, electromagnetic force, gravity
A “GUT” (grand unified theory) refers to theories that ________.
unify the strong force with the electromagnetic and weak forces
What do we mean by inflation?
a sudden and extremely rapid expansion of the universe that occurrred in a tiny fraction of a second during the universe’s first second of existence
Which of the following statements correctly summarizes the events in the early universe according to the Big Bang theory?
The universe began with the forces unified. During the first fraction of a second, the forces separated and there was a brief but important episode of inflation. Subatomic particles of both matter and antimatter then began to appear from the energy present in the universe. Most of the particles annihilated to make photons, but some became protons, neutrons, electrons, and neutrinos. The protons and neutrons underwent some fusion during the first three minutes, thereby determining the basic chemical composition of the universe.
Which statement about the cosmic microwave background is not true?
It is the result of a mixture of radiation from many independent sources, such as stars and galaxies.
The Big Bang Theory is supported by two major lines of evidence that alternative models have not successfully explained, what are they?
(1) the theory predicts the existence of and the specific characteristics of the observed cosmic microwave background; (2) the theory correctly predicts the observed overall chemical composition of the universe.
Measuring the amount of deuterium in the universe allows us to set a limit on ____________.
the density of ordinary (baryonic) matter the universe
The idea of dark matter arose to explain gravitational effects observed in galaxies and clusters of galaxies. However, studies of the early universe (especially the cosmic microwave background and of chemical abundances) also tell us something about dark matter. What do they tell us?
They add further support to the idea that dark matter really exists and is made of non-ordinary (nonbaryonic) matter, such as WIMPs
Which of the following observations cannot be explained by the Big Bang Theory unless we assume that an episode of inflation occurred?
the fact that the temperature of the cosmic microwave background is almost the same everywhere.
The idea of inflation makes one clear prediction that, until the discovery of an accelerating expansion, seemed to contradict the available observations. What is this prediction?
The universe should be geometrically “flat” (in the four dimensions of spacetime)
Olbers’s paradox is an apparently simple question, but its resolution suggests that the universe is finite in age. What is the question?
Why is the sky dark at night?
What happens when matter collides with anti-matter?
The two particles destroy each other, and create photons.
What is the current temperature of the universe?
a few degrees
The cosmic microwave background gives us a view of the universe when it was
380,000 years old.
Which of the following does not provide strong evidence for the Big Bang theory
observations of the amount of hydrogen in the universe
the current density of normal matter in the universe were 10 times as great as it is now, we would expect to observe
Which of the following does inflation help to explain?
the uniformity of the cosmic microwave background
Which of these pieces of evidence supports the idea that inflation really happened?
observations of the cosmic microwave background that indicate a flat geometry for the universe
Which of the following does inflation help to explain?
the origin of galaxies
What is the earliest time in the universe that we can directly observe?
a few hundred thousand years after the Big Bang
Why is the night sky is dark?
The universe is finite in age.
Which model(s) predicts that galaxies will eventually get closer together?
which model predicts that galaxies had the largest separations in the past
During the history of the universe, what important event occurred about 0.001 seconds after the Big Bang?
Most matter in the early universe was annihilated by antimatter
Which of the following important events occurred earliest in the history of the universe?
Spacetime rapidly expanded during a brief period of inflation
During the history of the universe, what important event occurred about 380,000 years after the Big Bang?
Light began to travel freely through the universe.
Essentially all the hydrogen nuclei that will ever exist in our universe was created __________.
by the time the universe was about 3 minutes old
Compared to when the cosmic microwave background was first released, the radiation of the cosmic microwave background today is __________.
fainter and has most of its photons at longer wavelengths
Approximately what is the current age of the universe in seconds?
4×10 17 s
Today, the temperature of the universe (that is, of the cosmic microwave background) is about 3 K . How many times hotter was the universe when it was 1 second old than it is today?
about 3,000,000,000 times
What was the approximate temperature of the universe when the universe was just 1 second old?
10 10 K