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 ________.
answer
one ten-billionth of a second after the Big Bang
question
What happens when a particle of matter meets its corresponding antiparticle of antimatter?
answer
The combined mass of the two particles is completely transformed into energy (photons).
question
What is the significance of the Planck time?
answer
Before it, conditions were so extreme that our current understanding of physics is insufficient to predict what might have occurred.
question
The four fundamental forces that operate in the universe today are ________.
A "GUT" (grand unified theory) refers to theories that ________.
answer
unify the strong force with the electromagnetic and weak forces
question
What do we mean by inflation?
answer
a sudden and extremely rapid expansion of the universe that occurred in a tiny fraction of a second during the universe's first second of existence
question
Which of the following statements correctly summarizes the events in the early universe according to the Big Bang theory?
answer
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 five minutes, thereby determining the basic chemical composition of the universe.
question
The current temperature of the universe as a whole is
answer
a few K.
question
Which of the following does not provide strong evidence for the Big Bang theory?
answer
observations of the amount of hydrogen in the universe
question
Which statement about the cosmic microwave background is NOT true?
answer
It is the result of a mixture of radiation from many independent sources, such as stars and galaxies.
question
In the past, the temperature of the universe was _____.
answer
hotter than it is today
question
The Big Bang theory is supported by two major lines of evidence that alternative models have not successfully explained. What are they?
answer
(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 primeval universe.
question
Which of the following does inflation help to explain?
answer
the origin of galaxies
question
Which of these pieces of evidence supports the idea that inflation really happened?
answer
observations of the cosmic microwave background that indicate a flat geometry for the universe
question
Which of the following statements can NOT be tested by science today?
answer
Prior to the Planck time, our universe emerged from another universe.
question
Which of the following statements explains why the night sky is dark?
answer
The universe has a finite age.
question
What is the earliest time in the universe that we can directly observe?
answer
a few hundred thousand years after the Big Bang
question
In principle, if we could see all the way to the cosmological horizon we could see the Big Bang taking place. However, our view is blocked for times prior to about 380,000 years after the Big Bang. Why?
answer
Before that time, the gas in the universe was dense and ionized and therefore did not allow light to travel freely.
question
If observations had shown that the cosmic microwave background was perfectly smooth (rather than having very slight variations in temperature), then we would have no way to account for ________.
answer
how galaxies came to exist
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