How do we determine the conditions that existed in the very early universe?
We work backward from current conditions to calculate what temperatures and densities must have been when the observable universe was much smaller in size.
Why can't current theories describe what happened during the Planck era?
We do not yet have a theory that links quantum mechanics and general relativity.
Which of the following statements best explains what we mean when we say that the electroweak and strong forces "froze out" at 10-38 second after the Big Bang?
These two forces first became distinct at this time.
According to the Big Bang theory, how many forces - and which ones - operated in the universe during the GUT era?
2 forces: gravity and a single force that later became the strong, weak, and electromagnetic forces
Laboratory experiments conducted with particle accelerators confirm predictions made by the theory that unifies _________.
the electromagnetic and weak forces into the electroweak force
What was the significance of the end of the era of nucleosynthesis, when the universe was about 5 minutes old?
The basic chemical composition of the universe had been determined.
According to the Big Bang theory, why do we live in a universe that is made of almost entirely of matter rather than antimatter?
During the first 0.001 second after the Big Bang, particles and antiparticles were made in almost but not perfectly equal numbers. Everything annihilated except the very slight excess of matter particles.
Which of the following is not an observed characteristic of the cosmic microwave background?
It contains prominent spectral lines of hydrogen, the primary chemical ingredient of the universe.
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?
Before that time, the gas in the universe was dense and ionized and therefore did not allow light to travel freely.
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 _________.
how galaxies came to exist
In stars, helium can sometimes be fused into carbon and heavier elements (in their final stages of life). Why didn't the same fusion processes produce carbon and heavier elements in the early universe?
By the time stable helium nuclei had formed, the temperature and density had already dropped too low for helium fusion to occur.
How does the idea of inflation account for the existence of the "seeds" of density from which galaxies and other large structures formed?
Inflation would have caused random, microscopic quantum fluctuations to grow so large in size that they became the seeds of structure.
Which of the following is not consistent with recent observations of the cosmic microwave background by the WMAP satellite?
The universe is at least 20 billion years old
Based on the results from the WMAP satellite, the overall composition of the universe is _________.
4% ordinary (baryonic) matter, 23% nonbaryonic dark matter, 73% dark energy
Which adjective does not necessarily describe a known feature of the early universe? (Be sure to consider the universe as a whole, not just the observable universe.)
The Big Bang theory seems to explain how elements were formed during the first few minutes after the Big Bang. Which hypothetical observation below (these are not real observations) would call our current theory into question?
The discovery of a galaxy with a helium abundance of only 10% by mass.
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