Chapter 26

Under what conditions would the expansion age of the universe be the actual length of time that has passed since the Big Bang?

Suppose astronomers were to discover that the value of Hubble's constant were twice as large as it is now thought to be. What effect would this discovery have on the expansion age of the universe?

Suppose we use Hubble's law to find that the galaxies at a distance of \(200 \mathrm{Mpc}\) were adjacent to the Milky Way 12 billion years ago. How long ago were the galaxies at 400 Mpc adjacent to the Milky Way?

What is meant by the statement that the surface of a ball has no center?

Describe two geometrical tests that could be used to distinguish positively curved universes from negatively curved universes.

Suppose you lived in a two-dimensional universe. Describe how you could use counts of distant galaxies to learn the curvature of space in your universe.

What is the curvature of the universe if its density is less than the critical density?

What is the value of \(\Omega_{0}\) if the universe is flat?

How do ancient supernovae contribute to the idea that expansion is accelerating?

Why did Einstein invent the cosmological constant?

What was the origin of the primordial neutrinos that are still present in the universe?

What happened to all of the radiation that was produced during the first 380 thousand years after the universe began?

The cosmic microwave background was emitted by gas at a temperature of about \(3000 \mathrm{K}\). Why, then, is the CMB brighter in the radio part of the spectrum than at visible wavelengths?

What is meant by the statement that the CMB has a temperature of \(2.74 \mathrm{K}\) ?

Why is the isotropy of the CMB a problem for the standard Big Bang model?

Why is the present flatness of the universe a problem for the standard Big Bang model?

Describe how inflation solves the flatness problem of the standard Big Bang.