Chapter 26

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?

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

Compare flat space universes with positively curved universes with respect to whether they are finite, whether they are bounded, and whether they have centers.

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?

Why did Einstein invent the cosmological constant?

How would dark energy affect the expansion of the universe?

How can globular clusters be used to place a lower limit on the age of the universe?

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 four hundred 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?

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

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

What is the fate of the universe if it has positive curvature and there is little or no dark energy?