21.The cosmic background radiation comes from a time after the : 1777275
21.The cosmic background radiation comes from a time after the origin of the universe
A.when protons and neutrons were first formed.
B.when the big bang first began to expand.
C.the inflationary period.
D.when gamma rays had enough energy to destroy nuclei.
E.when electrons began to recombine with nuclei to form atoms.
22.If the universe is flat
A.its age will be equal to 1/H.
B.its age will be equal two-thirds of 1/H.
C.the density of the universe is less than the critical density.
D.the density of the universe is greater than the critical density.
E.dark matter accounts for a small fraction of the density of the universe.
23.The flatness problem and horizon problem
A.are solved if there was a sudden inflation of the universe at time before recombination occurred.
B.show that the universe can be described as static and unchanging.
C.show that dark matter must be a small fraction of the total mass of the universe.
D.imply that the universe was once much colder than it is now.
E.imply that the inflationary theory is incorrect.
24.Galaxy seeds around which galaxies, clusters, and walls grey may have been
A.caused by hot dark matter.
B.caused by baryons.
C.the result of the separation of the electromagnetic and weak forces.
D.the result of freezing water molecules shortly after the universe became transparent to photons.
E.caused by defects in space-time.
25.The best determination of the Hubble constant using Cepheid variables found in distant galaxies by the Hubble telescope suggests
A.that the Hubble constant is about 0.07 km/sec/Mpc.
B.that the Hubble constant is about 7 km/sec/Mpc.
C.that the Hubble constant is about 70 km/sec/Mpc.
D.that the Hubble constant is about 700 km/sec/Mpc.
26.If a two-dimensional universe has a negative curvature,
A.the area of a circle will be greater than pr2.
B.the area of a circle will be equal to pr2.
C.the universe is infinite.
D.the universe is finite but bounded.
E.the universe will have a center.
27.Whether the universe is open, closed or flat depends on the ____ of the universe.
28.Current evidence suggests that the universe is
A.flat, infinite, and neither expanding nor contracting.
B.closed, finite, and slowing its expansion.
C.open, infinite, and slowing in its expansion.
D.static with no expansion.
E.flat, infinite, and accelerating in its expansion.
29.The age of the universe can be estimated or constrained from
A.the age of the oldest objects such as globular clusters
B.the distances of galaxies beyond our Local Group of galaxies
C.the rate of recession of the galaxies beyond Local Group
D.All of the above
30.The density of the universe is
A.equal to the critical density if the universe is closed.
B.equal to the critical density if the universe is flat.
C.greater than the critical density if the universe is flat.
D.greater than the critical density if the universe is open.
E.none of the above