The answers to these review questions are at the bottom of this page.

To determine if gravitational effects can be strong enough to stop the expansion of the Universe it is necessary to know the Universe's (Select one.)

A) material composition.

B) average mass density.

C) average redshift factor.

D) overall size.

E) matter/photon ratio.

2. The discovery that some clusters of galaxies do not have enough visible mass to maintain the structure of the cluster has become known as (Select one.)

A) the neutrino problem.

B) the missing mass problem.

C) Olbers's paradox.

D) the dark matter defect.

E) the cluster paradox.

3. The first multiparticle nucleus to form in the early Universe was probably the nucleus of (Select one.)

A) lithium.

B) helium.

C) deuterium.

D) boron.

E) tritium.

4. The force involved in chemical reactions is the (Select one.)
A) electromagnetic force.
B) strong force.
C) gravitational force.
D) weak force.

5. The force holding the nuclei of atoms together is the (Select one.)
A) weak force.
B) electromagnetic force.
C) gravitational force.
D) strong force.

6. The notion that all elementary particles are actually different energy states of tiny, one-dimensional elongated objects is called (Select one.)

A) grand unified theory.

B) superstring theory.

C) missing mass theory.

D) points of zero dimension.

E) tachyon theory.

7. A universe that has not expanded uniformly, but for some very short period in its history expanded rapidly, is called (Select one.)

A) inflationary.

B) flat.

C) oscillating.

D) open.

E) closed.

8. One success of the inflationary theory of the Universe is that it can explain why the Universe appears to be (Select one.)

A) oscillating.

B) closed.

C) open.

D) undergoing a phase transition.

E) flat.

9. The relative abundances of protons and neutrons was set when the age of the Universe was about (Select one.)

A) 1 s.

B) 10^-6 s

C) 10^-10 s

D) 10^-35 s

E) 100 s.

10. Theories that attempt to explain all known forces as different manifestations of a single, fundamental force are known as (Select one.)
A) Grand Unified Theories.
B) Inflationary theories.
C) Supersymmetric theories.
D) Relative theories.

11. The "horizon problem" relates to the early Universe's apparently uniform (Select one.)

A) density of planetary nebulae.

B) antimatter annihilation.

C) temperature.

D) age.

E) interstellar scattering.

12. The basic question concerning the future of the Universe is whether there is enough ______________ to overcome the expansion.

13. The current consensus value for the ratio of the actual density of the Universe to the critical density is ______________. (numerical answer!)

14. Recent observations of the expansion of the Universe using Type Ia supernovae indicate, surprisingly, that the expansion may be ______________.

15. A(n) _______________ has the same mass as its corresponding particle but is opposite in all other properties.

16. According to the standard model, heavy elements could not be formed until _____________ came into existence.

17. Until recently it was believed that there were ______________ fundamental forces.

18. The ____________ force, although weak, is important in astronomy because it operates over long distances.

19. The _____________ force is involved in radioactive decay.

20. The dominance of matter over antimatter in the Universe probably began when the Universe mainly consisted of ____________.

21. Six types of ______________ make up the particles in the nuclei of atoms.

22. The heaviest nucleus produced in the early Universe was ______________.

23. In inflationary theories of the Universe, the positive energy of all matter and electromagnetic radiation and the negative energy of the gravitational interactions among objects in the Universe are ______________.

1. B
2. B
3. C
4. A
5. D
6. B
7. A
8. E
9. A
10. A
11. C
12. density
13. matter
14. accelerating
15. antiparticle
16. stars
17. four
18. gravitational
19. weak
20. quarks
21. quarks
22. lithium
23. equal