Question : 11.Space-time will be flat ifA.the universe expanding.B.the universe accelerating.C.the average : 1777274

11.Space-time will be flat if
A.the universe is expanding.
B.the universe is accelerating.
C.the average density of the universe is equal to the critical density.
D.the universe is finite.
E.the universe is homogeneous and isotropic.

12.An open universe
A.has a negative curvature.
B.has zero curvature.
C.has a positive curvature.
D.is finite.
E.has a center.

13.Current observations indicate that the amount of baryonic matter and dark matter in the universe
A.is sufficient great enough to overcome the expansion of the universe.
B.implies that the universe is closed.
C.is mostly in the form of black holes and quasars.
D.are roughly equal.
E.implies that the universe is open.

14.The universe is said to be closed if

I.	gravity is strong enough to stop the expansion in a finite time.
II.	the density of the universe is less than the critical density.
III.	the universe is finite.

A.I & II
B.I & III
C.II & III
D.I, I, & III
E.none of the above

15.If the universe is closed, then its age will be
A.less than two-thirds of 1/H.
B.more than two-thirds of 1/H.
C.equal to 1/H.
D.equal to H squared.
E.equal to the square-root of H.

16.If the universe is closed and finite, then
A.the universe will expand forever
B.the universe has a center
C.the universe has an edge
D.none of the above

17.If the universe is closed and finite, then
A.the universe has a center and an edge.
B.the universe will expand forever.
C.the final fate of the universe will be very cold and of extremely low density .
D.the space-time of the universe is negatively curved.
E.none of the above

18.What was the temperature of the universe when the recombination took place that produced the cosmic background radiation we observe today?
A.about 2.7 K
B.about 300 K
C.about 3000 K
D.about 3 million K
E.about 3 billion K

19.In 1998, it was announced that the expansion of the universe is accelerating. What does this imply from the perspective of the big bang?
A.A force exists that we knew nothing about that causes the acceleration.
B.The universe must be closed.
C.The universe is finite.
D.The amount of dark matter must be greatly less than the amount of normal matter.
E.The universe must be infinitely old.

20.Measured ages of globular clusters suggests that the universe is about ...
A.1.4 billion years
B.14 billion years
C.140 billion years old.