Question

Choose the correct statements from the following list. (Give ALL correct answers, i.e., B, AC, BCD...)

A) A major difference between dark matter and dark energy is that one causes the univserse's expansion to slow down, the other to make it expand faster.
B) The critical density is the density needed to cause the Big Bang.
C) Assuming no dark energy, if the matter density of the universe is less than critical, the universe is open.
D) The inflationary model of the universe solves both the flatness and the horizon problems.
E) Assuming no dark energy, if the matter density of the universe is greater than critical, the universe is will expand forever.
F) Observations show us that the geometry of our universe must be very closed
G) The horizon problem in cosmology is that regions of the universe that should not have ever had thermal contact with one another have the same temperature.

Answer 1

SOLUTION:

A) A major difference between dark matter and dark energy is that one causes the universe's expansion to slow down, the other to make it expand faster. CORRECT.

B) The critical density is the density needed to cause the Big Bang.WRONG. (The critical density is the density needed to halt the expansion of our universe).

C) Assuming no dark energy, if the matter density of the universe is less than critical, the universe is open. CORRECT

D) The inflationary model of the universe solves both the flatness and the horizon problems. CORRECT

E) Assuming no dark energy, if the matter density of the universe is greater than critical, the universe is will expand forever. WRONG (If the matter density is greater than critical, the universe will collapse under gravity)

F) Observations show us that the geometry of our universe must be very closed. WRONG (The existence of dark energy shows that the universe isn't closed).

G) The horizon problem in cosmology is that regions of the universe that should not have ever had thermal contact with one another have the same temperature. CORRECT