Briefly explain why an expanding universe implies a beginning ...

[daltonest1984]

Briefly explain why an expanding universe implies a beginning (called a Big Bang).
 
  What will be an ideal response?

Question 2

Which statement about this cluster is not true?
 
  A) It contains some stars that are burning helium in their cores.
  B) It probably contains no young stars at all.
  C) It is likely to be located in the halo of the galaxy.
  D) It is likely to be spherical in shape.
  E) It is the type of cluster known as an open cluster of stars.

[234sdffa]

Answer to Question 1

The fact that the universe is expanding means the average distance between galaxies is growing, which implies that this average distance was smaller in the past. Extrapolating back in time, there must have been a time when the distance between galaxies (or their precursors) was zero, which must be the beginning of the universe.

Answer to Question 2

E