Question 12 The cosmic background
radiation comes from a time in the evolution of the universe when
a. "inflation" was occuring.
b. electrons began to recombine with nuclei
to form neutral atoms.
c. gamma rays had enough energy to destroy
nuclei.
d. gravity began to pull material together to form
galaxies.
Question 13 IF we were to observe that
the Hubble constant, H, was larger
for objects at greater distances, then that would imply that
a. the expansion rate of the universe is
accelerating.
b. the
expansion rate of the universe is slowing. (MISGRADED!)
c. the
expansion rate is constant with time.
OK, the easiest way to think of this is to realize
that the Hubble law says that
v = Hxd, so at larger distances, the slope would become STEEPER (remember, H is just the slope of the plot of d vs.
v). A steeper slope means that the velocity changes more quickly as the
distance changes. Larger distances mean earlier times. So, the expansion rate was faster in the past than it is now. That would mean that the expansion rate must
be slowing. But it is an ill-posed question I inherited
from another professor since
you can get this behavior for all sorts of universes. Its complicated. For instance, for constant expansion rate, t = 1/H,
so in the early universe (i.e.
large distances), the universe was younger and H had to be bigger!