The discovery of the expansion of the universe is one of the defining moments of 20th century astronomy. But
while Hubble’s law–the relation between a galaxy’s redshift and its distance–implies a beginning, the Big Bang
theory was not well accepted until additional evidence came to light. Discuss two additional lines of
observational evidence (the things that we can see or measure in some way) that support the idea that the
universe went through an extremely hot and dense period between 13 and 14 billion years ago. More recently,
two independent teams of astronomers (including Adam Riess, from the reading this week) discovered that the
rate of expansion is increasing. Describe why their discovery depended on observations of a new type of
standard candle.