A. Questions for Discussion

10.1. Hubble's Law and the expansion of the universe

The universe is expanding. Reflelct on how general relativity would answer the following questions:

1. 'What is the universe expanding into?'
2. 'If everything is moving away from us, does that mean we are at the centre of the universe?' (Why or why not?)
3. 'What does the expanding universe tell us about the age of the universe?'

10.2 FLRW Spacetime

1. Two sequences depicting an expanding universe are drawn below. Which of the two is a more accurate description of FLRW spacetime? Explain.
   
   
   
2. There is a special hypersurface in each FLRW spacetime which has constant curvature: zero, negative or positive. What implications (if any) does this have for the compatibility of relativity theory with presentism, the view that only the present is real?

B. Further Discussion (Optional)

• The Newtonian Bomb Universe. The three different kinds of expanding/collapsing universes can be described by the analogy of a Newtonian bomb. What is that analogy? What is correct about the Newtonian bomb analogy? What is incorrect about it?
• Which universe is ours? One of the big bang universes provides a good description of our own universe. Which one? Describe its properties in detail.
• Must there be a big bang? In light of Stephen Hawking's theorem, is it true that there must have been a big bang? Explain.