Is there just one big universe that is expanding, or are there lots of smaller universes that keep multiplying?

Question: Is there just one big universe that is expanding, or are there lots of smaller universes that keep multiplying?
- Keywords:
  expand,
  multiply,
  universe
Asked by Newstead,Melissa11 to Anne, Beth, COLFlight, Jon, Tom on 15 Oct 2015.
- Beth Healey answered on 15 Oct 2015:
  
  Hi Newstead and Melissa11!
  
  We’re not sure, there are different theories, good question though! This is one of the great things about being a space researcher because there are still so many things to find out!
  
  What do you think?

Question: Is there just one big universe that is expanding, or are there lots of smaller universes that keep multiplying?