I’ve heard the universe is getting bigger,but how can you tell? And can it ever get too big?

Question: I've heard the universe is getting bigger,but how can you tell? And can it ever get too big?
- Keywords:
  expansion,
  space,
  universe
Asked by dasilvathomas to Ed, Hayley, Jason, Nathan, Sophie on 14 Mar 2013. This question was also asked by slenderman.
- Jason King answered on 14 Mar 2013:
  
  We know it’s getting bigger, because if you track how all the stars you can see move really carefully, you can tell that they are all getting further away from each other. I’m no astronomer, but I think there’s still an argument about whether it will slow down and stop expanding and then start getting smaller again, or if it will keep on going.
- Hayley Evers-King answered on 15 Mar 2013:
  
  One of the most interesting bits of evidence for this is the doppler shift. You’ve probably seen or rather heard this in real life. When an ambulance or fire engine goes past you, the sound of the siren appears to change yes? Well the sound coming from the vehicle is actually the same, what’s happening is that the sound is being ‘stretched’ as it moves away from you (and more bunched up as it comes towards you). This same thing happens with light and we can look at far away stars and notice the colour of them tends to shift to more red – so they must be moving away from us!

Question: I've heard the universe is getting bigger,but how can you tell? And can it ever get too big?