So that cross sections at different instances always give a spherical universe of constant size and so of constant mass.
14 seconds sound clip from the Champagne for Caesar movie soundboard.
You can hear this line at 01:17:06 in the DVD version of the movie.
Quote context
[...]
- How does Einstein regard the space-time continuum?
- Well? We're running out of time. You want to make a stab at it?
- You have just five seconds, come on and try it.
- I'm sorry, but that's incorrect.
- Oh it's mine, all mine, as far as the eye can see!
- Tough luck, old man, but anyway, here are six cakes of Milady soap.
- I was almost sure that was the right answer.
[...]