This question already has an answer here:
I remember reading a novel as a teenager, all I remember is at the end of the book, a civilization was able to finally escape their dying world.
The book described little silver spaceships breaking through the outer shell of some alien experiment (A simulation?), and into this alien world. I think it was in a shed. Sorry I don't have anymore on it. I keep thinking it was "the Weapon Makers" but when I read the synopsis of that novel, it doesn't match that.
I think the "aliens" were doing a experiment that created a small universe and manipulated it study the evolution of the inhabitants, and they was able to break free and escape. I recall at the end the alien (child?) watched as several small silver spaceships broke through the outer shell (?) and escaped up into the sky...