Experiments with quantum fluctuations led to the understanding that child universes aren't difficult to create. Our universe is constantly spinning off new ones. You don't know it because they separate as soon as they are created.
The revolutionary discovery was that portals can be attached to spawned universes. This provides the ultimate research tool. We began modelling the Earth with alternate societies.
If a portal is discovered by it's world's inhabitants we always destroy it as a precaution. Doing so collapses the child universe.
I think I know how to identify a portal into our universe. I find this... disturbing.