Many Worlds Theory: Separating Physically or Superimposing?

[Forestman]

In the many worlds theory when universes split off from one another, do they actually separate physically, or are they merely superimposed on each other, but unable to have an effect on each other?

And if they separate from each other physically where do they go?

 

[Dmitry67]

they lose an ability to influence each other:
http://en.wikipedia.org/wiki/Quantum_decoherence

 

[Forestman]

Thanks Dmitry67