A girl standing on a floor would have two opposite forces acting on it. These forces are the weight and the normal force. Since no other forces are acting and that the girl is at rest, then the weight must equate to the normal force. Therefore, the supporting force would be:
F = mg = 55kg (9.81 m/s^2) = 539.55 N
In theroy, yes. But time travel has yet to happen and thus, we dont know. I would assume that that if an alternate universe were NOT created, it would cause a rip in the fabic of time creating a worm hole and allowing all entitys to pass through simultaneously,and that would cause great stress on it, possibly causing it to rip large enough to encase the whole universe and it would implode.