'Disk on the Sky' —The Search for an Alien Universe: “A Circular Bruise in the Cosmic Microwave Background”
A collision of one universe with another would leave what Perimeter Institute's Matthew Johnson, calls “a disk on the sky” – a circular bruise in the cosmic microwave background. That the search for such a disk has so far come up empty makes certain collision-filled models less likely. The Perimeter team is at work figuring out what other kinds of evidence a collision might leave behind. It’s the first time that anyone has produced a direct quantitative set of predictions for the observable signatures of bubble universe collisions. And though none of those signatures has so far been found, some of them are possible to look for.
So to start, forget the Big Bang; in the beginning was the vacuum. The vacuum simmered with energy (variously called dark energy, vacuum energy, the inflation field, or the Higgs field). Like water in a pot, this high energy began to evaporate – bubbles formed.