It's one thing to create a universe, but quite another to know where to keep it. After all, an eternally inflating universe might be expected to take up quite a bit of space - the cupboard under the stairs simply won't do.
Actually this wouldn't be a problem, Sakai says. For a start, the process warps space-time enormously, so that it is no longer the Euclidean space we are familiar with. This highly distorted space doesn't have the same geometry as normal space, so it's not as if the universe would blow up and engulf us.
Also, the baby universe has its own space-time and, as this inflates, the pressure from the true vacuum outside its walls continues to constrain it. As these forces compete, the growing baby universe is forced to bubble out from our space-time until its only connection to us is through a narrow space-time tunnel called a wormhole (see Graphic).
“Sitting inside the monopole, you would see space expanding in every direction”
In the end, space-time becomes so distorted that even this umbilical cord is severed. The baby universe's space-time is left entirely divorced from our own. If you were sitting inside the monopole, you would see space expanding, rushing out in every direction - just as it did after the big bang in our universe. The view from our universe, outside the monopole looking in, would be rather less spectacular.
“Once disconnected, the baby universe will be locked inside a microscopic black hole”
Sakai's calculations show that, once disconnected, the baby universe will be locked inside a microscopic black hole which will not appear to grow in size. This mini black hole will emit Hawking radiation and quickly evaporate from our universe. It will continue to grow its own space-time, but will leave behind little trace of its presence in our universe. "We would make this tiny little thing and before we know it, it has flown away - escaped from our grasp," Linde laments.