The Hidden Reality_ Parallel Universes and the Deep Laws of the Cosmos - Brian Greene [157]
Guth, together with Steven Blau and Eduardo Guendelman, showed that there’s no need to be concerned about an artificial phase of inflationary expansion ripping through our existing environment. The reason has to do with pressure. If an inflationary seed were created in the laboratory, it would harbor the inflaton field’s characteristic positive energy and negative pressure, but it would be surrounded by ordinary space in which the inflaton field’s value, and its pressure, would be zero (or nearly so).
We usually don’t ascribe much power to zero, but in this case zero makes all the difference. Zero pressure is larger than negative pressure, and so the pressure outside the seed would be larger than the pressure inside. This would subject the seed to a net external force pressing upon it, much like what your eardrums experience when deep-sea diving. It is the pressure differential is powerful enough to prevent the seed from expanding into the surrounding environment.
But this does not prevent the inflaton’s drive to expand. If you blow air into a balloon while tightly clasping its surface, the balloon will bubble out from between your hands. The inflaton seed can behave similarly. The seed can generate a new expanding spatial realm that sprouts from the original spatial environment, as illustrated by the little growing sphere in Figure 10.1. The calculations show that once the new expanding realm reaches a critical size, its umbilical cord to the parent space severs, as in the final image of Figure 10.1, and an independent inflating universe is born.
As enticing as the process might be—the artificial creation of a new universe—the view from the laboratory wouldn’t live up to the advance billing. It’s a relief that the inflationary bubble would not gobble up the surrounding environment, but the flip side is that there would be little evidence of the creation itself. A universe that expands by generating new space, which then detaches from ours, is a universe we can’t see. Indeed, as the new universe pinches off, its sole residue would be a deep gravitational well—you can see this in the last image of Figure 10.1—which would appear to us as a black hole. And since we have no capacity to see beyond a black hole’s edge, we wouldn’t even be assured that our experiment had been a success; without access to the new universe, we would have no means of establishing observationally that the universe had been created at all.
Figure 10.1 Because of the greater pressure in the ambient environment, an inflationary seed is forced to expand into newly formed space. As the bubble universe grows, it detaches from the parent environment, yielding a separate, expanding spatial domain. To someone in the ambient environment, the process looks like the formation of a black hole.
Physics protects us, but the price for safety is total separation from our handiwork. And that’s the good news.
The bad news for aspiring universe creators is a more sobering result derived by Guth and his MIT colleague Edward Farhi. Their careful mathematical treatment showed that the sequence depicted in Figure 10.1 requires an additional ingredient. Much as some balloons require that you give a strong initial burst of air, after which they more easily inflate, Guth and Farhi found that the nascent universe in Figure 10.1 needs a strong kick-start to get the inflationary expansion off and running. So strong that