The bottom will not fall out.

The bottom will not fall out

Ever since cosmologies that feature an inflationary universe were first proposed, there has been an underground current of apprehension among some physicists that the bottom might fall out of the universe, with disastrous consequences for all the objects and structures that we know in nature. In the older theories of the expanding universe, the cosmos expands at a constant rate throughout the ages. To get around some serious problems in that scenario, the inflationary cosmology proposes that there was at least one era when the cosmos expanded much faster than at the current rate (SN: 2/12/83, p. 108). However, while solving some problems, the inflationary scheme raised the specter of catastrophe by its treatment of the vacuum.

The vacuum is physicists' term for the lowest possible energy state, the zero level devoid of matter or energy. Everything that exists occupies energy levels above the vacuum, which is the rock bottom on which physics is based. Or perhaps not quite the rock bottom. Energy scales are relative. A state lower than the vacuum that we observe is conceivable, and the inflationary cosmology implies that such a state could exist for the universe.

If that is so, the universe as we see it is based on a false vacuum, and some appropriate nudge might send it crashing down to the true vacuum with a catastrophic rearrangement of physical structures and processes. Some physicists have feared that something in the laboratory, perhaps some very high-energy collisions of particles, could make a hole in the dike, so to speak, starting a process that would grow until everything in the cosmos was sucked into it and disastrously rearranged.

Now the man generally regarded as the originator of the inflationary idea, Alan H. Guth of Massachusetts Institute of Technology, says it can't happen. Guth, along with co-workers, calculates that if such a region based on a different vacuum got nucleated, it would develop as a universe separate from our own, and would not suck everything in our cosmos into itself. Such a new universe would connect to ours through an umbilicus that would look to us like a black hole.

Furthermore, such a different universe could probably not get started in the first place. It needs not some high-energy collision as a nucleus but an eternal singularity, Guth says. A singularity is a location where space-time becomes infinitely curved, and the laws and equations of physics become infinite or impossible to define. A singularity lurks in the center of every black hole, but these are temporal singularities: They form at some point in time, and they may disappear at some other point in time. The only eternal singularity cosmology knows is the one that started it all, the one at the origin of the Big Bang. Two of those don't seem to be possible.