They are out there, according to Tufts University cosmologist Alexander Vilenkin, and he makes this case in the September 2013 issue of Discover, although it isn’t spelled out in the preview. Bubble and baby universes are hot just now in cosmology.
Here’s cosmologist Vilenkin’s basic stance from Templeton’s page:
His first major paper on inflation and quantum cosmology, published in 1982, explained how the universe could have been created ex nihilo through quantum energy spacetime fluctuations. In another paper, the following year, he made the then astonishing suggestion that almost all inflationary models are eternal—once the process starts it continues without end like a chain reaction, stopping in one region of space only to start in another, ultimately spawning an infinite number of “pocket universes.” His variant account for the universe’s birth “by quantum tunneling from nothing,” involved a leap from no size at all—zero radius—to a radius large enough for inflation to take over. Continuing to explore the implications of this idea, he and Arvind Borde showed mathematically that a universe eternally inflating toward the future cannot be geodesically complete in the past, so that there must have existed in the indefinite past an initial “singularity,” an ultimate boundary, or beginning. Dr. Vilenkin is also a leading developer of the concept of cosmic strings—dense, linear “defects” in the fabric of space formed in the hot early universe, which he once thought might have a role in transforming matter and energy into galaxies. With Jaume Garriga, he has recently argued that there are an infinite number of regions of space the same size as our observable universe, but that their “histories”—or things that could possibly happen within these realms, including the evolution of intelligent life—are finite, so that every possible version of history will have occurred elsewhere. They call their work a “metaphysical exercise” and name their concept “many worlds in one.” A fellow of the American Physical Society, Dr. Vilenkin has been the recipient of a National Science Foundation Presidential Young Investigator Award and a research grant from the John Templeton Foundation. He is the author of more than 160 scientific papers and (with E. Paul Shellard) the book, Cosmic Strings and Other Topological Defects (Cambridge University Press, 1994 and 2000).
Cosmology is fun but the link with science often seems as imaginary as the imaginary time and space it sometimes relies on. But it’s August.