Expansion, turnaround, contraction and bounce. Those are the four components of a new model of the universe created by researchers at the University of North Carolina at Chapel Hill. Their work offers an alternative to the Big Bang theories in the marketplace and sets up a cyclical progression in which an infinite number of independent universes emerge from what’s left of matter just before the end of time.
Tough going, this. But think of the universe’s vast expansion pushing everything progressively further out until all matter disintegrates. This is the turnaround point, and it is here that each fragmented ‘patch’ of what had been matter collapses and contracts. “We discuss contraction which occurs with a very much smaller universe than in expansion,” write the researchers, “and with almost vanishing entropy because it is assumed empty of dust, matter and black holes.”
The key is that this collapse occurs individually, so that rather than causing the Big Bang to run in reverse, each patch becomes an independent universe that reinflates. Hence the ‘bounce.’
Lauris Baum and Paul Frampton, co-authors of the paper on this work, take aim at the key problem: entropy. The idea of an oscillating universe isn’t new, but the second law of thermodynamics says that entropy should increase from one cycle to the next. That leads straight back to an initial singularity and seems to rule out the idea of an infinitely cycling universe. But the discovery of dark energy and its possibiities in the cosmic mix inspired this new look at oscillations and their uses.
And the researchers get around the entropy problem by assuming that at the time of turnaround, any remaining entropy is in patches that are too remote for interaction. From the paper:
“The second law of thermodynamics continues to obtain for other causal patches, each with practically vanishing entropy at turnaround, but these are permanently removed from our universe, contracting instead into separate universes.”
Thus a kind of multiverse different from previous theories:
“…our proposal of deﬂation naturally leads to a multiverse picture, somewhat reminiscent of that predicted in eternal inﬂation, though here the proliferation of universes must be inﬁnite and originates at the opposite end of a cyclic cosmology, at its maximum rather than at its minimum size.”
The paper is Baum and Frampton, “Turnaround in Cyclic Cosmology,” slated to appear in Physical Review Letters and available as a preprint. I point you to the latter for the authors’ analysis of dark energy’s ‘equation of state’ (describing its pressure and density), which goes far beyond my mathematical powers but is vital to achieving the needed outcome. Thanks to Adam Rosalky and Larry Klaes for the pointer to this paper.