Siloto/Alamy
THESE days, cosmologists think of the big bang not as a single moment, but a longer period in which the nascent cosmos, then a ludicrously hot and dense soup, underwent a series of transformations before the universe we see today eventually emerged through a slower process of cooling and expansion.
But our understanding of this “hot big bang” remains sketchy at best. That means cosmologists have some freedom to generate new ideas about what really happened in the very early universe.
One intriguing possibility is that dark matter, the mysterious stuff thought to hold galaxies together, was formed in a…