A recent cosmological model combines two of the most eccentric ideas in contemporary physics to explain the nature of dark matter, the invisible substance that makes up about 85 percent of all matter in the universe. To understand it, it's necessary to look beyond the Big Bang we all know and consider two concepts that rarely intersect: cyclic universes and primordial black holes. There are different versions of the “multiverse.” The most popular model—that of the Marvel Cinematic Universe—proposes that there are as many universes as there are possibilities and that these versions of reality are parallel. Physics proposes something more sober and mathematically consistent: the cosmic bounce. In this model, the universe is not born from a singularity, but expands, contracts, and expands again in an endless cycle. Each “universe” is not parallel, but sequential—that is, one arises from the ashes of the previous one. Is it possible for something to survive the end of its universe and endure into the next? According to a paper published in Physical Review D, yes. Author Enrique Gaztanaga, a research professor at the Institute of Space Sciences in Barcelona, shows that any structure larger than about 90 meters could pass through the final collapse of a universe and survive the rebound. These "relics" would not only persist, but could also seed the formation of giant, unexplained structures observed in the early stages of the present-day universe. Moreover, they could be the key to understanding dark matter. For decades, the dominant explanation for dark matter has been that it is an unknown particle or particles. But after years of experiments without direct detections, physicists have begun to explore alternatives. One of them proposes that dark matter is not an exotic particle, but an abundant population of small black holes that we overlook. The idea is appealing, but it has a serious problem. For these black holes to explain dark matter, they would have to exist