" Multiverse Some cosmologists speculate that our observable universe is just an expanding bubble in a much wider sea of energy, which is also expanding. Since this wider universe contains many other bubbles in addition to ours, it is often called a multiverse. The Borde-Guth-Vilenkin theorem also applies to the multiverse as a whole, not just to the individual bubbles within it. Thus, even if there is a multiverse, it cannot be eternal in the past but must have had a beginning. "

― William Lane Craig , On Guard: Defending Your Faith with Reason and Precision