The current theory concerning empty space is that particle and anti-particle pairs are consistently popping into and out of existence, constantly annihilating one another (For more on this concept, check out these recent article describing scientific efforts to build the largest laser on Earth.) According to Poplawski, the conditions near the center of a black hole disrupt this mutual annihilation of particles, spawning the generation of an enormous amount of mass and energy which manifests itself as the big bang of another universe.
For those of you willing to brave the scientific jargon (including gems such as "Parker-Zel'dovich-Starobinskii quantum particle production in strong, anisotropic gravitational fields"), I encourage you to check out the paper.