Like part of a cosmic Russian doll, our universe may be nested inside a black hole that is itself part of a larger universe.

In turn, all the black holes found so far in our universe—from the microscopic to the supermassive—may be doorways into alternate realities.

According to a mind-bending new theory, a black hole is actually a tunnel between universes—a type of wormhole.

The matter the black hole attracts doesn't collapse into a single point, as has been predicted, but rather gushes out a "white hole" at the other end of the black one, the theory goes.

In a paper published in the journal Physics Letters B, Indiana University physicist Nikodem Poplawski presents new mathematical models of the spiraling motion of matter falling into a black hole.

His equations suggest such wormholes are viable alternatives to the "space-time singularities" that Albert Einstein predicted to be at the centers of black holes.

According to Einstein's equations for general relativity, singularities are created whenever matter in a given region gets too dense, as would happen at the ultra-dense heart of a black hole.

Einstein's theory suggests singularities take up no space, are infinitely dense, and are infinitely hot—a concept supported by numerous lines of indirect evidence but still so outlandish that many scientists find it hard to accept.

If Poplawski is correct, they may no longer have to. According to the new equations, the matter black holes absorb and seemingly destroy is actually expelled and becomes the building blocks for galaxies, stars, and planets in another reality.