Such a scenario in which the universe is born from inside a wormhole (also called an Einstein-Rosen Bridge) is suggested in a paper from Indiana University theoretical physicist Nikodem Poplawski in Physics Letters B.
In studying the radial motion through the event horizon (a black hole’s boundary) of two different types of black holes — Schwarzschild and Einstein-Rosen, both of which are mathematically legitimate solutions of general relativity — Poplawski admits that only experiment or observation can reveal the motion of a particle falling into an actual black hole. But he also notes that since observers can only see the outside of the black hole, the interior cannot be observed unless an observer enters or resides within.
“This condition would be satisfied if our universe were the interior of a black hole existing in a bigger universe,” he said. “Because Einstein’s general theory of relativity does not choose a time orientation, if a black hole can form from the gravitational collapse of matter through an event horizon in the future then the reverse process is also possible. Such a process would describe an exploding white hole: matter emerging from an event horizon in the past, like the expanding universe.”
A white hole is connected to a black hole by an Einstein-Rosen bridge (wormhole) and is hypothetically the time reversal of a black hole. Poplawski’s paper suggests that all astrophysical black holes, not just Schwarzschild and Einstein-Rosen black holes, may have Einstein-Rosen bridges, each with a new universe inside that formed simultaneously with the black hole.
“From that it follows that our universe could have itself formed from inside a black hole existing inside another universe,” he said.
By continuing to study the gravitational collapse of a sphere of dust in isotropic coordinates, and by applying the current research to other types of black holes, views where the universe is born from the interior of an Einstein-Rosen black hole could avoid problems seen by scientists with the Big Bang theory and the black hole information loss problem which claims all information about matter is lost as it goes over the event horizon (in turn defying the laws of quantum physics).
We consider the radial geodesic motion of a massive particle into a black hole in isotropic coordinates, which represents the exterior region of the Einstein-Rosen bridge (wormhole). The particle enters the interior region, which is regular and physically equivalent to the asymptotically flat exterior of a white hole, and the particle’s proper time extends to infinity. Since the radial motion into a wormhole after passing the event horizon is physically different from the motion into a Schwarzschild black hole, Einstein-Rosen and Schwarzschild black holes are different, though indistinguishable for distant observers, physical realizations of general relativity. We show that timelike geodesics in the field of a wormhole are complete because the expansion scalar in the Raychaudhuri equation has a discontinuity at the horizon, and because the Einstein-Rosen bridge is represented by the Kruskal diagram with Rindler’s elliptic identification of the two antipodal future event horizons.
The Einstein-Rosen bridge is the spherically symmetric solution to the Einstein field equations in vacuum if we solve these equations using isotropic coordinates, while the Schwarzschild metric is the spherically symmetric solution to the Einstein field equations in vacuum if we solve these equations using the Schwarzschild coordinates. The Schwarzschild black hole solution, singular at the center, does not exist in isotropic coordinates, while the Einstein-Rosen bridge solution, regular everywhere, exists in the Schwarzschild coordinates if we glue two Schwarzschild exterior sheets at their common event horizon. Both black hole solutions are mathematically legitimate.
Since the two solutions are indistinguishable for distant observers, which can only see the exterior sheet, the nature of the interior of a physical black hole cannot be satisfactorily determined, unless an observer enters or resides in the interior region. This condition would be satisfied if the universe were the interior of a black hole existing in a bigger universe. Because Einstein’s general theory of relativity does not choose an orientation for time, if a black hole can exist in the forward time collapse of a mass through an event horizon, then the time reversal of this process is possible: a white hole explosion of matter emerging from an event horizon in the past, like the expanding universe. Scenarios in which the universe is born from the interior of an Einstein-Rosen black hole may avoid many of the problems of the standard Big-Bang cosmology and the black hole information-loss problem. These scenarios, involving gravitational collapse of a sphere of dust in isotropic coordinates, and generalization of the results of the present paper to Schwarzschild-de Sitter and Kerr black holes, will be the subjects of subsequent papers.