Are we a universe within a universe?

• Position: YOUR LIFE

Could our universe be located within the interior of a wormhole which itself is part of a black hole that lies within a much larger universe? Such a scenario is suggested by theoretical physicist Nikodem Poplawski in Physics Letter B. Poplawski takes advantage of the Euclidean-based coordinate system called isotropic coordinates to describe the gravitational field of a black hole and model the radial geodesic motion of a massive particle into a black hole.

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 experimentation or observation can reveal the motion of a particle falling into an actual black hole, but he also notes that, since observers only can see the outside of the black hole, the interior cannot be viewed unless someone (or something) enters or resides within.

"This condition would be satisfied if our universe were the interior of a black hole existing in a bigger universe. Because [Albert] Einstein's general theory of relativity does not choose a time orientation, if a black hole can form from the...