Our universe might have originated from a black hole that lies within another universe.

The idea centers on how matter and energy falling into a black hole could in theory come out a “white hole” in another universe. In such a situation, both the black hole and the white hole are mouths of an Einstein-Rosen bridge, popularly known as a wormhole.
With that in mind, theoretical physicist Nikodem Poplawski at Indiana University conjectured that when a black hole forms upon the collapse of a dying star, a universe is born at the same time from the white hole on the other side of the wormhole.
“Our universe could have itself formed from inside a black hole existing inside another universe,” he said. This idea has been suggested before, and now Poplawski has expanded on the thinking.
Although a black hole forming from a star the size of our sun would only be about 2 miles wide, it does not mean that a universe which might originate from a black hole would stay that small.
“Our universe was small a long time ago and expanded,” Poplawski said. “From the other side, one would not see our expansion.” Essentially, a black hole could seem bigger on the “inside” than how it looked to someone outside.
If anyone survived a trip into a black hole and emerged in another universe, “it would be a one-way trip,” Poplawski noted. The event horizon of a black hole is boundary at which nothing inside can escape.
In theory, black holes do lose mass, however, as Hawking radiation — particles that emerge from the vacuum right next to their event horizons.
Black holes that lose more mass than they gain are expected to shrink and ultimately vanish. This does not mean any universe at the other end of the black hole would cease to exist, Poplawski explained. “We would just be disconnected from the other universe,” he said.
If our universe was born from a black hole in another universe, it would be impossible to cross its event boundary and see the other side, meaning one cannot prove or disprove this idea that way.
So how might one test this conjecture? One implication of Poplawski's concept is that our universe is “closed.”
“In cosmology, there are three models for our universe,” Poplawski explained. “The first is that it's closed, the second is that it's 'open,' and the third is that it's 'flat.'“
If it is closed, and one tries to venture to the edge of our universe, one would eventually loop back to where one started. “It would be like walking on the surface of the Earth — if you walk to the east, at some point you come back across the west,” Poplawski said.
If our universe is flat, and one tries to venture to its edge, one would never reach it, as it continued on infinitely. The same would hold true if the universe is open, “only it would be 'curved,'“ Poplawski said.
(Source: Space.com)