Do we live inside a baby universe that’s really a black hole on the outside?

One of the biggest existential questions that has puzzled humanity for as long as humans have been around is simply, “Where did all this come from?” After countless centuries of wondering and speculating, the 20th century brought with it our first scientific answers to that question. We learned that distant objects in the Universe are speeding away from one another: evidence that our Universe is expanding. We discovered that more distant galaxies appear younger, less massive, and with greater rates of star formation: evidence that our Universe evolves with time.

And we discovered a near-uniform background of blackbody radiation: evidence of an early, hot, dense, radiation-dominated state. All of these puzzle pieces, when put together, indicate that our Universe originated from a hot Big Bang some 13.8 billion years ago. But our Universe has a very curious property that not everyone appreciates.

If you add up the mass and energy of all the particles contained within the visible Universe, you can ask the question, “How big would the event horizon of a black hole with this mass be?” And the answer, perhaps surprisingly, is very close to the actual size of the cosmic horizon for our observable Universe. Additionally, there’s another related idea, made famous by Stephen Hawking, that each time we create a black hole in our Universe, it could give rise to a “baby Universe” that’s only accessible to an observer that crosses inside that black hole’s event horizon. Could our Universe, then, actually have been spawned by a black hole that was created in some sort of grand “parent Universe,” and do we give birth to a new Universe each time a new black hole is created?

It’s a fascinating idea worth exploring. Here’s what the science, at present, has to say about it. In the vicinity of a black hole, space flows like either a moving walkway or a waterfall, depending on how you want to visualize it.

At the event horizon, even if you ran (or swam) at the speed of light, there would be no overcoming the flow of spacetime, which drags you into the singularity at the center. Outside the event horizon, though, other forces (like electromagnetism) can frequently overcome the pull of gravity, causing even infalling matter to escape. Rotating black holes possess ring-like, not point-like, singularities.

The defining feature of a black hole is the existence of an event horizon: a boundary that tells a very different story for an object outside of it versus one inside of it. Outside of a black hole’s event horizon, any object will experience its gravitational effects, as the space will be curved by the black hole’s presence, but it can still escape. If it moves fast enough or accelerates quickly enough in the proper direction, it won’t necessarily fall into the black hole, but it could break free of the black hole’s gravitational influence.