But if we look further, could we find evidence that we are inside something even more remarkable, like a black hole?
A compact black hole is so dense that nothing, not even light, can escape its gravitational pull.
In one scenario, a black hole could have swallowed Earth long ago. But if this happened, the gravitational forces would be catastrophic, says Gaurav Khanna, a black hole physicist at the University of Rhode Island.
Does time slow down?
When Earth gets close to a black hole, time slows down. And depending on the size of the black hole, matter can be stretched into shapes resembling spaghetti. Khanna explains that even if the planet survives this “spaghettification” process, Earth would be confined by tiny, dense singularities where it would be incinerated by pressure and an immeasurable gravitational temperature.
Therefore, we can rule out the possibility of a black hole having swallowed Earth at some point in its history. Khanna says it would be obliterated instantly. But there is another way Earth could have ended up inside a black hole: it could have formed there.
Khanna says, “A black hole looks a lot like the Big Bang in reverse. … The math looks similar. While a black hole collapses to an extremely small, dense point, the Big Bang explosion started from such a point.
One theory suggests that the initial Big Bang was the singularity of a larger cosmic black hole. The dense center was compressed and compressed until it somehow exploded, and a newborn universe formed inside the black hole.”
This theory, called Schwarzschild cosmology, suggests that our expanding universe inside a black hole is part of the larger parent universe.
Is it possible for universes to exist within universes?
In theory, this scenario suggests that universes can exist within universes, much like Russian nesting dolls, and traveling back through a black hole – a feat that may be impossible, as even light cannot make a journey back – would unlock unknown realms, says Khanna.
However, this theory is difficult to prove; nothing can return through the event horizon of a black hole.
But if Earth were inside a black hole, experts have some estimates about the size of the cosmic abyss.
Scott Field, an associate professor of mathematics at the University of Massachusetts Dartmouth, says, “If we were inside a black hole, it would have to be extremely large. Earth would not just be squeezed into a black hole the size of a planet or even a black hole the size of the solar system. If that were the case, scientists would take notice.
There would be observable signs of the black hole’s rotation. Or, we would see subtle deformations caused by extreme gravitational forces – like time dilation and matter stretching…
For example, if Earth existed inside a black hole the size of Earth, humans would experience the effects of tidal forces, such as spaghettification and time dilation, as they move from one point to another on the globe, Field, who works on gravitational modeling, including black hole collisions, explains.
So, any black hole that Earth calls home would have to be enormous, on the scale of the universe, and vast enough that we couldn’t move far enough or fast enough to detect gravitational deformations, Field says.
Khanna states that from within a black hole in the universe, inhabitants of Earth “would have no way of knowing if another parent universe exists.” We would know nothing about it. So, it is safe to say that searching for our universal predecessors would be extremely challenging, to say the least. However, “it would be quite lovely” if this hypothesis turns out to be true.