Because our universe is actually the inside of a blackhole.

https://en.wikipedia.org/wiki/Black_hole_cosmology#Evidence

What the Wikipedia article calls "evidence" is not actually evidence. It's not things we actually observe that are predicted by this model. It's just stuff that can be made to sound plausible in the model, if you assume for the sake of argument that the model is true.

And there is also one huge reason to not think such models are viable. The Wikipedia article skates right by it:

"According to such scenarios, our observable universe was born in a black hole existing in a larger universe, where this black hole may, at some point, appear as a white hole."

The problem with this is, a white hole has a past horizon. In other words, it is an isolated system with a horizon around it, and infinite empty space outside the horizon. We have no evidence for any such thing, and how would it be possible anyway? The past horizon would have had to be "built in" to the universe from the start. It's not something that can be produced by a physical process, the way a black hole, with its future horizon, can be formed by gravitational collapse.

There is a video with John Baez and Philip Gibbs explaining why this is a common misconception. It's the same family of conceptual error, where things lining up just right allow incorrect conceptual reasoning to land at a correct answer shape, that allowed John Michell to work out the Schwarzschild radius of a star in the late 1700s.

With the blackhole universe picture, causal boundaries and spacetime's evolution aren't properly accounted for once we step out of a static picture.

Incidentally, the cosmic object we are more likely to be inside of is a white-hole.

https://www.youtube.com/watch?v=ULjLGTd3-4s

I'd heard that hypothesis, but not that we seem to have evidence for it too.

Absolutely wild, thanks for sharing.

> Any model of the observable universe being the interior of a black hole requires that the Hubble radius of the universe be equal to its Schwarzschild radius, which is proportional to its mass. This is indeed observed to be nearly satisfied, but might be a coincidence.

> The only way to test the idea that black holes create new universes is to measure the observable universe. Inflation generated by spin and torsion is consistent with the cosmic microwave background data from the Planck satellite.

But our universe also has black holes.

So what then, is it black holes all the way down?

Why there are anothder blackhole? Is there blackhole inside our blackhole?