Was our universe born inside a black hole in another universe?
The current explanation of the universe's origins relies on clumsy assumptions and can't explain most subatomic particles. A small tweak to general relativity solves these problems - and seemingly proves the universe must have come from a black hole elsewhere.

As it stands right now, the explanation for the universe's beginnings is built around a combination of Einstein's general relativity and observation of the ancient universe. Mixing these two theories together creates some problems - for instance, the universe is impossibly large according to its current rate of expansion, so astrophysicists have to invoke the idea of inflation, in which the early universe expanded at a tremendous rate within the first second after the Big Bang.

General relativity, however, can't explain inflation, so another theory is required to account for it. There's nothing technically wrong with that, but it's an inelegant solution, and physicists tend to prefer an all-encompassing explanation to a bunch of piecemeal solutions. That's not the only issue with the current explanation - it can't deal with many properties of subatomic particles, consigning them entirely to the realm of quantum mechanics.

Nikodem Poplawski of Indiana University thinks solving the latter problem can also solve the former, and that's just the start of the craziness. In a new paper, he explains that the standard version of general relativity totally ignores the intrinsic momentum of subatomic particles like protons and neutrons, but a modified version known as the Einstein-Cartan-Kibble-Sciama theory of gravity solves that problem. The theory states these particles interact repulsively, creating tiny amounts of a force called torsion.

Under normal circumstances, this is just an interesting bit of math, and torsion doesn't really affect anything. However, if densities are increased tremendously, then torsion has some very significant effects. Most intriguingly, torsion makes it impossible for black holes to form singularities. And if singularities are impossible, then what's at the center of black holes?

Poplawski has an audacious proposal: there are whole universes where we thought the singularities were. The torsion process allows for a massive energy buildup inside the event horizon, and this would allow for the creation of new particles through pair production, in which matter and antimatter are created in equal quantities. All it takes then is a small imbalance between the particles and antiparticles to form, and you've got a Big Bang on your hands.

What makes this idea appealing (beyond the fact that it just sounds so awesome) is that torsion explains inflation without requiring a new theory. That repulsive force is sufficient to explain how the universe expanded to its present extent, which means a single theory can explain the entire universe as it is now.

This potentially means that many of the black holes in our own universe are the incubators of entirely new universes, each separated by the infinite time gap of the event horizon. That said, some properties of the mother universe could trickle through to its daughters, and detecting some of these properties could actually provide experimental proof of the theory. In fact Poplawski speculates this inheritance of properties could solve another great mystery of cosmology.

The so-called arrow of time, in which time flows in one direction but not another, is a fundamental aspect of our experience. This isn't accounted for at all by physics, as all of its laws are apparently time-symmetric in that they work just as well whether time flows forwards or backwards. However, the passage of matter through the event horizon would provide a time asymmetry in the new universe, giving it a forward arrow to time. In that way, time itself is a gift of our mother universe on the other side of the black hole.

One problem being no-one can quite explain how there's a matter/antimatter imbalance when creation of a matter brequires the equivalent anti-matter.

As for the thread title - we can't tell, yet

The are we in a black hole concept was postulated more than a decade a go.