black hole
Concept drawing by Nasa showing the accretion lines from a black hole (Nasa)

The universe emerged from a collapsed star in a four-dimensional universe, a group of physicists have suggested.

Three scientists from the Perimeter Institute for Theoretical Physics have proposed an alternate theory to the Big Bang, where experts say the universe suddenly exploded from something smaller than a pinhead to an infinite size, and that it is still growing.

However, what sparked the explosion and subsequent expansion is not known.

Published in Scientific American, the cover story The Black Hole at the Beginning of Time says the Big Bang could be a 3D "mirage" of a collapsing star in a 4D universe.

The scientists say the Big Bang Theory is based on the idea of singularity – that the universe came from an extremely hot and dense spacetime where standard laws of physics do not apply. Singularities are extremely complex, and the Big Bang is an attempt at a relatively comprehensible explanation as a result.

Researchers Niayesh Afshoridi, Robert Mann and Razieh Pourhasan wrote: "Cosmology's greatest challenge is understanding the Big Bang itself," with Afshordi adding in an interview with Nature: "For all physicists know, dragons could have come flying out of the singularity."

milky way
Experts said they had discovered gravitational waves from Big Bang earlier this year. (Reuters)

They suggest the universe is a 3D mirage of an event horizon from a black hole inside a 4D universe.

In their hypothesis, the authors say our perception of the universe is too rudimentary to comprehend a 4D universe, alluding Plato's story of prisoners who live in a cave and see only flickering shadows cast on a wall from a fire.

"Their shackles have prevented them from perceiving the true world, a realm with one additional dimension," they said. "Plato's prisoners didn't understand the powers behind the sun, just as we don't understand the four-dimensional bulk universe. But at least they knew where to look for answers."

The authors suggest our universe burst into being when a star in a 4D universe collapsed into a black hole. The universe, they say, was never inside the singularity, but is just a feature of an imploded wreck of the 4D star.

In a 3D universe, black holes have 2D event horizons – boundaries that mark the point of no return. In a 4D universe, a black hole would have a 3D event horizon. However, the researchers also note that they do not know what a 4D universe looks like or how it came to be.