The big bang poses a big question: if it was indeed
the cataclysm that blasted our universe into existence 13.7 billion years ago,
what sparked it?
Three Perimeter Institute researchers have a new
idea about what might have come before the big bang. It’s a bit perplexing, but
it is grounded in sound mathematics, testable, and enticing enough to earn the
cover story in Scientific American, called “The Black Hole at the Beginning of
Time.” What we perceive as the big bang, they argue, could be the three-dimensional
“mirage” of a collapsing star in a universe profoundly different than our own.
“Cosmology’s greatest challenge is understanding the
big bang itself,” write Perimeter Institute Associate Faculty member Niayesh
Afshordi, Affiliate Faculty member and University of Waterloo professor Robert
Mann, and PhD student Razieh Pourhasan.
Conventional understanding holds that the big bang
began with a singularity – an unfathomably hot and dense phenomenon of
spacetime where the standard laws of physics break down. Singularities are
bizarre, and our understanding of them is limited.
“For all physicists know, dragons could have come
flying out of the singularity,” Afshordi says in an interview with Nature.
The problem, as the authors see it, is that the big
bang hypothesis has our relatively comprehensible, uniform, and predictable
universe arising from the physics-destroying insanity of a singularity. It
seems unlikely. So perhaps something else happened. Perhaps our universe was
never singular in the first place.
Their suggestion: our known universe could be the
three-dimensional “wrapping” around a four-dimensional black hole’s event
horizon. In this scenario, our universe burst into being when a star in a
four-dimensional universe collapsed into a black hole.
In our three-dimensional universe, black holes have
two-dimensional event horizons – that is, they are surrounded by a
two-dimensional boundary that marks the “point of no return.” In the case of a
four-dimensional universe, a black hole would have a three-dimensional event
horizon.
In their proposed scenario, our universe was never
inside the singularity; rather, it came into being outside an event horizon,
protected from the singularity. It originated as – and remains – just one
feature in the imploded wreck of a four-dimensional star.
The researchers emphasize that this idea, though it
may sound “absurd,” is grounded firmly in the best modern mathematics
describing space and time. Specifically, they’ve used the tools of holography
to “turn the big bang into a cosmic mirage.” Along the way, their model appears
to address long-standing cosmological puzzles and – crucially – produce
testable predictions.
Of course, our intuition tends to recoil at the idea
that everything and everyone we know emerged from the event horizon of a single
four-dimensional black hole. We have no concept of what a four-dimensional
universe might look like. We don’t know how a four-dimensional “parent”
universe itself came to be.
But our fallible human intuitions, the researchers
argue, evolved in a three-dimensional world that may only reveal shadows of
reality.
They draw a parallel to Plato’s allegory of the
cave, in which prisoners spend their lives seeing only the flickering shadows
cast by a fire on a cavern wall.
“Their shackles have prevented them from perceiving
the true world, a realm with one additional dimension,” they write. “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.”
0 Comments