THE BLACK HOLE AT THE BIRTH OF THE UNIVERSE
From the FMS Global News Desk of Jeanne Hambleton 7-Aug-2014
Source Perimeter Institute for Theoretical Physics
Newswise — 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.”
- Colin Hunter
DID A HYPER-BLACK HOLE SPAWN THE UNIVERSE?
Big Bang was mirage from collapsing higher-dimensional star, theorists propose
From the FMS Global News Desk of Jeanne Hambleton Nature | News by Zeeya Merali
It could be time to bid the Big Bang bye-bye. Cosmologists have speculated that the Universe formed from the debris ejected when a four-dimensional star collapsed into a black hole — a scenario that would help to explain why the cosmos seems to be so uniform in all directions.
The standard Big Bang model tells us that the Universe exploded out of an infinitely dense point, or singularity. But nobody knows what would have triggered this outburst: the known laws of physics cannot tell us what happened at that moment.
“For all physicists know, dragons could have come flying out of the singularity,” says Niayesh Afshordi, an astrophysicist at the Perimeter Institute for Theoretical Physics in Waterloo, Canada.
It is also difficult to explain how a violent Big Bang would have left behind a Universe that has an almost completely uniform temperature, because there does not seem to have been enough time since the birth of the cosmos for it to have reached temperature equilibrium.
To most cosmologists, the most plausible explanation for that uniformity is that, soon after the beginning of time, some unknown form of energy made the young Universe inflate at a rate that was faster than the speed of light. That way, a small patch with roughly uniform temperature would have stretched into the vast cosmos we see today. But Afshordi notes that “the Big Bang was so chaotic, it’s not clear there would have been even a small homogenous patch for inflation to start working on”.
On the brane
In a paper posted last week on the arXiv preprint server1, Afshordi and his colleagues turn their attention to a proposal2 made in 2000 by a team including Gia Dvali, a physicist now at the Ludwig Maximilians University in Munich, Germany. In that model, our three-dimensional (3D) Universe is a membrane, or brane, that floats through a ‘bulk universe’ that has four spatial dimensions.
Ashfordi’s team realized that if the bulk universe contained its own four-dimensional (4D) stars, some of them could collapse, forming 4D black holes in the same way that massive stars in our Universe do: they explode as supernovae, violently ejecting their outer layers, while their inner layers collapse into a black hole.
In our Universe, a black hole is bounded by a spherical surface called an event horizon. Whereas in ordinary three-dimensional space it takes a two-dimensional object (a surface) to create a boundary inside a black hole, in the bulk universe the event horizon of a 4D black hole would be a 3D object — a shape called a hypersphere. When Afshordi’s team modelled the death of a 4D star, they found that the ejected material would form a 3D brane surrounding that 3D event horizon, and slowly expand.
The authors postulate that the 3D Universe we live in might be just such a brane — and that we detect the brane’s growth as cosmic expansion. “Astronomers measured that expansion and extrapolated back that the Universe must have begun with a Big Bang — but that is just a mirage,” says Afshordi.
The model also naturally explains our Universe’s uniformity. Because the 4D bulk universe could have existed for an infinitely long time in the past, there would have been ample opportunity for different parts of the 4D bulk to reach an equilibrium, which our 3D Universe would have inherited.
The picture has some problems, however. Earlier this year, the European Space Agency’s Planck space observatory released data that mapped the slight temperature fluctuations in the cosmic microwave background — the relic radiation that carries imprints of the Universe’s early moments. The observed patterns matched predictions made by the standard Big Bang model and inflation, but the black-hole model deviates from Planck’s observations by about 4%. Hoping to resolve the discrepancy, Afshordi says that his is now refining its model.
Despite the mismatch, Dvali praises the ingenious way in which the team threw out the Big Bang model. “The singularity is the most fundamental problem in cosmology and they have rewritten history so that we never encountered it,” he says. Whereas the Planck results “prove that inflation is correct”, they leave open the question of how inflation happened, Dvali adds. The study could help to show how inflation is triggered by the motion of the Universe through a higher-dimensional reality, he says.