A theoretical physicist at UNC believes she has found a rather large hole in the popular scientific conception of the universe.
The university’s press office states flatly that Dr. Laura Mersini-Houghton has shown that “black holes do not exist,” and that, as a result, scientists are going to have to “reimagine the fabric of space-time, but also rethink the origins of the universe.”
Those cosmic claims may be slightly hyperbolic, but Mersini-Houghton herself believes that her paper published last week will disrupt our entire understanding of the light-eating, infinitely dense objects that supposedly haunt the universe. She says black holes likely can’t exist in the way they’ve been previously conceived.
Her conclusion, in short, is that collapsing stars should slow their self destruction before they truly become bottomless gravity wells.
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And if the Albanian-born professor’s equations prove right, then the theory fleshed out in her long, pensive walks through England in the last year may set a new benchmark in a debate that has long dominated the headiest heights of scientific debates.
“It’s a problem, of course, that every theoretical physicist thinks about now and then,” she said.
Black holes have been orbiting through astronomic theory since at least the 18th century, when parson John Michell imagined a “dark star” so heavy that its gravity sucked matter and energy back to its surface, blotting it out of the night sky, according to the American Museum of Natural History.
The modern theory of the black hole largely developed through the first half of the 20th century and by now is firmly rooted in the minds of many scientists and students alike.
“It’s one of the things that really starts to pique the interest of kids,” said Nick Eakes, an astronomy educator at UNC’s Morehead Planetarium and Science Center. “Maybe it’s the mysterious nature of it all, but it’s probably the thing they ask about most.”
That mystery has kept theorists’ questions coming, too. The theoretical objects aren’t directly observable and present serious contradictions and challenges for physicists, including questions about the “singularity” at the hole’s heart, where, in layman’s terms, gravity and physics go crazy.
Stephen Hawking famously took a series of bets with John Preskill and Kip Thorne on the nature of black holes.
“It’s the kind of Hollywood-type attraction, because of all the personalities involved in either side,” Mersini-Houghton said of her own long fascination.
“But the real motivation is that black holes are supposed to contain this singularity at the center, which is an incredibly exotic object. We can’t make sense of it with our physics.”
Her recent work on black holes, however, started at a much more human scale.
A new challenge
Mersini-Houghton spent the last academic year and this summer on research leave at the University of Cambridge in England. She’d recently wrapped up much of her work on the multi-verse – in peer-reviewed papers, she’d argued that variations in cosmic radiation were in fact the imprint of other universes, winning wide media coverage. She was ready for a new challenge.
A colleague at Cambridge, Donald Marolf of the University of California, had been working with other physicists on a new theory about black holes, positing that a high-energy “firewall” forms as mass is torn apart at the edge of the bottomless gravity well.
Mersini-Houghton ended up hearing a lot about this theory. She and Marolf often talked at the day care their daughters formed, and theoretical physicists’ small talk is rarely very small.
“Initially, I was just asking him what he’d been working on,” Mersini-Houghtson said.
A central paradox vexing physicists is the idea of information loss. Quantum theories say it’s impossible to destroy physical “information” about the structure of matter, which seems to clash with the idea that nothing ever escapes intact from a black hole’s point-of-no-return boundary, known as its event horizon.
“You could take all the stars around, stuff them down the throat of the black hole, and lose them forever,” Mersini-Houghton said. “And with quantum mechanics, that’s an absolute no-go.”
So celestial small talk with Marolf slowly gave way to relentless work.
“I looked at his papers, and I could see the way out,” she said.
Mersini-Houghton estimates she worked 12 hours per day on the project for about eight months, sketching out her equations with pen and paper, then turning over the thorny ideas in her head as she walked, equations from her notes projected in her mind’s eye.
“Once I got the answer, I put it in the drawer for a few months, checked and rechecked and discussed it with some very good people,” she said.
Heart of the theory
At the center of Mersini-Houghton’s work is the question of how a dying star becomes a black hole.
In popular theory, a large star that has just gone supernova might next begin to fall in on itself, unable to maintain its structure against the gravity of its own huge mass, according to the National Aeronautics and Space Administration. Black holes also could theoretically form when stars collide, NASA reports.
Mersini-Houghton’s theory diverges before the star’s mass can become the classic, inescapable black hole. Her papers show, she argues, that a collapsing star will avoid collapse-inducing imbalances of energy and mass by shedding “Hawking radiation,” a type of energy emission discovered by Stephen Hawking. The star may explode instead, she predicts.
Mersini-Houghton’s two papers are available on Cornell University’s arXiv server. The second paper, a more mathematically detailed collaboration with Harald Pfeiffer of the University of Toronto, hasn’t yet been peer reviewed. The earlier paper already has appeared in Physics Letters B.
Physical evidence to consider
Questions about the nature of the black hole aren’t new. In fact, Hawking himself argued earlier this year that the holes might hold on to stuff and eventually release it, rather than irreversibly eat it.
Still, Mersini-Houghton will face some tight scientific scrutiny of her theory, which would nullify the only real route that physicists have established for the creation of black holes, she said.
Ramesh Narayan, an astrophysicist at Harvard University, said that shifts in our understanding of black holes would eventually have to be reconciled with evidence of the phenomenon’s existence.
“What I can say is that we have a huge amount of evidence that compact objects with a wide range of mass ... exist in the universe,” Narayan wrote in an email, stressing that he was not evaluating the UNC professor’s mathematics. “The only reasonable model that we astrophysicists have for these objects is that they are black holes.”
Joe Polchinski, a theoretical physicist who collaborated on the “firewall” theory, said that the “usual equations” found that Hawking radiation had too small an effect to change the behavior of black holes, though he hasn’t yet reviewed Mersini-Houghton’s work.
William Unruh, a theoretical physicist at the University of British Columbia, is skeptical of the new research. In comments printed by the website IFL Science and confirmed by Unruh, the professor dismissed the paper as “nonsense” and a misunderstanding of Hawking radiation.
Mersini-Houghton, meanwhile, plans to further expand her research. She wants to address the question of what happens if some outside force destabilizes the collapsing star and see how the theory meshes with observational science.
She’s thinking of where to publish her second paper on the topic, and she hopes to get a word in with Hawking himself.
“For the foreseeable future,” she said, “it’s black holes.”
As for the kids who love to ask about black holes, Eakes, the planetarium educator, thinks they’ll be OK no matter what the truth turns out to be.
“They might have trouble adapting, but that’s the beautiful thing about science,” he said. “We, as scientists and astronomy educators, are excited for change.”