By Phil Berardelli
ScienceNOW Daily News
21 June 2007
If new calculations are correct, the universe just got even stranger. Scientists at Case Western Reserve University in Cleveland, Ohio, have constructed mathematical formulas that conclude black holes cannot exist. The findings--if correct--could revolutionize astrophysics and resolve a paradox that has perplexed physicists for 4 decades.
On the surface, a black hole seems like a simple concept. It's a point in space where gravity grows infinitely strong. At a particular distance from the center of the hole--called the event horizon--gravity is already so strong not even light can escape. So material falls in never to be seen again. Calculations support this theory, but they also support something stranger. In 1974, theoretical physicist Stephen Hawking showed that thanks to quantum mechanics matter can escape black holes in a tricky way. By random chance, a particle-antiparticle pair can flit into existence straddling the event horizon. One partner falls into the hole, while the other just barely makes it free. Because of this effect, dubbed Hawking radiation, a black hole slowly evaporates, so that anything that enters is eventually released over billions or even trillions of years. But how can black holes be both airtight and leaky?
Physicist Lawrence Krauss and Case Western Reserve colleagues think they have found the answer to the paradox. In a paper accepted for publication in Physical Review D, they have constructed a lengthy mathematical formula that shows, in effect, black holes can't form at all. The key involves the relativistic effect of time, Krauss explains. As Einstein demonstrated in his Theory of General Relativity, a passenger inside a spaceship traveling toward a black hole would feel the ship accelerating, while an outside observer would see the ship slow down. When the ship reached the event horizon, it would appear to stop, staying there forever and never falling in toward oblivion. In effect, Krauss says, time effectively stops at that point, meaning time is infinite for black holes. If black holes radiate away their mass over time, as Hawking showed, then they should evaporate before they even form, Krauss says. It would be like pouring water into a glass that has no bottom. In essence, physicists have been arguing over a trick question for 40 years.
Asked why then the universe nevertheless seems to be full of black holes, Krauss replies, "How do you know they're black holes?" No one has actually seen a black hole, he says, and anything with a tremendous amount of gravity--such as the supermassive remnants of stars--could exert effects similar to those researchers have blamed on black holes. "All of our calculations suggest this is quite plausible," Krauss says.
Not so fast, says astronomer Kimberly Weaver of NASA's Goddard Space Flight Center in Greenbelt, Maryland. Although she appreciates the physics the Case Western Reserve team is describing, the problem is "we have never observed any events that would back this up." At the site of the supermassive black hole at the center of the Milky Way, for example, she says astronomers routinely observe what looks like interstellar material disappearing without a trace. Also, no one has yet detected Hawking radiation, which would be prerequisite evidence for black hole evaporation, Weaver says.
Although it clearly presents the idea, I tend to think that article wasn't very well-written (in regard to some of the concepts). So I'll throw in an article from astronomy.com that adds a little more:
A research team concludes it is impossible to lose something inside a black hole.
"Nothing there," Case Western Reserve University physicists concluded about black holes after spending a year working to calculate black hole formation. The research may solve the information-loss paradox that has perplexed physicists for the past 40 years.
"It's complicated and very complex," said Case physicists Tanmay Vachaspati, Dejan Stojkovic, and Lawrence Krauss, referring to the overall problem and their particular approach to solving it.
The physicists set out to discover just what happens once something enters and collapses into a black hole. In current thinking, once this happens, all information is lost. Yet, the researchers thought, if all information is lost, then laws of quantum physics are defied.
"If you define the black hole as some place where you can lose objects, then there is no such thing, because the black hole evaporates before anything is seen to fall in," Vachaspati said.
The team argues that information would remain forever on the event horizon — the black hole's point of no return. The masses on the edge of the incipient black hole appear to be collapsing, but never actually fall inside the event horizon.
Researchers began by collapsing nonsingular matter to see if an event horizon formed, signaling the creation of a black hole.
They found while mass shrank in size, the matter never collapsed inside an event horizon. Evidence of pre-Hawking radiation — a non-thermal radiation that allows information to be recovered from the collapsing mass — may be the explanation for this.
"Non-thermal radiation can carry information in it unlike thermal radiation. This means that an outside observer watching some object collapse receives non-thermal radiation back and may be able to reconstruct all the information in the initial object, and so the information never gets lost," the team said.
According to the researchers, if new black holes form, information formed in the initial state would disappear in the black hole after a burst of thermal radiation.
Using Schrodinger formalism, the researchers suggest that information about energy emitted from radiation is long-evaporated before an event horizon forms.
"An outside observer will never lose an object down a black hole," Stojkovic said. "If you are sitting outside and throwing something into the black hole, it will never pass over, but will stay outside the event horizon, even if one considers the effects of quantum mechanics. In fact, since in quantum mechanics the observer plays an important role in measurement, the question of formation of an event horizon is much more subtle to consider."
The Case team's findings could be the beginning of a new era in black hole research. "From an external viewer's point it takes an infinite amount of time to form an event horizon, and the clock for the objects falling into the black hole appears to slow down to zero," said Krauss, director of Case's Center for Education and Research in Cosmology.
"This is one of the factors that led us to rethink this problem, and we hope our proposal at the very least will stimulate a broader reconsideration of these issues," Krauss added.
If black holes exist in the universe, the astrophysicists speculate, they were formed only at the beginning of time.