Friday, June 22, 2007
Black Holes Down the Drain?
Physicist Lawrence Krauss, well known for his activities against the attempts to inject Intelligent Design creationism into the Ohio public school system, along with Case Western Reserve colleagues, are trying to show, in a paper accepted for publication in Physical Review D, that black holes can't form. The paper is an attempt to solve a paradox posed as a result of a proposal by physicist Stephen Hawking. To begin with:
[A black hole is] 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. ...Krauss and his fellow authors
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.
... 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.Needless to say, unanimity has not struck the scientific community in a single stroke. One issue is, if black holes don't exist, why do they seem to be everywhere?
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. ...This doesn't sound like an issue that is going to disappear anytime soon.
Not so fast, says astronomer Kimberly Weaver of NASA's Goddard Space Flight Center in Greenbelt, Maryland. ... [T]he 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.