No More Black Holes?

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.


Original Post

A black hole is like a hole in the ground with a bottom, the things which actually fall in will coninue to fall, however before this they must actually approach the hole and fall in. The gravitational pull of a black hole outside of the event horizon may not be strong enough to pull on objects far in the distance.

Originally posted by Kai:

The gravitational pull of a black hole outside of the event horizon may not be strong enough to pull on objects far in the distance.

Would that be consistent with the characterization of "infinite gravity" then? It would seem like the gravity would actually be quite limited - except perhaps if something were right in it. Confused
Originally posted by MBM:
If a black hole has "infinite gravity" then why hasn't the entire universe gotten sucked into one any way? Confused
Black holes are really just a concept... No one knows if they exist as described...

If black holes do exist, whose to say that they aren't a key component to holding the universe together? Part of the gravitational balance... Like, for instance, in our solar system... the 8.5 planets rotate around the sun and have for millions of years, without getting sucked in... Maybe solar systems rotate around black holes in a similar fashion?
Originally posted by MBM:
If a black hole has "infinite gravity" then why hasn't the entire universe gotten sucked into one any way? Confused

What is meant by "infinite gravity"?

The field strength may be infinite at the source but I presume that is inside the event horizon. Beyond the event horizon it gets progressively weaker. Maybe everything eventually falls into a single black hole known as the big crunch but supposedly the rate of expansion of the universe is increasing which is why they came up with the idea of negative energy.

I confess when physics starts becoming virtually metaphysical I start to kind of lose interest. Even if I could develop my math skills to the point that I might understand it I wouldn't be able to do anything of practical value with it anyway. There are too many things that are just as interesting but way more down to Earth.


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