Many of you responded to yesterday's item about the work on naked singularities, arguing that in fact the team hadn't done anything new. I think that's partially my fault in not giving some more background, and since it's interesting stuff, here goes:
A black hole itself is typically created, physicists believe, when an object such as a star collapses in on itself. Its gravitational force twists space around it (as expressed in Einstein's theory of general relativity) so strongly that ultimately, light itself can't escape. The radius at which regular laws of physics break down is called the event horizon. Because nothing can pass out of this zone, there seems to be no way that scientists can observe the black hole, or singularity, that exists beyond this point, a phenomenon that's been dubbed the “cosmic censorship hypothesis.”
By the early 1990s, some physicists had suggested the notion of a
“naked” singularity, or one that did not have this event horizon, and might thus be observable from the outside. The idea was controversial enough to disgust Cambridge's Stephen Hawking, who in 1991 bet two proponents of the theory $100 and a T-shirt that no such phenomenon was possible.
It took six years for the bet to be concluded. A University of Texas supercomputer analysis showed that under specific conditions, a naked singularity could be formed. On the strength of this, Hawking reluctantly paid up, with the bet's bounty including T-shirts reading
“Nature Abhors a Naked Singularity.”
But perhaps fittingly for the mysteries of a black hole, other physicists argued that Hawking shouldn't have paid, because even though the naked singularity could exist, the probability of it forming was mathematically zero.
Tricky, yeah?
For more on the bet, a 1997 New York Times article outlines the story well here. And a Princeton professor's response on the zero-probability issue is here.
The new work from the Duke/Cambridge team, which I wrote about yesterday, could add new grist to that debate. Their argument is that a singularity could in effect shed its impenetrable event horizon under some conditions, and become directly observable through the phenomenon of gravitational lensing (in which a dense object bends space enough to split the light from background objects into multiple images).
However, I'm not at all qualified to critique the math -- the more detail-minded among you should certainly check out the full article in Physical Review D.
A Bet on a Cosmic Scale, And a Concession, Sort Of [New York Times]
Christodoulou Offers Strong Support for Cosmic Censorship, Says Naked Singularities Can't Really Exist [Princeton]
(Image: Artist's conception of a supermassive black hole -- not a naked one -- at the center of a galaxy. Credit: NASA/JPL-Caltech)
