The idea that spaceships might zip across the universe using black holes as a high-speed portal is a well-worn sci-fi cliché.
But the consensus among scientists of late is that black holes are so destructive, spaceships would be torn to subatomic bits if they tried such a thing.
Then again, maybe not. A new paper by University of Utah physicist Lior Burko, building on earlier work, raises the possibility that black holes may not annihilate everything, and that the potential for hyperspace travel is still open.
"One possibility is that black holes may allow us to travel to very remote places in the universe, or another universe entirely," said Burko in a telephone interview from his office in Salt Lake City. "It depends on the topology of the universe, which we do not know very well.... I'm not arguing it's a practical thing to do, but maybe in 1,000 years from now, maybe it would be simpler."
In Burko's scheme, black holes may be doorways to wormholes, theoretical constructs equivalent to tunnels, or shortcuts, between distant points of the universe, different points in time or even parallel universes.
Burko's ideas aren't new. Wormholes were popularized by Caltech physicist Kip Thorne in the 1980s, and were the interstellar vehicle of choice in Carl Sagan's influential novel Contact.
But subsequent black hole studies have suggested it would be impossible to use them as wormhole portals. The interiors of black holes are so infinitely dense that they exert massively destructive, "tide-like" distortions on approaching objects, ripping them into their constituent subatomic particles.
In fact, this infinitely dense interior gives black holes their potential for space and time travel. Inside a black hole, the very fabric of the universe is collapsed into a point of infinite curvature -- known as a "space-time singularity," where the laws of physics no longer apply.
However, Burko, a 34-year-old physicist from Israel, has suggested that some black holes may not be as destructive as others. Under certain circumstances, black holes may have "Cauchy horizon singularities," which may not be destructive but still act as openings to a wormhole.
Earlier work by Burko and others suggested weaker singularities were present in rotating black holes.
In a paper published in the March 28 issue of Physical Review Letters, Burko suggests that under certain conditions, hybrid singularities may exist. These hybrid singularities are composed of a strong sector, which is destructive, and a weak sector, which may not be. Any spacecraft entering the weak sector could possibly pass through without being damaged.
It's all theoretical, but the possibility of a weaker singularity doesn't rule out the potential of using black holes for interstellar travel.
"At the moment, we donÂ’t have compelling evidence that this kind of hyperspace travel is disallowed," said Burko. "It doesn't mean, of course, it is allowed, but we donÂ’t have compelling evidence to the contrary."
Princeton physicist Richard Gott, author of Time Travel in Einstein's Universe, said he hadn't read Burko's latest paper, but previous work on the subject reopened some interesting possibilities.
"It's certainly one of the possibilities that you can have a weak singularity," he said. "I characterize it like a speed bump. You hit it, and you come out in a new region. It could be a region of time travel, another universe or somewhere a great distance away. These are interesting possibilities and should be investigated further."
Burko noted that the theory rests on some unproven assumptions, and further work could debunk it. In addition, he said so little is known about quantum gravity -- the marriage of quantum physics and classic theories of gravity -- that as-yet-undiscovered laws may forbid hyperspace travel altogether.
Even if the idea of interstellar space travel through black holes is possible, traveling to a suitable black hole to try it out would be a problem.
Burko said the black hole at the center of the Milky Way may be a candidate, but it's 26,000 light years away. Traveling at near the speed of light -- the upper limit for an interstellar excursion -- the trip would take nearly 30,000 years!