But what conceivable good is it?
That's a question frequently tossed at physicists who work on those murky frontiers of science where progress isn't always clear and practical purpose is the farthest thing from anyone's mind.
These scientists spend their time on exotic pursuits like cooking up new states of matter, mapping the shape of the universe or fiddling around with mathematical strings in 11-dimensional space.
One might well ask: What for?
The traditional response of physicists has been to drag out Michael Faraday's legendary answer to Queen Isabella: When she asked what possible use could be found for the newly discovered phenomenon called electricity, Faraday reportedly replied, "Of what use is a newborn baby?"
Electricity is old news, of course, so physicists sometimes now update their story by telling us that all of modern computing and electronics is based on the understanding of the atom known as quantum mechanics--a bizarre set of behaviors that seemed about as technically promising at the time as the discovery of a new black hole.
But even quantum mechanics goes back to the early 20th century.
What, one might well ask the physicists, have you done for us lately?
One rather surprising answer surfaced during the meeting of the American Physical Society in Long Beach this spring: Einstein's theory of general relativity, of all things, guides the Global Positioning System that allows boaters, hikers and drivers to know exactly where they are all the time.
You can't get much more esoteric than Einstein's general relativity. In essence, the theory explained the familiar force of gravity as the curvature of space-time into an unseen fourth dimension. Like an elephant sitting on a water bed, heavy objects bend space-time into "gravity wells" that pull other objects in. The Earth can't escape the gravitational clutches of the sun because it's sitting in the sun's strong gravity well and can't climb out.
Time is not immune to the pull of gravity wells, either. So clocks close to strong gravitational sources run slower than clocks that are safely at a distance. This means that GPS satellites orbiting Earth tick away time faster than identical clocks on Earth.
(Curiously, Einstein's "other" or "special" relativity tells us that time slows down at the speeds the GPS satellites travel; however, the two effects do not exactly cancel out.)
Without general relativity, in other words, "GPS would fail," said physicist James Hartle, who directs the Institute for Theoretical Physics at UC Santa Barbara.
Of course, that's only general relativity's most obvious use. The theory also tells us that warped space-time bends light, so enormous concentrations of mass should act like lenses, forming images and distortions just like traditional lenses of glass or plastic.
Einstein thought the effect might never be seen, but today naturally occurring "gravity lenses" are the telescopes of choice for certain types of astronomy. Images of distant galaxies are bent into telltale, curved shapes, indicating that a lot of hidden, unseen matter lies between them and Earth. Such observations help measure the amount of matter in the universe.
Taken to extremes, general relativity produces such bizarre effects of severely warped space-time as black holes. Not so long ago black holes were nothing but a theoretical nightmare; today they are taken for granted, and a subject of intense scientific scrutiny.
"Black holes are no longer a theorist's dream," declared Hartle. "They have been detected."
As proof, he offered the work of UCLA astronomer Andrea Ghez, who has charted the orbits of stars around the black hole in our own Milky Way so convincingly that the hole almost seems visible.
And what good is a black hole, you ask? Of what conceivable use?
Looking to the distant future, there are wild ideas around for harnessing the energy of black holes--even using them for interstellar travel. These are highly speculative, to say the least.
More immediately, however, black holes promise to pay off big as pristine laboratories where fundamental physics can be explored in extreme conditions.
Of course, one can't travel into a black hole without getting crushed into oblivion. But that doesn't rule out riding into those dark recesses with the help of mathematics and imagination.
Using these tools, physicists have already established that the known laws of physics break down in the heart of black holes.
"That means we've got work to do," Ghez says. "It means we don't understand our physics."
It means, in other words, that black holes are almost surely portals to new physics, new understanding, new insights.
Who knows? They might even lead to a new generation of computers. Or something far more interesting still.