wow, what is the experiment?
Some theorists have suggested that gravity will behave differently at distances less than about one-five-hundredth of an inch. We're trying to test that hypothesis by looking at the gravitational force from a dense 4" diameter metal disk on a small pendulum as we move the
pendulumdisk towards and away from the diskpendulum.
wow! what would be the benefits of knowing whether or not gravity does behave differently at that small of a distance?
The short answer, in terms of practical applications, is we don't know yet--we'll let the engineers figure that out.
The long answer is that it would validate or invalidate proposed hypotheses, giving us a better picture of how the world actually works. Gravity is much weaker than the other forces between particles (electromagnetics and the forces responsible for nucleus cohesion and decay), and no one knows quite why. Our experiment could validate one hypothesis as to why it is. In some sense it would be a cultural achievement. What practical benefit is there from Sir Edmund Hillary reaching the peak of Mt. Everest, or from someone discovering a new species of animal, etc.?
Typically, practical application of scientific discoveries doesn't come for some time. Take Einstein's theory of relativity, for example. It's regarded as one of the greatest scientific breakthroughs in history, but now, a century after it was developed, the only current practical application I can think of for it is correction to the clocks on GPS satellites. That's pretty helpful, since GPS systems wouldn't work without it, but it's not indicative of the importance of the theory. It has enabled physics to progress and opened the development of other tested theories that have further enlarged our understanding of the world.
(I hope this isn't coming across as a rant. I do get this question just about every time I tell someone about our research, and I'm slowly figuring out better ways to answer it. Thanks for the interest!)
I can't take credit for the "cultural achievement" bit--I think I heard that from someone who'd heard Wolfgang Ketterle answer a question about what the benefit is to creating a Bose-Einstein condensate.