(Describer) In an animation, streams of light collide to create a globe filled with water. Title: Science Nation.

(Describer) A man pulls on coveralls, which he tucks into laced boots.

(male narrator) Physicist Dan McKinsey is suiting up to go deep...

(Describer) He goes down in an industrial elevator.

seriously deep, nearly a mile straight down an old mine shaft at the Sanford Underground Research Facility in Lead, South Dakota.

[elevator clunks]

(Describer) At the bottom, he rinses off the boots.

(narrator) He's not down here mining for gold, but for dark matter. With support from the National Science Foundation, McKinsey and a team of scientists from across the U.S. and Europe are hard at work on the large, underground xenon experiment, or LUX. So, dark matter would be something like 85% of the total amount of matter in the universe.

(Describer) Animated clouds turn around light.

(narrator) Dark matter is a scientific mystery. We can't see it or touch it, but physicists like McKinsey theorize it must exist, because without it the universe would look quite different.

(male) Dark matter is what causes things to clump gravitationally. Without dark matter, you wouldn't get galaxies and stars at the rate we do, and you and I probably wouldn't exist.

(narrator) The LUX experiment is designed to snare one possible type of dark matter: the WIMP, or...

(male) It would have been produced in enormous amounts in the Big Bang and would still be around in the right amount to be the dark matter.

(narrator) WIMPs actually aren't scarce. Theory holds they are everywhere, all around us all the time.

(Describer) Crowds move through a train station.

(male) It's not so different from thinking about there's radio waves going around us constantly, there's radiation from your cell phone going around us, lots of things we don't see with our eyes, but you can pick up with the right instruments.

(narrator) So why build LUX in an abandoned gold mine?

(Describer) A huge cylinder is built in fast-motion.

Physicists say WIMPs are hard to distinguish from ordinary background cosmic radiation. The mile of rock filters much of that out.

(Describer) Pipes bend around the finished structure.

The LUX instruments are sealed up inside this big water tank, which houses an inner vessel filled with liquid xenon.

(male) The xenon is sort of a magic potion for detecting WIMPs. It has all the right properties.

(narrator) The idea is to detect a WIMP hitting a liquid xenon atom head-on, creating a flash of light that would be picked up by sensors inside the liquid xenon vessel.

(Describer) They're round reflective disks.

(male) So with LUX we have the right kind of instrument to detect these WIMPs.

(narrator) The experiment has been running since 2013, and so far, they're still looking. McKinsey is optimistic. He says they have to keep pushing.

(male) This is what science is about. Science is about discovering new things. So, it's very exciting to be in a position where you have a chance of really discovering a fundamentally new thing about the universe. You know, we have that opportunity.

(narrator) So, it's back to the surface.

(Describer) The elevator door is closed.

When it comes to the search for WIMPs, the LUX team is confident they're sitting on a gold mine.

(Describer) A globe turns beside the title.

For Science Nation, I'm Miles O'Brien.