Between 1876 and 2002, the people of Lead, South Dakota, extracted $3.5 billion worth of gold from the Homestake mine. It was the town's main business, and when falling prices and diminishing returns finally shut it down, no one was sure what to do with the remaining 8,000-foot hole in the ground. Then, in 2007, the National Science Foundation decided that an 8,000-foot hole would be the perfect place to put its proposed Deep Underground Science and Engineering Laboratory, or DUSEL, a massive research complex that will include the world's deepest underground lab.
Now a team of physicists and former miners has converted Homestake's shipping warehouse into a new surface-level laboratory at the Sanford Underground Laboratory. They've painted the walls and baseboards white and added yellow floor lines to steer visitors around giant nitrogen tanks, locker-size computers and plastic-shrouded machine parts. Soon they will gather many of these components into the lab's clean room and combine them into LUX, the Large Underground Xenon dark-matter detector, which they will then lower halfway down the mine, where—if all goes well—it will eventually detect the presence of a few particles of dark matter, the as-yet-undetected invisible substance that may well be what holds the universe together.
The LUX project is just one of at least 10 efforts worldwide to find direct evidence of dark matter, and with a Nobel Prize and longer-term federal investment in play, the 50 researchers of LUX and 2,848 citizens of Lead (pronounced "leed") are pretty open about wanting to be first. But already there are problems.
For several hours now on this June afternoon, I've been watching through a window into the clean room as four physicists dressed in identical white Tyvek suits, latex gloves, blue booties, surgical masks and protective glasses prepare to connect two of the primary components of the detector. The inner cryostat is a hollow cylinder the size of a trash can that everyone refers to simply as "the can," and at the moment it is down below floor- level in a grate-covered pit. Hanging from a frame above the pit is the dome, which is a kind of lid for the can, and hanging from the dome itself is a complex assemblage called the skeleton. The idea is to carefully raise the can up around the skeleton, nesting one inside the other like a matryoska doll, until it connects with the dome cap, making a perfect seal.
The entire assemblage will eventually contain 31 gallons of –154°F liquid. xenon—the medium that will actually detect the dark matter— so precision is essential. But the various parts were machined at different sites, and without that perfect seal, air and impurities could infiltrate the experiment, potentially compromising the results. As Tom Shutt, a physicist at Case Western Reserve University and the co-founder of the LUX project, explains, "We've been on pins and needles to know how tight this can will be."
Before they lift the can, though, the team must complete the skeleton itself. Right now it consists of little more than six thin titanium straps hanging down from the inner rim of the dome. The next task is to insert the three thick disks that make up the bulk of the skeleton. One of the physicists, hand-operating a small forklift, raises one of the copper disks to waist-height, and the others adjust a temporary support that will hold it in place as they make final adjustments to bolt it to the titanium straps. This process continues for each of the three disks: Lift, tighten, adjust, confer, adjust.
The physicists work their way down the skeleton until finally they are on hands and knees, spinning bolts into the last copper slab, just about six inches from the floor. In slow succession, they sit back on their heels or stand up to observe their handiwork. Shutt, who was responsible for coordinating the fabrication of the can, is up next. He excuses himself and heads to the clean room's antechamber to suit up. (Common dust, the type one might drag in from anywhere, can have high levels of radioactivity that could obscure the signal if the detector does find dark matter.)
He is soon joined by an additional grad student, and the clean room is getting crowded. The six physicists wheel the skeleton-bearing frame to the side and open the pit's grate. One of them climbs down inside, connects two cables to the can, and scrambles out of the way. The cables are threaded through two pulleys on the frame, which the team slides back into place. They attach stacks of weights to the other ends of the cables, creating a simple elevator, and begin to slowly raise the can up and around the skeleton. Shutt stands to the side, his hands held palms out, fingers wiggling in anticipation like a kid waiting to open a gift.
Other scientists from the LUX project are gathering for the big moment—the moment when they will see if the can actually fits to form a functional detector—and I get elbowed over to the side window where the grad students have congregated. As the can nears the top, the murmurs die down. The skeleton is sliding perfectly into place. But, less than an inch from the dome, where the can should finally lock into place, it jams. Shutt and his team try to ease it up, and they try shoving it, but it just won't budge. The physicists suspect that the can's dimensions or the shape of the skeleton are off. Despite this apparent setback, they gamely pose for a few photos. Then they methodically lower the can back into the pit. They'll try again tomorrow.
No one knows what dark matter is, or if it even really exists. For now, it is just a placeholder, an x that must be plugged into various calculations in order to square astronomical observations with the rules of Newtonian physics. The name comes from Fritz Zwicky, a Swiss astronomer who in 1933 used two well-established methods to calculate the mass of the Coma cluster, a group of more than 1,000 galaxies. One calculation was extrapolated from the movement of eight galaxies in the cluster using Newton's second law of motion, which says, in essence, that the bigger the galaxy, the faster it spins. The other estimated the cluster's total mass by quantifying the amount of light given off by its stars.
The results should have been equal, but instead the movement-based number was an order of magnitude greater. The Coma galaxies were spinning much faster than would be predicted by the amount of overall light emitted. For the Newtonian equation to add up, there had to be more mass. Zwicky dubbed this missing bulk "dark matter."
Zwicky's work was largely ignored until 1970, when another astronomer, Vera Rubin, documented similar discrepancies in the Andromeda galaxy. Since then, researchers have found that the visible mass in hundreds of other galaxies is also too small to explain the rate of motion, at least within the context of our current understanding of physics. Astronomers have also discovered invisible "gravitational lenses" that cause light to bend around themselves—despite these lenses having no identifiable mass with which to distort the fabric of spacetime and bend light in the first place. All of this suggested that more than 80 percent of the matter in the universe was simply invisible to us.
Who's going to be the first to tell the author that a mile is 5,280ft, and that 4,850 isn't even a mile?
@shutterpod - he rounded off, you really don't have to be accurate for these things ;)
Which one of those guys is Gordon Freeman?
Whoops! Of course I know that a mile is 5,280 feet, not 2,580. I just forgot the crucial rule: coffee before writing headlines.
it says almost a mile, your ok! nice article def keep us posted.
Given that the Big Bang evidence now seems to point to a multiple non sequential bangs isn't it time to put Dark Matter in the pseudoscience section along with modified gravity laws etc. that propped up the Big Bang Theory.
The next Half-life installment should be set in Lead, South Dakota. Turns out dark matter is holding the universe AND Lead together.
It is always good to experiment to prove or disprove something - but I am tired of how every cosmology article is pushing dark matter relentlessly vs. the much more reasonable MOND theory.
This is like the last 3 decades of the (in my opinion) worthless string theory, academics like complicated improbably theories, and after many have invested their careers in it - they continue the tradition by becoming advisers to the next generation of grad students and the cycle repeats. Its some sort of theory peer pressure and momentum problem that resists change. There is also a huge "not invented here" component as well. (MOND is from Israel).
I think all articles need to start giving equal time to MOND - after all Ockham's razor suggests we should tend towards simpler theories, and MOND is just a long distance galactic tweak to Newton's laws of motions and fits everything perfectly (despite the endless attempts by the dark matter community to discount it and find contrived cases where it doesn't match the available data or assumptions). MOND may not be as "fun" since it is so easy - but "fun" should not be at the expense of the truth.
This is merely an opinion - in 20 years MOND will be king and dark matter a historical footnote in the annals of history - but to do so MOND requires more advocates in academia and the media since this unfortunately is partly a academic political and media popularity contest which has real implications on grant funding and numbers of those studying, verifying and refining the theory.
When will it finally be admitted that, although the proof of dark matter is exciting, the real reason for this unbelievable funding is for communications.....period. Once scientists can capture nutrinos as well as produce tou and muron nutrinos (the reason for the funding behind particle colliders) then dependence on satillites will be a thing of the past since nutrinos can pass through the planet as if it wasn't there.
I am Gordon Freeman... Any questions?
@ Gordon Freeman
I have a question. Do you take a crowbar down into that hole when you go? 'Cause I have a sneaking suspicion it will come in handy.
When will it finally be admitted that, although the proof of dark matter is exciting, the real reason for this unbelievable funding is for communications. <a href="http://www.istikbalnakliyat.com/" >evden eve nakliyat</a>
I found this article very humorous. Not only because of the reference to "Nerds looking for WIMPs", but because physicist want us to believe in something they think exists and are spending a lot of time and money trying to prove exists. Actually, I have no problem believing in things without physical proof, but it is ironic they usually can not do the same. Good luck.
What good is a clean room after it is filled with diamond and metal dust from all that grinding with the Dremel tool?