Everything about the ATLAS experiment is big.

Everything.

This massive particle collider, which serves as the key piece of machinery in the even more massive Large Hadron Collider in Geneva, Switzerland, is 148 feet long, 82 feet high and weighs 7,000 tons—approximately the same weight as the Eiffel Tower. Or one hundred Boeing 747s.

Designed to record and explore what happens when protons collide at nearly the speed of light, ATLAS will collect a staggering amount of data, too—enough to fill 100,000 data CDs per second, every second, or roughly equivalent to 50 billion phone calls being made at the same instant.

Even the team behind the development of the device is huge: In total, more than 2,000 people contributed from 37 different countries. More than 420 U.S. physicists, engineers, and graduate students hailing from 38 universities and four national laboratories were involved, including several physicists and graduate students from Penn. In fact, Penn has been a contributor to the project since Professor of Physics and Astronomy Brig Williams began working on it back in 1994.

And when the machine is turned on later this year, the discoveries it generates figure to be, scientists say, truly enormous. By slamming particies together millions of time each second, and then recording what happens in the explosions that ensue, ATLAS will give scientists a clearer picture than ever before of what happened in the earliest moments of the universe.

“With efforts at Penn since 1994, it’s been quite a while in the making,” says Penn Assistant Professor of Physics and Astronomy Evelyn Thomson, an ATLAS contributor. “The experiment should start running this year, and once it begins, it will probably run for much of the next decade. It’s going to run four to seven months a year, 24 hours a day, so it’s certainly a big project.”

Last month, ATLAS took a big step toward completion when the final pieces of the collider were lowered into the underground collision hall in Geneva. Once up and running, it will become the world’s most powerful particle accelerator, and should help the world scientific community answer some of the most fundamental questions about the universe. The work conducted there could, for instance, help scientists figure out where mass comes from, or what makes up the mysterious “dark matter” that, until now, has gone unidentified. The experiment may also explore extra dimensions of space or microscopic black holes. “We’re hoping, basically, to understand the fundamental nature of the universe,” says Thomson.

Maybe the most important answer to come out of the ATLAS project will be finding the origins and makeup for dark matter. Scientists know it exists. They just have no idea what it is.

“We recently found out, about 10 years ago, that all of the matter we know about—neutrons, protons, electrons, photons, etc.—only accounts for 5 percent of the energy in the universe,” Thomson says. “The other 95 percent, we don’t know what it is. Twenty-five percent of that appears to be dark matter. It doesn’t interact with light, but you can ‘see’ it because it has a gravitational effect.”

The Large Hadron Collider and ATLAS will help solve this mystery by, in effect, recreating conditions similar to what would have occurred after the Big Bang.

The experiment will work as follows: Protons will be accelerated in opposite directions inside the LHC, an underground circular tunnel nearly 17 miles in circumference, before crashing together in the center of the ATLAS detector. There, according to scientists, the collisions will create “tiny fireballs of primordial energy” that will be recorded by ATLAS and studied by scientists.

The massive machine will basically re-create the Big Bang 30 million times every second.

Scientists have some idea of what those tiny Big Bangs may reveal—but they’re not entirely sure, either. And that, Thomson says, is part of the excitement.

“In some ways we know what we’re looking for, and in some ways we don’t,” Thomson says. “But that may be interesting, too, because if we don’t find something that we’re looking for, we can rule those [theories] out and search for other things.”