April 26, 2011
It was a rainy Friday evening on campus. There was no free beer and no free t-shirts. And yet, a large and curious crowd braved the weather to hear Physics professor Mark Kruse explain the origins of the universe.
As it turns out, it’s been 14 billion years since the Big Bang and we still don’t know what went down.
“All the really interesting stuff happened less than a billionth of a second after the Big Bang,” Kruse said. The observable universe was 100 million km across (one thousand-trillionth its current size), with a toasty temperature of almost a million trillion degrees C.
“There were a lot of remarkable events going on during that first billionth of a second that we don’t fully understand and, without which, we wouldn’t be here,” Kruse said. That’s where the Large Hadron Collider comes in.
The Large Hadron Collider (LHC) near Geneva, Switzerland, is the world’s largest particle accelerator. In operation since early 2010, it uses electric fields to fling opposing beams of protons around a circular track until they reach 99.999999% the speed of light. When two protons collide (40 million times each second), a detector records the resulting debris of particles. These high-energy collisions approximate conditions found just after the Big Bang.
“If particles have more energy, then when you collide them, more things can happen,” Kruse said. “It’s like colliding two marbles together and getting two bowling balls. The energy of the collision is so great that it can create particles much more massive than the original particles.”
When these particles interact with a detector, they leave a little bit of energy behind. This energy acts like a signature, because different types of particles leave energy in different ways. According to Kruse, it’s like rolling various objects in the sand: you can identify an item by its tracks. A tennis ball doesn’t leave the same mark as a tennis shoe, and it’s the same for particles. Who knew?
Duke’s High Energy Physics Group is involved with the ATLAS detector, a 5-story-tall piece of machinery that weighs 7,000 tons (14 million pounds). Some of its components were built right here at Duke.
3,000 kilometers of cable connect the detector’s components to computers that analyze data from particle collisions. The detector produces several petabytes of data each year. For comparison, one petabyte equals 20 million four-drawer filing cabinets filled with text, or nearly all the photos on Facebook. Computer algorithms help scientists sort through this tremendous stack of data, but it’s still a lengthy process.
“For analysis of rare processes, we must find the signal events -- sometimes only produced every trillion or so collisions -- that decay instantly into a cascade of other particles and which look like several other processes that are produced orders of magnitude more frequently.” In other words, it’s difficult. New discoveries come only after all other possibilities have been excluded. However, “we’re really preparing ourselves to discover something new,” Kruse said.
Duke’s ATLAS team hopes to answer some of the weightiest question in science: What is the origin of mass? What is dark matter, and how can we detect it? Does the Higgs-boson particle exist? Most importantly, why are we here?
“You and everyone around you are intimately related to the questions we’re trying to answer at the Large Hadron Collider,” Kruse said. “If you’re trying to look at your ancestry and figure out where you came from... this is it. In some ways, the LHC is the ultimate ancestry.com.”
To learn more, see this TED Talk by Brian Cox.
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