The biggest physics experiment in history started up early this morning. At 4:27 A.M. eastern time, two proton beams made their first laps around the 27-kilometer tunnel of the Large Hadron Collider (LHC) outside Geneva. By late fall, once the behemoth has gotten warmed up, physicists at CERN hope to achieve particle collisions with an energy of five trillion electron volts; eventually, they’ll bump it up to seven trillion. As Nobel laureate and MIT Institute Professor Jerome Friedman wrote in our May/June issue, these collisions should help answer some of physics’s most fundamental questions: Why do particles have mass? Are there spatial dimensions beyond the ones we know? There will also likely be some surprises, if history is a guide.

But today’s switch-on, though momentous, was only the first step–what the New York Times this morning compared to turning on a car engine for the first time. That’s because this car needs to rev particles to near the speed of light, at temperatures near absolute zero. For a look at the immense and gorgeous inner workings of the accelerator, see our photo essay.