Leah Burrows

After two-years of upgrades and repairs, the Large Hadron Collider is back in the particle-smashing business—this time at double the energy of its first run.

Here’s the rub with friction: scientists don’t really know how it works. Sure, humans have been harnessing the power of friction since rubbing two sticks together to build a fire, but the physics of friction remains largely in the dark.