It is the gauge boson -- the force carrier -- for electromagnetism. It has no mass, no electric charge no weak charge, no color charge. It is the epitome of almost nothing at all. And yet everything we do in our everyday lives, from moving a mouse to running in the park relies on its mediation. It is just one of the many remarkable objects described in this series. Is it a force or is it matter? Find out in track 9 below, but don't skip the first eight to get to it, you might miss something important.