Wave–particle duality is frequently the first topic students encounter in elementary quantum
physics. Although this phenomenon has been demonstrated with photons, electrons, neutrons, and
atoms, the dual quantum character of the famous double-slit experiment can be best explained with
the largest and most classical objects, which are currently the fullerene molecules. The
soccer-ball-shaped carbon cages C60 are large, massive, and appealing objects for which it is clear
that they must behave like particles under ordinary circumstances. We present the results of a
multislit diffraction experiment with such objects to demonstrate their wave nature. The experiment
serves as the basis for a discussion of several quantum concepts such as coherence, randomness,
complementarity, and wave–particle duality. In particular, the effect of longitudinal ~spectral!
coherence can be demonstrated by a direct comparison of interferograms obtained with a thermal
beam and a velocity selected beam in close analogy to the usual two-slit experiments using light.