Pursuing those questions that keep my up at night (or keep me occupied when I'm up at night) - Is the universe, at it's most fundamental level, Analogue or Digital?
By which I mean, if the universe is analogue there are infinite subdivisions that can be applied to it - colors, heat, mass, all can be measured more and more precisely without hope of ever coming to an end. There is, then, an infinite possiblity of nuance, and the universe would then have to be considered to be a wave - or a complex pattern or interference of waves.
However, if the universe is digital everything at some fundamental level can be measured exactly, and that's the bottom of it. The mechanics of this in physics are known as "Quantum", however it should be noted that they have subdivided the atom into 6 varieties of quarks, and there are even more subdivisions that go farther still. So "Quantum Mechanics" describes a level of physics, but an intermediate level (albeit very small) between other levels that use waves to describe their properties.
Light is both a particle and a wave - see Wikipedia yet again for clarification. This explanation, however, while pandering to both possibilities raises more questions than it answers. If you've read the Wiki you'll understand.
Then there is always the possibility that the question is invalid - it is, after all, the universe, and there may be more than these 3 possibilities...