Everything we call real is made of things that cannot be regarded as real ~Niels Bohr This is the second part of a multi-part series on quantum mechanics. In part one,  I described and motivated particle-wave duality for light. I demonstrated that light waves are also particles (photons). But does this duality go the other way? Are particles like electrons also waves? As I hinted last time, the answer is yes. These are called matter waves, and their story is very interesting. The Mystery of the Emission Spectrum Last time, I discussed the emission spectrum of hydrogen, and the