Crystal Fire #3

Americans were latecomers to the quantum revolution. Europeans led the way in forming deeper and more fundamental insights about the quantum world. It was in the application of the new theoretical insights and experimental techniques that U.S. scientists excelled in the 1920s. They explored the internal structure and intrinsic properties of solids: color, hardness, conductivity, and so forth.

In the last quarter of the 19^th century, physicists became fascinated with cathode-ray tubes. In 1895 Roentgen discovered X-rays – so-called because he didn’t know what they were. X-rays excited the imagination, but much mystery about them remained. Were they waves or particles? Physicists searched for zebra-striped interference patterns like visible light produced. But if X-rays had wavelengths a thousand times shorter than visible light, any suitable diffraction grating would need spacing a thousand times smaller, less than a billionth of a meter. Nobody knew how to make such a fine grating. In 1912 two of Roentgen’s students found a wreath-like pattern of brights spots against a dark background directing X-ray beams onto a crystal of copper sulfate. Other crystals produced similar patterns. Max von Laue thought the interference patterns were caused by a three-dimensional lattice of objects within the crystals. William Henry Bragg and his son extended von Laue’s insights. All three received a Nobel Prize for their work.

Scientists could then peer inside crystals, where the atoms appeared to be arranged in layers, like eggs stacked in crates.

Physicists began to recognize the conductivity of metals had something to do with the availability of electrons within them. An excellent conductor like copper has plenty of free electrons. Good insulators, like glass or wood, have essentially none.

Chapter 3 has more about other discoveries in physics, such as Rutherford’s discoveries of the inner structure of atoms and Schröedinger’s wave equation. I will skip the details to stick to the main story of the book and avoid possible errors trying to summarize it.

Practical-minded Americans like Walter Brattain had little interest in the airy philosophical debates such as occurred between Niels Bohr and Albert Einstein. They were busy applying the new quantum tools to their study of matter. Plenty of unsolved problems about the nature and structure of atoms, molecules, metals, and crystals awaited exploration with the new methods.