What are the electronic structures of high-temperature superconductors at various points on their phase diagrams?[1] Can the transition temperature of high-temperature superconductors be brought up to room temperature?[1] Is Feynmanium the last chemical element that can physically exist? That is, what are the chemical consequences of having an element with an atomic number above 137, whose 1s electrons must travel faster than the speed of light?[1][2] Is Neutronium-4 possible? How can electromagnetic energy (photons) be efficiently converted to chemical energy?