“As the twentieth century continued to roar, the idea of information grew in status to an idea of global importance. Yet as the idea of information became more popular, we slowly began to forget about the physicality of information that had troubled Boltzmann. The word information became a synonym for the ethereal, the unphysical, the digital, the weightless, the immaterial. But information is physical. It is as physical as Boltzmann’s atoms or the energy they carry in their motion. Information is not tangible; it is not a solid or a fluid. It does not have its own particle either, but it is as physical as movement and temperature, which also do not have particles of their own.”