explanations are inevitably framed partly in terms of things we do not observe directly: atoms and forces; the interiors of stars and the rotation of galaxies; the past and the future; the laws of nature. The deeper an explanation is, the more remote from immediate experience are the entities to which it must refer. But these entities are not fictional: on the contrary, they are part of the very fabric of reality.
Along with Einstein, Mach, and Lorentz in his belief in the things we cannot see being real parts of our reality—attempts to describe reality.
