Two possible explanations for lack of observable neighbors are: 1) Any sufficiently advanced civilization will learn how to stimulate/entertain itself to the po

Two possible explanations for lack of observable neighbors are: 1) Any sufficiently advanced civilization will learn how to stimulate/entertain itself to the point of not needing external stimuli such as exploration and conquest. In other words, E.T. is too busy playing his holographic, neural-tapped X-Box to communicate or look for us. (E.M. Forrester's prophetic story, "The Machine Stops" foreshadowed this for mankind in 1909.) or possibility 2) A.I. and/or sentient life evolves into a higher-level, transdimensional abstraction beyond our perception and understanding (also known as the Singularity).