Nostalgia, underlying cosmological explanation for Weak but detectable interaction between two neighboring universes that are otherwise not causally connected. Manifests itself in humans as a feeling of missing a place one has never been, a place very much like one's home universe, or as a longing for versions of one's self that one will never, and can never know.

How to Live Safely in a Science Fictional Universe (Enhanced Edition): A Novel (ed. Knopf, 2010) - ISBN: 9780307379887