reality
Out of time: variations on alternate history

"How to time travel" by greywulf
Wikipedia resources
Alternate history or alternative history is a subgenre of speculative fiction (or some would say of science fiction) that is set in a world in which history has diverged from history as it is generally known. Alternate history literature asks the question, "What if history had developed differently?"
Virtual history, also referred to as counterfactual history, is a form of history which attempts to answer "what if" questions. It seeks to explore history and historical processes from the point of view of extrapolating a position in which certain key historical events did not happen or had an outcome which was different to that which did in fact occur.
Uchronia refers to a hypothetical time period of our world, in contrast to fictional lands or worlds. A concept similar to alternate history but different in the manner that uchronic times are not easily defined (mainly placed in some distant point near prehistory)
Parallel universe or alternate reality in science fiction and fantasy is a self-contained separate reality coexisting with our own. This separate reality can range in size from a small geographic region to an entire new universe, or several universes forming a multiverse.
Steampunk is a subgenre of speculative fiction which came into prominence in the 1980s and early 1990s. It concerns works set in the past, or a world resembling the past, in which modern technological paradigms occurred earlier in history, but were accomplished via the science already present in that time period.
Invasion literature (or the invasion novel) was a historical literary genre most notable between 1871 and the First World War (1914). The genre first became recognizable starting in England in 1871 with the short story The Battle of Dorking, a fictional account of an invasion of England by Germany.
Misery and suffering
"I believe that as a species, human beings define their reality through misery and suffering."
-- Agent Smith, in The Matrix
Douglas Adams and reality
"The fact that we live at the bottom of a deep gravity well, on the surface of a gas covered planet going around a nuclear fireball 90 million miles away and think this to be normal is obviously some indication of how skewed our perspective tends to be."
-- Douglas Adams
Williams and reality
"Reality...what a concept!"
-- Robin Williams
Lennon and reality
"Reality leaves a lot to the imagination."
-- John Lennon
Einstein and reality
"Reality is merely an illusion, albeit a very persistent one."
-- Albert Einstein
Freud and reality
"Illusions commend themselves to us because they save us pain and allow us to enjoy pleasure instead. We must therefore accept it without complaint when they sometimes collide with a bit of reality against which they are dashed to pieces."
-- Sigmund Freud