- Welcome to 1942!
- The Third-Reich is the dominant world power.
- Ancient Meteorite Revealed To Be Burnt Burger
- Cure For Senility Found, But Lost Before Being Recorded
- Japenese offensive on front lines a failure, thousands dead!
- This Space For Rent
- Moscow falls to the Reich!
- Timmy Falls Down Well, Climbing Needs Work
- Führer said to be in good health
Causal loopA causal loop is a paradox of time travel that occurs when a future event is the cause of a past event, which in turn is the cause of the future event. Both events then exist in spacetime, but their origin cannot be determined. A causal loop may involve an event, a person or object, or information. The terms boot-strap paradox, predestination paradox or ontological paradox are sometimes used in fiction to refer to a causal loop.
Grandfather paradoxThe consistency paradox or grandfather paradox occurs when the past is changed in any way, thus creating a contradiction. A time traveler can do anything that did happen, but can't do anything that didn't happen. Doing something that didn't happen results in a contradiction. Consistency paradoxes occur whenever changing the past is possible.
Fermi paradoxThe Fermi paradox can be adapted for time travel, and phrased "if time travel were possible, where are all the visitors from the future?" Answers vary, from time travel not being possible, to the possibility that visitors from the future can not reach any arbitrary point in the past, or that they disguise themselves to avoid detection.
According to the philosophical theory of compossibility, what can happen, for example in the context of time travel, must be weighed against the context of everything relating to the situation. If the past is a certain way, it's not possible for it to be any other way. What can happen when a time traveler visits the past is limited to what did happen, in order to prevent logical contradictions.