Predestination paradox

A predestination paradox, also called a causality loop, is a paradox of time travel. The idea is that when one travels back in time, one may influence events while in the past, such as causing, or undoing, the original reasons for the journey.

Suppose a man travels back in time and impregnates his great-great grandmother. The grandmother would thus give birth to one of the man's great grandparents, who would then give birth to his grandmother or father, who would then be able to give birth to one of the man's parents, and finally to the man himself. As a result, the man's very existence would be pre-determined by his time traveling adventure, and therein lies the paradox.

The Predestination paradox is very closely related to the Grandfather paradox.

One of the possible examples of this paradox is the death of Edith Keeler: if Doctor McCoy does not travel back in time accidentally and change the timeline by saving her, Captain Kirk does not follow him, does not fall in love with Keeler and does not leave her in the way of that certain truck.

The possibility remains, however, that the vehicle originally striking Keeler was different from the one that eventually did via Kirk and McCoy's interventions.

In order to stop him making advances on her, Beverly Crusher told Berlinghoff Rasmussen that she could be his great-great-great-great grandmother. (TNG: "A Matter of Time")

The Temporal Investigations agents Dulmur and Lucsly hated predestination paradoxes. (DS9: "Trials and Tribble-ations")

References

• TOS: "The City on the Edge of Forever"
• DS9: "Trials and Tribble-ations"
• VOY: "Relativity"
• Template:STA

See also:

• TNG: "Cause and Effect"
• VOY: "Future's End"