Ontological Paradox

An ontological paradox is a paradox of time travel that questions the existence and creation of information and objects that travel in time. It is very closely related to the predestination paradox and usually occurs at the same time. In simpler terms, an object is brought back in time, and it becomes the object that was initially brought back in time in the first place.

Definition

Because of the possibility of influencing the past while time traveling, one way of explaining why history does not change is by saying that whatever has happened was meant to happen. A time traveler attempting to alter the past in this model, intentionally or not, would only be fulfilling his role in creating history, not changing it. The Novikov self-consistency principle proposes that contradictory causal loops cannot form, but that consistent ones can. This theory, however, only makes sense if you're dealing with a wormhole or some other form of time travel where you end up in the same universe as you started. With actual time replication, which is what much of fiction calls "time travel" this could not be the case.

However, a scenario can occur where items or information are passed from the future to the past, which then become the same items or information that are subsequently passed back. This not only creates a loop, but a situation where these items have no discernible origin. Physical items are even more problematic than pieces of information, since they should ordinarily age and increase in entropy according to the Second law of thermodynamics. But if they age by any nonzero amount at each cycle, they cannot be the same item to be sent back in time, creating a contradiction.

The paradox raises the ontological questions of where, when and by whom the items were created or the information derived. Time loop logic operates on similar principles, sending the solutions to computation problems back in time to be checked for correctness without ever being computed "originally."

It is sometimes called the bootstrap paradox, in reference to the expression "pulling yourself up by your bootstraps", and the term was popularized by Robert A. Heinlein's story By His Bootstraps