Another resolution, of which the Novikov self-consistency principle can be taken as an example, holds that, if one were to travel back in time, the laws of nature or other intervening cause, would simply forbid the traveller from doing anything that could later result in their time travel not occurring. For example, a shot fired at the traveler's grandfather will miss, or the gun will jam, or misfire, or some other event will occur to prevent the attempt from succeeding. In effect, the traveller will be unable to change history, because for him it has already occurred.

Normally, in fiction, the time traveller does not merely fail to prevent the actions he seeks to prevent; he accidentally precipiates them. The oldest form of this may be the numerous folk tales involving prophecies -- where in the time travel is of information -- such as Oedipus Rex, wherein the very actions undertaken to thwart the decree of the prophecy bring it about: Cronus' swallowing of his children to prevent their usurping his power is what encouraged Zeus to overthrow him, and Oedipus's being abandoned led him to meet his mother without being aware of her presence.

This theory might lead to concerns about the existence of free will (in this model, free will may be an illusion). This theory also assumes that causality must be constant: i.e. that nothing can occur in the absence of cause, whereas some theories hold that an event may remain constant even if its initial cause was subsequently eliminated. It is also possible that the time travelers' intended action might be completed, but never successfully enough to result in cancellation—see Novikov self-consistency principle.

This premise was shown in the beginning of the 2002 movie version of The Time Machine, in which the main character cannot save his girlfriend by going back in time, as he only started building the time machine out of frustration of her death. This loop is not present in the original book. Likewise, in the film 12 Monkeys, the main character not only is unable to prevent a tragic past event from occurring, but even realizes that, as a child, he witnessed his adult self failing in the attempt.

Douglas Adams's Hitchhiker's Series and Harry Harrison's Technicolor Time Machine make use of this resolution for light-hearted and comic plots.

Closely related but distinct is the notion of the time line as self-healing. The time-traveler's actions are like throwing a stone in a large lake; the ripples spread, but are soon swamped by the effect of the existing waves. For instance, a time traveler could assassinate a politican who led his country into a disastrous war, but the politician's followers would then use his murder as a pretext for the war, and the emotional effect of that would cancel out the loss of the politican's charisma.

It also may not be clear whether the time traveler altered the past or precipitated the future he remembers, such as a time traveler who goes back in time to persuade an artist -- whose single surviving work is famous -- to hide the rest of the works to protect them. If, on returning to his time, he finds that these works are now well-known, he knows he has changed the past. On the other hand, he may return to a future exactly as he remembers, except that a week after his return, the works are found. Were they actually destroyed, as he believed when he traveled in time, and he has preserved them? Or was their disappearance occasioned by the artist's hiding them at his urging, and the skill with which they were hidden, and so the long time to find them, stemmed from his urgency?

Some science fiction stories suggest that causing any paradox will cause immense damage to, or the destruction of, everything the time traveller has ever affected in any way, which may be as wide-ranging as the entire universe. The plots of such stories tend to revolve around preventing paradoxes.

In Back to the Future Part II, it was speculated by Doc Brown that "the encounter could create a time paradox, the results of which could cause a chain reaction that would unravel the very fabric of the space-time continuum and destroy the entire universe! Granted, that's a worst-case scenario. The destruction might, in fact, be very localized, limited merely to our own galaxy". However, it must be noted that this is not the method of resolution in the Back to the Future trilogy for all time-travel paradoxes.

The 2005 Doctor Who series episode Father's Day provided a unique version of the destruction resolution. A paradox causes a wound in space-time, which attracts flying carnivorous monsters, Reapers. The Reapers act like bacteria around a real wound, devouring everything, starting with the youngest people and objects, until the wound is "sterilized" and the paradox resolved by its destruction.

In Stephen King's short story The Langoliers, a group of travelers pass through a strange time portal and end up in the past. Just when they realize what has happened to them, they see that the entire world around them is being eaten up by the Langoliers, strange creatures with razor sharp teeth devouring everything in their path, including the land and sky, as if somehow the past needs to be cleaned up to allow the future to continue properly.

In the 2001 film Donnie Darko, a rift in spacetime is created when a jet engine lands on the title character's house approximately 28 days before the plane carrying it flies over. This creates an unstable parallel (or tangent) universe which will cease to exist at the end of those 28 days if the engine is not returned to the primary universe. The laws of nature in the parallel universe are roughly the same, except characters and events close to the time portal are "manipulated" to return the engine to the primary universe before the parallel universe collapses on itself and becomes a blackhole of spacetime. If the portal were still open when this happened, it would destroy the primary universe and all of spacetime. How this works is never explained, but implies the idea of some universal defense mechanism.

One of the main assumptions of the grandfather paradox is that causality is an active physical force which can "follow" a time-traveller back through time. But it may very well be that this is not the case. In other words, if you traveled back to the year 1970 to kill your parents and prevent your birth in 1971, you would not disappear from history, because simply by travelling back to the year 1970, you would have established that you already existed in your adult form, complete with memories, in the year 1970. In effect, you would have prevented nothing but a redundant, younger copy of yourself from co-existing with you. Going back in time to prevent the premature existence of yourself would likewise only push back the time at which the existence of yourself was historically established.

Of course, while this would negate the grandfather paradox itself, it says nothing about other changes made to the timeline (for example: what if you killed someone else's parents?), and may assume a separation between the individual's timeline and the "main" timeline of the rest of the universe, essentially resulting in its own paradox -- that the lack of causality as an active force that affects the individual separately from the rest of reality in itself requires that causality be an active force that affects the individual separately from the rest of reality.

Questions like these lead some back to the simpler idea that time travel is by its very nature paradoxical and therefore logically impossible, on the same order as round squares and portable holes -- or at least, impossible under any of the conditions in which human life is thought to be able to exist.

These same questions also led Kurt Gödel to assert that the possibility of time travel would imply that time itself doesn't exist.