Time paradox (temporal paradox) - a paradoxical situation resulting from time-traveling in the opposite direction, as a result of any actions in the past such a journey can not be undertaken.
typical example is the grandfather paradox, when the hero, traveling back in time and kills his grandfather before he has time to conceive of his father. This is a paradox, because killing his grandfather, the hero prevents his own birth and thus prevents a journey through time, preventing his birth.
Different schools of thought in different ways considering how it will be resolved grandfather paradox, if a time machine yet invented. The essence of this hypothesis is that the time traveler can not simply create a paradox, because the natural flow of time did not allow him that. For example, it will appear in the wrong place and do not do anything, or he was prevented from various twists of fate, or even he himself unwittingly, to restore the course of events in the form in which they are remembered. This, incidentally, creates another paradox - the paradox of predestination, it - time loop where time travelers destined to travel in time and there to make some actions that have already occurred. Usually these actions necessitate travel in the future, an example is a call to itself.
A similar theory says that time travel is responsible for how the world is today, that is, actions of travelers in the past influence the present. On the other hand, in this case, travelers will seek to engage with the past as little as possible for fear of the consequences.