Novikov self-consistency principle
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The Novikov self-consistency principle, also known as the Novikov self-consistency conjecture, is a principle developed by Dr. Igor D. Novikov in the mid-1980s to solve the problem of paradoxes in time travel.
Stated simply, the Novikov consistency principle says that if an event exists that would give rise to a paradox, then the probability of that event happening is zero. Rather than consider the usual models for such a paradox, such as the grandfather paradox in which a time-traveller kills his own grandfather and prevents his own birth, Novikov used a mechanistic model which was more amenable to mathematics; a billiard ball being fired into a wormhole in such a way that it would go back in time and collide with its earlier self, thereby knocking it off course and preventing it from entering the wormhole in the first place.
Novikov found that there were many trajectories that could result from the same initial conditions. For example, the billiard ball could knock itself only slightly astray, resulting in its going into the past slightly off course, which winds up causing it to knock its past self only slightly astray; this "sequence" of events (actually a causal loop) is completely consistent and does not result in a paradox. Novikov found that the probability of such consistent events was nonzero, and the probability of inconsistent events was zero, so no matter what a time traveller might try to do he will always end up accomplishing consistent non-paradoxical actions.
In another example, let us examine the following situation: A person travels back in time to discover the cause of a famous fire. While in the building where the fire started, he or she accidentally knocks over a kerosene lantern and causes a fire, the same fire that would inspire him or her, years later, to travel back in time. This situation is entirely consistent -- after travelling back in time the person "fulfills" the events in the "past" which "already happened" (from the perspective of the future). In this example the person lacked free will -- it is impossible for him or her not to have set off the fire -- that would be inconsistent. Even if the person somehow knew that this would happen, he or she would be somehow bound to "follow" history by the self-consistency principle. Note that there are other equally plausible series of events for this case. For example, the fire could have never happened, and the person would then never travel back in time to discover its cause and make it happen. This is also entirely consistent. Thus we see that under this principle that may be many valid "solutions" to the same initial conditions.
Time loop logic is an application of this principle to (hypothetical) computers capable of sending information back through time.
The Novikov consistency principle assumes certain conditions about what sort of time travel is possible. Specifically, it assumes counterfactual definiteness which is the assertion that there is only one timeline and that multiple alternative timelines do not exist or are not accessible.
Some consider the Novikov self-consistency principle merely as a tautology, i.e., as a principle that cannot be false and does not need a justification.
See also
External links
- Notion of the Past & Can We Change It? - speech by Novikov
- From wormhole to time machine: Comments on Hawking's Chronology Protection Conjecture, which also addresses the Novikov self-consistency principle
- Einstein Physics prevent paradoxial time travel
- Blinovitch Limitation Effect - a pseudoscientific principle from the television series Doctor Who that sounds suspiciously similar to the Novikov self-consistency principlefr:Principe de cohérence de Novikov