Answer · confidence: partial
Does "messages can't change the past" really follow from how scientists explain time loops?
Research question: Does the idea that a message cannot change its own past, only fit with what already happened, actually follow from the self-consistency idea physicists use for loops?
The records show that the Novikov principle is tied to the claim that the past cannot be changed: the 1990 authors concluded that intelligent beings cannot change the past because such a change conflicts with self-consistency 518. The records do not show that this follows as a strict logical consequence, since taken alone the consistency constraint could be dismissed as a tautology and the principle adds a substantive assumption that local physics stays the same 7. Self-consistency is also not guaranteed for every body, as it may fail for extended objects such as gyroscopes 31, and a 2020 analysis found that the constraint does not uniquely determine one loop path 26. Critics such as Visser regard the principle as an ad hoc solution 6, and the facts do not address messages specifically. The newest fact is from 2025 16, about a year old as of October 2026.
Checked 2026-10-21. Only documented and supported facts are used.
Dig deeper on this questionSources
[1] supported
Novikov's self-consistency principle holds that anything a time traveler does in the past must already have been part of history, and the traveler cannot prevent their own trip back in time because that would be an inconsistency.
"Anything a time traveler does in the past must have been part of history all along, and the time traveler can never do anything to prevent the trip back in time from happening, since this would represent an inconsistency."Temporal paradox
[2] supported
The Novikov principle says any event that would cause a paradox or any change to the past has probability zero, so time paradoxes are impossible.
"The principle asserts that if an event exists that would cause a paradox or any "change" to the past whatsoever, then the probability of that event is zero."Novikov self-consistency principle
[3] supported
Some philosophers and scientists think time travel into the past need not be logically impossible as long as the past cannot be changed, and the Novikov self-consistency principle is cited as one such view.
"some philosophers and scientists believe that time travel into the past need not be logically impossible provided that there is no possibility of changing the past, [ 16 ] as suggested, for example, by the Novikov self-consistency principle"Temporal paradox
[4] supported
The 1990 authors stated the principle as requiring that only globally self-consistent solutions of physical laws can occur locally in the real Universe.
"We shall embody this viewpoint in a principle of self-consistency, which states that the only solutions to the laws of physics that can occur locally in the real Universe are those which are globally self-consistent."Novikov self-consistency principle
[5] supported
The authors concluded that intelligent beings cannot change the past, because such a change is incompatible with the principle of self-consistency.
"It certainly will imply that intelligent beings cannot change the past. Such change is incompatible with the principle of self-consistency."Novikov self-consistency principle
[6] supported
Novikov's views on self-consistency are not widely accepted, and critics such as Visser regard causal loops and the principle as an ad hoc solution.
"Novikov's views are not widely accepted. Visser views causal loops and Novikov's self-consistency principle as an ad hoc solution"Temporal paradox
[7] supported
Taken alone, the consistency constraint could be dismissed as a tautology, but the principle is meant to add a substantive assumption that local physics stays the same when time travel occurs.
"Given these assumptions, the constraint that time travel must not lead to inconsistent outcomes could be seen merely as a tautology , a self-evident truth that cannot possibly be false."Novikov self-consistency principle
[8] supported
In the simplified form, the Novikov self-consistency principle says that when someone travels to the past, the probability of acting in a way that changes an event that already happened to that traveler is close to zero.
"В упрощённой формулировке принцип самосогласованности постулирует, что при перемещении в прошлое вероятность действия, изменяющего уже случившееся с путешественником событие, будет близка к нулю."Принцип самосогласованности Новикова
[9] supported
Igor Novikov formulated the Novikov self-consistency principle in the mid-1980s, and it is said to resolve paradoxes tied to time travel that some Einstein field equation solutions theoretically allow.
"В середине 1980-х годов сформулировал принцип самосогласованности Новикова , разрешающий парадоксы , связанные с путешествиями во времени , теоретически допускаемыми некоторыми решениями уравнений Эйнштейна ."Новиков, Игорь Дмитриевич
[10] supported
Zeldovich and Novikov first mentioned the idea in the scientific literature in 1975, arguing that closed timelike curves need not lead to violations of causality, because events on such a curve can affect each other in a closed loop and be self-consistent.
"Впервые в научной литературе об этой идее упоминают Я. Б. Зельдович и И. Д. Новиков в 1975 году [ 5 ] , высказывая мнение о том, что существование замкнутых времениподобных линий не обязательно приводит к нарушению принципа причинности ."Принцип самосогласованности Новикова
[11] supported
The Novikov self-consistency principle is described as an important contribution to the theory of time travel.
"В середине 1980-х годов сформулировал принцип самосогласованности Новикова , явившийся важным вкладом в теорию путешествий во времени ."Новиков, Игорь Дмитриевич
[12] supported
The principle's rigorous formulation, in which only globally self-consistent solutions can occur locally in the real Universe, was given in 1990, as opposed to the simpler version used for the time-travel intuition.
"строгую формулировку принцип получил лишь в 1990 году"Принцип самосогласованности Новикова
[13] supported
Deutsch's D-CTC model assigns a definite form to the state of the chronology-violating system, while the postselected teleportation P-CTC model does not.
"D-CTCs assign a definite form to the state on this system, while P-CTCs do not."Quantum state tomography on closed timelike curves using weak measurements (2025)
[14] supported
The formal principle states that among all models allowed by known physical laws, only those that are globally self-consistent can exist locally in our Universe.
"который постулирует, что из всех возможных моделей, допускаемых известными законами физики, в нашей Вселенной локально могут существовать только те, которые глобально самосогласованы."Принцип самосогласованности Новикова
[15] supported
The consistency requirement is that the reduced state r must match across the CTC, meaning r has to satisfy a specific relation in every run of the experiment.
"r havetomatch,thatis,r hastosatisfyrelation(1)."Experimental simulation of closed timelike curves (2014)
[16] supported
The paper argues that, for any chronology-respecting input and unitary interaction, the unique state on the P-CTC can always be recovered.
"We show that, for any given combination of chronology-respecting input and unitary interaction, it is always possible to recover the unique state on the P-CTC"Quantum state tomography on closed timelike curves using weak measurements (2025)
[17] supported
Novikov's self-consistency principle is one of the classical proposals for reconciling closed timelike curves with physics, alongside Hawking's chronology protection conjecture.
"numerousefforts,suchasNovikov’sself-consistencyprinciple4to"Experimental simulation of closed timelike curves (2014)
[18] supported
The idea that the past cannot be changed is formalized in physics as the Novikov self-consistency principle, named after Russian physicist Igor Dmitriyevich Novikov.
"but in physics, it's known as the Novikov self-consistency principle, after Russian physicist Igor Dmitriyevich Novikov."Time Travel, Without the Pesky Paradoxes - Universe Today
[19] supported
In simplified form, Novikov's self-consistency principle postulates that when traveling into the past, the probability of an action that changes an event already experienced by the traveler tends to zero.
"В упрощённой форме он постулирует, что при перемещении в прошлое вероятность действия, изменяющего уже случившееся с путешественником событие, стремится к нулю."Причинно-следственная петля
[20] supported
The document states the principle of self-consistency as the requirement that only physical solutions which are globally self-consistent can occur locally in the real Universe.
"the only solutions to the laws of physics that can occur locally in the real Universe are those which are globally self-consis"Motion of a gyroscope on a closed timelike curve
[21] supported
The Novikov self-consistency conjecture says that only physical solutions that are globally self-consistent can occur locally in the real universe.
"the only solutions to the laws of physics that can occur locally in the real universe are those which are globally self-consistent"Lectures on Faster-than-Light Travel and Time Travel
[22] supported
Novikov's principle holds that closed causal loops may not violate the principle of causality, so they are hypothetically possible.
"Принцип самосогласованности Новикова утверждает, что существование причинных петель может не нарушать принцип причинности , то есть гипотетически возможно."Причинно-следственная петля
[23] supported
Lewis's reasoning in the grandfather paradox is that events must be compatible with all other relevant facts.
"His argument is essentially that events must be compatible with all other relevant facts."Motion of a gyroscope on a closed timelike curve
[24] supported
The self-consistency principle states that only solutions to the laws of physics that are globally self-consistent can occur locally in the real Universe.
"Мы формулируем эту точку зрения в виде принципа самосогласованности, который постулирует, что из всех возможных моделей, допускаемых известными законами физики, в нашей Вселенной локально могут существовать только те, которые глобально самосогласованы."Причинно-следственная петля
[25] supported
Lewis's central point is that time travel should be admitted provided it does not produce two events that are incompatible with each other.
"Lewis’s central point is that the possibility of time travel should be admitted, provided it does not lead to incon- sistencies in the shape of the occurrence of two events which are not compatible."Motion of a gyroscope on a closed timelike curve
[26] supported
The 2020 paper by Tobar and Costa found that a closed timelike curve's constraint does not uniquely determine one path, because there are multiple ways to form the loop, leaving room for choice.
"They found that CTCs allow for complex systems because the constraint of a time loop doesn't uniquely define a single path."Time Travel, Without the Pesky Paradoxes - Universe Today
[27] supported
A consistency paradox is any situation where changing the past removes the conditions that allowed or required changing the past in the first place.
"A consistency paradox is any situation where changing the past removes the conditions which allowed (or required) changing the past in the first place"Lectures on Faster-than-Light Travel and Time Travel
[28] supported
Zeldovich and Novikov were the first in the scientific literature to propose this idea, in 1975.
"В научной литературе впервые об этой идее в 1975 году заявили Я. Б. Зельдович и И. Д. Новиков"Причинно-следственная петля
[29] supported
The Novikov self-consistency principle is meant to resolve paradoxes of time travel that some solutions of Einstein's equations theoretically allow, namely those permitting closed timelike curves.
"Принцип самосогласованности Новикова — принцип, призванный разрешить парадоксы , связанные с путешествиями во времени , теоретически допускаемыми некоторыми решениями уравнений Эйнштейна, разрешающими существование замкнутых времениподобных линий ."Решения уравнений Эйнштейна
[30] supported
A rigorous formulation of the self-consistency principle appeared only in 1990, in a Physical Review D paper by Friedman, Morris, Novikov, Thorne and others.
"строгая формулировка принципа появилась лишь в 1990 году"Причинно-следственная петля
[31] supported
Self-consistency is guaranteed for a point particle considered in isolation because it has no internal structure, but this need not hold for extended bodies such as gyroscopes.
"Sinceapointparticlehasnointernal structure or other distinguishing features, self-consistency is guaranteed for CTCs considered in isolation. But the same need not be the case for extended bodies."Motion of a gyroscope on a closed timelike curve