When it comes to time travel and paradoxesthe first picture that comes to mind – it couldn’t be otherwise – is the family photo of Martin McFly (per century Michael J Fox), in which the silhouettes of the brother and sister gradually fade, almost disappearing: all because Marty moves into the past with the delorean built by friend doche accidentally seduced his mother before she met her father.
And here is the paradox: if Marty’s mother does not know her father, Marty cannot be born; and if Marty cannot be born, he cannot go back in time. The name of this problem – to be precise it’s a ‘antinomythat is, the kind of paradox that indicates the coexistence of two contradictory propositions that are both provable and defensible – is grandfather paradox: his first description of the science fiction author Rene Barjavelrefers to the hypothetical situation (analogous to that of Back to the Future, as well as many other time travel movies and books) in which a grandson goes back in time and kills his grandfather before he can meet his grandmother, before he can get married and have children; In this way, the action of the time traveler again makes both existence and time travel impossible.
Things got (even) more complicated. Recently, two physicists – Venkatesh Vilasiniof ETH Zurichand Roger Kolbeckof University of York – have indeed proposed a new bizarre approach to the paradox, the details of which are described in two articles (here and here) uploaded to the pre-print server ArXiv. Vilasini and Colbeck’s analysis focused on a specific case of Possible solutions to the grandfather paradoxthe so-called causal loop, or causal cyclewhich describes a (hypothetical) situation in which a certain event (an action, information, the existence of an object or a person) is among the causes of another event, which in turn is among the causes of the first.
In this situation there’s no point in talking about it anymore it causes an event: To understand why we can refer to the physicist’s instructive example Allen Everett. Suppose a time traveler provides the equations of theory of relativity to Albert Einstein before he formulates them and authorizes him to disclose them: In this case, the equations that end up in the textbooks have no real origin because (!) of this overlapping of causes.
As the New scientist In an in-depth study devoted to the subject, causality can be defined in two ways: the first implies describing the relationships between two entities in spacetime (i.e. how far apart they are and whether one comes before the other or vice versa), while the other the analysis of concerns flow of information from one entity to another. “We’re used to saying that Correlation does not mean causation – explains Vilasini – and instead we have focused on the opposite, ie on the fact that causality does not imply correlation, or more precisely the ability of the two entities to exchange signals. That is, going back to the previous example, the possibility that Einstein could discover his equations based on information from his future without ever communicating directly with the time traveler. All of this can happen in a universe similar to us, but not too much: “The three spatial dimensions of our universe – explain the two authors of the study – could change the equations of causal cycles and make them impossible, but we are not sure yet.” let alone us.