Causality Loops

If causality loops have recurred
Consequential-based logic's abjured.
Links acausal confuse
What begins, what ensues —
Life's a paradox, strange and absurd!

Causality loops are hypothetical constructs based on speculation that future events, if allowed to impact their own past causes, will lead to logical paradox, and are thus sometimes used to posit that acausal connection cannot therefore exist. Science fiction has many instances of such fanciful implications (they are collectively referred to as the predestination paradox). However, if one does not make the assumption that time-lines (an individual observer's past-present-future chain of causal events) are fixed for all observers (this is technically called an assumption on non-locality); and that if it is possible to revisit and change the past through an acausal connection; then perhaps subsequent events from that point on are within a new time-line for the acausal observer. Non-participating observers on other time-lines will be unaffected, though from then on exist in other worlds, inaccessible to the acausal observer (and vice versa). The implication here is that many time-lines (and thus worlds) may coexist.

However, an individual observer only perceives the time-line he is on. He is responsible — because of his acts and observations — for the world he exists in. Thus, a time-traveler can go back in time and kill his own grandfather and still exist, because the world from that point on unfolds differently to his prior recollection. He is on a new time-line. As such, there is no paradoxical causality loop in such a formulation, and the concept of free-will is preserved. Strange as it may sound, such many world interpretations of quantum mechanics are serious candidates explaining the underlying reality of the observable universe.