Anything that happens, happens.
Anything that, in happening, causes something else to happen, causes something else to happen.
Anything that, in happening, causes itself to happen again, happens again.
It doesn't necessarily do it in chronological order, though.
― Douglas Adams in the preface of his Sci Fi novel Mostly Harmless (1992)
In Science Fiction works involving time travel, causal loops are a common trope: Some event indirectly causes or enables itself.
Some examples even occur in the story presented in the popular online Esperanto course of lernu.net "La teorio Nakamura":
Said namesake Theory
is passed by Heleno (visiting from 2182) to Filipo Nakamura in 1982, who will later (somewhen in the early 21st century) publish it in an unimportant scientific journal, where it's mostly forgotten because it cannot be well understood yet. From there, the theory is rediscovered at some time after Filipo's death and
... once the advancement of the rest of the field of physics has caught up enough that the theory and its once too-novel-to-comprehend concepts can be readily understood, all physics students have to learn it. This includes Heleno,
thus enabling her to pass the theory on to young Filipo when she travels back to 1982.
Filipo's older self, visiting from 1982 from (probably again) 2012, instructs young 1982 Filipo to go to the 67th Universala Kongreso in Antwerp, Belgium and to meet
Lunjo
at the train station there and to invite her to a coffee. Older Filipo can tell younger Filipo that she'll accept the invitation and also what she'll wear (how young Filipo can recognize her despite never having seen her, yet), because he himself can remember
that very meeting he had with his then-future wife when he was 30 years younger.
So I came to wonder: How is the concept / term causal loop properly expressed in Esperanto?
The "causal" part seems straight forward: kaŭza
- definition from PIV
Rilata al kaŭzo, konsistiganta kaŭzon: kaŭza interrilato; la kuracado devas turni atenton al la kaŭza momento; kaŭza verbo (➞ faktitivo).
But what kind of loop is a causal loop?
- buklo (PIV, ReVo; not just locks of hair, but also loopy bands etc. and loops in graphs, so this might fit)
- lopo (PIV, ReVo; a looping when flying, so probably not?)
- maŝo (PIV, ReVo; can be a whole mesh or a single loop, so maybe?)
- banto (PIV, ReVo; a bow or knot, so probably not)
- fermita vojo (ReVo; technically the most fitting, but kinda lame, isn't it?)
(Let's ignore that some fictional timelines, such as in the movie plot of Predestination or the Jeremy Bearimy of The Good Place aren't simple rings but loop back in complex manners forming a knot, which would probably be nodo or in more involved cases plektaĵo in Esperanto.)
