Symbols change meaning over time, so how do you set up a warning system to warn people off of living near nuclear waste repositories for 10,000 years or more?
A radio show on design, 99% Invisible, tackles the problem, outlining the limitations and proposed solutions. The whole history of ideas is fascinating, but one of the most surrealistic is to bioengineer living Geiger counters, cats that change colours in the presence of radioactivity. Of course, this only works if you can also pass along understanding on why colour-changing kittens are a terrifying idea. The second half of the proposal is to publicize folk songs and stories driving home the moral that if you ever see these cats, run away.
While citing the longevity of moral codes from religions as a successful example, to me the idea evokes in the urban legend that Ring a Ring o' Roses is a warning of plague signs. Although folk lore historians doubt the veracity of the legend, if it were true, it's a good argument that a mere two centuries is enough to dilute a warning to incomprehensible. And if it's not true, it speaks to our capacity to seek out meaning and symbol where none was intended, creating another layer of complexity by needing to create a warning system that doesn't include unintended hidden messages.
It also brings up another problem: how do you keep the message on-track that it's not the cats that are evil, but the environmental conditions that prompt the cats to change colour? Otherwise, I can easily envision a future reminiscent of Anne McCafferey's world Pern from the Dragonrider's series, where a warning to monitor the spread of protective grubs transforms into an imperative to destroy the grubs on sight. A future that demonizes the very creatures we created to protect us seems far too plausible to me.
Even worse, given our long history of manipulating breeding, I can see future-humans modifying colour-changing cats to react to other stimuli, changing the warning of epic doom into furry, fashionable pets akin to mood rings.
So, what would you do to mark a nuclear waste facility for millennia into the future?