Arelith

So I've been toying with some ideas in my free time and one of the concepts i've been tossing around is the cultural shock when introducing a regreessive dark age-esk surface setting and isolationist subterranean civilizations.

I've been playing around with numerous elements and how to address them, but theres one I can't figure out.

Time.

How the hell does an underground civilization conceptualize time?

Shorter durations of time (minutes, seconds, hours) are used as precise ways to measure out a single day, which is however long it takes for a full day/night cycle. Something that doesn't exist underground.

Longer durations of time (weeks, months, years) are use to measure out how long it takes for a full rotation around the sun to pass. This can be tracked and verified via seasons, or if you wanted to be a bit more accurate, the positions of stars and costellations can be further used to track where in the year you are.

Absolutley none of this can be applied to an underground culture that either never goes to the surface, or very, very rarely goes up top.

That said, if the civilizations are going to be as advanced, if not moreso than whats on the surface, some metric of time has to have been created and used, as even "simple" mundane things such as cooking and smelting need to have some way to measure/track time in order to be efficent. However, everything I can think of is more or less inapplicable (day/night cycles, star locations, seasonal changes, etc).

This makes even simple questions like "how old are you" impossible to answer when there is nothing that can be compared or referenced.

Any ideas on how to tackle this?

The Valdemar books by Mercedes Lackey use “candlemarks” - markings on a candle that keep track of time based on the candle melting as it burns.

For longer term things, what about the life cycle or migration pattern of animals? Though I suppose that would depend on the fauna in the caves.

It would likely be something that more or less everyone can see/hear/relate to, as is the case with our night/day cycle and seasons.

Perhaps there are periodic seismic activity that happens with precise regularity? Some creatures that shed their fur/skin/horns/other horrific anatomy at regular intervals? Or perhaps a big river of either water or lava has a repeating pattern of highs and lows?

For short term time keeping, maybe the drip of water from a certain stalactite? For long term, the growth of a stalagmite? "I am three foot of stalagmite old!"?

I've read some interesting ideas based on following the cycle of the moon, because you're measuring the change in the moon's pull on the world rather than light. A series to look into (and worth reading through because they were fascinating) is Myst! The Book of Atrus, Ti'ana and D'ni. The way time is described in the D'ni society is pretty cool and I absolutely see a lot of similarities between them and Deep Imaskari in early Forgotten Realms.

While a surface dwelling civilization would likely conceptualize time based on celestial events like we do, an underground civilization would probably derive it off periodic natural phenomenons more characteristic to their environment: something like the life cycles of bioluminscent flora for instance - when the mushrooms glow/lie dormant/release spores/etc.

If it's something more localized, perhaps because of every year's monsoon, a large body of underground river and lake fills up, bringing a lot of organic matter and nutrients, attracting a lot of wildlife and mushroom cultivation growth in a parallel to the Nile in ancient Egypt.
So a year would be measured by the coming of the monsoon and in great celebration.

For more precise time measurement, water clocks are the best. One second could be translated in a story into one drippling, or one drip.

Magically adept societies are known to use magic to set a shared easily referenced measurement of time.

Menzo for instance has a giant pillar that is magically lit to glow in order to track time. Day's, cycles or periods would have to be manually tracked but thats pretty much the same as we do now. Just need the ability to mark it down and some kind of shared understanding will build up - likely relgious in nature.

Humanoid sleep cycles are also quite important, even in the realms most humanoids need to sleep on something like a daily basis. Even elves have to rest. That provides a reason to be somewhat close to a day as default, though it might not be the same specific 24 hours, and theres little reason it wouldn't fall out of sync if it isn't.

Also its worth looking at how isolated the community is, can they reach the surface or are they totally trapped. Even if the bit of the surface they see is uninhabitated or a crack in the roof of a cavern, they can see daylight or not.

Lastly, I can see the underdark experiencing temperature changes with the day/night and season cycles. Not as pronounced as the surface as the earth is effective at regulating its temperature, especially as you go deeper, but a sensitive species might be able to detect it.