How would an underground society measure time? [duplicate]

Question

I have a very mind-boggling question about time reckoning.

I have a race of Dwarves, that at the very beginning of their history lived only underground and were forbidden to reach the surface. They never saw sun or moon, day or night. The only one how knows about the concept of the normal passage of time was their King. He once sat among the gods, before he was sent to the normal world to lead the Dwarves.

I just want to disclaim that there is a very important reason for the Dwarves not being allowed to see the surface. So they must stay completely underground for the first 200 years let's say.

So the question now is what would be a reasonable way of telling time for them? Is there any logical and realistic way of explaining this or must I explain it with some kind of magical machine or item? How would such circumstances influence their days of the week and calendar?

Answer 1

I'd like to follow on to Daniel B's excellent water clocks answer, with water calendars, too.

Large bodies of water don't have to be on the surface to experience tidal effects. Depending on how fantastic your fantasy setting is, an underground sea may or may not be plausible, but many large real world cave systems communicate with the sea and water levels inside will rise and fall on a regular predictable cycle.

Tides are complicated things, and provide a natural basis for longer-period time measurement than could be provided by a water clock alone. Earth's tides have cycles with 12-ish-hour components (two high/low tides a day) and monthly components (spring tide-neap-tide cycle) and there are other components that might be detectable by suitably sensitive equipment of varying lengths (including daily and annually). Dwarves with a sea-linked cave system or huge underground sea will able able to identify "days" and "months" using a ruler alone.

Water will also seep into cave and mine systems from above, and the volume of water that makes it in will depend very much on the weather above. Though it depends on where the dwarves are in the world, there's a good chance that they'll have an annual change in surface water flux driven by rainy seasons or snowmelt that will provide a clear annual cycle indication even if it won't be nearly as precise or predictable as a tide.

Between the annual and monthly cycles, it should be possible to build a calendar and use that to synchronize your short-period clocks, such as Daniel B's water clocks.

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As an alternative, perhaps you could consider a Foucault pendulum. This is an interesting device whereby a very long pendulum appears to spontaneously start rotating and describing a sort of star-pattern across the ground, thanks to the rotation of the Earth.

Source

Over a period of time, the pendulum will return to its original position. This is called the period of precession, and can be calculated as $T = \frac{ {\mathrm d}}{2 \sin \phi}$ where $\mathrm d$ is the length of the day, and $\phi$ is the latitude of the pendulum. At the latitude of Almaty, to pick somewhere at random, the period would be a little over 17.5 hours. At the poles it would be 24 hours, at the equator it would never precess at all.

This could give an interesting local flavor to timekeeping, where "days" were subtly different lengths in different dwarven settlements. With an independent way to measure a period of time (such as a water clock) this might also allow a clever observer with some grasp of mathematics to make some assumptions about the nature of the world without ever having seen a sunrise. It might also inform underground navigation... travel east or west would not change the precession period, though travel north or south would. The change of period would inform how far you'd travelled, though given that Foucault pendulums need to be rather long this would only be useful for surveying with the aid of a large team of miners, rather than a personal tool.

Answer 2

Water clocks

The most natural way to develop a measurement of time is by a natural phenomenon that divides the passing of non-quantized time¹ into quantized time. As someone who has spent a fair amount of time in caves, in certain places there is a presence that is almost as universal as the sun, moon, and stars: the steady dripping of water.

Caves (on earth) are almost exclusively formed by erosion of water through limestone or karst, a process that is ongoing. Therefore, water is frequently continuing to penetrate, accumulate, and flow through them.

Surrounded by this omnipresent sound, the dwarves would find natural water clocks in their environment. Places where water flows or drips at a constant, reliable rate. Just as trees form natural sundials which are then artificially duplicated with more precise instruments, the dwarves would devise a more precise version of these natural water flows.

In fact, caves are perfect for water clocks, because the biggest flaw of the water clock as a system is that the viscosity of water changes by a significant percentage with the shift of daily temperatures, potentially creating a non-linear flow.

Temperatures in caves, however, fluctuate in the scale of fractional degrees daily, and only single-digit (or less) degrees over annual periods.

The units would be broken up by some arithmetic, arbitrary division as ours are.

As for the day-night cycle, it will likely correspond to the average of the circadian rhytm of the species. Cave-dwelling species have been shown to have (lessened, but still present) circadian rhythms, and absent of any specific declaration that they don't have them in the Q, I think it's reasonable to assume they would.

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1. Let's pretend we all agree that time is non-quantized for the purpose of this question.

Answer 3

Supposedly, your dwarves are still biological creatures, so they will have some natural circadian rhythm. Even without the sun, they would like to sleep for some time and eat several times a day. Most likely, their rhythms will be even more robust and less dependent on the artificial lightning then humans. The research says that even creatures in environments where the changes in lighting doesn't affect them, such as naked mole-rats, still have cyclical patterns of activity and sleep of almost precisely 24 hours.

So, the individual dwarf would understand the basic pattern of working period vs sleeping period, and the whole settlement would control and optimize those rhythms for communal activity.

Now, for the longer cycles. Possibly, your caves are not completely isolated from the outer worlds. There may be some changes of temperature, air flow or water flow depending on the conditions outside. They will be the 'seasons' for your dwarves. Obviously, they would not be called winter or spring. But there will be a season when the glaciers on the mountain start melting and the water level in the underground lake rises. Or the season when the warm air moves in the rightmost corridor, or cold air in the leftmost.

So, there will be some perceptible changes corresponding to the seasons outside - not completely rhythmical, not present every year, but significant enough that the dwarves themselves will notice them. And if they have at least some activity that depends on year-long cycle (breeding bats or growing mushrooms, for example), they would try to keep track of those patterns.

Water clocks, daily bells, yearly festivals - all that stuff would most likely still exist in their society.

There is a problem that for them there will be no 'objective' way to check the time - they will not be able to measure it by the position of the stars. Possibly, the timekeeping in different settlements will drift off, the day shifts would start at different time, the yearly festivals would move by the couple of days.

Timekeeping could even have deep cultural significance for them, being analogous to the concepts of 'thinking', 'speaking' or 'being civilized' for humans. A civilized dwarf keeps time carefully, always gets up with the morning bell, always checks his water clock, always keeps a calendar and celebrates the festivals.

Answer 4

Under the circumstances you describe there's really only one way they would develop a measure of time, distance, and the time it takes to travel it, most probably with paces in place of seconds and various multiples thereof.

Much as in the past when a rulers forearm length was the measure of a cubit this might differ from region to region and occasionally change with the ruler but would eventually be standardised.

For example a work shift might initially be measured by the time it takes to travel between two specific settlements (so, a choice entirely within your remit) a particular number of times and subdivided by the number of normal paces that takes.

That seems like the most likely and plausible outcome to me for your scenario.

There wouldn't be years as they have no seasons, the average lifespan may be used as a longer unit of measure subdivided by "sleeps" (which if they need as much sleep as often as us will correspond to roughly 24 of our hours), perhaps standardised against the lifespan of a famous individual.

The length of their pregnancies is another thing that might be used as a standard unit of measure.

Basically, without the days, seasons and years available to them, as they are to us on the surface, you need to look at what is in their environment against which time can be meaningfully measured.

Answer 5

If we think about a clock we can tell time because:

1. The clock has moving parts that change over time.
2. We have a sign/symbol system in order to make (clearer) distinctions, remember and categorize time.

Now in order to find out how ever underground living dwarves would invent/construct time measuring devices we need to look at what changes in the underground over time.

I can think of for example:

• Water Clock: Underground water or rivers
• Sand Glass Clock: Underground gravel or sand
• Fissure Clock: Fissures or rifts that change because of seismic activities
• Living Clock: Insect life that's much shorter than dwarven lifespans, and thus a death of an insect can mark a new time unit
• Growth Clock: Hair Growth (Either from an individual or a collective.)
• Sound Clock: Echos (If you e.g. have a very very large stone hall and play a large gong in there, you could wait until no one hears the gong anymore and then mark a time unit.)
• Gravity Clock: Gravity and drop time (Let's say your dwaves have a really deep hole and the drop in little rocks and mark a unit every time they hear a hit and then drop a new rock. If they are able to re-collect the already dropped rocks, that's a valid clock.)
• Roll Clock: A very rotund stone that rolls down a very long but not steep slide and always takes the same time to roll down that slide
• Heat Clock: A hot metal that gradually cools down until it's touchable (Let's say your dwarves are parcticing blacksmithing and one specific metal ball is always heated to roughly the same heat, and through visible black body radiation and sensible heat your dwarves can tell the difference between then and now.)

The next thing is a sign/symbol system in order tell the difference between time units. In the case of sand clocks this would be e.g. one full run-through of the sand. In the case of the Gravity Clock this might be the drop impact with an added checklist of e.g. strokes. 4 strokes form a gravity minute, 40 strokes a gravity hour and 960 strokes a gravity day.

So just look at what can change in your setting over time and add a sign/symbol system for the inhabitants to be able to interpret, write down and remember the time.

Answer 6

As a somewhat technical race, they would eventually develop a need to tell the change in time, from how long to heat ore to melt it (in the short term), time between meals(in the mid term) to when the crops will reach maturity (in the long term).

Mostly, its just guess work, but certain things may need at least a rudimentary form of time keeping. Melting ore? Just wait a while. Hungry? Just eat. Waiting for crops to ripen? Just watch them. But Forging and machining of complex items may need more precise time keeping.

For a short term time keeping strategy is to create a standardized funnel or chalice type item that has a very precise sized hole at the bottom that drips at a standardized interval. this device is kept full from cave condensation and excess is allowed to flow away from it. The drips strike a wheel that counts the drops to display some period of a cycle. This concept could arise from a bored dwarf watching the drips as they were waiting for their bread to cook and figured bread is perfect if they counted out 100 drips or so.

This machine will help the villagers tell when meals are, when work periods are and when to sleep. To ensure the proper work/rest cycles are met (week) the village period keeper, using a series of stones, tracks the "days of the week."

Beyond the king, any further concept of time may be arbitrary. With no moon, sun, stars, solstice and equinox, their minds would not be able to comprehend any other time scales other than their work/rest cycles. The king could dictate longer time scales to allow for crop rotations, but the people themselves would just have to push the "I believe" button on that. The village period keeper (time keeper) would be needed to track these cycles as no one else would be able to grasp the concept of the passage of time at those time scales.

Answer 7

For a time unit like a year you could have cave system / underground river that floods depending on the season above ground. Could be it only rains heavily topside a specific season of the year. Or maybe the water comes from melting glaciers during the summer. While in the winter the top soil is frozen solid for months at a time so the underground river dries out.

For a "day" cycle it would probably start from biology and culture, as in how long is a fair work shift and how much resting time is fair before the next work shift. I think this would be difficult to synchronize between settlements without somewhat advanced technology or magic. Maybe by sound?(blowing a horn), but I'm afraid the sound may die out too quickly.

Answer 8

All of these answers ignore the fact that times and dates are mostly used to coordinate meetings and such. The dripping of water in a certain cave somewhere is not going to help with that.

It's also not clear that a person's circadian rhythm is going to be able to function without sunlight, but there have been papers written about other types of animals: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5090016/

The most plausible mechanism for any sort of rhythm is that groups of dwarves living together will wake and eat at the same time. The most plausible form of time is one counting these "daily" cycles. But keep in mind that the lengths of the "days" may not be consistent, will be out of sync with actual days, and two colonies will be out of sync with each other.