Currently, there is no clock in nature that could work without human intervention for many tens, and even hundreds and thousands of years. In any watch, you need to periodically wind up the clockwork or change the batteries, set them on the signal of the exact time. And the need to follow the passage of time appeared in man a long time ago, at the dawn of civilization. 5-6 thousand years ago, during the megalithic epoch, in different parts of the world, people built structures that allowed them at least once a year to "set their clocks" and start over the exact time. Such a structure was probably the famous Stonehenge, over the Heel stone of which the sun has regularly risen on the summer solstice for 5 thousand years.

Why do I need a huge clock that can work without repair (this is a very important point, do not forget about it) for thousands of years?

You have an idea of ​​the pyramid, this is what unites you with the past. But we do not have anything like that for the future, we do not have a symbol that unites us with the future.

Thanks to the pyramids, now the average man in the street knows much more about Ancient Egypt than about Babylon, the Vedic civilization or the Sumerians. Perhaps, in the future, we will be spoken of as "those people who built that strange clock."

And here we come to the essence of my question: how should a watch (the structure of the mechanism and the materials from which the watch and its components be made) should be arranged, capable of working for about 100,000 years, without human intervention (without repair)?

Note: yes, I know that in 1993, fascinated by the idea of ​​such a "perpetual" clock, the famous American inventor, engineer, mathematician, professor of engineering and medicine at the University of Southern California, and, simply, the restless enthusiast William Daniel "Danny" Hillis proposed a project for the construction of a similar watch, but with a shelf life of ten thousand years (while I need one hundred thousand years), and Jeff Bezos even helped him to implement this idea, donating $ 42 million for this purpose.

However, as mentioned above, my watch should be able to work for several tens of thousands of years, which is several times longer than the shelf life of that project.

Addition: I ask you not to offer answers using repair nanorobots or some self-healing materials - it's too easy.

This watch must be of a mechanical nature (that is, it must have the same dial, something that shows the time and the corresponding mechanism), therefore no sundial (my watch is inside the building).

I would also like to mention that this watch is a cultural monument for future generations, so it should be located on the surface of the Earth (keep this in mind when taking into account the erosion and weathering of the materials from which the watch will be made).

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    $\begingroup$ I don't see a worldbuilding problem here. At most it's a plot detail. $\endgroup$
    – L.Dutch
    Nov 18, 2020 at 5:51
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    $\begingroup$ "You have an idea of ​​the pyramid, this is what unites you with the past." That was not the purpose of the pyramid. $\endgroup$
    – RonJohn
    Nov 18, 2020 at 6:21
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    $\begingroup$ Nothing human built has lasted even 10,000 years; over 100k years is talking geological time and will have to account for Ice Ages, earth movements and more. Even a big rock placed in a careful location will be subject to substantial erosion over this sort of time scale. $\endgroup$
    – David258
    Nov 18, 2020 at 12:28
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    $\begingroup$ @RonJohn But it kinda was ? Point of such big tombs is to make the dead guy inside "immortal", to carry him and his legacy into the future. So that next generations will remember him even thousands of years into the future. So it's not far-fetch to say that it is a bridge between the past and now. $\endgroup$
    – Jemox
    Nov 18, 2020 at 13:55
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    $\begingroup$ The entire history of mankind, from the earliest clay tablets of Sumer to the lastest SpaceX rocket, is less than 6,000 years. You are asking about a machine intended to work for a duration more than sixteen times longer than the entire history of human civilization. No, we do not have the faintest idea how to design and build such a thing. $\endgroup$
    – AlexP
    Nov 18, 2020 at 14:49

3 Answers 3


...Could work without human intervention for many tens, and even hundreds and thousands of years...

Impossible (based on any science I'm aware of)

Even Hillis' clock won't run without human intervention for anywhere near its lifespan.

  • The orbital speed of the earth changes, and that affects timekeeping. [1]

  • The rotational speed of the earth changes, and that affects timekeeping. [2]

  • The distance of the moon from the Earth changes, and that affects timekeeping. [3]

These are just some of what I expect to be a fair number of reasons why no time piece could possibly exist without human intervention for longer than a handful of years before needing recalibration. And this is assuming that the astronomical-length period you're talking about (100,000 years) doesn't include an asteroid or two with enough mass to give the Earth a good yank.

Your condition that there be no human intervention is a deal-killer.

Unless you don't care about how time is interpreted by Earthlings. You could set up an atomic-style clock that ticked away specific seconds based on the highly predictable half-life of a radioactive isotope. We do that already. The problem is that the count becomes meaningless if not calibrated against what's actually happening on the Earth. It isn't the length of a second that's important. It's the value of the clock as a timekeeping piece in real life.


  1. The OP believes that this is not a hard-science answer. It is, he/she simply hasn't realized that using the tag to create a fictional object invalidates the tag, which isn't magic. Adding it to, "How would you create FTL propulsion?" won't result in better answers, either. However, I did provide citations for my three principle assertions.

  2. Atomic clocks cannot operate without human intervention. They are amazingly accurate — but all they do is count seconds. If that's all that's required, then it's true that my answer is invalid — the result is the same. It's impossible given everything we know today about science. Materials degrade. Wars happen. Mother Nature is still more powerful than Humanity. (And to be frank, it's a waste of my time finding citations to prove any of those points, or any of the thousands of other ways anything manufactured today would decay. Sheesh.)

  3. If the OP thinks that solid science today can build a clock to his/her specifications, then by all means, answer your own question. Prove to me that what I've proposed isn't "solid science."

  4. The length of the Earth's day would increase 1.78 seconds over the course of 100,000 years. (Source) I might have jumped to the erroneous assumption that you wanted the clock to be accurate after that much time. If you're willing to give up 1.78 seconds, then what's the point of having a clock that can remain untouched for that long? (And that's only the effect of drag on the Earth's rotation. Nothing else....)

So... Unless the OP can prove otherwise to his/her own standard. I assert the project as conditioned is impossible.

And I'm willing to further assert that if someone on this site had a answer that would result in a clock that could last 100,000 years — they wouldn't post the answer here. They'd be talking to Bezos about getting a check for millions of dollars. No offense, French, but what are you expecting?

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    $\begingroup$ Sad to learn that it is impossible but glad to read an amazing answer. $\endgroup$ Nov 18, 2020 at 8:47
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    $\begingroup$ @TheSquare-CubeLaw I'd never give up hope. Science has this nasty habit of surprising us every day. For all I know, some soon-to-be-outrageously-wealthy fool will figure out how to do it next week. (And why is said person a fool? Because they don't know me well enough to buy me a creme soda with all that newfound swag....) $\endgroup$
    – JBH
    Nov 18, 2020 at 9:35
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    $\begingroup$ @MarvinKitfox, it's called "frame challenge" $\endgroup$
    – L.Dutch
    Nov 18, 2020 at 11:40
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    $\begingroup$ @Trish no just that it is inconsistent with the laws of physics as we know it, it is an important distinction. $\endgroup$
    – John
    Nov 18, 2020 at 15:57
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    $\begingroup$ @JBH Your answer is great, it includes a qualifier. I was just pointing out the flaw in MarvinKitfox's argument, science does not deal in absolutes. $\endgroup$
    – John
    Nov 18, 2020 at 17:09

FRAME CHALLENGE: A mechanical clock that will continue to operate over time comparable to the duration of the human species is impossible to design with current knowledge (especially under a "hard science" tag).

BUT: The clock you desire already exists, and predates humanity, though we only learned to read it with high accuracy within the past few centuries.

This clock is the Solar System.

The Earth itself provides a daily clock with its rotation relative to the sun. Earth's moon, and the positions of other planets (and their moons) provide a highly accurate clock over even geological time frames, if only you have the necessary instruments and knowledge to read it. This clock is accurate enough that it provided the very first measurement of the speed of light; has informed farmers when to plant their crops for millennia, and with modern instruments can be used to fix the date and time within seconds over a time frame of at least tens of millennia -- and will remain readable and comparably accurate over a much longer frame (billions of years).

The only thing necessary to ensure this clock remains readable over your desired time frame is to find a way to preserve the knowledge, both to make the instruments (astronomical telescopes and measuring instruments) and to interpret the positions of the planets and their moons.

  • $\begingroup$ This is nowhere close to a hard science answer $\endgroup$
    – user79911
    Nov 18, 2020 at 13:04
  • $\begingroup$ This watch must be of a mechanical nature (that is, it must have the same dial, something that shows the time and the corresponding mechanism), therefore no sundial (my watch is inside the building). I would also like to mention that this watch is a cultural monument for future generations, so it should be located on the surface of the Earth (keep this in mind when taking into account the erosion and weathering of the materials from which the watch will be made). $\endgroup$ Nov 18, 2020 at 13:07
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    $\begingroup$ Another answer has already established that your desired answer is impossible. I'll edit to clarify that this is a frame challenge, of sorts. $\endgroup$
    – Zeiss Ikon
    Nov 18, 2020 at 14:02

Mechanically impossible

Every interaction between two parts incurs friction. Friction is a force that transfers kinetic energy into thermal energy aka heat. The transfer of kinetic energy into thermal energy is a net loss of kinetic energy and means you need to add kinetic energy to keep the system moving at the same speed. This is due to Newton's laws and the first law of Thermodynamics:

In an inertial frame of reference, an object either remains at rest or continues to move at a constant velocity, unless acted upon by a force.

The total amount of energy in a system is constant but its forms can be converted

So we turn kinetic energy into thermal energy (heat) which then is dissipated into the atmosphere as the kinetic movement of atoms in the gases surrounding it. This happens on any parts rubbing against each other.

Where does the kinetic energy come from? In a normal windup clock, it comes from a spring that stores potential energy and releases it into kinetic energy, which results in movement and ultimately heat.

Since a Perpetuum Mobilee is not possible under the laws of thermodynamics any mechanical solution is impossible.

Digitally impossible

A digital solution runs into the same problem: you need an infinite potential reservoir of electric potential energy to keep a digital clock - like a nuclear clock - running. An RTG could run a clock for a few decades, but there is no way to have an energy source that runs for the amount of time you want without needing maintenance.

Non-Mechanical to the rescue?

I am only aware of one design of clock that does not need to be corrected and fixed over centuries but for occasional removal of debris: Solar clocks - or rather sundials. One of the oldest solar clocks that I am aware of and that is still in use is made from an obelisk and the surrounding place.

It might only be easy to read on some days of the year, but the Obelisk on the St. Peters Square does function as a solar clock together with the markers on the paving. The obelisk now stands there since 1586. The current paving is from 1817 and includes also shadow markers for when a new zodiac starts. There are also the long sectors for the equinox. Those are all still correct after 203 years! It always adjusts to the changing speeds of the planet, but it only allows relative measurements, no nighttime measurements, and the length of hours shifts with the year.

enter image description here

An older, dismantled sundial could be the Solarium Augusti of 10 BC, though that is disputed.

A Sundial Inside?!

Yes, they exist. To get a sundial inside a building to work, the sundial has to be included in the very construction of the building. Pinhole gnomons are a thing in several churches. St Sulpice has a pinhole, obelisk, and lines on the floor, together acting as a whole observatory!

A Rotunda with a pillar in the center and transparent roofing (or only one transparent tile) would allow sunlight to create a shadow finger and/or light point marker inside the building. This marker will wander over the marked floor and walls to indicate certain times and days. However, now you need to keep a building to stand for the required amount of time and keep the roofing all transparent - that is a different question and one that can't be solved.

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    $\begingroup$ heh, St Peters Square is a circle. $\endgroup$
    – user253751
    Nov 18, 2020 at 14:14
  • $\begingroup$ @user253751 St Peters Square is the whole stretch from the dome the photo was made from to the buildings that narrow down. $\endgroup$
    – Trish
    Nov 18, 2020 at 14:41
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    $\begingroup$ I upvoted this answer because it refocuses the problem. If the purpose of the project is to be a symbol to inspire future generations, then its design is secondary to its existence as a piece of art. A sundial, magnificent in scope, is a good idea (and that we already have a big nice one to use as a point of reference is even better). I'm still having trouble with the idea of any material, natural or man-made, capable of withstanding 100,000 years of time w/o human intervention, but this is likely as close as we can get today. $\endgroup$
    – JBH
    Nov 18, 2020 at 16:32

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