Time Measurement after Interstellar Expansion

How you ever wondered how we will measure time in the distant future once human race expands into the far reaches of the universe? I’ve been pondering this lately. You see, this is what I do. I noticed that “normal” people think about practical stuff most of the time. They ponder what they are going to eat for lunch, what household chores they want to do after work, what TV shows they are going to watch, what their friends are up to. If you leave them in a room with nothing to do, they tend to get fidgety and bored. Then they invent stuff they can do – they start cleaning the house, mowing the lawn and etc. Every time I see this, I am quite amazed because this is such an alien condition to me. If you put me in a room with no TV, no internet and no books to read, I will probably be pretty content to sit there and think, and will eventually try to find a piece of paper to jot down notes before I lose them.

So I think about stuff like measuring time in a distant future. Right now, our whole system is based largely on physical constraints. We measure time in days, based on the rotational speed of our planet, months based on our lunar cycle and years based on. This works pretty well for us here on earth, but these units will become completely meaningless once we start colonizing distant solar systems. Different planets will have different rotation speeds, orbital periods and their own seasons. Just to give you an example, Martian colonists will probably have change how they define an hour to keep the 24 hour cycle aligned with sunsets and sundowns. You see, Martian day is roughly 37 minutes longer than the Earth day. If they were to use Earth clocks to measure time, this offset would start adding up causing an interesting drift. Over the period of few months 8am would fall around their noon, then around supper time, and then back to morning hours. The same would happen to their year, which is 324 days longer than ours resulting in drifting seasons.

Initially most colonized planets will probably establish their own time keeping systems that will work locally. Whenever you will need to communicate to offworlders you will simply have to specify whether your figures are in local time or Earth time or whatever. It is a workable system, and one not much different from the headache we already have with our time zones here on Earth. It will simply be another layer of crap to keep track off. But eventually we will move our populations beyond worlds. At some point we will start building mega scale space habitats such as Dyson Spheres in which the day/night cycles and seasons will be human controlled. We will also likely migrate into virtual spaces as well. Unsleeping digital ghosts, or inhabitants of simulated worlds could borrow a time keeping system from a neighbor and use as their own. Or they could choose to use Earth standard time. But they would have no reason to. Days would probably seem very arbitrary to people living in environments where there are no natural nights. I could see such civilizations gravitating towards some sort of standardized, unified time keeping unit to replace the ancient planet bound time keeping concepts.

In fact, we already have such a unit – a second which is usually defined as:

The duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.

Not that easy to remember, but at least it is constant – it will always be the same whether you are living on an alien world, or inside a space hab of some sort. It is also an SI unit, which means it is already universal and widely accepted. Seconds may be the only time unit that will make sense to everyone in a distant. It even scales nicely.


  1. 1 hecto second is approximately 1.6 minutes
  2. 1 kilo second is around 16.6 minutes
  3. 1 mega second is 11.6 days
  4. 1 giga second is 31.7 years

It’s so intuitive I’m surprised we haven’t started using this years ago.. For example, if you wanted to step out for 15 minutes you could easily say “Back in a kilosec”. Assuming that our circadian rhythm does not change much from what it is now, you would be required to work approximately 30 kiloseconds (~8 hours) sleep for another 30 and bullshit around for 40 more. This would give us a nicely rounded 100 kilosecond cycle that would be roughly equivalent to an Earth day.

A mega second could be equivalent to our week, comprised of exactly 10 sleep/work/play cycles. Current drinking age in US would translate to a little over half a gigasecond. Lifespan of baseline humans would be somewhere between 2 and 3 gigaseconds. Historical dates on the other hand could be measured in tera- and petasecond offsets.

It’s workable, units are nice, scale well and are based on a universal, non-geography dependent constant. Of course a lot of worlds would probably cling to their preferred time system – especially if they have used it for generations. Still, seconds could be a nice universal standard that could be used as a base for conversions. This way when two worlds need to communicate, they merely have to encode their dates as seconds. For example, just leave unix time stamp on everything – the guys on the other side will then convert it to their preferred format at will.

What say you?

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8 Responses to Time Measurement after Interstellar Expansion

  1. jambarama UNITED STATES Mozilla Firefox Ubuntu Linux Terminalist says:

    While I’m sure relativity screws this up in someway, I wonder if using such small units in isolation increases the risk of error. I mean, if your measure of a second is off by .001, it isn’t a big deal when you’ve got other measures to check it against. Like it takes 60*60*24 seconds before the sun comes up again tomorrow. If patterns are more irregular on other planets (say they’ve got an elliptical orbit, or two suns), a second measure off by .001 might not be caught, and it’d cause some significant disparities between planets. Maybe that doesn’t matter, but if we have to pick a unit to base all time measurements on, I’d prefer a larger one.

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  2. What about relativity? Time passes at different rates for different observers. You might have to pick one frame of reference and base your time off of that. If you’re traveling in a very fast spaceship and you say, “This project will be completed within a megasecond” where it’s measured by the passage of time on Earth, that could turn from a week into 2 minutes.

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  3. Luke Maciak UNITED STATES Mozilla Firefox Linux Terminalist says:

    @ jambarama:

    Well, I’m assuming you would be using an atomic clocks. So elliptical orbits and all that stuff shouldn’t matter. You base it on the rate of decay of a cesium 133 atom.

    But yes, errors will be made but then again you can periodically sync your atomic clocks. Isn’t that what we do now? We have authoritative ntp servers and distributed networks that allow us to make sure we are all more or less on the same page.

    Also, I’m not sure how using a second would affect the risk of error. After all, we do use seconds right now – they are our basic time measurement unit. Just instead of using SI prefixes we lump seconds into minutes, hours, days, months and etc. But at the end of the day, we still have to do that bullshit with the leap second to make sure we don’t fall out of sync with the sun rises and sundowns.

    @ Chris Wellons:

    Oh, I did not think about that. I’d assume we would have some way of compensating for the time dilution. I mean we can calculate this based on the velocity, mass of the ship and length of the trip, no? So you can semi-accurately say that a ship time second is n standard seconds.

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  4. levinalex GERMANY Safari Mac OS says:

    You should read Vernor Vinges “A Deepness in the Sky”. It’s a great book and he depicts a society which uses exactly these units (“back in a ksec” is actually used there)

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  5. levinalex GERMANY Safari Mac OS says:

    @ levinalex

    This page goes into some more datail and gives more references and seems relevant. (and Accelerando is also a very nice book)

    The concept seems to be called Metric Time

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  6. Luke Maciak UNITED STATES Mozilla Firefox Windows Terminalist says:

    @ levinalex:

    You know, it’s funny but “A Deepness in the Sky” and “Accelerando” are on my Amazon wish list. I don’t remember correctly, but one of them might be in my most recent order that should arrive at my house any day now. If not, they are definitely going in on my next order.

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  7. SapientIdiot UNITED STATES Mozilla Linux Terminalist says:

    I’m pretty sure i’ve sat around and thought about this sort of thing before, but i never went anywhere in researching it. Nice work.

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  8. I think you’re right: seconds will end up being the universal unit to measure time. But whether or not local times will be synchronized with the time back on earth depends on whether we use FTL travel and communication.

    In early America, Boston, New York, and Washington D.C. all were on different time zones, off by a few minutes each (bell towers helped everyone within earshot be synchronized) – it took several days to travel between them and people didn’t have very accurate clocks. The need for synchronized time came with the invention of trains and the telegraph.

    If it takes 20 years to send a message to a colony, no one’s going to care if the clocks are synchronized. But it will matter if we have faster-than-light travel.

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