In a galactic civilization with multiple races, what would be an ideal calendar system that everyone could use? FTL travel is possible (please no answers involving the implications of FTL, for the purposes of this question it is entirely possible without any side effects such as time dilation). Instant communication to anywhere in the galaxy is also possible.

Would there be any way to create a calendar system that everyone could effectively use? A day on this calendar wouldn't have to be the same length as a day on earth, but it should still be close to a human sleep cycle (the other races would presumably have a sleep schedule similar to ours, but if there's any way a calendar could work with radically different schedules that would be great).

  • $\begingroup$ You want more than one timekeeping system. Local and galactic standard $\endgroup$ Feb 3, 2018 at 2:07

2 Answers 2


I agree with henry taylors answer in that when making new system that can span cultures and languages, you need to break them down into the smallest denominator and then build up. Then it can be more easily translated into different languages(unless you make an intergalactic language and number system aswell).

This is what I really want to say but didn't fit in comments.

You would probably get a galactic time and planetary time. Probably get planetary(jet) lag while getting used to the new days after comming to a new planet. Though I expect occassions to still run on the galactic calender, day to day life would be probably depend on the planet. I would expect planetary time to have days and seasons, so regular things might be;"see you tommorrow"(exactly the same as now) and "see you next summer"(instead of "see you next year"). While galactic time will probably only have measurements like months and years(no days). What happens to days off-planet? Well an electronic assistant can make sure you get enough rest(your on a spaceship, electronics are everywhere), if its a colony ship then lights might automatically dim to make an artificial day-night cycle.

Depending on the culture, it may become that people think of themselves like this; "I was born 18 summers ago or to be more accurate, I am 26 years old"


A calendar is a tool for measuring and subdividing time. Its components (such as Days, Months and Years) are just convenient packages of time. They assist calendar users in equating the passage of time to recognizable spans within their own lifetimes.

So ignoring the packaging, a calendar only needs two components. A starting point and a unit of measure. For the calendar to work across the entire galaxy, both of those components need to be absolute and immutable across all time and space.

I would propose that measuring every moment in time as its distance from the instant of the big bang, in units of atomic seconds where...

the official definition of a second is 9,192,631,770 cycles of the radiation that gets an atom of cesium to vibrate between two energy states.

(We might round that cycle count up to an even 10 billion just to make the math easier, but the rest of this answer assumes that we leave it the way it is stated above)

How we determine the exact instance of the big bang is probably beyond our current science, but hopefully we will figure that part out by the time we colonize the stars.

As for making such a system usable to "people", we would probably create new convenient packages for day to day use. A CentiSecond HectoSecond for 100 seconds could replace the minute. A KiloSec would then be about 16.667 of our minutes, so 4 of them could replace our hours. A MegaSec is only 277.778 of our hours, so that would be close enough to replace our weeks. In fact, it's 11.574 days the equivalent of our fortnight. And with adequate advancements in medicine, average human lifespans might someday reach 10 GigaSecs.

  • $\begingroup$ I remember an episode from the Bell Labs Science show which said the same thing. Some alien race wanted to know how they should set their clocks. $\endgroup$ Feb 3, 2018 at 2:07
  • $\begingroup$ I think you mean a hectosecond, centi- is 1/100 like centimeter and cents. Plus, saying "I'll be down in a hec" I think sounds better anyway $\endgroup$
    – Samwise
    Feb 3, 2018 at 21:13
  • $\begingroup$ @Samwise! Thanks for catching my error! $\endgroup$ Feb 5, 2018 at 7:20
  • $\begingroup$ thanks to relativity there is no immutable unit, Even using that definition of a second every ship will start falling massively out of since almost immediately. even from planet to plant it will vary since the planets are moving relative to each other. the twin paradox is pretty hard on universal timekeeping $\endgroup$
    – John
    Feb 5, 2018 at 7:36
  • $\begingroup$ It might be better to use binary as a compromise base. Just on Earth people have used systems with 20 or 60 as a base. In fact, base 60 is still kind of relevant in the context of time. Base 60 might actually be a decent alternative to decimal time as its selling point is that it is divisible in so many ways. It would be compatible with base 12 used by Rigellians for example. And base 15 used by several species of aliens. Not with base 7, though. $\endgroup$ Feb 5, 2018 at 7:38

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