How would several intelligent life forms, aka. Aliens or Foreigners to us, who roam around space (in something I would call space ships) and have never seen or heard about earth interpret time?

How would they define it, so that it fits in? (E.g. our earthly time system always kinda felt weird to me... should get changed, ngl)

What time format and divisions/partitions do you even use in space? (E.g. there is not really a day and night everywhere...)

  • $\begingroup$ VTC as a duplicate, but keep in mind that our definition of a second, despite the current definition, came to be in an entirely and hugely subjective manner based on planetary rotation, orbit, and lunar orbit, seasons, and other things - all of which would be different on another planet. In the end, the question isn't how you tell time - but you you synchronize time (that question's on here somewhere, too). $\endgroup$
    – JBH
    Commented Sep 7, 2020 at 17:38
  • 1
    $\begingroup$ Douglas Adams might suggest that they would work it out by comparing their various digital watches. $\endgroup$
    – user535733
    Commented Sep 7, 2020 at 20:09

2 Answers 2


Sleep is important, and being active as a group is also important. In a space ship they'll likely have two groups that sleep when the other is active to make sure the space ship is maintained at all times.

This means that these aliens will have something like a circadian rythm (https://en.m.wikipedia.org/wiki/Circadian_rhythm#:~:text=A%20circadian%20rhythm%20is%20a,oscillation%20of%20about%2024%20hours.) To make sure that they sleep enough.

The circadian rythm is linked to cell activity, with cells being less active during certain times. Even fish in perpetual darkness have this for some reason. Regardless of the actual length, it is likely that these aliens will base their time on this sleep cycle. "It is X time into the sleep cycle", "I am 80.000 cycles of sleep old", they'll likely have a word for "year" that is based on either their culture or on math. If they use a 10-digit system they might make a year 1000 sleep cycles for example.


Concepts like "days" only make sense with a day/night cycle, or if you have a race like humans who need sleep every 24 hours. So you're right, if there's no days, or no sleep, there's nothing to base your time on.

There is a place on earth with no day night cycle for parts of the year. Its discussed quite well on Wikipedia.

Basically they pick some place of importance (eg Greenwich England) and use the time there as their clock. (Technically they use UTC time, not GMT, but the difference is academic).

I would expect aliens in space to operate similar to humans in Antarctica, referencing their home planets clocks, even if they don't really make sense to their current day night cycle. They may be needed to help with a biological requirement (eg sleep), but if nothing else the ability to synchronise events "everyone be back from your mission by x" is a non negotiable. Not to mention its need for science and engineering work.

I'd expect aliens on a planet long term to derive at least a local calendar and clock to simplify life on that planet. But they'd probably choose to operate in their home time systems for anything like maths or physics.

Our Mars missions will use a custom clock to understand the conditions, but if were doing physics on the surface we'll be using old faithful metric earth seconds. If we change our time meanings we need to change measurements of energy, work, acceleration etc. Confusing this could be devastating.

A very large alien civilisation may create a galactic standard time or something. It's non trivial as the speed of light makes synchronisation provably impossible.

If we have no ftl, I'd suggest they base it on "spins of a pulsar" or something which can be observed galaxy wide. Technically events will never be in sync, "midnight" or a similar concept under the galactic calendar will propagate outwards like a wave travelling at the speed of light. The time day from the beacon will be used like our current time zones, eg "Earth is GST+707yrs."


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