[twodave]

Well the problem is a "second" is just a unit of rotation of the Earth on its axis. So you'd either need to use some other reference material than a rotating body in space or else use some arbitrary one (like Earth, since that's where we are from!) and choose a reference date (why not use one we're all familiar with? I know! We could use the UNIX epoch!).

Even if you did this, your universal time would just be a synchronizing tool. Each human consumer would expect it to be translated into the most relevant time to them. If you think it's hard getting people to adopt a standardized date/time on one planet, every planet you add to the system makes that an exponentially more difficult task.

[noir_lord]

> We could use the UNIX epoch!

Vernor Vinge got there way ahead of you, If you haven't read his books and given the way this community slants you are missing out.

> Take the Traders' method of timekeeping. The frame corrections were incredibly complex - and down at the very bottom of it was a little program that ran a counter. Second by second, the Qeng Ho counted from the instant that a human had first set foot on Old Earth's moon. But if you looked at it still more closely ... the starting instant was actually about fifteen million seconds later, the 0-second of one of Humankind's first computer operating systems.

[mey]

It was previously based on rotation of the earth. It was converted to atomic analysis of the caesium atom in 1967.

https://en.wikipedia.org/wiki/International_System_of_Units#...

[twodave]

Yes obviously we aren't sitting here measuring the earth's rotation to set our clocks. The point is the meaning of the number remains the same. Seconds, minutes and hours have meaning, and the meaning of those measured amounts of times is directly related to some fraction of the rotation of the planet we are currently sitting on. The point was moving this system of time-keeping to some other planet would discard much of its relevancy to our every-day life, which matters a lot.

[echlebek]

That's actually not true if you're using SI units for seconds.

"The SI unit of time is the second (s): The second is 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."

I'm not a physicist, but I think that's a universal definition - the rate of the periods should be constant everywhere in the universe.

So universal seconds are actually very easy to nail down. Dates are always a little more troublesome. Perhaps seconds since the start of the big bang would be a possibility.

[twodave]

The point wasn't to explain how we measure it or whether it is easy or not, the point is that the unit of measure was selected for its meaning, and that meaning has little relevance on other planets.

[wbl]

You are forgetting relativistic effects.

[dfox]

Because SI itself assumes that you and whatever you are measuring is in same relativistic frame of reference. When you start to take relativity into account the whole system breaks down horribly.