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> Time is tricky but there is a simple fact: it exists such a thing as the number of actual seconds elapsed since 'time x'

Yes and no: it might just exist theoretically, but we have no way to get at it. The closest we have is TAI, which is only an approximation of the time elapsed at mean sea level on the earthly geoid, because clocks fall victim to gravitational time dilatation and compression.

To accurately measure time you'd need a clock sitting perfectly still in space, and all other clocks in the universe would slowly drift behind it.

Not even that; relativity doesn't allow a single special frame of reference. There's no such thing as universal "time elapsed since x". Putting the clock in space would be as arbitrary choice as putting it on my roof (albeit definitely more practical).

I think the one who solves this problem ( at least for humanity ) would get a Nobel.

After the humans will wander thru space ( at some time - very probable), there will no time reference, but only time intervals ( like, day on a spaceship has 24h , etc ). So in this case, you would measure 86400 seconds and call it a new day. No more leap seconds, etc.

Now the UNIX makes sense: count seconds since a certain event in time and meajure from there on, internally. Want to display it? Then use special computation to render it in the format ( read timezone, add relativistic skew, etc ).

You're forgetting to factor in accuracy/resolution. TAI is completely perfect down to the picosecond level and further. That means you do have the number of actual seconds, milliseconds, microseconds, nanoseconds...

You only encounter issues with TAI once you get down to femtosecond or smaller levels.

> TAI is completely perfect down to the picosecond level and further.

I may have worded it badly, let's try again: TAI is "completely perfect" for the approximation it is: time elapsed at the geoid, which is a theoretical construct. That's an approximation for both "experienced time" and for anything which could be called "absolute time"

Oh that's easy to solve. Just mandate everyone live at sea level.

And stop the Earth from spinning, so we can get rid of that pesky oblateness and gravitational delta between the equator and poles.

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