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Comment by umvi | Hacker News Reader

Should we go ahead and make a SSCT (solar system coordinated time) as well?

That way I don't have to constantly be converting lunar timestamps, mars timestamps, etc. back to UTC (or the coordinated time of whichever celestial body I'm currently on) in order to paint a timeline of when events happened between my different devices spread out across the solar system.

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Wouldn't that need accounting for relativity? Distance to the gravity well (sun) affects the physical passage of time for you. Perhaps that's doable, but you can't count a sequence of numbers off and call it a day.

Time is local to a region though - there isn't any "Solar System Coordinated Time".

I guess pulsars may be our best bet for a universally coordinated time? We can detect the passage of time in a gravity well and create a well-centric system if need be!

Are you saying that a given pulsar acts as a giant sky clock? And that because it is far away — for some large value of far — it means that any clock inconsistencies across the solar system can be compensated for?

Pretty much, yes! Obviously the speed of light and orbital motion/distances make things tricky but not impossible.

I think I’m also saying that since time passes at different rates in different gravity scenarios, a single external reference may be the best way to coordinate time… even outside of our solar system.

Actually, “single external reference” might be wrong here. Using multiple pulsars might give us a better fix for our position +time solution across large distances.

Even cooler is that this has apparently and unsurprisingly already been explored.

These replies are intriguing, thanks. Do you have some good links / references I can follow?

Pulsar positioning system: https://arxiv.org/pdf/1704.03316.pdf

While not a primary source, it's still an answer to absolute time from pulsars: https://physics.stackexchange.com/questions/175981/can-you-u...

Well, no, pulsars periods drift due to change of alignment and emission process over time. Thought special and general relativity will drive any "global/solar system/galaxy"-wide precise time useless on long term anyway. The best is to keep track of long enough common measures ("day", "month") with decimal/fractions being connected to actual local times.

The Earth “day” also drifts over time. If you’ve ever thought today was longer than the last, then you are statistically correct!

Just hold still and avoid gravity wells. It’ll work out.

What is hold still? Relatively to what? Everything moves relatively to each other with a planet, solar system, galaxy, galaxy cluster, supercluster, filament, Universe...

I'd say define a "cycle" as greatest common divisor of all planets' rotation periods. Make it an equivalent of "solar system day/hour" or something.

The problem is these orbital periods are generally not rational multiples of each other, so their GCD is undefined (or 0, in a sense).

Some exceptions to this exist due to orbital resonance: Pluto and Neptune are in 2:3 resonance, and in the Jovian system Ganymede, Europa, and Io are in 1:2:4 resonance.

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