5 ms·
A relativistic framework to establish coordinate time on the Moon and beyond
- argumentofperi 2y agoNumerical evaluation of Eq. (4) yields a value 1.2695 × 10^−12(cos(f ) + e) or 0.1097(cos(f ) + e) μs/day. Typo?
- engineer_22 2y agoIn the abstract they hint that without a common clock communication could be inhibited
- teruakohatu 2y agoDo they? I don’t see that in the abstract, they do state that: > This understanding also underpins precise navigation in cislunar space and on celestial bodies' surfaces, thus playing a pivotal role in ensuring the interoperability of various position, navigation, and timing (PNT) systems spanning from Earth to the Moon and to the farthest regions of the inner solar system.
- karmakaze 2y ago> [...] and their inter-comparisons using clocks onboard orbiters at relatively stable Lagrange points as time transfer links is crucial for establishing reliable communications infrastructure.
- davidw 2y ago"I was in favour of space exploration until I realised what it'd mean for date time libraries" https://x.com/joe_jag/status/510048646482894848?lang=en https://x.com/joe_jag/status/510048646482894848?lang=en
- deleted 2y ago[deleted]
- jiehong 2y agoNice! It made me realise that we currently live in a time that can never be accurately referenced outside the planet. So no software can ever truly define 2024-07-11T00:00 on Pluto. It also makes me think that the Mass Relais in Mass Effects could actually also be atomic clocks forming this galactic time grid of reference, so in-game lore seems less implausible.
- WorldMaker 2y agoThere are interesting theories about how to use constellations of Pulsars as galactic "atomic clocks". Pulsars are generally extremely predictable in their emissions and with a big enough constellation, you can do old fashioned triangulation to get relative distance between yourself and enough pulsars to sync to some sort of standard time based on synchronicities in pulsar timing. I've not yet seen a full proposed standard for such a thing, but it's also not far from how GPS itself works and how GPS forms its standardized time, which is synced to Earth based atomic clocks but includes more relativistic effects. Most cellphones actually use GPS time rather than "atomic time" today, because they need GPS services in general and also because cell towers use a variant of GPS time in their communications with cell devices for complicated three dimensional dances like tower to tower hand-offs. It's kind of neat how even "Earth time" at its most accurate involves relative effects and triangulation in some of our most used and trusted devices. (Even NTP sync of non-cellphones uses IP pings as an approximate for triangulation to try to reduce error in syncing a laptop or desktop to nearby atomic clock sources. Though at least today in most internet usage, the Internet Protocol is less impacted by relativistic effects.)
- zokier 2y ago> how GPS itself works and how GPS forms its standardized time, which is synced to Earth based atomic clocks but includes more relativistic effects While the GPS satellites internal clocks might operate on whatever timescale, it is important to note that the time signal that is broadcast through GPS is strictly fixed offset from TAI without any additional relativistic shifts. And TAI is defined to use the geoid as reference frame. That is to say that if you have a clock synchronized to GPS signal then it should tick exactly at same rate as TAI and UTC.
- bloopernova 2y agoNow I'm wondering just how timekeeping would work with distance and/or high relative velocity. Would you observe "ship time" until you returned to base, and would then sync ship to base time?
- jerf 2y agoThat particular problem isn't necessarily materially different from the ships we already have that experience major time shifts every day. Time zones already create that problem and you can just look at the solutions we use today.
- ianburrell 2y agoThe ship would keep local time because that is easy to measure and fits with what people are doing. The point of establishing Moon time is that it is hard to keep using non-local Earth time. Keep in mind that there is difference between clock measuring seconds, and converting to days and times that requires choosing a calendar. The ship could use origin calendar, destination calendar to make people familiar, or some universal calendar. The problem with destination is that it won't sync properly until arrival. Or maybe they skew the calendar on the last leg. Also, don't need high relative velocity to have a difference. Considering relativistic space travel may be impossible; the only may be proposed warp drives.
- hlieberman 2y agoMissed opportunity to name it "stardate".
- deleted 2y ago[deleted]
- jvanderbot 2y agoIt strikes me as surprising to imply that we don't have time-keeping standards for solar system exploration that take into account relativistic differences. the CSPICE toolkit from JPL/NAIF has a bunch of routines to calculate local time, local time of arrival of events from other places (light cone, I suppose?), down to the nanosecond.
- jrcii 2y ago[dead]
- nynx 2y agoThat code exists for calculating those things does not mean there are timekeeping standards that support them.
- jvanderbot 2y agoTrue, should have mentioned (as sibling comment did) that the code _uses_ several timekeeping standards to do those calculations.
- zokier 2y agoThere definitely are various timescales and standards that take relativity into account https://en.wikipedia.org/wiki/Barycentric_Coordinate_Time https://en.wikipedia.org/wiki/Barycentric_Coordinate_Time https://en.wikipedia.org/wiki/Ephemeris_time https://en.wikipedia.org/wiki/Ephemeris_time https://en.wikipedia.org/wiki/Coordinate_time https://en.wikipedia.org/wiki/Coordinate_time Etc
- nickdothutton 2y agoI wonder if Sci-Fi novels contain any info on time representation, reference, and distribution.
- WorldMaker 2y agoThere's a lot of fascinating discussion around Star Trek's Stardate and its seemingly universal metric calendar and times referenced as decimal units of day: How does it adjust for relativity? Why did they choose the epoch they seemingly chose? (Not that many days before Enterprise's 5-Year-Mission, and seemingly still years into Starfleet's existence.) How do you account for the various obvious real world facts that many episodes just picked numbers that sounded cool or random and didn't pay attention if they were in the right order in the season or overall timeline? (Is that relativistic problems creeping in?) They are called Stardates implying the base unit is a Day, but it is an Earth-like 24 hour day or was it something else, perhaps in a compromise with other Federation planets? From the TNG era onward the various Writer's Bibles took an approach of 10,000 days per season to make the math easy if a script was given a Stardate in the right season and plenty of room for all the scripts in a season to have their own Stardates. If the Stardate day is a 24 hour Earth day equivalent then seasons were expected to take roughly 3 earth years. Or was that a sign that the Stardate day was about a third shorter than an Earth day and "five-year mission" did still just refer to Earth standard years? There are all kinds of fan theories. Some weird things in canon. Some weirder things in the books and other bits of Beta and Gamma "canon". (I did a bit too deep of a dive into Stardates recently as an offshoot of getting the idea to try to display a Stardate-like calendar and date stamps in the configurable calendar system of the Fantasy Grounds TTRPG hosting application.)
- akozak 2y agoIt's a neat idea that you could publish a paper like this that establishes a framework for thousands of years.
- alganet 2y ago> yielding 58.721 μs/day Can someone kind explain this unit for me? microseconds per day. Does that mean that the relativistic difference is cummulative? In other words, does it add up over time?
- nh23423fefe 2y agoits actually not a unit either. its a dimensionless ratio
- akira2501 2y ago6.79641e-10
- unholiness 2y agoThat's right. While a day passes on earth, a day minus 58.721 μs passes on the moon (which is moving faster than the Earth). This multiplies, so after a million days a clock on the moon will read 58 seconds behind a clock on the earth.
- pdonis 2y agoIt's the other way around: while a day passes on Earth, a day plus 58.721 microseconds passes on the Moon. The Moon clock gradually gets ahead of the Earth clock. In an Earth-centered inertial frame, the Moon is moving faster than the Earth, but it is also at a very high altitude, and the altitude effect, which speeds up the Moon clock relative to Earth, is much larger than the speed effect, which slows it down. (Note that the above only takes into account the effects of the Earth's gravity. The paper also takes into account the effects of the Moon's gravity, which don't change the above answer qualitatively but do add small corrections numerically, so the 58.721 microseconds per day is not the actual value the paper ends up with.)
- alganet 2y agoCool, thanks! I'm assuming this affects clocks (and things) but not time, right? Time itself is no different on the moon (it's not the future there). I know this must be true otherwise we would be surrounded by time travellers by now. So, where does this cancels out? My intuition says that if we have two clocks, each clock with a display and a laser pointing to each other, and we put one of them on the moon and the other on earth, someone observing it from a third equidistant point would see both lasers blinking at the same rate. If that's true (I don't know if it is) both of your answers are kinda right, aren't they? From earth, the moon clock ticks slower compared to earth clocks, therefore it lags behind. From the moon, the moon clock ticks faster compared to earth clocks, therefore it skips ahead, and vice-versa. I am not sure though, I feel like I'm missing something.