I Researchers calculate how much faster time passes on the Moon

[pinball1970]

TL;DR

A team of physicists with NASA's Jet Propulsion Laboratory at the California Institute of Technology has calculated more precisely how much faster time passes on the moon than on the Earth.

Fro phys.org

"The team in California has used math to calculate the difference in time passage between the Earth and moon, and also between both bodies and the solar system's barycenter.

In so doing, the team found that time on the moon ticks by at 0.0000575 seconds faster per day (57.50 µs/d) than it does on Earth. Based on that number, other calculations can be made—if a person were to live on the moon for 274 years, for example, they would be 5.76 seconds older than they would be had they lived on Earth all that time.

The work by the team is just the first step in establishing a standardized lunar time; meetings will have to be held between various entities to develop agreements, ensuring that everyone involved in lunar activity is on the same timetable."


paper here https://arxiv.org/abs/2406.16147

 

[anuttarasammyak]

The work by the team is just the first step in establishing a standardized lunar time; meetings will have to be held between various entities to develop agreements, ensuring that everyone involved in lunar activity is on the same timetable."

Has the standardized Earth time been established already ?

 

[pinball1970]

Has the standardized Earth time been established already ?

I took that as a given.

If they have accurately calculated that time on the moon is faster by a certain amount, it must be faster compared to a specific time on earth?

The paper is too far above my head unfortunately although I did look at it. Something for you guys.

 

[DaveC426913]

The team in California has used math to calculate

Ah yes - a marked advancement over the chicken bones and tea leaves of last year...

 

[pinball1970]

Ah yes - a marked advancement over the chicken bones and tea leaves of last year...


View attachment 348163

I nearly edited that but I thought I should quote directly.

It does read a bit naff.

 

[Vanadium 50]

I didn't read all 15 pages. Why is this interesting? Other than using math, of course.

 

[PeterDonis]

Has the standardized Earth time been established already ?

Yes, it's time on the geoid of the rotating Earth, as noted in the paper.

 

[DaveC426913]

I didn't read all 15 pages. Why is this interesting? Other than using math, of course.

"...ensuring that everyone involved in lunar activity is on the same timetable."

I think it's interesting that they seem to be anticipating a very active era of lunar ...er... activity.

Gotta keep them lunar trains running on time...

 

[Vanadium 50]

Good thing we had GPS and all these ppb-level corrections in 1969 or we never would have made it to the moon.

 

[Ibix]

It does sound a bit like a solution in search of a problem, doesn't it? Having a single well understood and clearly specified time standard would undoubtedly be useful if we were deploying GPS (LPS?) systems there, or doing other high precision relativity experiments. But we aren't, that I'm aware of.

Are there plans to put interferometric telescopes on the moon or something? Or LIGO type GW detectors?

 

[DrGreg]

if a person were to live on the moon for 274 years

A bizarre figure to choose as an example!

 

[Ibix]

A bizarre figure to choose as an example!

It's 100,000 days, which is a bit less arbitrary. Well, no less arbitrary, but at least round.

 

[DrGreg]

It's 100,000 days, which is a bit less arbitrary. Well, no less arbitrary, but at least round.

Ah I didn't realise. Explicable, but still a little bizarre. 27.4 years would have been a better example.

 

[pinball1970]

I didn't read all 15 pages. Why is this interesting? Other than using math, of course.

Yeah it's a new paper. I thought coordinating information between a fixed reference here and the moon would have been something of interest.

 

[pinball1970]

A bizarre figure to choose as an example!

Yeah. I don't know the long term plans of NASA

 

[Vanadium 50]

A bizarre figure to choose as an example!

We need an "oddly specific" emoji.

GPS (LPS?) s

GPS is fine. The moon is a globe.

 

[Ibix]

I thought coordinating information between a fixed reference here and the moon would have been something of interest.

I think it's a complex technical challenge, but kind of in the same sense a 100,000 piece jigsaw puzzle is. If you can do a 100 piece puzzle you can do the 100,000 piece one - if you have the patience.

The interesting question is why you would bother, and that section seems a bit light. The discussion at the end of the paper proposes some kinds of things you might use this for (a lunar GPS, basically, and then anything you'd use GPS for on Earth) but unless I missed something it all seems quite speculative. It's not "we need this for mission X", more like "this is an enabler for things that aren't even on the horizon yet".

GPS is fine. The moon is a globe.

One Star Trek novel (one of Diane Duane's, I think) had the Enterprise enter hephaestosynchronous orbit above Vulcan. I feel like there should be a better name than "lunar GPS"...

 

[Vanadium 50]

Isn't "geography of the moon" bad enough?

 

[pinball1970]

Isn't "geography of the moon" bad enough?

It's all relative I suppose.

 

[mathwonk]

mathematician weighing in here with arithmetic trivia. 274 years is a bit more than 100,000 days; in exactly 100,000 days the excess age would of course be about 5.75 and not 5.76. So the choice of time frame is still rather odd to me. I think I would have just said that in 100 years one ages a little over 2 seconds more.

 

[pinball1970]

mathematician weighing in here with arithmetic trivia. 274 years is a bit more than 100,000 days; in exactly 100,000 days the excess age would of course be about 5.75 and not 5.76. So the choice of time frame is still rather odd to me. I think I would have just said that in 100 years one ages a little over 2 seconds more.

They didn't include all the terms in the calculation either.

"...omitted O(c−4) terms in this expression, when evaluated at the Earth, contribute up to ∼ 9.74 × 10−17, too small to consider."

 

[Hornbein]

If is published then their goal has been achieved.

 

[ohwilleke]

Why is this interesting?

It builds intuition about the magnitude of gravitational effects on the passage of time in GR.

It is a bit like learning to use ºC without converting if you grew up using ºF. It helps to have benchmarks like normal human body temperature, room temperature, a chilly day, and a hot day to make sense of what the number mean through concrete examples.

I knew it was a small effect. But, without doing the math, I wouldn't have been able to guess if the effect was on the order of magnitude of a day, an hour, a minute, a second, or a microsecond per lifetime. Now I know: one or two seconds per lifetime. With a few more examples, in my head, I can better guess without calculating roughly what that kind of effect should be, as a reality check on any math that I do, and in deciding right off if this is a factor significant enough to include in a particular calculation.

 

[Vanadium 50]

It builds intuition about the magnitude of gravitational effects on the passage of time in GR.

Really? Whose intuition is better because of this? And why stop here? Why not Ganymede? Or Triton?

 

[ohwilleke]

Really? Whose intuition is better because of this?

Anyone he needs to understand how gravity impacts the passage of time.

And why stop here? Why not Ganymede? Or Triton?

Sure. And, maybe Jupiter, a white dwarf, and a few km out of the event horizon of Sgr A*. Intuition comes from examples, not rules. The more the merrier.

 

[Herman Trivilino]

Are there plans to put interferometric telescopes on the moon or something? Or LIGO type GW detectors?

I think they just want a standard that is as future-proof as possible.

 

[pinball1970]

In the interest of follow up (although I am aware that not many of you found it interesting/meaningful)

From the paper above.

"In conclusion, more work is needed to specify the details of the relativistic time and position transformations for various users in cislunar space (e.g., landers, orbiters, Earth-Moon Lagrange points). The introduction and maintenance of a self-consistent, fully-relativistic LCRS are essential for this purpose. Additionally, supporting this coordinate system for various practical applications (e.g., PNT services, frequency transfer, astronomy, lunar geology,fundamental physics) is crucial. This work is ongoing, and results will be reported when available."

This alert on Monday. https://iopscience.iop.org/article/10.3847/1538-3881/ad643a

From the abstract.

"This formalism is then used to compute the clock rates at Earth–Moon Lagrange points. Accurate estimation of the rate differences of coordinate times across celestial bodies and their inter comparisons using clocks on board orbiters at Lagrange points as time transfer links is crucial for establishing reliable communications infrastructure."

The first paper gives a difference of 57.5µs/d and this one gives 56.02µs/d

 

[jbriggs444]

crucial for establishing reliable communications infrastructure

The first paper gives a difference of 57.5µs/d and this one gives 56.02µs/d

High speed data circuits such as a DS-3 or an OC-3 have a frequency tolerance of 20 parts per million. That is 1.7 million microseconds per day.

Even on Earth, network links do not depend on externally synchronized clocks. One embeds timing information into the transmitted signal.

I've run reliable terrestrial communications networks without any need for externally synchronized clocks at the sub-microsecond level.

 

[pervect]

Has the standardized Earth time been established already ?

There are a number of standardized Earth times - the most relevant ones are probably TAI time, based on atomic clocks standardized to correct for altitude above sea level, https://en.wikipedia.org/wiki/International_Atomic_Time, and UTC time (the standard civil time), which differs from TAI time by a number of "leap seconds". The purpose of the leap seconds is to keep a version of the atomic time that is also synchronized to the Earth's rotation, as said rotation changes measurably. Rather than do this continuously, fixed offsets are added or subtracted from the atomic time as needed.

Traditionally, the Earth's rotation has been slowing down as it transfers angular momentum to the moon (via tidal interacations, but recently, for reasons that aren't entirely clear (there may be more current info on this out there if you do some research) the Earth's rotation has speed up.

There are a whole bunch of other time standards as well, if you really get into it. To name a few, TCB, TDB, GPS, and UT. There are some important ones I'm forgetting, all I can recall are the ICRS (International Celestial Reference Systems) and and GCRS (Geocentric Celestial Reference System), but those are coordinate system definitions which including both time and space. Those were adopted by the IAU, the Internatioanl Astronomical Union, most of the other time standards I mentioned are from the BIPM, the organization created by the treaty of the metre and the keeper of the SI standards.

https://spsweb.fltops.jpl.nasa.gov/portaldataops/mpg/MPG_Docs/Source Docs/USNO_Circular_5.1.pdf looks like it might be good reading if you want to get really technical.

 

[Vanadium 50]

Even on Earth, network links do not depend on externally synchronized clocks

Good thing, too. The speed in electronic cables varies by several ppm per degree. I expect fiber to be a little better, but mot much. You'd never keep sync across a city, let alone a country.