21 ms·
Might be O/T, but I found it really interesting how they mention "5,352 Martian solar days". Do we humans have plans in the pipeline for a universal time standa
by yingw787 8y ago
Might be O/T, but I found it really interesting how they mention "5,352 Martian solar days". Do we humans have plans in the pipeline for a universal time standard we can use wherever we are? Something that is a little more useful than "seconds since UNIX epoch" but something a little less terrestrial than UTC? Or is time going to be based wherever we land or travel (e.g. divide up Mars into time zones upon colonization)? If we don't have a formal ISO solution, it might be a good idea to start pinning one down; might be relevant by the time the standard is finalized.
- givinguflac 8y agoAgreed, I’d like it to be called “star date” like Star Trek but with fewer numbers involved.
- bch 8y agoTcl is ready for it: https://stackoverflow.com/questions/1024711/hidden-features-of-tcl-tk#comment838620_1026619 https://stackoverflow.com/questions/1024711/hidden-features-...
- scott_s 8y agoI was disappointed to recently learn that star dates were basically arbitrary: https://en.wikipedia.org/wiki/Stardate https://en.wikipedia.org/wiki/Stardate
- dahfizz 8y agoI don't really see the problem with standardizing on 'seconds since the epoch' for any interplanetary communication and having clients convert to something more meaningful to humans. Any other "universal" time format will be just as meaningless when days and seasons are all different lengths.
- tomp 8y agoYeah I don't entirely understand why we don't that already... Like, websites should be sending UNIX time to clients, and then the browser should display it in users local timezone/format.
- icebraining 8y agoHTML already has a <time> tag, which one can use to send a machine readable representation of the textual content; it would be easy for browsers to display it in local tz/format. Of course, almost nobody uses it, as usual. https://www.w3.org/TR/html52/textlevel-semantics.html#the-time-element https://www.w3.org/TR/html52/textlevel-semantics.html#the-ti...
- atoav 8y agoRelaticistic effects mean you have to resync clocks anyways, just like satelites in orbit need to do
- hermitdev 8y agoThe problem comes in due to relativity. Mars and Earth (and other planetoids) travel at different speeds. The very length of a second will drift over time.
- tomp 8y agoReally? Can't you just anchor to e.g. one revolution of the planet? That should be synchronizable...
- gmueckl 8y agoNo. You would have to observe the planet from your position and that observation changes based on how you move relative to the planet. The whole of SRT and GRT work in such a way that no general clock synchronization can ever exist for observers in different frames of reference. If you take a reference with you on a journey through the solar system, that reference will stay accurate for an observer travelling with it and drift as seen from an observer that stayed behind. Both views are accurate. Locally, the amount of time that has passed for each observer was different. If you would correct for any observed drift, you would mess with your fundamental unit of time in your local frame of reference and get incorrect measures of time passed in your own frame.
- tomp 8y agoWhat I had in mind is, you can observe your planet's position and velocity (relative e.g. to center/rotation of the galaxy), and the target planet's relative position and velocity, and use both to translate the observations into virtual "stationary" observations... And "unit of time" would be defined as 1/n of one planetary/galactic revolution, so every observer would be able to calculate their own "galactic time" independently. Well, maybe GPS already does something similar.
- gmueckl 8y agoThis would not work as what you have then is not a fixed unit, but something that keeps forever changing. And that is useless in metrology.
- wlesieutre 8y agoAt a certain point of accuracy you run into issues with this - seconds don't pass at the same rate due to relativistic effects (both speed and gravitational). An example we already deal with is GPS satellites orbiting Earth. Their clocks tick a little bit slower on account of how fast they're orbiting, and tick a bit faster on account of being further up Earth's gravity well. The gravitational effect is stronger, and the net effect is that a GPS clock advances an extra 38 microseconds over the course of a day (as measured by a clock on the ground). http://physicscentral.com/explore/writers/will.cfm http://physicscentral.com/explore/writers/will.cfm So when you try to standardize on "seconds since the epoch," the inevitable question is "Seconds according to who?"
- tlb 8y agoSeconds according to the atomic clocks at NIST. People operating clocks moving at relativistic speeds will apply the necessary corrections, as GPS satellites already do.
- teraflop 8y agoI don't think the relativistic effects would be a problem in practice. You can synchronize clocks on other planets to the UTC or TAI reference time, which are already specified in terms of the Earth's reference frame. Because of relativity, clocks on other planets would very slowly drift relative to UTC on Earth. But the drift is on the order of a few parts per billion (see e.g. [1]) which is comparable to what you'd expect anyway, even from a very high-quality temperature-controlled crystal oscillator. So it doesn't add any new clock synchronization difficulties that you wouldn't have anyway. For the most demanding applications -- the ones that require atomic clocks -- you would still need to take relativity into account. You can either measure time passing at the local rate (in cases where you need to know locally elapsed time to high precision) or you can measure UTC, which allows you to assign a consistent ordering to events on different planets. But for most ordinary purposes, the distinction is irrelevant. [1]: https://space.stackexchange.com/questions/33590/time-dilation-between-mars-and-earth-due-to-different-mass https://space.stackexchange.com/questions/33590/time-dilatio...
- wlesieutre 8y ago
- JumpCrisscross 8y ago> Do we humans have plans in the pipeline for a universal time standard we can use wherever we are? This fundamentally cannot exist. Any "universal" system would drift for observers on different planets. Having different times in New York and New Delhi isn't the worst right now; doing a calendar look-up for the time on Mars isn't as neat. But given we won't have real-time communication, it isn't as big of a problem either.
- relativitypro 8y agoProper time is an invariant that could be used for this... still corrections apply (as you suggest, for the two observers). https://en.m.wikipedia.org/wiki/Proper_time https://en.m.wikipedia.org/wiki/Proper_time
- yingw787 8y agoI know that system clock drift can be bounded to milliseconds using an atomic clock or GPS receiver, but I didn't know whether we could overcome synchronization difficulties when speed-of-light differences are significant. I thought we could package some coordinate reference system, directional travel metadata (I'm traveling 0.000002c this way), and current system clock time, and synchronize that way. Fantasy use case: Asteroid mining and traffic control. If you want to boost prepared asteroids to an orbit closer to Mars and you had a space station / spaceships to watch out for, different mining companies might want a clock protocol, a request buffer, and a map instead of synchronously planning, timing, and verifying each and every asteroid orbit change in a central location ("What do you mean you were using Earth time and not correcting for relativity??").
- ramses0 8y agoIf you ever get the chance go to the Royal Observatory in Greenwich, which has a great explanation of the difficulties (and values) associated with timekeeping: https://en.wikipedia.org/wiki/Royal_Observatory,_Greenwich#Observatory_museum https://en.wikipedia.org/wiki/Royal_Observatory,_Greenwich#O...
- etaoins 8y ago
- kharms 8y agoHow would such a standard handle time dilation?
- jerf 8y agoMost likely by declaring a standard reference frame and encoding standards for indicating amount of drift from it, tolerance of drift, and standards for how to update against it. A particularly forward-looking standard would encode information about the standard frame used within it, so we could switch from Sol-standard to galactic standard to cluster standard. Universal time is, of course, impossible in a relativistic universe, but (no sarcasm) that doesn't prevent us from trying, and getting to "close enough to work with for reasonable amounts of effort". Just as only a small portion of the world works on UTC directly right now, this time standard would be something computers would translate for people. Traveling at 80% the speed of light away from Earth in Earth's frame means you wouldn't want to directly use the resulting definition of a Standard Second for human time, but computers would be able to work with it.
- kharms 8y agoAn interesting challenge might be the computational cost of conversion to the "standard" reference given a speed near c. If a single CPU tick takes a "standard year" to compute how do you do you account for all ticks in your calculation?Is it possible to get to a sub-year standard time resolution in that scenario?
- nraynaud 8y agorecently I was wondering about time keeping on Mars, did they create a local clock network like we have with UTC here?
- kanox 8y agoEvery lander/rover keeps track of local solar time independently so they're effectively each in a separate timezone. I don't know what the orbiters use, presumably some variant of Julian day.
- dooglius 8y agoThere is BCT [0] which corrects for gravitational time dilation on Earth relative to the solar system, but I'm not aware of anything on a universal scale. It seems conceptually difficult to do synchronization if the communication round trip time, bounded below by the speed of light, is significant. [0] https://en.wikipedia.org/wiki/Barycentric_Coordinate_Time https://en.wikipedia.org/wiki/Barycentric_Coordinate_Time
- mattkrause 8y agoI think NTP uses some statistical tricks to get better synchronization than you'd expect over slow, laggy internet links. Possibly something like that could work.
- dooglius 8y agoIf we're talking interstellar travel, we're likely talking about spacecraft undergoing very significant acceleration and velocity. I'm not a physics expert, but from my understanding it seems that a starship would need to have a very accurate idea of its own acceleration vs reference time curve (relative to some reference frame) in order to calibrate its own ticking clock to the reference frame. For NTP, this isn't so much an issue because on Earth all the endpoints' clocks are all ticking at about the same rate.
- azernik 8y agoIt doesn't necessarily need a very good model of acceleration - you can probably get by with a) time at which a reference event is defined to have occurred, and b) distance to that event. From that and your locally-experienced acceleration you can (I think?) calculate relative speed and time drift.
- make3 8y agomust be Terran time, as literally all humans are currently either on Earth or orbiting around Earth, so literally everyone can relate
- magduf 8y ago>as literally all humans are currently either on Earth or orbiting around Earth The fact that this phrase of yours is literally true, and it's already 2019, makes me very sad.
- yingw787 8y agoHey cheer up now, there's no aliens we've found yet to compare to! We go our own pace and do our own thing, and Mister Rogers will always love you, and that's all that matters.
- deleted 8y ago[deleted]
- jrnichols 8y ago> Do we humans have plans in the pipeline for a universal time standard we can use wherever we are? this made me think of Swatch Internet Time, and whether or not it could have worked. https://en.wikipedia.org/wiki/Swatch_Internet_Time https://en.wikipedia.org/wiki/Swatch_Internet_Time
- myself248 8y agoThe reason I haven't tried to revive Swatch Internet Time is that it was based in GMT+1, which is just inane. I don't know if that little detail offended anyone else, but it sure torpedoed the idea for me.
- sixdimensional 8y agoI've always thought one would need a quantum clock to accomplish the same "instant" across the universe. Something that starts entangled and therefore stays in sync regardless of space and distance. That's a complete amateur physicist taking a stab at it!! I'm probably horribly wrong :)
- ajkjk 8y agoThat's not possible. Quantum mechanics doesn't give you clocks anyway, but if it did it still couldn't solve the problem of time dilation either.
- twodave 8y agoWell 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 8y ago> 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 8y agoIt 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#Base_units https://en.wikipedia.org/wiki/International_System_of_Units#...
- twodave 8y agoYes 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.
- DannyB2 8y agoAccording to relativity, you cannot get two different observers to agree on any kind of universal time, or even the order in which two events occurred. Observer A says that event X happened before Y. Observer B says that event Y happened before X. And they're both right from their POV.
- yingw787 8y agoHmm...would this only be relevant on the scale of nano/picoseconds, or seconds or higher granularity, given a frequent synchronization schedule?
- simcop2387 8y agoFor any speeds we'd be likely to be traveling, in system, it'd likely only be a problem for milliseconds if that. We'd still be able to correct for where things are as we approach them or plan to approach them.
- yingw787 8y agoYeah, I was thinking only of in the Solar System. Beyond that, the primary bound on commercializeable space is probably spacecraft propulsion, which will take a while.
- Symmetry 8y agoThe further apart the observers are and the larger their relative velocities the larger the effect is. There's nothing to stop the differential from being years in extreme cases.
- greiskul 8y agoYou are correct, but thankfully relativity tells us that in this case both events are independent, so neither can be the cause of the other, so it's not that bad of a disagreement. It's even useful as a consistency model for some distributed systems.
- duckerude 8y ago
- marzell 8y agoPlanck Seconds since the Birth of Jesus. Infallible. But seriously, since time is relative, you can only provide it with a reference included. i.e. Planck Seconds since x event (big bang/whatever) from the perspective of y. Similar to the notion of objective velocity... any object is stationary or moving only in reference to something else. Although I think we can get around that if we could get accurate measurements of quantum foam and determine if those foam bits all have velocity relative to each other.
- nekkoru 8y agoWhen exactly was Jesus born?
- james_s_tayler 8y agoI vote we switch to Metric Time. That'll solve all our problems.
- twic 8y ago> Something that is a little more useful than "seconds since UNIX epoch" Milliseconds since UNIX epoch!
- yingw787 8y agoI'm not sure about the usefulness of increasing precision if you can only guarantee a certain precision upon synchronization. I wonder if increased clock activity translates to increased clock temperature and increased clock variation. And I worry about more frequent logging and disk usage/space. But one thing I am sure of -- we would make good friends ;)
- emilfihlman 8y agoAny time period in itself is arbitrary. Our seconds, minutes, hours and days, years are sorta okay. Though I do see the irony with at the same time shaming imperial units. We'll highly likely stick with second as the base unit but create base 10 multiples on that .
- twic 8y agoUniversal, no. But the Darian calendar system has been carefully devised to fit Mars, the moons of Jupiter, and Titan, and as far as i know that's the closest anyone has got: http://ops-alaska.com/time/gangale_mst/abstract.htm http://ops-alaska.com/time/gangale_mst/abstract.htm
- basicplus2 8y agoA system based on SpaceTime with reference to the centre of the universe
- yingw787 8y agoI don't know. First we'd have to identify if there is one center of the universe; can we guarantee that the universe expands uniformly? I can't find anything online and I'm not a physicist. If there are multiple centroids of the universe, and they're all moving, we probably can't establish an eternal reference point. Also I think the confidence interval for instrumentation looking that far ahead would be so big comparative to current/possible local solutions, we're probably better off doing something in the Solar System instead. One advantage of synchronizing to some reference in the Solar System, and maybe setting clock boosters as floating checkpoints in space, is we will always be able to find our way home :)
- kanox 8y ago> Do we humans have plans in the pipeline for a universal time standard we can use wherever we are? Astronomy generally uses "Julian days" or "Julian years" which are measured in seconds since a certain calendar date. Since they're based on SI seconds intervals are independent of the Earth's movement and leap seconds and all that nonsense. Most popular epoch is J2000: measured since noon on 1 January 2000. Mars landers each track local solar time separately and a colony is likely to invent its own timezone with 24 hours and 39 minute days. You need this so that notions like "sunrise" and "sunset" make sense.
- sametmax 8y agoTime is not homogeneous accross the universe anyway, so what would be the absolute referential ? Best we can do is pick an arbitrary one, and then create algos and tables to convert from that. We already do that with UTC, and even with something that simple, it gets hard: politics gets in play, and we have to reajust our time slices with leap periods regularly.
- Yizahi 8y agoOne of the proposals for Mars in fiction was to use Earth 24 hours and then stop the clock for those additional 30 or 40 minutes Mars day has. Anyway, I suspect that humans will tend to use the most common standard, meaning some legacy standard and in case of time it is likely would be UNIX time. 110 volts AC too probably :)
- daddylonglegs 8y agoWell, the Martian solar day is a directly relevant measure for a mission that depends on charging batteries each day by solar power. I could see that being used for a lot of planning and operations. UTC (and international atomic time - TAI) is an average measure of elapsed time that already needs adjusting for relativistic time dilation. None of the accurate clocks used for TAI are at sea level but TAI is reported as though you had all your caesium atoms ringing away at sea level [0]. Everyone else adjusts their clocks with reference to this, making allowance for propagation delays where needed. This includes things like navigation satellites (GPS, Galileo, Glonass, BeiDou etc) which have accurate clocks and significant (for their operation) relativistic dilation. Since we already have to deal with relativity and propagation delay here on earth I suppose that, if your mission can still ping mission control here on Earth, then you can still set the system clock to UTC or TAI [1]. You will need a look up table for local sunrise times and the like but that seems quite simple compared to the mess that tzdata has to allow for back home. [0] As I write this I realise that I don't know if TAI will be adjusted for sea level changes or not. Anyone know? [1] Using TAI might save you from leap second problems while landing on an alien planet.
- benj111 8y agoThe problem you are always going to have is that the inhabitants of each planet will want their 'days' to line up with their day/night cycles. So even without relativity, you aren't going to get a unified date system that works for everyone. If that's the case Unix time then becomes a decent option, because it's equally human unreadable to everyone. Each planet can then have their own calendar based on that, and computers can deal with the nitty gritty