Submitted 10 months ago by randomaccount43543@lemmy.world to xkcd@lemmy.world
https://imgs.xkcd.com/comics/datetime_2x.png
Alt text:
It’s not just time zones and leap seconds. SI seconds on Earth are slower because of relativity, so there are time standards for space stuff (TCB, TGC) that use faster SI seconds than UTC/Unix time. T2 - T1 = [God doesn’t know and the Devil isn’t telling.]
From the wikipedia:
TCB ticks faster than clocks on the surface of the Earth by 1.550505 × 10−8 (about 490 milliseconds per year)
It’s amazing that this level of detail is relevant to anything.
Without considering this, most people wouldn’t be able to drive anywhere they haven’t been before anymore.
“Wouldn’t be able to” is a bit of a stretch, since Thomas Maps existed long before GPS. But it wouldn’t be so easy as it is now.
Thank you, but I gave up halfway through the list.
I got to “The day before Saturday is always Friday” and I was like waaaa?
Epoch is your friend, or use UTC. At least that’s my layman reasoning. I have no challenges working with DateTime except when I don’t know the underlying conditions applied from the source code.
This one is good (or evil, depends on how you see it):
Human-readable dates can be specified in universally understood formats such as 05/07/11.
That one’s really good.
Which one is it?
And is it 2011/2005 or rather 1911/1905, 1811/1805,…?
I really wish that list would include some explanations about why each line is a falsehood, and what’s actually true. Particularly the line:
The software will never run on a space ship that is orbiting a black hole.
If the author has proof that some software will run on a space ship that is orbiting a black hole, I’d be really interested in seeing it.
Technically isn’t the Earth itself a sort of space ship which is orbiting (…a star which is orbiting…) the black hole at the center of the Milky Way galaxy? Not really close enough for time dilation to be a factor, but still.
All links to the original article are dead and even archive.org doesn’t have a capture either. I guess the argument is along the lines of “it might not be relevant, when you’re scripting away some tasks for your small personal projects, but when you’re working on a widely used library or tool - one day, it might end up on a space vessel to explore whatever.”
E.g. my personal backup script? Unlikely. The Linux kernel? Somewhat plausible.
It’s a programmer thing. As you’re typing the code, you may suddenly realize that the program needs to a assume certain things to work properly. You could assume that time runs at a normal rate as opposed to something completely wild when traveling close to the speed of light or when orbiting a black hole.
In order to keep the already way too messy code reasonably simple, you decide that the program assumes you’re on Earth. You leave a comment in the relevant part of the code saying that this part shouldn’t break as long as you’re not doing anything too extreme.
Well in a very strict sense one can’t really say “never” (unless you can see into the Future), but it’s probably safe to go along with “It’s highly unlikelly and if it does I’ll fix it or will be long dead so won’t care”.
Does anyone know what is untrue about “Unix time is the number of seconds since Jan 1st 1970.”?
When a leap second happens, unix time jumps back by a second. See the section about leap seconds here: en.m.wikipedia.org/wiki/Unix_time
This post made my head hurt
Ah I’ve gotten to the point where I have to define what “frame” and epoch each time base is in before I’ll touch the representation of time( Unix,Gregorian, etc) .To be honest I’m probably just scratching the surface of time problem.
Hell probably the reason we haven’t seen time travellers is we suck at tracking time and you probably need to accurately know your time and place to a very good precision to travel to a given point and we can’t say where and when that is with enough accuracy to facilitate where to land. And people don’t want to land in the earth’s surface or 10000 km away from a stable orbit. Maybe some writer can build that out for a time travel book or to discount it for some reason lol
I recall a short story like that where someone died because they time traveled, but didn’t account for position.
Highly recommended
Then there’s continental drift, which as Indiana Jones reminded us this past summer, Archimedes didn’t know about when he built his time machine.
Pet peeve: brushing aside the time travel fantasy element, there is not a single shred of evidence of any type of connection between Archimedes and the Antikythera Mechanism.
Could you eli5 what frame and epoch are? I don’t get why aren’t unix timestamps a good enough way to store time, they seem pretty easy and intuitive
I just spent two days debugging a reporting endpoint that takes in two MM-YYYY parameters and tries to pull info between the first day of the month for param1 and the last day of the month for param2 and ended up having to set my date boundaries as
LocalDate startDate = new LocalDate(1, param1.getMonth(), param2.getYear()); //pretty straightforward, right?
//bump month by one, account for rollover, set endDate to the first of that month, then subtract one day int endMonth = param2.month == 12 ? param2.month + 1 : 1; LocalDate endDate = new LocalDate(1, endMonth, param2.year).minusDays(1);
This is extraordinarily simply for humans to understand intuitively, but to code it requires accounting for a bunch of backward edge/corner case garbage. The answer, of course, is to train humans to think in Unix epoch time.
Using YearMonth.atEndOfMonth would have been the easier choice there, I think
holy shit, yeah it would have. tyvm, I’ll be putting in a PR first thing monday!
In the example you gave, wouldn’t the year be off by one when param2.month is 12?
I was transcribing it from memory and that exact problem cost me like two hours when I was writing it the first time. Well spotted, now write me a unit test for that case.
Unix epoch time in UTC, making sure that your local offset and drift are current at the time of conversion to UTC…
i don’t even care if its wrong, I just want the code to be readable.
All dates and times shall be stored and manipulated in Unix time. Only convert to a readable format at the top of the UI, and forget trying to parse user inputs :P that’s just impossible
I picture this being read by the fred armisen “believe it or not, straight to jail” character
LOL whenever I have to work with DateTime systems that try to account for every possibility (and fail trying) I am reminded that in some disciplines, it’s acceptable to simplify drastically in order to do ‘close enough’ work.
I mean, if spherical cows are a thing because that makes the math doable, why not relativity-free date-time measures that are willing to ignore exotic edge cases like non-spherical livestock?
Because “relativity” isn’t even close to your biggest problem with time. The way we communicate time changes historically, unpredictably, without obvious record. The only way to know what time you’re talking about is to know exactly how you got your information. What location, measured at what time relative to recorded changes in the local time zone, with how much drift relative to the last time you synchronized to which ntp server, and so on. These things easily account for hours or days of error, not just nanoseconds.
Not even going to general relativity, as this comics suggests to experience time slowing down due to gravity, the events are not just at time, but also at particular location in space relative particular inertial system. Not specifying it, and not specifying the inertial system for which the final answer is needed makes it impossible to calculate even in special relativity.
Here’s the shortlist of horrors I’ve had to deal with in my career:
Things I’ve read about but haven’t needed to deal with personally:
it's all relative anyway
t2 - t1 = what even is time anyway???
We can divide by t and then we get 2-1=1. Simples!
Relevant Tom Scott video the answer depends on location, times, country, religion, and a bunch of other factors.
I wonder what fraction of xkcd readers have already seen this video… I imagine it is quite high. I know I’ve seen it multiple times. It’s a good one.
Tom Scott and Veritaseum.
Scrolled trough here just to search for this comment 😂
C++ user with operator overloading: “T2 minus T1.”
Let someone else implement the class. There’s probably a library for it.
Is there a straightforward way to know which overloading will be used or is it just a roulette every time you add a sketchy new library to your build?
That’s fine if T1 and T2 include a datetime with the exact local timezone. A simple timestamp or timestamp + utc offset won’t work.
That’s me in the bottom right corner over there.
Is it you in the bottom right spotlight over there?
Looks like they’ve lost something.
ericbomb@lemmy.world 10 months ago
We use datediff in sql and let God handle the rest.
“Oh but they’re in different time zones” “Oh did you account for if one is in day light savings and other isn’t” “Aren’t some of these dates stored in UTV and some local?”
Are all problems I do not care about.
Cosmonaut_Collin@lemmy.world 10 months ago
This is why we should just move to a universal time zone and stop with the day light savings.
nxdefiant@startrek.website 10 months ago
We have that, it’s called the Unix epoch, and the only thing it doesn’t account for is time dilation due to relativity.
The_Lurker@lemmy.world 10 months ago
Swatch’s Internet Beats are making more and sense every time Daylight Savings forces a timezones change. Why are we still using base 12 for time anyway?
photonic_sorcerer@lemmy.dbzer0.com 10 months ago
Give it a few more decades