6 ms·

Now we're going to have "lies programmers believe about time": 1. Seconds in one time system last the same amount of time as seconds in another time system 2.

Now we're going to have "lies programmers believe about time": 1. Seconds in one time system last the same amount of time as seconds in another time system 2. Seconds in the same time system last the same amount of time as each other 3. Time numbers are strictly increasing - the same time number can't happen again 4. [etc, kill me]

karmakurtisaani 5y ago
Just wait until we reach the proper space age and start traveling at speeds close to the speed of light. Taking into account the relativistic effects is going make more than a few coders switch carees to organic farming.
- nradov 5y ago
  GPS satellite designers already have to account for clock skew due to relativistic effects. A nice little real world confirmation of the theory.
- monocasa 5y ago
  Luckily clock skew already happens and is handled more or less by the current systems. The difference between the system moving at relativistic speeds versus a crystal being slightly out of spec add up to the same result. Incorrect number of ticks for a given proper time interval. That's part of the genius of Leslie Lamport, embracing the fact that your distributed clocks aren't consistent, so start looking at effects through distributed systems from a light cone perspective just like you do with relativity.
  - willis936 5y ago
    Clock skew is in error. Relativistic time dilation is not. Both clocks will be right and disagree. You can't escape answering the question: do I care about the time elapsed at home or the time elapsed here?
    - kuschku 5y ago
      We already define time relative to 1970-01-01, relative to the mean solar noon in Greenwich. We should also define the length of a second to mean "at sea level in Greenwich".
      - tialaramex 5y ago
        This just means the "length of a second" wanders around randomly and is thus useless. So now "a second" isn't any particular amount of time, and you've lost all ability to really measure time except in a vague inexact sense. The quest to eliminate irreproducibility from metrication is why SI did all that work to finally eliminate the kilogram prototype. The second was defined reproducibly decades ago because trying to define it based on our planet's inconstant spin was such a failure. The fact that the Earth's spin is not constant is perhaps frustrating, but like other facts just insisting it isn't true doesn't help you.
        kuschku 5y ago
        > This just means the "length of a second" wanders around randomly and is thus useless Why would it? My redefinition just means the length of a second is defined as a given number of cycles of caesium in a gravitational field equivalent to that of Greenwich. If you're in a different gravitational field, you'll just have to convert the values easily.
        fanf2 5y ago
        Right, but general relativity matters for how astronomers define their timescales, and how they are measured and maintained in practice: there are different scales for barycentric time (at the centre of gravity of the solar system), geocentric time (centre of the earth) and terrestrial time (on the surface of the rotating geoid). TAI is supposed to tick at the same rate as TT, so it depends on a model of an equal-gravitation version of sea level (the geoid) and the relative height of the time labs. In particular, NIST is a mile high in Colorado so their clocks tick a lot faster than (say) NPL by the Thames in west London.
- gorjusborg 5y ago
  I'd like to think my descendants will be beet farmers in a far away solar system.
- ISL 5y ago
  Those corrections (both special and general relativistic, with opposite signs) are already required to allow GPS to function.
- eftychis 5y ago
  We do: all these are taken into account for satellites. In particular GPS is one of the prime examples as it is affected by both special and general relativity and how fast time elapses is critical to its function.
- Swenrekcah 5y ago
  Probably takes some serious skills to be an organic farmer on Ceres.
  - bee_rider 5y ago
    Conveniently it turns out that the results are the same independent of your skill.
  - labster 5y ago
    It does, but you make more money than you would using standard farming methods and pesticides on Ceres.
npongratz 5y ago
We already do: https://infiniteundo.com/post/25326999628/falsehoods-programmers-believe-about-time https://infiniteundo.com/post/25326999628/falsehoods-program... HN discussion (among others less recent and/or less popular): https://news.ycombinator.com/item?id=19922062 https://news.ycombinator.com/item?id=19922062 More falsehoods: https://infiniteundo.com/post/25509354022/more-falsehoods-programmers-believe-about-time https://infiniteundo.com/post/25509354022/more-falsehoods-pr...
- nwallin 5y ago
  A collection of several falsehoods programmers believe lists, not just time: https://github.com/kdeldycke/awesome-falsehood https://github.com/kdeldycke/awesome-falsehood
2muchcoffeeman 5y ago
Why wouldn’t we decouple time from the earths orbit? Instead have 2 calendars: the normal date time is standardised, no leap anything and simply increases. The orbital time tracks the earths revolution around the sun. Sure, eventually the two will drift. But leap days account for 3 weeks-ish of time for the average person through out their life (let’s assume 80 years life span for arguments sake). So this doesn’t seem so hard to adjust to.
- deleted 5y ago
  [deleted]
- FredPret 5y ago
  Leap seconds are so much simpler than trying to wrangle two calendars with built in drift
  - 2muchcoffeeman 5y ago
    I'm not sure how you figure that. In my system, the time is simply a number that increments. No calculations are ever needed to correct anything. This is what most people use to schedule things. The second "clock" tracks position of the earth around the sun. You need it for the seasons. But this too is always exact. There will never be a situation where we need to adjust it. You can never reach the end of a year and be slightly short on the distance traveled around the sun. So one day Xmas is slightly warming than usual. But so what?
    - FredPret 5y ago
      Every person using their calendar is solving one simple problem in a simple way. But the real magic of the calendar is that billions of individuals use the same calendar for the same problem and thus we can all agree what day it is, every single day. So if there's an issue with the existing calendar, then simply adjusting our calendar by an amount really no-one will notice is by far the most practical solution. Almost every industry cycles with the season; we need the calendar to track it accurately.
wglb 5y ago
Here is one of many. Several are also shown in this thread: https://gist.github.com/timvisee/fcda9bbdff88d45cc9061606b4b923ca https://gist.github.com/timvisee/fcda9bbdff88d45cc9061606b4b...
vba616 5y ago
I took leap seconds for granted, then I read about Google "smearing" leap seconds. And then (on HN) I read about someone else working on a standard for smearing them differently than Google does, just because. ...aaaand there's an xkcd: https://xkcd.com/2266/ https://xkcd.com/2266/

karmakurtisaani 5y ago

Just wait until we reach the proper space age and start traveling at speeds close to the speed of light. Taking into account the relativistic effects is going make more than a few coders switch carees to organic farming.

nradov 5y ago
GPS satellite designers already have to account for clock skew due to relativistic effects. A nice little real world confirmation of the theory.
monocasa 5y ago
Luckily clock skew already happens and is handled more or less by the current systems. The difference between the system moving at relativistic speeds versus a crystal being slightly out of spec add up to the same result. Incorrect number of ticks for a given proper time interval. That's part of the genius of Leslie Lamport, embracing the fact that your distributed clocks aren't consistent, so start looking at effects through distributed systems from a light cone perspective just like you do with relativity.
- willis936 5y ago
  Clock skew is in error. Relativistic time dilation is not. Both clocks will be right and disagree. You can't escape answering the question: do I care about the time elapsed at home or the time elapsed here?
  - kuschku 5y ago
    We already define time relative to 1970-01-01, relative to the mean solar noon in Greenwich. We should also define the length of a second to mean "at sea level in Greenwich".
    - tialaramex 5y ago
      This just means the "length of a second" wanders around randomly and is thus useless. So now "a second" isn't any particular amount of time, and you've lost all ability to really measure time except in a vague inexact sense. The quest to eliminate irreproducibility from metrication is why SI did all that work to finally eliminate the kilogram prototype. The second was defined reproducibly decades ago because trying to define it based on our planet's inconstant spin was such a failure. The fact that the Earth's spin is not constant is perhaps frustrating, but like other facts just insisting it isn't true doesn't help you.
      - kuschku 5y ago
        > This just means the "length of a second" wanders around randomly and is thus useless Why would it? My redefinition just means the length of a second is defined as a given number of cycles of caesium in a gravitational field equivalent to that of Greenwich. If you're in a different gravitational field, you'll just have to convert the values easily.
      - fanf2 5y ago
        Right, but general relativity matters for how astronomers define their timescales, and how they are measured and maintained in practice: there are different scales for barycentric time (at the centre of gravity of the solar system), geocentric time (centre of the earth) and terrestrial time (on the surface of the rotating geoid). TAI is supposed to tick at the same rate as TT, so it depends on a model of an equal-gravitation version of sea level (the geoid) and the relative height of the time labs. In particular, NIST is a mile high in Colorado so their clocks tick a lot faster than (say) NPL by the Thames in west London.
gorjusborg 5y ago
I'd like to think my descendants will be beet farmers in a far away solar system.
ISL 5y ago
Those corrections (both special and general relativistic, with opposite signs) are already required to allow GPS to function.
eftychis 5y ago
We do: all these are taken into account for satellites. In particular GPS is one of the prime examples as it is affected by both special and general relativity and how fast time elapses is critical to its function.
Swenrekcah 5y ago
Probably takes some serious skills to be an organic farmer on Ceres.
- bee_rider 5y ago
  Conveniently it turns out that the results are the same independent of your skill.
- labster 5y ago
  It does, but you make more money than you would using standard farming methods and pesticides on Ceres.

npongratz 5y ago

We already do: https://infiniteundo.com/post/25326999628/falsehoods-programmers-believe-about-time https://infiniteundo.com/post/25326999628/falsehoods-program... HN discussion (among others less recent and/or less popular): https://news.ycombinator.com/item?id=19922062 https://news.ycombinator.com/item?id=19922062 More falsehoods: https://infiniteundo.com/post/25509354022/more-falsehoods-programmers-believe-about-time https://infiniteundo.com/post/25509354022/more-falsehoods-pr...

nwallin 5y ago
A collection of several falsehoods programmers believe lists, not just time: https://github.com/kdeldycke/awesome-falsehood https://github.com/kdeldycke/awesome-falsehood

2muchcoffeeman 5y ago

Why wouldn’t we decouple time from the earths orbit? Instead have 2 calendars: the normal date time is standardised, no leap anything and simply increases. The orbital time tracks the earths revolution around the sun. Sure, eventually the two will drift. But leap days account for 3 weeks-ish of time for the average person through out their life (let’s assume 80 years life span for arguments sake). So this doesn’t seem so hard to adjust to.

deleted 5y ago
[deleted]
FredPret 5y ago
Leap seconds are so much simpler than trying to wrangle two calendars with built in drift
- 2muchcoffeeman 5y ago
  I'm not sure how you figure that. In my system, the time is simply a number that increments. No calculations are ever needed to correct anything. This is what most people use to schedule things. The second "clock" tracks position of the earth around the sun. You need it for the seasons. But this too is always exact. There will never be a situation where we need to adjust it. You can never reach the end of a year and be slightly short on the distance traveled around the sun. So one day Xmas is slightly warming than usual. But so what?
  - FredPret 5y ago
    Every person using their calendar is solving one simple problem in a simple way. But the real magic of the calendar is that billions of individuals use the same calendar for the same problem and thus we can all agree what day it is, every single day. So if there's an issue with the existing calendar, then simply adjusting our calendar by an amount really no-one will notice is by far the most practical solution. Almost every industry cycles with the season; we need the calendar to track it accurately.

wglb 5y ago

Here is one of many. Several are also shown in this thread: https://gist.github.com/timvisee/fcda9bbdff88d45cc9061606b4b923ca https://gist.github.com/timvisee/fcda9bbdff88d45cc9061606b4b...

vba616 5y ago

I took leap seconds for granted, then I read about Google "smearing" leap seconds. And then (on HN) I read about someone else working on a standard for smearing them differently than Google does, just because. ...aaaand there's an xkcd: https://xkcd.com/2266/ https://xkcd.com/2266/