[FabHK]

I thought continuity provides an answer:

11:59:59.9999999999 is still AM.

12:00:00.0000000001 is clearly PM.

When should the AM switch to PM? My intuition says at the same time that the 11 switches to a 12 (and all the 9's switch to 0's). Thus, noon is pm.

Having said that, in reality the solution is banish the abominable 12 hour clock, and use the 24 hour clock.

That also removes the ambiguity whether "Midnight on January 1st 2017" means 2017-01-01 00:00 or 2017-01-01 24:00 == 2017-01-02 00:00.

[naikrovek]

I believe the actual answer is that there is no 12:00 AM or PM. You're meant to say "twelve noon" or "twelve midnight" rather than AM or PM for this exact reason.

"actual answer" is maybe a bit strong - I read it somewhere but I can't remember where. The site or book or wherever it was that I read that did seem quite authoritative on the matter, however!

[FabHK]

> I read it somewhere but I can't remember where.

Maybe in the stackoverflow answer we're discussing here? :-)

[naikrovek]

nah, I saw it in that answer but I replied before clicking the link. a bad practice, yes.

[mark-r]

That's just a cop-out. If you change the question from 11 AM to 11:01 AM it's still just as valid, and there's no need to argue about the ambiguity. Is there anybody who would seriously argue that 12:00 AM plus one minute should be 12:01 PM? That way lies madness.

[naikrovek]

12:00 isn't AM or PM. It straddles them, and isn't wholly either one because of it. That's what this is about. Some people could argue that noon is 12AM. Others can argue that it's 12PM. Both views have merit, and despite that, we need to agree on one or the other, because times are often written down and everyone needs to know what time is meant when someone writes "12AM." Since consensus on this has never been achieved, we just decided on something that people COULD agree on: noon and midnight.

The question isn't valid for 11AM vs 11:01AM, because crossing into 11:01AM doesn't put you into the afternoon like 12:01PM does. It's only a valid question at the transition time between AM and PM or vice versa. So, it was decided a LONG time ago to just skip the problem and say "twelve noon" or "midnight" (or "twelve midnight".)

[goialoq]

AM means "before noon". PM means "after noon"

12:00 noon is neither AM nor PM, and there'se no confusion.

The real question is why is the hour after midnight 12:01-12:59 AM.

Anyway, the real answer is that 0/12 and 13/1 are partial branch cuts and that "12" is used because "0" is awkward for mundane reasons, but retains some of its "0-ness"

https://en.wikipedia.org/wiki/Branch_point

[mark-r]

I'm not disagreeing that "noon" or "midnight" are less confusing, I'm simply saying there shouldn't be any ambiguity about 12AM or 12PM in the first place.

Any potential for confusion results from an ancient decision to designate noon/midnight as 12:00. If they had simply made them 1:00 instead then there'd be no trouble today.

[21]

Right. And what should I do if I'm a digital clock with limited space?

[naikrovek]

I imagine you're not pondering this problem if you're a clock.

[21]

You would need 3 leds on the display - AM/PM, noon, midnight

[FabHK]

How long would the noon and midnight LEDs burn?

[goialoq]

The quantum of resolution in the UI. Usually 1 minute

[mywittyname]

Well, since 9.9999999... = 10 [0], then 50 + 9.999999... = 50 + 10

Given that, to you claim, 11:59.59.99999[...] is still AM, then 11:59:60 is still AM, thus 12:00:00 is still AM.

[0] https://www.youtube.com/watch?v=SDtFBSjNmm0

/s

[FabHK]

Well, while the numbers of nines is finite, it's still AM.

I'm arguing for switching the very moment the number of nines is infinite, or, in other words, they've turned into (an equally infinite number of) zeros.

[jjoonathan]

Limits work from both directions. 12:00:00.1 is PM, 12:00:00.00001 is PM, so 12:00:00 is PM. Contradiction. /s, it's all in good fun :)

[barbs]

Even if you're right, by the time the words come out of your mouth, it's now PM.

That's how I remember it anyway :)

[fallingfrog]

That's true for every hour though. The same argument applies to 10:59:59.99999 and 11:00:00

Pop quiz: How many hours passed between 11am and 12am?

[imustbeevil]

The point is that a nanosecond after noon is "post meridiem".

[Finnucane]

But whose 24 hour clock? Should we all be on GMT? That's arbitrary and eurocentric. And let's get rid of those pesky arbitrary time zones too. We should all be able to have our own personal time zones.

[Fnoord]

> But whose 24 hour clock?

The one from your current timezone, obviously. And if you omit your timezone, you obviously mean your current timezone; the one you're residing in. If you're in Paris and you tell your kid dinner is at 6 PM then you mean local time. If your kid then comes home at 7 PM and says oh I thought you meant UK time then that's obviously your kid being a smartass. Even if you are both from UK. Why? Because it isn't practical to stick to a timezone you're not residing in.

Wether we're talking about 6 PM or 18 and 7 PM or 19 makes zero difference to your argument.

24H notation is just simpler and more practical. You don't have to resort to keyboard, it even takes up less space, and most importantly the context is less relevant ie. if AM/PM is omitted you still know what's up.

The only reason people stick to 24H notation, or imperial system for that matter, is "because we've always done it like this" ie. an argumentum ad antiquitatem. Not because it is better. Backwards compatibility comes with a price. You should always question whether the price is worth it.

I can think of one problem with the 24H system: analogue clocks like watches and churches. They use 12 hours. But when you watch that, that's communication to you as a human instead of human to human. And you know whether it is morning or evening, day or night, unless you're in a truly strange mental state.

[beambot]

Even if you eliminate time zones, you still end up having to do lookups whenever you're communicating across zones. E.g. "If I call my brother now from SFBA, is it normal daytime hours in Switzerland?" Knowing that right now is 15:00 GMT doesn't help answer that question.

[deadbunny]

What? The 24hour clock has nothing to do with timezones. 11:00 is the same as 11am and 21:00 is the same as 9pm whatever your timezone.

[ljm]

Measuring time over 24 hours rather than 12*2 hours makes it abundantly clear what part of the day you're referring to, no matter what timezone it is. It's not about putting everyone on the same time, but describing it without ambiguity.

This is especially important in language, where in some cultures the word 'tonight' actually translates to what you'd call 'last night' in English, for example.

[coldtea]

>But whose 24 hour clock? Should we all be on GMT? That's arbitrary and eurocentric.

Doesn't matter. Anything would be arbitrary. Just pick one and be done with it, and we already have GMT and UTC.

[Goladus]

So long as we're being completely arbitrary without any regard whatsoever natural language sensibility, let's just convert time to a metric/decimal system.

In 1998, the Swiss watch company Swatch introduced the concept of a decimal Internet Time in which the day is divided into 1000 'beats' so that each beat is equal to 1 minute 26.4 seconds. The beats were denoted by the @ symbol, so that, for example, @250 denotes a time period equal to six hours.

So far this system has not caught on

http://www.abc.net.au/science/articles/2011/11/15/3364432.ht...

[function_seven]

Sorry if I misinterpreted your response, but do you think doing away with timezones in "normal" life would be a net gain? I think it would add way more confusion than it would eliminate. (e.g. "Let's have dinner Wednesday night" would be very confusing in some parts of the world. "Is that the Wednesday night just after Tuesday night? Or the one just before Thursday night?")

[coldtea]

>Sorry if I misinterpreted your response, but do you think doing away with timezones in "normal" life would be a net gain? I think it would add way more confusion than it would eliminate.

It's the exact same information needed both today and after doing away with timezones.

If you're in the same place as the other person, there's no confusion at all. If everybody uses GMT, you know e.g. that diner around your parts (e.g. London) is around 19:00 (7pm). If you live in California you know that diner around your parts is around 03:00 (3am).

If you're in different countries, e.g. one is in London and the other is in California, "Let's have a Skype at around 11:00" is unambiguous -- it will be 11:00 at both your clocks.

Lastly, if you're in different countries and you want to call someone in California, and wonder whether now (11:00 GMT) is a good time, you just have to know the offset number (the sun rises there 8 hours later) which is the same as knowing the timezone.

Without timezones, it's only knowing the "part of the day" (whether it's late or dusk or sunrise time etc) in another place that requires knowing an offset (similar to knowing the timezone offset today).

All other calculations and coordination is vastly simplified.

>(e.g. "Let's have dinner Wednesday night" would be very confusing in some parts of the world. "Is that the Wednesday night just after Tuesday night? Or the one just before Thursday night?")

How is that confusing? Assuming we're talking about dinner, it would have to be dinner time in the place those people live. So, e.g. a little before or after sunset time on Wednesday. Whether that corresponds to 7pm or 2am or 12pm, people will know when it's that time where they live.

[function_seven]

What are we trying to solve by moving the world to UTC? We can't change when the sun rises and sets, nor can we change our circadian rhythms. So what we're left with is the fact that different parts of the world do things at different times. Using timezones, we set the start, midpoint, and end of the day to common numbers. If we ditch timezones and move to UTC-everywhere, we still have timezones. They're just implicit now. And we also have the new burden of our day changing while the sun is still up.

You waive off my dinner example as if "dinner" is a rigid set time. It's not. I'm in New York and I eat dinner at 6pm sometimes. Other times I eat at 8pm. Under UTC, this means that I sometimes have dinner on Wednesday at 23:00 and other times I wait until Thursday at 01:00. Asking someone over for "dinner on Wednesday" would always be ambiguous.

Here are some other confusing examples, if the dinner one doesn't illustrate it:

(At work)

    "What days do you have off this week?" 

    "I got Tuesday/Wednesday and Friday/Saturday off"

(At school)

    "When is the paper due?"

    "Tuesday"

    "The class that starts on Tuesday or the 
    one that ends on Tuesday?"

There's a reason we have the days change when most of us are asleep. It's a lot easier. A day encapsulates a day.

We could acclimate to all of this, sure. But we'd still have timezones. It wouldn't be immediately obvious to the Londoner that 11:00 is a terrible Skype time for her California colleagues (3am). So I don't see the gain here. Dealing with time differences is a fundamental aspect of living on a ball Earth.

[coldtea]

>We could acclimate to all of this, sure. But we'd still have timezones. It wouldn't be immediately obvious to the Londoner that 11:00 is a terrible Skype time for her California colleagues (3am)

Yeah, I addressed that though. We'd still need to know the offsets sunrise-wise or cultural-wise (e.g. 10pm is late to call in some countries, absolutely normal in others).

>So I don't see the gain here.

It's trading local time reference points (like the sun etc), for global coordination (in an increasingly interconnected and real-time planet) -- so everybody immediately knows what time X is everywhere. It's not meant to eliminate the fact that sunrise times etc are different, just to keep a stable frame of reference without timezones for time (one would still need the offsets to know whether it's night or day in place Y at time X).

>Dealing with time differences is a fundamental aspect of living on a ball Earth.

Doesn't mean there's one and only one way to deal with those though. Or that people don't spend a lot of time in the real-time, non-spherical, always-on, web too nowadays.

[QuercusMax]

Sounds like you'd love SwatchBeats[1].

1. https://en.wikipedia.org/wiki/Swatch_Internet_Time