Why don't the whole planet just use UTC+00:00 / Universal Time without time zones?

Because we like midnight to happen at night, and noon to happen during the day

And you'd still have to adjust to local time anyway! Travel three timezones and now noon is at 9 instead of 12. Your alarm to wake up at 6, now needs to be at 3.
- Literally sounds a lot worse. Imagine telling your friend in Europe from the USA "ugh, I have to get up at 10 AM for work!" And the european responds with "10am is pretty late!"
- Why would you want to get up every day at 6 am from three time zones over?
- Not very convenient if a date change happens during your typical workday and that your meeting is from Monday 23:00 o’clock until Tuesday 1:00 o’clock. I mean, sure, we could deal with it, but locally it only adds new complexity.
  Sure, you could talk with anyone in the world and agree on a time without misunderstandings, but as soon as you want to know if people in the other country are even awake at that time, or if it’s during business hours, you need to do the same calculations as before and need to look up how many hours the schedule is shifted in that country, similar to before.
  My Anki deck (flashcards app) would like to know when it’s the next day. It now uses a standard (configurable) value worldwide (4:00 o’clock, to allow for late nights). If we used UTC everywhere, a standard value wouldn’t make any sense, and you would have to know the local offset, and change it when you are traveling.
  Taking about traveling: instead of just changing the time zone on your devices and be done with it, you need to look up what time you should go to sleep and wake up and at what time the stores open to fit the local schedule and none of the hours that you’re used to would make any sense. Let’s have dinner at 19:00 o’clock. No, wait, that’s in the early morning here.
  We already have UTC as a standard reference, and we don’t need to adopt it for local time, as long as the offset is clear when communicating across borders. Digital calendars already take time zones into account, so when I’m inviting people from overseas, they know at what time in their local timezone the meeting starts.
  The issue is not the time zones, but the fact that we live on a sphere revolving around a star and that our biological system likes to be awake when it’s light outside.
This is exactly right. People don't wan to change, even if the new way is demonstrably superior. Look at the adoption of the Metric system in England and the (almost) adoption in the US.
- UTC isn't even demonstrably superior.
- and the (almost) adoption in the US.
  For example:
  1 bushel is exactly 64 dry pints.
  1 dry pint is exactly 107521/92400 liquid pints.
  1 liquid pint is exactly 231/8 cubic inches.
  We formally defined the inch in terms of the metric system in the 1950s as being precisely 2.54 centimeters.
  Thus making the bushel exactly 220244188543/6250000 cubic centimeters.¹
  ¹ Unless you're talking about an oat bushel, a barley bushel, a wheat bushel, or a few other exceptions.

I believe no one else mentioned this but... China is a case study of why this is a terrible idea

The entire PRC uses the same time zone, even though in any other parts of the world, China should have been split to at least 3 different timezones

It is very disorienting to try and go for breakfast in Tibet at 9 am to find that nothing is open and the sun is just out... So yeah. Imagine if this is extended to 12-hr differences

Wikipedia has a nice summary of this

The cultural relationship with time is more important than its absolute measurement.

Tell that to the trains.
- Trains still accepted that noon should be near the middle of the day. Time zones came from railroads trying to standardize time.

So you want to abolish time zones.

That would make time more unrelated to the sun, which is pretty important.

We could just get used to the fact that in this location 6 PM means noon and in this other location it's 3 PM
It's changing all the time anyway, so time is almost never aligned with the sun.
- Sounds a lot like getting used to time zones. Just get used to it being 3pm there when it's 6pm here
- Yeah, the number on the clock is just a number. Does it matter if it says 12 or 6 or 20?
  That said, if we were going to a universal time zone, I would definitely get rid of AM/PM and do 24-hour clock.

Because that would be a nightmare. "I'll meet you for lunch at 2AM", "No, I had a huge breakfast yesterday". You would need to relearn the times every time you went to a different place, "oh, right, the restaurants only serve lunch until 10AM" or "Sorry sir, but there's an extra fee for night time services starting 1PM". Those are much more likely day-to-day phrases than scheduling a meeting with someone from another continent. And you don't gain anything by this, because whenever you're communicating across timezones you can simply use UTC as a standard and everyone knows how to convert that to their own time. So there's no good reason and a lot of drawbacks.

I am baffled that needs explanation!
Only because we're already familiar with the current way of doing things, though. If we had all been on UTC for our entire lives, it would be a simple matter of getting to a new place, asking when local noon is, and going about our business.
"Hey, when is local noon here?"
"'bout 0330."
"Cool, thanks. Want to get together for drinks tomorrow night? Say, around 1045?"
They're all just numbers. They have no inherent meaning, only what we imbue then with.
It would get a little bit tricky with the date switching over in the middle of the day, of course. In my mind, that's the biggest reason.
- So every time you deal with somebody in a different location, you can't assume anything about the hours and times you have to ask them or go look it up Even if you have a decent idea where they live because you're not going to know the time disparity of every city out there.
- Why exactly is asking for "what time is the local noon" more convenient than asking "what timezone is this"?
  How is "local noon is at 2:45" somehow easier to adjust to than "adjust your clock by X hours"? You don't need to relearn every thing like what time breakfast is served when local noon is 08:50.
- Answer quickly, if noon is 0330 what time is dinner, what is a 9-5 job and what time do you expect to have breakfast. There are lots of adjustments you will need to make, whereas with the current system you know that as a general rule you can expect dinner at around 8, most people to work 9-5, and places to serve breakfast at 8 or 9, so you switch your clock when you arrive and you're done.
  If you're a local who never moved timezones z then yeah it makes no difference what the numbers are, you would get used to waking up at 9PM and switching date midway through the day, there might even be 2 different words for tomorrow, one for the next day one for the next date, but the moment you traveled to a different location all of your years of being used to general time where things happen go out the window, it's much more of a hassle than adjusting your clock and assuming times will be mostly similar.

It would make it even harder for people to understand when it was in a different timezone. Right now I know that 11pm is late for anyone on thier own timezone. But with no timezone, I would say, the meeting is at 23:00. Thats mid morning for me, what is that for you... the answer is way less exact, and harder to covert.
So you day is my day minus half a morning?

Because the vast majority of people aren't terminally online and/or affected by timezones.

Milliseconds since the epoch is the only true time

2 more bits could have kept us in the same epoch pretty much forever. What were they thinking??
- You get over 584 million years in 2^64 ms. 66-bit computers are a bit tough to come by!

I see this argument all the time. Forget all the tradition, "people like noon near solar noon", all that.

Date changes mid day some places and not others would be a nightmare for so many things.

What're you doing on the Tuesday half of June 15/16th?

This sounds like something legitimately terrifying, but I'm struggling to make it concrete. Could you expand on the example a bit?
- Take some place currently having UTC+12 time zone, say Marshall Islands. Midnight by UTC, the moment date changes, is exactly noon there. So how should people there talk about time? There is no "Tuesday the 15th of May" there, because every day is one part one date, other part another date
  So yeah. For computers and programmers "whole planet lives in UTC" might look like a boon (for a time I myself wished for it), but only until they start facing other, more twisted problems
This happens anyway. I literally have meetings every week where it's Tuesday night for everyone else on the meeting, and Wednesday morning for me.
- That's different, your day remains Wednesday their day remains Tuesday, they're talking about going to lunch on Tuesday and coming back on Wednesday, do you call that your Tuesday lunch? Tuesday Dinner? Wednesday breakfast? Wednesday lunch?

Here are some reasons told through what-if.

TL;DR: People like to sleep in the dark generally, and businesses that close are open when more people are awake.

You still sleep at night and have businesses open during the day. It's just that the numbers displayed on the clock are different when this happens. Maybe standard business hours are 2-10 or 14-22 instead of 9-17 (I advocate 24-hour clock instead of AM/PM).
- The issue (as the link illustrates, but I didn't go into detail) comes with long distance communication. Time zones serve as a rough approximation for 'where is the sun' at a specific place that you want to communicate/trade with and that is a rough approximation for 'when are people/places likely to be awake/open. Without that you Would need to find published hours for people/places and that can be tough.
  Replacing time zones isn't impossible of course, but it's definitely not as simple as 'just use UTC+0'. That shifts the inconvenience elsewhere

So if I'm in Vancouver BC it would go from Friday to Saturday in the mid afternoon? Is Friday night the first night of the weekend or the last night of the work week?

Most people don't have to deal with booking a meeting a few timezones away or anything else where it would be an advantage on a regular basis.

It's convenient if the date, and possibly weekday, changes at night.

Swatch Internet Time tried doing something like that

tried
https://f-droid.org/en/packages/eu.mirkodi.swatchbeatclock/
Can still do it!

Because timezones were a result of town specific clocks, which were a result of people liking certain hours happening generally in line with where the sun is, like "noon" which still technically refers to when the sun is at its highest point.

Time zones were the result of railroads getting towns to abandon their town specific clocks because of railroads.
- This really fails to acknowledge the hodegpode, anything goes chaos that was towns choosing their own noon based around someone with a watch and a bell looking at the shadow on a stick a few times a year.
  Sometimes standardization isn't simply a terror induced by capitalism, and has accrual benefits.
Well, the result of railroads needing to standardize time tables.
Prior to that, towns had their own local time, and often it was approximate at best, based on a guy looking at a shadow and keeping time with inaccurate tools.
Imagine trying to explain to the people of Bumblefuck, IA that the train departs Nowheresville, IA at 10:30, and is a 30 minute trip, but the train arrives in Bumblefuck at 10:52 because the town clock is the one guy that winds his watch every day.
Its a simple matter to define noon as whatever utc time you want for wherever you are

Because who the hell wants to say it's 11 in the morning while it's dark out?

"No one," sourly thought a reader in Longyearbyen, Norway. "No one, dammit."
Longyearbyen experiences midnight sun from between 18 April and 24 August (128 days), polar night from 27 October to 15 February (111 days), and civil polar night from 13 November to 29 January. However, due to shading from mountains, the sun is not visible in Longyearbyen until around 8 March.
For no time zones? 🙋‍♂️
- Do you also want the day to change from Sunday to Monday in the middle of your Sunday morning? Or do we change days at different hours everywhere?

Because "the markets open at 9" is an international standard that everyone can count on. You could stagger it so that one country's market opens at 10, then another at 12, and so on, but then what if one country chooses a different standard? What if a restaurant picks a different convention than businesses in one area? Time zones are great because once you understand them, you'll always know how time works locally, anywhere in the world with a single piece of information, it's a truly successful standard.

- I can see how someone that doesn't understand the words would think that.
  It's not every sentence, sheesh. It's like two of them.

I'm now imagining that playing out.

"France, we're thinking about adopting British time as the global standard. Do you have any thoughts or input on the matter?"

But again, why should most of us waste our time when we’re almost never troubled by time zone changes?
But won't you think of the poor developers who have to occasionally write software that handles local times?!
(Or the poor international business person who has to coordinate virtual meetings around the globe?!?)

It's because a lot of the way humans go about their life is based on traditions. Getting everybody to switch from a system that already works pretty well is just a hassle.

Examples:

English spelling is faaar from phonetic and children take longer to learn how to spell than in Spanish for example. (though, cough, enough, plough instead of something like thouğ, koff, enaf and the US plow)
Metric system adopted globally would streamline a lot of global industries that have no cater to each system.
Driving right side everywhere. Sweden switched but asking India to switch makes way less sense.
Date formats. Arguably the best if everyone uses ISO 8601 but nobody does.

I do use ISO 8601

TL:DR -> https://thelemmy.club/comment/19143233

Examples:

The year doesn't start at the shortest day (Persian calendar is better in that regard).
month length is not evenly distributed. Why is February shorter?
time is almost never power of 10: there is 12, 60, 24
time zones are used to follow alliances: see al the nations that went to CET after fall of URSS
you can easily estimate your local time by looking at the sun
Holidays tend to happen on the same approximate dates even when major cultural changes happen. See how Christianity took over a lot of things from Romans.

because despite all the technological advancement, we still live enclosed in these self-ambulatory lumps of flesh that crave the sun.

Living in the same timezone doesn't mean waking up and going to bed at the same time.
You can still consider whatever time the sun gets up in your area as morning and the dusk will tell you when it's evening.
- What's the point of having the same time zone when people are not going by it?
  Like, "hey when you go to Singapore you gotta pay attention as the shops open at 22:00 and close at 13:00"!

This is a surprisingly divisive topic every time I see it or suggest it. I reckon the divisor is "people who use and work across timezones a lot" and "people who don't". Fuck I hate timezones.

You know who hates time zones the most? Programmers.

That would be shifting from timezone to "workzone" or "noonzone". At this moment you need to setup a meeting with people, then you ask which is their timezone. With global UTC timezone, then you need to ask, which are your work hours? (workzone).

With global UTC timezone, then you need to ask, which are your work hours?
Which would be beautiful because you'd instantly gain an intuitive understanding of how that overlaps with your own work hours instead of having to do a conversion.
- You're doing a conversion when you ask that question. My point is, there is no gain, is just converting one system for another that requires the exact work. Then we'll have tables of "workzones per country" and we need to do the same conversion to setup a meeting.

because we sleep at night and are active during the day, and so we need to track that in a way that is universal. if i mention 12:00, people understand that it is noon where i am, and if i mention 22:00, they know it's bedtime.

the whole point of time zones is to have time cohesion in a wider region within margin of error of solar noon, so people on the far east and far west of a time zone are close enough to solar noon at 12:00. you can take a train to a neighbouring city without having to worry about needing to adjust your timekeeping devices by a few minutes.

to put your scenario into perspective, china has already done what you suggested on a smaller scale: the entire country is on UTC+8 for the sake of "unity" and "national cohesion". beijing loves it; 12:00 is still noon there! except it ain't in xinjiang and tibet. xinjiang has its own unofficial xinjiang time zone of UTC+6, and so people have to specify which time zone they're talking about and convert times between the two time zones in conversation because the uyghers use xinjiang time and the han chinese use beijing time, and you can imagine the confusion and also technical issues that has arisen from that.

imagine that, but 12 times worse. no thanks, i'll do the simple math of converting time zones if i ever need to communicate internationally.

fuck daylight savings. take that shit out back.

On the other hand, we could refine time zones so they’re continuous instead of discrete chunks. Then every step you take adjusts the time. Would be more “accurate.”

We should also all work 9am-5pm of course.

Edit: it would be wild because in the USA the shops would open in the middle of the night etc.

That's 9:00 - 17:00.
Who are you, a service employee? In our country, office workers' shifts are 7-15 and factory workers' 6-14, plus 14-22 and 22-6 in two/three-shift operations. The workday opening hours of small businesses are approximately:
Convenience shops: 6-7 to 18-21 (overwhelmingly run by the Vietnamese minority)
Pubs: 10-16 to 20-24
Bakeries: 6 to 15-16
Clothes stores, jewelry etc.: 8-10 to 16-18 (closest to a "9-5")
Hairdressers, massage parlors: by appointment, usually 10-20
People who ever work after 16:00 are a minority.
- To be fair, a lot of office jobs (in Prague at least) are 9-17, or 8-16. Unless you meant government offices, which do open earlier with standart 8(7.5)hr shift

Almost a century ago, the fascist dictator of Spain wanted to appease Hitler and decided to move the timezone from the UK one to the German one. With daylight savings the situation in summer was a bit ridiculous: dark until 9 am and sun until 10 pm, it was very confusing as a tourist to have all the stores to open so late in morning and go out to eat dinner so late

I can't imagine what kind of mess would be going to Japan as a tourist on UTC+0

Long discussion here. I feel I'd like to add two things. First: we already do. If you coordinate international video calls or conference live streams, you'll say it starts 14:00 UTC. That is something we can do and regularly do. Some companies will use the timezone of their headquarters, though.

Furthermore: Once you're already in the process of changing how time works, don't do a half-assed job. Go all the way and make it metric. Do away with all the 12/24 and 60s. And make things divisible by 1000.

Base 10/100 is inferior to 12/60 when it comes to splitting.
10 can only be divided by 10,5,2, and 1. 100 only adds 4, 25, and 50 to that.
12 is divisible by 12,6,4,3,2, and 1. 60 adds 5,10,15,20, and 30.
What is time other than measuring the movements of circles and spheres? The rotation of the earth, the revolution around the sun. It makes sense for us to use the same basic 12/60/360 tools we use for circles, degrees. The “metric” measurement of circles is radians, which would require factoring pi into our measurement of time, and that would be way more complicated.
- That is correct. We'd gain a few things though. For example I could easily tell how much time passed between 8:47am and 3:22pm without doing all the gymnastics. Or maybe how many days it is until a certain date. As of now that's just a lot of irregular 30s and 31s and then the last of February and you almost need a look-up table for that with all the extra rules and exceptions.
  Main thing I wanted to say, once you decouple time from the timezones, you're somewhat on the way of making earth's spin meaningless. You'd end up going to work at 14:50 and returning home at 23:20 anyway (for example). Maybe you'll advance into a new day randomly while at it. I don't see how that's fundamentally different to just working from 250 until 600. And I think I can as easily remember to pick up the kids at 2am or at 100 ticks. Also some calculations wirh the 60 are really annoying. Netflix will show a movie is 155 minutes, it's now x o clock and do I get to bed at 10:30pm? That'd also be easier with metric. And once I look at kids these days, they don't know how to read those circular clocks in the first place. So drawing time on a circle might be an arcane, old concept to them, and we don't need to bother with the circle for much longer...
  (There is some sarcasm hidden in these words.)
  (Edit: And dividing the circle is another thing. Why not use radians, or better tau? I mean I get that 360 has a lot of divisors. But why do I need to remember that 3/4 of a circle is 270 degrees, why can't I just say three quarters of the circle? Or store a concept of how much 200 degrees is in my brain if the calculator returns this? I think it'd be far easier if it gave that to me in fractions of the whole circle. I have a rough concept of what 55% and a bit is...)

Same reason some people use miles instead of kilometers, or that most people use Windows even if they hate it.

Inertia is a powerful force.

Maybe it would be easier if the earth would be flat :)

Momentum

Why should the UK get to be the only place with an accurate local time? I don't want to live on UK time.

100% because 0 is set to UK/France. Utc 0 should have been somewhere in the middle of pacific if it was ever intended to be adopted. Now why would India or smt set their clocks to UK?

As someone who mostly lives on UTC it's such a sad wasted opportunity and it'll never be widely adopted.

For the same reason the whole planet does not use the metric system (I'm looking at you america, you old faded superpower).

Because base 10 is vastly inferior to base 12? Go ahead, divide a kilometer into thirds without repeating decimals YOU CANT WHERES YOUR ANTOIN LAVOISER NOW
Babylon was right.
- ⅓km
- Americans saying the metric system is dumb while reasoning that its bad because they can't do decimals and fractions properly will never not be funny.
  "omg 1/3km is 333.33 metres! it doesnt make any sense!"
  1 foot = 0.33 yards? "totally logical, so easy!"
  5280 feet in a mile? "wow so simple"
  10mm in a cm, 100cm in a m, 1000m in a km? "its impossible to grasp!"
  you guys think you're so ahead of the rest of the world, while crashing probes into Mars and not knowing a 1/3 pounder is bigger than a 1/4 pounder, but everyone else easily converting volume to weight to temperature to distance at every order of magnitude are just laughing at you.
So how come the rest of the planet besides America hasn't transitioned to a single time zone yet?

Well the solution to our "not enough bits" problem has been generally available for 20 years. Signed bigint time would cover from the Permian Period until 290 million years from now, down to ms precision. That ought to be good enough for most use cases.

I work with someone who does 9-5 in the next state, a messily -4 hours away.

They get to work when I have lunch, when I'm waiting on something from them in the afternoon they're just dealing with morning shit. When their system crashes at 4:50 in the afternoon as usual I'm making dinner.

So does this colleague suddenly have to work 9-5 in +0 time. Or do they keep working real 9-5?

Worst of all, he sees a bit of daylight on the sunrise commute home. Yet I as a +10 would never see the sun.

How do you propose any of this work?

Your 9-5 is his 11-4
So does this colleague suddenly have to work 9-5
Worst of all, he sees a bit of daylight on the sunrise commute home. Yet I as a +10 would never see the sun.
Everyone who works a daylight job would work a daylight job with Universal Time. We exist under Universal Time right now, and yet you (and the majority of other people in the world) work during the day. Nothing would change.
Everyone would work whatever part of the day they work right now, except the numbers would change. And you'd have to learn what numbers mean "get up", "lunch", "dinner", and "sleep" because they won't be what you're used to.
The current clock numbers are entirely arbitrary. (And they repeat!) When you were a kid, you had to learn what the hours meant relative to what part of the day it was. Under universal time, you would simply relearn that. Children learning it now would never know the difference. They would think local time is weird.
I don't understand why every time this conversation comes up, there are always people who think that it means you'd have to change when you sleep, live, and work relative to the sun. I just don't get it. It just seems like such an odd conclusion to me.