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

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

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

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.

So you want to abolish time zones.

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

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?

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.

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

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.

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?

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).

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?

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?

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

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.

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.

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.

Milliseconds since the epoch is the only true time