Okay. I work in Minneapolis and need to schedule a meeting with someone in London. How do I know what UTC time is during daylight hours for both participants? Well, we can use a formula that will tell us where the sun in the sky for a given longitude. But that's kind of a chore. So let's break ranges of longitude into zones and create a lookup table. Hang on a minute...
I've just traveled to Tokyo from Minneapolis. What time do I need to set my alarm to, to wake up an hour before most businesses open? Well, I can use trigonometry to figure out what UTC time the sun will rise at this location on Earth. But that's kind of a chore, so presumably each city will have an offset from UTC time that they all agree on to begin business hours. Hang on a minute...
Fine.. so I'm going to have a teleconference with a company in NYC. Due to what you wrote above I now have an idea of what UTC time window to plan for - after all, I want to be able to reach them during their working hours.
Then on Friday I have to schedule a teleconf with a company in Japan. When do they work, relative to UTC? You forgot to add that, so I have to find it somewhere.
Hm, wouldn't it be nice if my computer could keep track of the working hours everywhere in the world. Let's make a database of that.. There's just one issue: How is this any better than using the timezone system we already have? Using that, I can figure out the local time in those places, and I can safely assume that they'll at least be working from around 09:00 local time. Having to instead keep track of their working hours relative to UTC doesn't seem like much of an improvement to me.
Except for most people it is almost never a problem because most people aren’t scheduling phone calls or meetings with unfamiliar locations.
The benefit is obvious: things that happen at the same time have the same number associated with them. Just like we currently coordinate dates using a shared calendar, we coordinate times. And that has a local benefit as well. Aside from no more daylight savings time which we can achieve using other means, we also know when world events happen as they are being reported, we know when certain things take effect for countries that span multiple timezones now, we know the exact difference between any two given time points without asking “but where are they happening?”
Again, imagine that we had unified time and some country somewhere said “hey we are using the same format but doing our own variable offset from it”. That would be absolutely asinine. We are used to timezones and think they benefit us because of that familiarity. In reality we have had variable time even in the same timezones before and it was universally a bad idea that was shut down soon as people started traveling.
Oh and consider that due to cultural differences your example of scheduling meetings is already flawed: do you know if Tokyo wraps up the workday at 4pm or 6pm? Is there an hour or two hour lunch break in Barcelona? When do people actually come to work in Rome? Are banks open on Saturdays in Baghdad? Timezones do not solve these issues whatsoever so you still need to do the lookup of “when are people actually around” when scheduling a meeting outside of your culture.
2) If you want to let everybody in the world know when something specific happens (e.g. the launch of the first manned Mars mission), then you specify the time in UTC. But.. that's what we do already. Or at least those with some sense. There's still no need to force Joe Nobody to get to work at 14:00 (assuming a single world time zone) when the sun rises.. there's no advantage for people elsewhere in the world. You yourself argued that "most people aren't scheduling phone calls or meetings with unfamiliar locations". So, what's the advantage here?
3) I happen to use a calendar which is coordinated with others - it happens automatically, when they schedule something. And it has zero problem with the time - it's not just date. There's zero to gain by using UTC as localtime everywhere. That does nothing for the calendar.
4) Cultural differences in work hours: They absolutely exist. So what would having everybody use UTC help with? You still have to know those differences. It's even worse then, because if my stepson tells me "I have to work to 10AM" then I know it's late, for him. I know it instantly. If he had said "..have to work to 13 UTC" then I'm lost. I don't immediately see that he's actually working very late. I'll have to think "let's see.. he's in Tokyo, so that would be, hmm, this many hours difference from here.. is there an issue here? Oh wait, "you're working really late, will you be you okay?"
5) And that statement ".. most people aren't scheduling phone calls or meetings with unfamiliar locations". That's false. We're not in the 19th or even the 20th century anymore. The internet is a thing, and tons of people are in daily contact with people from all over the world. Just a moment ago I got a message from an airbnb guest, for example.
I also think that your using the example of submarines -- notoriously an onerous lifestyle that very few are capable of living -- pretty much torpedoes your implicit suggestion that this would not be too much of a change.
You did that on porpoise I hope.
And the reason why people don’t just do that is because it is a network effect problem. We all need to buy into it. Like the metric system or driving on the same side of the road.
And people do this. Haven’t you seen people who routinely talk to people outside their timezones sign their email with their location and/or UTC work hours?
You have plans to go to the theatre on Tuesday after work.
Is that 0100 on Tuesday (after finishing at 2300 on Monday) or 0100 on Wednesday (after finishing at 2300 on Tuesday)
The solution is to just use UTC. That’s it. That means in NYC you’d get to work at 13:00 and go home at 21:00, which used to be 9am-5pm. That’s it. Your whole transition has been completed. The rest is just what your calendar says. Niece’s recital on Thursday at 19:00, beers with Greg at 23:00 on Friday, etc. It really isn’t hard to imagine.