There's no reason 1200 should be midday. If we changed this today the next generation would never stop to think about how "weird it is that it's dark at 1200" where they live.
Of course, nothing stops people from using UTC only for the situation where it's really useful: long-distance coordination. (And as mentioned in other comments, that's often done already.)
The current use of timezones seems primarily designed to ease adjustment for those traveling between them. Work starts at 9 AM in region-X, you move to region-Y, adjust your time and work starts at the "same" time.
Today I think however there are a lot more cases of cross-timezone communications, and a lot of people are telecommuting to work and various events. It may be time to move on and adjust to better support distance communication and telecommuting.
The national networks can advertise that a popular show comes on at 8 pm, and it will everywhere.
So, it's better to keep the second problem ('what time is morning?') more accessible, since you need that in both cases.
So what do you optimize for? For the ability to live your life anywhere you go with the same basic assumptions you and everyone else grew up with about when people wake up, are at work, eat, etc., or do you optimize for the convenience of the occasional synchronization of multi-locale events?
If your wake up, jet lagged, look at your watch, and it says 1800, are you too late for breakfast? Are you too early to call someone you came to visit? The fact that you didn't have to reset your watch for the local time means you know exactly what's going on back in the place you left. Great. Too bad you don't have any idea what's going on where you actually are. You can save yourself the trouble of setting your watch, and be confused about when to do what all day long, or you can set your watch once and be completely oriented to your new locale by lifelong instinct.
Given the choice of having to do a clock calculation to synchronize occasional events versus having to get used to a different daily life pattern everywhere you live, visit, or even call, I'll take the former.
Use UTC for synchronizing events. Use local time for living life.
To me, something like “in Japan, people usually start their workday at 2100 (or at 2000 in winter)” seems less complex than “in Japan, people usually start their workday at 8:00, which is 2100 (or 2000 in winter)”.
> If your wake up, jet lagged, look at your watch, and it says 1800, are you too late for breakfast?
If you wake up, jet lagged, look at your watch, and it says 18:00—which place this time refers to?
I think having global time would be simpler (though it's impossible anyway due to politics and people's inertia).
[... and thank god, because DST was nothing but a huge pain when I lived in countries that did have it. It has no place in the modern world.]
That's not how calls to Japan currently work, and I make plenty of them. You check the world clocks on your phone and see that it's 6:00am in Tokyo. You know what 6:00am means: it means what it has always meant for you and everyone else, everywhere in the world, since you and they were born. You decide to give them a call later. The end.
Life in different places on the globe is not synchronized just because you assign everyone the same universal clock time. You can either look up the local time in Japan, and know immediately what that means, or you can look up your clock time here, know immediately the clock time in Japan, and still not know what you need to figure out: what's going on right now in Japan. You still have to look that up somehow, but the answer won't be a simple local time that everyone understands intuitively, because local time maps differently to the daily cycle of life in every locale.
I think having global time would be simpler
Well, everyone's watches would say the same thing. That's the good news. The bad news is that they would all mean something different.
though it's impossible anyway due to politics and people's inertia
The inertia of things that work well in practice is a valuable shield against seemed-like-a-good-idea-at-the-time theories. I find UTC very useful for viewing astronomical events. When I need it, it's just another clock. It doesn't mean it needs to replace the far more useful local time for daily life.
Your in London, UK and schedule a meeting for your team at 9:00 in New York, LA, Tokyo and Bangalore.
Who is awake? Who is asleep? Who's workday ended?
You live in Paris, your mother lives in Hawaii. You want to call here when you get off work. Did you wake her up? Is she at work?
Timezones give you a general idea about what it going on at that part of the world. You lose that information without them.
Instead of everywhere starting their workday at 9am UTC like you're imagining, London would start their workday at 9am UTC, New York would start their workday at 4am UTC, Los Angeles would start their workday at 1am UTC.
9am is the morning everywhere in a time zone, 3 hours before noon when the sun is highest and the work day ends at 5~6pm. Seasons don't matter here.
"What time is it in Sao Paulo?" "7pm" "Damn they've gone home for the day." Whether it is winter or summer, that doesn't change this.
Heck, if you happened to call someone in France in the afternoon you might disturb them from their siesta!
In Spain, maybe. There is no concept of "siesta" in France.
You're creating an issue by extending something to absurdity.
Specifics like that aren't going to be communicated with any system, but removing timezones removes the general idea that is communicated with 9am or 7pm.
So Spanish people typically siesta between 1100 to 1300 UTC. Imagine, my home country is UK. I work between 0900 to 1800 UTC. Imagine I travel to US and need to call my Spanish friend. In the US, when I reach the east-coast I realize that I work between 0200 to 1100 UTC. At once I can deduce when to call my Spanish friend; it is before I leave my work at 1100 UTC.
Frankly, even I had not thought through completely the UTC based scenario, until now. I am now even more convinced that it's the most convenient way forward.
With a common time reference, you wouldn't need to map between time-zones.
Also for communication you still need to keep a table of when the sun rises and sets in each place; still need to keep in mind "they're x hours ahead/behind."
I travel extensively and work regularly with people in every time zone, and have thought long and hard about this problem. I don't think abandoning time zones is the solution, but abandoning DST globally would certainly help a lot.
http://www.timeanddate.com/worldclock/
And there are several ways to use it, it can even help set up a meeting between cities (click on a city to see more)
I'm curious if there's any data on how well that works for them versus, say, the US or Canada.