Bad idea. You would still have different people in different places experiencing different parts of their day, even if you put them all on UTC or had no clocks at all. You still have to figure out what they are doing before you call and figure out whether it is too late to call, or too early, or they ought to still be in the office, etc., one way or another.
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.
> You still have to figure out what they are doing before you call
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).
...seems less complex than “in Japan, people usually start their workday at 8:00, which is 2100 (or 2000 in winter)”.
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.
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.