You are misunderstanding how it would work. People would still be awake when it's light out and asleep when it's dark.
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.
Actually, that's exactly how I know it would work. I'm pointing out the information your going to loose without having timezones because people are still going to get up and go to sleep basically following a solar day. Are people in Paris awake at 9:00 or asleep? Are people in LA working or not? Without a table, say a table that says what time of day it is in particular zones, 9:00 tells you nothing.
Nit: If we eradicate timezones, lets also get rid of this am/pm nonsense. New York wouldn't start at 1am, they would start at 1h00 (or 01:00, or 01h00, or however you want to notate it).
Not really. Two places with the same timezone may have completely different day and night schedules. The northen hemisphere is flooded with sunlight during Northen summer, while the souther hemisphere gets very little sunlight during this time.
Extend the issue out, when I want to call my mother around the world, how do I know she's not ill today, took the day off and went to bed early?
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.
Siesta is an essential part of daily schedule in many places. “Took the day off”, “ill”, “went to bed early” are obviously extraordinary circumstances.
Because instead of just remembering that Spanish people siesta from 1200-1400 local time, you might as well translate it to UTC and make it even more complicated to remember?
It is possible that it appears complicated because it is not common to use UTC. But let's try to imagine the scenario further...
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.
When does your Argentine friend siesta? When does your Japanese friend get off work? What's a good time to phone your friend in Australia? You've just landed in Tokyo--when should you be getting to sleep? You still have to do time zone calculations, but you don't have the time zones anymore.
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.