Time zones are a relatively recent invention. They date back to the 19th Century and were designed to reconcile the needs of the then-new railroad industry with the ingrained habits of a population new to clocks.
They were a good idea at the time, but in the modern world they cause more trouble than they are worth. Now that several generations of humanity are accustomed to abstracting time away from the happenstance of where the sun is located, it's time to do away with this barbarous relic of the past. Everyone on the planet should operate according to a single time — Greenwich Mean Time would be suggested by tradition — and then local schedules could differ from place to place according to personal taste and local practicality.
Before the 19th Century, time was generally reckoned with reference to the local position of the sun. Noon was when the sun was at its peak. Midnight was when the peak was furthest away. Sundials and other instruments could directly measure solar position, but with time not generally kept very precisely there simply wasn't a lot of precise scheduling happening. Then came reliable and relatively affordable mechanical clocks, at which point western towns generally began keeping a local mean solar time. Now noon would be exactly 24 hours after the previous noon every day of the year regardless of astronomical perturbations.
But noon in Boston took place earlier than Worcester which was earlier than noon in Hartford which was earlier than noon in New York which was earlier than noon in Philadelphia.
This created a significant practical problem for railroad operators. They needed to schedule the arrival and departure of trains fairly precisely, and wanted to be able to characterize the entire system without reference to dozens of separate time scales. Railroads in the UK and United States began implementing railroad time, and over the decades persuaded governments to adopt it legally. The key conceit of railroad time is the use of time zones. A wide band of territory will all use the same time, and then it will suddenly jump one hour into the next zone.
Time zones are a mess
The simple way to accomplish the dream of railroad time would be to divide the globe into 24 equal slices. The problem, however, is that it is difficult for people to collaborate across time zone boundaries. Consequently, the real world time zones follow what's more of a political and economic logic than a geographical one. Argentina has extensive commercial ties to Brazil, and Brazil's main economic centers are on the coast, so Argentina is in the same time zone Sao Paulo and Rio rather than that of the Brazilian towns directly to its north.
Northern Idaho is connected via I-90 to Spokane and Seattle to its west, but not to Boise to its south so the Couer d'Alene area is on Pacific Time rather than Mountain Time. India has broken with the general scheme and adopted a half-hour staggered time zone so as to place the entire country on one time.
Yet while these zig-zags and 30-minute zones destroy the pristine geometry of railroad time, they serve a very practical purpose. It is genuinely annoying to schedule meetings, calls, and other arrangements across time zones. The need to constantly specify which time zone you're talking about is a drag. Commuting across time zones would be more annoying still, which is why the suburbs of Chicago that are located in Indiana use Illinois' Central Time rather than Indianapolis' Eastern Time.
But the ultimate solution to this problem is not a lot of ad hoc deviations. It's to shift the world to one giant time zone.
One time to rule them all
Whenever I mention this idea in conversation, people accuse me of wanting to force California office workers to show up at the wee hours of the dawn. This is nonsense. As you may have noticed, it is right now the case that different businesses open at different times. In my neighborhood, Starbucks opens before the other retailers while the bars close later. The McDonalds operates 24 hours a day, but the other eateries don't. The falafel shop stays open later on weekends when there are more late-night drunken revelers.
What's more, my intensive research has revealed that even people who start working at similar times actually live on different personal schedules. Commutes vary, for example. Some people get to the gym before work. Some people have to get their children up and fed and off to school.
All of which is to say that within a given time zone, the point of a common time is not to force everyone to do everything at the same time. It's to allow us to communicate unambiguously with each other about when we are doing things.
If the whole world used a single GMT-based time, schedules would still vary. In general most people would sleep when it's dark out and work when it's light out. So at 23:00, most of London would be at home or in bed and most of Los Angeles would be at the office. But of course London's bartenders would probably be at work while some shift workers in LA would be grabbing a nap. The difference from today is that if you were putting together a London-LA conference call at 21:00 there'd be only one possible interpretation of the proposal. A flight that leaves New York at 14:00 and lands in Paris at 20:00 is a six-hour flight, with no need to keep track of time zones. If your appointment is in El Paso at 11:30 you don't need to remember that it's in a different time zone than the rest of Texas.
This has always been the underlying logic of the railroad time scheme — clockface times should be abstracted away from considerations of solar position. But the initial introduction of railroad time was controversial. It struck people as unnatural. Today, however, we are very accustomed to the idea that time zone boundaries should be bent for the sake of convenience and practicality. That means we should move to the most convenient and most practical time system of all — a single Earth Time for all of humanity.