Consider this. Suppose I want to phone someone who lives in Japan and I live in the UK. Japan is +9 hours ahead of UK local time (GMT). Therefore I know if I phone slightly before lunch then I'll be phoning them in the evening.

Now suppose we all had the same time. If I phoned them just before lunch, which would mean shortly before 12:00 in the UK then I'd have to try and figure out what Japan would be doing at that time. Would 12:00 in Japan be early morning, late at night, would they be eating a meal, would they be at work? Now I have to remember where in the day different times are for different counties. However, with timezones all I need to remember is a numerical value and I can easily figure out where Japan is in the progression of a day (i.e morning, evening, night).

You need to remember the exact same bits of information in both cases, so I don't see the problem. In one case you remember it as "time difference" ("now is 12:00 +9 there"), in the other case you remember it as earlyness/lateness compared to you ("12:00 here is LIKE 12:00 +9 there").

So that would need the same exact effort.

The man benefit would be for the "let's meet at the same time online" etc coordination stuff -- where's its brain-dead easy when everybody has the same time.

Ok, but I know a lot of people who are available at work at times which do not match the "usual" work hours. Also shops have no universal opening times, some open at 7, some at 10, so you always have to check if the other side is available before calling (or just try).

I guess calling would also be easier if the used system can show if the other side is available like Skype or even better when she is available.

How would you know if it is appropriate to call someone in some other part of the globe? One way or another you have to do a lookup.

A) Everyone uses UTC. Now you have to know the business hours in Tokyo because it is not universally 8-6 anymore.

B) Everyone uses local time. Now you have to know their local time.

As an example:

I don't know where you are, you don't know where I am. I tell you I am available from @300-@800 if you want to Skype today. Let me know which time is good for you.

Which would be scenario A. You just did the lookup of finding that 0xEA's business hours are from @300 to @800.

Sure, you would have to know that. But you have to look up if the business you want to contact is open on Sunday anyway, even if they are local. Or what time they close today.

Or you have to try to figure out the whole no work on Friday thing in the middle east and Monday being part of the weekend. You always have to look it up.

What made this dream cool in the digital age is I could just have hours that I'm available and if I wanted to work late at night, I could. I considered myself a 'hardcore hacker' in '98 and what appealed was how well this lined up with my natural inclination to hack on code from 10pm to 5am every day, despite being in high school.

I didn't care or need to know where my IRC friends were. We could collaborate none the less.

If I say something like "I had to catch a 6am flight", that means something to you without knowing what time zone I'm in. Absolute and relative times are both useful.

> If I say something like "I had to catch a 6am flight", that means something to you without knowing what time zone I'm in.

But it's really meaningful only in the sense that it's early morning, so that the same information could be conveyed by saying "I had to catch an early-morning flight." (More precise information than that could always be conveyed: "I had to catch a flight 1 hour before sunrise", or whatever.)

Where it matters, UTC is widely used, for example in aviation. And local times - based on time zones – are representations of UTC too.