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Comment by kjrfghslkdjfl | Hacker News Reader

You're confusing time with calendar.

If I want to meet an alien species in Jupiter we're not going to coordinate using Earth's calendar. Doesn't mean it's impossible to meet just because they don't know Earth's calendar, we just have to specify a point in TIME without resorting to Earth's calendars. And points in TIME don't depend on timezone changes. Points in the calendar do.

A "timezone" is a map from point in time to point in the calendar. And a "timezone change" is an operation that takes a point in time from one point in the calendar to a different point in the calendar.

> The quirk is that the offset to UTC might not be static because of timezone changes,

An offset to UTC by definition does not depend on timezone, the same way that integers don't depend on timezones. 5 is 5 regardless of the timezone. If I say offset=3711, that has nothing to do with timezones.

You're confusing time with calendar.

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I don't think aliens would care about UTC. And it seems a bit pedantic to separate it, humans tend to store times related to events on Earth.

> If you want to represent a point in a calendar, use local timezone.

And actually, going back to the original comment, this part was covered by the article. Storing timezone doesn't cover the case of a location switching between timezones.

So it seems the article can't be summed up in a simple rule like the original comment contends.

I didn't say aliens would care about UTC, did I? I said that we would have to specify a point in time without resorting to calendars. I didn't say we would use offset to UTC, because aliens don't know UTC either. But presumably they can measure time, so we could e.g. measure a point in time as an offset to "now". We would also have to use units that they understand. Not seconds, but perhaps Cesium revolutions.

> And it seems a bit pedantic to separate it

I would say that the fact that you can't see a distinction between time and a calendar is precisely the reason you're confused. So I wouldn't consider it pedantic.

No, you are absolutely right about the distinction, I didn't see it as useful since the article is dealing with calendars here, eg. time of event at some location. I don't think I've used time without a calendar so it seems a bit abstract to do so.

Every time you say "wait a second" you're using time without a calendar or a timezone. You're referring to a point in time as an offset (1 second) to "now" which is the point in time when you say it, and its the same point regardless of which timezone you're in, or whether there's a timezone change in between.

You wanted to make a point that time does not depend on physical location, while you chose an example that proves otherwise.

There is no absolute time in spacetime, so your calendar invite from an alien friend would include not only the coordinates on Jupiter but also a time value relative to something. Possibly Earth. Maybe even UTC, as observed on Earth.

Please don't bring relativity into this except as a fun side note. It doesn't make a meaningful difference for actual objects in space, because they all share basically the same reference frame.

Timekeeping is hard enough already. Let's leave the aliens aspect out of it.

You might be right. I was trying to disentangle "time" from "calendar" by showing that just because someone doesn't know anything about calendars doesn't mean you can't coordinate with them to meet at a future point in time, and THEREFORE you should indeed use an offset to represent points in time and local timezone to represent points in a calendar as I originally claimed.

In retrospective I wish I'd chosen a less fantastical example, because of course people are gonna get distracted. "Aliens" was not the point. But now I can't be bothered anymore, losing interest fast.

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