A Guide to



Universal And Local Metric Time

Part Of A Guide To Metric Time

Universal Metric Time

One of the goals of Metric Time should be to create a common reference of time that can be used by people communicating over the Internet or other global systems. This is where the concept of universal time comes in. Universal time, in general, is a standard reference time that is the same everywhere (Relativity not withstanding). The Metric Time system will use Universal Metric Time (UMT) as its reference time.

The current ABT system uses a universal time called, oddly enough, Universal Time (UT), or sometimes Greenwich Mean Time (GMT) since it is basically the local time in Greenwich, England (but not exactly). UT is based on the Earth's actual rotation rate and can vary. Coordinated Universal Time (UTC) is measured using highly accurate atomic clocks and synchronized periodically to UT by the addition or subtraction of seconds.

UMT will be handled the same as UT. There will also be a Coordinated Universal Metric Time (UMTC) that will correspond with UTC in function. The important differences between ABT and MT universal times are:

  1. UMT shall be kept using a decimalized system as outlined here.
  2. UMT shall be measured from the International Date Line (180° longitude), not the Greenwich Prime Meridian.

The last difference needs explaining (or rather justification). Previously in my proposal, I advocated making UMT merely a decimalized version of UT. However, after communications with Jonathan Jay I have decided to follow his lead; Greenwich should be put behind us as we move into the 21st century. A universal time reference should, if possible, be based in a neutral location, not parochially chosen due to the sordid history of colonialism and imperialism. Also, by placing the UMT meridian at the IDL we will be synchronizing the start of the day and the start of the clock.

(I should also here mention another universal time system that has gained some celebrity as of late. Internet Time, introduced by Swatch, is a decimalized time system that aims to be the clock of the Net. However, Swatch has made the rather self-serving decision to center Internet Time on their headquarters in Biel, Switzerland. This makes this system unacceptable as an impartial global time reference.)

Usage of UMT

UMT -- not local MT -- should be used in any forum whose members are in different parts of the world, such as on the Internet. UMT should also be used by businesses and for announcing events of interest beyond an immediate locality, such as conferences or bombings. Basically, whenever possible use UMT. In this way it will serve its role as a universal temporal reference. (See next subsection for discussion of local time usage.)

To avoid confusion and make explicit that you are using UMT, always label it as such. For example:

98.765 UMT

Or when spoken:

"98.765 universal"

Local Times

Should you use UMT exclusively or both UMT and local MT? The issues involved here are relevant to all universal time systems, so a lot of what follows digresses a bit from merely proposing a specific system.

Local solar time is very real. People actually live their lives by it. Given the effect light exposure can have on circadian rhythms, it's not much of a stretch to say local time is a fact of biology. It needs to be accounted for. In light of this, there are two related problems, or inadequacies, with using only universal time that need to be addressed:

  1. Daily Activity Mapping: Most of us use the local clock time as a conceptual landscape of the day that is landmarked with our regular activities, such as waking, having lunch, and going to bed. When we travel to a different time zone and must adapt to their local solar time, we find it convenient to simply adopt their local clock time and apply our daily map to its familiar -- if offset -- landscape. We do something like this too when either communicating with or thinking about people in other time zones, imagining where they are on our map of the day by "what time it is there".

    For example: most people are at work by 9:00 am local time according to my conceptual day map. This is probably true for most of the world, local customs aside. If someone in India tells me it's 10:00 am there, I assume that she has been in the office for probably around an hour. Now what if I and everyone else only used ABT Universal Time? If I lived in Greenwich, 9:00 am would be the place on my day map marked "should be at work by now". But for someone in India, her day map would have "lunch should be over by now" marked at 9:00 am. We may have a common reference for absolute temporal events, but we no longer have a common reference for how we live our day.

  2. Communication of Day Map: How do you tell someone when they can expect to find you at work or at lunch? With the current local clock time system you tell the person "what time it is here" (or tell him your time zone which he then uses to calculate "what time it is there"). Once the person has your local clock time, he can use his day map to tell where you are and where you will soon be. If we lived in a world with no local times and only universal time, how would we express where we are in our day?

    One method would be to ask a person questions like "When do you get to work?" The problem with this is that for every time zone you would have to create a separate day map, each with different landmarks on it ("People in Greenwich get to work at 0900 UTC and leave at 1700 UTC, whereas people in Mumbai get to work at 1430 UTC and leave at 2230 UTC, while people in Seattle..."). That's a lot to remember.

    Another method might be to ask a person "What's your time zone?" You would then figure how many hours/half-hours difference there is between you and calculate where on your day map the person would be. The problem with this is that it is too easy to slip into what amounts to local time only with everyone using their own day maps ("That person is at what's like my 0900 UTC"). This not only defeats the purpose of universal time, but could lead to confusion for individuals (especially if they travel: "It's 1200 UTC, and where I am now that's like 0900 UTC back home, and since I'm traveling west, in two hours it will be like 1000 UTC... or will it?").

    With an universal-time-only system, there isn't a way to communicate a day map that isn't cumbersome or doesn't introduce a bastardized version of local time.

So, what should we do to address these points? Here are two solutions:

  1. We need a common map of our day that is easy to communicate. Since we are talking about a local solar day, we basically need a way to say "When the sun is at this place in the sky, I and others do this" and "The sun is now at this place in the sky." Does this sound familiar? We've just reinvented the clock! In other words: we should use local times somewhat as we do now. However, the use of local times (Local Metric Time or LMT) should be strictly limited to expressing daily activity periods ("People are at work by 37.5 LMT") and communicating your location's temporal offset ("It's 50.0 LMT here"), never used beyond that context, and should always be labeled "LMT" or "local" ("It's 98.7 local") if the time zone is understood. In situations where the time zone is not a given, always state it ("It's 98.7 PST").

  2. Only use universal time and let databases and software agents keep track of where people are in their day ("Hal, is Sr. Sanchez in his office now?" "I'm sorry Dave. I'm afraid he isn't.").

Time Zones

If we are to have local times, we need time zones. (Actually, we would need them even without local time since having everyone in a region operating in phase is economically beneficial.) Currently, local time is based on time zones which are a whole number of ABT hours or half-hours from UT. In a decimalized time system this could be awkward since the zones would often be fractional or even non-finite (i.e. PST is -33.3333... centidays from UT). There are two options for dealing with this:

  1. Create new Metric Time Zones. This is a long term solution that could be a part of a project to decimalize the longitude/latitude system. Although ultimately making the world more base-10 friendly, this option is fraught with all sorts of political and economic concerns as to exactly where to draw the lines for the new zones.

  2. Leave things as they are. This is of course the easiest option. since the technology to automatically convert from UMT to LMT is ubiquitous we would only rarely have to do it manually or mentally. This is what we should do in the short term, at least.