Metric Time, as is oh so cleverly softlinked to this node, will never happen. That said, let's run through a brief explanation of it.

Metric Time (abbreviated MT) is the Base 10 alternative to plain, old, Base 60 Anglo-Babylonian timekeeping that we all *know* and love. (abbreviated ABT)
LMT is short for Local Metric Time, which is offset for whichever time zone you happen to be in.
UMT is short for Universal Metric Time, equivalent to what would be GMT in ABT time.

Here's the most common system of Metric Time, first used during the French Revolution:
10 days in a metric week
100 metric seconds in a metric minute
100 metric minutes in a metric hour
10 metric hours in a day

Sounds pretty simple and metricky, huh? Well this has a big problem. Dividing the metric day into 10 different slices makes a metric hour last about 2.5 ABT hours. You can't make metric hour-long TV programs or schedule a metric hour-long appointment. You'll only fit a few of them in per day! People would have to resort to using clumsier prefixes to divide their schedules into - a centiday for example (approx. 14.4 ABT minutes)




Now, the following is a more real-world system using the day (equal to one solar day) as the base unit.

deciday(dd) = 1/10 day (Metric hour)
centiday(cd) = 1/100 day
milliday(md) = 1/1000 day (Metric minute)
microday(µd) = 1/1000000 day (Metric decisecond)
etc...

How is Metric Time formatted?
00.0 LMT = 12:00 midnight ABT, local
50.0 LMT = 12:00 noon ABT, local
00.0 UMT = 12:00 noon ABT, GMT
50.0 UMT = 12:00 midnight ABT, GMT
50.000 LMT = 12:00:00 noon ABT, local
02.425 LMT = 12:34:56AM ABT, local
Note that the trailing zeros are never dropped.

How do I convert from ABT to Metric time?
MT = ((s/86400)+(m/1440)+(h/ 24))*10x
Where X is what unit you are solving for:
Days x=0
Decidays x=1
Centidays x=2
Millidays x=3
Quintoday x=5
Microdays x=6

How do I convert from Metric time to ABT?
h = abs(d * 24)
m = abs(((d * 24) - h) * 60)
s = abs(((((d * 24) - h) * 60) - m) * 60)

Then, ABT = h : m : s

How do I convice my friends, relatives, and coworkers to start using Metric Time?
You don't.

I pine for the day (Metric of course) when my watch will display atomic, binary, metric time. :)

Metric time would basically be the metric alternative of the measurement of the passage of time. Since there currently is no standard for metric time, this is my proposal of what I think it should be.
{Note: you should be familiar with the way the metric system works}


What should designate one unit of time?

In going with the tradition of basing metric measurement with other metric measurements through some common element of nature (such as 1 Liter was defined as a 10 cm cube of water), I propose basing the measurement of time off of the speed of light. To place the duration of a single time unit within a reasonably understandable quantity, I arbitrarily decided that it would work best to define one metric time unit as the amount of time it takes light to travel one billion meters (1 x 109 m). For more precision, I am taking the speed of light as the amount of time it takes light to travel in a complete void (e.g. complete vacuum and without gravitational distortion) assuming that is possible to accurately measure.

(Or see di5tortion's writeup below where he puts more thought into it and chooses to use 1 x 1012 m rather than 1 x 109 m. I agree that that might be a better choice for practicality.)


What should the basic metric time unit be called?

I must admit, I am not very good at coming up with names for things, however, the name that made the most sense to me was chron. ('chron' as in the prefix for time, so a chronometer would actually measure time in chrons.) The word chron is only one syllable and easy to pronounce (“KRon”). It also works well with all of the metric suffixes (millichron, megachon, centichon, etc.). As for the symbol of chron in shorthand, I could only come up with the lowercase letter ‘q’ from the English alphabet since it’s not used much elsewhere.


How is a chron compared to the current standard measurements of time?

Assuming the speed of light is something around 299,792,458 m/s, one chron (1 q) would be about 3.33564 seconds.

1 q = 3.33564 sec
1 sec = 0.299792 q

Some common numbers:

One hour = 1079.25 q = 1.08 kq
Time it takes the Earth to make one full revolution (1 day) = 259021 q = 259 kq
Time it takes the Earth to make one full orbit (1 year) = 9460730 q = 9.46 Mq
The speed of light = 1 Gm / q (by definition)


Should everybody switch over to this new system?

Right now it doesn't really make much sense to switch away from our current system. Our current measurements of time is based on the natural astronomic system of Earth, and as long as the majority of the human species dwells on or in the orbit of Earth, it would be best to commonly use the current time system. Metric time would be more advantageous in hypothetical physics problems and deep space travel.

The SI unit for time is the second (s). While it may be sensible to develop a new set of units for time using base ten, it would not be 'metric,' and integrating the new unit into SI would be non-trivial.

The main problem is that SI has many derived units related to the second. First of all, the newton (N) would have to go. The newton is the SI unit of force (much like the pound), and is defined as 1 kg*m/s2. It would be necessary to replace the second in this equation with the new time unit, which would create a new unit for force which is not equal to the newton. Then we'd have to get rid of the pascal (Pa), which is a unit for pressure. It is defined as 1 N/m2. This wouldn't be quite so painful because despite the fact that it is the official SI unit, most people use atmospheres or millimeters of mercury instead. This is very silly, but it's what people seem to do.

The next one to go out the window would be the joule (J), which is defined as 1 N * m. Although the second does not seem to appear in this equation, the newton does, and since we're tossing that, we need to also toss any other units based on it. Now we have to get rid of the watt (W), which is a unit of power - 1 J/s. Then the volt, a unit of electric potential, which is 1 J/C. Speaking of coulombs, (charge) either they go or the ampere goes. The ampere is a unit of electric current equal to 1 C/s, and there is some disagreement over which is the base unit.

There's more, but the point of all this is that a new time system may or may not be worth implementing, but it would be a much more complicated matter than advocates make it out to be. Changing any base unit would totally alter the metric system itself. Actually, you could change the unit for time without changing any of the derived units, but then you'd need to use weird conversion factors, which kind of defeats the purpose of SI.

IMHO, our time system doesn't really need changing. The thing that seems to bug people is not the second itself, but rather how it relates to minutes, hours, and days. However, these units are good enough for everyday use by non-scientists, and scientists don't use them anyway. Sure, the second might not relate to the day in a sensible manner (86,400 seconds per day), but none of the other metric units are based on properties of the planet Earth*, so why should the unit for time be? In any case, most chemists and physicists always record the time in seconds, so they don't need to care about how long a day is.


*I've gotten a couple complaints about this statement, but I stand by it and will attempt to justify it. The meter was originally meant to be 1/10,000,000th of the distance from the north pole to the equator, but in reality it is more like 1/10,018,800th. The meter is still fixed at its original length, however, so it is not based on an accurate measurement of the Earth, and furthermore it is now defined based on the speed of light.

The degree Celsius was based on the melting and boiling points of water at sea level, but the kelvin, an absolute unit, has 273.16 fixed at the triple point of water. While the unit size is contrived to be identical to that of the degree Celsius, it is not nominally based on it.

Finally we come to the Atmosphere. 1 atm is equal to the pressure at sea level. Well, I'll just say that this is not an SI unit, so it doesn't count.

Given that SI already uses the second as a unit of time (as Rubyflame points out supra), here are some conversions:

Standard to metric:

  • One minute = 60 s
  • One hour = 3.6 ks
  • One day = 86.4 ks
  • One week = 604.8 ks
  • One fortnight = 1.2096 Ms
  • One month varies from 2.4192 Ms (28 days) to 2.6784 Ms (31 days). The average month (one-twelfth of a 365 1/4 -day year) is 2.6298 Ms.
  • One average year (365 1/4 days) is 31.5576 Ms.

Metric to standard:

  • 1 decasecond (das) = 10 seconds
  • 1 hectosecond (hs) = 1 minute 40 seconds
  • 1 kilosecond (ks) = 16 minutes 40 seconds
  • 1 megasecond (Ms) = 11 days 13 hours 46 minutes 40 seconds
  • 1 gigasecond (Gs) ≈ 31 years 8 months 7 days 19 hours 46 minutes 40 seconds (based on the average year and the average month)

I so far like Monolith's chron unit, as well as FREETACO's system. My idea is for the chron to be used mainly by people living in space, especially people who will be working in space transport one day.

There are two things that this unit needs to work for. It needs to be both useful as a unit of measuring stand-alone time (19 seconds till liftoff) and time as compared to the passage of it (it is 1800 hours). But before we go into doing this arbitrarily, we need to consider some other factors. In other words, we need to compromise between Monolith's and FREETACO's systems and then innovate. Compromise and innovate.

Where will it be used?

Since it will be used mainly in space, we need it to work well for the people who work in space. This presents another argument altogether.

Who will be using it?

Well, people who work and/or live in space, of course, although I'm sure it can be adapted to other uses. One important thing to factor in here is that we are making this system for the future, not for now.

Why is it necessary?

Living on a Terran timetable when you're living on Luna is stupid. Living on a Terran timetable when you're living in orbit around Venus is stupid. Especially when you're travelling between planets, and spend a lifetime doing this, it is necessary to base your time system on something that doesn't change. Monolith's writeup proposed the use of the speed of light for this. I couldn't agree more.

So tell me about this new system.

Note from Monolith's writeup that one of his chrons would equal the amount of time it would take for light to travel one billion (1 x 109) meters. I had three options when choosing the base unit for this, but there were some things I needed to consider before just picking one arbitrarily. The three options were to make the base unit equivalent to 1.08 hours, 10.8 hours, or .108 hours. To have this be compatible with space operations, I tried for the 1.08 hours in hopes of making one of the space "days" equivalent to 10 chrons.

The Space Day

A day needs to have time for all of the basic functions of life. 10.8 hours is way too little to accomodate work, sleep, and play. 21.6 hours isn't. One needs plenty of time to sleep in space (sleep prevents accidents, and keeps you fit), and 9-10 hours is an optimal amount of sleeping time. A 10.8 hour day would work nicely assuming that the first day would be used mainly for work and play (7-8 hours work, the remaining amount play), and the majority (9-10 hours) of the next day would be used for sleep, with the rest for play. This gives about 4 hours of free time every cycle.

Why didn't you just make it a 21.6 hour day?

Because then it wouldn't be Base 10, now would it? Besides, if a cycle would be equivalent to a "day" then it's no problem, right?

Recap

Note that all figures are approximate.
One decachron (daq) (space day) == 10 q == 10.792 hours (556 minutes)
One chron (q) == 1.0792 hours (55.59 minutes)
One decichron (dq) == 0.107 hours (5.559 minutes)
One centichron (cq) == 0.0107 hours (0.5559 minutes) (33.3564 seconds)
One millichron (µq) == 0.0093 hours (3.33564 seconds)

So how will this work with one's daily schedule?

Well, for one thing, let's stop thinking in hours and seconds, and start thinking in chrons. Otherwise, this is going to get pretty confusing.

One cycle would equal 20 chrons. This is equivalent to one of our days. Let's break it down into the human necessities.

1 q - Wake up / Clean
0.5 q - Breakfast
4 q - Work
0.5 q - Lunch
4 q - Work ----- That's 10 chrons so far.
3 q - Dinner / Free Time
7 q - Sleep

There would be 5 cycles in a week. In other words, it's a five day week. This works out nicely to being 100 chrons in a week. A 50-cycle year is also a good idea, since it works out to a nice 10,000 chron year. Interested yet?

Practical Details

Unless you never intend on walking on your homeworld again (assuming its Earth), zero-g exercises are important to do every day when you're in space. To allow time for this, things like TV, music, or internet-surfing can be combined into the same time period as your exercise, when needed. For example, in addition to .2 or so chrons of exercise in the morning, one would spend about 1 chron of their dinner/free time to exercise and at the same time watch the news, since riding a stationary bike isn't a really mind-consuming exercise.

Since being in space is expensive, days in which you are free would be limited. One day every decacycle free could work well.

Conclusion

This system obviously won't be in use for a while, as it is only practical when one spends a lot of time in space, or travels between celestial bodies very frequently.

Let it be noted that practicality and adherence to Base 10 were my main concerns when working the system out.


Excalibre informed me of something fun-- the circadian cycle. I guess a 24 hour schedule wouldn't be SO bad-- it would work nicely, in fact, since you can have three 8 hour shifts.

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