Why does the United States keep using "old" date representations and imperial system, while being in the minority?

The answer is quite simple. Freedom. In the United States individuals are free to choose whichever system they want to use, and the government does not yet have enough power to force them to use a different system. So the milk bottler that has been bottling his milk in gallons, half gallons, quarts, pints and half pints will continue to do so, because that is what he is tooled for, and that is also what his customers demand and understand. He has a considerable economic advantage to continue using the same units. We have a constitution that is supposed to limit the power of the government, and so far that has prevented a switch of units by fiat.

In order to understand this answer, it is instructive to look at the metrication process in Britain. All it takes is a little research into this Britain's history with the metric system to see that this question is kind of based upon a false premise. I have found news articles lamenting the fact that Britain uses a mixture of imperial and metric units (Will British people ever think in metric? http://www.bbc.co.uk/news/magazine-16245391). I recall a time I was visiting one of my English friends from college. I sat down by him on the bed and my weight created a depression, pulling him toward me. He jumped up and exclaimed: "Good Lord, you must weigh 16 stone!". He was spot on by the way, that is almost exactly my weight.

Ok, so now back to the history. Below is an excerpt from wikipedia on the Metrication of the U.K. (http://en.wikipedia.org/wiki/Metrication_in_the_United_Kingdom)

Adopting the metric system had been discussed in the Parliament as early as 1818 and some industries and even some government agencies had metricated, or were in the process of metricating by the mid 1960s. However, a formal government policy to support metrication was not agreed until 1965. This policy, initiated in response to requests from industry, was to support voluntary metrication, with costs picked up where they fell. In 1969 the government created the Metrication Board as a Quango to promote and coordinate metrication. In 1978, after some carpet retailers reverted to pricing by the square yard rather than the square metre, government policy shifted, and they started issuing orders making metrication mandatory in certain sectors. In 1980 government policy shifted again to prefer voluntary metrication, and the Metrication Board was abolished. By the time the Metrication Board was wound up, all the economic sectors that fell within its remit except road signage and parts of the retail trade sector had metricated. The treaty of accession to the European Economic Community (EEC), which the United Kingdom joined in 1973, obliged the United Kingdom to, incorporate into domestic law all EEC directives, including the use of a prescribed SI-based set of units for many purposes within five years. By 1980 most pre-packaged goods were sold using the prescribed units. Mandatory use of prescribed units for retail sales took effect in 1995 for packaged goods and in 2000 for goods sold loose by weight. The use of "supplementary indications" or alternative units (generally the traditional imperial units formerly used) was originally to have been permitted for only a limited period. However, that period had to be extended a number of times due to public resistance, until in 2009 the requirement to ultimately cease use of traditional units alongside metric units was finally removed.

The Quango (quasi-autonomous non-governmental organisation) was active from 1969 to 1980. This period represented the largest jump forward in metrication since the process began.

By the time the Metrication Board was wound up, all the economic sectors that fell within its remit except road signage and parts of the retail trade sector had metricated.

These Quangos are non-governmental organizations to which the government gives power and funding. Because these Quangos are non-governmental and somewhat autonomous, they can exert power against the will of the people and the people have very little recourse. These Quangos appear to be a failed experiment in autocracy, as the UK is in the process of defunding and eliminating many of them. There have also been accusations that the appointments to them are based more upon political patronage than qualifications, and they are very expensive for the services they provide.

In his recollection of his time serving as head of the Metrication Quango, Jim Humble, appears to validate the 'metrication by force' hypothesis

High Street retailers found enormous commercial advantage in reverting to sales by the square yard. Consumers could not be persuaded to believe that goods costing, for example, £10 per square yard or £12 per square metre were virtually priced the same. Consumers bought, in very significant volume, the apparently cheaper priced imperial version. Metrication of carpet sales entered into full scale reverse and the Chambers of Trade and retail associations pressed for firm Government leadership, i.e. compulsory cut-off.

What would have been the result if the members of the Quango were elected officials, answerable to their constituents? Compare to the Metrication Process for the same time frame in the US.

Voluntary conversion was initiated (1975), and the United States Metric Board (USMB) was established for planning, coordination, and public education. The public education component led to public awareness of the metric system, but the public response included resistance, apathy, and sometimes ridicule.[7] In 1981, the USMB reported to Congress that it lacked the clear Congressional mandate necessary to bring about national conversion. Because of this ineffectiveness and an effort of the Reagan administration — particularly from Lyn Nofziger's efforts[8] as a White House advisor to the Reagan administration, to reduce federal spending — the USMB was disbanded in the autumn of 1982.

The USMB in the US reported that they were unable to bring about change because they lacked the Congressional mandate necessary to bring about national conversion. Translation: They did not have enough power to force the people to incur the costs of switching. It is clear that in both of these cases that the cost to switching to metric system was quite high, and individuals are unwilling to foot the costs unless it is by force. Indeed, it seems that they had a considerable economic advantage to staying with their existing systems.

it would be too easy to just wake up and actually LOOK at the metric system, see the logic of how easily you can specify how many centimeters are in 5.3 kilometers (so, the first clue is that the actual prefixes in the metric system MEAN SOMETHING- aka centimeter has 100 to a meter, as centi would indicate. then you have kilometer- which would indicate 1000 meters... so you have 5,300 meters times 100, and thus even a moron can see that 53,000 centimeters constitute 5.3 kilometers)

instead, people in usa rely on what people everywhere else rely on on all manner of issues: stubbornness and ingrained habitual responses. these are actually the way the entire human race deals with change. it just so happens that the entire course of history since the industrial revolution has contributed towards ingraining this particular set of practices in americans, much the way the irish or polish ingrained the potato into their cuisine: it just sort of stuck.

trying to promote change, while often perceived as helpful or necessary, in an uphill battle when dealing with humans due to this "conservatism in spurts" whereby certain systems may be very flexible but suddenly harden as usage piles on. This is much as a production web server will often never get its updates and minor fixes, as there simply is no more concept of downtime for maintainence. oops.

I can suggest a reason for continuing report weather Imperial Units. The benefit of Fahrenheit is that its scale is more granular. For every degree Celsius you get 1.8 more degrees of precision in Fahrenheit. Which when reporting the weather in Celsius it is almost only reported in whole numbers. Most of the time it's not a big deal, until it's very hot or cold in human terms. That's the second benefit of Fahrenheit, at 0 and 100 it's uncomfortable but not fatal to people

• Fahrenheit
  • 0: Very Cold
  • 100: Very Hot
• Celsius
  • 0: Cold
  • 100: Dead
• Kelvin
  • 0: Dead
  • 100: Dead

The sheer size of the install base will ensure that American Customary measures will stick around in fact, if not in name. For example, if we go metric and a kid tosses a baseball through my window, I'll replace it with one that measures 122 cm wide by 91.5 cm high -- but that's just a 4-foot by 3-foot window dressed up in metric numbers. This extends to all sorts of things: for example, if you don't want to go around re-threading every single screw hole in the country, you'll wind up producing things like a M6.35x1.27 bolt -- the same thing as the UTS 1/4"-20 bolt, but with numbers that are far more awkward.

There's one thing people usually forget about "customary" measurement systems (aka "imperial" in this case): they are evolved over considerable period of time in the society, and thus are much more convenient for use in everyday life (where complex calculations are usually not required).

Lame examples were edited out due to popular opposition.

Natural fractions are also more intuitive then decimal one (one third, one quarter, etc). Thus, base 12 (as oft used in "customary" measures) is better for many purposes then base 10 (more prime factors to think with). Revolutionary (as in "French Revolution") French system (the direct precursor to SI) tried to mandate decimal measures for time and angular quantities - those were not accepted by anybody and faded into complete obscurity, while base 12 is alive and kicking.

Another interesting feature of customary systems, especially related to volume, was the use of base 2 system (each next measure is exactly twice the volume/weight of the preceding one).

In fact, while introducing many important innovations, French system was notoriously bad in choosing its étalons for most common measures. It was not mandated by lack of knowledge, but by a misplaced desire to remove the entirety of Ancien Régime legacy. Truly, customary foot makes a much better base length than a meter - apart from being more convenient in everyday life, the speed of light could be trivially defined as 1e9 feet per second, avoiding the need to work with a very cumbersome metric 'c' constant (to achieve this, modern definition of foot needs to be adjusted by only 2%; this is well within the original "customary" precision of foot definition).

Considering the above, it is not surprising that USA had never switched to the metric system:

1. Relatively weak federal government and strongish local one, along with strongly opinionated population (with legal means to stand by their opinion) meant that people had a chance to stick to system they find convenient. For comparison, in continental Europe, metric system was introduced by the decree of the governments and with considerable level of violent oppression.
2. Lack of real incentive, as most professional activities employ customized measurement systems (a good dozen of those is employed in physics/chemistry) or work with fixed sets of measurements. Standardization of those sets is of much more real importance than the underlying system employed, and it can be said that USA has much better standardization institutions than any other nation (NIST, ANSI, etc.).
3. In the modern era all non-trivial computations are done by computers, which can do arbitrary unit conversions at negligible computational costs.

We can conclude from the above that large scale measurement system conversion will be a completely pointless exercise, which explains why USA never bothered (and probably would not bother in the future).

I'll start with about the only place actual history comes into this: why it started.

In English there are two ways to say dates:

America's official birthday is on the fourth of July, seventeen seventy-six.

and

America's official birthday is July fourth, seventeen seventy-six.

You may notice that the second way is far shorter. It requires no prepositions, which means it is much less awkward a phrasing. Easier for both the mouth and the ear. So it shouldn't surprise even a non-English speaker that this is the preferred and traditional way to say it for much of the English-speaking world.

When writing a date out numerically, what you are essentially doing is abbreviating. So if in English one typically speaks a date as "month day, year", then the proper way to abbreviate it (assuming slashes as separators) would naturally be MM/DD/YYYY. Any other way is going to confuse people (even if there is some standard somewhere saying it should be that way).

So where did the other order come from? Well, it turns out that in French, the natural way to speak a date is in fact "day month, year". So for a Frenchman, abbreviating dates as "DD/MM/YYYY" is the natural abbreviation. The Francophone world insists on that ordering, and will accept no other (as it would be confusing to them).

I won't get into the politics of who "won" when the EU standardized things. However, it should at least be noted that the capitol of the EU is in a Frankaphone country.

The USA is a much larger country (in just about every sense) than the UK, and does not have to worry nearly so much about French sensibilities. So it does dates the way its people want to do dates. If people in other countries have a problem with that, then they have a problem.

Now this being said, IMHO both systems are old systems. The "modern" way to do dates is in fact YYYY-MM-DD (aka: ISO 8601). This format is much easier for computers (and by extension, us Computer Scientists) to deal with.

The conversion to SI is a fairly different story, although the enemy is still established mindshare. Presidents Ford and Carter actually tried to move the US to metric back in the 70's. The general public balked, both were defeated in their next elections, and the next President (Regan) abolished the ineffective agency in charge of the effort. Today the USA uses Metric units in many of the sciences, but for the most part happily sticks to English units.

Generally it is probably the case that the USA is so large and self-sufficient of a society, that any radical change in units from what everyone is used to is nearly impossible. The vast majority of the population never has to deal with a non-USA person, so changing something everyone already understands solely for the benefit of this rarely dealt with non-USA person is just not going to fly.

My answer is more about the metric system then about dates.

About dates, also consider that there are Chinese, Hebrew and Islamic calendar, which are much more different from the Christian one.

According to Wikipedia:

In 1866, Congress authorized the use of the metric system and supplied each state with a set of standard metric weights and measures. In 1875, the United States solidified its commitment to the development of the internationally recognized metric system by becoming one of the original seventeen signatory nations to the Metre Convention or the Treaty of the Metre.

But several decades later:

Congress passed the Metric Conversion Act of 1975 "to coordinate and plan the increasing use of the metric system in the United States". Voluntary conversion was initiated, and the United States Metric Board (USMB) was established for planning, coordination, and public education. The public education component led to public awareness of the metric system, but the public response included resistance, apathy, and sometimes ridicule. In 1981, the USMB reported to Congress that it lacked the clear Congressional mandate necessary to bring about national conversion. Because of this ineffectiveness and an effort of the Reagan administration — particularly from Lyn Nofziger's efforts as a White House advisor to the Reagan administration, to reduce federal spending — the USMB was disbanded in the autumn of 1982.

And even more recently:

On December 31, 2012, a petition was created on the White House's petitioning system, petitioning the White House to "Make the Metric system the standard in the United States, instead of the Imperial system." On January 10, 2013, this petition garnered over 25,000 signatures - exceeding the threshold needed to require the Obama Administration to officially respond to the petition. Patrick D. Gallagher, director of the National Institute of Standards and Technology, provided the official response stating that customary units were defined in the metric system, thus making the nation "bilingual" in terms of measurement systems.

Se also Metrication opposition (Wikipedia).

With regard to imperial measurement, there is actually an interesting reason (at least in my opinion) why the US was not an early adopter of it. Thomas Jefferson had actually developed his own base-10 system of measurement (I believe he even attempted a base-10 system of time), and, had US relations been better with post-Revolution France, we may well have become one of the earliest adopters. Unfortunately, such was not the case:

The evolving political situation didn't help matters. Although France supported the American colonies during the Revolutionary War, it became hostile to the U.S. after Jay's Treaty was ratified in 1795. The French viewed the treaty, which eliminated British control of posts in the Northwest Territories and provided America a limited right to trade in the West Indies, as a blossoming alliance between the U.S. and England. France retaliated by sending privateers to target American merchant ships. By the time John Adams became president in 1797, the hostilities between the U.S. and France had grown quite intense. It's no surprise, then, that in 1798, France snubbed the U.S. when it invited dignitaries from foreign countries to travel to Paris to learn about the metric system.

Why isn't the U.S. on the metric system?

Now, granted, that does not explain why the US did not adopt the metric system, for instance, 40 years later, or 140 years later for that matter. Actually, technically speaking the US has adopted it since 1866 (see the same article above for more details), but as everyone living in the States knows, technical adoption is not the same as the population accepting it.

At this point, the largest reason we still cling to the imperial system is inertia. So much is in place that we think of via imperial measurements - your weight is in pounds, your height in inches, your milk in gallons, and so on - that at this point it would be a lot of work to change. Nevertheless, attempts were made as recently as the 1970s to switch over to the French system, and we're beginning to see metrics encroaching on all aspects of our lives as we accept the reality of global trade.

Edit: As pointed out in the comments, I realize this answer doesn't deal with the history of metrication in America. I intended it only as an answer to "why does the US keep using their systems?" However, other answers here do a very good job outlining the history, and I encourage everyone to check those out too.

As a non-American, I've always found it amusing that the 3 countries that officially cling to Imperial units are Liberia, Myanmar, and the United States. Quite a motley crew!

Anyway, for the US there are a number of reasons why it'll be hard to switch to metric/24-hour clocks/logical(!) date formats. Many of these reasons have already been mentioned.

But the simplest thing is probably a thought experiment for non-Americans: Imagine your own country wanted to switch to American units and formats. How receptive would you be to that idea?

Now setting aside the scientific arguments for using SI units, I imagine you would be very hesitant. It's not a lack of will, but an abundance of opposition.

These units and formats touch everybody's lives, meaning everyone is a stakeholder. Everything from grocery shopping to weather forecasts to your calendar would suddenly be a pain to figure out - just like it's a pain to figure out for non-Americans visiting the country. If you've grown up with one system, you've internalized it to such a degree that switching to anything else will seem completely ridiculous.

From the simple (replacing all your cookbooks) to the complex (retooling entire industries and changing every single road sign, to name a few), it's just a hornet's nest.

Sure, you can use rational arguments for why SI units etc. are just plain smarter, but if you're dealing with hundreds of millions of people, rational arguments tend not to work.

Add to that a certain anti-authoritarian streak that has defined much of American history and politics. If the US government declared that the country should switch to metric, I'd bet many would say that that's government interference in their lives. And they'd be right, because - as mentioned - it literally does affect everyone.

There could also be a wee bit of isolationism and perhaps even exceptionalism: Why should America even care what others are doing? And why should America follow anyone else?

And to many it will just seem like the stupidest thing to spend time and tax payer money on. To American eyes, there's no problem to solve. The US is self-reliant on almost everything, so as an American you never, ever have to deal with SI units for anything in your daily life. Goods are produced, sold, bought, and consumed by the pound, by the ounce, and by the gallon. No tricky conversions necessary.

Of course, the difference in units do cause problems. But it's not something the general public has to concern itself with. For instance, in 1999 an (unmanned) spacecraft was lost because one part of the system used Imperial units, while the rest used SI units. While that's the butt of many a joke (and a loss to science, but mostly a joke), it's again not something that affects anyone's daily life - especially since the craft crashed on Mars, not Earth.

So, in the end: Yes, America should absolutely switch to metric! It's crazy that they still use those weird systems :)