The principle of "path dependence" in economics means that when you make your first choice, the future path is irreversibly determined. An example that best illustrates the principle of "path dependence" is the rail gauge. The rail gauge used in the United States is 4.85 feet. Where did this come from? It turned out to be the standard for British railways because the early American railways were designed and built by the British. So where does the British standard come from? The answer is that the original British railway was designed by people who built tram tracks, and 4.85 feet is the standard for tram tracks.

We continue to trace the source, where does the standard of tram tracks come from? It turned out that the wheel width of the carriage was the standard. Then the wheel width of the carriage - where did this 4.85 feet come from? The answer is in the hands of the ancient Romans. 4.85 feet is the width of the ancient Roman chariot. So why did the ancient Romans use 4.85 feet as the wheel of the chariot? The answer is that 4.85 feet is the butt width of the horses of two pull carts.

This statement may be too story-telling, but it is mostly a fact that is well documented: the international standard for railway gauges in 1937 was 1435 mm (4.85 ft), and this is the first American railroad specification in 1835. It is inherited from the British specifications. According to the British steam engine-driven railroad designer George Stephenson's son, Robert later recalled in Congress that the 1435mm rail width was not determined by his father, but from his hometown. He said that the rail width of 1435mm, "there is no scientific theoretical basis, purely because someone is already using it."

Today, you are sitting in the spacious Chinese high-speed rail. The rail gauge at your feet is the width of the two horses ass – 1435mm. History is so incredible, the 45-minute TV series is also determined by a roll of film in the industrial age, just as the length of a foot is determined by the length of the footprint of a king's foot.

In 1937, the International Railway Association made a unified regulation: 1435mm is the international standard gauge, the gauge of 1520mm or more is the wide rail, and the narrow rail below 1067mm. About 60% of the world's railways use international standard gauges, but even now, there are 30 different gauges in the world. China's existing railways use an international standard gauge of 1435mm. It should be reminded that the gauge gauge for measuring the gauge width is the mandatory verification measuring instrument specified in China's “Measurement Law”! (Source: China Metrology Network)