The length of one second

The "stopped one second" took an Olympic medal away from Korean fencer Shin A-lam. She was an unfortunate case in the London Summer Olympics. Her four years of toil disappeared in vain in the single second. The unfortunate second passed only after her German counterpart attacked her three times to score the winning point. The Korea Research Institute of Standards and Science said it took 1.42 seconds for three attacks, indicating that the scoring occurred when the match was over. Germany’s Britta Heidemann, the winner, stressed that the timer’s one second could mean 1.99 second, but a second on a timer measuring every 10 seconds means 0.01 to 1 second.

The scientific definition of a second has changed over time. Before 1956, a second was 1/86,400th of the mean solar day in the rotation of the earth. Due to irregular rotation, however, a second was redefined as 1/31,556,925.9747 of the tropical year for 1900 January 0 at 12 hours ephemeris time in terms of the revolution of the earth from 1956. In 1967, the 13th General Conference on Weights and Measures defined a second as the duration of 9,192,631,770 cycles of microwave light absorbed or emitted by cesium. Cesium is a substance with the least margin of error. The cesium clock has a margin of error of just one second every 30,000 years.

The think tank, which provides Korea’s standard time information to broadcasters, banks and telecom companies, uses several cesium clocks. The accuracy of time is needed not just in sports, which require 1/100ths of a second in accuracy. Telecom companies need an accuracy of 1/100,000 second to prevent congestion and GPS needs that of 1/1,000,000,000 second. Had the London Olympics measured time with a cesium clock, Korea’s Park Tae-hwan would have won a silver medal and China’s Sun Yang a bronze.

In sports, a second is never short. If a pitcher throws a ball at 150 kilometers per hour, the ball flies 18.4 meters in 0.44 second and gets stuck in the catcher’s mitt. A batter hits a ball after considering the quality and direction of the ball and the defense’s loopholes for a shorter period of time. A soccer player who takes a penalty kick sends a ball at the speed of more than 120 kilometers per hour and sends the ball 10.97 meters in about half a second toward the goal. Fencing, however, is not a ball game. The speed of brandishing a sword is a world different from that of a ball. Korea’s Choi Byung-chul, who took bronze in the men’s individual foil Tuesday, said, “Even if I play with a child, it’s impossible for me to attack three times within one second.”

Editorial Writer Lee Hyeong-sam (hans@donga.com)