This is a meter. But it’s not THE meter. The meter isn’t a physical object, locked
away in a secret vault somewhere. The meter is a math problem. Take the distance light travels in one second
and cut it into this many chunks, that’s how we define a meter. But why that number? Why not this many chunks? Or this many? It’s the fundamental unit of the metr-ic
system, a unit built into the very foundations of physics, so surely something in the basic
laws of the universe explains why a meter is… a meter. But that’s not the case. The real story is full of discovery, deception,
and a lot of people getting their heads cut off. [OPEN] 1789. The French people have a lot of problems with
the monarchy, and now Louis was gonna hear about it. In their airing of grievances the people included
demands to fix France’s system of weights and measures. It was a confusing mess. Every town and trade basically measured things
how they wanted. This was not a new problem. The Ancient Egyptian cubit was said to be
the length of a man’s arm, and the English inch was three pieces of barley laid end to
end. But whose arm and whose barley? In France, a pound of bread sometimes really
was lighter than a pound of lead. Its people were using some 250,000 different
measures, which made trade difficult and cheating easy. A pint of beer in Paris? Two-thirds the size of a pint in St. Denis! If ever there were an injustice worthy of
REVOLUTION, it was that. France’s revolutionary spirit wanted united
and equal measures for a united and equal people, but French savants, being the Enlightened
dudes they were, set their goal even higher: a universal measure, for all nations, derived
from nature itself. Rulers? Who needs ‘em. The basic unit of length would be called the
“meter”, and all other units derived from that. The divisions of those units would be decimal,
and given prefixes from Greek and Latin so the whole thing would sound old and important. All that was left to do was invent the meter. One smart choice was the length of a pendulum
swinging once per second. Thomas Jefferson even agreed to make some
measurements, and join America into this new “metric system”. Problem solved, right? Wrong. First they had to agree on the length a second. Some French savants wanted to throw out the
day we use, and replace it with a decimal day. Since no one could agree on a second, the
pendulum meter was dropped. In its place, a meter defined as one ten millionth
the distance between the North Pole and the equator, along a meridian passing through
France. England and the USA refused to accept a measure
based on a French line and… well, we all know how that turned out. In 1791, two men set out to make the meter. Their plan? Measure latitude at the ends, then meet in
the middle. Do a little multiplication and you’ve measured
the Earth! Unfortunately they don’t make 1000-km tape
measures. Instead, Méchain and Delambre would mark
a series of triangles across France. Walking off just one side of a triangle in
the north and south, they could use those angles to calculate the length of every link
in the chain, proving trigonometry IS good for something after all. This was their tool. The repeating circle was two telescopes mounted
on a ring. Zero in on two distant markers, and measure
the angle between them. But a single measurement was guaranteed to
have some error. The repeating circle was rotated and remeasured,
rotated and remeasured, each time adding the new angle to the previous sum. Divide by the number of measurements, and
the average angle would be more precise than any single measurement. These would be the most precise surveying
measurements ever attempted, giving the world an error-free meter. Unfortunately, as soon as they set off, things
in France went to H-E-double hockey sticks. Revolution was in full swing, the King was
in jail (then dead), and France was at war with basically everyone (but especially Spain). In city after city people assumed the scientists
with the funny tools were royal spies, and each time they barely kept their heads. But hooray! There was a revolution against the revolution,
and after seven years of struggle, the triangles were connected. In 1799, pages and pages of calculations were
reviewed, the distance from the north pole to the equator was determined, and a platinum
meter was cut, one ten-millionth as long. Mankind finally had a definitive, universal
measure derived from nature. There was just one problem: The meter was,
and is, wrong. To the calculate the meter, they needed an
accurate measure of earth’s curvature. Since Newton, scientists knew Earth’s cross-section
was an ellipse, not a circle. But the results of the meter expedition claimed
Earth was twice as squished as scientists had thought. It wasn’t, they just picked a bad line to
measure. Worse, the curve isn’t smooth. This was a big discovery, but it also invalidated
the whole premise of the meter. Earth is too irregular to be its own measure. But rather than admit 7 years of wasted time,
the new triangulations were combined with older measures for Earth’s curvature, and
the meter ended up being… an estimate, a physical object, the opposite of what it was
supposed to be. (Plus, it turns out one of the guys fudged
as bunch of his data, but that’s a whole other story) Of course, today we don’t measure
the meter based on a hunk of metal. Or do we? In 1960, the meter was redefined as a number
of atomic wavelengths, but that was calculated to match the old platinum bar. And in 1983, the meter was redefined again,
as the distance light will travel in 1/299,792,458ths of a second, but that number was also chosen
to match the old hunk of metal. Based on satellite measurements of Earth’s
average curvature, today we know that ten million meters from pole to equator would
leave you about 2 km shy. The meter was invented as a perfect ratio,
but even our meter, based on the speed of light, carries an old error, two tenths of
a millimeter shorter than it should be. Of course it’s still *a* meter… because
we say it is. But if you shake the basic laws of the universe,
a meter doesn’t fall out. It’s just another invention. But as inventions go, it was revolutionary. Stay curious.
