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.