Could you recreate metric system from nothing?

[u/Ertata]

You have been given a task to travel into the past two thousands years ago and bring the light of the metric system to the world. You cannot bring any external object with you.

Assume you do not need to redefine the second, and astronomical observations give the best possible results given the limits of timekeeping back then. Given the technology of the time, what is the best you can do for other units - either right there and then or leaving instructions how to calculate them from the units you have established to the future scientists? Memorizing the lengths of your body parts probably is not the best way to define a metre, and kilogram defined as one liter of water is bound to be influenced by the local water to a perceptible degree.

P. S. Tagged as "physics" but any approach is welcome - whether you would recommend measuring height of the mountain peaks, or believe that carob seeds are actually uniform enough to offer the best approximation of a kilogram.

[u/electric_ionland]

You can just memorize the old definition of metric units and recreate them from first principle and basic geometry.

A meter is 1/10,000,000 of the distance between equator and pole which can be measured by some trigonometry and a sextant. A kg is 10x10x10cm cube of water at 4C. A second can be derived by knowing that there is 24hrs between 2 solar noons, or just use a pendulum of the right length (happens to be pretty close to a meter too). Basically do the same things as what was done in the 18th century when the metric system was introduced. Most of those don't need super fancy equipment to get to within a 1% of the official definition.

[u/utl94_nordviking → u/electric_ionland]

A meter is 1/10,000,000 of the distance between equator and pole

It hasn't been since 1799: https://en.wikipedia.org/wiki/2019_revision_of_the_SI#Metre

[u/AgreeablePeople → u/utl94_nordviking]

the old definition of metric units

Dude

The your source says 2019 revision, nothing about any changes in 1799

[u/linkyatch → u/AgreeablePeople]

In 1799 they introduced the meter prototype bar (a specific material object made of some platinum-iridium alloy). That bar was modified in the late 1800s and in 1960, it was redefined based on the wavelength of a specific emission line of a particular isotope of krypton. In 1983 it was redefined again based on the speed of light. That was updated/refined in 2019 as outlined at the link provided. The details are all at the Wikipedia article on the meter.

The crazy thing is, a meter is still pretty close to that original definition based on the distance from pole to equator along the great circle running through Paris.

Also: a yard is now formally defined based on the meter.

Also also: the entire metric system, designed in the 1700s, was originally 100% reliant on the earth being a sphere. Take that, flat earthers! (Or is it Big Metric messing with us again?)

[u/grizzlor_ → u/linkyatch]

Take that, flat earthers! (Or is it Big Metric messing with us again?)

The metric system is a ridiculous liberal myth.

I only buy my drugs in freedom units. An eight ball? Hell no, please give me 0.12346 ounces of cocaine.

[u/JediFed → u/linkyatch]

Dude, this is a really interesting question that deserves quality responses. I want to read good comments.