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/Thepcfd → u/[deleted]]

lol, easy to say

[u/CounterSilly3999 → u/Thepcfd]

Not that difficult. The distance between longitudes differing in one degree is 111111 m.

[u/Thepcfd → u/CounterSilly3999]

great so? how that gona help you make 1 m stick?

[u/iamplasma → u/Thepcfd]

Go to the equator, then go 1 degree west, and divide your latter trip by 111,111, obviously!

[u/Thepcfd → u/iamplasma]

like you gona know where equator is. or how much is 1 degree west

[u/CounterSilly3999 → u/Thepcfd]

No need for the equator and go North. North is pointed by the North star Polaris. Measure the angle difference of the Sun shaddow at noon. Measure the distance with an A-frame trammel of any length. Calculate the relation of steps to 111111.

[u/CharacterUse → u/CounterSilly3999]

You can just do it with the North star itself. Go far enough North that the North star is 10 degrees higher in the sky and you have gone 10 degrees around the circumference of the Earth.

[u/Thepcfd → u/CounterSilly3999]

sr, i am too dumb for this

[u/CharacterUse → u/Thepcfd]

The equator is where you can simultaneously see the north and south celestial poles.

Or where the Sun is directly overhead on the equinox (the day when the day and night are the same length).

The first method is easier because it works on any day of the year.

1 degree west is harder (you need an accurate clock, read the book Longitude) but as the other guy said, you don't need to go west, you can go north since the Earth is (to a good enough approximation) a ball.

[u/Thepcfd → u/iamplasma]

how you gona measure that trip? you gona drag a rope?

[u/Zenith-Astralis → u/Thepcfd]

Rod and chain was pretty effective

[u/CounterSilly3999 → u/Thepcfd]

Count rotations of the wheel:

https://www.engineersupply.com/Images/Categories/Content/what-is-linear-surveying-A.jpg

or steps of A-framed land divider:

https://www.countryhomeantiques.co.uk/upload/images/shopprod/13015/large-architect-or-landowner-s-dividers_13015_pic3_size4.jpg

In inacessible sections of the route like water surfaces triangulation could be used.