How could SI units be derived from scratch without the use of modern technology?
How could SI units be derived from scratch without the use of modern technology?
Think "you wake up in the woods naked," Dr. Stone-style tech reset. How could humans acquire a 1-gram weight, a centimeter ruler, an HH:MM:SS timekeeping device, etc. starting with natural resources?
My best guess was something involving calibrating a mercury thermometer (after spending years developing glassblowing and finding mercury, lol) using boiling water at sea level to mark 100 ° C and then maybe Fahrenheit's dumb ice ammonium chloride brine to mark -17.7778 ° C, then figuring out how far apart they should be in millimeters on the thermometer (er, somehow). I can already think of several confounding variables with that though, most notably atmospheric pressure.
I feel like the most important thing to get would be a length measurement since you can then get a 1 gram mass from a cubic centimeter of distilled water.
That's as far as I got with this thought experiment before deciding to ask the internet. I actually asked on Reddit a while back but never got any responses.
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The metre was originally defined in 1791 (...) as one ten-millionth of the distance from the equator to the North Pole along a great circle, so the Earth's circumference is approximately 40000 km.
https://en.m.wikipedia.org/wiki/MetreThe kilogram was originally defined in 1795 during the French Revolution as the mass of one litre (1/1000 m³) of water.
https://en.m.wikipedia.org/wiki/Kilogram... and the last major SI unit is the second which of course you know is (originally was) 1/86400 day.
Please notice about the Celsius scale : the second reference point isn't a mixture of ice and salt but rather pure water freezing point.
Now how can we as naked humans develop technology to figure this out is something of historical proportion, that's a quite amazing story !
Your definition of the meter leaves out the most interesting part. Yes, it was 1,000, 000th the distance of the equator to the North Pole, but how far is that? That wasn't known accurately in the 18th Century. So, two Frenchmen, Delambre and Mechain conducted the longest meridian survey every attempted. They also did so while half of Europe was at war with one another. It was an amazingly dangerous endeavor. There is also significant evidence they totally flubbed and hand-waived their results. So, although their science ended up being questioned, the process and method was accepted and the Meter was defined.
Re Celsius 0 °: the reason I thought perhaps Fahrenheit's Weird Brine might be a more absolute thing to take de novo temperature from was because I don't actually know the answer to "how can you ensure water is exactly freezing temperature?" If it's solid ice it could be colder, if it's liquid it's probably warmer, and even if it's a bucket of cold distilled water with distilled water ice in it, isn't it still likely hotter than 0 ° C? I feel like there's probably something involving equilibrium between solid and liquid water that would be difficult to sus out
Not that Weird Brine is any better really 🤦♀️
if you have both liquid and solid water at equilibrium then you have zero degrees Celsius. Pressure has minimal effects ...at plus or minus 0.5 atmosphere. of course if you go to a hundred or a thousand atmosphere then there is an effect of pressure.
Small pieces of ice will equilibrate their temperature faster in water.
Surface tension has minimal effect on melting temperature unless you go to extremely small pieces of ice meaning less than one micron, ...which is not possible to achieve anyway because such small ice pellet with fuse rapidly to form larger ones.Ah, so at sea level a bucket of ice water would make a decent approximation of 0 ° C, then, I suppose.
Didn't know really tiny ice particles spontaneously fused, this is neat to know
Yes a bucket of a mixture of small ice pellets, say a few millimeter size, plus water, (this bucket being enveloped with some insulation) would be a great zero degrees Celsius reference point.
if you want something more precise you can read this :
https://en.m.wikipedia.org/wiki/Celsius... "the actual melting point of ice is very slightly (less than a thousandth of a degree) below 0 °C." ...
isotopic distribution of heavy and light elements in water also has a very slight effect on melting point. So, rainwater and water distilled from ocean will not melt at the (exact) same temperature.
See : Vienna Standard Mean Ocean Water https://en.m.wikipedia.org/wiki/Vienna_Standard_Mean_Ocean_Water
Now, about small particle fusing together this is true not only of ice but of any material.
it's called sintering and it is caused by diffusion and a lowering of the surface energy.
This process is faster when the material is near it's melting temperature and faster yet if in contact with any miscible liquid phase.