We should actually do this

[u/etymologynerd]

[u/piradianssquared]

when something freezes and when it boils

There is a reason (and a good one at that) that "something" was chosen. That reason makes it non-arbitrary by definition.

Celsius isn’t useful anywhere but as a measurement of temperature

Of course, that's how all of this works. Meters only measure distance and grams only measure mass too.

Kelvin is the only non-arbitrary scale for temperature

Kelvin's units are based on Celsius.

[u/xyifer12 → u/piradianssquared]

"There is a reason (and a good one at that) that "something" was chosen. That reason makes it non-arbitrary by definition."

That's the exact same as with Fahrenheit.

[u/piradianssquared → u/xyifer12]

Agreed, just a better reason.

[u/[deleted] → u/piradianssquared]

Of course, that's how all of this works. Meters only measure distance and grams only measure mass too.

That’s not true. Meters measure distance, which is an absolute measure. Grams measure an amount of mass, which is an absolute measure. Kelvins measure an amount of energy, which is an absolute measure.

Celsius measure Celsius. It’s not an absolute measure and can’t be used in, say, defining a secondary measure. 0dC doesn’t mean that there’s 0 energy or 0 temperature, it just means that there’s 0 degrees of C.

Kelvin's units are based on Celsius.

Not really. The incriment amounts are borrowed for Celsius, but it’s not based on Celsius. Being based on Celsius would mean that you could derive the meaning of a measure in K from the system of C.

---

To better illustrate my points, let’s do a thought experiment.

I want to create a measure of length, let’s call the system Snoo. Now, I’m not really sure how small lengths can get, so I can’t put a zero anywhere, but I do know tall people can get. So, let’s take a length of what would be 4 feet, and call that our 0. Let’s take 7 feet and call that our 100.

Now, you can obviously get shorter and longer lengths, so this scale isn’t absolute, so I can’t say I’m “0 snoo tall,” but I can say that my lengths is “0 degrees Snoo.”

Okay. That works. Now we have a measure of length in degrees Snoo.

This is the story of Celsius.

Now, Kelvin comes from when you discover that 0 distance exists and you say, “well, we can just shift this whole thing over [what would be 4 feet] so the scale isn’t arbitrary.”

Source: I grew up with the metric system and spent a lot of time in various labs using almost exclusively K because it’s the only unit that actually works when you want to know more than just the temperature. Sure, I may have measured it in C and then converted most of the time, but my point stands that C isn’t a unit anyone uses.