eli5: If absolute 0 is only theoretical, how do we know what it is in Celsius and fereignheit

Question

eli5: If absolute 0 is only theoretical, how do we know what it is in Celsius and fereignheit

In: 0

Answer 1

If I tell you a woolly mammoth weighs 1200 kilograms, you can convert that to pounds because the formula to convert between those units is well defined. The mammoth is entirely theoretical, at no point did you need to weigh a physical mammoth, in fact they are long dead.

0 Kelvin is a known point on the temperature scale that we just happen to think cannot possibly exist in reality, but we know how to convert between Kelvin and Celsius and Fahrenheit using basic formulae so I don’t see what you think would be difficult about that.