Isn’t it quite a big coincidence that this value would only have 2 decimal points on a scale that puts the temperature value of water boiling and freezing at whole numbers?
In: Mathematics
[deleted]
Cuz in reality it likely isn’t, but for practical uses going to more decimal places isn’t that helpful. The same way that we round pi to 3.14 instead of using 3.14159…
Like in many engineering applications we don’t even use 273.15, we just round it to 273. Absolute Zero is just a hypothetical point where you cool a gas down to the point where its Volume is 0. But gas is matter, physical atoms, it is impossible to make those atoms have no volume.
Because nowadays we define the Celsius scale in terms of Kelvin and not the freezing and boiling points of water.
0 degrees C is defined to be exactly 273.15 degrees K.
The Celsius scale was already in use when we began to realize that applications of the gas laws and other aspects of physics imply an absolute zero point in temperature. So we figured out, theoretically, that it is very close to -273.15 *C.
Then, later, we ***re***defined the Celsius scale in terms of absolute zero and the triple point of water, and dropped the boiling point as an anchor. Now, absolute zero is -273.15 by definition, the freezing point of water is still generally at 0 *C (depending on pressure, impurities, etc.), but the boiling point is no longer keyed to 100, and is actually closer to 99.98 *C.
The boiling and melting points of water aren’t that precise, because it varies with armospheric pressure. While the original definition of the Celsius referred to those, the current definition is actually defined based on the Triple Point of water, which is a more reproducible standard, and absolute zero, which is a universal constant. (Actually, the current current definition is to do with the Boltzmann constant, but that’s unimportant for our purposes)
Basically, the reason why there’s only two decimal places of precision is because that’s the definition of the Celsius.
This comes up any time a unit or scientific constant is redefined: you can pick an exact value as long as it is within the previous value’s imprecision. It won’t mess up previous uses if the change in value is less then the uncertainty in the value.
The freezing and boiling points of water aren’t as well defined as you think. Atmospheric pressure and contaminates in the water can very easily change it.
We now base our definition of Kelvin on absolute 0 and the triple point of pure water.
Odds are that our current scale doesn’t line up exactly with the one proposed by Celsius, but even if it’s off by a whole degree, we probably won’t notice because of how imprecise thermometers have been for centuries.
The point is now we have a very good idea of how it all lines up.
They changed the Celsius scale to make that work. -273.16°C is absolute zero, by definition. And 0.01°C is the temperature of water at its triple point, by definition.*
Defining the Celsius scale this way is more precise than the classic freezing/boiling point of water definition, since the temperatures at which water freezes and boils can vary depending on several things, in ways that absolute zero and the triple point don’t.
^(*This definition is no longer in use as of 2019. Now, the degree Celsius is defined in terms of absolute zero and the Boltzmann constant, which relates temperature and energy across the universe. But the value we assign that constant was chosen to keep the degree Celsius as close as possible to the prior water-based definition.)
The guy who came up with Kelvin which starts 0° at absolute zero was using Celsius for all his measurements because that’s what scientists do. So his new way of measuring temperature was Celsius that started zero at the coldest possible temp instead of starting zero at when water freezes
It’s not really that much of a coincidence. Celsius is basically designed to measure the temperature between boiling and freezing. It just so happens that the difference between freezing and absolute 0 is roughly 2.5 times as big as that. So that’s why there’s the same number of 0s.
Latest Answers