Didn't we mess up with the temperature?

[Meson080]

The following passage has been extracted from the book "The Feynman Lectures on Physics-Vol l":

The mean kinetic energy is a property only of the "temperature." Being a property of the "temperature," and not of the gas, we can use it as a definition of the temperature. The mean kinetic energy of a molecule is thus some function of the temperature. But who is tell us what scale to use to use for the temperature? We may arbitrarily define the scale of the temperature so that the mean energy is linearly proportional to the temperature. The best way to do it would be to call the mean energy itself "the temperature." That would be the simplest possible function. Unfortunately, the scale of temperature has been chosen differently, so instead of calling it temperature directly we use a constant conversion factor between the energy of a molecule and a degree of absolute temperature called a degree kelvin.

The constant of proportionality is k=1.38 χ 10^-23 joule for every degree. So if T is a absolute temperature, our definition says that the mean kinetic energy is (3/2) kt (The 3/2 is put in as a matter of convenience, so as to get rid of it somewhere else.)

From the above passage, at absolute zero, by definition, mean kinetic energy of a molecule should be zero-"completely frozen." There is a giant principle which stands against the view of atoms getting completely frozen; the following passage from the same book introduces the principle:

As we decrease the temperature, the vibration decreases
and decreases until, at absolute zero, there is a minimum amount of vibration
that the atoms can have, but not zero...

Remember that when a crystal is cooled to absolute zero, we said that the atoms do not stop moving, they still
jiggle. Why? If they stopped moving, we would know where they were and that
they had zero motion, and that is against the uncertainty principle. We cannot
know where they are and how fast they are moving, so they must be continually
wiggling in there!

Aren't the above two passages in contradiction with each other? Didn't we mess up with temperature?

The question is also asked in Physics Stack Exchange, interested folks can visit the page: Didn't we mess up with the temperature?

My other related thread died early, if anyone wants to give life to it once again, please visit the page: Feynman's quote

 

[Astronuc]

The concept or notion of 'temperature' predates our knowledge/understanding of QM, the uncertainty principle and absolute zero.

As far as humans are concerned, ice, or frozen water is a good basis for 0, as in 0°C. For all intents and purposes, the molecules in ice are frozen solid. Whether or not the atoms are still vibrating is largely irrelevant in common everyday experience.

http://www.brannan.co.uk/who-invented-the-thermometer

FYI - Inventing Temperature: Measurement and Scientific Progress (Oxford Studies in Philosophy of Science)
https://www.amazon.com/dp/0195337387/?tag=pfamazon01-20

http://www.nist.gov/pml/div685/grp01/

The Kelvin and Temperature Measurements
http://www.nist.gov/calibrations/upload/106-1-01.pdf

If temperature is a measure of some mean kinetic energy, or translational motion of an atom or molecule, then if it's very very small, it's effectively zero.BTW - A Solid Like No Other: Frigid, solid helium streams like a liquid
http://www.phschool.com/science/science_news/articles/solid_helium.html

 

[D H]

In the first passage, Feynman was writing about an ideal gas, a substance that does not exist. In the second passage, he was writing about the behaviors of real substances. So no, there's no contradiction between those two passages.

 

[Meson080]

In the first passage, Feynman was writing about an ideal gas, a substance that does not exist.

So, ideal gas concept or kinetic "Theory" of gases is not consistent with the principles (laws) of nature.

 

[D H]

The concept of an ideal gas and the kinetic theory of gases predates quantum mechanics.

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