Following the recent decision to change the definition of SI units, I understand that Kelvin is no longer defined in terms of the number 1/273.16. Does that mean that absolute zero is no longer necessarily 0K?

Edit: What are the proposed realizations in the New SI for the kilogram, ampere, kelvin and mole? is helpful but doesn’t address absolute zero.

  • $\begingroup$ Related: physics.stackexchange.com/q/147433 $\endgroup$ – user191954 Nov 17 '18 at 10:40
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    $\begingroup$ @Chair But that is about all of the SI revision. This question is just about temperature. $\endgroup$ – Pieter Nov 17 '18 at 10:49

No, it means that the triple point of water is not defined as exactly 273.16 kelvin when the new definition takes effect in May. The revision fixes the value of the Boltzmann constant. Zero remains zero.

The practical temperature scale ITS-90 (for calibrating thermometers) has not changed by this decision. In the future, maybe a different method of calibration will be prescribed for ambient temperatures, but that is not likely to be anytime soon. In that sense, the triple point of water remains at 273.16 K.


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