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Can the temperature of a black body be defined without using radiation? Energy spectrum of black body is a function of temperature so when we say a given blackbody is at temperature $T$ we measure the energy of radiation (ultimately photons) to assign $T$ using following kind of graph enter image description here

In other words, is it possible to operationally define the temperature of a black body without going through the route of detecting photons?

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Temperature is defined thermodynamically as the energy change as the entropy changes: $$T=\left( \frac{dU}{dS}\right)_{P,V},$$ entirely independently of radiation. To operationally measure a temperature of a body without measuring photons you will have to use a thermometer or something similar.

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