It senses a temperature change
How?
Any sensor is an energy converter. No matter what you try to measure, you always deal with energy transfer from the object of measurement to the sensor. The process of sensing is a particular case of information transfer, and any transmission of information requires transmission of energy.
http://www.kelm.ftn.uns.ac.rs/liter...ModernSensorsPhysicsDesignAndApplications.pdf
Look what I found on page 3.
That's so weird, because I've always said that the warmer emitter can't tell the temperature of the cooler target in order to adjust the "dimmer switch" if the cooler target never emits.
This neat book, not sure if it's the same one you supposedly took your passage from, says there is always a transmission of energy.
And on page 106.......
106 3 Physical Principles of Sensing
Fig. 3.43. Thermal radiation exchange between an object and a thermal radiation sensor.
from the sensor toward the object must also be taken into account. A thermal sensor is capable of responding only to a net thermal flux (i.e., flux from the object minus flux from itself). The surface of the sensor which faces the object has emissivity εs (and, subsequently, reflectivity ρs =1−εs). Because the sensor is only partly absorptive, not the entire flux, .b0, is absorbed and utilized. A part of it, .ba, is absorbed by the sensor and another part, .br, is reflected (Fig. 3.43) back toward to object.20 The reflected flux is proportional to the sensor’s coefficient of reflectivity:
It's weird, the nice diagram shows energy going both ways.......not one way
tell me, what do you thing positive flux, and negative flux means?
Positive means the net flux flows toward the sensor, in other words, the target is hotter.
That means the sensor receives more energy from the target than it sends toward the target.
Negative means the net flux flows toward the target, in other words, the target is cooler.
That means the sensor sends more energy to the target than it receives from the target
Thanks again for that nice source. It's always fun when you link something that disproves your claims.