Wikipedia says:
In a wireless communications receiver, the equivalent input noise temperature \$T_{eq}\$ would equal the sum of two noise temperatures:
$$T_{eq} \ = \ T_{ant} \ + \ T_{sys}$$
I understand that these values of \$T\$ are related to temperatures, but they are not themselves actual temperatures that one measures with a thermometer.
If I put a 273K ice cube in my 357K coffee (no pun intended) I'd get cooler coffee, not 630K coffee. The same applies if they are two streams of fluid mixing rather than static objects.
In another setting; at given frequency, the noise power of an external radio source, like a blackbody source, would scale as the fourth power of temperature, not linearly.
I need help understanding why noise temperatures are simply added, even though in the real world the last thing we'd think of doing is adding two temperatures together.