We say the cosmic microwave background radiation “has a temperature” of 2.7K.
Does this mean it has a temperature in the way we say the air around a warm lightbulb has a temperature of 120° or in the sense that the mix of electromagnetic waves given off by the lightbulb are like those emitted by a blackbody at 3000K?
Is the temperature of the electromagnetic field at some point in space the temperature “of the space” in which the field exists, or the temperature of a black body that would emit the spectrum of the EM field in the space if the blackbody were there at that moment.
I hear people speak as if the first, but I think they mean the second. Yes?