Gravity has no temperature, too. Fields don’t have temperatures. But it is irrelevant to the temperature-question. Every existent is made out of quarks. They don’t have a temperature, because at that level the term temperature becomes meaningless. So if you isolate every quark in my stove, you cannot say that it has a temperature, because the quarks it consists of have none.
All of which proves that the concept “temperature” has meaning only in certain contexts, i.e. only when applied to entities that possess that attribute. The universe is not an entity, so it cannot be one of the entities to which the concept of temperature applies.
You can say, “The mean temperature of all the matter that we have managed to measure is X degrees.” Likewise, you can say, “The mean wavelength of all the radiation that we have managed to measure is X nanometers.” That does not mean that the universe has a temperature and a wavelength.
You cannot attribute a wavelength to the universe, because at that scale the concept of wavelength becomes meaningless. Even humans don’t have wavelength, because already there it becomes pointless. But here concepts like temperature find meaning and they don’t lose it if you expand your focus, even to the entire universe.
This is a selective application of the fallacy of composition. You rule out the notion of the universe having a wavelength because it contains existents to which the concept of wavelength does not apply. But you arbitrarily insist that it can have a temperature, despite the fact that it contains existents to which the concept of temperature does not apply.
At this point, you have given good examples of the things to which the concepts of temperature and wavelength can apply – and you have given good examples of the things to which these terms can not apply. What you have not done is show why either of these terms should apply to a collection that includes all of the things you have mentioned, the things to which the concepts apply and the things to which they do not apply. This is a textbook example of the fallacy of composition.
There are electromagnetic waves coming through the window next to me. I don’t have to care about them because they are irrelevant for the question. Still the glass has a temperature.
My processor is hot even though the voltage isn’t. I see no problem at all.
You see no problem because you do not grasp the distinction between an existent, which has a metaphysical existence and attributes of its own, versus a collection, which has only an epistemological existence and does not have a separate, metaphysical existence (apart from the enitities it comprises) and which cannot, therefore, be ascribed the characteristics of an existent.
The coin-example didn’t mention how the dollar bills and the coins are arranged. For a loosely arranged bunch of coins and bills, I would measure the rigidity of the bills and the coins separately and then I can calculate a mean based on volume or weight. If you have them glued together, they are as rigid as the weakest link. You have to further define what you mean by rigidity.
This does not deserve much of a response. I think it is quite clear what rigidity means in this example. The point is that it is non-sense to say that the money collection is simultaneously rigid and non-rigid. The fact that you can glue the pieces of money together or measure the rigidity and calculate a mean changes nothing. It is still non-sense to speak of the collection as being simultaneously rigid and non-rigid.
But I will simplify it even further. Here is the essence of your error. The number 2 is even. The number 3 is odd. If we put them together in a collection, we will have the number 5. According to your argument, 5 is both odd and even. Or, 5 is 50% even and 50% odd.
For the temperature of the universe you have to define that you want the mean temperature.
But if I throw a bunch of ice cubes into my glass of orange juice, this arrangement does have a temperature and I can calculate the mean temperature despite any gravity or electromagnetic fields that may be in the glass.
So what? This issue is not what you can measure and calculate about any particular existents. The issue is whether you can ascribe the attributes of entities to things that are not entities, like the universe. You cannot.