As another example, we have only indirect evidence that fusion of protons occurs in the sun and stars, yet few doubt that fusion does occur.
But is fusion the only mechanism by which stars emit radiation and generate heat? Could it be possible that some stars generate heat simply by friction between gases cause by gravity?
I meant without. But I am actually on topic. It was stated that you don't have to directly observe fusion at the center of the sun to know it is occurring. The idea is that we can infer based on the evidence. It is actually the neutrino emission that is the dead ringer for fusion. Without that, I don't know that we can know that fusion is going on for sure by inference. I was trying to show that there are other possibilities besides the one that was said to be "obvious" by inference. I was trying to figure out if it was possible for a star with the mass and size of our sun to generate the heat it does without the help of fusion. I am not sure my question has been adequately answered. The point I am make that has to do with the topic here is that there are often other possibilities that can be inferred from the evidence when it is impossible to take direct measurements. Just because a conclusion can be reached by inference, doesn't mean it is the correct inference.