The very nature of the study of physics has created a long history of untestable theories to fill in the gaps. Because candidate theories that can be tested eit

The very nature of the study of physics has created a long history of untestable theories to fill in the gaps. Because candidate theories that can be tested either solve the problem or remove themselves from contention, so until the problem is solved, the untestable ones are the only ones that last any significant amount of time. The theory of luminiferous ether had a large amount of circumstantial experimental evidence for quite a long time, but all it really was, was a placeholder waiting for an actual explanation. Theories like that will always exist on the frontiers of science. It’s not really unique to physics either. Miasma theory played a similar role in the history of biology for instance.