In physics, theories need math. That's how you predict, gather evidence, verify, disprove, and support. But EU theory isn't big on math. In fact, "Mathematics is not physics," Thornhill said. While that equation aversion makes the theory pretty much a nonstarter for "mainstream" astronomers, it is the exact thing that appeals to many adherents.
"We know stars generate energy through nuclear fusion, not plasma discharge; we know craters are formed from asteroid and comet impacts, not huge electric arcs; we absolutely know that special and general relativity work, despite some EU proponents' claims," said Plait, who has tangled with EU commenters a time or two. "From what I've seen, most EU claims are on the cranky end of [the] scale. That's why most astronomers ignore it: No evidence for it, tons of evidence against it, and no support mathematically or physically."
EU makes few predictions. It doesn't have a unified framework, or mathematical laws underpinning it. The underlying physics doesn't go far beyond, "It's electric."