Really? What's the prediction, exactly?

Our best physics arguably predict that when you run electricity through a filament in a vacuum, the filament will emit light. It's a very specific, very detailed prediction, based entirely on phenomena we understand very well through extensive experimental observations.

In the case of predicting that aliens should/could have visited Earth by now, what are the extensive experimental observations? What are the phenomena we understand very well? What are the details of the prediction. What, specifically, is being predicted?

Incidentally, "our best physics"? A lot of the stuff you've listed under that heading in this thread seems to me to be more like "our most speculative and so far un-falsifiable physics, plus some conjectures about what might happen if we make a bunch of unsupported assumptions".