It is important to consider the chance of us having evidence of B, assuming that B was actually happening. We have an absence of evidence for æther, but we are

It is important to consider the chance of us having evidence of B, assuming that B was actually happening. We have an absence of evidence for æther, but we are pretty certain that if it exists, we would have evidence of it. Our confidence of that is strong enough to state with some confidence that æther does not exist. For practical intents and purposes, we can say that the absence of evidence of æther is evidence that it does not exist. Not all absences of evidence are made equal, some are more significant than others.