I often see people quote Sagan's "extraordinary claims require extraordinary evidence," typically when "extraordinary" is defined as "alternative to the currently accepted wisdom."
Anyone who defines it that way is missing the point, by making the mistake of defining science as just another belief system. The reason science works is because it's based on the evidence. The "currently accepted wisdom" is, ideally, based on the evidence we have. If a model is supported by a great deal of evidence, then naturally it's going to take some pretty compelling evidence to prove that the model needs to be changed. It's silly to treat it as some kind of ideological war, because if the facts support the new idea, it will eventually win out against any resistance, because it's simply true
. Even if there's a generation of scientists who resist accepting it, eventually enough evidence and experiments will support it that there will be no choice but to accept it. And conversely, if the idea is wrong, then the evidence won't be there to support it and it will fall by the wayside.
Look at quantum physics. Initially, when its ideas started to be formulated in the late 19th and early 20th centuries, there was a lot of resistance in the scientific community to its ideas, since they were very extraordinary claims that went against all conventional wisdom. Even Einstein didn't want to believe in it. But today it's been confirmed by such overwhelming evidence that it's become the foundation of modern physics. Its principles are used and affirmed every day in technologies such as the ones that enable me to type these words into an electronic device that sends them out to other electronic devices around the world. The fact that people didn't initially believe in it didn't matter, because it was true
, and reality trumps belief every single time.