I am doing research for a new book and would like to hope to elicit informed responses to the following question:
The flat earth and geocentric world are examples of wrong scientific beliefs that were held for long periods. Can you name your favorite example and for extra credit why it was believed to be true?
Please note that I am interested in things we once thought were true and took forever to unlearn. I am looking for wrong scientific beliefs that we've already learned were wrong, rather than those the respondent is predicting will be wrong which makes it different from the usual Edge prediction sort of question.