The recent resurrection of the name Brontosaurus well illustrates the temporary nature of all scientific understanding. Because scientific understanding is based on our best known knowledge and interpretation of that knowledge, there’s the possibility that with more knowledge or with better interpretation, pieces of our understanding could be wrong.
We live in a world, however temporary, in which Brontosaurus is real again. For the sake of this thought experiment, let’s assume that other subjects, small and large, are also just as easy to change from unreal to real, or real to unreal. Other than the obvious answer of Pluto being a planet again*, what’s the scientific fact/theory/idea that you would undo?
Give a link to the fact/theory/idea if it’s something that might be kind of niche in its level of popular science understanding, and tell why it’s something you want to undo and what the implications of its undoing would be. All(?) answers get a picture of a pizza roll, the best answer gets a picture of two pizza rolls.