People once thought that world was flat or nearly flat. It was considered a bit crazy to think of it as a big ball. But it is. You can prove it. One of the big ideas in science is that ideas can be tested. Scientists test claims. If one scientist claims that she or he can fill a balloon with invisible gas using vinegar and baking soda, other scientists can try it and see if they get the same result. Sometimes ideas are wild, extraordinary. And, the claims that go with these way-out ideas are pretty extraordinary as well. The round Earth is an example of an extraordinary claim that needed extraordinary proof. But, there are many people, who believe in extraordinary claims without looking for extraordinary proof. We scientists are always on the lookout.