What are historical misconception or scientific hypothesis that are so cool you wish they were true?
For example, the medical concept of humours, which regulated a persons temperament and were tied to certain fluids in the body, or phlogiston, a substance that existed in objects and made them more likely to burn, which was disproved when it was determined that burning objects gained mass.
These theories were all, of course, eventually disproven, but how cool would it be if radio waves and light actually traveled through an omnipresent substance?
What other theories do you think would be cool if they were real, and how would they change the world today?