What is pseudoscience? The answer to that question is more difficult than you might think. In trying to answer the question, we can learn a lot more about what science is, how it is practiced, and what goes into producing new scientific knowledge. Based on the work of historian of science Michael Gordin and several collections in the Niels Bohr Library & Archives, this episode examines pseudoscientific theories based on Einstein’s theory of relativity. Some of the pseudoscientists included in the collection think that Einstein was flat-out wrong–that he missed some vital information or that his theory is simply too confusing and unintuitive to understand. If physicists largely agree that the theory of relativity isn’t quite intuitive, then maybe it makes sense to hear out these anti-Einsteinians to get a sense of how they understand science. Other individuals included in these collections agree with Einstein but push relativity in interesting directions. One tries to make a case for a 6,000 year old universe. Another tells us how to build a time machine to help Muhammad Ali meet Thomas Edison. We conclude with Ralph Hartley, a practicing and accomplished scientist. Hartley was born eight years after Einstein and never accepted his ideas about the universe, offering instead a much older explanation of how gravity works. Through these stories we’ll learn about what constitutes legitimate science. Unsurprisingly, real science meets the tests that scientists set for legitimacy.