Richard Feynman once said of the scientific process, “The first principle is that you must not fool yourself — and you are the easiest person to fool.” The idea that scientists might be fooling themselves (whether out of ignorance or in order to preserve their jobs) is a common accusation made by skeptics of scientific disciplines ranging from climate change to cosmology. It’s easy to dismiss such criticism as unfounded, but it does raise an interesting question: how can we tell that we’re not fooling ourselves?

The popular view of science is that experiments should be repeatable and falsifiable. If you have a scientific model, that model should make clear predictions, and those predictions must be testable in a way that can either validate or disprove your model. It is sometimes assumed by critics that this means the only true sciences are those that can be done in a laboratory setting, but that’s only part of the story. Observational sciences such as cosmology are also subject to this test, since new observational evidence can potentially disprove our current theories. If, for example, I observe a thousand white swans I might presume that all swans are white. But the observation of a single black swan can overturn my ideas. A scientific theory is therefore never absolute, but always tentative, depending on whatever subsequent evidence arises.

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