What does quantum mechanics, the most successful theory ever proposed by physics, teach us about reality? The starting point for most philosophers of physics is that quantum mechanics must somehow provide a description of the world as it is independently of us, the users of the theory.

This has led to a large number of incompatible worldviews. Some believe the implication of quantum mechanics is that there are parallel worlds as in the Marvel Comic universe; some believe it implies signals that travel faster than light, contradicting all that Einstein taught us. Some say it implies that the future affects the past.

According to QBism, an approach developed by Christopher Fuchs and me, the great lesson of quantum mechanics is that the usual starting point of the philosophers is simply wrong. Quantum mechanics does not describe reality as it is by itself. Instead, it is a tool that helps guide agents immersed in the world when they contemplate taking actions on parts of it external to themselves.

The use of the word "agent" rather than the familiar "observer" highlights that quantum mechanics is about actions that participate in creating reality, rather than observations of a reality that exists independently of the agent.

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