The word theory is used differently in science to how it is in common speech. In science, a "theory" represents humanity's best possible explanation for something given everything we know. For example, the theory of gravity gives a reason for why things are attracted to each other, namely the bending of spacetime.

Theories don't become laws, either. Laws in science describe what happens, and theories describe how. To go back to gravity, the law of gravity is an equation that can tell you exactly how much two objects will be attracted to each other, but it can't explain how that happens. That's what the theory is for.

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