Physicists invoke demons—not supernatural beings, but imaginary creatures that embody impossible scenarios. These thought experiments have become legendary tools for exploring the limits of physics. According to Physics World, science writer Robert P Crease examines four such demons from the history of physics. Each one reveals something profound: about entropy, information, determinism, or the nature of reality itself. From thermodynamics to quantum mechanics, these mythical creatures have helped shape how scientists understand the natural world, turning impossible questions into paths to discovery.

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