Six easy roads to the Planck scale

Understand

We give six arguments that the Planck scale should be viewed as a fundamental minimum or boundary for the classical concept of spacetime, beyond which quantum effects cannot be neglected and the basic nature of spacetime must be reconsidered.

• The arguments are elementary, heuristic, and plausible, and as much as possible rely on only general principles of quantum theory and gravity theory.
• The paper is primarily pedagogical, and its main goal is to give physics students, non-specialists, engineers etc.
• an awareness and appreciation of the Planck scale and the role it should play in present and future theories of quantum spacetime and quantum gravity.