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Concept

Planck time

A clock face showing the time as 11:00 against a dark green background, symbolizing the concept of Planck time.

The duration light takes to cross a Planck length, approximately 5.39 × 10⁻⁴⁴ seconds. It is constructed from the speed of light, Newton's gravitational constant, and Planck's constant, and is widely conjectured to mark the scale at which quantum-mechanical effects on spacetime itself become unavoidable. No experiment has come within thirty orders of magnitude of probing it directly.

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