The observable universe and the mystery of the Planck length

Video of Planck length: why string theory is hard to test | Britannica

Introduction to Light

Kilogram: Mass and Planck's Constant

Quantum mechanics originated from Max Planck's attempt to solve the black body radiation problem—how ideal objects emit electromagnetic radiation. Classical physics predicted infinite energy at high frequencies (the "ultraviolet catastrophe"), but experiments showed radiation peaks and then falls. Planck resolved this by proposing that energy is quantized in discrete units of hf (frequency times Planck’s constant), introducing the concept of energy quantization and the foundation of quantum mech