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Introduction
The Planck constant (h) is the most important number you have never heard of. Its value, approximately 4.14×10⁻¹⁵ eV·s, is the reason World Quantum Day is celebrated on April 14 (4.14). This guide explains its discovery, meaning, and why it is the bedrock of modern physics.
For the main celebration overview, read our World Quantum Day 2026 article.
Who Discovered the Planck Constant?
German physicist Max Planck introduced the constant in 1900 to solve the “ultraviolet catastrophe”. He proposed that energy comes in tiny, discrete packets called quanta, with energy given by E = h × f.
Why Is It So Important?
The Planck constant sets the scale of the quantum world. It appears in the Heisenberg uncertainty principle and now defines the kilogram. Without it, atoms would collapse.
For the basics of quantum computing, see our Quantum Computing Basics Guide .
Comparison Table – Units
| Unit | Value | Use |
|---|---|---|
| Joule‑seconds (J·s) | 6.62607015 × 10⁻³⁴ | SI, kilogram definition |
| Electronvolt‑seconds (eV·s) | 4.14 × 10⁻¹⁵ | World Quantum Day |
Real‑World Applications
Planck’s constant underpins LEDs, solar panels, atomic clocks, and GPS. To see how quantum principles apply to computing, read our Quantum vs Classical Computing Comparison .
FAQ
Q1: What is Planck’s constant in simple terms?
A: It describes the size of energy packets (quanta).
Q2: Why is World Quantum Day on April 14?
A: Because the constant rounds to 4.14×10⁻¹⁵ eV·s.
Q3: Who discovered it?
A: Max Planck in 1900.
Q4: Is it the same everywhere?
A: Yes, it is a fundamental constant of nature.
Conclusion
The Planck constant is the silent ruler of the quantum realm. Celebrate it on World Quantum Day. For more on quantum applications, see our Quantum Computing Applications 2026 and Post‑Quantum Cryptography Explained .
