6 constants · 5 exact by definition · 1 still measured
The Universal Constants
A handful of numbers set how fast light goes, how hard gravity pulls and how big an atom is. Run the famous experiment that found each one, then see where it comes from and what would break if it changed.
- Exact since 1983 The speed of light 299,792,458 m/s How fast is light, and how did anyone time something that quick? 12 min · Run the experiment →
- Measured The gravitational constant 6.67430 × 10⁻¹¹ N m²/kg² How hard does gravity pull, and how do you weigh the Earth? 13 min · Run the experiment →
- Exact since 2019 The Planck constant 6.62607015 × 10⁻³⁴ J s Why does light come in tiny packets, and how big is one? 13 min · Run the experiment →
- Exact since 2019 The elementary charge 1.602176634 × 10⁻¹⁹ C Is electric charge smooth, or does it come in lumps? 12 min · Run the experiment →
- Exact since 2019 The Boltzmann constant 1.380649 × 10⁻²³ J/K What is temperature, really, and how hot is one molecule? 12 min · Run the experiment →
- Exact since 2019 The Avogadro constant 6.02214076 × 10²³ per mole How many atoms are in a spoonful, and how did anyone count them? 13 min · Run the experiment →