Planck energy

Two ways of reading the same number make the Planck scale vivid. In particle terms it is 1.22 × 10¹⁹ GeV, a quadrillion times the LHC's 13.6 TeV, unreachable by any accelerator that fits in a solar system. In everyday terms it is 1.96 gigajoules — the kinetic energy of a 1.4-tonne car at about 190 km/h, or roughly half a tonne of TNT. The difference is that the Planck energy is concentrated on a single particle.

This is where the four forces are conjectured to unify and where a graviton exchange becomes as strong as a photon exchange. Nature does get close: the highest-energy cosmic ray ever recorded, the 1991 "Oh-My-God" particle, carried 3 × 10²⁰ eV — a single proton with the energy of a well-struck baseball, yet still eight orders of magnitude below E_P. Some quantum-gravity models predict tiny energy-dependent delays in gamma-ray bursts suppressed by E_P; none has been seen.