2026
CLM-LR-DRAFT-C-1= 299792458 m/sEXACT VALUESI definition of the metreSource: Speed of light in vacuum ↗
PROVEN
Limits RegistryPUBLIC RECORDLimits RegistryPUBLIC RECORDLimits RegistryPUBLIC RECORDLimits RegistryResearch Console →The speed of light in vacuum is one of the few physical constants whose value is exact by definition rather than measurement — the 1983 SI redefinition of the metre fixed it precisely, making it the ultimate speed limit for information and matter in relativity.
The question, scope, and sources behind this Registry record.
What is the SI-defined value of c, the speed of light in vacuum?
Current frontiers derived from accepted Claims.
The accepted equality closes this optimization result.
Assertions tied to evidence, attribution, and review.
The frontier as it changed over time.
Only accepted Claims matching the current specification contribute to the displayed bounds. Strict inequalities remain open; contradictory Claims require editorial review.