Wavelength Independence of the Velocity of Light in Space

Abstract

BECAUSE of the great distances involved, time measurements on astronomical events afford the best possibility for a high precision determination of the relative velocities of electromagnetic radiation at different wavelengths¹. A discussion of flare stars, observed nearly simultaneously at optical and radio wavelengths, resulted in a relative uncertainty Δc/c of 4 × 10⁻⁷ over the wavelength range 0.54 microns–1.2 m. This gives a value of the product p=(c/Δc) (λ₂/λ₁) of about 5 × 10¹², which is a factor of 10 greater than that which has been achieved in the laboratory².