Ives–Stilwell

Plate 27 speaks for itself: “Moving clocks run slow, measured in hydrogen.”

The Physics

Ives and Stilwell looked at light from fast hydrogen ions, forward and backward. The first-order Doppler shifts cancel in the midpoint, which is shifted by time dilation alone.

Δλ ≈ β² λ₀ / 2

• Δλ: midpoint shift of the forward and backward lines, m
• β: v/c, dimensionless
• λ₀: rest wavelength, m

Fast hydrogen atoms from a canal-ray beam. Ives & Stilwell, 1938.

Sources

• H. E. Ives, G. R. Stilwell, J. Opt. Soc. Am. 28, 215 (1938).

On the poster

Plate 027, “Ives–Stilwell”: the pixel-art plate with its slogan “Moving clocks run slow, measured in hydrogen.”, the key equation and the facts panel shown above. Pixelated Physics. Physics. Personified.