Figure 21-7: The Gravitational Slowing of Time and the Gravitational Redshift (a) Clocks at different heights in a gravitational field tick at different rates. Assume that identical clocks were first brought together and set to the same time. After being placed on different floors and left to tick for a while, the stronger gravity on the lower floor (closer to Earth) results in less time passing for that clock. In stronger gravity, time passes more slowly. (b) The oscillations of a light wave constitute a type of clock. As a light wave climbs from the ground floor toward the top floor, its oscillation frequency becomes lower and its wavelength becomes longer.