Figure 12-31Time Slows Down Near Matter (a) Two clocks in space set at exactly the same time are (b) brought to Earth and the Moon. From a vantage point far from Earth and the Moon, the clock on Earth is ticking more slowly than the clock on the Moon. This occurs because mass slows down the flow of time, and Earth has more mass (and a higher density, which adds to the effect) than the Moon.