0.00000000000000004. That's the minuscule factor by which time speeds up if you're elevated just one foot higher from the surface of the Earth, according to new study in Science that cleverly demonstrates Einstein's general relativity on a human scale. Don't rush to move into the basement to extend your life, though: That tiny speck of a difference would account for just about a billionth of a second over the span of the year. Gravity is the key player in this time variance: