Everyday time dilation.

Einstein showed that time is relative. Maybe you've heard of the twin paradox? That is a thought experiment, in which someone who goes on a high-speed rocket journey returns to Earth younger than their stay-behind twin.

Well, time dilation has been well-demonstrated, but generally only at fairly high speeds; we've never thought of it as something that's relevant or detectable in everyday experience (for those of us who don't ride rocket-ships).

But.

In a recent paper in Science, researchers at NIST used novel "optical clocks" to detect time dilation at everyday speeds, and, perhaps most spectacularly, due to one foot of elevation: They showed that their clocks can be used to detect the difference in the rate of passage of time due to a change in one foot in elevation with respect to the gravitational field of the earth!