General relativity has readers feeling upside down

It’s all relative

In “Earth is young at heart” (SN: 6/25/16, p. 5), Emily Conover reported that Earth’s core is more than two years younger than the planet’s surface, according to new calculations. Thanks to the effect of gravity on the passage of time, a clock placed at Earth’s core will tick fractions of a second slower than a clock at the surface.