A beautiful essay about the nature of time by Tom Vanderbilt. My favorite excerpt:
"For now, such clocks can at least confirm the old physics. “If you were to lift this clock up a centimeter of elevation,” Hume told me, “you would be able to discern a difference in the ticking rate.” The reason is Einstein’s theory of relativity: Time differs depending on where you are experiencing it. When standing upright, your head exists at a slightly different timescale than your feet. But with this accuracy comes a sobering reality. “There are not just two times,” notes the physicist Carlo Rovelli in The Order of Time. “Times are legion: a different one for every point in space.” What we think of the present, he writes, “does not extend throughout the universe.” Rather, “it is like a bubble around us.” The “well-defined now,” as he calls it, “is an illusion.”"
Found via The Browser.