At the hazy dawn of the twentieth century, through the byways of mental meandering and mathematical play, Albert Einstein arrived at a revelation about the nature of the universe while working as a clerk at the Swiss patent office — a new relationship between space and time, the warp and weft of a single fabric that hammocks energy and matter into the lucid dream of reality. It took years for Arthur Eddington’s dramatic eclipse expedition to confirm Einstein’s theory by watching light bend along the curvature of spacetime against the screen of totality rather than follow the straight lines Newton predicted. “New theory of the universe,” the London Times proclaimed under the heading REVOLUTION IN SCIENCE, “Newtonian ideas overthrown.” But no one, not even Einstein himself, imagined that this purely theoretical revolution would have practical applications that would alter the fabric of human life — relativity was the paragon of “useless knowledge.” Today, GPS governs everything from air traffic to world banking, relying heavily on relativity: A centerpiece of Einstein’s insight was that time dilations due to gravity and velocity make a clock in space run at a slightly different pace from a clock on Earth; the incredible accuracy of the atomic clocks on satellites, which must sync up with the clocks on Earth in order to yield coordinates, means that the minutest misalignment in time can result in immense dislocation in space. One million taxi trips in New York City. (Data from nyc.gov visualized with kepler.gl.)Building on Hedy Lamarr’s technology for remote-controlling torpedoes, GPS was developed by the U.S. Department of Defense as a military technology two decades after Einstein’s death. (I wrote Traversal largely to reckon with this tendency of civilization to turn the most succulent fruits of our search for truth into grenades for power, and to celebrate its counterpoints, which are many and which in the end prevail — we must believe they do, or perish.) But science, which is the reverence of nature, may have the last word.Within two decades of its invention, Venezuelan cattle rancher turned biologist and conservationist Eduardo Alvarez pioneered the use of GPS as a tool of field biology. The wildlife tracking it made possible revolutionized conservation, shedding light on the movements and habits of animals too elusive or wide-ranging for close and consistent human observation. Sandhill crane migration. (Study data visualized with kepler.glIt all began with a creature most of us have never encountered or even know exists. Just out of school, Alvarez was charged with environmental evaluations of a dam-damaged river in Venezuela’s Guri Lake basin. In the decade he spent there, he kept hearing local stories about encounters with a living mystery of the rainforest — the rare harpy eagle. So named by Linnaeus for the harpies of Greek mythology — half-woman, half-bird creatures personifying the storm winds — Harpia harpyja is our planet’s largest-taloned bird and one of its most vulnerable, its native habitat shrinking exponentially with the destruction of the Amazon. Harpy eagle. (Photograph: Bill Abbott.)Alvarez grew fascinated with this curious creature that looks like a character out of Lewis Carroll’s mind. Within a decade, he had founded a conservation program, pioneering GPS tracking to protect these strange, silent birds and their vanishing world. Today, GPS is used in the conservation of an astonishing array of wildlife, from orcas to pandas. But, in an ouroboros kind of way, none of it would exist without birds: It was in the avian brain that evolution invented the dream-rich REM sleep as a laboratory for practicing the possible, and it was in a dream that Einstein arrived at the central insight of relativity. Every harpy eagle, every heron and every sparrow, carries on its wings the wondrous worlds we enter at night where we may find the deepest, most elusive truths.Einstein’s birthplace on the sleeping Earth seen from the International Space Station, which remains in orbit thanks to GPS. (Photograph: NASA.)donating = lovingFor seventeen years, I have been spending hundreds of hours and thousands of dollars each month composing The Marginalian (which bore the outgrown name Brain Pickings for its first fifteen years). It has remained free and ad-free and alive thanks to patronage from readers. I have no staff, no interns, no assistant — a thoroughly one-woman labor of love that is also my life and my livelihood. If this labor makes your own life more livable in any way, please consider lending a helping hand with a donation. Your support makes all the difference.newsletterThe Marginalian has a free weekly newsletter. It comes out on Sundays and offers the week’s most inspiring reading. Here’s what to expect. Like? Sign up.