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When Will Time End
Time is flying by on this busy, crowded planetas life changes and evolves from second to second. At the same time, the arc of the humanlifespan is getting longer: 67 years is the global average, up from just 20 years in theStone Age. Modern science provides a humbling perspective.Our lives, indeed even that of the human species, are just a blip compared to the Earth, at4.5 billion years and counting, and the universe, at 13.7 billion years. It now appears the entire cosmos is livingon borrowed time. It may be a blip within a much grander sweep of time. When, we nowask, will time endé
Our lives are governed by cycles of wakingand sleeping, the seasons, birth and death. Understanding time in cyclical terms connectsus to the natural world, but it does not answer the questions of science. What explains Earth's past, its geologicaleras and its ancient creaturesé And where did our world come fromé How and when willit endé In the revolutions spawned by Copernicus and Darwin, we began to see time as an arrow,in a universe that's always changing. The 19th century physicist, Ludwig Boltzmann,found a law he believed governed the flight of Time's arrow. Entropy, based on the 2ndlaw of thermodynamics, holds that states of
disorder tend to increase. From neat, orderly starting points, the elements,living things, the earth, the sun, the galaxy. are all headed eventually to states of highentropy or disorder. Nature fights this inevitable disintegration by constantly reassemblingmatter and energy into lower states of entropy in cycles of death and rebirth. Will entropy someday win the battle and putthe breaks on time's arrowé Or will time, stubbornly, keep moving forwardé We are observers, and pawns, in this cosmicconflict. We seek mastery of time's workings,
even as the clock ticks down to our own certainend. Our windows into the nature of time are the mechanisms we use to chart and measurea changing universe, from the mechanical clocks of old, to the decay of radioactive elements,or telescopes that measure the speed of distant objects. Our lives move in sync with the 24hour day,the time it takes the Earth to rotate once. Well, it's actually 23 hours, 56 minutesand 4.1 seconds if you're judging by the stars, not the sun. Earth got its spin atthe time of its birth, from the bombardment of rocks and dust that formed it. But it'sgradually losing it to drag from the moon's
gravity. That's why, in the time of the dinosaurs,a year was 370 days, and why we have to add a leap second to our clocks about every 18months. In a few hundred million years, we'll gain a whole hour. The daynight cycle is so reliable that ithas come to regulate our internal chemistry. The fading rays of the sun, picked up by ourretinas, set our socalled â€œcircadian rhythmsâ€� in motion. That's when our brains beginto secrete melatonin, a hormone that tells our bodies to get ready for sleep.
Finally, in the light of morning, the flowof melatonin stops. Our blood pressure spikesâ€¦ body temperature and heart rate rise as wemove out into the world. Our days, and our lives, are short in cosmic terms. But withour minds, we have learned to follow time's trail out to longer and longer intervals. We know from precise measurements that theEarth goes around the sun every 365.256366 days. Much of the solar energy that hits ourplanet is reflected back to space or absorbed by dust and clouds. The rest sets our planetin motion. You can see it in the ebb and flow of heatin the tropical oceans, the annual melting