How Long Would It Take to Walk a Light-Year ?

    

      If you had started just before the first dinosaurs appeared, you’d probably be finishing your hike just about now. Here’s how it breaks down. One light-year —the distance light travels in one year, used as the yardstick for interstellar distances—is about 5.9 trillion miles (9.5 trillion km). If you hoofed it at 20 minutes a mile, it would take 225 million years to complete your journey (not including stops for meals or the restroom). Even if you hitched a ride on NASA’s Mach 9.8 X-43A hypersonic scramjet, it would take more than 90,000 years to cover the distance. You’d need to bring a big backpack, too: Walking such a distance requires substantial supplies. The average adult burns about 80 calories per mile walked, so you’d need about six trillion granola bars to fuel your trip. You’d also produce a heap of worn-out shoes. The typical pair of sneakers will last you 500 miles (800 km), so you’d burn through some 11.8 billion pairs. And all that effort wouldn’t get you anywhere, astronomically speaking: The closest star to the Sun, Proxima Centauri, Is 4.22 light-years away.