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. If you hoofed it at a moderate pace of 20 minutes a mile, it would take you 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 9.68 X-43A hypersonic scramjet, the fastest aircraft in the world, it would take about 95,000 years to cover the distance.
You'll need to bring a big bag, too; walking such a distance requires substantial supplies. The average adult burns about 80 calories per mile walked, so you'd need two trillion PowerBars to fuel your trip. You'd also produce a heap of worn-out shoes. The typical pair of sneakers will last you 500 miles, so you'd burn through some 11.8 billion pairs of shoes. And all that effort wouldn't get you very far, astronomically speaking: The closest star to the sun, Proxima Centauri, is 4.22 light-years away.
This article appeared in the September 2008 issue of Popular Science magazine.