If you had a magic green wand, how would you change the world? Share your out-of-the-box, pie-in-the-sky big idea with GOOD and Babelgum — both green-minded media companies — and it could be featured in Big Ideas, a new weekly series featuring celebs sharing their green ideas, and GOOD Magazine’s Fall 2009 issue.

To enter, just answer this question: “If there weren’t any pesky practical limitations, what world-changing device would you invent?” Then submit your answer through the Big Ideas website by Aug. 25. For inspiration, watch some of the Big Ideas episodes — like the one below by Imogen Heap, who’d like “spherical bubbles that are see-through living spaces.”

Got an idea more creative than Imogen Heap’s? Then enter the contest — and good luck!