While batteries and hydrogen fuel cells are variously bandied about as appropriate power sources for cars, and high-speed trains (also electric, or diesel-electric hybrid) an excellent choice for longer-range travel, the question remains of how airplanes will fly without energy-intensive aviation fuel. After all, you can't really run a jet-plane equivalent on batteries. Alternatives like airships and "gravity planes" are interesting, but have substantive drawbacks, mostly regarding speed. And virtual reality (even with "claytronic" avatars) is still nowhere close to being a strong alternative to face-to-face contact.
Blogger and occasional WorldChanging commenter "Engineer-Poet" tackles the question of post-oil aviation in a new post on his blog, The Ergosphere. The post is particularly interesting in the way he peels down the issues and lays out just where the solutions could come from. The short answer is liquid methane, which actually has some advantages over current jet fuels. The entire argument is worth reading, so don't just go by this one-sentence summary.
