I can't tell you what joy xkcd gives me:
Everybody Jump What would happen if everyone on earth stood as close to each other as they could and jumped, everyone landing on the ground at the same instant? —Thomas Bennett (and many others)
This is one of the most popular questions submitted to this blog. It’s been examined before, including by a ScienceBlogs post and a Straight Dope article. They cover the kinematics pretty well. However, they don’t tell the whole story.