There was a reader input in an LXF issue recently that the world jump day wouldn't have any impact besides the fact that people commonly all over the world would have some fun together. There was a suggestion? on jumping in one spot but that wouldn't be viable because of the physics. The fact is that there wouldn'd being any jumping at all. If all humans where to be gathered together at one spot giving every human a square-meter to stand on we would all be melting away.