World Jump Day is the first global flash mob event scheduled for July 20, 2006 at 11:39.13 UTC, at which time the organization plans to have 600 million people from the western hemisphere jump simultaneously (currently the site claims that there are 600,256,820 registered jumpers as of July 20, 2006 (less than 12 hours before the event; according to World Stats, this would be almost 50% of all internet users. There are strong reasons to doubt this figure.). They claim this will move the Earth out of its current orbit, and into a new one, one that will not cause global warming. The site is an art installation, and in no way serious.
The World Jump Day website gave the jump time as 11:39:13 GMT, but the countdown on the same site was (as of May 6 2006) counting down to 10:39:13 GMT. There seemed to have been a confusion between the GMT or UTC time and the UK legal time 11:39:13 which takes into account daylight savings time. Recently the countdown was adjusted to reach zero at 11:39:13 GMT.
World Jump Day's claim is completely unscientific. There are a number of reasons to reject the thesis:
* It is impossible to permanently change the Earth's orbit using the planet's own mass (which includes that of the world's population) unless such mass is ejected from the Earth at escape velocity (see Newton's third law of motion). The center of gravity of the system containing the earth and its population of humans will remain in the exact same orbit it was always in throughout the jump. However, for the very brief moment when the jumpers are in the air, the Earth's orbit would be moved a tiny bit - only to be restored to its exact same location by the force of gravity acting between the jumpers and the planet while they are in the air.
* Even ejecting such mass from the Earth (or colliding to it from outer space), the resulting energy would be equivalent to only 2% of the energy released by a modern hydrogen bomb, shifting the Earth's orbit just a small fraction of the radius of a single atom [1]
* Since the Earth's orbit is elliptic, there are already great variations in its distance from the Sun (about 5,000,000 km) with no generally noticeable changes in temperature.
* Applying a brief force to the surface of the earth would not move its orbit further from the sun - it would merely change the shape of the ellipse - so at some times of year the earth would actually be closer to the sun whilst at others it would be further away.
* Time Zones! There are 600 thousand people going to jump and they all live in different areas! The time zone changes aren't accurate enough for everyone to hit the ground at the EXACT same time. And since the time is so precise, there will be variations in the jump speed height, ETC. So jumping will not do anything, just make you look like an idiot.
