UPDATE: The Earth Didn't Move For Me.
We jumped, really, but I guess enough of you out there slept in. For shame. ::ABC News
OK it is finally here. Rockies may crumble, Gibraltar may tumble, They're only made of clay but Jump Day is here to stay. We have no doubt that the Intarweb will crash along with most masonry buildings under the shock but TreeHugger will be up as soon as electricity returns and we can find our dialup modems. If it works, we will all live in a cooler, better world. Get ready to jump, today, at 11:39 GMT. Do NOT use the Jump Day site calculator- it did not take daylight saving time into account. See you after the jump! ::World Jump Day
All kinds of people say it is a hoax, an art piece by one Torsten Lauschmann, a german artist living in Glasgow, who has also busked across Europe with a solar powered sound system. Others point out that it just can't work, for reasons shown below the fold. However if we don't jump and it gets warmer, we will regret it, maybe not today but soon and for the rest of our lives. 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 
* 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. ::Wikipedia