Originally posted by rhbI think one reason would be that it would be imposible to get everyone to jump at the same time as even a second off would ruin it.
it'll never work!
Is there any proof that it would affect the orbit at all? I would expect it would have a far smaller effect then the tides.
Okay, folks, let's look at this. Suppose everybody on the planet weighed 100kg (which is an overestimate, 70kg is more like it, probably less). Suppose that there were ten billion people (another overestimate - there are about 6.4 billion at the time of writing). Suppose that they all jumped ten metres in the air (a huge overestimate, fifty centimetres is more likely and probably much less). Suppose they were all at the exact same point on Earth (which they won't be, thus mitigating the effects of the jump). And lastly, suppose that they all jumped at precisely the same instant, which of course they will not, seeing as the time difference between the fastest watch and the slowest will likely be over five minutes.
Altogether that's a mass of one billion tonnes of humanity jumping ten metres in the air.
The Earth has a mass of... let's be nice and round it WAY down to 10exp21 tonnes. That's a trillion times heavier than all of humanity. Which means the distance the Earth moves when everybody jumps will be one trillionth of the distance that all the people jumped: that is to say, 10exp-11 metres, or about half the radius of a hydrogen atom.
It gets better. Even assuming the Earth did move by some significant distance when everybody jumped, just think about it: it'd move right back again! You jump up, the Earth goes down: you fall down, the Earth comes up to meet you. Jumping up and down to try to move the Earth is like mounting a fan on a sailboat, pointing the fan at the sail, and expecting the boat to move forwards. It just doesn't work!
Cut'n'pasted from here: (Which lists real cool ways to destroy the Earth)
http://qntm.org/moving