Matt Jones' Random Acts of Verbiage

Whilst blog browsing, I came across a post from last week: Stop World Jump Day Before It’s Too Late. I must be out of the loop or something because I had never heard of this. Reading that post made me think two things: either 1) people are complete idiots, or 2) it is a hoax. So I went to the World Jump Day website. There isn’t much info up there now as the “event” has already happened (July 20th). The just of the “event” was that if they could get 600,000,000 people in the Western hemisphere to all jump at the exact time they could change the orbit of the earth so as to reduce the effects of global warming. For those that don’t understand physics (or the sheer impossibility of cooridinating the precise movements of 600,000,000 people), this is impossible. And seeing that the website pointed to lambda omega lambda, a german techie/computer science student orginzation, I figured this must be a hoax because nerds like that wouldn’t actually believe this would work. Then I went to Wikipedia, as I often do, to see what it had to say. Their article states that it is apparently an art installation by some German guy. I also found this pretty funny:

The counter for the site, measuring registered jumpers, was also inaccurate. The number of registered jumpers would go both up and down. For a point of reference, at 21:37 on 18th July 2006, it was at 598,196,296 but just 15 minutes later it had dropped to around 598,106,000. Less than 12 hours before the event the site’s counter read that there were 600,256,820 registered jumpers, over 50% of all internet users.

Heh. This is an awesome hoax because I have no doubt that there are plenty of people willing to believe this (just like the number of people willing to blame global warming on us…). I am curious as to how many people believe this. Has anyone come across this and believed it?

Does anyone want me to explain why the science of this is bad?

UPDATE: Physics!

So here is the deal, two objects with mass will always have a gravitational force between them (F = G*m(1)*m(2)/r^2 where G is the gravitational constant, m(1) and m(2) are the masses of the two objects, and r is the distance between the two points). The center of gravity (also called the center of mass) lies between the two points. If we have two equal masses separated by 2 meters, the center of mass will be at 1 meter away from each of them. If one mass is 99kg and the second is 1kg, the center of mass will be 1/50th of a meter away from the larger object because that object as much more mass (see here for how I calculated that). In that example, the center of mass was 99% closer to the heavy body and yet there was only a 98kg difference in mass. So if we move the scale up to me and Earth size, we will see that, for all purposes, the center of mass is in the middle of the Earth (the Earth is 10^23 times more massive that a person is, that’s a 1 with 23 zeroes). This means that if I jump a meter in the air (which is a huge jump) I am not going to change the center or gravity (1 meter is only .00000784% of the radius). If I can’t change the center of gravity, I can’t change the earth’s orbit. Not only that, but because the force of gravity is attractive, I just fall towards the earth again (and according to Newton’s 3rd law, the Earth falls towards me). So even if I could move the center of gravity during my jump, it would go back to exactly the same place when I reach the ground again. So here is the just of what I am saying: The earth’s own mass (including us) cannot be used to change its center of gravity.

The idea is to change the Earth’s orbit by changing its center of mass. The center of mass of the Earth-Sun system cannot be changed by us jumping on it because us jumping on it does not even change the center of mass of the Earth-me system. The only way to change the center of mass of the Earth-Sun system would be to change our mass somehow. Even if it was possible for the supposed 600,000,000 people to leave the Earth (and therefore reduce its mass and therefore the center of mass of the Earth-Sun system), it would not be enough! Let’s assume that the average person has a mass of 70kg (I have no idea of this is correct). That means that the total mass of the 600,000,000 people would be 42 billion kg (4.2*10^10 kg). The Earth has a mass of 5.97*10^24 kg. So all of those people leaving the Earth entirely would only reduce the mass of the earth by .0000000000007035%!! This is NOT a substantial amount!

It comes to this: people jumping will not cause a change in the center of mass of the Earth so the center of mass of the Earth-Sun system will not change so the orbit will not change. Even having those people leave the earth will not cause a significant change in the mass of the Earth so that will not even change the center of gravity (by a significant amount) of the Earth. I probably made this too long and confused things more… but I hope it helped!