Our planet, space and the Chinese is something that has has
bothered children all over the world for many years. Even adults sometimes think
about these things. The question of whether the Great Wall of China is
viewable from the moon is one of those things, and the question of the jumping
Chinese is another. Why don't we investigate this last question once and for all
Let's do the math, without the physics. We could use Newton's laws in
order to calculate the forces involved, but that would only give us a number that
would be hard to interpret. Let's just try to do an estimate that we then can
translate into something we can relate to instead.
Assume that one billion people would be
participating this event. That would be hard enough to synchronize, but
theoretically another billion jumpers would be able to squeeze in on that side
of earth. We don't want people interfering on the other side of the earth, mind
you. It's a factor 2, which we can account for later, if needed. Anyhow, one
billion people, each weighing 60 kg (~130 lbs), would have the weight of
6 ·1010 kg. Earth has the mass 6 ·1024
The earth weighs 6 ·1024 / 6 ·1010 = 1014
times more than one billion people. That is
100,000,000,000,000 times more. This number is of course hard to comprehend, but
it gives a hint that there would be no noticeable effect on Earth at all.
Let's scale this down to something we can relate to: a housefly. We all
know how it is when a fly lands on you. If you're lucky, you feel an itch, but
often you feel nothing. The ordinary housefly does not make a noticeable impact
on you; it does not make you stumble or lose your balance. A housefly weighs
about 40 mg, 40 thousands of a gram, or 4 ·10-2 g, or 4 ·10-5
kg. Something weighing a factor 1014 times more would
therefore weigh 4 ·10-5 kg x 1014 = 4 ·109 kg,
or 4 million kilograms. Lead weighs 11 350 kg/m3, which means
that it would take 4 · 109 kg / 11350 kg/m3 =
352 400 m3 of lead to come up in this weight. This corresponds to a
cube of lead with the side 3√( 352 400) = 70 meters (76
yards or 230 feet). This is the side of the cube of lead that our imaginary fly would
So, we therefore conclude that:
The effect that one billion people would have on earth, is
the same as a housefly would have on a lead cube with sides 70 meters long.
We realize that increasing the amount of people would have little impact.
Just add one fly for each billion people. It wouldn't matter at all, would it? Earth would not notice our effort.