What if every single person on Earth jumped at the exact same time? Could it cause an earthquake or would we not even be able to tell? First things first, let’s talk about the Earth’s rotation.The Earth spins, that’s why we have night and day, and it spins quickly. At the equator, the Earth is spinning at more than 1,000 MPH. Now, a spinning ice skater can speed up by moving mass closer to the center and the Earth is no different. In fact, if you get down on the ground right now and move your mass closer to Earth’s center, technically, you will speed up Earth’s rotation, making this day shorter. Now, the change that you would make to the Earth’s rotation is way smaller than we could even measure, but it is calculable, and the impact can be quite impressive when you talk about redistributing more mass than just one person.
For instance, last year, the earthquake in Japan redistributed so much of Earth’s mass towards the center, that every day since then has been 1.8 microseconds shorter. But, that was a giant geological event. What can us humans do to the Earth all on our own? There are more than 7 billion of us now. What if we all got together in one place and jumped? What would that even look like? Interestingly, if you took the entire human population of Earth and had them all live in one place with the same density that people live in New York City, you could fit everyone, all of us, into the state of Texas. But that’s living, not standing around in a crowd, which is how we would probably want to do the jump.
If every single person alive right now on Earth stood shoulder to shoulder, you could fit all of us into the city of Los Angeles. It would be an incredible sight to behold, a mere 500 square miles containing every single person on Earth. Then, we jump. Unfortunately, not much happens. Our collective mass compared to the mass of the entire Earth is like nothing. In fact, Dot Physics calculated that if all of us were to get together in one location and all jump 30 cm into the air at the exact same time, we would push Earth away from us a tiny amount. Earth would only move away from us about 1/100th of the width of a single Hydrogen Atom. And here’s another thing. Because we’re all jumping and then going back to where we started, Earth is just going to move back to where it started.
So, our big jump won’t be able to change Earth’s position in space, but, 7 billion people all jumping together has to cause some sort of seismic activity, isn’t it? So, let’s say you have a lot of people all together in one place and you have them all jump on: 1-2-3! That is what BBC did with 50,000 people and discovered that a kilometer and a half away, it only registered a .6 on the Richter scale. You would need 7 million times more people than even live on Earth right now to jump at once to recreate the earthquake that recently happened in Japan. So, compared to the size of the Earth, we’re not much. But don’t get too discouraged. Our collective jump would contain a lot of energy.
The Straight Dope calculated that even if only the people who lived in China got together and jumped, their jump would be the equivalent of 500 tons of TNT. Of course, 500 tons of TNT doesn’t do much to an Earth that weighs 6 sextillion 588 quintillion tons. But keep this in mind. Even though you, or even a large group of us, can’t do much to change Earth’s location or rotation, we can affect it a little bit. Newton’s Third Law guarantees this. If you weigh 150 pounds, the Earth is pulling you down with a force of 150 pounds. But, you are also pulling up on the Earth with a force of 150 pounds. If you fall 3 meters, the Earth has pulled you down 3 meters. But, you have also exerted a equal and opposite force on the Earth. Of course, it’s a lot bigger. So, if you fall 3 meters, you pull the Earth up about a billionth of the width of a proton, which isn’t bad. So, the next time you move your body, the next time you jump, think about this. You just affected the Earth as much as it affected you. You’ve got that kind of power.