If every single human on Earth jumped at the exact same time, would it cause a planet-wide earthquake, or would we not notice anything at all? It’s probably not something you’ve ever considered, but now that the question’s out there, you’re curious, aren’t you? Well, don’t worry, because Michael from Vsauce is here to run us through the awesome physics of this conundrum, and says the answer has everything to do with how quickly our Earth is rotating at this very moment.
At the equator, Earth is spinning at more than 1,600 km/h – that’s really fast. And the amazing thing is, in much the same way as a spinning ice-skater is able to speed up when they move their arms and legs closer to their body, because more mass in the centre means a faster spin, you can actually speed up Earth’s rotation. “If you get down on the ground right now, and move your mass closer to Earth’s centre, technically, you will speed up Earth’s rotation, making this day shorter,” says Michael.
Sure, the effect you’d have on Earth’s rotation would be so minuscule, no machine on the planet would be sensitive enough to measure it, but it’s still calculable, and this is how we can figure out the impact of the world’s population redistributing their mass away from and then towards Earth’s centre in one big jump. And we don’t even need a hypothetical scenario like that to see the effects. According to the video above, an earthquake that hit Japan in 2011 redistributed so much of Earth’s mass towards the centre, that every day since then has been 0.000018 seconds shorter.
So what about if we got all 7 billion humans and made them gather in one place and perform one Earth-sized jump? How would that fare against the colossal movement of tectonic plates that was the Japan earthquake? Firstly, we’d have to find somewhere to put everyone, and Michael says that if we took the entire population and needed to put them in one place with the density of New York City, you could fit every single person into the state of Texas. WTF.