Here's a fun hypothetical: what would happen if everyone on the planet jumped at the exact same time? Could the Earth move, or – as legend has it – could our planet's rotation even slow down?
Unfortunately, given the insurmountable problems in choreographing the event, we cannot say for certain what would happen. However, a few people have investigated the question, with one physicist calculating that we could at least temporarily shift our host planet a tiny fraction.
In one experiment performed for BBC's Earth Lab, science journalist and presenter Greg Foot attempted to answer the question by getting a crowd of 50,000 people to all jump up at the same time, measuring the resulting quake in the ground from 1.5 kilometers (almost 1 mile) away.
"And then with a bit of math I can scale that up and see what would happen if everyone around the Earth jumped at the same time, and whether that would change the speed of the spin of the Earth," Foot explains in the video.
Earthquakes, if they are large enough, can affect the speed of the Earth's spin. In 2011, the massive earthquake that hit Japan slightly accelerated Earth's spin, shortening our days by about 1.8 microseconds. Therefore, Foot believed in the idea that if everyone jumped at the same time, we might be able to affect the Earth's spin.
Sure enough, from a kilometer and a half away the team were still able to detect an earthquake that read 0.6 on the Richter scale. However, scaling that up, he figured out that it wasn't enough.
"Earthquakes don't affect the planet's spin until they reach at least eight, and for this you'd need seven million times more people than currently live on the planet," he concluded. "So the urban legend is completely untrue. You cannot shift the planet if everyone jumps at the same time; you can't even change how fast it spins. There's no truth in it at all."
But, could we move the planet at all? To this, physicist Rhett Allain has an answer. Allain loosely estimated the average weight of humans and children and the mass of the Earth, assumed that everyone jumped 0.3 meters (1 foot, for ease of calculation), and assumed that everyone would be performing the jump in the same place, to avoid our jumps canceling each other out.
Based on the 7 billion people alive at the time, Allain calculated that the Earth would be moved about a hundredth of the radius of a single hydrogen atom.
"After all the people jump they would 'fall' back down – move towards the Earth," he added to Live Science's series Life's Little Mysteries. "During this time, the Earth would move back up. All would be as it once was."