What would happen if everyone jumped at the same time?

We humans love to break records, and messing with gravity seems to be one of our species' odd and enduring obsessions. But what would happen if we decided to take things to the next level by convincing every human on earth to jump at exactly the same time?

First, some math. According to a 2013 biomass study cited in Live Science, the combined mass of humanity is around 632 billion pounds. To provide a convenient handle on that number, picture a perfectly balanced (and enormous) scale with 15 million Eiffel Towers on one side, and all human beings on the other. At first glance, the question of what would happen if everyone jumped at the same time seems a simple matter of physics: something akin to: "what would happen if a 632 billion pound bowling ball collided with a much larger 1.3 x 10 to the 25th (which is the weight of the Earth) pound bowling ball?"

Unfortunately, it's not that easy. The answer depends on how the jumping occurred, and whom you ask. 

Imagine first a scenario in which everyone stayed exactly where they currently live. From a physics standpoint, this is similar to grains of rice hitting a hot air balloon from all sides at once. According to a Live Science article relying on the work of University of Southern Louisiana physicist Rhet Allain, the tiny fluctuations in gravity from every person's leap would amount to ... well... nothing. It'd just get chalked up to being the largest flash mob in history, someone would develop a line of cool "I jumped" merchandise, and everyone would just sheepishly move on with their lives.

Scenario two is a little more complicated. Imagine that everyone flew to the same location and jammed tightly together into one area occupying roughly the size of Los Angeles — and that at the appointed time, every human in existence jumped around a foot into the air. What would happen next is the subject of some debate. 

According to Professor Allain, this would indeed affect our planet. He calculates that at the moment humanity's collective weight crashed back to the ground, the Earth would shift its course. Unfortunately, if one lonely astronaut happened to be orbiting the planet to observe the phenomenon, they probably wouldn't notice. The planet would move off-course by approximately the radius of one hydrogen atom. Then the Earth would instantly right itself and resume its original course. And humanity would fly home — dejected but unharmed. 

Other experts paint a less rosy picture. Take as one example this joint presentation by Ohio State University physicist Dr. Paul Sutter and Sandia National Laboratories astrophysicist Mark Boslough. In their model, immediately after the jump, every human on Earth would double over in agony, their eardrums perforated by the sound of 14.6 billion shoes striking the ground at once. Then, as people lay writhing in pain, a massive earthquake of up to eight on the Richter scale would shatter the ground around them. When those people who were still conscious finally stumbled to their feet (wishing they'd stuck with video game jumping,) they'd be greeted with the hellish vista of a hundred-foot tsunami bearing down on them, a wave of oceanic vengeance punishing humankind for its collective jumping hubris. Not a great day. And one that would definitely put humanity's less important terrible decisions into a more favorable light. 

So, to recap. The best answer to what would happen if everyone jumped at the same time is that it would either be utterly anticlimactic or completely cataclysmic. Either way, it's probably not a great idea.