What if everyone jumped at once?

This question comes from Thomas and  many other people, who all asked:  

What would happen if everyone on earth stood  as close to each other as they could, jumped,  

and landed on the ground all at the same instant? This is one of the most popular questions  

submitted to What If. It’s been examined before,  including by a ScienceBlogs post and a Straight  

Dope article. They cover the physics pretty  well. However, they don’t tell the whole story. 

At the start of the scenario, the entirety  of Earth’s population has been magically  

transported together into one place. This crowd takes up an area the size  

of Rhode Island. In fact, let’s assume they  – I mean, we – are actually in Rhode Island. 

At the stroke of noon, everyone jumps. As discussed elsewhere, the jump doesn’t  

really affect the planet. Earth outweighs us  by a factor of over ten trillion. On average,  

we humans can vertically jump maybe half a meter  – and that’s when we’re not shoulder to shoulder  

in the middle of a crowd. Even if everyone did  jump that high, and the ground were rigid and  

responded instantly, the Earth would still only  be pushed down by less than an atom’s width. 

Next, everyone falls back to the ground. Technically, this delivers a lot of energy  

into the Earth, but it’s spread out over  a large enough area that it doesn’t do  

much more than leave footprints in a lot of  gardens. A slight pulse of pressure spreads  

through the North American continental crust and  dissipates with little effect beyond moving the  

needle of a few local seismometers. The sound of twelve billion feet  

hitting the ground does create a loud,  drawn-out roar which lasts many seconds. 

Eventually, the air grows quiet. Seconds pass. Everyone looks around. 

There are a lot of uncomfortable  glances. Someone coughs. 

A cell phone comes out of a pocket. Within  seconds, the rest of the world’s seven billion  

phones follow. All of them—even those compatible  with the region’s towers—are displaying some  

version of “NO SIGNAL”. The cell networks have  all collapsed under the unprecedented load. 

Outside Rhode Island, abandoned machinery begins  grinding to a halt, airplanes drift through the  

skies on auto-pilot trajectories, food starts  burning on abandoned kitchen stoves, soccer balls  

complete their trajectories into now-vacant goals,  and empty playground swings gradually drift to a  

halt. Back in Rhode Island, people – many people  – begin to wonder: how do we get everyone home? 

The T. F. Green airport in Warwick, Rhode Island  handles a few thousand passengers a day (I just  

flew out of there. They have the nicest bathrooms  of any airport I’ve ever seen. Very impressive.  

This is not part of the recording). Assuming  they got things organized (including sending  

out scouting missions to retrieve fuel),  they could run at 500% capacity for a hundred  

years without making a dent in the crowd. The addition of all the nearby airports  

doesn’t change the equation much. Nor does  the region’s light rail system. Crowds climb  

on board container ships in the deepwater port  of Providence, but stocking sufficient food and  

water for a long sea voyage proves a challenge. Rhode Island’s million cars are commandeered.  

Moments later, I-95, I-195, and I-295 become the  sites of the largest traffic jam in the history  

of the planet. Most of the cars are blocked  by the crowds, but a lucky few get out and  

begin wandering the abandoned road network. Some make it past New York or Boston before  

running out of fuel. Since the electricity is  probably not on at this point, rather than find  

a working gas pump, it’s easier to just abandon  the car and get in a new one. After all, who can  

stop you? All the cops are in Rhode Island. The edge of the crowd spreads outward into  

southern Massachusetts and Connecticut. Any two  people who meet are unlikely to have a language  

in common, and almost nobody knows the area. Even if people cooperate, everybody is hungry  

and thirsty. Grocery stores are immediately  emptied and woefully insufficient. Fresh water is  

hard to come by and there’s no efficient system  for distributing it. Sanitation is a disaster  

and healthcare infrastructure nonexistent. Within weeks, Rhode Island is a graveyard  

of billions (including most  of the people who submitted  

this question, and probably you and me, too). The survivors spread out across the face of the  

world and struggle to build a new civilization  atop the ruins of the old. Our species staggers  

on, but our population has been greatly reduced.  And most importantly: the Earth’s rotation and  

orbit are completely unaffected—it spins along  exactly as it did before our species-wide jump. 

Note to future civilizations:  let’s not try that again.