Have you ever wondered what the world would be like if everyone suddenly disappeared?
What would happen to all our stuff? What would happen to our houses, our schools, our neighborhoods, our cities?
Who would feed the dog? Who would cut the grass? Although it's a common theme in movies, TV shows, and books, the end of humanity is still a strange thing to think about.
But as an associate professor of urban design – that is, someone who helps towns and cities plan what their communities will look like – it's sometimes my job to think about prospects like this.
So much silence
If humans just disappeared from the world, and you could come back to Earth to see what had happened one year later, the first thing you'd notice wouldn't be with your eyes.
It would be with your ears.
The world would be quiet. And you would realize how much noise people make. Our buildings are noisy. Our cars are noisy. Our sky is noisy. All of that noise would stop.
You'd notice the weather. After a year without people, the sky would be bluer, the air clearer. The wind and the rain would scrub clean the surface of the Earth; all the smog and dust that humans make would be gone.
Home sweet home
Imagine that first year, when your house would sit unbothered by anyone.
Go inside your house – and hope you're not thirsty, because no water would be in your faucets. Water systems require constant pumping. If no one's at the public water supply to manage the machines that pump water, then there's no water.
But the water that was in the pipes when everyone disappeared would still be there when the first winter came – so on the first cold snap, the frigid air would freeze the water in the pipes and burst them.
There would be no electricity. Power plants would stop working because no one would monitor them and maintain a supply of fuel. So your house would be dark, with no lights, TV, phones, or computers.
Your house would be dusty. Actually, there's dust in the air all the time, but we don't notice it because our air conditioning systems and heaters blow air around. And as you move through the rooms in your house, you keep dust on the move too. But once all that stops, the air inside your house would be still and the dust would settle all over.
The grass in your yard would grow – and grow and grow until it got so long and floppy it would stop growing. New weeds would appear, and they would be everywhere.
Lots of plants that you've never seen before would take root in your yard. Every time a tree drops a seed, a little sapling might grow. No one would be there to pull it out or cut it down.
You'd notice a lot more bugs buzzing around. Remember, people tend to do everything they can to get rid of bugs. They spray the air and the ground with bug spray. They remove bug habitat. They put screens on the windows. And if that doesn't work, they swat them.
Without people doing all these things, the bugs would come back. They would have free rein of the world again.
On the street where you live
In your neighborhood, critters would wander around, looking and wondering.
First the little ones: mice, groundhogs, raccoons, skunks, foxes and beavers. That last one might surprise you, but North America was once rich with beavers.
Bigger animals would come later – deer, coyotes and the occasional bear. Not in the first year, maybe, but eventually.
With no electric lights, the rhythm of the natural world would return. The only light would be from the Sun, the Moon, and the stars. The night critters would feel good they got their dark sky back.
Fires would happen frequently. Lightning might strike a tree or a field and set brush on fire, or hit the houses and buildings. Without people to put them out, those fires would keep going until they burned themselves out.
Around your city
After just one year, the concrete stuff – roads, highways, bridges, and buildings – would look about the same.
Come back, say, a decade later, and cracks in them would have appeared, with little plants wiggling up through them. This happens because the Earth is constantly moving. With this motion comes pressure, and with this pressure come cracks.
Eventually, the roads would crack so much they would look like broken glass, and even trees would grow through them.
Bridges with metal legs would slowly rust. The beams and bolts that hold the bridges up would rust too. But the big concrete bridges, and the interstate highways, also concrete, would last for centuries.
The dams and levees that people have built on the rivers and streams of the world would erode. Farms would fall back to nature. The plants we eat would begin to disappear. Not much corn or potatoes or tomatoes anymore.
Farm animals would be easy prey for bears, coyotes, wolves, and panthers. And pets? The cats would go feral – that is, they would become wild, though many would be preyed upon by larger animals. Most dogs wouldn't survive, either.
Like ancient Rome
In a thousand years, the world you remember would still be vaguely recognizable. Some things would remain; it would depend on the materials they were made of, the climate they're in, and just plain luck.
An apartment building here, a movie theater there, or a crumbling shopping mall would stand as monuments to a lost civilization. The Roman Empire collapsed more than 1,500 years ago, yet you can see some remnants even today.
If nothing else, humans' suddenly vanishing from the world would reveal something about the way we treated the Earth.
It would also show us that the world we have today can't survive without us and that we can't survive if we don't care for it.
To keep it working, civilization – like anything else – requires constant upkeep.