I *love* these about 32 billion times more than XKCD itself–which I do, in fact like. But these I *really* like. Like all good scifi, they address the human ramifications of physical, scientific facts. SF, more so than any other literary sub-sect, seeks to directly address the question of how humans react to the things humans have done, and to try to fully imagine and enact how that plays out.
Everybody Jump
What would happen if everyone on earth stood as close to each other as they could and jumped, everyone landing on the ground at the same instant?
—Thomas Bennett (and many others)
This is one of the most popular questions submitted to this blog. It’s been examined before, including by a ScienceBlogs post and a Straight Dope article. They cover the kinematics pretty well. However, they don’t tell the whole story.
Let’s take a closer look.
At the start of the scenario, the entire Earth’s population has been magically transported together into one place.
This crowd takes up an area the size of Rhode Island. But there’s no reason to use the vague phrase “an area the size of Rhode Island”. This is our scenario; we can be specific. They’re actually in Rhode Island.
At the stroke of noon, everyone jumps.
As discussed elsewhere, it 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 on a good day. Even if the Earth were rigid and responded instantly, it would 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. The sound of all those feet hitting the ground creates 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.
. . .
—Thomas Bennett (and many others)
This is one of the most popular questions submitted to this blog. It’s been examined before, including by a ScienceBlogs post and a Straight Dope article. They cover the kinematics pretty well. However, they don’t tell the whole story.
Let’s take a closer look.
At the start of the scenario, the entire Earth’s population has been magically transported together into one place.
This crowd takes up an area the size of Rhode Island. But there’s no reason to use the vague phrase “an area the size of Rhode Island”. This is our scenario; we can be specific. They’re actually in Rhode Island.
At the stroke of noon, everyone jumps.
As discussed elsewhere, it 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 on a good day. Even if the Earth were rigid and responded instantly, it would 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. The sound of all those feet hitting the ground creates 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.
. . .
These are also quite nice; the “one-way” mirror section is a little weak, but the final answer is rock solid: Short Answer Section