As you’d expect, air resistance would slow down an arrow, and eventually it would stop . . . after flying very, very far. Fortunately, for most of that flight, it wouldn’t be much of a danger to anyone.
Let’s go over what would happen in more detail.
Say you fire the arrow at 85 meters per second. That’s about twice the speed of a major-league fastball, and a little below the 100 m/s speed of arrows from high-end compound bows.
The arrow would slow down quickly. Air resistance is proportional to speed squared, which means that when it’s going fast, the arrow would experience a lot of drag.
After ten seconds of flight, the arrow would have traveled 400 meters, and its speed would have dropped from 85 m/s to 25 m/s; 25 m/s is about how fast a normal person could throw an arrow.
At that speed, the arrow would be a lot less dangerous.
We know from hunters that small differences in arrow speed make big differences in the size of the animal it can kill. A 25-gram arrow moving at 100 m/s could be used to hunt elk and black bears. At 70 m/s, it might be too slow to kill a deer. Or, in our case, a space deer.
Once the arrow leaves that range, it’s no longer particularly dangerous . . . but it’s not even close to stopping.
After five minutes, the arrow would have flown about a mile, and it would have slowed to roughly walking speed. At that speed, it would experience very little drag; it would just cruise along, slowing down very gradually.
At this point, it would have gone much farther than any Earth arrow can go. High-end bows can shoot an arrow a distance of a couple hundred meters over flat ground, but the world record for a hand bow-and-arrow shot is just over a kilometer.
This record was set in 1987 by archer Don Brown. Brown set his record by firing slender metal rods from a terrifying contraption that only vaguely resembled a traditional bow.
As the minutes stretch into hours and the arrow slows down more and more, the airflow changes.
Air has very little viscosity. That is, it’s not gooey. That means things flying through the air experience drag because of the momentum of the air they’re shoving out of the way—not from cohesion between the air molecules. It’s more like pushing your hand through a bathtub full of water than a bathtub full of honey.
After a few hours, the arrow would be moving so slowly that it would be barely visible. At this point, assuming the air is relatively still, the air would start acting like honey instead of water. And the arrow would, very gradually, come to a stop.
The exact range would depend heavily on the precise design of the arrow. Small differences in an arrow’s shape can dramatically change the nature of the airflow over it at low speeds. But at minimum, it would probably fly several kilometers, and could conceivably go as far as 5 or 10.
Here’s the problem: Currently, the only sustained zero-g environment with an Earth-like atmosphere is the International Space Station. And the largest ISS module, Kibo, is only 10 meters long.
This means that if you actually performed this experiment, the arrow would fly no more than 10 meters. Then, it would either come to a stop . . . or really ruin someone’s day.
1Also, you don’t usually shoot astronauts with a bow and arrow — at least not for an undergraduate degree.
Sunless Earth
Q. What would happen to the Earth if the Sun suddenly switched off?
—Many, many readers
A. This is probably the single most popular submission to What If.
Part of why I haven’t answered it is that it’s been answered already. A Google search for “what if the Sun went out” turns up a lot of excellent articles thoroughly analyzing the situation.
However, the rate of submission of this question continues to rise, so I’ve decided to do my best to answer it.
If the Sun went out . . .
We won’t worry about exactly how it happens. We’ll just assume we figured out a way to fast-forward the Sun through its evolution so that it becomes a cold, inert sphere. What would the consequences be for us here on Earth?
Let’s look at a few . . .
Reduced risk of solar flares: In 1859, a massive solar flare and geomagnetic storm hit the Earth. Magnetic storms induce electric currents in wires. Unfortunately for us, by 1859 we had wrapped the Earth in telegraph wires. The storm caused powerful currents in those wires, knocking out communications and in some cases causing telegraph equipment to catch fire.
Since 1859, we’ve wrapped the Earth in a lot more wires. If the 1859 storm hit us today, the Department of Homeland Security estimates the economic damage to the US alone would be several trillion dollars—more than every hurricane that has ever hit the US combined. If the Sun went out, this threat would be eliminated.
Improved satellite service: When a communications satellite passes in front of the Sun, the Sun can drown out the satellite’s radio signal, causing an interruption in service. Deactivating the Sun would solve this problem.
Better astronomy: Without the Sun, ground-based observatories would be able to operate around the clock. The cooler air would create less atmospheric noise, which would reduce the load on adaptive optics systems and allow for sharper images.
Stable dust: Without sunlight, there would be no Poynting–Robertson drag, which means we would finally be able to place dust into a stable orbit around the Sun without the orbits decaying. I’m not sure whether anyone wants to do that, but you never know.
Reduced infrastructure costs: The Department of Transportation estimates that it would cost $20 billion per year over the next 20 years to repair and maintain all US bridges. Most US bridges are over water; without the Sun, we could save money by simply driving on a strip of asphalt laid across the ice.
Cheaper trade: Time zones make trade more expensive; it’s harder to do business with someone if their office hours don’t overlap with yours. If the Sun went out, it would eliminate the need for time zones, allowing us to switch to UTC and give a boost to the global economy.
Safer children: According to the North Dakota Department of Health, babies younger than six months should be kept out of direct sunlight. Without sunlight, our children would be safer.
Safer combat pilots: Many people sneeze when exposed to bright sunlight. The reasons for this reflex are unknown, and it may pose a danger to fighter pilots during flight. If the Sun went dark, it would mitigate this danger to our pilots.
Safer parsnip: Wild parsnip is a surprisingly nasty plant. Its leaves contain chemicals called furocoumarins, which can be absorbed by human skin without causing symptoms . . . at first. However, when the skin is then exposed to sunlight (even days or weeks later), the furocoumarins cause a nasty chemical burn. This is called phytophotodermatitis. A darkened Sun would liberate us from the parsnip threat.
In conclusion, if the Sun went out, we would see a variety of benefits across many areas of our lives.
Are there any downsides to this scenario?
We would all freeze and die.
Updating a Printed Wikipedia
Q. If you had a printed version of the whole of (say, the English) Wikipedia, how many printers would you need in order to keep up with the changes made to the live version?
—Marein Könings
A. This many.
If a date took you home and you saw a row of working printers set up in his or her living room, what would you think?
That’s surprisingly few printers! But before you try to create a live-updating paper Wikipedia, let’s look at what those printers would be doing . . . and how much they’d cost.
Printing Wikipedia
People have considered printing out Wikipedia before. One student, Rob Matthews, printed every Wikipedia featured article, creating a book several feet thick.
Of course, that’s jus
t a small slice of the best of Wikipedia; the entire encyclopedia would be a lot bigger. Wikipedia user Tompw has set up a tool that calculates the current size of the whole English Wikipedia in printed volumes. It would fill a lot of bookshelves.
Keeping up with the edits would be hard.
Keeping up
The English Wikipedia currently receives about 125,000 to 150,000 edits each day, or 90–100 per minute.
We could try to define a way to measure the “word count” of the average edit, but that’s hard bordering on impossible. Fortunately, we don’t need to—we can just estimate that each change is going to require us to reprint a page somewhere. Many edits will actually change multiple pages—but many other edits are reverts, which would let us put back pages we’ve already printed.1 One page per edit seems like a reasonable middle ground.
For a mix of photos, tables, and text typical of Wikipedia, a good inkjet printer might put out 15 pages per minute. That means you’d need only about six printers running at any given time to keep pace with the edits.
The paper would stack up quickly. Using Rob Matthews’ book as a starting point, I did my own back-of-the-envelope estimate for the size of the current English Wikipedia. Based on the average length of featured articles vs. all articles, I came up with an estimate of 300 cubic meters for a printout of the whole thing in plain text form.
By comparison, if you were trying to keep up with the edits, you’d print out 300 cubic meters every month.
$500,000 per month
Six printers isn’t that many, but they’d be running all the time. And that gets expensive.
The electricity to run them would be cheap—a few dollars a day.
The paper would be about 1 cent per sheet, which means you’ll be spending about a thousand dollars a day on paper. You’d need to hire people to manage the printers 24/7, but that would actually cost less than the paper.
Even the printers themselves wouldn’t be too expensive, despite the terrifyingly fast replacement cycle.
But the ink cartridges would be a nightmare.
Ink
A study by QualityLogic found that for a typical inkjet printer, the real-life cost of ink ran from 5 cents per page for black-and-white to around 30 cents per page for photos. That means you’d be spending four to five figures per day on ink cartridges.
You definitely want to invest in a laser printer. Otherwise, in just a month or two, this project could end up costing you half a million dollars:
But that’s not even the worst part.
On January 18, 2012, Wikipedia blacked out all its pages to protest proposed Internet-freedom-limiting laws. If, someday, Wikipedia decides to go dark again, and you want to join the protest . . .
. . . you’ll have to get a crate of markers and color every page solid black yourself.
I would definitely stick to digital.
1The filing system that would be required for this would be mind-bending. I’m fighting the urge to start trying to design it.
Facebook of the Dead
Q. When, if ever, will Facebook contain more profiles of dead people than of living ones?
—Emily Dunham
“Put on your headphones!” “Can’t. Ears fell off.”
A. Either the 2060s or the 2130s.
There are not a lot of dead people on Facebook.1 The main reasons for this is that Facebook—and its users—are young. The average Facebook user has gotten older over the last few years, but the site is still used at a much higher rate by the young than by the old.
The past
Based on the site’s growth rate, and the age breakdown of its users over time,2 there are probably 10 to 20 million people who created Facebook profiles who have since died.
These people are, at the moment, spread out pretty evenly across the age spectrum. Young people have a much lower death rate than people in their 60s or 70s, but they make up a substantial share of the dead on Facebook simply because there have been so many of them using it.
An elderly Cory Doctorow cosplaying by wearing what the future thinks he wore in the past.
The future
About 290,000 US Facebook users probably died in 2013. The worldwide total for 2013 is likely several million.3 In just seven years, this death rate will double, and in seven more years it will double again.
Even if Facebook closes registration tomorrow, the number of deaths per year will continue to grow for many decades, as the generation who was in college between 2000 and 2020 grows old.
The deciding factor in when the dead will outnumber the living is whether Facebook adds new living users—ideally, young ones—fast enough to outrun this tide of death for a while.
Facebook 2100
This brings us to the question of Facebook’s future.
We don’t have enough experience with social networks to say with any kind of certainty how long Facebook will last. Most websites have flared up and then gradually declined in popularity, so it’s reasonable to assume Facebook will follow that pattern.4
In that scenario, where Facebook starts losing market share later this decade and never recovers, Facebook’s crossover date—the date when the dead outnumber the living—will come sometime around 2065.
But maybe it won’t. Maybe it will take on a role like the TCP protocol, where it becomes a piece of infrastructure on which other things are built, and has the inertia of consensus.
If Facebook is with us for generations, then the crossover date could be as late as the mid-2100s.
That seems unlikely. Nothing lasts forever, and rapid change has been the norm for anything built on computer technology. The ground is littered with the bones of websites and technologies that seemed like permanent institutions ten years ago.
It’s possible the reality could be somewhere in between.5 We’ll just have to wait and find out.
The fate of our accounts
Facebook can afford to keep all our pages and data indefinitely. Living users will always generate more data than dead ones,6 and the accounts for active users are the ones that will need to be easily accessible. Even if accounts for dead (or inactive) people make up a majority of their users, it will probably never add up to a large part of its overall infrastructure budget.
More important will be our decisions. What do we want for those pages? Unless we demand that Facebook deletes them, they will presumably, by default, keep copies of everything forever. Even if they don’t, other data-vacuuming organizations will.
Right now, next of kin can convert a dead person’s Facebook profile into a memorial page. But there are a lot of questions surrounding passwords and access to private data that we haven’t yet developed social norms for. Should accounts remain accessible? What should be made private? Should next of kin have the right to access email? Should memorial pages have comments? How do we handle trolling and vandalism? Should people be allowed to interact with dead user accounts? What lists of friends should they show up on?
These are issues that we’re currently in the process of sorting out by trial and error. Death has always been a big, difficult, and emotionally charged subject, and every society finds different ways to handle it.
The basic pieces that make up a human life don’t change. We’ve always eaten, learned, grown, fallen in love, fought, and died. In every place, culture, and technological landscape, we develop a different set of behaviors around these same activites.
Like every group that came before us, we’re learning how to play those same games on our particular playing field. We’re developing, through sometimes messy trial and error, a new set of social norms for dating, arguing, learning, and growing on the Internet. Sooner or later, we’ll figure out how to mourn.
1At the time I wrote this, anyway, which was before th
e bloody robot revolution.
2You can get user counts for each age group from Facebook’s create-an-ad tool, although you may want to try to account for the fact that Facebook’s age limits cause some people to lie about their ages.
3Note: In some of these projections, I used US age/usage data extrapolated to the Facebook userbase as a whole, because it’s easier to find US census and actuarial numbers than to assemble the country-by-country for the whole Facebook-using world. The US isn’t a perfect model of the world, but the basic dynamics — young people’s Facebook adoption determines the site’s success or failure while population growth continues for a while and then levels off — will probably hold approximately true. If we assume a rapid Facebook saturation in the developing world, which currently has a faster-growing and younger population, it shifts many of the landmarks by a handful of years, but doesn’t change the overall picture as much as you might expect.
4I’m assuming, in these cases, that no data is ever deleted. So far, that’s been a reasonable assumption; if you’ve made a Facebook profile, that data probably still exists, and most people who stop using a service don’t bother to delete their profiles. If that behavior changes, or if Facebook performs a mass purging of its archives, the balance could change rapidly and unpredictably.
5Of course, if there’s a sudden rapid increase in the death rate of Facebook users — possibly one that includes humans in general — the crossover could happen tomorrow.
6I hope.
What If? Page 18