What if I wrote a book?

For the last couple years, I’ve been answering your science questions on What If.

Today, I’m excited to announce that the What If? book is coming!

What If?: Serious Scientific Answers to Absurd Hypothetical Questions will be published September 2nd by Houghton Mifflin Harcourt. Starting today you can pre-order it from your favorite bookseller (Barnes & NobleAmazonIndie Bound).  There are also foreign editions, including a UK and Commonwealth edition and a German edition.

As I’ve sifted through the letters submitted to What If every week, I’ve occasionally set aside particularly neat questions that I wanted to spend a little more time on. This book features my answers to those questions, along with revised and updated versions of some of my favorite articles from the site. (I’m also including my personal list of the weirdest questions people have submitted.)

Preorder today to get a copy as soon as it comes out!

The Baby Name Wizard

The OKCupid statistics blog, by Christian Rudder, is amazing. Sadly, it hasn’t updated since 2011, around when OKCupid was bought by Match.com. (Rudder says the timing was a coincidence—he took time off for another project, and the blog may return soon!)

In the meantime, I’d like to recommend another unexpectedly engrossing blog: The Baby Name Wizard blog, by Laura Wattenberg (creator of the amazing Name Voyager graphing tool).

I find the Baby Name Wizard blog fascinating because, like the OK Cupid Blog, it combines two key ingredients:

  • Access to rich data about something that comes up all the time in our lives
  • The ability to find and tell the stories in that data

The reason I like the blog has nothing to do with naming babies. (I’m not allowed to name babies, anyway.)

I like it because we all encounter names every day, all the time, in every part of our life. We all have feelings and opinions about what names mean, but if you’re like me, they were mostly unconscious, unquestioned, and never subject to any statistical rigor. (Freakonomics has a well-known chapter about naming trends, which Wattenberg takes issue with).

Nevaeh (“Heaven” backward) is currently a more popular baby name than Sarah.  Brooklyn is more popular than either, and Sophia is more popular than all three combined. In 20 years, those names will conjure up images of college kids, and Brandon and Sarah will sound as much like Mom and Dad names as Gary and Debby do to my generation.

If you’re like most people, you probably had some opinions when you read the names in the last paragraph. But maybe the biggest thing I’ve learned from reading this blog is that the reactions and stereotypes that names provoke often reveal more interesting stories than the names themselves.

For example, you may have heard the urban legend about a mother who named her daughter Le-a, pronounced “Ledasha”. Wattenberg dissects this urban legend in an insightful essay (Part 1, Part 2, Part 3), which explains how apocryphal names like Le-a serve, across a wide variety of communities, as proxies for talking about race.

Here are a few of the other things I’ve learned from the blog:

That’s just a tiny sampling; if you think any of it sounds interesting, I recommend browsing through the blog’s extensive archives.

Asteroid 4942 Munroe

Whoa. There’s an asteroid named after me!

Amazing xkcd readers Lewis Hulbert and Jordan Zhu noticed that the International Astronomical Union—the organization in charge of official astronomical naming—was taking suggestions for what to name small Solar System objects. They submitted my name for asteroid (4942) 1987 DU6, and it was subsequently renamed 4942 Munroe.

I’m really touched. I spent all weekend telling everyone who wanted to listen (and probably some who didn’t) about the asteroid.

The first thing I did was try to figure out whether 4942 Munroe was big enough to pose a threat to Earth. I was excited to learn that, based on its albedo (brightness), it’s probably about 6-10 kilometers in diameter. That’s comparable in size to the one that killed the dinosaurs—definitely big enough to cause a mass extinction!

I texted Phil Plait to let him know that 4942 Munroe is four or five times the diameter of 165347 Philplait.

Unfortunately Fortunately, it’s in a fairly stable circular orbit between Mars and Jupiter, so it’s unlikely to hit the Earth any time soon.

4942 Munroe (!!!) is large enough that it would have noticeable gravity, although not much. If you were walking on the surface and you tripped and fell, it’d take you a minute to hit the ground. You could get into orbit around it by traveling at jogging speed, and might even escape its gravity entirely with a good jump.

Thank you so much. This is the coolest thing.

1190: Time

On Friday, xkcd #1190—Timecame to an end.

It was a huge project, but since it was all concealed within a single comic panel, I thought I’d end with this short post to explain what was going on. If you want to see the story yourself before I spoil anything, you can use one of the many excellent third-party Time explorers, like the Geekwagon viewer, or one of the others listed here.

When the comic first went up, it just showed two people sitting on a beach. Every half hour (and later every hour), a new version of the comic appeared, showing the figures in different positions. Eventually, the pair started building a sand castle.

There was a flurry of attention early on, as people caught on to the gimmick. Readers watched for a while, and then, when nothing seemed to be happening, many wandered away—perhaps confused, or perhaps satisfied that they’d found a nice easter-egg story about castles.

But Time kept going, and hints started appearing that there was more to the story than just sand castles. A few dedicated readers obsessively cataloged every detail, watching every frame for clues and every changing pixel for new information. The xkcd forum thread on Time grew terrifyingly fast, developing a subculture with its own vocabulary, songs, inside jokes, and even a religion or two.

And as Time unfolded, readers gradually figured out that it was a story, set far in the future, about one of the strangest phenomena in our world: The Mediterranean Sea sometimes evaporates, leaving dry land miles below the old sea level … and then fills back up in a single massive flood.

(A special thank you to Phil Plait for his advice on the far-future night sky sequence, and to Dan, Emad, and everyone else for your help on various details of the Time world.)

Time was a bigger project than I planned. All told, I drew 3,099 panels. I animated a starfield, pored over maps and research papers, talked with biologists and botanists, and created a plausible future language for readers to try to decode.

I wrote the whole story before I drew the first frame, and had almost a thousand panels already drawn before I posted the first one. But as the story progressed, the later panels took longer to draw than I expected, and Time began—ironically—eating more and more of my time. Frames that went up every hour were sometimes taking more than an hour to make, and I spent the final months doing practically nothing but drawing.

To the intrepid, clever, sometimes crazy readers who followed it the whole way through, watching every pixel change and catching every detail: Thank you. This was for you. It’s been quite a journey; I hope you enjoyed the ride as much as I did!

P.S. A lot of people have asked if I can sell some kind of Time print collection (or a series of 3,099 t-shirts, where you run to the bathroom and change into a new one every hour). I’m afraid I don’t have anything like that in the works right now. I just made this because I thought it would be neat, and now that it’s done, my only plan is to spend the next eleven thousand years catching up on sleep. If you liked the project, you’re always welcome to donate via PayPal (xkcd@xkcd.com) or buy something from the xkcd store. Thank you.

Dictionary of Numbers

I don’t like large numbers without context. Phrases like “they called for a $21 billion budget cut” or “the probe will travel 60 billion miles” or “a 150,000-ton ship ran aground” don’t mean very much to me on their own. Is that a large ship? Does 60 billion miles take you outside the Solar System? How much is $21 billion compared to the overall budget? (That last question is  why I made my money chart.)

A friend of mine, Glen Chiacchieri, has created a Chrome extension to help solve this problem: Dictionary of Numbers. It searches the text in your browser for quantities it understands and inserts contextual statements in brackets. It might turn the phrase “315 million people” into “315 million people [≈ the population of the United States]“.

As Glen explains, he once read an article about US wildfires which mentioned that the largest fire of the year had burned “300,000 acres.” This didn’t mean much to Glen:

I have no idea how much 300,000 acres is [...] But we need to understand this number to answer the obvious question: how much of the United States was on fire? This is why I made Dictionary of Numbers.

Dictionary of Numbers helpfully informs me that 300,000 acres is about the area of LA or Hong Kong.

Wolfram|Alpha provides a lookup service like this, but you have to load the site and type in the quantity you’re curious about, which I never remember to do. (It’s also often short on good points of comparison.)

Dictionary of Numbers is a new project, so it’s got its share of glitches and rendering hiccups; it’s very much a work in progress. You can submit bug reports, feedback, and suggestions for data sources via a link on the project’s website.

I think these kinds of tools are a great idea, and I want to encourage them. Intelligence is all about context, and when computers get better at providing it, they make us smarter.

The extension can even be surprisingly funny, like when it seems to be making an oblique suggestion for how to solve a problem—e.g. “The telescope has been criticized for its budget of $200 million [≈ Mitt Romney net worth].” It can also come across as unexpectedly judgmental. Glen told me about complaint he got from a user: “I installed your extension and then forgot about it … until I logged into my bank account. Apparently my total balance is equal to the cost of a low-end bicycle. Thanks.”

You can get Dictionary of Numbers here.

A morbid Python script

Comics #493 and #893 involve actuarial tables, which are tables for calculating the probability that someone of a given age will die within a given amount of time.

One evening, when I was feeling morbid, I wrote a Python script to calculate death probabilities for any collection of people: actuary.py (.txt). It takes a list of ages and genders and produces various statistics. Here’s the report for the nine living people who have walked on the moon:

~$ python actuary.py 81m 82m 80m 81m 80m 81m 76m 78m 77m
There is a 5% chance of someone dying within 0.08 years (by 2012).
There is a 50% chance of someone dying within 1.1 years (by 2013).
There is a 95% chance of someone dying within 4.08 years (by 2016).

There is a 5% chance of everyone dying within 10.78 years (by 2023).
There is a 50% chance of everyone dying within 16.12 years (by 2028).
There is a 95% chance of everyone dying within 22.57 years (by 2035).

Probability of all dying in 1.0 year: <0.001%
Probability of a death within 1.0 year: 46.32%

And here’s the table for four of the main stars of the original Star Wars (Harrison Ford, Carrie Fisher, Mark Hammill, James Earl Jones):

~$ python actuary.py 69m 55f 60m 81m 10
There is a 5%  chance of someone dying within 0.42 years (by 2012).
There is a 50% chance of someone dying within 4.74 years (by 2017).
There is a 95% chance of someone dying within 12.83 years (by 2025).

There is a 5%  chance of everyone dying within 18.17 years (by 2030).
There is a 50% chance of everyone dying within 31.28 years (by 2043).
There is a 95% chance of everyone dying within 42.62 years (by 2055).

Probability of all dying in 10.0 years:   0.272%
Probability of a death within 10.0 years: 85.94%

Of course, these are based on average death rates based only on age and gender. Adding more specific information about the people in question will refine the calculation. For example, I’d guess former astronauts are more likely to be in good health—and have longer life expectancies—than the rest of us.

Groundhog Day correction

A number of people have mentioned an issue with today’s comic—in the movie Groundhog Day, it’s actually implied that Phil, Bill Murray’s character, didn’t have sex with Rita. He took her home to his room, but they woke up in the same clothes they fell asleep in. I haven’t seen the movie in a number of years, but I think they’re right—and bit of Googling suggests that I’m not the only one who was confused on that point.

Groundhog Day is, like Office Space, a comedy containing a gimmick that really sticks with you, even as the rest of the story fades. Or, at least, it did with me—I’ve probably seen the movie a couple of times, but I think I’ve spent a lot more time dwelling on the time loop scenario it describes. Now that people have raised the question, I’m not even sure that I interpreted the scene this way when I was watching it.

From a sci-fi point of view, the whole idea that the time loop was broken by emotional/personal development seemed kind of cheesy, but I just chalked that up to one of those things movies do because that’s how we like stories to work. Nobody wants a movie where the climax consists of an hour of excitedly inferring and testing revisions to the standard model of physics. (Or, at least, there aren’t enough of us to support a big-budget movie.) So while drawing my comic, I remembered that the time loop ended after he took Rita back to his room, and I filled in the typical romanticized Sleeping Beauty idea that I assumed had gone with it.

I appreciate the corrections—in addition to being a reminder to double-check pop culture references, it’s driven home for me what a neat, original movie Groundhog Day really is.

And now I wonder what kind of misconceptions I have about Ghostbusters.

I’m visiting CNU on April 4th

I’ll be in Newport News, Virginia this April 4th to give a talk at my old school, Christopher Newport University.

I’m really looking forward to it! The chaos of the past year and a half didn’t leave me with much time or energy for travel or events, so it’ll be fun to get out and meet people again. I’m also looking forward to seeing the campus, which I hear has changed substantially since I left.

The talk isn’t limited to CNU students, so if you live nearby, you’re welcome to come! Admission is free, but since space is limited, you’ll need to reserve tickets here.

Hope to see you there!


Almost four years ago, I posted a comic laying out the Geohashing algorithm. The algorithm generated a set of random latitudes and longitudes each day, spread out across the globe so there was generally always one within a few dozen miles of every location. I figured they could be used for hiking destinations, sightseeing, meetups, or whatever else people came up with.

I wanted to make an algorithm that anyone could implement, which didn’t rely on a central authority or ongoing support from any one maintainer. I also wanted to make it impossible to know the locations more than a day or so in advance, so that if geohashing became popular in an area, no one could publish a list of future locations that woud give property owners, park rangers, or local police time to prepare. So each day’s coordinates are randomized using the most recent Dow Jones opening price, which isn’t known until the morning of that day—or, in the case of weekends, a day or two in advance, which helps with planning larger weekend trips.

In the days after I posted the comic, there was a flurry of geohashing activity, which quieted down as the initial novelty wore off. But it didn’t die, and for the past several years there’s been a small but vibrant community building around the Geohashing Wiki. There are numerous daily expeditions, and they’ve taken some beautiful pictures and come up with a lot of neat tools, games, and achievements.

One of the many things they did was use a tweaked version of the algorithm to come up with a globalhash, a single coordinate for the day somewhere on the planet (biased toward the areas near the poles). They’re usually over the ocean, but a few of the land ones have been reached.

Yesterday’s globalhash fell less than a kilometer from the South Pole. User Carl-Johan got in touch with the Scott-Amundsen research station, and later that day, the hash was reached by Katie Hess, Dale Mole, and Joselyn Fenstermacher of the US, Robert Schwarz of Germany, and Sven Lidström of Sweden.

Wow. Just wow. Congratulations.

If you want to look up today’s geohash for your location, you can use this online tool, or one of the others listed on the Coordinate Calculators page.