Math Puzzle

This cool puzzle (and solution) comes from my friend Mike.

Alice secretly picks two different real numbers by an unknown process and puts them in two (abstract) envelopes.  Bob chooses one of the two envelopes randomly (with a fair coin toss), and shows you the number in that envelope.  You must now guess whether the number in the other, closed envelope is larger or smaller than the one you’ve seen.

Is there a strategy which gives you a better than 50% chance of guessing correctly, no matter what procedure Alice used to pick her numbers?

I initially thought there wasn’t, or that the problem was paradoxically defined, but it turns out that it’s perfectly valid and the answer is “Yes.”  See my first comment for an example of one such winning strategy.

This puzzle is similar to, but not the same as, the two envelopes paradox.  For more time-devouring reading, see Wikipedia’s List of Paradoxes.

Android Bug Reports, Songs, Rovers

The following is a partial list of bugs in Android (or associated software) which have impacted my actual life in some way.  Some may have been fixed since I last encountered them.

  • When navigation is muted, but you hit volume down just to be safe, it unmutes and starts blaring, waking other passengers on the bus.
  • Sometimes the GPS stops getting locks on satellites until the phone is rebooted.  (This may be related to the GPSStatus app, installed to avoid this kind of thing.)  To be fair, satellites are very small and far away, so you can hardly blame it for having trouble.
  • You can say “Call <contact name>”, and contact names+addresses show up in the navigation search with “navigate to” options, but you can’t say “Navgiate to <contact name>” like you can with all other major actions.  This means you have to type their full address to find out which exit to take from the traffic circle, and it’s really hard to type while holding the wheel steadily to the left like that.
  • Sometimes, when arranging home screen icons, you feel sad and you’re not sure why.
  • If you follow Google’s guidelines and have your own Jabber DNS records set up in a particular way on your Google Apps server, it screws up Google Talk’s ability to authenticate, which in turn (for some bizarre reason) causes all app downloads to hang midway through.  This is rare enough that the error messages are not Googleable.  But don’t worry, it’s easy to figure out as long as you’ve read all of the source code to Android and to Google’s servers, which is good practice when you get any product.
  • Sometimes the home screen icons all disappear.  The only thing which fixes this is a restart, going through five menus to kill the “Home screen” process, or crying quietly for hours until the icons start to feel sorry for you and come back.
  • Occasionally, when swiping the lock sideways to unlock the phone, the lock button images are rotated by 90 degrees.  This is probably connected to your Jabber server somehow.
  • Sometimes an Android user will think they hear someone say their name, but they’re not sure, so they say ‘Yes?’, but then it turns out it was something else.
  • Maps Navigation doesn’t cache your route, so if you drive through an area with bad cell coverage, it may silently stop notifying you of upcoming turns, and you won’t realize anything’s wrong until you discover you’ve taken NH Route 2 all the way to the White Mountains, which are very cold.
  • Latitude doesn’t update well on either end.  Often times, it will tell you someone was in a particular place “5 minutes ago”, and then 10 minutes later — after multiple restarts — it will still say it got that last update from them “5 minutes ago” even if they’re actively using Maps, so you have no idea whether they’ve left.  This can continue for hours as you slowly run out of air in the closet.
  • The phone occasionally locks on full brightness and turns off the keyboard backlight, which is fixed by un-checking and then re-checking the “automatic brightness” checkbox, also about five menus deep, which is hard to see when you’re squinting because the screen is so bright.  Fortunately, it never gets very dark where I live in Boston.  Unfortunately, it’s extremely dark at night in the White Mountains.
  • Navigation instructions silence things like podcasts players, but don’t pause them.  Thus, to hear that missing sentence or two, you have to switch over to the podcast app and hit ‘back’ several times, then swerve your car to avoid the stupid stop sign that shouldn’t be in the middle of the sidewalk to begin with.
  • Google Voice doesn’t do push notifications, so you often get voicemails quite some time after the caller leaves them, sometimes after you’ve already called them back.  This can make you call your doctor back again and have a really confusing conversation where you accidentally get a second prescription. Which you can then get filled and sell on the street. Come to think of it, this bug might be a feature.
  • If you stop for gas, sometimes navigation suspends, but doesn’t resume when you start driving again (or just disappears without notifying you), so you miss the upcoming turn and think you’re already on I-95, and by the time you discover your mistake and turn around you’ve lost enough time that you totally get to the conference too late to catch Richard Stallman doing his acapella Bad Romance cover which is the whole reason you paid the entry fee in the first place.
  • If you have several Google accounts, there’s no way to select which one to use for Google Checkout purchases.  It just picks whichever one it notices first, even if it’s one from an old Google account tied to your mom’s credit card, so now she might know that you bought the app to turn the phone into a vibrator.  (The app doesn’t really work since the vibrate motor is too weak, but the reviews by people who don’t understand its purpose are hilarious.)
  • If you have a secondary account that it’s decided to use for Checkout, and you want to delete it so the phone will use your primary one, you can’t.  Why?  Because that account is used for an essential service and so can’t be deleted.  As far as I can guess, that service is Google Checkout.  This bug report is dedicated to Joseph Heller.
  • Google Chrome in OS X follows the Apple guidelines concerning the green “+” button, and has it make the window no bigger than it deems necessary to fit the current page’s contents.  This annoys a lot of people. Since there are no OS X Chrome extensions, the best workaround seems to be registering and putting a giant <div> there.  Whenever you need to maximize, you load that page before hitting the green button.  (This bug is not, technically, related to Android in any way.)
  • There’s a Fantastic Contraption app on iPhone, but not Android. This is probably a feature rather than a bug, since it means Android users can spend time on things other than playing Fantastic Contraption.

These issues aside, I’m really happy with my Droid.  The screen is incredible, it’s much faster and easier to use than the G1, and I wouldn’t trade away the physical keyboard and persistent SSH for anything.

I just about fell out of my chair when I saw this.  Thank you to everyone who appeared in it, and to Olga and Elaine for doing whatever black magic they did to get them all together. <3. (Side note: I met Neil Gaiman once, back when I was in college, when his book tour came near my town. At the signing afterward, I talked awkwardly to him for what seemed like several minutes while he signed stuff for our group. Later, my friends pointed out that I was speaking too quietly for him to hear—or, in fact, to notice that I was standing there at all. I’ve been quietly embarrassed about that ever since and this video makes me feel better.)

If anyone is still sad about my Spirit comic, maybe this person’s rewrite – author unknown, found on a random image page – might provide some comfort.  Also, I got a couple of nice letters from members of the Spirit/Opportunity teams, and it’s very clear how proud they are of these little rovers. Next, Europa!

Books and Laptops and Bugs

Hey!  To anyone in the Boston area who wants to get an xkcd book signed, I’ll be doing a signing event at MIT this Thursday (the 17th).  It’s in Room 26-100 from 6:00 to 8:00 PM.  Details are here.  The event is free, and there will be books for sale there.  I’ve been pretty busy signing prints for the store to keep up with the massive flood of Christmas orders, but I wanted to get in a free non-charity event for people who wanted to get books signed but couldn’t afford tickets.

Speaking of which, here are pictures of the xkcd school nearing completion in Laos:

Thanks for all suggestions for the dedication plaque thing! Here’s what we ended up going with:

“Do not train children to learning by force and harshness, but direct them to it by what amuses their minds, so that you may be better able to discover with accuracy the peculiar bent of the genius of each.” – Plato.

This school is a gift from the readers of XKCD, an internet comic strip. The world is full of exciting things to discover. We hope you find some of them.

Thanks, everyone.  <3

I posted a while back about getting an x200s laptop.  A big part of my decision was based on its durability — reviews touted the roll cage and carbon-fiber composite casing.  Sadly, it doesn’t seem to hold up very well in my daily use.  The case has cracked in five or six places, and some of these breaks have warped the frame.  It also just feels flimsy.  The related computers in the line (the x301, the x200, etc) are reportedly a lot sturdier.

Long and boring story short, I decided to repair and resell it, and use the money to get a 13-inch Macbook Pro.  It’s significantly heavier than the x200s, but I have a Droid now (which I quite like) and it’s helped remove a lot of my need for an ultraportable laptop.  I’ve been using an OS X desktop (a Mac Mini) as my main desktop machine for a couple years now, and I’m tired of rebooting my laptop to Windows when traveling to get to Photoshop (Wine et. al. don’t quite cut it).  The things I use Linux for (programming and playing with random toys/projects) are, on the other hand, easily done in VMs.  So for me, an OS X laptop seems like a logical choice, and so far I’ve been largely happy with it.

I love the multitouch trackpad (I’ve installed jitouch to expand the set of available gestures), and VMs seem to run nicely.  Supposedly the battery’s lifespan is much improved from the old 250 cycles.  If not, expect a post in about a year and a half about me blowing up my apartment while attempting to replace the battery with an off-brand one.  I may die, but at least I’ll prove the TSA wrong. This laptop has the bonus of being more powerful than my old desktop, which I can now resell to another friend (making the laptop my primary computer), and actually come out ahead on this whole affair.

So long as I’m blabbing about recent gadget experience: Amazon’s support/replacement for broken Kindles is amazing (“We’ll rush-ship you a new one immediately! Just send the old one back to us whenever. So sorry!”). The Droid is proving excellent, though it seems like each day brings a hilarious new Android bugs. For example, it turns out having certain kinds of DNS records for the Jabber server for your Google Apps account for your domain can, starting last week, through a complicated series of events, cause Market downloads to freeze and keep you from updating any apps on the phone.  That was a fun bug to try to track down, but it’s trumped in sheer weirdness by the Droid’s 24.5-day Autofocus bug, which is itself the weirdest bug story since The Case of the 500-Mile Email.

Signed Book Timeline

When I put my book up for sale, I thought it would be neat to offer the option of a signed copy to people who ordered in the first 24 hours. It was a popular option (more popular than we expected), and some people are wondering why they took so long to get there (most should have arrived last week, the last few American copies should have arrived by now, and overseas orders will be shipping outas soon as I finish signing them).  I had put a note on the order page warning that the signed copies would take longer to ship; if anyone’s interested in why they took as long as they did, here’s the story:

The regular copies were shipped immediately, and continue to ship on time.  The people who ship the books get them out fast — orders are generally shipped within 36 hours of when we get them.  The signed books started shipping out within a few days of the initial sale, and generally arrived promptly.  The books were being printed right up to the publication date, so I didn’t actually have a large stock of them beforehand.  Since I had no idea how popular the signed copies would be, I put up a note saying that the signed books might take longer to ship, since I’d be signing them after they were ordered.  This meant they had to be shipped to me first, before going to the shipping people.  It turned out (to my delight and horror) that they were extremely popular, and we had to raise the price just to make sure there wouldn’t be more orders than I had time to sign.

Since I was going on the book tour soon after the book went up for sale, we had the bulk of the books sent out to the reddit offices in San Francisco.  For the week after my book tour, I sat up late at one of their desks signing books (and working my way through the entire run of The West Wing).  I got all those signed by the end of the week (leaving an impressive callous on my right middle finger) and left the reddit office full of boxes for FedEx.  They picked them up Monday the 28th and took them to the shipping place in Virginia.  Because of the weight, they had to go ground, so they took all of that week to go there.  Those books shipped out within 36 hours of arriving, so they should have arrived late last week.

I got back to Boston, and later that week the next set of books arrived there.  I signed a large set of those, which finished off the US orders, and they went to the distribution office for shipping out sometime last week.  For the last week, I’ve been signing boxes of mainly European orders (followed by Australia and other overseas, which take longer to ship), and I should be finishing those up in the next handful of days.  Then there’s a four-or-five day delay as they’re sent to the shipping people (too heavy to send by anything but FedEx Ground), and they’ll go out then.  I apologize to anyone whose signed books took longer than they expected to arrive.  If you have any questions or problems regarding your order, email

Thank you so much to everyone who ordered a book.  If you’re interested, there are some pictures of the xkcd school site in Laos over on the BreadPig blog.


Just a note: thank you to everyone who made it to the events. We raised enough money to build a school!  It’ll be in the Salavan Province, on Road No. 13 South.  We’re not going to torment the kids’ ability to learn phonetics by calling it The XKCD School, but we will be writing a dedication which will go on a plaque.  You guys made this happen — does anyone have any suggestions for what it should say?

Also, I’m currently happily hiding out for a while working on drawing and other projects, but I’ll hopefully be doing some less fundraise-y free signing events around Boston in the next month or two.  I’ll let you know once we have any places or dates!

Physics for Entertainment

Update: I’m finally home after a month or so of nonstop events, including several xkcd book fund-raisers/signings.  I met tons of cool people, we raised a lot of money for the EFF and Room to Read, and at one point I signed a book for a robot.  Thank you to everyone who ordered a copy, by the way!  I hope you like it.  They’re shipping out nicely, and we’re about ready to order a second printing.

The events and travel were a huge amount of fun, and I loved getting to talk to (or at) so many of you cool people.  But I’m an introvert at heart, and after doing that much socializing I feel a powerful urge to hide in my room for about a month.  At some point in my travels I seem to have picked up a cold that’s been keeping me down for a couple days, so it’s just as well that I don’t have any more events on the immediate calendar.  There’s no fever, so it’s not swine flu, but it’s keeping me awake at night and I’m going through a lot of tissues and cough medicine.  But it should blow over in a couple days, and then I’ll get to spend a while quietly working on new projects!

While I’m doing that, here’s a bit about a neat book I found recently:

Physics for Entertainment:

Physics for Entertainment was written by Yakov Perelman in the 1920′s (in Russian) and updated periodically through the 1930′s.  There are actually two parts to it, but Volume 1 is long out-of-print (though findable online — more on that later).  The book I have is a 1975 translation of Volume 2. The book is a series of a few hundred examples, no more than one or two pages each, asking a question that illustrates some idea in basic physics.

It’s neat to see what has and hasn’t changed in the last century or so.  Many of the examples he uses seem to be straight out of a modern high school physics textbook, while others were totally new to me.  And some of the answers to the questions he poses seem obvious, but others made me stop and think.  The diagram to the right shows a design for a fountain with no pump — it took me a while to get why it works.  (For an easier-to-build variant, click here.)  Later in the book, he explains the physics of that drinking bird toy.

It’s written in a fun, engaging, conversational style, as if he’s in the room chatting with you about these neat ideas.

There are a lot of diagrams:

And it’s hard not to like the guy:

“If you’ll bear with me for a moment, let’s analyze this fairy tale from a physics standpoint …”  That’s a man after my own heart.

He also spends a lot of time discussing why various perpetual-motion machines won’t work.  it’s interesting to see that there was as thriving a community of free energy people a century ago as there is now, many of their designs based on the same misapplications of physics.

Lastly, when he talks about space travel — from a pre-space-age perspective — he turns starry-eyed and poetic:

I alternate wildly between thinking that it’s totally crazy that we clawed our way up out of the atmosphere and walked on the moon, and thinking that it’s a shame that it turned out to be so boring.  But I really desperately want to see more missions to places like the Jovian moons. If it turns out one of them is teeming with life, we’re gonna feel awfully silly about how long we spent shuffling around in the Martian dust.  Also, Kepler is really exciting, putting us in a much better place to speculate about life in the galaxy.

You can get the printed Volume 2 on Amazon, while Volume 1 was supposedly unavailable for translation or reprint.  However, I mentioned this book at one of the events recently, and reader Matthias Kübel emailed me to let me know Volume 1 is available free online!  I’m looking forward to reading through it.

xkcd: volume 0

The xkcd book is now officially available in the store! (There are also a handful of new shirts available for preorder, and we’ve got the signed prints back in stock).

It’s been fun putting it all together.  It was neat to go back through various huge stacks of old drawings, some on the back of school assignments, and scan them at print resolution.  I also had fun with the marginal notes.  I’m really excited to finally have it in print, and I’m looking forward to seeing people and signing copies at the release events this weekend.  I’m also excited about getting back to work on some other projects which have been on hold for a bit, at least one of which will involve lakes and a recently-acquired Arduino.

P.S. Thank you so much for the help with the phone this weekend.  Through a bizarre set of exploits, I’ve gotten it unlocked without losing any data (for details, see the edits to the previous post).

I need G1 tech support.

Note: for anyone with a G1 with this same problem who found this entry by Googling, you don’t have to lose any data — we eventually found a workaround that doesn’t require a factory reset.  Details are at the bottom of this post.

I’ve hit the end of the flowchart, it’s 3 AM, and I’m turning to you all.

I’m at my cousin’s wedding and I’ve been locked out of my G1 phone.  I was idly playing with the screen unlock pattern (it’s fun to draw G1 unlock patterns) and it eventually said I’d made too many attempts and asked for my Google account email and password.  I typed them in.

They don’t work.  (Edit: and the username/password are correct — they work fine for logging in via the web, and they’ve worked recently in other parts of the phone.) I tried every variation on the email (it’s an email, not and every password I’ve ever used for anything Google-related.  It still says ‘incorrect username or password’.  It’s the middle of the night, I’m exhausted, and I was about to set my phone as an alarm clock to wake me up for the wedding.

I’ve googled around and found lots of other people with the same problem.  They seem to suggest it’s simply an Android bug, and the only solution is a factory reset of the phone.  This will lose all my app data.  Music, photos, and contact lists will be saved, but I’ll have to redownload all my apps, and I’ll lose my call history, Google Tracks, saved games, Shazam tagged songs, and a pile of text messages containing useful information and/or sentimental minimalist poems.

The phone is not a dev/rooted phone, so a few hacks I found with ADB won’t work.  Does anyone know anything else I can do, or is this an unfixable bug?  I just want my phone back.  I would really appreciate any help anyone can give.  I’ll watch here for a little bit, then find something else to use as an alarm and see if there’s a solution in the morning.

Thank you in advance.

Edit: I’ve used the bug mentioned in #28 here (thanks, Julian!) to successfully get to the home screen.  I couldn’t believe it actually worked, but it does — you can unlock the phone by getting a call and flipping the screen open and shut repeatedly while tapping ‘home’.  Now I can get into the phone by opening the keyboard, but if I just try to touch ‘menu’ it’s still locked.  This is still annoying, but I can deal with it for now (I’ll let it finish syncing and try reboots and stuff).  Thank you so much, internet.  <3

Edit #2: Thanks to Dan Egnor over at Google, I’ve gotten the last piece.  The phone was tied to my Google Apps account rather than my Google account, which have the same email address as their name (and I had tried the passwords for both, of course).  By changing the password for the Google Apps account (not the Google account), I made the phone fail to sync, which prompted me for a new password — which was then saved properly.  When the lockout screen came up next, I entered that password, and my phone is back.  So, in summary, to fix this without wiping your phone, you:

  1. Get someone to call you.
  2. After answering, flip the screen open and shut repeatedly, tapping the “home” button every few flips.  Eventually you’ll drop through to your home screen.  This may take a few tries.
  3. Go into your security settings and disable the unlock pattern.  You can now bypass the lockout just by opening the keyboard.
  4. Change the password on your account, which may be your Google Apps account if you have one.
  5. In a few moments, your phone will fail to sync with email and prompt you for a password.  Enter the new password.
  6. You can now log in with the new password.  Lock your screen, press menu to try unlocking it, and enter your new information.  This should unlock your phone.


There’s an xkcd book!

xkcd: volume 0 will be released in the xkcd store next week, and I’m going to some events in New York and California next weekend to celebrate the release and also help out some nonprofits.

The book contains strips chosen by me from the first 600 xkcd comics, including many of my favorites plus some which were acted out by fans or otherwise had a weird real-world effect.  The project took a little longer than expected because I went back and redid the comic selection and page layout myself.  I also reconstructed a lot of the old comics from scans (many high-res versions of early comics were missing, and others were lost in my 2007 laptop theft).  Throughout the process, I added various marginal notes and doodles.  It will be initially available in the xkcd store (and possibly later in some bookstores).

The book is being published by BreadPig, an adorable company set up by reddit founder Alexis Ohanian.  A portion of the profits go toward build a school in Laos, via the charity Room to Read.  There’s a possibility we’ll get to name the school; I wanted to name it ‘the xkcd school’ because of how confused it would make the kids who are trying to learn English phonetics, but I think they’re vetoing that idea.

We’ll be in New York on September 19th, San Francisco on September 21st, and Silicon Valley on September 22nd.  For more information on the events, check out the BreadPig announcement.  I’ll be doing some events to raise money for Room to Read and the EFF, including a Q&A where the questions are selected by reddit users.  You can add questions and vote here (hey, Reddit admins — if I bribe you with free copies of the book, will you artificially vote down the terrifying Romanian question?).

I hope to see you at the events!