# Nautilus, The Riddler, and Brain Pickings

Welcome to this week’s Math Munch!

Sometimes math pops up in places when you aren’t even looking for it. This week I’d like to share three websites that I enjoy. What they have in common is that they all cover a wide range of subjects—astronomy, politics, pop culture—but also host some great math if you know where to look for it.

First up is a site called Nautilus. In their own words, “We are here to tell you about science and its endless connections to our lives.” Each month they publish articles around a theme. This month’s theme is “Heroes.” Included in Nautilus’s mission is discussing mathematics, and you can find their math articles on this page. Here are a few articles to get you started. Read about how Penrose tiles have made the leap from nonrepeating abstraction to the real world—including to kitchen items. Learn about one of math’s beautiful monsters and how it shook the foundations of calculus. Or you might be interested in learning about how a mathematician is using computers to change the way we write proofs.

Next, you might think that, since the presidential election is now over, you won’t be heading to Nate Silver’s FiveThirtyEight quite as often. But do you know about the site’s column called The Riddler? Each week Oliver Roeder shares two puzzles, the newer Riddler Express and the Riddler Classic. Readers can send in their solutions, and some get featured on the website—that could be you! Here are a couple of puzzles to get you started, and you can also check out the full archive. The Puzzle of the Lonesome King asks about the chances that someone will win a prince-or-princess-for-a-day competition. Can You Win This Hot New Game Show? asks you to come up with a winning strategy for a round of Highest Number Wins. And Solve The Puzzle, Stop The Alien Invasion is just what is says on the tin.

The third site I’d like to point you to is Brain Pickings. It’s a wide-ranging buffet of short articles on all kinds of topics, written and curated by Maria Popova. If you search Brain Pickings for math, all kinds of great stuff will pop up. You can read about John ConwayPaul Erdős, Margaret WertheimBlaise Pascal, and more. You’ll find book recommendations, videos, history, and artwork galore. I particularly want to highlight Maria’s article about the trailblazing African American women who helped to put a man on the moon. Their story is told in the book Hidden Figures by Margot Lee Shetterly, and the feature film by the same name is coming soon to a theater near you!

I hope you find lots to dig into on these sites. Bon appetit!

# Making Pi, Transcending Pi, and Cookies

Welcome to this week’s Math Munch– and happy Pi Day!

What does pi look like? The first 10,000 digits of pi, each digit 0 through 9 assigned a different color.

You probably know some pretty cool things about the number pi. Perhaps you know that pi has quite a lot to do with circles. Maybe you know that the decimal expansion for pi goes on and on, forever and ever, without repeating. Maybe you know that it’s very likely that any string of numbers– your birthday, phone number, all the birthdays of everyone you know listed in a row, followed by all their phone numbers, ANYTHING– can be found in the decimal expansion of pi.

But did you know that pi can be approximated by dropping needles on a piece of paper? Well, it can! If you drop a needle again and again on a lined piece of paper, and the needle is the same length as the distance between the lines, the probably that the needle lands on a line is two divided by pi. This experiment is called Buffon’s needle, after the French naturalist Buffon.

If the angle the needle makes with the lines is in the gray area (like the red needle’s angle is), it will cross the line. If the angle isn’t, it won’t. The possible angles trace out a circle. The closer the center of the needle (or center of the circle) is to the line, the larger the gray area– and the higher the probability of the needle hitting the line.

This may seem strange to you– but if you think about how the needle hitting a line has a lot to do with the distance between the middle of the needle and the nearest line and the angle it makes with the lines, maybe you’ll start to think about circles… and then you’ll get a clue about the connection between this experiment and pi. Working out this probability exactly requires some pretty advanced mathematics. (Feeling ambitious? Read about the calculation here.) But, you can get some great experimental results using this Buffon’s needle applet.

Click on the picture to try the applet.

I had the applet drop 500 needles. Then, the applet used the fact that the probability of the needle hitting a line should be two divided by pi and the probability it measured to calculate an approximation for pi. It got… well, you can see in the picture. Pretty close, right?

Here’s another thing you might not know: pi is a transcendental number. Sounds trippy– but, like some other famous numbers with letter names, like e, pi can never be the solution to an algebraic equation involving whole numbers. That means that no matter what equation you give me– no matter how large the exponent, how many negatives you toss in, how many times you multiply or divide by a whole number– pi will never, ever be a solution. Maybe this doesn’t sound amazing to you. If not, check out this video from Numberphile about transcendental numbers. Numbers like pi and e don’t do mathematical things we’re used to numbers doing… and it’s pretty weird.

Still curious about transcendental numbers? Here’s a page listing the fifteen most famous transcendental numbers. My favorite? Definitely the fifth, Liouville’s number, which has a 1 in each consecutive factorial numbered place.

Finally, maybe you don’t like pi. Maybe you like cookies instead. Lucky for you, you can do many mathematical things with cookies, too. Like make cookie tessellations! This mathematical artist and baker made cookie cutters in the shapes of tiles from Escher tessellations and used them to make mathematical cookie puzzles. Beautiful, and certainly delicious.

If you happen to have a 3D printer, you can make your own Escher cookie cutters. Here’s a link to print out the lizard cutter. If you don’t have a 3D printer, you could try printing out a 2D image of an Escher tessellation and tracing a tile onto a sheet of paper. Cut out the tile, roll out your dough, and slice around the outside of the tile to make your cookies. If you do it right, you shouldn’t have to waste any dough…

Here’s hoping you eat some pi or cookies on pi day! Bon appetit!

# Virtual Hyenas, Markov Chains, and Random Knights

Welcome to this week’s Math Munch!

It’s amazing how a small step can lead to a chain reaction of adventure.

Arend Hintze

Recently a reader named Nico left a comment on the Math Munch post where I shared the game Loops of Zen. He asked why the game has that name. Curious, I looked up Dr. Arend Hintze, whose name appears on the game’s title page. This led me to Arend’s page at the Adami Lab at Michigan State University. Arend studies how complex systems—especially biological systems—evolve over time.

Here is a video of one of Arend’s simulations. The black and white square is a zebra. The yellow ones are lions, the red ones are hyenas, and guess who’s hungry?

Arend’s description of the simulation is here. The cooperative behavior in the video—two hyenas working together to scare away a lion—wasn’t programmed into the simulation. It emerged out of many iterations of systems called Markov Brains—developed by Arend—that are based upon mathematical structures called Markov chains. More on those in a bit.

You can read more about how Arend thinks about his multidisciplinary work on biological systems here. Also, it turns out that Arend has made many more games besides Loops of Zen. Here’s Blobs of Zen, and Ink of Zen is coming out this month! Another that caught my eye is Curve, which reminds me of some of my favorite puzzle games. Curve is still in development; here’s hoping we’ll be able to play it soon.

Arend has agreed to do an interview with Math Munch, so share your questions about his work, his games, and his life below!

Eric Czekner

Arend’s simulations rely on Markov chains to model animal behavior. So what’s a Markov chain? It’s closely related to the idea of a random walk. Check out this video by digital artist, musician, and Pure Data enthusiast Eric Czekner. In the video, Eric gives an overview of what Markov chains are all about and shows how he uses them to create pieces of music.

On this page, Eric describes how he got started using Markov chains to make music, along with several of his compositions. It’s fascinating how he captures the feel of a song by creating a mathematical system that “generates new patterns based on existing probabilities.”

Now there’s a big idea: exploring something randomly can capture structures that might be hard to perceive otherwise. Here’s one last variation on the Markov chain theme that involves a pure math question. This blog post ponders the question: what happens when a knight takes a random walk—or random trot?—on a chessboard? It includes some colorful images of chessboards along the way.

 How likely it is that a knight lands on each square after five moves, starting from b1. How likely it is that a knight lands on each square after 200 moves, starting from b1.

The blogger—Leonid Kovalev—shows in his analysis what happens in the long run: the number of times a knight will visit a square will be proportional to the number of moves that lead to that square. For instance, since only two knight moves can reach a corner square while eight knight moves can reach a central square, it’s four times as likely that a knight will finish on a central square after a long, long journey than on a corner square. This idea works because moving a knight around a chessboard is a “reversible Markov chain”—any path that a knight can trace can also be untraced. The author also wrote a follow-up post about random queens.

It’s amazing the things you can find by chaining together ideas or by taking a random walk. Thanks for the inspiration for this post, Nico. Keep those comments and questions coming, everyone—we love hearing from you.

Bon appetit!

Welcome to this week’s Math Munch!

Abraham Lincoln, figuring out a word problem.
Can you decipher his steps?

About a month ago I ran across an article about Abraham Lincoln and math. Lincoln is often celebrated as a self-made frontiersman who had little formal education. The article describes how two professors from Illinois State University recently discovered two new pages of math schoolwork done by Lincoln, which may show that he had somewhat more formal schooling than was previously believed. The sheet shows the young Abe figuring problems like, “If 4 men in 5 days eat 7 lb. of bread, how much will be sufficient for 16 men in 15 days?” Here are some further details about the manuscript’s discovery from the Illinois State University website and a high-quality scan of Lincoln’s figuring from the Harvard University Library.

Lincoln is also known for his study of Euclid’s Elements—that great work of mathematics from ancient times. Lincoln began to read the Elements when he was a young lawyer interested in what exactly it means to “prove” something. Euclid’s work even made a brief appearance in the recent movie about Lincoln. Thinking about Lincoln and math got me to wondering about how our presidents in general have interacted with the subject. Certainly they must all have had some kind of experience with math! In my searching and remembering, I’ve run across these tidbits about Ulysses S. Grant, James Garfield, and President Obama. Still, my searches haven’t turned up so very much. Maybe you’ll keep your eyes open for further bits of mathy presidential trivia?

Next up, check out these math problems about blinking on a wonderful online resource called Bedtime Math. Every day, the site posts a few math problems that parents and children can share and ponder at bedtime—just like families often do with storybooks. Bedtime Math was founded by Laura Bilodeau Overdeck. She is involved with several math-related nonprofits and is the mother of three kids. Bedtime Math grew out of the way that Laura shared math problems with her own children. A few of my favorite Bedtime Math posts are “You Otter Know” and “Booking Down the Hall“.

Today’s Bedtime Math is titled “Space Saver” and contains some problems about hexagon tilings and our mathematical chum, the honeybee. Here is today’s “big kid” problem: If a bee builds 5 hexagons flush in a horizontal row, how many total sides did the bee make, given the shared sides? I hope you find some problems to enjoy at Bedtime Math. You can sign up to receive their daily email of problems on the righthand side of the Bedtime Math frontpage.

Zome inventor Paul Hildebrandt and
a mathy PCMI Fourth of July float!

Did you know that people blink differently when they lie? I’ve been thinking a lot these past few weeks about frauds and fakes as I’ve worked with some teacher friends on this year’s PCMI problem sets. PCMI—the Park City Math Institute—is a math event held each summer that gathers math professors, math teachers, and college math students to do mathematics together for three weeks. It all happens in beautiful Park City, Utah. The first week of PCMI coincides with the Fourth of July, and the PCMI crew always makes a mathy entry in the local Independence Day Parade!

The theme of the high school teachers’ program this year is “Probability, Randomization, and Polynomials”. The first problem set introduces the following conundrum:

Suppose you were handed two lists of 120 coin ﬂips, one real and
one fake. Devise a test you could use to decide which was which.
Be as precise as possible.

Which is real? Which is fake?

If you understand what this problem is all about, then you can understand my recent fascination with frauds! Over to the left I’ve shared two sequences I concocted. One I made by actually flipping a coin, while the other I made up out of my head. Can you tell which is which?

For more sleuthing fun, check out this applet on Khan Academy, which challenges you to distinguish lists of coin flips. Some are created by a fair coin, others are made by an unfair coin, and still others are made by human guesses. This coin-flipping challenge is a part of Khan Academy’s Journey into Cryptography series. You should also know that the PCMI problem sets from previous years are all online, filed by years under “Class Notes”. They are rich with fantastic, brain-teasing problems that are woven together in expert fashion.

And finally, to go along with your Bedtime Math, how about a little bedtime poetry? Check out the video below.

Sweet dreams, and bon appetit!