Wikimedia Commons
Wikimedia Commons

Edsger Dijkstra, Computer Scientist

Wikimedia Commons
Wikimedia Commons

In our Retrobituaries series, we highlight interesting people who are no longer with us. Today let's explore the life of Edsger Dijkstra, who died at 72 in 2002. 

If you’ve used a computer or smart phone in the last few decades, you’ve come into contact with the work of Edsger Dijkstra. Since his death in 2002, his research in the field of computer science has in many ways only grown more important. Here are a few things you didn’t know about his life and his science. 

If you took his computer science class, you probably didn’t touch a computer.

Professor Dijkstra once said, “Computer science is no more about computers than astronomy is about telescopes,” and he taught his courses accordingly. He was a proponent of elegance in mathematical proofs, whereby puzzles are solved with efficiency and aesthetic sensitivity.

Grades were determined by the final exam, which was neither written on a piece of paper nor typed on a computer. Rather, students were given individual oral examinations in his office or at his home. The conversational exams lasted hours at a time, and students were asked how they might prove various mathematical propositions. They were then challenged to write out their proofs on a chalkboard. After the exam, students were offered a beer if they were of age, or a cup of tea, if they were not. 

He didn’t use email. Or a word processor.

Dijkstra was famous for his general rejection of personal computers. Instead of typing papers out using a word processor, he printed everything in longhand. He wrote well over a thousand essays of significant length this way, and for most of his academic career, they proliferated by ditto machine and fax. Each essay was given a number and prefixed with his initials, EWD.

Students who emailed Dijkstra were asked to include a physical mailing address in the letter. His secretary would print the message, and he would respond by hand.

Computers weren’t the only technology he shunned. He refused to use overhead projectors, calling them “the poison of the educational process.”


Use Google Maps? You can thank Dijkstra.

Among his profound contributions to computer science is a solution to the “single source shortest-path problem.” The solution, generally referred to as Dijkstra’s algorithm, calculates the shortest distance between a source node and a destination node on a graph. (Here is a visual representation.) The upshot is that if you’ve ever used Google Maps, you’re using a derivation of Dijkstra’s algorithm. Similarly, the algorithm is used for communications networks and airline flight plans. 

He “owned” a nonexistent company.

In many of his more humorous essays, he described a fictional company of which he served as chairman. The company was called Mathematics, Inc., and sold mathematical theorems and their maintenance. Among the company’s greatest triumphs was proving the Riemann hypothesis (which it renamed the Mathematics, Inc. Theorem), and then it unsuccessfully attempted to collect royalties on all uses of the mathematical conjecture in the real world. Evidence was never given of the proof, of course, because it was a trade secret. Mathematics Inc. claimed to have a global market share of 75 percent.

He was the first programmer in the Netherlands.

In the 1950s, his father suggested that he attend a Cambridge course on programming an Electronic Delay Storage Automatic Calculator, or EDSAC. Dijkstra did, believing that theoretical physics (which he was studying at the time at Leiden University) might one day rely upon computers. The following year, he was offered a job at Mathematisch Centrum in Amsterdam, making him the first person in the Netherlands to be employed as something called a “programmer.” (“A programmer?” he recalled of the moment he was offered the position. “But was that a respectable profession? For after all, what was programming? Where was the sound body of knowledge that could support it as an intellectually respectable discipline?” He was then challenged by his eventual employer to make it a respectable discipline.) 

This would later cause problems. On his marriage application in 1957, he was required to list his profession. Officials rejected his answer—”Programmer”—stating that there was no such job.

Previously on Retrobituaries: Albert Ellis, Pioneering Psychologist. See all Retrobituaries here.

The Math Behind the Classic Eye Chart Is Surprisingly Complex

Next time you're forced to take a vision exam at the DMV, take a moment to appreciate the complex math that went into the eye chart. What seems like a fairly straightforward way to assess eyesight is actually the result of specific calculations that can tell you a lot about how the human eye works.

As The Verge explains in the video below, eye charts measure one aspect of healthy vision: visual acuity. This is our ability to make out fine details in our surroundings—kind of like the resolution of a computer screen, but instead of pixels, it's measured in degrees. It's easy for our eyes to tell the difference between two points of light coming from different directions, but if those points start to move closer together they will eventually blur into one. The angle created just as two lines of light become too close for our eyes to distinguish them is called the resolution limit. In healthy adults, it measures one-sixtieth of a degree, or one arcminute wide.

When a doctor asks you to read an eye chart, the resolution limit is what they're looking for. The letters in the middle of an eye chart are all designed to be exactly one arcminute thick. If your vision is sharp, you should be able tell the difference between the white spaces and the black lines of the text from 20 feet away. 

A perfect 20/20 score on an eye chart test doesn't mean you have perfect vision: Visual acuity, along with color, contrast, and depth perception, are all important parts of healthy eyesight. And a higher resolution limit isn't always a sign of a permanent problem: For people who spend their days staring at a screen, it may be caused by the eye fatigue brought on by Computer Vision Syndrome. If this is a problem for you, here are some ways to tweak your behavior.

[h/t The Verge]

Could You Pass the Mensa Intelligence Test?

The biggest perk of being in Mensa just might be the bragging rights. Membership is reserved for society’s most elite intellectuals, and the only path to induction is to score in the 98th percentile or higher on their notorious IQ test. Think you have the smarts to join the top .0001 percent of thinkers? Before you apply for the real thing, flex your brain by answering a few sample questions from the test.

The practice questions shared on Popular Science cover the skills Mensa looks for in its members: verbal, spatial, and mathematical reasoning. To ace the test, you’ll need to be just as capable of recognizing obscure vocabulary as you are of doing complex math in your head.

The real Mensa IQ test is really two tests: a timed test with 50 questions and one with seven sections. (Scoring in the 98th percentile on either test qualifies you to join.) Answering all four of the questions posted to PopSci correctly doesn’t necessarily mean you’re intelligent enough for Mensa, but it should give you a confidence boost if you’re thinking about applying. If you do miss a question or two, maybe hold off on taking the official test until you’ve had more time to prepare: Scoring below the 98th percentile bars you from joining the exclusive club for life. You can take the practice test now by heading over to PopSci.

[h/t Popular Science]


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