The Lava Lamps That Help Keep The Internet Secure

At the headquarters of Cloudflare, in San Francisco, there’s a wall of lava lamps: the Entropy Wall. They’re used to generate random numbers and keep a good bit of the internet secure: here’s how.

For a technical overview of the Entropy Wall click here.

Video by YouTuber Tom Scott

Read more: http://twistedsifter.com/videos/the-lava-lamps-that-help-keep-the-internet-secure/

In Math, Profs Use This Puzzle To Teach a Valuable Lesson About Problem Solving

Graphic by Krauss

The missing square puzzle is an optical illusion used in mathematics classes to help students reason about geometrical figures; or rather to teach them not to reason using figures, but to use only textual descriptions and the axioms of geometry.
 
It depicts two arrangements made of similar shapes in slightly different configurations. Each apparently forms a 13×5 right-angled triangle, but one has a 1×1 hole in it. [source]

Graphic by Trekky0623

The key to the puzzle is the fact that neither of the 13×5 “triangles” is truly a triangle, because what appears to be the hypotenuse is bent. In other words, the “hypotenuse” does not maintain a consistent slope, even though it may appear that way to the human eye. [source]

Graphic by Krauss

According to Martin Gardner, this particular puzzle was invented by a New York City amateur magician, Paul Curry, in 1953. However, the principle of a dissection paradox has been known since the start of the 16th century. [source]

Graphic by Krauss

Read more: http://twistedsifter.com/2017/07/profs-use-this-puzzle-to-teach-lesson-about-problem-solving/

Carl Sagan Explains How Eratosthenes Knew the Earth Was Curved Over 2,200 Years Ago

In this excerpt from episode 1 of Carl Sagan’s ‘Cosmos’, he explains how the Greek scholar, Eratosthenes, knew the Earth was curved over 2,200 years ago.

Read more: http://twistedsifter.com/videos/how-eratosthenes-knew-the-earth-was-curved/