RandomUnder500 publishes short, well-sourced explainers on science, history, psychology and the world around us. Every entry is under 500 words.https://randomunder500.com/https://randomunder500.com/articles/the-rule-of-72/https://randomunder500.com/articles/the-rule-of-72/Divide 72 by an interest rate and you get the years it takes to double. Here is where the shortcut came from, why it works, and three places it changes the picture.Tue, 10 Nov 2026 20:54:00 GMTMoneycompound interestinflationmental mathshttps://randomunder500.com/articles/the-year-ten-days-disappeared/https://randomunder500.com/articles/the-year-ten-days-disappeared/In October 1582, millions of people went to bed on the 4th and woke up on the 15th. Here is why the calendar had to skip ahead, and what it still affects.Mon, 09 Nov 2026 21:24:00 GMTHistorycalendarsastronomytimekeepinghttps://randomunder500.com/articles/tardigrades/https://randomunder500.com/articles/tardigrades/Tardigrades can survive space, deep freezing and decades without water. But the popular story of an unkillable animal leaves out the interesting part.Mon, 09 Nov 2026 21:12:00 GMTBiologyanimalsextremophilesevolutionhttps://randomunder500.com/articles/the-mandela-effect/https://randomunder500.com/articles/the-mandela-effect/Thousands of people share the same false memories, from a monocle that never existed to a movie line never spoken. Here is what the science says.Mon, 09 Nov 2026 20:31:00 GMTPsychologymemorycognitionperception