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RandomUnder500

An index of explained things

Curious about everything.
Explained in under 500 words.

Clear, sourced explainers on how the world works and why we believe what we do. No filler, no hot takes. Just the facts that matter, in the time it takes to finish a coffee.

10 entries · 8 topics
A slice of watermelon and a round biscuit lying on a pale tiled kitchen floor in soft daylight, with crumbs beside the biscuit.Latest · No.010
● Science · 14 November 2026 · 2 min readThe Five-Second Rule: What Really Decides How Dirty Dropped Food GetsBacteria don't wait five seconds before jumping onto dropped food. What matters more is what you dropped and what it landed on.
The indexNewest first
  1. No.009Dog Years Don't Work Like That: Why the Times-Seven Rule Is WrongMultiplying a dog's age by seven is a tidy rule of thumb. A study of how DNA changes with age found dogs grow up far faster than that, then slow down.● Biology14 November 2026 · 2 min
  2. No.008Can You Catch Up on Sleep at the Weekend?A weekend lie-in feels like paying back a sleep debt. The research says it helps less than you think, and the real problem may be the swing itself.● Health14 November 2026 · 2 min
  3. No.007Green Snot Doesn't Mean You Need AntibioticsMany people see green mucus as proof of an infection that needs treating. The colour comes from your own immune cells, and it says little about bacteria.● Health13 November 2026 · 2 min
  4. No.006The Password Rules Were Wrong: Why Length Beats ComplexitySymbols, numbers and a new password every few months: the rules came from one 2003 document, and its author later said he regretted them.● Technology13 November 2026 · 2 min
  5. No.005Why You Shouldn't Wash Raw Chicken, and What Actually Keeps You SafeNearly half of cooks rinse raw chicken to make it cleaner. It doesn't, and the research points to a bigger risk most kitchens overlook.● Food13 November 2026 · 2 min
  6. No.004The Rule of 72: A 500-Year-Old Trick for Seeing How Fast Money GrowsDivide 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.● Money10 November 2026 · 2 min
  7. No.003The Year Ten Days Disappeared: How the Calendar Was FixedIn 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.● History9 November 2026 · 2 min
  8. No.002Tardigrades: The Toughest Animals on Earth Are Not IndestructibleTardigrades can survive space, deep freezing and decades without water. But the popular story of an unkillable animal leaves out the interesting part.● Biology9 November 2026 · 2 min
  9. No.001The Mandela Effect: Why Millions Remember Things That Never HappenedThousands 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.● Psychology9 November 2026 · 2 min
Topics