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Number 21: Weighing the soul

Welcome to 2024 and I hope your New Year’s resolutions are holding up. If you’re counting calories with unusual focus at the moment, I've got a number story to blow your mind! And does the human soul really weigh 21 grams...?

Tour de Carb

Each July the world’s best cyclists compete in the Tour de France over 21 stages, covering 3500 kilometres (and some incredibly hilly terrain!)

Compared to the 2000 calories an average adult burns per day, a Tour cyclist can melt through 6000 calories (25,000 kj)!!!

The Inside Science website, run by the American Institute of Physics, calculated this energy demand and worked out if you only ate jelly doughnuts, you’d need to chow through 32 a day to consume 6000 calories.

Or if you don’t like jelly doughnuts, perhaps try these 6000 calories equivalents:

  • 10 Burger King Whoppers

  • 24 Snickers bars

  • 58 bananas

  • 243 carrots

  • Or perhaps you’d like to try cycling the entire Tour fuelled by 220 bottles of red wine (though I’m not at all confident that this would get you to the finish line!)

Send me your favourite 6000 calorie meal (along with the breakdown of what foods contain how many calories) and the tastiest offering will win a lip-smacking signed copy of one of my books! Enter here

21 grams of BS!

“The Human Soul weighs precisely 21 grams”

This meme has crept into everything from a local coffee shop of mine to the 2003 feature film starring Sean Penn and Naomi Watts.

But where did this complete non-truth come from?

We owe it all to Duncan MacDougall’s 1907 study which hypothesised that souls have a physical weight and set about trying to prove it.

He chose 6 patients in nursing homes whose death was obviously imminent (4 tuberculosis sufferers, 1 diabetic and 1 ... unspecified dying person) and placed their entire beds on

industrial scales sensitive to within 5.6 grams.

One of his subjects seemed, at the precise moment of death, to lose 21.3 grams of weight…and MacDougall’s infamy was as assured as his certainty that he’d measured the weight of a soul.

Obviously his woefully small sample size, unscientific methods and the fact that only a single subject met his hypothesis rendered his research meaningless.

But good on you for having a crack, MacDougall.

Fascinating fast facts about 21!

Precious time!

High-end watches contain actual jewels – usually rubies or sapphires – to help their internal mechanisms move smoothly. While a fully jewelled watch has 17 gems, a real baller of a watch contains 21 to 25. E.g. the Vacheron Constantin Égérie Moon Phase ($137,000 including free delivery – gee thanks pal!)

It’s hip to be triangular

The diagram shows that 21 = 1 + 2 + 3 = 4 + 5 = 6 and hence we say 21 is the 6th ‘triangular’ number. It is also the total number of dots on a standard die. Neither of these facts explain why African elephants have 21 pairs of ribs. FYI humans typically have 12 pairs and most dogs 13.


While some crazy lawn bowlers like to change it up, the Laws of the Sport of Bowls stipulate that the winner in a game of singles is the first to 21 points. Whereas in table tennis, a ‘set’ was reduced from first to 21 points with 5 serves each, to first to 11 points with 2 serves each in an effort to modernise the game in 2001.

Hip to be (21) squares

You can easily divide a square into 4 smaller squares of equal size. But if the smaller squares have to all be different sizes, you need 21 squares, and there is only one way you can do it. The solution (pictured below) was found by Dutch computer scientist and mathematician A.J. W. Duijvestijn in 1978 and looks awesome!

Game Set Math

The awesome card game Set involves cards that have 1, 2 or 3 of the same image on them. Each of the images can be one of 3 colours, shapes and shades.

This means there are 4 variables (number of images, their colour, shape and shade) and therefore 3 x 3 x 3 x 3 = 81 cards in the deck.

You turn over cards and if 3 cards have a matching quality – e.g. they are all purple or they all contain 3 images etc. – they form a set.

Using a wonderful mathematical tool called “the pigeonhole principle”, we know that if you turn over 21 cards, there must be a set contained within them.

But what is really cool is that late last year a Large Language Model AI Algorithm made a mathematical breakthrough on a much more complicated version of this card game problem.

That’s all from me for now. If you'd like more geeky fun, please check out my other newsletters below, or connect with me on LinkedIn and X.

Yours in numbers,


Jump back to: Tour de Carb | 21 Grams | Precious Time | Game, Set, Math | Hip to be Square


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