As a legend goes, when the game of chess was invented in India, the ruler of those days wanted to reward its inventor. And so they asked for the following: Place a grain of rice on the first square of the chess board. Then, on the next day, place two grains of rice on the following square. 4 grains of rice on the following day & square, and so on, always doubling the amount of rice grains, until each square of the chess board is filled.

Put yourself in the rulers shoes for a moment — do you think that’s a meager reward? How much rice would you really have to give the inventor of chess?

In the story, the ruler agreed to this reward, thinking it would be easy to fulfill. And indeed, after the first week, the ruler would only have to give a total of 127 grains of rice¹, which isn’t all that much. Things look much the same in the second week: Now the reward totals 16.383 grains of rice, which amounts to not quite 0,5kg of rice². By the end of the third week, the ruler has given out about 60kg of rice in total³.

During the fourth week is where things get interesting: at the end, the ruler owes over 7 tons of rice. By day 32, or halfway through the chess board, the ruler owes around 124 tons of rice in total. In the end, after 64 days, the ruler would have needed to amass 534.955.578.137 tons of rice⁴. That’s a lot of rice!⁵

To put this into perspective, in 2017, the entire annual rice production on earth totalled about 688.2 million tons. At that rate, it would take 777 years to fulfill the debt to chess’ inventor⁶.

Unless you’ve heard of this story before⁷, you probably vastly underestimated the amount of rice that would end up on the board. A chess board doesn’t look that big, and in the beginning, the amounts you’re dealing with are tiny. But this story is a prime example of exponential growth. If something doubles in size every day, even if it starts out very tiny, at some point it will start growing at a rate we humans aren’t really equipped to think about.

As you might have guessed, this story is really about why containing the rate of COVID-19 infections is so important. Just as the grains of rice grew slowly, until it suddenly grew extremely fast, so too did the amount of infected people grow in China, and Italy, and everywhere else where people were tested positive.

But just as unintuitive exponential growth is to us, so is how sensitive it is to changing conditions. And that’s the good news: Early measures, even if their (apparent) effect is fairly small, can make an enormous difference later (YouTube).

(Graphic by Toby Morris (Spinoff.co.nz))

So: Stay at home, and wash your hands. And if you do go outside, keep your distance.

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Some grocery items are obvious panic buys: Water, bread, flour, eggs, pasta, or soap and hand sanitizer. But some other items are less obvious: why are the toilet paper shelves empty? A consumer behavior research explains why everyone is hoarding toilet paper.

Modelling the Curve

How do mathematicians model the spread of the virus? Numberphile explains the Coronavirus curve (YouTube).

Virtual Pandemic

Usually, when mathematicians and scientists try to model pandemics, they have to rely on simulations, and hope the chosen parameters mirror reality closely enough. And they know that there are a lot of factors that are hard to pin down, most of all how humans behave during times of crisis. But before COVID-19, those models got help from an unexpected corner: What a WoW virtual outbreak taught us about how humans behave in epidemics.

Plague Friends

There is no vaccine for COVID-19. But there are a lot of other diseases that are far more dangerous that we do have vaccines for. But more and more people decide not to vaccinate their children. The COVID-19 pandemic is a stark reminder of what could happen to us with other diseases: How Anti-Vaccine Sentiment Took Hold in the United States.

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