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Cancellation calculus: The maths of cancelled events

Cancellation calculus: The maths of cancelled events

The maths says we can't stop the spread of disease – but it can help us keep it under control.

Cancellation calculus: The maths of cancelled events

You’ve probably seen a rush of events cancelled by now, and sadly, Particle Under the Stars is no exception – but why does this keep happening?

Disease spread is a maths equation, and cancelling events helps us control one of the variables: how long does this virus take to spread?

What does social distancing actually do?

The best way to think about infection is a chain reaction.

“It’s a bit like the inside of a nuclear reactor,” says Shyam Drury, Scitech’s resident Maths Multiplier.

Image|Dave Mosher / Gfycat

Each person, on average, will infect a certain number of other people. That number is different for every disease, and it’s called r0.

For the COVID-19, r0 seems to be around 2.5. That means if we do nothing, each person infected will infect two to three others.

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Image|Particle
If we do nothing, the disease will spread …

One part of that equation is how long the virus is infectious, and how it spreads, which we can’t change. The other part, though, is called the contact rate – and that we can change. We can affect how long the virus takes to spread, by controlling how many people are around us.

“In our nuclear reaction analogy, social distancing is like the moderator – it slows the reaction down,” Shyam says.

“It’s the difference between a controlled reaction and a complete meltdown.”

What is ‘the curve’ anyway?

‘The curve’ is the graph we get when we look at how many people are sick at once.

“You can see how, in each step of the spread, there are twice as many new people to get infected as the time before. If you put these together in a graph showing how many people are infected at once, it starts to curve up,” says Shyam.

“It drops off after a peak, because eventually everyone who is going to get infected does, while others recover.”

 The same number of people get infected in each graph – you can count them, if you like. . View Larger
The same number of people get infected in each graph – you can count them, if you like.
But in one scenario, we aren’t overwhelming the health system. . View Larger
But in one scenario, we aren’t overwhelming the health system.

Here’s the thing: if everyone gets sick together, there are quickly more people sick than there are hospital beds.

“People may end up at risk not because we don’t know how to treat them, but because they can’t get a bed,” says Shyam.

Social distancing gives people time to get treated before the next wave of sick people arrive. We might all still get sick, but we get to have some control over how quickly – and that gives our hospitals time to do their thing.

Isn’t this a bit of an overreaction?

Unlike quarantine, which just separates people who might have been infected from the rest of us, social distancing separates everyone from each other.

It’s all about keeping r0 as low as possible. The virus can’t spread to everyone at your movie night if the the movie night never happens. It has to reach those people one by one instead, and that takes longer.

A bit like the Y2K bug back in the 90s, it’s going to take a lot of effort to do this right – but if we do, it’ll look like nothing happened.

So what should I do?

As much as it pains us to say it: you shouldn’t buy tickets to our movie nights right now – or anyone else’s, for that matter.

Beyond that, you should get your news and advice from somewhere trustworthy, and try to follow it.

Stay safe out there everyone, and we’ll see you soon.

Video|Simon Pegg / Nick Frost
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