Keep A Distance of Two Arms: Intuitive Social Distancing Advice

The experts have great tools for science, but not for real life. How do we keep a distance of 1.5 metres? It’s not easy — but ancient wisdom can tell us what to do.

Social Distancing: “Is this far enough, officer?”

Which genius decided on the rules for social distancing?

This is the official advice from the Australian government on public gatherings during this COVID-19 coronavirus outbreak.

I don’t know how long 1.5 metres is, and I don’t have a ruler on me. Neither do my neighbours, and who knows if the other people around me know the number of centimetres in a metre.

Imagine standing in a queue, and you are standing too close to the person in front. The police catch you, and now you find yourself being questioned and lectured about the importance of the public health measures.

“If you’ve got a room, if you’ve got a premise, if you’ve got a meeting room or something like that, that’s 100 square metres, then you can have 25 people in that room,” Prime Minister Scott Morrison said on Friday.

Source: The Courier

If it were already hard enough to estimate length, then how are we supposed to estimate population density?

Population density = Population / Area
Area = Length * Length.
Count the number of people
Estimate length, take the square to get area.
Divide these two numbers

Too difficult.

During this outbreak, it is important to do everything we can to slow the course of the outbreak. But this advice seems to be developed by experts, for ordinary people who do not think like experts. Experts love to use precise measurements and fragile models whose predictions depend on assumptions.

Unfortunately, the public needs convenient rules of thumb.

An Alternative Rule For Social Distancing

Here is a simple alternative which is simpler and more intuitive.

Arm span. License.

The arm span (distance between fingertips when arms are extended sideways) of an individual is approximately equal to their height.

If we think of a typical adult height of 1.7m, then an arm span (can be thought of as 2 arms and torso) is also around ~1.7cm, which is slightly more than the official government recommendation of 1.5m. The torso makes the difference, so 1.5 metres is about 2 arm lengths.

Therefore, telling people to stay 1.5 metres away from each other is roughly equivalent to telling them to keep a distance of 2 arms lengths, or 1 arm span. But the difference is that this alternative is convenient for practical use. It also makes intuitive sense, because now it’s clear that the idea behind the distance is to prevent people from accidentally touching each other when they extend their arms.

Ancient Units of Measurement

Ancient people didn’t have these measurements and units like we do now. Well, they eventually had to, but it was difficult. They couldn’t mass produce rulers and scales on factory lines. They didn’t have supermarkets and stationery stores where ordinary people could buy measuring equipment. They had to use what was available to them.

And what is more available than a human’s own body parts?

Old measurement systems were based on body-parts. Very similar across civilizations despite their separation. Not perfectly precise, but it works!
3 — palm. 4 — span. 5~6 — finger.

The Metric System vs. The “Body” System

There is a tradeoff between precision and convenience. The metric system is more precise, but often requires measuring tools. The systems which utilize body-parts sacrifice precision, but are more intuitive, convenient and have no learning curve. Everyone who speaks the language knows what an “arm” or a “finger” is.

Moreover, these body-part systems are Lindy. They have been widely used cross-culturally (developed independently?) and over time. Why? — because it works.

Unfortunately, these systems are now becoming obsolete because the influence of academia is too strong. We should not think that everything ought to be measured precisely. For example, look at a recipe book, then look at the way people actually cook. Do they use precise tools or rough estimates?

An Egyptian measuring tool — one Egyptian cubit. This image is licensed under the Creative Commons Attribution 2.0 Generic license.

Don’t get me wrong. The metric system is still a good system. We have a need for precision, and the metric system satisfies that need. Even ancient societies sought precision — they built roads and buildings, which required measuring tools and a somewhat standardized system.

But not everyone aspires to be extraordinary. Not everyone has the inspiration or the ambition to perform these amazing feats of science — and that is perfectly okay. Most people want to live humble and ordinary lives.

Simplify your message

Let’s not be blinded by expertise and complicate the message. If we are caught up in a problem (coronavirus outbreak), and we all have to contribute to the solution, then let’s simplify the solution.

  1. Keep a distance of more than two arm lengths from others during this COVID-19 outbreak, so that you can’t accidentally touch people around you.
  2. In an indoor area, make sure there is enough space so that everyone is able to swing their arms around without accidentally touching someone else. More people is too many. (And ensure it is well-ventilated.)

Math, stats, data. Influenced by the complex systems perspective. I prefer to take the critical view.

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