On May 10, Mr. @BorisJohnson proposed a simple equation to determine #COVID Alert Level. He then explained how the reopening policy could be shaped based on this "Threat Level".

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* Fast forward to tweet # 11 if you already know Dimensional Analysis.

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See this @wikipedia article for a technical description:

en.wikipedia.org/wiki/Dimension…

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In physics, there are seven fundamental dimensions. The most commonly used dimensions are Mass (M), Length (L), and Time (T).

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Newton's second law is often written as F = ma, or Force = mass × acceleration. Acceleration is the rate of change of velocity:

a = v/t.

Velocity = distance / time, so:

[v] = L/T,

where [ ] denotes dimension (or physical unit) of a variable.

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[a] = (L/T)/T=L/T^2.

Therefore, F = ma tells us that:

[F] = ML/T^2.

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[E] = M (L/T)^2 = ML^2/T^2,

Note that c is the speed of light, which means it has the same dimension as velocity:

[c] = [v] = L/T.

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However, an equation with incompatible dimensions CANNOT be correct.

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Covid Alert Level (C) is dimensionless, i.e., it has the dimension of a pure number:

[C] = 1.

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[day] = [time] = T, so:

[i] = P/T.

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[C] = [R] + [i],

or

1 = 1/T + P/T.

This is mathematically impossible for the same reason that one cannot write the following equation:

Wall = Snake + Oil.

3 variables with 3 different units!

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doi.org/10.1016/j.ecol…

This indicator combines many variables to determine the sustainability state of a society.

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It is also unnecessary, because in the epidemic system, we have simple, clear variables that can guide the reopening policy/decisions: DAILY NEW CASES & DAILY DEATHS.

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hindawi.com/journals/cmmm/…

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Below, I will provide examples of countries that are past the rapid transmission phase of #coronavirus, countries that are close to success, & countries that are far from ready to reopen.

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dw.com/en/spike-in-so…

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#BritishColumbia #Vancouver can safely reopen as it has ~10 daily new cases.

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Politicians should not confuse people with incorrect equations & ad hoc indicators when daily new cases can show our safety status so clearly.

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A big thank you to @bing for the plots and datasets. And thank you all for reading my thread!

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