* Fast forward to tweet # 11 if you already know Dimensional Analysis.
In physics, there are seven fundamental dimensions. The most commonly used dimensions are Mass (M), Length (L), and Time (T).
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.
[a] = (L/T)/T=L/T^2.
Therefore, F = ma tells us that:
[F] = ML/T^2.
[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.
However, an equation with incompatible dimensions CANNOT be correct.
Covid Alert Level (C) is dimensionless, i.e., it has the dimension of a pure number:
[C] = 1.
[day] = [time] = T, so:
[i] = P/T.
[C] = [R] + [i],
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!
This indicator combines many variables to determine the sustainability state of a society.
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.
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.
Politicians should not confuse people with incorrect equations & ad hoc indicators when daily new cases can show our safety status so clearly.
A big thank you to @bing for the plots and datasets. And thank you all for reading my thread!