Archive for the 'Obfuscatory Math' category

Bad Math from the Bad Astronomer

Jan 17 2014 Published by under Bad Algebra, Bad Math, Bad Physics, Obfuscatory Math

This morning, my friend Dr24Hours pinged me on twitter about some bad math:

And indeed, he was right. Phil Plait the Bad Astronomer, of all people, got taken in by a bit of mathematical stupidity, which he credulously swallowed and chose to stupidly expand on.

Let's start with the argument from his video.


We'll consider three infinite series:

S1 = 1 - 1 + 1 - 1 + 1 - 1 + ...
S2 = 1 - 2 + 3 - 4 + 5 - 6 + ...
S3 = 1 + 2 + 3 + 4 + 5 + 6 + ...

S1 is something called Grandi's series. According to the video, taken to infinity, Grandi's series alternates between 0 and 1. So to get a value for the full series, you can just take the average - so we'll say that S1 = 1/2. (Note, I'm not explaining the errors here - just repeating their argument.)

Now, consider S2. We're going to add S2 to itself. When we write it, we'll do a bit of offset:

1 - 2 + 3 - 4 + 5 - 6 + ...
    1 - 2 + 3 - 4 + 5 + ...
==============================
1 - 1 + 1 - 1 + 1 - 1 + ...

So 2S2 = S1; therefore S2 = S1=2 = 1/4.

Now, let's look at what happens if we take the S3, and subtract S2 from it:

   1 + 2 + 3 + 4 + 5 + 6 + ...
- [1 - 2 + 3 - 4 + 5 - 6 + ...]
================================
   0 + 4 + 0 + 8 + 0 + 12 + ... == 4(1 + 2 + 3 + ...)

So, S3 - S2 = 4S3, and therefore 3S3 = -S2, and S3=-1/12.


So what's wrong here?

To begin with, S1 does not equal 1/2. S1 is a non-converging series. It doesn't converge to 1/2; it doesn't converge to anything. This isn't up for debate: it doesn't converge!

In the 19th century, a mathematician named Ernesto Cesaro came up with a way of assigning a value to this series. The assigned value is called the Cesaro summation or Cesaro sum of the series. The sum is defined as follows:

Let \(A = {a_1 + a_2 + a_3 + ...}\). In this series, \(s_k = Sigma_{n=1}^{k} a_n\). \(s_k\) is called the kth partial sum of A.

The series \(A\) is Cesaro summable if the average of its partial sums converges towards a value \(C(A) = lim_{n rightarrow infty} frac{1}{n}Sigma_{k=1}^{n} s_k\).

So - if you take the first 2 values of \(A\), and average them; and then the first three and average them, and the first 4 and average them, and so on - and that series converges towards a specific value, then the series is Cesaro summable.

Look at Grandi's series. It produces the partial sum averages of 1, 1/2, 2/3, 2/4, 3/5, 3/6, 4/7, 4/8, 5/9, 5/10, ... That series clearly converges towards 1/2. So Grandi's series is Cesaro summable, and its Cesaro sum value is 1/2.

The important thing to note here is that we are not saying that the Cesaro sum is equal to the series. We're saying that there's a way of assigning a measure to the series.

And there is the first huge, gaping, glaring problem with the video. They assert that the Cesaro sum of a series is equal to the series, which isn't true.

From there, they go on to start playing with the infinite series in sloppy algebraic ways, and using the Cesaro summation value in their infinite series algebra. This is, similarly, not a valid thing to do.

Just pull out that definition of the Cesaro summation from before, and look at the series of natural numbers. The partial sums for the natural numbers are 1, 3, 6, 10, 15, 21, ... Their averages are 1, 4/2, 10/3, 20/4, 35/5, 56/6, = 1, 2, 3 1/3, 5, 7, 9 1/3, ... That's not a converging series, which means that the series of natural numbers does not have a Cesaro sum.

What does that mean? It means that if we substitute the Cesaro sum for a series using equality, we get inconsistent results: we get one line of reasoning in which a the series of natural numbers has a Cesaro sum; a second line of reasoning in which the series of natural numbers does not have a Cesaro sum. If we assert that the Cesaro sum of a series is equal to the series, we've destroyed the consistency of our mathematical system.

Inconsistency is death in mathematics: any time you allow inconsistencies in a mathematical system, you get garbage: any statement becomes mathematically provable. Using the equality of an infinite series with its Cesaro sum, I can prove that 0=1, that the square root of 2 is a natural number, or that the moon is made of green cheese.

What makes this worse is that it's obvious. There is no mechanism in real numbers by which addition of positive numbers can roll over into negative. It doesn't matter that infinity is involved: you can't following a monotonically increasing trend, and wind up with something smaller than your starting point.

Someone as allegedly intelligent and educated as Phil Plait should know that.

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Obfuscatory Vaccination Math

Nov 07 2010 Published by under Bad Math, Obfuscatory Math

Over at my friend Pal's blog, in a discussion about vaccination, a commenter came up with the following in an argument against the value of vaccination:

Mathematical formula:

100% – % of population who are not/cannot be vaccinated – % of population who have been vaccinated but are not immune (1-effective rate)-% of population who have been vaccinated but immunity has waned – % of population who have become immune compromised-(any other variables an immunologist would know that I may not)

What vaccine preventable illnesses have the result of that formula above the necessary threshold to maintain herd immunity?

I don’t know if the population is still immune to Smallpox, but I would hope that that is just a science fiction question. Smallpox was eradicated, but that vaccine did have the highest number of adverse reaction (I’m sure PAL will correct me if that statement is wrong)

It's a classic example of what I call obfuscatory mathematics: that is, it's an attempt to use fake math in an attempt to intimidate people into believing that there's a real argument, when in fact they're just hiding behind the appearance of mathematics in order to avoid having to really make their argument. It's a classic technique, frequently used by crackpots of all stripes.

It's largely illegible, due to notation, punctuation, and general babble. That's typical of obfuscatory math: the point isn't to use math to be comprehensible, or to use formal reasoning; it's to create an appearance of credibility. So let's take that, and try to make it sort of readable.

What he wants to do is to take each group of people who, supposedly, aren't protected by vaccines, and try to put together an argument about how it's unlikely that vaccines can possibly create a large enough group of protected people to really provide herd immunity.

So, let's consider the population of people. Per Chuck's argument, we can consider the following subgroups:

  • \(u\) is the percentage of the population that does not get vaccinated, for whatever reason.
  • \(v\) is the percentage of people who got vaccinated; obviously equal to \(1 - u\).
  • \(n\) is the percentage of people who were vaccinated, but who didn't gain any immunity from their vaccination.
  • \(w\) is the percentage of people who were vaccinated, but whose immunity from the vaccine has worn off.
  • \(i\) is the percentage of people who were vaccinated, but who have for some reason become immune-compromised, and thus gain no immunity from the vaccine.

He's arguing then, that the percentage of effectively vaccinated people is \(1.0 - u - nv - wv - iv\). And he implies that there are other groups. Since herd immunity requires a very large part of the population to be immune to a disease, and there are so many groups of people who can't be part of the immune population, then with so many people excluded, what's the chance that we really have effective herd immunity to any disease?

There's a whole lot wrong with this, ranging from the trivial to the moderately interesting. We'll start with the trivial, and move on to the more interesting.

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44 responses so far