## Horror films

Posted by chrisrick13 on December 1, 2009

It is obvious: there are a lot of horror films around.

I have just watched an hour long film that is the most terrifying thing I have ever watched:

I stumbled across it while converting my erroneous rule of 72 to a rule of 70 in my previous blog entry.

It talks about exponential growth. Don’t let that word frighten you there is no maths in it. It uses the rule of 70. You can see how compound interest works, where your pension is going, what is happening to oil reserves, what is happening to population. Dr Bartlett gives an absorbing talk.

The most frightening thing is that his numbers carry authority. But even if he is, say, 100% out in a value for the year 2020 of some feature, due to exponential growth he will be right just 1 year later.

From his talk I have made some simple deductions: We are rapidly moving our world from one that can support the current world population poorly, to one that will be capable of supporting a much lower population. At the same time we are increasing population at a rate that will double it in 35 years. I have no idea what a sustainable population is, but our rate of consumption is continuously reducing that sustainable level. Population increase is bringing the crunch point forward and making the sustainable population count much lower.

Dr Bartlett’s trick is not to get involved in deductions he just shows some very simple stuff. The simplicity of it is what is so scary. Plenty of people have made the deduction that I made a long time ago. This video shows very simply how it must be right.

It is obvious: there are a lot of horror films around and I’m not talking fiction.

## Bill said

I think that the exponential model is frequently used

at low population densitiesas it gives a quick and simple view of how it will grow. However such an approach does not work for higher population densities. For example the population of the US was about 4 million in 1790 and grew to 63 million in 1890. During this period it grew at a rate very close to that predicted by an exponential curve, which is as Malthus would have calculated. If you look at the population from that point on it has diverged by a very high degree and a Belgium Mathematician Verhulst argued that, when there were issues (such as limited resources) then there were counterbalancing forces to slow done such growth.In fact the equation that can/should be used is the Logistic (Logistic Recurrence Relation) where the change in population is not rP (rate of growth * Population at the start) but rP(1-P/E) [the new term, E, is the equilibrium population]. Verhulst (in the early 1900s predicted a ‘final’ Belgium population of 9.4 million and its about 10 million now, not far out…

This equation fits much better and predicts that the population rise will tend to slow as it approaches E (well to be honest only if 0<r<1). I'm sure a mathematician will take issue with my comments but I think they are broadly correct(?)

Bill

## chrisrick13 said

You are right on the maths. Clearly these exponential curves do not carry on. I wrote about curves and lines for predicting things in a earlier blog. They only fit until something causes them not to. I think he is saying that if this rate is sustained (of whatever)then there is a predictable end point. So something will change before that end point…but that end point is very close for everything. That is what scares me. We have already abrogated the chance to choose.

The only answer is reduced population, but as we go on using resources and growing our populations we lower the number that the populations have to go to and increase the number of people that have to go! Anyone for a war, a good disease (natural or terrorist spread), or some natural event like a slipped ice-shelf?

Living in a world with zero growth will be an interesting new experience for all of us – not far away now.

Spend all your money now and then throw yourself on the mercy of the state. You will be there soon anyway!