Tag Archives: The scientific method

Extrapolating your way

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There is a very powerful scientific reasoning tool that I use, that, it occurs to me, I wasn’t actually taught… the simple art of extrapolation.

Most people have a pretty good idea of what extrapolating is – its where you look at a trend and predict what will happen if that trend persists. 

For example, if I said it took me 6 months to save £500, I can use extrapolation to predict how long it will take me to save £2000; its something we do all the time – yesterday I was driving down from Bristol, I could count off the the miles, and knowing the distance, I could predict if I would make it for dinner (I didn’t).

Scientists use this too. A good example is the way we can calculate the temperature of “absolute zero” by looking at the volume of a balloon as you heat it up. If you had a balloon at 25C, and you heat it to about 55C its volume would increase by about 10%. What does that tell us? It tells if we cooled it, it would eventually have no volume – and that this would happen at around -275C (-273.15C actually) – absolute zero.

Of course, the method relies upon assumptions – usually the assumption that the trend will continue in the same way (people often use the term “linear” to represent relationships that form straight lines when plotted on a graph).

What if the relationship is non-linear? For example, if little James is 5 feet tall when he is 10, how tall will he be when he is 20? Clearly he won’t be 10ft tall – that is because the relationship between height and age is “non-linear”.

Most of us are smart enough to extrapolate without knowing the jargon, but when the relationships get complicated a bit of maths and jargon can help.

For example, if we want to examine the population of bacteria in a petri dish, or the spread of a virus (or a rumour) through a population, our mental arithmetic is not always up to it. Luckily, some scientists have realised even these complex affairs have some predictability and although “non-linear”, they can still be modelled – graphs can be plotted and extrapolations made.

If this interests you, I refer you to books on epidemiology; I will move onto another sort of extrapolation – one used to check people’s theories by identifying ‘impossible’ extrapolations.

Let’s say, for example, that the want to predict  how the obesity epidemic will progress in the coming decades. If the media says obesity in a certain group increased from 14-24% between 1994 and 2004, and then goes on to predict that obesity will therefore reach 34% by 2014, does this withstand scrutiny?

Never mind that the definition of obesity may be faulty (BMI), never mind that they are extrapoliting from 2 data points – let’s rather ask if the linear trend is justifiable. This can be done by extrapolating the prediction to try to break it. 

If the model is right, obesity will go on increasing and soon enough 100% (or more!) of the population will be obese. This is clearly wrong – obesity is not likely to get everyone – vast swaths of the population are likely to be immunised to some extent against obesity due to active lifestyles and good dietary educations, or perhaps its in their genes, the lucky things. 

The truth will of course be more complex – the first group to become obese will be the most vulnerable, so an increase from 14-24% may incorporate that group, but each successively 10% will be harder fought.  All this is enough to suggest the predictions made for 2014 are doubtful, and those that go further are downright shameless. But it doesn’t stop them…

I am sure you can think of other suspicious trend-based predictions, like those for peak-oil or global warming. They could do with some improvements, so get to it!

 

The scientific method defined (well hypothesised at any rate)

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I recently realised that the jury is out on exactly what science and the scientific method are (or should be, at least).

Some would say that science is the endeavour to understand the world, answer the “how” behind the ocean tides, rainbows or seed germination. So the scientific method is any way we might do this. Sounds reasonable to me.

However, some would say that science is the business of ‘facts’ or ‘truth’ and proofs. We do experiments to ‘prove’ our hypothesis. This is the definition I would like to take issue with.

Theories and facts confused…

I get really agitated when I hear people say that evolution is a ‘fact’. Not because I’m a  nutty young earth creationist (I’m not), because no-one has yet furnished a proof. But, you may argue, there’s loads of evidence, its clearly a fact.

But evidence is not the same as proof.

Even if something is 99.999% sure, it is still not sure.

I think the trouble comes because people are never taught that those ‘theorems’ and ‘proofs’ they learned in maths class are not quite the same as the theories and evidence in the scientific method.

So is maths a science? Well, yes, sort of. But while it can deal with real things, like counting sheep, it actually deals with a sort of imaginary world (the so-called Platonic ‘world of ideas’). The whole of maths is a mental construct with no known (‘proven’) basis is reality. But nonsense, you say, of course there are numbers in the real world! Well so there are, but there are no proofs!

Proofs are only possible is a fully ‘understood’ world, and because the world of maths is underpinned by a set of axioms, it is, more or less, ‘understood’. But the real world in which we live is not like that. We don’t understand how the brain works, we don’t know how many dimensions there are, we don’t even know if there is a god.

So does that mean we don’t know anything? The media (and opponents of science) use this uncertainty to undermine science. “You can’t prove there is no God, because there is!” Hey presto, a proof of God.

No, science and the scientific method doesn’t do proofs and facts. So what does it do?

Let’s consider the old chestnut, evolution. People had a book that explained the marvellous spectrum of life, from the caterpillar to the jellyfish. This was good enough for many years. But some clever folks started to question why God would bother to make different tortoises on different islands, and why He would go to all the trouble of putting dinosaur bones in certain rocks and why he would disguise their uranium-lead isotopes to make them look millions of years old.

So a theory was proposed (Darwin’s natural selection) that explained the incredible story of species and, for good measure, predicted that humans are apes, which went down well in the church.

Since then, loads and loads of observations have been made that confirm the theory (with the odd tweak). Its a theory that would have been easy to disprove. If it was wrong, some animals that couldn’t have logically been explained by the theory would have cropped up. But they haven’t.

But all this evidence is not proof. And the lack of a disproof isn’t a proof.

The same is true for all accepted theories. The sun and the moon are thought to cause the tides. If that a fact?

If you ask a scientist, even a good one, he/she may well say yes, its a fact. Because it is so darn likely to be right. Because there is no good alternative theory. Because non-one is disputing it. Because the maths is just so neat. Because the theory can make predictions. All good reasons to accept a theory. But they do not make it fact.

So we do know ‘stuff’, plenty of stuff, facts to all intents and purposes, but not strictly facts in the sense of logical proof.

So what is the scientific method, then?

Science is the system of theories and hypotheses about the nature of reality that have not yet been disproven and which are ranked by the weight of evidence in their favour.

It is like a model of the world that we are ever refining, chucking out wrong theories, refining the ones that work. The scientific method is that refinement process. Well that is my hypothesis. The truth may be altogether different!