Thursday, February 04, 2010

Science for Non-Scientists: Part 2 - Theories and Stuff

From Hypothesis to Law

Following on from part 1, a basic discussion of the Scientific Method, I'm now going to move to looking at theories. In science ideas move thought a series of stages which signify their acceptance. This is an important concept because as the idea moves though the stages, it also signifies the amount of facts and data they backup that idea. Broadly these are;

- 1. Hypothesis:
This is an idea that you wish to test out, a premiss or a concept. It is an idea waiting for evidence. However, confusingly this is what in normal language we would call a 'Theory'. A hypothesis can be anything: 'I think the moon is made of cheese', 'I think the planet is warming', 'I think milk comes from cows' - anything. There is also the null-hypothesis, which is where your stated premiss is a negative, so for example 'I don't think the moon is made of cheese', 'I don't think the earth is warming' etc. The null-hypothesis works by taking your hypothesis, then you then try to disprove it - this is considered a better method because you avoid the problem of confirmation bias (where you search for information that confirms of your prejudices, rather than what might be true). Hypothesis (and their nulls) are weak ideas that can (and are) easily overturned by contrary data and experiments.

- 2. Theory: This is a framework that explains lots of facts. It is what a hypothesis can become if you've gathered lots and lots of data and/or done lots and lots experiments and other people doing other experiments and data gathering that all arrive at the same point. Theories are not easy to get to in science and once something is considered a theory it is a mark of huge importance. It means that lots of divergent paths have come together to all underline the same point over and over. It is the opposite to what the word means in everyday speech. So when Darwin first published 'On the Origin of Species' it was a hypothesis - now, with it's added parts and divergent lines of evidence from biology, ecology, palaeontology, genetics and more it is considered a theory. Theories are strong ideas that are hard to overturn because not only would you need to produce data that the current cannot account for, but you would need to explain what happens to all the other lines of evidence that back up the theory.

Theories also tend to consist of inter-locking parts that work together. While a theory is hard to overturn, the interlocking parts can and are often modified, downgraded, upgraded etc. So when Darwin proposed evolution he only had one and a half parts of what the theory is today; he got natural selection and he sort of understood that there where other bits that had to exist for the theory to work, but didn't have the mechanisms to prove it. Later research filled the gaps and added the transmission of genes and random mutation of genes into the mix to complete the theory. Since then the relative importance of each of the bits has been/is debated and moved around - but the core idea of evolution only gets stronger as the evidence piles up.

- 3. Laws: A constant that is universal. This is the top stage for an idea in science. They are so strong that it is considered almost nothing can break them. They tend to be used for stuff where there are measurable and definable aspects to them - where mathematical predictions are at their core. An example would be Newton's Laws of Motion - for which there are definite measurements you can take that always end up being predicted by the laws. Laws can be overturned, but not very often. It would be a major, major event for this to happen.

So I hope you can see how ideas in science move though stages, if the idea is robust - it gathers more and more evidence and passes up the hierarchy of terms from hypothesis to theory to law. Like a martial arts student going from white belt to red belt to block belt as they accumulate skills and experience.

The Abuse of Theories

Put even more simply, a hypothesis is an opinion whereas a theory and a law is a fact. This is where you see people failing to grasp the concepts; they confuse opinion with fact. So a common pseudo-attack on evolution is to say something like, "If it is a fact, why do they call it a theory?" - this is a huge fail because that person does not understand what a theory in science is.

The second common mistake is to not understand that a theory is a robust and complex body of facts and ideas. Take the example of global warming denial; when a new bit of evidence comes out that suggests one aspect of the theory does not operate quite as it was thought, they assume the whole theory is broken and thus disproved. Not so, it means the theory may well get modified to account for the new data. This might sound a bit sneaky, but again remember that theories of large interlocking ideas with lots of evidence behind them; one part of the idea can easily be modified without breaking how they work together - indeed you expect modifications of the whole as the data piles up. Theories almost never stay the same - as new data arrives, it needs to be accounted for and so the theory advances - evolves, if you will. Here's an example; Some recent NASA research showed a cooling of the upper atmosphere. Denialists jumped on this as proof that the earth was not cooling. However, if they had bothered to read the whole thing, they'd see that one of the interlocking parts that the theory of global warming predicts is that this warming has no implications for climate change in the troposphere, a fundamental prediction of climate change theory is that the upper atmosphere will cool in response to increasing carbon dioxide.

1 comment:

Dan said...

Good post!

Newton's Laws of Motions are another example of how ideas evolve in science, as they breakdown close to the speed of light, but do apply in all normal situations. The three laws were updated by Einstein's Theory of Relativity which explains what happens in certain extreme conditions. The Laws of Motion are still laws, but ones that are now known to apply only within certain constraints. An example of how subsequent information adds to idea rather than throws it out of the window.