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What is science and how do we decide?

Scientific Method.

This is the name given to a general set of techniques used to investigate new phenomena and gather new knowledge. It is the core method used in all sciences, though it can also be used in disciplines which are not themselves regarded as sciences.

The basic method can be represented as series of steps as follows:
  • 1. Observe some aspect of the universe.
  • 2. Invent a tentative description, called a hypothesis, that is consistent with what you have observed.
  • 3. Use the hypothesis to make predictions.
  • 4. Test those predictions by experiments or further observations and modify the hypothesis in the light of your results.
  • 5. Repeat steps 3 and 4 until there are no discrepancies between theory and experiment and/or observation.

This can be illustrated by the following diagram:

Certain consequences follow from this.
  • 1. If a hypothesis cannot be tested then scientific method cannot be used and such a hypothesis cannot be said to be a truly scientific one.
  • 2. At no stage is the process complete. New observations can occur at any time and must still be consistent with the theory, otherwise we must go back to steps 3 and 4 once again.
  • 3. It follows from 2 that we can never finally say that a theory is 'true' since there is always the possibility that a new experiment or observation might not fit into the theory. From this it is easy to show that the whole concept of 'proof' is illusionary.

The idea that proof is not possible, in an absolute sense, is known as the problem of induction and was first clearly set-out by David Hume*. A simple example, often used to illustrate the problem, is the problem of Sunrise.
Observation leads to a hypothesis that the sun will rise tomorrow morning. This is based on numerous examples of it happening and can be tested repeatedly and will always be shown to work. Is the hypothesis, therefore, TRUE? A moment's consideration tells us that no, the hypothesis cannot be true. One day it is certain that the sun will not rise. It has a finite lifespan and will change in the future into a red-giant and then into a white-dwarf. The hypothesis, therefore, whilst apparently being correct, is not true.

This limitation applies to all hypotheses and this is what we mean by the problem of induction. This problem occupied some of the best minds in philosophy and was not satisfactorily solved until last century when Karl Popper** suggested that the solution was to adopt a model using 'refutation' rather than proof as the test.
The solution, argued Popper, was to turn the problem on it's head. It is evident that no number of confirmations can ever prove a theory is correct, for once and all, but it is also evident that one single example is enough to show the hypothesis is wrong. A single observation or result which does not agree with the predictions of the hypothesis is enough to show that the hypothesis is incorrect. Science, he argued, should therefore abandon any notion of trying to prove hypotheses correct and should, instead, be based on trying to falsify or refute hypotheses. Accordingly, any hypothesis which cannot be tested, with a view to refuting it, cannot be said to be a scientific hypothesis. This, he argues, is the crucial difference, or demarcation, between science and non-science. If it can be tested then it is scientific, if not, it is not.

This was accepted and incorporated into science, and now forms the basis of the standard methodology. Any new scientific hypothesis must be testable. Ideally it should, itself, state clearly what observations or results would prove the hypothesis to be invalid. The easier it is to refute a hypothesis the more powerful that hypothesis potentially is, since it must therefore contain very specific predictions and consequences.

This can be illustrated by considering two predictions:
  • It will rain tomorrow
  • It will rain in central Manchester tomorrow afternoon

The first prediction is almost a truism since chance alone will ensure it is true - it will almost certainly rain somewhere on earth tomorrow. Thus it contains little, if any, information. It is also hard to refute - you would need to monitor the entire earth for a whole day.
The second prediction is much less likely to be true by chance alone. It therefore contains much more information. It is also relatively easy to test since all we need do is monitor Manchester for half a day.

So modern scientific method is based on falsification or refutation as a core principle. In practice this means that new hypotheses are subjected to a process of 'peer-review' in which a panel of experts in the field concerned will try their best to falsify any new hypothesis. This is done before the hypothesis can be published in the scientific literature (journals) of the field in question.

It follows from this that it is incorrect to speak of concepts such as 'proved' and 'true' when considering scientific hypotheses and theories, because such terminology is misleading. Science does not claim 'truth', it claims, rather, that a particular theory represents the best understanding we currently have of a set of phenomena, and offers the best model currently available for explaining and making predictions about the said phenomena.

Finally, we should distinguish between the terms used when talking about scientific theory. The important ones are 'Hypothesis', 'Law' and 'Theory'.

A rational explanation, based on observation(s), of a particular phenomenon, which can be tested and, therefore, refuted.

A scientific statement which explains a particular phenomenon and is accepted as fact, since it has not been refuted. A law must be universal - ie it cannot simply apply in one particular circumstance, it must be true in all cases. A scientific law may be discovered by a single scientist and will be one of many laws contained in an overall theory. It is normally expressed as a mathematical equation or set of equations

A scientific theory is a larger statement which explains a group of phenomena and represents the work of many scientists. A theory is a dynamic thing since it will constantly evolve as new laws and hypotheses emerge and particular elements of the theory are refined and changed.

*Full text of Hume's 'An Enquiry Concerning Human Understanding'
**Full text of Popper's 'Science as Falsification'
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