[S01] Theories & evidence

There are lots of different branches of science, such as chemistry, biology, physics, etc. But generally speaking, there are four main components in scientific research :

1. Theories - These are the hypotheses, laws and facts about the empirical world.
2. The world - All the different objects, processes and properties of the universe.
3. Explanations and predictions - We use our theories to explain what is going on in the world, and to make predictions. Most predictions are about the future, but we can also have predictions about the past (retrodictions). For example, a geological theory about the earth's history might predict that certain rocks contains a high percentage of iron. A crucial part of scientific research is to test a theory by checking whether its predictions are correct or not.
4. Data (evidence) - The information that is gathered from observations or experiments. We use data to test our theories. They might also inspire new directions in research.

So in order to understand a scientific theory, we need to be able to say: (1) which are the laws, principles and facts included in the theory, (2) what do these theories tell us about the nature of the world, (3) what can it predict and what can it explain, and (4) what are the main pieces of evidence used to support the theory, and whether there might be evidence against the theory.

§1. Two misconceptions

Here are two misconceptions about science which seem rather common:

• Some people like to say that nothing can be proven in science, so it is all based on faith, just like religion. What is right about this view is that most scientific claims cannot be proven because scientists are not 100% certain. But this does not mean that accepting them is solely a matter of faith, because we can still have very strong evidence supporting them. In life, we have to be content with probability, not absolute certainty. We cannot prove with 100% certainty that you will die if you jump out of an airplane without a parachute. In fact quite a few people have survived. But of course it would be very stupid for you to try it just because there is no such proof.
• In science, a set of claims and principles about some particular subject matter is called a "theory". Sometimes this misleads some people because in ordinary language, "theory" is often used to talk about a tentative hypothesis with little evidence to support it. So now and then there are people who say things like "evolution is just a theory", "Einstein's theories are just that -- theories". These claims are not really helpful and not very clear. It is true that they are regarded as theories, but it does not mean they are speculative hypotheses on a par with any other wild guesses that people might come up with. A scientific theory can be a claim that is strongly supported by a wide range of evidence. Saying that it is "just" a theory would not be fair.