# 16.3 Scientific proof

### Black swans vs white coats

Before you read this post, I suggest you read post 16.1 and post 16.2

How often have you read or heard the phrase “Scientifically proven”? If you’ve read my first two posts, you may suspect that scientists can’t prove that anything is true. And you would be right.

Science can only show that some ideas are wrong. As a result of observing the world around us or by logical argument (often relying on mathematics) a scientist may come up with a new idea. But is that idea true?

Experiments are intended to test such ideas. Designing an experiment is not always as simple as it may seem. Suppose you want to find if a lump of plastic supporting a weight gradually reduces in height over a period of several days. This seems like a really simple idea to test – just take a lump of plastic, put a weight on it and measure its height at the same time every day. But suppose the weather is getting colder. Then the block would shrink because its temperature is decreasing. How would you know that the weight was having any effect? Such effects have to be anticipated and controlled if the experiment is to be reliable.

Suppose an experiment supports an idea. The idea is not necessarily true. It may be true for the conditions that the experimenter has chosen but there may be other conditions that have yet to tried, or even thought of, where the predictions of the new idea are false. For example, Newton’s laws (Post 16.2) were thought to be universally true for over 200 years. Their predictions were correct for objects as large as planets and as small as molecules. It wasn’t until they couldn’t predict the behaviour of very small particles that scientists realised that there were problems.

Currently most people believe that Darwin’s theory of evolution and Einstein’s theory of relativity are correct. But we don’t know what will be observed in the future that might contradict these ideas.

Think about the colour of swans. A few hundred years ago science was studied only in Europe and parts of Asia. All the adult swans seen by zoologists would have been white. So I guess they believed that all swans were white. The first zoologist to go to Australia and see a black swan must have been very surprised! This single observation shows the idea that all swans are white is false. The observation of a million white swans did not show that it was true.

So the man in the white coat on the television telling us that something is “scientifically proven” has been proved to be false – by a black swan!

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Follow-up posts

20.1 Mathematical proof and science