The Diffraction Pattern That Changed The World -Mental Model 055

Scientific Method

The systematic observation, measurement, and experiment, and the formulation, testing, and modification of a hypothesis.


Example: Let’s see how the scientific method was used to discover the structure of DNA.


Scientists had discovered the chemical composition of DNA and that is carried genetic information. But the question remained…


> Question: How is genetic information stored in DNA? What is the mechanism?


The scientists Pauling, Crick and Watson hypothesised that…


> Hypothesis: DNA has a helical (spiral) structure.


Let’s get some background info before we look at the prediction. An X-ray beam is used to view DNA because atoms are too small to be seen using a microscope.


A beam of X-ray radiation focused on an object and through to a photographic film on the far side will produce a series of spots on the film. Those spots are formed by the X-ray radiation diffracting off the structure they passed through.


The predication is…


> Prediction: If DNA had a helical structure then its X-ray diffraction pattern would be X-shaped.


> Experiment: Rosalind Franklin performed X-ray diffraction on DNA which produced an X-shaped photo.


> Analysis: When Watson saw the photo, he recognised the helical structure, which proved his hypothesis.


Wisdom: “Nullius in Verba / On no man’s word.” — Royal Society of London


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