Experiment!: Planning, Implementing and Interpreting

6.4 Reflections on the Exhibition

Recapitulating our definition, an experiment changes the state of a system to produce an organized response, in purpose to answer a specific question. We added that the response of interest must arise from the treatment imposed by the experimenter. If these criteria are not fulfilled it is an observational study, where measurements are made without attempting to influence the response. One reason why observational studies are sometimes mistaken for experiments is that building and operating measurement devices often require a great deal of practical manipulation, though measurements in themselves are only a way of observation. Looking at the experiments in our gallery we see that they all change the state of a system in order to study the resulting response. For example, Harvey obstructed blood flows in various ways to observe how the vessels were emptied or filled, and Feynman put an O-ring in cold water to see if its resiliency was affected.

Exercise 6.2: As all seven examples in the gallery are experiments they should provide good evidence for causation. For each experiment, give at least one example of a causal relationship revealed by the experiment.

These experiments are captivating in that they use rather simple means to interact with things that often cannot be seen or touched: the minute capillaries that transfer blood from the arteries to the veins, the DNA of viruses, subatomic particles like electrons, not to mention female birds’ ...