Experiment!: Planning, Implementing and Interpreting

2.4 Consequences of Falsification

When the scientific knowledge grows within a field, the theories of that field are sometimes affected. New insights are not always compatible with current theory. There are, in principle, three possible scenarios in such cases. The theory may be modified to explain more aspects of the world, it may be completely replaced, or, sometimes, it is not affected at all. We will continue to use the laws of planetary motion as examples to illustrate these scenarios.

Today, few physics undergraduates learn about Ptolemy's theory for planetary motion. This is because it has been proven wrong and has been successively replaced with better theories. Ptolemy lived in the second century of the Common Era (CE) and his theory was based on Aristotle's cosmology, stating that the earth was situated at the center of the universe with the sun and planets revolving around it. The planets moved in perfect circles with uniform motion, since nothing in heaven could deviate from perfection.

Readers who have studied the motions of the planets in the night sky may have noticed a curious effect called retrograde motion. Looking night after night at the planet Mars, for example, it seems to move westward relative to the backdrop of the stars. At some point it suddenly makes a halt and starts to move backwards. Later, the backwards motion ceases and the planet continues in the westward direction. This motion makes perfect sense in a heliocentric system, where the earth revolves ...