Our parents and our teachers tell us what is right and what is wrong from an early age. We may also learn from our own experience. In this way, we learn not to touch a hot stove and we develop a system of beliefs about how the world works. It is only through experiment that we can verify whether a belief is true, although not all beliefs can be subjected to experimental verification. Experimental proof can overthrow even beliefs that have been popular for hundreds of years. It was in this way that after 1200 years of use, the Earth-centered model of the solar system proposed by Ptolemy was eventually superseded by the Copernican model with the Sun at the center.