Topic 14

Paradigms in Macroscopic Physics -

What They Are and How They Change

Paradigms We Have considered:

Geocentric Universe - Earth is the center; all planets, our Moon, and the stars all revolve around Earth; orbits defined by concentric spheres each with its own rotation axis (embedded in the next sphere outward) or by circular orbits (deferents) with smaller circular orbits on top ofthem (epicycles); Euclidean geometry; static universe;

Solar-Centered Universe - The Sun is the center; all planets including Earth, our Moon, and the stars revolve around the Sun; orbits are elliptical with the Sun at one focus; predicatable pattern of planetary revolution period versus distance from the Sun; Euclidean geometry; static universe;

Expanding Universe - The Sun and Solar System just one of billions, no special place; Universe is composed of countless galaxies all moving away from one another at high speeds; Universe curvilinear and defined by Riemannian (non-Euclidean) geometry; Universe probably finite in size (mass) andformed from Big-Bang about 15-20 billion years ago;

Aristotelian View of Matter/Motion - All matter made up of air, water, fire, earth; heavy materials (rich in water and earth) fall downward at speeds proportional to weight while light objects (rich in air and fire) rise upward at speeds proporitonal to weight; all horizontal motion artificial and due to external causes;

Galilean/Newtonian Motion - All motion governed by simple physical laws; one important force is that of gravity; Euclidean geometry;

Relativistic World - Newtonian mechanics only appropriate for individual reference frames or between reference frames moving slowly relative to one another; Lorentz transformations define behavior when reference frames moving at relativistic speeds with respect to one another;

Ways we Change from One Paradigm to Another:

There is no single way for one paradigm to supplant another one. Some possible ways include:

1) A key idea which better explains observations

2) A key experiment which is obviously correct but cannot be explained by current paradigm

3) A slow accumulation of ideas and experimental observations with very slow natural translation from one paradigm to another