26. one point, from Lectures 25, 26, and 28, short answer, pictures, symbols

(a) .2 Geodesic. Give a general definition of a geodesic. (.1) Give the argument that light travels on a geodesic. (.1)

(b) .4 Mass Causes Curvature. Explain how mass causes the curvature of spacetime. This explanation must include how mass, dynamics, kinematics, and mathematics are all related. (.4) It is acceptable to use a diagram instead of a paragraph to answer this.

(c) .4 Gravitational Lensing. What is meant by gravitational lensing? (.1) How did a solar eclipse enable observation of this lensing? Draw the eclipse observation in two pictures, one before and one during the eclipse. (.2) (The second picture could be the one on p. 145 of the book.) What does gravitational lensing have to do with dark matter? (.1)

Revised October 26, 1997.