TOPICS 1. From Newton’s Gravity to Einstein’s Spacetime 2. “Seeing” Spacetime with Gyroscopes 3. The Science Instrument in a Force-Free Environment ACTIVITIES Assumptions about Gravity Equivalence Principle Curved Spacetime Models Frame-Dragging GRAVITY PROBE B: Examining Einstein’s Spacetime with Gyroscopes An Educator’s Guide

Uncovering Assumptions about Gravity 1. What does the ball represent? The magnet? The magnetic field? 2. How does the ball “know” that the magnet is there? How does the magnet “pull” the ball toward it? 3. In what ways does this model NOT accurately demonstrate Newton’s gravity? In what ways is gravity different than a magnetic force?

NO HYPOTHESIS In the Principia (1687), Newton states that “there is a power of gravity pertaining to all bodies, proportional to the … quantities of matter which they contain.” As the story goes, when Newton was questioned about how his “power of gravity” transmitted from one body to another, he responded, “I make no hypothesis.”

Which wagon is harder to push? Which wagon hits first? swimmingpool

Microscopic Angles of GP-B Geodetic effect milliarcseconds (ST curvature) Frame-dragging milliarcseconds GP-B tolerance milliarcseconds

Gyroscopic Performance Orders of Magnitude Earth-based navigational gyros GP-B gyroscopes Drift Rate (degrees/hour)

Materials -- fused silica, coated with niobium Diameter inches Sphericity -- < 0.3 millionths of an inch (40 atomic layers) Homogeneity -- < 2 parts per million Roundest Gyroscope in the World Roundest Object in the Universe (Almost)

Mach's principle Inertial effects of mass are not innate in a body, but arise from its relation to the totality of all other masses, i.e., to the universe as a whole. Hence, the “local” behavior of matter is influenced by the “global” properties of the universe. Why do gyroscope’s stay oriented? rotational inertia Where does a gyroscope’s “inertia” come from?

Ultra-Low Temperatures for Superconductivity 273 Kelvin Niobium = 9.25K Lead = 4.15K Mercury = 3.72K Aluminum = 1.10K Tungsten = K GP-B Probe Temperature 10K 5K 0K 1.8K METALS