TOPICS1. 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?

swimming swimming

poolpool

Microscopic Angles of GP-B

Geodetic effect ---------- 6600 milliarcseconds(ST curvature)

Frame-dragging ------------ 42 milliarcseconds

GP-B tolerance ------------- 0.5 milliarcseconds

Gyroscopic Performance

Orders of Magnitude

10 10 10 10 10 10 10 10-12-10 -14-8-6-4-20

Earth-based navigational

gyros

GP-B gyroscopes

Drift Rate (degrees/hour)

Materials -- fused silica, coated with niobium

Diameter --- 1.5 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 SuperconductivityUltra-Low Temperatures for Superconductivity

273 Kelvin

Niobium = 9.25K

Lead = 4.15KMercury = 3.72K

Aluminum = 1.10K

Tungsten = 0.0019K

GP-B ProbeTemperature

10K

5K

0K

1.8K

METALS