Gravity Probe B
Videos
Gravity Probe B (GP-B) was a satellite-based experiment to test two unverified predictions of general relativity: the geodetic effect and frame-dragging. This was to be accomplished by measuring, very precisely, tiny changes in the direction of spin of four gyroscopes contained in an Earth-orbiting satellite at 650 km (400 mi) of altitude, crossing directly over the poles.
Image: Artist concept of Gravity Probe B
Image: Gravity Probe B logo (KSC 03PD3038)
At the time, the fused quartz gyroscopes created for Gravity Probe B were the most nearly perfect spheres ever created by humans. The gyroscopes differ from a perfect sphere by no more than 40 atoms of thickness. One is pictured here refracting the image of Albert Einstein in background.
Gravity Probe B before launch
Spacetime
Videos
In physics, spacetime is a mathematical model that fuses the three dimensions of space and the one dimension of time into a single four-dimensional continuum. Spacetime diagrams are useful in visualizing and understanding relativistic effects such as how different observers perceive where and when events occur.
Henri Poincaré
Hermann Minkowski
Figure 1–4. Hand-colored transparency presented by Minkowski in his 1908 Raum und Zeit lecture