Albert Einstein had two theories about relativity. They were known as the Special Theory and the General Theory. Both have been confirmed many times with experiment and shown to be valid. The Special Theory challenges our intuition about time, length, and mass in our surroundings. These quantities are assumed to be constants even if they are moving with respect to us as observers. Einstein said that is not true. They vary and their values are dependent upon how fast they are moving with respect to us. Time slows, lengths contract in the direction of motion, and mass increases as objects increase their speed with respect to us. The only thing that remains constant is the speed of light measured by observers. These effects are small and negligible for normal human produced speeds. The changes to these dimensions is exponential as the they approach higher fractions of the speed of light.
The universe has a speed limit.
General Relativity combines special relativity and Newton’s law of universal gravitation, describing gravity as a geometric property of space and time, or Space-time. Space-time is said to have curvature and is affected by the energy and momentum of whatever matter and radiation are present. On May 4, 2011, Stanford and NASA scientists reported confirmation of two predictions of Albert Einstein’s General Theory of relativity, concluding one of the space agency’s longest-running projects. The experiment was known as Gravity Probe B. Within the spacecraft were four ultra-precise gyroscopes to measure two parts of Einstein’s theory about gravity. The first is the geodetic effect, or the warping of space and time around a gravitational body. The second is frame-dragging, which is the amount a spinning object pulls space and time with it as it rotates.
The geodetic effect is often modeled with the idea of a bowling ball warping a rubber sheet. Here, the fabric of space is warped by the masses that are present in it. The more massive objects warp space more ‘deeply’. The Moon follows this warp of space as it orbits Earth. The Earth and other objects in space do not actually rest on a stretchy fabric. This is only meant as a visual aid for a much more complex mathematical and physical description of the relationship.
The Gravity Probe B experiment is simple in concept. Click the image below for an animation. It only takes one minute of your time to view it. The spacecraft monitors the spin axis of ultra-precise gyroscopes by comparing their axis to the direction of a guide star.
The second relativistic effect is that of frame dragging caused by the spinning of a massive object, such as Earth, in the fabric of space. Visualize the effect of slowly rotating the honey dipper in a jar of honey. Dragging movements of the dipper cause subtle effects on the honey farther away. These effects in space are incredibly difficult to measure. They require the ultra-precision of the four gyroscopes in the spacecraft.
Gravity Probe B was able to measure both effects, which occur at right angles to each other. The goal of the GP-B experiment was to measure the geodetic effect to an accuracy of ~0.01%. The frame-dragging effect, which has not previously been directly measured, was to be measured to an accuracy ~1%.
This award winning animated sequence below shows how the probe was able to make those measurements over the course of about a year of data collection starting in August 2004. Click the image below for an animation. It only takes three minutes of your time to view it.
Physics advances experimentally in two ways. 1) Known effects are measured with higher accuracy. 2) Previously untested phenomena are investigated. The geodetic effect was known to ~1% by analyzing the Earth and Moon system around the Sun. Gravity Probe-B attempted to improve on that by 100x. The frame-dragging effect has not been measured directly before. It is so minuscule around a planet the size of our Earth. The spacecraft was testing something that had never been investigated this way. The frame-dragging effect is of particular interest to physicists and cosmologists who study black holes. Like the air in a spinning tornado or hurricane, the frame-dragged space around a black hole has enormous potential for destruction.
The importance of the measurements to the astronomy community and those who study black holes was expressed by Kip Thorne one of the world’s leading experts on black holes. In this video, he made the following comments on the significance of the frame-dragging effect:
“The black dot in the center of the drawing in the video represents a black hole. It is surrounded by an accretion disc of gas, shown in yellow, that we believe is forced into the equatorial plane of the black hole by the dragging of spacetime in that vicinity. Jets of energy [blue light in the video clip drawing] shoot out in both directions along the spin axis produced by frame-dragging around the black hole. Furthermore, the interaction of the frame-dragging around black holes with magnetic fields is responsible for the enormous and destructive power generation that produces the jets of energy streaming out of these objects.”
We live all our lives within the influence of the effects of space-time and the warp cause by masses and their motions. These effects are miniscule. What really is impressive is the action at the places where our normal and commonplace becomes rare, where the exotic is commonplace. It would seem the stuff of science fiction.