Gravitational and relativity physics is perhaps the most fundamental area of physics.
Gravity is the weakest of the four known forces, yet paradoxically it is the most dominant
because it acts from very large distances. In fact, every bit of matter in the universe
is under the gravitational influence of every other bit of matter, even if infinitesimally so.
Relativity theories propose that gravitational forces apply equivalently to all bodies.
Furthermore, Einstein's theory of general relativity puts gravity at the heart of the
structure of the universe, proposing that even the orderly space-time structure of the
universe can be "warped" near a body of large mass, such as the Sun or even the Earth.
This warp near massive bodies affects even clocks. While these changes to the very fabric
of space and time near a large body are dramatic in their importance, they are also very
subtle and difficult to measure accurately. Yet, they must be taken into account even in
routine astronomy observations and in measuring the position of satellites and planets.
Advanced technologies must be applied to detect and characterize these minute changes so
that the corrections caused by relativistic phenomena can be precise.
Several missions and experiments presently under development to improve the accuracy of
measurements of gravity effects are described briefly in this section. All of these
experiments make use of the nearest large body, the Earth, to measure the distortion of
space-time.
- Gravity Probe B measures how Earth distorts the space around it, and how Earth
drags nearby space as it rotates. GP-B is scheduled to be launched May 1, 2002.
Learn more about the science objectives, and about the many technology developments
that have been necessary for this experiment, at its web site http://einstein.stanford.edu/.
Be sure to follow the progress of this pioneer relativity experiment.
- Satellite Test of the Equivalence Principle (STEP) will compare a body's inertial
mass to its gravitational mass to the remarkable resolution of a part in 1018!
For more information on STEP visit http://einstein.stanford.edu/STEP/index.html.
- The Superconducting Microwave Oscillator (SUMO) will place a high-stability clock
in orbit around the Earth to test Einstein's prediction that time varies depending on the
strength of gravity, the 'gravitational red shift.' SUMO has a web site -
http://bigben.stanford.edu/sumo/
- The Primary Atomic Reference Clock in Space (PARCS) experiment will place a precise
laser-cooled atomic clock in orbit to measure the red shift
and to detect other effects of Einstein's theory of general relativity.
- The Satellite Energy Exchange (SEE) experiment will measure G and its change
with time by tracking the motions of two bodies in Earth orbit. The gravity attraction
of the larger test mass, the 'shepherd,' causes the smaller mass to approach, then recede
from the shepherd. To learn more go to http://GRAVITY.PHYS.UTK.EDU/see/.
