Equivalence Principle of Gravity TWO

Terrestrial and Spaceborne Tests of the Equivalence Principle of Gravity
Dr James D Phillips, Harvard Smithsonian Center for Astrophysics

Since before Galileo Galilei, experimenters have used free fall to
investigate gravity. The motivation has varied. In 2006, we test general
relativity. GR is founded upon the Einstein equivalence principle, which
states that all sufficiently small test objects, subject only to gravity,
fall the same, independent of their size, composition, location and the
time. Theories of quantum gravity such as string theory and supersymmetry
predict violations of the equivalence principle, setting the stage for
modern experimental tests. The most sensitive test at present employs a
torsion pendulum with a composition dipole, and is sensitive to small
components of gravitational acceleration perpendicular to the suspension
fiber. The highest sensitivity is Delta-g/g = 4x10^-13. These experiments
are reaching the limit imposed by thermal noise in the fiber. Furthermore,
various groups including our own are considering a space-based test
achieving a sensitivity as high as 10^-20, and a torsion fiber suspension
is a poor starting point. Therefore, we began a terrestrial equivalence
principle test of the Galilean type, employing freely-falling masses. This
experiment will improve the terrestrial limit on EP violation by one order
of magnitude, and would serve as the basis for a space-based version.
Significant obstacles must be overcome. For example, the test masses are
launched at 5 m/s, but the transverse vibration must be held to 10
micron/s. Test mass separation must be measured with an accuracy of 10^-14
m incremental, and 3x10^-8 m absolute, which we will accomplish with
optical metrology. Transverse velocity must be measured to 0.25 nm/s,
which we will accomplish with capacitance gauges. We are building up these
technologies, and expect to achieve state of the art sensitivity within a
few years. Along the way, we have learned things we didn.t want to know
about the friction in steel cable, and how inappropriate ball bearings are
for this work.


Please see http://nesosa.org/2006/oct.phtml for additional information.

Thursday Oct 26, 2006 Waltham MA


tags astronomy gravity Galileo string_theory NASA

Category:

Howto & Style

Tags:

• astronomy
• gravity
• Galileo
• string_theory
• NASA
• optic_society
• physics

[earlyphilosophy]

appearantly this is an experiment designed to accurately test the equivalence of gravitational and inertial mass.

Look up "The Principle of Equivalence" in Wikipedia or somewhere else.

[costel13112002]

what is this guy talking about?