Equivalence Principle of Gravity ONE

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

Category:

Howto & Style

Tags:

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

[nspinicelli]

good speech, but for the love of god, please control the camera!

[astrophoto]

Camera control: improvement would requior stand up, tripod, and diligent attention. Any of these is more effort than I want.

These videos get done because they are so astonishingly easy.

This talk is the most popular one of those posted. I wish I saw why! :)

best wishes

[nspinicelli]

Well , the way I prop up my camera for videos and prolonged exposures is by setting the camera down and propping it up with the lens cap. It should elevate the camera just enough to capture the subject, and is completely still (granted the cap doesn't slip or the camera isn't bumped of course).  Have a great weekend!

[astrophoto]

If line of sight permits I sometimes put the camera onto the table. But unmoving video is visually deadly. The projection screen sometimes changes slowly and, with this system, this camera doesn't have enought resolution to show detail without zooming.

I'm not "for hire". A capable video crew would not be reasonably priced.  :)

[MisterSym]

If you have a second camera, you might want to try shooting one at the PowerPoint presentation, and the primary (one w/ best audio) at the presenter. A simple in-screen edit can put both videos together and better conveys the presentation as a whole to the viewer.

[astrophoto]

when cost, effort, and time are unlimited, anything is possible. These videos are a note pad made with trivial effort. I'm suprised that the result was usable. To me, this style is better than the wide angle camera from the back of the room unmoving for an hour where an audio recording without video would be nearly as good.

I'm amazed by the amount of interest that this garners.

ttyl

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[gyulaszasz]

Ihr macht wohl Witze, Galilei's UFF stimmt garnicht!

[nfexp]

bless you ! :)

[photographer]

I agree. But I don't see how a greater effort will gain anything except few complaints.I'm astonished I get legable recording with trivial effort. I'd have to bring a tripod, stand up, and give diligent attention. The information will be only trivially more understandable. (BTW: after the first paragraph, I didn't understand a thing which befuddles me completely wondering who is looking. :)

Thanks for the note.

[crowleyjohn301]

this is the most annoying cameraman...EVER! didn't your mother ever tell you to stop fidgeting...jesus! why are you even there?

[strata88]

this cameraman is not paying attention at all...sneezing, mixing sugar packets in his glass, moving the camera around constantly...

[seph0000]

i wanna stab the camera guy

[Giraffepotamus]

didnt really watch video..

but i heard there is a laser pointer somewhere

cool!