Re: Einstien

Mark F. wrote:
> A satellite was launched a while ago (1 year) to prove something with
> relativity and Einstein.
> Something about 3 ball made perfectly smooth and put in orbit in a
> satellite.
>
> Dose anyone remember the mission or what they found??

The mission is Gravity Probe B. (Why B? Because there was also a
Gravity Probe A, which tested a different prediction of general
relativity.) In GPB, the three spheres are made of quartz, polished
to within a few nanometers of perfect sphericity--an accuracy of about
one part in 10 million. They are isolated from outside buffeting by
an outer shell, and are set to spinning.

In doing so, they act as gyroscopes, so their axis of rotation should
remain pointing in the same direction if they were not subject to a
gravitational influence. In Newtonian mechanics, even gravity has no
effect on the gyros (because they're perfectly spherical), but in
general relativity, the axis of the gyros will precess ever so
slightly--about 1/100,000 of a degree per year. This is due to a
phenomenon called *frame dragging*. GPB is designed to measure the
precession and see if it in fact matches the predictions of general
relativity. We'll know one way or the other in a year or two.

In Gravity Probe A, a maser was sent up in orbit, to be used as a
clock. General relativity predicts that clocks higher up in a
gravitational field run faster than clocks further down, by a specific
amount, and GPA verified this to about one part in 10,000.

--
Brian Tung <brian@xxxxxxx>
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
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My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt
.

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