Detecting Tectonic plate shifts

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by KoenigMKII</i>
<br />Well if we use laser gyro's as gravimeters, the speed of light being reflected continuously between mirrors can be used to amplify any tiny accelerations the geosynchronous satellite due to a "gravity signal" from a tectonic plate.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">The gravitational acceleration of a geosynchronous satellite due to the gravity of the entire Earth is roughly 20 cm/sec/sec.

Let's suppose our earthquake is a giant one and moves a million cubic kilometers up by one meter. That is a motion of a mass of 1/2,000,000 of Earth's mass, which is therefore responsible before it is moved for 1/2,000,000 of the satellite's acceleration, or 0.000 01 cm/sec/sec. The Earthquake changes the distance of that mass by 1 meter at a total distance of 40 million meters. So the distance is changed by that ratio, and the distance squared is changed by twice that ratio, or 1/20,000,000 of the acceleration.

That brings us to the bottom line. The earthquake changes the acceleration of our geosynchronous satellite by less than 10^-12 cm/sec/sec. That is one ten-thousandth of an Angstrom total distance change after two seconds.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">Because the detecting satellite (in MM at least) experiences the gravity flutuation instantaneously and the 25,000 mile height of the satellite should give a 0.13 millisecond "light time" delay for the SR model, don't we get a chance to see the difference?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Sure. In 0.13 milliseconds, the one satellite will get a head start of a hundred-millionth of an Angstrom or so.

Do these figures begin to show what your idea is up against? -|Tom|-

Quote from Tom:-

"Sure. In 0.13 milliseconds, the one satellite will get a head start of a hundred-millionth of an Angstrom or so."


Ko's reply:-

Yes I give up

A tectonic plate doesn't move enough to be detectable at that distance, even during a nightmare earth quake.

If I say move the satellite to low orbit to increase the acceleration, the light time shrinks and the experiment gets impossible. Catch 22.

The apparatus could not be that sensitive, even a laser gyro uses light with a wavelength that is going to put a limit on "resolving" and minute signal like that.

The only other thing I could do is switch to a more massive signal source. For a low earth orbit GPS satellite, the only thing I can think of is the changing relative postion of the moon as the satellite orbits.

If gravity in a three body problem is light time delayed, would the satellite stay in its current orbit?

Since the moon is massive, distant, and the satellite is moving rapidly relative to it, doesn't it give a chance to detect the difference in gravity propagation speeds between SR and MM for a LEO GPS satellite??

Sorry to harp on

I quote myself:-
"Since the moon is massive, distant, and the satellite is moving rapidly relative to it, doesn't it give a chance to detect the difference in gravity propagation speeds between SR and MM for a LEO GPS satellite??"

I reply to myself:-
&lt;sigh&gt; This is wrong because the detector is moving not the gravity source(s). POW! Shoots down own arguement.. heh

Now I can see why Tom's "text book" example involves two ultra massive Neutron stars rotating arround each other.

The only problem with that example is it is far, far away from our solar system and is 'politically' too easy to ignore. Thats why I tried to think of something closer.

It seems SR will torture a new generation of physics students &lt;sad grin&gt;

It is an entertaining idea if nothing else so chear up-you haven't lost anything.

Gravimetric instruments are useless aboard a manmade satellite. Einstein explained very well that, for an observer in an elevator, there is no way to distinguish between changes of gravity from outside the elevator vs. changes of acceleration of the elevator. On a satellite, any change in external sources of gravity would equally affect all parts of a gravimetric instrument, so the output of the instrument would be the same before and after -- i.e., zero.

The only evidence of changes of Earth gravity would be the minute changes in the orbits of the satellites, which would only be detectible after the passage of considerable time.