Re: Tsunami's impact on Gravity Probe B

twloehfelm_at_gmail.com
Date: 01/19/05 

Date: 19 Jan 2005 07:55:48 -0800

I am inclined to disagree with your analyses, Tom and David-

I wasn't implying that Gravity Probe B would send data back to earth
that said "the earth's rotations changes right....NOW!"
But consider the hypotheses that went into designing the Gravity Probe
B experiment:

1) A massive spinning object, such as the earth, drags space and time
as it spins.
2) We can not only measure that effect, but we can predict the
magnitude of it.

No "strain gauge with instant feedback" or "massive spinning neutron
stars" required, and even the "speed of transmission" of gravity is
irrelevant.

Let's say, for the sake of argument, that earth is spinning at some
constant (or at least very accurately predictable) rate. The GPB
experiment says that, given that rate of rotation, we expect to see a
frame shift of some value x after a certain amount of time. I am well
aware that "it will take months of operation to reliably detect frame
dragging", but after those months of operation we will have some value
"x arcseconds of frame dragging in y months", so GPB will provide a
rate of change.

Now, there is some predicted value for that rate of change that, I
imagine, assumed that earth would rotate at a constant or predictable
rate. If, 6 months into a 12 month measurement, that rate changed (and
remained at the changed value), so must the predicted degree of frame
dragging. All I am asking is: if there is a discrepancy between the
predicted and measured frame shift, might that discrepancy be corrected
by taking into account the fact that the earth's rotation changed from
the initial assumptions?

I recognize that the sensitivity of the measuring instrument is the
limiting factor, but I am also aware that GPB is exquisitely sensitive.
And if you have a prediction for a velocity (arcseconds/time)
measurement, and that velocity is determined by the rotation of an
object, and the rotation of that object changes from what you assumed
it would be, your prediction will no longer be accurate. You'll have
to account for the change in the rotating object.

That accounting factor might say that "your measurements are accurate
if you assume that on December 26 the earth's rotational velocity
changed by this much from what you initially assumed it would be."

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