Gravity Probe B is the relativity gyroscope experiment conducted by NASA and Stanford University to test two predictions of Einstein's general theory of relativity. GPB is essentially looking for the effects caused by the mass of the Earth bending space-time around the Earth as Einstein's theories suggest. One observable should be the geodetic effect estimated to be about 6 arc seconds per year. The other is a frame dragging effect of about .042 arc seconds per year. GPB will look for these effects by tracking a guide star, about 300 light years away, and seeing how the gyros move in relation to the known proper motion of this relatively fixed point in space. Important to our purposes, the GPB technology appears ideally suited to determine if our solar system is curving through space.

GPB is not concerned with subtle motions of the earth, such as nutation or theoretical luni-solar precession, as it will float about 400 miles above the earth (in a polar orbit) free from these effects. It will keep one of the outer gyros in freefall position as the spacecraft orbits the earth, while the earth orbits the sun. Consequently, the spacecraft will track the earth's larger motions (orbital, and binary if it exists) as it moves with the earth through space, without mimicking its lesser gyrations. As readers of this site know one predication of binary theory is that the observable commonly called the “precession of the equinox” is not due to local forces wobbling the earth but is principally a result of the solar system's motion through space in its binary orbit. In short, we believe a moving solar system is responsible for producing the observable called the precession of the equinox, while the earth wobbles very little relative to objects inside the solar system.

In order to isolate the geodetic effect and the very small GR effect, the GPB team has to separate out a number of unwanted signals. One, the well-known aberration of light due to the motion of the spacecraft around the Earth (slightly changing the telescopes orientation to the guide star with each orbit), amounts to +-5” per orbit, and is easy to identify due to the short periodicity. Another, the aberration of light due to the Earth’s annual orbit around the sun (carrying the spacecraft with it), may be less obvious because the Earth only went around the sun once during the GPB data collection period. But it too is a well-known effect, and quite large (+- 20.148”p/y), and therefore should also be readily identifiable.

Now here is our part: If BRI is correct that the Earth also has a third motion, moving with the Sun in a roughly 24,000-year orbit (producing the bulk of the observable known as the precession of the equinox [360 degrees divided by 25,800 years = 50” of geometric precession p/y [1]) then there should be a third aberration, unexpected under current theory. However, because the periodicity of this motion is so long in relation to the data gathering period of the spacecraft (showing less than 1/12,000th of the binary waveform peak to trough in one year) it would likely only be detected as drift rather than any obvious cycle, but the effect will be fairly large, on the order of 50”p/y. Hence, it would mimic general precession even though there is no cause for such an observation because the spacecraft is not wobbling like the earth. [2] This would be overwhelming evidence that the bulk of the observable of general precession of the Earth is actually due to the motion of the SS, and very little to local effects.

The Stanford team has a big task in separating the enormous amount of data received into identifiable signals, each with a known and justifiable cause. If they cannot justify each and every signal then their attempt to isolate the small geodetic and frame dragging effects will lack credibility. Beyond the binary effect, other theorists are suggesting some small noises that may also have to be separated out, if they exist. However, none of these is of the magnitude of the binary (precession of the equinox) observable. So while the analysis might take some time, we expect the largest surprising effect will be a roughly 50”p/y signal that seems to show no periodicity, that looks like drift and coincidentally mimics the precession of the equinox observable.

The GPB program has cost approximately $800 million. Some have argued this cost is unnecessary, as Einstein's predictions have been largely proven through other experiments. However, if GPB proves that the observable of precession is due very little to local effects and mostly due to the heretofore unknown motion of the solar system curving through space, then it will be well justified. Some of the attendant implications of such a find include:

The delta between a tropical year and a sidereal year, long known to be the value of precession, would now be recognized as simply the observable of a solar system that curves through space.

A tropical year, now thought to represent a motion of the Earth around the Sun that is 50” less than 360 degrees, would now be understood as a 360 degree motion of the Earth around the Sun. The reason the background stars change at the rate of about 50”p/y is due to the solar system curving through space at this rate, not because the Earth wobbles 50”p/y.

The sidereal year would now be seen as a period that is about 50”p/y longer than one Earth orbit around the Sun. The extra motion has been offset or masked in the solar system’s journey through space.

As an astronomer friend of mine once said, “"sometimes the real value of experiment is in what you don't expect to find." GPB could unexpectedly prove to make one of the most fortuitous finds in the history of astronomy.

[1] This is the rough current rate. The rate will change over time subject to the eccentricity of the orbit according to Kepler's laws.