[X] My Assistant

[remcook]

http://www.planetary.org/news/2005/pioneer_anomaly_faq.html

The planetary society may be checking it out...

The Planetary Society has committed to raise the funds to preserve the priceless Pioneer data from destruction.


After years of analysis, but without a final conclusion, NASA, astonishingly, gave up trying to solve the "Pioneer Anomaly" and provided no funds to analyze the data. The Pioneer data exists on a few hundred ancient 7- and 9-track magnetic tapes, which can only be read on "antique" outdated computers. The agency is going to scrap, literally demolish, the only computers able to access and process that data in the next few months!

[The Messenger]

All of these approaches use assumptions we should not be making. If there is a variation in the permeabiliy of space to mass necessary to explain the phenomena I outlined above, there is almost certainly a corresponding gradient in the speed of light.

This can be demonstrated with the Galileo paradox:

Put Galileo on the Dark side of Mercury, rolling his balls to measure the gravitational constant. Because of the nearby mass of the sun, the balls will roll slower, which would cause Galileo, not knowing about GR, to underestimate the G constant. EXCEPT Galileo's clock is also ticking slower, so the value would be very close to correct.

Watching the experiment from an Earth frame of reference, the balls would appear to roll slower, and a GR space curvature correction must be used to explain the phenomena.

Three things: 1) The same observations can be interpreted as a time or space dilation, depending upon the frame of reference. 2) Performing the experiment on Mercury, Galileo could be completely oblivious to the need for GR to explain the results from Earth. 3) It is relatively simple to transfer both frames of reference to a single coordinate system where the absolute pathlength through a given volume of space varies as a function of mass.

Magueijo eluded to this transformation in Faster Than the Speed of Light, where he found it difficult to prove his theory required a new physical concept; and not just a transformation of GR into a completely compatible coordinate system, where pathlengths and the speed of light vary, not time and space curvature. (I am of the opinion that this mathematic transformation provides a better conceptual bases for GR phenomenon.)

So any attempts to measure unknown or poorly characterized forces must also address an untested assumption in measurement theory: the Speed of light is an absolute constant that is not mass dependent; or more exactly: Current GR perameters correctly compensate for mass-dependant effects upon light.

Again, existing solar probes have tightly constrained any deviations from established GR constraints: Bertotti has used Cassini to constrain unexpected GR variance to a factor of 2.3x10^-5 near the Earth's orbit. Perhaps the best solar constraint on the speed of light is the Pioneer Anomally itself - 8x10^-9m/s^2, but this is only beyond the obital distance of Saturn. (Notice that since we use the two-way speed of light to determine the position of the Pioneer probes, the acceleration of the probes could be away from, rather than towards the sun, as long as it is of the same magnitude as any change in the speed of light.)

Bertotti, B., Iess, L., Tortora, P., “A test of general relativity using radio links with the Cassini spacecraft,” Nature 425, 374-376 (2003).

http://lanl.arxiv.org/PS_cache/gr-qc/pdf/0411/0411082.pdf

Again, much of the science needed to nail down these possible discrepancies can be extracted from the current generation of probes, but only if the experimentors are aware of the unbridled parameters and the need for additional onstraints.

Edited to add:

One more question about LISA - unless and until the current LIGO generation of gravity antenna detect ANY gravitational phenomena, should we be vesting in another experiment? IAOTO the waves do exist, but we may be searching with the wrong kind of antenna.

[jamescanvin]

Heading off topic but...

One more question about LISA - unless and until the current LIGO generation of gravity antenna detect ANY gravitational phenomena, should we be vesting in another experiment? IAOTO the waves do exist, but we may be searching with the wrong kind of antenna.

Well LISA will be serching in a completely different frequency band. A band which should include waves from binary neutron stars which pretty much must exists given current observations (and at a known amplitude), unlike LIGO which can only detect much more exotic and theoretical objects and mergers. So yes I do think it's worth investing in, even given the non-detections at LIGO.