Read the paper by Anderson, Lang et. al. on the archive as gr/0104064 (extensive bibliography at the end). Some of these people, as well as those whom they consulted, were on the original Pioneer science and engineering teams – no one in the world knows the spacecraft systems as well as they do. The most critical factor in rejecting the heat flow hypothesis as the origin of the anomaly is that the decay of the on-board supply of fuel in the RTG should have been seen by now, and is not.

Furthermore, the authors did not, as you put it, claim that thermal emission was “not significant”. On the contrary, they analyzed the problem very thoroughly, and stated flatly among their conclusions that “it is hard to resist the notion that [RTG thermal emission] must somehow be the origin of the effect”. Also, the debate is not “raging” – real science is about neither fashions nor fads, and those who do it are not given to “rages”.

But the most interesting statement, and in hindsight the one that rings most true, is this, in reference to a possible cosmological origin of the anomaly – “This possibility necessitates a cautionary note on phenomenology: At this point in time, with the limited results available, there is a phenomenological equivalence between the aP and at points of view. But somehow, the choice one makes affects one’s outlook and direction of attack. If one has to consider new physics one should be open to both points of view. In the unlikely event that there is new physics, one does not want to miss it because one had the wrong mind set.” It is precisely this “wrong mind set” that, these days, has allowed theoretical particle physics to be dominated by a non-theory that is patent nonsense as science, and in past days, caused Poincare and Hilbert to miss relativity, Lorentz to indulge himself with deformable electrons, etc. etc. The Mercury perihelion anomaly was itself tiny almost beyond measure – 43″ per century. Almost, but not quite – and some people trusted their instruments more than their models, and believed what they were being told.

Today, it seems that instruments can never be trusted – that instead, we must ignore what is real in favor of what is fashionable. The last thing people need now, it seems, is new physics, when the existing models at all scales are already under attack from so many directions. Every time some new effect is discovered, whether this tiny anomaly painstakingly recorded and reduced, or the clumping of galaxies, or the essential role of non-linearity in general relativity, the orthodoxy are all too ready to leap on the heretics while they apply patch upon patch to the decadent models. The real issue in physics is one of mind-set – one must know history, and have faith in his own eyes and brain.

As for the Pioneer anomaly, paraphrasing someone – “and yet it accelerates”.

I could indeed point out that the Pioneers are spin-stabilized but I’m not sure what the point is. They are better than the Voyagers, true, but the orientations of the Pioneers are really not all that well known. It is one of the sources of uncertainty in the measurement, as pointed out in the conference session by the speaker.

“The physics community” doesn’t believe in string theory. There are some physicists who think it is the best candidate for quantum gravity and the dedication of some to the theory could be called belief. But the whole physics community? No way. There are aggressive and common debates on this topic within physics.

You claim the Pioneer anomaly is real, yet you provide no evidence for that claim. The anomaly is real in the sense that is is unexplained for now, but do you mean it is a sign of new physics rather than unexplained effects? For some reason you seem more willing to believe that the anomaly is a sign of new physics but want to ignore studies about it, like the one discussed here. That doesn’t seem to be a very scientific attitude, so if you have extra evidence that members of physics community doesn’t know about it, I’m sure they’d be keen to hear it. But dismissing studies that provide more information doesn’t seem like a strong argument for supporting the existence of new exotic physics.

The main conclusion of the talk was that the more the anomaly is studied, the more it seems that the unexplained effect can be accounted for by non-exotic means. The speaker himself pointed out that one of the largest factors still hasn’t been taken into account: the changing optical properties of the Pioneers as they travel. This could be enough to explain the anomaly quite well.

As for your comment about the WMAP data, I’m not sure what you are talking about. Care to explain?

Since you are a science reporter, you might point out that the Pioneers are spin-stabilized, making them excellent test platform for probing gravity over long periods, unlike the Voyagers.

Now, as for the tenor of this report, I find it astonishing, particularly comments made on behalf of “the physics community”. Those people in fact believe string theory – “believe” I say, because there is no theory to know – here, we are talking about real numbers from a real thing regarding a real aspect of nature. The Pioneer anomaly is not only real, it is probably the most interesting thing to come out of observational gravitation since the Mercury perihelion anomaly, which as we know was finally resolved by general relativity.

I will not ever bother mentioning the relevant papers – find them yourself. Suffice to say that this one report makes not the slightest difference as to the reality of this effect. After what was done with, and to, the WMAP data, these people are not to be trusted.

-drl

But is it really worth the cost of doing it when that would mean a lot of other more important science couldn’t be performed? I suspect we probably agree on the answer to that.

The anomalous acceleration is about one ten-billionth of the gravitational acceleration at the earth’s surface so we are talking about a tiny tiny effect, and a significant number of unknowns about the condition of the spacecraft.

Well believe it or not, if I dare say: in the last call for mission ideas from the European Space Agency here, we indeed found one dedicated “Pioneer Anomaly Mission” proposal, along with two or three others that featured dedicated “Pioneer” measures as “valuable” add-ons. (out of some 70 total IIRC)

Needless to say all of these were filtered in the complex, peer-reviewed elimination process that led to the present set of tentative ESA missions; still, it tells a lot on the (poor) level we are now in physics, er, credulity level…

Hervé

But I like to think it’s justified because of a comment Isaac Asimov once made: “The most exciting phrase to hear in science, the one that heralds new discoveries, is not ‘Eureka!’ (I’ve found it!), but ‘That’s funny…’”

I think that describes the situation here quite nicely.