Dark Matter or Modified Gravity ?

twofish-quant

And then have a good point. LCDM doesn't work that well at explaining the behavior of galaxy formation, because its was never intended as a theory of individual galaxy formation. People are extrapolating LCDM into this area, but the fact that it doesn't work well is hardly a surprise. If I use a hammer as a saw, it's going to have problems.

LCDM also doesn't explain the green house effect, the fact that the earth has one moon, or why there is evil in the world. Why can't you get good airline coffee? LCDM doesn't explain that. Well, it must be wrong......

Old Smuggler

The scientific method is about testing theories. Just to come up with a flexible mainstream model
where some choice of parameters will fit the data does not automatically shut out other models.
Rather, if more models fit the data equally well, the "best" one is the one with the least number of
parameters. This is what Occam's razor is all about.

The Turyshev paper depends heavily on the "discovered" decay of the anomaly. Since this
"discovery" is probably due to mismodelling of the data, chances are that the model will not be
correct. The lesson learned here is that mere parameter-fitting in a flexible model should not be
sufficient to be called a "settled explanation", even if many people apparently think so.

clamtrox

I still don't understand what your claim is. If you claim that it's possible that there exists an alternative explanation for Pioneer anomaly, then I am not really interested to continue this "argument", as what you are saying is then trivially true.

If your claim is that the article I cited is wrong, then fine; I'm by no means an expert in FEM and all that stuff you need to model the thermal emissions. Perhaps you should publish an article about it. Regardless, I find claims like "GR can't explain the Pioneer anomaly" very dubious, even if the best modelling is done somehow wrong.

If your claim is that since modelling the thermal emissions of Pioneer is so complicated, a "simpler" explanation by modified gravity theories is somehow automatically preferred, then I strongly disagree with you. Just because there are complicated -- but in theory perfectly well understood -- phenomena, doesn't mean that we should look to modify our existing theories. One does not look to modify the theory of gravity just because it's very difficult to calculate the precession of Mercury caused by all the other planets. Only after it's clear that the prevailing theory cannot account for all of the precession, it makes sense to look to look for modifications.

Old Smuggler

My claim is that the data do not constrain the thermal model sufficiently to reach a conclusion of any reasonable
degree of confidence. On the contrary, the fact that the "observed" decay of the anomaly goes as
1/r² indicates that the thermal modelling is fundamentally misguided. For this reason, an objective
view would be to regard the case as open until data of sufficient quality are obtained. Such data can
only be obtained from a dedicated mission craft specifically equipped to settle the case, so that an
explanation based on known physics local to the craft can be confirmed or ruled out.