Because I can see the non-dust pattern with naked eyes...
Just three days ago, I wrote a blog post about BICEP2. So I wasn't terribly excited to write down another blog post once the Planck Collaboration published a paper claiming that the BICEP2 could be due to dust, especially because I don't find the Planck paper to be terribly new, interesting, insightful, or game-changing.
A random image, taken from Perceiving randomness: egalitarian bias
They've been saying similar things since the spring and the arguments they presented today don't seem stronger than the previous ones.
Their fits don't seem to be too good without the error margins and as far as I can say, they are inflating the errors by inventing various kinds of "extra errors" (such as the "conversion error") in order to dilute and obfuscate the signal that they may have failed to discover, despite their superior gadgets and huge funding. This production of spurious errors sort of reminds me of Gerhard Schröder's invention of new taxes such as the environmental tax, the beverage tax, the bad weather tax, and others (Schröder wasn't a sufficiently arrogant hardcore thief to propose a carbon tax, however!).
Much of this tension is a clash of personalities. I think that what BICEP2 has shown is the experimental science of the best kind and unless some embarrassing error emerges (I really mean something like a loosened OPERA cable: it hasn't emerged so far), I will continue to think of them highly even if their discovery is ultimately reduced to dust (or another background). Like proper stereotypical experimenters, they didn't really believe a word that the theorists like to say (all proper experimenters think that gravity is actually caused by leprechauns and GR is just a theorists' fairy-tale for babies to sleep smoothly; but if a theorist needs the experimenters to empirically determine something, the good experimenters are as reliable as a vacuum cleaner). However, after they spent a very long time by efforts to show that their signal is due to something else, they published a paper with the discovery claim and it was undoubtedly right that they did so. Science couldn't operate if the publication of a discovery were viewed as a blasphemy.
On the other hand, I do feel that the Planck folks have the lack of audacity combined with prejudices and the plan to "just impose new limits" is their modus operandi, a dogma predetermined to direct their behavior for years to come. I am even afraid that they will abuse their stronger political power and their joint paper with BICEP2 (to be out in November 2014) already has a predetermined qualitative conclusion now – it will be just a new limit on \(r\), the tensor-to-scalar ratio.
But let me stop with these ethical questions which are clearly dividing the people. There is a scientific substance. Everyone who is interested in cosmology would love to know whether the imprints of the primordial gravitational waves have been seen. I agree with those who say that this discovery, if true, is the greatest discovery in many years if not decades or a century. I would probably place it above the Higgs boson discovery because unlike the Higgs boson, it wasn't really guaranteed.
However, we must ask: is the discovery real?
Of course that I am not 100.00000% sure. But I still think it's significantly more likely than not that the BICEP2 discovery is genuine and the pattern they see is simply not dust. Why? Because it clearly doesn't look like dust. What do I mean?
Just look at the key "photograph" of the BICEP2 field with the polarized CMB signal. My question for you is the following: Can you distinguish this picture from the picture of the "colorful smoke" at the top of this blog post? I sincerely hope you can. But why are these two pictures so different?
The BICEP2 picture is very regular in some very specific way: you may talk about a preferred length scale, the typical distance of adjacent red blobs (or adjacent blue blobs). It pretty much looks as if the adjacent, nearby blue blobs (or adjacent red blobs) wanted to be a rather well-defined distance from each other – and the distance is something like 1/7 of the width of the picture (about 4° steps in the declination, the vertical axis – or about 8° steps in the right ascension on the horizontal axis; note that \(\Delta \phi\) has to be multiplied by \(\sin\theta\) to get a distance on the unit sphere). Do you agree? Needless to say, the step \(\Delta\theta=4^\circ\) exactly corresponds to \(\ell=90\) because one may squeeze \(90\) waves per \(4°\) on a circle that has \(360^\circ\) in total.
On the other hand, the colorful smoke at the top doesn't seem to have a preferred length scale. To a large extent, it is self-similar. If you need to know, the colors in the "coloful smoke" picture were computed from functions defined by Fourier series, and the coefficients in the momentum representation were random numbers comparable to a (decreasing) power law of the momentum, to guarantee that the color is sort of continuous.
If you work on the sphere, the "momentum modes" become "spherical harmonics" and \(\ell\), the orbital angular momentum, replaces \(|\vec k|\). OK. What is the decomposition of the pictures to the spherical harmonics?
Open the new Planck paper on page 8. You find Figure 2 over there which has two similar (electric, magnetic spectral) parts and the top one-half of each part features three red almost straight lines (top) and three blue almost straight lines (bottom) which are the predictions for the dust. These monotonic predictions may leak to the polarization data and the resulting polarization, in the bottom part of the pictures, is less monotonic but it is still monotonic enough. The slopes are small and the local maxima are very mild.
It simply looks very different from the BICEP2 spectrum that seems to have a pretty clear local maximum near \(\ell=90\) or so while the \(\ell=50\) harmonics are weaker by a factor of two.
I don't want to say which particular increase or decrease in the BICEP2 spectrum most visibly contradicts the predictions from the "dust" hypothesis. If I wanted to choose the criterion that, in my opinion, discriminates between the BICEP2 observations and the predictions of dust more sharply, it's the presence of a preferred length scale (preferred value of \(\ell\approx 90\), or preferred angular scale in the sky) that the BICEP2 seems to clearly and "repeatedly" see while, as far as I can say, all dust-like explanations would tend to predict a self-similar smoke-like pattern that has no finite preferred angular scale.
It's my feeling that if you quantified some "confidence level" telling you "how strongly BICEP2 sees a preferred finite angular scale smaller than the size of the window", you would get a pretty high confidence. And the fact that this preferred angular scale \(\ell\approx 90\) agrees with the predictions of inflationary cosmology is one more consistency check for me to be even more certain.
Again, I am in no way 100.00000% certain that the gravitational waves are being seen over there. Of course that if there is a risk of something like a "loose cable" in the BICEP2 apparatuses, the confidence level may go to 50% or lower. But if there is no risk of an embarrassing error and the competing hypotheses are really dust-like, I feel that my confidence is still above 99% that what BICEP2 doesn't see a dust/smoke because that would have a much more self-similar, scaleless appearance.
For those reasons, it looks like Planck is a victim of a confirmation bias, a team looking for excuses why they haven't seen those things before their competition and trying to sell their own "absence of evidence" as "evidence of absence".