No certainty yet about the validity of the BICEP2's 2014 discovery
Two or three days before the preprint will appear on the arXiv, BICEP2/KeckArray have released their joint analysis with Planck:
The new joint paper is framed as a discovery of the B-modes at 7 standard deviations but these B-modes are presented as "dust and gravitational waves combined". This literally means that all probabilities of their model are obtained as sums (integrals, the so-called marginalization) over models with all possible values of the tensor-to-scalar ratio, \(r\).
When the high-depth, window-only BICEP2 data are mixed with the low-depth, global Planck data – just like if you dilute your favorite whisky in water at a 100-to-1 ratio, it becomes impossible to discover the primordial gravitational waves separately, the paper confirms. Instead, one may impose one of the usual Planck-like upper bounds on \(r\), namely \(r\lt 0.12\) at the 95% confidence level. This is slightly higher – more signal-like – than all the previous upper bounds coming from Planck.
Needless to say, virtually all science inkspillers totally misinterpret the new release when they write (or spill) say that "it disproved the gravitational waves". It didn't disprove a damn thing. It confirmed the discovery of the B-modes but was unable to reproduce the discovery of the primordial gravitational waves themselves.
I must mention Dennis Overbye of the New York Times as a positive exception. He really is a class above almost all of his fellow writers and his article – and the corrected title (with the word "obscures" instead of "rebuts") – is more accurate than others. Still, the article is bad, with weird claims such as "the paper has no evidence of inflation". Wow, how can say such a thing? Even in the absence of a measurement of an exact \(r\), this is a nontrivial paper verifying many features of inflation.
I don't see how this paper differs from the numerous informal "combos" of the BICEP2 and Planck datasets done by the theorists, for example from the paper by Colley and Gott that concluded that the primordial gravitational waves are shown there (in the combination of the experimental datasets) and \(r=0.11\pm 0.04\) because the B-mode signal seems to be about half dust, half gravitational waves.
Your humble correspondent doesn't feel comfortable about this very method of "forced collaboration" proposed by the "stronger team that hasn't discovered anything". I think it's a tricky way for Planck to "link itself" to the discovery when it's done again even though this collaboration has clearly nothing to do with the discovery.
Well, I still think that the primordial gravitational wave signal is there because of the clear "local maximum" of various BB-spectra and cross-correlations near \(\ell\approx 100\) which no existing model without primordial gravitational waves seems to predict. Lensing of dust only gives one monotonic curves in this interval of \(\ell\).
Ron Cowen of the tabloid named Nature will be my exemplary inkspiller of choice. His title is "Gravitational waves discovery now officially dead". That surely sounds impressive or funny, depending on your point of view, but science cannot make discoveries "officially dead".
The last time when someone tried to make a discovery "officially dead" was in 1633 when Galileo Galilei was was forced to participate in a trial that "officially" decided that heliocentrism was wrong. "Eppur si muove," Galileo mentioned (although this proclamation was probably just silent, because he would have been executed if he were loud). And no doubts about it, the Earth continued to revolve, indeed! ;-)
Science obviously doesn't care about "official authorities" in this sense.
So sorry, this is a different paper by a different collaboration using a different method that got (somewhat) different results and it in no way proves that the March 2014 discovery was wrong. And the hypothesis that \(r\approx 0.12\), for example, is compatible with both powers up to approximately 2-sigma deviations and in this sense, none of the two papers "disproves" the other one.
The arrogance of some people with which they make themselves "official" is manifesting itself at other points of Ron Cowen's rant, too. He teams up with an equally arrogant member of Planck:
Planck researcher George Efstathiou of the University of Cambridge, UK, says that the conclusion is no surprise. “I don’t know why people are so excited,”he says. “There’s nothing dramatic here form the science point of view.”The results of the joint analysis are not a surprise because to dilute BICEP2's signal with Planck's non-signal was the very plan of this joint analysis from the beginning. People are still excited by the BICEP2's discovery of the primordial gravitational waves because if it is true, it is one of the greatest experimental discoveries in cosmology for decades.
Efstathiou characterized the 29 January leak as both “unfortunate” and “careless”. “The BICEP people felt that they had not handled the publicity right the first time” and that everyone was eager to make public the joint analysis in a more cautious manner.
And what about the "leak" stuff? This is clearly a completed paper that was, according to all the information I can have, finalized for the arXiv submission. Mr Efstathiou is just trying to act as a bully and show his loud voice and "muscles" because that's how he may be more visible than by doing research in cosmology.
BICEP2 + Keck Array are doing the right thing by not being secretive and by avoiding bureaucratic unjustified delays before they provide the scientific public with the results of their work. Mr Efstathiou should learn to do it in this way, too.