The BICEP2 announcement was hailed as an “epic discovery,” and there was talk about scientists popping the corks of champagne bottles in a celebration. But in the past several weeks some scientific papers have been released which in various ways rain on the party of those who wanted to claim that the theory of cosmic inflation had been verified.
Almost immediately after the BICEP2 announcement, a scientific paper by Liu and others was released which casts severe doubt on whether the BICEP2 b-mode polarizations really do come from cosmic inflation or the Big Bang. The paper described a source of dust-related "galactic radio loop" radiation that may well account for the radiation detected by the BICEP2 team. The paper noted that the dust source of radiation “crosses the very region of the sky from which the BICEP 2 experiment has recently detected a B-mode polarisation signal,” and noted that this "galactic radio loop" radiation peaks at 120 to 130 gigahertz, which is almost the exact frequency used by the BICEP2 team (150 gigahertz). The paper also noted that this source of radiation was not accounted for by the BICEP2 team. The paper caused several science web sites to have stories such as this: The Big “Gravitational Wave” Finding May Have Actually Just Been Some Dust. See also this later paper by a much larger team mentioning the same source of radiation, described as "magnetic dipole emission from ferromagnetic inclusions within interstellar grains."
Another recent scientific paper raining on the party of the cosmic inflation celebrants is this paper by Hu and others. The BICEP2 findings conflicted with the findings of a much larger scientific team (the Planck team), in regard to something called the tensor-to-scalar ratio. In an attempt to resolve this discrepancy, the BICEP2 team trotted out a kind of farfetched theoretical contraption called the vanishing scalar index running model. But Hu's paper blows the whistle on this, like an NFL official throwing a flag on a football play. Hu's paper points out that when you sum up all the latest observations (from Planck, WMAP, and BICEP2) “the vanishing scalar index running model is strongly disfavored,” with a high three-sigma confidence level (a 99.7% confidence level).
Hu's paper shows that the BICEP2 team's observations indicate a “blue tilt” in their polarization observations, and the paper notes that “this blue-tilt spectrum is not consistent with the prediction of the standard single field inflationary paradigm.” That's a big downer for the proponents of the cosmic inflation theory, as it seems to suggest that the BICEP2 observations contradict the main predictions of cosmic inflation theory, instead of confirming them. In fact, a few years back this scientific paper ended by saying, “More strikingly, if B-mode polarization is found and is shown to be due to gravitational waves, then if the spectrum is slightly blue one would have falsified the inflationary paradigm.” Such a slightly blue spectrum has apparently being found in the BICEP2 observations, an embarrassment for cosmic inflation proponents who are trying to wiggle their way out of this dilemma.
The BICEP2 B-Mode Signal: Slightly blue
Another problem for cosmic inflation advocates is a recent paper on a topic called primordial non-Gaussianity. Primordial perturbations are tiny little lumps in the cosmic background radiation, tiny little blips in the Big Bang believed to be like the seeds of future galaxies. Most versions of the cosmic inflation theory (and basically all of the simplest versions) have predicted that these primordial perturbations should be almost perfectly Gaussian, that is, having the shape of a bell-shaped curve or normal distribution. If, however, scientists find evidence that these primordial perturbations were non-Gaussian, it would almost seem to put the inflation theory on life-support. Primordial non-Gaussianity is like poison to the theory of cosmic inflation. If the cosmic inflation theory is Superman, then primordial non-Gaussianity is kryptonite.
The WMAP space satellite observed the cosmic background radiation for nine years. Quite a few scientific papers based on the data from that satellite did actually report evidence for primordial non-Gaussianity, as you can see by reading the papers here. But a team studying data from the Planck satellite reported no evidence of primordial non-Gaussianity. However, the confidence level in their study was low, only 68%.
But on April 1 of this year a team of scientists reported a study on primordial non-Gaussianity based on quasars. They found a significant degree of primordial non-Gaussianity (between 46 and 158), with a confidence of 95%, much higher than the 65% confidence level reported by the Planck team. These results are rather toxic for the theory of cosmic inflation. They suggest that the main prediction of the typical cosmic inflation theory – almost perfectly Gaussian primordial fluctuations – simply is not true. This paper has received almost no attention from the proponents of cosmic inflation, some of whom seem to fulsomely hail any study that may favor their theory, and pay little attention to studies that conflict with their theory.
A distant quasar (Credit: NASA)