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Our future, our universe, and other weighty topics

Thursday, May 15, 2014

A Talk at Princeton Deflates the Grandiose Super-inflated BICEP2 Claims

In March the BICEP2 study announced observations that were hailed as a “smoking gun” proof of the theory of cosmic inflation, a theory that originated as an attempt to explain away various eerie problems of fine-tuning or “unnatural coordination” in the Big Bang (problems known as the horizon problem and the flatness problem). But this week rumors have been swirling that the findings of the BICEP2 study may not hold up. However, the supporters of the cosmic inflation theory have kept saying that the BICEP2 findings “remain robust.”

Today may be the day that BICEP2 goes from “robust” to “bust.” A scientist has just finished a talk at Princeton University which spells bad news for anyone thinking that BICEP2 has provided any evidence for the theory of cosmic inflation.

The talk was delivered by scientist Raphael Flauger, and the slide show from his talk can be downloaded here.

BICEP2 detected what is known as b-mode polarization, something that could be produced by cosmic inflation in the universe's first second, but which can also be produced by ordinary things that do not come from the Big Bang: gravitational lensing, synchrotron radiation and dust (all originating long after the universe was born). The question is: can the BICEP2 observations be explained by ordinary things like dust and gravitational lensing, or can they only be explained by assuming some super-special cosmic inflation in the universe's first second?

Flauger presents updated models of the combined effects of dust polarization and gravitational lensing, which he shows in the graph below (from page 39 of the pdf) :

BICEP2 foreground

The colored bands are the b-mode polarization effects we would expect to see from dust, other ordinary foreground effects, and gravitational lensing, according to Flauger. Notice that they overlap almost exactly with the BICEP2 observations. In fact, if one uses a combination of the BICEP2 observations and similar preliminary observations from a related team (Keck), then basically 9 out of 9 observations can be explained by assuming ordinary, run-of-the-mill things like dust and gravitational lensing (not the super-special cosmic inflation from the universe's first second).

This result is devastating to the grandiose, super-inflated claims of those claiming that BICEP2 has provided evidence for cosmic inflation. The Princeton presentation suggests the BICEP2 observations do not come from the Big Bang or the dawn of time. 

Flauger then uses another, different way of estimating the foreground contribution of dust and gravitational lensing, one based on what are called column densities. He gets the same result: a model indicating that all BICEP2 observations can be explained by the dust, gravitational lensing, and other ordinary foreground effects. In fact, Flauger gets the same predictions using two different techniques, which suggests he's on the right track. Below is page 52 of his presentation: 
BICEP2 foreground

Yesterday I published a blog post arguing for the same thing, that the BICEP2 observations can be explained by ordinary dust and gravitational lensing, not from some super-special cosmic inflation at the dawn of time. It is nice to have my conclusion supported the next day by a presentation at Princeton University.

It may not quite yet be the day for the fervent BICEP2 advocates to wave the white flag, but I would suggest that they at least get one ready (along with an explanation of exactly why they told us with such assurance again and again that some ambiguous observations were proof of something from the universe's first second).  Postscript: the Resonaances blog (written by a physicist) has just come out with a post which pretty much says the same thing I say in this post, commenting on the same Princeton talk, and suggesting that the BICEP2 result "will not stand."   

Post-postscript: After repeatedly writing as if it was a decided fact that the BICEP2 observations are gravitational waves from primordial cosmic inflation,  physicist Sean Carroll now tweets that it is merely "even money" that such is the case.   

Post-post-postscript. In this article in the scientific journal Nature, it is explained that two recent scientific papers have concluded that there is no significant evidence that the BICEP2 signals are from cosmic inflation or gravitational waves, with dust and cosmological lensing being an equally plausible explanation.