Gravitational waves, part II

Planck cosmic microwave background

Remember how, back in March, the science-heads were agog about new evidence of gravity waves from the Big Bang? I wrote a happily awed post about it, in which this sentence is particularly relevant:

Of course, the results must be replicated for this discovery to be confirmed…

Ahem. Well, it seems that confirmation is not going to happen this year. Or for a few years, if ever.

The BICEP team was attempting to locate gravity waves by isolating primordial radiation from surrounding “noise,” or other forms of light polarization. When you’re looking back in time 13 billion years or so, you’re talking very, very, very faint light. Light that is easily interfered with. BICEP’s paper indicated that all sources of interference had been anticipated and accounted for, including interstellar dust.

Here’s the problem: the data that the BICEP team used to control for interstellar dust was not raw data. It came from a PowerPoint slide that was presented at a conference. Of course it would have been great if the BICEP team had been given access to the actual data rather than the processed results from a PowerPoint PDF, but the original slide was presented by the European Space Agency’s Planck team—which was in direct competition with BICEP.

So BICEP used this slide to locate an area of space relatively free of interstellar dust, and that’s where the telescope was aimed. BICEP also used the slide to estimate the amount of dust in that area, and then subtract it from the collected data.

Naturally, as soon as BICEP released its not-yet-peer-reviewed paper, the Planck team pounced on it and performed its own analysis of dust distribution. Their conclusion: that stuff is everywhere, including the point of space BICEP used in its study. The abstract says:

We show that even in the faintest dust-emitting regions there are no “clean” windows where primordial CMB B-mode polarization could be measured without subtraction of dust emission.

Thus BICEP’s results are in question because the point of space its scientists thought was relatively free of interstellar dust isn’t that free after all. Which means that the polarization patterns BICEP detected may not be signs of gravity waves, but rather signs of…dust.

There is good news, however. In the course of its analysis, Planck identified several areas that would make better candidates for trying to detect gravity wave polarization. And the last line of the abstract says:

The present uncertainties will be reduced through an ongoing, joint analysis of the Planck and BICEP2 data sets.

In other words, “Let’s work together.”

(The image is of Plank’s measurement of the cosmic microwave background.)


About Fletcher DeLancey

Socialist heathen and Mac-using author of the Chronicles of Alsea, who enjoys pondering science, politics, well-honed satire (though sarcastic humor can work, too) and all things geeky.
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