Still no Primordial Gravitational Waves…

During March 2014 this blog received the most traffic it has ever had (reaching almost 10,000 hits per day at one point). The reason for that was the announcement of the “discovery” of primordial gravitational waves by the BICEP2 experiment. Despite all the hype at the time I wasn’t convinced. This is what I said in an interview with Physics World:

It seems to me though that there’s a significant possibility of some of the polarization signal in E and B [modes] not being cosmological. This is a very interesting result, but I’d prefer to reserve judgement until it is confirmed by other experiments. If it is genuine, then the spectrum is a bit strange and may indicate something added to the normal inflationary recipe.

I also blogged about this several times, e.g. here. It turns out I was right to be unconvinced as the signal detected by BICEP2 was dominated by polarized foreground emission. The story is summarized by these two news stories just a few months apart:

Anyway, the search for primordial gravitational waves continues. The latest publication on this topic came out earlier this month in Physical Review Letters and you can also find it on the arXiv here. The last sentence of the abstract is:

These are the strongest constraints to date on primordial gravitational waves.

In other words, seven years on from the claimed “discovery” there is still no evidence for anything but polarized dust emission…

One Response to “Still no Primordial Gravitational Waves…”

  1. Steve Hargrove Says:

    …..yes, but this paper places the tightest constraints I am aware of on the r-n parameter space. Many popular = inflation theories are now dust!

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