[breput]

"The collaboration stopped short of claiming outright detection, opting to describe their results instead as strong evidence of the expected gravitational wave background. That said, "In our statistical analyses, there's a less than 1-in-1,000 chance of nature giving our results without gravitational waves being present," NANOGrav chair Stephen Taylor of Vanderbilt University said during a press briefing." (from the Ars Technica article)

That is far short of the usual 5-sigma (1-in-3,500,000) threshold. So I guess interesting results but not really a major discovery?

[raattgift]

Would it be a major discovery even with 5-sigma, given that it confirms what everyone thought anyway, namely that there are quite a lot of tens-to-hundreds-of-nanohertz gravitational waves, enough to support the idea of a stochastic background?

That is, "General Relativity's right about gravitation yet again". Interesting, because it's yet another way of confirming the theory (at the linear level and a flavour of the equivalence principle), but not at all startling.

What's intriguing is that pulsar timing arrays ("PTA") like NANOGrav, CPTA, EPTA, InPTA, PPTA etc may be seeing more gravitational waves than expected. Assuming the sources are all SMBH binaries in ~month-long mutual orbits, then maybe there are more SMBHs than expected, or they binarize more commonly than expected or earlier in the universe than expected, or through some unexpectedly popular channel other than galaxy mergers. Pulsar timing arrays appear likely to produce increasingly useful data about galaxy formation, mergers, and evolution.

I think that having both LIGO (Hz-kHz, so ~stellar mass) and PTAs (~nHz, and much larger mass) giving views into different parts of the spectrum in gravtiational wave astronomy is pretty major. That LIGO appeared to work at all was awfully cool; and now we have these large international PTA collabs appearing to work too. I am tempted to compare high-end early 20th century optical telescopes at the dawn of radio telescopes: same electromagnetic spectrum, but sensitivity to different wavelengths, with different wavelengths associated with different phenomena and different objects.

PS: I like InPTA's set of cartoons at https://twitter.com/InPTA_GW/status/1674208503395934208 (thread).

[ftxbro]

> "In our statistical analyses, there's a less than 1-in-1,000 chance of nature giving our results without gravitational waves being present"

I wonder how many science experiments were done on earth yesterday. It was probably more than a thousand. This is why if you are doing science, you should always do the sciences that will give amazing headlines if you are right. Maybe you will be one of that day's lucky one in a thousand!

[tobinfricke]

This is an unnecessarily cynical point of view.

There has been 1 pulsar-timing experiment looking for gravitational waves and it produced this positive, 1-in-1000 result. Seems extremely promising.