5 ms·

If this events are so rare (that we don't even know how rare they are), how is it possible that they achieved the required certainty (5 sigma)? I guess you cou

• cdelsolar 11y ago
  Both detectors detected the same event at slightly different times
  • 1024core 11y ago
    About 7ms apart, which ties in well with the distance between the two detectors.
• davrosthedalek 11y ago
  It's not a counting experiment, which makes the calculation of a false positive rate somewhat harder. The key for LIGO is certainly that they saw the signal coincident at two stations, far apart.
• antognini 11y ago
  The detection uncertainty is a separate matter from the predicted rate. Sure, if you had a strong prior that GWs should be detected once in a billion years, then you would want a better detection. But as it is the priors on the detection are pretty weak and this is totally consistent with what is expected.
• dragonwriter 11y ago
  Others have answered other aspects of this, but as I understand it, it is not the case that we don't know how rare they (BH-BH events) are because they are so rare, we don't know how rare they are, because we don't have a really good model for them. So, we don't know how often we'd expect to detect them, once we had a detector.
  • jcoffland 11y ago
    I believe the issue is that we don't know of they are rare at all. Perhaps they occur quite frequently. That is the big question.
• drx 11y ago
  From the paper: "To account for the search background noise varying across the target signal space, candidate and background events are divided into three search classes based on template length. The right panel of Fig. 4 shows the background for the search class of GW150914. The GW150914 detection- statistic value of ρˆ_c = 23.6 is larger than any background event, so only an upper bound can be placed on its false alarm rate. Across the three search classes this bound is 1 in 203 000 years. This translates to a false alarm probability < 2 × 10^−7, corresponding to 5.1σ. A second, independent matched-filter analysis that uses a different method for estimating the significance of its events [85,86], also detected GW150914 with identical signal parameters and consistent significance" (https://dcc.ligo.org/LIGO-P150914/public https://dcc.ligo.org/LIGO-P150914/public). Take a look at Figure 4 as well. In case you'd like to dig deeper, the 85 and 86 mentioned are: [85] K. Cannon et al., Astrophys. J. 748, 136 (2012). [86] S. Privitera, S. R. P. Mohapatra, P. Ajith, K. Cannon, N. Fotopoulos, M. A. Frei, C. Hanna, A. J. Weinstein, and J. T. Whelan, Phys. Rev. D 89, 024003 (2014),
• 21 11y ago
  This is about detection. To put it another way, you need a single black swan to prove that black swans exists (to whatever sigma).
  • rdancer 11y ago
    But gravitational waves are a phenomenon without equivalent. Nothing like that had been observed before. (Am I wrong?) W̶h̶e̶n̶ ̶t̶h̶e̶ ̶L̶H̶C̶ ̶d̶e̶t̶e̶c̶t̶e̶d̶ ̶H̶i̶g̶g̶s̶,̶ ̶f̶o̶r̶ ̶e̶x̶a̶m̶p̶l̶e̶,̶ ̶t̶h̶e̶y̶ ̶h̶a̶d̶ ̶b̶e̶e̶n̶ ̶f̶i̶n̶d̶i̶n̶g̶ ̶p̶a̶r̶t̶i̶c̶l̶e̶s̶ ̶f̶o̶r̶ ̶m̶i̶l̶l̶i̶o̶n̶s̶ ̶o̶f̶ ̶m̶a̶n̶-̶y̶e̶a̶r̶s̶,̶ ̶a̶n̶d̶ ̶ s̶o̶ ̶i̶t̶ ̶s̶t̶a̶n̶d̶s̶ ̶ t̶o̶ ̶r̶e̶a̶s̶o̶n̶ ̶t̶h̶a̶t̶ ̶t̶h̶e̶y̶ ̶o̶n̶l̶y̶ ̶n̶e̶e̶d̶e̶d̶ ̶o̶n̶e̶ ̶e̶v̶e̶n̶t̶ ̶t̶o̶ ̶b̶e̶ ̶c̶e̶r̶t̶a̶i̶n̶ ̶t̶h̶e̶y̶'̶v̶e̶ ̶f̶o̶u̶n̶d̶ ̶ i̶t̶.̶ Why are the researchers certain that their equipment and methodology results can be trusted to such high degree, if there ever has been one positive measurement?
    • pja 11y ago
      The Higgs detection was not a single event but resulted from the statistical analysis of many events.
      • rdancer 11y ago
        Thank you for correcting me!
    • cdelsolar 11y ago
      Because of the shape of the event, detection in two places, and more importantly, it matching the signature of the theoretical event extremely closely (especially the ringing at the end)
    • yaks_hairbrush 11y ago
      This comment is making the page formatting gross. Those special characters with the strike-throughs make the entire page over-wide, thus requiring horizontal scrolling to read comments.