81 00:06:47,360 --&amp;gt; 00:06:49,920 working out which of these are elementary, 82 00:06:49,920 --&amp;gt; 00:06:54,120 is a problem that's defined particle physics for over 60 years 83 00:06:54,120 --&amp;gt; 00:06:59,480 and has required an extraordinary coming together of theory and experiment.