We have built up a vast amount of scientific knowledge. In the previous chapters, I have briefly sketched out a tiny amount of it, just to provide a framework for my argument about the physical world inside our diving bell. Scientific knowledge is based on careful observations of that world, always followed by publishing them for anyone else to repeat, criticize and argue about. The French poet Valery wrote in 1932 that ‘science is the aggregate of the recipes which always work’. The result is ‘public knowledge’, testable at any time by anybody who cares to take the trouble. The questioner merely has to repeat the observation or the experiment, and observe the result. It is, or should be, quite independent of the state of mind of that questioner. He or she may be massively ecstatic or massively depressed; it doesn’t matter. Either way, the observation will come out the same.