This is not true! There are techniques to determine causality passively. Here is one such example, which takes advantage of the behavior of noise to choose between "temperature causes altitude" and "altitude causes temperature": [PDF] http://papers.nips.cc/paper/3548-nonlinear-causal-discovery-...
I think that paper is using a heuristic that, for some problems, is a good guess which direction the causal direciton is.
Use your common sense though. Do you think we would have built the modern world (e.g. electricity) by passive observation of the world, or does really getting to the truth require controlled experiments?
All experiments require repeat measurements for confidence. None of this means that passive methods are impossible, which is what you were saying earlier.
That paper had no proof attached, because it's a heuristic and can easily be fooled by a bad setting. So maybe some causal relationship that are obvious can be learnt passively. But what I am saying is entirely consistent with what Pearl is saying in the article. To get to the next level of ai you need an experimenting agent. Passive methods in general are impossible for untangling causal relationship.
