  It is a fact that both (1868) [WA I, 96] and (1871b) [WA I, 284] mention external disturbances as an ingredient in the motivation for the ergodic hypothesis. This might be taken as evidence for ‘interventionalism’, i.e., the viewpoint that such external influences are crucial in the explanation of thermal phenomena (see Blatt 1959, Ridderbos &amp; Redhead 1998). Yet even though Boltzmann clearly expressed the thought that these disturbances might help to motivate the ergodic hypothesis, he never took the idea very seriously. The marginal note in the 1868 paper mentioned above indicated that, even if the system is disturbed, there is still no easy proof of the ergodic hypothesis, and all his further investigations concerning this hypothesis assume a system that is either completely isolated from its environment or at most acted upon by a static external force. Thus, interventionalism did not play a significant role in his  thinking.[9] 