High Quality Content by WIKIPEDIA articles! Wittgenstein's rod is a thought experiment attributed to 20th century philosopher Ludwig Wittgenstein. THe set-up is as follows: a rod passes through a sleeve, in which it can smoothly slide. THe sleeve is tangentially affixed to a wall at its lengthwise center, forming a pivot. ONe end of the rod is moved in a circle whose plane is parallel to the wall. THe question of the thought experiment is what shape does the other end of the rod describe? The seemingly obvious answer is a circle, but in fact it describes an inverted cardioid.