 This example nicely illustrates many of the most common features of what it means to engage in the conduct of thought experiments: we visualize some situation that we have set up in the imagination; we let it run or we carry out an operation; we see what happens; finally, we draw a conclusion. The example also illustrates the fallibility of thought experiments. Since the time of Lucretius, we’ve learned how to conceptualize space so that it could be both finite and unbounded. Imagine a circle, which is a one-dimensional space. As we move around, there is no edge, but it is nevertheless finite. The universe might be a three-dimensional version of this topology. It is, therefore, true that we must try to be mindful of unexpected limitations due to “physical scale effects” (Klee 2008), or other such things, when imagining counterfactual scenarios.