 Theorizing about thought experiments usually turns on the details or the patterns of specific cases. Familiarity with a wide range of examples is crucial for commentators, and the list is very long (see, e.g., Stuart et al. 2018, pp. 558–560) We will provide a few here. One of the most beautiful early instances (found in Lucretius, De Rerum Natura 1.951–987; see Bailey 1950, pp. 58–59) attempts to show that space is infinite: if there is a purported boundary to the universe, we can toss a spear at it. If the spear flies through, it isn’t a boundary after all; if the spear bounces back, then there must be something beyond the supposed edge of space, a cosmic wall that stopped the spear, a wall that is itself in space. Either way, there is no edge of the universe; thus, space must be infinite.