The crystallisation achieved by the artist condenses space into a metastable state. This is clearly the case because work must be exerted by the artist during the condensation process. Although the crystallisation of space results in a metastable state, the state is a very long-lived state; the large amount of mass that would have to shift amounts to a large activation barrier between the metastable crystallised state and the lower energy equilibrium state. It nonetheless remains possible that a "crystal" of space subject to a sudden force or disturbance could suddenly acquire sufficient energy to overcome the activation barrier and pass into it equilibrium decomposed state. Due to the endothermic nature of the crystallisation process, such as sudden change of state would bill exothermic and result in the emitting of a relatively large amount of energy in the form of noise.

The question of how best to describe the long-range order in reciprocal spaces remains an open question. It seems to be the case that the simple three-dimensional reciprocal space is insufficient to describe the order of the crystal. Perhaps the six-dimensional reciprocal space approach that has been used to discuss quasi-crystals might provide an appropriate formalism. A careful study of the density-density correlation functions should reveal some interesting behaviour. Within the crystal, it is probably the case that the pair-correlation function is rotationally symmetric with a large maximum constituting the first coordination shell followed by successive maxima whose peaks slowly decay to unity.

The large surface-area-to-volume ratio suggests that the surface energy of crystallised space is not significantly larger than the bulk energy. While some may find this surprising and, perhaps, even counter-intuitive, the difficulty in achieving the crystallisation of space in the first place argues for a very low, in absolute terms, value for the bulk energy. Although bulk energies can be determined to a surprisingly good degree of accuracy using the local density approximation within density functional theory, the resolution of this question must await the improvement of techniques for calculating the surface energy. This very problem has motivated the introduction of a promising approach to the calculation of surface energies using the concept of a local energy density. It is certainly to be hoped that this procedure will shed light on the subject.

It should be clear that the crystallisation of space, which is in and of itself, a remarkable achievement, has opened several new avenues to pursue and considerations, which, when elucidated, will add to our understanding of the world in which we find ourselves.

Krzysztof Rapcewicz ( received his Ph.D. in Theoretical Physics from Cornell University)