 One particularly bad scenario for experimental testability is related to the speculation (in the context of the ‘mass density’ version) that the cause of spontaneous collapse may be connected with gravitation. Tegmark (1993, Table 2) quotes some admittedly uncertain estimates for the suppression of interference due to a putative quantum gravity, but they are quantitatively very close to the rate of destruction of interference due to the GRW collapse (at least outside of the microscopic domain). Similar conclusions are arrived at in the more detailed work by Kay (1998). If there is indeed such a quantitative similarity between these possible effects, then it would become extremely difficult to distinguish between the two. In the presence of gravitation, any positive effect could be interpreted as support for either collapse or decoherence. And in those cases in which the system is effectively shielded from decoherence (say, if the experiment is performed in free fall), then if the collapse mechanism is indeed triggered by gravitational effects, no collapse should be expected  either.[32]