One proposal is that of scale invariance. There is growing evidence that gravity may be nonperturbatively renormalizable as described by the asymptotic safety program, which requires the existence of a non-Gaussian fixed point at high energies towards which the couplings defining the theory flow. At such a fixed point gravity must be scale invariant, and hence Newton's constant must be dimensionless. Only in 2-dimensional spacetime is Newton's constant dimensionless, and so in this scenario going to higher energies and hence flowing towards the fixed point should correspond to the dimensionality of spacetime reducing to the value 2. This explanation is not entirely satisfying as it does not explain why such a fixed point should exist in the first place.