We investigate the class of ultralocal metrics on the configuration sp
ace of canonical gravity. It is described by a parameter alpha, where
alpha = 0.5 corresponds to general relativity. For alpha less than a c
ritical value the signature is positive definite, while for all other
values it is indefinite. We show that in the positive definite case gr
avity becomes repulsive. From the primordial helium abundance we find
that alpha must lie between 0.4 and 0.55.