  The magnitude and sign of the gravitational coupling $1/G$ depend on the
relations between different contributions from scalar, fermionic and vector
fields. In principle, this may give the zero and negative values of $1/G$ in
some hypothetical Universes with the proper relations between the fermionic and
bosonic species. We consider different conjectures related to gravity, such as
the wave function collapse caused by gravity, entropic gravity, and maximum
force. We find that some of them do not work in the Universes with zero or
negative $1/G$, and thus cannot be considered as universal. Thus the extension
of the gravitational coupling to $1/G \leq 0$ provides the test on the
universality of the proposed theories of gravity.
