Agreed, Anna. Andy, I think, defines objective as what cannot be changed. I follow Julian in finding that confusing. Andy gave the example that human activity cannot change the fact that the world is round. Yet with enough atomic bombs humans could certainly change that fact! Less depressingly, human activity changes our material circumstances all the time, and we often employ mathematics in order to do this.
At the risk of repeating myself, I think we need to work hard to escape from false dichotomies such as objective/subjective, social/real, conventional/natural...
Brian Rotman has suggested that we need “to demolish the widely held metaphysical belief that mathematical signs point to, refer to, or invoke some world, some supposedly objective eternal domain, other than that of their own human, that is time bound, changeable, subjective and finite, making” (1987, p. 107).