Sam Harris' metaphor for objective morality is the "Moral Landscape" where higher peaks represent better states of well-being and vice-versa.
He asks us to imagine the deepest possible valley that represents the worst possible state for the maximum number of conscious creatures. Morality is about moving away from that position. There will be numerous places in the landscape of equal height just as there are equally moral positions and states of well-being.
In this landscape there is no need to know how high the highest possible peak is: no absolute state of moral perfection. Just as we cannot define perfect human health but we can take steps to objectively improve our health relative the the worse possible state - nothing is more unhealthy than a corpse.
I found it to be useful metaphor. His book is well worth your time. Substituting "god says...." for difficult answers is not satisfying.