After working through my previous argument and MisterChris's idea about objective morality, I thought of something interesting since most of my evidence was from science. Maybe science could prove objective morality?
Idea: Because science is applied philosophy and the closest representation of the universe, it is the best idea we have which we should follow more than any other ideal. For example, it is beyond a reasonable doubt that the force of gravity exists, that the speed of light is a constant in a vacuum, etc.
As science tells us how things should act, logically, this extends to how humans should act as well. Again, we have nothing better to go on, because science is the only thing that can be proved time and time again, under countless different conditions and universally applicable.
Science tells us our genes and pre-determined instincts push us towards a specific set of morals. For example, we have evolved to naturally survive, because only those who survive long enough can reproduce their offspring. We have evolved to protect ourselves and our culture. These ideas have not changed regardless of where you are on earth, neither when in history you pick the person.
Because there are inherent values that humans value and actions that we tend to do as science predict, science tells us the objective morality. After all, every other force in the universe has some law that affects it, not affected by human thought (except perhaps quantum mechanics).