This was the question of Sam Harris’s TED talk which was a sales pitch for his book “The Moral Landscape“. I think science cannot answer moral questions. Science can help creating a cure for cancer or design a better gas chamber with equal efficiency. It is utterly incapable of telling if one is more ethical than the other. There is no litmus test for morality.
Science is great at finding methods for making something. Good decisions are not an exception. Science can shed the light on how to make better decisions as this excellent video by Mariano Sigman and Dan Ariely shows. It cannot tell what these decisions are.
Notice the difference between the two videos. The second video is focused on the method. It does not comment on the morality of a particular decision and does not mention religion or any social group at all. Harris’s video, to the contrary, is full of anti-religious (Islamophobic, in particular) examples, and appeals to emotions rather than intellect while being completely unsound intellectually. As a sales pitch, it worked great creating controversy and sparking heated discussions among scientists, philosophers, and religious people. But it did nothing to make this world better.