What's good, and what's evil? Traditionally, religion and philosophy have answered these questions, pushing science to the side, asking it to stick to the world of natural laws and knowable facts. But Sam Harris wants to change things. At TED, he's arguing that science (particularly neuroscience) can address moral questions precisely because these questions fall into the world of knowable facts. And, even better, science can provide definitive, highly objective answers to such questions. Just as there are scientific answers to all questions in physics, so there are clear answers in the moral realm. This applies, for example, to whether children should be subjected to corporal punishment, or how society deals with very meaningful gender questions. (Things get a little emotional on this topic at about 11 minutes in.) The upshot is that Harris isn't buying a radically relativist position on morality, and this will disappoint many post-modernists. The Enlightenment project is alive and well, ready to make its comeback.
Update: You can find a rebuttal to Harris’s thesis from physicist Sean Carroll here. Thanks Mike for pointing that out.