By GEORGE JOHNSON (NYT)

Maybe the pivotal moment came when Steven Weinberg, a Nobel laureate in physics, warned that

Or perhaps the turning point occurred at a more solemn moment, when Neil deGrasse Tyson, director of the Hayden Planetarium in New York City and an adviser to the Bush administration on space exploration, hushed the audience with heartbreaking photographs of newborns misshapen by birth defects