From John Horgan:
Even when fortified by the latest findings from neuroscience, genetics, and other fields, social science will never approach the precision and predictive power of the hard sciences. Physics addresses phenomena—electrons, elements, electromagnetism, the nuclear forces, gravity—that are relatively simple, stable and amenable to precise mathematical definition. Gravity works in exactly the same way whether you measure it in 17th-century England or 21st-century America, in Zambia or on Alpha Centauri. Every neutron is identical to every other neutron.
In contrast, the basic units of social systems—people—are all different from each other; each person who has ever lived is unique in ways that are not trivial but essential to our humanity. Each individual mind also keeps changing in response to new experiences—reading Thus Spoke Zarathustra, watching Lord of the Rings, banging your head on the ice while playing pond hockey, having a baby, teaching freshman composition. Imagine how hard physics would be if every electron were the unique product of its entire history.
Societies also vary markedly across space and time. France in 2013 is radically different than it was in Comte’s era. The United States today is quite different than it was a century, a decade or a year ago. Social scientists are chasing a moving target, one they can never catch. As anthropologist and archetypal softy Clifford Geertz once wrote, social scientists can construct only “hindsight accounts of the connectedness of things that seem to have happened: pieced-together patternings, after the fact.”
Here is the biggest difference between social and hard science: Protons, plasmas and planets are oblivious to what scientists say about them. Social systems, on the other hand, consist of objects that watch television; listen to the radio; read newspapers, journals, books, and blogs; and consequently change their behavior. In other words, social-science theories can transform societies if people believe in them.