You can find a lot of different definitions of post-modernism. Here is one from Wikipedia, which seems appropriate because in some sense at its very core Wikipedia adopts a post-modernist approach to truth. Post-modernism rejects objective truth, or at least man’s ability ever to identify such truth. As applied to science, post-modernists would say that what we call scientific “truth” in in fact the results of social, cultural, and political forces within and acting on the scientific community.
Some elements of post-modernism actually provide a useful critique of science. Its focus on biases and resulting observational blindness to certain results that falsify ones pre-conceived notions are useful caveats in a scientific process. But the belief that a rational scientific process is not just difficult but impossible leads to all kinds of crazy conclusions. Many in hard core postmodern circles would argue that since objective truth is impossible anyway, scientific findings should be guided by what is most socially useful. As Steven Schneider of Stanford says vis a vis climate:
We have to offer up scary scenarios, make simplified, dramatic statements, and make little mention of any doubts we have. Each of us has to decide what the right balance is between being effective and being honest.
And speaking of Steven Schneider, he is coauthor of a recent study appearing in the Proceedings of the National Academy of Sciences that has really made it plain to me that climate is becoming the first post-modern physical science. Just note the incredible approach to his study, and how much it mirrors the precepts of post-modernism: To decide who is right and wrong in climate science between skeptics and alarmists, the study authors have … wait for it .. counted them and measured their relative influence in academic circles. Since the authors count more alarmists than skeptics, and judge that the alarmists are more influential in academic circles, then they must be right! After all, truth is determined by those with the most political and cultural influence, not by silly stuff like testing hypotheses against observational data.