The term "junk science" (see also pseudo-science and pseudoscience) has transformed in recent years from an appropriate description of poorly constructed scientific reasoning to a label placed on any theory or hypothesis that goes against the scientific hegemony. It has become a derogatory label that gets pasted onto those who put forth ideas that challenge the generally accepted hypotheses concerning the functioning of the world, and in my opinion has morphed from a definition into an accusation.

Now, it should be noted that a large majority of what is labelled junk science is in fact just that; a series of conclusions that are based upon faulty understanding of the facts at hand and, at times, a frightening disregard for logic. As examples, one could look at young-earth creationism, UFO conspiracies, much of the arguments that challenge the safety of Genetically Modified Organisms. However, this label has also been placed upon those who challenge the relative safety of breast implants, those who support vegetarianism as a healthier alternative, the link between vaccines and autism in children and the challenges to current global warming theories.

The danger of this term, in my mind, is that it has been adopted in the popular press and has a powerful connotation. It supposes that those who support the latter hypotheses are in fact unable or unwilling to reason. However, the very nature of science necessitates constant challenge and doubt; we cannot improve on a theory or hypothesis without someone presenting alternative interpretations. We should not be so quick as to dismiss alternative explanations as nutty or insane without at least considering the fact that they may contain some element of truth. Human history has taught us that our understanding of the universe, while adequate for the present, normally appears to be frighteningly false in the future. And as Santayana tells us:

"Those who are ignorant of history are doomed to repeat it."

That being said, I think it should also be noted that just because an alternative theory (see above) that challenges current belief should not be rejected without thorough consideration, we cannot allow opportunistic politicians and policy makers to use that theory to either push forward a personal agenda or to avoid making the difficult decisions that must be made today. I cite, as examples, the terribly slow movement in the USA on issues relating to global warming and ozone depletion; frequently, inaction is justified by stating that certain scientists do not agree with the beliefs of the majority. While we shouldn't label the doubters as junk scientists (before careful consideration), we should strongly state that while alternative hypotheses exist the scientific consensus is that global warming is a fact, and policy makers should act upon those theories. This should also be the case for questions concerning GMOs, breast implants, pollutants, and vaccines.