Within science it's obvious you can have "bad" science, but in the real world it's different; that troubles me. Science can be "bad" for many reasons; small sample sizes, using incorrect tests or overstating your results to name a few. Bad science ranges from the inconsequential to life-threatening. An example of bad science causing real damage was Andrew Wakefield's investigation into the supposed connection between the measles, mumps, and rubella vaccine, and autism. The findings have been shown to be incorrect but the initial media storm undeniably means there are concerned and well-meaning parents who still refuse to vaccinate their children.

Another "bad" science is pseudoscience; things that sound science-like but really have little or no substance. Pseudoscience is often harmless, like ghost hunters, but can be malevolent. Anti-vaccine proponents and climate-change deniers have the potential to cause either personal or societal damage and thrive on "facts and figures" that sound scientific but are hokum.

My friend's response concerned me because it showed something worrying with science; something scientists are partially responsible for perpetuating. It's the image of scientists as authority figures speaking absolute facts. As Nobel laureate Peter Doherty says: "If you want absolutes speak to a politician or a pope." Scientists don't do absolutes. Indeed we don't really deal with "facts", not how most people understand them.

In science you form an explanation for what is causing a phenomenon; a hypothesis. You test your hypothesis through experimentation, these experiments are designed to try to disprove your hypothesis. Whenever you fail to disprove it, you provide evidence to support your hypothesis. But importantly, you never prove your hypothesis, it never becomes fact.

Even as a scientist this was hard to wrap my head around, but it underpins science, it's why scientists are always qualifying their statements with "we are confident that" rather than "we know that". It's an important nuance; it means science isn't fixed, it's not dogmatic; there's always room to move and evolve. Don't get me wrong, I'm not saying that we don't "know" anything. Eventually, with enough evidence, the probability that a hypothesis is correct becomes indistinguishable from "fact". Examples include that vaccines protect against disease and that species arise through evolution.